Asymmetric Planetary Nebulae V20-25 June 2010, Bowness-on-Windermere
Planetary Nebulae Surveys: Past Present and FuturePlanetary nebulae (PN) are among the most complex, varied and fascinating of celestial phenomena. They are important probes of nucleosynthesis processes, mass loss and Galactic abundance gradients and are responsible for a large fraction of the chemical enrichment of the interstellar medium, including the seeding of pre-biotic carbon. PN are also useful kinematical probes due to their rich emission line spectra that enables their detection to large distances. These scientific drivers and others motivate the search for and study of PN in our Galaxy, Magellanic Clouds and further afield.
In this review I briefly cover the legacy of the major Acker and Kohoutek PN compilations and the recent, significant progress in PN surveys, including the MASH and the IPHAS PN catalogues which have doubled Galactic PN numbers. I then discuss the prospects for future PN surveys in our Galaxy and the increasing role and importance that multi-wavelength data is playing in both the detection of PN and the elimination of PN mimics that have biased previous work. Current efforts and prospects for PN detections in external galaxies are also discussed due to their use in compiling the PN luminosity function where the constancy of the fit to bright end cut-off acts as a standard candle for the cosmic distance scale.
Hunting for Clues to Shaping Mechanisms in the Progenitors of Aspherical Planetary NebulaeCo-authors: Mark Morris, Carmen Sanchez Contreras, Mark Claussen
Pre-Planetary Nebulae are believed to represent a relatively short, intermediate evolutionary phase in the evolution of AGB stars to Planetary Nebulae (PNe). Our unbiased, high-resolution imaging surveys with HST of young PNe and PPNe have shown very strong morphological similarities between these classes. As a result, our morphological scheme for PPN classification has been easily extended to young PNe (with the preservation of virtually all of the primary and secondary descriptors, and the addition of a few new secondary ones).
These results show that the primary shaping of PNe begins before the PN phase. We have therefore been carrying out multiwavelength studies of PPNe and their progenitors (i.e., nascent PPNe or NPPNe) to search for clues to the physical mechanisms which are responsible for the shapes of PNe. This talk will focus on some important clues which we have uncovered so far. These include (i) potential signatures and probes of disks: Halpha emission with very broad wings and submillimeter excesses indicative of substantial masses of large dust grains, (ii) very massive collimated outflows and episodic jets (collimated jets can become active at the very late AGB phase, as shown by an HST imaging survey of a small sample of NPPNe), and (iii) far-ultraviolet excesses in AGB stars, resulting directly or indirectly from the presence of binary companions.
Proto-planetary Nebulae with the Spitzer Space TelescopeCo-author: Joe Hora
The transition from Asymptotic Giant Branch star to Planetary Nebula is short lived and mysterious. Though it lasts only a few thousand years, it is thought to be the time when the asymmetries observed in subsequent phases arise. However, there are very few that we have caught in the act; those that have been identified are shrouded in thick clouds of dust and molecular gas. Thus, infrared observations are needed to reveal these objects at their most pivotal moment. I present preliminary results of a Spitzer program on targets spanning the range from post-AGB stars to young Planetary Nebulae, with the goal of determining the genesis of asymmetry in these objects.
Imaging Planetary Nebulae with Herschel-PACS and SPIRECo-authors: M.J. Barlow, G.C. Van de Steene, K. Exter, M.A.T. Groenewegen, and the MESS consortium
In this presentation we will discuss the images of Planetary Nebulae that have recently been obtained with PACS and SPIRE on board the Herschel satellite. This will at least include results for NGC 6720 (the Ring nebula), NGC 650 (the little Dumbell nebula), and NGC 6543 (the Cat's Eye nebula). An outlook on future observations will also be included.
Symmetric and Asymmetric Circumstellar Dust Shells in Evolved Stars Revealed by AKARICo-authors: T. Ueta, I. Yamamura, Y. Nakada, N. Matsunaga, Y. Ita, M. Matsuura, H. Fukushi, H. Mito, T. Tanabe, T. Sorahana, O. Hashimoto
We present the results of far-infrared imaging observations toward 144 evolved stars to investigate their cold dust shells with the Far-Infrared Surveyor onboard the infrared astronomy satellite ``AKARI.'' Both circularly symmetric and asymmetric dust shells have been found for the sample, which consists of M-type, S-type, and carbon stars, planetary nebulae, and a few supergiants. We also present detailed analysis of a circularly symmetric, detached dust shell of the carbon star U Hya and discuss the origin of the detached shell.
Morphological Structures of Planetary NebulaeSince various structural components of planetary nebulae manifest themselves differently, a combination of optical, infrared, submm, and radio techniques is needed to derive a complete picture of planetary nebulae. The effects of projection and limited surface brightness sensitivity can also make the derivation of the true 3-D structure difficult. Using a number of examples, we show that bipolar and multipolar nebulae are much more common than usually inferred from morphological classifications of apparent structures of planetary nebulae. We put forward a new hypothesis that the bipolar and multipolar lobes of PN are not regions of high-density ejected matter, but the result of ionization and illumination. The visible bright regions are in fact volume of low densities (cleared by high-velocity outflows) where the UV photons are being channelled through. We suggest that multipolar nebulae with similar lobe sizes are not caused by simultaneous ejection of matter in several directions, but by leakage of UV photons into those directions.
A view of the solar neigbourhood: the local population of PN and their mimicsCo-author: Quentin A. Parker
We have, for the first time, compiled a reasonably complete, volume-limited census of PN out to 3.0 kpc from the Sun. Such samples are fundamental but unfortunately rare in astronomy. The ability to generate this census rests, in large part, on the application of our new, empirical H-alpha surface brightness radius (SB-r) relation which we have shown can provide distances accurate to 20-30$%$. Our technique is the only statistical method that is applicable to the very faintest PNe, which are selected against in radio surveys. Such PN numerically dominate any volume-limited sample, so it is crucial to include them in any statistically valid sampleu. We will use this census of >400 objects to answer some long-standing statistical questions regarding the overall population of Galactic disk PN and their central stars. Estimates of the local volume density and scale height also rest on having an accurate census of nearby PN. We have also refined a range of classification tools to weed out a range of mimics that have contaminated both Galactic and extragalactic PN catalogues in the past. However, evidence is increasing that the PN 'phenomenon' is heterogeneous, and PN-like nebulae are likely to be formed from multiple evolutionary scenarios. In particular, we look at the relationships between classical, close-binary, and H-deficient PNe, and between these nebulae and the strongly aximsymmetric outflows surrounding some symbiotic and B[e] stars.
Zinc Abundances in Planetary Nebulae: Tracers of their Parent PopulationsCo-authors: T.R. Geballe, N.C. Sterling
We searched for the 3.625 micron [Zn IV] fine-structure line in 21 planetary nebulae in the Milky Way and its satellite dwarf galaxies, and detected it in 14 objects. Our measurements were obtained with GNIRS on Gemini South, CGS 4 on UKIRT, and SpeX on the IRTF. The gas-phase abundance of Zn relative to H is an effective surrogate for elemental Fe/H, due to the relatively mild depletion of Zn compared to the often severe and uncertain depletion of Fe into dust in nebular environments. In two planetary nebulae in the Large Magellanic Cloud and the Sagittarius dwarf galaxy, Zn is found to be deficient by factors of 4 and 5 respectively relative to solar Zn/H; in addition, Zn is more deficient than O measured in the same nebulae. The Zn/H abundances of the Milky Way planetary nebulae in our sample range from essentially solar to about one-tenth solar. Several objects display Zn/H deficiencies of a factor of three or greater yet have nearly solar O/H. We suggest that these nebulae share the chemical abundance signature common to many metal-poor stars, such that O and other alpha species show elevated abundances relative to the Fe group elements. Our new approach of measuring Zn provides the first clear opportunity to assess the initial elemental Fe/H abundances of planetary nebula progenitor stars, offering new insight and constraints on their parent stellar populations.
Iron depletion onto dust grains in Galactic planetary nebulaeCo-author: M. Rodriguez
Although the progenitors of planetary nebulae (PNe), asymptotic giant branch (AGB) stars, are considered the most efficient source of circumstellar dust in the Galaxy, it remains unknown how much dust do PNe have and whether this dust is destroyed or modified during their lifetime. We study the dust present in a sample of 48 low-ionization Galactic PNe through the analysis of their iron depletion factor, the ratio between the expected abundance of iron and the one measured in the gas phase. The derived depletion factors are consistently high in all the objects, suggesting that more than 80% of their iron atoms are condensed into dust grains. However, the depletions cover a wide range, with a difference in the iron abundance of a factor of ~100 for the objects with the highest and lowest depletion factors. What is the reason behind this difference? We do not find any significant correlation between the derived iron abundances and parameters that can be related to the age of the PN, such as surface brightness or electron density. This suggests that no significant destruction of dust grains is taking place in these objects. Could the difference be related to the characteristics of the AGB progenitors? We explore this issue looking for a relation between iron abundance and morphological type, taking into account both the global morphology of the PNe and their small scale structures.
A new [OIII] Galactic Bulge Planetary Nebulae Luminosity FunctionCo-authors: Q. Parker, G. Jacoby
The Planetary Nebulae Luminosity Function (PNLF) describes the collective luminosity evolution for a given population of Planetary Nebulae (PNe). A major paradox in current PNLF studies is in explaining the observed strong constancy of the absolute magnitude of the brightest PNe regardless of galaxy type and age. The progenitor central-star mass required to produce such bright PNe should have evolved beyond the PNe phase in old, red elliptical galaxies whose stellar populations are ~10Gyr. The bulge of our Galaxy is predominantly old (Zoccali et al., 2003) and can therefore be used as a proxy for an elliptical galaxy but one whose broad PN population is resolvable and accessible to ground based telescopes and hence offering prospects for unraveling this conundrum. We have used the MOSAIC-II camera on the Blanco 4-m at CTIO, to carefully target ~80 square degrees of the Galactic Bulge and consequently establish accurate [OIII] fluxes for 85 % of Bulge PNe currently known from the Acker and MASH catalogues. Construction of the [OIII] Bulge PNLF has allowed us to investigate placement of PNe population sub-sets according to morphology and spectroscopy within the PNLF and most importantly, whether just one of these population sub-sets constitutes the bright-end of the LF. Our excellent, deep data also offers exciting prospects for significant new PNe discoveries.
A New Luminosity Function for Planetary Nebulaee in the Large Magellanic CloudCo-author: Q. Parker A deep AAO/UKST H-alpha multi-exposure stack of the LMC's central 25deg2 was used to uncover several thousand candidate emission line sources. Follow-up confirmatory spectroscopy by the 2dF and FLAMES multi-object spectroscopy systems on the AAT and ESO VLT led to the discovery of 460 new LMC PNe while independently recovering all 169 previously known PNe in the LMC’s central area. This work is now being extended to the outer regions of the LMC through access to the MCELS data where several thousand additional compact emission candidates have been found. Subsequent preliminary follow-up spectroscopy on the 2dF AAOmega system on the AAT has so far led to a further 100 new faint PNe being discovered from the first 56 deg2 of the outer LMC. Again all previously known PNe were independently recovered. A large fraction of these new LMC PNe are ≥3 times fainter than those previously known, tripling numbers accrued from all surveys over the last 80 years. We have been able to provide the most complete and accurate Planetary Nebula Luminosity Function (PNLF) across a whole galaxy ever assembled. This can be used to accurately predict the number of stars in the PN evolutionary stage in each luminosity bin compared to the luminosity and mass of the whole galaxy. This is not currently possible for any galaxy other than the LMC/SMC, as dust obscures too much of our own Galaxy and other galaxies are too distant to identify faint PNe. The well determined 50 kpc LMC distance, modest, 35 degree inclination angle and disk thickness ~500pc, mean that LMC PNe are effectively co-located. With low extinction, we can better estimate absolute line fluxes. Our new LMC PNLF, complete to 7 mag below the brightest, provides a unique probe into the LMC's chemical and dynamical evolution. The overall shape of the function depends on the central star mass and on the variation of the nebula optical depth with time. This makes the overall shape of the [OIII] PNLF an important diagnostic for galactic chemical evolution. In particular, the faint end of the function reflects core stellar evolution. We present and compare the [OIII] and H-beta PNLFs and show the implied implications for evolution, PN masses and dynamical time scales.
Symmetric vs. asymmetric planetary nebulae: morphology and chemical abundancesCo-author: R. D. D. Costa
Planetary nebulae (PN) are observed in a variety of morphological aspects, leading to several classification systems in the literature based on their observed shapes, especially using high resolution optical images. Most PN can be classified as round, elliptical, bipolar, and point-symmetric objects, although the exact attribution of a given type may be affected by the lack of adequate resolution or by projection effects. Generally, the observed morphologies can be attributed either to projection effects on a basic tridimensional structure, or to the effect of different physical processes such as binary evolution, rotation, magnetic fields, etc., on the origin and evolution of the nebulae. The second approach seems to be favoured by recent work both on galactic and extragalactic planetary nebulae, in view of some correlations between the observed shapes and some evolutionary properties of the nebulae and their progenitor stars. Among these correlations, those involving the observed chemical composition are particularly important, as theoretical models for intermediate mass stars predict important differences between nebulae ejected by low- or high mass stars, which may be detectable by the study of the nebular chemical composition. Some of these differences are indeed observed, so that they can be used in the investigation of the origin and evolution of the nebulae and their progenitor stars. In this work we analyse a large sample of galactic and Magellanic Cloud planetary nebulae based on their chemical composition and observed morphologies. A recent morphological classificatin system is adopted, and several elements are considered, namely He, C, N, O, S, Ne, and Ar in order to investigate the main correlations involving these elements and the different PN types. Special emphasis is given to the observed differences between symmetric (e.g. round or elliptical) nebulae and those that present some degree of asymmetry (e. g. bipolars or bipolar core objects). The results are then compared with previous findings on the relationship between the nebular chemical abundances and the considered morphological types.
Mass loss at the AGB and beyond and the asymmetry conundrumI guess that in this meeting we will all agree that one of the yet most intriguing aspects of stellar evolution is how stars like our Sun can lead to the formation of the most bizarre objects in space, the Planetary Nebulae (PNe). Our current understanding is that PNe should be the result of the (post-AGB) evolution of the circumstellar envelopes (CSEs) around red giant and super-giant stars, which in turn are the result of the heavy mass loss that these stars undergo while at the AGB.
The evolution of these nebulae/envelopes includes a drastic transformation both in shape and kinematics, from the simple spherical and radially expanding CSEs, to the full variety of forms and velocity fields displayed in the PN zoo. It is believed that this metamorphosis is due to a mechanism that either stars operating at the late AGB or early post-AGB phases, or, if present before, it does not reveals itself till these stages of the late stellar evolution.
To better study this transformation process and the mechanism behind, we must target nebulae around AGB stars, i.e., regular CSEs, or early post-AGB stars, the so called pre-Planetary Nebulae (pPNe). In either case, the central stars are still too much cool to ionize the nebulae around them, and so CSEs and pPNe mostly consist in molecular gas. Therefore, the composition, physics, structure and dynamics of these objects are best studied by means molecular spectroscopy, which can provide high spatial (sub-arcsecond) and spectral (better than 1 km/s) resolution images of these objects.
These observations reveal that, although inhomogeneities are present at small scales, envelopes around AGB stars are in general quite spherically symmetric at larger scales. Quasi-periodic variations in the mass loss rate are also detected, but yet preserving the overall roundish shape of these envelopes. This may not be case of semirregular variables and symbiotic systems, were a significant prevalence of aspherical structures is being detected.
On the contrary, pPNe appear as much bizarre as PNe, displaying a large variety of shapes and kinematics: self-similar structures in which the expansion velocity is proportional to the distance to central stars, hour-glass structures, Keplerian rotating disks, jets working its way out inside fossil CSEs, multipolar winds, etc. In summary, from the point of view of the molecular line observations, the enigma is still there.
Structure and shaping processes within the extended atmosphere of AGB starsCo-authors: D. Boboltz, I. Karovicova, K. Ohnaka, M. Scholz
We present recent studies using the near-infrared instrument AMBER of the VLT Interferometer (VLTI) to investigate the structure and shaping processes of the extended atmosphere of AGB stars.Spectrally resolved near-infrared AMBER observations of the Mira variable S Ori have revealed wavelength-dependent apparent angular sizes. These data were successfully compared to dynamic model atmospheres, which predict wavelength-dependent radii because of geometrically extended molecular layers. Most recently, AMBER closure phase measurements of several AGB stars have also revealed wavelength-dependent deviations from 0/180 deg., indicating asymmetric morphologies. The variation of closure phase with wavelength might indicate a complex non-spherical stratification of the extended atmosphere, and may reveal whether observed asymmetries are located near the photosphere or in the outer molecular layers.Concurrent observations of SiO masers located within the extended molecular layers provide us with additional information on the morphology, conditions, and kinematics of this shell. These observations promise to provide us with new important insights into the shaping processes at work during the AGB phase. With improved imaging capabilites at the VLTI, we expect to extend the successful story of imaging studies of planetary nebulae to the photosphere and extended outer atmosphere of AGB stars.
Unfolding properties of mass loss at the tip of the Asymptotic Giant BranchPlanetary nebulae (PNe) form in the remains of the final mass-loss stages on the preceding asymptotic giant branch (AGB). In order to understand the formation and evolution of PNe it is important to use a proper description of the AGB wind. I will present our unique approach of measuring the mass-loss evolution of the AGB wind using observations of weak halos of PNe, both densities and kinematics can hereby be measured. In comparison to more commonly used methods we measure the gas directly, avoiding the need for supplementary models. I will also present our approach towards a more extended study - more observations are needed in order to more precisely predict physical properties of this decisive stage of stellar evolution.
Unexplained AGB asymmetriesCo-authors: I. Bains, M. Szymczak, J. A. Yates
Maps of water and hydroxyl masers in the winds of AGB stars reveal subtle asymmetries. Multi-epoch observations show that most circumstellar envelopes supporting bright masers are close to spherical but with uneven filling. The dominant wind direction is radial and there is no significant rotation or other signs of companions at a velocity resolution <=0.2 km/s. The stars do appear to posess dynamically significant magnetic fields but the origin of these is not fully understood. Future observations will test the suggestions from current data, that clumping scales and asymmetries are determined at the origin of mass loss, from the stellar surface itself.
The magnetic field of the evolved star W43ACo-authors: W. Vlemmings, H.J. van Langevelde
The majority of the observed planetary nebulae exhibit elliptical or bipolar structures. Recent observations have shown that asymmetries already start during the last stages of the AGB phase. Theoretical modeling has indicated that magnetically collimated jets may be responsible for the formation of the non-spherical planetary nebulae. Direct measurement of the magnetic field of evolved stars is possible using polarization observations of different maser species occurring in the circumstellar envelopes around these stars. The aim of this project is to measure the Zeeman splitting caused by the magnetic field in the OH and H2O maser regions occurring in the circumstellar envelope and bipolar outflow of the evolved star W43A. We compare the magnetic field obtained in the OH maser region with that measured in the H2O maser jet. We used the UK Multi-Element Radio Linked Interferometer Network (MERLIN) to observe the polarization of the OH masers in the circumstellar envelope of W43A. Additionally, we used the Green Bank Telescope (GBT) observations to measure the magnetic field strength obtained previously in the H2O maser jet. We report a measured magnetic field of approximately 100 micro-gauss in the OH maser region of the circumstellar envelope around W43A. The GBT observations reveal a magnetic field strength B|| of ~30 mG changing sign across the H2O masers at the tip of the red-shifted lobe of the bipolar outflow. We also find that the OH maser shell shows no sign of non-spherical expansion and likely has an expansion velocity that is typical for the shells of regular OH/IR stars. The GBT observations confirm that the magnetic field collimates the H2O maser jet, while the OH maser observations show that a strong large scale magnetic field is present in the envelope surrounding the W43A central star. The magnetic field in the OH maser envelope is consistent with that extrapolated from the H2O measurements, confirming that magnetic fields play an important role in the entire circumstellar environment of W43A.
Morphology of Planetary Nebulae with Water Maser EmissionCo-authors: Y. Gomez, H. Imai. J.M. Torrelles, G. Anglada, N. Patel
In order to better understand the formation of asymmetric structures in planetary nebula, we have studied two of the three planetary nebulae that are known to harbor water maser emission: K3-35, IRAS 17347-3139. These objects show a clear bipolar morphology with a narrow waist; the water maser emission arises from the central region and in the case of K 3-35 it is also found located at the surprisingly large distance of ~4000 AU from the central star (near the tips of the bipolar lobes). Several mechanism have been proposed to explain the bipolar morphology of PNe; in the case of K3-35 we believe that we may be observing some of them at the same time: i) a disk-like structure traced by the H2O masers, ii) a precessing bipolar jet probably due to the presence of a binary companion and iii) circular polarization in the OH 1665 MHz masers, which suggests the presence of a magnetic field. A detailed modeling of all these observational results might shed light on the formation of asymmetrical structures in planetary nebula. On the other hand, we also present the first high angular images of the ionized gas (in radio continuum at lambda=3.6, 1.3 and 0.7 cm) of IRAS 17347-3139. The results support the presence of a collimated wind which might be shaping the bipolar lobes. Additionally, the 0.7 cm images show an equatorial structure that has been interpreted as a high density ionized torus in which the water maser emission would be arising.
Magnetic fields around AGB, post-AGB and (P-)PNeI will review the current observational evidence for strong magnetic fields throughout the envelopes of evolved stars. Specifically, the role of high resolution maser polarization observations and dust/line polarization in the submm regime will be addressed. While current observations are limited in sample size, strong magnetic fields appear ubiquitous at all stages of (post-)AGB evolution. Recent observations also give strong support to a field structure that is maintained from close to the star to several thousands of AU distance. While its origin is still unlear, the magnetic field is thus a strong candidate for shaping the stellar outflows on the path to the planetary nebula phase and might even play a role in determining the stellar mass-loss.
Dust in AGB stars, post-AGB and planetary nebulaeMass loss from AGB stars is important for stellar evolution during AGB, post-AGB and planetary nebula phase. In addition, gas and dust ejected from these stars contribute to chemical evolution of galaxies. To investigate the quantity of mass loss from stars, as well as to investigate the properties of dust, we have made systematic spectral and photometric surveys of these stars in the Large Magellanic Cloud (LMC). We found AGB stars are indeed important dust ejecting sources in the LMC. Dust grains appear to be processed as the stars evolve from AGB to PN phase. It is not clear if morphology of stars affects on chemical processes in these stars. It is previously known that crystalline silicates in oxygen-rich stars have been more frequently detected in PNe with disks; otherwise, no systematic difference found in dust properties and morphology.
A VISIR/VLT imaging survey of post-AGB starsCo-authors: T. Verhoelst , D. Mekarnia, A.A. Zijlstra, O. Suarez, O. Chesneau, R. Szczerba, H. Van Winckel, Ph. Benjoya
We will present the results from first large mid-infrared imaging survey of post-AGB stars envelopes using a 8m class telescope. We observed ~90 post-AGB stars using VISIR on the VLT. The observations were obtained under excellent conditions, leading to the obtention of multi-wavelengths diffraction-limited images with a resolution of 0.3 arcsecond. Our sample contains all the post-AGB stars brighter than 10 Jansky at 10 microns observable with the VLT and also includes some R CBr stars, water fountain sources, RV Tau stars, close AGB stars and Red Supergiants. About half of the sources are resolved, some for the first time. The images reveal a wealth of different structures, such as discs, jets (some precessing), torii, discs and detashed shells. The mid-infrared wavelength range is sensitive to direct dust emission from the envelope. This allows us to study the physical properties (size, mass...) of these different observed structures and their role in the shaping process. This survey will bring a new view on the mophological classification of post-AGB envelopes and be complementary to the surveys done in the optical and near-infrared (and thus sensitive to scattered light).
Point-Symmetric Planetary Nebulae: a wide visionCo-authors: Roberto Vazquez, Maria Eugenia Contreras, Lorenzo Olguin, Paco Guillen
Morphological classification is a very important path in the initial stages of the study of many disciplines. In astronomy, and particularly in the case of Planetary Nebulae (PNe) it is important that this classification evolves to become a way that allows us to infer physical parameters, evolution tracks, common origin or some other understanding of the nature of the object of study. In many descriptive catalogues Point symmetric Planetary Nebulae (Ps-PNe) are thought to be a proper class in the wide range of morphologies displayed by PNe. They are generally characterized by an S-shaped structure with the central star being the point of reflection and collimated pairs of knots/blobs tracing, apparently, the occurrence of different mass loss episodes. Our group intends to better explain the characteristics of those objects which make them so specific from the other morphological classes and identify a (possible) common origin for their formation. Also, we present a global cross-analysis of a group of Ps-PNe as well as a more detailed physical and kinematical study of three objects as examples (NGC 6309, NGC 7354, and Pe 1-17). The combination of narrow band imaging, high and low resolution spectroscopy and modelling (using the morpho-kinematic tool Shape) is giving new insights in the understanding of those somehow complex structures.
Properties of post-AGB objects as inferred from the 2nd release of the Torun catalogueThe Torun catalogue of Galactic post-AGB and related objects is an evolving catalogue containing astrometric, photometric and spectroscopic data for all know post-AGB objects and candidates in our Galaxy. The second release of our catalogue includes a significant number of new objects and all available HST images. It also opens access to the part of catalogue containing the possible post-AGB objects (objects which nature has not yet been sufficiently confirmed).
During may talk I will address 3 topics:
1) Post-AGB objects with M-type central stars as a precursors of post-AGBs with circumstellar arcs;
2) A correlation between spectral energy distribution of post-AGB objects, their HST images and binarity;
3) Properties of post-AGB objects with determined shapes of their VLT images.
195-670um spectra of post-AGB objects and planetary nebulae obtained with the Herschel-SPIRE spectrometerCo-author: R. Wesson, J. Cernicharo, M. Matsuura, and the Herschel MESS Consortium team
As part of the Herschel SPIRE instrument's Guaranteed Time programme, high signal to noise spectra have been obtained with the SPIRE Fourier Transform Spectrometer of a number of carbon-rich and oxygen-rich post-AGB objects and planetary nebulae. The spectra have a resolving power that ranges from 350 at 650um to 1150 at 200um and reveal a host of emission lines attributable to a wide range of molecular species. Targets that have been observed include AFGL 2688, AFGL 618, NGC 7027, HD 161796, AFGL 4106 and NGC 6302. Their spectra will be presented, together with abundances and physical conditions that have been derived from the spectra.
Models of Planetary Nebulae EvolutionIn this talk I review various models that have been proposed for the shaping of planetary nebulae. In particular I focus on the ways these models refer back to processes involving the evolution of the central source. Particular emphasis will paid to the role of magnetic fields, binary companions and ionizing radiation.
Large Scale Asymmetries in PNeCo-author: Arturo Manchado, Guillermo Garcia-Segura
We relate the origin of second-order asymmetries in Planetary Nebulae (PNe), those arising from the interaction of the evolving star with the Interstellar Medium (ISM), to the properties of their environment. The proper motion of the star has been shown to be responsible for the formation of bow-shocks structures in PNe, and this star-ISM interaction process can be traced back to the Asymptotic Giant Branch phase with the formation of cometary tails. We have systematically explored the impact that the star´s motion through the ISM has on the formation and evolution of the PNe progenitors. Models for a range of relative velocities and ISM conditions expected for low-and intermediate mass progenitor stars evolving in the Galaxy will be presented and compared with observed objects that show morphological features of interaction with the ISM. We will present the observed spatial distribution of this sample within the Galaxy, their radial velocity dispersion, Galactic height distribution and the nebular properties. We show how the observed properties compared with the models of the interaction.
Lumps and bumps: mapping molecular shocks in clumpy post-AGB outflowsCo-author: K.P. Forde Shock-excited molecular hydrogen traces the interaction between the faster winds blowing during the post-AGB phase and the earlier slower moving AGB envelope. H2 emission has been detected in several highly asymmetrical post-AGB objects and provides a tool to investigate this phase during which the AGB material is being excavated and sculpted as a planetary nebula forms. We have used integral field spectroscopy to map the distribution, excitation and kinematics of H2 on spatial scales down to the 2-micron diffraction limit of the VLT and over a range of stellar spectral types from M to B. We present some of these results, finding evidence for excitation in curved shocks, such as bow shocks, where the outflow interacts with clumpy material. We see further cases of objects with equatorial H2 emission, similar to that in the Egg Nebula. We also show how, in at least one object, the presence of CO bandheads in emission can be used to probe into the central obscured regions close to the star and infer that mass-loss is ongoing.
Fast, gusty winds blowing from the core of the pre-planetary nebula M2-56Co-author: C. Cortijo-Ferrero, L.F. Miranda, A. Castro-Carrizo, V. Bujarrabal
In contrast to envelopes around Asymptotic Giant Branch (AGB) stars, which are in general spherical and expand slowly, planetary and pre-planetary nebulae (PNe, pPNe) present clear departures from sphericity as well as collimated, fast winds. To date, post-AGB winds remain very poorly characterized by direct observations and, indeed, the process (or processes) that triggers and drives post-AGB jet-like winds is still a mystery. I will present results from a recent study based on ground-based spectroscopy and imaging (ground-based and with HST) that reveal M2-56 as a unique, key object that makes possible for the first time witnessing the current, variable post-AGB wind activity at its core and tracking the rapid evolution of the circumstellar material shocked by short-lived, post-AGB mass ejections. Some of the stunning results from our work include the discovery of: 1) proper motions and other structural changes in the fast, shocked-lobes, 2) an intense burst of Halpha emission from the core (within 0.5 arcsec) that had vanished in less than 3 years, which we interpret as an indication of a sudden, bipolar mass ejection at high velocity (500 km/s), 3) an emerging, central HII region with expansion velocities of up to 1200 km/s, 4) an equatorial flow with a linear velocity gradient that suggests simultaneous bipolar and equatorial mass ejections, etc. The data presented here unveil the complex post-AGB mass-loss history of this object, whose rapid evolution is driven by multiple episodes of mass outflow, not regularly spaced in time, leading to different nebular components. The successive multiple post-AGB winds in M2-56 are characterized by ejection speeds increasing with time. In contrast, the mass-loss rate and linear momentum show a time decreasing trend.
3-D Study of the Glowing Eye Nebula, NGC 6751Co-authors: Ma. T. Garcia-Dimaz, J. A. Lispez, W. G. Steffen, M. G Richer
In this talk I present a detailed, multiwavelength spectral and image analysis of the complex planetary nebula, NGC 6751. This PN consists of multiply shells and a bipolar outflow. Using the Manchester Echelle Spectrometer (MES) at San Pedro Martir Observatory in Baja California, we acquired optical, high spectral resolution, longslit observations across this nebula, with particular focus on the highly structured inner region near the out flowing jets. Inserting the observed profiles into the interactive program SHAPE, we were able to derive the 3-D morpho-kinematic model of the nebula that closely resembles the observed profiles and image of NGC 6751. The inner region consists of a filamentary bubble surrounded by a clumpy ring. The ring is tilted with-respect-to the line-of-sight and is encircled by a disk-like structure. Emanating from the central regions are two, point-symmetric jets which flow into two lobes seen in a ground based, Gemini image. Farther out are a faint inner halo and a fragmented outer halo. This nebula lies in the galactic plane and appears to be moving through a gas-rich environment. Deep, ground-based images indicate a veil-like structure to the NE, which is most likely nearby ISM. Our spectra indicate a large velocity difference between this gas and NGC 6751, confirming that this structure is indeed ISM material.
Modelling the H2 Infrared Emission of Cometary Knotsco-athors: Albert Zijlstra, Mikako Matsuura, Ruth Gruenwald, Rafael Kimura
The comparison between images of the ionized gas and the H2 emission of planetary nebulae (PNe) shows that at least part of the molecular emission is produced inside the ionized region. Most or all of such emission is produced inside cometary knots. Cometary knots are comet-shaped structures observed inside the ionized region of several PNe. They are believed to be clumps of dense neutral gas. Most of the H2 emission of the cometary knots seems to be produced in a thin layer between the ionized diffuse gas and the neutral material of the knot. This is probably a mini photodissociation region (PDR). However, PDR models published so far cannot fully explain all the characteristics of the H2 emission of the knots. In this work, we use the photoionisation code Aangaba to study the H2 emission of cometary knots, particularly that produced in the H+/H0 interface of the knot, where most of the H2 emission seems to be produced. Our results show that the production of molecular hydrogen in such region may explain several characteristics of the observed emission, particularly the high excitation temperature of the H2 infrared lines.
Stellar evolution from the main sequence to the post-AGB phaseI will briefly review the evolution of (single) low and intermediate-mass stars from the main sequence to the post-AGB phase. These stars evolve through core H and He-burning before entering the asymptotic giant branch (AGB) phase. During the AGB, recurrent mixing events may occur that can significantly change the composition of the envelope, with enrichments in carbon, nitrogen and heavy elements synthesized by the slow neutron capture process observed. The details of dredge-up are still not well understood but likely depend on mass, metallicity, and evolutionary state. The AGB phase is terminated once mass loss has eroded the envelope and envelope ejection occurs. The brief post-AGB phase is characterized by stars evolving at near constant luminosity toward higher effective temperatures. If the ejected envelopes have sufficient time to become ionized by the hot central stars then it will be observed as a PN. I will review current evolutionary models and discuss uncertainties in the stellar modelling of the AGB and post-AGB phase.
New Atomic Data for Determining Neutron-Capture Element Abundances in Planetary NebulaeCo-authors: Michael C. Witthoeft, Alejandro Aguilar, David A. Esteves, Brendan M. McLaughlin, Connor P. Ballance, A. L. D. Kilcoyne, Ronald A. Phaneuf, Rene C. Bilodau, P. H. Norrington
The detection of neutron(n)-capture elements (atomic number Z>30) in the spectra of a large number of Galactic PNe has enabled investigations of s-process enrichments in these objects. These studies can reveal important details of nucleosynthesis and evolution during the AGB phase of PN progenitor stars. However, since only one or two ions of a given n-capture element can generally be detected in individual PNe, abundance determinations require corrections for unobserved ions. Such corrections rely on the availability of atomic data for processes that govern the ionization structure of a PN (e.g., photoionization cross-sections and rate coefficients for various recombination processes). Until recently, these data were unknown for virtually all n-capture element ions. For the first five ions of Se, Kr, and Xe -- the -- -- three most widely detected n-capture -- -- elements in PNe -- we have calculated the electronic structure, photoionization cross-sections, and radiative and dielectronic recombination rate coefficients using a multi-configuration Breit-Pauli atomic structure code. Charge transfer rate coefficients have been determined for Se, Kr, and Xe ions with a multichannel Landau-Zener code. To calibrate our computational results, we have measured experimental absolute photoionization cross-sections of several Se and Xe ions. These atomic data can be incorporated into photoionization codes, which we will use to derive analytical ionization corrections (and hence abundances) for Se, Kr, and Xe in PNe. Using Monte Carlo simulations, we will investigate the effects of atomic data uncertainties on the derived abundances of these elements, thereby illuminating the ionic systems and atomic processes that require further analysis. These results are critical for honing nebular spectroscopy into a more effective and reliable tool for investigating s-process enrichments in AGB stars, and the role of PNe in the chemical evolution of trans-iron elements.
The connection between sequence D and sequence E red giant variables and asymmetric planetary nebulaeCo-author: P. Wood
Stars showing Long Secondary Periods, known as sequence D variables, make up about 30% of all luminous AGB variables. This is similar to the fraction of planetary nebulae that are known to be asymmetric. One of the models for sequence D variables is that they are binaries; a favourite explanation for asymmetric planetary nebulae. However, recent observations of the sequence D stars rule out binarity as an explanation. If there is a connection between sequence D variables and asymmetric planetary nebulae, it is not due to binarity. Sequence E variables are ellipsoidal red giant binaries, in which a red giant is distorted by its unseen orbiting companion. We have used the observed frequency of sequence E binaries relative to non-variable red giants to estimate the fraction of low mass stars in the LMC that terminate their red giant evolution by a common envelope event, potentially producing an asymmetric planetary nebula.
The Evolutionary History of the R Coronae Borealis StarsThe R Coronae Borealis (RCB) stars are rare hydrogen-deficient carbon-rich supergiants, all apparently single stars which are consistent with being post-AGB stars. RCB stars undergo massive declines of up to 8 mag due to the formation of carbon dust at irregular intervals. The mechanism of dust formation around RCB stars is not well understood but the dust is thought to form in or near the atmosphere of the stars. Their rarity may stem from the fact that they are in an extremely rapid phase of the evolution or in an evolutionary phase that most stars do not undergo. Several evolutionary scenarios have been suggested to account for the RCB stars including, a merger of two white dwarfs (WDs), or a final helium shell flash in a PN central star. The large overabundance of 18O found in most of the RCB stars favors the WD merger scenario while the presence of Li in the atmospheres of five of the RCB stars favors the FF scenario. In particular, the measured isotopic abundances imply that many, if not most, RCB stars are produced by WD mergers, which may be the low-mass counterparts of the more massive mergers thought to produce type Ia supernovae. I will present recent visible and IR observations of various RCB stars obtained with HST, Spitzer and ground-based telescopes.
Wolf-Rayet Central Stars of Planetary NebulaeCo-authors: Quentin Parker, Orsola De Marco, David Frew
Over the past decade, the number of those central stars of planetary nebulae (CSPNe) known to exhibit the Wolf-Rayet (WR) phenomenon has grown substantially. Many of these new discoveries have resulted from the Macquarie/AAO/Strasbourg H-Alpha (MASH) PN survey. While WR CSPNe constitute a relatively rare stellar type (~10 % of CS), there are indications that the proportion of PNe harbouring them may increase as spectroscopy of more central stars is carried out. In this talk, I will discuss new [WR] discoveries by the MASH group, as well as potential insights into the environments that produce them and their evolutionary sequence.
UV Spectroscopy of the Central Star of the Planetary Nebula A43Co-authors: F. Friederich, T. Rauch, K. Werner, J.W. Kruk
About 25% of all post-AGB stars are hydrogen-deficient. The PG1159 stars belong into this group with a typical abundance pattern He:C:O = 33:50:17 (by mass). Only four of about 40 known PG1159 stars exhibit H in their spectra. The exciting star of the planetary nebula A43 is one of these so-called hybrid PG1159 stars. We present preliminary results of an on-going spectral analysis of it by means of NLTE model-atmosphere techniques based on UV spectra obtained with FUSE, HST/GHRS, and IUE as well as on optical observations.
Modeling ejecta of massive starsTo paraphrase an old adage, there are two certainties in the life of a massive star: death and mass-loss. However, the mass-loss 'tax' can come in myriad guises, from steady radiation-driven winds to episodic eruptive outbursts. The mass loss rarely conforms to the idealization of spherical symmetry; structuring is observed in ejecta on both large scales (e.g., disks, bipolar lobes, spirals) and small scales (e.g., clumps). In the preponderance of cases, the mechanisms underlying the structure involve one or more of stellar astrophysics' Four Horsemen of the Apocalypse: instabilities, rapid rotation, magnetic fields and binarity. In this review, I'll discuss the variety of approaches that are being used to model these complex phenomena, and highlight some of the recent successes in explaining the diverse morphologies of ejecta from massive stars.
Eta Carinae, the Most Brutal Binary BipolarEta Carinae, one of the most extreme and fascinating objects in our Galaxy, is a supermassive interacting binary at the centre of a bipolar nebula, expanding at about 500 km/s. Finding the mechanisms behind Eta's appearance and behaviour is the main goal of this investigation. The binary has a semimajor axis of 15.4 AU, a period of 5.54 years and an extremely large eccentricity: at least 0.7 and maybe as large as 0.9. This large value has a dramatic influence on the flow and shock patterns in and around the binary. I presume that the gaseous `skirt' surrounding Eta is an equatorial `excretion disk' formed by the interacting binary, that the bipolar `Homunculus' nebula above and below this plane is due to the collision between the material ejected in the 1840 `Giant Eruption' and the disk, and the `Little Homunculus' similarly in the smaller 1890 eruption. I have extensively explored the general types of flow pattern expected here, an am constructing specific models for quantitative comparison with this wonderful object, which many believe to be a key to understanding a variety of hitherto unexplained phenomena in and around massive stars, be they binary or single.
A New Class of Luminous Transients and their Connection to Planetary NebulaeRecent discoveries of transients in nearby galaxies are challenging our understanding of mass-loss in "low-mass" massive stars. I will present two supernova-like transients discovered in 2008 in the nearby galaxies NGC 6946 and NGC 300 for which we have identified the progenitors as dust-enshrouded stars in Spitzer images. This new class of dusty luminous transients has progenitors that are extremely rare compared to known stellar populations identified in the mid-infrared. I will discuss the implications of these findings in the context of "low-mass" massive stars (i.e., close to 8 Msun) and connect it to proto-planetary nebulae and electron-capture supernovae.
Models of jets in PNeSome of the theoretical ideas that have been developed for HH jets have direct applications to jets in PNe. An example of this is the theory of jets from variable sources. One of the main differences between PNe and HH jets is that the sources of asymmetric PNes are binary stars, and this binary nature is likely to have strong effects on the dynamics of the jets. We explore three of these effects:
- the jet from a compact star will propagate within the (possibly latitude-dependent) wind from a giant companion,
- the orbital motion of the jet source will introduce an extra component to the ejection velocity, inducing a spiral pattern in the path of the jet beam,
- as a result of the presence of the companion star, the accretion disk around the jet source is likely to precess, possibly also inducing a spiral pattern in the jet beam path.
We explore the above effects individually, and also the combination of an orbital motion plus a precession. Finally, we also explore the effects of an ejection velocity time-variability.
The Turbulent Destruction of Circumstellar CloudsCo-authors: Sam Falle, Tom Hartquist
The interaction of an astrophysical shock or shell with a cloud typically occurs at high Reynolds number, and in such cases will be highly turbulent. However, the formation of fully developed turbulence is usually prevented by the artificial viscosity inherent in hydrodynamical simulations. We study the nature of turbulent shock-cloud and shell-cloud interactions using a subgrid compressible k-epsilon turbulence model, and demonstrate a new mechanism for forming tails.
Physical conditions and excitation of FLIERsCo-authors: A.C. Raga, G. Mellema, A. Esquivel, P. Velázquez
A fraction of all PNe and PPNe show high velocity knots (Fast Low Ionization Emission Regions or FLIERs), with line ratios and radial velocities which differ signicantly from the surrounding nebular gas. The spectra of these features show evidence of shock excitation. However, the actual physical/dynamical configuration of FLIERs is not clear at all. We present the results of axisymmetric simulations of an initially spherical cloudlet, moving away from a photoionizing source. These simulations include a detailed calculation of both the transfer of ionizing radiation and the non-equilibrium ionization state of the gas. From these simulations, we predict the spectra of a bow-shock that is illuminated by an ionizing flux from the post-shock direction, which we compare with the observed properties of FLIERs.
Non-homologous expansion of planetary nebula shellsCo-authors: Maria Teresa Garcia, Jose Alberto Lopez, Francisco Tamayo
The state of the kinematic expansion of planetary nebulae shells provides information towards their evolutionary stage and the processes that have lead to their current structure. If the expansion of a nebula shell deviates systematically from a homologous expansion, it is likely that dynamical processes, rather than a ballistic expansion, are still at work. We present theoretical and observational evidence for non-homologous expansion of planetary nebula shells. The observational analysis is based on a sample of images and position-velocity diagrams of the San Pedro Martir Kinematic Catalog of Planetary Nebulae. 3D morpho-kinematic modeling of the kinematics several PNe shows additional evidence for the presence of non-homologous expansion of bipolar planetary nebula shells.
'Sphericalization' of mature PN by the effects of geometry-changing, magnetized and radiatively cooling stellar windsCo-authors: Frank Adam, De Marco Orsola, Balick Bruce, Blackman Eric, Kastner Joel H, Kaminski Erica
We present recent 2.5-MHD Eulerian-grid numerical simulations of radiatively cooling and magnetized interacting winds. Using MHD models of evolving stellar winds we investigate the flow dynamics and morphologies that result from a evolving central outflow whose velocity, mass loss rate, magnetic field strength and opening angle vary with time. Our goal is to investigate the long term evolution of PN morphologies. In particular we wish to address the observational issue that most pre-PN are bipolar but most older PN are elliptical. We do this by tracking increase in wind velocity, decrease in mass loss and episodic change in wind geometry from spherical (AGB) to collimated (PPN) and back to spherical again (PN). Our goal is to explain the "sphericalization" of mature PN even if they begin in PPN stage as bipolar jets.
Mira: it's a wonderful prospectCo-authors: A. A. Zijlstra, T. J. O'Brien, M. Seibert Since being named 'wonderful' in the 17th century for its peculiar brightness variability, Mira A has been the subject of extensive research and become the prototype for a whole class of 'Mira' variable stars. The primary star in a binary system, Mira A is reaching the end of its life and currently undergoing an extended period of enhanced mass-loss. Recent observations have revealed a surrounding arc-like structure and a stream of material stretching 12 light years away in opposition to the arc. In this talk, I will present our recent modelling of this cometary appearance as a bow shock with an accompanying tail of material ram-pressure-stripped from the head of the bow shock and predict the form of the PNe which Mira A will eventually produce, drawing parallels with the highly-evolved PNe Sh 2-68.
Observations of dusty tori and compact disksThe recent high angular resolution observations have shown that the transition between a globally symmetrical giant and a source surrounded by a spatially complex environment occur relatively early, as soon as the external layers of the stars are not anymore tightly bound to the core of the star. I will present many examples of high angular resolution observations that show the complexity of the late stages circumstellar environments, and how dusty torus and stratified disks are observed by means of high resolutions techniques, in the near and mid-IR. I shall discuss in particular the broad range of circumstances and time scales for which more or less bipolar nebulae together with disks are observed; Many examples will be provided covering some post-AGB disks, the dusty environment around born-again stars and recent novae, and disks encountered around more massive evolved sources.
Dusty discs in Galactic and extragalactic post-AGB binariesWe present our study on the discs around binary post-AGB stars, a class which may contain the progenitors of bipolar planetary nebulae. By combining a wide range in observational data and techniques, like photometry, interferometry, radial velocity monitoring and spectroscopy, we study in detail the binary nature of the central stars, as well as the geometry and mineralogy of their circumstellar environment. Thanks to the release of the Spitzer SAGE LMC survey, we also find a large sample of similar extragalactic evolved disc sources. We now have a sample of about 45 Galactic and 25 extragalactic sources for which we perform a full spectral fitting, using Spitzer high-resolution spectra, and a 2D disc modelling, using a passively irradiated flared disc with a puffed up inner rim. In this talk we present the results on the disc geometry and chemical composition, and look for possible similarities or differences between the Galactic and LMC disc sources.
Dusty discs around evolved stars observed at high angular resolutionCo-authors: A.Zijlstra, O.Chesneau, P.Tuthill
We present the discovery of dusty, edge-on discs around evolved stars at different evolutionary stages. Menzel 3, M2-9 and Sakurais Object were observed with MIDI on the Very Large Telescope Interferometer (VLTI) providing a resolution of ~0.01 arcsec in the mid-infrared. The first two objects contain disks composed of silicate dust, while the last contains a disc-like structure of carbonaceous material. The dusty discs are aligned with the minor axis of the bipolar nebulae (or a density enhancement on the round nebula for the last object) and their inner rim radii are less than 100AU. Characterising the dusty discs in the core of these nebulae and at different evolutionary stages, provides invaluable constraints on the processes that lead to these impressive nebulae. The properties of each disc have been explored with the means of radiative transfer modelling. We also present the first images of the cores of M2-9 and V Hya, observed in the near-infrared with Sparse Aperture Masking (SAM) on the Very Large Telescope.
A circumbinary dust disc in the making: the semi-detached evolved binary SS LeporisCo-authors: E. Van Aarle, B. Acke, and A. Jorissen
In the past few years, dusty discs have been observed around several evolved objects, especially around Post-AGB binaries, but also at the center of Planetary Nebulae. This lends support to the hypothesis that such circumbinary discs play a crucial role in the formation of multipolar (proto-)planetary nebulae. The formation of such discs could, according to theory, occur in different ways, among which a common envelope phase or wind accretion, when one component of a binary system ascends a giant branch. However, observational counterparts of these proposed evolutionary events are sparse, and in none of them, a dusty disc has been directly observed. We present a combined interferometric and spectroscopic analysis of the A+M binary SS Leporis, and show it to be forming a circumbinary dust disc through non-conservative mass transfer. We discuss a possible cause for the low detection rate of such systems so far.
IR Excess of Central Stars of Planetary NebulaeCo-authors: You-Hua Chu, Robert Gruendl, Kate Su, Orsola De Marco, Thomas Rauch, Kevin Volk
Inspired by the prevalance of WDs with mid-IR excesses being central stars of planetary nebulae (CSPNs), we have examined archival Spitzer IRAC and/or MIPS observations of 66 PNe and found IR excesses for six, and possibly more, CSPNs. Among these six, CSPN He 2-99 is WC star, which is commonly associated with circumstellar dust; CSPN NGC 2346 is a known binary with circumstellar dust; CSPNs NGC 2438, NGC 6804, NGC 6853, and NGC 7139 are not known to be binaries. We have obtained Spitzer IRS and Gemini NIRI and Michelle spectra of some of these CSPNs to detemine the nature of the IR emission. We have also obtained KPNO echelle obsevations to search for spectral features and variations arising from possible companions. We will report the results in this paper.
HERMES Survey of Binarity in Evolved starsCo-authors: H. Van Winckel, R. Oestensen, K. Exter, A. Jorissen, S. Van Eck, G. Van de Steene
One of the reasons that we are now already on the 5th version of the APN series, is that the impact of binarity on our global understanding of the late stellar evolution is still far from clear. Confirmed or suspected classes of evolved binaries are so prominent (and so poorly understood), that also our understanding of the final phases of single stars may very well be blurred. Indeed, a rich zoo of peculiar evolved objects are born from the interactions between the loosely bound envelope of a (super)giant, and the gravitational pull of a companion. One of the major shortcomings to binary evolution predictions and theoretical binary evolutionary channels in general, is that the many parameters involved are not well constrained by systematics. Here we report on our project to overcome this and bring the different classes of (suspected) evolved binaries into an, as yet undisclosed, evolutionary connection. Our spectrograph HERMES is a new optical echelle spectrograph mounted on the 1.2m Flemish telescope Mercator on La Palma. It was build by a consortium of Belgian Insitutes (KULeuven, ULB, Royal Observatory) with contributions from the Geneva Observatory and Landessternwarte Tautenburg. Our new spectrograph is a unique tool to study binary evolutionary channels and we use it continuously from May 2009 onwards to focus on the wide variety of distinct (suspected or proven) classes of binary stars with evolved components. By combining high S/N single observations with low S/N timeseries, we aim at quantifying the orbital and chemical characteristics of every distinct subgroup. The suspected orbital periods range from days (sdB stars, PNe) to years (post-AGB, Ba star family, J-type silicate stars etc.) so the sampling rate is tuned to the expected behavior. The ultimate goal of this long program is to connect the zoo of different objects into a sound evolutionary picture that would account for the chemical peculiarities and the dynamical constraints set by the orbital distribution and binarity rates. We will discuss our project, the unique capabilities of HERMES, and present the first results of our program.
Binary central stars of PNAre companions needed to shape non spherical PN? Theoretically the influence of a companion is still the only way to induce an axis of symmetry in the outflow from an AGB star. But theories are only good if they can be tested. We do not yet have an observational answer to this question, but several failed and successful (but partial) attempts have opened the way to more tests. I will review the progress that has been made towards and observational answer to the "binary hypothesis", in particular in the last 3 years, since the establishment of the under the PlaN-B coalition (which took place at the "Asymmetric PN IV" meeting, in July 2007).
The binary central stars of PNe with the shortest orbital periodCo-authors: P. Rodriguez-Gil, R. Corradi, B. Miszalski, D. Jones, M. Rubio-Dimez
Close binarity can play a significant role in the shaping of planetary nebulae (PNe) as the system evolves through the common-envelope phase. We will present the detection of the shortest orbital periods among PN binary central stars. These are Hen 2-428, a bipolar PN, and V458 Vul, a recent nova surrounded by a mildly bipolar planetary nebula. The properties of the central stars of these systems, of their nebulae, the formation scenarios, and their possible fate will be discussed.
Are Planetary Nebulae and Proto-Planetary Nebulae Shaped by a Binary? Results of Long-Term Radial Velocity and Light Curve Studies”Planetary nebulae (PNe) and proto-PNe (PPNe) commonly reveal a bipolar or ellipsoidal nebula. The current working hypothesis is that this axial symmetry is caused by a binary companion. To test this hypothesis, we are carrying out a long-term radial velocity study of seven bright PPNe. They each have spectral types of F-G with many sharp lines that allow good precision (< 1 km/s). Initial observations made in 1991-1995 have been combined with our current observations from 2007-2009, all made with the 1.2-m Coude telescope at the Dominion Astrophysical Observatory. In several cases, we have been able to include additional published radial velocities. All of the PPNe are found to vary within a full range of 10 km/s due to pulsation, with amplitudes of ~2.0 km/s and periods of 35-130 days. Similar pulsation periods are found from our complementary light curve studies, but these light curves show no evidence for binary interaction. Only one PPN, IRAS 22272+5435, shows evidence of additional velocity variation due to a long-period binary companion. The resulting limits on possible binary companions to these PPNe will be presented and the implications of these results for the binary model will be discussed. These observations are continuing. We recently initiated a near-infrared radial velocity study of three edge-on bipolar PPNe in which the central star is obscured in the visible but can be seen in the near-infrared. This research is funded in part by grants from the NSF.
Post-AGB stars in the LMC as tracers of (binary) stellar evolutionCo-authors: H. Van Winckel, T. Lloyd Evans, P. Wood, T. Ueta
The few known post-AGB objects in the Galaxy display very diverse observational characteristics. Despite the very detailed studies of many of them, there is no consensus on how the individual objects may be linked by evolutionary channels. In the Galaxy, it is shown that there is a clear correlation between binarity of the central star, and the presence of a stable circumbinary disc in the system. With poorly known distances and hence luminosities, it is, however, most difficult to interpret the results on the individual post-AGB stars in the broader theoretical context of (chemical) stellar evolution. In this contribution we will report on our project to overcome this problem by focusing on a large sample of post-AGB stars with known distances: those in the LMC. Via cross-correlation of the SPITZER SAGE catalogue with optical catalogues we selected a sample of 1500 LMC post-AGB candidates based on their - color index and estimated luminosity. We determined the fundamental properties of the central stars of 99 of these objects using low resolution optical spectra that we obtained at Siding Spring and SAAO. About half of the objects in our sample show an SED that is indicative of a disc rather than an expanding and cooling AGB remnant. Our final catalog of good candidate post-AGB stars will be presented and evaluated. We also will present the first results of our ongoing detailed study of the photospheric abundances of the LMC post-AGB stars.
The Physical Characteristics of Binary Central Stars of Planetary NebulaeA number of efforts are underway to detect close binary stars in planetary nebulae. The primary goal of these studies is to determine the binary fraction of central stars. The next stage is a detailed analysis of the binaries to determine physical parameters for the systems. These analyses can be combined with population synthesis models, common envelope evolution models, and observed properties of nebulae to further understand the impact of binarity on PN formation. I will summarize the current knowledge of close binary central star properties, what conclusions we can draw with the current data, some of the surprises encountered, and what may be accomplished in the future. Among the issues I will discuss are the relationships between these close binaries and double degenerates, SN Ia progenitors, and cataclysmic variables.
Variability of Central Stars of Planetary Nebulae in the ASAS surveyCo-authors: Albert A. Zijlstra, Krzysztof Gesicki
The All Sky Automated Survey (ASAS) survey monitors the brightness of the objects up to ~14 magnitude of the southern hemisphere. The collected data allows for analysis of the variability of bright central stars of the planetary nebulae. We present the first results of our research.
Symbiotic Stars as Testbeds for Binary Shaping MechanismsBinarity has been proposed as the root cause of bipolar structure in planetary nebulae (PNe). The nebulae around symbiotic stars can look like PNe, and they are known to contain binaries. The mechanisms by which symbiotic binaries generate asymmetric structure may thus be relevant for understanding the formation of asymmetric PNe. I will discuss four mechanisms by which bipolar structure appears to be generated in symbiotic stars: 1) accretion disks and jets; 2) gravitational focusing; 3) common envelope interactions; and 4) stellar rotation. Since PNe can also be thought of as very slow analogs of nova explosions, I will also briefly review current ideas about the generation of bipolar structure in novae.
Barium Stars RevisitedCo-author: Tijl Dermine, Ross Church, Lionel Siess
The barium stars are G/K giants which contain copious amounts of barium but are not evolved enough to have made it themselves. Instead they acquired their heavy metal from a now dead AGB companion star. Canonical theory of mass transfer and tidal circularization suggests that barium stars with periods less than about twenty years should have circular orbits. That they do not is a serious problem for our understanding of binary-star physics. We investigate by simulating populations of Ba stars and find that our models only match the observed eccentricities and periods if we introduce some exotic new physics, namely a stellar kick at the end of the AGB.
Tides and Tidal Engulfment: Two Populations of Companions Around White DwarfsThe presence of a close, low-mass companion is thought to play a substantial and perhaps necessary role in shaping post-Asymptotic Giant Branch and Planetary Nebula outflows. During post-main-sequence evolution, radial expansion of the primary star, accompanied by intense winds, can significantly alter the binary orbit via tidal dissipation and mass loss. To investigate this, we couple stellar evolution models (from the zero-age main-sequence through the end of the post-main sequence) to a tidal evolution code. The binary's fate is determined by the initial masses of the primary and the companion, the initial orbit (taken to be circular), and the Reimers mass-loss parameter. For a range of these parameters, we determine whether the orbit expands due to mass loss or decays due to tidal torques. Where a common envelope (CE) phase ensues, we estimate the final orbital separation based on the energy required to unbind the envelope. These calculations predict period gaps for planetary and brown dwarf companions to white dwarfs. The upper end of the gap is the shortest period at which a CE phase is avoided. The lower end is the longest period at which companions survive their CE phase. For binary systems with 1 Msun progenitors, we predict no Jupiter-mass companions with periods <~270 days. Once engulfed, Jupiter-mass companions do not survive a CE phase. For binary systems consisting of a 1 Msun progenitor with a companion 10 times the mass of Jupiter, we predict a period gap between ~0.1 and ~380 days. These results are consistent with both the detection of a ~50 MJ brown dwarf in a ~0.003 AU (~0.08 day) orbit around the white dwarf WD 0137-349 and the tentative detection of a ~2 MJ planet in a >~2.7 AU (>~4~year) orbit around the white dwarf GD66.
Mass Transfer in Mira-type BinariesCo-authors: Ph. Podsiadlowski
Mass transfer in detached, wind interacting binaries which consist of a Mira variable and a compact companion, is generally assumed to occur via Bondi-Hoyle-Littleton (BHL) accretion. However, the accretion rates and outflow geometries that result from this mass-transfer mechanism cannot adequately explain the observations of the nearest and best studied symbiotic binary, Mira. Thus, we propose a new mass-transfer mode for Mira-type binaries, which we call 'wind Roche-lobe overflow' (wind RLOF). Utilising 3D Smoothed Particle Hydrodynamic (SPH) simulations which incorporate a mass-loss prescription for the Mira, including dust formation, cooling and pulsation-induced shocks, and the accretion of wind material onto the companion star, we show that wind RLOF can occur if the wind acceleration zone (the dust forming regions in Miras) lies close to, or is a significant fraction of, the Roche-lobe radius. In this case, the slow wind material does not escape from the system, but rather fills the donor star's Roche lobe and flows onto the companion through the inner Lagrangian point, L1, similar to the case of standard Roche-lobe overflow. Importantly, we show that the circumstellar outflows which result from wind RLOF tend to be highly aspherical and strongly focused towards the binary orbital plane. Furthermore, the subsequent mass-transfer rates are at least an order of magnitude greater than the analogous BHL values. We discuss the implications of these results for the shaping of bipolar (proto)-planetary nebulae and other related systems e.g. the outflows of symbiotic binaries.
Asymmetry in Common Envelope EjectaWe have performed a parameter study of common envelope ejecta morphology using the smoothed particle hydrodynamics code Gadget2. Amongst other factors, we assess the effects of deposition energy, angular momentum and envelope structure on the final ejecta morphology. We explore the possibilities that this has for the formation of bipolar planetary nebulae.
What can novae tell us about planetary nebulaeThere are several similarities between the evolution of a nova outburst and of the subseqeuent remnant, and that of a PN. The way in which a nova eruption evolves may show us the evolution of a PN (or possibly a subset thereof) in fast forward. This talk will draw parallels between nova eruptions and PNe.
Exploring the Morphology of the Expanding Nebular Remnants of NovaeCo-authors: M. F. Bode, M. J. Darnley, U. Munari
I report studies of several novae which are known or suspected to be recurrent. I will discuss our early morpho-kinematical modelling of the evolution of the optical spectra taken after outburst for two recent novae. In addition, in the case of the known recurrent nova RS Ophiuchi, this is also coupled with HST imaging. Results suggest that remnant shaping happens very early in a nova outburst and the geometries of the nebular remnants are derived. Overall, these results emphasise the need for coordinated imaging and spectroscopy if we are to truly understand remnant shaping in these systems together with the wider implications for studies of shaping mechanisms in other astronomical objects.
Modelling of the 2006 outburst of the recurrent nova RS Ophiuchi: synthetic X-ray spectra and discrepancies between post-shock and X-ray temperaturesCo-authors: T.J. O'Brien, K.L. Page, M. Lloyd, M.F. Bode, A.P. Beardmore Following the Swift X-ray observations of the 2006 outburst of the recurrent nova RS Ophiuchi, we developed hydrodynamical models of mass ejection from which the forward shock velocities were used to estimate the ejecta mass and velocity. In order to further constrain our model parameters, we present here synthetic X-ray spectra from our hydrodynamical calculations which we compare directly to the Swift data. An extensive set of simulations was carried out to find a model which best fits the spectra up to 100 days after outburst. We find a good fit at high energies but require additional absorption to match the low energy emission. We estimate the ejecta mass to be in the range (2-5) 10-7 Msun and the ejection velocity to be greater than 6000 km s-1 (and probably closer to 10,000 km s-1). We also find that estimates of shock velocity derived from gas temperatures via standard model fits to the X-ray spectra are much lower than the true shock velocities.
Multiwavelength modeling the SED of stellar explosionsStellar explosions represent an important phase of the stellar evolution, during which a significant amount of particles and photons can be injected into the interstellar medium. Extreme conditions that develop during outbursts, can be derived from the energy distribution throughout the entire spectrum (SED). The spectrum of exploding objects consists of different components of radiation, whose contributions are a function of the outburst evolution. In my presentation I will introduce a method of disentangling the composite spectrum from the soft X-ray to radio wavelengths, observed during outbursts of selected objects. Particularly, I will demonstrate the multiwavelength modeling the SED for the outbursts of the recurrent symbiotic nova RS Oph, explosion of the classical nova V1974 Cyg, and for a Z And-type bursts produced by the classical symbiotic star AG Dra.
Prediction of Close Binarity based on Nebula MorphologyCo-authors: Romano Corradi, David Jones, Miguel Santander-Garcia, Pablo Rodriguez-Gil and Maria del Mar Rubio Diez
A thorough search of the OGLE-III microlensing project has more than doubled the total sample of PNe known to have close binary central stars. This larger sample of nearly 40 PNe has enabled close binary induced morphological trends to be revealed for the first time. Canonical bipolar nebulae, low-ionisation structures and polar outflows are all identified within the sample and are tentatively associated with binarity. We describe the first survey aimed towards predicting close binarity based on these features using the Mercator telescope. An overview of survey results will be presented including the discovery of the shortest known period and confirmation of binarity in newly found PNe with impressive jet systems.
The kinematics and morphology of planetary nebulae with close binary coresCo-authors: Ma. T. Garcia-Diaz, M.G. Richer, M. Lloyd, J. Meaburn
In this work we present the results of a kinematical survey of planetary nebulae with known or suspected close binary nuclei. The kinematic information is analyzed together with images for the sample nebula from different sources. The sample under study does not show a particular correlation with morphology, complex shapes or the presence of bipolar collimated outflows. Only the presence of thick equatorial structures (toroids) seem to dominate the sample.
Abell 41: nebular shaping by a binary central star?Co-authors: M. Lloyd, J.A. López, J. Meaburn, D.L. Mitchell, T.J. O'Brien, D. Pollacco, M.M. Rubio-Díez, M. Santander-García, N.M.H. Vaytet
We present the first detailed spatio-kinematical analysis of the planetary nebula Abell 41, which is known to contain the well-studied, close-binary system MT Ser. Current evolutionary theories predict that if the binary has influenced the shaping of the nebula, its orbital plane should be aligned perpendicular to the nebular symmetry axis, as such this object represents an important test case. Detailed spatio-kinematic modelling of Abell 41 has been performed, based on deep narrow-band WHT-ACAM imagery and high resolution MES-SPM longslit spectroscopy. The best fitting model reveals the nebula to have a bipolar hourglass-like structure, with a symmetry axis which lies approximately perpendicular to the orbital plane of the central binary system. This provides strong evidence that the close-binary system, MT Ser, has directly affected the shaping of its nebula, Abell 41.
The Necklace planetary nebula: equatorial and polar outflows from a post-common-envelope systemCo-authors: B. Miszalski, M. Santander-García, P. Rodríguez-Gil
We present observations of a new planetary nebula discovered through the IPHAS Halpha survey of the Northern Galactic Plane. Its remarkable morphology, consisting of a bright equatorial ring, a faint pair of lobes, and low-ionization polar jet motivated us to further investigate the object through long-slit spectroscopy and photometric monitoring. These data allowed us to determine the kinematical, geometrical, physical and chemical properties of the nebula, and to detect a close binary central star displaying strong irradiation effects. The tight association between this distinctive morphology and binarity in PNe will be discussed.
Multi-Epoch Imaging Observations of CRL618Co-Authors: Thomas Gomez, Adam Frank, Javier Alcolea, Romano Corradi, Dejan Vinkovic
HST images of CRL618 from 1998, 2002, and 2009 show a surprising and highly non-uniform growth pattern in each of the "fingers" of shocked emission. Although the proper motions are all radial, many of the knots near the tips of the fingers appear to lurch forward, as if the working surface of the flow is encountering a highly nonuniform medium. The knots that are coincident with faint rings seen in deep images are highly variable. The structure of the apparent "wake" of the tips of the fingers also varies, perhaps the results of shear instabilities or turbulence.
The Expanded Very Large Array and Asymmetric Planetary NebulaeThe Expanded Very Large Array (EVLA) is beginning to come on-line, with early science observations begun in March 2010. In this talk, I'd like to describe and extol the characteristics of the EVLA as it pertains to the topic of the meeting. In doing this, I will also report on the how the science commissioning of the EVLA is progressing and how the commissioning effort is organized around what we call Open and Resident Shared Risk Observing. The ten times increase in continuum sensitivity of the EVLA over the VLA will enable many new, exciting observations on AGB stars, pre-planetary nebulae, and planetary nebulae. A few examples: the detection of many "radio photospheres" of AGB stars; deep observations for radio continuum emission from pre-planetary nebulae, which may come from either ionized gas (photo-ionization or shock ionization) or cold dust and large grain emission; imaging of the radio continuum of ionized gas in planetary nebula --- the EVLA will return us to the measurement of physical properties in planetary nebulae, but with a lot more sensitivity. Although the sensitivity of spectroscopy will not be improved by the EVLA over the VLA, many exciting projects will be opened up because of the large simultaneous bandwidths and many spectral channels of the EVLA, as compared with the VLA. Radio recombination lines in a given receiver band may be observed all at once and stacked to provide extra sensitivity (for example, six recombination lines would be available in the 2 - 4 GHz receiver, and all could be observed simultaneously). Spectral imaging surveys of molecular emission in AGB stars or pre-planetary nebulae will be accessible. If time permits,I will also talk about Very Long Baseline Array (VLBA) observations of water masers in the so-called "water-fountain" nebulae, and in particular about the interesting and important object IRAS16342-3814. New VLBA and VLA observations suggest that new masers have arisen at low velocities (as compared with the high blue- and red-shifted velocities) and the VLBA observations will be able to show us just where these masers have arisen with respect to the high velocities. A new episode of jet emission near the central source has perhaps begun.
Prospects for Asymmetric PNe with ALMAMillimeter and sub-millimeter observations have made fundamental contributions to our current understanding of the transition from AGB stars to white dwarfs. The approaching era of ALMA brings significantly enhanced observing capabilities at these wavelengths that promise to push back the frontiers in a number of ways. We examine the scientific prospects of this new era for PNe, with an emphasis on how developments may contribute to the goals of the asymmetric PNe community.
On the construction of a database to search for ICFs that account for asymmetrical nebulaeCo-authors: M. L. Leal-Ferreira, H. Monteiro In this contribution we study, through spectroscopic mapping, the physical and chemical parameters of the planetary nebula NGC 40. The spectroscopic mapping technique consists of interpolating the observed slit profiles to construct a two-dimensional map for a given emission line. The maps of NGC 40 have been constructed from 16 parallel longslit spectra obtained with NOT+ALFOSC. This technique has the advantage of allowing to investigate the spatial variations of each of the analyzed parameters (extinction coefficient, electron density and temperature and chemical abundances) throughout the nebulae. We, first, show that the flux measurements based on the spectroscopic mapping technique agree with the direct measurements from a single slit. We, then, obtained maps from 31 emission lines and the extinction, electron density and temperature and chemical abundances maps were derived from them. We, finally, found that the extinction, electron density and helium abundance maps show significant spatial variations. On the other hand, there is no variation in the electron temperature map. These results confirm the necessity of spatial resolution when studying the physical and chemical parameters of planetary nebulae (PNe), and show the potential of the technique for the analysis of other photoionized nebulae as well.
The study described above is part of a project aimed at revisiting the ionization-correction factors (ICFs) to account for asymmetrical nebulae. The present ICF -that represent the unseen ionization fractions of PNe optical spectra- were derived using 1D photoionization codes, under the assumption that all the PNe are spherical (e.g., Kingsburgh & Barlow 1994). In order to find a set of more reliable equations that can safely be applied to the case of asymmetrical PNe it is mandatory to revisit the ICF formulation. This procedure requires good quality spectra -to map the PNe by using multiple longslit (as in the case of NGC 40; Leal-Ferreira et al. 2010) and IFU (Monteiro et al. 2010) spectroscopy- as well detailed 3D modeling, for which we are using MOCASSIN (Ercolano et al. 2003). Putting together all the 3D model fitting data we are obtaining we will finally come up with a new set of ICFs with which to determine elemental abundances of N, O, Ne, S, Ar, and S of asymmetric nebulae.