The 41st Young European Radio Astronomers Conference
University of Manchester/Jodrell Bank Observatory, 18-20 July 2011
List of abstracts
Participant talk abstracts
[CII] in M33 major axis (HERM33ES)
We study the photoelectric heating as an approximation of the [CII]/TIR ratio, the correlation between [CII] and other data presented and use [CII] and CO(J=1-0) (calculated through CO (J=2-1)) to study the characteristics of photodissociation regions (PDRs) in the major axis of M33. In addition, we will continue a study from several authors (Stacey et al. 2010, Hailey-Dunsheath et al. 2010, Gracia-Carpio et al. 2011) who have represented galactic and extragalactic studies of [CII] and CO (J=1-0) trying to find common behaviors in different kinds of objects. This work will be followed by studies of specific M33 major axis regions in small-scale, using spectroscopic [CII] data obtained with Herschel/HIFI.
In this work we use ISO/LWS [CII] observations along M33 major axis to make a large-scale study of the PDR and the photoelectric heating in the regions observed. Supplementing these data, we also use data from HERM33ES Herschel Key Project from FIR continuum (Herschel SPIRE, PACS and Spitzer MIPS), CO(J=2-1) (IRAM 30m), HI (VLA) and Halpha (Burrel-Shmidt).
Radio Nebulae around Luminous Blue Variable Stars
Luminous Blue Variable stars (LBVs) are massive and unstable post-MS stars undergoing different phases of instability, characterized either by photometric and spectroscopic variability or by mass-loss episodes. As a consequence of the mass-loss phenomenon, LBVs show circumstellar ejection nebulae, traced by dust and/or gas emission. A systematic study of a sample of LBVs, based on the comparison between radio and IR observations, is ongoing. The aim of this study is deriving the mass-loss properties for a better understanding of the LBV phenomenon in the wider context of massive star evolution. Among the most interesting aspects of this study is the gas and dust distribution in the ejecta, revealing sometime symmetric or asymmetric environments, sometime single or multiple events associated with mass-loss during the LBV phase. We present our EVLA and ATCA radio observations of some LBV candidates, which provide us knowledge of the ionizing flux, the distribution and the physical conditions of the ionized gas.
AMI-LA radio continuum observations of low mass young stars
I will present 16 GHz observations of a sample of low-mass young stars. These sources are selected to match the target sample for the e-MERLIN legacy project on the morphology and time evolution of thermal jets associated with low mass young stars. I will draw correlations between the radio luminosity and a number of global properties for these systems, and use these correlations along with the spectral indices for these sources, to place limits on the physical mechanisms responsible for the radio emission.
Deep Radio Observations of the Subaru/XMM-Newton Deep Field
I will present deep radio observations of the Subaru/XMM-Newton Deep Field from the Very Large Array at 1.4 GHz. The central 0.7 square degrees of the map coincides with the UDS field, for which multi-wavelength data is available. The analysis of the radio population conducted using multi-wavelength data from optical, infrared and X-ray bands will be discussed here.
Compact HII regions toward Methanol Maser traced sources of Massive Star Formation
We present the results of 8.64-GHz radio continuum observations made during the Methanol MultiBeam (MMB) high resolution 6.7GHz methanol maser positioning campaign (conducted using Australia Telescope Compact Array (ATCA)). We categorise the 105 observed continuum sources as either Hyper-Compact, Ultra-Compact or Compact HII regions and attempt to remove distance ambiguity based on source size and emission measure estimates.
As both HII regions and the 6.7GHz methanol maser are both massive star formation tracers they have been used in proposed evolutionary tracer timelines (e.g Breen et al. 2010), we investigate whether there are any physical differences between closely associated maser-HII region pairs and those for which the separation would suggest they are associated with different protostellar objects.
Kinematics of the ionized stellar wind of the massive star MWC349A
Disks around massive stars seem to play a key role both in their formation process and in the supergiant B[e] evolutionary stage. Unveiling the characteristics of the system formed by the ionized stellar outflow and the disk is essential to understand both evolutionary stages. To this, we have studied the MWC349A star, prototype of massive star with a ionized outflow expanding at nearly constant velocity and whose evolutionary stage is under debate (pre-main sequence or supergiant B[e]). To date, it is along with Cepheus A HW2 the only known object with masers in recombination lines. A 3D radiative transfer model applied to the H30alpha line has allowed to constrain the stellar wind kinematics. The obtained result has been supported by the consistency of the predicted results of our model with the observations of the other observed recombination lines. It seems to indicate that the stellar wind is originated by the disk photo-evaporation, what means an essential step forward in the understanding of the mechanisms originating winds around massive stars.
Radio Emission from Massive Stars
I will report on two projects: The COBRaS E-Merlin survey of Cygnus OB2 and the BOSS search for bow shocks around massive stars.
The Cygnus OB2 association is a nearby (1.2-1.8 kpc) young (~2-3 Myr) massive star cluster, that is tremendously rich in massive stars with strong stellar winds. The region will be studied using e-MERLIN as part of the COBRaS (Cygnus OB2 Radio Survey) project. The COBRaS project will enable studies of this region in areas of 1) mass-loss from massive stars, 2) radio astrometry yielding information on cluster dynamics, 3) binarity and colliding stellar winds and 4) ongoing and triggered star formation.
The BOw Shock Survey (BOSS) is a multiwavelength search for bow shocks around massive stars. I will briefly discuss this project and present results with the VLA and GMRT on one particular object, which is a runaway star from Cyg OB2.
Radio spectra and morphology of Radio-Loud Broad Absorption Line Quasars
About 15% of the quasar population show broad absorption lines in their spectra generated from outflows with velocities up to 0.2 c. We selected a complete sample of Radio Loud Broad Absorption Line Quasars from the Sloan Digital Sky Survey, in order to study their spectral properties and orientation features at radio wavelengths. At the moment two models have been presented to explain these objects: an orientation model (Elvis 2000) and an evolutionary scenario (Becker et al. 2000). Results from our radio campaign will be presented, focusing on the spectral and morphological properties that can discriminate between the two models.
Radio characteristics of Broad Absorption Lines (BAL) quasars
Broad absorption lines (BALs), seen in a small fraction of both the radio-quiet and radio-loud quasar populations, are probably caused by the outflow of gas with high velocities and are part of the accretion process. The presence of BALs is the geometrical effect and/or it is connected with the quasar evolution. It has been believed that BALQSO occurs only among radio-quiet galaxies. However, in 2000 Becker et al. discovered the representative sample of radio-loud objects which exhibits broad absorption troughs. The radio morphologies of radio-loud BAL quasars provide important additional information about their orientation and the direction of the outflow.
Using the final release of FIRST survey combined with a A Catalog of BAL QSOs (SDSS/DR3), we have constructed a new sample of compact radio-loud BAL QSOs, which makes the majority of radio-loud BAL QSOs. The main goal of this project is to study the origin of BALs by analysis the BAL QSOs radio morphology, their orientation and jets evolution, using EVN at 1.6 GHz and VLBA at 5 and 8.4 GHz.
The Molecular Environments of Methanol Maser Sources
Methanol masers trace a very early phase in the formation of high mass stars. In this project observations of a range of molecular lines will be used to study the properties of the dense cores in which these stars are forming. With observations of over 200 sources, these data will also be used to investigate whether the properties of the cores vary with location in the Galaxy.
A JCMT HARP survey of molecular outflows associated with 6.7 GHz methanol masers
The 6.7 GHz methanol maser is a valuable tracer of early massive star formation and is a promising candidate with which to unravel the early stages in the formation of a high mass star. Despite this promise, the precise evolutionary phase traced by the maser is not yet clear. I will describe the preliminary results of a JCMT HARP survey for outflows associated with methanol masers, which is aimed at determining the number, frequency and dynamical lifetime of outflows associated with the masers. I will also discuss the application of new 3D methods of outflow identification to the HARP Galactic Plane Survey.
VLBI observations of spacecraft with EVN radio telescopes
PRIDE, the Planetary Radio Interferometry and Doppler Experiment initiative, focuses at enhancing the scientific return of prospective planetary missions by involving in the Earth-based segment of the missions a network of radio telescopes. PRIDE provides a direct characterisation of the planetary orbiters and surface elements (landers) signals by means of their Doppler and VLBI tracking. Such the tracking enables estimates of the spacecraft (S/C) state vectors which can be used for a variety of scientific applications. The experiment is beneficial to literally any planetary mission since PRIDE's requirements to the onboard instrumentation are minimal and are met on most planetary mission S/C irrespective to PRIDE.
In this work, we present some preliminary results of recent test VLBI observations of spacecraft carried out using the European VLBI Network (EVN) telescopes in the phase-referencing mode. Some peculiarities of such the observations are described, for a S/C being a near-field source when observing with an Earth-based VLBI array of telescopes. The results of a narrow-band signal processing of the S/C signal, as well as test broad-band processing using the new software correlator SFX at the Joint Institute for VLBI in Europe (JIVE) are also presented.
The interplanetary scintillation of the power scintillation sources in the decreasing phase near the minimum of solar activity cycle 23
The results of interplanetary scintillation observation of power scintillation sources 3C048 and 3C298 are presented, which were carried by the radio telescope LPA at the frequency of 111 MHz during the low solar activity. The radial dependences of scintillation index were obtained, which showed the impact of the low-latitude heliospheric current sheet. The solar wind speed was estimated via temporal scintillation spectra, and good agreement with values derived by diversity technique was showed.
WSRT and LOFAR observations of the Lockman Hole
One of the most debated issues about the sub-mJy radio sources, responsible for the steepening of the 1.4 GHz sources counts, is the origin of their radio emission. In order to shed light on the physical properties of sub-mJy sources an important role is played by multi-frequency radio observation: radio spectral indices may help to constrain the origin of the radio emission allowing to distinguish between self-absorbed AGN cores and optically thin synchrotron emission. With the aim of studying the physics properties and the spectral index of the faint radio population, I have analysed a WSRT data of the Lockman Hole. The Lockman Hole was observed with the WSRT at 1.4 GHz. The data reduction was performed by myself. The Lockman Hole was also observed with LOFAR at 58 MHz as part of the commissioning of the telescope. This is the first LOFAR observation of a deep field.
H2CO in the Horsehead nebula
Photodissociation region (PDR) models are used to understand the evolution of the far-UV illuminated matter both in our Galaxy and in external galaxies. The spectacular instrumental improvements, which happens in radioastronomy with the advent of Herschel, ALMA and NOEMA, call for matching progresses in PDR modeling. While it is now confirmed that some interstellar species are mostly formed in the gas phase (CO for instance) and others on grains (CH3OH, Garrod et al. 2007), the chemical routes for other species, like H2CO, are still debated because it is likely that solid and gas phase processes are both needed. The availability of well defined observations is essential here to discriminate between chemical assumptions about the important grain surface processes: adsorption, desorption and reactivity. Due to its closeness (~400 pc) and simple geometry, the Horsehead PDR is particularly well suited to investigate the grain surface chemistry.
We present observations of 7 transitions of formaldehyde (H2CO) toward two positions: the edge of the nebula exposed to the UV-field (PDR), and a colder region (cold core) shielded from the UV radiation. A non-LTE Montecarlo radiative transfer code is used to determine the H2CO abundance from the observed intensities and line profiles. We find that the H2CO abundance is very similar in the warm PDR and in the cold dense core. The inferred abundances are compared with PDR models, including both gas-phase and grain surface reactions, in order to study the dominant formation routes of H2CO. Pure gas-phase chemistry models fail to reproduce the observed H2CO abundance by a factor ~10 in the PDR, while surface grain chemistry increases the H2CO abundance up to 3 orders of magnitude in the PDR.
Planetary Nebuale Distances using the Radio Expansion Parallax Technique
The methods that use statistical techniques to measure the distance to planetary nebulae (PNe) can provide accuracies as good as 50% on average, but when they are applied to individual objects the errors can be as large as a factor of 2 or even more. This derives a very uncertain estimation of the galactic location and physical parameters of PNe.
One technique that has proven effective is the so-called expansion parallax method, which is based on the comparison of the angular expansion of the source on the plane of the sky, with the velocity expansion along the line of sight measured from the width of some appropriately chosen spectral lines. In principle, the angular expansion could be measured using any tracer, but the free-free radio emission from the ionised gas has been, by far, the most popular choice. I will present the results of applying this technique to the PNe M2-43, IC 418 and NGC 6881.
Determining broad-band spectra of radio galaxies with the EVLA
Determining the shape of the energy spectrum of an electron population producing synchrotron radiation can often give key insights into the underlying physics of a radio source. Poor sampling in frequency space has traditionally meant that distinguishing between various models that predict a particular electron energy spectrum has been hard to achieve. I will show how the capability of the upgraded EVLA to observe at widely spaced frequencies and broad bandwidths allows the problem of determining spectral shape to be overcome and will demonstrate the use of this new capability to test the validity of spectral ageing models in the lobes of FRII radio galaxies.
Radio maps for the REXCESS cluster sample
We present fluxes and radio maps for the REXCESS cluster sample. The REXCESS sample consists of 33 local (z<0.2) clusters drawn from the flux-limited REFLEX catalogue. It is the first time where this sample is completely mapped in the 610 MHz band. We chose this unique sample in order to fully sample the cluster luminosity function, unbiased from x-ray luminosities and cluster dynamical state. The data for these maps were collected by using the GMRT in Pune, India. After mapping the individual sources and determining the fluxes, the maps will be investigated to examine the different types of radio outburst and there influence on cluster heating. Additionally it will give information about the injection of energy by larger scale central radio emission.
Radio Observations of the massive star forming region G305
We have undertaken a multi wavelength study of the G305 star forming complex. This intense region of massive star formation is estimated to be forming > 30 O7 stars (Clark & Porter 2004). Numerous studies of small regions have been carried out, until recently studies of the entire complex have been hampered by the large degree scale. Recent improvements in instrumentation have allowed us to map the entire region in unprecedented detail in an attempt to unravel the star formation mechanisms and history. Here we present results of two sets of observations using the MOPRA radio telescope and the Australia Telescope Compact Array (ATCA) interferometer, to study the molecular and ionised environment of G305.
G305 is a giant HII complex at a distance of ~4 kpc and extending over 1.5 x 1 degrees it is one of the closest, largest and most intense regions of massive star formation in the galaxy. With multiple HII regions, IR hotspots, maser emission, and YSOs located around the periphery of the central HII region. These factors makes it an excellent laboratory in which to study massive star formation, and so we have undertaken a multi wavelength observational campaign designed to study the star formation across the G305 complex.
Here I will discuss the results of recent Mopra telescope 12 mm and ATCA 3 & 6 cm radio observations. Mopra 12 mm observations have uncovered several large ammonia (1,1), (2,2) and (3,3) clumps and numerous H2O masers within the region. We comment on the general properties of the molecular material and the relation to a variety of star formation tracers.
ATCA 3 & 6 cm observations were carried out using the newly commissioned CABB. The large degree scale size of G305 required us to perform one of the largest mosaics with the new CABB system to date. I will discuss the distribution and properties of the compact and diffuse emission, compare these observations to the molecular material and star formations tracers. I will present an almost complete census of UC HII regions in G305, measure the propagation of massive star formation into the surrounding molecular clouds, determine the properties of stellar sources with the central clusters and determine their energy input.
A Laboratory Test-bed for a Spectral and Spatial Interferometry
The astronomical community is showing a growing interest in the observation of sub-millimetre waves with high angular resolution (sub arc second) and sensitivity in both spatial and spectral domain. This is the so-called Spectral-Spatial Interferometry, multi-Fourier Transform Spectroscopy or Double Interferometry (Mariotti and Ridgway (1988); Ohta et al. (2006, 2007)). With increased spatial and spectral information, a number of interesting science cases can be investigated. For example, in the far infrared, this system could characterise gas, ice and dust in disks undergoing planetary formation, resolve the cosmic Infra Red Background, investigate the formation and evolution of AGN and trace Milky Way type galaxy formation, among others. Here a test-bed for spatial and spectral interferometry in the 5-30 cm−1 band is described, and first experimental results are presented. The performance of the test-bed is analyzed.
VLBI mapping of M15 - A proper motion analysis
The globular cluster M15 hosts two low-mass X-ray binaries (LMXB) and at least eight millisecond pulsars (MSP) detected via pulsed radio searches. Using multi-epoch 1.6 GHz VLBI observations at high spectral resolution, we detect the already known MSPs and perform a model independent proper motion analysis. Furthermore, we search for new radio sources being potential candidates for new LMXBs or MSPs in the vicinity of the core of M15. Combining the proper motion results of all sources under consideration we will be able to further constrain the central mass distribution in the cluster and, in case of high proper motions near the core, find further evidence for the central object being an intermediate mass black hole. I will present preliminary results from the first four of a total of six observation epochs.
Solar corona observations at decameter wavelengths
The antenna system UTR-2 (Ukrainian T-shaped radio telescope, Mark 2) of the Braude Radio Observatory (Kharkov, Ukraine) has been used to observe the radio emission from the quiet Sun in the frequency range 16.5-33 MHz. The monitoring of solar corona has been carried out during the summer-autumn of 2010. The investigations included the measurement of solar flux density and the determination of angular equatorial and polar diameters of solar corona from day to day. Moreover the heliograph capability of UTR-2 was applied too. Preliminary results are presented.
Luminosity and density evolution of extragalactic radio sources
The counting of radio sources is a strong tool for the investigation of evolution of extragalactic sources. Additional information can also be obtained from the "power-linear size" diagram (P-D), which is analogues to the Hertzsprung-Russell diagram. On it there is clear evidence for the existence of a "main sequence" and the "sequence of giants". The "main sequence" consists mostly of the FR I sources. The "sequence of giants" consists of radio loud compact sources and quasars, and FR II sources, which grow in giant radio galaxies. Such evolution can be described with a theory based on the idea of fast adiabatic expansion of the source's extended parts (cocoons) and the synchrotron radiation of particles in these structures. Fixing the bulk kinetic power delivered to the cocoons by the jets, it is possible to obtain P-D tracks for FR II sources.
In my work I have taken a sample of radio sources, constructed the P-D tracks, and divided all sources into two types: ones which belong to the "main consequence", and others to the "sequence of giants". As for the last sequence, it can be considered as an independent evolutionary track of some radio source classes. These defined samples I have used for the estimation of their independent and joint radio luminosity and density evolution, through which it is possible to obtain fruitful results.
High precision pulsar timing at Nançay
The Nançay radiotelescope is one of the largest decimetric instruments in Europe. We propose to present the pulsar observation programs dedicated to different studies, and in particular, that of gravitational wave detection through regular high-precision timing measurements.
HI-mass comparison of nearby galaxies (EBHIS and THINGS)
The Effelsberg-Bonn HI Survey (EBHIS) is aiming to map the neutral hydrogen of the full northern hemisphere (Dec > -5 deg). The spectrometers of the 100-m dish cover the Milky Way HI gas and in parallel the extragalactic sky out to a distance of 270 Mpc.
First correlation studies between EBHIS and The HI Nearby Galaxy Survey (THINGS) - performed with the Very Large Array (VLA) - disclose towards some of the galaxies of the studied ensemble a significant discrepancy in the derived HI mass. This discrepancy can be attributed entirely to the lack on information due to "missing spacings" of radio interferometers.
I will briefly present the EBHIS-data-reduction pipeline and motivate further work on the necessity for the combination of single dish and radio interferometric data in order to produce high-quality maps of the gas mass distribution.
Investigating the FR dichotomy through jet evolutionary tracks and environmental interactions
The extended lobes and jets of radio galaxies often exhibit clear evidence of interaction with the cluster environment. But the mechanism of this feedback process, and the effect it has on both the jet and host galaxy evolution remains unclear. I will review analytic models that describe self-similar jet evolution for the radio-loud FR classified sources and investigate the regimes where external environmental effects might become significant. Using the radio power-jet length (PD) diagram as a tool to track this evolution, I plot the luminosities and newly-measured linear sizes of 433 FR sources, cross-matched in the FIRST, NVSS, and SDSS catalogues. This large sample of sources displays the same FRII/FRI dichotomy seen in earlier PD diagrams based around the 3CRR sample. By closely investigating the morphologies of the sub-set of sources that lay close to the dividing line, we hope to find trends that suggest the nature of the dichotomy, and whether it is dominated by intrinsic or environmental effects.
Variability of methanol maser in the massive star formation regions
Star formation constitutes one of the basic problems of astrophysics due to the fact that stars are fundamental objects of astronomy. Shu et al. (1987) reviews the theory of low mass star formation from the molecular cloud via accretion disk-outflow. The formation of high mass stars is still not well understood. They may also be formed through accretion disk plus outflow (Shu et al. 1987) or by collision-coalescence which was proposed by Wolfire & Cassinelli (1987) and Bonnell et al. (1998), but most observations support the accretion disk-outflow model.
The brightest methanol masers occur at 6668 MHz and 12178 MHz and are found in the star forming regions containing very young massive protostars even before the formation of an ultra-compact HII region (Longmore et al. 2007). These masers serve as useful tools to study these regions.
This talk will be on the analysis of the time series of 6668 MHz and 12178 MHz methanol maser emission lines in some of the sources which were showing periodic variations in monitoring before the 26 meter Hartebeesthoek Radio Astronomy Observatory (HartRAO) Telescope bearing failure in 2008. After the telescope was repaired in 2010, the programme to monitor these sources was restarted. These two methanol emission lines are radiatively pumped which implies that their variability could be due to the decrease or increase in the seed photons at the radio frequency, or the infra-red radiation field that pumps the masers. Since there has been a two year gap in the monitoring program of these sources, we want to establish whether the periodic variations continue. Such periodic behaviour has not been seen in other maser species in star forming regions, so it can provide new insights into what is happening in these regions.
Determination of the inhomogeneity of the microwave background maps angular power spectrum
A new method for analyzing the inhomogeneity in the microwave background maps, based on the behaviour of the angular power spectrum is proposed. We represent the change in the variance of the power spectrum of the hemisphere background signal in the form of a new map, which characterises the homogeneity (heterogeneity) in the background to second order. We use this method of analysis of the WMAP signal for maps with a resolution L<100. As a result, we detected the asymmetry of the ILC signal connected with the eclipse coordinate system, and it is also observed for the signal channel data in WMAP.
The High Time Resolution Universe Legacy Survey
The extreme conditions found in and around pulsars make them fantastic natural laboratories, providing insights to a rich variety of aspects of fundamental physics and astronomy. To discovery more pulsars we have begun the High Time Resolution Universe Legacy (HTRU) survey; a blind survey of the northern sky with the 100-m Effelsberg radio telescope in Germany and a twin survey of the southern sky with the 64-m Parkes radio telescope in Australia. Blind pulsar surveys are the only way to significantly increase the known population of pulsars in an unbiased way. Surveys of this type allow us to remain sensitive to all varieties of pulsars, ranging from the slowly rotating isolated magnetars to exotic relativistic binary systems such as a theoretical pulsar-black hole binary. In particular, the HTRU survey uses multi-beam receivers and backends constructed with recent advancements in technology, providing unprecedentedly high time and frequency resolution. Here I will summarise the scientific motivation and the specifications of the HTRU survey. I will provide an overview of the standard pulsar searching pipeline, as well as the innovative segmented search technique which aims to increase our chances of discoveries of highly accelerated relativistic binary systems. I will discuss the computational challenges arising from the processing of the petabyte-sized HTRU survey data and our current progress in the survey.
On the structure of pulsar magnetosphere
The angle BETA between rotation and magnetic axes are calculated by two methods for 283 radio pulsars at the wavelength 10 cm, 132 ones at 20 cm and 80 objects at the wavelength near 30 cm. The common average of the angle BETA is 43.5 degrees. Some effects which can give errors in the values of BETA are discussed. There are no correlations between values of BETA and pulsar ages.
Application and limitations of redundancy calibration in phased arrays
In new phased array developments, a fundamental question is whether the geometrical redundant baselines in a regularly arranged phased array are really redundant. Based on real and simulated data, we demonstrate that for a phased array station, a regular arrangement of station elements is necessary but not sufficient to fulfill redundancy calibration requirements. This is due to the electromagnetic interaction between closely spaced antenna elements which leads to non-identical beams and possibly correlated noise. Each of these deterministic effects introduces a bias on the estimated calibration results. Understanding the nature of these effects has helped us to determine applicability and limitations of the redundancy calibration for a given phased array, which are presented in this paper.
CO in the Circumstellar Envelope of Betelgeuse with CARMA
The massive M supergiant Betelgeuse (alpha ori, M2 Iab) is one of the best studied stars in the sky. Its large angular diameter allows detailed spatially-resolved studies of the star and its circumstellar environment. Such studies can yield information on the physical processes that drive the observed large mass loss rates from these highly evolved stars. Here we report our CARMA (Combined Array for Research in Millimeter-wave Astronomy) 230 GHz (1.3 mm) radio interferometric observations of Betelgeuse that reveal the complex structure of its circumstellar environment.
Dealing with LOFAR interference
LOFAR is a new radio telescope built in and around the Netherlands that will probe the universe between 10 and 200 MHz. Most of LOFAR‚s hardware has been installed and the next step is writing the required algorithms to process LOFAR‚s data. One such algorithm is the detection of interference. Since LOFAR is built in a populated environment, care has to be taken to deal with interference from terrestrial origin. A detection pipeline was written that removes interference in an automated way. This pipeline is now in use and the radio environment around LOFAR is being analyzed. Results show a relatively benign radio environment with a loss of data of a few per cent due to interference.
Probing the field of radio astronomy with the SKA and the Hartebeesthoek Radio observatory: an engineer's perspective
The Square Kilometre Array (SKA) is an international project to build the world’s largest and most sensitive radio telescope interferometer. It will consist of thousands of antennas distributed over many kilometers, with the hosting country being either South Africa or Australia. This talk will give some background on the SKA technologies, pathfinders and Key Science Projects and also consider the system design options for the SKA Pulsar science case. The Hartebeesthoek Radio Astronomy Observatory (HartRAO) is the only major radio astronomy observatory in Africa; with KAT-7 in testing and the MeerKAT still in it's design phase. Some of my research work at HartRAO is presented, which includes data analysis of the pointing model for the 26m radio telescope and evaluating the performance of the GPS-disciplined Rubidium and Hydrogen Maser frequency standards. I will also talk about our project to build a 1.4GHz receiver for a commercial satellite TV antenna as well as calibrating data at 22GHz for observing water masers in Orion.
e-MERLIN and the COBRaS legacy Project
As one of the 12 legacy programmes given ~300 hrs observing time on the newly enhanced e-MERLIN; the Cygnus OB2 Radio Survey (COBRaS) (homepage: http://www.homepages.ucl.ac.uk/~ucapdwi/cobras/) is an intensive deep-field mapping of the Cyg OB2 association in the Cygnus region of our Galaxy. This will provide the most detailed census for the most massive OB association in the northern hemisphere. A range of astrophysical problems and themes will be investigated including: mass loss and evolution of massive stars; the formation, dynamics and content of massive OB associations and the frequency of massive binaries and the incidence of non-thermal radiation.
As part of of the initial ground work for this project, extensive meta-data catalogues were amalgamated from various catalogues from the Virtual Observatory database. In this talk I will discuss; investigations into JHK photometric techniques which can help identify possible OB candidates and other spectral classes; theoretical mass loss models as described by Vink et al. 2001 along with stellar parameters from Martins et al. 2005, Searle et al. 2008 and Prinja et al 1990 which pave the way to calculate theoretical mass loss rates for smooth winds of O stars and B supergiants, and the predicted 6cm fluxes resulting from the thermal free-free radiation in their winds. This will be essential for the study of clumped winds which is an early goal for this project.
Over the months following from when this abstract was written; the first e-MERLIN pointings are expected. In the event of obtaining data, this will also be included in the presentation as part of the 'early science' from e-MERLIN and COBRaS.
Spectral Analysis of Timing Noise in NANOGrav Pulsars
The NANOGrav collaboration seeks to detect gravitational waves from distant supermassive black hole sources using a pulsar timing array. In order to search for gravitational waves, it is necessary to have a good characterization of the timing noise for each pulsar of the pulsar timing array. Red noise is common in millisecond pulsars, and we need to quantify how much red noise is present for each pulsar. This can be done by looking at the power spectra of the pulsar timing residuals. However because the pulsar data are non-uniformly sampled, one cannot simply do a Fourier analysis. Also, commonly used least-square fitting methods such as the Lomb-Scargle analysis are not adequate for steep red spectra. Instead, we compute the power spectra of NANOGrav pulsar timing residuals using the Cholesky transformation, which eliminates spectral leakage. This is done with the help of the TEMPO2 "SpectralModel" plugin developed by William Coles and George Hobbs.
Circular polarization of AGN on VLBI scale. New application of gain transfer method
We applied the gain transfer technique, which was developed by Homan and Wardle in 1999, to the single-source VLBI experiment. We obtained images of the parsec-scale circular polarization of the blazar 0716+714 at 22 and 5 GHz at three epochs. Blazar 0420-014, initially observed as EVPA calibrator, was used as a circular polarization calibrator. Here we present images of circular polarization of 0716+714, discuss sources of errors and their significance and propose a list of circularly unpolarized compact sources that can be used as circular polarization calibrations for other short single-source VLBI experiments.
Plasma radio emission from inhomogeneous collisional plasma
We consider the production of radio waves via plasma emission involving Langmuir waves from a flare-accelerated electron beam in a dense plasma with density perturbations. We numerically solve the system of nonlinear kinetic equations for the particles, Langmuir waves and electromagnetic waves. We include the effects of collisions on electrons and waves, and of random fluctuations in the plasma density on Langmuir waves. We follow the temporal evolution of the system, and obtain an estimate of the radio emission produced.
The overall systematic trends in the kinematics of massive star forming regions. Observations of HC3N* in hot cores
Since hot molecular cores are considered the cradle of massive stars, the study of their gas kinematics is key to better understand the physical processes leading to massive star formation. Previous observations of rotational transitions from vibrationally excited levels of HC3N (hereafter HC3N*) towards the Sgr B2M and Sgr B2N hot cores, revealed the existence of two systematic trends in these high-mass star forming regions: i) a decrease of the linewidth with increasing energy of the vibrational levels involved in the transition; and ii) an increase of the linewidth with the size of the HC3N* emitting region. Since these systematic trends may be related to the global processes of high-mass star formation, it is necessary to clearly establish whether these trends are also found toward other hot cores with different total luminosities or gas masses. Here, we present observations of several rotational transitions of HC3N* toward a sample of 10 hot cores whose luminosities span from several 103 to ~108 solar luminosities. Our results show that the systematic trends for the HC3N* linewidths to decrease with increasing energy of the transition, and to decrease with the size of the emitting region, are preserved toward the observed hot cores. This is explained by the fact that the emission from the lower energy transitions of HC3N* likely shows a contribution from high-velocity shocked gas arising from molecular outflows. This suggests that molecular outflows are the major agent, over collapse and/or rotation, affecting the global kinematics in massive star forming regions. In addition, our HC3N* data reveals a clear correlation between the linewidths of the HC3N* 1v6 and 1v7 lines and the total luminosity measured in these regions, suggesting that HC3N* is an excellent tool to link the gas kinematics of hot cores with their global properties such as total luminosity or mass.
F-Gamma program: Probing the AGN physics via broad-band radio variability studies
The F-GAMMA program (Fermi-GST AGN Multi-frequency Monitoring Alliance) is meant to investigate the physics of AGNs via a multi-frequency monitoring approach. Blazars are AGNs that show intense variability in flux and polarisation and super-luminal motions due to small viewing angles to the jet axis. Hence, there is very extreme physics at work and despite decades of study the exact physics are still unclear. A method to distinguish between different emission models are the multi-frequency variability studies. The Fermi-GST scans the entire sky every three hours. So, for the first time it provides densely sampled gamma-ray light curves which can be cross-correlated with radio, optical or other light curves. To fully exploit these features 65 Fermi-GST detectable blazars are being monitored monthly in radio wavelength since 2007. The core program involves observations with the 100-m Effelsberg telescope at 8 frequencies between 2.6 and 43 GHz, the 30-m IRAM telescope at 86, 145 and 240 GHz and the APEX 12-m telescope at 345 GHz. Spectra simultaneous within a week are produced for cross-band studies.
In this talk results of time series analysis studies will be presented in an attempt to search for characteristic timescales and study the brightness temperatures and variability Doppler factors of these objects. Furthermore, it will be shown that all the spectra can be grouped in only 9 phenomenological classes of spectral variability pattern. Seven of these classes are clearly dominated by spectral evolution and can be interpreted as a quiescent optically thin spectrum with a super-imposed flaring event. The different classes can be explained by different redshifts and intrinsic-source/flare parameters as simulations showed. The other 2 classes vary self-similarly with almost no apparent shift of the peak frequency implying that a totally different mechanism is at work.
From all this it is concluded that only two mechanisms have been observed to produce variability. Given that none of these sources was found to switch mode, the variability mechanism must be a finger-print of the source or it depends on conditions that do not change within the time covered by F-GAMMA program.
The Sunyaev-Zel'dovich effect in the Bullet Cluster
The Sunyaev-Zel'dovich (SZ) effect offers an opportunity to probe the properties of the intracluster plasma in galaxy clusters through its interaction with the cosmic microwave background radiation. I will present the detection of the SZ effect at 870 micrometers in the Bullet Cluster of Galaxies, at redshift 0.3. I will discuss the techniques used to remove background submillimeter galaxies and the filtering applied to extract the extended SZ emission. By modeling the data the distribution and properties of the hot gas in the cluster can be constrained.
Searching the giant radiogalaxies in NVSS survey
Giant radio galaxies are the largest radio sources in the Universe. Their size being about 1 Mpc is comparable with a galaxy cluster. To the present, only about 150 giant radio galxies are known over the flux density of 150 mJy. Using NVSS catalog to search for structures larger than 4 arcmin, we select canditates to the giant radio galaxies under this flux density limit.
Are core-dominated triple sources concealed double-doubles?
The term "core-dominated triple" (CDT) radio source was coined for an object which, as seen in FIRST maps, is featured by a relatively bright, point-like central component straddled with a pair of much weaker, often diffuse lobes. We are testing a hypothesis that CDTs could be "concealed" double-double radio sources (DDRS). Typically, the separation of the inner lobes in DDRSs is not less than one order of magnitude compared to that of the outer lobes. It may happen, though, that this ratio is lower and so the inner part is too compact to be properly imaged in the maps encompassing the outer one. As a result, the source does not appear in FIRST maps as a DDRS but as a CDT, and only high-resolution observations can prove that the alleged core is actually a compact double. We observed the cores of 15 CDTs with MERLIN and those that were still unresolved were followed up with the EVN. This way, we discovered a few "concealed" DDRS, i.e. DDRS where the inner double is very young.
New data of radio emission from three AXPs
Anomalous X-ray pulsars (AXPs) are a group of 9 X-ray sources showing periodical pulsation at periods in the 2-12 s range. The main problem is the source of energy, because their X-ray luminosities much higher than can be provided by the rotational kinetic-energy losses. Many attempts have been made to detect radio emission. The first detection of periodical pulsations from the AXP 1E 2259+586 have been made at the frequency 111 MHz by Malofeev (Malofeev et al., 2001, 2005). The second transient AXP XTE J1810-197 and the third AXP candidate 1E1547.0-5408 (Camilo et al., 2006, 2007) have been detected in the large frequency band 0.69-42 GHz. In this report we present new data for three AXPs 1E 2259+586, 4U 0142+61 and XTE J1810-197 at low frequencies. The observations were carried out on two sensitive transit radio telescopes in the range 42-112 MHz. The flux densities and mean pulse profiles, the estimation of the distances and integrated radio luminosities are presented. We used new digital receivers to obtain pulse profiles and dynamic spectra. Comparison with X-ray data shows large differences in the mean pulse widths and luminosities.
Binary pulsar searching with GPUs
GPUs (Graphical Processing Units) are increasingly being used for general purpose computing in science and engineering. I have been looking into the application of GPUs to searching for pulsars in short-period binary systems where their pulse period has been Doppler shifted. This makes finding these pulsars through conventional search techniques very time consuming and it is hoped GPUs could address this.
Using millimetre observations to constrain variations of dust properties in circumstellar disks
Grain growth in protoplanetary disks is the first step towards the formation of the rocky cores of planets. Dust evolution models predict that grains grow, migrate and fragment in the disk and predict varying dust properties as a function of radius, disk age and physical properties.
To constrain grain growth and migration in protoplanetary disks high-angular resolution observations at more then one (sub-)mm wavelength are currently being performed to detect possible radial variations of the dust properties.
I will present initial results of including radial dependent grain growth at the midplane of two layers passive disks. Our models predict variations of the disk emission as a function of radius as a consequence of the different grain distribution as a function of radius. The aim is to compare the prediction of these models against spatially resolved multi-frequency observations of the disk around some circumstellar disks.
Nulling and intermittent pulsars
Pulsars are extremely magnetised, rapidly rotating neutron stars which produce beams of electromagnetic radiation that sweep across the Earth. They exhibit a variety of interesting phenomena which allow us to gain insight into the physics of the emission process in these extreme magnetic fields. Intermittent pulsars are instrumental in this study due to their meta-stable configurations which result in abrupt cessation or re-activation of their radio emission. Their behaviour is believed to be tied to transient particle flow in the radio emission region. In the case of PSR B1931+24, the long-term modulation in the radio emission has been linked with the spin-down rate of the pulsar. Thus, offering a unique opportunity to study how magnetospheric changes can affect the magnetic braking of pulsars. Since the discovery of this behaviour in B1931+24, several other sources have been found to show similar radio emission modulation. Results from the analysis of the radio emission behaviour of these sources are presented, along with an update of the work carried out on observations of PSR B1931+24.
Invited talk abstracts
LOFAR: Opening up a new window on the Universe
LOFAR - the Low Frequency Array is a radio telescope operating at frequencies below 200 MHz. It will enable the sky to be studied in a region of the electro-magnetic spectrum that is almost entirely unexplored, certainly at this high spatial resolution and sensitivity. I will present the LOFAR concept, the new capabilities of the telescope and the progress to date, including the first commissioning observations and the emergence of the International LOFAR Telescope (ILT), incorporating LOFAR stations from all over Europe. I will also describe the scientific goals of the project, briefly touching upon the multi-disciplinary aspects of the system. Finally, I will explain how LOFAR is a scientific and technological pathfinder for the Square Kilometre Array (SKA), a global 1.5 Billion Euro project that aims to be under construction later in this decade.
Measuring Einstein's last great legacy: wrinkles in space-time
In 1915 Einstein predicted the existence of traveling disturbances in space-time called "gravitational waves". Almost 100 years later we still have not directly detected such waves. However, models suggest that the universe is filled with them. A number of experiments are now on the brink of detecting gravitational waves, including the International Pulsar Timing Array in which Jodrell Bank plays a key part. Gravitational wave observatories will allow us to see the essential nature of exotic objects that can only be indirectly observed by eye, such as black holes, gamma-ray bursts, and supernova explosions. The IPTA is sensitive to massive black holes with masses billions of times that of the sun. Black hole binary systems are prodigious sources of gravitational waves that will alter the arrival times of pulsar signals. We expect that in the next 10 years we will detect the signature of thousands of massive black holes merging with other massive black holes early in the history of our universe.
Gas and radio galaxies: a story of love and hate
Gas in radio galaxies is an important component that plays different roles. Gas can feed the AGN and make it active but dense gas can also be an obstacle for radio jets and (temporarily) destroy their flow. The characteristics of the different phases of gas in the circumnuclear regions of active nuclei hold clear signatures of the influences that the black hole activity has on its surroundings. I will review these effects based on some recent results obtained in the study of neutral hydrogen and CO. In particular, I will concentrate on the effects of radio jets in generating the strong negative feedback of the kind invoked in current scenarios for galaxy evolution.
The Story of Jodrell Bank
A talk covering the history of the observatory from its origins after the second world war through the Mk1 Telescopes role in the early days of the space race to the present day. Key highlights of its research will be described along with the development of MERLIN and its roles in European VLBI, the SKA and PLANCK mission.
e-MERLIN: an update
In this presentation I will be giving an update regarding the latest developments with e-MERLIN during its commissioning period. I will outline what has been achieved so far and give a timeline for the final delivery of this greatly enhanced imaging telescope, illustrated by some recent images from commissioning tests. I will also outline some planned e-MERLIN observations in my own research area of extragalactic star-formation as we look forward to a new era of imaging capability.
Science with ALMA
The Atacama large Millimetre/sub-mm Array is about to start its first open science observing. When complete, it will detect spectral line emission from CO or CII in a normal galaxy like the Milky Way at a redshift of z=3, in less than 24 hours amd image the gas kinematics in protostars and in protoplanetary disks around young Sun-like stars in the nearest molecular clouds. It will provide sub-arcsec resolution images in all the atmospheric windows from 50 GHz to about 1 THz. I will outline the current capabilities and progress, the science potential of ALMA and how you can go about using it.
SKA and its pathfinders
The Square Kilometer Array will be the largest radio telescope in theworld, spreading out over an entire continent. It will revolutionize manyareas of astronomy and astrophysics. It is also an enormous engineeringchallenge. I will introduce some of the pathfinder instruments being builtaround the world and how they are leading to the SKA. I will also discuss some of the science that will be enabled by the SKA and highlight some of the specific engineering challenges.
Cosmic Microwave Background radiation and the Planck Satellite at Jodrell Bank
The University of Manchester, through Jodrell Bank, was involved in the construction of the two lowest frequency channels of the Low Frequency Instrument (LFI) for the Planck satellite. We have had many years experience of building cryogenically cooled low-noise amplifiers for Cosmic Microwave background experiments on Tenerife, which gave us the heritage to be able to do the same for Planck. I will describe what the aim of the mission was, give a few details of the adventure that was our first involvement in a modern space project, and end with a taster of the astronomical results so far released.