ESTRELA

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Early-stage training site for European long-wavelength astronomy

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Introduction

ESTRELA is a Marie Curie Early Stage Training-Site programme funded by the EU. The programme offers opportunities for PhD positions starting between September 2006 and September 2007. The general information on the programme can be found on ESTRELA home page, where the application form, details on particpating institutes and all possible project may be found. Below we give additional details on the ESTRELA projects at JIVE.

At JIVE the positions are implemented in close collaboration with the astronomy departments at Leiden and Groningen university: Sterrewacht Leiden and Kapteyn Institute Groningen. Depending on the subject of their thesis research the students will be based at either of these university towns. The construction also ensures the students will be able to conclude their thesis research in 4 years, as is the norm in the Netherlands. The primary supervisor will be a member of the JIVE staff and frequent visits to Dwingeloo are anticpated. The Dwingeloo radio-observatory has excellent visitor facilities including a guesthouse.

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Background on projects

Below we provide details on the projects at JIVE. The same numbering is used below as on the ESTRELA project list.

V1. Astrometry of methanol masers

• Supervisor: Huib van Langevelde
• Based at: Leiden

Methanol molecules can be abundant in regions where the activity of forming stars evaporates the dust grains on which they form. The presence of methanol is an important diagnostic for star formation activity; in some cases these regions give rise to maser emission in the radio waveband, and the understanding of the methanol maser sources can be improved greatly by monitoring their positions over a few years. Not only can this establish their 3D dynamics, but also their accurate association with sources known at other wavelengths. Moreover, the same observations can establish distances to these star-forming regions by directly measuring the annual parallax. The EVN and MERLIN offer the only high resolution imaging capability at the 6.7 GHz methanol frequency that can perform these observations for a large number of sources. The proposed programme is uniquely suited for observing with eVLBI. It is anticipated that this project is carried out in collaboration with Onsala Space Observatory, Sweden.

Methanol emission form the source G23.657-0.127 shows a remarkable ring structure around the supposed position of a young star. Proper motions studies may reveal whether this ring is expanding or maybe rotating.

More detailed information may be obtained from these sources:

• Bartkiewicz et al paper 2005 paper on this ring source.
• Recent presentation on methanol masers.
• Phillips and van Langevelde paper on methanol masers in W51

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V2. Faint and transient radio sources

• Supervisor: Mike Garrett
• Based at: Groningen

Some of the most exciting recent astrophysics involves the study of transient phenomena, such as gamma-ray bursts (probably the signature of hugely energetic, distant, massive supernovae); and also the very faint radio source population which has hitherto been difficult to study. In the next 2 years, these studies will be revolutionised by the capabilities of LOFAR (Low Frequency Array), which will detect transient events, and of real-time e-VLBI observations with the e-EVN which will follow them up at high resolution. It will be important to ensure that young PhD students are involved in these exciting new instrumental projects, which will study the after-glow emission associated with supernova and gamma-ray burst events, and outbursts from active stars such as X-ray binaries. With a real-time observing capability, the e-EVN will be the premier high-resolution instrument to observe such transient phenomena, and will be a crucial tool in trying to understand the underlying emission mechanisms. LOFAR will also be extremely sensitive, allowing us to study exceptionally faint radio sources that have been magnified by the gravitational lensing effect of intervening clusters. We will use these observations, together with lens modelling, to study the details of these objects, which are responsible for a significant fraction of the star formation in the Universe and are therefore extremely important for cosmology as well as for planning for the SKA.

High resolution VLBI observations of SGR1806-20 showing the expansion of the radio emission associated with the giant flare of 27 December 2004. The flare is thought thought to be the largest explosion observed by humans in the galaxy since the SN 1604 supernova observed by Johannes Kepler in 1604.

More detailed information may be obtained from these sources:

• Preprint by Fender et al. (2005) on this same magnetar.
• Presentation by Mike Garrett on the flare in 1806-20.
• Recent conference proceeding by Paragi et al (2005) on detecting gamma ray bursts with e-VLBI.

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V3. Pulsar proper motion

• Supervisor: Huib van Langevelde and Bob Campbell.
• Based at: Leiden

The large telescopes of the EVN are ideally suited for pulsar observations, and the unique Mk5 bandwidth capacity would make this the most sensitive array in the world. A missing component for this research is the operational capability of pulsar gating at the data processor at JIVE. However, testing this could be part of a project that would be ideally suited for a technically inclined student. Combined with ionospheric calibration methods, currently being implemented under the ALBUS effort, this could allow the proper motion studies of weak pulsars. The association of pulsars with OB associations in order to constrain their origin is an important problem in astronomy. This project will be carried out in collaboration with several other groups in the ESTRELA consortium and probably will include a stay at Jodrell Bank Observatory.

Monte Carlo simulations of the possible birthplaces for PSRB1929+10 and PSRB2021+51 in relation to known OB associations. Red diamonds are the current locations, and from proper motion and age estimates it is simulated where these pulsars could possibly have formed, when a massive binary star explodes.

More detailed information may be obtained from these sources:

• Campbell paper on the perspectives of pulsar observing with the EVN.
• Campbell et al. 1996 on determining the proper motion of pulsars.
• Recent example by Chatterjee et al. (2005) on accurate astrometry of pulsar proper motions.

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V4. High fidelity imaging of normal OH masers shells

• Supervisor: Huib van Langevelde
• Based at: Leiden

Soon the EVN and MERLIN telescopes will be combined in a more intimate fashion, allowing correlation of all mutual baselines, albeit at a limited bandwidth. This offers unique imaging capabilities at the frequencies and spatial scales of OH maser shells, which are seen around some stars, which have become unstable red giants at the end of their life. High dynamic range images are needed to derive the underlying density and abundance structure in the circumstellar shells. Combined with recently developed 3D radiative transfer code, this will allow us to study the formation of masers in these shells and address the problem of deviation from spherical symmetry in these object that are evolving into the spectacular planetary nebulae. This project involves the first use of new instrumentation, as well as innovative data processing issues, but there is also a possibility to start theoretical modeling on radiative transfer in these masers. This project will be done in close collaboration with Jodrell Bank Observatory.

OH maser emission from the expanding shells around evolved stars can be imaged with long baseline interferometry. At different projected velocities the shell projects into rings (image from Chapman et al).

More detailed information may be obtained from these sources:

• General presentation on these maser stars.
• Recent paper by Vlemmings et al (2003) on OH maser observations raising a couple of questions on OH maser propagation.
• Van Langevelde and Spaans 1993 paper on theoretical radiative transfer in these shells.

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