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Unveiling the history of the Galaxy with its fossil stars

Final Report Summary - GALFOS (Unveiling the history of the Galaxy with its fossil stars)

The GALFOS project searched for very cool White dwarfs (WDs) belonging to the thick disc and halo populations of our Galaxy. These WDs are very old remnants of high mass progenitors (up to 8 solar masses) allowing to probe the early phases of our Galaxy. This project uses data from the WFCAM TRANSIT SURVEY (WTS), which is a variability survey carried out in the zyJHK filters with the UKIRT telescope. We have stacked images on a month-by-month basis to create deep images in the J band. From these we measured proper motions of all the objects detected, with an accuracy of approx. 5 milliarcseconds per year (mas/yr). Simulations of the Galactic population of WDs allowed us to predict the number of observable white dwarfs in the fields (more than 1500 white dwarfs with proper motion higher than 10 mas/yr). This assumes a standard initial mass function (IMF), but numbers could be much higher for a top heavy IMF. We checked with the simulated Galactic white dwarf population that proper motion criteria allow a good distinction between thin disk white dwarfs on the one hand and thick disk and halo white dwarfs on the other hand, which allow us to define a clean, but still well sized sample of white dwarfs from the earliest Galactic populations.

GALFOS uses optical data to complete the photometric spectral energy distributions of the objects detected. We have been awarded with observing time at different observatories: 6 nights at INT at el Roque de los Muchachos observatory (December 2009, December 2010), 20 nights at the 3.5m telescope at CAHA observatory (May 2010, December 2010, May 2011, December 2011). The fellow reduced and analysed the optical data obtained from these observing runs. Then, these data were cross-matched with the IR data from the WTS and a list of high proper motion cool white dwarf candidates was obtained. A paper explaining the project and the first results is in preparation and soon ready for submission. The fellow also characterised the WD candidates obtaining stellar parameters and linking each WD to a Galactic population depending on the proper motion.

Dr Catalan has also been actively involved with other work in the hosting institute, in particular collaborating with the low-mass group in the field of wide binaries containing white dwarfs, which is linked to the topic of her PhD thesis. This collaboration has resulted in a recent paper.

The Fellow has also furthered her work with other European collaborators, especially with the Insititut de Ciencies de l'Espai (Barcelona, Spain). Dr Catalan is the second supervisor of a PhD student, whose thesis is focused in the age dating of main sequence stars (belonging to wide binaries) using the white dwarf companion. These results have been published recently in A&A. Thanks to the collaboration of the fellow with this Spanish institution we could apply for observing time at the GTC telescope in the Canary Islands, the largest in the northern hemisphere. Time has been granted and spectroscopic observations of the high-proper motion white dwarf candidates will be obtained in July 2011.

The IEF has helped Dr Catalan to develop her research profile into that of an independent researcher. She has developed skills in writing successful scientific proposals, leading observing runs, supervising postgraduate students, and expanding her own analysis skills to include a wide range of wavelengths and new techniques, for instance optical and IR photometry. She has also gained experience in education and outreach through work associated with the 'East of England Science Learning Centre', the host institute's teaching observatory, undergraduate teaching at the host institute.