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|Title:||The white dwarf cooling sequence of the Galactic bulge||Authors:||Calamida, Annalisa
Sahu, K. C.
Brown, T. M.
Bond, H. E.
Ferguson, H. C.
Valenti, J. A.
|Issue Date:||2014||Number:||223||First Page:||315.08||Abstract:||We present F606W,F814W (V,I)-band time-series data of ~1 million stars in the low-reddening Sagittarius window in the Galactic bulge. Images were collected with the Advanced Camera far Surveys (ACS) and the Wide Field Camera 3 mounted on the Hubble Space Telescope. The total field of view is ~ 17x18 arcminutes, which was observed approximately every two weeks for two consecutive years, with the principal aim to detect a hidden population of isolated black holes and neutron stars in the Galactic disk through astrometric microlensing. Here we present some results based on the combined deep images of the four ACS fields. The final photometric catalog of ~ 1 million stars reaches down to V ~ 31 mag. Proper motions were also measured, with an accuracy of better than ~ 0.15 mas/yr at V ~ 26 mag in both coordinates. We were then able to separate disk and bulge stars and obtain a clean bulge color-magnitude diagram. Together with several candidate extreme horizontal branch (EHB) stars we were able to identify for the first time a clearly defined white dwarf (WD) cooling sequence in the bulge. The comparison between theory and observations shows that a fraction of the WDs is systematically redder than the canonical cooling tracks for CO-core DA WDs. This evidence would suggest the presence of He-core WDs in the bulge, formed in close binaries, as has been found in some Galactic globular and open clusters. The presence of close binaries in the EHB and WD bulge population is further supported by the finding of two EHB ellipsoidal variables and a candidate dwarf nova in outburst in one of the ACS fields.||URI:||http://hdl.handle.net/20.500.12386/12653||Bibcode ADS:||2014AAS...22331508C|
|Appears in Collections:||3.02 Abstract in Atti di convegno|
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