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Title: First detection of the white dwarf cooling sequence of the galactic bulge

We present Hubble Space Telescope data of the low-reddening Sagittarius window in the Galactic bulge. The Sagittarius Window Eclipsing Extrasolar Planet Search field (∼3'× 3'), together with three more Advanced Camera for Surveys and eight Wide-Field Camera 3 fields, were observed in the F606W and F814W filters, approximately every two weeks for 2 yr, with the principal aim of detecting a hidden population of isolated black holes and neutron stars through astrometric microlensing. Proper motions were measured with an accuracy of ≈0.1 mas yr{sup –1} (≈4 km s{sup –1}) at F606W ≈ 25.5 mag, and better than ≈0.5 mas yr{sup –1} (≈20 km s{sup –1}) at F606W ≈ 28 mag, in both axes. Proper-motion measurements allowed us to separate disk and bulge stars and obtain a clean bulge color-magnitude diagram. We then identified for the first time a white dwarf (WD) cooling sequence in the Galactic bulge, together with a dozen candidate extreme horizontal branch stars. The comparison between theory and observations shows that a substantial fraction of the WDs (≈30%) are systematically redder than the cooling tracks for CO-core H-rich and He-rich envelope WDs. This evidence would suggest the presence of a significant number of low-mass WDs and WD-main-sequencemore » binaries in the bulge. This hypothesis is further supported by the finding of two dwarf novae in outburst, two short-period (P ≲ 1 day) ellipsoidal variables, and a few candidate cataclysmic variables in the same field.« less
Authors:
; ; ; ; ; ; ; ; ;  [1] ; ; ;  [2] ;  [3] ;  [4] ;  [5]
  1. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
  2. Osservatorio Astronomico di Teramo—INAF, Via M. Maggini, I-64100 Teramo (Italy)
  3. Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool L3 5RF (United Kingdom)
  4. Osservatorio Astronomico di Roma—INAF, Via Frascati 33, I-00040 Monte Porzio Catone (Italy)
  5. University of Michigan-Dearborn, 4901 Evergreen Road, Dearborn, MI 48128 (United States)
Publication Date:
OSTI Identifier:
22365454
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 790; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ACCURACY; APPROXIMATIONS; BLACK HOLES; CARBON MONOXIDE; COMPARATIVE EVALUATIONS; DETECTION; ECLIPSE; FILTERS; HYPOTHESIS; MASS; NEUTRON STARS; NOVAE; PLANETS; PROPER MOTION; SPACE; STAR EVOLUTION; TELESCOPES; WHITE DWARF STARS