TY - JOUR
T1 - First detection of the white dwarf cooling sequence of the galactic bulge
AU - Calamida, A.
AU - Sahu, K. C.
AU - Anderson, J.
AU - Casertano, S.
AU - Cassisi, S.
AU - Salaris, M.
AU - Brown, T.
AU - Sokol, J.
AU - Bond, H. E.
AU - Ferraro, I.
AU - Ferguson, H.
AU - Livio, M.
AU - Valenti, J.
AU - Buonanno, R.
AU - Clarkson, W.
AU - Pietrinferni, A.
PY - 2014/8/1
Y1 - 2014/8/1
N2 - 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-1 (≈4 km s-1) at F606W ≈ 25.5 mag, and better than ≈0.5 mas yr-1 (≈20 km s-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-sequence 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.
AB - 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-1 (≈4 km s-1) at F606W ≈ 25.5 mag, and better than ≈0.5 mas yr-1 (≈20 km s-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-sequence 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.
UR - https://www.scopus.com/pages/publications/84904637274
UR - https://www.scopus.com/pages/publications/84904637274#tab=citedBy
U2 - 10.1088/0004-637X/790/2/164
DO - 10.1088/0004-637X/790/2/164
M3 - Article
AN - SCOPUS:84904637274
SN - 0004-637X
VL - 790
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 164
ER -