skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

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

Abstract

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

Citation Formats

Calamida, A., Sahu, K. C., Anderson, J., Casertano, S., Brown, T., Sokol, J., Bond, H. E., Ferguson, H., Livio, M., Valenti, J., Cassisi, S., Buonanno, R., Pietrinferni, A., Salaris, M., Ferraro, I., and Clarkson, W., E-mail: calamida@stsci.edu. First detection of the white dwarf cooling sequence of the galactic bulge. United States: N. p., 2014. Web. doi:10.1088/0004-637X/790/2/164.
Calamida, A., Sahu, K. C., Anderson, J., Casertano, S., Brown, T., Sokol, J., Bond, H. E., Ferguson, H., Livio, M., Valenti, J., Cassisi, S., Buonanno, R., Pietrinferni, A., Salaris, M., Ferraro, I., & Clarkson, W., E-mail: calamida@stsci.edu. First detection of the white dwarf cooling sequence of the galactic bulge. United States. doi:10.1088/0004-637X/790/2/164.
Calamida, A., Sahu, K. C., Anderson, J., Casertano, S., Brown, T., Sokol, J., Bond, H. E., Ferguson, H., Livio, M., Valenti, J., Cassisi, S., Buonanno, R., Pietrinferni, A., Salaris, M., Ferraro, I., and Clarkson, W., E-mail: calamida@stsci.edu. Fri . "First detection of the white dwarf cooling sequence of the galactic bulge". United States. doi:10.1088/0004-637X/790/2/164.
@article{osti_22365454,
title = {First detection of the white dwarf cooling sequence of the galactic bulge},
author = {Calamida, A. and Sahu, K. C. and Anderson, J. and Casertano, S. and Brown, T. and Sokol, J. and Bond, H. E. and Ferguson, H. and Livio, M. and Valenti, J. and Cassisi, S. and Buonanno, R. and Pietrinferni, A. and Salaris, M. and Ferraro, I. and Clarkson, W., E-mail: calamida@stsci.edu},
abstractNote = {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-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.},
doi = {10.1088/0004-637X/790/2/164},
journal = {Astrophysical Journal},
number = 2,
volume = 790,
place = {United States},
year = {Fri Aug 01 00:00:00 EDT 2014},
month = {Fri Aug 01 00:00:00 EDT 2014}
}