J/ApJ/790/164 Candidate bulge WDs in the SWEEPS field (Calamida+, 2014)
First detection of the white dwarf cooling sequence of the Galactic bulge.
Calamida A., Sahu K.C., Anderson J., Casertano S., Cassisi S., Salaris M.,
Brown T., Sokol J., Bond H.E., Ferraro I., Ferguson H., Livio M.,
Valenti J., Buonanno R., Clarkson W., Pietrinferni A.
<Astrophys. J., 790, 164 (2014)>
=2014ApJ...790..164C 2014ApJ...790..164C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, white dwarf ; Stars, nearby ; Milky Way ; Photometry, HST ;
Proper motions
Keywords: stars: abundances - stars: evolution
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'x3'), 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 (∼4 km/s) at F606W ∼25.5 mag, and better than
∼0.5 mas/yr (∼20 km/s) 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.
Description:
We observed the Sagittarius Window Eclipsing Extrasolar Planet Search
(SWEEPS) field (l=0°, b=-2.65°) in the Galactic bulge in 2004
and again in 2011, 2012, and 2013 with the Hubble Space Telescope
(HST), using the Wide-Field Channel of the Advanced Camera for Survey
(ACS; proposals GO-9750, GO-12586, PI: Sahu). The SWEEPS field covers
∼3.3'x3.3' in a region of relatively low extinction in the bulge
(E(B-V)≲0.6 mag; Oosterhoff & Ponsen, 1968BANS....3...79O 1968BANS....3...79O). The
2004 observations were taken in the F606W (wide V) and F814W (wide I)
filters over the course of one week (for more details, see Sahu et al.
2006Natur.443..534S 2006Natur.443..534S). The new data were collected between 2011 October
and 2013 October, with a ∼2 week cadence, for a total of 60 F606W- and
61 F814W-band images.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 53 74 List of the Candidate Bulge WDs in the
SWEEPS Field
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See also:
J/A+A/549/A147 : Abundances of microlensed bulge dwarf stars. V.
(Bensby+, 2013)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- ID Candidate bulge WD identifier (1)
4- 5 I2 h RAh Hour of Right Ascension (J2000)
7- 8 I2 min RAm Minute of Right Ascension (J2000)
10- 14 F5.2 s RAs Second of Right Ascension (J2000)
16 A1 --- DE- Sign of the Declination (J2000)
17- 18 I2 deg DEd Degree of Declination (J2000)
20- 21 I2 arcmin DEm Arcminute of Declination (J2000)
23- 27 F5.2 arcsec DEs Arcsecond of Declination (J2000)
29- 33 F5.2 mag F814Wmag F814W-band apparent magnitude
35- 39 F5.2 mag F606Wmag F606W-band apparent magnitude
41- 46 F6.2 mas/yr pmGLAT Proper motion along GLAT
48- 53 F6.2 mas/yr pmGLON Proper motion along GLON
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Note (1): The first two stars are the ellipsoidal variables.
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History:
From electronic version of the journal
(End) Prepared by Tiphaine Pouvreau [CDS] 28-Mar-2017