J/ApJ/730/67 Radial velocities of low-mass white dwarfs (Brown+, 2011)
The binary fraction of low-mass white dwarfs.
Brown J.M., Kilic M., Brown W.R., Kenyon S.J.
<Astrophys. J., 730, 67 (2011)>
=2011ApJ...730...67B 2011ApJ...730...67B
ADC_Keywords: Stars, white dwarf ; Radial velocities ; Photometry, infrared ;
Stars, double and multiple
Keywords: stars: evolution - stars: low-mass - white dwarfs
Abstract:
We describe spectroscopic observations of 21 low-mass (≤0.45M☉)
white dwarfs (WDs) from the Palomar-Green survey obtained over four
years. We use both radial velocities and infrared photometry to
identify binary systems, and find that the fraction of single,
low-mass WDs is ≤30%. We discuss the potential formation channels for
these single stars including binary mergers of lower-mass objects.
However, binary mergers are not likely to explain the observed number
of single low-mass WDs. Thus, additional formation channels, such as
enhanced mass loss due to winds or interactions with substellar
companions, are likely.
Description:
Our sample of thirty ≤0.45M☉ low-mass WDs is taken from the PG
survey, a comprehensive survey of blue stellar objects with B≲16.1
(Green et al. 1986, Cat. II/207). The PG survey covers 10714deg2
with an estimated completeness of 84%. Liebert et al. (2005,
Cat. J/ApJS/156/47) fit stellar atmosphere models to the 348 DA WDs in
the PG survey and identify 30 WDs with mass less than 0.45M☉.
This is the sample of WDs studied here.
For nine objects we obtain deep near-infrared photometry using the
Peters Automated Infrared Imaging Telescope (PAIRITEL).
We obtain spectroscopy for the 21 low-mass WDs with no previously
known radial velocity variability. The other nine WDs are known binary
systems published elsewhere. To verify our data reduction and analysis
procedures, we re-observed one of the known binaries, PG 2331+290, and
confirmed its 4hr orbital period. We obtained 720 spectra between 2007
October and 2010 April using the FAST spectrograph on the Fred
Lawrence Whipple Observatory 1.5m telescope. This spectrograph setup
provides a wavelength range of 3500-5500Å at a spectral resolution
of 1.7Å.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 43 31 Physical parameters
table2.dat 110 31 Binary orbital parameters
table4.dat 39 731 Radial velocity measurements (for 22 WDs)
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/207 : Palomar-Green catalog UV-excess stellar objects (Green+ 1986)
J/MNRAS/413/1121 : SDSS post-common envelope binaries. X (Rebassa-Mansergas+
2011)
J/MNRAS/417/1210 : DA-white dwarfs from SDSS and UKIDSS (Girven+, 2011)
J/ApJ/723/1072 : The ELM survey. I. Low-mass white dwarfs (Brown+, 2010)
J/ApJ/712/585 : Apparent velocity measurements of DA WDs (Falcon+, 2010)
J/AJ/135/1239 : Spectral distances to DA white dwarfs (Holberg+, 2008)
J/AJ/132/1221 : VJHK and SDSS photometry of DA white dwarfs (Holberg+, 2006)
J/ApJS/156/47 : White dwarfs from the Palomar Green Survey (Liebert+, 2005)
J/AJ/124/1118 : RVs of high-velocity white dwarfs (Silvestri+, 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Star name
12 A1 --- f_Name [b] b: photometric binary (see table 3)
14- 17 F4.2 Msun Mass ? Mass (1)
19- 23 I5 K Teff ? Effective temperature (1)
25- 29 F5.2 mag Vmag ? V-band magnitude (1)
31- 36 F6.3 mag Jmag ? J-band magnitude (2)
38- 42 F5.3 mag e_Jmag ? Jmag uncertainty
43 A1 --- f_Jmag [p] p: our PAIRITEL photometry
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Note (1): Mass, Teff, and Vmag are from Liebert et al. (2005,
Cat. J/ApJS/156/47).
Note (2): Jmag is from Cutri et al. (2003, Cat. II/246), except for those
objects (*) with our own photometry.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Object name
12- 13 A2 --- r_Per [a-fMg ] References and notes (3)
15- 20 F6.4 d Per ? Orbital period
22- 27 F6.4 d e_Per ? Per uncertainty
29- 31 I3 km/s K Velocity semiamplitude K (or standard deviation
of the velocities for the 14 objects with no
orbital fits)
32 A1 --- u_K Uncertainty flag on K
34- 35 I2 km/s e_K ? K uncertainty
37- 39 I3 km/s V0 Systemic velocity Γ
41- 42 I2 km/s e_V0 ? Γ uncertainty
44- 52 F9.4 d T0 ? Time of spectroscopic conjunction (T0-2450000)
54- 59 F6.4 d e_T0 ? T0 uncertainty
61- 68 E8.3 --- Ftest ? F-test significance
69- 70 A2 --- f_Ftest [Hd/No] Flag on Ftest (4)
72- 77 F6.4 Msun MF ? Mass function MF
78 A1 --- u_MF Uncertainty flag on MF
80- 85 F6.4 Msun e_MF ? MF uncertainty
87- 88 A2 --- l_M2 [≥] Limit flag on M2
89- 92 F4.2 Msun M2 ? Minimum companion mass M2
93 A1 --- u_M2 Uncertainty flag on M2
95- 96 A2 --- l_tau [≤] Limit flag on tau
97-103 F7.1 Gyr tau ? Maximum merger time τ
104 A1 --- u_tau Uncertainty flag on tau
106-110 A5 --- Notes Note(s) (5)
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Note (3): References as follows:
a = Morales-Rueda et al. 2005MNRAS.359..648M 2005MNRAS.359..648M;
b = Marsh 1995MNRAS.275..828M 1995MNRAS.275..828M;
c = Holberg et al. 1995ApJ...452L.133H 1995ApJ...452L.133H;
d = Nelemans et al. 2005MNRAS.356..753N 2005MNRAS.356..753N;
e = Orosz et al. 1999AJ....117.1598O 1999AJ....117.1598O;
f = Marsh et al. 1995MNRAS.275..828M 1995MNRAS.275..828M.
Mg = PG 1458+172 is a new pre-cataclysmic binary discovered in our survey.
The optical spectrum of this object shows Balmer lines both in absorption
and emission and an MgI triplet (5167.321Å, 5172.684Å, and
5183.604Å) in emission as seen in Figure 3. Strong Hα emission
is also evident in the SDSS spectroscopy. The radial velocity variation
of the emission lines is about 190° out of phase with the Balmer
absorption lines from the WD primary. We use the H and Mg emission lines
to fit an independent orbit to the secondary (Mg). See section 3.4.
Note (4): Flag as follows:
No = No detectable period
Hd = High dispersion : Curiously, of the WDs for which we cannot fit orbits,
two objects (PG 0846+249 and PG 1320+645) have significant velocity
variability. Although we require more data to constrain a period for
these two WDs, we consider them probable binary systems.
Note (5): Notes as follows:
1 = Probable single WD.
2 = Infrared color excess, M-dwarf companion.
3 = Velocity variable, unconstrained orbit.
4 = Double-lined spectroscopic binary.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Name Object name
13- 23 F11.6 d HJD Heliocentric Julian date; (HJD-2450000.0)
25- 30 F6.1 km/s HRV Heliocentric radial velocity
32- 36 F5.1 km/s e_HRV Uncertainty in HRV
38- 39 A2 --- n_HRV [Mg ] MgI triplet lines (for PG 1458+172,
see Note (3) above).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 17-Sep-2012