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J/ApJ/839/23    Subdwarf A stars vs ELM WDs radial velocities    (Brown+, 2017)

The physical nature of subdwarf A stars: white dwarf impostors. Brown W.R., Kilic M., Gianninas A. <Astrophys. J., 839, 23-23 (2017)> =2017ApJ...839...23B (SIMBAD/NED BibCode)
ADC_Keywords: Stars, white dwarf ; Binaries, eclipsing ; Radial velocities ; Abundances, [Fe/H] Keywords: binaries: close; binaries: eclipsing; Galaxy: stellar content; stars: atmospheres; white dwarfs Abstract: We address the physical nature of subdwarf A-type (sdA) stars and their possible link to extremely low mass (ELM) white dwarfs (WDs). The two classes of objects are confused in low-resolution spectroscopy. However, colors and proper motions indicate that sdA stars are cooler and more luminous, and thus larger in radius, than published ELM WDs. We demonstrate that surface gravities derived from pure hydrogen models suffer a systematic ∼1dex error for sdA stars, likely explained by metal line blanketing below 9000K. A detailed study of five eclipsing binaries with radial velocity orbital solutions and infrared excess establishes that these sdA stars are metal-poor ∼1.2M main sequence stars with ∼0.8M companions. While WDs must exist at sdA temperatures, only ∼1% of a magnitude-limited sdA sample should be ELM WDs. We conclude that the majority of sdA stars are metal-poor A-F type stars in the halo, and that recently discovered pulsating ELM WD-like stars with no obvious radial velocity variations may be SX Phe variables, not pulsating WDs. Description: Our sample is comprised of 11 subdwarf A-type (sdA) stars suspected of being eclipsing binaries (S. O. Kepler 2015, private communication) and 11 previously unpublished extremely low mass (ELM) white dwarf (WD) candidates that have sdA-like temperatures summarized in Table 1. We obtain time-series spectroscopy for all 22 objects and time-series optical photometry for 21 objects. We also obtain JHK infrared photometry for 6 objects. We obtain time-series spectroscopy for 20 of the 22 objects with the 6.5m MMT telescope. We obtain spectra for the two brightest objects with the 1.5m Tillinghast telescope at Fred Lawrence Whipple Observatory. We obtain additional spectra for six objects with the 4m Mayall telescope at Kitt Peak National Observatory. The spectra were mostly acquired in observing runs between 2014 December and 2016 December. We search the Catalina Surveys Data Release 2 (Drake+ 2009, J/ApJ/696/870) and find time-series V-band photometry for 21 of the 22 objects. Six objects show significant eclipses. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 50 22 Summary of observations table2.dat 79 22 Stellar atmosphere parameters table5.dat 61 274 Radial velocity data
See also: VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006) II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012) J/ApJS/99/135 : Rotation and Spectral Peculiarities (Abt+ 1995) J/A+A/339/123 : PSR J1012+5307 evolutionary tracks (Driebe+ 1998) J/PASP/110/863 : A Stellar Spectral Flux Library: 1150 - 25000 A (Pickles 1998) J/ApJ/573/359 : Rotational velocities of B stars from BSC (Abt+, 2002) J/AJ/131/582 : Cool white dwarfs in the SDSS (Kilic+, 2006) J/AJ/136/2070 : SEGUE stellar parameter pipeline. III. (Allende Prieto+, 2008) J/ApJ/696/870 : Catalina Real-time Transient Survey (CRTS) (Drake+, 2009) J/ApJ/723/1072 : The ELM survey. I. Low-mass white dwarfs (Brown+, 2010) J/A+A/529/A75 : Limb-darkening coefficients (Claret+, 2011) J/MNRAS/417/1210 : DA-white dwarfs from SDSS and UKIDSS (Girven+, 2011) J/ApJ/743/138 : Spectroscopic survey of bright white dwarfs (Gianninas+, 2011) J/AJ/141/89 : SEGUE stellar parameter pipeline. IV. (Smolinski+, 2011) J/A+A/557/A19 : Mass and age of extreme low-mass white dwarfs (Althaus+, 2013) J/ApJ/769/66 : The ELM survey. V. White dwarf binaries (Brown+, 2013) J/A+A/568/A7 : Model SDSS colors for halo stars (Allende Prieto+, 2014) J/ApJ/794/35 : Binary white dwarfs atmospheric parameters (Gianninas+, 2014) J/MNRAS/448/2260 : White dwarf candidates in SDSS DR10 (Gentile Fusillo+, 2015) J/ApJ/812/167 : The ELM survey. VI. 11 new ELM WD binaries (Gianninas+, 2015) J/MNRAS/446/4078 : New white dwarf stars in SDSS DR10 (Kepler+, 2015) J/ApJ/818/155 : The ELM survey. VII. 15 new ELM WD cand. (Brown+, 2016) J/A+A/595/A35 : Low-mass helium WDs evolutionary models (Istrate+, 2016) J/MNRAS/455/3413 : New WD and subdwarf stars in SDSS DR12 (Kepler+, 2016) J/A+A/600/A50 : Catalog of hot subdwarf stars (Geier+, 2017) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 4 A4 --- Set Set: sdA = subdwarf A-type stars or sdAL = sdA-like extremely low mass (ELM) WD candidates 6- 9 A4 --- --- [SDSS] 11- 31 A21 --- Name SDSS designation (JHHMMSS.sss+DDMMSS.ss) 33- 34 I2 --- Nsp [4/27] Number of spectroscopic measurements 36- 38 A3 --- Var RV variable star? 40- 42 I3 --- Nph [0/757] Number of photometric measurements 44- 46 A3 --- Ecl Eclipsing? 48- 50 A3 --- IRex IR excess?
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 4 A4 --- Set Set: sdA = sdA stars or sdAL = sdA-like ELM WD candidates 6- 13 A8 --- AName Abbreviated name used in the article 15- 18 I4 K Teff [6652/8466] Gianninas effective temperature (1) 20- 22 I3 K e_Teff [111/232] Teff uncertainty 24- 28 F5.3 [cm/s2] logg [4.7/6.1] Gianninas log surface gravity (1) 30- 34 F5.3 [cm/s2] e_logg [0.06/0.6] logg uncertainty 36- 39 I4 K TeffK [6786/8355]? Kepler effective temperature (2) 41- 45 F5.3 [cm/s2] loggK [5.3/6.4]? Kepler log surface gravity (2) 47- 50 I4 K TeffS [6769/7906]? SEGUE stellar parameter pipeline effective temperature 52- 54 I3 K e_TeffS [46/286]? TeffS uncertainty 56- 60 F5.3 [cm/s2] loggS [3.5/4.4]? SEGUE stellar parameter pipeline log surface gravity 62- 66 F5.3 [cm/s2] e_loggS [0.09/0.4]? loggS uncertainty 68- 73 F6.3 [Sun] [Fe/H] [-1.8/-0.3]? SEGUE stellar parameter pipeline metallicity 75- 79 F5.3 [Sun] e_[Fe/H] [0.01/0.3]? [Fe/H] uncertainty
Note (1): We fit the summed spectra to a grid of pure hydrogen atmosphere models that span 4000K<Teff<35000K and 4.5<logg<9.5 (Gianninas+ 2011, J/ApJ/743/138 ; 2014ApJ...781..104G, 2015, J/ApJ/812/167). We apply the Tremblay+ (2013A&A...559A.104T, 2015ApJ...809..148T) 1D to 3D corrections to all of the temperatures and gravities. See section 4.2 for further explanations. Note (2): Kepler values come from Kepler+ (2015, J/MNRAS/446/4078 and 2016, J/MNRAS/455/3413).
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1- 4 A4 --- --- [SDSS] 6- 26 A21 --- Name SDSS designation (JHHMMSS.sss+DDMMSS.ss) 28- 35 A8 --- AName Short named used in article 37- 47 F11.6 d HJD Heliocentric Julian Date; JD-2450000, based on UTC 49- 55 F7.2 km/s HRV [-486/339] Heliocentric radial velocity (1) 57- 61 F5.2 km/s e_HRV [3/51] Uncertainty in HRV
Note (1): The heliocentric radial velocity is uncorrected for the white dwarf gravitational redshift.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 08-Nov-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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