J/ApJS/190/77 Detailed analysis of cool WDs in the SDSS (Kilic+, 2010)
A detailed model atmosphere analysis of cool white dwarfs in the Sloan Digital Sky Survey. Kilic M., Leggett S.K., Tremblay P.-E., Von Hippel T., Bergeron P., Harris H.C., Munn J.A., Williams K.A., Gates E., Farihi J. <Astrophys. J. Suppl. Ser., 190, 77-99 (2010)> =2010ApJS..190...77K
ADC_Keywords: Stars, white dwarf ; Photometry, ugriz ; Photometry, infrared ; Spectral types ; Surveys Keywords: stars: atmospheres - stars: evolution - white dwarfs Abstract: We present optical spectroscopy and near-infrared photometry of 126 cool white dwarfs (WDs) in the Sloan Digital Sky Survey (SDSS DR3). Our sample includes high proper motion targets selected using the SDSS and USNO-B astrometry and a dozen previously known ultracool WD candidates. Our optical spectroscopic observations demonstrate that a clean selection of large samples of cool WDs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic Survey Telescope data sets) is possible using a reduced proper motion diagram and a tangential velocity cut-off (depending on the proper motion accuracy) of 30km/s. Our near-infrared observations reveal eight new stars with significant absorption. We use the optical and near-infrared photometry to perform a detailed model atmosphere analysis. More than 80% of the stars in our sample are consistent with either pure hydrogen or pure helium atmospheres. However, the eight stars with significant infrared absorption and the majority of the previously known ultracool WD candidates are best explained with mixed hydrogen and helium atmosphere models. The age distribution of our sample is consistent with a Galactic disk age of 8Gyr. A few ultracool WDs may be as old as 12-13Gyr, but our models have problems matching the spectral energy distributions of these objects. There are only two halo WD candidates in our sample. However, trigonometric parallax observations are required for accurate mass and age determinations and to confirm their membership in the halo. Description: We obtained low-resolution spectroscopy of 98 targets using the 9.2m HET in the queue mode and the Marcario Low Resolution Spectrograph (LRS). Our observations were performed between 2004 October and 2006 July. We obtained JHK photometry of 126 WDs using the Near Infra-Red Imager and Spectrometer (NIRI) on Gemini-North, the 0.8-5.4um medium-resolution spectrograph and imager (SpeX) on the Infrared Telescope Facility (IRTF), and the Wide-Field Camera (WFCAM) on the United Kingdom Infra-Red Telescope (UKIRT). The IRTF observations were obtained on several observing runs between 2004 December and 2006 April. The UKIRT observations (of J0146+1404 and J2239+0018) were performed on UT 2007 September 20. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 101 156 Optical and near-infrared photometry of cool white dwarfs table2.dat 101 26 Spectroscopically identified subdwarf stars table3.dat 77 125 Best-fit model physical parameters assuming logg=8
See also: B/wd : Spectroscopically Identified White Dwarfs (McCook+, 2008) II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009) J/AJ/127/3034 : Proper-motion catalog combining USNO-B and SDSS (Munn+, 2004) J/ApJ/607/426 : Catalog of white dwarfs in SDSS-DR1 (Kleinman+, 2004) J/AJ/131/582 : Cool white dwarfs in the SDSS (Kilic+, 2006) J/ApJS/167/40 : SDSS4 confirmed white dwarfs catalog (Eisenstein+, 2006) J/A+A/448/579 : Sample of confirmed WDs in GSC-II survey (Carollo+, 2006) J/MNRAS/382/515 : SDSS ultracool and halo WD candidates (Vidrih+, 2007) Byte-by-byte Description of file: table.dat
Bytes Format Units Label Explanations
1- 18 A18 --- SDSS SDSS name (HHMMSS.ss+DDMMSS.s) (1) 20- 24 F5.2 mag umag u-band AB magnitude (2) 26- 30 F5.2 mag gmag g-band AB magnitude (2) 32- 36 F5.2 mag rmag r-band AB magnitude (2) 38- 42 F5.2 mag imag i-band AB magnitude (2) 44- 48 F5.2 mag zmag z-band AB magnitude (2) 50- 54 F5.2 mag Jmag ? NIRI J-band magnitude (1.250um) 56- 59 F4.2 mag e_Jmag ? Jmag uncertainty 61- 65 F5.2 mag Hmag ? NIRI H-band magnitude (1.635um) 67- 70 F4.2 mag e_Hmag ? Hmag uncertainty 72- 76 F5.2 mag Kmag ? NIRI Ks-band magnitude (2.150um) 78- 81 F4.2 mag e_Kmag ? Kmag uncertainty 83- 87 A5 --- SpT Spectroscopic classification 89 I1 --- r_SpT [1-9]? Reference (for table 1 only) (3) 91- 94 I4 mas/yr pmRA ? Proper motion in RA (for table2 only) (4) 96- 99 I4 mas/yr pmDE ? Proper motion in Dec (for table2 only) (4) 101 I1 --- Nep [4/6]? Number of epochs (for table2 only) (5)
Note (1): In table 1, 234405.54-142923.5 is a misprint for 234405.54+142923.5; corrected at CDS. Note (2): The photometric calibration is based on the SDSS standard star system tied to the survey data with the Photometric Telescope (Hogg et al., 2001AJ....122.2129H). The SDSS photometry is in the AB system. We use the corrections given in Eisenstein et al. (2006, Cat. J/ApJS/167/40) for the u-, i-, and z-band photometry. Note (3): Source of the optical spectroscopic observations as follows: 1 = Kilic et al. 2006, Cat. J/AJ/131/582; 2 = This paper; 3 = SDSS; 4 = Oppenheimer et al. 2001, Cat. J/other/Sci/292.698; 5 = Gates et al., 2004ApJ...612L.129G; 6 = Oswalt et al., 1996Natur.382..692O; 7 = Hintzen 1986AJ.....92..431H; 8 = Carollo et al. 2006, Cat. J/A+A/448/579; 9 = Vennes & Kawka, 2003ApJ...586L..95V. Note (4): The proper motion measurements are from Munn et al. (2004, Cat. J/AJ/127/3034). Note (5): Number of epochs an object is detected in the USNO-B + SDSS.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 11 A11 --- Name Object name (JHHMM+DDMMA) 13- 16 I4 K Teff Effective temperature 18- 21 I4 K e_Teff Teff uncertainty 23- 25 I3 pc Dist Distance 27- 30 F4.1 Gyr Age Cooling age 32- 35 A4 --- Comp Composition (logH/He) 37- 42 A6 --- SpT Spectral type 43- 47 I5 mas/yr pmRA Proper motion in RA 49- 52 I4 mas/yr pmDE proper motion in Dec 54- 58 A5 --- Pec [a-f, ] Peculiarities (1) 60- 77 A18 --- SDSS SDSS name (HHMMSS.ss+DDMMSS.s) (added by CDS)
Note (1): Note as follows: a = Hα is clearly visible and in good agreement with the best-fit pure H model; b = Hα is barely visible and cannot be confirmed; c = the pure helium fit is significantly better; d = the object has to be H rich for the Hα line to be visible at this temperature; e = the fit is poor and unusual, and the photometry seems offset; f = mild infrared absorption could be fitted with mixed models but the Hα line would be incompatible with predictions.
History: From electronic version of the journal
(End) Emmanuelle Perret [CDS] 29-Sep-2010
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