A hot white dwarf luminosity function from the Sloan Digital Sky Survey

Abstract

Aims. We present a hot white dwarf (WD) luminosity function (LF) using data taken from the Sloan Digital Sky Survey (SDSS) Data Release 4. We present and discuss a combined LF, along with separate DA and non-DA as LFs. We explore the completeness of our LFs and interpret a sudden drop in the non-DA LF near 2 M bol as a transition of the non-DA WD atmosphere into the DA one during WD evolution. Our LF extends roughly between −0.5 < M bol < 7 or equivalently, ∼120 000 K > T eff > ∼25 000 K. Our LF should now be useful for estimates of recent star formation and for studies of neutrino and other potential particle emission losses in hot WDs. Methods. To create a sample whose completeness can be characterized fully, we used stars whose spectra were obtained via the SDSS's "hot standard" target selection criteria. The hot standard stars were purposefully targeted to a high level of completeness by the SDSS for calibration purposes. We are fortunate that many of them are hot white dwarfs stars. We further limited the sample to stars with fitted temperatures exceeding 23 500 K and log g > 7.0. We determined stellar distances for our sample based on their absolute SDSS g filter magnitudes, derived from WD stellar atmosphere model fits to the SDSS stellar spectra. Results. We compared our LF with those of other researchers where overlap occurs; however, our LFs are unique in their extension to the most luminous/hottest WDs. The cool end of our LF connects with the hot end of previously determined SDSS WD LFs and agreement here is quite good. It is also good with previous non-SDSS WD LFs. We note distinct differences between the DA and non-DA LFs and discuss the reliability of the DA LF at its hot end. We have extended the range of luminosities covered in the most recent WD LFs. The SDSS sample is understood quite well and its exploration should contribute to a number of new insights into early white dwarf evolution.

Limits on the neutrino magnetic dipole moment from the luminosity function of hot white dwarfs

“…Fortunately, differences between DA-only and DA+DB WDLFs are most likely on the order of 10 to 20% (De Gennaro et al 2008), values which are within the error bars of our averaged WDLF (Table 1). Indeed, when a χ 2 -test was performed on the individual WDLFs derived from the SDSS, they all yielded similar conclusions, regardless of whether they were DA-only WDLFs (De Gennaro et al 2008) 7 or DA+DB WDLFs (Harris et al 2006;Krzesinski et al 2009). In short, the comparison of our theoretical WDLFs with all the WDLFs derived from the SDSS suggest that models with μ 12 < 5 agree better with the observed disk WDLFs.…”

“…A systematic exploration of the impact of the uncertainties in the SFR of the disk in the past Gyr needs to be made to estimate systematic errors in the comparison of theoretical and inferred WDLFs. Finally, it would be interesting to test the impact of a magnetic dipole moment on the pre-white dwarf stages and (2006) and Krzesinski et al (2009). The inset shows the value of the χ 2 per degree of freedom ν of the χ 2 -test.…”

“…When dealing with the data of Harris et al (2006), Rowell & Hambly (2011), and Krzesinski et al (2009), we took M 1 Bol = 10 and M 2 Bol = 13. We emphasize that the theoretical WDLFs need to be normalized to fit each observed WDLF.…”

“…Using the same technique, but based on the SDSS DR4 and constraining it solely to spectroscopically derived DA-WDs, De Gennaro et al (2008) derived a DA-only WDLF in the range 5.2 < M Bol < 12.4. Also from the SDSS-DR4, but based on the color-selection technique, which works well at high luminosities, Krzesinski et al (2009) derived high-luminosity WDLFs (both a H-rich-only WDLF and a H-deficient WDLF) for the range 0 < M Bol < 7. Using the WDLFs of Harris et al (2006) and Krzesinski et al (2009), we constructed a WDLF for DA+DB white dwarfs (from now on SDSS-WDLF).…”

A Deep Proper Motion Catalog Within the Sloan Digital Sky Survey Footprint. Ii. The White Dwarf Luminosity Function

“…Thus, even the earliest LFs for hot WDs contained hundreds of stars, including those produced from the Palomar-Green (Green 1980;Fleming et al 1986;Liebert et al 2005;Bergeron et al 2011) and Kiso (Ishida et al 1982;Wegner & Darling 1994;Limoges & Bergeron 2010) ultraviolet excess surveys. LFs generated from modern largescale spectroscopic surveys have been based on samples of thousands of hot WDs, including those from the Sloan Digital Sky Survey (SDSS; Hu et al 2007;DeGennaro et al 2008;Krzesinski et al 2009) and the Anglo-Australian 2dF QSO Redshift Survey (Vennes et al 2002(Vennes et al , 2005. Thus, the bright end of the WDLF is defined with high statistical significance.…”