Cool White Dwarfs in the Sloan Digital Sky Survey

Kilic, Mukremin; Munn, Jeffrey A.; Harris, Hugh C.; Liebert, James; Hippel, Ted von; Williams, Kurtis A.; Metcalfe, T. S.; Winget, D. E.; Levine, S. E.

doi:10.1086/497962

Cited by 104 publications

(170 citation statements)

References 48 publications

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“…For halo field WDs, these estimates are 11.4 ± 0.7 Gyr (Kalirai 2012), 11-11.5 Gyr (Kilic et al 2012), and 10.5 +2.0 −1.5 (Kilic et al 2017). Although broadly consistent, these studies all use somewhat different techniques.…”

Section: Hierarchical Analysismentioning

confidence: 70%

“…The Kilic et al (2012) analysis depends on photometry and trigonometric parallaxes, as does our work, yet at that point only two halo WDs were available for their study. The Kilic et al (2017) study is based on the halo WD luminosity function isolated by Munn et al (2017). Although this sample contains 135 likely halo WDs, there are as yet no trigonometric parallaxes or spectroscopy to independently constrain their masses.…”

Section: Hierarchical Analysismentioning

confidence: 99%

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A hierarchical model for the ages of Galactic halo white dwarfs

Dyk

Hippel

et al. 2017

Monthly Notices of the Royal Astronomical Society

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In astrophysics, we often aim to estimate one or more parameters for each member object in a population and study the distribution of the fitted parameters across the population. In this paper, we develop novel methods that allow us to take advantage of existing software designed for such case-by-case analyses to simultaneously fit parameters of both the individual objects and the parameters that quantify their distribution across the population. Our methods are based on Bayesian hierarchical modelling which is known to produce parameter estimators for the individual objects that are on average closer to their true values than estimators based on case-by-case analyses. We verify this in the context of estimating ages of Galactic halo white dwarfs (WDs) via a series of simulation studies. Finally, we deploy our new techniques on optical and near-infrared photometry of ten candidate halo WDs to obtain estimates of their ages along with an estimate of the mean age of Galactic halo WDs of 12.11 +0.85 −0.86 Gyr. Although this sample is small, our technique lays the ground work for large-scale studies using data from the Gaia mission.

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Section: Hierarchical Analysismentioning

confidence: 70%

Section: Hierarchical Analysismentioning

confidence: 99%

A hierarchical model for the ages of Galactic halo white dwarfs

Dyk

Hippel

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…Finally, Bergeron & Leggett (2002) argued that all white dwarfs cooler than 4000 K have mixed H/He atmospheres. Many of these early findings have been corroborated by the wealth of data obtained from recent large surveys, like the Sloan Digital Sky-Survey Kilic et al 2006). Accordingly, we have have produced a second set of simulations, and we refer to them as model B, following these observational results.…”

Section: The Fraction Of Da and Non-da White Dwarfsmentioning

confidence: 74%

“…After all, and as pointed out by Gyuk & Gates (1999), the thick disk population presents a reasonable alternative to a halo population of lenses. Several observational (Oppenheimer et al 2001;Kilic et al 2006;Harris et al 2006;Vidrih et al 2007) works have addressed this question, but this is still a controversial issue, and a definitive answer still requires more theoretical and observational efforts.…”

Section: Introductionmentioning

confidence: 99%

White dwarfs with hydrogen-deficient atmospheres and the dark matter content of the Galaxy

Torres

Camacho

Isern

et al. 2010

A&A

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Context. The nature of the several microlensing events observed by the MACHO team towards the Large Magellanic Cloud (LMC) is still a subject of debate. Low-mass substellar objects and stars with masses larger than ∼1 M have been ruled out as major components of a massive astrophysical compact halo object (MACHO) galactic halo, while stars of half a solar mass seem to be viable candidates. Main sequence stars have been already discarded, and there are tight restrictions on the role played by white dwarfs with hydrogendominated atmospheres. Aims. In this paper we evaluate the contribution to the dark matter content of the Galaxy of white dwarfs with hydrogen-deficient atmospheres. Methods. For this purpose we use a Monte Carlo simulator which incorporates up-to-date evolutionary sequences of white dwarfs with hydrogen-rich and hydrogen-deficient atmospheres. We also take into account detailed descriptions of the thick disk and the halo of our Galaxy as well as of a reliable model of the LMC. Results. We find that the contribution of white dwarfs with hydrogen-deficient atmospheres moderately increases the theoretical estimate of the optical depth with respect to the value obtained when only hydrogen-rich white dwarfs are considered. We also find that the contribution of the thick disk population of white dwarfs is comparable to the halo contribution. However, the contributions of both the halo and the thick disk white-dwarf populations are still insufficient to explain the number of events observed by the MACHO team. Conclusions. Finally, we find that the contribution to the halo dark matter of the entire population under study is less than 10% at the 95% conficence level.

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“…We recognize that modern CCD observations have significantly higher precision than photographic images from the past. However, our interest is in the possibility of using this largely neglected observational material on the most densely star-studded regions in the sky to harvest astrophysically interesting targets (for which there would be some baseline temporal information) for follow up by present day surveys (Munn et al 2004;Kilic et al 2006;Finch et al 2007;Becker et al 2004). Figure 10 shows the statistical HRD for the VSC sample of 55 × 10 3 stars using the values of (B − V) 0 This figure illustrates how a statistical HRD allows one to classify a star on the probability, from its kinematical properties, that it is a MS I, RG I, WD I, SD II, RG II or HB II star.…”

Section: Construction Of the Variability Sample Catalog (Vsc)mentioning

confidence: 99%

A variability sample catalogue selected from the Sydney Observatory Galactic Survey

Fresneau

Osborn²

2009

A&A

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Context. A set of 55 × 10 3 stars brighter than about B-magnitude 14 and having at least three observations are identified in the Sydney Observatory Galactic Survey, carried out over the years 1892-1932 along the galactic equator section l ∈ [275. Short-term (30 min) and long-term (decades) magnitude variations in the data set are analyzed. Aims. Evidence is sought for a correlation between short-term and long-term variabilities which would identify stars in a non-quiescent phase. Methods. We use a reduced proper motion diagram to classify the stars in our sample into probable dwarfs, giants and other types. The validity of the kinematical classification is checked using objective-prism spectroscopic classification for 10 × 10 3 early-type stars. A search is made for statistical correlations between our variability indicators and physical and kinematical stellar properties. Results. We find that suspected photospheric activity for giant and dwarf stellar candidates is correlated with the time to cross the galactic thin disk. We estimate a significant apparent B-magnitude variation of ±0.25 over the 40 years of photographic observations, and candidates for monitoring for possible photospheric activity at the present time are selected employing a statistical colour-diagram which uses the total proper motion component as a distance indicator. Conclusions. Follow up studies of our tentative findings are suggested. Toward this aim the derived data for the set of 55 × 10 3 stars with variability information is archived as the variability Sample Catalogue. The data for a set of 2.4 × 10 5 stars along the section of the galactic equator l ∈ [275 • , 335 • ], |b| ≤ 7 • , and a set of of 1.7 × 10 5 stars along the section of the galactic meridian 330 • ± 5 • , b ∈ [−64 • , −7 • ] is also archived as a quick-look facility for seeking long-term magnitude changes since the century-old photographic observations were obtained.

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Cool White Dwarfs in the Sloan Digital Sky Survey

Cited by 104 publications

References 48 publications

A hierarchical model for the ages of Galactic halo white dwarfs

A hierarchical model for the ages of Galactic halo white dwarfs

White dwarfs with hydrogen-deficient atmospheres and the dark matter content of the Galaxy

A variability sample catalogue selected from the Sydney Observatory Galactic Survey

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