Ultracool white dwarfs and the age of the Galactic disc★

Gianninas, A.; Curd, Brandon; Thorstensen, J. R.; Kilic, Mukremin; Bergeron, P.; Andrews, Jeff J.; Canton, Paul; Agüeros, Marcel A.

doi:10.1093/mnras/stv545

Cited by 38 publications

(58 citation statements)

References 59 publications

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“…Few intrinsically faint WDs have parallax measurements. Gianninas et al (2015) obtained parallaxes for 54 cool WDs, and all 6 of their ultracool WDs ( < T 4000 K eff ) have masses less than 0.4M ☉ , versus the typical mass for hotter WDs of~M 0.6 ☉ assumed in our analysis. A 4000K pure hydrogen atmosphere WD with a mass of 0.3M ☉ is ∼0.7 mag brighter than a 0.6M ☉ WD of the same temperature and atmospheric composition.…”

Section: Disk Resultsmentioning

confidence: 69%

“…The overall impression of Figure 23 is that it is consistent with our high adopted fraction of hydrogen atmosphere WDs past the turnover, and that clearly more accurate infrared photometry has the potential to allow unambiguous classification of atmospheric composition for stars cooler thanT 4000 K eff . Kilic et al (2010a) fraction of helium WDs we've adopted (see also Gianninas et al 2015).…”

Section: Disk Resultsmentioning

confidence: 99%

See 1 more Smart Citation

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

Munn¹,

Harris²,

Hippel³

et al. 2016

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Section: Disk Resultsmentioning

confidence: 69%

Section: Disk Resultsmentioning

confidence: 99%

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

Munn¹,

Harris²,

Hippel³

et al. 2016

Self Cite

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“…However, from MS and WD populations, it has been shown that oldest stars within the disk have an age of 8-10 Gyr (e.g. Oswalt et al 1996;Bergeron et al 1997;del Peloso et al 2005;Salaris 2009;Haywood et al 2013;Gianninas et al 2015).…”

Section: Star Formation Historymentioning

confidence: 99%

The binarity of the local white dwarf population

Toonen

Hollands

Gänsicke

et al. 2017

A&A

174

194

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Context. As endpoints of stellar evolution, white dwarfs (WDs) are powerful tools to study the evolutionary history of the Galaxy. In particular, the multiplicity of WDs contains information regarding the formation and evolution of binary systems. Aims. Can we understand the multiplicity of the local WD sample from a theoretical point of view? Population synthesis methods are often applied to estimate stellar space densities and event rates, but how well are these estimates calibrated? This can be tested by a comparison with the 20 pc sample, which contains ≃ 100 stars and is minimally affected by selection biases. Methods. We model the formation and evolution of single stars and binaries within 20 pc with a population synthesis approach. We construct a model of the current sample of WDs and differentiate between WDs in different configurations, that is single WDs, and resolved and unresolved binaries containing a WD with either a main-sequence (MS) component or with a second WD. We also study the effect of different assumptions concerning the star formation history, binary evolution, and the initial distributions of binary parameters. We compile from the literature the available information on the sample of WDs within 20 pc, with a particular emphasis on their multiplicity, and compare this to the synthetic models. Results. The observed space densities of single and binary WDs are well reproduced by the models. The space densities of the most common WD systems (single WDs and unresolved WD-MS binaries) are consistent within a factor two with the observed value. We find a discrepancy only for the space density of resolved double WDs. We exclude that observational selection effects, fast stellar winds, or dynamical interactions with other objects in the Milky Way explain this discrepancy. We find that either the initial mass ratio distribution in the Solar neighbourhood is biased towards low mass-ratios, or more than ten resolved DWDs have been missed observationally in the 20 pc sample. Furthermore, we show that the low binary fraction of WD systems (∼25%) compared to Solartype MS-MS binaries (∼50%) is consistent with theory, and is mainly caused by mergers in binary systems, and to a lesser degree by WDs hiding in the glare of their companion stars. Lastly, Gaia will dramatically increase the size of the volume-limited WD sample, detecting the coolest and oldest WDs out to ≃ 50 pc. We provide a detailed estimate of the number of single and binary WDs in the Gaia sample.

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“…c Paper II is Kilic et al (2012). d Paper III is Gianninas et al (2015). e Paper IV is Dame et al (2016).…”

Section: Simulation Studymentioning

confidence: 99%

“…from the literature (Kilic et al 2010(Kilic et al , 2012Gianninas et al 2015;Dame et al 2016). The atmospheric compositions and priors on distance moduli for these 10 stars are listed in Table 4.…”

Section: Analysis Of a Group Of Candidate Halo White Dwarfsmentioning

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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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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Ultracool white dwarfs and the age of the Galactic disc★

Cited by 38 publications

References 59 publications

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

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

The binarity of the local white dwarf population

A hierarchical model for the ages of Galactic halo white dwarfs

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