Cool White Dwarfs Identified in the Second Data Release of the Ukirt Infrared Deep Sky Survey

Lodieu, N.; Leggett, S. K.; Bergeron, P.; Nitta, A.

doi:10.1088/0004-637x/692/2/1506

Cited by 8 publications

(16 citation statements)

References 55 publications

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“…One of the solutions is usually better than the other one. The cooler solution with a temperature of 3480 K explains the overall SED significantly better than the warmer solution (of Lodieu et al 2009) over the 0.4-2.2 μm range. Clearly, J2242+0048 is one of the coolest WDs known.…”

Section: Mixed H/he Atmosphere Wdsmentioning

confidence: 85%

A Detailed Model Atmosphere Analysis of Cool White Dwarfs in the Sloan Digital Sky Survey

Kilic

Leggett

Tremblay

et al. 2010

ApJS

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138

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We present optical spectroscopy and near-infrared photometry of 126 cool white dwarfs (WDs) in the Sloan Digital Sky Survey (SDSS). 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 30 km s −1 . 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 8 Gyr. A few ultracool WDs may be as old as 12-13 Gyr, 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.

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Section: Mixed H/he Atmosphere Wdsmentioning

confidence: 85%

A Detailed Model Atmosphere Analysis of Cool White Dwarfs in the Sloan Digital Sky Survey

Kilic

Leggett

Tremblay

et al. 2010

ApJS

Self Cite

138

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“…We have reviewed the properties of the published LAS white dwarf sample (Lodieu et al 2009;Leggett et al 2011) and updated two compositions given the predictions of improved model atmospheres including the Lyα red wing opacity. We have also computed 2D and 3D simulations but have shown that the multi-dimensional effects are negligible for the predicted spectra.…”

Section: Resultsmentioning

confidence: 99%

White Dwarfs in the Ukirt Infrared Deep Sky Survey Data Release 9

Tremblay

Leggett

Lodieu

et al. 2014

ApJ

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We have identified eight to ten new cool white dwarfs from the Large Area Survey (LAS) Data Release 9 of the United Kingdom InfraRed Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS). The data set was paired with the Sloan Digital Sky Survey (SDSS) to obtain proper motions and a broad ugrizY JHK wavelength coverage. Optical spectroscopic observations were secured at Gemini Observatory and confirm the degenerate status for eight of our targets. The final sample includes two additional white dwarf candidates with no spectroscopic observations. We rely on improved 1D model atmospheres and new multi-dimensional simulations with CO5BOLD to review the stellar parameters of the published LAS white dwarf sample along with our additional discoveries. Most of the new objects possess very cool atmospheres with effective -2temperatures below 5000 K, including two pure-hydrogen remnants with a cooling age between 8.5 and 9.0 Gyr, and tangential velocities in the range 40 km s −1 ≤ v tan ≤ 60 km s −1 . They are likely thick disk 10-11 Gyr-old objects. In addition we find a resolved double degenerate system with v tan ∼ 155 km s −1 and a cooling age between 3.0 and 5.0 Gyr. These white dwarfs could be disk remnants with a very high velocity or former halo G stars. We also compare the LAS sample with earlier studies of very cool degenerates and observe a similar deficit of helium-dominated atmospheres in the range 5000 < T eff (K) < 6000. We review the possible explanations for the spectral evolution from helium-dominated towards hydrogen-rich atmospheres at low temperatures.

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“…This parameter is useful to separate solar-metallicity stars from subdwarfs and white dwarfs (Jones 1972;Evans 1992;Salim & Gould 2002;Lépine & Shara 2005;Burgasser et al 2007;Lodieu et al 2009). A reduced proper motion diagram is shown in Fig.…”

Section: Sample Selectionmentioning

confidence: 99%

New ultracool subdwarfs identified in large-scale surveys using Virtual Observatory tools

Lodieu

Contreras

Osorio

et al. 2012

A&A

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Aims. The aim of the project is to improve our knowledge of the low-mass and low-metallicity population to investigate the influence of metallicity on the stellar (and substellar) mass function. Methods. We present the results of a photometric and proper motion search aimed at discovering ultracool subdwarfs in large-scale surveys. We employed and combined the Fifth Data Release (DR5) of the UKIRT Infrared Deep Sky Survey (UKIDSS) Large Area Survey (LAS) and the Sloan Digital Sky Survey (SDSS) Data Release 7 complemented with ancillary data from the Two Micron All-Sky Survey (2MASS), the DEep Near-Infrared Survey (DENIS) and the SuperCOSMOS Sky Surveys (SSS). Results. The SDSS DR7 vs. UKIDSS LAS DR5 search returned a total of 32 ultracool subdwarf candidates, only two of which are recognised as a subdwarf in the literature. Twenty-seven candidates, including the two known ones, were followed-up spectroscopically in the optical between 600 and 1000 nm, thus covering strong spectral features indicative of low metallicity (e.g., CaH), 21 with the Very Large Telescope, one with the Nordic Optical Telescope, and five were extracted from the Sloan spectroscopic database to assess (or refute) their low-metal content. We confirm 20 candidates as subdwarfs, extreme subdwarfs, or ultra-subdwarfs with spectral types later than M5; this represents a success rate of ≥60%. Among those 20 new subdwarfs, we identify two early-L subdwarfs that are very likely located within 100 pc, which we propose as templates for future searches because they are the first examples of their subclass. Another seven sources are solar-metallicity M dwarfs with spectral types between M4 and M7 without Hα emission, suggesting that they are old M dwarfs. The remaining five candidates do not have spectroscopic follow-up yet; only one remains as a bona-fide ultracool subdwarf after revision of their proper motions. We assigned spectral types based on the current classification schemes and, when possible, we measured their radial velocities. Using the limited number of subdwarfs with trigonometric parallaxes, we estimated distances ranging from ∼95 to ∼600 pc for the new subdwarfs. We provide mid-infrared photometry extracted from the WISE satellite databases for two subdwarfs and discuss their colours. Finally, we estimate a lower limit of the surface density of ultracool subdwarfs about 5000-5700 times lower than that of solar-metallicity late-M dwarfs.

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Cool White Dwarfs Identified in the Second Data Release of the Ukirt Infrared Deep Sky Survey

Cited by 8 publications

References 55 publications

A Detailed Model Atmosphere Analysis of Cool White Dwarfs in the Sloan Digital Sky Survey

A Detailed Model Atmosphere Analysis of Cool White Dwarfs in the Sloan Digital Sky Survey

White Dwarfs in the Ukirt Infrared Deep Sky Survey Data Release 9

New ultracool subdwarfs identified in large-scale surveys using Virtual Observatory tools

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