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Post Info TOPIC: SDSS J073842.56+183509.6
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SDSS J073842.56+183509.06
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Title: Detailed compositional analysis of the heavily polluted DBZ white dwarf SDSS J073842.56+183509.06: A window on planet formation?
Authors: P. Dufour, M. Kilic, G. Fontaine, P. Bergeron, C. Melis, J. Bochanski

We present a new model atmosphere analysis of the most metal contaminated white dwarf known, the DBZ SDSS J073842.56+183509.06. Using new high resolution spectroscopic observations taken with Keck and Magellan, we determine precise atmospheric parameters and measure abundances of 14 elements heavier than helium. We also report new Spitzer mid-infrared photometric data that are used to better constrain the properties of the debris disk orbiting this star. Our detailed analysis, which combines data taken from 7 different observational facilities (GALEX, Gemini, Keck, Magellan, MMT, SDSS and Spitzer) clearly demonstrate that J0738+1835 is accreting large amounts of rocky terrestrial-like material that has been tidally disrupted into a debris disk. We estimate that the body responsible for the photospheric metal contamination was at least as large Ceres, but was much drier, with less than 1% of the mass contained in the form of water ice, indicating that it formed interior to the snow line around its parent star. We also find a correlation between the abundances (relative to Mg and bulk Earth) and the condensation temperature; refractory species are clearly depleted while the more volatile elements are possibly enhanced. This could be the signature of a body that formed in a lower temperature environment than where Earth formed. Alternatively, we could be witnessing the remains of a differentiated body that lost a large part of its outer layers.

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Blobrana


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RE: SDSS J073842.56+183509.6
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A Ceres-like Dwarf Planet Swallowed by a White Dwarf Star

A Canadian-U.S. team led by Patrick Dufour (University of Montreal) discovered the most metal-rich white dwarf known to date by examining thousands of stars from the Sloan Digital Sky Survey. Their analysis, based on follow-up observations using the Gemini North telescope and the Multiple-Mirror Telescope (MMT), shows a clear signature of a tidally destroyed dwarf planet that once orbited the parent star.
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Blobrana


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Cannibalisme stellaire : mise en évidence d'une planète naine engloutie par une étoile naine blanche

Une équipe d'astrophysiciens canadiens et américains dirigée par Patrick Dufour, chercheur postdoctoral au Département de physique de l'Université de Montréal et membre du Centre de recherche en astrophysique du Québec (CRAQ), a découvert en examinant des milliers de spectres du Sloan Digital Sky Survey, une étoile naine blanche dont la composition de surface est la plus riche en éléments lourds connue à ce jour. Leur analyse, basée sur des observations obtenues au télescope Gemini Nord (Hawaii) et au MMT (Multiple-Mirror Telescope, Arizona), démontre clairement qu'une planète naine, de masse équivalente à Cérès de notre système solaire, s'est engouffrée dans une étoile de type « naine blanche ».
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Title: The Discovery of the Most Metal-Rich White Dwarf: Composition of a Tidally Disrupted Extrasolar Dwarf Planet
Authors: P. Dufour, M. Kilic, G. Fontaine, P. Bergeron, F.-R. Lachapelle, S. J. Kleinman, S. K. Leggett

Cool white dwarf stars are usually found to have an outer atmosphere that is practically pure in hydrogen or helium. However, a small fraction have traces of heavy elements that must originate from the accretion of extrinsic material, most probably circumstellar matter. Upon examining thousands of Sloan Digital Sky Survey spectra, we discovered that the helium-atmosphere white dwarf SDSS J073842.56+183509.6 shows the most severe metal pollution ever seen in the outermost layers of such stars. We present here a quantitative analysis of this exciting star by combining high S/N follow-up spectroscopic and photometric observations with model atmospheres and evolutionary models. We determine the global structural properties of our target star, as well as the abundances of the most significant pollutants in its atmosphere, i.e., H, O, Na, Mg, Si, Ca, and Fe. The relative abundances of these elements imply that the source of the accreted material has a composition similar to that of Bulk Earth. We also report the signature of a circumstellar disk revealed through a large infrared excess in JHK photometry. Combined with our inferred estimate of the mass of the accreted material, this strongly suggests that we are witnessing the remains of a tidally disrupted extrasolar body that was as large as Ceres.

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