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The cool magnetic DAZ white dwarf NLTT 10480
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SYSNO ASEP 0367844 Document Type J - Journal Article R&D Document Type Journal Article Subsidiary J Článek ve WOS Title The cool magnetic DAZ white dwarf NLTT 10480 Author(s) Kawka, Adela (ASU-R) ORCID, RID
Vennes, Stephane (ASU-R) ORCID, RIDSource Title Astronomy & Astrophysics. - : EDP Sciences - ISSN 0004-6361
Roč. 532, August (2011), A7/1-A7/8Number of pages 8 s. Language eng - English Country FR - France Keywords white dwarfs ; individual star NLTT 10480 Subject RIV BN - Astronomy, Celestial Mechanics, Astrophysics R&D Projects IAA300030908 GA AV ČR - Academy of Sciences of the Czech Republic (AV ČR) IAA301630901 GA AV ČR - Academy of Sciences of the Czech Republic (AV ČR) GAP209/10/0967 GA ČR - Czech Science Foundation (CSF) LC06014 GA MŠMT - Ministry of Education, Youth and Sports (MEYS) CEZ AV0Z10030501 - ASU-R (2005-2011) UT WOS 000293283600018 DOI 10.1051/0004-6361/201117078 Annotation We have identified a new cool magnetic white dwarf in the New Luyten Two-Tenths (NLTT) catalogue. The high proper-motion star NLTT 10480 shows weak Zeeman-split lines of calcium as well as characteristic Halpha and beta Zeeman triplets. Using VLT X-shooter spectra, we measured a surface-averaged magnetic field BS about 0.5 MG. The relative intensity of the pi and sigma components of the calcium and hydrogen lines imply a high inclination. The optical-to-infrared V - J colour index and the Ca I/Ca II ionization balance indicate a temperature between 4900 and 5200 K, while the Balmer line profiles favour a higher temperature of 5400 K. The discrepancy is potentially resolved by increasing the metallicity to 0.03 × solar, hence increasing the electron pressure. However, the measured calcium abundance and abundance upper limits for other elements (Na, Al, Si, and Fe) imply a low photospheric metallicity. Assuming diffusion steady-state, a calcium accretion rate of log M(g s-1) = 5.6 plus/minus 0.3 is required to sustain a calcium abundance of log n(Ca)/n(H) = -10.30 plus/minus 0.30 in the white dwarf atmosphere. We examine the implications of this discovery for the incidence of planetary debris and weak magnetic fields in cool white dwarf stars. Based on observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile under programme ID 080.D-0521, 082.D-0750 and 086.D-0562. Workplace Astronomical Institute Contact Radka Svašková, bibl@asu.cas.cz, Tel.: 323 620 326 Year of Publishing 2012
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