Spectroscopic classification and Gaia DR2 parallaxes of new nearby white dwarfs among selected blue proper motion stars

• Verfasst von: Scholz, Ralf-Dieter [VerfasserIn]
• Verfasst von: Jahreiß, Hartmut [VerfasserIn]
• Titel: Spectroscopic classification and Gaia DR2 parallaxes of new nearby white dwarfs among selected blue proper motion stars
• Verf.angabe: R.-D. Scholz, H. Meusinger, A. Schwope, H. Jahreiß, and I. Pelisoli
• E-Jahr: 2018
• Jahr: 07 November 2018
• Umfang: 15 S.
• Fussnoten: Gesehen am 11.12.2019
• Titel Quelle: Enthalten in: Astronomy and astrophysics
• Ort Quelle: Les Ulis : EDP Sciences, 1969
• Jahr Quelle: 2018
• Band/Heft Quelle: 619(2018) Artikel-Nummer A31, 15 Seiten
• ISSN Quelle: 1432-0746
• DOI: doi:10.1051/0004-6361/201833700
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1587611341

Abstract

<i>Aims.<i/> With our low-resolution spectroscopic observing programme for selected blue proper motion stars, we tried to find new white dwarfs (WDs) in the solar neighbourhood.<i>Methods.<i/> We used the Lépine & Shara Proper Motion (LSPM) catalogue with a lower proper motion limit of 150 mas yr<sup>−1<sup/> and the Second US Naval Observatory CCD Astrograph Catalog (UCAC2) for proper motions down to about 90 mas yr<sup>−1<sup/>. The LSPM and UCAC2 photometry was combined with Two Micron All Sky Survey (2MASS) near-infrared (NIR) photometry. Targets selected according to their blue optical-to-NIR and NIR colours were observed mainly at Calar Alto. The spectra were classified by comparison with a large number of already known comparison objects, including WDs, simultaneously observed within our programme. <i>Gaia<i/> DR2 parallaxes and colours were used to confirm or reject spectroscopic WD candidates and to derive improved effective temperatures.<i>Results.<i/> We found ten new WDs at distances between 24.4 pc and 79.8 pc, including six hot DA WDs: GD 221 (DA2.0), HD 166435 B (DA2.2), GD 277 (DA2.2), 2MASS J19293865+1117523 (DA2.4), 2MASS J05280449+4105253 (DA3.6), and 2MASS J05005185-0930549 (DA4.2). The latter is rather bright (<i>G<i/> ≍ 12.6) and with its <i>Gaia<i/> DR2 parallax of ≍14 mas it appears overluminous by about 3 mag compared to the WD sequence in the <i>Gaia<i/> DR2 colour-magnitude diagram. It may be the closest extremely low mass (ELM) WD to the Sun. We further classified 2MASS J07035743+2534184 as DB4.1. With its distance of 25.6 pc it is the second nearest known representative of its class. With GD 28 (DA6.1), LP 740-47 (DA7.5), and LSPM J1919+4527 (DC10.3) three additional cool WDs were found. <i>Gaia<i/> DR2 parallaxes show that four of our candidates, but also two previously supposed WDs (WD 1004+665 and LSPM J1445+2527) are in fact distant Galactic halo stars with high tangential velocities. Among our rejected WD candidates, we identified a bright (<i>G<i/> = 13.4 mag) G-type carbon dwarf, LSPM J0937+2803, at a distance of 272 pc.