<i>Gaia</i> white dwarfs within 40 pc – I. Spectroscopic observations of new candidates
P-E Tremblay, Mark Hollands, N. P. Gentile Fusillo, J McCleery, Paula Izquierdo, B. T. Gänsicke, Elena Cukanovaite, D. Koester, Warren R. Brown, S. Charpinet, Tim Cunningham, Jay Farihi, N. Giammichele, V. Van Grootel, J. J. Hermes, Matthew J. Hoskin, S. Jordan, S. O. Kepler, S. J. Kleinman, Christopher J. Manser, T. R. Marsh, D. de Martino, A. Nitta, S. G. Parsons, Ingrid Pelisoli, R. Raddi, A. Rebassa–Mansergas, J-J Ren, M. R. Schreiber, R. Silvotti, Odette Toloza, Silvia Toonen, Santiago Torres
Abstract
ABSTRACT We present a spectroscopic survey of 230 white dwarf candidates within 40 pc of the Sun from the William Herschel Telescope and Gran Telescopio Canarias. All candidates were selected from Gaia Data Release 2 (DR2) and in almost all cases, had no prior spectroscopic classifications. We find a total of 191 confirmed white dwarfs and 39 main-sequence star contaminants. The majority of stellar remnants in the sample are relatively cool (〈Teff〉 = 6200 K), showing either hydrogen Balmer lines or a featureless spectrum, corresponding to 89 DA and 76 DC white dwarfs, respectively. We also recover two DBA white dwarfs and 9–10 magnetic remnants. We find two carbon-bearing DQ stars and 14 new metal-rich white dwarfs. This includes the possible detection of the first ultra-cool white dwarf with metal lines. We describe three DZ stars for which we find at least four different metal species, including one that is strongly Fe- and Ni-rich, indicative of the accretion of a planetesimal with core-Earth composition. We find one extremely massive (1.31 ± 0.01 M⊙) DA white dwarf showing weak Balmer lines, possibly indicating stellar magnetism. Another white dwarf shows strong Balmer line emission but no infrared excess, suggesting a low-mass sub-stellar companion. A high spectroscopic completeness (&gt;99 per cent) has now been reached for Gaia DR2 sources within 40-pc sample, in the Northern hemisphere (δ &gt; 0°) and located on the white dwarf cooling track in the Hertzsprung–Russell diagram. A statistical study of the full northern sample is presented in a companion paper.