Gaia white dwarfs within 40 pc – I. Spectroscopic observations of new candidates

• Published in: Monthly notices of the Royal Astronomical Society Vol. 497; no. 1; pp. 130 - 145
• Main Authors: Tremblay, P-E, Hollands, M A, Gentile Fusillo, N P, McCleery, J, Izquierdo, P, Gänsicke, B T, Cukanovaite, E, Koester, D, Brown, W R, Charpinet, S, Cunningham, T, Farihi, J, Giammichele, N, van Grootel, V, Hermes, J J, Hoskin, M J, Jordan, S, Kepler, S O, Kleinman, S J, Manser, C J, Marsh, T R, de Martino, D, Nitta, A, Parsons, S G, Pelisoli, I, Raddi, R, Rebassa-Mansergas, A, Ren, J-J, Schreiber, M R, Silvotti, R, Toloza, O, Toonen, S, Torres, S
• Format: Journal Article
• Language: English
• Published: Oxford University Press (OUP): Policy P - Oxford Open Option A 01-09-2020
• Subjects: Astrophysics; Sciences of the Universe; Solar and Stellar Astrophysics; solar neighbourhood; stars: statistics; white dwarfs
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/staa1892

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 (>99 per cent) has now been reached for Gaia DR2 sources within 40-pc sample, in the Northern hemisphere (δ > 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.