Spectroscopic identification of white dwarfs in galactic clusters. IV. NGC 2168.

The authors have performed spectroscopic observations of 3 faint blue objects located in the field of the intermediate age galactic cluster NGC 2168 and proposed by Romanishin and Angel (1981) as white dwarf candidates. NGC 2168-3 and -4 are very hot white dwarfs with T_eff = 37,500K and 44,000K, respectively. NGC 2168-1 is much fainter (V ≈ 21.5) and cooler (9500K) and cannot be a cluster member according to its distance and cooling age. A fourth WD candidate (2168-2) could not be observed spectroscopically due to its faintness (V ⪆ 22) and is probably not a hot cluster member. Depending on the assumed value for reddening, the masses of NGC 2168-3 and -4 are between 0.6 and 0.8 M_sun;. The results for NGC 2168 are compared with those for NGC 2516, a cluster with nearly the same age and turnoff-mass (≡5 M_sun;) where the three WD members have smaller radii and somewhat higher masses of ⪆1 M_sun; (Reimers and Koester, 1982).