New results from a survey of faint proper-motion stars - A probable deficiency of very low luminosity degenerates

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view Abstract Citations (112) References (72) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New results from a survey of faint proper-motion stars: a probable deficiency of very low luminosity degenerates. Liebert, J. ; Dahn, C. C. ; Gresham, M. ; Strittmatter, P. A. Abstract Spectroscopic classifications and broad-band colors are presented largely for faint Luyten proper-motion stars with > 1" yr -`. Our primary goal was to find nearby white dwarfs of very low luminosity (VLL)-i.e., with Mbol > + which recent theoretical calculations predict substantial numbers. The only possible case, LP 131-66, is discussed in detail elsewhere. Furthermore, no additional artificially red "blanketed" stars like LP 701-29 were found. Questions concerning the completeness of Luyten's catalogs are discussed, specifically for very faint stars of large proper motion; we believe that the catalogs are 50% complete for stars with m < 18.0 in finished Luyten Palomar fields. We also consider the likelihood of finding VLL objects as brighter, very nearby (<5 pc) stars, and as common proper-motion companions to nearby K-M dwarfs. It is concluded that there is probably a large deficiency of VLL degenerates relative to the predicted numbers from (1) the Shaviv-Kovetz 0.6 M0 cooling curve, (2) normalized to Green's empirical density of hot stars, and (3) with the assumption of a constant white dwarf birthrate. We consider it unlikely that the deficiency in VLL stars will be completely explained by drastic errors in the cooling theory. In particular, we consider the possibilities that Debye cooling might begin at higher luminosities than predicted or that Stevenson s insolubility effects could produce additional gravitational enefgy in a crystallizing core. Yet the empirical deficiency becomes even worse when one assumes a conventional" disk star-formation picture-a disk age of 15 x 10 years with star formation much greater in the past. Alternatively, if most disk star formation occurred 1010 years ago, a curtailment of white dwarfs in the VLL interval can be explained. These results thus support the view that the stellar disk is effectively much younger than the currently accepted age of the halo. In addition to white dwarfs, the search plan uncovered several new M dwarfs of very low luminosity and a substantial number of very cool subdwarfs. Contrary to previous experience, not one M dwarf with probable Mv > +15 showed strong line emission at Ha; most were observed at least twice, though at moderate (6-12 A) resolution. Individual discussions of white dwarfs include (1) the classification of the fourth Praesepe cluster member LB 1847 (EG 60) as DA, (2) the abundances of GD 401 (Gr 451), (3) two DB stars BPM 70524 and LB 433, and (4) some nonvariable DA stars. Finally, we report that GD 439 has a subdwarf G spectrum with a very strong CH band; the proper motion constrains Mv to be +4, making this another carbon subdwarf candidate. Subject headings: stars: late-type - stars: proper-motion - stars: stellar statistics - stars: white dwarfs Publication: The Astrophysical Journal Pub Date: October 1979 DOI: 10.1086/157384 Bibcode: 1979ApJ...233..226L Keywords: Astronomical Spectroscopy; Late Stars; Stellar Luminosity; Stellar Motions; White Dwarf Stars; Astronomical Catalogs; Searching; Astrophysics; Low-Luminosity Stars:Stellar Statistics; Nearby Stars:White Dwarfs; Proper-Motion Stars:Surveys full text sources ADS | data products SIMBAD (84)