J/ApJS/94/749 J/ApJS/94/749 RI photometry of cool dwarfs J D Kirkpatrick J T McGraw T R Hess J Liebert D W McCarthy Jr. Astrophys. J. Suppl. Ser. 94 749 1994 1994ApJS...94..749K I/98 : NLTT Catalogue (Luyten, 1979) J/AJ/106/773 : Mass-luminosity relation (Henry+, 1993) Photometry, RI Stars, dwarfs Stars, late-type stars: low-mass, brown dwarfs stars: luminosity function, mass function The luminosity function at the end of the main sequence is determined from V, R, and I data taken by the CCD/Transit Instrument (CTI), a dedicated telescope surveying an 8.25' wide strip of sky centered at {delta}=+28deg, thus sampling Galactic latitudes of +90deg down to -35deg. A selection of 133 objects chosen via R-I and V-I colors has been observed spectroscopically at the 4.5m Multiple Mirror Telescope to assess contributions by giants and subdwarfs and to verify that the reddest targets are objects of extremely late spectral class. Eighteen dwarfs of type M6 or later have been discovered, with the latest being of type M8.5. Data used for the determination of the luminosity function cover 27.3deg^2^ down to a completeness limit of R=19.0. This luminosity function, computed a V, I, and bolometric magnitudes, shows an increase at the lowest luminosities, corresponding to spectral types later than M6, an effect suggested in earlier work by Reid & Gilmore and Leggett & Hawkins. When the luminosity function is segregated into north Galactic and south Galactic portions, it is found that the upturn at faint magnitudes exists only in the southern sample. In fact, no dwarfs with M_I_>=12.0 are found within the limiting volume of the 19.4deg^2^ northern sample, in stark contrast to the smaller 7.9deg^2^ area at southerly latitudes where seven such dwarfs are found. This fact, combined with the fact that the Sun is located ~10-40pc north of the midplane, suggests that the latest dwarfs are part of a young population with a scale height much smaller than the 350pc value generally adopted for other M dwarfs. These objects comprise a young population either because the lower metallicities prevalent at earlier epochs inhibited the formation of late M dwarfs or because the older counterparts of this population have cooled beyond current detection limits. The latter scenario would hold if these late-type M dwarfs are substellar. The luminosity function data together with an empirical derivation of the mass-luminosity relation (from Henry & McCarthy, 1993, Cat. <J/AJ/106/773>) are used to compute a mass function independent of theory. This mass function increases toward the end of the main sequence, but the observed density of M dwarfs is still insufficient to account for the missing mass. If the increases seen in the luminosity and mass functions are indicative of a large, unseen, substellar population, brown dwarfs may yet add significantly to the mass of the Galaxy.

Object Object name --- mr Red magnitude number=1 Magnitudes as listed in the NLTT catalogue (Cat. <I/98>). mag mpg Photographic magnitude number=1 Magnitudes as listed in the NLTT catalogue (Cat. <I/98>). mag col Luyten's color class --- pm Total proper motion arcsec/yr RAh Right ascension (1987.5) number=2 Predicted coordinates for epoch and equinox 1987.5. h RAm Right ascension (1987.5) number=2 Predicted coordinates for epoch and equinox 1987.5. min RAs Right ascension (1987.5) number=2 Predicted coordinates for epoch and equinox 1987.5. s DEd Declination (1987.5) number=2 Predicted coordinates for epoch and equinox 1987.5. deg DEm Declination (1987.5) number=2 Predicted coordinates for epoch and equinox 1987.5. arcmin DEs Declination (1987.5) number=2 Predicted coordinates for epoch and equinox 1987.5. arcsec CTI CTI name --- n_CTI Note number=3 c: In Table 1. d: Luyten 1979 (Cat. <I/98>) appears to have overestimated this object's proper motion. The CTI star listed in the table has been confirmed from CTI images to be the proper motion object (LP 323-25 = LHS 2723) in question. --- l_Rmag Limit flag on Rmag --- Rmag CTI R (or V if n_Rmag=V) magnitude mag n_Rmag V: CTI V magnitude in Rmag column --- R-I CTI R-I colour index mag e_R-I rms uncertainty on R-I mag Note Notes --- James Marcout, Patricia Bauer CDS 1997Jun24 UNKNOWN UNKNOWN Prepared via OCR at CDS. J_ApJS_94_749.xml