Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs

August 2002 • 2002AJ....124.1170D

Authors • Dahn, Conard C. • Harris, Hugh C. • Vrba, Frederick J. • Guetter, Harry H. • Canzian, Blaise • Henden, Arne A. • Levine, Stephen E. • Luginbuhl, Christian B. • Monet, Alice K. B. • Monet, David G. • Pier, Jeffrey R. • Stone, Ronald C. • Walker, Richard L. • Burgasser, Adam J. • Gizis, John E. • Kirkpatrick, J. Davy • Liebert, James • Reid, I. Neill

Abstract • Trigonometric parallax determinations are presented for 28 late-type dwarfs and brown dwarfs, including eight M dwarfs with spectral types between M7 and M9.5, 17 L dwarfs with spectral types between L0 and L8, and three T dwarfs. Broadband photometry at CCD wavelengths (VRIz*) and/or near-IR wavelengths (JHK) is presented for these objects and for 24 additional late-type dwarfs. Supplemented with astrometry and photometry from the literature, including 10 L and two T dwarfs with parallaxes established by association with bright, usually Hipparcos primaries, this material forms the basis for studying various color-color and color-absolute magnitude relations. The I-J color is a good predictor of absolute magnitude for late M and L dwarfs. MJ becomes monotonically fainter with I-J color and with spectral type through late L dwarfs, then brightens for early T dwarfs. The combination of z*JK colors alone can be used to classify late M, early L, and T dwarfs accurately, as well as to predict their absolute magnitudes, but is less effective at untangling the scatter among mid- and late L dwarfs. The mean tangential velocity of these objects is found to be slightly less than that for dM stars in the solar neighborhood, consistent with a sample with a mean age of several Gyr. Using colors to estimate bolometric corrections and models to estimate stellar radii, effective temperatures are derived. The latest L dwarfs are found to have Teff~1360 K.


IPAC Authors


Davy Kirkpatrick

Senior Scientist