Key points are not available for this paper at this time.
The U.S. Naval Observatory CCD trigonometric parallax program is described in detail, including the instrumentation employed, observing procedures followed, and reduction procedures applied. Astrometric results are presented for 72 stars ranging in apparent brightness from V = 15.16 to 19.58. Photometry is presented for the parallax stars and for all 426 individual reference stars employed in the astrometric solutions. Seventeen of the 23 stars with V(tau) greater than 200 km/s form a well-delineated sequence of extreme subdwarfs covering M(V) between 11.5 and 14.5 in the M(V) vs V - I diagram. The transformation to the M(bol) vs log T(eff) plane is presented and the results are compared with various model interior computations. The coolest members of the extreme subdwarf sequence appear to be near the hydrogen-burning minimum mass limit for stars with metallicities of (M/H) about -2.
Monet et al. (Sat,) studied this question.