Paper: astro-ph/0512108
Date: Mon, 5 Dec 2005 14:21:16 GMT (116kb)

Title: The Space Interferometry Mission Astrometric Grid Giant-Star Survey. I.
Stellar Parameters and Radial Velocity Variability

Authors: Dmitry Bizyaev (1,2), Verne V. Smith (1,3), Jose Arenas (4), Doug
Geisler (4), Steven R. Majewski (5), Richard J. Patterson (5), Katia Cunha
(1,6), Cecilia Del Pardo (7), Nicholas B. Suntzeff (8), Wolfgang Gieren (4)
((1) NOAO, (2) Sternberg Astronomical Institute, Russia, (3) McDonald
Observatory, UT Austin, (4)Universidad de Concepcion, Chile, (5) Univ. of
Virginia, (6)Observatorio Nacional, Brazil, (7) UTEP (8) CTIO, Chile)

Comments: Astronomical Journal, in press, 22 pages, 11 Postscript figures, uses
aastex.cls
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We present results from a campaign of multiple epoch echelle spectroscopy of
relatively faint (V = 9.5-13.5 mag) red giants observed as potential
astrometric grid stars for the Space Interferometry Mission (SIM PlanetQuest).
Data are analyzed for 775 stars selected from the Grid Giant Star Survey
spanning a wide range of effective temperatures (Teff), gravities and
metallicities. The spectra are used to determine these stellar parameters and
to monitor radial velocity (RV) variability at the 100 m/s level. The degree of
RV variation measured for 489 stars observed two or more times is explored as a
function of the inferred stellar parameters. The percentage of radial velocity
unstable stars is found to be very high -- about 2/3 of our sample. It is found
that the fraction of RV-stable red giants (at the 100 m/s level) is higher
among stars with Teff \sim 4500 K, corresponding to the calibration-independent
range of infrared colors 0.59 < (J-K_s)_0 < 0.73. A higher percentage of
RV-stable stars is found if the additional constraints of surface gravity and
metallicity ranges 2.3< log g < 3.2 and -0.5 < [Fe/H] < -0.1, respectively, are
applied. Selection of stars based on only photometric values of effective
temperature (4300 K < Teff < 4700 K) is a simple and effective way to increase
the fraction of RV-stable stars. The optimal selection of RV-stable stars,
especially in the case when the Washington photometry is unavailable, can rely
effectively on 2MASS colors constraint 0.59 < (J-K_s)_0 < 0.73. These results
have important ramifications for the use of giant stars as astrometric
references for the SIM PlanetQuest.

\\ ( http://arXiv.org/abs/astro-ph/0512108 , 116kb)