Understanding the Effects of Starspots and Pulsations of K Giants on the SIM Astrometric Grid

Details Understanding the Effects of Starspots and Pulsations of K Giants on the SIM Astrometric Grid Understanding the Effects of Starspots and Pulsations of K Giants on the SIM Astrometric Grid

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aas...203.4903c&link_type=abstract

American Astronomical Society Meeting 203, #49.03; Bulletin of the American Astronomical Society, Vol. 35, p.1284

Astronomy and Astrophysics

Astronomy

Scientific paper

The Space Interferometry Mission (SIM), scheduled for launch in 2009, will be able to perform ˜1 micro-arcsec (μ as) astrometry in a narrow-angle mode (within ˜1o) and ˜4 μ as astrometry in a wide-angle model (within ˜15o). In order to achieve such high precision astrometry, SIM requires a set of astrometrically stable stars spread quasi-uniformly across the sky - collectively known as ``the grid''. The grid will be composed of 1302 early K giant (K0 - K2 III) stars, located at ≳ 1000 pc. The stars must be astrometrically stable to ˜4 μ as over the 5 year lifetime of the SIM mission. Here we model the effect of starspots on the astrometric position of the photocenter. We find for early-type K giants that starspots shift the apparent photocenter by ≲ 1 μ as. Additionally, a radial velocity program with a precision of 50 m/s is being performed to remove giant stars with stellar and sub-stellar companions from the grid. Here we model the effect of pulsations on the intrinsic radial velocity stability of the giant stars. We find the early K giants are atmospherically stable to ≲ 50 m/s, as determined empirically in earlier studies. We attribute the cause of milli-magnitude photometric variability observed in giant stars (III) to stellar pulsations and not starspots.

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