Physics – Optics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20916202w&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #162.02; Bulletin of the American Astronomical Society,
Physics
Optics
Scientific paper
STEPS (STEllar Planet Survey) is a ground-based, optical astrometric survey of 30 nearby M dwarfs from the Hale 5-meter telescope with the goal of discovering extrasolar planets. Since astrometry measures center of light motion about the center of mass, a degeneracy exists between luminous and non-luminous secondaries. This degeneracy can be removed by high-resolution imaging. Using the Keck II laser guide star adaptive optics system (LGSAO), we imaged four candidate binary systems. Stellar companions were discovered for two of the four stars (G 78-28 and GJ 231.1B), but no luminous companions were detected for the remaining two stars. This raises the possibility of substellar companions around these stars. The companion to G 78-28 lies 2.19 ± 0.10 AU from the 0.370 ± 0.034 solar mass primary and has a mass of 0.195 ± 0.021 solar masses. The full orbit of GJ 231.1BC has not been observed, because its > 26 year period is almost three times the temporal baseline of STEPS. Thus, the primary and secondary component masses of 0.25 ± 0.06 and 0.12 ± 0.02 solar masses, respectively, are based on mass-luminosity relations in the literature. To calibrate the NIRC2 detector pixel scale and nominal rotation, we imaged the core of M5 and correlated stellar positions against an archival, public image from the Hubble Space Telescope Planetary Camera. We find the pixel scale for the narrow camera mode of 9.970 ± 0.012 mas/pix is consistent with other values from the literature, and we find that rotation information in image headers is accurate to better than 1 degree.
Kulkarni Sanjeev R.
Pravdo Steven Howard
Shaklan Stuart B.
Wiktorowicz Sloane
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