arXiv subjects
Publications and source records attributed to D. A. Fischer.
We report observations of the G0 subgiant eta Boo made in 1998, in Balmer-line equivalent width with the 2.5-m Nordic Optical Telescope and in velocity with the 24-inch Lick CAT. In both data sets we see an excess in the power spectrum, with oscillation frequencies that confirm the earlier observations by Kjeldsen et al. (1995).
HD 89744 is an F7 V star with mass 1.4 M, effective temperature 6166 K, age 2.0 Gy and metallicity [Fe/H]= 0.18. The radial velocity of the star has been monitored with the AFOE spectrograph at the Whipple Observatory since 1996, and evidence has been found for a low mass companion. The data were complemented by additional data from the Hamilton spectrograph at Lick Observatory during the companion's periastron passage in fall 1999. As a result, we have determined the star's orbital wobble to have period P = 256 d, orbital amplitude K = 257 m/s, and eccentricity e = 0.7. From the stellar mass we infer that the companion has minimum mass m2 sin i = 7.2 MJup in an orbit with semi-major axis a2 = 0.88 AU. The eccentricity of the orbit, among the highest known for extra-solar planets, continues the trend that extra-solar planets with semi-major axes greater than about 0.15 AU tend to have much higher eccentricities than are found in our solar system. The high metallicity of the parent star reinforces the trend that parent stars of extra-solar planets tend to have high metallicity
We have enlarged the sample of stars in the planet search at Lick Observatory. Doppler measurements of 82 new stars observed at Lick Observatory, with additional velocities from Keck Observatory, have revealed two new planet candidates. The G3V/IV star, HD 195019, exhibits Keplerian velocity variations with a period of 18.27 d, an orbital eccentricity of 0.03 +/- 0.03, and M sin i = 3.51 M_Jup. Based on a measurement of Ca II H&K emission, this star is chromospherically inactive. We estimate the metallicity of HD 195019 to be approximately solar from ubvy photometry. The second planet candidate was detected around HD 217107, a G7V star. This star exhibits a 7.12 d Keplerian period with eccentricity 0.14 +/- 0.05 and M sin i = 1.27 M_Jup. HD 217107 is also chromospherically inactive. The photometric metallicity is found to be [Fe/H] = +0.29 +/- 0.1 dex. Given the relatively short orbital period, the absence of tidal spin-up of HD 217107 provides a theoretical constraint on the upper limit of the companion mass of < 11 M_Jup.
Doppler measurements of the M4 dwarf star, Gliese 876, taken at both Lick and Keck Observatory reveal periodic, Keplerian velocity variations with a period of 61 days. The orbital fit implies that the companion has a mass of, M = 2.1 MJUP /sin i, an orbital eccentricity of, e = 0.27+-0.03, and a semimajor axis of, a = 0.21 AU. The planet is the first found around an M dwarf, and was drawn from a survey of 24 such stars at Lick Observatory. It is the closest extrasolar planet yet found, providing opportunities for follow--up detection. The presence of a giant planet on a non-circular orbit, 0.2 AU from a 1/3 M_Sun star, presents a challenge to planet formation theory. This planet detection around an M dwarf suggests that giant planets are numerous in the Galaxy.