The Penn State-Toruń Centre for Astronomy Planet Search stars

Abstract

Aims. We present basic atmospheric parameters (T eff , log g, v t , and [Fe/H]) as well as luminosities, masses, radii, and absolute radial velocities for 348 stars, presumably giants, from the ∼1000 star sample observed within the Penn State-Toruń Centre for Astronomy Planet Search with the High Resolution Spectrograph of the 9.2 m Hobby-Eberly Telescope. The stellar parameters (luminosities, masses, radii) are key to properly interpreting newly discovered low-mass companions, while a systematic study of the complete sample will create a basis for future statistical considerations concerning the appearance of low-mass companions around evolved low-and intermediate-mass stars. Methods. The atmospheric parameters were derived using a strictly spectroscopic method based on the LTE analysis of equivalent widths of Fe I and Fe II lines. With existing photometric data and the Hipparcos parallaxes, we estimated stellar masses and ages via evolutionary tracks fitting. The stellar radii were calculated from either estimated masses and the spectroscopic log g or from the spectroscopic T eff and estimated luminosities. The absolute radial velocities were obtained by cross-correlating spectra with a numerical template. Results. We completed the spectroscopic analysis for 332 stars, 327 of which were found to be giants. A simplified analysis was applied to the remaining 16 stars, which had incomplete data. The results show that our sample is composed of stars with effective temperatures ranging from 4055 K to 6239 K, with log g between 1.39 and 4.78 (5 dwarfs were identified). The estimated luminosities are between log L/L = −1.0 and 3 and lead to masses ranging from 0.6 to 3.4 M . Only 63 stars with masses larger than 2 M were found. The radii of our stars range from 0.6 to 52 R with the vast majority between 9−11 R . The stars in our sample are generally less metal-abundant than the Sun with median [Fe/H] = −0.15. The estimated uncertainties in the atmospheric parameters were found to be comparable to those reached in other studies. However, due to lack of precise parallaxes, the stellar luminosities and, in turn, the masses are far less precise, within 0.2 M in best cases and 0.3 M on average.

Masses and luminosities for 342 stars from the PennState-Toruń Centre for Astronomy Planet Search

“…3 mathematical formalism and examples of the constructed probability distribution function are provided. The results, a comparison with parameters obtained by Zieliński et al (2012) and others is presented in Sect. 4 while Sect.…”

“…After we published the results of the spectroscopic analysis for the first group of stars observed in our project (Zieliński et al 2012), eight of the objects then became targets of other studies. These revealed near perfect agreement in effective temperatures, log g, and metallicities.…”

“…Given the very approximate methodology applied in Zieliński et al (2012) for deriving stellar masses, we decided to revise the previous results using a more sophisticated approach. The purpose of this paper is to find a better way to constrain masses, ages, radii and, when no parallax is available, also luminosities for red giants, as presented in Zieliński et al (2012).…”

“…The purpose of this paper is to find a better way to constrain masses, ages, radii and, when no parallax is available, also luminosities for red giants, as presented in Zieliński et al (2012). We do this using a Bayesian probability approach (da Silva et al 2006).…”

“…Stellar atmospheric parameters, together with uncertainties (required in further mass, age, and luminosity determination) were taken from Zieliński et al (2012) where, the effective temperatures, surface gravities, metallicities and microturbulence velocities were derived using TGVIT (Takeda et al 2005) from spectra obtained with the Hobby-Eberly Telescope (HET, Ramsey et al 1998) and its High Resolution Spectrograph (HRS, Tull 1998) that was operated in the queue scheduled mode (Shetrone et al 2007). …”