P. Zieliński

A PLANET IN A 0.6 AU ORBIT AROUND THE K0 GIANT HD 102272

We report the discovery of one or more planet-mass companions to the K0-giant HD 102272 with the Hobby-Eberly Telescope. In the absence of any correlation of the observed periodicities with the standard indicators of stellar activity, the observed radial velocity variations are most plausibly explained in terms of a Keplerian motion of at least one planet-mass body around the star. With an estimated stellar mass of 1.9 M ☉, the minimum mass of the confirmed planet is 5.9 MJ . The planets orbit is characterized by a small but nonzero eccentricity e = 0.05 and a semimajor axis of 0.61 AU, which makes it the most compact planet discovered so far around GK spectral type giants. This detection adds to the existing evidence that, as predicted by theory, the minimum size of planetary orbits around intermediate-mass giants is affected by both planet-formation processes and stellar evolution. The currently available evidence of another planet around HD 102272 is insufficient to obtain an unambiguous two-orbit solution.

SUBSTELLAR-MASS COMPANIONS TO THE K-GIANTS HD 240237, BD +48 738 AND HD 96127

We present the discovery of substellar-mass companions to three giant stars by the ongoing Penn State-Torun Planet Search conducted with the 9.2 m Hobby-Eberly Telescope. The most massive of the three stars, K2-giant HD 240237, has a 5.3 M{sub J} minimum mass companion orbiting the star at a 746 day period. The K0-giant BD +48 738 is orbited by a {>=}0.91 M{sub J} planet which has a period of 393 days and shows a nonlinear, long-term radial velocity (RV) trend that indicates a presence of another, more distant companion, which may have a substellar mass or be a low-mass star. The K2-giant HD 96127 has a {>=}4.0 M{sub J} mass companion in a 647 day orbit around the star. The two K2-giants exhibit a significant RV noise that complicates the detection of low-amplitude, periodic variations in the data. If the noise component of the observed RV variations is due to solar-type oscillations, we show, using all the published data for the substellar companions to giants, that its amplitude is anti-correlated with stellar metallicity.

The Penn State-Toruń Centre for Astronomy Planet Search stars - I. Spectroscopic analysis of 348 red giants

Aims. We present basic atmospheric parameters (Teff ,l ogg, vt ,a nd [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-Toru´ n 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 Teff 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

PTPS Candidate Exoplanet Host Star Radii Determination with CHARA Array

We propose to measure the radii of the Penn State - Torun Planet Search (PTPS) exoplanet host star candidates using the CHARA Array. Stellar radii estimated from spectroscopic analysis are usually inaccurate due to indirect nature of the method and strong evolutionary model dependency. Also the so-called degeneracy of stellar evolutionary tracks due to convergence of many tracks in the giant branch decreases the precision of such estimates. However, the radius of a star is a critical parameter for the calculation of stellar luminosity and mass, which are often not well known especially for giants. With well determined effective temperature (from spectroscopy) and radius the luminosity may be calculated precisely. In turn also stellar mass may be estimated much more precisely. Therefore, direct radii measurements increase precision in the determination of planetary candidates masses and the surface temperatures of the planets.

The Pennsylvania—Toruń Planet Search: Target Characteristics and Recent Results

More than 450 stars hosting planets are known today but only approximately 30 planetary systems were discovered around stars beyond the Main Sequence. The Pennsylvania‐Torun Planet Search, putting an emphasis on extending studies of planetary system formation and evolution to intermediate‐mass stars, is oriented towards the discoveries of substellar‐mass companions to a large sample of evolved stars using high‐precision radial velocity technique. We present the recent status of our survey and detailed characteristic for ∼350 late type giant stars, i.e. the new results of radial velocity analysis and stellar fundamental parameters obtained with extensive spec‐troscopic method. Moreover, in the future we will make an attempt to perform the statistical study of our sample and searching the correlations between the existence of substellar objects and stellar atmospheric parameters according to previous works which investigated the planetary companion impact on the evolution of the host stars.

The Pennsylvania-Toruń search for planets around evolved stars with HET

Searches for planets around giants represent an essential complement to ’traditional’ surveys, because they furnish information about properties of planetary systems around stars that are the descendants of the A-F main sequence (MS) stars with masses as high as ~5 M ⊙ . As the stars evolve off the MS, their effective temperatures and rotation rates decrease to the point that their radial velocity variations can be measured with a few ms −1 precision. This offers an excellent opportunity to improve our understanding of the population of planets around stars that are significantly more massive than the Sun, without which it would be difficult to produce abroad, integrated picture of planet formation and evolution. Since 2001, about 30 such objects have been identified, including our five published HET detections (Niedzielski et al . 2007; Niedzielski et al . 2009a; Niedzielski et al . 2009b). Our work has produced the tightest orbit of a planet orbiting a K-giant identified so far (0.6 AU), and the first convincing evidence for a multiplanet system around such as star (Niedzielski et al . 2009a). Our most recent discoveries (Niedzielski et al . 2009b) have identified new multiplanet systems, including a very intriguing one of two brown dwarf-mass bodies orbiting a 2.8 M ⊙ , K2 giant. This particular detection challenges the standard interpretation of the so-called brown dwarf desert known to exist in the case of solar-mass stars. Along with discoveries supplied by other groups, our work has substantially added to the emerging evidence that stellar mass positively correlates with masses of substellar companions, all the way from red dwarfs to intermediate-mass stars. We present current status and forthcoming results from the Pennsylvania-Torun Search for Planets performed with the Hobby-Eberly Telescope (HET) since 2004.

The PSU/TCfA search for planets around evolved stars. Stellar parameters and activity indicators of targets.

The main objective of the Penn State/Torun Centre for Astronomy Search for Planets around Evolved Stars is the detection of planetary systems around massive, evolved stars. We are also interested in the evolution of these systems on stellar evolution timescales. In this paper we present our approach to determine the basic physical parameters of our targets GK-giants. We also discuss the stellar activity indicators used in our survey: line bisector and curvature, and Halpha variability.