Companions to Kepler giant stars: A long-period eccentric substellar companion to KIC 3526061 and a stellar companion to HD 187878

Context. Our knowledge of populations and occurrence of planets orbiting evolved intermediate-mass stars is still incomplete. In 2010 we started a planet-search program among 95 giant stars observed by the Kepler mission to increase the sample of giant stars with planets and with reliable estimates of stellar masses and radii. Aims. We present the two systems KIC 3526061 and HD 187878 from our planet-search program for which we could characterise their companions. Methods. We used precise stellar radial velocity measurements taken with four different echelle spectrographs to derive an orbital solution. We used Gaia astrometric measurements to obtain the inclination of the HD 187878 system and Kepler photometric observations to estimate the stellar mass and radius. Results. We report the discovery of a sub-stellar and a stellar companion around two intermediate-mass red giant branch stars. KIC 3526061 b is most likely a brown dwarf with a minimum mass of 18.15 Jupiter masses in a long-period eccentric orbit, with the orbital period 3552 d and orbital eccentricity 0.85. It is the most evolved system found having a sub-stellar companion with such a large eccentricity and wide separation. HD 187878 B has a minimum mass of 78.4 Jupiter masses. Combining the spectroscopic orbital parameters with the astrometric proper motion anomaly we derived an orbital inclination 9.8 deg, which corresponds to the companion's mass in the stellar regime of 0.51 Sun mass. Conclusions. A sub-stellar companion of KIC 3526061 extends the sample of known red giant branch stars with sub-stellar companions on very eccentric wide orbits and might provide a probe of the dynamical evolution of such systems over time.Comment: 14 pages, 11 figures. Accepted to A&

Chromospheric activity in K giant stars

In this bachelor thesis, we analyze chromospheric activity of two K giant stars, HD 187878 and KIC 3526061, which have been monitored for the past 10 years and have shown variations in their radial velocities that could be caused either by a star's companion, a yet to be discovered type of stellar oscillations or a modulation due to stellar surface features as a result of stellar activity. We explain the physics and theory behind the measurements and we apply it directly to observed data. After the procession of data, we look for periodicities and discuss the results.

Chromosférická aktivita u červených obrů

In this bachelor thesis, we analyze chromospheric activity of two K giant stars, HD 187878 and KIC 3526061, which have been monitored for the past 10 years and have shown variations in their radial velocities that could be caused either by a star's companion, a yet to be discovered type of stellar oscillations or a modulation due to stellar surface features as a result of stellar activity. We explain the physics and theory behind the measurements and we apply it directly to observed data. After the procession of data, we look for periodicities and discuss the results. 1V tejto bakalárskej práci analyzujeme chromosférickú aktivitu dvoch hviezd typu K, HD 187878 a KIC 3526061, ktoré boli monitorované posledných 10 rokov a vykazovali zmeny radiálnych rýchlostí, ktoré mohli byť spôsobené buď spoločníkom hviezdy, zatiaľ neobjaveným typom oscilácií hviezdy alebo moduláciou spôsobenou vlastnosťami povrchu hviezdy v dôsledku jej aktivity. Vysvetľujeme fyziku a teóriu, ktorá stojí za meraniami, a aplikujeme ju priamo na pozorované údaje. Po spracovaní údajov hľadáme periodicity a diskutujeme o výsledkoch. 1Astronomický ústav UKAstronomical Institute of Charles UniversityFaculty of Mathematics and PhysicsMatematicko-fyzikální fakult