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تسجيل مستخدم جديدRetired A Stars Revisited: An Updated Giant Planet Occurrence Rate as a Function of Stellar Metallicity and Mass
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Exoplanet surveys of evolved stars have provided increasing evidence that the formation of giant planets depends not only on stellar metallicity ([Fe/H]), but also the mass ($M_star$). However, measuring accurate masses for subgiants and giants is far more challenging than it is for their main-sequence counterparts, which has led to recent concerns regarding the veracity of the correlation between stellar mass and planet occurrence. In order to address these concerns we use HIRES spectra to perform a spectroscopic analysis on an sample of 245 subgiants and derive new atmospheric and physical parameters. We also calculate the space velocities of this sample in a homogeneous manner for the first time. When reddening corrections are considered in the calculations of stellar masses and a -0.12 M$_{odot}$ offset is applied to the results, the masses of the subgiants are consistent with their space velocity distributions, contrary to claims in the literature. Similarly, our measurements of their rotational velocities provide additional confirmation that the masses of subgiants with $M_star geq 1.6$ M$_{odot}$ (the Retired A Stars) have not been overestimated in previous analyses. Using these new results for our sample of evolved stars, together with an updated sample of FGKM dwarfs, we confirm that giant planet occurrence increases with both stellar mass and metallicity up to 2.0 M$_{odot}$. We show that the probability of formation of a giant planet is approximately a one-to-one function of the total amount of metals in the protoplanetary disk $M_star 10^{[Fe/H]}$. This correlation provides additional support for the core accretion mechanism of planet formation.
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(abridged) We have obtained precise radial velocities for a sample of 373 G and K type giants at Lick Observatory regularly over more than 12 years. Planets have been identified around 15 giant stars; an additional 20 giant stars host planet candidat
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The study of planet occurrence as a function of stellar mass is important for a better understanding of planet formation. Estimating stellar mass, especially in the red giant regime, is difficult. In particular, stellar masses of a sample of evolved
planet-hosting stars based on spectroscopy and grid-based modelling have been put to question over the past decade with claims they were overestimated. Although efforts have been made in the past to reconcile this dispute using asteroseismology, results were inconclusive. In an attempt to resolve this controversy, we study four more evolved planet-hosting stars in this paper using asteroseismology, and we revisit previous results to make an informed study of the whole ensemble in a self-consistent way. For the four new stars, we measure their masses by locating their characteristic oscillation frequency, $mathrm{ u}_{mathrm{max}}$, from their radial velocity time series observed by SONG. For two stars, we are also able to measure the large frequency separation, $mathrm{Delta u}$, helped by extended SONG single-site and dual-site observations and new TESS observations. We establish the robustness of the $mathrm{ u}_{mathrm{max}}$-only-based results by determining the stellar mass from $mathrm{Delta u}$, and from both $mathrm{Delta u}$ and $mathrm{ u}_{mathrm{max}}$. We then compare the seismic masses of the full ensemble of 16 stars with the spectroscopic masses from three different literature sources. We find an offset between the seismic and spectroscopic mass scales that is mass-dependent, suggesting that the previously claimed overestimation of spectroscopic masses only affects stars more massive than about 1.6 M$_mathrm{odot}$.
We investigate the formation of double-peaked asymmetric line profiles of CO in the fundamental band spectra emitted by young (1-5Myr) protoplanetary disks hosted by a 0.5-2 Solar mass star. Distortions of the line profiles can be caused by the gravi
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ant star HD 208897 using an iodine (I2) absorption cell. The measurements were made at TUB.ITAK National Observatory (TUG, RTT150) and Okayama Astrophysical Observatory (OAO). For the origin of the periodic variation seen in the RV data of the star, we adopted a Keplerian motion caused by an unseen companion. We found that the star hosts a planet with a minimum mass of m2sini=1.40MJ, which is relatively low compared to those of known planets orbiting evolved intermediate-mass stars. The planet is in a nearly circular orbit with a period of P=353 days at about 1 AU distance from the host star. The star is metal rich and located at the early phase of ascent along the red giant branch. The photometric observations of the star at Ankara University Kreiken Observatory (AUKR) and the HIPPARCOS photometry show no sign of variation with periods associated with the RV variation. Neither bisector velocity analysis nor analysis of the Ca II and Halpha lines shows any correlation with the RV measurements.
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