Chemical abundances and kinematics of 257 G-, K-type field giants. Setting a base for further analysis of giant-planet properties orbiting evolved stars
V. Zh. Adibekyan, L. Benamati, N. C. Santos, S. Alves, C. Lovis, S. Udry, G. Israelian, S. G. Sousa, M. Tsantaki, A. Mortier, A. Sozzetti, J. R. De Medeiros
We performed a uniform and detailed abundance analysis of 12 refractory elements (Na, Mg, Al, Si, Ca, Ti, Cr, Ni, Co, Sc, Mn, and V) for a sample of 257 G- and K-type evolved stars from the CORALIE planet search program. To date, only one of these stars is known to harbor a planetary companion. We aimed to characterize this large sample of evolved stars in terms of chemical abundances and kinematics, thus setting a solid base for further analysis of planetary properties around giant stars. This sample, being homogeneously analyzed, can be used as a comparison sample for other planet-related studies, as well as for different type of studies related to stellar and Galaxy astrophysics. The abundances of the chemical elements were determined using an LTE abundance analysis relative to the Sun, with the spectral synthesis code MOOG and a grid of Kurucz ATLAS9 atmospheres. To separate the Galactic stellar populations both a purely kinematical approach and a chemical method were applied. We confirm the overabundance of Na in giant stars compared to the field FGK dwarfs. This enhancement might have a stellar evolutionary character, but departures from LTE may also produce a similar enhancement. Our chemical separation of stellar populations also suggests a "gap" in metallicity between the thick-disk and high-alpha metal-rich stars, as previously observed in dwarfs sample from HARPS. The present sample, as most of the giant star samples, also suffers from the B - V colour cut-off, which excludes low-log g stars with high metallicities, and high-logg star with low-[Fe/H]. For future studies of planet occurrence dependence on stellar metallicity around these evolved stars we suggest to use a sub-sample of stars in a "cut-rectangle" in the logg - [Fe/H] diagram to overcome the aforementioned issue.
A scatter plot of exoplanet mass against red giant host star radius demonstrates an interesting positive trend: larger stars have more massive planets. This implies that the evolution of a star towards a red giant affects the masses of planets in the system.
In the near future we will have ground- and space-based telescopes that are designed to observe and characterize Earth-like planets. While attention is focused on exoplanets orbiting main sequence stars, more than 150 exoplanets have already been detected orbiting red giants, opening the intriguing question of what rocky worlds orbiting in the habitable zone of red giants would be like and how to characterize them. We model reflection and emission spectra of Earth-like planets orbiting in the habitable zone of red giant hosts with surface temperatures between 5200 and 3900 K at the Earth-equiv…
Context. Following the first discovery of a planet orbiting a giant star in 2002, we started the CORALIE radial-velocity search for companions around evolved stars (CASCADES). We present the observations of three stars conducted at the 1.2 m Leonard Euler Swiss telescope at La Silla Observatory, Chile, using the CORALIE spectrograph. Aims. We aim to detect planetary companions to intermediate-mass G- and K- type evolved stars and perform a statistical analysis of this population. We searched for new planetary systems around the stars HD22532 (TIC 200851704), HD64121 (TIC 264770836), and HD6912…
Driven largely by multiple ground-based radial-velocity (RV) surveys and photometric space missions such as Kepler and K2, the discovery of new exoplanets has increased rapidly since the early 2000s. However, due to a target selection bias in favor of main-sequence stars, only a handful of transiting planets have been found orbiting evolved hosts. These planets, most of which are giants, hold important information regarding the formation and evolution of planetary systems. In this thesis, I sought to increase the sample of known giant planets orbiting red-giant stars, focusing on data from NAS…
New and updated stellar parameters for 71 evolved planet hosts. On the metallicity - giant planet connection
目前仍有争议的是，著名的矮恒星金属丰度-巨行星相关性是否也适用于巨恒星。因此，精确的金属丰度非常重要。不同的方法可以提供不同的结果，导致行星宿主分析的差异。为了研究不同的分析方法对演化恒星金属丰度标度的影响，我们比较了不同的铁谱线列表，用于演化恒星的大气参数推导。因此，我们使用了71颗演化恒星的样本。有了这些新的均匀参数，我们重新审视了演化恒星的金属丰度-巨行星联系。基于局部热力学平衡（LTE）下的Kurucz模式，通过MOOG程序进行光谱分析，以获得大气参数。使用了两个不同的铁线列表集，一个是一般的冷FGK恒星，另一个是巨大的FGK恒星。使用Padova模型通过等时线拟合计算质量。然后对演化恒星和红巨星的各种不同样本的金属丰度分布进行了科尔莫戈罗夫-斯米尔诺夫检验（KS检验）。所有的参数都可以用一个专门为冷的和类似太阳的恒星设计的线列表集进行比较，以提供更准确的温度。使用此线路列表集导出的所有参数均为首选，因此可用于未来分析。我们发现，进化的行星宿主比拥有巨行星的矮星更缺乏金属。然而，在寻找行星的巨大恒星样本中存在偏见。由于颜色的限制，富含金属的低重力恒星被排除在样本之外，这使得很难将矮星与巨星进行比较。此外，相对于没有行星的红巨星，没有发现有行星的红巨星（$\log g < 3.0$ \，dex）的金属丰度增强。
We report the discovery of a transiting planet first identified as a candidate in Sector 1 of the Transiting Exoplanet Survey Satellite (TESS), and then confirmed with precision radial velocities. HD1397b has a mass of ${\rm M_P}$ = $0.335_{-0.018}^{+0.018}$ ${\rm M_J}$, a radius of ${\rm R_P}$ = $1.021_{-0.014}^{+0.015}$ ${\rm M_J}$, and orbits its bright host star ($V = 7.8$ mag) with an orbital period of $11.53508 \pm 0.00057 $ d, on a moderately eccentric orbit ($e$ = 0.210 $\pm$ 0.038). With a mass of ${\rm M}_{\star}$ = $1.284_{-0.016}^{+0.020}$ ${\rm M}_{J}$, a radius of ${\rm R}_{\star…
The fate of planets around rapidly evolving stars is not well understood. Previous studies have suggested that relative to the main sequence population, planets transiting evolved stars ($P$ $<$ 100 d) tend to have more eccentric orbits. Here we present the discovery of TOI-4582 b, a 0.94 $\pm$ 0.12 R$_\mathrm{J}$, 0.53 $\pm$ 0.05 M$_\mathrm{J}$ planet orbiting an intermediate-mass subgiant star every 31.034 days. We find that this planet is also on a significantly eccentric orbit ($e$ = 0.51 $\pm$ 0.05). We then compare the population of planets found transiting evolved (log$g$ $<$ 3.8) stars…
Hot Neptunes, gaseous planets smaller than Saturn ($\sim$ 3-8 R$_\oplus$) with orbital periods less than 10 days, are rare. Models predict this is due to high-energy stellar irradiation stripping planetary atmospheres over time, often leaving behind only rocky planetary cores. We present the discovery of a 6.2 R$_\oplus$(0.55 R$_\mathrm{J}$), 19.2 M$_\oplus$(0.060 M$_\mathrm{J}$) planet transiting a red giant star every 4.21285 days. The old age and high equilibrium temperature yet remarkably low density of this planet suggests that its gaseous envelope should have been stripped by high-energy…
We report initial results of a large radial velocity survey of K dwarfs up to a distance of 50 pc from the Solar System, to look for stellar, brown dwarf, and jovian planets using radial velocities from the CHIRON spectrograph on the CTIO/SMARTS 1.5m telescope. We identify three new exoplanet candidates orbiting host stars in the K dwarf survey, and confirm a hot Jupiter from TESS orbiting TOI 129. Our techniques are confirmed via five additional known exoplanet orbiting K dwarfs, bringing the number of orbital solutions presented here to 9, each hosting an exoplanet candidate with a minimum m…
A gas giant planet which survives the giant branch stages of evolution at a distance of many au and then is subsequently perturbed sufficiently close to a white dwarf will experience orbital shrinkage and circularization due to star-planet tides. The circularization timescale, when combined with a known white dwarf cooling age, can place coupled constraints on the scattering epoch as well as the active tidal mechanisms. Here, we explore this coupling across the entire plausible parameter phase space by computing orbit shrinkage and potential self-disruption due to chaotic f-mode excitation and…
We report the discovery of a second planet orbiting the K giant star 7 CMa based on 166 high-precision radial velocities obtained with Lick, HARPS, UCLES and SONG. The periodogram analysis reveals two periodic signals of approximately 745 and 980 d, associated to planetary companions. A double-Keplerian orbital fit of the data reveals two Jupiter-like planets with minimum masses $m_b\sin i \sim 1.9 \,\mathrm{M_{J}}$ and $m_c\sin i \sim 0.9 \,\mathrm{M_{J}}$, orbiting at semi-major axes of $a_b \sim 1.75\,\mathrm{au}$ and $a_c \sim 2.15\,\mathrm{au}$, respectively. Given the small orbital separ…
Upper atmospheres of Hot Jupiters are subject to extreme radiation conditions that can result in rapid atmospheric escape. The composition and structure of the upper atmospheres of these planets are affected by the high-energy spectrum of the host star. This emission depends on stellar type and age, which are thus important factors in understanding the behaviour of exoplanetary atmospheres. In this study, we focus on Extrasolar Giant Planets (EPGs) orbiting K and M dwarf stars. XUV spectra for three different stars - epsilon Eridani, AD Leonis and AU Microscopii - are constructed using a coron…
According to core-accretion formation models, the conditions under which gas giants will form around M dwarfs are very restrictive. Also, the correlation of the occurrence of these planets with the metallicity of host stars is still unknown due to the intrinsic faintness of M dwarfs in the optical and some intricacies in their spectra. Interestingly, NASA's TESS mission has started to create a growing sample of these systems, with eleven observed planets located in close-in orbits: contrary to what is expected for low stellar masses. Tidal interactions with the host star will play a key role i…
Exploring atmospheres of hot mini-Neptunes and extrasolar giant planets orbiting different stars with application to HD 97658b, WASP-12b, CoRoT-2b, XO-1b and HD 189733b
The tidal interaction of an orbiting giant planet with a star near the Kraft break: the excitation of $r$-modes and the retention of orbital and spin angular momenta misalignment
The Pan-Pacific Planet Search -- IX. A menagerie of companions orbiting evolved stars
University of Southern Queensland（南昆士兰大学）；Max Planck Institute for Astronomy（马克斯·普朗克天文学研究所）；Department of Astronomy & Astrophysics, University of Chicago（芝加哥大学天文与天体物理系）；Department of Physical Sciences, Kutztown University（库茨敦大学物理科学系）；Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney（悉尼大学物理学院悉尼天体物理研究所）；Institute for Astronomy, University of Hawai‘i（夏威夷大学天体物理研究所）；School of Physics, UNSW Sydney（新南威尔士大学悉尼分校物理学院）；Department of Physics, National University of Singapore（新加坡国立大学物理系）
The composition and structure of the upper atmospheres of Extrasolar Giant Planets (EGPs) are affected by the high-energy spectrum of their host stars from soft X-rays to EUV. This emission depends on the activity level of the star, which is primarily determined by its age. We focus upon EGPs orbiting K- and M-dwarf stars of different ages. XUV spectra for these stars are constructed using a coronal model. These spectra are used to drive both a thermospheric model and an ionospheric model, providing densities of neutral and ion species. Ionisation is included through photo-ionisation and elect…
We present fundamental stellar parameters and chemical abundances for a sample of 86 evolved stars with planets and for a control sample of 137 stars without planets. The analysis was based on both high S/N and resolution echelle spectra. The goals of this work are i) to investigate chemical differences between stars with and without planets; ii) to explore potential differences between the properties of the planets around giants and subgiants; and iii) to search for possible correlations between these properties and the chemical abundances of their host stars. In agreement with previous studi…
Extrasolar satellites are generally too small to be detected by nominal searches. By analogy to the most active body in the Solar System, Io, we describe how sodium (Na I) and potassium (K I) $\textit{gas}$ could be a signature of the geological activity venting from an otherwise hidden exo-Io. Analyzing $\sim$ a dozen close-in gas giants hosting robust alkaline detections, we show that an Io-sized satellite can be stable against orbital decay below a planetary tidal $\mathcal{Q}_p \lesssim 10^{11}$. This tidal energy is focused into the satellite driving a $\sim 10^{5 \pm 2}$ higher mass loss…
We report the discovery of a substellar companion around the giant star HIP67537. Based on precision radial velocity measurements from CHIRON and FEROS high-resolution spectroscopic data, we derived the following orbital elements for HIP67537$\,b$: m$_b$sin$i$ = 11.1$^{+0.4}_{-1.1}$ M$_{\rm {\tiny jup}}$, $a$ = 4.9$^{+0.14}_{-0.13}$ AU and $e$ = 0.59$^{+0.05}_{-0.02}$. Considering random inclination angles, this object has $\gtrsim$ 65% probability to be above the theoretical deuterium-burning limit, thus it is one of the few known objects in the planet to brown-dwarf transition region. In add…
The abundance and properties of planets orbiting binary stars - circumbinary planets - are largely unknown because they are difficult to detect with currently available techniques. Results from the Kepler satellite and other studies indicate a minimum occurrence rate of circumbinary giant planets of ~10 %, yet only a handful are presently known. Here, we study the potential of ESA's Gaia mission to discover and characterise extrasolar planets orbiting nearby binary stars by detecting the binary's periodic astrometric motion caused by the orbiting planet. We expect that Gaia will discover hundr…
An Aligned Very-Low-Mass Star Orbiting an M dwarf and Obliquity Patterns Across Giant Planets, Brown Dwarfs, and Binary Stars
Westlake University（西湖大学）；Université de Montréal（蒙特利尔大学）；Observatoire du Mont-Mégantic, Université de Montréal（蒙特利尔大学马格尼克天文台）；Université de Genève（日内瓦大学）；Observatoire de Genève, Département d’Astronomie, Université de Genève（日内瓦大学天文学系日内瓦天文台）
The red giant branch (RGB) of globular clusters (GCs) is home to some exotic stars, which may provide clues on the formation of multiple stellar populations in GCs. It is well known that binary interactions are responsible for many exotic stars. Thus, it is important to understand what fraction of stars on the RGB of GCs is the result of binary interactions. In this paper, we performed a binary population synthesis study to track the number of post-binary-interaction (post-BI) stars that appear on the RGB, with particular emphasis on the evolved blue straggler stars (E-BSSs). Assuming an initi…
Asteroseismology has revealed that cores of red giants rotate about one order of magnitude faster than their convective envelopes. This paper attempts an explanation for this rotational state in terms of the theory of angular momentum transport in stellar convection zones. A differential rotation model based on the theory is applied to a sequence of evolutionary states of a red giant of one solar mass. The model computations show a rotation of about ten times faster in the cores compared to the stellar surface. This rotational state is caused by the non-diffusive downward convective transport …
GEMS JWST: A sub-Solar metallicity atmosphere for giant planet TOI-5293Ab orbiting a rapidly changing M-dwarf
Carnegie Science（卡内基科学）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Johns Hopkins APL（约翰斯·霍普金斯大学应用物理实验室）；University of Maryland, College Park（马里兰大学帕克分校）；University of Zürich（苏黎世大学）
RV surveys of evolved stars allow us to probe a higher stellar mass range compared to main-sequence samples. Differences between the planet populations can be caused by either the differing stellar mass or stellar evolution. To properly disentangle the effects of both, the planet population around giant stars needs to be characterized as accurately as possible. Our goal is to investigate the giant planet occurrence rate around evolved stars and determine its dependence on stellar mass, metallicity, and orbital period. We combine data from the Lick, EXPRESS, and PPPS giant star surveys, yieldin…
The CARMENES radial-velocity survey is currently searching for planets in a sample of 387 M dwarfs. Here we report on two Saturn-mass planets orbiting TYC 2187-512-1 ($M_\star = 0.50 M_\odot$) and TZ Ari ($M_\star = 0.15 M_\odot$), respectively. We obtained supplementary photometric time series, which we use along with spectroscopic information to determine the rotation periods of the two stars. In both cases, the radial velocities also show strong modulations at the respective rotation period. We thus modeled the radial velocities as a Keplerian orbit plus a Gaussian process representing the …
CORALIE radial-velocity search for companions around evolved stars (CASCADES) IV: New planetary systems around HD 87816, HD 94890, and HD 102888 and an update on HD 121056
基于 CORALIE 数据，在 HD 87816、HD 94890 和 HD 102888 周围发现五个新大质量行星及一个亚恒星伴星，并更新了 HD 121056 外伴星周期，增进了对中等质量恒星行星种群的理解。
Validated planet candidates need not lie on long-term stable orbits, and instability triggered by post-main-sequence stellar evolution can generate architectures which transport rocky material to white dwarfs, polluting them. The giant planet HD 131399Ab orbits its parent A star at a projected separation of about 50-100 au. The host star, HD 131399A, is part of a hierarchical triple with HD 131399BC being a close binary separated by a few hundred au from the A star. Here, we determine the fate of this system, and find that (i) stability along the main sequence is achieved only for a favourable…
The growing database of exoplanets have shown us the statistical characteristics of various exoplanet populations, providing insight towards their origins. Observational evidence suggests that the process by which gas giants are conceived in the stellar disk may be disparate from that of smaller planets. Using NASA's Exoplanet Archive, we analyzed a correlation between the planet mass and stellar metallicity of low-mass exoplanets (MP < 0.13 MJ) orbiting spectral class G, K, and M stars. The correlation suggests an exponential law relationship between the two that is not fully explained by obs…
Our knowledge of the populations and occurrence rates of planets orbiting evolved intermediate-mass stars lags behind that for solar-type stars by at least a decade. Some radial velocity surveys have targeted these low-luminosity giant stars, providing some insights into the properties of their planetary systems. Here we present the final data release of the Pan-Pacific Planet Search, a 5-year radial velocity survey using the 3.9m Anglo-Australian Telescope. We present 1293 precise radial velocity measurements for 129 stars, and highlight six potential substellar-mass companions which require …
The detection of mixed modes in subgiants and red giants by the CoRoT and \emph{Kepler} space-borne missions allows us to investigate the internal structure of evolved low-mass stars. In particular, the measurement of the mean core rotation rate as a function of the evolution places stringent constraints on the physical mechanisms responsible for the angular momentum redistribution in stars. It showed that the current stellar evolution codes including the modelling of rotation fail to reproduce the observations. An additional physical process that efficiently extracts angular momentum from the…
Study of the impact of the post-MS evolution of the host star on the orbits of close-in planets. II. A giant planet in a close-in orbit around the RGB star HIP63242
The advent of asteroseismology as the golden path to precisely characterize single stars naturally led to synergies with the field of exoplanetology. Today, the precise determination of stellar masses, radii and ages for exoplanet-host stars is a driving force in the development of dedicated software and techniques to achieve this goal. However, as various approaches exist, it is clear that they all have advantages and inconveniences and that there is a trade-off between accuracy, efficiency, and robustness of the techniques. We aim to compare and discuss various modelling techniques for exopl…
The space-borne missions CoRoT and Kepler opened up a new opportunity for better understanding stellar evolution by probing stellar interiors with unrivalled high-precision photometric data. Kepler has observed stellar oscillation for four years, which gave access to excellent frequency resolution that enables deciphering the oscillation spectrum of evolved red giant branch and asymptotic giant branch stars. The internal structure of stars in the upper parts of the red and asymptotic giant branches is poorly constrained, which makes the distinction between red and asymptotic giants difficult. …
We report the discovery of eight new giant planets, and updated orbits for four known planets, orbiting dwarf and subgiant stars using the CORALIE, HARPS, and MIKE instruments as part of the Calan-Hertfordshire Extrasolar Planet Search. The planets have masses in the range 1.1-5.4MJs, orbital periods from 40-2900 days, and eccentricities from 0.0-0.6. They include a double-planet system orbiting the most massive star in our sample (HD147873), two eccentric giant planets (HD128356b and HD154672b), and a rare 14 Herculis analogue (HD224538b). We highlight some population correlations from the sa…
We report an unbiased radio line survey towards the circumstellar envelopes of evolved stars at the frequency range from 20 to 25 GHz, aiming to obtain a more complete unbiased picture of the chemical evolution in the final stages of stellar evolution. The observation sample includes the asymptotic giant branch (AGB) star IRC+10216, the proto-planetary nebulae (PPNs) CRL\,2688 and CRL\,618, and the young planetary nebula (PN) NGC\,7027, representing an evolutionary sequence spanning about 10,000 years. Rotational transitions from cyanopolyyne chains and inversion lines from ammonia are detecte…
Some red giant envelopes present spiral structures (seen either in dust scattered stellar continuum or in molecular line emission), the most striking example probably being AFGL 3068. This object has been modeled (both analytically and numerically) in terms of a wind ejected from a star in orbit around a binary companion. We revisit both analytical models and 3D simulations of a wind from an orbiting red giant star, and extend the numerical simulations to the case of a binary with two red giants with strong winds. We find that most two-wind models on the orbital plane show a "double spiral" st…
We report on the discovery and characterization of the transiting planet K2-39b (EPIC 206247743b). With an orbital period of 4.6 days, it is the shortest-period planet orbiting a subgiant star known to date. Such planets are rare, with only a handful of known cases. The reason for this is poorly understood, but may reflect differences in planet occurrence around the relatively high-mass stars that have been surveyed, or may be the result of tidal destruction of such planets. K2-39 is an evolved star with a spectroscopically derived stellar radius and mass of $3.88^{+0.48}_{-0.42}~\mathrm{R_\od…
