- ID:
- ivo://CDS.VizieR/J/ApJS/190/1
- Title:
- A survey of stellar families
- Short Name:
- J/ApJS/190/1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a comprehensive assessment of companions to solar-type stars. A sample of 454 stars, including the Sun, was selected from the Hipparcos catalog with {pi}>40mas, {sigma}{pi}/{pi}<0.05, 0.5<=B-V<=1.0 (~F6-K3), and constrained by absolute magnitude and color to exclude evolved stars. These criteria are equivalent to selecting all dwarf and subdwarf stars within 25pc with V-band flux between 0.1 and 10 times that of the Sun, giving us a physical basis for the term "solar-type". New observational aspects of this work include surveys for (1) very close companions with long-baseline interferometry at the Center for High Angular Resolution Astronomy Array, (2) close companions with speckle interferometry, and (3) wide proper-motion companions identified by blinking multi-epoch archival images. In addition, we include the results from extensive radial-velocity monitoring programs and evaluate companion information from various catalogs covering many different techniques. The results presented here include four new common proper-motion companions discovered by blinking archival images. Additionally, the spectroscopic data searched reveal five new stellar companions. Our synthesis of results from many methods and sources results in a thorough evaluation of stellar and brown dwarf companions to nearby Sun-like stars. The overall observed fractions of single, double, triple, and higher-order systems are 56%+/-2%, 33%+/-2%, 8%+/-1%, and 3%+/-1%, respectively, counting all confirmed stellar and brown dwarf companions.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/857/119
- Title:
- Asymmetry of oscillations in 43 Kepler stars
- Short Name:
- J/ApJ/857/119
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Oscillation properties are usually measured by fitting symmetric Lorentzian profiles to the power spectra of Sun-like stars. However, the line profiles of solar oscillations have been observed to be asymmetrical for the Sun. The physical origin of this line asymmetry is not fully understood; though, it should depend on the depth dependence of the source of wave excitation (convective turbulence) and details of the observable (velocity or intensity). For oscillations of the Sun, it has been shown that neglecting the asymmetry leads to systematic errors in the frequency determination. This could subsequently affect the results of seismic inferences of the solar internal structure. Using light curves from the Kepler spacecraft, we have measured mode asymmetries in 43 stars. We confirm that neglecting the asymmetry leads to systematic errors that can exceed the 1{sigma} confidence intervals for seismic observations longer than one year. Therefore, the application of an asymmetric Lorentzian profile should be favored to improve the accuracy of the internal stellar structure and stellar fundamental parameters. We also show that the asymmetry changes sign between cool Sun-like stars and hotter stars. This provides the best constraints to date on the location of the excitation sources across the Hertzsprung-Russel diagram.
- ID:
- ivo://CDS.VizieR/J/MNRAS/444/3517
- Title:
- BCool survey of solar-type stars
- Short Name:
- J/MNRAS/444/3517
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a major high-resolution spectropolarimetric BCool project magnetic survey of 170 solar-type stars. Surface magnetic fields were detected on 67 stars, with 21 classified as mature solar-type stars, a result that increases by a factor of 4 the number of mature solar-type stars on which magnetic fields have been observed. In addition, a magnetic field was detected for 3 out of 18 of the subgiant stars surveyed. For the population of K-dwarfs, the mean value of |Bl| (|Bl|_mean_) was also found to be higher (5.7G) than |Bl|_mean_ measured for the G-dwarfs (3.2G) and the F-dwarfs (3.3G). For the sample as a whole, |Bl|_mean_ increases with rotation rate and decreases with age, and the upper envelope for |Bl| correlates well with the observed chromospheric emission. Stars with a chromospheric S-index greater than about 0.2 show a high magnetic field detection rate and so offer optimal targets for future studies. This survey constitutes the most extensive spectropolarimetric survey of cool stars undertaken to date, and suggests that it is feasible to pursue magnetic mapping of a wide range of moderately active solar-type stars to improve our understanding of their surface fields and dynamos.
- ID:
- ivo://CDS.VizieR/J/A+A/655/A117
- Title:
- Carbon and oxygen in microlensed bulge dwarfs
- Short Name:
- J/A+A/655/A117
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Next to H and He, carbon is, together with oxygen, the most abundant element in the Universe and widely used when modelling the formation and evolution of galaxies and their stellar populations. For the Milky Way bulge, there are currently essentially no measurements of carbon in un-evolved stars, hampering our abilities to properly compare Galactic chemical evolution models to observational data for this still enigmatic stellar population. We aim to determine carbon abundances for our sample of 91 microlensed dwarf and subgiant stars in the Galactic bulge. Together with new determinations for oxygen this forms the first statistically significant sample of bulge stars that have C and O abundances measured, and for which the C abundances have not been altered by the nuclear burning processes internal to the stars. Our analysis is based on high-resolution spectra for a sample of 91 dwarf and subgiant stars that were obtained during microlensing events when the brightnesses of the stars were highly magnified. Carbon abundances were determined through spectral line synthesis of six CI lines around 9100{AA}, and oxygen abundances using the three OI lines at about 7770{AA}. One-dimensional (1D) MARCS model stellar atmospheres calculated under the assumption of local thermodynamic equilibrium (LTE) were used, and non-LTE corrections were applied when calculating the synthetic spectra for both C and O. Carbon abundances was possible to determine for 70 of the 91 stars in the sample and oxygen abundances for 88 of the 91 stars in the sample. The [C/Fe] ratio evolves essentially in lockstep with [Fe/H], centred around solar values at all [Fe/H]. The [O/Fe]-[Fe/H] trend has an appearance very similar to that observed for other alpha-elements in the bulge, with the exception of a continued decrease in [O/Fe] at super-solar [Fe/H], where other alpha-elements tend to level out. When dividing the bulge sample into two sub-groups, one younger than 8Gyr and one older than 8Gyr, the stars in the two groups follow exactly the elemental abundance trends defined by the solar neighbourhood thin and thick disks, respectively. Comparisons with recent models of Galactic chemical evolution in the [C/O]-[O/H] plane show that the models that best match the data are the ones that have been calculated with the Galactic thin and thick disks in mind. We conclude that carbon, oxygen, and the combination of the two support the idea that the majority of the stars in the Galactic bulge have a secular origin; that is, they are formed from disk material. We cannot exclude that a fraction of stars in the bulge could be classified as a classical bulge population, but it would have to be small. More dedicated and advanced models of the inner region of the Milky Way are needed to make more detailed comparisons to the observations.
- ID:
- ivo://CDS.VizieR/J/MNRAS/505/L79
- Title:
- Characteristic time of stellar flares
- Short Name:
- J/MNRAS/505/L79
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- Using the short-cadence data (1-min interval) of the Kepler space telescope, we conducted a statistical analysis for the characteristic time of stellar flares on Sun-like stars (SLS). Akin to solar flares, stellar flares show rise and decay light-curve profiles, which reflect the two distinct phases (rise phase and decay phase) of the flare process. We derived characteristic times of the two phases for the stellar flares of SLS, resulting in a median rise time of about 5.9min and a median decay time of 22.6min. It is found that both the rise time and the decay time of the stellar flares follow a lognormal distribution. The peak positions of the lognormal distributions for flare rise time and decay time are 3.5min and 14.8min, respectively. These time values for stellar flares are similar to the time-scale of solar flares, which supports the idea that stellar flares and solar flares have the same physical mechanism. The statistical results obtained in this work for SLS can be a benchmark of flare characteristic times when comparing with other types of stars.
- ID:
- ivo://CDS.VizieR/J/ApJ/709/447
- Title:
- Chemical composition of OGLE-2007-BLG-514S
- Short Name:
- J/ApJ/709/447
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a high-resolution spectrum of a microlensed G dwarf in the Galactic bulge with spectroscopic temperature T_eff_=5600+/-180K. This I~21mag star was magnified by a factor ranging from 1160 to 1300 at the time of observation. Its high metallicity ([Fe/H]=0.33+/-0.15dex) places this star at the upper end of the bulge giant metallicity distribution. Using a Kolmogorov-Smirnov test, we find a 1.6% probability that the published microlensed bulge dwarfs share an underlying distribution with bulge giants, properly accounting for a radial bulge metallicity gradient. We obtain abundance measurements for 15 elements and perform a rigorous error analysis that includes covariances between parameters. This star, like bulge giants with the same metallicity, shows no alpha enhancement. It confirms the chemical abundance trends observed in previously analyzed bulge dwarfs. At supersolar metallicities, we observe a discrepancy between bulge giant and bulge dwarf Na abundances.
- ID:
- ivo://CDS.VizieR/J/AJ/160/239
- Title:
- Cluster difference imaging photometric survey. II.
- Short Name:
- J/AJ/160/239
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the discovery of TOI837b and its validation as a transiting planet. We characterize the system using data from the NASA Transiting Exoplanet Survey Satellite mission, the ESA Gaia mission, ground-based photometry from El Sauce and ASTEP400, and spectroscopy from CHIRON, FEROS, and Veloce. We find that TOI837 is a T=9.9mag G0/F9 dwarf in the southern open cluster IC2602. The star and planet are therefore 35_-5_^+11^ million years old. Combining the transit photometry with a prior on the stellar parameters derived from the cluster color-magnitude diagram, we find that the planet has an orbital period of 8.3days and is slightly smaller than Jupiter (R_p_=0.77_-0.07_^+0.09^R_Jup_). From radial velocity monitoring, we limit M_p_sin(i) to less than 1.20M_Jup_(3{sigma}). The transits either graze or nearly graze the stellar limb. Grazing transits are a cause for concern, as they are often indicative of astrophysical false-positive scenarios. Our follow-up data show that such scenarios are unlikely. Our combined multicolor photometry, high-resolution imaging, and radial velocities rule out hierarchical eclipsing binary scenarios. Background eclipsing binary scenarios, though limited by speckle imaging, remain a 0.2% possibility. TOI837b is therefore a validated adolescent exoplanet. The planetary nature of the system can be confirmed or refuted through observations of the stellar obliquity and the planetary mass. Such observations may also improve our understanding of how the physical and orbital properties of exoplanets change in time.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/20
- Title:
- C/O and Mg/Si for solar neighborhood's stars
- Short Name:
- J/ApJ/831/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The carbon-to-oxygen ratio in a protoplanetary disk can have a dramatic influence on the compositions of any terrestrial planets formed. In regions of high C/O, planets form primarily from carbonates, and in regions of low C/O, the ratio of magnesium to silicon determines the types of silicates that dominate the compositions. We present C/O and Mg/Si ratios for 852 F, G, and K dwarfs in the solar neighborhood. We find that the frequency of carbon-rich dwarfs in the solar neighborhood is <0.13% and that 156 known planet hosts in the sample follow a similar distribution as all of the stars as a whole. The cosmic distribution of Mg/Si for these same stars is broader than the C/O distribution and peaks near 1.0, with ~60% of systems having 1<=Mg/Si<2, leading to rocky planet compositions similar to the Earth. This leaves 40% of systems that can have planets that are silicate-rich and that may have very different compositions than our own.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A34
- Title:
- Complete line list and solar values
- Short Name:
- J/A+A/634/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Open clusters are recognised as excellent tracers of the Galactic thin disc properties. At variance with intermediate-age and old open clusters, for which a conspicuous number of studies is now available, until a few years ago clusters younger than 150Myr had been mostly overlooked in terms of their chemical composition (with few exceptions). On the other hand, previous investigations seem to indicate an anomalous behaviour of young clusters, which include (but is not limited to) slightly sub-solar iron (Fe) abundances and extreme, unexpected barium (Ba) enhancements. In a series of papers, we plan to expand our comprehension of this topic and investigate whether these chemical peculiarities are instead related to abundance analysis techniques. We present here a new determination of the atmospheric parameters for 23 dwarf stars observed by the Gaia-ESO survey in five young open clusters (age less than 150Myr) and one star forming region (NGC 2264). We exploit a new method based on titanium (Ti) lines to derive spectroscopic surface gravity and, most important, microturbulence parameter. A combination of Ti and Fe lines have been used to obtain effective temperatures. We also infer abundances of FeI, FeII, TiI, TiII, NaI, MgI, AlI, SiI, CaI, CrI and NiI. Our findings are in fair agreement with Gaia-ESO iDR5 results for effective temperatures and surface gravities, but suggest that for very young stars the microturbulence parameter is over-estimated when Fe lines are employed. This impacts the derived chemical composition, causing the metal content of very young clusters to be under-estimated. Our clusters display a metallicity [Fe/H] between +0.04 and +0.12; thus they are not more metal-poor than the Sun. Although based on a relatively small sample size, our explorative study suggests that we may not need to call for ad hoc explanations to reconcile the chemical composition of young open clusters with Galactic chemical evolution models.
- ID:
- ivo://CDS.VizieR/J/AJ/160/96
- Title:
- CORALIE and PFS radial velocities of HD 86226
- Short Name:
- J/AJ/160/96
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Transiting Exoplanet Survey Satellite (TESS) mission was designed to find transiting planets around bright, nearby stars. Here, we present the detection and mass measurement of a small, short-period (~4days) transiting planet around the bright (V=7.9), solar-type star HD86226 (TOI-652, TIC22221375), previously known to host a long-period (~1600days) giant planet. HD86226c (TOI-652.01) has a radius of 2.16{+/-}0.08R_{Earth}_ and a mass of 7.25_-1.12_^+1.19^M_{Earth}_, based on archival and new radial velocity data. We also update the parameters of the longer-period, not-known-to-transit planet, and find it to be less eccentric and less massive than previously reported. The density of the transiting planet is 3.97g/cm^3^, which is low enough to suggest that the planet has at least a small volatile envelope, but the mass fractions of rock, iron, and water are not well- constrained. Given the host star brightness, planet period, and location of the planet near both the "radius gap" and the "hot Neptune desert," HD86226c is an interesting candidate for transmission spectroscopy to further refine its composition.
