- ID:
- ivo://CDS.VizieR/J/AJ/138/312
- Title:
- Activity of bright solar analogs
- Short Name:
- J/AJ/138/312
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present 14 years of contemporaneous photometric and spectroscopic observations of 28 solar analog stars, taken with the Tennessee State University Automatic Photometric Telescopes at Fairborn Observatory and the Solar-Stellar Spectrograph at Lowell Observatory. These are the best observed and most nearly Sun-like of the targets in our magnitude-limited (V<=7.5) sample. The correlations between luminosity and activity reveal the expected inverse activity-brightness correlations for active stars. Strong direct correlations between activity and brightness are not prevalent for the less active solar age stars, but are precision limited.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/687/1264
- Title:
- Age estimation for solar-type dwarfs
- Short Name:
- J/ApJ/687/1264
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- While the strong anticorrelation between chromospheric activity and age has led to the common use of the CaII H and K emission index (R'_HK_=L_HK_/L_bol_) as an empirical age estimator for solar-type dwarfs, existing activity-age relations produce implausible ages at both high and low activity levels. We have compiled R'_HK_, data from the literature for young stellar clusters, richly populating for the first time the young end of the activity-age relation. Combining the cluster activity data with modern cluster age estimates and analyzing the color dependence of the chromospheric activity age index, we derive an improved activity-age calibration for F7-K2 dwarfs (0.5<B-V<0.9mag). We also present a more fundamentally motivated activity-age calibration that relies on conversion of R'_HK_ values through the Rossby number to rotation periods and then makes use of improved gyrochronology relations.
- ID:
- ivo://CDS.VizieR/J/ApJ/745/24
- Title:
- A search for new companions with CHARA
- Short Name:
- J/ApJ/745/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a comprehensive search for new companions to nearby solar-type stars using the separated fringe packet (SFP) technique at the Center for High Angular Resolution Astronomy (CHARA) Array. Our search included 636 observations of 186 stars, searching for companions with separations of approximately 8-80 mas and moderate brightness ratios ({Delta}K<~1.5). This survey was undertaken to support a comprehensive assessment of companions to solar-type stars within 25 pc. We detected separated fringe companions to two stars (HD 3196 and 79096) and found faint companion signatures to two more stars (HD 98231 and 137763). All of these companions are previously known by spectroscopic methods, and three of them have speckle interferometric observations as well. The faint companion seen to HD 98231 represents the first visual detection of this spectroscopic companion. Our null detection for new companions implies that the presumed gap between spectroscopic and visual techniques has largely been filled for nearby solar-type stars, thanks to systematic radial-velocity observations over multiple decades and a thorough coverage using visual techniques, especially speckle interferometric observations. We also generate simulated fringe packets to derive detection limits for SFP binaries using the CHARA Array.
- ID:
- ivo://CDS.VizieR/J/MNRAS/495/2363
- Title:
- Asteroseismology of 36 Kepler subgiants. I.
- Short Name:
- J/MNRAS/495/2363
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The presence of mixed modes makes subgiants excellent targets for asteroseismology, providing a probe for the internal structure of stars. Here we study 36 Kepler subgiants with solar-like oscillations and report their oscillation mode parameters. We performed a so-called peakbagging exercise, i.e. estimating oscillation mode frequencies, linewidths, and amplitudes with a power spectrum model, fitted in the Bayesian framework and sampled with a Markov Chain Monte Carlo algorithm. The uncertainties of the mode frequencies have a median value of 0.180uHz. We obtained seismic parameters from the peakbagging, analysed their correlation with stellar parameters, and examined against scaling relations. The behaviour of seismic parameters (e.g. {Delta}{nu}, {nu}_max_, {epsilon}_p_) is in general consistent with theoretical predictions. We presented the observational p-g diagrams: {gamma}_1_-{Delta}u for early subgiants and {Delta}{Pi}_1_-{Delta}u for late subgiants, and demonstrate their capability to estimate stellar mass. We also found a logg dependence on the linewidths and a mass dependence on the oscillation amplitudes and the widths of oscillation excess. This sample will be valuable constraints for modelling stars and studying mode physics such as excitation and damping.
- 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.
- 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/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.
