- ID:
- ivo://CDS.VizieR/J/AJ/144/8
- Title:
- Spectroscopy of ~100 G/K/M-type Sco-Cen complex members
- Short Name:
- J/AJ/144/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have spectroscopically identified ~100 G-, K-, and M-type members of the Scorpius-Centaurus complex. To deduce the age of these young stars we compare their Li {lambda}6708 absorption line strengths against those of stars in the TW Hydrae association and {beta} Pictoris moving group. These line strengths indicate that Sco-Cen stars are younger than {beta} Pic stars whose ages of ~12Myr have previously been derived from a kinematic traceback analysis. Our derived age, ~10Myr, for stars in the Lower Centaurus Crux and Upper Centaurus Lupus subgroups of ScoCen is younger than previously published ages based on the moving cluster method and upper main-sequence fitting. The discrepant ages are likely due to an incorrect (or lack of) cross-calibration between model-dependent and model-independent age-dating methods.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/574/A124
- Title:
- Spectroscopy of solar twins and analogues
- Short Name:
- J/A+A/574/A124
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Many large stellar surveys have been and are still being carried out, providing huge amounts of data, for which stellar physical parameters will be derived. Solar twins and analogues provide a means to test the calibration of these stellar catalogues because the Sun is the best-studied star and provides precise fundamental parameters. Solar twins should be centred on the solar values. This spectroscopic study of solar analogues selected from the Geneva-Copenhagen Survey (GCS) at a resolution of 48000 provides effective temperatures and metallicities for these stars. We test whether our spectroscopic parameters, as well as the previous photometric calibrations, are properly centred on the Sun. In addition, we search for more solar twins in our sample. The methods used in this work are based on literature methods for solar twin searches and on methods we developed in previous work to distinguish the metallicity-temperature degeneracies in the differential comparison of spectra of solar analogues versus a reference solar reflection spectrum.
- ID:
- ivo://CDS.VizieR/J/PASP/118/1690
- Title:
- Spitzer solar-type stars list
- Short Name:
- J/PASP/118/1690
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We provide an overview of the Spitzer Legacy Program, Formation and Evolution of Planetary Systems, that was proposed in 2000, begun in 2001, and executed aboard the Spitzer Space Telescope between 2003 and 2006. This program exploits the sensitivity of Spitzer to carry out mid-infrared spectrophotometric observations of solar-type stars. With a sample of 328 stars ranging in age from 3Myr to 3Gyr, we trace the evolution of circumstellar gas and dust from primordial planet-building stages in young circumstellar disks through to older collisionally generated debris disks. When completed, our program will help define the timescales over which terrestrial and gas giant planets are built, constrain the frequency of planetesimal collisions as a function of time, and establish the diversity of mature planetary architectures. In addition to the observational program, we have coordinated a concomitant theoretical effort aimed at understanding the dynamics of circumstellar dust with and without the effects of embedded planets, dust spectral energy distributions, and atomic and molecular gas line emission. Together with the observations, these efforts will provide an astronomical context for understanding whether our solar system and its habitable planets a common or a rare circumstance. Additional information about the FEPS project can be found on the team Web site.
- ID:
- ivo://CDS.VizieR/J/ApJ/871/187
- Title:
- Spot parameters on KIC solar-type stars
- Short Name:
- J/ApJ/871/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Active solar-type stars show large quasi-periodic brightness variations caused by stellar rotation with star spots, and the amplitude changes as the spots emerge and decay. The Kepler data are suitable for investigations of the emergence and decay processes of star spots, which are important to understand the underlying stellar dynamo and stellar flares. In this study, we measured the temporal evolution of the star-spot area with Kepler data by tracing the local minima of the light curves. In this analysis, we extracted the temporal evolution of star spots showing clear emergence and decay without being disturbed by stellar differential rotation. We applied this method to 5356 active solar-type stars observed by Kepler and obtained temporal evolution of 56 individual star spots. We calculated the lifetimes and emergence/decay rates of the star spots from the obtained temporal evolution of the spot area. As a result, we found that the lifetimes (T) of star spots range from 10 to 350days when the spot areas (A) are 0.1%-2.3% of the solar hemisphere. We also compared them with sunspot lifetimes and found that the lifetimes of star spots are much shorter than those extrapolated from an empirical relation of sunspots (T{propto}A), while being consistent with other research on star-spot lifetimes. The emergence and decay rates of star spots are typically 5x10^20^Mx/hr (8MSH/hr) with an area of 0.1%-2.3% of the solar hemisphere and mostly consistent with those expected from sunspots, which may indicate the same underlying processes.
- ID:
- ivo://CDS.VizieR/J/AJ/160/130
- Title:
- SpT & NIR color excess of Solar-type stars
- Short Name:
- J/AJ/160/130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Although solar-analog stars have been studied extensively over the past few decades, most of these studies have focused on visible wavelengths, especially those identifying solar-analog stars to be used as calibration tools for observations. As a result, there is a dearth of well-characterized solar analogs for observations in the near-infrared, a wavelength range important for studying solar system objects. We present 184 stars selected based on solar-like spectral type and V-J and V-K colors whose spectra we have observed in the 0.8-4.2{mu}m range for calibrating our asteroid observations. Each star has been classified into one of three ranks based on spectral resemblance to vetted solar analogs. Of our set of 184 stars, we report 145 as reliable solar-analog stars, 21 as solar analogs usable after spectral corrections with low-order polynomial fitting, and 18 as unsuitable for use as calibration standards owing to spectral shape, variability, or features at low to medium resolution. We conclude that all but five of our candidates are reliable solar analogs in the longer wavelength range from 2.5 to 4.2{mu}m. The average colors of the stars classified as reliable or usable solar analogs are V-J=1.148, V-H=1.418, and V-K= 1.491, with the entire set being distributed fairly uniformly in R.A. across the sky between -27{deg} and +67{deg} in decl.
- ID:
- ivo://CDS.VizieR/J/A+A/393/225
- Title:
- Starspot cycles of six young solar analogues
- Short Name:
- J/A+A/393/225
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A long-term photometric monitoring of a selected sample of solar analogues has been carried out since early nineties as part of "The Sun in tim" project, which is aimed at a multiwavelength study of stars with solar-like global properties, but with different ages and thus at different stages of their evolution. The extended time sequence of ground-based observations collected over more than a decade as part of this program has revealed the existence of starspot cycles. Also from these data it is possible to investigate surface differential rotation of the stars. In this paper we present the photometry collected to date and report on cycles search for a selected subsample of five young single G0-G5V stars with ages between ~130Myr and 700Myr: EK Dra, {pi}^1^ UMa, HN Peg, {kappa}^1^ Cet, BE Cet. Also we include in this study the Pleiades-age (~130Myr) K0V star DX Leo (HD 82443). All the cited stars show activity cycles whose period is, furthermore, the first determined from photometric data. They are compared to those activity cycles derived from CaII H&K emission fluxes and differences are discussed. All the cycle periods, except for EK Dra, fit well the empirical relations with global stellar parameters derived from larger stellar samples. The following results are also inferred from the present study: i) the fastest rotating stars tend to have longer cycles; ii) the range in the observed cycle lengths seems to converge with stellar age from a maximum dispersion around the Pleiades' age towards the solar cycle value at the Sun's age; iii) the overall short- and long-term photometric variability increases with inverse Rossby number with very high correlation degree, indicating that the level of magnetic activity at least in photosphere is still controlled by the stellar rotation even on the longest time scales; iiii) the increase with inverse Rossby number of the long-term overall photometric variability seems to level off at the highest rotation rate, which may be interpreted as due to a saturation in the level of photospheric magnetic activity around the activity maximum.
- ID:
- ivo://CDS.VizieR/J/PASJ/63/1035
- Title:
- Stellar parameters and abundances of 99 giants
- Short Name:
- J/PASJ/63/1035
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present basic stellar parameters of 99 late-type G giants based on high-resolution spectra obtained by the High Dispersion Spectrograph attached to Subaru Telescope. These stars are targets of a Doppler survey program searching for extra-solar planets among evolved stars, with a metallicity of -0.8<[Fe/H]<+0.2. We also derived their abundances of 15 chemical elements, including four {alpha}-elements (Mg, Si, Ca, Ti), three odd-Z light elements (Al, K, Sc), four iron peak elements (V, Cr, Fe, Ni), and four neutron-capture elements (Y, Ba, La, Eu). Kinematic properties reveal that most of the program stars belong to the thin disk.
- ID:
- ivo://CDS.VizieR/J/A+A/458/873
- Title:
- Stellar parameters of metal-rich solar-type stars
- Short Name:
- J/A+A/458/873
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To date, metallicity is the only parameter of a star that appears to clearly correlate with the presence of planets and their properties. To check for new correlations between stars and the existence of an orbiting planet, we determine accurate stellar parameters for several metal-rich solar-type stars. The purpose is to fill the gap of the comparison sample presented in previous works in the high metal-content regime.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/480
- Title:
- Stellar X-ray sources in the COSMOS survey
- Short Name:
- J/ApJ/725/480
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an analysis of the X-ray properties of a sample of solar- and late-type field stars identified in the Chandra Cosmic Evolution Survey (COSMOS), a deep (160ks) and wide (~0.9deg^2^) extragalactic survey. The sample of 60 sources was identified using both morphological and photometric star/galaxy separation methods. We determine X-ray count rates, extract spectra and light curves, and perform spectral fits to determine fluxes and plasma temperatures. Complementary optical and near-IR photometry is also presented and combined with spectroscopy for 48 of the sources to determine spectral types and distances for the sample. We find distances ranging from 30pc to ~12kpc, including a number of the most distant and highly active stellar X-ray sources ever detected. Overall the sample is typically more luminous than the active Sun, representing the high-luminosity end of the disk and halo X-ray luminosity functions. The halo population appears to include both low-activity spectrally hard sources that may be emitting through thermal bremsstrahlung, as well as a number of highly active sources in close binaries.
- ID:
- ivo://CDS.VizieR/J/ApJS/209/5
- Title:
- Superflares of Kepler stars. I.
- Short Name:
- J/ApJS/209/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By extending our previous study by Maehara et al. (2012, Cat. J/other/Nat/485.478), we searched for superflares on G-type dwarfs (solar-type stars) using Kepler data for a longer period (500 days) than that (120 days) in our previous study. As a result, we found 1547 superflares on 279 G-type dwarfs, which is much more than the previous 365 superflares on 148 stars. Using these new data, we studied the statistical properties of the occurrence rate of superflares, and confirmed the previous results, i.e., the occurrence rate (dN/dE) of superflares versus flare energy (E) shows a power-law distribution with dN/dE{prop.to}E^-{alpha}^, where {alpha}~2. It is interesting that this distribution is roughly similar to that for solar flares. In the case of the Sun-like stars (with surface temperature 5600-6000K and slowly rotating with a period longer than 10 days), the occurrence rate of superflares with an energy of 10^34^-10^35^erg is once in 800-5000yr. We also studied long-term (500 days) stellar brightness variation of these superflare stars and found that in some G-type dwarfs the occurrence rate of superflares was extremely high, ~57 superflares in 500 days (i.e., once in 10 days). In the case of Sun-like stars, the most active stars show a frequency of one superflare (with 10^34^erg) in 100 days. There is evidence that these superflare stars have extremely large starspots with a size about 10 times larger than that of the largest sunspot. We argue that the physical origin of the extremely high occurrence rate of superflares in these stars may be attributed to the existence of extremely large starspots.
