Related papers: Probing Galactic variations in the fine-structure …
We report the latest statistical analyses of superflares on solar-type (G-type main-sequence; effective temperature is 5100 - 6000 K) stars using all of the $Kepler$ primary mission data, and $Gaia$-DR2 (Data Release 2) catalog. We updated…
Context: Massive amounts of spectroscopic data obtained by stellar surveys are feeding an ongoing revolution in our knowledge of stellar and Galactic astrophysics. Analysing these data sets to extract the best possible astrophysical…
Extreme precision radial-velocity spectrometers enable extreme precision stellar spectroscopy. Searches for low-mass exoplanets around solar-type stars are limited by the physical variability in stellar spectra, such as the short-term…
Large spectroscopic surveys aim to consistently compute stellar parameters of very diverse stars while minimizing systematic errors. We explore the use of stellar clusters as benchmarks to verify the precision of spectroscopic parameters in…
We conduct a line-by-line differential analysis of a sample of 125 co-moving pairs of stars (dwarfs and subgiants near solar metallicity). We obtain high precision stellar parameters with average uncertainties in effective temperature,…
We carried out spectroscopic observations with Subaru/HDS of 50 solar-type superflare stars found from Kepler data. More than half (34 stars) of the target stars show no evidence of the binary system, and we confirmed atmospheric parameters…
We conducted high dispersion spectroscopic observations of 50 superflare stars with Subaru/HDS, and measured the stellar parameters of them. These 50 targets were selected from the solar-type (G-type main sequence) superflare stars that we…
The observable spectrum of an unresolved binary star system is a superposition of two single-star spectra. Even without a detectable velocity offset between the two stellar components, the combined spectrum of a binary system is in general…
We report on the results of high dispersion spectroscopy of two `superflare stars', KIC 9766237, and KIC 9944137 with Subaru/HDS. Superflare stars are G-type main sequence stars, but show gigantic flares compared to the Sun, which have been…
An abundance analysis is presented of 60 metal-poor stars drawn from catalogues of nearby stars provided by Ariyanto et al. (2005) and Schuster et al. (2006). In an attempt to isolate a sample of metal-weak thick disc stars, we applied the…
To understand the formation and evolution of solar-type stars in the solar neighborhood, we need to measure their stellar parameters to high accuracy. We present a catalogue of accurate stellar parameters for 451 stars that represent the…
We investigate sulphur abundance in 74 Galactic stars by using high resolution spectra obtained at ESO VLT and NTT telescopes. For the first time the abundances are derived, where possible, from three optical multiplets: Mult. 1, 6, and 8.…
We have observed 152 nearby solar-type stars with the Infrared Spectrometer (IRS) on the Spitzer Space Telescope. Including stars that met our criteria but were observed in other surveys, we get an overall success rate for finding excesses…
Various effective temperature scales have been proposed over the years. Despite much work and the high internal precision usually achieved, systematic differences of order 100 K (or more) among various scales are still present. We present…
Binarity is often invoked to explain peculiarities that can not be explained by the standard theory of stellar evolution. Detecting orbital motion via the Doppler effect is the best method to test binarity when direct imaging is not…
Aims. To obtain limits on the variation of the fine-structure constant alpha and the electron-to-proton mass ratio mu over different cosmological epochs. Methods. A new approach based on the comparison of redshifts of far infrared (FIR)…
We examine contributions of second order physical processes to results of stellar evolution calculations amenable to direct observational testing. In the first paper in the series (Young et al. 2001) we established baseline results using…
Binary stars are as common as single stars. Binary stars are of immense importance to astrophysicists because that they allow us to determine the masses of the stars independent of their distances. They are the cornerstone of the…
We need to resolve the individual stars for binary fraction determinations of stellar systems. Therefore, it is not possible to obtain the binary fractions for dense or distant stellar systems. % We proposed a method to determine the binary…
Radial velocity observations of stars are entering the sub-m/s domain revealing fundamental barriers for Doppler precision experiments. Observations of the Sun as a star can easily overcome the m/s photon limit but face other obstacles. We…