Search results for "Surface gravity"
showing 8 items of 8 documents
Gaia -ESO Survey: Analysis of pre-main sequence stellar spectra
2015
This paper describes the analysis of UVES and GIRAFFE spectra acquired by the Gaia-ESO Public Spectroscopic Survey in the fields of young clusters whose population includes pre-main sequence (PMS) stars. Both methods that have been extensively used in the past and new ones developed in the contest of the Gaia-ESO survey enterprise are available and used. The internal precision of these quantities is estimated by inter-comparing the results obtained by such different methods, while the accuracy is estimated by comparison with independent external data, like effective temperature and surface gravity derived from angular diameter measurements, on a sample of benchmarks stars. Specific strategi…
The Gaia-ESO survey: Metallicity of the chamaeleon i star-forming region
2014
Context. Recent metallicity determinations in young open clusters and star-forming regions suggest that the latter may be characterized by a slightly lower metallicity than the Sun and older clusters in the solar vicinity. However, these results are based on small statistics and inhomogeneous analyses. The Gaia-ESO Survey is observing and homogeneously analyzing large samples of stars in several young clusters and star-forming regions, hence allowing us to further investigate this issue. Aims. We present a new metallicity determination of the Chamaeleon I star-forming region, based on the products distributed in the first internal release of the Gaia-ESO Survey. Methods. 48 candidate member…
Coronal properties of G-type stars in different evolutionary phases
2005
We report on the analysis of XMM-Newton observations of three G-type stars in very different evolutionary phases: the weak-lined T Tauri star HD 283572, the Zero Age Main Sequence star EK Dra and the Hertzsprung-gap giant star 31 Com. They all have high X-ray luminosity (10^31 erg/s for HD 283572 and 31 Com and 10^30 erg/s for EK Dra). We compare the Emission Measure Distributions (EMDs) of these active coronal sources, derived from high-resolution XMM-Newton grating spectra, as well as the pattern of elemental abundances vs. First Ionization Potential (FIP). We also perform time-resolved spectroscopy of a flare detected by XMM from EK Dra. We interpret the observed $EMD$s as the result of …
The Gaia-ESO Survey: matching chemodynamical simulations to observations of the Milky Way
2017
The typical methodology for comparing simulated galaxies with observational surveys is usually to apply a spatial selection to the simulation to mimic the region of interest covered by a comparable observational survey sample. In this work, we compare this approach with a more sophisticated post-processing in which the observational uncertainties and selection effects (photometric, surface gravity and effective temperature) are taken into account. We compare a 'solar neighbourhood analogue' region in a model MilkyWay-like galaxy simulated with RAMSES-CH with fourth release Gaia-ESO survey data. We find that a simple spatial cut alone is insufficient and that the observational uncertainties …
Universal Relations for Gravitational-Wave Asteroseismology of Protoneutron Stars
2019
State-of-the-art numerical simulations of core-collapse supernovae reveal that the main source of gravitational waves is the excitation of proto-neutron star modes during post-bounce evolution. In this work we derive universal relations that relate the frequencies of the most common oscillation modes observed, i.e. g-modes, p-modes and the f-mode, with fundamental properties of the system, such as the surface gravity of the proto-neutron star or the mean density in the region enclosed by the shock. These relations are independent of the equation of state, the neutrino treatment, and the progenitor mass and hence can be used to build methods to infer proto-neutron star properties from gravit…
Thermal conduction and modeling of static stellar coronal loops
1993
We have modeled stellar coronal loops in static conditions for a wide range of loop length, plasma pressure at the base of the loop and stellar surface gravity, so as to describe physical conditions that can occur in coronae of stars ranging from low mass dwarfs to giants as well as on a significant fraction of the Main-Sequence stars.
Optical spectroscopy of X-ray sources in the Taurus molecular cloud: discovery of ten new pre-main sequence stars
2008
We have analyzed optical spectra of 25 X-ray sources identified as potential new members of the Taurus molecular cloud (TMC), in order to confirm their membership in this SFR. Fifty-seven candidates were previously selected among the X-ray sources in the XEST survey, having a 2MASS counterpart compatible with a PMS star based on color-magnitude and color-color diagrams. We obtained high-resolution optical spectra for 7 of these candidates with the SARG spectrograph at the TNG telescope, which were used to search for Li absorption and to measure the Ha line and the radial and rotational velocities; 18 low-resolution optical spectra obtained with DOLORES for other candidate members were used …
The Second APOKASC Catalog: The Empirical Approach
2018
We present a catalog of stellar properties for a large sample of 6676 evolved stars with APOGEE spectroscopic parameters and \textit{Kepler} asteroseismic data analyzed using five independent techniques. Our data includes evolutionary state, surface gravity, mean density, mass, radius, age, and the spectroscopic and asteroseismic measurements used to derive them. We employ a new empirical approach for combining asteroseismic measurements from different methods, calibrating the inferred stellar parameters, and estimating uncertainties. With high statistical significance, we find that asteroseismic parameters inferred from the different pipelines have systematic offsets that are not removed b…