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Absolute parameters for AI Phoenicis using WASP photometry <i>(Corrigendum)</i>
摘要： An error has been noted in the linear ephemeris for AI Phe, shown in Eq. (2) of the paper. The correct ephemeris is This is typographical error and has no effect on any of the timing analysis presented in the paper. HJD Pri. Min. = 2 455 805.24370(21) + 24.592483(17) E.
关键词： stars: fundamental parameters,errata,binaries: eclipsing,stars: evolution,addenda,stars: solar-type
更新于2025-09-23 15:22:29
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Empirical photometric calibration of the <i>Gaia</i> red clump: Colours, effective temperature, and absolute magnitude
摘要： Context. Gaia Data Release 1 allows the recalibration of standard candles such as the red clump stars. To use those stars, they first need to be accurately characterised. In particular, colours are needed to derive interstellar extinction. As no filter is available for the first Gaia data release and to avoid the atmosphere model mismatch, an empirical calibration is unavoidable. Aims. The purpose of this work is to provide the first complete and robust photometric empirical calibration of the Gaia red clump stars of the solar neighbourhood through colour–colour, effective temperature–colour, and absolute magnitude–colour relations from the Gaia, Johnson, 2MASS, Hipparcos, Tycho-2, APASS-SLOAN, and WISE photometric systems, and the APOGEE DR13 spectroscopic temperatures. Methods. We used a 3D extinction map to select low reddening red giants. To calibrate the colour–colour and the effective temperature–colour relations, we developed a MCMC method that accounts for all variable uncertainties and selects the best model for each photometric relation. We estimated the red clump absolute magnitude through the mode of a kernel-based distribution function. Results. We provide 20 colour versus G ? Ks relations and the first Teff versus G ? Ks calibration. We obtained the red clump absolute magnitudes for 15 photometric bands with, in particular, MKs = (?1.606 ± 0.009) and MG = (0.495 ± 0.009) + (1.121 ± 0.128) (G ? Ks ? 2.1). We present a dereddened Gaia-TGAS HR diagram and use the calibrations to compare its red clump and its red giant branch bump with Padova isochrones.
关键词： stars: fundamental parameters,stars: atmospheres,dust, extinction,stars: abundances
更新于2025-09-23 15:21:21
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The X-shooter Spectral Library (XSL)
摘要： We present the ?rst release of the X-shooter Spectral Library (XSL). This release contains 237 stars. The spectra in this release span a wavelength range of 3000–10 200 ? and have been observed at a resolving power of R ≡ λ/Δλ ～ 10 000. The spectra were obtained at ESO’s 8-m Very Large Telescope (VLT). The sample contains O–M, long-period variable, C and S stars. The spectra are ?ux-calibrated and telluric-corrected. We describe a new technique for the telluric correction. The wavelength coverage, spectral resolution, and spectral type of this library make it well suited to stellar population synthesis of galaxies and clusters, kinematical investigation of stellar systems, and the study of the physics of cool stars.
关键词： stars: fundamental parameters,galaxies: stellar content,stars: atmospheres,stars: AGB and post-AGB,stars: abundances
更新于2025-09-23 15:19:57
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Solar twins in the ELODIE archive
摘要： A large dataset of ～2800 spectra extracted from the ELODIE archive was analysed in order to ?nd solar twins. Stellar spectra closely resembling the spectrum of the Sun were selected by applying a purely di?erential method, directly on the ?uxes. As solar reference, 18 spectra of asteroids, Moon, and blue sky were used. Atmospheric parameters and di?erential abundances of eight chemical elements were determined for the solar twin candidates after a careful selection of appropriate lines. The Li feature of the targets was investigated and additional information on absolute magnitude and age was gathered from the literature. HIP 076114 (HD 138573) is our best twin candidate; it looks exactly like the Sun in all these properties.
关键词： stars: fundamental parameters,stars: solar-type,stars: atmospheres,stars: abundances
更新于2025-09-23 15:19:57
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Deep SDSS optical spectroscopy of distant halo stars
摘要： Aims. We analyze a sample of tens of thousands of spectra of halo turno? stars, obtained with the optical spectrographs of the Sloan Digital Sky Survey (SDSS), to characterize the stellar halo population “in situ” out to a distance of a few tens of kpc from the Sun. In this paper we describe the derivation of atmospheric parameters. We also derive the overall stellar metallicity distribution based on F-type stars observed as ?ux calibrators for the Baryonic Oscillations Spectroscopic Survey (BOSS). Methods. Our analysis is based on an automated method that determines the set of parameters of a model atmosphere that reproduces each observed spectrum best. We used an optimization algorithm and evaluate model ?uxes by means of interpolation in a precomputed grid. In our analysis, we account for the spectrograph’s varying resolution as a function of ?ber and wavelength. Our results for early SDSS (pre-BOSS upgrade) data compare well with those from the SEGUE Stellar Parameter Pipeline (SSPP), except for stars with log g (cgs units) lower than 2.5. Results. An analysis of stars in the globular cluster M 13 reveals a dependence of the inferred metallicity on surface gravity for stars with log g < 2.5, con?rming the systematics identi?ed in the comparison with the SSPP. We ?nd that our metallicity estimates are signi?cantly more precise than the SSPP results. We also ?nd excellent agreement with several independent analyses. We show that the SDSS color criteria for selecting F-type halo turno? stars as ?ux calibrators e?ciently excludes stars with high metallicities, but does not signi?cantly distort the shape of the metallicity distribution at low metallicity. We obtain a halo metallicity distribution that is narrower and more asymmetric than in previous studies. The lowest gravity stars in our sample, at tens of kpc from the Sun, indicate a shift of the metallicity distribution to lower abundances, consistent with what is expected from a dual halo system in the Milky Way.
关键词： techniques: spectroscopic,stars: atmospheres,methods: observational,Galaxy: halo,stars: Population II,stars: fundamental parameters
更新于2025-09-23 15:19:57
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Spectroscopic study of solar twins and analogues
摘要： Context. 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. Aims. This spectroscopic study of solar analogues selected from the Geneva-Copenhagen Survey (GCS) at a resolution of 48 000 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. Methods. 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. Results. We derive spectroscopic parameters for 148 solar analogues (about 70 are new entries to the literature) and verify with a-posteriori differential tests that our values are well-centred on the solar values. We use our dataset to assess the two alternative calibrations of the GCS parameters; our methods favour the latest revision. We show that the choice of spectral line list or the choice of asteroid or time of observation does not affect the results. We also identify seven solar twins in our sample, three of which are published here for the first time. Conclusions. Our methods provide an independent means to differentially test the calibration of stellar catalogues around the values of a well-known benchmark star, which makes our work interesting for calibration tests of upcoming Galactic surveys.
关键词： stars: fundamental parameters,stars: solar-type,stars: abundances
更新于2025-09-19 17:15:36
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Benchmark stars for <i>Gaia</i> Fundamental properties of the Population II star HD?140283 from interferometric, spectroscopic, and photometric data
摘要： Metal-poor halo stars are important astrophysical laboratories that allow us to unravel details about many aspects of astrophysics, including the chemical conditions at the formation of our Galaxy, understanding the processes of diffusion in stellar interiors, and determining precise effective temperatures and calibration of colour-effective temperature relations. To address any of these issues the fundamental properties of the stars must first be determined. HD 140283 is the closest and brightest metal-poor Population II halo star (distance = 58 pc and V = 7.21), an ideal target that allows us to approach these questions, and one of a list of 34 benchmark stars defined for Gaia astrophysical parameter calibration. In the framework of characterizing these benchmark stars, we determined the fundamental properties of HD 140283 (radius, mass, age, and effective temperature) by obtaining new interferometric and spectroscopic measurements and combining them with photometry from the literature. The interferometric measurements were obtained using the visible interferometer VEGA on the CHARA array and we determined a 1D limb-darkened angular diameter of θ1D = 0.353 ± 0.013 milliarcsec. Using photometry from the literature we derived the bolometric flux in two ways: a zero reddening solution (AV = 0.0 mag) of Fbol of 3.890 ± 0.066 × 10?8 erg s?1 cm?2, and a maximum of AV = 0.1 mag solution of 4.220 ± 0.067 × 10?8 erg s?1 cm?2. The interferometric Teff is thus between 5534 ± 103 K and 5647 ± 105 K and its radius is R = 2.21 ± 0.08 R⊙. Spectroscopic measurements of HD 140283 were obtained using HARPS, NARVAL, and UVES and a 1D LTE analysis of Hα line wings yielded Teff spec = 5626 ± 75 K. Using fine-tuned stellar models including diffusion of elements we then determined the mass M and age t of HD 140283. Once the metallicity has been fixed, the age of the star depends on M, initial helium abundance Yi, and mixing-length parameter α, only two of which are independent. We derive simple equations to estimate one from the other two. We need to adjust α to much lower values than the solar one (～2) in order to fit the observations, and if AV = 0.0 mag then 0.5 ≤ α ≤ 1. We give an equation to estimate t from M, Yi (α), and AV. Establishing a reference α = 1.00 and adopting Yi = 0.245 we derive a mass and age of HD 140283: M = 0.780 ± 0.010 M⊙ and t = 13.7 ± 0.7 Gyr (AV = 0.0 mag), or M = 0.805 ± 0.010 M⊙ and t = 12.2 ± 0.6 Gyr (AV = 0.1 mag). Our stellar models yield an initial (interior) metal-hydrogen mass fraction of [Z/X]i = ?1.70 and log g = 3.65 ± 0.03. Theoretical advances allowing us to impose the mixing-length parameter would greatly improve the redundancy between M, Yi, and age, while from an observational point of view, accurate determinations of extinction along with asteroseismic observations would provide critical information allowing us to overcome the current limitations in our results.
关键词： stars: fundamental parameters,techniques: spectroscopic,surveys,stars: individual: HD 140283,techniques: interferometric,stars: Population II
更新于2025-09-19 17:15:36
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HIDES spectroscopy of bright detached eclipsing binaries from the <i>Kepler</i> field – III. Spectral analysis, updated parameters and new systems
摘要： We present the latest results of our spectroscopic observations and refined modelling of a sample of detached eclipsing binaries, selected from the Kepler Eclipsing Binary Catalog, that are also double-lined spectroscopic binaries (SB2s). New high-resolution spectra obtained with the HIgh-Dispersion Echelle Spectrograph (HIDES), attached to the 1.88-m telescope of the Okayama Astrophysical Observatory, have supplemented the previous observations. This has allowed us to improve the physical parameters of some systems, and to characterize three previously omitted objects. All the obtained radial velocities were combined with Kepler photometry, in order to derive a full set of orbital and physical parameters. Ten out of eleven SB2s have their component spectra tomographically disentangled, and spectral analysis was performed with ISPEC, in order to derive the effective temperatures of components and the metallicities of the systems. By comparing our results with theoretical models, we assess the age and evolutionary status of the studied objects. We find a good match to all systems but one. We have derived distances from the parameters determined in this way, and we compare them with those from the Gaia Data Release 2. For systems previously studied by other authors, our new results lead to better consistency between observations and models.
关键词： binaries: eclipsing,stars: fundamental parameters,stars: late-type,binaries: spectroscopic,stars: evolution
更新于2025-09-19 17:15:36
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LEMONY – a library of empirical medium-resolution spectra by observations with the NAOC Xinglong 2.16-m and YNAO Gaomeigu 2.4-m telescopes
摘要： In this study, we expand the coverage and improve the homogeneity of the distribution of MILES template stars in the parameter space, as well as extend the wavelength coverage of the template spectra to the far red beyond the CaII triplet. To achieve this, we have carried out a major observational campaign using two long-slit spectrographs: the OMR mounted on the National Astronomy Observatory of China (NAOC) 2.16-m telescope and the Yunnan Faint Object Spectrograph and Camera (YFOSC) mounted on the Yunnan Astronomical Observatory (YNAO) 2.4-m telescope. The original sample is based on the MILES library, supplemented by 918 stars selected from the PASTEL data base. In total, 822 OMR and 1324 YFOSC spectra have been collected and reduced, covering the wavelength ranges λλ3800–5180 and λλ5150–9000, respectively. The spectra have a mean resolution full width at half-maximum of ～3.3 ? and are wavelength- and ?ux-calibrated to an accuracy of ～20 km s?1 and ～5 per cent, respectively. The spectra are further corrected for systematic errors in the wavelength calibration to an accuracy of ～4 km s?1 by cross-correlating with the theoretical spectra. Almost all the spectra have an average signal-to-noise ratio better than 100 per pixel. Combined with the MILES spectra, there are now 1731, 1542, 1324 and 1273 stars with spectra covering λλ3800–5180, λλ3800–7500, λλ5150–9000 and λλ3800–9000, respectively. In this paper, we describe our template star selection, the observation and data reduction, and we present the reduced spectra collected hitherto.
关键词： stars: fundamental parameters,techniques: imaging spectroscopy
更新于2025-09-19 17:15:36
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A CO-multilayer outer atmosphere for eight evolved stars revealed with VLTI/AMBER
摘要： We determine the physical parameters of the outer atmosphere of a sample of eight evolved stars, including the red supergiant α Scorpii, the red giant branch stars α Bootis and γ Crucis, the K giant λ Velorum, the normal M giants BK Virginis and SW Virginis, and the Mira star W Hydrae (in two different luminosity phases) by spatially resolving the stars in the individual carbon monoxide (CO) first overtone lines. We used the Astronomical Multi-BEam combineR (AMBER) instrument at the Very Large Telescope Interferometer (VLTI), in high-resolution mode (λ/(cid:5)λ ≈ 12 000) between 2.28 and 2.31 μm in the K band. The maximal angular resolution is 10 mas, obtained using a triplet telescope configuration, with baselines from 7 to 48 m. By using a numerical model of a molecular atmosphere in a spherical shells (MOLsphere), called PAMPERO (an acronym for the ‘physical approach of molecular photospheric ejection at high angular resolution for evolved stars’), we add multiple extended CO layers above the photospheric MARCS model at an adequate spatial resolution. We use the differential visibilities and the spectrum to estimate the size (R) of the CO MOLsphere, its column density (NCO) and temperature (Tmol) distributions along the stellar radius. The combining of the χ 2 minimization and a fine grid approach for uncertainty analysis leads to reasonable NCO and Tmol distributions along the stellar radius of the MOLsphere.
关键词： techniques: high angular resolution,stars: atmospheres,stars: AGB and post-AGB,stars: fundamental parameters,methods: numerical,methods: observational
更新于2025-09-11 14:15:04