Line profile variations in classical Cepheids

Kovtyukh, V. V.; Andrievsky, S. M.; Luck, R. E.; Gorlova, Nadya

doi:10.1051/0004-6361:20030130

Cited by 66 publications

(85 citation statements)

References 31 publications

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“…To determine the effective temperature T eff , we employed the line depth ratios method of Kovtyukh (2007), which comes from the work of Kovtyukh & Gorlova (2000). The ratios of the central depths of carefully chosen pairs of lines that have a very different dependence on T eff are entered in previously calibrated relations.…”

Section: Methodsmentioning

confidence: 99%

Type II Cepheids in the Milky Way disc

Lemasle

Kovtyukh

Bono

et al. 2015

A&A

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Context. A robust classification of Cepheids into their different sub-classes and, in particular, between classical and Type II Cepheids, is necessary to properly calibrate the period-luminosity relations and for populations studies in the Galactic disc. Type II Cepheids are, however, very diverse, and classifications based either on intrinsic (period, light curve) or external parameters (e.g., [Fe/H], |z|) do not provide a unique classification. Aims. We want to ascertain the classification of two Cepheids, HQ Car and DD Vel, that are sometimes classified as classical Cepheids and sometimes as Type II Cepheids. Methods. To achieve this goal, we examine both their chemical composition and the presence of specific features in their spectra. Results. We find emission features in the Hα and in the 5875.64 Å He I lines that are typical of W Vir stars. The [Na/Fe] (or [Na/Zn]) abundances are typical of thick-disc stars, while BL Her stars are Na-overabundant ([Na/Fe] > +0.5 dex). Finally, the two Cepheids show a possible (HQ Car) or probable (DD Vel) signature of mild dust-gas separation that is usually observed only in long-period type II Cepheids and RV Tau stars. Conclusions. These findings clearly indicate that HQ Car and DD Vel are both Type II Cepheids from the W Vir sub-class. Several studies have reported an increase in the Cepheids' abundance dispersion towards the outer (thin) disc. A detailed inspection of the Cepheid classification, in particular for those located in the outer disc, will indicate whether this feature is real or simply an artefact of the inclusion of type II Cepheids belonging to the thick disc in the current samples.

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Section: Methodsmentioning

confidence: 99%

Type II Cepheids in the Milky Way disc

Lemasle

Kovtyukh

Bono

et al. 2015

A&A

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“…The effective temperature for each program star was determined using the method described in detail in Kovtyukh & Gorlova (2000). That method is based on the use of relations between effective temperature and the line depth ratios (each ratio is for the weak lines with different excitation potentials of the same chemical element).…”

Section: Stellar Parametersmentioning

confidence: 99%

Using Cepheids to determine the galactic abundance gradient

Andrievsky¹,

Kovtyukh

Luck

et al. 2002

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138

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Abstract.A number of studies of abundance gradients in the galactic disk have been performed in recent years. The results obtained are rather disparate: from no detectable gradient to a rather significant slope of about −0.1 dex kpc −1 . The present study concerns the abundance gradient based on the spectroscopic analysis of a sample of classical Cepheids. These stars enable one to obtain reliable abundances of a variety of chemical elements. Additionally, they have well determined distances which allow an accurate determination of abundance distributions in the galactic disc. Using 236 high resolution spectra of 77 galactic Cepheids, the radial elemental distribution in the galactic disc between galactocentric distances in the range 6-11 kpc has been investigated. Gradients for 25 chemical elements (from carbon to gadolinium) are derived. The following results were obtained in this study. Almost all investigated elements show rather flat abundance distributions in the middle part of galactic disc. Typical values for iron-group elements lie within an interval from ≈−0.02 to ≈−0.04 dex kpc −1 (in particular, for iron we obtained d[Fe/H]/dRG = −0.029 dex kpc −1 ). Similar gradients were also obtained for O, Mg, Al, Si, and Ca. For sulphur we have found a steeper gradient (−0.05 dex kpc −1 ). For elements from Zr to Gd we obtained (within the error bars) a near to zero gradient value. This result is reported for the first time. Those elements whose abundance is not expected to be altered during the early stellar evolution (e.g. the iron-group elements) show at the solar galactocentric distance [El/H] values which are essentially solar. Therefore, there is no apparent reason to consider our Sun as a metal-rich star. The gradient values obtained in the present study indicate that the radial abundance distribution within 6-11 kpc is quite homogeneous, and this result favors a galactic model including a bar structure which may induce radial flows in the disc, and thus may be responsible for abundance homogenization.

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“…Gray 1989;Strassmeier & Schordan 2000), and supergiants (e.g. Kovtyukh & Gorlova 2000). To the best of our knowledge, this technique has not been extended to the lowmass star regime, however, most likely because of the difficulties in analysing their optical spectrum, which is mainly covered by molecular bands (in particular TiO and water) that blend or hide most of the atomic lines commonly used in the spectral analysis of solar-type stars.…”

Section: Introductionmentioning

confidence: 99%

Stellar parameters of early-M dwarfs from ratios of spectral features at optical wavelengths

Maldonado

Affer

Micela

et al. 2015

A&A

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Context. Low-mass stars have been recognised as promising targets in the search for rocky, small planets with the potential of supporting life. As a consequence, Doppler search programmes using high-resolution spectrographs like HARPS or HARPS-N are providing huge quantities of optical spectra of M dwarfs. However, determining the stellar parameters of M dwarfs using optical spectra has proven to be challenging. Aims. We aim to calibrate empirical relationships to determine accurate stellar parameters for early-M dwarfs (spectral types M0-M4.5) using the same spectra as those that are used for radial velocity determinations, without the necessity of acquiring IR spectra or relying on atmospheric models and/or photometric calibrations. Methods. Our methodology consists of using ratios of pseudo-equivalent widths of spectral features as a temperature diagnostic, a technique frequently used in solar-type stars. Stars with effective temperatures obtained from interferometric estimates of their radii are used as calibrators. Empirical calibrations for the spectral type are also provided. Combinations of features and ratios of features are used to derive calibrations for the stellar metallicity. Our methods are then applied to a large sample of M dwarfs that are currently being observed in the framework of the HARPS GTO search for extrasolar planets. The derived temperatures and metallicities are used together with photometric estimates of mass, radius, and surface gravity to calibrate empirical relationships for these parameters. Results. A long list of spectral features in the optical spectra of early-M dwarfs was identified. This list shows that the pseudoequivalent width of roughly 43% of the features is strongly anticorrelated with the effective temperature. The correlation with the stellar metallicity is weaker. A total of 112 temperature sensitive ratios were identified and calibrated over the range 3100−3950 K, providing effective temperatures with typical uncertainties of about 70 K. Eighty-two ratios of pseudo-equivalent widths of features were calibrated to derive spectral types within 0.5 subtypes for stars with spectral types between K7V and M4.5V. We calibrated 696 combinations of the pseudo-equivalent widths of individual features and temperature-sensitive ratios for the stellar metallicity over a metallicity range from −0.54 to +0.24 dex, with estimated uncertainties in the range of 0.07−0.10 dex. We provide our own empirical calibrations for stellar mass, radius, and surface gravity. These parameters depend on the stellar metallicity. For a given effective temperature, lower metallicities predict lower masses and radii as well as higher gravities.

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Line profile variations in classical Cepheids

Cited by 66 publications

References 31 publications

Type II Cepheids in the Milky Way disc

Type II Cepheids in the Milky Way disc

Using Cepheids to determine the galactic abundance gradient

Stellar parameters of early-M dwarfs from ratios of spectral features at optical wavelengths

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