The stellar temperature scale for stars of spectral types from O8 to F6 and the standard deviation of the MK spectral classification

Theodossiou, E.; Danezis, E.

doi:10.1007/bf00643019

Cited by 28 publications

(20 citation statements)

References 47 publications

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“…Some of our spectra were suffering from strong sky-line residuals that were flagged using the spectral atlas of Rousselot et al (2000) and removed. Spectra of B-type standards star were corrected from their intrinsic features and divided by black bodies at the appropriate temperature (Theodossiou & Danezis 1991). G-type standard star spectra were divided by reference spectra (smoothed at R = 1500 in the H + K band) of G-type stars from the IRTF spectral library 2 (Rayner et al 2009, hereafter R09).…”

Section: Spectral Extractionmentioning

confidence: 99%

A library of near-infrared integral field spectra of young M–L dwarfs

Bonnefoy

Chauvin

Lagrange

et al. 2014

A&A

147

204

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Context. At young ages, low surface gravity affects the atmospheric properties of ultracool dwarfs. The impact on medium-resolution near-infrared (NIR) spectra has only been slightly investigated at the M-L transition so far. Aims. We present a library of NIR (1.1-2.45 µm) medium-resolution (R ∼ 1500-2000) integral field spectra of 15 young M6−L0 dwarfs. We aim at deriving updated NIR spectral type, luminosity, and physical parameters (T eff , log g, M, L/L ) for each source. This work also aims at testing the latest generation of BT-SETTL atmospheric models. Methods. We estimated spectral types using spectral indices and the spectra of young objects classified in the optical. We used the 2010 and 2012 releases of the BT-SETTL synthetic spectral grid and cross-checked the results with the DRIFT-PHOENIX models to derive the atmospheric properties of the sources. Results. We do not find significant differences between the spectra of young companions and those of young isolated brown dwarfs in the same spectral type range. We derive infrared spectral types L0 ± 1, L0 ± 1, M9.5 ± 0.5, M9.5 ± 0.5, M9.25 ± 0.25, M8 +0.5 −0.75 , and M8.5 ± 0.5 for AB Pic b, Cha J110913-773444, USco CTIO 108B, GSC 08047-00232 B, DH Tau B, CT Cha b, and HR7329B, respectively. The BT-SETTL and DRIFT-PHOENIX models yield close T eff and log g estimates for each source. The models seem to show a 600 +600 −300 K drop in the effective temperature at the M-L transition. Assuming the former temperatures are correct, we then derive new mass estimates that confirm that DH Tau B, USco CTIO 108B, AB Pic b, KPNO Tau 4, OTS 44, and Cha1109 lie inside or at the boundary of the planetary mass range. We combine the empirical luminosities of the M9.5-L0 sources to the T eff to derive semi-empirical radii estimates that do not match "hot-start" evolutionary models predictions at 1-3 Myr. We use complementary data to demonstrate that atmospheric models are able to reproduce the combined optical and infrared spectral energy distribution, together with the NIR spectra of these sources simultaneously. But the models still fail to represent the dominant features in the optical. This issue raises doubts on the ability of these models to predict effective temperatures from NIR spectra alone. Conclusions. The library provides templates for characterizing other young and late type objects. The study advocates the use of photometric and spectroscopic information over a broad range of wavelengths to study the properties of very low-mass young companions to be detected with the planet imagers (Subaru/SCExAO, LBT/LMIRCam, Gemini/GPI, VLT/SPHERE).

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Section: Spectral Extractionmentioning

confidence: 99%

A library of near-infrared integral field spectra of young M–L dwarfs

Bonnefoy

Chauvin

Lagrange

et al. 2014

A&A

147

204

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“…Most of the T eff values were in works that deal with only a reduced number of stars and use different techniques (Hunger & Groote 1999;Zboril et al 1997;Glagolevskij 2002;Theodossiou & Danezis 1991;Adelman & Pyper 1985;Kaufmann & Theil 1980). Table 9 compares the BCD effective temperatures with those obtained by Glagolevskij (2002), Zboril et al (1997) and Kaufmann & Theil (1980).…”

Section: T Eff Determinationmentioning

confidence: 99%

Fundamental parameters of He-weak and He-strong stars

Cidale¹,

Arias²,

Torres³

et al. 2007

A&A

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Context. He-weak and He-strong stars are chemically peculiar AB objects whose He lines are anomalously weak or strong for their MK spectral type. The determination of fundamental parameters for these stars is often more complex than for normal stars due to their abundance anomalies. Aims. We discuss the determination of fundamental parameters: effective temperature, surface gravity, and visual and bolometric absolute magnitudes of He-weak and He-strong stars. We compare our values with those derived independently from methods based on photometry and model fitting. Methods. We carried out low resolution spectroscopic observations in the wavelength range 3400-4700 Å of 20 He-weak and 8 He-strong stars to determine their fundamental parameters by means of the Divan-Chalonge-Barbier (BCD) spectrophotometric system. This system is based on the measurement of the continuum energy distribution around the Balmer discontinuity (BD). For a few He-weak stars we also estimate the effective temperatures and the angular diameters by integrating absolute fluxes observed over a wide spectral range. Non-LTE model calculations are carried out to study the influence of the He/H abundance ratio on the emergent radiation of He-strong stars and on their T eff determination. Results. We find that the effective temperatures, surface gravities and bolometric absolute magnitudes of He-weak stars estimated with the BCD system and the integrated flux method are in good agreement between each other, and they also agree with previous determinations based on several different methods. The mean discrepancy between the visual absolute magnitudes derived using the hipparcos parallaxes and the BCD values is on average ±0.3 mag for He-weak stars, while it is ±0.5 mag for He-strong stars. ForHe-strong stars, we note that the BCD calibration, based on stars in the solar environment, leads to overestimated values of T eff . By means of model atmosphere calculations with enhanced He/H abundance ratios we show that larger He/H ratios produce smaller BD which naturally explains the T eff overestimation. We take advantage of these calculations to introduce a method to estimate the He/H abundance ratio in He-strong stars. The BD of HD 37479 suggests that the T eff of this star remains fairly constant as the star spectrum undergoes changes in the intensity of H and He absorption lines. Data for the He-strong star HD 66765 are reported for the first time.

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“…For a solar composition T eff = 11 000 K and log g = 3.50 while for models with 10 times solar metals T eff = 10 750 K and log g = 3.50. Kroll (1987), from near infrared photometry, assigned T eff = 13 800 K to α Scl while Theodossiou & Danezis (1991) estimate T eff = 11 500 K and log g = 3. The catalogue of Cayrel de Strobel et al (1992) reports T eff = 15 750 K, log g = 3.4, and a +0.7 dex iron overabundance with respect to the sun.…”

Section: Atmospheric Parametersmentioning

confidence: 99%

Elemental abundance studies of CP stars

López-García

Adelman

Pintado

2001

A&A

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Abstract. Fine analyses of the magnetic CP stars α Scl and HD 170973 are presented using ATLAS9 model atmospheres which have same bulk metallicity as the deduced abundances. The light elements are mostly solar except for silicon, and all the heavier elements except nickel in HD 170973, which is solar, are greatly overabundant. The iron peak elements are typically 10 times overabundant, Sr is of order of 1000 times solar, Y and Zr are of order of 100 times solar. The rare earths are 1000 or more times overabundant.

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The stellar temperature scale for stars of spectral types from O8 to F6 and the standard deviation of the MK spectral classification

Cited by 28 publications

References 47 publications

A library of near-infrared integral field spectra of young M–L dwarfs

A library of near-infrared integral field spectra of young M–L dwarfs

Fundamental parameters of He-weak and He-strong stars

Elemental abundance studies of CP stars

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