Line‐Depth Ratios: Temperature Indices for Giant Stars

Gray, David F.; Brown, Kevin I. T.

doi:10.1086/320811

Cited by 62 publications

(65 citation statements)

References 22 publications

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“…In fact this is not too surprising as LDR papers describing much wider ranges of (B − V ) (and hence temperature) (e.g. Strassmeier & Schordan 2000;Gray & Brown 2001), show essentially linear distributions in the range of our LDR and T (B−V ) 0 values. Therefore, the analysis that follows always uses linear fits with consideration taken for errors in both coordinates (Press et al 2002).…”

Section: Converting Depth Ratios To Temperaturessupporting

confidence: 66%

“…Whilst LDRs perhaps require more reduction effort than some of these methods, they have many advantageous qualities. For instance, line depths are measured downward from the continuum so they should not suffer from zero-point errors, they should be applicable to composite spectra, and, unlike photometric methods, are independent of interstellar extinction and, within sensible limits, sky quality (Gray & Brown 2001).…”

Section: Introductionmentioning

confidence: 99%

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Line-depth-ratio temperatures for the close binary ν Octantis: new evidence supporting the conjectured circumstellar retrograde planet

Ramm¹

2015

Monthly Notices of the Royal Astronomical Society

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We explore the possibly that either starspots or pulsations are the cause of a periodic radialvelocity signal (P ∼ 400 days) from the K-giant binary ν Octantis (P ∼ 1050 days, e ∼ 0.25), alternatively conjectured to have a retrograde planet. Our study is based on temperatures derived from 22 line-depth ratios (LDRs) for ν Oct and twenty calibration stars. Empirical evidence and stability modelling provide unexpected support for the planet since other standard explanations (starspots, pulsations and additional stellar masses) each have credibility problems. However, the proposed system presents formidable challenges to planet-formation and stability theories: it has by far the smallest stellar separation of any claimed planet-harbouring binary (a bin ∼ 2.6 AU) and an equally unbelievable separation ratio (a pl /a bin ∼ 0.5), hence the necessity that the circumstellar orbit be retrograde.The LDR analysis of 215 ν Oct spectra acquired between 2001-2007, from which the RV perturbation was first revealed, have no significant periodicity at any frequency. The LDRs recover the original 21 stellar temperatures with an average accuracy of 45 ± 25 K. The 215 ν Oct temperatures have a standard deviation of only 4.2 K. Assuming the host primary is not pulsating, the temperatures converted to magnitude differences strikingly mimic the very stable photometric Hipparcos observations 15 years previously, implying the long-term stability of the star and demonstrating a novel use of LDRs as a photometric gauge. Our results provide substantial new evidence that conventional starspots and pulsations are unlikely causes of the RV perturbation. The controversial system deserves continued attention, including with higher resolving-power spectra for bisector and LDR analyses.

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Section: Converting Depth Ratios To Temperaturessupporting

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Line-depth-ratio temperatures for the close binary ν Octantis: new evidence supporting the conjectured circumstellar retrograde planet

Ramm¹

2015

Monthly Notices of the Royal Astronomical Society

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“…The use of ∼70−100 calibrations per spectrum reduces the uncertainty to 5−25 (1σ) K. This precision indicates that these 100 calibrations are weakly sensitive to non-LTE effects, metallicity, surface gravity, micro-and macroturbulence, rotation, and other individual stellar parameters. These relations have been calibrated with the reference stars in common with Gray & Brown (2001) Fig. 2).…”

Section: Effective Temperature T Effmentioning

confidence: 99%

Elemental abundances in the atmosphere of clump giants

Mishenina¹,

Bienaymé

Gorbaneva³

et al. 2006

A&A

135

161

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Aims. The aim of this paper is to provide the fundamental parameters and abundances for a large sample of local clump giants with a high accuracy. This study is a part of a big project, in which the vertical distribution of the stars in the Galactic disc and the chemical and dynamical evolution of the Galaxy are being investigated. Methods. The selection of clump stars for the sample group was made applying a colour-absolute magnitude window to nearby Hipparcos stars. The effective temperatures were estimated by the line depth ratio method. The surface gravities (log g) were determined by two methods (the first one was the method based on the ionization balance of iron and the second one was the method based on fitting of the wings of the Ca i 6162.17 Å line). The abundances of carbon and nitrogen were obtained from the molecular synthetic spectrum, and the Mg and Na abundances were derived using the non-LTE approximation. The "classical" models of stellar evolution without atomic diffusion and rotation-induced mixing were employed. Results. The atmospheric parameters (T eff , log g, [Fe/H], V t ) and Li, C, N, O, Na, Mg, Si, Ca, and Ni abundances in 177 clump giants of the Galactic disc were determined. The underabundance of carbon, overabundance of nitrogen, and "normal" abundance of oxygen were detected. A small sodium overabundance was found. A possibility of a selection of the clump giants based on their chemical composition and the evolutionary tracks was explored. Conclusions. The theoretical predictions based on the classical stellar evolution models are in good agreement with the observed surface variations of the carbon and nitrogen just after the first dredge-up episode. The giants show the same behaviour of the dependencies of O, Mg, Ca, and Si (α-elements) and Ni (iron-peak element) abundances vs. [Fe/H] as dwarfs do. This allows us to use such abundance ratios to study the chemical and dynamical evolution of the Galaxy.

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“…described by Gray & Johanson (1991) and others, line-depth ratios (LDRs) of properly selected line pairs are an excellent diagnostic of effective temperature that allow for relative measurements with a precision as small as a few kelvins, not only in dwarfs but also in giants (Gray & Brown 2001). The conversion to an absolute temperature scale, however, necessarily depends on an external color-temperature calibration, since LDR variations are usually compared with corresponding changes in a color index such as B À V , which is an easier quantity to measure than temperature.…”

Section: Additional Spectroscopic Constraintsmentioning

confidence: 99%

HipparcosAstrometric Orbit and Evolutionary Status of HR 6046

Torres

2007

Astron J

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The previously known, 6 yr single-lined spectroscopic binary HR 6046 has been speculated in the past to contain a compact object as the secondary. A recent study has redetermined the orbit with great accuracy and shown that the companion is an evolved but otherwise normal star of nearly identical mass to the primary, which is also a giant. The binary motion was detected by the Hipparcos mission but was not properly accounted for in the published astrometric solution. Here we use the Hipparcos intermediate data in combination with the spectroscopic results to revise that solution and establish the orbital inclination angle for the first time, and with it the absolute masses M A ¼ 1:38 þ0:09 À0:03 M and M B ¼ 1:36 þ0:07 À0:02 M . Aided by other constraints, we investigate the evolutionary status and confirm that the primary star is approaching the tip of the red giant branch, while the secondary is beginning its first ascent.

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Line‐Depth Ratios: Temperature Indices for Giant Stars

Cited by 62 publications

References 22 publications

Line-depth-ratio temperatures for the close binary ν Octantis: new evidence supporting the conjectured circumstellar retrograde planet

Line-depth-ratio temperatures for the close binary ν Octantis: new evidence supporting the conjectured circumstellar retrograde planet

Elemental abundances in the atmosphere of clump giants

HipparcosAstrometric Orbit and Evolutionary Status of HR 6046

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