The effective temperatures and colours of G and K stars

Bell, R. A.; Gustafsson, B.

doi:10.1093/mnras/236.3.653

Cited by 153 publications

(156 citation statements)

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“…We may add though that we never saw a flare in our long-term BVRI photometric monitoring. & Gustafsson (1989) predicted an angular diameter of 0.91 mas based on the apparent bolometric flux of 30.5 × 10 −15 W cm −2 . It is also listed in the CHARM-2 catalog (Richichi et al 2005).…”

Section: Rotational Modulationmentioning

confidence: 99%

Rotation and magnetic activity of the Hertzsprung-gap giant 31 Comae

Strassmeier¹,

Granzer²,

Kopf³

et al. 2010

A&A

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Context. The single rapidly-rotating G0 giant 31 Comae has been a puzzle because of the absence of photometric variability despite its strong chromospheric and coronal emissions. As a Hertzsprung-gap giant, it is expected to be at the stage of rearranging its moment of inertia, hence likely also its dynamo action, which could possibly be linked with its missing photospheric activity. Aims. Our aim is to detect photospheric activity, obtain the rotation period, and use it for a first Doppler image of the star's surface. Its morphology could be related to the evolutionary status. Methods. We carried out high-precision, white-light photometry with the MOST satellite, ground-based Strömgren photometry with automated telescopes, and high-resolution optical echelle spectroscopy with the new STELLA robotic facility. Results. The MOST data reveal, for the first time, light variations with a full amplitude of 5 mmag and an average photometric period of 6.80 ± 0.06 days. Radial-velocity variations with a full amplitude of 270 m s −1 and a period of 6.76 ± 0.02 days were detected from our STELLA spectra, which we also interpret as due to stellar rotation. The two-year constancy of the average radial velocity of +0.10 ± 0.33 km s −1 confirms the star's single status, as well as the membership in the cluster Melotte 111. A spectrum synthesis gives T eff = 5660 ± 42 K, log g = 3.51 ± 0.09, and [Fe/H] = −0.15 ± 0.03, which together with the revised Hipparcos distance, suggests a mass of 2.6 ± 0.1 M and an age of ≈540 Myr. The surface lithium abundance is measured to be nearly primordial. A detection of a strong He i absorption line indicates nonradiative heating processes in the atmosphere. Our Doppler images show a large, asymmetric polar spot, cooler than T eff by ≈1600 K, and several small low-to-mid latitude features that are warmer by ≈300-400 K and are possibly of chromospheric origin. We computed the convective turnover time for 31 Com as a function of depth and found on average τ C ≈ 5 days. Conclusions. 31 Com appears to be just at the onset of rapid magnetic braking and Li dilution because its age almost exactly coincides with the predicted onset of envelope convection. That we recover a big polar starspot despite the Rossby number being larger than unity, and thus no efficient (envelope) dynamo is expected, leads us to conclude that 31 Com still harbors a fossil predominantly poloidal magnetic field. However, the increasing convective envelope may have just started an interface dynamo that now is the source of the warm surface features and the corresponding UV and X-ray emission.

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Section: Rotational Modulationmentioning

confidence: 99%

Rotation and magnetic activity of the Hertzsprung-gap giant 31 Comae

Strassmeier¹,

Granzer²,

Kopf³

et al. 2010

A&A

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“…Since then, a number of authors have applied the IRFM to determine effective temperatures in stars with different spectral types and metallicities (e.g. Bell & Gustafsson 1989;Alonso et al 1996a;Ramírez & Meléndez 2005a;Casagrande et al 2006;González Hernández & Bonifacio 2009). The main ingredient of the IRFM is infrared photometry, with the homogeneous and all-sky coverage provided by 2MASS being the de facto choice nowadays.…”

Section: Introductionmentioning

confidence: 99%

An absolutely calibratedT_effscale from the infrared flux method

Casagrande¹,

Ramírez²,

Meléndez

et al. 2010

A&A

721

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985

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Various effective temperature scales have been proposed over the years. Despite much work and the high internal precision usually achieved, systematic differences of order 100 K (or more) among various scales are still present. We present an investigation based on the infrared flux method aimed at assessing the source of such discrepancies and pin down their origin. We break the impasse among different scales by using a large set of solar twins, stars which are spectroscopically and photometrically identical to the Sun, to set the absolute zero point of the effective temperature scale to within few degrees. Our newly calibrated, accurate and precise temperature scale applies to dwarfs and subgiants, from super-solar metallicities to the most metal-poor stars currently known. At solar metallicities our results validate spectroscopic effective temperature scales, whereas for [Fe/H] < ∼ −2.5 our temperatures are roughly 100 K hotter than those determined from model fits to the Balmer lines and 200 K hotter than those obtained from the excitation equilibrium of Fe lines. Empirical bolometric corrections and useful relations linking photometric indices to effective temperatures and angular diameters have been derived. Our results take full advantage of the high accuracy reached in absolute calibration in recent years and are further validated by interferometric angular diameters and space based spectrophotometry over a wide range of effective temperatures and metallicities.

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“…Fekel & Marshall (1991) found that the best fit to the spectrum of HD 33798 in the 6430 Å region is obtained with κ Gem, a G8 III star. This spectral type corresponds to an effective temperature of 4970 K (Bell & Gustafsson 1989). V390 Aurigae is the primary of the visual binary ADS 3812 whose secondary is 0.358 ± 0.011 away and ∆m V = 1.85 ± 0.08 fainter (ESA 1997).…”

Section: Introductionmentioning

confidence: 99%

The corona of V390 Aurigae (HD 33798)

Gondoin

2003

A&A

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Abstract. V390 Aurigae (HD 33798) is a rapidly rotating, lithium rich, late-type giant whose distinctive characteristics include a high X-ray luminosity observed by the XMM-Newton space observatory. Series of lines of highly ionized Fe and several Lyman lines of hydrogen-like ions and triplet lines of helium-like ions are visible in the reflection grating spectra, most notably from O and Ne. X-ray emission from plasma at high temperature (T > 10 7 K) indicates intense flaring activity on this star. Analysis results suggest a scenario where the corona of V390 Aurigae is dominated by large magnetic structures similar in size to interconnecting loops between solar active regions but significantly hotter. The interaction of these structures could explain the permanent flaring activity on large scales that is responsible for heating plasma to high temperatures. The intense activity on V390 Aurigae is related to its evolutionary position at the bottom of the red giant branch. It is anticipated that the rotation of the star will spin-down in the future, thus decreasing the efficiency of its α − Ω dynamo with the suppressing of large scale magnetic structures in its corona.

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The effective temperatures and colours of G and K stars

Cited by 153 publications

References 0 publications

Rotation and magnetic activity of the Hertzsprung-gap giant 31 Comae

Rotation and magnetic activity of the Hertzsprung-gap giant 31 Comae

An absolutely calibratedT_effscale from the infrared flux method

The corona of V390 Aurigae (HD 33798)

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The effective temperatures and colours of G and K stars

Cited by 153 publications

References 0 publications

Rotation and magnetic activity of the Hertzsprung-gap giant 31 Comae

Rotation and magnetic activity of the Hertzsprung-gap giant 31 Comae

An absolutely calibratedTeffscale from the infrared flux method

The corona of V390 Aurigae (HD 33798)

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An absolutely calibratedT_effscale from the infrared flux method