Determining the effective temperatures of G- and K-type giants and supergiants based on observed photometric indices

Lyubimkov, L. S.; Poklad, D. B.

doi:10.3103/s0884591314050055

Cited by 5 publications

(5 citation statements)

References 22 publications

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“…As has already been noted in the Introduction, to confirm the status of the star HD 77361 with greater reliability, we applied a fundamentally different technique to determine T eff . For this purpose, we used two independent methods: the recently developed photometric method of Lyubimkov and Poklad(2014) and the spectroscopic method of Kovtyukh (2007). The former was proposed to determine the effective temperature T eff for G and K giants and supergiants.…”

Section: The Technique For Determining the Fundamental Parameters T E...mentioning

confidence: 99%

The cool giant HD 77361—a super Li-rich star

et al. 2015

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Super Li-rich stars form a very small and enigmatic group whose existence cannot be explained in terms of the standard stellar evolution theory. The goal of our study is to check the reality of this group of cool giants based on an independent technique. We have carried out such a check using the K giant HD 77361 (HR 3597), which has previously been assigned to this rare type, as an example. We have redetermined the effective temperature T eff and surface gravity log g for this star. We have applied two different methods, photometric and spectroscopic, to estimate T eff (the accuracy of the Li-abundance determination depends significantly on this parameter). The value of log g has been found from the highly accurate parallax of this nearby star. To apply the photometric method of determining T eff , we have performed UBV observations of the star, which yielded V = 6.18 ± 0.03, B -V = 1.13 ± 0.01, and U -B = 1.18 ± 0.05. The following parameters of the star have been found: effective temperature T eff = 4370 ±100 K, surface gravity log g = 2.30 ± 0.10, iron abundance log (Fe) = 7.49 ± 0.14, microturbulence V t =1.1 ± 0.2 km s -1 , rotational velocity Vsini = 4.5 km s -1 , and mass M = 1.3 ± 0.2 M  . The lithium abundance has been determined from a non-LTE analysis of three Li I lines: the resonance line at 6707.8 Å and the subordinate lines at 6103.6 and 8126.4 Å (the latter in a blend with a CN molecular line). We have found a high lithium abundance, log (Li) = 3.75 ± 0.11, which exceeds considerably the initial abundance log (Li) = 3.2 ± 0.1 for young stars in the solar neighborhood. Thus, we have confirmed that the K giant HD 77361 actually belongs to the type of super Li-rich stars. It is noted that a high lithium abundance in such cool giants is inconsistent with predictions of the standard stellar evolution theory and may suggest a recent synthesis of lithium in these stars.

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Section: The Technique For Determining the Fundamental Parameters T E...mentioning

confidence: 99%

The cool giant HD 77361—a super Li-rich star

et al. 2015

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“…For cold K-giants these models may manifest differences in the photometric indices Q and [c 1 ] (see Ref. 14), but in studies of elemental abundance for these kinds of stars, no significant differences were found between the ATLAS9 and MARCS models. It is important that these are all stationary, one-dimensional atmospheric models.…”

Section: Discussionmentioning

confidence: 99%

“…One of these reliable and popular methods is the infrared flux method (IRFM). As a first step we used the photometric method developed by Lyubimkov and Poklad [14], referred to below as LP'14, to determine T eff for G-and K-giants and supergiants, and calibrated on the basis of IRFM data. This method is based on using the indices Q and [c 1 ] in the UBV and uvby photometric systems, respectively.…”

Section: 1determination Of the Effective Temperature T Effmentioning

confidence: 99%

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Three Nearby K-Giants with Planets: Accurate Determination of Basic Parameters, Including an Analysis of Metallicity Based on Fe I Lines

2019

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Fundamental parameters, including the effective temperature T eff , surface gravity logg, mass M, luminosity L, radius R, and age t, are determined for three bright, nearby K-giants, β Gem (K0 III), μ Leo (K2 III), and α Tau (K5 III). It is notable that around all three stars the giant planets have been found. Our results are compared with published high-precision data for benchmark stars included in the Gaia project. Very good agreement was obtained for all three giants with these data for the basic parameters T eff , logg, and M, although our technique of their determination was simpler. Special attention was devoted to analy-sis of the Fe I lines which are the basis of a simultaneous determination of the metallicity index [Fe/H] and microturbulent parameter V t . The equivalent widths W of the Fe I lines are automatically measured from published spectra for the benchmark stars. An analysis of Fe I lines from the list of "golden lines" selected in a study of benchmark stars led to the conclusion that the excitation potential E l of the low level of the lines plays an substantial role in determining [Fe/H] and V t . It is shown that in the case of the early K-giants β Gem and μ Leo with temperatures T eff between 4400 and 4900 K for lines in the range of W from 100 to 300 mÅ there is a dependence of the [Fe/H] and V t values on E l . This dependence was not taken into account earlier is studies of the K-giants, in particular in the Fe I lines analysis of the benchmark stars. It is shown that a correct accounting for it leads an ambiguity in the determination of [Fe/H] and V t for β Gem and μ Leo. In the case of the coolest K-giant α Tau (Aldebaran) with a temperature T eff = 3920K, this effect seems to be less pronounced. Recommendations are given for the Crimean Astrophysical Observatory, RAN, Russia;Fe I lines selection for [Fe/H] and V t determination. It is sonfirmed for the example of the three stars studied here that the non-LTE effects in the Fe I lines for the K-giants with normal metallicity are very minor, so they cannot be the reason of the revealed ambiguity in [Fe/H] and V t . values. The low ratios of the carbon 12 C/ 13 C and oxygen 16 O/ 17 O isotopes confirm that all three giants passed the phase of deep convective mixing.

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“…In this case, the infrared flux method (IRFM) seems to be the most precise photometric method of the T eff determination for cool stars like ours. As the first step, we used the photometric method, which has been developed by Lyubimkov & Poklad (2014) for the T eff derivation for G‐ and K‐type giants and supergiants and calibrated on the IRFM data. This technique is based on an application of the observed indices Q and [ c1 ] that are free from interstellar extinction.…”

Section: Determination Of Basic Parametersmentioning

confidence: 99%

Fundamental parameters and non‐local thermodynamic equilibrium abundances of key light elements for nine bright and nearby K giants

et al. 2021

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For nine bright K giants within 100 pc of the sun, the fundamental parameters and the non-local thermodynamic equilibrium (LTE) abundances of three key light elements (Li, C, and O) are accurately determined. These stars are of special interest due to the planets detected around them. Their fundamental parameters are found to be typical for K giants; in particular, these stars have effective temperatures T eff = 3,920-4,830 K, surface gravities log g = 1.20-2.85, masses M = 1.2-2.8 M ⊙ , and ages t = 0.4-5.4 Gyr (the pronounced anticorrelation between ages t and masses M exists). The microturbulent parameter V t derived from Fe I lines varies between 1.2 and 1.9 km s −1 ; the metallicity index [Fe/H] forfive stars is close to the normal (zero) value, for other four stars it varies between −0.3 and −0.4 dex. All the giants are on the red giant branch stage and passed the first-dredge-up (FDU) phase. This conclusion is confirmed by the published low isotope ratios 12 C/ 13 C and 16 O/ 17 O. Basing on the non-LTE analysis of Li I, C I, and O I lines, we determined abundances of lithium, carbon, and oxygen, three tracers of stellar evolution. The carbon deficiency −0.3 dex is found for the giants, which is quite expectable for these post-FDU objects.The oxygen abundance is likely to be unchanged, whereas for the C/O ratio we obtained (after correction due to galactic chemical evolution) the mean value [C/O] cor = −0.22 ± 0.10 that is in very good agreement with the theory. The lithium abundance is not detected for seven of nine program giants; this result is quite expectable for the post-FDU stars. We determined the Li abundance with the confidence only for two giants, namely, log ϵ(Li) = 0.92 for β Gem and log ϵ(Li) = 0.45 for μ Leo; this result contradicts the standard theory. Hypothetical engulfment by a star of a giant planet could solve the problem.

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Determining the effective temperatures of G- and K-type giants and supergiants based on observed photometric indices

Cited by 5 publications

References 22 publications

The cool giant HD 77361—a super Li-rich star

The cool giant HD 77361—a super Li-rich star

Three Nearby K-Giants with Planets: Accurate Determination of Basic Parameters, Including an Analysis of Metallicity Based on Fe I Lines

Fundamental parameters and non‐local thermodynamic equilibrium abundances of key light elements for nine bright and nearby K giants

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