Determination of effective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5)

Astronomy and Astrophysics Supplement Series, Jul 2018

We have applied the InfraRed Flux Method (IRFM) to a sample of 475 dwarfs and subdwarfs in order to derive their effective temperatures with a mean accuracy of about 1.5%. We have used the new homogeneous grid of theoretical model atmosphere flux distributions developed by Kurucz (1991, 1993) for the application of the IRFM. The atmospheric parameters of the stars cover, roughly, the ranges: 3500 K 8000 K; -3.5 ≤ [Fe/H] ; 3.5 ≤ log(g) . The monocromatic infrared fluxes at the continuum, and the bolometric fluxes are derived using recent results, which satisfy the accuracy requeriments of the work. Photometric calibrations have been revised and applied to estimate metallicities, although direct spectroscopic determinations were preferred when available. The adopted infrared absolute flux calibration, based on direct optical measurements of angular stellar diameters, sets the effective temperatures determined using the IRFM on the same scale than those obtained by direct methods. We derive three temperatures, TJ, TH and TK, for each star using the monochromatic fluxes at different infrared wavelengths in the photometric bands J, H, and K. They show good consistency over 4000 K, and no trend with wavelength may be appreciated. We provide a detailed description of the steps followed for the application of the IRFM, as well as the sources of the errors associated to the different inputs of the method, and their transmission into the final temperatures. We also provide comparison with previous works.

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Determination of effective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5)

Astron. Astrophys. Suppl. Ser. Determination of e ective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5)? A. Alonso S. Arribas C. Mart nez-Roger Instituto de Astrof sica de Canarias La Laguna (Tenerife) Spain Electronic mail: | We have applied the InfraRed Flux Method (IRFM) to a sample of 475 dwarfs and subdwarfs in order to derive their e ective temperatures with a mean accuracy of about 1.5%. We have used the new homogeneous grid of theoretical model atmosphere flux distributions developed by Kurucz (1991, 1993) for the application of the IRFM. The atmospheric parameters of the stars cover, roughly, the ranges: 3500 K Te 8000 K; −3.5 [Fe/H] +0:5; 3.5 log(g) 5. The monocromatic infrared fluxes at the continuum, and the bolometric fluxes are derived using recent results, which satisfy the accuracy requeriments of the work. Photometric calibrations have been revised and applied to estimate metallicities, although direct spectroscopic determinations were preferred when available. The adopted infrared absolute flux calibration, based on direct optical measurements of angular stellar diameters, sets the e ective temperatures determined using the IRFM on the same scale than those obtained by direct methods. We derive three temperatures, TJ , TH and TK , for each star using the monochromatic fluxes at di erent infrared wavelengths in the photometric bands J , H, and K. They show good consistency over 4000 K, and no trend with wavelength may be appreciated. We provide a detailed description of the steps followed for the application of the IRFM, as well as the sources of the errors associated to the di erent inputs of the method, and their transmission into the nal temperatures. We also provide comparison with previous works. stars; fundamental parameters | stars; Population II | stars; subdwarfs | stars; general 1. Introduction The stellar e ective temperatures might be, in principle, determined following a fundamental or direct method based on the combination of the bolometric fluxes and the angular diameter measurements according to the equation: Te = ( 4 )1=4 −1=2FB1=o4l; (1) where is the Stefan-Boltzmann constant, is the angular diameter of the star, and FBol is the bolometric flux measured on the surface of the earth. However, in practice, we need atmosphere models to perform secondary corrections to both the angular diameter measurement (limb darkening) and FBol (interstellar absorption). The Sun is obviously the only exception, since its limb darkening can be empirically determined, and its interstellar absorption is negligible. In any event, the main di culty a ecting the direct procedure is the limited number of stars with a reliable measurement of their angular Send o print requests to: A. Alonso ?Table 4 is only available in electronic form at CDS Tables 1-3 are also available via ftp 130.79.128.5 diameter (see for instance Table 4 from Mozurkewich et al. 1991). This problem is remarkably severe for the low main sequence, as there are no direct measurements of angular diameter for stars later than F5V, with the above mentioned exception of the Sun. For this reason, relatively large uncertainties still remain on the scale of stellar effective temperatures in the low main sequence, especially when the e ect of metallicity is considered. Thus, we are compelled to use semi-direct methods, which require, as a basis, atmosphere models in addition to observational information (see the review by B¨ohmVitense 1981) . Among the di erent methods of this type the Infrared Flux Method (hereafter IRFM; Blackwell et al. 1990, and references therein) seems especially adequate to analyse the temperatures of F, G, and K stars. The IRFM has been successfully applied to di erent samples of population I stars (e.g. Blackwell et al. 1990; Bell & Gustafsson 1989; Saxner & Hammarb¨ack 1985) . However, the works based on the IRFM devoted to metal poor stars (Magain 1987; Arribas & Mart nez-Roger 1987, 1989) are restricted to rather limited samples. The present paper is part of a long term programme aimed to a better de nition of the scale of temperatures for F, G, and K dwarfs and subdwarfs, using the IRFM. calibration for the infrared flux of Vega, which scales the This work is relevant to three main topics: (a) analysis of IRFM temperatures to those derived by direct methods, the global behaviour of atmosphere models (e.g., Magain is proposed. Thirdly, a method to obtain bolometric fluxes 1987) , (b) the correct interpretation of the observed HR for metal poor stars was devised in Alonso et al. (1995 , diagram (e.g., Arribas & Mart nez-Roger 1988, 1989) , and Paper III). Last, but not least, we have used the improved (c) ne spectroscopic analysis for abundance determina- grid of atmosphere models computed recently by Kurucz tions of metal poor stars (e.g., King 1994) . (1991, 1993). The general programme has been focussed on the im- This paper provides detailed information on (...truncated)


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A. Alonso, S. Arribas, C. Martínez-Roger. Determination of effective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5), Astronomy and Astrophysics Supplement Series, pp. 227-254, Volume 117, Issue 2, DOI: 10.1051/aas:1996153