Empirical Calibration of the Physical Parameters of Solar-like stars using uvby-Str\"omgren Photometry

TL;DR

This study empirically calibrates physical parameters of solar-like stars using uvby-Strömgren photometry, establishing correlations and defining solar analogs with specific color and temperature ranges.

Contribution

It provides a new empirical calibration method for effective temperature and gravity of solar-like stars based on uvby-Strömgren photometry, and proposes refined criteria for solar analogs.

Findings

Strong correlation between (b-y)o and Teff allowing polynomial expression.

Defined solar analogs with specific color indices and physical parameters.

Identified discrepancies in the (m1)o index related to solar metallicity.

Abstract

We present an empirical calibration of the physical parameters of A, F and early G-type stars of luminosity class V. We have used a statistical approach based on a sample of about 15 000 stars having both uvby-Str\"omgren photomerty (Hauck & Mermilliod 1998) and spectral types taken from SIMBAD. Stars closer than 70 pc have been considered reddening-free. In this paper we present the results for 1900 stars within 70 pc. Mean unreddened measurements have been used as input to CHORIZOS (Ma\'iz-Apell\'aniz 2004). By assuming "solar metallicity" ([Fe/H]=0), we have been able to determine effective temperatures (Teff) and surface gravities (log g) for each spectral type. We have found a tight correlations among the observations and the derived physical parameters; for example, Teff can be expressed as a cubic polynomial in (b-y)o. From the distribution of colors and indices for 128 stars and their associated physical parameters we have proposed an alternative definition for solar-analogs: stars whose classification is G2 V with (b-y)o=0.3927+/-0.0190, (m1)o = 0.1901+/-0.0143, and (c1)o=0.3302+/-0.0388, Teff=5930+/-145, and log g =4.70+/-0.33. These values are consistent with previous empirical results; however, (m1)o differs from a recent model-based value for this index derived by Mel\'endez et al. (2010). This discrepancy points out the actual solar metallicity problem. We suggest that our sample of solar analogs could be useful for searches of solar twins and exoplanets.