A new implementation of the infrared flux method using the 2MASS catalogue

TL;DR

This paper introduces a new implementation of the infrared flux method (IRFM) using the 2MASS catalogue, providing improved temperature calibrations for stars, especially metal-poor ones, by directly comparing theoretical fluxes with observed magnitudes.

Contribution

The paper presents a fully self-consistent IRFM implementation in the 2MASS system and new empirical temperature calibrations for stars, including metal-poor stars, based on an extended sample.

Findings

Derived new effective temperature scales that are hotter by ~54-64K for most stars.

Provided temperature calibrations specifically for metal-poor stars with [Fe/H]<-2.5.

Recommended the new calibrations for use with 2MASS photometry, especially for metal-poor stars.

Abstract

We present a new implementation of the infrared flux method (IRFM) using the 2MASS catalogue. We compute the theoretical quantities in the 2MASS JHKs filters by integrating theoretical fluxes computed from ATLAS models, and compare them directly with the observed 2MASS JHKs magnitudes. This is the main difference between our implementation of the IRFM and that of Ramirez & Melendez, since to introduce new stars at the lowest metallicities they transform the 2MASS JHKs magnitudes into the TCS photometric system. We merge in our sample the dwarfs stars from Alonso and collaborators with the stars in the sample of Ramirez & Melendez, Casagrande et al., Christlieb et al. and Bonifacio et al. The final number of stars in our sample is 555 dwarf and subgiant field stars, and 264 giant field stars. We derive a new bolometric flux calibration using the available Johnson-Cousins UBVRI and the 2MASS JHKs photometry. We also compute new Teff versus colour empirical calibrations using our extended sample of stars. We derive effectives temperatures for almost all the stars in the Alonso et al. sample and find that our scales of temperature are hotter by ~64K(dT=104K,N=332 dwarfs) and ~54K(dT=131K,N=202 giants). The same comparison with the sample of Ramirez & Melendez for stars with [Fe/H]<-2.5 provides a difference of ~-87K(dT=194K,N=12 dwarfs) and ~61K(dT=62K,N=18 giants). Our temperature scale is slightly hotter than that of Alonso et al. and Ramirez & Melendez for metal-rich dwarf stars but cooler than that of Ramirez & Melendez for metal-poor dwarfs. We have performed a fully self-consistent IRFM in the 2MASS photometric system. For those who wish to use 2MASS photometry and colour-temperature calibrations to derive effective temperatures, especially for metal-poor stars, we recommend our calibrations.