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

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.

💡 Research Summary

The paper presents a fully self‑consistent implementation of the Infrared Flux Method (IRFM) that operates directly in the 2MASS photometric system, thereby eliminating the intermediate transformation to the TCS system that was required in previous works such as Ramírez & Meléndez (2005). The authors compute theoretical fluxes for the 2MASS J, H, and Kₛ filters by integrating ATLAS9 model spectra over the actual 2MASS filter transmission curves. These synthetic fluxes are then compared directly with observed 2MASS magnitudes, which removes a source of systematic error that becomes especially important for very metal‑poor stars where colour transformations are poorly constrained.

The stellar sample is assembled from several high‑quality sources. It includes the dwarf and sub‑giant stars from Alonso et al. (1996, 1999) together with the stars used by Ramírez & Meléndez, Casagrande et al., Christlieb et al., and Bonifacio et al. After merging, the final catalogue contains 555 dwarf/sub‑giant field stars and 264 giant field stars, for a total of 819 objects spanning a wide range in effective temperature (≈4000–7000 K), metallicity (−4.0 ≲