A reevaluation of the 2MASS zero points using CALSPEC spectrophotometry complemented with Gaia Data Release 2 parallaxes

Abstract

Context. 2MASS is the reference survey in the near-infrared (NIR) part of the spectrum due to its whole-sky coverage, large dynamic range, and proven calibration uniformity. However, previous studies disagree on the value of the zero points (ZPs) for its three bands JHK at the hundredth of a magnitude level. The disagreement should become more noticeable now that Gaia provides whole-sky optical photometry calibrated below that level. Aims. We want to establish the value of the 2MASS ZPs based on NICMOS/HST spectrophotometry of the CALSPEC standard stars and test it with the help of Gaia DR2 parallaxes. Methods. We have computed the synthetic JHK photometry for a sample of stars using the HST CALSPEC spectroscopic standards and compared it with their 2MASS magnitudes to evaluate the ZPs. We have tested our results by analyzing a sample of FGK dwarfs with excellent 2MASS photometry and accurate Gaia DR2 parallaxes. Results. The Vega ZPs for 2MASS J, H, and K are found to be −0.025 ± 0.005, 0.004 ± 0.005, and −0.015 ± 0.005 mag, respectively. The analysis of the FGK sample indicates that the new ZPs are more accurate than previous ones.