Calibration of the photometric G passband for Gaia Data Release 1^⋆

Centro de Astrobiología, CSIC-INTA, campus ESAC, camino bajo del castillo s/n, 28 692 Villanueva de la Cañada, Spain
e-mail: jmaiz@cab.inta-csic.es

Received: 25 October 2017
Accepted: 29 November 2017

Abstract

Context. On September 2016 the first data from Gaia were released (DR1). The first release included photometry for over 10⁹ sources in the very broad G system.

Aims. The aims here are to test the correspondence between G magnitudes in DR1 and the synthetic equivalents derived using spectral energy distributions from observed and model spectrophotometry; to correct the G passband curve; and to measure the zero point in the Vega system.

Methods. I have computed the synthetic G and Tycho-2 B_TV_T photometry for a sample of stars using the Next Generation Spectral Library (NGSL) and the Hubble Space Telescope (HST) CALSPEC spectroscopic standards.

Results. I have found that the nominal G passband curve is too blue for the DR1 photometry, as shown by the presence of a color term in the comparison between observed and synthetic magnitudes. A correction to the passband applying a power law in λ with an exponent of 0.783 eliminates the color term. The corrected passband has a Vega zero point of 0.070 ± 0.004 mag.