Calibration of the photometric G passband for Gaia Data Release 1

Apellaniz, J. M. 2017. Calibration of the photometric G passband for Gaia Data Release 1. Astronomy and Astrophysics 608, DOI: 10.1051/0004-6361/201732167

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 BTVT 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 lambda with an exponent of 0.783 eliminates the color term. The corrected passband has a Vega zero point of 0.070 +/- 0.004 mag.

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