A cross-calibration between Tycho-2 photometry and Hubble Space Telescope spectrophotometry

By analyzing a well-calibrated sample of 256 stars observed with both Hipparcos and HST, I show that Tycho-2 photometry and HST spectrophotometry are accurate and stable enough to obtain a precise cross-calibration. Based on this analysis, I obtain the following photometric zero points with respect to Vega for Tycho-2: 0.020 +/- 0.001 (B-T - V-T) 0.078 +/- 0.009 (B-T), and 0.058 +/- 0.009 (V-T).