THE GRONBECH-OLSEN PHOTOMETRY - TRANSFORMATIONS TO A HYADES-COMA SYSTEM

In this paper, we consider the zero points of six sets of Stromgren-be ta photometry. The color-index system to which our results are referre d is a ''Hyades-Coma'' system composed of photometry by Crawford and F erry (1966, AJ, 71, 206) and Crawford and Barnes (1969, AJ, 74, 407). For V magnitudes, we use measurements by Taylor and Joner (1992, PASP, 104, 911). Our results are as follows. (1) The zero points of photome try by Gronbech and Olsen (1976, A&AS, 25, 213; 1977, A&AS, 27, 443) a re offset from those of the Hyades-Coma system. The offsets can amount to several mmag; they appear for V and all color indices except beta, and depend on right ascension and (usually) declination. (2) These of fsets can be applied to photometry by Stetson (1991, AJ, 102, 589), wh o reduced his results to the Gronbech-Olsen system. After correction, Stetson's results for a set of ''transfer stars'' differ from comparab le data published by Crawford and Barnes (1970, AJ, 75, 978). (3) A di rect comparison of the transfer stars to the Hyades yields consistency between the Hyades-Coma and Crawford-Barnes zero points (for the tran sfer stars specifically). This result supports a conclusion drawn by T aylor and Joner, and suggests that there is some problem with the zero points of Stetson's transfer-star data. (4) From Stetson's corrected data, one finds that the Crawford-Perry zero points for the Hyades are consistent with the Crawford-Barnes zero points for Coma. This result agrees with a conclusion drawn by Taylor and Joner from their own dat a, and suggests that the problem postulated for Stetson's transfer-sta r data does not extend to his results for the Hyades and Coma.