|
Description
New absolute proper motions referred directly to external galaxies, photographic photometry, and cluster membership probabilities have been determined for over 600 faint stars in the Hyades region. These have been used to investigate the Hyades convergent point and distance. A detailed review of the foundations of the convergent-point method, its applicability to the Hyades, the several mathematical variations of the method, and its possible role in producing the apparent discrepancy between previous Hyades proper motion results and "secondary" Hyades distance indicators, has been carried out. The convergent-point method, as applied to the Hyades, is entirely valid, and cannot be the source of any significant error in the Hyades distance. Systematic errors in meridian circle proper motions are implicated as the cause of the observed Hyades distance discrepancy. The convergent-point analysis of the new absolute Hyades proper motions represents the first Hyades distance determination independent of all meridian circle proper motion systems. The resulting Hyades distance modulus is m-M=3.42, significantly greater than all previous values from proper motions, and in agreement with predictions of the Hyades distance from stellar structure theory, and with the results of "secondary" distance indicators. Incorporating this value, the most likely value of the mean Hyades distance modulus from all sources is m-M=3.29+/-0.08. The quoted error represents a larger and more realistic estimate of the true errors than has been previously stated. Significant effects of the increased Hyades distance on the cosmic distance scale and other questions of general astronomical importance are briefly discussed.
|
