Ultraviolet photometry of stars obtained with the Celescope experiment in the Orbiting Astronomical Observatory

Abstract

We have used the television photometers in the Celescope OAO experiment to measure the far ultraviolet brightnesses of several thousand stars, including parts of the constellations Draco, Lyra, Puppis, Vela, Taurus, and Orion; and the Moon. As of this date (22 July 1969), three of our four cameras continue to operate satisfactorily, and we are making measurements in additional star fields distributed throughout the sky. Our shortest wavelength band, which includes the Lyman α line of atomic hydrogen, provides information on the Earth's outer atmosphere, as well as on star brightnesses. The intensity of the Lyman α radiation from the geocorona is a maximum when the Sun is near the horizon as seen by the OAO, and a minimum when the Sun is in the nadir. The direction that the telescope points does not much affect the measured intensities.

Because of the heavy logistic problems of identification, calibration, and measurement for so many stars and because of the survey character of the program, the scientific interpretation of the results is, as expected, lagging the measurement program. However, one consistent picture beginning to emerge from our data is that our observed stars are about equally divided between those that fall within 0.5 magnitude of the predicted ultraviolet brightnesses and those that are significantly fainter than predicted. Most of the giant stars we observe exhibit these ultraviolet deficiencies. Since some of these giants are stars for which little or no interstellar reddening is predicted, we attribute the observed deficiencies to the stars themselves.

Many of the objects we observe do not have accurate ground-based published data regarding magnitude, color, and spectral type; new ground-based observations of these objects are required to ensure satisfactory interpretation of our results.