The UV spectra of nearby white dwarfs and the nature of the local interstellar medium.

Abstract

Detailed results from analysis of the IUE ultraviolet data obtained in the directions of the white dwarfs G191-B2B, W1346, HD 149499B, and Sirius B are presented. It is found that the sun is embedded in a low-density cloud extending to about 2-3 pc in most directions, with some evidence suggesting that the sun may be near the edge of the cloud. This H I cloud is surrounded by a rather extensive region of very low density, hot interstellar medium. The apparent elemental depletions of C, N, O, Si, Mg, and possibly Fe are low in the solar neighborhood. The sun is moving through the cloud at a relative velocity of about 20 km/s, which agrees with previous space observations. The present observations rule out the existence of small 'cloudlets' within the local ISM of the type currently envisaged by the model of McKee and Ostriker (1977), but does not rule out larger, sparser clouds.