The Local Interstellar Medium toward the Center of Loop I

Abstract

The present study of the local insterstellar medium toward the center of Loop I analyzes optical and UV spectra of nearby stars within the l = 310-330 deg, b = 15-25 deg area. The analysis of the UV spectra reveals a sudden gas-column density increase as a function of distance from 10 to the 18th to 10 to the 20th/sq cm, suggesting the presence of a wall of gas 40 + or - 25 pc from the sun; this constrains the distance to the boundary of the soft X-ray emitting cavity around the sun, or 'Local Bubble', in the direction toward the Loop I center. At greater distances, the approximately constant N(H I), in conjunction with the lack of interstellar components in the optical spectra, are suggestive of the presence of another low-density gas column which can be identified with the Loop I Bubble.