Further optical and UV spectroscopy of stars in the direction of the Riegel & Crutcher cold cloud
Abstract
Further optical and UV spectral data are presented for four stars in the direction of the Riegel & Crutcher cold cloud. Two of the stars lie close in position to the area covered by our previous optical, UV and radio studies near l=10 deg, while the other two stars lie near l=15 deg. The stars range in distance from about 140 pc to 1.5 kpc. The RC cold cloud gas is detected (at a velocity of ~+3 km s^-1) towards a star at a distance of about 150 pc, in agreement with previous cloud distance estimates. The spectra of the more distant stars contain components at higher velocities; components at +20 and +40 km s^-1 may be identified with peculiar-velocity gas associated with the Sagittarius arm, seen elsewhere in the general field, while a component at -60 km s^-1 may be stellar or interstellar in nature. A component at -20 km s^-1 seen towards previously studied stars in the field is not clearly identified in the spectra of the present stars. The atomic column densities of the Riegel & Crutcher cloud component do not vary greatly across the field, although the CH and CH^+ column densities are more variable. The CH/CH^+ column density ratio remains fairly constant, however, at a value that is consistent with the CH^+ being formed in a warm boundary layer. Along the HD 167264 sightline, the cold gas has an electron density of the order of 0.05-0.1 cm^-3 and a space density of the order of 100-300 cm^-3.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- December 1996
- DOI:
- 10.1093/mnras/283.3.1089
- Bibcode:
- 1996MNRAS.283.1089K
- Keywords:
-
- STARS: DISTANCES;
- ISM: ATOMS;
- ISM: CLOUDS;
- ISM: GENERAL;
- ISM: STRUCTURE;
- ULTRAVIOLET: STARS