Publication Date:
2014-01-29
Description:
High spectral resolution (~80 000) and signal-to-noise observations from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project (UVES-POP) are used to study the interstellar molecular lines CN (3874 Å), CH + (3957, 4232 Å) and CH (3886, 4300 Å) towards 74 O- and B-type stellar sightlines. Additionally, archive data are presented for 140 ELODIE early-type stellar sightlines at R = 42 000, plus 25 FEROS at R = 48 000 and 3 UVES at R 〉 50 000, mainly in the CH + (4232 Å) and CH (3886, 4300 Å) transitions. Detection rates are ~45 per cent for CN and ~67 per cent for the other lines in the POP sample, and ~10–15 per cent for CH + and CH lines in the additional sample. CH and CH + are well correlated between log[ N (CH) cm –2 ]~12–14, implying that these clouds are CH + -like CH and not CN-like CH. CH is also very well correlated with Na i D in the range log[ N (Na i cm –2 ]) ~12.2–14.2. A few sightlines show tentative velocity shifts of ~2 km s –1 between CH and CH + , which appear to be caused by differences in component strength in blends, and hence do not provide firm evidence for shocks. Finally, we describe a search for 13 CH + in a sightline towards HD 76341. No 13 CH + is detected, placing a limit on the 13 CH + to 12 CH + ratio of ~0.01. If a formal fit is attempted, the equivalent width ratio in the two isotopes is a factor ~90 but with large errors.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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