Optical spectroscopy of the M 15 intermediate velocity cloud

Details Optical spectroscopy of the M 15 intermediate velocity cloud Optical spectroscopy of the M 15 intermediate velocity cloud

Jun 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002a%26a...387.1057s&link_type=abstract

Astronomy and Astrophysics, v.387, p.1057-1065 (2002)

Astronomy and Astrophysics

Astrophysics

6

Ism: Clouds, Ism: Abundances, Ism: Individual Objects: M 15 Ivc, Ism: Individual Objects: Complex Gp

Scientific paper

We present echelle spectrograph observations in the Na D lines, at resolutions of 6.2-8.5 km s-1, for 11 stars located in the line-of-sight to the M 15 intermediate velocity cloud (IVC), which has a radial velocity of ~ +70 km s-1 in the Local Standard of Rest. This cloud is a part of IVC Complex gp. The targets range in magnitude from mV=13.3-14.8. Seven of the observed stars are in the M 15 globular cluster, the remaining four being field stars. Three of the observed cluster stars are located near a peak in intensity of the IVC H I column density as observed at a resolution of ~ 1 arcmin. Intermediate velocity gas is detected in absorption towards 7 stars, with equivalent widths in Na D2 ranging from ~ 0.09-0.20 Å, corresponding to log10(NNa cm-2) ~ 11.8-12.5, and Na I/H I column density ratios (neglecting the H II component) ranging from ~ (1-3)x10-8. Over scales ranging from 30 arcsec to 1 arcmin, the Na I column density and the Na I/H I ratio varies by upto 70 per cent and a factor of ~ 2, respectively. Combining the current sightlines with previously obtained Na I data from Kennedy et al. (\cite{Kennedy98}b), the Na I/H I column density ratio over cluster sightlines varies by upto a factor of ~ 25, when using H I data of resolution ~ 2x1 arcmin. One cluster star, M 15 ZNG-1, was also observed in the Ca I (lambdaair =4226.728 Å) and Ca II (lambdaair =3933.663 Å) lines. A column density ratio N(Ca I)/N(Ca II) < 0.03 was found, typical of values seen in the warm ionised interstellar medium. Towards this sightline, the IVC has a Na I/Ca II column density ratio of ~ 0.25, similar to that observed in the local interstellar medium. Finally, we detect tentative evidence for IV absorption in K I (lambdaair =7698.974 Å) towards 3 cluster stars, which have N(K I)/N(H I) ratios of ~ 0.5-3x10-9. Based on observations made with the Apache Point Observatory 3.5-m, USA, Very Large Telescope, Chile, and William Herschel Telescope, La Palma, Spain.

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