Volume 387, Number 3, June I 2002
|Page(s)||1057 - 1065|
|Published online||17 May 2002|
Optical spectroscopy of the M 15 intermediate velocity cloud *
Astrophysics and Planetary Science Division, Department of Pure and Applied Physics, The Queen's University of Belfast, University Road, Belfast, BT7 1NN, UK
2 Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
3 Isaac Newton Group, Apartado de Correos 368, Santa Cruz de La Palma, Tenerife 38780, Canary Islands, Spain
Corresponding author: J. V. Smoker, email@example.com
Accepted: 14 March 2002
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 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)10-8. 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]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 ~21 arcmin. One cluster star, M 15 ZNG-1, was also observed in the Ca i ( Å) and Ca ii ( 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 ( Å) towards 3 cluster stars, which have N(K i)/N(H i) ratios of ~0.5-310-9.
Key words: ISM: clouds / ISM: abundances / ISM: individual objects: M 15 IVC / ISM: individual objects: complex gp
© ESO, 2002
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.