CaII K interstellar observations towards early-type disc and halo stars, abundances and distances of intermediate- and high-velocity clouds

Details CaII K interstellar observations towards early-type disc and halo stars, abundances and distances of intermediate- and high-velocity clouds CaII K interstellar observations towards early-type disc and halo stars, abundances and distances of intermediate- and high-velocity clouds

Jul 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006mnras.370..151s&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Volume 370, Issue 1, pp. 151-162.

Astronomy and Astrophysics

Astronomy

5

Stars: Early-Type, Ism: Clouds, Ism: General, Ism: Structure

Scientific paper

We present CaII K (λair = 3933.661Å) interstellar observations towards 20 early-type stars, to place lower distance limits to intermediate- and high-velocity clouds (IHVCs) in their lines of sight. The spectra are also employed to estimate the Ca abundance in the low-velocity gas towards these objects, when combined with Leiden-Dwingeloo 21-cm HI survey data of spatial resolution . Nine of the stars, which lie towards IHVC complexes H, K and gp, were observed with the intermediate dispersion spectrograph on the Isaac Newton Telescope at a resolution R = λ/Δλ of 9000 (~33kms-1) and signal-to-noise ratio (S/N) per pixel of 75-140. A further nine objects were observed with the Utrecht Echelle Spectrograph on the William Herschel Telescope at R = 40000 (~7.5kms-1) and S/N per pixel of 10-25. Finally, two objects were observed in both CaII K and NaI D lines using the 2D COUDÉ spectrograph on the McDonald 2.7-m telescope at R = 35000 (~8.5 kms-1). The abundance of CaII K {log10(A) = log10[N(CaII K)]-log10[N(HI)]} plotted against HI column density for the objects in the current sample with heights above the Galactic plane (z) exceeding 1000pc is found to obey the Wakker & Mathis (2000) relation. Also, the reduced column density of CaII K as function of z is consistent with the larger sample taken from Smoker et al. (2003). Higher S/N observations than those previously taken towards HVC complex H stars HD13256 and HILT 190 reinforce the assertion that this lies at a distance exceeding 4000pc. No obvious absorption is detected in observations of ALS10407 and HD357657 towards IVC complex gp. The latter star has a spectroscopically estimated distance of ~2040pc, although this was derived assuming the star lies on the main sequence and without any reddening correction being applied. Finally, no CaII K absorption is detected towards two stars along the line of sight to complex K, namely PG1610+529 and PG1710+490. The latter is at a distance of ~700pc, hence placing a lower distance limit to this complex, where previously only an upper distance limit of 6800pc was available.

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