Abstract
We present high-resolution (R=λ/Δλ~ 40000) CaII K
interstellar observations (λair= 3933.66Å)
towards 88 mainly B-type stars, of which 74 are taken from the
Edinburgh-Cape or Palomar-Green surveys, and 81 have |b| > 25°.
The majority of the data come from previously existing spectroscopy,
although also included are 18 new observations of stars with echelle
spectra taken with UVES on the Very Large Telescope UT2 (Kueyen). Some
49 of the sample stars have distance estimates above the Galactic plane
(|z|) >= 1 kpc, and are thus good probes of the halo interstellar
medium. Of the 362 interstellar Ca K components that we detect, 75 (21
per cent) have absolute values of their LSR velocity values exceeding 40
km s-1. In terms of the deviation velocity for the sightlines
with distance estimates, 46/273 (17 per cent) of components have
velocity values exceeding those predicted by standard Galactic rotation
by more than 40 km s-1. Combining this data set with previous
observations, we find that the median value of the reduced equivalent
width (REW) of stars with |z| >= 1 kpc (EW×sin|b|) is ~115
mÅ (n= 80), similar to that observed in extragalactic sightlines
by Bowen. Using data of all z distances, the REW at infinity is found to
be ~130 mÅ, with the scaleheight (l) of the CaII K column density
distribution being ~800 pc (n= 196) and reduced column density at
infinity of log[N(CaII K) cm-2]~12.24. This implies that ~30
per cent of CaII K absorption occurs at distances exceeding ~1 kpc. For
nine sightlines with distance exceeding 1 kpc and with a companion
object within 5°, we find that all but two have values of CaII
reduced equivalent width the same to within ~20 per cent, when the REW
of the nearest object is extrapolated to the distance of the further of
the pair, and assuming l= 800 pc. For 29 of our sightlines with |z|
>= 1 kpc and a HI detection from the Leiden-Dwingeloo survey
(beamsize of 0.5°), we find log(N(CaII K)/N(HI)) ranging from -7.4
to -8.4. Values of the CaII K abundance relative to neutral hydrogen
(log[N(CaIIK)cm-2]-log[N(HI)cm-2]) are found to be
more than ~0.5dex higher in stars with distances exceeding ~100 pc, when
compared with the (log[N(CaII K) cm-2]-
log[N(Htot) cm-2]) values found in nearby
sightlines such as those in Wakker & Mathis (2000). Finally, stellar
CaII K equivalent widths of the sample are determined for 26 objects.
Original language | English |
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Pages (from-to) | 119-134 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 346 |
Issue number | 1 |
DOIs | |
Publication status | Published - 1 Nov 2003 |
Keywords / Materials (for Non-textual outputs)
- stars: early-type
- ISM: clouds
- ISM: general
- ISM: structure