52 research outputs found
Interstellar and Circumstellar Optical & Ultraviolet Lines Towards SN1998S
We have observed SN1998S which exploded in NGC3877, with the UES at the WHT
and with the E230M echelle of STIS aboard HST. Both data sets were obtained at
two seperate epochs. From our own Galaxy we detect interstellar absorption
lines of CaII, FeII, MgI, and probably MnII from the edge of the HVC Complex M.
We derive gas-phase abundances which are very similar to warm disk clouds in
the local ISM, which we believe argues against the HVC material having an
extragalactic origin. At the velocity of NGC3877 we detect interstellar MgI,
MgII, MnII, CaII, & NaI. Surprisingly, one component is seen to increase by a
factor of ~1 dex in N(NaI) and N(MgI) between the two epochs over which the
data were taken. Unusually, our data also show narrow Balmer, HeI, and
metastable FeII P-Cygni profiles, with a narrow absorption component
superimposed on the bottom of the profile's absorption trough. Both the broad
and narrow components of the optical lines are seen to increase substantially
in strength between the two epochs. Most of the low-ionization absorption can
be understood in terms of gas co-rotating with the disk of NGC 3877, providing
the SN is at the back of an HI disk with a similar thickness to that of our own
Galaxy. However, the variable absorption components, and the classic P-Cygni
emission profiles, most likely arise in slow-moving circumstellar outflows
originating from the red supergiant progenitor of SN1998S. [Abridged.]Comment: Accepted by ApJ, 26 pages including 9 figure
The Far Ultraviolet Spectroscopic Explorer Survey of OVI Absorption in the Disk of the Milky Way
To probe the distribution and physical characteristics of interstellar gas at
temperatures T ~ 3e5 K in the disk of the Milky Way, we have used the Far
Ultraviolet Spectroscopic Explorer (FUSE) to observe absorption lines of OVI
toward 148 early-type stars situated at distances 1 kpc. After subtracting off
a mild excess of OVI arising from the Local Bubble, combining our new results
with earlier surveys of OVI, and eliminating stars that show conspicuous
localized X-ray emission, we find an average OVI mid-plane density n_0 = 1.3e-8
cm^-3. The density decreases away from the plane of the Galaxy in a way that is
consistent with an exponential scale height of 3.2 kpc at negative latitudes or
4.6 kpc at positive latitudes. Average volume densities of OVI along different
sight lines exhibit a dispersion of about 0.26 dex, irrespective of the
distances to the target stars. This indicates that OVI does not arise in
randomly situated clouds of a fixed size and density, but instead is
distributed in regions that have a very broad range of column densities, with
the more strongly absorbing clouds having a lower space density. Line widths
and centroid velocities are much larger than those expected from differential
Galactic rotation, but they are nevertheless correlated with distance and
N(OVI), which reinforces our picture of a diverse population of hot plasma
regions that are ubiquitous over the entire Galactic disk. The velocity
extremes of the OVI profiles show a loose correlation with those of very strong
lines of less ionized species, supporting a picture of a turbulent, multiphase
medium churned by shock-heated gas from multiple supernova explosions.Comment: Accepted for publication in ApJS. Preprint with full resolution
images and all 148 spectra available at
http://www.astro.princeton.edu/~dvb/o
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