57 research outputs found
CalFUSE v3: A Data-Reduction Pipeline for the Far Ultraviolet Spectroscopic Explorer
Since its launch in 1999, the Far Ultraviolet Spectroscopic Explorer (FUSE)
has made over 4600 observations of some 2500 individual targets. The data are
reduced by the Principal Investigator team at the Johns Hopkins University and
archived at the Multimission Archive at Space Telescope (MAST). The
data-reduction software package, called CalFUSE, has evolved considerably over
the lifetime of the mission. The entire FUSE data set has recently been
reprocessed with CalFUSE v3.2, the latest version of this software. This paper
describes CalFUSE v3.2, the instrument calibrations upon which it is based, and
the format of the resulting calibrated data files.Comment: To appear in PASP; 29 pages, 13 figures, uses aastex, emulateap
Opacity in the upper atmospheres of active stars II. AD Leonis
We present FUV and UV spectroscopic observations of AD Leonis, with the aim
of investigating opacity effects in the transition regions of late-type stars.
The C III lines in FUSE spectra show significant opacity during both the
quiescent and flaring states of AD Leonis, with up to 30% of the expected flux
being lost during the latter. Other FUSE emission lines tested for opacity
include those of O VI, while C IV, Si IV and N V transitions observed with STIS
are also investigated. These lines only reveal modest amounts of opacity with
losses during flaring of up to 20%. Optical depths have been calculated for
homogeneous and inhomogeneous geometries, giving path lengths of ~20-60 km and
\~10-30 km, respectively, under quiescent conditions. However path lengths
derived during flaring are ~2-3 times larger. These values are in excellent
agreement with both estimates of the small-scale structure observed in the
solar transition region, and path lengths derived previously for several other
active late-type stars.Comment: 13 pages, 4 figures, 4 Tabels, accepted A&
A search for line intensity enhancements in the far-UV spectra of active late-type stars arising from opacity
Radiative transfer calculations have predicted intensity enhancements for
optically thick emission lines, as opposed to the normal intensity reductions,
for astrophysical plasmas under certain conditions. In particular, the results
are predicted to be dependent both on the geometry of the emitting plasma and
the orientation of the observer. Hence in principle the detection of intensity
enhancement may provide a way of determining the geometry of an unresolved
astronomical source. To investigate such enhancements we have analyzed a sample
of active late-type stars observed in the far ultraviolet spectral region.
Emission lines of O VI in the FUSE satellite spectra of epsilon Eri, II Peg and
Prox Cen were searched for intensity enhancements due to opacity. We have found
strong evidence for line intensity enhancements due to opacity during active or
flare-like activity for all three stars. The O VI 1032/1038 line intensity
ratios, predicted to have a value of 2.0 in the optically thin case, are found
to be up to ~30% larger during several orbital phases. Our measurements,
combined with radiative transfer models, allow us to constrain both the
geometry of the O VI emitting regions in our stellar sources and the
orientation of the observer. A spherical emitting plasma can be ruled out, as
this would lead to no intensity enhancement. In addition, the theory tells us
that the line-of-sight to the plasma must be close to perpendicular to its
surface, as observations at small angles to the surface lead to either no
intensity enhancement or the usual line intensity decrease over the optically
thin value. For the future, we outline a laboratory experiment, that could be
undertaken with current facilities, which would provide an unequivocal test of
predictions of line intensity enhancement due to opacity, in particular the
dependence on plasma geometry.Comment: 10 Pages, 8 Figures, and 2 Tables; Accepted in A&
The FUSE survey of OVI absorption in and near the Galaxy
We present FUSE observations of OVI absorption in a sample of 100
extragalactic targets and 2 distant halo stars. We describe the details of the
calibration, alignment in velocity, continuum fitting, and manner in which
contaminants were removed (Galactic H2, absorption intrinsic to the background
target and intergalactic Ly-beta lines). We searched for OVI absorption in the
velocity range -1200 to 1200 km/s. With a few exceptions, we only find OVI
between -400 and 400 km/s; the exceptions may be intergalactic OVI. We discuss
the separation of the observed OVI absorption into components associated with
the Galactic halo and components at high-velocity, which are probably located
in the neighborhood of the Galaxy. We describe the measurements of equivalent
width and column density, and we analyze the different contributions to the
errors. We conclude that low-velocity Galactic OVI absorption occurs along all
sightlines - the few non-detections only occur in noisy spectra. We further
show that high-velocity OVI is very common, having equivalent width >65 mAA in
50% of the sightlines and >30 mAA in 70% of the high-quality sightlines. The
high-velocity OVI absorption has velocities relative to the LSR of
+/-(100--330) km/s; there is no correlation between velocity and absorption
strength. We present 50 km/s wide OVI channel maps. These show evidence for the
imprint of Galactic rotation. They also highlight two known HI high-velocity
clouds (complex~C and the Magellanic Stream). The channel maps further show
that OVI at velocities <-200 km/s occurs along all sightlines in the region
l=20-150, b200 km/s occurs along all sightlines
in the region l=180-300, b>20 (abbreviated).Comment: 85 pages, 127 figures, 13 color figures, 3 tables, AASTeX preprint
format. All figures are in PNG format due to space concerns. Bound copies of
manuscript and two accompanying articles are available upon request.
submitted to ApJ
FUSE Observations of Interstellar Gas Towards the LMC Star Sk -67 05
We report on measurements of interstellar O VI, H2, P II, Si II, Ar I, and Fe II absorption along the line of sight to Sk -67 05, a B0 Ia star in a diffuse H II region in the western edge of the Large Magellanic Cloud (LMC). We find log N(O VI) = 14.40 +/- 0.04 in the Milky Way (MW) component and, using the C IV column density from previous IUE observations, N(C IV) / N(O VI) = 1.00 +/- 0.16, a value similar to other halo measurements made with FUSE. In the LMC component, log N(O VI) = 13.89 +/- 0.05, and N(C IV) / N(O VI) < 0.4 (3 sigma), since only an upper limit on N(C IV) is available. Along this sightline the LMC is rich in molecular hydrogen, log N(H2) = 19.50 +/- 0.08; in the MW log N(H2) = 14.95 +/- 0.08. A two-component fit for the excitation temperature of the molecular gas in the LMC gives T_01 = 59 +/- 5 K for J=0,1 and T_ex = 800 +/- 330 K for J=3,4,5. For the MW, T_01 = 99 (+30/-20) K; no excitation temperature could be determined for the higher rotational states. The MW and LMC gas-phase [Fe/P] abundances are ~0.6 and ~0.7 dex lower, respectively, than solar system abundances. These values are similar to [Fe/Zn] measurements for the MW and LMC towards SN 1987A
Far Ultraviolet Spectroscopic Explorer Observations of the Supernova Remnant N49 in the Large Magellanic Cloud
We report a Far Ultraviolet Spectroscopic Explorer satellite observation of the supernova remnant N49 in the Large Magellanic Cloud, covering the 905 -- 1187 A spectral region. A 30'' square aperture was used, resulting in a velocity resolution of ~100 km/s. The purpose of the observation was to examine several bright emission lines expected from earlier work and to demonstrate diffuse source sensitivity by searching for faint lines never seen previously in extragalactic supernova remnant UV spectra. Both goals were accomplished. Strong emission lines of O VI 1031.9 A, 1037.6 A and C III 977.0 A were seen, Doppler broadened to +/- 225 km/s and with centroids red-shifted to 350 km/s, consistent with the LMC. Superimposed on the emission lines are absorptions by C III and O VI 1031.9 at +260 km/s, which are attributed to warm and hot gas (respectively) in the LMC. The O VI 1037.6 A line is more severely affected by overlying interstellar and H2 absorption from both the LMC and our galaxy. N III 989.8 A is not seen, but models indicate overlying absorption severely attenuates this line. A number of faint lines from hot gas have also been detected, many of which have never been seen in an extragalactic supernova remnant spectrum
FUSE observations of the HI interstellar gas of IZw18
We present the analysis of FUSE observations of the metal-deficient dwarf
galaxy IZw18. We measured column densities of HI, NI, OI, ArI, SiII, and FeII.
The OI/HI ratio (log(OI/HI)=-4.7^{+0.8}_{-0.6}) is consistent with the O/H
ratio observed in the HII regions (all uncertainties are 2-sigma). If the
oxygen is depleted in the HI region compared to the HII regions, the depletion
is at most 0.5dex. This is also consistent with the log(O/H) ratios ~-5
measured with FUSE in the HI regions of other blue compact dwarf galaxies. With
log(NI/OI)=-2.4^{+0.6}_{-0.8}, the measured NI/OI ratio is lower than expected
for primary nitrogen. The determination of the NII column density is needed to
discriminate between a large ionization of NI or a possible nitrogen
deficiency. The neutral argon is also apparently underabundant, indicating that
ionization into ArII is likely important. The column densities of the other
alpha-chain elements SiII and ArI favor the lower edge of the permitted range
of OI column density, log(N(OI))~16.3.Comment: Accepted for publication in A&
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