19 research outputs found
Spectroscopic observations of the candidate sgB[e]/X-ray binary CI Cam
We present a compilation of spectroscopic observations of the sgB[e] star CI
Cam. This includes data from before, during, and after its 1998 outburst. The
object shows a rich emission line spectrum originating from circumstellar
material, rendering it difficult to determine the nature of either star
involved or the cause of the outburst. We collate pre-outburst data to
determine the state of the system before this occurred and provide a baseline
for comparison with later data. During the outburst all lines become stronger,
and hydrogen and helium lines become significantly broader and asymmetric.
After the outburst, spectral changes persist for at least three years, with
FeII and [NII] lines still a factor of ~2 above the pre-outburst level and HeI,
HeII, and NII lines suppressed by a factor of 2-10. We find that the spectral
properties of CI Cam are similar to other sgB[e] stars and therefore suggest
that the geometry of the circumstellar material is similar to that proposed for
the other objects: a two component outflow, with a fast, hot, rarefied polar
wind indistinguishable from that of a normal supergiant and a dense, cooler
equatorial outflow with a much lower velocity. We suggest that CI Cam is among
the hotter members of the class and is viewed nearly pole-on. The nature of the
compact object and the mechanism for the outburst remain uncertain, although it
is likely that the compact object is a black hole or neutron star, and that the
outburst was precipitated by its passage through the equatorial material. We
suggest that this prompted a burst of supercritical accretion resulting in
ejection of much of the material, which was later seen as an expanding radio
remnant. [Abbreviated]Comment: 25 pages including figures. Accepted for publication in A&
Herschel-SPIRE FTS Spectroscopy of Evolved Stars
We present far-infrared and submillimetre spectra of evolved objects observed with the SPIRE Fourier-transform spectrometer on board the Herschel Space Observatory. The observations cover wavelengths 195â670 ÎŒm, a region of the electromagnetic spectrum hitherto difficult to study. The far-infrared spectra of these objects are rich and complex. We determine physical conditions from observations of the rotational lines of several molecules, and present initial large velocity gradient models for AFGL 618. We detect water in AFGL 2688 for the first time, and confirm its presence in AFGL 618 in both ortho and para forms. In addition, we detect of the J = 1â0 line of CH+ in NGC 7027. Finally, we present new HerschelâSPIRE spectroscopic observations of both O-rich and C-rich evolved sources, and discuss preliminary investigations into their physical conditions
Herschel-SPIRE FTS spectroscopy of the carbon-rich objects AFGL 2688, AFGL 618, and NGC 7027
We present far-infrared and submillimetre spectra of three carbon-rich
evolved objects, AFGL 2688, AFGL 618 and NGC 7027. The spectra were obtained
with the SPIRE Fourier transform spectrometer on board the Herschel Space
Observatory, and cover wavelengths from 195-670 um, a region of the
electromagnetic spectrum hitherto difficult to study in detail. The far
infrared spectra of these objects are rich and complex, and we measure over 150
lines in each object. Lines due to 18 different species are detected. We
determine physical conditions from observations of the rotational lines of
several molecules, and present initial large velocity gradient models for AFGL
618. We detect water in AFGL 2688 for the first time, and confirm its presence
in AFGL 618 in both ortho and para forms. In addition, we report the detection
of the J=1-0 line of CH+ in NGC 7027.Comment: Accepted for A&A Herschel special issue. 4 tables, 2 figures
Relationship between thiol-disulphide homeostasis and visual evoked potentials in patients with multiple sclerosis
PACS and SPIRE spectroscopy of the red supergiant VY CMa
With a luminosity >105 Lâ and a mass-loss rate of âŒ2 Ă 10-4 Mâ yr-1, the red supergiant VY CMa truly is a spectacular object. Because of its extreme evolutionary state, it could explode as supernova any time. Studying its circumstellar material, into which the supernova blast will run, provides interesting constraints on supernova explosions and on the rich chemistry taking place in such complex circumstellar envelopes. We have obtained spectroscopy of VY CMa over the full wavelength range offered by the PACS and SPIRE instruments of Herschel, i.e. 55-672 micron. The observations show the spectral fingerprints of more than 900 spectral lines, of which more than half belong to water. In total, we have identified 13 different molecules and some of their isotopologues. A first analysis shows that water is abundantly present, with an ortho-to-para ratio as low as âŒ1.3:1, and that chemical non-equilibrium processes determine the abundance fractions in the inner envelope. © 2010 ESO
Silicon in the dust formation zone of IRC+10216
The interstellar medium is enriched primarily by matter ejected from evolved
low and intermediate mass stars. The outflows from these stars create a
circumstellar envelope in which a rich gas-phase and dust-nucleation chemistry
takes place. We observed the nearest carbon-rich evolved star, IRC+10216, using
the PACS (55-210 {\mu}m) and SPIRE (194-672 {\mu}m) spectrometers on board
Herschel. We find several tens of lines from SiS and SiO, including lines from
the v=1 vibrational level. For SiS these transitions range up to J=124-123,
corresponding to energies around 6700K, while the highest detectable transition
is J=90-89 for SiO, which corresponds to an energy around 8400K. Both species
trace the dust formation zone of IRC+10216, and the broad energy ranges
involved in their detected transitions permit us to derive the physical
properties of the gas and the particular zone in which each species has been
formed. This allows us to check the accuracy of chemical thermodynamical
equilibrium models and the suggested depletion of SiS and SiO due to accretion
onto dust grains.Comment: 5 pages, 3 figures, 7 pages in online appendix, Astronomy &
Astrophysics in pres
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