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IAUC 8675: RS Oph

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                                                  Circular No. 8675
Central Bureau for Astronomical Telegrams
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
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     T. Iijima, Osservatorio Astrofisico, Asiago, writes that high-
dispersion spectra (resolution 16000; range 420-680 nm) of RS Oph
were taken with an echelle spectrograph mounted on the 1.82-m
reflector at the Mt. Ekar station of the Astronomical Observatory
of Padova on Feb. 18.2 and 19.2 UT.  The spectra show broad
emission lines of H I, He I, Fe II multiplets 27, 37, 38, 42, 43,
48, 49, and 74, and some Ti II lines.  The emission lines of He II
were not yet detected.  The FWHM of H I and He I lines are about
1800 km/s, and those of the Fe II lines are roughly 800 km/s.  Very
narrow emission components, whose widths are comparable to the
resolution limit of the spectrograph, are seen on the top of the
broad emission components.  The narrow components are very weak for
H I and He I lines, while their heights are larger than those of
the broad components for several Fe II lines.  The line of [N II]
575.5-nm shows only the narrow component.
     M. F. Bode, Liverpool John Moores University; T. J. O'Brien
and R. J. Davis, University of Manchester; J. Osborne and K. L.
Page, University of Leicester; G. Schwarz, West Chester University;
S. Starrfield and J.-U. Ness, Arizona State University; J. Krautter,
University of Heidelberg; J. Drake, Smithsonian Astrophysical
Observatory; A. Evans, Keele University; and S. P. S. Eyres,
University of Central Lancashire, report that Swift XRT
observations of the latest outburst of RS Oph (IAUC 8671) show this
to be a very bright and rapidly evolving x-ray source:  "The first
observations, obtained on Feb. 16.21 UT (3.38 days after reported
outburst), gave a total XRT countrate of 11.8 +/- 0.2 counts/s.
The x-ray spectrum could be well fitted with a strongly absorbed
high-temperature thermal bremsstrahlung model plus an Fe K line and
absorption edge:  kT > 70 keV (90-percent confidence), E_line =
6.66 +/- 0.02 keV, E_edge = 7.18 +/- 0.09 keV, and N_H = (2.3 +/-
0.1) x 10**(22) cm**(-2).  Observations on Feb. 17.89 show the
source to be around three times brighter in the XRT band, and the
spectrum shows clear evidence of line emission from other elements
as well as Fe.  A preliminary solar abundance spectral fit requires
four temperature components plus an Fe K line and absorption edge.
In this fit, N_H = (1.7 +0.11/-0.22) x 10**(22) cm**(-2).  We note
that these fits may not be unique and should be considered simply
empirical at this stage.  Detailed hydrodynamic modelling is now in
progress.  Observations and modelling of the previous outburst in
1985 (see, e.g., O'Brien et al. 1992, MNRAS 255, 683) suggest that
RS Oph will continue to evolve rapidly in the x-ray range over the
coming weeks.  We also urge continued monitoring at other
wavelengths, in particular optical spectroscopy, for the next
several months.  Swift observations are ongoing."

                      (C) Copyright 2006 CBAT
2006 February 21               (8675)            Daniel W. E. Green

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