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Date: 13 Oct 93 00:45:00 EST
From: "STARS::HRSSHORE" <HRSSHORE%STARS.decnet@hrs.gsfc.nasa.gov>
Subject: IUE Observations of Nova Sgr 1993
Ultraviolet development of N Sgr 1993
Steve Shore, Sumner Starrfield
IUE observations of N Sgr 93 have been obtained with IUE starting on
21 Sept. The first (Vilspa) spectra on 17 Sept. probably caught the
nova at UV minimum, but we have not seen this spectrum. The spectrum
during the past month has been typical of the optically thick stage in
a relatively slow nova. We cannot distinguish the subclass from the
UV data; any possible P Cyg stage, typical of an ONeMg nova in early
outburst, has yet to occur.
The short wavelength interval (SWP, 1200-2000 A) has increased in
integrated flux by about a factor of 10 since that first spectrum and
the windows at about 1300, 1600, and 1700 A have not become optically
thin. The most substantial change has been the steady increase in the
flux shortward of 1500 A -- the longer wavelengths have slowly
decreased as the windows have become progressively brighter. The 1300
A feature may also contain O I 1300. The SWP maximum appears to have
been reached on about 8 Oct. and the nova is now in a broad maximum,
with the interval at maximum light being comparable to Nova LMC 1992.
The rise time was about the same as OS And 1986 and other relatively
slow novae. The long wavelength (LWP, 2100 - 3300 A) region has been
dominated by Mg II 2800. The profile has become progressively more
asymmetric relative to the interstellar absorption lines, with a red
wing extending to about 2500 km/s. No P Cyg has been detected on the
blueward side of the line. The profile may be showing some absorption
from the excited state Mg II doublet (the h and k satellite lines
arising from the upper level of the resonance transitions). The
continuum in the vicinity of the resonance lines has remained unchanged
since about 21 Sept. No other strong emission lines have been
detected (Al II 2640 is also present). The LWP flux has been
decreasing as the SWP flux has been rising. The Mg II line profile is
otherwise featureless, unlike N Cyg 92 which showed knotty structure
comparable with the optical lines. Observations will now cease with
IUE because of operational constraints. The following is the table of
measured IUE fluxes for comparison with anybody's optical data. The
columns list the image number (SWP), julian date, integrated
1200-2000A flux (erg/cm^2/s) and the flux corrected for a guessed-at
reddening of E(B-V)=0.4.
Any observers with optical data wishing to compare their results with
the IUE spectra should contact Steve Shore
(hrsshore@stars.gsfc.nasa.gov). The nova should start the transition
to the nebular spectrum within a couple of weeks, for anyone in the
southern hemisphere still able to observe this star.
48694 9251.0368 3.580320e-11 7.43064264e-10 1500 1592
48705 9253.0819 3.831770e-11 7.84549589e-10 1500 1592
48807 9260.0931 7.709045e-11 1.54938262e-09 660 1592
48847 9265.7604 7.507954e-11 1.52108188e-09 600 1592
48848 9265.8160 8.782813e-11 1.78940395e-09 900 1591
48849 9265.8639 9.279517e-11 1.89627972e-09 900 1592
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