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Date: Wed, 7 Apr 93 21:50:44 GMT
From: rab@simplicio.as.utexas.edu (Bob Benjamin)
Subject: Infrared update on N Cyg 1992
Here's an update on the IR spectrum of Nova Cygni 1992 (soon to be an IAU
Circular). The trend toward higher and higher ionization continues.
H. Dinerstein and R. Benjamin report that infrared spectroscopy by
D. Lester, N. Gaffney, and B. Smith at the McDonald Observatory 2.7 m
reflector shows the appearance of new infrared coronal lines,
[Al IX] 2.040 microns and [S IX] 1.250 microns. The ionization energy to
create these ions are 285 eV and 328eV, respectively. Both lines are clearly
resolved from neighboring lines. The [S IX] 1.250 micron line was
tentatively detected by Woodward and Greenhouse (IAUC 5653) with
a reported line strength of 0.08 times that of the adjacent Paschen
beta line. This strength was consistent, however, with an identification
as He I 1.253 microns, which had been observed as early as June 1992,
before the onset of the coronal phase. On 2.4 April 1993 UT, we find the
strength of the 1.25 micron feature is now a factor of 8 too strong to be
due to He I alone; it had increased to about 0.6 times the strength of
Paschen beta. Therefore, we regard it as highly likely that [S IX] is now
present. Further confirmation that the level of ionization in the
ejecta has continued to increase since our previous epoch of
observations (10 December 1992) is seen in the ratio
[Si VII] 2.47 microns/[Si VI] 1.96 microns, which increased from about
1.6 to 3.5 between Dec 1992 and April 1993, while the absolute fluxes of
both lines dropped. These new infrared spectra supplement and confirm the
recent report of very high ionization species ([Fe X], [Ar X], and possibly
[Fe XIV]) in the optical spectrum of V1974 Cygni by Garnavich (IAUC 5746).
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