Central Bureau for Astronomical Telegrams
IAUC 5925: N Cas 1993
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Circular No. 5925
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
NOVA CASSIOPEIAE 1993
S. N. Shore, Indiana University, South Bend; S. Starrfield and
P. H. Hauschildt, Arizona State University; G. Sonneborn, Goddard
Space Flight Center; and R. Gonzalez-Riestra, International Ultraviolet
Explorer (IUE) Observatory, Vilspa, report: "Observations of
N Cas 1993 have been obtained with the IUE satellite since shortly
after the report of its discovery (IAUC 5902). The first spectra
(1993 Dec. 12.1 UT) showed the nova at ultraviolet (UV) minimum
with most of the opacity coming from overlapping absorption lines
from the iron group elements: the 'iron curtain'. We have been
obtaining IUE spectra at about 4-day intervals since that time, which
reveal that the ejected material has remained in an extremely
optically thick shell stage. The wavelength region around 280 nm is a
blend of both Fe II and Mg II. This blend displays a pseudo-P-Cyg
profile with a broad absorption trough that extends to a velocity
of about -1600 km/s. Interstellar Mg II h and k absorption lines
are superposed on emission from the nova; they have mean velocities
of -35 km/s but extend to nearly -60 km/s. Windows in the Fe II
absorption spectrum have recently begun to appear at 158 nm and
longer wavelengths, and changes in the spectral energy distribution
imply a slowly growing temperature for the ejecta. An ultraviolet
rise of a factor of three occurred around Dec. 22, but after that
time the nova has remained at nearly constant integrated UV flux
(through 1994 Jan. 12). A preliminary upper limit of E(B-V) = 0.6
is derived from the UV-to-optical flux ratio. The interstellar Mg
II and Na I lines suggest a distance of 4-6 kpc. We note that the
optical light curve is similar to that of a DQ Her-type of nova
(Payne-Gaposchkin 1957, The Galactic Novae, p. 13). Such a nova
will form an optically-thick dust shell about 60-90 days after
maximum light in the optical. Our stellar-atmosphere modeling
indicates that the slow spectral evolution is consistent with steady-
state ejection over the past month. The optical light curve, the
relatively slow UV spectral evolution, the steady state mass ejection,
and the detection of CO molecular lines in the infrared (IAUC
5916, 5922) lead us to expect that this nova will also form
optically-thick dust (Shore and Starrfield 1994, Sky Telesc., in press);
infrared observations will be necessary to confirm this expectation."
H. Mikuz, Ljubljana, Slovenia, reports that a prediscovery
photograph, taken by J. Prudic (Ljubljana) on 1993 Dec. 4.95 UT
with a 58-mm f/2 lens and T-Max 400 film, shows this object at mpv
= 8.0 (comparison stars from AAVSO Atlas).
1994 January 20 (5925) Daniel W. E. Green
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