Issue |
A&A
Volume 451, Number 2, May IV 2006
|
|
---|---|---|
Page(s) | 563 - 580 | |
Section | Stellar structure and evolution | |
DOI | https://doi.org/10.1051/0004-6361:20053984 | |
Published online | 02 May 2006 |
Spectral evolution of the slowest classical nova V723 Cassiopeiae in the decline stage
Astronomical Observatory of Padova, Asiago Section, Osservatorio Astrofisico, 36012 Asiago (Vi), Italy e-mail: iijima@astras.pd.astro.it
Received:
4
August
2005
Accepted:
15
November
2005
The spectral evolution of an extremely slow nova V723 Cas was monitored
at Asiago Observatory for seven years. Observations in the long
pre-maximum stage, which lasted more than four months, were reported in our
previous paper. Here, we report the spectral evolution in the decline stage
from January 1996 to December 2001. The spectra just after maximum
luminosity showed prominent emission lines of H I, He I, Fe II, Ti II, Si II,
Na I, etc. P Cygni type absorption components appeared on H I, He I, and Fe II lines about two months after maximum when the nova performed the second
brightening. The radial velocities of the absorption components of H I and
He I lines varied from -600 km s-1 in February to -1600 km s-1 in June 1996.
Broad emission wings of H I and He I lines that were red-shifted by about
1000 km s-1 were detected in the same season. When the third brightening
began in July 1996, a new absorption system of H I and He I appeared in
which the blue-shift changed from -1000 km s-1 in July 1996 to -1600 km s-1
in February 1997. Prominent emission lines of highly ionized ions such as
[Fe VI], [Fe VII], and [Ca V] emerged in the period between May 30 and July 1, 1997. This nova probably entered the nebular stage in this period. The
interval from maximum luminosity
to the beginning of nebular stage is about 18 months, which is still longer
than those of the other extremely slow novae: 10 months of RR Pic or 8 months
of HR Del. Some emission lines of [Fe IV], which were not found on the
spectra of usual classical novae, were detected on the spectra in the nebular
stage. The ionization state grew with time to have a coronal emission
line [Fe X] λ6375 in November 1999 and later. The interstellar extinction is
estimated at and the distance to the nova at about
kpc, while the mass of the ejecta may be about
. The abundance of helium is estimated at
N(He)/N(H) =
. The abundance of oxygen is not so different from those of usual
classical novae, while a rather low abundance of nitrogen is noticed. The
abundance of neon is roughly comparable to that of a neon nova QU Vul.
Key words: stars: individual: V723 Cassiopeiae / novae, cataclysmic variables / ISM: general
© ESO, 2006
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