99 research outputs found
A Modeling of the Super-Eddington Luminosity in Nova Outbursts: V1974 Cygni
We have modeled nova light curves exceeding the Eddington luminosity. It has
been suggested that a porous structure develops in nova envelopes during the
super Eddington phase and the effective opacity is much reduced for such a
porous atmosphere. Based on this reduced opacity model, we have calculated
envelope structures and light curves of novae. The optically thick wind model
is used to simulate nova winds. We find that the photospheric luminosity and
the wind mass-loss rate increase inversely proportional to the reducing factor
of opacities, but the wind velocity hardly changes. We also reproduce the
optical light curve of V1974 Cygni (Nova Cygni 1992) in the super-Eddington
phase, which lasts 13 days from the optical peak 1.7 mag above the Eddington
luminosity.Comment: 8 pages, 4 figures, to appear in ApJ
Eclipsing Binaries Showing Light Time Effect
Four eclipsing binaries, which show apparent changes of period, have been
studied with respect to a possible presence of the light time effect. With a
least squares method we calculated new light elements of these systems, the
mass function of the predicted third body, and its minimum mass. We discuss the
probability of the presence of such bodies in terms of mass function, changes
in radial velocity and third light in solution of light curves.Comment: 4 pages, 4 figures, 1 table, conference proceeding
The nature of premaximum halts of classical nova outbursts: V723 Cassiopeiae and V463 Scuti
We present a new interpretation of long premaximum halts of nova outbursts.
For V723 Cas (Nova Cas 1995) and V463 Sct (Nova Sct 2000), we have reproduced
light curves, excluding the brightness maxima, starting from the long
premaximum halt through the late decay phase of the outbursts using a
steady-state optically thick wind model. When the hydrogen-rich envelope of the
white dwarf (WD) is massive enough, the star expands to \sim 100 R_\sun or over
and its surface temperature decreases to below 7000 K. At this supergiant
mimicry stage, the changes in both the photospheric radius and the temperature
are small against the large increase in the envelope mass. These changes cause
a saturation in visual magnitude that lasts a long time before it begins to
decline. This saturation is known as the premaximum halt of a classical nova
outburst. The visual magnitude during the saturation is close to the bolometric
magnitude, which is an upper limit for a given WD mass. Since the WD masses are
estimated to be 0.59 M_\sun for V723 Cas and 1.1 M_\sun for V463 Sct by fitting
the decline rate of nova light curves, we can determine the absolute magnitude
of premaximum halts. It is a refined Eddington luminosity. Thus, the premaximum
halt of a nova works as a standard candle.Comment: corrections for distance estimate of V463 Sct and several typos, 8
pages including 5 figures, to appear in ApJL, 2004 September
Multiwavelength evidence for a 15-year periodic activity in the symbiotic nova V1016 Cygni
The ~15.1 years period found in the long-term UBV photoelectric and
photographic photometry of the symbiotic nova V1016 Cyg is detected also in the
(J-K) colour index and in the UV continuum and emission line fluxes from IUE
and HUT spectra. It could be interpreted either as the effect of recurrent
enhanced mass loss episodes from the Mira type variable companion to a hot
component along its ultra-wide orbit (proposed from recent HST observations) or
the true orbital period of the inner, unresolved binary of a triple system. A
410-day delay of the maximum of UV emission lines fluxes with respect to the
maximum of continuum was found. The pulsation period of the Mira type variable
was improved to 474+/-6 days.Comment: 7 pages, 7 PostScript figures. Accepted for pubblication in A&
Toward a unified light curve model for multi-wavelength observations of V1974 Cygni (Nova Cygni 1992)
We present a unified model for optical, ultraviolet (UV), and X-ray light
curves of V1974 Cygni (Nova Cygni 1992). Based on an optically thick wind model
of nova outbursts, we have calculated light curves and searched for the best
fit model that is consistent with optical, UV, and X-ray observations. Our best
fit model is a white dwarf (WD) of mass 1.05 M_\sun with a chemical composition
of X=0.46, C+N+O=0.15, and Ne = 0.05 by mass weight. Both supersoft X-ray and
continuum UV 1455 \AA light curves are well reproduced. Supersoft X-rays
emerged on day ~ 250 after outburst, which is naturally explained by our model:
our optically thick winds cease on day 245 and supersoft X-rays emerge from
self-absorption by the winds. The X-ray flux keeps a constant peak value for ~
300 days followed by a quick decay on day ~ 600. The duration of X-ray flat
peak is well reproduced by a steady hydrogen shell burning on the WD. Optical
light curve is also explained by the same model if we introduce free-free
emission from optically thin ejecta. A t^{-1.5} slope of the observed optical
and infrared fluxes is very close to the slope of our modeled free-free light
curve during the optically thick wind phase. Once the wind stops, optical and
infrared fluxes should follow a t^{-3} slope, derived from a constant mass of
expanding ejecta. An abrupt transition from a t^{-1.5} slope to a t^{-3} slope
at day ~ 200 is naturally explained by the change from the wind phase to the
post-wind phase on day ~ 200. The development of hard X-ray flux is also
reasonably understood as shock-origin between the wind and the companion star.
The distance to V1974 Cyg is estimated to be ~ 1.7 kpc with E(B-V)= 0.32 from
the light curve fitting for the continuum UV 1455 \AA.Comment: 8 pages, 4 figures, to appear in the Astrophysical Journa
Non-LTE Modeling of Nova Cygni 1992
We present a grid of nova models that have an extremely large number of
species treated in non-LTE, and apply it to the analysis of an extensive time
series of ultraviolet spectroscopic data for Nova Cygni 1992. We use
ultraviolet colors to derive the time development of the effective temperature
of the expanding atmosphere during the fireball phase and the first ten days of
the optically thick wind phase. We find that the nova has a pure optically
thick wind spectrum until about 10 days after the explosion. During this
interval, we find that synthetic spectra based on our derived temperature
sequence agree very well with the observed spectra. We find that a sequence of
hydrogen deficient models provides an equally good fit providing the model
effective temperature is shifted upwards by ~1000 K. We find that high
resolution UV spectra of the optically thick wind phase are fit moderately well
by the models. We find that a high resolution spectrum of the fireball phase is
better fit by a model with a steep density gradient, similar to that of a
supernova, than by a nova model.Comment: 24 pages, 17 figures, Accepted by Astrophysical Journa
The Distance and Morphology of V723 Cassiopeiae (NOVA CASSIOPEIA 1995)
We present spatially resolved infrared spectra of V723 Cas (Nova Cassiopeia
1995) obtained over four years with the integral field spectrograph OSIRIS on
Keck II. Also presented are one epoch of spatially unresolved spectra from the
long slit spectrograph NIRSPEC on Keck II. The OSIRIS observations made use of
the laser guide star adaptive optics facility that produced diffraction-limited
spatial resolution of the strong coronal emission features in the nova ejecta.
We remove the point-like continuum from V723 Cas data cubes to reveal details
of the extended nebula and find that emission due to [Si VI] and [Ca VIII] has
an equatorial ring structure with polar nodules-a strikingly different
morphology than emission due to [Al IX], which appears as a prolate spheroid.
The contrast in structure may indicate separate ejection events. Using the
angular expansion and Doppler velocities observed over four epochs spaced at
one year intervals, we determine the distance to V723 Cas to be 3.85+0.23-0.21
kpc. We present the OSIRIS three-dimensional data here in many ways: as
narrowband images, one- and two-dimensional spectra, and a volume rendering
that reveals the true shape of the ejecta.Comment: 37 pages, 8 figure
Elemental Abundances in the Ejecta of Old Classical Novae from Late-Epoch Spitzer Spectra
We present Spitzer Space Telescope mid-infrared IRS spectra, supplemented by
ground-based optical observations, of the classical novae V1974 Cyg, V382 Vel,
and V1494 Aql more than 11, 8, and 4 years after outburst respectively. The
spectra are dominated by forbidden emission from neon and oxygen, though in
some cases, there are weak signatures of magnesium, sulfur, and argon. We
investigate the geometry and distribution of the late time ejecta by
examination of the emission line profiles. Using nebular analysis in the low
density regime, we estimate lower limits on the abundances in these novae. In
V1974 Cyg and V382 Vel, our observations confirm the abundance estimates
presented by other authors and support the claims that these eruptions occurred
on ONe white dwarfs. We report the first detection of neon emission in V1494
Aql and show that the system most likely contains a CO white dwarf.Comment: 22 pages, 12 figure
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