112 research outputs found
Complex Velocity Fields in the Shell of T Pyxidis
We present spatially-resolved, moderate-resolution spectrophotometry of the
recurrent nova T Pyx and a portion of the surrounding shell. The spectrum
extracted from a strip of width 10'' centered on the star shows well-known,
strong emission lines typical of old novae, plus a prominent, unfamiliar
emission line at 6590 Angstroms. This line, and a weaker companion at 6540
Angstroms which we also detect, have been previously reported by Shahbaz et
al., and attributed to Doppler-shifted H alpha emission from a collimated jet
emerging from T Pyx. We demonstrate that these lines are instead due to [NII]
6548, 6584 from a complex velocity field in the surrounding nebula. The
comments of past workers concerning the great strength of HeII 4686 in T Pyx
itself are also reiterated.Comment: 8 pages including 2 figures; Accepted for publication in The
Astrophysical Journal Letter
The Amazing Old Nova Q Cygni: A Far Ultraviolet Synthetic Spectral Analysis
Q Cygni (Nova Cygni 1876) is the third oldest old novae (after WY Sge and
V841 Oph) with a long orbital period of 10.08 hours and spectroscopic
peculiarities in the optical including the presence of variable wind outflow
revealed by optical P Cygni profiles in the HeI lines and H alpha beta (Kafka
et al. 2003). We have carried out a synthetic spectral analysis of a far
ultraviolet IUE archival spectrum of Q Cygni using our optically thick, steady
state, accretion disk models and model white dwarf photospheres. We find that
the accretion light of a luminous accretion disk dominates the FUV flux of the
hot component with a rate of accretion 2-3 1.E-9 Msun/yr. We find that Q Cygni
lies at a distance of 741 \pm 110 pc . The implications of our results for
theoretical predictions for old novae are presented.Comment: PASP, August 201
Chandra observations of the recurrent nova CI Aql after its April 2000 outburst
We report the results of two Chandra observations of the recurrent nova CI
Aql at 14 and 16 months after its outburst in April 2000, respectively. The
X-ray emission is faint in both cases, without any noticeable change in
spectrum or intensity. Although the emission is very soft, it is not luminous
enough to be due to late-time H-burning. This implies that the luminous
supersoft phase ended even before the time predicted by the most recent
calculations. The details of the X-ray spectrum, together with the fact that
the observed X-ray intensity is brighter than pre-outburst (1992/1993), suggest
that the observed X-ray emission is either due to ionization of the
circumstellar material or due to the shocks within the wind and/or with the
surrounding medium.Comment: 10 pages ApJ style with 5 figures; accepted for publication in Ap
A Catalog and Atlas of Cataclysmic Variables - The Living Edition
The Catalog and Atlas of Cataclysmic Variables (Edition 1 - 1993) and Edition
2 - 1997) has been a valuable source of information for the cataclysmic
variable (CV) community. However, the goal of having a central location for all
objects is slowly being lost as each new edition is generated. There can also
be a long time delay between new information becoming available on an object
and its publication in the catalog. To eliminate these concerns, as well as to
make the catalog more accessible, we have created a web site which will contain
a ``living'' edition of the catalog. We have also added orbital period
information, as well as finding charts for novae, to the catalog.Comment: LaTeX, 8 pages, 4 ps-figures, accepted by PAS
A Theoretical Light-Curve Model for the Recurrent Nova V394 Coronae Austrinae
A theoretical light curve for the 1987 outburst of V394 Coronae Austrinae
(V394 CrA) is modeled to obtain various physical parameters of this recurrent
nova. We then apply the same set of parametersto a quiescent phase and confirm
that these parameters give a unified picture of the binary. The early visual
light curve (1-10 days after the optical maximum) is well reproduced by a
thermonuclear runaway model on a very massive WD close to the Chandrasekhar
limit (1.37 +- 0.01 M_sun). The ensuing plateau phase (10-30 days) is also
reproduced by the combination of a slightly irradiated MS and a fully
irradiated flaring-up disk with a radius ~1.4 times the Roche lobe size. The
best fit parameters are the WD mass 1.37 M_sun, the companion mass 1.5 M_sun
(0.8-2.0 M_sun is acceptable), the inclination angle of the orbit i~65-68
degree, and the flaring-up rim ~0.30 times the disk radius. The envelope mass
at the optical peak is estimated to be ~6 x 10^{-6} M_sun, which indicates an
average mass accretion rate of 1.5 x 10^{-7} M_sun yr^{-1} during the quiescent
phase between the 1949 and 1987 outbursts. In the quiescent phase, the observed
light curve can be reproduced with a disk size of 0.7 times the Roche lobe size
and a rather slim thickness of 0.05 times the accretion disk size at the rim.
About 0.5 mag sinusoidal variation of the light curve requires the mass
accretion rate higher than ~1.0 x 10^{-7} M_sun yr^{-1}, which is consistent
with the above estimation from the 1987 outburst. These newly obtained
quantities are exactly the same as those predicted in a new progenitor model of
Type Ia supernovae.Comment: 9 pages including 4 figures, to appear in the Astrophysical Journal,
Part
Survey of long-term variability of stars I. Reliability of magnitudes in old star catalogues
The comparison of visual magnitudes of stars compiled in old catalogues is
expected to yield information about their long-term magnitude variations. In
seven old catalogues whose historical data have been intensively compared, 2123
sampled stars have been studied, disregarding stars that we could not identify,
double stars which could be misidentified, or stars observed under poor
conditions, and known variable stars with large amplitude discrepancies. The
independence of stellar magnitude catalogues is demonstrated by comparing seven
old studies to each other, suggesting that the magnitude estimates in each
catalogue reflect the brightness at each observational period. Furthermore, by
comparing them with a modern star catalogue, the magnitude differences show a
Gaussian distribution. Therefore, if they are sufficiently larger than the
deduced standard deviations, the magnitude variations between the catalogues
can be considered real. Thus, the stellar magnitudes compiled in old studies
can be used as scientific data within the average intrinsic uncertainty. These
seven old catalogues can be used as data for the survey of the long-term
variability of stars.Comment: 7 pages including 2 figures, accepted for publication in A&
Sakurai's Object: characterizing the near-infrared CO ejecta between 2003 and 2007
We present observations of Sakurai's Object obtained at 1â5 ÎŒm between 2003 and 2007. By fitting a radiative transfer model to an echelle spectrum of CO fundamental absorption features around 4.7 ÎŒm, we determine the excitation conditions in the line-forming region. We find 12C/13C = 3.5+2.0â1.5, consistent with CO originating in ejecta processed by the very late thermal pulse, rather than in the pre-existing planetary nebula. We demonstrate the existence of 2.2 Ă 10â6â€MCO†2.7 Ă 10â6 Mâ of CO ejecta outside the dust, forming a high-velocity wind of 500 ± 80 km sâ1. We find evidence for significant weakening of the CO band and cooling of the dust around the central star between 2003 and 2005. The gas and dust temperatures are implausibly high for stellar radiation to be the sole contributor
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