345 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
CK Vul as a Candidate Eruptive Stellar Merging Event
CK Vul (Nova Vul 1670) is one of the most mysterious objects among erupting
stellar objects. Past studies have suggested that CK Vul is a final
helium-flash object resembling V605 Aql and V4334 Sgr (Sakurai's object). The
peculiar outburst light curve of CK Vul, however, had no similar counterpart
among the known eruptive objects. Furthermore, the presence of hydrogen in the
proposed remnant seems to contradict with the final helium-flash scenario. We
propose that the peculiarities of CK Vul can be naturally understood if we
consider a merging of main-sequence stars, following a new interpretation by
Soker and Tylenda (astro-ph/0210463), which was proposed to explain the
peculiar eruptive object V838 Mon. In this case, the 1670 outburst of CK Vul
may be best understood as a V838 Mon-like event which occurred in our vicinity.Comment: 3 pages, 1 figure, submitted to Astron. Astrophy
Recovery of the old nova V840 Ophiuchi: A carbon rich system
We present optical spectroscopy and multi colour photometry of the old nova
V840 Oph. We rediscovered the nova based on its position in the colour--colour
diagrams. It stands out as a very blue object with an additional red component.
We present the first optical spectroscopy of this candidate and confirm its
nova character. Furthermore, V840\,Oph has been found as one of very few
cataclysmic variables showing C IV emission at lambda = 580/1 nm. From the
analysis of the carbon lines it seems probable that V840 Oph contains actually
a carbon-rich secondary star. So far, only the nova-like QU Car has been known
to have such a companion. We furthermore find spectroscopic evidence that V840
Oph has a hot, dense accretion disc or stream and is probably a magnetic
system.Comment: 7 pages, 6 figures, accepted by A&
The born again (VLTP) scenario revisited: The mass of the remnants and implications for V4334 Sgr
We present 1-D numerical simulations of the very late thermal pulse
(VLTP) scenario for a wide range of remnant masses. We show that by taking
into account the different possible remnant masses, the observed evolution of
V4334 Sgr (a.k.a. Sakurai's Object) can be reproduced within the standard
1D-MLT stellar evolutionary models without the inclusion of any
reduced mixing efficiency. Our simulations hint at a consistent picture with
present observations of V4334 Sgr. From energetics, and within the standard MLT
approach, we show that low mass remnants \hbox{(\msun)} are
expected to behave markedly different than higher mass remnants
\hbox{(\msun)} in the sense that the latter are not expected to
expand significantly as a result of the violent H-burning that takes place
during the VLTP. We also assess the discrepancy in the born again times
obtained by different authors by comparing the energy that can be liberated by
H-burning during the VLTP event.Comment: Submitted to MNRAS. In includes an appendix regarding the treatment
of reduced convective motions within the Mixing Length Theor
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
Multivariate characterization of hydrogen Balmer emission in cataclysmic variables
The ratios of hydrogen Balmer emission line intensities in cataclysmic
variables are signatures of the physical processes that produce them. To
quantify those signatures relative to classifications of cataclysmic variable
types, we applied the multivariate statistical analysis methods of principal
components analysis and discriminant function analysis to the spectroscopic
emission data set of Williams (1983). The two analysis methods reveal two
different sources of variation in the ratios of the emission lines. The source
of variation seen in the principal components analysis was shown to be
correlated with the binary orbital period. The source of variation seen in the
discriminant function analysis was shown to be correlated with the equivalent
width of the H line. Comparison of the data scatterplot with
scatterplots of theoretical models shows that Balmer line emission from T CrB
systems is consistent with the photoionization of a surrounding nebula.
Otherwise, models that we considered do not reproduce the wide range of Balmer
decrements, including "inverted" decrements, seen in the data.Comment: Accepted by PAS
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