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 $ad-hoc$ 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{($M\lesssim0.6$\msun)} are expected to behave markedly different than higher mass remnants \hbox{($M\gtrsim0.6$\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$\beta$ 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