QU Carinae: Supernova Ia in the making?

Variable NaI absorption lines have been reported in a number of type Ia supernovae (SNeIa). The presence of this circumstellar material suggests that cataclysmic variables (CVs) with a giant donor star may be the progenitors of these SNeIa (Patat et al. 2007). We present echelle spectra of the CV QU Carinae which strengthen the connection between CVs of the V Sge class, the Accretion Wind Evolution scenario, variable wind features, variable NaI absorption, and SNIa. This thread not only provides insight into the spectral peculiarities of QU Car, but also links SNeIa as a class with their parent systems.Comment: Accepted for publication to MNRAS. 23 pages (4 figures, 3 tables

3D simulations of RS Oph: from accretion to nova blast

RS Ophiuchi is a recurrent nova with a period of about 22 years, consisting of a wind accreting binary system with a white dwarf (WD) very close to the Chandrasekhar limit and a red giant star (RG). The system is considered a prime candidate to evolve into an SNIa. We present a 3D hydrodynamic simulation of the quiescent accretion and the subsequent explosive phase. The computed circumstellar mass distribution in the quiescent phase is highly structured with a mass enhancement in the orbital plane of about a factor of 2 as compared to the poleward directions. The simulated nova remnant evolves aspherically, propagating faster toward the poles. The shock velocities derived from the simulations are in agreement with those derived from observations. For v_RG = 20 km/s and for nearly isothermal flows, we derive a mass transfer rate to the WD of 10% of the mass loss of the RG. For an RG mass loss of 10^{-7} solar masses per year, we found the orbit of the system to decay by 3% per million years. With the derived mass transfer rate, multi-cycle nova models provide a qualitatively correct recurrence time, amplitude, and fastness of the nova. Our simulations provide, along with the observations and nova models, the third ingredient for a deeper understanding of the recurrent novae of the RS Oph type. In combination with recent multi-cycle nova models, our results suggests that the WD in RS Oph will increase in mass. Several speculative outcomes then seem plausible. The WD may reach the Chandrasekhar limit and explode as an SN Ia. Alternatively, the mass loss of the RG could result in a smaller Roche volume, a common envelope phase, and a narrow WD+WD system. Angular momentum loss due to graviational wave emission could trigger the merger of the two WDs and - perhaps - an SN Ia via the double degenerate scenario.Comment: Accepted by Astronomy & Astrophysics Letters, 4 pages, 5 figures; Version with high resolution figures and movie can be found at http://www.astro.phys.ethz.ch/staff/folini/private/research/rsoph/rsoph.htm

Five-Year Optical and Near Infrared Observations of the Extremely Slow Nova V1280 Scorpii

We present optical ($B$, $V$, $R_{\rm c}$, $I_{\rm c}$ and $y$) and near infrared ($J$, $H$ and $K_{\rm s}$) photometric and spectroscopic observations of a classical nova V1280 Scorpii for five years from 2007 to 2011. Our photometric observations show a declining event in optical bands shortly after the maximum light which continues $\sim$ 250 days. The event is most probably caused by a dust formation. The event is accompanied by a short ($\sim$ 30 days) re-brightening episode ($\sim$ 2.5 mag in $V$), which suggests a re-ignition of the surface nuclear burning. After 2008, the $y$ band observations show a very long plateau at around $y$ = 10.5 for more than 1000 days until April 2011 ($\sim$ 1500 days after the maximum light). The nova had taken a very long time ($\sim$ 50 months) before entering the nebular phase (clear detection of both [\ion{O}{iii}] 4959 and 5007) and is still continuing to generate the wind caused by H-burning. The finding suggests that V1280 Sco is going through the historically slowest evolution. The interval from the maximum light (2007 February 16) to the beginning of the nebular phase is longer than any previously known slow novae: V723 Cas (18 months), RR Pic (10 months), or HR Del (8 months). It suggests that the mass of a white dwarf in the V1280 Sco system might be 0.6 M_\mathrm{\sun} or smaller. The distance, based on our measurements of the expansion velocity combined with the directly measured size of the dust shell, is estimated to be 1.1 $\pm$ 0.5 kpc.Comment: 17 pages, 14 figures, accepted for publication in A&

Equilibria of a Self-Gravitating, Rotating Disk Around a Magnetized Compact Object

We examine the effect of self-gravity in a rotating thick-disk equilibrium in the presence of a dipolar magnetic field. In the first part, we find a self-similar solution for non-self-gravitating disks. The solution that we have found shows that the pressure and density equilibrium profiles are strongly modified by a self-consistent toroidal magnetic field. We introduce 3 dimensionless variables $C_B$, $C_c$, $C_t$ that indicate the relative importance of toroidal component of magnetic field ($C_B$), centrifugal ($C_c$) and thermal ($C_t$) energy with respect to the gravitational potential energy of the central object. We study the effect of each of them on the structure of the disk. In the second part, we investigate the effect of self-gravity on the these disks; thus we introduce another dimensionless variable ($C_g$) that shows the importance of self-gravity. We find a self-similar solution for the equations of the system. Our solution shows that the structure of the disk is modified by the self-gravitation of the disk, the magnetic field of the central object, and the azimuthal velocity of the gas disk. We find that self-gravity and magnetism from the central object can change the thickness and the shape of the disk. We show that as the effect of self-gravity increases the disk becomes thinner. We also show that for different values of the star's magnetic field and of the disk's azimuthal velocity, the disk's shape and its density and pressure profiles are strongly modified.Comment: 7 page with 6 figures, Accepted for MNRA

A New Interpretation for the Second Peak of T Coronae Borealis Outbursts: A Tilting Disk around a Very Massive White Dwarf

A new interpretation for the second peak of T Coronae Borealis (T CrB) outbursts is proposed based on a thermonuclear runaway (TNR) model. The system consists of a very massive white dwarf (WD) with a tilting accretion disk and a lobe-filling red-giant. The first peak of the visual light curve of T CrB outbursts is well reproduced by the TNR model on a WD close to the Chandrasekhar mass ($M_{\rm WD} \gtrsim 1.35 ~M_\odot$), while the second peak is reproduced by the combination of the irradiated M-giant and the irradiated tilting disk. The derived fitting parameters are the WD mass $M_{\rm WD} \sim 1.35 ~M_\odot$, the M-giant companion mass $M_{\rm RG} \sim 0.7 M_\odot$ ($0.6-1.0 M_\odot$ is acceptable), the inclination angle of the orbit i \sim 70 \arcdeg, and the tilting angle of the disk i_{\rm prec} \sim 35 \arcdeg. These parameters are consistent with the recently derived binary parameters of T CrB.Comment: 6 pages including 2 figures, to be published in ApJ Letter

QU Carinae: a SNeIa progenitor?

Optical spectra obtained in 2006-07 of the nova-like cataclysmic variable QU Car are studied for radial velocities, line profiles, and line identifications. We are not able to confirm the reported 10.9 hr orbital period from 1982,partly because our sampling is not ideal for this purpose and also, we suspect, because our radial velocities are distorted by line profile changes due to an erratic wind. P-Cygni profiles are found in several of the emission lines, including those of C IV. Carbon lines are abundant in the spectra, suggesting a carbon enrichment in the doner star. The presence of [O III] 5007\AA and [N II] 6584\AA is likely due to a diffuse nebula in the vicinity of the system. The wind signatures in the spectra and the presence of nebular lines are in agreement with the accretion wind evolution scenario that has been suggested to lead to SNeIa. We argue that QU Car is a member of the V Sge subclass of CVs, and a possible SNeIa progenitor. It is shown that the recent light curve of QU Car has ~1 mag low states, similar to the light curve of V Sge, strengthening the connection of QU Car with V Sge stars, supersoft x-ray sources, and SNeIa progenitors.Comment: Accepted in the Astronomical Journal. 11 pages, 3 tables, 5 figure

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

The unusual Nova Cygni 2006 (V2362 Cyg)

Context: Optical nova lightcurves often have structures, such as rapid declines and recoveries, due to nebular or dusty phases of the ejecta. Nova Cygni 2006 (V2362 Cyg) underwent an unusual brightening after an early rapid decline. The shape of the lightcurve can be compared to that of V1493 Aql, but the whole event in that case was not as bright and only lasted a couple of weeks. V2362 Cyg had a moderately fast decline of t_2 = 9.0 before rebrightening, which lasted 250 days after maximum. Aims: We present an analysis of our own spectroscopic investigations in combination with AAVSO photometric data covering the whole rebrightening phase until the return to the final decline. Methods: We used the medium resolution spectroscopy obtained in ten nights over a period of 79 nights to investigate the change of the velocity structure of the ejecta. The publicly available AAVSO photometry was used to analyze the overall properties and the energy of the brightening. Results: Although the behavior of the main outburst (velocity, outburst magnitude, and decline timescales) resembles a ``normal'' classical nova, the shell clearly underwent a second fast mass ejecting phase, causing the unusual properties. The integrated flux during this event contributes ~ 40 % to the total radiation energy of the outburst. The evolution of the H_alpha profile during the bump event is obtained by subtracting the emission of the detached shells of the main eruption by a simple optically thin model. A distance of D ~ 7.5 {+3.0}{-2.5} kpc and an interstellar extinction E(B-V) = 0.6 +/- 0.1 was also derived.Comment: 4 pages, 4 Postscript figures, accepted for A&A Letter

34) Pieranski, P. Contemp. Phys. 1983, 24, 25. (35) Okubo, T

However, we have no information on the stoichiometric charge number on the surface of tungstic acid colloid. Thus, we estimated the amount of free protons from the solution conductance and from the reference values of equivalent conductance of protons. The evaluated D 1 values for our system were in the range of several thousand angstroms. This correction term then became quite significant for the smaller colloids. The triangles in The significance of the Debye-length has often been pointed out for the solution properties of various colloids and polyelectrolytes in salt-free systems such as the ordered solution structure in monodispersed l a t i c e~,~~-~~ conformation of ionic flexible polymer^,^*-^^ and very low mobility of spherical colloids at ex- tremely low ionic ~t r e n g t h .~* -~~ Next, we examined the viscosity effect of solvent on the relaxation times. In Conclusions A new and convenient way of determining the rotational diffusion coefficient (D,) was successfully achieved by the SP-SF and C S F techniques for the ellipsoidal colloids of tungstic acid. The significant contribution of Debye-screening-length to the D, has been described, particularly in salt-free systems. (32) Ito, K.; Ise, N:; Okubo; T.'J

Effects of rotation on the helium burning shell source in accreting white dwarfs

We investigate the effects of rotation on the behavior of the helium burning shell source in accreting carbon-oxygen white dwarfs, in the context of the single degenerate Chandrasekhar mass progenitor scenario for Type Ia supernovae (SNe Ia). We model the evolution of helium accreting white dwarfs of initially 1 Msun, assuming four different constant accretion rates (2, 3, 5 and 10 times10^{-7} Msun/yr). In a one-dimensional approximation, we compute the mass accretion and subsequent nuclear fusion of helium into carbon and oxygen, as well as angular momentum accretion, angular momentum transport inside the white dwarf, and rotationally induced chemical mixing. Our models show two major effects of rotation: a) The helium burning nuclear shell source in the rotating models is much more stable than in corresponding non-rotating models -- which increases the likelihood of accreting white dwarfs to reach the stage of central carbon ignition. This effect is mainly due to rotationally induced mixing at the CO/He interface which widens the shell source, and due to the centrifugal force lowering the density and degeneracy at the shell source location. b) The C/O-ratio in the layers which experience helium shell burning -- which may affect the energy of a SN Ia explosion -- is strongly decreased by the rotationally induced mixing of alpha-particles into the carbon-rich layers. We discuss implications of our results for the evolution of SNe Ia progenitors.Comment: 12 pages, 9 figures, to appear in A&