Marcos P. Diaz

The 1991 V603 Aquilae campaign - Superhumps and P-dots

We report the results of an intensive program of photometry of the old nova V603 Aquilae during 1991. The coverage totaled 207 hr, spread over 66 nights. The mean value of the 3.5 hr photometric period was 0.14640 (±6) days, but the instantaneous value increased over the course of the 5 month observing season. This is a drift in the period rather than a truly secular effect, since the observed rate of increase is much too high to be consistent with period measurements in previous years. New spectroscopic observations confirm the radial velocity curve and O d .138 period found by Kraft in 1962. The low amplitude in v rad and the relatively narrow emission lines require a very low binary inclination; i∼20° is likely. The inequality of photometric and spectroscopic periods is thus established beyond doubt and is the outstanding puzzle

The peculiar nova V1309 Scorpii/nova Scorpii 2008 - A candidate twin of V838 Monocerotis

Aims. Nova Scorpii 2008 was the target of our Director Discretionary Time proposal at VLT+UVES in order to study the evolution, origin and abundances of the heavy-element absorption system recently discovered in 80% of classical novae in outburst. Methods. The early decline of nova Scorpii 2008 was monitored with high resolution echelle spectroscopy at 5 different epochs. The analysis of the absorption and the emission lines show many unusual characteristics. Results. Nova Scorpii 2008 is confirmed to differ from a common classical nova as well as a symbiotic recurrent nova, and it shows characteristics which are common to the so called, yet debated, red-novae. The origin of this new nova remains uncertain.

Double-periodic blue variables in the Magellanic Clouds

We report the discovery, based on an inspection of the OGLE-II database, of a group of blue variables in the Magellanic Clouds showing simultaneously two kinds of photometric variability: a short-term cyclic variability with typical amplitudeI 0:05 mag and period P1 between 4 and 16 days and a sinusoidal, long-term cyclic oscillation with much larger amplitudeI 0:2 mag with period P2 in the range of 150-1000 days. We find that both periods seems to be coupled through the relationship P2= 35:2 0:8 P1. In general, the short term variability is reminiscent of those shown by Algol-type binaries. We propose that the long-term oscillation could arise in the precession of a elliptical disc fed by a Roche-lobe filling companion in a low mass ratio Algol system.

A search for brown dwarf like secondaries in cataclysmic variables

We present VTL/ISAAC infrared spectroscopy of a sample of short-orbital-period cataclysmic variables that are candidates for harbouring substellar companions. We have detected the K I and Na I absorption lines of the companion star in VY Aqr. The overall spectral distribution in this system is best fitted with an M9.5 type dwarf spectrum, implying a distance of 100 ′ 10 pc. VY Aqr seems to fall far from the theoretical distribution of secondary star temperatures around the orbital period minimum. Fitting of the IR spectral energy distribution (SED) was performed by comparing the observed spectrum with late-type templates. The application of such a spectral fitting procedure suggests that the continuum shape in the 1.1-2.5 μm spectral region in short-orbital-period cataclysmic variables may be a useful indicator of the companions spectral type. SED fitting for RZ Leo and CU Vel suggests M5-type dwarf companions, and distances of 340 ′ 110 and 150 ′ 50 pc, respectively. These systems may be placed in the upper evolution branch for short-period cataclysmic variables.

THE SPECTRAL EVOLUTION AND EJECTA OF RECURRENT NOVA U Sco IN THE 2010 OUTBURST

Synoptic spectroscopic observations of the U Sco 2010 outburst from maximum light to quiescence as well as a contemporaneous X-ray observation are presented and analyzed. The X-ray spectrum 52 days after outburst indicates a hot source (kTbb ~ 70 eV). . Narrow line components from the irradiated companion atmosphere were observed in hydrogen and helium optical recombination lines. The formation of a nebular spectrum is seen for the first time in this class of recurrent novae, allowing a detailed study of the ejecta using photoionization models. Unusual [OIII] auroral-to-nebular line ratios were found and possible scenarios of their origin are discussed. The modeling of the emission line spectrum suggests a highly heterogeneous ejecta with mass around or above 3 x 10-6 Msun

A Statistical Study of Accretion Disk Model Spectra for Cataclysmic Variables

We have performed a statistical test of the currently used accretion disk models for cataclysmic variables (CVs) using a set of 33 CVs with steady disks (10 old novae and 23 nova-like systems). The mass transfer rate () for each system was also calculated. Ultraviolet (UV) data were fitted by model spectra using a multiparametric optimization method, aiming to constrain the values. It was verified that these accretion disk models fail to fit both color and flux simultaneously, as previously noted when composite stellar atmosphere models were fitted to the UV spectra of CVs by Wade. By applying such models to a sample of novae and nova-like CVs, we confirm that the limb-darkening effect must be taken into account when estimating mass transfer rates, especially for high-inclination systems. Important fitting degeneracies of the basic disk parameters are analyzed. Our simulations suggest that to reproduce the observations a revision of the temperature profile, at least in the innermost parts of the disk, seems to be required, and possibly the vertical distribution of the viscosity should be revised. In addition, an optically thin layer or an extended disk component should be considered. This component may be physically represented by a disk wind and/or a chromosphere. A physical description of the emission-line profiles may help to break the degeneracies that appear when only the continuum is analyzed. The average value of found for nova-like systems is ~9.3 ? 10-9 M? yr-1, while ~1.3 ? 10-8 M? yr-1 is found for old classical novae. No clear evidence is found for either the presence or absence of a correlation between and the orbital period. Such correlation analysis was performed for high accretion rate systems (15 nova-like systems and 10 old novae), but we were not able to find a well-defined correlation as found by Patterson. By measuring the equivalent width of the emission lines (C IV ?1550 and He II ?1640) we found a lack of systems with low and strong UV emission lines. A correlation between the equivalent width of such lines and the orbital inclination (i) was also confirmed.

The Eclipsing Precataclysmic Binary RR Caeli

Photometric and some spectroscopic observations of the white dwarf–red dwarf binary RR Cae (V = 14.36 mag) are presented. The light curve confirms an earlier report of deep eclipses. An orbital period of 0.303695 days is derived. Small out-of-eclipse variations—at least partly explicable as the result of reflection and tidal distortion—and a weak secondary eclipse are also detected. The phase of the latter suggests an eccentric orbit that, however, has yet to be confirmed. The Hα absorption line of the white dwarf contains a narrow emission core. Otherwise, the red spectrum is dominated by absorption structures of a very late (~M6) main-sequence star. Eclipse simulations permit a unique solution for the orbital inclination and the component radii in units of their separation. This, in turn, leads to a self-consistent solution for the absolute values of numerous system parameters, the most important of which are the masses estimated by using theoretical and empirical mass-radius relationships (M1 = 0.365 M⊙; M2 = 0.089 M⊙). A photometric parallax of 12 pc is derived. The future evolution of this precataclysmic binary is briefly discussed.

Discovery of a cataclysmic variable with a sub-stellar companion

We nd that the ROSAT source 1RXS J105010.3-140431 is a cataclysmic variable with orbital period of 88.6 min and a spectrum closely resembling WZ Sge. In particular, emission lines are flanked by Stark-broadened absorption wings probably originating in the photosphere of a compact object. The Balmer absorption lines can be modeled by the spectrum of a DA white dwarf with 13 000 <T e < 24 000 K. The strong absorption lines allowed us to obtain direct radial velocities of the white dwarf using the cross-correlation technique. We nd an extremely low white dwarf radial velocity half amplitude, Kwd =4 1k m s 1 . This is consistent with the upper limit obtained from the H emission line wing K< 20 km s 1 . The corresponding mass function is incompatible with a main sequence secondary, but is compatible with a post orbital period minimum cataclysmic variable with a brown dwarf-like secondary. The formal solution gives a secondary mass of 10{20 Jovian masses. Doppler maps for the emission lines and the hypothesis of black-body emission indicate a steady state (T r 3=4 ) accretion disk mainly emitting in H and an optically thicker hotspot with a strong contribution to the higher order Balmer lines and He I 5875. As in other long cycle length dwarf novae, evidence for inner disk removal is found from the analysis of the emission lines.

A cyclic bipolar wind in the interacting binary V 393 Scorpii

V 393 Scorpii is a double periodic variable characterized by a relatively stable non-orbital photometric cycle of 253 d. Mennickent et al. argue for the presence of a massive optically thick disc around the more massive B-type component and describe the evolutionary stage of the system. In this paper, we analyse the behaviour of the main spectroscopic optical lines during the long non-orbital photometric cycle. We study the radial velocity of the donor determining its orbital elements and find a small but significant orbital eccentricity (e = 0.04). The donor spectral features are modelled and removed from the spectrum at every observing epoch using the light-curve model given by Mennickent et al. We find that the line emission is larger during eclipses and mostly comes from a bipolar wind. We also find that the long cycle is explained in terms of a modulation of the wind strength; the wind has a larger line and continuum emissivity at the high state. We report the discovery of highly variable chromospheric emission in the donor, as revealed by the Doppler maps of the emission lines Mg ii 4481 and C i 6588. We discuss notable and some novel spectroscopic features like discrete absorption components, especially visible at blue depressed O i 7773 absorption wings during the second half-cycle, Balmer double emission with V/R curves showing ‘Z-type’ and ‘S-type’ excursions around secondary and main eclipses, respectively, and Hβ emission wings extending up to ± 2000 km s−1. We also discuss possible causes for these phenomena and for their modulations with the long cycle.

An analysis of the light curve of the post common envelope binary MT Serpentis

Photometric observations of MT Ser, the central star of the planetary nebula Abell 41 are presented. The periodic modulations detected by Grauer & Bond (1983) are conrmed, thus rmly establishing the binary nature of MT Ser. The signicantly enlarged time base permits us to derive more accurate ephemeris. The orbital period is either P1 =0 :113226533 days or twice that value, P2 =0 :226453066 days. We analyze the light curve (after a careful subtraction of the nebular contribution) with the Wilson-Devinney light curve synthesis routine. Since it is not a priori clear which is the true orbital period of MT Ser, two radically dierent models, one based on P1 the other on P2 are considered: (1) A low temperature component orbiting around a hot sub-dwarf. The variability is then due to a reflection eect together with ellipsoidal variations of one or both components. (2) Two hot sub- dwarfs of similar temperature and luminosity, partially eclipsing each other and exhibiting ellipsoidal variations. In both models, the primary as well as the secondary component are required to almost ll their respective Roche lobes. A contact conguration is possible. Pros and cons can be found for either of the two models. A nal decision between them has to await the observations of a radial velocity curve. The orbital period is currently decreasing at a rate of _ P=P = 1:15 10 9 d 1 . Interpreting this as due to mass loss via a stellar winds permits us to