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Cycles in the cataclysmic variable V795 Herculis
Aims: We investigate the photometric activity of the cataclysmicvariable (CV) V795 Her. We pay attention to the time evolution of thelength of its superhump cycle Psh. We investigate how wellthe superhump profile is reproduced in the individual phases?sh of Psh. We also analyze the mutualrelation of the intensity of the superhump light and the superimposedrapid intensity variations. Methods: We used the photometricV-band CCD observations obtained between 2008 and 2010. The observingrun on a given night consisted of a dense series of V-band images (exp.time of 20 s), which enabled us to investigate the superhump profile andthe superimposed rapid changes. Results: We identified severaltime segments characterized by a relatively stable Psh andmean intensity level. We find that inside such a segment, the smoothedprofile of the intensity curve folded with Psh displays thelargest scatter of the residuals of the mean profile in?sh of the peak intensity and during the decay from thispeak. A zone of quiescence occurs at ?sh ? 0.6-0.7.The profile of these residuals can be explained if the strength andluminosity of the spiral arms undergo large variations on a timescalemuch shorter than the segment's duration, as predicted in a previouslydeveloped model, while the conditions for the disk precession remainmuch more stable. The formation of these arms is considerably fasterthan their fading. We find that the emission of the superimposed shortcycle (~0.01-0.02 d) in this CV depends on ?sh. Weconclude that it does not come from pulsations of the white dwarf or,generally, from the close vicinity of this accretor. We argue that it isflickering with the site in the disk region that produces the superhump.This flickering is not located in the impact of the stream on the disk.V795 Her is a borderline case in the sense that its disk is close to theswitch to the cool state. We explain the suppression of thethermal-viscous instability of the disk in V795 Her as caused by thetidal force that is also the reason for the superhumps. This tidalheating can also help to keep the accretion disks in other permanentsuperhumpers in the hot state.The data are only available at the CDS via anonymous ftp tocdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/540/A15
| ASAS Photometry of ROSAT Sources. I. Periodic Variable Stars Coincident with Bright Sources from the ROSAT All Sky Survey
Photometric data from the ASAS - South (declination less than 29°)survey have been used for identification of bright stars located nearthe sources from the ROSAT All Sky Survey Bright Source Catalog (RBSC).In total 6028 stars brighter than 12.5 mag in I- or V-bands have beenselected and analyzed for periodicity. Altogether 2302 variable starshave been found with periods ranging from 0.137 d to 193 d. Most ofthese stars have X-ray emission of coronal origin with a few cataclysmicbinaries and early type stars with colliding winds. Whenever it waspossible we collected data available in the literature to verify periodsand to classify variable objects.The catalog includes 1936 stars (1233 new) considered to be variable dueto presence of spots (rotationally variable), 127 detached eclipsingbinary stars (33 new), 124 contact binaries (11 new), 96 eclipsing starswith deformed components (19 new), 13 ellipsoidal variables (4 new), 5miscellaneous variables and one pulsating RR Lyr type star (blended withan eclipsing binary). More than 70% of new variable stars haveamplitudes smaller than 0.1 mag, but for ASAS 063656-0521.0 we havefound the largest known amplitude of brightness variations due to thepresence of spots (up to ?V=0.8 mag). The table with the compileddata and figures with light curves can be downloaded from Acta AstronomicaArchive.
| A critical analysis of three near-infrared photometric methods of estimating distances to cataclysmic variables
A critical analysis of three methods of estimating distances tocataclysmic variables (CVs) is performed. These methods, by Ak et al.,Beuermann, and Knigge, all use near-infrared (JHK or Ks)magnitudes and the Barnes-Evans relation. We compare all threemethods to distances measured by trigonometric parallax by Thorstensen,with Hubble Space Telescope, and with the HIPPARCOS spacecraft.We findthat the method of Ak et al. works best overall for all CVs, predictingdistances on the average 4% less than those measured by trigonometricparallaxes. The method of Beuermann overestimates distances by 52%. Themethod of Knigge underestimates distances by 26%, although this was onlyever meant as a lower limit, since it assumes all light comes from thesecondary star.
| On the Progenitors of Galactic Novae
Of the approximately 400 known Galactic classical novae, only 10 ofthem, the recurrent novae, have been seen to erupt more than once. Atleast eight of these recurrents are known to harbor evolved secondarystars, rather than the main-sequence secondaries typical in classicalnovae. In this paper, we propose a new nova classification system, basedsolely on the evolutionary state of the secondary and not (like thecurrent schemes) based on the properties of the outbursts. Usingarchival optical and near-infrared photometric observations of a sampleof 38 quiescent Galactic novae we show that the evolutionary state ofthe secondary star in a quiescent system can be predicted and severalobjects are identified for follow-up observations: CI Aql, V2487 Oph, DILac, and EU Sct.
| Do novae have optically thick winds during outburst with large deviations from spherical symmetry?
Context. The evidence for the presence of optically thick winds that areproduced by classical novae after optical maximum has been challenged inrecent papers. In addition, signs of orbital phase-dependent photometricvariations, sometimes seen quite early in the development of novaoutbursts, are hard to interpret in the framework of optically thickenvelopes and especially winds. Aims: A general discussion of theassumption of optically thick winds with increasing ejection velocitiesduring the early stages of novae after their explosion is needed, alsoto clarify ideas about novae and in particular to contribute to theunderstanding of the behaviour of novae V1500 Cyg and V1493 Aql, whichshow phase-dependent variations during the very early decline after theoutburst. Methods: We considered possible ways of overcoming theapparent contradiction of phase-ependent variations through theproduction of deviations from spherical symmetry of the winds and madeorder-of-magnitude estimates for different theoretical scenarios thatmight produce these deviations. Results: We found that largedeviations from the spherical symmetry of the optically thick winds inearly phases after the explosion can easily explain the problem ofvariations. In particular, the presence of a magnetic field might havehad a non-negligible effect on the wind of V1500 Cyg, while at thepresent there is not enough information available concerning V1493 Aql. Conclusions: Optically thick winds/envelopes are almost certainlypresent in the early stages after the optical maximum of a nova, whileit is difficult to make pure Hubble-flow models fit the observations ofthose stages. New more detailed observational and theoretical work, inparticular including the effects of magnetic fields on the winds, isneeded.
| U Scorpii 2010 outburst: observational evidence of an underlying ONeMg white dwarf
This paper presents U Sco nebular spectra collected in the periodMarch-May 2010 after the binary outburst on Jan. 28, 2010. The spectradisplay strong [Nev] and [Neiii] lines that can be used to compute therelative abundance of [Ne/O]. The value obtained ([Ne/O] = 1.69) ishigher than the typical [Ne/O] abundance found in classical novae fromCO progenitors and suggests that U Sco has a ONeMg white-dwarfprogenitor. It follows that U Sco will not explode as a SN Ia but rathercollapse to become a neutron star or a millisecond pulsar.Based on observations carried out at the ESO's VLT+X-Shooter underprogram 284.D-5041.
| An extensive optical study of V2491 Cyg (Nova Cyg 2008 N.2), from maximum brightness to return to quiescence
The photometric and spectroscopic evolution of the He/N and very fastNova Cyg 2008 N.2 (V2491 Cyg) is studied in detail. A primary maximumwas reached at V = 7.45 ± 0.05 on April 11.37 (±0.1) 2008UT, followed by a smooth decline characterized by t2V=4.8 days, and thena second maximum was attained at V = 9.49 ± 0.03, 14.5 days afterthe primary one. This is the only third nova to have displayed asecondary maximum, after V2362 Cyg and V1493 Aql. The development andenergetics of the secondary maximum is studied in detail. The smoothdecline that followed was accurately monitored until day +144 when thenova was 8.6 mag fainter than maximum brightness, well into its nebularphase, with its line and continuum emissivity declining ast-3. The reddening affecting the nova was EB-V =0.23 ± 0.01, and the distance of 14 kpc places the nova at aheight above the galactic plane of 1.1 kpc, larger than typical for He/Nnovae. The expansion velocity of the bulk of ejecta was 2000 km/s, withcomplex emission profiles and weak P-Cyg absorptions during theoptically thick phase, and saddle-like profiles during the nebularphase. Photo-ionization analysis of the emission line spectrum indicatesthat the mass ejected by the outburst was 5.3 × 10-6M&sun; and the mass fractions to be X = 0.573, Y = 0.287, Z =0.140, with those of individual elements being N = 0.074, O = 0.049, Ne= 0.015. The metallicity of the accreted material was [Fe/H] = -0.25, inline with ambient value at the nova galacto-centric distance. Additionalspectroscopic and photometric observations at days +477 and +831 showthe nova returned to the brightness level of the progenitor and to haveresumed the accretion onto the white dwarf.
| On the Rebrightenings of Classical Novae during the Early Phase
We report on the spectral evolution of 6 classical novae (V1186 Sco,V2540 Oph, V4745 Sgr, V5113 Sgr, V458 Vul, and V378 Ser), based onlow-resolution spectra obtained at the Fujii-Bisei Observatory and theBisei Astronomical Observatory, Japan. In the light curves, these 6novae show several rebrightenings during the early phase lasting˜10 d after the first maximum in fast novae, and ˜100 d inslow novae. The early spectra of all of these novae had emission lineswith a P-Cygni profile at the maximum brightness. The absorptioncomponent of the P-Cygni profiles then disappeared after the maximum,and reappeared when the novae brightened to the next maximum. We suggestthat the re-appearance of the absorption component at the rebrighteningcan be attributable to a re-expansion of the photosphere after it onceshifts sufficiently inside. From the light curves, we found that thetime intervals of the rebrightenings of these 6 novae show a similarsystematic trend, which is applicable to all types of novae; fast andslow, and Fe II type and hybrid type. Moreover, we note the differencebetween the spectra at the rebrightenings during the early phase and atthe rebrightening in V2362 Cyg, and at the oscillation during thetransition phase in V1494 Aql, which means a difference in the physicalmechanism of the rebrightening during the early phase and the lateroscillations.
| Orbital and spin phase-resolved spectroscopy of the intermediate polar EX Hya using XMM-Newton data
We present the orbital phase-resolved spectra of an intermediate polar,EX Hya, together with the spin phase-resolved spectra during twodifferent epochs using the X-ray Multi-Mirror Mission (XMM-Newton),European Photon Imaging Camera (pn instrument). We find that the sourceat the two epochs has the same X-ray luminosity of ˜6.5 ×1031 erg s-1. We detect spectral variationsbetween the 2000 and 2003 observations of the source. We fitted thespectrum using a neutral hydrogen absorption model with or withoutcovering fraction together with Gaussians for emission lines, twocollisional equilibrium plasma emission models (MEKAL) and acooling-flow plasma emission model (VMCFLOW). We find that two of thethree emission components (kT= 0.6-0.8 and 1.3-1.7 keV) fitted by theMEKAL models are almost constant over the spin and orbital phases andalso over the two different epochs with the normalization varyingdirectly proportional to the flux when the data are folded according tothe orbital and spin phase indicating that the slight variation may bedue to occultation. The emission modelled by the VMCFLOW changes overthe spin and orbital phases and the 2000 and 2003 observations revealtwo different ranges of temperatures (3-33 and 8-61 keV, respectively)that model the shock zone in the accretion column(s). The ratios of thespin maximum to minimum and the orbital maximum to minimum spectra alongwith the increase in the plasma temperatures indicate that the spectrumgets harder in the minimum phases of both orbital and spin periods. Inthe 2003 observation, a 6.4 keV fluorescent Fe emission line is presentat the orbital minima in a range of phases from 0.9 to 1.3 and it isabsent otherwise. This indicates that there is reflection from the discmost likely from a large bulge at the accretion impact zone.
| Infrared Spectroscopic Observations of the Secondary Stars of Short-period Sub-gap Cataclysmic Variables
We present K-band spectroscopy of short-period, "sub-gap" cataclysmicvariable (CV) systems obtained using ISAAC on the Very Large Telescope.We show the infrared (IR) spectra for nine systems below the 2-3 hrperiod gap: V2051 Oph, V436 Cen, EX Hya, VW Hyi, Z Cha, WX Hyi, V893Sco, RZ Leo, and TY PsA. We are able to clearly detect the secondarystar in all but WX Hyi, V893 Sco, and TY PsA. We present the firstdirect detection of the secondary stars of V2051 Oph, V436 Cen, anddetermine new spectral classifications for EX Hya, VW Hyi, Z Cha, and RZLeo. We find that the CO band strengths of all but Z Cha appear normalfor their spectral types, in contrast to their longer period cousinsabove the period gap. This brings the total number of CVs and pre-CVswith moderate resolution (R >~ 1500) IR spectroscopy to 61 systems:19 pre-CVs, 31 non-magnetic systems, and 11 magnetic or partiallymagnetic systems. We discuss the trends seen in the IR abundancepatterns thus far and highlight a potential link between anomalousabundances seen in the IR with the C IV/N V anomaly seen in theultraviolet. We present a compilation of all systems with sufficientresolution IR observations to assess the CO band strengths and, byproxy, obtain an estimate on the C abundance on the secondary star.
| The Spectral Evolution and Ejecta of Recurrent Nova U Sco in the 2010 Outburst
Synoptic spectroscopic observations of the U Sco 2010 outburst frommaximum light to quiescence as well as a contemporaneous X-rayobservation are presented and analyzed. The X-ray spectrum 52 days afteroutburst indicates a hot source (kT bb ~ 70 eV). Narrow-linecomponents from the irradiated companion atmosphere were observed inhydrogen and helium optical recombination lines. The formation of anebular spectrum is seen for the first time in this class of recurrentnovae, allowing a detailed study of the ejecta using photoionizationmodels. Unusual [O III] auroral-to-nebular line ratios were found andpossible scenarios of their origin are discussed. The modeling of theemission line spectrum suggests highly heterogeneous ejecta with massesaround or above 3 × 10-6 M sun.
| The peculiar dust shell of Nova DZ Cru (2003)
We present Spitzer Space Telescope observations of the `peculiarvariable' DZ Cru, identified by Rushton et al. as a classical nova. Adust shell, on which are superimposed a number of features, is prominentin the 5-35?m range some 4 yr after eruption. We suggest that thedust in DZ Cru is primarily hydrogenated amorphous carbon in whichaliphatic bands currently predominate and which may become eitherpredominantly aromatic as the dust is photoprocessed by ultravioletradiation from the stellar remnant or more likely completely destroyed.
| Catalog of 93 Nova Light Curves: Classification and Properties
We present a catalog of 93 very-well-observed nova light curves. Thelight curves were constructed from 229,796 individual measuredmagnitudes, with the median coverage extending to 8.0 mag below peak and26% of the light curves following the eruption all the way toquiescence. Our time-binned light curves are presented in figures and ascomplete tabulations. We also calculate and tabulate many propertiesabout the light curves, including peak magnitudes and dates, times todecline by 2, 3, 6, and 9 mag from maximum, the time until thebrightness returns to quiescence, the quiescent magnitude, power-lawindices of the decline rates throughout the eruption, the break times inthis decline, plus many more properties specific to each nova class. Wepresent a classification system for nova light curves based on the shapeand the time to decline by 3 mag from the peak (t 3). Thedesignations are "S" for smooth light curves (38% of the novae), "P" forplateaus (21%), "D" for dust dips (18%), "C" for cusp-shaped secondarymaxima (1%), "O" for quasi-sinusoidal oscillations superposed on anotherwise smooth decline (4%), "F" for flat-topped light curves (2%),and "J" for jitters or flares superposed on the decline (16%). Ourclassification consists of this single letter followed by the t3 value in parentheses; so, for example, V1500 Cyg is S(4),GK Per is O(13), DQ Her is D(100), and U Sco is P(3).
| Unresolved X-ray emission in M31 and constraints on progenitors of classical novae
We investigate unresolved X-ray emission from M31 based on an extensiveset of archival XMM-Newton and Chandra data. We show that extendedemission, found previously in the bulge and thought to be associatedwith a large number of faint compact sources, extends to the disc of thegalaxy with similar X-ray to K-band luminosity ratio. We also detectexcess X-ray emission associated with the 10-kpc star-forming ring. TheLX/SFR (star formation rate) ratio in the 0.5-2 keV bandranges from zero to ~1.8 × 1038 (ergs-1)/(Msolaryr-1), excluding theregions near the minor axis of the galaxy where it is ~1.5-2 timeshigher. The latter is likely associated with warm ionized gas of thegalactic wind rather than with the star-forming ring itself. Based onthis data, we constrain the nature of classical nova (CN) progenitors.We use the fact that hydrogen-rich material, required to trigger theexplosion, accumulates on the white dwarf surface via accretion.Depending on the type of the system, the energy of accretion may beradiated at X-ray energies, thus contributing to the unresolved X-rayemission. Based on the CN rate in the bulge of M31 and its X-ray surfacebrightness, we show that no more than ~10 per cent of CNe can beproduced in magnetic cataclysmic variables, the upper limit being ~3 percent for parameters typical of CN progenitors. In dwarf novae,>~90-95 per cent of the material must be accreted during outbursts,when the emission spectrum is soft, and only a small fraction inquiescent periods, characterized by rather hard spectra.
| K-band Spectroscopy of (Pre-)Cataclysmic Variables: Are Some Donor Stars Really Carbon Poor?
We present a new sample of K-band spectral observations for cataclysmicvariables (CVs): non-magnetic and magnetic as well as present-day andpre-CVs. The purpose of this diverse sample is to address the recentclaim that the secondary stars in dwarf novae are carbon deficient,having become so through a far more evolved evolution than the currentparadigm predicts. Our new observations, along with previous literatureresults, span a wide range of orbital period and CV type. In general,dwarf novae in which the secondary star is seen show weak to no COabsorption while polar and pre-CV donor stars appear to have normal COabsorption for their spectral type. However, this is not universal. Thepresence of normal looking CO absorption in the dwarf nova SS Aur andthe hibernating CV QS Vir and a complete lack of CO absorption in thelong-period polar V1309 Ori cloud the issue. A summary of the literaturepointing to non-solar abundances including enhanced N V/C IV ratios ispresented. It appears that some CVs have non-solar abundance materialaccreting onto the white dwarf suggesting an evolved secondary starwhile for others CO emission in the accretion disk may play a role.However, the exact mechanism or combination of factors causing the COabsorption anomaly in CVs is not yet clear.
| XID II: Statistical Cross-Association of ROSAT Bright Source Catalog X-ray Sources with 2MASS Point Source Catalog Near-Infrared Sources
The 18,806 ROSAT All Sky Survey Bright Source Catalog (RASS/BSC) X-raysources are quantitatively cross-associated with near-infrared (NIR)sources from the Two Micron All Sky Survey Point Source Catalog(2MASS/PSC). An association catalog is presented, listing the mostlikely counterpart for each RASS/BSC source, the probability Pid that the NIR source and X-ray source are uniquelyassociated, and the probability P no-id that none of the2MASS/PSC sources are associated with the X-ray source. The catalogincludes 3853 high quality (P id>0.98) X-ray-NIR matches,2280 medium quality (0.98 >= P id>0.9) matches, and4153 low quality (0.9 >= P id>0.5) matches. Of the highquality matches, 1418 are associations that are not listed in the SIMBADdatabase, and for which no high quality match with a USNO-A2 opticalsource was presented for the RASS/BSC source in previous work. Thepresent work offers a significant number of new associations withRASS/BSC objects that will require optical/NIR spectroscopy forclassification. For example, of the 6133 P id>0.92MASS/PSC counterparts presented in the association catalog, 2411 haveno classification listed in the SIMBAD database. These 2MASS/PSC sourceswill likely include scientifically useful examples of known sourceclasses of X-ray emitters (white dwarfs, coronally active stars, activegalactic nuclei), but may also contain previously unknown sourceclasses. It is determined that all coronally active stars in theRASS/BSC should have a counterpart in the 2MASS/PSC, and that the uniqueassociation of these RASS/BSC sources with their NIR counterparts thusis confusion limited.
| 57-second oscillations in Nova Centauri 1986 (V842 Cen)
High-speed photometry in 2008 shows that the light curve of V842 Cenpossesses a coherent modulation at 56.825 s, with sidebands at 56.598and 57.054 s. These have appeared since this nova remnant was observedin 2000 and 2002. We deduce that the dominant signal is the rotationperiod of the white dwarf primary and the sidebands are caused byreprocessing from a surface moving with an orbital period of 3.94 h.Thus, V842 Cen is an intermediate polar (IP) of the DQ Herculissubclass, is the fastest rotating white dwarf among the IPs and is thethird fastest known in a cataclysmic variable. As in other IPs, we seeno dwarf nova oscillations, but there are often quasi-periodicoscillations in the range 350-1500 s. There is a strong brightnessmodulation with a period of 3.78 h, which we attribute to negativesuperhumps, and there is an even stronger signal at 2.886 h which is ofunknown origin but is probably a further example of that seen in GW Liband some other systems. We used the Swift satellite to observe V842 Cenin the ultraviolet and in X-rays, although no periodic modulation wasdetected in the short observations. The X-ray luminosity of this objectappears to be much lower than that of other IPs in which the accretionregion is directly visible.
| On the Accretion Rates of SW Sextantis Nova-like Variables
We present accretion rates for selected samples of nova-like variableshaving IUE archival spectra and distances uniformly determined using aninfrared method by Knigge. A comparison with accretion rates derivedindependently with a multiparametric optimization modeling approach byPuebla et al. is carried out. The accretion rates of SW Sextantisnova-like systems are compared with the accretion rates of non-SWSextantis systems in the Puebla et al. sample and in our sample, whichwas selected in the orbital period range of three to four and a halfhours, with all systems having distances using the method of Knigge.Based upon the two independent modeling approaches, we find nosignificant difference between the accretion rates of SW Sextantissystems and non-SW Sextantis nova-like systems insofar as opticallythick disk models are appropriate. We find little evidence to suggestthat the SW Sex stars have higher accretion rates than other nova-likecataclysmic variables (CVs) above the period gap within the same rangeof orbital periods.
| New Stars and telescopes: Nova research in the last four centuries
This article gives a brief overview of 400 years of research in thefield of novae and related stars. Important objects, first applicationsof various observing techniques, and early ideas of the interpretationof phenomena are listed. Also, the historical evolution of theclassification of novae and related stars (supernovae, dwarf novae), aswell as their use as distance indicators is discussed.
| The Search for SW Sextantis Stars
13 out of 48 nova-likes in the 2.8-4 h orbital period range areeclipsing SW Sex stars - these are all the eclipsing cataclysmicvariables (CVs) in this range. Apparently, SW Sex stars are veryfrequent and probably represent an important stage in CV evolution, asthey densely gather just above the period gap and exhibit extremely highmass transfer rates. As the physical properties of SW Sex stars havenothing to do with their inclination, this suggests that all non- orweakly-magnetic CVs in the 2.8-4 h period range are physically similarto the SW Sex stars. Here, we present our project on the search fornon-eclipsing SW Sex type stars. We perform time-resolved opticalspectroscopy of all sufficiently bright old novae and nova-like CVs inthe orbital period range between 2.8 and 4 h and search forcharacteristic SW Sex behaviour. Eventually we want to quantify theimpact of the SW Sex phenomenon at the upper boundary of the orbitalperiod gap.
| New X-Ray Observations of the Old Nova CP Puppis and of the More Recent Nova V351 Puppis
We present X-ray observations of the field containing Nova Puppis 1942(CP Pup) and Nova Puppis 1991 (V351 Pup), done with ASCA in 1998, andwith XMM-Newton in 2005. The X-ray and UV luminosity of CP Pup seem tohave remained approximately constant since the last X-ray observationsof the 1980s, while the optical luminosity has decreased. The X-rayproperties of this nova are explained by a high-mass white dwarf (WD)accreting at low rate, in agreement with the nova theory given the largeamplitude and other characteristics of the 1942 outburst. Assuming adistance of 1600 pc, the X-ray luminosity of CP Pup is L x =2.2 × 1033 erg s-1 in the 0.15-10 keV rangecovered with EPIC, compatible with a magnetic system. The RGS gratingspectrum shows a few prominent emission lines, and it is fitted with acooling flow with mass accretion rate \dot{m}<1.6 ×10-10 M sun yr-1. We also detected theO VII complex at 21.6-21.8 Å that does not arise in the coolingflow. Most likely this feature originates in a wind or in the novashell. The RGS and EPIC spectra are fitted only with thermal models witha very high shock temperature, T > 60 keV, indicating a WD with M> 1.1 M sun. The X-ray flux is modulated with thespectroscopic period of 1.47 hr detected in the optical. Since CP Pup isnot an eclipsing system, this is better understood if magnetic accretionoccurs: we discuss this possibility and its implications in detail. V351Pup was detected with XMM-Newton, but not with ASCA. It is a faint,nonsupersoft X-ray source with luminosity L x sime 3 ×1031 erg s-1, a factor of 50 less than measuredwith ROSAT in 1993.
| The secrets of T Pyxidis. II. A recurrent nova that will not become a SN Ia
Aims: We compare the observed and theoretical parameters for thequiescent and outburst phases of the recurring nova T Pyx. Methods: IUE data were used to derive the disk luminosity and the massaccretion rate, and to exclude the presence of quasi-steady burning atthe WD surface. XMM-NEWTON data were used to verify this conclusion. Results: By various methods, we obtained L_disk 70L? and dot{M} 1.1 × 10-8M? yr-1. These values were about twice ashigh in the pre-1966-outburst epoch. This allowed the first directestimate of the total mass accreted before outburst, M_accr =dot{M}_pre-OB \cdot ? t, and its comparison with the criticalignition mass M_ign. We found M_accr and M_ign to be in perfectagreement (with a value close to 5 × 10-7M?) for M1 1.37 M?, whichprovides a confirmation of the thermonuclear runaway theory. Thecomparison of the observed parameters of the eruption phase, with thecorresponding values in the grid of models by Yaron and collaborators,provides satisfactory agreement for values of M1 close to1.35 M? and log dot{M} between -8.0 and -7.0, but theobserved value of the decay time t3 is higher than expected.The long duration of the optically thick phase during the recordedoutbursts of T Pyx, a spectroscopic behavior typical of classical novae,and the persistence of P Cyg profiles, constrains the ejected mass M_ignto within 10-5-10-4 M?. Therefore,T Pyx ejects far more material than it has accreted, and the mass of thewhite dwarf will not increase to the Chandrasekhar limit as generallybelieved in recurrent novae. A detailed study based on the UV dataexcludes the possibility that T Pyx belongs to the class of thesupersoft X-ray sources, as has been postulated. XMM-NEWTON observationshave revealed a weak, hard source and confirmed this interpretation.
| RRPictoris: an old nova showing superhumps and QPOs
We present time-resolved V photometry of the old nova RRPictoris(RRPic). Apart from the hump-like variability, the light curves show thestrong flickering and random variation typical for RRPic. We do not findany convincing evidence for the previously reported eclipse. Theextrapolated eclipse phase coincides with a broad minimum, but comparingthe overall shape of the light curve suggests that the eclipse shouldactually be located around phase 0.2. The orbital period which we derivefrom these data agrees well with the old one, any uncertainty is toosmall to account for the possible phase shift. Apart from the 3.48hperiod, which is usually interpreted as the orbital one, we find anadditional period at P = 3.78h, which we interpret as the superhumpperiod of the system; the corresponding precession period at 1.79d isalso present in the data. We also find indications for the presence of a13min quasi-periodic oscillation.
| RR Pic (1925): a Chandra X-ray view
We present the Chandra ACIS-S3 data of the old classical nova RR Pic(1925). The source has a count rate of 0.067 +/- 0.002 counts-1 in the 0.3-5.0 keV energy range. We detect the orbitalperiod of the underlying binary system in the X-ray wavelengths. We alsofind that the neutral hydrogen column density differs for orbitalminimum and orbital maximum spectra with values0.25+0.23-0.18 × 1022 and0.64+0.13-0.14 ×1022cm-2 at 3? confidence level. The X-rayspectrum of RR Pic can be represented by a composite model ofbremsstrahlung with a photoelectric absorption, two absorption linescentered around 1.1-1.4 keV and five Gaussian lines centered at emissionlines around 0.3-1.1 keV corresponding to various transitions of S, N,O, C, Ne and Fe. The bremsstrahlung temperature derived from the fitsranges from 0.99 to 1.60 keV and the unabsorbed X-ray flux is found tobe 2.5+0.4-1.2 ×10-13ergcm-2s-1 in the 0.3-5.0 keVrange with a luminosity of 1.1 +/- 0.2 1031ergs-1at 600 pc. We also detect excess emission in the spectrum possiblyoriginating from the reverse shock in the ejecta. A fit with a coolingflow plasma emission model shows enhanced abundances of He, C, N, O andNe in the X-ray emitting region indicating existence of diffusivemixing.
| Spatial distribution and galactic model parameters of cataclysmic variables
The spatial distribution, galactic model parameters and luminosityfunction of cataclysmic variables (CVs) in the solar neighbourhood havebeen determined from a carefully established sample of 459 CVs. Thesample contains all of the CVs with distances computed from theperiod-luminosity-colours (PLCs) relation of CVs which has been recentlyderived and calibrated with 2MASS photometric data. It has been foundthat an exponential function fits best to the observationalz-distributions of all of the CVs in the sample, non-magnetic CVs anddwarf novae, while the sech2 function is more appropriate fornova-like stars and polars. The vertical scaleheight of CVs is 158± 14 pc for the 2MASS J-band limiting apparent magnitude of 15.8.On the other hand, the vertical scaleheights are 128 ± 20 and 160± 5 pc for dwarf novae and nova-like stars, respectively. Thelocal space density of CVs is found to be ˜3 ×10-5 pc-3 which is in agreement withthe lower limit of the theoretical predictions. The luminosity functionof CVs shows an increasing trend toward higher space densities at lowluminosities, implying that the number of short-period systems should behigh. The discrepancies between the theoretical and observationalpopulation studies of CVs will almost disappear if for the z-dependenceof the space density the sech2 density function is used.
| The hydrogen-deficient knot of the `born-again' planetary nebula Abell 58 (V605 Aql)
We have analysed deep optical spectra of the `born-again' planetarynebula Abell 58 and its hydrogen-deficient knot, surrounding V605 Aql,which underwent a nova-like eruption in 1919. Our analysis shows thatthe extinction towards the central knot is much higher than previouslythought, with c(Hβ) = 2.0. The outer nebula is less reddened, withc(Hβ) = 1.04. We find that the outer nebula has a Ne/O ratio higherthan the average PN value.The electron temperature we derive for the central knot varies widelydepending on the diagnostic used. The [OIII] nebular-to-auroraltransition ratio gives a temperature of 20800K, while the ratio of the[NII] nebular and auroral lines gives Te = 15200K. The heliumline ratios λ5876/λ4471 and λ6678/λ4471imply temperatures of 350 and 550K, respectively. Weaklytemperature-sensitive OII recombination line ratios imply similarly lowelectron temperatures. Abundances derived from recombination lines arevastly higher than those found from collisionally excited lines, withthe abundance discrepancy factor (ADF) for O2+ reaching 89 -the second highest known value after that found for thehydrogen-deficient knots in Abell 30. The observed temperaturediagnostics and abundances support the idea that, like Abell 30, theknot of Abell 58 contains some very cold ionized material. Although thecentral star is carbon-rich (C/O > 1), the knot is found to beoxygen-rich, a situation not predicted by the single-star `born-again'theory of its formation.We compare the known properties of Abell 58 to those of Abell 30,Sakurai's Object and several novae and nova remnants. We argue that theabundances in the ejecta observed in A30 and A58 have more in commonwith neon novae than with Sakurai's Object, which is believed to haveundergone a final helium flash. In particular, the C/O ratio of lessthan unity and the presence of substantial quantities of neon in theejecta of both Abell 30 and Abell 58 are not predicted by very latethermal pulse models.
| Nova V5116 Sagittarii and searching for superhumps in nova remnants
Aims:We present the period analysis of unfiltered photometricobservations of V5116 Sgr (Nova Sgr 2005 #2) and search for superhumpcandidates in novae remnants. Methods: The PDM method for periodanalysis was used. The masses of the novae componets we are estimatedfrom the secondary mass - orbital period and primary mass - decline timerelations. Results: We find that 13 nights of V5116 Sgrobservations in the year 2006 are modulated with a period of 0.1238± 0.0001 d (2.9712 ± 0.0024 h). Following the shape of thephased light curves and no apparent change in the value of theperiodicity in different subsamples of the data, we interpreted theperiod as orbital in nature. The binary system then falls within theperiod gap of the orbital period distribution of cataclysmic variables.From the maximum magnitude - rate of decline relation, we estimated amaximum absolute visual magnitude of M_Vmax = -8.85 ± 0.04 magusing the measured value of decline t2 = 6.5 ± 1.0 d.The mass-period relation for cataclysmic variables yields a secondarymass estimate of about 0.26 ± 0.05 {M}_&sun;. We propose thatV5116 Sgr is a high inclination system showing an irradiation effect ofthe secondary star. No fully developed accretion disc up to the tidalradius with the value lower than 3.5 × 1010 cm isprobable. The mass ratio was estimated in a few novae and the presenceor absence of superhumps in these systems was compared with the massratio limit for superhumps of about 0.35. We find that, in the majorityof novae with expected superhumps, this variability has not been foundyet. Therefore, more observations of these systems is encouraged.
| A Statistical Study of Accretion Disk Model Spectra for Cataclysmic Variables
We have performed a statistical test of the currently used accretiondisk models for cataclysmic variables (CVs) using a set of 33 CVs withsteady disks (10 old novae and 23 nova-like systems). The mass transferrate () for each system was also calculated. Ultraviolet (UV) data werefitted by model spectra using a multiparametric optimization method,aiming to constrain the values. It was verified that these accretiondisk models fail to fit both color and flux simultaneously, aspreviously noted when composite stellar atmosphere models were fitted tothe UV spectra of CVs by Wade. By applying such models to a sample ofnovae and nova-like CVs, we confirm that the limb-darkening effect mustbe taken into account when estimating mass transfer rates, especiallyfor high-inclination systems. Important fitting degeneracies of thebasic disk parameters are analyzed. Our simulations suggest that toreproduce the observations a revision of the temperature profile, atleast in the innermost parts of the disk, seems to be required, andpossibly the vertical distribution of the viscosity should be revised.In addition, an optically thin layer or an extended disk componentshould be considered. This component may be physically represented by adisk wind and/or a chromosphere. A physical description of theemission-line profiles may help to break the degeneracies that appearwhen only the continuum is analyzed. The average value of found fornova-like systems is ~9.3 × 10-9 Modotyr-1, while ~1.3 × 10-8 Modotyr-1 is found for old classical novae. No clear evidence isfound for either the presence or absence of a correlation between andthe orbital period. Such correlation analysis was performed for highaccretion rate systems (15 nova-like systems and 10 old novae), but wewere 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 lowand strong UV emission lines. A correlation between the equivalent widthof such lines and the orbital inclination (i) was also confirmed.
| A new absolute magnitude calibration with 2MASS for cataclysmic variables
Using reliable trigonometric measurements, we find that the absolutemagnitude of cataclysmic variables depends on the orbital period andde-reddened (J ‑ H)0 and (H ‑Ks)0 colours of 2MASS (Two Micron All Sky Survey)photometric system. The calibration equation covers the ranges0.032d < Porb ⩽ 0.454d,‑0.08 < (J ‑ H)0 ⩽ 1.54, ‑0.03 <(H ‑ Ks)0 ⩽ 0.56 and 2.0
| SWSextantis stars: the dominant population of cataclysmic variables with orbital periods between 3 and 4h
We present time-series optical photometry of five new cataclysmicvariables (CVs) identified by the Hamburg Quasar Survey (HQS). The deepeclipses observed in HS 0129+2933 (= TT Tri), HS 0220+0603 and HS0455+8315 provided very accurate orbital periods of 3.35129827(65),3.58098501(34) and 3.56937674(26) h, respectively. HS 0805+3822 showsgrazing eclipses and has a likely orbital period of 3.2169(2) h.Time-resolved optical spectroscopy of the new CVs (with the exception ofHS 0805+3822) is also presented. Radial velocity studies of the Balmeremission lines provided an orbital period of 3.55 h for HS 1813+6122,which allowed us to identify the observed photometric signal at 3.39 has a negative superhump wave. The spectroscopic behaviour exhibited byall the systems clearly identifies them as new SW Sextantis (SW Sex)stars. HS 0220+0603 shows unusual NII and SiII emission lines suggestingthat the donor star may have experienced nuclear evolution via the CNOcycle.These five new additions to the class increase the number of known SWSex stars to 35. Almost 40 per cent of the total SW Sex population donot show eclipses, invalidating the requirement of eclipses as adefining characteristic of the class and the models based on a highorbital inclination geometry alone. On the other hand, as more SW Sexstars are identified, the predominance of orbital periods in the narrow3-4.5 h range is becoming more pronounced. In fact, almost half the CVswhich populate the 3-4.5 h period interval are definite members of theclass. The dominance of SW Sex stars is even stronger in the 2-3 hperiod gap, where they make up 55 per cent of all known gap CVs. Thesestatistics are confirmed by our results from the HQS CVs. Remarkably, 54per cent of the Hamburg nova-like variables have been identified as SWSex stars with orbital periods in the 3-4.5 h range. The observation ofthis pile-up of systems close to the upper boundary of the period gap isdifficult to reconcile with the standard theory of CV evolution, as theSW Sex stars are believed to have the highest mass-transfer rates amongCVs.Finally, we review the full range of common properties that the SW Sexstars exhibit. Only a comprehensive study of this rich phenomenologywill prompt to a full understanding of the phenomenon and its impact onthe evolution of CVs and the accretion processes in compact binaries ingeneral.
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