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Register a new userIdentification of SRGt 062340.2-265715 as a bright, strongly variable, novalike cataclysmic variable
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We report the identification and follow-up of the transient SRG 062340.2-265715 detected with both instruments on board the Spektrum-Roentgen-Gamma mission. Optical spectroscopy of the G=12.5 counterpart firmly classifies the object as a novalike cataclysmic variable (CV) at a distance of 495 pc. A highly significant TESS period of 3.941 hours, tentatively identified with the orbital period of the binary, could not be found when the object was reobserved with TESS two years later. The newer high-cadence TESS data revealed quasi-periodic oscillations around 25 min, while ground-based photometry indicated periodic variability at 32 min. Located in very sparsely populated regions of color-magnitude diagrams involving X-ray and optical magnitudes and colors, the new object could be an X-ray underluminous magnetic CV, an intermediate polar, or an overluminous nonmagnetic CV. The lack of uniquely identified spin and orbital periods prevents a final classification. The site of X-ray production in the system, L(X, bol) = 4.8 x 10^{32} erg/s, remains to be understood given its high variability on long and short timescales.
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We analyzed a Kepler light curve of KIC 8751494, a recently recognized novalike cataclysmic variable in the Kepler field. We detected a stable periodicity of 0.114379(1) d, which we identified as being the binarys orbital period. The stronger photometric period around 0.12245 d, which had been detected from the ground-based observation, was found to be variable, and we identified this period as being the positive superhump period. This superhump period showed short-term (10-20 d) and strong variations in period most unexpectedly when the object entered a slightly faint state. The fractional superhump excess varied as large as ~30%. The variation of the period very well traced the variation of the brightness of the system. The time-scales of this variation of the superhump period was too slow to be interpreted as the variation caused by the change in the disk radius due to the thermal disk instability. We interpreted that the period variation was caused by the varying pressure effect on the period of positive superhumps. This finding suggests that the pressure effect, in at least novalike systems, plays a very important (up to ~30% in the precession rate) role in producing the period of the positive superhumps. We also described a possible detection of the negative superhumps with a varying period of 0.1071-0.1081 d in the Q14 run of the Kepler data. We also found that the phase of the velocity variation of the emission lines reported in the earlier study is compatible with the SW Sex-type classification. Further, we introduced a new two-dimentional period analysis using least absolute shrinkage and selection operator (Lasso) and showed superior advantage of this method.
We report on the discovery of J0644+3344, a bright deeply eclipsing cataclysmic variable (CV) binary. Spectral signatures of both binary components and an accretion disk can be seen at optical wavelengths. The optical spectrum shows broad H I, He I, and He II accretion disk emission lines with deep narrow absorption components from H I, He I, Mg II and Ca II. The absorption lines are seen throughout the orbital period, disappearing only during primary eclipse. These absorption lines are either the the result of an optically-thick inner accretion disk or from the photosphere of the primary star. Radial velocity measurements show that the H I, He I, and Mg II absorption lines phase with the the primary star, while weak absorption features in the continuum phase with the secondary star. Radial velocity solutions give a 150+/-4 km/s semi-amplitude for the primary star and 192.8+/-5.6 km/s for the secondary. The individual stellar masses are 0.63-0.69 Mdot for the primary and 0.49-0.54 Mdot for the secondary. The bright eclipsing nature of this binary has helped provide masses for both components with an accuracy rarely achieved for CVs. This binary most closely resembles a nova-like UX UMa or SW Sex type of CV. J0644+3344, however, has a longer orbital period than most UX UMa or SW Sex stars. Assuming an evolution toward shorter orbital periods, J0644+3344 is therefore likely to be a young interacting binary. The secondary star is consistent with the size and spectral type of a K8 star, but has an M0 mass.
We report the discovery of a new cataclysmic variable (CV) among unidentified objects from the ASCA Galactic Plane Survey made using the Virtual Observatory data mining. First, we identified AX J194939+2631 with IPHAS J194938.39+263149.2, the only prominent H-alpha emitter among 400 sources in a 1 arcmin field of the IPHAS survey, then secured as a single faint X-ray source found in an archival Chandra dataset. Spectroscopic follow-up with the 3.5-m Calar Alto telescope confirmed its classification as a CV, possibly of magnetic nature. Our analysis suggests that AX J194939+2631 is a medium distance system (d ~ 0.6 kpc) containing a late-K or early-M type dwarf as a secondary component and a partially disrupted accretion disc revealed by the double-peaked H-alpha line. However, additional deep observations are needed to confirm our tentative classification of this object as an intermediate polar.
We present the results of MeerKAT radio observations of eleven nearby novalike cataclysmic variables. We have detected radio emission from IM Eri, RW Sex, V3885 Sgr and V603 Aql. While RW Sex, V3885 Sgr and V603 Aql had been previously detected, this is the first reported radio detection of IM Eri. Our observations have doubled the sample of non-magnetic CVs with sensitive radio data. We observe that at our radio detection limits, a specific optical luminosity $gtrsim 2.2times 10^{18}$ erg/s/Hz (corresponding to $M_V lesssim 6.0$) is required to produce a radio detection. We also observe that the X-ray and radio luminosities of our detected novalikes are on an extension of the $L_{X} propto L_{R}^{sim 0.7}$ power law originally proposed for non-pulsating neutron star low-mass X-ray binaries. We find no other correlations between the radio emission and emission in other wavebands or any other system parameters for the existing sample of radio-detected non-magnetic CVs. We measure in-band (0.9-1.7 GHz) radio spectral indices that are consistent with reports from earlier work. Finally, we constructed broad spectral energy distributions for our sample from published multi-wavelength data, and use them to place constraints on the mass transfer rates of these systems.
We present new photometry and spectroscopy of the 94m eclipsing binary LSQ1725-64 that provide insight into the fundamental parameters and evolutionary state of this system. We confirm that LSQ1725-64 is a magnetic cataclysmic variable whose white dwarf has a surface-averaged magnetic field strength of $12.5 pm 0.5$ MG measured from Zeeman splitting. The spectral type and colour of the secondary, as well as the eclipse length, are consistent with other secondaries that have not yet evolved through the period minimum expected for cataclysmic variables. We observe two different states of mass transfer and measure the transition between the two to occur over about 45 orbital cycles. In the low state, we observe photometric variations that we hypothesize to arise predominantly from two previously heated magnetic poles of the white dwarf. Our precise eclipse measurements allow us to determine binary parameters of LSQ1725-64 and we find it contains a high mass ($0.97 pm 0.03 M_{odot}$) white dwarf if we assume a typical mass-radius relationship for a CO core white dwarf. We also measure an eclipse of the accretion stream after the white dwarf eclipse, and use it to estimate an upper limit of the mass transfer rate. This derived limit is consistent with that expected from angular momentum loss via gravitational radiation alone.
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