A 9-h CV with one outburst in 4 yr of Kepler data

During a visual search through the Kepler main-field light curves, we have discovered a cataclysmic variable (CV) that experienced only a single 4-d long outburst over four years, rising to three times the quiescent flux. During the four years of non-outburst data the Kepler photometry of KIC 5608384 exhibits ellipsoidal light variations ('ELVs') with a ∼12 per cent amplitude and period of 8.7 h. Follow-up ground-based spectral observations have yielded a high-quality radial velocity curve and the associated mass function. Additionally, H α emission lines were present in the spectra even though these were taken while the source was presumably in quiescence. These emission lines are at least partially eclipsed by the companion K star. We utilize the available constraints of the mass function, the ELV amplitude, Roche lobe filling condition, and inferred radius of the K star to derive the system masses and orbital inclination angle: Mwd ≃ 0.46 ± 0.02 M☉, MK ≃ 0.41 ± 0.03 M☉, and i ≿ 70◦. The value of Mwd is the lowest reported for any accreting WD in a CV. We have also run binary evolution models using MESA to infer the most likely parameters of the pre-cataclysmic binary. Using the mass-transfer rates from the model evolution tracks we conclude that although the rates are close to the critical value for accretion disc stability, we expect KIC 5608384 to exhibit dwarf nova outbursts. We also conclude that the accreting white dwarf most likely descended from a hot subdwarf and, most notably, that this binary is one of the first bona fide examples of a progenitor of AM CVn binaries to have evolved through the CV channel

Low Frequency Flickering of TT Arietis:Hard and Soft X-ray Emission Region

Using archival ASCA observations of TT Arietis, X-ray energy spectra and power spectra of the intensity time series are presented for the first time. The energy spectra are well-fitted by a two continuum plasma emission model with temperatures around 1 keV and 10 keV. A coherent feature at about 0.643 mHz appeared in the power spectra during the observation.Comment: 9 pages in PostScript including figures, accepted for publication in Astrophysics and Space Science, available at http://astroa.physics.metu.edu.tr/preprints.htm

The WEBT campaign on the blazar 3C 279 in 2006

The quasar 3C279 was the target of an extensive multiwavelength monitoring campaign from January through April 2006, including an optical-IR-radio monitoring campaign by the Whole Earth Blazar Telescope (WEBT) collaboration. In this paper we focus on the results of the WEBT campaign. The source exhibited substantial variability of optical flux and spectral shape, with a characteristic time scale of a few days. The variability patterns throughout the optical BVRI bands were very closely correlated with each other. In intriguing contrast to other (in particular, BL Lac type) blazars, we find a lag of shorter- behind longer-wavelength variability throughout the RVB ranges, with a time delay increasing with increasing frequency. Spectral hardening during flares appears delayed with respect to a rising optical flux. This, in combination with the very steep IR-optical continuum spectral index of ~ 1.5 - 2.0, may indicate a highly oblique magnetic field configuration near the base of the jet. An alternative explanation through a slow (time scale of several days) acceleration mechanism would require an unusually low magnetic field of < 0.2 G, about an order of magnitude lower than inferred from previous analyses of simultaneous SEDs of 3C279 and other FSRQs with similar properties

DE CVn: A Bright, Eclipsing Red Dwarf - White Dwarf Binary

Contains fulltext : 35976.pdf (preprint version ) (Open Access)DE CVn is a relatively unstudied eclipsing binary where one of the components is an M dwarf. Its brightness makes it an ideal system for a detailed study in the context of common-envelope evolution of a detached white dwarf - red dwarf binary with a relatively short orbital period (~8.7 hours). We present a detailed study of the basic parameters (e.g. orbital period, components' masses, spectral type) for this system from photometric and spectroscopic studies. The eclipses observed during several photometric observing runs were used to derive the ephemeris. We have used spectroscopic data to derive the radial velocity variations of the emission lines and these are used to determine the components' masses and the orbital separation. The secondary component in DE CVn is an M3 main-sequence star and the primary star, which is not visible in the spectra, is a cool white dwarf with a temperature of ~8000 K. From the photometry and spectroscopy together, we have set a limit on the binary inclination. This system is a post-common-envelope system where the progenitor of the present day white dwarf was a low-mass star (M<2 Msun). The time before DE CVn becomes a semi-detached system is longer than the Hubble time

Confirmation of 1RXS J165443.5–191620 as an intermediate polar and its orbital and spin periods

Aims: We investigate the physical nature of the X-ray emitting source 1RXS J165443.5-191620 through optical photometry and time-resolved spectroscopy. Methods: Optical photometry is obtained from a variety of telescopes all over the world spanning about 27 days. Additionally, time-resolved spectroscopy is obtained from the MDM observatory. Results: The optical photometry clearly displays modulations consistent with those observed in magnetic cataclysmic variables: a low-frequency signal interpreted as the orbital period, a high-frequency signal interpreted as the white dwarf spin period, and an orbital sideband modulation. Our findings and interpretations are further confirmed through optical, time-resolved, spectroscopy that displays H-alpha radial velocity shifts modulated on the binary orbital period. Conclusion: We confirm the true nature of 1RXS J165443.5-191620 as an intermediate polar with a spin period of 546 seconds and an orbital period of 3.7 hours. In particular, 1RXS J165443.5-191620 is part of a growing subset of intermediate polars, all displaying hard X-ray emission above 15keV, white dwarf spin periods below 30 minutes, and spin-to-orbital ratios below 0.1.Comment: 7 pages, 9 figures, 6 tables, accepted for publication in A&