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Register a new userThe Superoutburst Duration versus Orbital Period Relation for AM CVn stars
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We examine the relationship between superoutburst duration $t_{rm dur}$ and orbital period $P_{rm orb}$ in AM CVn ultra-compact binary systems. We show that the previously determined steep relation derived by Levitan et al (2015) was strongly influenced by the inclusion of upper limits for systems with a relatively long orbital period in their fit. Excluding the upper limit values and including $t_{rm dur}$ values for three systems at long $P_{rm orb}$ which were not considered previously, then $d log (t_{rm dur})/ d log (P_{rm orb})$ is flat as predicted by Cannizzo & Nelemans(2015)
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We consider initial stage of the evolution of AM CVn type stars with white dwarf donors, which is accompanied by thermonuclear explosions in the layer of accreted He. It is shown that the accretion never results in detonation of He and accretors in AM CVn stars finish their evolution as massive WDs. We found, for the first time, that in the outbursts the synthesis of n-rich isotopes, initiated by the ${mathrm{^{22}{Ne}(alpha,n)^{25}Mg}}$ reaction becomes possible.
This paper presents new CCD BVRI light curves of the newly discovered RS CVn eclipsing binary V1034 Her in 2009 and 2010, which shapes are different from the previous published results. They show asymmetric outside eclipse and we try to use a spot model to explain the phenomena. Using the Wilson-Devinney program with one-spot or two-spots model, photometric solutions of the system and starspot parameters were derived. Comparing the two results, it shows that the case of two spots is better successful in reproducing the light-curve distortions. For all the spot longitudes, it suggests that the trend towards active longitude belts and each active longitude belts might be switch. Comparing the light curves of 2009 and 2010, it indicates that the light curve changes on a long time scale of one year, especially in phase 0.25. In addition, we also collected the values of the maximum amplitudes of photometric distortion of the short-period RS CVn binary. We found for the first time that there is a trend of increasing activity with decreasing the orbital period. Finally, fitting all available light minimum times including our newly obtained ones with polynomial function confirmed that the orbital period of V1034 underwent up increase.
We report the discovery of a one magnitude increase in the optical brightness of the 59.63 minute orbital period AM CVn binary SDSS J113732.32+405458.3. Public $g$, $r$, and $i$ band data from the Zwicky Transient Facility (ZTF) exhibit a decline over a 300 day period, while a few data points from commissioning show that the peak was likely seen. Such an outburst is likely due to a change in the state of the accretion disk, making this the longest period AM CVn binary to reveal an unstable accretion disk. The object is now back to its previously observed (by SDSS and PS-1) quiescent brightness that is likely set by the accreting white dwarf. Prior observations of this object also imply that the recurrence times for such outbursts are likely more than 12 years.
Phase-resolved spectroscopy of four AM CVn systems obtained with the William Herschel Telescope and the Gran Telescopio de Canarias (GTC) is presented. SDSS,J120841.96+355025.2 was found to have an orbital period of 52.96$pm$0.40,min and shows the presence of a second bright spot in the accretion disc. The average spectrum contains strong Mg,{sc i} and Si,{sc i/ii} absorption lines most likely originating in the atmosphere of the accreting white dwarf. SDSS,J012940.05+384210.4 has an orbital period of 37.555$pm$0.003 min. The average spectrum shows the Stark broadened absorption lines of the DB white dwarf accretor. The orbital period is close to the previously reported superhump period of 37.9,min. Combined, this results in a period excess $epsilon$=0.0092$pm$0.0054 and a mass ratio $q=0.031pm$0.018. SDSS,J164228.06+193410.0 displays an orbital period of 54.20$pm$1.60,min with an alias at 56.35,min. The average spectrum also shows strong Mg,{sc i} absorption lines, similar to SDSS,J120841.96+355025.2. SDSS,J152509.57+360054.50 displays an period of 44.32$pm$0.18,min. The overall shape of the average spectrum is more indicative of shorter period systems in the 20-35 minute range. The accretor is still clearly visible in the pressure broadened absorption lines most likely indicating a hot donor star and/or a high mass accretor. Flux ratios for several helium lines were extracted from the Doppler tomograms for the disc and bright spot region, and compared with single-slab LTE models with variable electron densities and path lengths to estimate the disc and bright spot temperature. A good agreement between data and the model in three out of four systems was found for the disc region. All three systems show similar disc temperatures of $sim$10,500 K. In contrast, only weak agreement between observation and models was found for the bright spot region.
We present results of our analysis of up to 15 years of photometric data from eight AM CVn systems with orbital periods between 22.5 and 26.8 min. Our data has been collected from the GOTO, ZTF, Pan-STARRS, ASAS-SN and Catalina all-sky surveys and amateur observations collated by the AAVSO. We find evidence that these interacting ultra-compact binaries show a similar diversity of long term optical properties as the hydrogen accreting dwarf novae. We found that AM CVn systems in the previously identified accretion disc instability region are not a homogenous group. Various members of the analysed sample exhibit behaviour reminiscent of Z Cam systems with long super outbursts and standstills, SU UMa systems with regular, shorter super outbursts, and nova-like systems which appear only in a high state. The addition of TESS full frame images of one of these systems, KL Dra, reveals the first evidence for normal outbursts appearing as a precursor to super outbursts in an AM CVn system. Our results will inform theoretical modelling of the outbursts of hydrogen deficient systems.
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