Context. The Nova HR Del, discovered in 1967, was found to be exceptionally bright in the optical and UV during the whole lifetime of the IUE satellite (ending in 1996) and appears to still be extremely luminous today. The reason for this continuing activity is not clear, but continuing weak thermonuclear burning might be involved. Aims. We therefore need to better understand the processes at play in HR Del. Methods. HR Del was thus monitored over several years, both in broad band photometry and spectroscopically in the Hα spectral region.Results. The profile of the Hα line shows two components: a narrow, central component and broader wings. The former is most easily understood as the result of an accretion disk whose geometry might lead it to partly occult certain regions of itself. That component shows something like an S wave with an orbital phase dependence, suggesting that it could be due to a spot bright in Hα. The wide component must come from another region, with a probably non-negligible contribution from the material ejected during the 1967 outburst. Non-orbital variations of the Hα equivalent width were found both on long and short time scales. Similar variations were found in the photometry, showing a component with a clear dependence on the orbital phase, however with no obvious relation with the Hα variations. Conclusions. The orbital part of the photometric variations can be explained by irradiation of the companion, while the properties of Hα are explicable by the presence of an accretion disk and a spot bright in Hα.
New high-precision CCD photometric light curves of two contact binary stars, TYC 1337-1137-1 and TYC 3836-0854-1, are displayed and analyzed by using the Wilson-Devinney (W-D) program. The light curve solutions show that both of them are low-mass ratio, deep overcontact binary systems with a mass ratio of q=0.1716±0.0010 and a high fillout factor of f=76.0±2.9% for TYC 1337-1137-1, and q=0.1900±0.0032 and f=79.4±7.9% for TYC 3836-0854-1, respectively. These results indicate that they are near the end evolutionary stage of contact binaries. The absolute parameters were calculated by using the new method of mass-radius relationship (0.238 ± 0.009 M e and 1.386 ± 0.050 M e for TYC 1337-1137-1, 0.228 ± 0.014 M e and 1.20 ± 0.07 M e for TYC 3836-0854-1, respectively). The preliminary orbital period analysis suggests that long-term period increases exist for both of them, which may be interpreted in two possible ways. A first possibility is mass transfer conservation from the less massive component to the more massive one leading to an orbital period increase. In this case, when their orbital angular momentum is less than three times the total spin angular momentum, they may evolve into a rapidly rotating single star. A second possibility is that the parabolic variation in the (O − C) diagram is only a part of a long-period cyclic change caused by a potential third body. In future, more high-precision observations of these two binaries are needed to confirm the form of orbital period changes.
DV UMa is an eclipsing dwarf nova with an orbital period of ∼ 2.06 h, which lies just at the bottom edge of the period gap. To detect its orbital period changes we present 12 new mid-eclipse times by using our CCD photometric data and archival data. Combining with the published mid-eclipse times in quiescence, spanning ∼ 30 yr, the latest version of the O − C diagram was obtained and analyzed. The best fit to those available eclipse timings shows that the orbital period of DV UMa is undergoing a cyclic oscillation with a period of 17.58(±0.52) yr and an amplitude of 71.1(±6.7) s. The periodic variation most likely arises from the light-travel-time effect via the presence of a circumbinary object because the required energy to drive the Applegate mechanism is too high in this system. The mass of the unseen companion was derived as M 3 sin i ′ = 0.025(±0.004)M ⊙ . If the third body is in the orbital plane (i.e. i ′ = i = 82.9• ) of the eclipsing pair, it would match to a brown dwarf. This hypothetical brown dwarf is orbiting its host star at a separation of ∼ 8.6 AU in an eccentric orbit (e = 0.44).
Continuing the project undertaken by Kato et al. (2009), we collected times of superhump maxima for 56 SU UMa-type dwarf novae mainly observed during the 2013–2014 season and characterized these objects. We detected negative superhumps in VW Hyi and indicated that the low number of normal outbursts in some supercycles can be interpreted as a result of disk tilt. This finding, combined with the Kepler observation of V1504 Cyg and V344 Lyr, suggests that disk tilt is responsible for modulating the outburst pattern in SU UMa-type dwarf novae. We also studied the deeply eclipsing WZ Sge-type dwarf nova MASTER OT J005740.99+443101.5 and found evidence of a sharp eclipse during the phase of early superhumps. The profile can be reproduced by a combination of the eclipse of the axisymmetric disk and the uneclipsed light source of early superhumps. This finding shows the lack of evidence for a greatly enhanced hot spot during the early stage of WZ Sge-type outburst. We detected growing (stage A) superhumps in MN Dra and give a suggestion that some of SU UMa-type dwarf novae situated near the critical condition of tidal instability may show long-lasting stage A superhumps. The large negative period derivatives reported in such systems can be understood as a result of the combination of stage A and B superhumps. Two WZ Sge-type dwarf novae, AL Com and ASASSN-13ck, showed a long-lasting (plateau-type) rebrightening. In the early phase of their rebrightenings, both objects showed a precursor-like outburst, suggesting that the long-lasting rebrightening is triggered by a precursor outburst.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.