Perfect fluid tori orbiting Kehagias-Sfetsos naked singularities

We construct perfect fluid tori in the field of the Kehagias-Sfetsos (K-S) naked singularity representing spherically symmetric vacuum solution of the modified Ho\v{r}ava quantum gravity that is characterized by a dimensionless parameter $\omega M^2$, combining the gravitational mass parameter $M$ of the spacetime with the Ho\v{r}ava parameter $\omega$ reflecting the role of the quantum corrections. In dependence on the value of $\omega M^2$, the K-S naked singularities demonstrate a variety of qualitatively different behavior of their circular geodesics that is fully reflected in the properties of the toroidal structures. In all of the K-S naked singularity spacetimes the tori are located above an "antigravity" sphere where matter can stay in stable equilibrium position, that is relevant for the stability of the orbiting fluid toroidal accretion structures.Comment: 44 pages, 27 figures multi panel

Survey of Period Variations of Superhumps in SU UMa-Type Dwarf Novae

We systematically surveyed period variations of superhumps in SU UMa-type dwarf novae based on newly obtained data and past publications. In many systems, the evolution of superhump period are found to be composed of three distinct stages: early evolutionary stage with a longer superhump period, middle stage with systematically varying periods, final stage with a shorter, stable superhump period. During the middle stage, many systems with superhump periods less than 0.08 d show positive period derivatives. Contrary to the earlier claim, we found no clear evidence for variation of period derivatives between superoutburst of the same object. We present an interpretation that the lengthening of the superhump period is a result of outward propagation of the eccentricity wave and is limited by the radius near the tidal truncation. We interpret that late stage superhumps are rejuvenized excitation of 3:1 resonance when the superhumps in the outer disk is effectively quenched. Many of WZ Sge-type dwarf novae showed long-enduring superhumps during the post-superoutburst stage having periods longer than those during the main superoutburst. The period derivatives in WZ Sge-type dwarf novae are found to be strongly correlated with the fractional superhump excess, or consequently, mass ratio. WZ Sge-type dwarf novae with a long-lasting rebrightening or with multiple rebrightenings tend to have smaller period derivatives and are excellent candidate for the systems around or after the period minimum of evolution of cataclysmic variables (abridged).Comment: 239 pages, 225 figures, PASJ accepte

Photometry of the Didymos System across the DART Impact Apparition

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the satellite of binary near-Earth asteroid (65803) Didymos. This demonstrated the efficacy of a kinetic impactor for planetary defense by changing the orbital period of Dimorphos by 33 minutes. Measuring the period change relied heavily on a coordinated campaign of lightcurve photometry designed to detect mutual events (occultations and eclipses) as a direct probe of the satellite’s orbital period. A total of 28 telescopes contributed 224 individual lightcurves during the impact apparition from 2022 July to 2023 February. We focus here on decomposable lightcurves, i.e., those from which mutual events could be extracted. We describe our process of lightcurve decomposition and use that to release the full data set for future analysis. We leverage these data to place constraints on the postimpact evolution of ejecta. The measured depths of mutual events relative to models showed that the ejecta became optically thin within the first ∼1 day after impact and then faded with a decay time of about 25 days. The bulk magnitude of the system showed that ejecta no longer contributed measurable brightness enhancement after about 20 days postimpact. This bulk photometric behavior was not well represented by an HG photometric model. An HG 1 G 2 model did fit the data well across a wide range of phase angles. Lastly, we note the presence of an ejecta tail through at least 2023 March. Its persistence implied ongoing escape of ejecta from the system many months after DART impact

droke

droke nA wooded valley, surrounded by barrens.DNE-cit JH 11/73Used I and SupUsed I and SupNot use

The triple system CG Aurigae

Several new precise times of eclipses were measured for eclipsing binary CG Aur as a part of our long-term observational project for studying eclipsing binaries with an eccentric orbit. Based on a current O - C diagram, we found for the first time that its orbit is slightly eccentric (e = 0.124) and that times of minima besides the slow apsidal motion show very rapid changes with a period about 700 days only, caused very probably by the third body orbiting the eclipsing pair. The relativistic contribution to the total apsidal-motion rate is significant being about 33%.Web of Science16640440

Rapid apsidal motion in V381 Cassiopeiae

V381 Cas is a relatively bright and early-type eclipsing binary system. Several new times of its eclipses were measured as part of our long-term observational project of eccentric eclipsing binaries. Based on a current O–C diagram solution, we found for the first time that its orbit is slightly eccentric (e = 0.025) and shows a very rapid apsidal advance with short period of about 20 years only. The relativistic and third body effects are negligible, being about 3% of the total apsidal motion rate

Apsidal motion in five eccentric eclipsing binaries

Aims. As part of the long-term Ondrejov and Ostrava observational projects, we aim to measure the precise times of minimum light for eccentric eclipsing binaries, needed for accurate determination of apsidal motion. Over fifty new times of minimum light recorded with CCD photometers were obtained for five early-type and eccentric-orbit eclipsing binaries: V785 Cas (P = 2.(d)70, e = 0.09), V821 Cas (1.(d)77, 0.14), V796 Cyg (1.(d)48, 0.07), V398 Lac (5.(d)41, 0.23), and V871 Per (3.(d)02, 0.24). Methods. O-C diagrams of binaries were analysed using all reliable timings found in the literature, and new elements of apsidal motion were obtained. Results. We derived for the first time or improved the relatively short periods of apsidal motion of about 83, 140, 33, 440, and 70 years for V785 Cas, V821 Cas, V796 Cyg, V398 Lac, and V871 Per, respectively. The internal structure constants, log k(2), for V821 Cas and V398 Lac are then found to be -2.70 and -2.35, under the assumption that the component stars rotate pseudosynchronously. The relativistic effects are weak, up to 7% of the total apsidal motion rate.Web of Science549art. no. A10

Relativistic apsidal motion in eccentric eclipsing binaries

Context. The study of apsidal motion in detached eclipsing binary systems is known to be an important source of information about stellar internal structure as well as the possibility of verifying of General Relativity outside the Solar System. Aims. As part of the long-term Ondřejov and Ostrava observational projects, we aim to measure precise times of minima for eccentric eclipsing binaries, needed for the accurate determination of apsidal motion, providing a suitable test of the effects of General Relativity. Methods. About seventy new times of minimum light recorded with photoelectric or CCD photometers were obtained for ten eccentric-orbit eclipsing binaries with significant relativistic apsidal motion. Their O–C diagrams were analysed using all reliable timings found in the literature, and new or improved elements of apsidal motion were obtained. Results. We confirm very long periods of apsidal motion for all systems. For BF Dra and V1094 Tau, we present the first apsidal-motion solution. The relativistic effects are dominant, representing up to 100% of the total observable apsidal-motion rate in several systems. The theoretical and observed values of the internal structure constant k2 were compared for systems with lower relativistic contribution. Using the light-time effect solution, we predict a faint third component for V1094 Tau orbiting with a short period of about 8 years

Apsidal motion in eccentric eclipsing binaries: CW Cephei, V478 Cygni, AG Persei, and IQ Persei

Aims. About thirty new times of minimum light recorded with photoelectric or CCD photometers were obtained for four early-type eccentric-orbit eclipsing binaries CW Cep ( P = 2.(d)73, e = 0.029), V478 Cyg (2.(d)88, 0.016), AG Per (2.(d)03, 0.071), and IQ Per (1.(d)74, 0.076). Methods. Their O-C diagrams were analysed using all reliable timings found in the literature, and elements of apsidal motion were improved. Results. We confirm relatively short periods of apsidal motion of about 46, 27, 76, and 124 years for CW Cep, V478 Cyg, AG Per, and IQ Per, respectively. The corresponding internal structure constants, log k(2), are then found to be -2.12, -2.25, -2.15, and -2.36, under the assumption that the component stars rotate pseudosynchronously. The relativistic effects are negligible, being up to 8% of the total apsidal motion rate in all systems. Using the light-time effect solution, we have predicted a faint third component orbiting with a period of about 39 years for CW Cep.Web of Science45631083107