arXiv subjects

Sergey Shugarov

Publications and source records attributed to Sergey Shugarov.

5 recordsLinked to original sources

arXiv2025

Photometric Analysis of TCP J20171288$+$1156589 -- WZ Sge Type Dwarf Nova with Delayed Ordinary Superhumps Emergence

We present the results of photometric analysis of WZ Sge type dwarf nova TCP J20171288$+$1156589. This object exhibited an outburst with a large amplitude of $>7.9$ magnitudes and was observed for over a month. The photometric evolution of the superoutburst was atypical for WZ Sge-type dwarf novae. Periodogram analisys reveals early superhumps with the most probable period of $0.0611\pm0.0001$ days during the initial decline. After a plateau phase of approximately 11 days, ordinary superhumps (likely stage B) emerged with a period of $0.0616\pm0.0001$ days, corresponding to a superhump excess of $\epsilon=0.008$ correspondingly. This delay in the onset of ordinary superhumps is an unusual feature among WZ Sge stars. We evaluated the main parameters of the system: mass ratio $q=M_{RD}/M_{WD}=0.06\pm0.005$, yielding component masses of $M_{WD}\sim1.0\pm0.15M_{\odot}$ for the white dwarf and $M_{RD}=0.06\pm0.01M_{\odot}$ for the donor. The estimated distance to the system is $\sim850$ pc, and the binary separation is $a=0.67\pm0.03R_{\odot}$.

astro-ph.SR↗

arXiv2020

X-ray Spectra and Light Curves of Cooling Novae and a Nova-Like

We present X-ray observations of novae V2491 Cyg and KT Eri about 9 years post-outburst, of the dwarf nova and post-nova candidate EY Cyg, and of a VY Scl variable. The first three objects were observed with XMM-Newton, KT Eri also with the Chandra ACIS-S camera, V794 Aql with the Chandra ACIS-S camera and High Energy Transmission Gratings. The two recent novae, similar in outburst amplitude and light curve, appear very different at quiescence. Assuming half of the gravitational energy is irradiated in X-rays, V2491 Cyg is accreting at $\dot{m}=1.4\times10^{-9}-10^{-8}M_\odot/yr$, while for KT Eri, $\dot{m}<2\times10^{-10}M_\odot/yr$. V2491 Cyg shows signatures of a magnetized WD, specifically of an intermediate polar. A periodicity of ~39 minutes, detected in outburst, was still measured and is likely due to WD rotation. EY Cyg is accreting at $\dot{m}\sim1.8\times10^{-11}M_\odot/yr$, one magnitude lower than KT Eri, consistently with its U Gem outburst behavior and its quiescent UV flux. The X-rays are modulated with the orbital period, despite the system's low inclination, probably due to the X-ray flux of the secondary. A period of ~81 minutes is also detected, suggesting that it may also be an intermediate polar. V794 Aql had low X-ray luminosity during an optically high state, about the same level as in a recent optically low state. Thus, we find no clear correlation between optical and X-ray luminosity: the accretion rate seems unstable and variable. The very hard X-ray spectrum indicates a massive WD.

astro-ph.HE↗

arXiv2020

Classical Nova Persei 2018 outburst from the dwarf nova V392 Per

On 2018, April 29, a bright classical nova (CN) Per 2018 was discovered. Its progenitor is a well-known dwarf nova V392 Per. In this contribution, we analyze $UBVR_{C}I_{C}$ photometry and optical spectroscopy of the CN V392 Per. From the $V$ light curve (LC) we found the brightness decline times t$_{2,V}$ = 3 d, t$_{3,V}$ = 10 d and calculated absolute magnitude of the nova at maximum $MV_{max}$ = -9.30 ${\pm}$0.57 using the new $MV_{max}$ - t$_{3}$ "universal" decline law and $MV_{15}$ relations, adopting the Gaia data for CNe. We determined the colour excess $E_{B-V}$ = 0.90$\pm$0.09 and distance to the nova $d$ = 3.55$\pm$0.6 kpc. The optical spectrum obtained in brightness maximum resembles that of the F2 supergiant. Its bolometric luminosity computed by fitting the continuum by atmospheric and black-body models is in agreement with the luminosity, that we have found from photometry. We estimated the mass of the ONe white dwarf in V392 Per as $M_{wd}$ = 1.21 M$_{\odot}$. The CN Per 2018 can be classified as a fast super-Eddington nova with an outburst LC of plateau type. Nova displayed He/N spectrum classification, large expansion velocities, and triple-peaked emission-line profiles during the decline, explained by equatorial ring seen nearly face on and a bipolar flow aligned almost with the line of sight. The post maximum spectra of CN Per 2018 and available radio data were used to estimate the inclination angle of the system as $i\sim$ 9$^{\circ}$. The difference in intensity of redward and blueward emission bumps is possible to explain by about 1.5 times higher density of the receding outtflow. The rapid increase of the bipolar outflow radial velocities by $\sim$300 km/s around day 5 after the maximum was caused by the fast bipolar winds from the burning white dwarf after shrinking of its pseudophotosphere.

astro-ph.SR↗

arXiv2012

Detection of Change in Supercycles in ER Ursae Majoris

We examined data on about 20 years of observations of ER UMa available in AAVSO, VSNET, AFOEV, NSVS, VSOLJ databases together with published light curves. The obtained O-C diagram revealed a systematic change of the supercycle (time interval between two successive superotbursts) within 43.6 and 59.2 d. The time-scale of this change variation is from 300 to $\sim$ 1900 d. The number of normal outbursts within the supercycles also varied from 4 to 6 although no strong correlation between this number and supercycle length was found. We suggest that appearance of negative superhumps is responsible for the observed variations of number of normal outbursts. Our results generally confirms the expectations by the thermal-tidal instability theory.

astro-ph.SR↗

arXiv2011

MN Dra - In-the-Gap Dwarf Nova With Negative Superhumps

The multi-site photometric observations of MN Dra were made over 77 nights in August-November, 2009. The total exposure was 433 hours. During this time the binary underwent two superoutbursts and five normal outbursts. During the course of first superoutburst period of positive superhumps decreased with extremely large $\dot P = -1.5 \times 1.0^{-4}$ for SU UMa-like dwarf novae, confirming known behavior of MN Dra [1]. Between the superoutbursts MN Dra displayed negative superhumps. Their period changed cyclically around 0.096-day value.

astro-ph.SR↗