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NSVS 2569022:a peculiar binary among W UMa stars with extremely small mass ratios

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Research in Astronomy and Astrophysics 2018年第10期18卷 123-130页

作者： Diana P.Kjurkchieva velimir A.popov Nikola I.Petrov Department of Physics and Astronomy Shumen University Institute of Astronomy and NAO Bulgarian Academy of Sciences

Photometric observations of the W UMa binary NSVS 2569022 are presented. The light curve solution reveals that both components are of F spectral type （temperatures T1 = T2 = 6100 K）. NSVS 2569022 undergoes a total eclipse of W subtype and the mass ratio is well-determined. Its extremely small value of only 0.077 implies that the target will probably experience instability and a possible merger. This value ranks NSVS 2569022 in sixth place among binaries with the smallest mass ratio. Based on an empirical relation of ＂period - total mass＂ for low mass-ratio binaries, we estimate the global parameters of NSVS 2569022： masses M1 = 1.17 M⊙ and M2 = 0.09 M⊙; radii R1 = 1.19 R⊙ and R2 = 0.38 R⊙; luminosities L1 = 1.73 L⊙ and L2 = 0.17L⊙. An analysis of the characteristics of binaries with extremely low-mass ratios is made. NSVS 2569022 turns out to be a peculiar binary among W UMa stars with extremely small mass ratios due to its unexpectedly small fill-out factor of only 0.014 （slightly overcontact configuration）.

关键词： binaries eclipsing - binaries close - stars fundamental parameters - stars individual(NSVS 2569022)

New observations and transit solutions of the inflated exoplanets HAT-P-40b and HAT-P-51b

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Research in Astronomy and Astrophysics 2021年第2期21卷 157-160页

作者： Diana P.Kjurkchieva Nikola I.Petrov velimir A.popov Department of Physics and Astronomy Shumen University115 Universitetska str.9700 ShumenBulgaria Institute of Astronomy and NAO Bulgarian Academy of SciencesTsarigradsko shossee 721784 SofiaBulgaria

We present high-precision photometric observations of the transiting exoplanets HAT-P-40 b and HAT-P-51 b by the Rozhen 2-m *** newly-observed transit of HAT-P-40 b is the first one with a complete *** orbital periods of the two targets were *** modeled the observed transits and found bigger stellar radii than those derived from the stellar *** planet radii of HATP-40 b and HAT-P-51 b obtained from our transit solutions are bigger than the values calculated by the empirical relations for Jupiter-mass and Saturn-mass planets *** values reveal the highlyinflated nature of the two targets,especially that of HAT-P-51 *** established that the best transit solutions correspond to a quadratic limb-darkening *** fitted limb-darkening coefficients of HAT-P-40 are close to the theoretical ones while those of HAT-P-51 are a little *** precise astrometric Gaia distances of the two targets are smaller by 6%–7%than the calculated values from the stellar *** propose the Gaia distances to be used for improvement of the stellar models as well as for more reliable calculation of the parameters of the known exoplanets.

关键词： (Stars )planetary systems-techniques photometric-Stars individual(HAT-P-40 and HAT-P-51)

Observations and light curve solutions of a selection of middle-contact W UMa binaries

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Research in Astronomy and Astrophysics 2018年第4期18卷 105-114页

作者： Diana Petrova Kjurkchieva velimir Angelov popov Doroteya Lyubenova Vasileva Nikola Ivanov Petrov Department of Physics Shumen University IRIDA Observatory Rozhen NAO Institute of Astronomy and NAO Bulgarian Academy of Sciences

Photometric observations in Sloan g′and i′ bands of W UMa binaries NSVS 4340949,T-Dra0–00959,GSC 03950–00707,NSVS 4665041,NSVS 4803568,MM Peg,MM Com and NSVS4751449 are *** light curve solutions revealed that the components of each target are of G and K spectral *** binaries of the sample have middle-contact configurations whose fillout factors are within the range 0.2–*** only exception is NSVS 4751449 which is in deeper contact（fillout factor of 0.55）.It precisely obeys the relation between mass ratio and fillout factor for deep,low mass ratio overcontact *** of the eclipses of almost all targets（except MM Peg）is an occultation and their photometric mass ratios and solutions could be accepted with *** found that the target components have almost equal temperatures but differ considerably in size and *** components of the partially-eclipsed MM Peg have close *** solutions reveal that NSVS 4340949,T-Dra0–00959,NSVS 4803568 and MM Com are of W subtype while GSC 03950–00707,NSVS 4665041,MM Peg and NSVS 4751449 are of A *** subclassification is well-determined for all totallyeclipsed *** targets confirm the trends in which W-subtype systems have smaller periods and lower temperatures than A subtype binaries.

关键词： binaries close — binaries eclipsing — stars fundamental parameters — stars late-type

Photometric observations and light curve solutions of the W UMa stars NSVS 2244206,NSVS 908513,CSS J004004.7+385531 and VSX J062624.4+570907

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Research in Astronomy and Astrophysics 2016年第9期16卷 15-22页

作者： Diana Petrova Kiurkchieva velimir Angelov popov Doroteya Lyubenova Vasileva Nikola Ivanov Petrov Department of Physics Shumen University115Universitetska Str.1712 ShumenBulgaria IRIDA Observatory 17A Prof.Asen Zlatarov Str.SofiaBulgaria Institute of Astronomy and National Astronomical Observatory Bulgarian Academy of Sciences72Tsarigradsko Shose Blvd.1784 SofiaBulgaria

Photometric observations in Sloan 9＇ and i＇ bands of four W UMa stars, NSVS 2244206, NSVS 908513, CSS J004004.7＋385531 and VSX J062624.4＋570907, are presented. The light curve solutions reveal that all targets have overcontact configurations with fillout factors within 0.15-0.26. Their components are G-K spectral types and are almost in thermal contact. They are also relatively close in size and luminosity： the radius ratios r2/r1 are within 0.75-0.90; the luminosity ratios 12/11 are within 0.53-0.63. The results of the light curve solution of CSS J004004.7＋385531 imply the weak limb-darkening effect of its primary component and possible presence of additional absorbing features in the system.

关键词： methods data analysis -- stars fundamental parameters -- stars binaries eclipsing individ-ual (NSVS 2244206, NSVS 908513, CSS J004004.7+385531, VSX J062624.4+570907)

The W UMa binaries USNO-A2.0 1350-17365531,V471 Cas,V479 Lac and V560 Lac:light curve solutions and global parameters based on Gaia distances

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Research in Astronomy and Astrophysics 2019年第1期19卷 141-148页

作者： Diana P.Kjurkchieva velimir A.popov Yordanka Eneva Nikola I.Petrov Department of Physics and Astronomy Shumen University Medical University Institute of Astronomy and NAO Bulgarian Academy of Sciences

We present photometric observations in Sloan filters g′, i′of the eclipsing W UMa stars USNOA2.0 1350-17365531, V471 Cas, V479 Lac and V560 Lac. The sinusoidal-like O-C diagram of V471 Cas indicates the presence of a third body with mass 0.12 M_⊙(a red dwarf) at distance 897 R_⊙. The O-C diagram of V479 Lac reveals a period decrease of d P/dt =-1.69 × 10-6d yr-1. The results of the light curve solutions are:(i) the targets are overcontact binaries with small fill-out factors;(ii) their components are F–K stars, comparable in size, whose temperature differences are below 80 K;(iii) all targets undergo partial eclipses and to limit the possible mass ratios we carried out two-step q-search analysis. The target global parameters(luminosities, radii, masses) were obtained on the basis of their Gaia distances and the results of our light curve solutions. The obtained total mass of V560 Lac turns out to be smaller than the lower mass limit for presently known W UMa binaries of 1.0-1.2 M_⊙, i.e. this target is a peculiar overcontact system.

关键词： binaries:close binaries:eclipsing methods:data analysis stars:fundamental parameters stars:individual(USNO-A2.0 1350-17365531,V471 Cas,V479 Lac,V560 Lac)

Observations and light curve solutions of the W UMa binaries V796 Cep,V797 Cep,CSS J015341.9+381641 and NSVS 3853195

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Research in Astronomy and Astrophysics 2017年第5期17卷 31-38页

作者： Diana Petrova Kjurkchieva velimir Angelov popov Sunay Ibryamov Ibryamov Doroteya Lyubenova Vasileva Nikola Ivanov Petrov Department of Physics Shumen University115 Universitetska Str.9712 ShumenBulgaria IRIDA Observatory Rozhen NAOBulgaria Institute of Astronomy and NAO Bulgarian Academy of Sciences72 Tsarigradsko Shose Blvd.1784 SofiaBulgaria

Photometric observations in Sloan g′and i′bands of four W UMa binaries, V796 Cep,V797 Cep, CSS J015341.9＋381641 and NSVS 3853195, are presented. Our observations showed that CSS J015404.1＋382805 and NSVS 3853195 are the same star. We determined the initial epochs T_0 of all targets and found improved values for the period of NSVS 3853195. The light curve solutions of our data revealed that the components of each target are almost the same in terms of mass, temperature,radius and luminosity. The stellar components are G and K spectral types and undergo partial *** systems have barely-overcontact configurations and can be classified as H subtype W UMa *** established that the relation between the luminosity ratio l_2/l_1 and mass ratio q of our targets is approximately l_2/l_1 = q^（1.5）.

关键词： stars: binaries: eclipsing -- stars: fundamental parameters -- stars: individual (V796 Cep,V797 Cep CSS J015341.9+381641 NSVS 3853195)

V2551 Cyg:a pulsating star with enigmatic peculiarities

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Research in Astronomy and Astrophysics 2017年第7期17卷 57-66页

作者： Diana P.Kjurkchieva velimir A.popov Dragomir V.Marchev Kenneth T.Menzies Nikola I.Petrov Department of Physics Shumen University IRIDA Observatory Rozhen NAO Tigh Speuran Observatory Institute of Astronomy and NAO Bulgarian Academy of Sciences

Intensive photometric and spectral observations of the variable star V2551 Cyg are *** light curve shape reveals that the target is a pulsating star, contrary to its previous classification as an eclipsing binary. The period and amplitude of the light curve, the amplitudes of color changes and the radial velocity curve of V2551 Cyg are similar to those of a high-amplitude δ Scuti variable. The target seems to pulsate with the fundamental mode. However, V2551 Cyg exhibits several important peculiarities：（i） the decreasing branch of its light curve is steeper than the increasing one;（ii） the radial velocity curve has a flat section in the phase range 0.7-1.2 and short increase of the negative radial velocity at phase 0.7;（iii） the rotational velocity is quite big for a HADS star;（iv） the Fourier coefficients of V2551 Cyg are quite different from those of HADS stars. The target classification is difficult due to these peculiarities.

关键词： stars variables delta Scuti - stars variables RR Lyrae - stars individual (V2551 Cyg)