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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)

A long-term UBVRI photometric study of the pre-main sequence star V350 Cep

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Research in Astronomy and Astrophysics 2014年第10期14卷 1264-1268页

作者： sunay ibryamov Evgeni Semkov Stoyanka Peneva Institute of Astronomy and National Astronomical Observatory Bulgarian Academy of Sciences72 Tsarigradsko Shose Blvd1784 SofiaBulgaria

Results from UBVRI optical photometric observations of the pre-main se- quence star V350 Cep during the period 2004-2014 are presented. The star was dis- covered in 1977 due to its remarkable increase in brightness by more than 5 mag （R）. In previous studies, V350 Cep was considered to be a potential FUor or EXor eruptive variable. Our data suggest that during the period of observations the star maintains its maximum brightness with low amplitude photometric variations. Our conclusion is that V350 Cep was probably an intermediate object between FUors and EXors, similar to V1647 Ori.

关键词： stars pre-main sequence -- stars variable T Tauri -- stars individual(V350 Cep)

Long-term V(RI) CCD photometry of pre-main-sequence stars in the association Cepheus OB3

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Research in Astronomy and Astrophysics 2021年第8期21卷 91-98页

作者： sunay ibryamov Gabriela Zidarova Evgeni Semkov Stoyanka Peneva Department of Physics and Astronomy University of Shumen115Universitetska Str.9700 ShumenBulgaria Institute of Astronomy and National Astronomical Observatory Bulgarian Academy of Sciences72Tsarigradsko Shose Blvd.1784 SofiaBulgaria

Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are *** stars are located in the association Cepheus OB3,in the field of the young star V733 *** observations,especially concerning the long-term variability of the stars,are missing in the *** present the first longterm V(RI)c monitoring for them,that cover 13 *** from our study indicate that all of the investigated stars manifest strong photometric *** presented paper is a part of our program for the photometric study of pre-main-sequence stars located in active star-forming regions.

关键词： stars:pre-main sequence stars:variables:T Tauri Herbig Ae/Be techniques:photometric methods:observational data analysis stars:individual

BV(RI )c photometric study of three variable PMS stars in the field of V733 Cephei

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Research in Astronomy and Astrophysics 2020年第12期20卷 221-228页

作者： sunay ibryamov Evgeni Semkov Stoyanka Peneva Kristina Gocheva Department of Physics and Astronomy University of Shumen115Universitetska Str.9700 ShumenBulgaria Institute of Astronomy and National Astronomical Observatory Bulgarian Academy of Sciences72Tsarigradsko Shose Blvd.1784 SofiaBulgaria

This paper reports results from the first long-term BV(RI)c photometric CCD observations of three variable pre-main-sequence stars collected during the period from February 2007 to January 2020. The investigated stars are located in the field of the PMS star V733 Cep within the Cepheus OB3 association. All stars from our study show rapid photometric variability in all-optical passbands. In this paper, we describe and discuss the photometric behavior of these stars and the possible reasons for their variability. In the light variation of two of the stars, we found periodicity.

关键词： stars:pre-main sequence stars:variables:T Tauri,Herbig Ae/Be techniques:photometric methods:observational,data analysis stars:individual(2MASS J22534654+6234582,2MASS J22533629+6231446,2MASS J22531578+6235262)

Long-term BV RI photometric light curves of 15 PMS stars in the star-forming region IC 5070

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Research in Astronomy and Astrophysics 2018年第11期18卷 63-74页

作者： sunay ibryamov Evgeni Semkov Teodor Milanov Stoyanka Peneva Department of Physics and Astronomy Faculty of Natural Sciences University of Shumen Institute of Astronomy and National Astronomical Observatory Bulgarian Academy of Sciences

This paper reports results from the multicolor photometric observations of 15 pre-main sequence stars collected in the period September 2010-October 2017. The stars from our study are located in the star-forming HII region IC 5070. These objects were previously detected as either emission line stars, flare stars, T Tauri variables or Herbig Ae/Be stars. Photometric observations, especially concerning the long-term behavior of the objects, are missing in the literature. We present the first photometric monitoring for all stars from our study. The analysis of the obtained BV RI photometric data allows us to draw the conclusion that all investigated objects are variable stars. In the case of LkHα 146,we identified previously unknown periodicity in its photometric variability.

关键词： stars: pre-main sequence stars: variables: T Tauri Herbig Ae/Be stars: individual

Light curve solutions of six eclipsing binaries at the lower limit of periods for W UMa stars

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Research in Astronomy and Astrophysics 2015年第9期15卷 1493-1503页

作者： Diana P.Kjurkchieva Dinko P.Dimitrov sunay I.ibryamov Department of Physics Shumen University Institute of Astronomy and National Astronomical Observatory Bulgarian Academy of Sciences

Photometric observations are presented in V and I bands of six eclipsing binaries at the lower limit of the orbital periods for W UMa stars. Three of them are newly discovered eclipsing systems. The light curve solutions reveal that all shortperiod targets are contact or overcontact binaries and six new binaries are added to the family of short-period systems with estimated parameters. Four binaries have com- ponents that are equal in size and a mass ratio near 1. The phase variability shown by the V-I colors of all targets may be explained by lower temperatures on their back surfaces than those on their side surfaces. Five systems exhibit the O＇Connell effect that can be modeled by cool spots on the side surfaces of their primary components. The light curves of V1067 Her in 2011 and 2012 are fitted by diametrically opposite spots. Applying the criteria for subdivision of W UMa stars to our targets leads to ambiguous results.

关键词： methods: data analysis -- catalogs -- stars: fundamental parameters-- stars: binaries: eclipsing: individual (1SWASP J173828.46+111150.2 1SWASPJ174310.98+432709.6 ≡ V1067 Her NSVS 11534299 NSVS 10971359 NSVS11234970 NSVS 11504202)

Long-term photometric behavior of the PMS stars V977 Cep and V982 Cep in the vicinity of NGC 7129

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Research in Astronomy and Astrophysics 2017年第2期17卷 77-88页

作者： sunay I. ibryamov Evgeni H. Semkov Teodor R. Milanov Stoyanka P. Peneva Department of Theoretical and Applied Physics University of Shumen BG-9712 Shumen Bulgaria Institute of Astronomy and National Astronomical Observatory Bulgarian Academy of Sciences BG-1784 Sofia Bulgaria

Long-term BVRI photometric light curves of the pre-main sequence stars V977 Cep and V982 Cep during the period from 2000 October to 2016 August are presented. The stars are located in the vicinity of the reflection nebula NGC 7129. Our photometric data show that both stars exhibit strong photometric variability in all optical passbands, which is typical for Classical T Tauri stars. Using our observational data we analyze the reasons for the observed brightness variations. In the case of V977 Cep we identify previously unknown periodicity in its light curve.

关键词： stars: pre-main sequence -- variables: T Tauri -- stars: individual (V977 Cep V982 Cep)

Study of the Long-term BVR_(c)I_(c) Photometric Variability of Eight PMS Stars in the Young Open Cluster Trumpler 37

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Research in Astronomy and Astrophysics 2023年第8期23卷 117-126页

作者： sunay ibryamov Gabriela Zidarova Evgeni Semkov Stoyanka Peneva Department of Physics and Astronomy Faculty of Natural SciencesUniversity of Shumen115Universitetska Str.9700 ShumenBulgaria Institute of Astronomy and National Astronomical Observatory Bulgarian Academy of Sciences72Tsarigradsko Shose Blvd.1784 SofiaBulgaria

This paper reports results from our long-term BV(RI)_(c) photometric CCD observations of eight pre-main sequence stars collected from 2008 June to 2022 *** stars are located in the young open cluster Trumpler 37,in the field of GM *** observational data indicate that all stars from our study exhibit variability in all-optical passbands,typical for young *** this paper,we describe and discuss the photometric behavior of the stars and the possible reasons for their *** two of the objects,we identified periodicity in their light variation.

关键词： stars pre-main sequence-stars variables T Tauri-Herbig Ae/Be

Long-term Photometric Study of the Pre-main Sequence Star V1180 Cas

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Research in Astronomy and Astrophysics 2022年第12期22卷 284-291页

作者： Asen Mutafov Evgeni Semkov Stoyanka Peneva sunay ibryamov Institute of Astronomy and National Astronomical Observatory Bulgarian Academy of SciencesBG-1784SofiaBulgaria Department of Physics and Astronomy Faculty of Natural SciencesUniversity of Shumen115Universitetska Str.9700 ShumenBulgaria

In this paper results from the optical photometric observations of the pre-main sequence star V1180 Cas are *** star is a young variable associated with the dark cloud Lynds 1340,located at a distance of 600 pc from the Sun in the star-forming region in Cassiopeia.V1180 Cas shows large amplitude variability,interpreted as a combination of accretion-induced and extinction-driven *** data from VRI CCD photometric observations of the star were collected from September 2011 to February *** our monitoring,we recorded several brightness dips with large amplitudes of up to 5 mag(I band).At the same time,increases in brightness over periods of several weeks have also been *** this paper,we compare the photometric data obtained for V1180 Cas with observations of other low-mass pre-main sequence objects.

关键词： stars:variables:T Tauri Herbig Ae/Be stars:pre-main sequence stars:evolution