143 citations · 896 across the 61 of their papers we have counts for
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Photometric monitoring of PMS stars with the telescopes at Rozhen Observatory
Evgeni Semkov, Sunay Ibryamov, Stoyanka Peneva +1
For several decades we have been performing photometric monitoring of some of the star formation regions. Significant place in our program take observations of objects of the type…
Study of the long-term photometric variability of eight PMS stars in the young open cluster Trumpler 37
Sunay Ibryamov, Gabriela Zidarova, Evgeni Semkov +1
This paper reports results from our long-term photometric CCD observations of eight pre-main-sequence stars collected from June 2008 to October 2022. These stars are l…
Long-term Photometric Study of the Pre-main Sequence Star V1180 Cas
Asen Mutafov, Evgeni Semkov, Stoyanka Peneva +1
In this paper results from the optical photometric observations of the pre-main-sequence star V1180 Cas are reported. The star is a young variable associated with the dark cloud Ly…
Long-term optical photometry of the PMS stars V2764 Ori and LkH 301 in the field of the McNeil's Nebula
G. Zidarova, S. Ibryamov, E. Semkov +1
In this paper, we present results from long-term photometric observations of the pre-main-sequence stars V2764 Ori and LkH 301, located in the field of the McNeil's…
The FUor star V2493 Cyg (HBC 722) -- eleven years at maximum brightness
Evgeni Semkov, Sunay Ibryamov, Stoyanka Peneva
At the time of stellar evolution, young stellar objects go through processes of increased activity and instability. Star formation takes place in several stages during which the st…
Long-term optical photometric monitoring of the FUor star V900 Mon
Evgeni Semkov, Stoyanka Peneva, Sunay Ibryamov
We present results from photometric monitoring of V900 Mon, one of the newly discovered and still under-studied object from FU Orionis type. FUor phenomenon is very rarely observed…
New Results from Long-time Photometric Study of UX Orionis Star GM Cephei
Asen Mutafov, Evgeni Semkov, Stoyanka Peneva +1
New results from long-term optical photometric observations of the pre-main sequence star GM Cep from UX Orionis type are reported. During ongoing photometric monitoring of the GM…
Long-term CCD photometry of pre-main-sequence stars in the association Cepheus OB3
Sunay Ibryamov, Gabriela Zidarova, Evgeni Semkov +1
Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented. These stars are locat…
A new prolonged decrease event in the brightness of the young stellar object V2492 Cygni
Sunay Ibryamov, Evgeni Semkov
Results from the BV(RI)c photometric observations of the young stellar object V2492 Cyg collected in the period from April 2018 to September 2020 are presented. These observations…
BV(RI)c photometric study of three variable PMS stars in the field of V733 Cephei
Sunay Ibryamov, Evgeni Semkov, Stoyanka Peneva +1
This paper report 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…
Intra-night flickering of RS Ophiuchi: III. Modes of quasi-periods in the minute scale and their evolution
Ts. B. Georgiev, R. K. Zamanov, S. Boeva +7
We study the photometric behavior of the recurrent nova RS Oph by 58 monitoring light curves (LCs), taken by 5 telescopes. All LCs show repeating time structures with some quasi-pe…
International observational campaign of the 2014 eclipse of EE Cep
D. Pieńkowski, C. Gałan, T. Tomov +64
Context. EE Cep is one of few eclipsing binary systems with a dark, dusty disk around an invisible object similar to ε Aur. The system is characterized by grey and asymmetric eclip…
Photometric and spectroscopic study of 5 pre-main sequence stars in the vicinity of NGC 7129
Evgeni H. Semkov, Sunay I. Ibryamov, Stoyanka P. Peneva
We present results from long-term optical photometric and spectroscopic observations of 5 pre-main sequence stars, located in the vicinity of the bight nebula NGC 7129. We obtained…
New four-color optical photometry of the young stars V521 Cyg and FHO 27
Sunay Ibryamov, Evgeni Semkov
Results from new BVRI photometric observations of the pre-MS stars V521 Cyg and FHO 27 collected during the period from February 2015 to July 2019 are presented. These stars are em…
New light curve solution of V568 Peg and first determination of its fundamental parameters
Diana Kjurkchieva, Sunay Ibryamov
We present V, Rc photometric observations of the short-period W UMa star V568 Peg. They allowed us to improve its period. The light curve solution revealed that V568 Peg is an over…
Intra-night flickering of RS Ophiuchi: I. Sizes and cumulative energies of time structures
Ts. B. Georgiev, R. K. Zamanov, S. Boeva +7
We analyzed 29 pairs of time series in B and V bands of the recurrent nova RS Oph. The observations were carried out in 2008-2017 with duration 0.6 - 3.6 hours, with time resolutio…
Long-term BVRI photometric light curves of 15 PMS stars in the IC 5070 star-forming region
Sunay Ibryamov, Evgeni Semkov, Teodor Milanov +1
This paper reports the results from the multicolor photometric observations of 15 pre-main sequence stars collected in the period 2010 September - 2017 October. The stars from our…
Multicolor photometric behavior of the young stellar object V1704 Cygni
Sunay Ibryamov, Evgeni Semkov, Stoyanka Peneva +1
Results from BVRI photometric observations of the pre-main sequence star V1704 Cyg collected during the time period from August 2010 to December 2017 are presented. The star is loc…
V2492 Cygni: Optical BVRI variability during the period 2010-2017
Sunay I. Ibryamov, Evgeni H. Semkov, Stoyanka P. Peneva
Results from BVRI photometric observations of the young stellar object V2492 Cyg collected during the period from August 2010 to December 2017 are presented. The star is located in…
Observations and light curve solutions of ultrashort-period eclipsing binaries
Diana P. Kjurkchieva, Dinko P. Dimitrov, Sunay I. Ibryamov +1
Photometric observations in V and I bands and low-dispersion spectra of ten ultrashort-period binaries (NSVS 2175434, NSVS 2607629, NSVS 5038135, NSVS 8040227, NSVS 9747584, NSVS 4…
Long-term photometric observations in the field of the star formation region NGC7129
Evgeni Semkov, Stoyanka Peneva, Sunay Ibryamov +1
We present results from long-term optical photometric observations of the Pre-Main Sequence (PMS) stars, located in the star formation region around the bright nebula NGC 7129. Usi…
Observations and light curve solutions of the eclipsing stars CSS J075205.6+381909 and NSVS 691550
D. Kjurkchieva, V. Popov, D. Vasileva +2
The paper presents observations and light curve solutions of the eclipsing stars CSS J075205.6+381909 and NSVS 691550. As a result their initial epochs were determined. The target…
A deep decrease event in the brightness of the PMS star V350 Cep
Evgeni H. Semkov, Sunay I. Ibryamov, Stoyanka P. Peneva
New photometric data from CCD UBVRI observations of the PMS star V350 Cep during the period from March 2014 to May 2017 are presented. In the period April-May 2016 we registered a…
Observations and light curve solutions of the W UMa binaries V796 Cep, V797 Cep, CSS J015341.9+381641 and NSVS 3853195
D. P. Kjurkchieva, V. A. Popov, S. I. Ibryamov +2
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…