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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 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.
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We present our photometric observations of GM Cep, a solar type variable in the young (~4 Myr) open cluster Trumpler 37. The star is known as a classical T Tauri star with a circumstellar disk and active accretion. GM,Cep was suspected to undergo an outburst, thus a candidate for an EXor-type variable. In our monitoring campaign observations in 2010-2011, GM Cep experienced a ~0.82 mag brightness decrease in the R band lasting for 39 days, and frequent, transient flare-like episodes with amplitude < 1 mag, each lasting for about 10 days. The brightening was accompanied with a bluer color, presumably arising from increased accretion activity. Interestingly, the star also turned bluer in the fading phase. Combining the AAVSO and literature data, we found a quasi-cyclic peroid of ~311 days for the fading event. A possible mechanism for the fading could be obscuration by a clump of dust around the star. We proposed that GM Cep therefore should be a UXor-type variable in the transition phase between grain coagulation and planetesimal formation process in the circumstellar disk.
We report the discovery of 19 variable stars and two blue-stragglers in the field of the open cluster NGC6866. Three of the variable stars we classify as delta Sct, two, as gamma Dor, four, as WUMa, two, as ellipsoidal variables, and one, as an eclipsing binary. Seven stars show irregular variability. Two of the pulsators, a delta Sct star NGC 6866-29 and a gamma Dor star NGC6866-21, are multiperiodic. From an analysis of proper motions, we conclude that the delta Sct stars, one of the gamma Dor stars and both blue-stragglers are very probable members of the cluster. The position on the color-magnitude diagram of seven other variables suggests that they also belong to the cluster. The eclipsing binary, which we discover to be a new high-velocity star, and the seven irregular variables are non-members. Then, we discuss in detail the age and metallicity of open clusters that host gamma Dor stars and we show that none of these parameters is correlated with the number of gamma Dor stars in cluster.
Results from UBVRI photometric observations of the pre-main sequence star GM Cep obtained in the period April 2011 - August 2014 are reported in the paper. Presented data are a continuation of our photometric monitoring of the star started in 2008. GM Cep is located in the field of the young open cluster Trumpler 37 and over the past years it has been an object of intense photometric and spectral studies. The star shows a strong photometric variability interpreted as a possible outburst from EXor type in previous studies. Our photometric data for a period of over six years show a large amplitude variability (Delta V ~ 2.3 mag.) and several deep minimums in brightness are observed. The analysis of the collected multicolor photometric data shows the typical of UX Ori variables a color reversal during the minimums in brightness. The observed decreases in brightness have a different shape, and evidences of periodicity are not detected. At the same time, high amplitude rapid variations in brightness typical for the classical T Tauri stars also present on the light curve of GM Cep. The spectrum of GM Cep shows the typical of classical T Tauri stars wide H/alpha emission line and absorption lines of some metals. We calculate the outer radius of the H/alpha emitting region as 10.4 +/-0.5 Rsun and the accretion rate as 1.8 x 10 E-7 Msun/yr.
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 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 BVRI photometric data allows to draw a conclusion that all investigated objects are variable stars. In the case of LkHa 146 we identified previously unknown periodicity in its photometric variability.
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 Cep four deep minimums in brightness are observed. The collected multicolour photometric data shows the typical of UXor variables colour reversal during the minimums in brightness. Recent $BVRI$ photometric observations of GM Cep have been collected from November 2014 to October 2020.
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