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TOPIC: GM Cephei

Blobrana

L

Posts: 131433

Date: Feb 27 10:08 2015

2MASS J21381731+5731220	Permalink

Title: The unusual photometric variability of the PMS star GM Cep Author: E. Semkov, S. Ibryamov, S. Peneva, T. Milanov, K. Stoyanov, I. Stateva, D. Kjurkchieva, D. Dimitrov, V. Radeva 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 multicolour photometric data shows the typical of UX Ori variables a colour 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. Read more (792kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Mar 27 00:59 2012

GM Cephei	Permalink

Title: A Possible Detection of Occultation by a Proto-planetary Clump in GM Cephei Authors: The YETI Collaboration: W. P. Chen, S. C.-L. Hu, R. Errmann, Ch. Adam, S. Baar, A. Berndt, L. Bukowiecki, D. P. Dimitrov, T. Eisenbeib, S. Fiedler, Ch. Ginski, C. Gräfe, J. K. Guo, M. M. Hohle, H. Y. Hsiao, R. Janulis, M. Kitze, H. C. Lin, C. S. Lin, G. Maciejewski, C. Marka, L. Marschall, M. Moualla, M. Mugrauer, R. Neuhäuser, T. Pribulla, St. Raetz, T. Röll, E. Schmidt, J. Schmidt, T. O. B. Schmidt, M. Seeliger, L. Trepl, C. Briceño, R. Chini, E. L. N. Jensen, E. H. Nikogossian, A. K. Pandey, J. Sperauskas, H. Takahashi, F. M. Walter, Z.-Y. Wu, X. Zhou GM Cep in the young (~4 Myr) open cluster Trumpler 37 has been known to be an abrupt variable and to have a circumstellar disk with very active accretion. Our monitoring observations in 2009-2011 revealed the star to show sporadic flare events, each with brightening of < 0.5 mag lasting for days. These brightening events, associated with a colour change toward the blue, should originate from an increased accretion activity. Moreover, the star also underwent a brightness drop of ~1 mag lasting for about a month, during which the star became bluer when fainter. Such brightness drops seem to have a recurrence time scale of a year, as evidenced in our data and the photometric behaviour of GM Cep over a century. Between consecutive drops, the star brightened gradually by about 1 mag and became blue at peak luminosity. We propose that the drop is caused by obscuration of the central star by an orbiting dust concentration. The UX Orionis type of activity in GM Cep therefore exemplifies the disk inhomogeneity process in transition between grain coagulation and planetesimal formation in a young circumstellar disk. Read more (67kb, PDF) __________________

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