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A sudden brightness decrease of the young pre-MS object GM Cep

ATel #11004; U. Munari (INAF - Osservatorio Astronomico di Padova, Italy), F. Castellani (ANS Collaboration, Italy), T. Giannini, S. Antoniucci, D. Lorenzetti (INAF - Osservatorio Astronomico di Roma, Monte Porzio, Italy)
on 24 Nov 2017; 14:38 UT
Credential Certification: Simone Antoniucci (antoniucci@oa-roma.inaf.it)

Subjects: Optical, Variables, Young Stellar Object, Pre-Main-Sequence Star

In the framework of our EXor monitoring programme dubbed EXORCISM (EXOR OptiCal and Infrared Systematic Monitoring - Antoniucci et al. 2013 PPVI, Lorenzetti et al. 2007 ApJ 665, 1182; Lorenzetti et al. 2009 ApJ 693, 1056), we observed a new fading of the optical brightness of the Young Stellar Object (YSO) GM Cep (d=870 pc). This is a well studied variable (Semkov & Peneva 2012 APSS,338,95; Ibryamov et al. 2015 PASA,32,11; Xiao, Kroll, & Henden 2010 AJ, 139, 1527; Sicilia-Aguilar et al. 2008 ApJ,673,382-3) whose light-curve is dominated by recurrent brightness dims, interpreted as non-periodical eclipse events due to orbiting dust structures that move along the line of sight (UXor-type variability - Grinin 1988). Our photometry has been obtained on Nov 23.81 (UT) with the ANS Collaboration 40cm telescope ID-66 and provides V=14.91, B-V=1.31, V-R=0.92, V-I=1.95 (errors about ± 0.01). The estimated drop in the V-band is of about 2 mag. Our photometric colors are in agreement with those provided by Semkov & Peneva (2012), confirming the blueing effect typical of the UXor variables at low luminosity levels. A (quasi-)simultaneous flux-calibrated low-res spectrum (3500-8000 Å, 2.31 Å/pix) has been also collected on Nov. 23.71 (UT) with the Asiago 1.22m + B&C spectrograph (depicted in this figure). The Hα integrated flux is 8.9 ± 0.1 10-14 erg/cm2/s, the Hβ emission component fills the absorption one, while Hγ e Hδ are in absorption, as well as CaII and BaII. LiI detection is within 1σ noise. Unfortunately, GM Cep is embedded within a strong nebulosity that causes an intense background. Remarkably, our spectrum is the first one obtained during a deep brightness minimum, therefore it can be adopted as a solid reference for establishing future variations.