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 (email@example.com)
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.