Optical and near-IR photometry indicate that HBC722 is now fading
ATel #3165; D. Lorenzetti (INAF - Osservatorio Astronomico di Roma, Monte Porzio, Italy), A. A.Arkharov (Central Astronomical Observatory of Pulkovo, Russia), E. N.Kopatskaya, V. M.Larionov (Astronomical Institute of St. Petersburg University, Russia), T. Giannini (INAF - Osservatorio Astronomico di Roma, Monte Porzio, Italy)
on 14 Feb 2011; 10:38 UT
Credential Certification: Dario Lorenzetti (dloren@mporzio.astro.it)
Subjects: Infra-Red, Optical, Star, Variables
As a target of a monitoring program of EXor variables, we are observing the pre-Main Sequence star HBC722 in NGC 7000/IC 5070 (see also ATel#2854). A large amplitude (> 3 mag) outburst of this object has recently provoked a considerable observational interest (Miller et al. 2010 arXiv:1011.2063v1; Semkov et al. 2010 arXiv:1011.1647v1). Both papers refer to HBC722 as a FUOri candidate mainly because of the presence of absorption lines in its optical and near-IR spectrum. Remarkably, one of the most typical features of this class with respect to the EXor variables is the long lasting (many years) post-outburst brightness instead of the occurrence of repetitive outbursts each followed by a relatively rapid (months) decling phase toward the pre-outburst quiescent status.
We observed HBC722 in different occasions (between September 2010 and January 2011). Visual (R band) photometry was obtained at the LX-200 16" telescope from St.Petersburg (Russia), while near-IR data (JHK bands) are from 1m AZT-24 telescope of Campo Imperatore (Italy). The following magnitudes were obtained (typical errors are less than 0.02 mag):
| JD-2400000 | R | J | H | K |
|---|
| 55440.49 | | 10.06 | 9.17 | 8.68 |
| 55440.30 | 12.88 | | | |
| 55500.28 | | 10.19 | 9.23 | 8.71 |
| 55504.30 | | 10.20 | 9.26 | 8.75 |
| 55506.24 | | 10.20 | 9.25 | 8.70 |
| 55507.25 | | 10.20 | 9.26 | 8.68 |
| 55513.29 | | 10.27 | 9.33 | 8.76 |
| 55514.24 | | 10.28 | 9.32 | 8.75 |
| 55515.26 | | 10.25 | 9.31 | 8.76 |
| 55516.28 | | 10.30 | 9.34 | 8.85 |
| 55561.12 | 13.44 | | | |
| 55577.25 | 13.66 | | | |
| 55588.22 | 13.73 | | | |
Our data indicate that the source is steadily declining, thus the possibility of a FUOri event should be reconsidered maybe in favour of an EXor one. Actually, this source is a well known candidate to undergo intermittent accretion (EXor) events. Indeed, Cohen & Kuhi (1979 ApJS 41, 743) provided the following magnitudes H = 11.12 +/- 0.04, K = 10.26 +/- 0.03, while about 20yrs later 2MASS gave H = 12.21 +/- 0.04, K = 11.46 +/- 0.04, pointing out a significant variability (more than 1 mag) as a common and repetitive feature of HBC722.
