Continuous brightening of the eruptive variable V2493 Cyg (HBC 722)
ATel #5023; S. Antoniucci (INAF-Osservatorio Astronomico di Roma, Monte Porzio, Italy), A. Arkharov, S. Klimanov (Pulkovo Observatory, St. Petersburg Russia), D. Lorenzetti, T. Giannini, A. Di Paola (INAF-Osservatorio Astronomico di Roma, Monte Porzio, Italy), V. Larionov (Astronomical Institute of St. Petersburg University, Russia; Pulkovo Observatory, Russia)
on 27 Apr 2013; 18:44 UT
Credential Certification: Simone Antoniucci (antoniucci@oa-roma.inaf.it)
Subjects: Infra-Red, Variables, Young Stellar Object, Pre-Main-Sequence Star
As anticipated (Lorenzetti et al. 2009 ApJ 693, 1056), we are constantly monitoring the eruptive variable V2493 Cyg (otherwise called HBC 722) in the near-IR with the AZT24 1m-telescope (Campo Imperatore, Italy).
Since its outburst in Aug. 2009 (Miller et al. 2011 ApJ 730, 80; ATel #2801, ATel #2854) this source has been widely monitored (Kospal et al. 2011 A&A 527, A133, Lorenzetti et al. 2012 ApJ 749, 188; Semkov et al. 2012 A&A 542, 43) both in the optical and near-IR bands. After the outburst (of about 4 mag in V), the object showed a slow decline of 1.5 mag starting from Oct. 2010 (ATel #3165), with small brightness fluctuations around this level. In Oct. 2011 another increase of luminosity was observed and the source reached the same brightness level as that of the initial outburst (ATel #4123).
Now we report a further near-IR brightening of about 1 mag above the original outburst level. In particular, (since Oct. 2011) we have been observing a constant increase of brightness, which is summarized in the Table below:
| MJD | J | H | K |
| 55808 | 10.67 | 9.61 | 9.02 |
| 55863 | 10.30 | 9.34 | 8.85 |
| 55864 | 10.33 | 9.35 | 8.83 |
| 55868 | 10.29 | 9.33 | 8.85 |
| 55875 | 10.29 | 9.29 | 8.81 |
| 55878 | 10.30 | 9.34 | 8.81 |
| 55882 | 10.27 | 9.31 | 8.81 |
| 55886 | 10.24 | 9.27 | 8.81 |
| 56044 | 9.88 | 8.93 | 8.44 |
| 56049 | 9.85 | 8.89 | 8.39 |
| 56056 | 9.80 | 8.84 | 8.40 |
| 56390 | 9.31 | 8.37 | 7.90 |
| 56396 | 9.30 | 8.35 | 7.85 |
Typical errors of the reported near-IR magnitudes are less than 0.04 mag.
As expected (Lorenzetti et al. 2012), the source is becoming bluer while brightening (ΔJ = 1.37, ΔH = 1.26, ΔK = 1.17). After the main outburst, some controversy arose about the proper classification of this source as a FUor object, characterized by accretion bursts of long duration (> tens of years), or as an EXor, displaying accretion events lasting one year or less with a recurrent time of months to years. The presented data indicate a steady, roughly linear (in magnitude) increase of brightness, whose relatively slow rate of about -0.07 mag/month in J (with no sign of an imminent return to a quiescent state) seems more compatible with the FUor hypothesis.
