Rapid variability of the EXor star NY Ori
ATel #8828; D. Lorenzetti (INAF - Osservatorio Astronomico di Roma, Monte Porzio, Italy), A. A.Arkharov, N. Efimova (St. Petersburg Pulkovo Observatory, Russia), T. Giannini, S. Antoniucci, A. Di Paola (INAF - Osservatorio Astronomico di Roma, Monte Porzio, Italy), V. M.Larionov (Astronomical Institute of St. Petersburg University, Russia)
on 16 Mar 2016; 14:22 UT
Credential Certification: Dario Lorenzetti (dloren@mporzio.astro.it)
Subjects: Infra-Red, Variables, Young Stellar Object, Pre-Main-Sequence Star
We report on a rapid brightness variability of the classical EXor star NY Ori observed with the AZT24 1m IR telescope (Campo Imperatore, Italy), as a part of our program EXORCISM (EXOR OptiCal
and Infrared Systematic Monitoring - Antoniucci et al. 2013 PPVI; Lorenzetti et al. 2009 ApJ 693, 1056). Our observations covering a period of more than 4 years (since 2011 Oct. to 2015
Dec.) are summarized in the Table below:
| JD-2400000.5 | J(mag) | H(mag) | K(mag) |
| 55863.6 | 10.69 | 9.43 | 8.50 |
| 55868.6 | 10.84 | 9.46 | 8.50 |
| 55874.6 | 10.46 | 9.23 | 8.33 |
| 55879.6 | 10.27 | 9.11 | 8.17 |
| 55881.5 | 10.26 | 9.29 | 8.10 |
| 55885.5 | 10.59 | 9.33 | 8.39 |
| 56561.5 | 10.42 | 9.28 | 8.41 |
| 56577.5 | 10.59 | 9.12 | 8.21 |
| 56591.5 | 10.06 | 8.97 | 8.09 |
| 56644.4 | 10.71 | 9.37 | 8.41 |
| 56728.3 | 9.38 | 8.80 | 8.13 |
| 56730.3 | 10.81 | 9.47 | 8.48 |
| 56736.3 | 10.66 | 9.45 | 8.50 |
| 56948.6 | 10.75 | 9.41 | 8.34 |
| 56958.6 | 10.46 | 9.20 | 8.28 |
| 56959.6 | 10.39 | 9.13 | 8.23 |
| 56960.6 | 10.48 | 9.24 | 8.28 |
| 56962.6 | 10.17 | 9.04 | 8.16 |
| 56963.6 | 10.45 | 9.24 | 8.32 |
| 56975.5 | 11.03 | 9.58 | 8.51 |
| 57015.5 | 10.05 | 8.99 | 8.14 |
| 57339.5 | 10.01 | 8.96 | 8.20 |
| 57341.5 | 9.86 | 8.87 | 8.14 |
| 57343.5 | 9.64 | 8.64 | 7.91 |
| 57346.6 | 9.95 | 9.23 | 8.16 |
| 57357.5 | 9.88 | 8.74 | 8.14 |
| 57358.5 | 9.96 | 8.35 | 8.22 |
| 57360.5 | 10.08 | 9.00 | 8.21 |
Magnitude errors are less than 0.03 mag. The light-curves are shown in
this figure. To study variations
on a short timescale (days) we list below the differences in
brightness (expressed as ΔJmag) observed for any pair of subsequent dates
spaced by Δt from 1 to 6 days. The fluctuations are significantly larger than the photometric
errors. Remarkable is the fading of about 1.4 mag that occurred within just two days
(between 56728.3 and 56730.3). Similar fluctuations occur at a lesser extent in H, K bands.
| Δt(days) | ΔJ (mag) |
| 1 | +0.07, -0.09, -0.28, -0.08 |
| 2 | +0.01, -1.43, -0.31, +0.015, +0.22, -0.12 |
| 3 | -0.31 |
| 4 | -0.33 |
| 5 | -0.15, +0.19 |
| 6 | +0.38, +0.17, +0.15 |
Given the random cadence of our
observations, we conclude that NY Ori undergoes continuous variations too rapid to be due to disk accretion
events. We do not rule out EXor-type variability on longer timescales, but signal that other phenomena (e.g. hotspots onto the
stellar surface) may have a major impact. Observations of different EXors on a short timescale are encouraged to ascertain whether or not the
NY Ori phenomenology is a typical feature of the entire class.
