Gaia16aye: a flaring object of uncertain nature in Cygnus
ATel #9376; V. Bakis (Akdeniz Univ.), U. Burgaz (Ege Univ.), T. Butterley (Durham Univ.), J. M. Carrasco (Institut de Ciencies del Cosmos-Univ. of Barcelona), V. S. Dhillon (Univ. of Sheffield), M. Dominik (Univ. St Andrews), A. Floers (INAF OAPd), L. K. Hardy (Univ. of Sheffield), G. Leto (INAF OACT), S. P. Littlefair (Univ. of Sheffield), J. R. Maund (Univ. of Sheffield), P. Ochner (INAF OAPd), A. Pastorello (INAF OAPd), A. Piascik (Liverpool JMU), L. Rhodes (Univ. of Sheffield), R. Z. Sanchez (INAF OACT), K. V. Sokolovsky (IAASARS NOA/SAI/ASC Lebedev), I. Steele (Liverpool JMU), S. Taubenberger (ESO), G. Terreran (INAF OAPd), L. Tomasella (INAF OAPd), R. W. Wilson (Durham Univ.), L. Wyrzykowski (Warsaw Univ. Astronomical Obs.), A. M. Zubareva (INASAN/SAI)
on 15 Aug 2016; 20:40 UT
Credential Certification: Kirill Sokolovsky (firstname.lastname@example.org)
Subjects: Optical, Microlensing Event, Star, Transient, Variables
A Gaia science alert was triggered on 2016-08-05 when the object
Gaia16aye (19:40:01.13 +30:07:53.4, J2000) was found 1.2m brighter
than during previous Gaia observations (the latest of which was
conducted on 2016-06-20). The previous 22 Gaia detections of the
source (starting from 2014-10-30) show no variability greater
than 0.05m RMS.
Follow-up ground-based observations started on 2016-08-09 reveal
a red source (V=14.9, B-V=1.6) gradually brightening at a rate of
about 0.1m/day without changing its color and showing no fast
variability (apart from the long-term brightening trend).
The observations obtained on 2016-08-13 show the object reached
V=13.8 (B-V=1.6) and its brightening rate increased to 0.6m/day.
The photometric measurements were conducted with the 0.6m telescope
of the SAI Southern Station in Crimea, the pt5m telescope at
the Roque de los Muchachos observatory on La Palma (Hardy et al.
2015, MNRAS, 454, 4316), the 0.8m telescopi Joan Oro at
l'Observatori Astronomic del Montsec, the 0.6m Akdeniz Univ. UBT60
in the TUBITAK National Observatory, Antalya, and the 0.8m
telescope at Serra La Nave. The combined lightcurve can
be found at
The spectra of Gaia16aye obtained with the 1.22m Asiago telescope
on 2016-08-11 and the 2.0m Liverpool Telescope (La Palma) on
2016-08-12 are consistent with a normal K8-M2 type star.
No emission lines are detected. Inspection of 159 unfiltered images
of the NMW nova patrol archive
obtained in 2011-2013 indicates that the object was always fainter
than a nearby V=14.2 star.
The physical nature of the flare remains uncertain. The lightcurve
shape showing an isolated brightening event is unusual for red
irregular variables which typically have lightcurves showing
a series of waves of changing amplitudes. The possibilities of
a FUor/EXor young stellar object flare or a cataclysmic variable
are not supported by the absence of emission lines in the spectrum.
An absence of emission lines would be consistent with an FU Ori
event if the absorption lines were broad and correspond to a higher
temperature, which is not observed. Many cataclysmic variables show
strong Balmer absorption lines during outburst while others show
emission - the effect may be inclination dependent. Strong Balmer
absorption is not observed in Gaia16aye: EW(Halpha) ~ 1.1+/-0.1 A.
A bright microlensing event like the one discovered by A. Tago on
October 31, 2006 (CBET #711, #718; Fukui et al. 2007, ApJ, 670,
423; Gaudi et al., 2008, ApJ, 677, 1268) is not excluded, but
a well-sampled long-term lightcurve is needed to test this
possibility. If the star is a nearby red dwarf rather than
a distant giant, the probability of a microlensing event would be
low. We encourage further observations to determine a nature of
this flaring object. Archival information about (non-)variability
and spectra of this object in the past would be also very valuable.
The photometric calibrations for the pt5m, Joan Oro, and UBT60
observations were obtained using the Cambridge Photometric
designed and maintained by Sergey Koposov and Lukasz Wyrzykowski.
We acknowledge ESA Gaia, DPAC and the
Photometric Science Alerts Team.
Gaia16aye science alert page