Publications (2)0 Total impact
ABSTRACT: Context. V2492 Cyg is a young eruptive star that went into outburst in 2010.
The near-infrared color changes observed since the outburst peak suggest that
the source belongs to a newly defined sub-class of young eruptive stars, where
time-dependent accretion and variable line-of-sight extinction play a combined
role in the flux changes.
Aims. In order to learn about the origin of the light variations and to
explore the circumstellar and interstellar environment of V2492 Cyg, we
monitored the source at ten different wavelengths, between 0.55 \mu m and 2.2
\mu m from the ground and between 3.6 \mu m and 160 \mu m from space.
Methods. We analyze the light curves and study the color-color diagrams via
comparison with the standard reddening path. We examine the structure of the
molecular cloud hosting V2492 Cyg by computing temperature and optical depth
maps from the far-infrared data.
Results. We find that the shapes of the light curves at different wavelengths
are strictly self-similar and that the observed variability is related to a
single physical process, most likely variable extinction. We suggest that the
central source is episodically occulted by a dense dust cloud in the inner
disk, and, based on the invariability of the far-infrared fluxes, we propose
that it is a long-lived rather than a transient structure. In some respects,
V2492 Cyg can be regarded as a young, embedded analog of UX Orionis-type stars.
Conclusions. The example of V2492 Cyg demonstrates that the light variations
of young eruptive stars are not exclusively related to changing accretion. The
variability provided information on an azimuthally asymmetric structural
element in the inner disk. Such an asymmetric density distribution in the
terrestrial zone may also have consequences for the initial conditions of
ABSTRACT: Context. In August 2010, the sudden optical brightening of two young stellar
objects, located in the North America/Pelican Nebula Complex, was announced.
Early observations indicated that these objects may belong to the FUor or EXor
class of young eruptive stars. The eruptions of FUors and EXors are often
explained by enhanced accretion of material from the circumstellar disk to the
protostar. Aims. In order to determine the true nature of these two objects, we
started an optical and near-infrared monitoring program, and complemented our
data with archival observations and data from the literature. Methods. We plot
and analyze pre-outburst and outburst spectral energy distributions (SEDs),
multi-filter light curves, and color-color diagrams. Results. HBC 722
brightened monotonically in about two months, and the SED obtained during
maximum brightness indicates the appearance of a hot, single-temperature
blackbody. The current fading rate implies that the star will return to
quiescence in about a year, questioning its classification as a bone fide FUor.
The outburst of VSX J205126.1+440523 happened more gradually, but reached an
unprecedentedly high amplitude. At 2.5 months after the peak, its light curves
show a deep minimum, when the object was close to its pre-outburst optical
brightness. Further monitoring indicates that it is still far from being
quiescent. Conclusions. The shape of the light curves, the bolometric
luminosities and accretion rates suggest that these objects do not fit into the
classic FUor group. Although HBC 722 exhibit all spectral characteristics of a
bona fide FUor, its luminosity and accretion rate is too low, and its timescale
is too fast compared to classical FUors. VSX J205126.1+440523 seems to be an
example where quick extinction changes modulate the light curve.