1,690 research outputs found
The large amplitude outburst of the young star HBC 722 in NGC 7000/IC 5070, a new FU Orionis candidate
We report the discovery of a large amplitude outburst from the young star HBC
722 (LkHA 188 G4) located in the region of NGC 7000/IC 5070. On the basis of
photometric and spectroscopic observations, we argue that this outburst is of
the FU Orionis type. We gathered photometric and spectroscopic observations of
the object both in the pre-outburst state and during a phase of increase in its
brightness. The photometric BVRI data (Johnson-Cousins system) that we present
were collected from April 2009 to September 2010. To facilitate transformation
from instrumental measurements to the standard system, fifteen comparison stars
in the field of HBC 722 were calibrated in the BVRI bands. Optical spectra of
HBC 722 were obtained with the 1.3-m telescope of Skinakas Observatory (Crete,
Greece) and the 0.6-m telescope of Schiaparelli Observatory in Varese (Italy).
The pre-outburst photometric and spectroscopic observations of HBC 722 show
both low amplitude photometric variations and an emission-line spectrum typical
of T Tau stars. The observed outburst started before May 2010 and reached its
maximum brightness in September 2010, with a recorded Delta V~4.7 mag.
amplitude. Simultaneously with the increase in brightness the color indices
changed significantly and the star became appreciably bluer. The light curve of
HBC 722 during the period of rise in brightness is similar to the light curves
of the classical FUors - FU Ori and V1057 Cyg. The spectral observations during
the time of increase in brightness showed significant changes in both the
profiles and intensity of the spectral lines. Only H alpha remained in
emission, while the H beta, Na I 5890/5896, Mg I triplet 5174, and Ba II
5854/6497 lines were in strong absorption.Comment: 4 pages, 6 figures, accepted for publication in A&
Optical spectroscopy of EX Lupi during quiescence and outburst: Infall, wind, and dynamics in the accretion flow
We explore the accretion mechanisms in EX Lupi, prototype of EXor variables,
during its quiescence and outburst phases. We analyse high-resolution optical
spectra taken before, during, and after its 2008 outburst. In quiescence and
outburst, the star presents many permitted emission lines, including typical
CTTS lines and numerous neutral and ionized metallic lines. During the
outburst, the number of emission lines increases to over a thousand, with
narrow plus broad component structure (NC+BC). The BC profile is highly
variable on short timescales (24-72h). An active chromosphere can explain the
metallic lines in quiescence and the outburst NC. The dynamics of the BC line
profiles suggest an origin in a hot, dense, non-axisymmetric, and non-uniform
accretion column that suffers velocity variations along the line-of-sight on
timescales of days. Assuming Keplerian rotation, the emitting region would be
located at ~0.1-0.2 AU, consistent with the inner disk rim, but the velocity
profiles of the lines reveal a combination of rotation and infall. Line ratios
of ions and neutrals can be reproduced with a temperature of T~6500 K for
electron densities of a few times 10cm in the line-emitting
region. The data confirm that the 2008 outburst was an episode of increased
accretion, albeit much stronger than previous EX Lupi and typical EXors
outbursts. The line profiles are consistent with the infall/rotation of a
non-axisymmetric structure that could be produced by clumpy accretion during
the outburst phase. A strong inner disk wind appears in the epochs of higher
accretion. The rapid recovery of the system after the outburst and the
similarity between the pre-outburst and post-outburst states suggest that the
accretion channels are similar during the whole period, and only the accretion
rate varies, providing a superb environment for studying the accretion
processes.Comment: 15 pages plus 26 pages online material, accepted by A&
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