Publications of the MPIfR
Optical & Infrared
Interferometry Group
Malbet, F.; Lachaume, R.; Berger,
J.-P.; Colavita, M.; Di Folco, E.; Eisner, J.; Millan-Gabet, R.;
Ségransan, D.; Traub, W.
New insights on the AU-scale circumstellar
structure of FU Orionis
Astronomy and Astrophysics, v.437, p.627-636 (2005)
Abstract
We report new near-infrared, long-baseline interferometric observations
at
the AU scale of the pre-main-sequence star FU Orionis with the PTI,
IOTA and
VLTI interferometers. This young stellar object has been observed on 42
nights
over a period of 6 years from 1998 to 2003. We have obtained 287
independent
measurements of the fringe visibility with 6 different baselines
ranging from
20 to 110 meters in length, in the H and K bands. Our extensive
(u,v)-plane
coverage, coupled with the published spectral energy distribution data,
allows
us to test the accretion disk scenario. We find that the most probable
explanation for these observations is that FU Ori hosts an active
accretion
disk whose temperature law is consistent with standard models. We are
able to
constrain the geometry of the disk, including an inclination of 55 deg
and a
position angle of 47 deg. In addition, a 10 percent peak-to-peak
oscillation is
detected in the data (at the two-sigma level) from the longest
baselines, which
we interpret as a possible disk hot-spot or companion. However, the
oscillation
in our best data set is best explained with an unresolved spot located
at a
projected distance of 10 AU at the 130 deg position angle and with a
magnitude
difference of DeltaK = 3.9 and DeltaH = 3.6 mag moving away from the
center at
a rate of 1.2 AU/yr. we propose to interpret this spot as the signature
of a
companion of the central FU Ori system on an extremely eccentric orbit.
We
speculate that the close encounter of this putative companion and the
central
star could be the explanation of the initial photometric rise of the
luminosity
of this object.
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