3,886 research outputs found
Line Structure in the Spectrum of FU Orionis
New high-resolution spectra of FU Ori, obtained with the HIRES spectrograph
at the Keck I telescope in 2003-2006, make it possible to compare the optical
line profiles with those predicted by the self-luminous accretion disk model. A
dependence of line width on excitation potential and on wavelength, expected
for a Keplerian disk, is definitely not present in the optical region, nor is
the line duplicity due to velocity splitting. The absorption lines observed in
the optical region of FU Ori must originate in or near the central object, and
here their profiles are shown to be those expected of a rigidly rotating
object. They can be fitted by a rapidly rotating (v sin i = 70 km/s)
high-luminosity G-type star having a large dark polar spot, with axis inclined
toward the line of sight. Over these years, the radial velocity of FU Ori has
remained constant to within +/-0.3 km/s, so there is no indication that the
star is a spectroscopic binary. These results apply to the optical region
( \AA); more distant, cooler regions of the disk contribute in
the infrared.Comment: 14 pages, 11 figures, accepted by A
The Unusual Object IC 2144/MWC 778
IC 2144 is a small reflection nebula located in the zone of avoidance near
the Galactic anticenter. It has been investigated here largely on the basis of
Keck/HIRES optical spectroscopy (R ~ 48,000) and a SpeX spectrogram in the
near-IR (R = 2000) obtained at the NASA IRTF. The only star in the nebula that
is obvious in the optical or near-IR is the peculiar emission-line object MWC
778 (V = 12.8), which resembles a T Tauri star in some respects. What appear to
be F- or G-type absorption features are detectable in its optical region under
the very complex emission line spectrum; their radial velocity agrees with the
CO velocity of the larger cloud in which IC 2144 is embedded. There are
significant differences between the spectrum of the brightest area of the
nebula and of MWC 778, the presumed illuminator, an issue discussed in some
detail. The distance of IC 2144 is inferred to be about 1.0 kpc by reference to
other star-forming regions in the vicinity. The extinction is large, as
demonstrated by [Fe II] emission line ratios in the near-IR and by the strength
of the diffuse interstellar band spectrum; a provisional value of A_V of 3.0
mag was assumed. The SED of MWC 778 rises steeply beyond about 1 m, with a
slope characteristic of a Class I source. Integration of the flux distribution
leads to an IR luminosity of about 510 L_solar. If MWC 778 is indeed a F- or
G-type pre--main-sequence star several magnitudes above the ZAMS, a population
of faint emission Halpha stars would be expected in the vicinity. Such a
search, like other investigations that are recommended in this paper, has yet
to be carried out.Comment: 36 pages, 13 figures, accepted by A
The 2008 extreme outburst of the young eruptive variable star Ex Lupi
In early 2008, the young low-mass star EX Lupi, the prototype of the EXor
class of eruptive variables, optically brightened by over five magnitudes for a
period of 7 months. The previous time a change of such amplitude had been
observed in EX Lup was over 50 years ago. In this Letter we present new optical
and near-IR high resolution spectroscopy of EX~Lup during the 2008 outburst. We
investigate the physical characteristics of the outburst both soon after it
began and some four months later, and consider the energetics and kinematics
observed. Emission line strengths, widths, and profiles changed significantly
between the two observations. Also, modeling of the 2.2935 um CO overtone
bandhead emission suggests that an inner gap in the circumstellar gas disk
around the star may be present and it is from the inner edge of the gas disk
that the CO overtone emission probably arises. We derive a mass accretion
luminosity and rate during the extreme outburst of ~2+-0.5~Lsun and
~2+-0.5x10^-7 Msun yr^-1, respectively, which suggests that this outburst was
indeed one of the strongest witnessed in EX Lup, yet not as strong as those
observed in FU Orionis stars.Comment: 5 pages, 4 figure
Review of cometary spectra
The spectra of comet Kohoutek, comet Bradfield, and comet Mrkos are reviewed and compared in relation to stellar spectroscopy and evolution. The possibility of observing the absorption spectrum of a comet and direct measurement of Doppler shifts due to expansion or streaming motions in comets are considered along with the spectra of giant comets, such as, comet Minkowski, comet Baade, and comet Lovas. A speculative explanation for possible intrinsic abundance differences between comets is given
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&
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