1,111 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
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 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 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&
Profiles of Strong Permitted Lines in Classical T Tauri Stars
We present a spectral analysis of 30 T Tauri stars observed with the Hamilton
echelle spectrograph over more than a decade. One goal is to test
magnetospheric accretion model predictions. Observational evidence previously
published supporting the model, such as emission line asymmetry and a high
frequency of redshifted absorption components, are considered. We also discuss
the relation between different line forming regions and search for good
accretion rate indicators.
In this work we confirm several important points of the models, such as the
correlation between accretion and outflow, broad emission components that are
mostly central or slightly blueshifted and only the occasional presence of
redshifted absorption. We also show, however, that the broad emission
components supposedly formed in the magnetospheric accretion flow only
partially support the models. Unlike the predictions, they are sometimes
redshifted, and are mostly found to be symmetric. The published theoretical
profiles do not have a strong resemblance to our observed ones. We emphasize
the need for accretion models to include a strong turbulent component before
their profiles will match the observations. The effects of rotation, and the
outflow components, will also be needed to complete the picture.Comment: 25 pages including 9 figures, 3 tables, accepted for publication in
the Astronomical Journa
Efficient creation of molecules from a cesium Bose-Einstein condensate
We report a new scheme to create weakly bound Cs molecules from an atomic
Bose-Einstein condensate. The method is based on switching the magnetic field
to a narrow Feshbach resonance and yields a high atom-molecule conversion
efficiency of more than 30%, a factor of three higher than obtained with
conventional magnetic-field ramps. The Cs molecules are created in a single
-wave rotational quantum state. The observed dependence of the conversion
efficiency on the magnetic field and atom density shows scattering processes
beyond two-body coupling to occur in the vicinity of the Feshbach resonance.Comment: 7 pages, 4 figures, submitted to Europhysics Letter
IRAS 05436-0007 and the Emergence of McNeil's Nebula
We present a study of McNeil's Nebula, a newly appeared reflection nebula in
the L1630 cloud, together with photometry and spectroscopy of its source. New
IR photometry compared to earlier 2MASS data shows that the star has brightened
by about 3 magnitudes in the near-infrared, changing its location in a J-H/H-K
diagram precisely along a reddening vector. A Gemini NIRI K-band spectrum shows
strong CO-bandhead emission and Br-gamma is in emission, indicative of strong
accretion. A Gemini GMOS optical spectrum shows only a red, heavily veiled
continuum, with H-alpha strongly in emission and displaying a pronounced P
Cygni profile, with an absorption trough reaching velocities up to 600 km s-1.
This implies significant mass loss in a powerful wind. However, no evidence is
found for any shocks, as commonly seen in collimated outflows from young stars.
Apparently the eruption has dispersed a layer of extinction and this, together
with the intrinsic brightening of the IRAS source, has allowed an earlier
outflow cavity to be flooded with light, thus creating McNeil's Nebula.Comment: 9 pages, 5 figure
Radio Spectra and NVSS Maps of Decametric Sources
We constructed radio spectra for ~1400 UTR-2 sources and find that 46% of
them have concave curvature. Inspection of NVSS maps of 700 UTR sources
suggests that half of all UTR sources are either blends of two or more sources
or have an ultra-steep spectrum (USS). The fraction of compact USS sources in
UTR may be near 10%. Using NVSS and the Digitized Sky Survey(s) we expect to
double the UTR optical identification rate from currently ~19%.Comment: 2 pages, no figures; to appear in Proc. "Observational Cosmology with
the New Radio Surveys", eds. M. Bremer, N. Jackson & I. Perez-Fournon, Kluwer
Acad. Pres
Observation of Feshbach-like resonances in collisions between ultracold molecules
We observe magnetically tuned collision resonances for ultracold Cs2
molecules stored in a CO2-laser trap. By magnetically levitating the molecules
against gravity, we precisely measure their magnetic moment. We find an avoided
level crossing which allows us to transfer the molecules into another state. In
the new state, two Feshbach-like collision resonances show up as strong
inelastic loss features. We interpret these resonances as being induced by Cs4
bound states near the molecular scattering continuum. The tunability of the
interactions between molecules opens up novel applications such as controlled
chemical reactions and synthesis of ultracold complex molecules
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