394 research outputs found
A close view on the protoplanetary disk in the Bok globule CB26
We present new sub-arcsecond-resolution near-infrared polarimetric imaging
and millimetre interferometry data on the circumstellar disk system in the Bok
globule CB26. The data imply the presence of a M > 0.01 M_sun edge-on disk of
>400 AU in diameter, being in Keplerian rotation around a young ~0.35 M_sun
star. The mm dust emission from the inner 200 AU is highly optically thick, but
the outer parts are optically thin and made of small dust grains. Planetesimal
growth in the inner disk could neither be comfirmed nor excluded. The outer
optically thin part of the disk is strongly warped. We argue that the CB 26
disk is a very young protoplanetary disk and show that it is comparable to the
early solar system.Comment: Conference proceeding "Origins of stars and planets: The VLT view",
ESO, Garching, April 24-27 200
Molecular Hydrogen in the Lagoon: H2 line emission from Messier 8
The 2.12 micron v=1-0 S(1) line of molecular hydrogen has been imaged in the
Hourglass region of M8. The line is emitted from a roughly bipolar region,
centred around the O7 star Herschel 36. The peak H2 1-0 S(1) line intensity is
8.2 x 10E-15 erg s-1 cm-2 arcsec-2. The line centre emission velocity varies
from -25 kms in the SE lobe to +45 kms in the NW lobe. The distribution is
similar to that of the CO J=3-2 line. The H2 line appears to be shock-excited
when a bipolar outflow from Herschel 36 interacts with the ambient molecular
cloud. The total luminosity of all H2 lines is estimated to be ~ 16 Lsun and
the mass of the hot molecular gas ~9 x 10E-4 Msun (without any correction for
extinction).Comment: 11 pages, 4 figures (1 in colour). Submitted to Publications of the
Astronomical Society of Australia, December 200
Detection of an optical filament in the Monogem Ring
The Monogem Ring is a huge bright soft X-ray enhancement with a diameter of ~
25\degr. This 0.3 kpc distant structure is a peculiar Galactic supernova
remnant in that it is obviously visible only in X-rays, due to its expansion
into a region of extremely low ambient density: hence, practically no optical
emission or a neutral HI shell was expected to be detectable. - Here we report
on the discovery of a very faint arc-like nebula on a POSS II R film copy, at
the south-eastern borders of the MR. Spectroscopy revealed this filament to
have a very large [SII] 6716+6731/Halpha ratio of up to ~ 1.8,
indicating shock excitation, and a low density of N_e <100 cm^{-3}. There is no
hint of [OIII] emission in the spectra. On deep wide-field direct images in
Halpha and in [SII] the nebula appears as a ~ 20 arcmin long, thin (~ 1
arcmin), structured filament, stretching N-S. We believe that this filament
belongs to the MR and became visible due to the interaction of the expanding
remnant with a mild density increase in the interstellar medium. Only one other
possible optical filament of the MR has been reported in the literature, but no
spectrum was provided.Comment: 6 pages, 4 figures, of which 2 in jpeg format and degraded because of
size constraints. Accepted for publication in A&
The power of low-resolution spectroscopy: On the spectral classification of planet candidates in the ground-based CoRoT follow-up
Planetary transits detected by the CoRoT mission can be mimicked by a
low-mass star in orbit around a giant star. Spectral classification helps to
identify the giant stars and also early-type stars which are often excluded
from further follow-up.
We study the potential and the limitations of low-resolution spectroscopy to
improve the photometric spectral types of CoRoT candidates. In particular, we
want to study the influence of the signal-to-noise ratio (SNR) of the target
spectrum in a quantitative way. We built an own template library and
investigate whether a template library from the literature is able to reproduce
the classifications. Including previous photometric estimates, we show how the
additional spectroscopic information improves the constraints on spectral type.
Low-resolution spectroscopy (1000) of 42 CoRoT targets covering a
wide range in SNR (1-437) and of 149 templates was obtained in 2012-2013 with
the Nasmyth spectrograph at the Tautenburg 2m telescope. Spectral types have
been derived automatically by comparing with the observed template spectra. The
classification has been repeated with the external CFLIB library.
The spectral class obtained with the external library agrees within a few
sub-classes when the target spectrum has a SNR of about 100 at least. While the
photometric spectral type can deviate by an entire spectral class, the
photometric luminosity classification is as close as a spectroscopic
classification with the external library. A low SNR of the target spectrum
limits the attainable accuracy of classification more strongly than the use of
external templates or photometry. Furthermore we found that low-resolution
reconnaissance spectroscopy ensures that good planet candidates are kept that
would otherwise be discarded based on photometric spectral type alone.Comment: accepted for publication in Astronomische Nachrichten; 12 pages, 4
figures, 7 table
Near-infrared polarimetric observations of the afterglow of GRB 000301C
Based on near-infrared polarimetric observations we constrain the degree of
linear polarization of the afterglow light of GRB 000301C to less than 30% 1.8
days after the burst.Comment: To appear in: Proc. 20th Texas Symposium on Relativistic
Astrophysics, eds. J. C. Wheeler and H. Marte
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