1,228 research outputs found
A Study Of The White HeartâRot Of Locust, Caused By Trametes Robiniophila
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141421/1/ajb205691.pd
Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
Context: Absorption by molecules in the Earth's atmosphere strongly affects
ground-based astronomical observations. The resulting absorption line strength
and shape depend on the highly variable physical state of the atmosphere, i.e.
pressure, temperature, and mixing ratio of the different molecules involved.
Usually, supplementary observations of so-called telluric standard stars (TSS)
are needed to correct for this effect, which is expensive in terms of telescope
time. We have developed the software package molecfit to provide synthetic
transmission spectra based on parameters obtained by fitting narrow ranges of
the observed spectra of scientific objects. These spectra are calculated by
means of the radiative transfer code LBLRTM and an atmospheric model. In this
way, the telluric absorption correction for suitable objects can be performed
without any additional calibration observations of TSS. Aims: We evaluate the
quality of the telluric absorption correction using molecfit with a set of
archival ESO-VLT X-Shooter visible and near-infrared spectra. Methods: Thanks
to the wavelength coverage from the U to the K band, X-Shooter is well suited
to investigate the quality of the telluric absorption correction with respect
to the observing conditions, the instrumental set-up, input parameters of the
code, the signal-to-noise of the input spectrum, and the atmospheric profiles.
These investigations are based on two figures of merit, I_off and I_res, that
describe the systematic offsets and the remaining small-scale residuals of the
corrections. We also compare the quality of the telluric absorption correction
achieved with moelcfit to the classical method based on a telluric standard
star. (Abridged)Comment: Acc. by A&A; Software available via ESO:
http://www.eso.org/sci/software/pipelines/skytools
Improved orbital solution and masses for the very low-mass multiple system LHS 1070
We present a refined orbital solution for the components A, B, and C of the
nearby late-M type multiple system LHS 1070. By combining astrometric
datapoints from NACO/VLT, CIAO/SUBARU, and PUEO/CFHT, as well as a radial
velocity measurement from the newly commissioned near infrared high-resolution
spectrograph CRIRES/VLT, we achieve a very precise orbital solution for the B
and C components and a first realistic constraint on the much longer orbit of
the A-BC system. Both orbits appear to be co-planar. Masses for the B and C
components calculated from the new orbital solution (M_(B+C) = 0.157 +/- 0.009
M_sun) are in excellent agreement with theoretical models, but do not match
empirical mass-luminosity tracks. The preliminary orbit of the A-BC system
reveals no mass excess for the A component, giving no indication for a
previously proposed fourth (D) component in LHS 1070.Comment: published in A&A, 2008, 484, 429; added CFHT acknowledgemen
A New Ultra-dense Group of Obscured Emission-Line Galaxies
We present the discovery of an isolated compact group of galaxies that is
extremely dense (median projected galaxy separation: 6.9 kpc), has a very low
velocity dispersion ( = 67 km s), and where all
observed members show emission lines and are morphologically disturbed. These
properties, together with the lack of spirals and the presence of a prominent
tidal tail make this group one of the most evolved compact groups.Comment: 15 pages,LaTeX, 2figures. A Postscript figure with spectra is
available at ftp://astro.uibk.ac.at/pub/weinberger/ . Accepted for
publication in ApJ Letter
Symmetry Detection in Large Scale City Scans
In this report we present a novel method for detecting partial symmetries in very large point clouds of 3D city scans. Unlike previous work, which was limited to data sets of a few hundred megabytes maximum, our method scales to very large scenes. We map the detection problem to a nearestneighbor search in a low-dimensional feature space, followed by a cascade of tests for geometric clustering of potential matches. Our algorithm robustly handles noisy real-world scanner data, obtaining a recognition performance comparable to state-of-the-art methods. In practice, it scales linearly with the scene size and achieves a high absolute throughput, processing half a terabyte of raw scanner data over night on a dual socket commodity PC
Candidate Tidal Dwarf Galaxies in the Compact Group CG J1720-67.8
This is the second part of a detailed study of the ultracompact group CG
J1720-67.8: in the first part we have focused the attention on the three main
galaxies of the group and we have identified a number of candidate tidal dwarf
galaxies (TDGs). Here we concentrate on these candidate TDGs. Absolute
photometry of these objects in BVRJHKs bands confirms their relatively blue
colors, as we already expected from the inspection of optical and near-infrared
color maps and from the presence of emission-lines in the optical spectra. The
physical conditions in such candidate TDGs are investigated through the
application of photoionization models, while the optical colors are compared
with grids of spectrophotometric evolutionary synthesis models from the
literature. Although from our data self-gravitation cannot be proved for these
objects, their general properties are consistent with those of other TDG
candidates. Additionally we present the photometry of a few ``knots'' detected
in the immediate surroundings of CG J1720-67.8 and consider the possibility
that these objects might belong to a dwarf population associated with the
compact group.Comment: Accepted for publication in the Astrophysical Journa
V605 Aql: The Older Twin of Sakurai's Object
New optical spectra have been obtained with VLT/FORS2 of the final helium
shell flash (FF) star, V605 Aql, which peaked in brightness in 1919. New models
suggest that this star is experiencing a very late thermal pulse. The evolution
to a cool luminous giant and then back to a compact hot star takes place in
only a few years. V605 Aql, the central star of the Planetary Nebula (PN), A58,
has evolved from T5000 K in 1921 to 95,000 K today. There are
indications that the new FF star, Sakurai's Object (V4334 Sgr), which appeared
in 1996, is evolving along a similar path. The abundances of Sakurai's Object
today and V605 Aql 80 years ago mimic the hydrogen deficient R Coronae Borealis
(RCB) stars with 98% He and 1% C. The new spectra show that V605 Aql has
stellar abundances similar to those seen in Wolf-Rayet [WC] central stars of
PNe with ~55% He, and ~40% C. The stellar spectrum of V605 Aql can be seen even
though the star is not directly detected. Therefore, we may be seeing the
spectrum in light scattered around the edge of a thick torus of dust seen
edge-on. In the present state of evolution of V605 Aql, we may be seeing the
not too distant future of Sakurai's Object.Comment: 12 pages, 1 figure, ApJ Letters in pres
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