1,854 research outputs found
Chandra Spectroscopy Of The Hot Star β Crucis And The Discovery Of A Pre-Main-Sequence Companion
In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, beta Crucis (beta Cru; B0.5 III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half widths of 150 km s(-1). The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channelling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (h nu \u3e 1 keV) X-rays, modulated on the known optical period of 4.58 h, which is the period of the primary beta Cephei pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion\u27s X-ray spectrum is relatively hard and variable, as would be expected from a post-T Tauri star. The age of the beta Cru system (between 8 and 10 Myr) is consistent with this interpretation which, if correct, would add beta Cru to the roster of Lindroos binaries - B stars with low-mass pre-main-sequence companions
Chandra Spectroscopy Of The Hot Star β Crucis And The Discovery Of A Pre-Main-Sequence Companion
In order to test the O star wind-shock scenario for X-ray production in less luminous stars with weaker winds, we made a pointed 74-ks observation of the nearby early B giant, beta Crucis (beta Cru; B0.5 III), with the Chandra High Energy Transmission Grating Spectrometer. We find that the X-ray spectrum is quite soft, with a dominant thermal component near 3 million K, and that the emission lines are resolved but quite narrow, with half widths of 150 km s(-1). The forbidden-to-intercombination line ratios of Ne IX and Mg XI indicate that the hot plasma is distributed in the wind, rather than confined near the photosphere. It is difficult to understand the X-ray data in the context of the standard wind-shock paradigm for OB stars, primarily because of the narrow lines, but also because of the high X-ray production efficiency. A scenario in which the bulk of the outer wind is shock heated is broadly consistent with the data, but not very well motivated theoretically. It is possible that magnetic channelling could explain the X-ray properties, although no field has been detected on beta Cru. We detected periodic variability in the hard (h nu \u3e 1 keV) X-rays, modulated on the known optical period of 4.58 h, which is the period of the primary beta Cephei pulsation mode for this star. We also have detected, for the first time, an apparent companion to beta Cru at a projected separation of 4 arcsec. This companion was likely never seen in optical images because of the presumed very high contrast between it and beta Cru in the optical. However, the brightness contrast in the X-ray is only 3:1, which is consistent with the companion being an X-ray active low-mass pre-main-sequence star. The companion\u27s X-ray spectrum is relatively hard and variable, as would be expected from a post-T Tauri star. The age of the beta Cru system (between 8 and 10 Myr) is consistent with this interpretation which, if correct, would add beta Cru to the roster of Lindroos binaries - B stars with low-mass pre-main-sequence companions
The KELT-South Telescope
The Kilodegree Extremely Little Telescope (KELT) project is a survey for new
transiting planets around bright stars. KELT-South is a small-aperture,
wide-field automated telescope located at Sutherland, South Africa. The
telescope surveys a set of 26 degree by 26 degree fields around the southern
sky, and targets stars in the range of 8 < V < 10 mag, searching for transits
by Hot Jupiters. This paper describes the KELT-South system hardware and
software and discusses the quality of the observations. We show that KELT-South
is able to achieve the necessary photometric precision to detect transits of
Hot Jupiters around solar-type main-sequence stars.Comment: 26 pages, 13 figure
SOLID WASTE DISPOSAL SITE CHARACTERIZATION USING NON-INTRUSIVE ELECTROMAGNETIC SURVEY TECHNIQUES AND GEOSTATISTICS
Prior to the research reported in this paper, a site-specific hydrogeologic investigation was developed for a closed solid waste facility in Eastern Nebraska using phased subsurface characterizations. Based on the findings of this prior investigation, a surface based geoelectric survey using electromagnetic induction to measure subsurface conductivity was implemented to delineate the vertical and horizontal extent of buffed waste and subsurface contamination. This technique proved to be a key non-intrusive, cost-effective element in the refinement of the second phase of the hydrogeologic investigation.
Three-dimensional ordinary kriging was used to estimate conductivity values at unsampled locations. These estimates were utilized to prepare a contaminant plume map and a cross section depicting interpreted subsurface features. Pertinent subsurface features were identified by associating a unique range of conductivity values to that of solid waste, saturated and unsaturated soils and possible leachate migrating from the identified disposal areas
SOLID WASTE DISPOSAL SITE CHARACTERIZATION USING NON-INTRUSIVE ELECTROMAGNETIC SURVEY TECHNIQUES AND GEOSTATISTICS
Prior to the research reported in this paper, a site-specific hydrogeologic investigation was developed for a closed solid waste facility in Eastern Nebraska using phased subsurface characterizations. Based on the findings of this prior investigation, a surface based geoelectric survey using electromagnetic induction to measure subsurface conductivity was implemented to delineate the vertical and horizontal extent of buffed waste and subsurface contamination. This technique proved to be a key non-intrusive, cost-effective element in the refinement of the second phase of the hydrogeologic investigation.
Three-dimensional ordinary kriging was used to estimate conductivity values at unsampled locations. These estimates were utilized to prepare a contaminant plume map and a cross section depicting interpreted subsurface features. Pertinent subsurface features were identified by associating a unique range of conductivity values to that of solid waste, saturated and unsaturated soils and possible leachate migrating from the identified disposal areas
The Architecture of the GW Ori Young Triple Star System and Its Disk: Dynamical Masses, Mutual Inclinations, and Recurrent Eclipses
We present spatially and spectrally resolved Atacama Large
Millimeter/submillimeter Array (ALMA) observations of gas and dust orbiting the
pre-main sequence hierarchical triple star system GW Ori. A forward-modeling of
the CO and CO =2-1 transitions permits a measurement of
the total stellar mass in this system, , and the
circum-triple disk inclination, . Optical spectra spanning
a 35 year period were used to derive new radial velocities and, coupled with a
spectroscopic disentangling technique, revealed that the A and B components of
GW Ori form a double-lined spectroscopic binary with a day
period; a tertiary companion orbits that inner pair with a day
period. Combining the results from the ALMA data and the optical spectra with
three epochs of astrometry in the literature, we constrain the individual
stellar masses in the system (,
, ) and
find strong evidence that at least one (and likely both) stellar orbital planes
are misaligned with the disk plane by as much as . A -band light
curve spanning 30 years reveals several new 30 day eclipse events
0.1-0.7~mag in depth and a 0.2 mag sinusoidal oscillation that is clearly
phased with the AB-C orbital period. Taken together, these features suggest
that the A-B pair may be partially obscured by material in the inner disk as
the pair approaches apoastron in the hierarchical orbit. Lastly, we conclude
that stellar evolutionary models are consistent with our measurements of the
masses and basic photospheric properties if the GW Ori system is 1 Myr
old.Comment: 26 pages, 15 figures, accepted to Ap
Deriving Telescope Mueller Matrices Using Daytime Sky Polarization Observations
Telescopes often modify the input polarization of a source so that the
measured circular or linear output state of the optical signal can be
signficantly different from the input. This mixing, or polarization
"cross-talk", is defined by the optical system Mueller matrix. We describe here
an efficient method for recovering the input polarization state of the light
and the full 4 x 4 Mueller matrix of the telescope with an accuracy of a few
percent without external masks or telescope hardware modification. Observations
of the bright, highly polarized daytime sky using the Haleakala 3.7m AEOS
telescope and a coude spectropolarimeter demonstrate the technique.Comment: Accepted for publication in PAS
Towards the understanding of the cocoa transcriptome: Production and analysis of an exhaustive dataset of ESTs of Theobroma cacao L. generated from various tissues and under various conditions
Theobroma cacao L., is a tree originated from the tropical rainforest of South America. It is one of the major cash crops for many tropical countries. T. cacao is mainly produced on smallholdings, providing resources for 14 million farmers. Disease resistance and T. cacao quality improvement are two important challenges for all actors of cocoa and chocolate production. T. cacao is seriously affected by pests and fungal diseases, responsible for more than 40% yield losses and quality improvement, nutritional and organoleptic, is also important for consumers. An international collaboration was formed to develop an EST genomic resource database for cacao. Fifty-six cDNA libraries were constructed from different organs, different genotypes and different environmental conditions. A total of 149,650 valid EST sequences were generated corresponding to 48,594 unigenes, 12,692 contigs and 35,902 singletons. A total of 29,849 unigenes shared significant homology with public sequences from other species. Gene Ontology (GO) annotation was applied to distribute the ESTs among the main GO categories. A specific information system (ESTtik) was constructed to process, store and manage this EST collection allowing the user to query a database. To check the representativeness of our EST collection, we looked for the genes known to be involved in two different metabolic pathways extensively studied in other plant species and important for T. cacao qualities: the flavonoid and the terpene pathways. Most of the enzymes described in other crops for these two metabolic pathways were found in our EST collection. A large collection of new genetic markers was provided by this ESTs collection. This EST collection displays a good representation of the T. cacao transcriptome, suitable for analysis of biochemical pathways based on oligonucleotide microarrays derived from these ESTs. It will provide numerous genetic markers that will allow the construction of a high density gene map of T. cacao. This EST collection represents a unique and important molecular resource for T. cacao study and improvement, facilitating the discovery of candidate genes for important T. cacao trait variation. (Résumé d'auteur
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