1,564 research outputs found
New detections of H2O masers in planetary nebulae and post-AGB stars using the Robledo-70m antenna
Aims: We investigated the possible relationship between the evolutionary
stage of post-AGB stars and planetary nebulae (PNe) and the presence of water
masers in their envelopes.
Methods: We have used NASA's 70-m antenna in Robledo de Chavela (Spain) to
search for the water maser transition at 22235.08 MHz, towards a sample of 105
sources with IRAS colour characteristic of post-AGB stars and PNe at
declination >-32 deg. 83% of the sources in the sample are post-AGB stars, 15%
PNe or PN candidates, while only 2% seem to be HII regions.
Results: We have detected five water masers, of which four are reported for
the first time: two in PNe (IRAS 17443-2949 and IRAS 18061-2505), a ``water
fountain'' in a post-AGB star (IRAS 16552-3050), and one in a source previously
catalogued as a PN, but whose classification is uncertain (IRAS 17580-3111).
Conclusions: The unexpected detections of water masers in two objects among
the small subset of PNe led us to suggest that the PNe harbouring water masers
are a special type of massive, rapidly evolving PNe.Comment: 15 pages, 7 figures. Accepted for publication in Astronomy and
Astrophysic
Seasonal home range variation and spatial ecology of peregrine falcons (Falco peregrinus) in coastal Humboldt County, CA
Peregrine falcons (Falco peregrinus) are renowned for their migratory habits, with ‘peregrinus’ often translated as ‘wanderer’ or ‘pilgrim’. However, their migratory habits may differ by population and some peregrine may falcons forgo migration when climate and resources remain stable. To examine peregrine falcon home range and space use, I fitted GPS-satellite transmitters to nine breeding adults in coastal northern California, an area with a mild climate and abundant waterbird populations. I used kernel density estimates and time-local convex hulls to examine seasonal home ranges and within-home range habitat use. All nine peregrine falcons remained resident in their territories year-round, and home ranges continued to center around the location of the nesting structure (i.e. bridge or cliff face) even during winter. Home range sizes were larger in the breeding season than in winter, indicating that peregrines did not need to travel farther to find food during the winter and that local conditions were conducive to year-round occupancy. Intensity of space use within the home range was influenced by several environmental covariates, including distance to water, distance to nest site, elevation, prey density, terrain ruggedness and habitat type. Peregrine falcons preferred habitat types associated with nest sites, where they remained year-round, and with open areas such as mud flats, beaches, some agricultural lands, and inland standing water. Intensity of use decreased with distance from bodies of water, distance from nest sites, and terrain ruggedness. Intensity of use was positively associated with elevation and an index of prey density. Our results demonstrate non-random space use within the home range and provide new information about previously unstudied non-migratory behaviors of coastal breeding peregrines in Humboldt County, California
Paper Session III-B - Space Station On-Orbit Assembly and Operation
The United States and its international partners are well on the way to developing Space Station Freedom which will be a very large orbiting facility with many capabilities for conducting space operations. Adjustments in the program content and station design have been implemented as a result of the recent restructure activity. This paper addresses the assembly and operations aspects of SSF. Assembly is achieved by sequential shuttle launches which carry portions of the station building the capability through the Manned Tended Capability and then on to Permanent Manned Capability. The pre-integrated truss segment resulting from the program restructure activity is shown and assembly techniques using the orbiter described. Both pay load and station operations are examined. The pay load operations include the conduct of materials processing and life science missions. These rely heavily on the microgravity capability of the Space Station. Station operations examined include EVA for assembly and maintenance and reboost techniques
Chlorite composition and geothermometry: a comparative HRTEM/AEM-EMPA-XRD study of Cambrian basic lavas from the Ossa Morena Zone, SW Spain
15 páginas, 8 figuras, 4 tablasChlorites from Cambrian basaltic vesicular lavas, characterized by relatively high Xc (0.81–0.98), gave temperatures of formation of 285 to 350°C (Cathelineau’s empirical geothermometer). Both the Xc and temperature calculations gave results which were too high for the diagenetic conditions indicated by the interbedded shale mineralogy. The HRTEM and XRD studies indicate the absence of smectite layers in these chlorites; i.e. according to lattice images, the actual value of Xc is 1. The chlorite composition in these basaltic lavas must, therefore, be explained in relation to their whole-rock geochemistry, with which a good correlation has been found. The basaltic lavas are characterized by relatively high FeO/MgO ratios (3.2831.66) and must be considered as an Fe-rich system, with similar chemical behaviour to pelitic rocks. In these cases, direct chlorite formation, without a previous smectite precursor, is a normal occurrence and the Xc calculation and empirical geothermometric calculations are inadequate.Proyecto de investigación BTE2000-0582 del Ministerio de Ciencia y TecnologÃa, y el Grupo de Investigación RNM-0179 de la Junta de AndalucÃa.Peer reviewe
Probabilistic and deterministic results of the ANPAF analog model for Spanish wind field estimations
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Interstitial lithium doping in SrTiO3
Strontium titanate (SrTiO3) has received much attention due to its wide range of potential applications including in electrochemical devices such as solid oxide fuel cells and capacitors. The stability and safety features of SrTiO3 led to the development of promising electrodes for Li-ion batteries. Here, we use density functional theory simulations to examine the incorporation of lithium from its gas-phase and bulk forms. The results show that a single Li atom is thermodynamically stable in bulk SrTiO3 with respect to its gas-phase and slightly unfavourable compared to its bulk. Multiple Li incorporation up to six is also considered and the incorporation is exoergic with respect to both gas-phase and bulk forms. Charge analysis confirmed the presence of Li+ ions in the lattice. Li incorporation turns the insulating nature of SrTiO3 into metallic and non-magnetic into magnetic. Lithium incorporation facilitates the formation of Sr, Ti and O vacancies. The loss of Li2O is exoergic suggesting that oxygen vacancy mediated-self diffusion will be promoted
First detection of thermal radio jets in a sample of proto-brown dwarf candidates
We observed with the JVLA at 3.6 and 1.3 cm a sample of 11 proto-brown dwarf
candidates in Taurus in a search for thermal radio jets driven by the most
embedded brown dwarfs. We detected for the first time four thermal radio jets
in proto-brown dwarf candidates. We compiled data from UKIDSS, 2MASS, Spitzer,
WISE and Herschel to build the Spectral Energy Distribution (SED) of the
objects in our sample, which are similar to typical Class~I SEDs of Young
Stellar Objects (YSOs). The four proto-brown dwarf candidates driving thermal
radio jets also roughly follow the well-known trend of centimeter luminosity
against bolometric luminosity determined for YSOs, assuming they belong to
Taurus, although they present some excess of radio emission compared to the
known relation for YSOs. Nonetheless, we are able to reproduce the flux
densities of the radio jets modeling the centimeter emission of the thermal
radio jets using the same type of models applied to YSOs, but with
corresponding smaller stellar wind velocities and mass-loss rates, and
exploring different possible geometries of the wind or outflow from the star.
Moreover, we also find that the modeled mass outflow rates for the bolometric
luminosities of our objects agree reasonably well with the trends found between
the mass outflow rates and bolometric luminosities of YSOs, which indicates
that, despite the "excess" centimeter emission, the intrinsic properties of
proto-brown dwarfs are consistent with a continuation of those of very low mass
stars to a lower mass range. Overall, our study favors the formation of brown
dwarfs as a scaled-down version of low-mass stars.Comment: 18 pages, 8 figures, 14 tables, accepted by the Astrophysical Journa
A refutation to 'A new A-P compartment boundary and organizer in holometabolous insect wings'.
We respond to a recent report by Abbasi and Marcus who present two main findings: first they argue that there is an organiser and a compartment boundary within the posterior compartment of the butterfly wing. Second, they present evidence for a previously undiscovered lineage boundary near wing vein 5 in Drosophila, a boundary that delineates a "far posterior" compartment. Clones of cells were marked with the yellow mutation and they reported that these clones always fail to cross a line close to vein 5 on the Drosophila wing. In our hands yellow proved an unusable marker for clones in the wing blade and therefore we reexamined the matter. We marked clones of cells with multiple wing hairs or forked and found a substantial proportion of these clones cross the proposed lineage boundary near vein 5, in conflict with their findings and conclusion. As internal controls we showed that these same clones respect the other two well established compartment boundaries: the anteroposterior compartment boundary is always respected. The dorsoventral boundary is mostly respected, and is crossed only by clones that are induced early in development, consistent with many reports. We question the validity of Abbasi and Marcus' conclusions regarding the butterfly wing but present no new data.Arising from: R. Abbasi and J. M. Marcus Sci. Rep. 7, 16337 (2017); https://doi.org/10.1038/s41598-017-16553-5 .WELLCOME TRUST 107060/Z/15/
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