19,893 research outputs found
Discovery of a Shell of Neutral Atomic Hydrogen Surrounding the Carbon Star IRC+10216
We have used the Robert C. Byrd Green Bank Telescope to perform the most
sensitive search to date for neutral atomic hydrogen (HI) in the circumstellar
envelope (CSE) of the carbon star IRC+10216. Our observations have uncovered a
low surface brightness HI shell of diameter ~1300" (~0.8 pc), centered on
IRC+10216. The HI shell has an angular extent comparable to the far
ultraviolet-emitting astrosphere of IRC+10216 previously detected with the
GALEX satellite, and its kinematics are consistent with circumstellar matter
that has been decelerated by the local interstellar medium. The shell appears
to completely surround the star, but the highest HI column densities are
measured along the leading edge of the shell, near the location of a previously
identified bow shock. We estimate a total mass of atomic hydrogen associated
with IRC+10216 CSE of M_HI~3x10e-3 M_sun. This is only a small fraction of the
expected total mass of the CSE (<1%) and is consistent with the bulk of the
stellar wind originating in molecular rather than atomic form, as expected for
a cool star with an effective temperature T_eff<~2200 K. HI mapping of a 2 deg
x 2 deg region surrounding IRC+10216 has also allowed us to characterize the
line-of-sight interstellar emission in the region and has uncovered a link
between diffuse FUV emission southwest of IRC+10216 and the Local Leo Cold
Cloud.Comment: Accepted to MNRAS. 16 pages. A version with full resolution figures
may be found at
http://www.haystack.mit.edu/hay/staff/lmatthew/Matthews_etal_IRC+10216.pd
HI emission from the red giant Y CVn with the VLA and FAST
Imaging studies with the VLA have revealed HI emission associated with the
extended circumstellar shells of red giants. We analyse the spectral map
obtained on Y CVn, a J-type carbon star on the AGB. The HI line profiles can be
interpreted with a model of a detached shell resulting from the interaction of
a stellar outflow with the local interstellar medium. We reproduce the spectral
map by introducing a distortion along a direction corresponding to the star's
motion in space. We then use this fitting to simulate observations expected
from the FAST radiotelescope, and discuss its potential for improving
ourdescription of the outer regions of circumstellar shells.Comment: accepted for publication in RA
An HI Imaging Survey of Asymptotic Giant Branch Stars
We present an imaging study of a sample of eight asymptotic giant branch
(AGB) stars in the HI 21-cm line. Using observations from the Very Large Array,
we have unambiguously detected HI emission associated with the extended
circumstellar envelopes of six of the targets. The detected HI masses range
from M_HI ~ 0.015-0.055 M_sun. The HI morphologies and kinematics are diverse,
but in all cases appear to be significantly influenced by the interaction
between the circumstellar envelope and the surrounding medium. Four stars (RX
Lep, Y UMa, Y CVn, and V1942 Sgr) are surrounded by detached HI shells ranging
from 0.36 to 0.76 pc across. We interpret these shells as resulting from
material entrained in a stellar outflow being abruptly slowed at a termination
shock where it meets the local medium. RX Lep and TX Psc, two stars with
moderately high space velocities (V_space>56 km/s), exhibit extended gaseous
wakes (~0.3 and 0.6 pc in the plane of the sky), trailing their motion through
space. The other detected star, R Peg, displays a peculiar "horseshoe-shaped"
HI morphology with emission extended on scales up to ~1.7 pc; in this case, the
circumstellar debris may have been distorted by transverse flows in the local
interstellar medium. We briefly discuss our new results in the context of the
entire sample of evolved stars that has been imaged in HI to date.Comment: Accepted to AJ. A version with full resolution figures is available
at http://www.haystack.mit.edu/hay/staff/lmatthew/matthews_HI_survey.pd
The effects of swimming fatigue on shoulder strength, range of motion, joint control, and performance in swimmers
Purpose
To investigate the effects of training induced fatigue on shoulder strength, ROM, joint position sense, and stroke length in elite competitive swimmers.
Methods
Seventeen national level swimmers performed maximum isometric strength (internal and external rotation), ROM, and joint position sense tests before and after a fatiguing 8 × 100 m training set. Stroke length, heart rate, blood lactate and blood glucose levels were recorded throughout.
Results
Peak blood lactate, blood glucose levels, and heart rate increased significantly (P<0.001) post-training confirming fatigue. Reductions were observed in stroke length of both arms (P<0.001), external rotation range of motion (P<0.001, −5.29°, Right shoulder; P = 0.04, −3.18°, Left shoulder) and joint position sense in their dominant (breathing side) arm (P = 0.03).
Conclusions
This investigation revealed a reduction in stroke length across both arms and also an arm bias in swimming whereby a greater reduction in both external rotation range and joint position sense was observed in the dominant arm when fatigued. This has highlighted a relationship between fatigue and potential mechanism of shoulder pathology in swimmers
Recent Experiments with Bose-Condensed Gases at JILA
We consider a binary mixture of two overlapping Bose-Einstein condensates in
two different hyperfine states of \Rb87 with nearly identical magnetic moments.
Such a system has been simply realized through application of radiofrequency
and microwave radiation which drives a two-photon transition between the two
states. The nearly identical magnetic moments afford a high degree of spatial
overlap, permitting a variety of new experiments. We discuss some of the
conditions under which the magnetic moments are identical, with particular
emphasis placed on the requirements for a time-averaged orbiting potential
(TOP) magnetic trap.Comment: 9 pages, 5 figures; corrected post-publication editio
Galactic Center Youth: Orbits and Origins of the Young Stars in the Central Parsec
We present new proper motions for the massive, young stars at the Galactic Center, based on 10 years of diffraction limited data from the Keck telescopes. Our proper motion measurements now have uncertainties of only 1-2 km/s and allow us to explore the origin of the young stars that reside within the sphere of inflience of the supermassive black hole whose strong tidal forces make this region inhospitable for star formation. Their presence, however, may be explained either by in situ star formation in an accretion disk or as the remnants of a massive stellar cluster which spiraled in via dynamical friction. Earlier stellar velocity vectors were used to postulate that all the young stars resided in two counter-rotating stellar disks, which is consistent with both of the above formation scenarios. Our precise proper motions allow us, for the frst time, to determine the orbital parameters of each individual star and thereby to test the hypothesis that the massive stars reside in two stellar disks. Of the 26 young stars in this study that were previously proposed to lie on the inner, clockwise disk, we find that nearly all exhibit orbital constraints consistent with such a disk. On the other hand, of the 7 stars in this study previously proposed to lie in the outer, less well-defhed counter-clockwise disk, 6 exhibit inclinations that are inconsistent with such a disk, bringing into question the existence of the outer disk. Furthermore, for stars in the inner disk that have eccentricity constraints, we find several that have lower limits to the eccentricity of more than 0.4, implying highly eccentric orbits. This stands in contrast to simple accretion disk formation scenarios which typically predict predominantly circular orbits
Growth inhibition of cytosolic Salmonella by caspase-1 and caspase-11 precedes host cell death
Sensing bacterial products in the cytosol of mammalian cells by NOD-like receptors leads to the activation of caspase-1 inflammasomes, and the production of the pro-inflammatory cytokines interleukin (IL)-18 and IL-1β. In addition, mouse caspase-11 (represented in humans by its orthologs, caspase-4 and caspase-5) detects cytosolic bacterial LPS directly. Activation of caspase-1 and caspase-11 initiates pyroptotic host cell death that releases potentially harmful bacteria from the nutrient-rich host cell cytosol into the extracellular environment. Here we use single cell analysis and time-lapse microscopy to identify a subpopulation of host cells, in which growth of cytosolic Salmonella Typhimurium is inhibited independently or prior to the onset of cell death. The enzymatic activities of caspase-1 and caspase-11 are required for growth inhibition in different cell types. Our results reveal that these proteases have important functions beyond the direct induction of pyroptosis and proinflammatory cytokine secretion in the control of growth and elimination of cytosolic bacteria
CO and HI observations of an enigmatic cloud
An isolated HI cloud with peculiar properties has recently been discovered by
Dedes, Dedes, & Kalberla (2008, A&A, 491, L45) with the 300-m Arecibo
telescope, and subsequently imaged with the VLA. It has an angular size of ~6',
and the HI emission has a narrow line profile of width ~ 3 km/s.
We explore the possibility that this cloud could be associated with a
circumstellar envelope ejected by an evolved star.
Observations were made in the rotational lines of CO with the IRAM-30m
telescope, on three positions in the cloud, and a total-power mapping in the HI
line was obtained with the Nancay Radio Telescope.
CO was not detected and seems too underabundant in this cloud to be a
classical late-type star circumstellar envelope. On the other hand, the HI
emission is compatible with the detached-shell model that we developed for
representing the external environments of AGB stars.
We propose that this cloud could be a fossil circumstellar shell left over
from a system that is now in a post-planetary-nebula phase. Nevertheless, we
cannot rule out that it is a Galactic cloud or a member of the Local Group,
although the narrow line profile would be atypical in both cases.Comment: Accepted for publication in Astronomy and Astrophysic
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