3,634 research outputs found
Infrared photometry of the 1982-4 eclipse of Epsilon Aurigae
The infrared photometry of epsilon Aur performed prior to and during the ingress phase of the recent eclipse allowed the first solid determination of the temperature of the secondary object. The eclipse depth was significantly less at lambda 5 micrometers than in the near-infrared. This is explained by a model of the secondary as an opaque and very cool object with a temperature of approx. 500 K. During eclipse, the secondary blocks approximately 45% of the near infrared radiation from the primary star. At the same time, the radiation from the secondary remains completely unobscured, resulting in a shallower light curve at longer wavelengths. This phenomenon is well known in the study of eclipsing binary stars; if the two stars have different colors, then the net color of the system changes during eclipse. In the case of epsilon Aur, the eclipsing object has a color deep in the infrared, so the effect is only noticeable there
Nearby main sequence stars with cool circumstellar material
The discovery of the so-called Vega phenomenon was one of the most important and unexpected results of the IRAS mission. Several nearby main sequence stars were found to possess clouds of solid grains emitting strongly in the far-IR. Three of these objects were marginally resolved by IRAS. This phenomenon appears to be widespread and not limited to proto-planetary epochs. Possible connection of this phenomenon to the existing of planets is discussed
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BACKGROUND: It has been hypothesised that an upregulation of the neuropeptide substance P (SP) and its preferred receptor, the neurokinin-1 receptor (NK-1 R), is a causative factor in inducing tenocyte hypercellularity, a characteristic of tendinosis, through both proliferative and antiapoptotic stimuli. We have demonstrated earlier that SP stimulates proliferation of human tenocytes in culture. AIM: The aim of this study was to investigate whether SP can mediate an antiapoptotic effect in tumour necrosis factor-α (TNF-α)-induced apoptosis of human tenocytes in vitro. RESULTS: A majority (approximately 75%) of tenocytes in culture were immunopositive for TNF Receptor-1 and TNF Receptor-2. Exposure of the cells to TNF-α significantly decreased cell viability, as shown with crystal violet staining. TNF-α furthermore significantly increased the amount of caspase-10 and caspase-3 mRNA, as well as both BID and cleaved-poly ADP ribosome polymerase (c-PARP) protein. Incubation of SP together with TNF-α resulted in a decreased amount of BID and c-PARP, and in a reduced lactate dehydrogenase release, as compared to incubation with TNF-α alone. The SP effect was blocked with a NK-1 R inhibitor. DISCUSSION: This study shows that SP, through stimulation of the NK-1 R, has the ability to reduce TNF-α-induced apoptosis of human tenocytes. Considering that SP has previously been shown to stimulate tenocyte proliferation, the study confirms SP as a potent regulator of cell-turnover in tendon tissue, capable of stimulating hypercellularity through different mechanisms. This gives further support for the theory that the upregulated amount of SP seen in tendinosis could contribute to hypercellularity
Mid-infrared Imaging of a Circumstellar Disk Around HR 4796: Mapping the Debris of Planetary Formation
We report the discovery of a circumstellar disk around the young A0 star, HR
4796, in thermal infrared imaging carried out at the W.M. Keck Observatory. By
fitting a model of the emission from a flat dusty disk to an image at
lambda=20.8 microns, we derive a disk inclination, i = 72 +6/-9 deg from face
on, with the long axis of emission at PA 28 +/-6 deg. The intensity of emission
does not decrease with radius as expected for circumstellar disks but increases
outward from the star, peaking near both ends of the elongated structure. We
simulate this appearance by varying the inner radius in our model and find an
inner hole in the disk with radius R_in = 55+/-15 AU. This value corresponds to
the radial distance of our own Kuiper belt and may suggest a source of dust in
the collision of cometesimals. By contrast with the appearance at 20.8 microns,
excess emission at lambda = 12.5 microns is faint and concentrated at the
stellar position. Similar emission is also detected at 20.8 microns in residual
subtraction of the best-fit model from the image. The intensity and ratio of
flux densities at the two wavelengths could be accounted for by a tenuous dust
component that is confined within a few AU of the star with mean temperature of
a few hundred degrees K, similar to that of zodiacal dust in our own solar
system. The morphology of dust emission from HR 4796 (age 10 Myr) suggests that
its disk is in a transitional planet-forming stage, between that of massive
gaseous proto-stellar disks and more tenuous debris disks such as the one
detected around Vega.Comment: 9 pages, 4 figures as LaTex manuscript and postscript files in
gzipped tar file. Accepted for publication in Astrophysical Journal Letters.
http://upenn5.hep.upenn.edu/~davidk/hr4796.htm
Three newly-discovered M-dwarf companions of Solar Neighbourhood stars
We present low-resolution spectroscopy of newly-discovered candidate
companions to three stars in the Solar Neighbourhood. All three companions are
M dwarfs, with spectral types ranging from M4 to M9.5. In two cases, G85-55`B'
(M6) and G87-9`B' (M4), we have circumstantial evidence from spectroscopy,
photometry and limited astrometry that the systems are physical binaries; in
the third, G216-7B (M9.5), comparison of POSS II IIIaF plate material and the
2MASS image indicates common proper motion. The primary star in this system,
G216-7A (M0), appears itself to be an unresolved, nearly equal-mass binary. All
three low-mass companions are highly likely to be stellar in nature, although
G216-7B lies very close to the hydrogen-burning limit.Comment: Accepted for publication in PASP; 21 pages, 6 figure
The Inner Rings of Beta Pictoris
We present Keck images of the dust disk around Beta Pictoris at 17.9 microns
that reveal new structure in its morphology. Within 1" (19 AU) of the star, the
long axis of the dust emission is rotated by more than 10 degrees with respect
to that of the overall disk. This angular offset is more pronounced than the
warp detected at 3.5" by HST, and in the opposite direction. By contrast, the
long axis of the emission contours at ~ 1.5" from the star is aligned with the
HST warp. Emission peaks between 1.5" and 4" from the star hint at the presence
of rings similar to those observed in the outer disk at ~ 25" with HST/STIS. A
deconvolved image strongly suggests that the newly detected features arise from
a system of four non-coplanar rings. Bayesian estimates based on the primary
image lead to ring radii of 14+/-1 AU, 28+/-3 AU, 52+/-2 AU and 82+/-2 AU, with
orbital inclinations that alternate in orientation relative to the overall disk
and decrease in magnitude with increasing radius. We believe these new results
make a strong case for the existence of a nascent planetary system around Beta
Pic.Comment: 5 pages, 2 figures, PDF format. Published in ApJL, December 20,200
Radial Distribution of Dust Grains Around HR 4796A
We present high-dynamic-range images of circumstellar dust around HR 4796A
that were obtained with MIRLIN at the Keck II telescope at lambda = 7.9, 10.3,
12.5 and 24.5 um. We also present a new continuum measurement at 350 um
obtained at the Caltech Submillimeter Observatory. Emission is resolved in Keck
images at 12.5 and 24.5 um with PSF FWHM's of 0.37" and 0.55", respectively,
and confirms the presence of an outer ring centered at 70 AU. Unresolved excess
infrared emission is also detected at the stellar position and must originate
well within 13 AU of the star. A model of dust emission fit to flux densities
at 12.5, 20.8, and 24.5 um indicates dust grains are located 4(+3/-2) AU from
the star with effective size, 28+/-6 um, and an associated temperature of
260+/-40 K.
We simulate all extant data with a simple model of exozodiacal dust and an
outer exo-Kuiper ring. A two-component outer ring is necessary to fit both Keck
thermal infrared and HST scattered-light images. Bayesian parameter estimates
yield a total cross-sectional area of 0.055 AU^2 for grains roughly 4 AU from
the star and an outer-dust disk composed of a narrow large-grain ring embedded
within a wider ring of smaller grains. The narrow ring is 14+/-1 AU wide with
inner radius 66+/-1 AU and total cross-sectional area 245 AU^2. The outer ring
is 80+/-15 AU wide with inner radius 45+/-5 AU and total cross-sectional area
90 AU^2. Dust grains in the narrow ring are about 10 times larger and have
lower albedos than those in the wider ring. These properties are consistent
with a picture in which radiation pressure dominates the dispersal of an
exo-Kuiper belt.Comment: Accepted by Astrophysical Journal (Part1) on September 9, 2004. 13
pages, 10 figures, 2 table
Measuring the Interplanetary Medium with a Solar Sail
NASA has been considering a solar sail that would accelerate a craft to a
high velocity (~ 14 AU/yr) by the time it reached 5 AU. Then the sail would be
dropped and the craft would coast alone to deep space. We propose that the sail
be retained longer. Then the density of the interplanetary medium could be
determined by measuring the drag force on the huge sail using radiometric
navigational data. Such an experiment would yield an independent, new type of
measurement of the interplanetary medium and should be pursued.Comment: 12 page
Force balance and membrane shedding at the Red Blood Cell surface
During the aging of the red-blood cell, or under conditions of extreme
echinocytosis, membrane is shed from the cell plasma membrane in the form of
nano-vesicles. We propose that this process is the result of the
self-adaptation of the membrane surface area to the elastic stress imposed by
the spectrin cytoskeleton, via the local buckling of membrane under increasing
cytoskeleton stiffness. This model introduces the concept of force balance as a
regulatory process at the cell membrane, and quantitatively reproduces the rate
of area loss in aging red-blood cells.Comment: 4 pages, 3 figure
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