4,904 research outputs found
Disk Evolution in Young Binaries: from Observations to Theory
The formation of a binary system surrounded by disks is the most common
outcome of stellar formation. Hence studying and understanding the formation
and the evolution of binary systems and associated disks is a cornerstone of
star formation science. Moreover, since the components within binary systems
are coeval and the sizes of their disks are fixed by the tidal truncation of
their companion, binary systems provide an ideal "laboratory" in which to study
disk evolution under well defined boundary conditions.
In this paper, we review observations of several inner disk diagnostics in
multiple systems, including hydrogen emission lines (indicative of ongoing
accretion), and color excesses (evidence of warm inner disks), and
polarization (indicative of the relative orientations of the disks around each
component). We examine to what degree these properties are correlated within
binary systems and how this degree of correlation depends on parameters such as
separation and binary mass ratio. These findings will be interpreted both in
terms of models that treat each disk as an isolated reservoir and those in
which the disks are subject to re-supply from some form of circumbinary
reservoir, the observational evidence for which we will also critically review.
The planet forming potential of multiple star systems is discussed in terms of
the relative lifetimes of disks around single stars, binary primaries and
binary secondaries. Finally, we summarize several potentially revealing
observational problems and future projects that could provide further insight
into disk evolution in the coming decadeComment: 16 pages, 7 figures, chapter in Protostars and Planets
Effects of magnesium treatment in a model of internal capsule lesion in spontaneously hypertensive rats
<p><b>Background and Purpose:</b> The study aim was to assess the effects of magnesium sulfate (MgSO4) administration on white matter damage in vivo in spontaneously hypertensive rats.</p>
<p><b>Methods:</b> The left internal capsule was lesioned by a local injection of endothelin-1 (ET-1; 200 pmol) in adult spontaneously hypertensive rats. MgSO4 was administered (300 mg/kg SC) 30 minutes before injection of ET-1, plus 200 mg/kg every hour thereafter for 4 hours. Infarct size was measured by T2-weighted magnetic resonance imaging (day 2) and histology (day 11), and functional recovery was assessed on days 3 and 10 by the cylinder and walking-ladder tests.</p>
<p><b>Results:</b> ET-1 application induced a small, localized lesion within the internal capsule. Despite reducing blood pressure, MgSO4 did not significantly influence infarct volume (by magnetic resonance imaging: median, 2.1 mm3; interquartile range, 1.3 to 3.8, vs 1.6 mm3 and 1.2 to 2.1, for the vehicle-treated group; by histology: 0.3 mm3 and 0.2 to 0.9 vs 0.3 mm3 and 0.2 to 0.5, respectively). Significant forelimb and hindlimb motor deficits were evident in the vehicle-treated group as late as day 10. These impairments were significantly ameliorated by MgSO4 in both cylinder (left forelimb use, P<0.01 and both-forelimb use, P<0.03 vs vehicle) and walking-ladder (right hindlimb score, P<0.02 vs vehicle) tests.</p>
<p><b>Conclusions:</b> ET-1–induced internal capsule ischemia in spontaneously hypertensive rats represents a good model of lacunar infarct with small lesion size, minimal adverse effects, and a measurable motor deficit. Despite inducing mild hypotension, MgSO4 did not significantly influence infarct size but reduced motor deficits, supporting its potential utility for the treatment of lacunar infarct.</p>
NICMOS Images of the GG Tau Circumbinary Disk
We present deep, near-infrared images of the circumbinary disk surrounding
the pre-main-sequence binary star, GG Tau A, obtained with NICMOS aboard the
Hubble Space Telescope. The spatially resolved proto-planetary disk scatters
roughly 1.5% of the stellar flux, with a near-to-far side flux ratio of ~1.4,
independent of wavelength, and colors that are comparable to the central
source; all of these properties are significantly different from the earlier
ground-based observations. New Monte Carlo scattering simulations of the disk
emphasize that the general properties of the disk, such as disk flux, near side
to far side flux ratio and integrated colors, can be approximately reproduced
using ISM-like dust grains, without the presence of either circumstellar disks
or large dust grains, as had previously been suggested. A single parameter
phase function is fitted to the observed azimuthal variation in disk flux,
providing a lower limit on the median grain size of 0.23 micron. Our analysis,
in comparison to previous simulations, shows that the major limitation to the
study of grain growth in T Tauri disk systems through scattered light lies in
the uncertain ISM dust grain properties. Finally, we use the 9 year baseline of
astrometric measurements of the binary to solve the complete orbit, assuming
that the binary is coplanar with the circumbinary ring. We find that the
estimated 1 sigma range on disk inner edge to semi-major axis ratio, 3.2 <
Rin/a < 6.7, is larger than that estimated by previous SPH simulations of
binary-disk interactions.Comment: 40 pages, 8 postscript figures, accepted for publication in Ap
The Ursinus Weekly, May 19, 1958
Haag prexy of men\u27s student government • Annual banquet held by Varsity Club Tues., May 13 • Seniors feted at annual banquet • Special editorial: Customs • Dr. Cooke speaks on mental difficulties of our children • Election results for officers are announced • Ottenberg speaks on the problems of skid rowers • Editorial: Leadership and service • Inner peace • Letters to the editor • To the hilt • Against me • Cindermen whip Washington squad; Lose to Dickinson • Tennis team picks up first two wins; Loses close tilt • Bears nine win two; Beaten by Wilkes, 3-2 • Drexel defeated by lacrosse team • West Chester wallops JV varsity softball teams • Tennis team routs strongest rival • Dr. Hugh Borton to speak at foreign traders dinner • Library accessionshttps://digitalcommons.ursinus.edu/weekly/1408/thumbnail.jp
The Ursinus Weekly, May 19, 1958
Haag prexy of men\u27s student government • Annual banquet held by Varsity Club Tues., May 13 • Seniors feted at annual banquet • Special editorial: Customs • Dr. Cooke speaks on mental difficulties of our children • Election results for officers are announced • Ottenberg speaks on the problems of skid rowers • Editorial: Leadership and service • Inner peace • Letters to the editor • To the hilt • Against me • Cindermen whip Washington squad; Lose to Dickinson • Tennis team picks up first two wins; Loses close tilt • Bears nine win two; Beaten by Wilkes, 3-2 • Drexel defeated by lacrosse team • West Chester wallops JV varsity softball teams • Tennis team routs strongest rival • Dr. Hugh Borton to speak at foreign traders dinner • Library accessionshttps://digitalcommons.ursinus.edu/weekly/1408/thumbnail.jp
Biomass burning and urban air pollution over the Central Mexican Plateau
Observations during the 2006 dry season of highly elevated concentrations of cyanides in the atmosphere above Mexico City (MC) and the surrounding plains demonstrate that biomass burning (BB) significantly impacted air quality in the region. We find that during the period of our measurements, fires contribute more than half of the organic aerosol mass and submicron aerosol scattering, and one third of the enhancement in benzene, reactive nitrogen, and carbon monoxide in the outflow from the plateau. The combination of biomass burning and anthropogenic emissions will affect ozone chemistry in the MC outflow
Investigating disk evolution: A high spatial resolution mid-infrared survey of T Tauri stars
We present a high spatial resolution, 10-20 micron survey of 65 T Tauri
binary stars in Taurus, Ophiuchus, and Corona Australis using the Keck 10 m
telescopes. Designed to probe the inner ~1 AU region of the circumstellar disks
around the individual stellar components in these binary systems, this study
increases the number of binaries with spatially resolved measurements at 10
micron by a factor of ~5. Combined with resolved near-infrared photometry and
spectroscopic accretion diagnostics, we find that ~10% of stars with a
mid-infrared excess do not appear to be accreting. In contrast to an actively
accreting disk system, these passive disks have significantly lower
near-infrared colors that are, in most cases, consistent with photospheric
emission, suggesting the presence of an inner disk hole. In addition, there
appears to be a spectral type/mass dependence associated with the presence of a
passive disk, with all passive disks occurring around M type stars. The
possibility that the passive disks are caused by the presence of an as yet
undetected companion at a small separation (0.3-3 AU) is possible for any
individual system, however, it cannot account for the spectral type dependence
of the passive disk sample as a whole. We propose that these passive disks
represent a subset of T Tauri stars that are undergoing significant disk
evolution. The fraction of observed passive disks and the observed spectral
type dependence can both be explained by models of disk evolution that include
disk photoevaporation from the central star. (abridged).Comment: 51 pages, 3 figures, to be published in ApJ, January 200
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