1,939 research outputs found
Production of Milky Way structure by the Magellanic Clouds
Previous attempts at disturbing the galactic disk by the Magellanic Clouds
relied on direct tidal forcing. However, by allowing the halo to actively
respond rather than remain a rigid contributor to the rotation curve, the
Clouds may produce a wake in the halo which then distorts the disk. Recent work
reported here suggests that the Magellanic Clouds use this mechanism to produce
disk distortions sufficient to account for both the radial location, position
angle and sign of the HI warp and observed anomalies in stellar kinematics
towards the galactic anticenter and LSR motion.Comment: 8 pages, uuencoded compressed PostScript, no figures, html version
with figures and mpeg simulations available at
http://www-astro.phast.umass.edu/Preprints/martin/martin1/lmc_online.htm
Effect of the Milky Way on Magellanic Cloud structure
A combination of analytic models and n-body simulations implies that the
structural evolution of the Large Magellanic Cloud (LMC) is dominated by its
dynamical interaction with the Milky Way. Although expected at some level, the
scope of the involvement has significant observational consequences. First, LMC
disk orbits are torqued out of the disk plane, thickening the disk and
populating a spheroid. The torque results from direct forcing by the Milky Way
tide and, indirectly, from the drag between the LMC disk and its halo resulting
from the induced precession of the LMC disk. The latter is a newly reported
mechanism that can affect all satellite interations. However, the overall
torque can not isotropize the stellar orbits and their kinematics remains
disk-like. Such a kinematic signature is observed for nearly all LMC
populations. The extended disk distribution is predicted to increase the
microlensing toward the LMC. Second, the disk's binding energy slowly decreases
during this process, puffing up and priming the outer regions for subsequent
tidal stripping. Because the tidally stripped debris will be spatially
extended, the distribution of stripped stars is much more extended than the HI
Magellanic Stream. This is consistent with upper limits to stellar densities in
the gas stream and suggests a different strategy for detecting the stripped
stars. And, finally, the mass loss over several LMC orbits is predicted by
n-body simulation and the debris extends to tens of kiloparsecs from the tidal
boundary. Although the overall space density of the stripped stars is low,
possible existence of such intervening populations have been recently reported
and may be detectable using 2MASS.Comment: 15 pages, color Postscript figures, uses emulateapj.sty. Also
available from http://www-astro.phast.umass.edu/~weinberg/weinberg-pubs.htm
Evolution of the Small Magellanic Cloud
Based on the results of N-body simulations on the last 2.5 Gyr evolution of
the Large and Small Magellanic Clouds (LMC and SMC, respectively) interacting
with the Galaxy, we firstly show when and where the leading arms (LAs) of the
Magellanic stream (MS) can pass through the Galactic plane after the MS
formation. We secondly show collisions between the outer Galactic HI disk and
the LAs of the MS can create giant HI holes and chimney-like structures in the
disk about 0.2 Gyr ago. We thirdly show that a large amount of metal-poor gas
is stripped from the SMC and transfered to the LMC during the tidal interaction
between the Clouds and the Galaxy about 0.2 and 1.3 Gyr ago. We thus propose
that this metal-poor gas can closely be associated with the origin of LMC's
young and intermediate-age stars and star clusters with distinctively
low-metallicities with [Fe/H] < -0.6.Comment: 4 pages, 3 figures, to appear in the proceedings of ``Galaxies in the
Local Volume'', Sydney, 8 to 13 July, 200
Tidal Streams as Probes of the Galactic Potential
We explore the use of tidal streams from Galactic satellites to recover the
potential of the Milky Way. Our study is motivated both by the discovery of the
first lengthy stellar stream in the halo (\cite{it98}) and by the prospect of
measuring proper motions of stars brighter than 20th magnitude in such a stream
with an accuracy of yr, as will be possible with the Space
Interferometry Mission (SIM). We assume that the heliocentric radial velocities
of these stars can be determined from supporting ground-based spectroscopic
surveys, and that the mass and phase-space coordinates of the Galactic
satellite with which they are associated will also be known to SIM accuracy.
Using results from numerical simulations as trial data sets, we find that, if
we assume the correct form for the Galactic potential, we can predict the
distances to the stars as a consequence of the narrow distribution of energy
expected along the streams. We develop an algorithm to evaluate the accuracy of
any adopted potential by requiring that the satellite and stars recombine
within a Galactic lifetime when their current phase-space coordinates are
integrated backwards. When applied to a four-dimensional grid of triaxial
logarithmic potentials, with varying circular velocities, axis ratios and
orientation of the major-axis in the disk plane, the algorithm can recover the
parameters used for the Milky Way in a simulated data set to within a few
percent using only 100 stars in a tidal stream.Comment: Revised version - original algorithm generalised to be applicable to
any potential shape. LaTeX, 12 pages including 3 figures. To be published in
ApJ Letter
Stanley's conjecture for critical ideals
Let S=K[x_1,x_2,...,x_n] be a polynomial ring in n variables over a field K.
Stanley's conjecture holds for the modules I and S/I, when I is a critical
monomial ideal. We calculate the Stanley depth of S/I when I is a canonical
critical monomial ideal. For non critical monomial ideals we show the existence
of a Stanley ideal with the same depth and Hilbert function.Comment: 5 page
The Magellanic Stream and the density of coronal gas in the Galactic halo
The properties of the Magellanic Stream constrain the density of coronal gas
in the distant Galactic halo. We show that motion through ambient gas can
strongly heat Stream clouds, driving mass loss and causing evaporation. If the
ambient gas density is too high, then evaporation occurs on unreasonably short
timescales. Since heating dominates drag, tidal stripping appears to be
responsible for producing the Stream. Requiring the survival of the cloud MS IV
for 500 Myr sets an upper limit on the halo gas density n_H< 10^{-5} cm^{-3} at
50 kpc, roughly a factor of 10 lower than that estimated from the drag model of
Moore & Davis (1994). Implications for models of the evolution of gas in galaxy
halos are discussed.Comment: 4 pages, 1 figure, in press, ApJ
Selective Hydrogenation and Transfer Hydrogenation for Post-Functional Synthesis of Trifluoromethylphenyl Diazirine Derivatives for Photoaffinity Labeling
Elucidation of protein functions on the basis of structureâactivity relationships can reveal the mechanisms of homeostasis functions in life and is one of the greatest interests of scientists. In the human body, many proteins are activated and/or inactivated by ligands to maintain homeostasis. Understanding the mechanism of molecular interactions between small bioactive ligands and proteins is an important step in rational drug design and discovery. ! Photoaffinity labeling, which is one of the most familiar approaches for chemical biology analysis, was initiated using diazocarbonyl derivatives in 1962 (Singh et al., 1962). Many researchers have subsequently tried to establish alternative approaches for the direct identification of target proteins for the bioactive small ligands. These approaches are based on the affinity between the ligand and the target protein (Figure 1). Several reviews are published for the recent applications of photoaffinity labeling (Tomohiro et al., 2005; Hashimoto & Hatanaka, 2008). To archive photoaffinity labeling, researchers have to prepare photoaffinity labeling ligands. The native ligands must be modified by photoreactive compounds (photophores) by organic synthesi
Neuroimaging of serotonin transporters in post-stroke pathological crying
Pathological crying (PC) is a neuropsychiatric disorder characterized by an excessive tendency towards crying after brain damage. To elucidate the role of serotonin neurotransmission for PC, a pilot study was performed using single photon emission computed tomography with [123I]ÎČ-CIT to estimate central (midbrain/pons and thalamus/hypothalamus) serotonin transporter (SERT) densities in 15 stroke patients who did or did not have PC. SERT binding ratios in midbrain/pons were significantly lower in the PC subgroup
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