6,936 research outputs found
Time-Series Ensemble Photometry and the Search for Variable Stars in the Open Cluster M11
This work presents the first large-scale photometric variability survey of
the intermediate age (~200 Myr) open cluster M11. Thirteen nights of data over
two observing seasons were analyzed (using crowded field and ensemble
photometry techniques) to obtain high relative precision photometry. In this
study we focus on the detection of candidate member variable stars for
follow-up studies. A total of 39 variable stars were detected and can be
categorized as follows: 1 irregular (probably pulsating) variable, 6 delta
Scuti variables, 14 detached eclipsing binary systems, 17 W UMa variables, and
1 unidentified/candidate variable. While previous proper motion studies allow
for cluster membership determination for the brightest stars, we find that
membership determination is significantly hampered below V=15,R=15.5 by the
large population of field stars overlapping the cluster MS. Of the brightest
detected variables that have a high likelihood of cluster membership, we find
five systems where further work could help constrain theoretical stellar
models, including one potential W UMa member of this young cluster.Comment: 38 pages, 13 figures, accepted for December 2005 AJ, high-resolution
version available upon reques
Homogeneous cooling of rough, dissipative particles: Theory and simulations
We investigate freely cooling systems of rough spheres in two and three
dimensions. Simulations using an event driven algorithm are compared with
results of an approximate kinetic theory, based on the assumption of a
generalized homogeneous cooling state. For short times , translational and
rotational energy are found to change linearly with . For large times both
energies decay like with a ratio independent of time, but not
corresponding to equipartition. Good agreement is found between theory and
simulations, as long as no clustering instability is observed. System
parameters, i.e. density, particle size, and particle mass can be absorbed in a
rescaled time, so that the decay of translational and rotational energy is
solely determined by normal restitution and surface roughness.Comment: 10 pages, 10 eps-figure
Coefficient of restitution for elastic disks
We calculate the coefficient of restitution, , starting from a
microscopic model of elastic disks. The theory is shown to agree with the
approach of Hertz in the quasistatic limit, but predicts inelastic collisions
for finite relative velocities of two approaching disks. The velocity
dependence of is calculated numerically for a wide range of
velocities. The coefficient of restitution furthermore depends on the elastic
constants of the material via Poisson's number. The elastic vibrations absorb
kinetic energy more effectively for materials with low values of the shear
modulus.Comment: 25 pages, 12 Postscript figures, LaTex2
A Deep Chandra Observation of the AGN Outburst and Merger in Hickson Compact Group 62
We report on an analysis of new Chandra data of the galaxy group HCG 62, well
known for possessing cavities in its intragroup medium (IGM) that were inflated
by the radio lobes of its central active galactic nucleus (AGN). With the new
data, a factor of three deeper than previous Chandra data, we re-examine the
energetics of the cavities and determine new constraints on their contents. We
confirm that the ratio of radiative to mechanical power of the AGN outburst
that created the cavities is less than 10^-4, among the lowest of any known
cavity system, implying that the relativistic electrons in the lobes can supply
only a tiny fraction of the pressure required to support the cavities. This
finding implies additional pressure support in the lobes from heavy particles
(e.g., protons) or thermal gas. Using spectral fits to emission in the
cavities, we constrain any such volume-filling thermal gas to have a
temperature kT > 4.3 keV. For the first time, we detect X-ray emission from the
central AGN, with a luminosity of L(2-10 keV) = (1.1 +/- 0.4) x 10^39 erg s^-1
and properties typical of a low-luminosity AGN. Lastly, we report evidence for
a recent merger from the surface brightness, temperature, and metallicity
structure of the IGM.Comment: Accepted to MNRAS, 14 pages, 9 figure
Granular Collapse as a Percolation Transition
Inelastic collapse is found in a two-dimensional system of inelastic hard
disks confined between two walls which act as an energy source. As the
coefficient of restitution is lowered, there is a transition between a state
containing small collapsed clusters and a state dominated by a large collapsed
cluster. The transition is analogous to that of a percolation transition. At
the transition the number of clusters n_s of size s scales as with .Comment: 10 pages revtex, 5 figures, accepted by Phys Rev E many changes and
corrections from previous submissio
Inelastic collapse of a randomly forced particle
We consider a randomly forced particle moving in a finite region, which
rebounds inelastically with coefficient of restitution r on collision with the
boundaries. We show that there is a transition at a critical value of r,
r_c\equiv e^{-\pi/\sqrt{3}}, above which the dynamics is ergodic but beneath
which the particle undergoes inelastic collapse, coming to rest after an
infinite number of collisions in a finite time. The value of r_c is argued to
be independent of the size of the region or the presence of a viscous damping
term in the equation of motion.Comment: 4 pages, REVTEX, 2 EPS figures, uses multicol.sty and epsf.st
Sand as Maxwell's demon
We consider a dilute gas of granular material inside a box, kept in a
stationary state by shaking. A wall separates the box into two identical
compartments, save for a small hole at some finite height . As the gas is
cooled, a second order phase transition occurs, in which the particles
preferentially occupy one side of the box. We develop a quantitative theory of
this clustering phenomenon and find good agreement with numerical simulations
- …