8,173 research outputs found
Initial radio-frequency gas heating experiments to simulate the thermal environment in a nuclear light bulb reactor
Initial radio frequency gas heating experiments to simulate thermal environment in nuclear light bulb reacto
Kondo Insulator description of spin state transition in FeSb2
The thermal expansion and heat capacity of FeSb2 at ambient pressure agrees
with a picture of a temperature induced spin state transition within the Fe
t_{2g} multiplet. However, high pressure powder diffraction data show no sign
of a structural phase transition up to 7GPa. A bulk modulus B=84(3)GPa has been
extracted and the temperature dependence of the Gruneisen parameter has been
determined. We discuss here the relevance of a Kondo insulator description for
this material.Comment: Physical Review B in press (2005
Searching for Planets in the Hyades V: Limits on Planet Detection in the Presence of Stellar Activity
We present the results of a radial velocity survey of a sample of Hyades
stars, and discuss the effects of stellar activity on radial velocity
measurements. The level of radial velocity scatter due to rotational modulation
of stellar surface features for the Hyades is in agreement with the predictions
of Saar & Donahue (1997)- the maximum radial velocity rms of up to ~50 m/s,
with an average rms of ~16 m/s. In this sample of 94 stars, we find 1 new
binary, 2 stars with linear trends indicative of binary companions, and no
close-in giant planets. We discuss the limits on extrasolar planet detection in
the Hyades and the constraints imposed on radial velocity surveys of young
stars.Comment: To appear in the June 2004 issue of A
The CIV-MgII Kinematics Connection in <z>~0.7 Galaxies
We have examined Faint Object Spectrograph data from the Hubble Space
Telescope Archive for CIV 1548,1550 absorption associated with 40 MgII
2796,2803 absorption-selected galaxies at 0.4 < z < 1.4. We report a strong
correlation between MgII kinematics, measured in 6 km/s resolution HIRES/Keck
spectra, and W_r(1548); this implies a physical connection between the
processes that produce "outlying velocity" MgII clouds and high ionization
galactic/halo gas. We found no trend in ionization condition,
W_r(1548)/W_r(2796), with galaxy-QSO line-of-sight separation for 13 systems
with confirmed associated galaxies, suggesting no obvious ionization gradient
with galactocentric distance in these higher redshift galaxies. We find
tentative evidence (2-sigma) that W_r(1548)/W_r(2796) is anti-correlated with
galaxy color; if further data corroborate this trend, in view of the
strong CIV-MgII kinematics correlation, it could imply a connection between
stellar populations, star formation episodes, and the kinematics and ionization
conditions of halo gas at z~1.Comment: Accepted to Astrophysical Journal Letters; 4 pages; 3 figures;
emulateapj.st
The Physical Conditions of Intermediate Redshift MgII Absorbing Clouds from Voigt Profile Analysis
[Slightly Abridged] We present a detailed statistical analysis of the column
densities, N, and Doppler parameters, b, of MgII absorbing clouds at redshifts
0.4<z<1.2. We use the HIRES/Keck data and Voigt profile (VP) fitting results
presented by Churchill & Vogt (Paper I). The sample is comprised of 175 clouds
from 23 systems along 18 quasar lines of sight. In order to understand whether
inferred conditions could be "false", we performed extensive simulations of our
VP analyses. In brief, we find: (1) N(FeII) and N(MgII) are correlated at the
9-sigma level. There is a 5-sigma anti-correlation between N(MgI)/N(MgII) and
N(MgII). (2) Power-law fits to the distributions of N(MgII), N(FeII), and
N(MgI) yielded power-law slopes of -1.6, -1.7, and -2.0. (3) The modes of the
Doppler parameter distributions were ~5 km/s for MgII and FeII and ~7
km/s for MgI. The clouds are consistent with being thermally broadened, with
temperatures in the 30-40,000K range. (4) A two-component Gaussian model to the
velocity two-point correlation function yielded velocity dispersions of 54 km/s
and 166 km/s. The narrow component has roughly twice the amplitude of the
broader component. The width and amplitude of the broader component decreases
as equivalent width increases. (5) From photoionization models we find that the
column density ratios are most consistent with photoionization by the
extragalactic background, as opposed to stars. Based upon N(MgI)/N(MgII), it
appears that at least two-phase ionization models are required to explain the
data.Comment: Accepted to the Astronomical Journal (January 2003
Charmonium Suppression by Comover Scattering in Pb+Pb Collisions
The first reports of and production from experiment NA50 at
the CERN SPS are compared to predictions based on a hadronic model of
charmonium suppression. Data on centrality dependence and total cross sections
are in good accord with these predictions.Comment: 9 pages, latex, 6 figures, epsf, figure added and text modified to
clarify result
Galaxy Interactions in Compact Groups II: abundance and kinematic anomalies in HCG 91c
Galaxies in Hickson Compact Group 91 (HCG 91) were observed with the WiFeS
integral field spectrograph as part of our ongoing campaign targeting the
ionized gas physics and kinematics inside star forming members of compact
groups. Here, we report the discovery of HII regions with abundance and
kinematic offsets in the otherwise unremarkable star forming spiral HCG 91c.
The optical emission line analysis of this galaxy reveals that at least three
HII regions harbor an oxygen abundance ~0.15 dex lower than expected from their
immediate surroundings and from the abundance gradient present in the inner
regions of HCG 91c. The same star forming regions are also associated with a
small kinematic offset in the form of a lag of 5-10 km/s with respect to the
local circular rotation of the gas. HI observations of HCG 91 from the Very
Large Array and broadband optical images from Pan-STARRS suggest that HCG 91c
is caught early in its interaction with the other members of HCG 91. We discuss
different scenarios to explain the origin of the peculiar star forming regions
detected with WiFeS, and show that evidence point towards infalling and
collapsing extra-planar gas clouds at the disk-halo interface, possibly as a
consequence of long-range gravitational perturbations of HCG 91c from the other
group members. As such, HCG 91c provides evidence that some of the
perturbations possibly associated with the early phase of galaxy evolution in
compact groups impact the star forming disk locally, and on sub-kpc scales.Comment: 25 pages, 21 figures, MNRAS accepted. Until publication of the
article, the interactive component of Figure 4 is available at this URL:
http://www.mso.anu.edu.au/~fvogt/website/misc.htm
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