1,550 research outputs found
X-ray Supercavities in the Hydra A Cluster and the Outburst History of the Central Galaxy's Active Nucleus
A 227 ksec Chandra Observatory X-ray image of the hot plasma in the Hydra A
cluster has revealed an extensive cavity system. The system was created by a
continuous outflow or a series of bursts from the nucleus of the central galaxy
over the past 200-500 Myr. The cavities have displaced 10% of the plasma within
a 300 kpc radius of the central galaxy, creating a swiss-cheese-like topology
in the hot gas. The surface brightness decrements are consistent with empty
cavities oriented within 40 degrees of the plane of the sky. The outflow has
deposited upward of 10^61 erg into the cluster gas, most of which was propelled
beyond the inner ~100 kpc cooling region. The supermassive black hole has
accreted at a rate of approximately 0.1-0.25 solar masses per year over this
time frame, which is a small fraction of the Eddington rate of a ~10^9 solar
mass black hole, but is dramatically larger than the Bondi rate. Given the
previous evidence for a circumnuclear disk of cold gas in Hydra A, these
results are consistent with the AGN being powered primarily by infalling cold
gas. The cavity system is shadowed perfectly by 330 MHz radio emission. Such
low frequency synchrotron emission may be an excellent proxy for X-ray cavities
and thus the total energy liberated by the supermassive black hole.Comment: 8 pages, 3 figures; Submitted to ApJ, revised per referee's
suggestion
The mission oriented terminal area simulation facility
The Mission Oriented Terminal Area Simulation (MOTAS) was developed to provide an ATC environment in which flight management and flight operations research studies can be conducted with a high degree of realism. This facility provides a flexible and comprehensive simulation of the airborne, ground-based and communication aspects of the airport terminal area environment. Major elements of the simulation are: an airport terminal area environment model, two air traffic controller stations, several aircraft models and simulator cockpits, four pseudo pilot stations, and a realistic air-ground communications network. MOTAS has been used for one study with the DC-9 simulator and a series of data link studies are planned in the near future
Dust Properties and Star-Formation Rates in Star-Forming Dwarf Galaxies
We have used the Spitzer Space Telescope to study the dust properties of a
sample of star-forming dwarf galaxies. The differences in the mid-infrared
spectral energy distributions for these galaxies which, in general, are low
metallicity systems, indicate differences in the physical properties, heating,
and/or distribution of the dust. Specifically, these galaxies have more hot
dust and/or very small grains and less PAH emission than either spiral or
higher luminosity starburst galaxies. As has been shown in previous studies,
there is a gradual decrease in PAH emission as a function of metallicity.
Because much of the energy from star formation in galaxies is re-radiated in
the mid-infrared, star-formation rate indicators based on both line and
continuum measurements in this wavelength range are coming into more common
usage. We show that the variations in the interstellar medium properties of
galaxies in our sample, as measured in the mid-infrared, result in over an
order of magnitude spread in the computed star-formation rates.Comment: 25 pages, 11 figures, 4 tables, ApJ accepte
CORMASS: A Compact and Efficient NIR Spectrograph for Studying Low-Mass Objects
CorMASS (Cornell Massachusetts Slit Spectrograph) is a compact,
low-resolution (R=300), double-pass prism cross-dispersed near-infrared (NIR)
spectrograph in operation on the Palomar Observatory 60-inch telescope. Its
2-dimensional spectral format provides simultaneous coverage from lambda ~ 0.75
microns to lambda ~ 2.5 microns (z'JHK bands). A remotely operated cold flip
mirror permits its NICMOS3 detector to function as a K_s slit viewer to assist
object placement into the 2 arcsec x 15 arcsec slit. CorMASS was primarily
designed for the rapid spectral classification of low-mass stellar and
sub-stellar objects identified by the Two-Micron All Sky Survey (2MASS).
CorMASS' efficiency and resolution also make it a versatile instrument for the
spectral observation and classification of many other types of bright objects
(K<14) including quasars, novae, and emission line objects.Comment: To be published in Feb 2001 PASP, 19 pages, 12 Figures, High
Resolution file can be retrieved from
ftp://iras2.tn.cornell.edu/pub/wilson/papers/cormass.ps.g
Abundances in galactic H2 regions, 3: G25.4-0.2, G45.5+0.06, M8, S159 and DR22
Measurements of the ARII (6.99 microns), ArIII (8.99 microns), NeII (12.81 microns), SIII (18.71 microns), and SIV (10.51 microns) lines are presented for five compact HII regions along with continuum spectroscopy. From these data and radio data, lower limits to the elemental abundances of Ar, S, and Ne were deduced. The complex G25.4-0.2 is only 5.5 kpc from the galactic center, and is considerably overabundant in all these elements. Complex G45.5+0.06 is at seven kpc from the galactic center, and appears to be approximately consistent with solar abundance. The complex S159 in the Perseus Arm, at 12 kpc from the galactic center, has solar abundance, while M8 in the solar neighborhood may be somewhat overabundant in Ar and Ne. Complex DR 22, at 10 kpc from the galactic center in the Cygnus Arm, is overabundant in Ar. A summary of results from a series of papers on abundances is given
AWM 4 - an isothermal cluster observed with XMM-Newton
We present analysis of an XMM observation of the poor cluster AWM 4. The
cluster is relaxed and its X-ray halo is regular with no apparent substructure.
Azimuthally averaged radial spectral profiles suggest that the cluster is
isothermal to a radius of at least 160 kpc, with no evidence of a central
cooling region. Spectral mapping shows some significant temperature and
abundance substructure, but no evidence of strong cooling in the cluster core.
Abundance increases in the core, but not to the extent expected, and we find
some indication of gas mixing. Modeling the three dimensional properties of the
system, we show that ongoing heating by an AGN in the dominant elliptical, NGC
6051, is likely to be responsible for the lack of cooling. We also compare AWM
4 to MKW 4, a cluster of similar mass observed recently with XMM. While the two
systems have similar gravitational mass profiles, MKW 4 has a cool core and
somewhat steeper gas density profile, which leads to a lower core entropy. AWM
4 has a considerably larger gas fraction at 0.1 R200, and we show that these
differences result from the difference in mass between the two dominant
galaxies and the activity cycles of their AGN. We estimate the energy required
to raise the temperature profile of MKW 4 to match that of AWM 4 to be 9x10^58
erg, or 3x10^43 erg/s for 100 Myr, comparable to the likely power output of the
AGN in AWM 4.Comment: Accepted for publication in MNRAS, 18 pages, 1 colour and 11 b&w
postscript figures, corrected author affiliatio
The Kondo Effect in the Presence of Magnetic Impurities
We measure transport through gold grain quantum dots fabricated using
electromigration, with magnetic impurities in the leads. A Kondo interaction is
observed between dot and leads, but the presence of magnetic impurities results
in a gate-dependent zero-bias conductance peak that is split due to an RKKY
interaction between the spin of the dot and the static spins of the impurities.
A magnetic field restores the single Kondo peak in the case of an
antiferromagnetic RKKY interaction. This system provides a new platform to
study Kondo and RKKY interactions in metals at the level of a single spin.Comment: 5 pages, 4 figure
Twenty Years of Timing SS433
We present observations of the optical ``moving lines'' in spectra of the
Galactic relativistic jet source SS433 spread over a twenty year baseline from
1979 to 1999. The red/blue-shifts of the lines reveal the apparent precession
of the jet axis in SS433, and we present a new determination of the precession
parameters based on these data. We investigate the amplitude and nature of
time- and phase-dependent deviations from the kinematic model for the jet
precession, including an upper limit on any precessional period derivative of
. We also dicuss the implications of these results
for the origins of the relativistic jets in SS433.Comment: 21 pages, including 9 figures. To appear in the Astrophysical Journa
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