7,861 research outputs found
Evidence for a 3 x 10^8 solar mass black hole in NGC 7052 from HST observations of the nuclear gas disk
We present an HST study of the nuclear region of the E4 radio galaxy NGC
7052, which has a nuclear disk of dust and gas. The WFPC2 was used to obtain B,
V and I broad-band images and an H_alpha+[NII] narrow-band image. The FOS was
used to obtain H_alpha+[NII] spectra along the major axis, using a 0.26 arcsec
diameter circular aperture. The observed rotation velocity of the ionized gas
is V = 155 +/- 17 km/s at r = 0.2 arcsec from the nucleus. The Gaussian
dispersion of the emission lines increases from sigma = 70 km/s at r=1 arcsec,
to sigma = 400 km/s on the nucleus.
To interpret the gas kinematics we construct axisymmetric models in which the
gas and dust reside in a disk in the equatorial plane of the stellar body. It
is assumed that the gas moves on circular orbits, with an intrinsic velocity
dispersion due to turbulence. The circular velocity is calculated from the
combined gravitational potential of the stars and a possible nuclear black hole
(BH). Models without a BH predict a rotation curve that is shallower than
observed (V_pred = 92 km/s at r = 0.2 arcsec), and are ruled out at > 99%
confidence. Models with a BH of 3.3^{+2.3}_{-1.3} x 10^8 solar masses provide
an acceptable fit.
NGC 7052 can be added to the list of active galaxies for which HST spectra of
a nuclear gas disk provide evidence for the presence of a central BH. The BH
masses inferred for M87, M84, NGC 6251, NGC 4261 and NGC 7052 span a range of a
factor 10, with NGC 7052 falling on the low end. By contrast, the luminosities
of these galaxies are identical to within 25%. Any relation between BH mass and
luminosity, as suggested by independent arguments, must therefore have a
scatter of at least a factor 10.Comment: 39 pages, LaTeX, with 16 PostScript figures. Submitted to the
Astronomical Journal. Postscript version with higher resolution figures
available from http://sol.stsci.edu/~marel/abstracts/abs_R22.htm
Electron-beam-induced shift in the apparent position of a pinned vortex in a thin superconducting film
When an electron beam strikes a superconducting thin film near a pinned
vortex, it locally increases the temperature-dependent London penetration depth
and perturbs the circulating supercurrent, thereby distorting the vortex's
magnetic field toward the heated spot. This phenomenon has been used to
visualize vortices pinned in SQUIDs using low-temperature scanning electron
microscopy. In this paper I develop a quantitative theory to calculate the
displacement of the vortex-generated magnetic-flux distribution as a function
of the distance of the beam spot from the vortex core. The results are
calculated using four different models for the spatial distribution of the
thermal power deposited by the electron beam.Comment: 9 pages, 6 figures, resubmitted to PRB with referee-suggested
revisions, includes new paragraph on numerical evaluatio
Progress report on the ultra heavy cosmic ray experiment (AO178)
The Ultra Heavy Cosmic Ray Experiment (UHCRE) is based on a modular array of 192 side-viewing solid state nuclear track detector stacks. These stacks were mounted in sets of four in 48 pressure vessels employing sixteen peripheral Long Duration Exposure Facility (LDEF) trays. The extended duration of the LDEF mission has resulted in a greatly enhanced scientific yield from the UHCRE. The geometry factor for high energy cosmic ray nuclei, allowing for Earth shadowing, was 30 sq m-sr, giving a total exposure factor of 170 sq m-sr-y at an orbital inclination of 28.4 degrees. Scanning results indicate that about 3000 cosmic ray nuclei in the charge region with Z greater than 65 were collected. This sample is more than ten times the current world data in the field (taken to be the data set from the HEAO-3 mission plus that from the Ariel-6 mission) and is sufficient to provide the world's first statistically significant sample of actinide (Z greater than 88) cosmic rays. Results to date are presented including details of ultra-heavy cosmic ray nuclei, analysis of pre-flight and post-flight calibration events and details of track response in the context of detector temperature history. The integrated effect of all temperature and age related latent track variations cause a maximum charge shift of +/- 0.8 e for uranium and +/- 0.6 e for the platinum-lead group. The precision of charge assignment as a function of energy is derived and evidence for remarkably good charge resolution achieved in the UHCRE is considered. Astrophysical implications of the UHCRE charge spectrum are discussed
WFPC2 Images of the Central Regions of Early-Type Galaxies - I. The Data
We present high resolution R-band images of the central regions of 67
early-type galaxies obtained with the Wide Field and Planetary Camera 2 (WFPC2)
aboard the Hubble Space Telescope (HST). Our sample strikingly confirms the
complex morphologies of the central regions of early-type galaxies. In
particular, we detect dust in 43 percent of all galaxies, and evidence for
embedded stellar disks in a remarkably large fraction of 51 percent. In 14 of
those galaxies the disk-like structures are misaligned with the main galaxy,
suggesting that they correspond to stellar bars in S0 galaxies. We analyze the
luminosity profiles of the galaxies in our sample, and classify galaxies
according to their central cusp slope. To a large extent we confirm the clear
dichotomy found in previous HST surveys: bright, boxy ellipticals with shallow
inner cusps (`core' galaxies) on one hand and faint, disky ellipticals with
steep central cusps (`power-law' galaxies) on the other hand. The advantages
and shortcomings of classification schemes utilizing the extrapolated central
cusp slope are discussed, and it is shown that this cusp slope might be an
inadequate representation for galaxies whose luminosity profile slope changes
smoothly with radius rather than resembling a broken power-law. In fact, we
find evidence for an `intermediate' class of galaxies, that cannot
unambiguously be classified as either core or power-law galaxies, and which
have central cusp slopes and absolute magnitudes intermediate between those of
core and power-law galaxies.Comment: 44 pages, 7 Postscript figures. Accepted for publication in the
Astronomical Journal. The associated Appendix with figures of luminosity
profiles, contour plots and isophotal parameters for all galaxies is
available at http://www.astro.washington.edu/rest/centralpro
A Possible Role for Calcitonin-Gene-Related Peptide in the Regulation of the Smooth Muscle Tone of the Bladder and Penis
Observations of microquasars with the MAGIC telescope
We report on the results from the observations in very high energy band (VHE,
E_gamma > 100GeV) of the black hole X-ray binary (BHXB) Cygnus X-1. The
observations were performed with the MAGIC telescope, for a total of 40 hours
during 26 nights, spanning the period between June and November 2006. We report
on the results of the searches for steady and variable gamma-ray signals,
including the first experimental evidence for an intense flare, of duration
between 1.5 and 24 hours.Comment: Contribution to the 30th ICRC, Merida Mexico, July 2007 on behalf of
the MAGIC Collaboratio
Changes in Penile Hemodynamics after Intracavernous Injection of Prostaglandin E1 and Prostaglandin I2 in Pigtailed Monkeys
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