225 research outputs found
The Surface Brightness Fluctuations and Globular Cluster Populations of M87 and its Companions
Using the surface brightness fluctuations in HST WFPC-2 images, we determine
that M87, NGC 4486B, and NGC 4478 are all at a distance of ~16 Mpc, while NGC
4476 lies in the background at ~21 Mpc. We also examine the globular clusters
of M87 using archived HST fields. We detect the bimodal color distribution, and
find that the amplitude of the red peak relative to the blue peak is greatest
near the center. This feature is in good agreement with the merger model of
elliptical galaxy formation, where some of the clusters originated in
progenitor galaxies while other formed during mergers.Comment: 5 pages, 2 figure
Kepler-413b: a slightly misaligned, Neptune-size transiting circumbinary planet
We report the discovery of a transiting, Rp = 4.347+/-0.099REarth,
circumbinary planet (CBP) orbiting the Kepler K+M Eclipsing Binary (EB) system
KIC 12351927 (Kepler-413) every ~66 days on an eccentric orbit with ap =
0.355+/-0.002AU, ep = 0.118+/-0.002. The two stars, with MA =
0.820+/-0.015MSun, RA = 0.776+/-0.009RSun and MB = 0.542+/-0.008MSun, RB =
0.484+/-0.024RSun respectively revolve around each other every
10.11615+/-0.00001 days on a nearly circular (eEB = 0.037+/-0.002) orbit. The
orbital plane of the EB is slightly inclined to the line of sight (iEB =
87.33+/-0.06 degrees) while that of the planet is inclined by ~2.5 degrees to
the binary plane at the reference epoch. Orbital precession with a period of
~11 years causes the inclination of the latter to the sky plane to continuously
change. As a result, the planet often fails to transit the primary star at
inferior conjunction, causing stretches of hundreds of days with no transits
(corresponding to multiple planetary orbital periods). We predict that the next
transit will not occur until 2020. The orbital configuration of the system
places the planet slightly closer to its host stars than the inner edge of the
extended habitable zone. Additionally, the orbital configuration of the system
is such that the CBP may experience Cassini-States dynamics under the influence
of the EB, in which the planet's obliquity precesses with a rate comparable to
its orbital precession. Depending on the angular precession frequency of the
CBP, it could potentially undergo obliquity fluctuations of dozens of degrees
(and complex seasonal cycles) on precession timescales.Comment: 48 pages, 13 figure
Physical Conditions in the Seyfert Galaxy NGC 2992
This paper presents long slit spectral maps of the bi-cone shaped extended
narrow line region (ENLR) in the Seyfert galaxy NGC 2992. We investigate the
physical properties of the ENLR via emission line diagnostics, and compare the
observations to shock and photoionization models for the excitation mechanism
of the gas. The line ratios vary as a function of position in the ENLR, and the
loci of the observed points on line ratio diagrams are shown to be most
consistent with shock+precursor model grids. We consider the energetics of a
nuclear ionizing source for the ENLR, and perform the q-test in which the rate
of ionizing photons from the nucleus is inferred from measurements of the
density and ionization parameter. The q-test is shown to be invalid in the case
of NGC 2992 because of the limitations of the [S II]6717/6731 density
diagnostic. The excitation of the gas is shown to be broadly consistent with
the kinematics, with higher [N II]6583/H-alpha present in the more dynamically
active region. We also show that the pressure associated with the X-ray
emitting plasma may provide a large fraction of the pressure required to power
the ENLR via shocks.Comment: 55 pages, 49 figures, ApJ accepted September 9, 1998. Figures 1a-f
are provided in jpeg forma
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
ASCA Observations of the Composite Warm Absorber in NGC 3516
We obtained X-ray spectra of the Seyfert 1 galaxy NGC~3516 in March 1995
using ASCA. Simultaneous far-UV observations were obtained with HUT on the
Astro-2 shuttle mission. The ASCA spectrum shows a lightly absorbed power law
of energy index 0.78. The low energy absorbing column is significantly less
than previously seen. Prominent O~vii and O~viii absorption edges are visible,
but, consistent with the much lower total absorbing column, no Fe K absorption
edge is detectable. A weak, narrow Fe~K emission line from cold
material is present as well as a broad Fe~K line. These features are
similar to those reported in other Seyfert 1 galaxies. A single warm absorber
model provides only an imperfect description of the low energy absorption. In
addition to a highly ionized absorber with ionization parameter and
a total column density of , adding a lower
ionization absorber with and a total column of significantly improves the fit. The contribution of
resonant line scattering to our warm absorber models limits the Doppler
parameter to at 90\% confidence. Turbulence at the sound
speed of the photoionized gas provides the best fit. None of the warm absorber
models fit to the X-ray spectrum can match the observed equivalent widths of
all the UV absorption lines. Accounting for the X-ray and UV absorption
simultaneously requires an absorbing region with a broad range of ionization
parameters and column densities.Comment: 14 pages, 4 Postscript figures, uses aaspp4.sty To appear in the
August 20, 1996, issue of The Astrophysical Journa
A Radio Study of the Seyfert Galaxy IC 5063: Evidence for Fast Gas Outflow
New radio continuum (8 GHz and 1.4 GHz) and HI 21 cm line observations of the
Seyfert 2 galaxy IC 5063 (PKS 2048-572) were obtained with the Australia
Telescope Compact Array (ATCA). The 8 GHz image reveals a linear triple
structure (~4'', 1.5 kpc) oriented perpendicular to the optical polarization
position angle. It is aligned with the inner dust lane and shows strong
morphological association with the narrow emission line region (NLR). At 21 cm,
very broad (~700 km/s) HI absorption is observed against the strong continuum
source. This absorption is almost entirely blueshifted, indicating a fast net
outflow, but a faint and narrow redshifted component is also present. In IC
5063 we see clear evidence for strong shocks resulting from the radio
plasma-ISM interaction in the central few kpc. However, the energy flux in the
radio plasma is an order of magnitude smaller than the energy emitted in
emission lines. Thus, shocks are unlikely to account solely for the global
ionization of the emission line region, particularly at large distances.
The HI emission outlines a warped disk associated with the system of dust
lanes some ~2' (~38 kpc) in radius. The lack of kinematically disturbed gas
outside the central few kpc, coupled with the disk warp and close morphological
connection of the inner dust lanes and the large-scale ionized gas, support the
idea that the gas at large radii is photoionized by the central region, while
shadowing effects are important in defining its X-shaped morphology. The
kinematics of the ionized and of the neutral gas suggests the existence of a
dark halo.Comment: 18 pages, 8 Postscript figures, 3 jpeg figures, Postscript preprint
is available from http://jhufos.pha.jhu.edu/~zlatan/papers.htm
M87: A Misaligned BL LAC?
The nuclear region of M87 was observed with the Faint Object Spectrograph
(FOS) on the Hubble Space Telescope (HST) at 6 epochs, spanning 18 months,
after the HST image quality was improved with the deployment of the corrective
optics (COSTAR) in December 1993. From the FOS target acquisition data, we have
established that the flux from the optical nucleus of M87 varies by a factor ~2
on time scales of ~2.5 months and by as much as 25% over 3 weeks, and remains
unchanged (<= 2.5%) on time scales of ~1 day. The changes occur in an
unresolved central region <= 5 pc in diameter, with the physical size of the
emitting region limited by the observed time scales to a few hundred
gravitational radii. The featureless continuum spectrum becomes bluer as it
brightens while emission lines remain unchanged. This variability combined with
the observations of the continuum spectral shape, strong relativistic boosting
and the detection of significant superluminal motions in the jet, strongly
suggest that M87 belongs to the class of BL Lac objects but is viewed at an
angle too large to reveal the classical BL Lac properties.Comment: 12 pages, 3 Postscript figure
Stabilized micelles as delivery vehicles for paclitaxel
Paclitaxel is an antineoplastic drug used against a variety of tumors, but its low aqueous solubility and active removal caused by P-glycoprotein in the intestinal cells hinder its oral administration. In our study, new type of stabilized Pluronic micelles were developed and evaluated as carriers for paclitaxel delivery via oral or intravenous route. The pre-stabilized micelles were loaded with paclitaxel by simple solvent/evaporation technique achieving high encapsulation efficiency of approximately 70%. Gastrointestinal transit of the developed micelles was evaluated by oral administration of rhodamine-labeled micelles in rats. Our results showed prolonged gastrointestinal residence of the marker encapsulated into micelles, compared to a solution containing free marker. Further, the oral administration of micelles in mice showed high area under curve of micellar paclitaxel (similar to the area of i.v. Taxol®), longer mean residence time (9-times longer than i.v. Taxol®) and high distribution volume (2-fold higher than i.v. Taxol®) indicating an efficient oral absorption of paclitaxel delivered by micelles. Intravenous administration of micelles also showed a significant improvement of pharmacokinetic parameters of micellar paclitaxel vs. Taxol®, in particular higher area under curve (1.2-fold), 5-times longer mean residence time and lower clearance, indicating longer systemic circulation of the micelles
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