28 research outputs found
The Color Distributions of Globular Clusters in Virgo Elliptical Galaxies
This Letter presents the color distributions of the globular cluster (GC)
systems of 12 Virgo elliptical galaxies, measured using data from the Hubble
Space Telescope. Bright galaxies with large numbers of detected GC's show two
distinct cluster populations with mean V-I colors near 1.01 and 1.26. The GC
population of M86 is a clear exception; its color distribution shows a single
sharp peak near V-I=1.03. The absence of the red population in this galaxy, and
the consistency of the peak colors in the others, may be indications of the
origins of the two populations found in most bright elliptical galaxies.Comment: 5 pages, 1 figure, to be published in ApJ Letters Corrections to
introductio
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
Qatar Exoplanet Survey : Qatar-3b, Qatar-4b and Qatar-5b
We report the discovery of Qatar-3b, Qatar-4b, and Qatar-5b, three new
transiting planets identified by the Qatar Exoplanet Survey (QES). The three
planets belong to the hot Jupiter family, with orbital periods of
=2.50792 days, =1.80539 days, and =2.87923 days.
Follow-up spectroscopic observations reveal the masses of the planets to be
=4.31 , =6.10 , and
= 4.32 , while model fits to the transit light
curves yield radii of = 1.096 , =
1.135 , and = 1.107 . The
host stars are low-mass main sequence stars with masses and radii =
1.145 , = 0.896 ,
= 1.128 and = 1.272 ,
= 0.849 and = 1.076
for Qatar-3, 4 and 5 respectively. The V magnitudes of the three
host stars are =12.88, =13.60, and =12.82. All three
new planets can be classified as heavy hot Jupiters (M > 4 ).Comment: 13Pages, 8Figure
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
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
Are Seyfert Narrow Line Regions Powered by Radio Jets?
We argue that the narrow line regions of Seyfert galaxies are powered by the
transport of energy and momentum by the radio-emitting jets and consequently
that the ratio of the radio power to jet energy flux is much smaller than is
usually assumed for radio galaxies. This can be partially attributed to the
smaller ages () of Seyferts compared to radio galaxies but one
also requires that either the magnetic energy density is more than an order of
magnitude below the equipartition value, or more likely, that the internal
energy densities of Seyfert jets are dominated by thermal plasma. If Seyfert
jets are initially dominated by relativistic plasma, then an analysis of the
data on jets in five Seyfert galaxies shows that all but one of these would
have mildly relativistic jet velocities near 100 pc in order to power the
respective narrow-line regions. However, observations of jet-cloud interactions
in the NLR provide additional information on jet velocities and composition via
the momentum budget. Our analysis of a jet-cloud interaction in NGC 1068,
implies a shocked jet pressure much larger than the minimum pressure of the
radio knot, a velocity and a jet temperature
implying mildly relativistic electrons but thermal protons. The jet mass flux
at this point , is an order of magnitude higher than
the mass accretion rate into the black hole, strongly indicating entrainment.
The initial jet mass flux , comparable to the mass
accretion rate and is consistent with the densities inferred for accretion disc
coronae from high energy observations, together with an initially mildly
relativistic velocity and an initial jet radius of order 10 gravitational
radii.Comment: LaTeX2e, uses astrobib.sty, 4 postscript figures; submitted to Ap