2,763 research outputs found
The Gamma-Ray Detected Narrow-Line Seyfert 1 Galaxy 1H 0323+342: Swift Monitoring and Suzaku Spectroscopy
As a radio-loud narrow-line Seyfert 1 galaxy (NLS1) detected by Fermi/LAT in
GeV -rays, 1H 0323+342 is a remarkable Active Galactic Nucleus (AGN)
showing properties characteristic of both NLS1s and blazars. Here we present
results of simultaneous X-ray and UV/optical monitoring observations on 1H
0323+342 taken with the UV/Optical Telescope (UVOT) and X-ray Telescope (XRT)
onboard the Swift satellite over six years from 2006. Overall, the object
showed statistically correlated variations in both the UV and X-ray bands on
timescales of years as well as on timescales of days. A deep Suzaku observation
reveals X-ray variability on timescales as short as a few tens of thousand
seconds, and an X-ray spectrum typical of Seyfert galaxies. The broad-band
spectral energy distribution, for which the data of UV and X-ray observations
taken on 2009 July 26-27 were used, can be well modeled with a simple one-zone
leptonic jet model plus accretion disk/corona emission. The latter is
predominantly responsible for the UV/optical and X-ray (0.3-10 keV) emission
and their observed variations. The correlated UV-X-ray variability on the
timescale of days is consistent with reprocessing of the X-ray radiation by the
accretion disk. The shortest timescale and large normalized excess variance of
the X-ray variability detected with Suzaku suggest a relatively small black
hole mass of the order of , consistent with the estimation based
on the broad H line in the optical.Comment: 38 pages, 12 figures, in press, accepted by AJ (first submitted on
2014 July 7th
To help allies, send security guarantees, not nuclear bombs
Despite the end of the Cold War more than two decades ago, the U.S. still deploys nuclear weapons in several countries. But does deploying these weapons act as a deterrent to conflict, making these countries safer? In new research which analyses the effects of such nuclear deployments, Matthew Fuhrmann and Todd S. Sechser find that their presence does little, when compared with alliance guarantees. They write that having an alliance with a nuclear armed ally is actually more effective in preventing armed conflicts than the local deployment of the weapons themselves
Simultaneous Radio to (Sub-) mm-Monitoring of Variability and Spectral Shape Evolution of potential GLAST Blazars
The Large Area Telescope (LAT) instrument onboard GLAST offers a tremendous
opportunity for future blazar studies. In order to fully benefit from its
capabilities and to maximize the scientific return from the LAT, it is of great
importance to conduct dedicated multi-frequency monitoring campaigns that will
result comprehensive observations. Consequently, we initiated an effort to
conduct a GLAST-dedicated, quasi-simultaneous, broad-band flux-density (and
polarization) monitoring of potential GLAST blazars with the Effelsberg and
OVRO radio telescopes (11cm to 7mm wavelength). Here, we present a short
overview of these activities which will complement the multi-wavelengths
activities of the GLAST/LAT collaboration towards the 'low-energy' radio bands.
Further we will give a brief outlook including the extension of this
coordinated campaign towards higher frequencies and future scientific aims.Comment: 3 pages, to appear in the Proceedings of the First GLAST Symposium,
Stanford University, February 200
Fictive Impurity Approach to Dynamical Mean Field Theory: a Strong-Coupling Investigation
Quantum Monte Carlo and semiclassical methods are used to solve two and four
site cluster dynamical mean field approximations to the square lattice Hubbard
model at half filling and strong coupling. The energy, spin correlation
function, phase boundary and electron spectral function are computed and
compared to available exact results. The comparision permits a quantitative
assessment of the ability of the different methods to capture the effects of
intersite spin correlations. Two real space methods and one momentum space
representation are investigated. One of the two real space methods is found to
be significantly worse: in it, convergence to the correct results is found to
be slow and, for the spectral function, nonuniform in frequency, with
unphysical midgap states appearing. Analytical arguments are presented showing
that the discrepancy arises because the method does not respect the pole
structure of the self energy of the insulator. Of the other two methods, the
momentum space representation is found to provide the better approximation to
the intersite terms in the energy but neither approximation is particularly
acccurate and the convergence of the momentum space method is not uniform. A
few remarks on numerical methods are made.Comment: Errors in previous versions corrected; CDMFT results adde
Planet-Induced Emission Enhancements in HD 179949: Results from McDonald Observations
We monitored the Ca II H and K lines of HD 179949, a notable star in the
southern hemisphere, to observe and confirm previously identified planet
induced emission (PIE) as an effect of star-planet interaction. We obtained
high resolution spectra (R ~ 53,000) with a signal-to-noise ratio S/N >~ 50 in
the Ca II H and K cores during 10 nights of observation at the McDonald
Observatory. Wide band echelle spectra were taken using the 2.7 m telescope.
Detailed statistical analysis of Ca II K revealed fluctuations in the Ca II K
core attributable to planet induced chromospheric emission. This result is
consistent with previous studies by Shkolnik et al. (2003). Additionally, we
were able to confirm the reality and temporal evolution of the phase shift of
the maximum of star-planet interaction previously found. However, no
identifiable fluctuations were detected in the Ca II H core. The Al I lambda
3944 A line was also monitored to gauge if the expected activity enhancements
are confined to the chromospheric layer. Our observations revealed some
variability, which is apparently unassociated with planet induced activity.Comment: 11 pages, 11 figures, 5 tables; Publications of the Astronomical
Society of Australia (in press
Sub-Saturn Planet Candidates to HD 16141 and HD 46375
Precision Doppler measurements from the Keck/HIRES spectrometer reveal
periodic Keplerian velocity variations in the stars HD 16141 and HD 46375. HD
16141 (G5 IV) has a period of 75.8 d and a velocity amplitude of 11 m/s,
yielding a companion having Msini = 0.22 Mjup and a semimajor axis, a = 0.35
AU. HD 46375 (K1 IV/V) has a period of 3.024 d and a velocity amplitude of 35
m/s, yielding a companion with Msini=0.25 Mjup, a semimajor axis of a = 0.041
AU, and an eccentricity of 0.04 (consistent with zero). These companions
contribute to the rising planet mass function toward lower masses.Comment: 4 Figure
A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres
We highlight the importance of gaseous TiO and VO opacity on the highly
irradiated close-in giant planets. The atmospheres of these planets naturally
fall into two classes that are somewhat analogous to the M- and L-type dwarfs.
Those that are warm enough to have appreciable opacity due to TiO and VO gases
we term the ``pM Class'' planets, and those that are cooler we term ``pL
Class'' planets. We calculate model atmospheres for these planets, including
pressure-temperature profiles, spectra, and characteristic radiative time
constants. We show that pM Class planets have hot stratospheres 2000 K
and appear ``anomalously'' bright in the mid infrared secondary eclipse, as was
recently found for planets HD 149026b and HD 209458b. This class of planets
absorbs incident flux and emits thermal flux from high in their atmospheres.
Consequently, they will have large day/night temperature contrasts and
negligible phase shifts between orbital phase and thermal emission light
curves, because radiative timescales are much shorter than possible dynamical
timescales. The pL Class planets absorb incident flux deeper in the atmosphere
where atmospheric dynamics will more readily redistribute absorbed energy. This
will lead to cooler day sides, warmer night sides, and larger phase shifts in
thermal emission light curves. Around a Sun-like primary this boundary occurs
at 0.04-0.05 AU. The eccentric transiting planets HD 147506b and HD
17156b alternate between the classes. Thermal emission in the optical from pM
Class planets is significant red-ward of 400 nm, making these planets
attractive targets for optical detection. The difference in the observed
day/night contrast between ups Andromeda b (pM Class) and HD 189733b (pL Class)
is naturally explained in this scenario. (Abridged.)Comment: Accepted to the Astrophysical Journa
Detailed analysis of Balmer lines in cool dwarf stars
An analysis of H alpha and H beta spectra in a sample of 30 cool dwarf and
subgiant stars is presented using MARCS model atmospheres based on the most
recent calculations of the line opacities. A detailed quantitative comparison
of the solar flux spectra with model spectra shows that Balmer line profile
shapes, and therefore the temperature structure in the line formation region,
are best represented under the mixing length theory by any combination of a low
mixing-length parameter alpha and a low convective structure parameter y. A
slightly lower effective temperature is obtained for the sun than the accepted
value, which we attribute to errors in models and line opacities. The programme
stars span temperatures from 4800 to 7100 K and include a small number of
population II stars. Effective temperatures have been derived using a
quantitative fitting method with a detailed error analysis. Our temperatures
find good agreement with those from the Infrared Flux Method (IRFM) near solar
metallicity but show differences at low metallicity where the two available
IRFM determinations themselves are in disagreement. Comparison with recent
temperature determinations using Balmer lines by Fuhrmann (1998, 2000), who
employed a different description of the wing absorption due to self-broadening,
does not show the large differences predicted by Barklem et al. (2000). In
fact, perhaps fortuitously, reasonable agreement is found near solar
metallicity, while we find significantly cooler temperatures for low
metallicity stars of around solar temperature.Comment: 17 pages, 9 figures, to appear in A&
Ten Low Mass Companions from the Keck Precision Velocity Survey
Ten new low mass companions have emerged from the Keck precision Doppler
velocity survey, with minimum (msini) masses ranging from 0.8 mjup to 0.34
msun. Five of these are planet candidates with msini < 12 mjup, two are brown
dwarf candidates with msini ~30 mjup, and three are low mass stellar
companions. Hipparcos astrometry reveals the orbital inclinations and masses
for three of the (more massive) companions, and it provides upper limits to the
masses for the rest. A new class of extrasolar planet is emerging,
characterized by nearly circular orbits and orbital radii greater than 1 AU.
The planet HD 4208b appears to be a member of this new class. The mass
distribution of extrasolar planets continues to exhibit a rapid rise from 10
mjup toward the lowest detectable masses near 1 msat.Comment: 26 pages, TeX, plus 13 postscript figure
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