168 research outputs found
The First Detection of [O IV] from an Ultraluminous X-ray Source with Spitzer. II. Evidence for High Luminosity in Holmberg II ULX
This is the second of two papers examining Spitzer Infrared Spectrograph
(IRS) observations of the ultraluminous X-ray source (ULX) in Holmberg II. Here
we perform detailed photoionization modeling of the infrared lines. Our
analysis suggests that the luminosity and morphology of the [O IV] 25.89 m
emission line is consistent with photoionization by the soft X-ray and far
ultraviolet (FUV) radiation from the accretion disk of the binary system and
inconsistent with narrow beaming. We show that the emission nebula is
matter-bounded both in the line of sight direction and to the east, and
probably radiation-bounded to the west. A bolometric luminosity in excess of
10 erg s would be needed to produce the measured [O IV] flux. We
use modeling and previously published studies to conclude that shocks likely
contribute very little, if at all, to the high-ionization line fluxes observed
in the Holmberg II ULX. Additionally, we find that the spectral type of the
companion star has a surprisingly strong effect on the predicted strength of
the [O IV] emission. This finding could explain the origin of [O IV] in some
starburst systems containing black hole binaries.Comment: Accepted by Ap
Dynamical evolution and spin-orbit resonances of potentially habitable exoplanets. The case of GJ 581d
GJ 581d is a potentially habitable super-Earth in the multiple system of
exoplanets orbiting a nearby M dwarf. We investigate this planet's long-term
dynamics, with an emphasis on its probable final rotation states acquired via
tidal interaction with the host.
The published radial velocities for the star are re-analysed with a benchmark
planet detection algorithm, to confirm that there is no evidence for the
recently proposed two additional planets (f and g). Limiting the scope to the
four originally detected planets, we assess the dynamical stability of the
system and find bounded chaos in the orbital motion. For the planet d, the
characteristic Lyapunov time is 38 yr. Long-term numerical integration reveals
that the system of four planets is stable, with the eccentricity of the planet
d changing quasi-periodically in a tight range around 0.27, and with its
semimajor axis varying only a little.
The spin-orbit interaction of GJ 581d with its host star is dominated by the
tides exerted by the star on the planet. We model this interaction, assuming a
terrestrial composition of the mantle. Besides the customarily included secular
parts of the triaxiality-caused and tidal torques, we also include these
torques' oscillating components. It turns out that, dependent on the mantle
temperature, the planet gets trapped into the 2:1 or an even higher spin-orbit
resonance. It is very improbable that the planet could have reached the 1:1
resonance. This enhances the possibility of the planet being suitable for
sustained life
Spitzer Observations of MF 16 Nebula and the associated Ultraluminous X-ray Source
We present Spitzer Infrared Spectrograph (IRS) observations of the
ultra-luminous X-ray source (ULX) NGC 6946 X-1 and its associated nebula MF 16.
This ULX has very similar properties to the famous Holmberg II ULX, the first
ULX to show a prominent infrared [O IV] emission line comparable to those found
in AGN. This paper attempts to constrain the ULX Spectral Energy Distribution
(SED) given the optical/UV photometric fluxes and high-resolution X-ray
observations. Specifically, Chandra X-ray data and published Hubble optical/UV
data are extrapolated to produce a model for the full optical to X-ray SED. The
photoionization modeling of the IR lines and ratios is then used to test
different accretion spectral models. While either an irradiated disk model or
an O-supergiant plus accretion disk model fit the data very well, we prefer the
latter because it fits the nebular parameters slightly better. In this second
case the accretion disk alone dominates the extreme-UV and X-ray emission,
while an O-supergiant is responsible for most of the far-UV emission.Comment: 26 pages, 7 figures, accepted by Ap
FINANCIAL CONSTRAINS IN THE HEALTH SECTOR: ROMANIAN PLACE IN EUROPEAN PERSPECTIVE WITH A FOCUS ON RHEUMATIC DISEASE
Health represents both a personal and social asset different valued by individuals and populations. Personal
education, previous experience, sex, income or housing variables contribute to a higher or lower prioritization of
health care. Different actors interfere their forces and interests in this area: industry is interested in profit, administration is interested in a healthier and productive population, politicians are interested in accomplishing their
agenda, patients want to pay less and receive more benefits etc. As European Union is still very inhomogeneous
in terms of wealth, education or previous experience with health sector is clear that a large pool of differences
could observed among EU28 countries.
Objectives. In this paper we are analyzing EU official statistical data to understand these differences and find
practical conclusions for what Romanian health system intend to be.
Methods. Analyses of EU statistics public available in Eurostat directory.
Results. We analyzed how developed and what are the outcomes of EU health sector with a focus on Romania
and rheumatology field.
Discussions and conclusions. There is no a clear link between different components of health sector and the
way these are financed and the outcome
The Nature of the UV/optical Emission of the Ultraluminous X-Ray Source in Holmberg II
We report on UV and X-ray spectroscopy and broad-band optical observations of
the ultraluminous X-ray source in Holmberg II. Fitting various stellar spectral
models to the combined, non-simultaneous data set, we find that normal
metallicity stellar spectra are ruled out by the data, while low metallicity, Z
= 0.1 Z_{\odot}, late O-star spectra provide marginally acceptable fits, if we
allow for the fact that X-ray ionization from the compact object may reduce or
eliminate UV absorption/emission lines from the stellar wind. By contrast, an
irradiated disk model fits both UV and optical data with chi^2/dof=175.9/178,
and matches the nebular extinction with a reddening of
E(B-V)=0.05^{+0.05}_{-0.04}. These results suggest that the UV/optical flux of
Holmberg II X-1 may be dominated by X-ray irradiated disk emission.Comment: 9 pages, 1 table, 6 figures, accepted by Ap
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