470 research outputs found
Orbital Evolution of Planets around Intermediate-Mass Giants
Around low- and intermediate-mass (1.5-3 M_sun) red giants, no planets have
been found inside 0.6 AU. Such a paucity is not seen in the case of 1 M_sun
main sequence stars. In this study, we examine the possibility that
short-period planets were engulfed by their host star evolving off the main
sequence. To do so, we have simulated the orbital evolution of planets,
including the effects of stellar tide and mass loss, to determine the critical
semimajor axis, a_crit, beyond which planets survive the RGB expansion of their
host star. We have found that a_crit changes drastically around 2 M_sun: In the
lower-mass range, a_crit is more than 1 AU, while a_crit is as small as about
0.2 AU in the higher-mass range. Comparison with measured semimajor axes of
known planets suggests that there is a lack of planets that only planet
engulfment never accounts for in the higher-mass range. Whether the lack is
real affects our understanding of planet formation. Therefore, increasing the
number of planet samples around evolved intermediate-mass stars is quite
meaningful to confirm robustness of the lack of planets.Comment: 4 pages, 3 figures, Part of PlanetsbeyondMS/2010 proceedings
http://arxiv.org/html/1011.660
Influence of Addition of Polyols and Food Emulsifiers on the Retrogradation Rate of Starch
The influence of polyols and emulsifiers on hardening of non-glutinous rice starch gels has been investigated. The polyols and emulsifiers were added at concentrations of 6% (w/w) and 0.2% (w/w), respectively , to starch gels (starch content, 30%). The hardening rate and the initial viscoelastic values of gels were computed by analyzing static linear viscoelastic parameters (creep compliance) of the gels stored at 0 C for up to 3,000 minutes.
Hardening of gels, i.e., retrogradation of starch, could be described by a first order kinetic equation. Polyols prevented the retrogradation of starch, and formed rigid and stable gel matrices. Emulsifiers also retarded starch retrogradation and stabilized the gel network.
The use of the two food additives was successful in retarding the retrogradation of starch. It follows that these effects might be attributed to the water-structure formation effect of polyols and the complex-formation of starch chains with emulsifier molecules
Macro-scale ore-controlling faults revealed by micro-geochemical anomalies
Whereas the mechanism of fluid flow, and thus structural control, linked with mineral deposit formation is quite understood, the specific structures that likely provided controls on mineralization at certain geographic scales are not readily known for a given region unless it is well-explored. This contributes uncertainty in mineral prospectivity analysis in poorly-explored regions (or greenfields). Here, because the spatial distribution of mineral deposits has been postulated to be fractals (i.e., the patterns of these features are self-similar across a range of spatial scales), we show for the first time that micro-geochemical anomalies (as proxies of micro-scale patterns of ore minerals), from few discrete parts of the Sossego iron-oxide copper-gold (IOCG) deposit in the Carajas Mineral Province (CMP) of Brazil, exhibit trends of macro-scale faults that are known to have controlled IOCG mineralization in the CMP. The methodology described here, which led to this novel finding, would help towards detecting mineral exploration targets as well as help towards understanding structural controls on mineralization in greenfields9CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTĂFICO E TECNOLĂGICO - CNPQFUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULO - FAPESP2014-9/401316; 2017-3/3097122015/11186-3FAPESP (Sao Paulo Research Foundation)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [2015/11186-3]; CNPq (Brazilian National Council for Scientific and Technological Development)National Council for Scientific and Technological Development (CNPq) [2014-9/401316, 2017-3/309712]; Vale Compan
Fermi-LAT Study of Gamma-ray Emission in the Direction of Supernova Remnant W49B
We present an analysis of the gamma-ray data obtained with the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of
SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a
significance of 38 sigma is found to coincide with SNR W49B. The energy
spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The
luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy
range. There is no indication that the gamma-ray emission comes from a pulsar.
Assuming that the SNR shell is the site of gamma-ray production, the observed
spectrum can be explained either by the decay of neutral pi mesons produced
through the proton-proton collisions or by electron bremsstrahlung. The
calculated energy density of relativistic particles responsible for the LAT
flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either
gamma-ray production mechanism.Comment: 9 pages, 10 figure
Planet Engulfment by ~1.5-3 Solar-Mass Red Giants
Recent radial-velocity surveys for GK clump giants have revealed that planets
also exist around ~1.5-3 Msun stars. However, no planets have been found inside
0.6 AU around clump giants, in contrast to solar-type main-sequence stars, many
of which harbor short-period planets such as hot Jupiters. In this study we
examine the possibility that planets were engulfed by host stars evolving on
the red-giant branch (RGB). We integrate the orbital evolution of planets in
the RGB and helium burning (HeB) phases of host stars, including the effects of
stellar tide and stellar mass loss. Then we derive the critical semimajor axis
(or the survival limit) inside which planets are eventually engulfed by their
host stars after tidal decay of their orbits. Especially, we investigate the
impact of stellar mass and other stellar parameters on the survival limit in
more detail than previous studies. In addition, we make detailed comparison
with measured semimajor axes of planets detected so far, which no previous
study did. We find that the critical semimajor axis is quite sensitive to
stellar mass in the range between 1.7 and 2.1 Msun, which suggests a need for
careful comparison between theoretical and observational limits of existence of
planets. Our comparison demonstrates that all those planets are beyond the
survival limit, which is consistent with the planet-engulfment hypothesis.
However, on the high-mass side (> 2.1 Msun), the detected planets are orbiting
significantly far from the survival limit, which suggests that engulfment by
host stars may not be the main reason for the observed lack of short-period
giant planets. To confirm our conclusion, the detection of more planets around
clump giants, especially with masses > 2.5 Msun, is required.Comment: 12 pages, 6 figures, 1 table, accepted for publication in Ap
Fermi-LAT Discovery of Extended Gamma-ray Emission in the Direction of Supernova Remnant W51C
The discovery of bright gamma-ray emission coincident with supernova remnant
(SNR) W51C is reported using the Large Area Telescope (LAT) on board the Fermi
Gamma-ray Space Telescope. W51C is a middle-aged remnant (~10^4 yr) with
intense radio synchrotron emission in its shell and known to be interacting
with a molecular cloud. The gamma-ray emission is spatially extended, broadly
consistent with the radio and X-ray extent of SNR W51C. The energy spectrum in
the 0.2-50 GeV band exhibits steepening toward high energies. The luminosity is
greater than 1x10^{36} erg/s given the distance constraint of D>5.5 kpc, which
makes this object one of the most luminous gamma-ray sources in our Galaxy. The
observed gamma-rays can be explained reasonably by a combination of efficient
acceleration of nuclear cosmic rays at supernova shocks and shock-cloud
interactions. The decay of neutral pi-mesons produced in hadronic collisions
provides a plausible explanation for the gamma-ray emission. The product of the
average gas density and the total energy content of the accelerated protons
amounts to 5x10^{51}(D/6kpc)^2 erg/cm^3. Electron density constraints from the
radio and X-ray bands render it difficult to explain the LAT signal as due to
inverse Compton scattering. The Fermi LAT source coincident with SNR W51C sheds
new light on the origin of Galactic cosmic rays.Comment: 17 pages, 4 figures, 1 table. Accepted for ApJ Letters. Contact
authors: Y. Uchiyama, S. Funk., H. Tajima, T. Tanak
Fermi-LAT Observation of Supernova Remnant S147
We present an analysis of gamma-ray data obtained with the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the region
around SNR S147 (G180.0-1.7). A spatially extended gamma-ray source detected in
an energy range of 0.2--10 GeV is found to coincide with SNR S147. We confirm
its spatial extension at >5sigma confidence level. The gamma-ray flux is (3.8
\pm 0.6) x 10^{-8} photons cm^{-2} s^{-1}, corresponding to a luminosity of 1.3
x 10^{34} (d/1.3 kpc)^2 erg s^{-1} in this energy range. The gamma-ray emission
exhibits a possible spatial correlation with prominent Halpha filaments of
S147. There is no indication that the gamma-ray emission comes from the
associated pulsar PSR J0538+2817. The gamma-ray spectrum integrated over the
remnant is likely dominated by the decay of neutral pi mesons produced through
the proton--proton collisions in the filaments. Reacceleration of pre-existing
CRs and subsequent adiabatic compression in the filaments is sufficient to
provide the required energy density of high-energy protons.Comment: 12 pages, accepted for publication in Ap
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