5,660 research outputs found
A New Channel for the Detection of Planetary Systems Through Microlensing: I. Isolated Events Due to Planet Lenses
We propose and evaluate the feasibility of a new strategy to search for
planets via microlensing. This new strategy is designed to detect planets in
"wide" orbits, i.e., with orbital separation, greater than .
Planets in wide orbits may provide the dominant channel for the microlensing
discovery of planets, particularly low-mass (e.g., Earth-mass) planets. This
paper concentrates on events in which a single planet serves as a lens, leading
to an isolated event of short duration. We point out that a distribution of
events due to lensing by stars with wide-orbit planets is necessarily
accompanied by a distribution of shorter- duration events. The fraction of
events in the latter distribution is proportional to the average value of
, where is the ratio between \pl and stellar masses. The position
of the peak or peaks also provides a measure of the mass ratios typical of
planetary systems. We study detection strategies that can optimize our ability
to discover isolated short-duration events due to lensing by planets, and find
that monitoring employing sensitive photometry is particularly useful. If
planetary systems similar to our own are common, even modest changes in
detection strategy should lead to the discovery of a few isolated events of
short duration every year. We therefore also address the issue of the
contamination due to stellar populations of any microlensing signal due to
low-mass MACHOs. We describe how, even for isolated events of short duration,
it will be possible to test the hypothesis that the lens was a planet instead
of a low-mass MACHO, if the central star of the planetary system contributes a
measurable fraction of the baseline flux.Comment: 37 pages, 6 figure. To be published in the Astrophysical Journal.
This is part one of a series of papers on microlensing by planetary systems
containing wide-orbit planets; the series represents a reorganization and
extension of astro-ph/971101
Improved Detection Rates for Close Binaries Via Astrometric Observations of Gravitational Microlensing Events
In addition to constructing a Galactic matter mass function free from the
bias induced by the hydrogen-burning limit, gravitational microlensing allows
one to construct a mass function which is less affected by the problem of
unresolved binaries (Gaudi & Gould). However, even with the method of
microlensing, the photometric detection of binaries is limited to binary
systems with relatively large separations of of their combined
Einstein ring radius, and thus the mass function is still not totally free from
the problem of unresolved binaries. In this paper, we show that by detecting
distortions of the astrometric ellipse of a microlensing event with high
precision instruments such as the {\it Space Interferometry Mission}, one can
detect close binaries at a much higher rate than by the photometric method. We
find that by astrometrically observing microlensing events, of
binaries with separations of can be detected with the detection
threshold of 3%. The proposed astrometric method is especially efficient at
detecting very close binaries. With a detection threshold of 3% and a rate of
10%, one can astrometrically detect binaries with separations down to .Comment: total 14 pages, including 5 Figures and no Table (For figure 1,
please send a request mail to [email protected]), accepted to
ApJ (Vol 525, 000), updated versio
Second Backbend in the Mass A ~ 180 Region
Within the framework of selfconsistent cranked Hartree-Fock- Bogoliubov
theory(one-dimensional) we predict second backbend in the yrast line of Os-182
at , which is even sharper than the first one observed
experimentally at .
Around such a high spin the structure becomes multi-quasiparticle type, but
the main source of this strong discontinuity is a sudden large alignment of
i_13/2 proton orbitals along the rotation axis followed soon by the alignment
of j_15/2 neutron orbitals. This leads to drastic structural changes at such
high spins. When experimentally confirmed, this will be observed for the first
time in this mass region, and will be at the highest spin so far.Comment: 13 pages, 4 ps figure
Almost ï¨-duals of some sequence spaces
Ansari and Shukla [1] have generalized the notion of ï¡-duals and developed the concept of almostï¨ï€Âduals by using the concept of absolutely almost convergence. P Chandra and B.C. Tripathy [8] have introduced the concept of ï¨-duals. We have introduced the concept of almost ï¨-duals and determined almost ï¨-duals of some sequence spaces
Evaluation of antimicrobial property of Spirogyra species
Spirogyra species is an important genus of filamentous green algae (Chlorophyta) in showing its antimicrobial activity against number of bacteria and fungi. In present study the effect of Petroleum ether, methanol and chloroform extract of Spirogyra species was screened against three bacteria and three plant pathogenic fungi for their level of antimicrobial potential. Thin layer chromatography was used to assay for the compounds and pure fractions obtained were tested for their antimicrobial property and were found to be effective on the entire test organism except for Clavibacter sp. and Curvularia sp.Â
Occurrence of parasites in selected fish species in Gandoman Lagoon, Iran
This study was carried out to investigate occurrence of parasite in selected cyprinid fish species in Gandoman Lagoon, in the vicinity of Gandoman City, Chaharmahal & Bakhtyari Province. A total of 90 fish specimens including Cyprinus carpio, Carassius auratus gibelio, Capoeta aculeata , C.damascina, Chondrostoma regium and Alburnus alburnus from Gandoman were examined during spring and summer 2007. Ten species of parasites were found, including Ichthyophthirius multifiliis, Trichodina sp. (Cilliophora), Myxobolus musayevi, Myxobolus sp. (Myxozoa), Dactylogyrus extensus, D.lenkorani (Monogenea), Diplostomum spathaceum, Tylodelphys clavata (Digenea). Argulus foliaceus and Lernea cyprinacea (Crustaceans). 77.7% of fishes were infected to parasites and 22.3 % did not show any infection. Chondrostoma regium and Alburnus alburnus are reported as new hosts for D. extensus
Characterizations of Prime and Minimal Prime Ideals of Hyperlattices
In this paper, we define an ideal and prime ideal of hyperlattices (hyper join and hyper meet operation) .We obtain results on ideals of lattice in the sense of hyperlattice .We prove some results on prime ideals of hyperlattices. A result analogous to separation theorem is obtained for hyperlattices in respect of prime ideals. Further, we extend the classical result of Nachbin for hyperlattices. Also we furnish some characterizations of minimal prime ideals of hyperlattices
Probing the Mass Fraction of MACHOs in Extragalactic Halos
Current microlensing searches calibrate the mass fraction of the Milky Way
halo which is in the form of Massive Compact Halo Objects (MACHOs). We show
that surveys like the Sloan Digital Sky Survey (SDSS) can probe the same
quantity in halos of distant galaxies. Microlensing of background quasars by
MACHOs in intervening galaxies would distort the equivalent width distribution
of the quasar emission lines by an amplitude that depends on the projected
quasar-galaxy separation. For a statistical sample of detectable at the >2sigma
level out to a quasar-galaxy impact parameter of several tens of kpc, as long
as extragalactic halos are made of MACHOs. Detection of this signal would test
whether the MACHO fraction inferred for the Milky-Way halo is typical of other
galaxies.Comment: 12 pages, 2 figures, submitted to ApJ Letter
- …