17,450 research outputs found
Frequency of Solar-like Systems and of Ice and Gas Giants Beyond the Snow Line from High-magnification Microlensing Events in 2005-2008
We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval –4.5 200) microlensing events during 2005-2008. The sampled host stars have a typical mass M_(host) ~ 0.5 M_⊙, and detection is sensitive to planets over a range of planet-star-projected separations (s ^(–1)_(max)R_E, s_(max)R_E), where R_E ~ 3.5 AU(M_(host)/M_⊙)^(1/2) is the Einstein radius and s_(max) ~ (q/10^(–4.3))^(1/3). This corresponds to deprojected separations roughly three times the "snow line." We show that the observations of these events have the properties of a "controlled experiment," which is what permits measurement of absolute planet frequency. High-magnification events are rare, but the survey-plus-follow-up high-magnification channel is very efficient: half of all high-mag events were successfully monitored and half of these yielded planet detections. The extremely high sensitivity of high-mag events leads to a policy of monitoring them as intensively as possible, independent of whether they show evidence of planets. This is what allows us to construct an unbiased sample. The planet frequency derived from microlensing is a factor 8 larger than the one derived from Doppler studies at factor ~25 smaller star-planet separations (i.e., periods 2-2000 days). However, this difference is basically consistent with the gradient derived from Doppler studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in planet-star separation, 2 dex in mass ratio, and 0.3 dex in host mass. Finally, if all planetary systems were "analogs" of the solar system, our sample would have yielded 18.2 planets (11.4 "Jupiters," 6.4 "Saturns," 0.3 "Uranuses," 0.2 "Neptunes") including 6.1 systems with two or more planet detections. This compares to six planets including one two-planet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems
Measuring the Rotation Speed of Giant Stars From Gravitational Microlensing
During some gravitational lensing events, the lens transits the face of the
star. This causes a shift in the apparent radial velocity of the star which is
proportional to its rotation speed. It also changes the magnification relative
to what would be expected for a point source. By measuring both effects, one
can determine the rotation parameter . The method is especially useful
for K giant stars because these have turbulent velocities that are typically
large compared with their rotation speed. By making a series of radial velocity
measurements, one can typically determine to the same accuracy as the
individual radial velocity measurements. There are approximately 10
microlensing transit events per year which would be suitable to make these
measurements.Comment: 11 pages including 1 embedded figur
Microwave Scattering and Noise Emission from Afterglow Plasmas in a Magnetic Field
The microwave reflection and noise emission (extraordinary mode) from cylindrical rare‐gas (He, Ne, Ar) afterglow plasmas in an axial magnetic field is described. Reflection and noise emission are measured as a function of magnetic field near electron cyclotron resonance (ω ≈ ω_c) with electron density as a parameter (ω_p < ω). A broad peak, which shifts to lower values of ω_c/ω) as electron density increases, is observed for (ω_c/ω) ≤ 1. For all values of electron density a second sharp peak is found very close to cyclotron resonance in reflection measurements. This peak does not occur in the emission data. Calculations of reflection and emission using a theoretical model consisting of a one‐dimensional, cold plasma slab with nonuniform electron density yield results in qualitative agreement with the observations. Both the experimental and theoretical results suggest that the broad, density‐dependent peak involves resonance effects at the upper hybrid frequency ((ω_h)^2 = (ω_c)^2 + (ω_p)^2) of the plasma
Sgr A* ``Visual Binaries'': A Direct Measurement of the Galactocentric Distance
We present a new geometrical method for measuring the distance to the
Galactic center (R_0) by solving for the Keplerian orbit of individual stars
bound to the black hole associated with the Sgr A* from radial velocity and
proper motion measurements. We identify three stars to which the method may be
applied, and show that 1-5 % accuracy of R_0 can be expected after 15 years of
observing, and 0.5-2 % after 30 years of observing, depending on what the
orbital parameters of these three stars turn out to be. Combining the
measurements of the three stars with favorable orbital parameters leads to even
more precise values. In the example that we present, such combined solution
yields 4 % accuracy already by the year 2002. All these estimates assume that
annual position measurements will continue to be made with the 2 mas precision
recently reported by Ghez et al. The precision of the distance measurement is
relatively insensitive to the radial velocity errors, provided that the latter
are less than 50 km/s. Besides potentially giving an estimate of R_0 that is
better than any currently in use, the greatest advantage of this method is that
it is free from systematic errors.Comment: Submitted to ApJ, 14 pages, 8 figure
Lax Operator for the Quantised Orthosymplectic Superalgebra U_q[osp(2|n)]
Each quantum superalgebra is a quasi-triangular Hopf superalgebra, so
contains a \textit{universal -matrix} in the tensor product algebra which
satisfies the Yang-Baxter equation. Applying the vector representation ,
which acts on the vector module , to one side of a universal -matrix
gives a Lax operator. In this paper a Lax operator is constructed for the
-type quantum superalgebras . This can in turn be used to
find a solution to the Yang-Baxter equation acting on
where is an arbitrary module. The case is included
here as an example.Comment: 15 page
Microlensing Detections of Moons of Exoplanets
We investigate the characteristic of microlensing signals of Earth-like moons
orbiting ice-giant planets. From this, we find that non-negligible satellite
signals occur when the planet-moon separation is similar to or greater than the
Einstein radius of the planet. We find that the satellite signal does not
diminish with the increase of the planet-moon separation beyond the Einstein
radius of the planet unlike the planetary signal which vanishes when the planet
is located well beyond the Einstein radius of the star. We also find that the
satellite signal tends to have the same sign as that of the planetary signal.
These tendencies are caused by the lensing effect of the star on the moon in
addition to the effect of the planet. We determine the range of satellite
separations where the microlensing technique is optimized for the detections of
moons. By setting an upper limit as the angle-average of the projected Hill
radius and a lower limit as the half of the Einstein radius of the planet, we
find that the microlensing method would be sensitive to moons with projected
separations from the planet of for a Jupiter-mass planet, for a Saturn-mass planet, and for a Uranus-mass planet. We compare the
characteristics of the moons to be detected by the microlensing and transit
techniquesComment: 6pages, 6 figure
Avoidance of the real and anxiety about the unreal: attachment style and video-gaming
In this article, the authors discuss the light and dark side of attachments and attachment style in physical and digital worlds. They argue that many games offer opportunities for the generation of new and meaningful attachments to both physical and digital others. They discuss two ‘fundamental attachment errors’ and show how these can lead to both ‘light’ outcomes, in terms of opportunities to learn more secure attachment patterns, and ‘dark’ outcomes, where existing dysfunctional behaviours become more pronounced. The authors argue that the avatars which children adopt online have important consequences for their psychosocial development, and that these are mediated through the degree to which the real self is differentiated from the avatar. It is proposed that attachment is a key force in understanding play, and that studying its manifestations and effects in digital playscapes may contribute to understanding the effects of life online, and how insecure attachments may become secure
Empirical Study of Simulated Two-planet Microlensing Event
We undertake the first study of two-planet microlensing models recovered from
simulations of microlensing events generated by realistic multi-planet systems
in which 292 planetary events including 16 two-planet events were detected from
6690 simulated light curves. We find that when two planets are recovered, their
parameters are usually close to those of the two planets in the system most
responsible for the perturbations. However, in one of the 16 examples, the
apparent mass of both detected planets was more than doubled by the unmodeled
influence of a third, massive planet. This fraction is larger than, but
statistically consistent with, the roughly 1.5% rate of serious mass errors due
to unmodeled planetary companions for the 274 cases from the same simulation in
which a single planet is recovered. We conjecture that an analogous effect due
to unmodeled stellar companions may occur more frequently. For seven out of 23
cases in which two planets in the system would have been detected separately,
only one planet was recovered because the perturbations due to the two planets
had similar forms. This is a small fraction (7/274) of all recovered
single-planet models, but almost a third of all events that might plausibly
have led to two-planet models. Still, in these cases, the recovered planet
tends to have parameters similar to one of the two real planets most
responsible for the anomaly.Comment: 21 pages, 9 figures, 2 tables; submitted to ApJ; for a short video
introducing the key results, see https://www.youtube.com/watch?v=qhK4a6sbfO
Anomaluos RR Lyrae (V-I)_0 colors in Baade's Window
We compare (V-I)_0-(V-K)_0 color-color and (V-I)_0-log P period-color
diagrams for Baade's Window and local RRab Lyrae stars. We find that for a
fixed log P the Baade's Window RR Lyrae stars are ~0.17 magnitudes redder in
(V-I)_0 than the local RR Lyrae stars. We also show that there is no such
effect observed in (V-K)_0. We argue that an extinction misestimate towards
Baade's Window is not a plausible explanation of the discrepancy. Unlike
Baade's Window RR Lyrae stars, the local ones follow a black-body color-color
relation and are well approximated by theoretical models. We test two
parameters, metallicity and surface gravity, and find that their effects are
too small to explain the (V-I)_0 discrepancy between the two groups of stars.
We do not provide any explanation for the anomalous (V-I)_0 behavior of the
Baade's Window RR Lyrae stars. We note that a similar effect for clump giant
stars has been recently reported by Paczynski and we caution that RR Lyrae
stars and clump giants, often used as standard candles, can be subject to the
same type of systematics.Comment: 10 pages, 7 figures, submitted to Ap
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