19,960 research outputs found
Planetary Microlensing: Present Status and Long-term Goals
Massive gravitational microlensing programs were begun about a decade ago as
a means to search for compact baryonic dark matter in the Galaxy, but before
the first events were detected the technique was also proposed as a means of
detecting extra-solar planets in our Galaxy. Current microlensing planet
searches, which have been underway for four years, are sensitive to jovian-mass
planets orbiting a few to several AU from their parent Galactic stars. Within
two years, sufficient data should be in hand to characterize or meaningfully
constrain the frequency of massive planets in this range of parameter space,
nicely complementing information about planets at smaller orbital radii now
being provided by radial velocity searches. In principle, the technique could
be pushed to smaller planetary masses, but only if a larger number of faint
microlensed sources can be monitored with higher precision and temporal
sampling. The VST on Paranal, with spectroscopic follow-up with the VLT, may be
the ideal instrument for such an ambitious program.Comment: Invited Review at VLT Opening Symposium, Antofagasta, Chile, March
1999. To appear in the Springer-Verlag series ``ESO Astrophysics Symposia'
Optimal Survey Strategies and Predicted Planet Yields for the Korean Microlensing Telescope Network
The Korean Microlensing Telescope Network (KMTNet) will consist of three 1.6m
telescopes each with a 4 deg^{2} field of view (FoV) and will be dedicated to
monitoring the Galactic Bulge to detect exoplanets via gravitational
microlensing. KMTNet's combination of aperture size, FoV, cadence, and
longitudinal coverage will provide a unique opportunity to probe exoplanet
demographics in an unbiased way. Here we present simulations that optimize the
observing strategy for, and predict the planetary yields of, KMTNet. We find
preferences for four target fields located in the central Bulge and an exposure
time of t_{exp} = 120s, leading to the detection of ~2,200 microlensing events
per year. We estimate the planet detection rates for planets with mass and
separation across the ranges 0.1 <= M_{p}/M_{Earth} <= 1000 and 0.4 <= a/AU <=
16, respectively. Normalizing these rates to the cool-planet mass function of
Cassan (2012), we predict KMTNet will be approximately uniformly sensitive to
planets with mass 5 <= M_{p}/M_{Earth} <= 1000 and will detect ~20 planets per
year per dex in mass across that range. For lower-mass planets with mass 0.1 <=
M_{p}/M_{Earth} < 5, we predict KMTNet will detect ~10 planets per year. We
also compute the yields KMTNet will obtain for free-floating planets (FFPs) and
predict KMTNet will detect ~1 Earth-mass FFP per year, assuming an underlying
population of one such planet per star in the Galaxy. Lastly, we investigate
the dependence of these detection rates on the number of observatories, the
photometric precision limit, and optimistic assumptions regarding seeing,
throughput, and flux measurement uncertainties.Comment: 29 pages, 31 figures, submitted to ApJ. For a brief video explaining
the key results of this paper, please visit:
https://www.youtube.com/watch?v=e5rWVjiO26
Short-duration lensing events: I. wide-orbit planets? free-floating low-mass objects? or high-velocity stars?
Short duration lensing events tend to be generated by low-mass lenses or by
lenses with high transverse velocities. Furthermore, for any given lens mass
and speed, events of short duration are preferentially caused by nearby lenses
(mesolenses) that can be studied in detail, or else by lenses so close to the
source star that finite-source-size effects may be detected, yielding
information about both the Einstein ring radius and the surface of the lensed
star. Planets causing short-duration events may be in orbits with any
orientation, and may have semimajor axes smaller than an AU, or they may reach
the outer limits of their planetary systems, in the region corresponding to the
Solar System's Oort Cloud. They can have masses larger than Jupiter's or
smaller than Pluto's. Lensing therefore has a unique potential to expand our
understanding of planetary systems. A particular advantage of lensing is that
it can provide precision measurements of system parameters, including the
masses of and projected separation between star and planet. We demonstrate how
the parameters can be extracted and show that a great deal can be learned. For
example, it is remarkable that the gravitational mass of nearby free-floating
planet-mass lenses can be measured by complementing observations of a
photometric event with deep images that detect the planet itself. A fraction of
short events may be caused by high-velocity stars located within a kpc. Many
high-velocity lenses are likely to be neutron stars that received large natal
kicks. Other high-speed stars may be members of the halo population. Still
others may be hypervelocity stars that have been ejected from the Galactic
Center, or runaway stars escaped from close binaries, possibly including the
progenitor binaries of Type Ia supernovae.Comment: 17 pages; 2 figures; submitted to ApJ 3 July 200
Illuminating Hot Jupiters in caustic crossing
In recent years a large number of Hot Jupiters orbiting in a very close orbit
around the parent stars have been explored with the transit and doppler effect
methods. Here in this work we study the gravitational microlensing effect of a
binary lens on a parent star with a Hot Jupiter revolving around it. Caustic
crossing of the planet makes enhancements on the light curve of the parent star
in which the signature of the planet can be detected by high precision
photometric observations. We use the inverse ray shooting method with tree code
algorithm to generate the combined light curve of the parent star and the
planet. In order to investigate the probability of observing the planet signal,
we do a Monte-Carlo simulation and obtain the observational optical depth of
. We show that about ten years observations of Galactic
Bulge with a network of telescopes will enable us detecting about ten Hot
Jupiter with this method. Finally we show that the observation of the
microlensing event in infra-red band will increase the probability for
detection of the exo-planets.Comment: 8 pages, 7 figures, accepted in MNRA
Short-duration lensing events: II. Expectations and Protocols
Ongoing microlensing observations by OGLE and MOA regularly identify and
conduct high-cadence sampling of lensing events with Einstein diameter crossing
time, tau_E, of 16 or fewer days. Events with estimated values of tau_E of one
to two days have been detected. Short duration events tend to be generated by
low-mass lenses or by lenses with high transverse velocities. We compute the
expected rates, demonstrate the expected ranges of parameters for lenses of
different mass, and develop a protocol for observing and modeling
short-duration events. Relatively minor additions to the procedures presently
used will increase the rate of planet discovery, and also discover or place
limits on the population of high-speed dim stars and stellar remnants in the
vicinity of the Sun.Comment: 17 pages; 3 figures; submitted to ApJ 3 July 200
Rapidly Rotating Lenses: Repeating features in the lightcurves of short period binary microlenses
Microlensing is most sensitive to binary lenses with relatively large orbital
separations, and as such, typical binary microlensing events show little or no
orbital motion during the event. However, despite the strength of binary
microlensing features falling off rapidly as the lens separation decreases, we
show that it is possible to detect repeating features in the lightcurve of
binary microlenses that complete several orbits during the microlensing event.
We investigate the lightcurve features of such Rapidly Rotating Lens (RRL)
events. We derive analytical limits on the range of parameters where these
effects are detectable, and confirm these numerically. Using a population
synthesis Galactic model we estimate the RRL event rate for a ground-based and
space-based microlensing survey to be 0.32fb and 7.8fb events per year
respectively, assuming year-round monitoring and where fb is the binary
fraction. We detail how RRL event parameters can be quickly estimated from
their lightcurves, and suggest a method to model RRL events using timing
measurements of lightcurve features. Modelling RRL lightcurves will yield the
lens orbital period and possibly measurements of all orbital elements including
the inclination and eccentricity. Measurement of the period from the lightcurve
allows a mass-distance relation to be defined, which when combined with a
measurement of microlens parallax or finite source effects, can yield a mass
measurement to a two-fold degeneracy. With sub-percent accuracy photometry it
is possible to detect planetary companions, but the likelihood of this is very
small.Comment: 16 pages, 14 figures, accepted for publication in MNRAS. Equation 21
simplifie
Multicolor pyrometer for materials processing in space
The program goals are to design, construct, and program a prototype imaging pyrometer capable of measuring the temperature distribution across the surface of a moving object suspended in space. The approach is to utilize an optical system which operates at short wavelengths compared to the peak of the blackbody spectrum for the temperature range of interest, thus minimizing errors associated with a lack of knowledge about heated sample emissivity. An analysis of the system's temperature measurement capability based on the camera's responsivity was performed and bound to be satisfactory. Details for the evolving optical design and the progress towards construction of a working model are discussed. Details of the algorithm developed for selecting the optimum colors to be used by the pyrometer are reported. Though final selection of the colors will have to await a final design of the optical system, results using a preliminary optical design are presented
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