8,905 research outputs found
Microlens Parallax Asymmetries Toward the LMC
If the microlensing events now being detected toward the Large Magellanic
Cloud (LMC) are due to lenses in the Milky Way halo, then the events should
typically have asymmetries of order 1% due to parallax from the reflex motion
of the Earth. By contrast, if the lenses are in the LMC, the parallax effects
should be negligible. A ground-based search for such parallax asymmetries would
therefore clarify the location of the lenses. A modest effort (2 hours per
night on a 1 m telescope) could measure 15 parallax asymmetries over 5 years
and so marginally discriminate between the halo and the LMC as the source of
the lenses. A dedicated 1 m telescope would approximately double the number of
measurements and would therefore clearly distinguish between the alternatives.
However, compared to satellite parallaxes, the information extracted from
ground-based parallaxes is substantially less useful for understanding the
nature of the halo lenses (if that is what they are). The backgrounds of
asymmetries due to binary-source and binary-lens events are estimated to be
approximately 7% and 12% respectively. These complicate the interpretation of
detected parallax asymmetries, but not critically.Comment: Submitted to ApJ, 17 pages, including 2 embedded figure
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
A Fiber Optic Probe for the Detection of Cataracts
A compact fiber optic probe developed for on-orbit science experiments was used to detect the onset of cataracts, a capability that could eliminate physicians' guesswork and result in new drugs to 'dissolve' or slow down the cataract formation before surgery is necessary. The probe is based upon dynamic light scattering (DLS) principles. It has no moving parts, no apertures, and requires no optical alignment. It is flexible and easy to use. Results are presented for excised but intact human eye lenses. In a clinical setting, the device can be easily incorporated into a slit-lamp apparatus (ophthalmoscope) for complete eye diagnostics. In this set-up, the integrated fiber optic probe, the size of a pencil, delivers a low power cone of laser light into the eye of a patient and guides the light which is backscattered by the protein molecules of the lens through a receiving optical fiber to a photo detector. The non-invasive DLS measurements provide rapid determination of protein crystalline size and its size distribution in the eye lens
Development of a versatile laser light scattering instrument
NASA Lewis Research Center is providing and coordinating the technology for placing a compact Laser Light Scattering (LLS) instrument in a microgravity environment. This will be accomplished by defining and assessing user requirements for microgravity experiments, coordinating needed technological developments, and filling technical gaps. This effort is striving to brassboard and evaluate a miniature multi-angle LLS instrument. The progress of the program is reported
Search for hidden turbulent gas through interstellar scintillation
Stars twinkle because their light propagates through the atmosphere. The same
phenomenon is expected when the light of remote stars crosses a Galactic - disk
or halo - refractive medium such as a molecular cloud. We present the promising
results of a test performed with the ESO-NTT and the perspectives of detection.Comment: Structure and dynamics of disk galaxies, Petit Jean Mountain : United
States (2013). arXiv admin note: substantial text overlap with
arXiv:1208.637
Development of a versatile laser light scattering instrument
A versatile laser light scattering (LLS) instrument is developed for use in microgravity to measure microscopic particles of 30 A to above 3 microns. Since it is an optical technique, LLS does not affect the sample being studied. A LLS instrument built from modules allows several configurations, each optimized for a particular experiment. The multiangle LLS instrument can be mounted in the rack in the Space Shuttle and on Space Station Freedom. It is possible that a Space Shuttle glove-box and a lap-top computer containing a correlator card can be used to perform a number of experiments and to demonstrate the technology needed for more elaborate investigations. This offers simple means of flying a great number of experiments without the additional requirements of full-scale flight hardware experiments
Study of a Strategy for Parallax Microlensing Detection Towards the Magellanic Clouds
In this article, we have investigated the possibility to distinguish between
different galactic models through the microlensing parallax studies. We show
that a systematic search for parallax effects can be done using the currently
running alert systems and complementary photometric telescopes, to distinguish
between different lens distance distributions. We have considered two galactic
dark compact objects distributions, with total optical depths corresponding to
the EROS current upper limits. These models correspond to two extreme
hypothesis on a three component galactic structure made of a thin disc, a thick
disc, and a spherically symmetric halo. Our study shows that for sub-solar mass
lenses, an exposure of staryr toward LMC should allow to
distinguish between these two extreme models. In addition the self-lensing
hypothesis (lensing by LMC objects) can efficiently be tested through the
method proposed here.Comment: 10 pages, 12 eps figures. To be published in A&A (accepted version).
Minor changes: - Discussion added on the differential velocity of the thick
galactic disk with respect to the thin disk. - Quality and lisibility of
figures improved. - Typo errors correcte
A New Channel for the Detection of Planetary Systems Through Microlensing: II. Repeating Events
In the companion paper we began the task of systematically studying the
detection of planets in wide orbits () via microlensing surveys.
In this paper we continue, focusing on repeating events. We find that, if all
planetary systems are similar to our own Solar System, reasonable extensions of
the present observing strategies would allow us to detect 3-6 repeating events
per year along the direction to the Bulge. Indeed, if planetary systems with
multiple planets are common, then future monitoring programs which lead to the
discovery of thousands of stellar-lens events will likely discover events in
which several different planets within a single system serve as lenses, with
light curves exhibiting multiple repetitions. In this paper we discuss
observing strategies to maximize the discovery of all wide-orbit planet-lens
events. We also compare the likely detection rates of planets in wide orbits to
those of planets located in the zone for resonant lensing. We find that,
depending on the values of the planet masses and stellar radii of the lensed
sources (which determine whether or not finite source size is important), and
also on the sensitivity of the photometry used by observers, the detection of
planets in wide orbits may be the primary route to the discovery of planets via
microlensing. We also discuss how the combination of resonant and wide-orbit
events can help us to learn about the distribution of planetary system
properties (S 6.1). In addition, by determining the fraction of short-duration
events due to planets, we indirectly derive information about the fraction of
all short-duration events that may be due to low-mass MACHOs (S 6.2).Comment: 51 pages, 7 figures. To be published in the Astrophysical Journal, 20
February 1999. This completes the introduction to the discovery of planets in
wide orbits begun in astro-ph/9808075, also to appear in ApJ on 20 February
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