9,030 research outputs found

    Microlens Parallax Asymmetries Toward the LMC

    Get PDF
    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

    Get PDF
    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 vsin‚Ā°iv\sin i. 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 vsin‚Ā°iv\sin i 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

    Get PDF
    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

    Get PDF
    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

    Full text link
    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

    Get PDF
    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

    Full text link
    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 8√ó1078\times 10^7 star√ó\timesyr 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

    Sur les traces de la matière dans le cosmos

    No full text
    Archeop

    A New Channel for the Detection of Planetary Systems Through Microlensing: II. Repeating Events

    Full text link
    In the companion paper we began the task of systematically studying the detection of planets in wide orbits (a>1.5REa > 1.5 R_E) 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 199
    • ‚Ķ
    corecore