We conducted a search for occultations of bright stars by Kuiper Belt Objects (KBOs) to estimate the density of subkilometer KBOs in the sky. We report here the first results of this occultation ...survey of the outer solar system conducted in 2007 June and 2008 June/July at the MMT Observatory using Megacam, the large MMT optical imager. We used Megacam in a novel shutterless continuous-readout mode to achieve high-precision photometry at 200 Hz, which with point-spread function convolution results in an effective sampling of ~30 Hz. We present an analysis of 220 star hours of data at a signal-to-noise ratio of 25 or greater, taken from images of fields within 3DG of the ecliptic plane. The survey efficiency is greater than 10% for occultations by KBOs of diameter d >= 0.7 km, and we report no detections in our data set. We set a new 95% confidence level upper limit for the surface density capital sigma N (d) of KBOs larger than 1 km: capital sigma N (d >= 1 km) <= 2.0 X 108 deg-2, and for KBOs larger than 0.7 km capital sigma N (d >= 0.7 km) <= 4.8 X 108 deg-2.
We have analyzed the first 3.75 years of data from the Taiwanese American Occultation Survey (TAOS). TAOS monitors bright stars to search for occultations by Kuiper Belt objects (KBOs). This data set ...comprises 5 X 105 star hours of multi-telescope photometric data taken at 4 or 5 Hz. No events consistent with KBO occultations were found in this data set. We compute the number of events expected for the Kuiper Belt formation and evolution models of Pan & Sari, Kenyon & Bromley, Benavidez & Campo Bagatin, and Fraser. A comparison with the upper limits we derive from our data constrains the parameter space of these models. This is the first detailed comparison of models of the KBO size distribution with data from an occultation survey. Our results suggest that the KBO population is composed of objects with low internal strength and that planetary migration played a role in the shaping of the size distribution.
The nature of dark matter remains mysterious, with luminous material accounting for at most ∼25 per cent of the baryons in the Universe. We accordingly undertook a survey looking for the microlensing ...of stars in the Large Magellanic Cloud (LMC) to determine the fraction of Galactic dark matter contained in massive compact halo objects (MACHOs). The presence of the dark matter would be revealed by gravitational lensing of the light from an LMC star as the foreground dark matter moves across the line of sight. The duration of the lensing event is the key observable parameter, but gives non-unique solutions when attempting to estimate the mass, distance and transverse velocity of the lens. The survey results to date indicate that between 8 and 50 per cent of the baryonic mass of the Galactic halo is in the form of MACHOs (ref. 3), but removing the degeneracy by identifying a lensing object would tighten the constraints on the mass in MACHOs. Here we report a direct image of a microlens, revealing it to be a nearby low-mass star in the disk of the Milky Way. This is consistent with the expected frequency of nearby stars acting as lenses, and demonstrates a direct determination of a lens mass from a microlensing event. Complete solutions such as this for halo microlensing events will probe directly the nature of the MACHOs.
We present a methodology to discover outliers in catalogues of periodic light curves. We use a cross-correlation as the measure of ‘similarity’ between two individual light curves, and then classify ...light curves with lowest average ‘similarity’ as outliers. We performed the analysis on catalogues of periodic variable stars of known type from the MACHO and OGLE projects. This analysis was carried out in Fourier space and we established that our method correctly identifies light curves that do not belong to those catalogues as outliers. We show how an approximation to this method, carried out in real space, can scale to large data sets that will be available in the near future such as those anticipated from the Panoramic Survey Telescope & Rapid Response System (Pan-STARRS) and Large Synoptic Survey Telescope (LSST).
The Taiwanese-American Occultation Survey (TAOS) operates four fully automatic telescopes to search for occultations of stars by Kuiper Belt Objects. It is a versatile facility that is also useful ...for the study of initial optical GRB afterglows. This paper provides a detailed description of the TAOS multi-telescope system, control software, and high-speed imaging.
•An experimental investigation has been conducted on an adjustable TADTAR.•This new design allows for an adjustment of the TADTAR resonator length.•Matching between frequency output of TAE and ...frequency required by TAR is achieved.•The length adjustment of the resonator alters the performance of the TADTAR.•Through the resonator adjustment, a single device could have different operating points.
An experimental investigation is conducted on a new adjustable thermoacoustically-driven thermoacoustic refrigerator (TADTAR). This refrigerator comprises of a thermoacoustic engine which drives a thermoacoustic refrigerator. This study aims to demonstrate the possibility to alter the TADTAR performance through the adjustment of specific design parameters. An adjustable resonator, which consisted of stacks, spacing couplings and shell-tube heat exchangers was designed and built. Six different honeycomb ceramic stacks were investigated. For each system, three different stack configurations were studied. Measurements of temperature difference across the refrigerator stack and sound pressure levels at steady states were used to determine the performance of the device. Through the adjustment of the length and the insertion of the heat exchanger, the performance of the device with a longer resonator was relatively higher. This study shows that an adjustable resonator successfully alters the frequency output of the thermoacoustic engine to match the frequency required by the thermoacoustic refrigerator and achieve resonance. In addition, this study demonstrates the possibility to change the geometrical configuration of the device and ultimately alter the performance of the TADTAR. Through the adjustment of the length of the resonator, this study shows that a single device could have different operating points. This creates new possibilities to introduce control system able to adjust the geometry of thermoacoustic system while in operation.
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