117818525
Proton irradiation effect on SCDs
The Low Energy X-ray Telescope is one of the main payloads on the Hard X-ray Modulation Telescope satellite. Swept charge devices (SCDs) are selected as detectors for the Low Energy X-ray Telescope. As SCDs are sensitive to proton irradiation, irradiation tests were carried out on the HI-13 accelerator at the China Institute of Atomic Energy. The beam energy was measured to be 10 MeV at the SCD. The proton fluence delivered to the SCD was 3x10(8)protons/cm(2) over two hours. By comparing the performance before and after irradiation, it is concluded that proton irradiation affects both the dark current and the charge transfer inefficiency of the SCD. The energy resolution of the proton-irradiated SCD is 212 eV@5.9 keV at -60 degrees C, while it before irradiated is 134 eV. Moreover, better performance can be reached by lowering the operating temperature of the SCD in orbit.
118659723
Search for TeV-antiprotons in space from the shadowing of cosmic rays by the moon with the L3+C detector
A search for antiprotons in the primary cosmic ray flux has been performed by observing the Moon shadow with the muon data collected by the L3+C experiment at CERN during 1999 and 2000. The angular resolution ofthe detector and its dependences on the muon energy and zenith angle are obtained at the event level with a Monte Carlo simulation and the analysis of real double muon data using a maximum likelihood method. The Moon shadow effect is observed in three muon momentum bands > 100 GeV/c, 65 100 GeV/c and 30 65 GeV/c with a significance of 7.0 0",5.80" and 5.2 0" respectively. Two dimensional maximum likelihood analyses are performed, both with binned data and unbinned data. The unbinned method gives a smaller uncertainty on the measurement of the antiproton to proton ratio. For a muon momentum cut at 70 GeV/c, the antiproton to proton ratio is measured to be -0.12 ±O.ll and an upper limit ofthis ratio is estimated to be 0.08 (at 90% confidence level) for primary energies in the range 0.8 TeV to 2.4 TeV. In addition, the above mentioned angular resolution is confirmed by the Moon shadow observation and the pointing precision of the detector is determined to be better than 0.1 0 •
116433269
A Search for Astrophysical Point Sources and a Solar Anisotropy measurement
The L3 detector at LEP, CERN, has been employed for the search of point sources through the observation of muons with energies above 20, 30, 50, and 100 GeV. Excesses lasting for only one day, as well as steady emissions of single muon events pointing to a particular direction in the sky were searched for in the data obtained from mid July to October 1999 and from April to November 2000. Special attention was also given to a selection of known γ-sources. No statistically significant excess has been observed for any direction or particular source in the time periods considered. In addition a dedicated study of the angular distribution of muons above 20 GeV revealed evidence for a Solar anisotropy of the primary flux.
1567381
The structure of the Galactic halo : SDSS versus SuperCOSMOS
The halo structure at high Galactic latitudes near both the north and south poles is studied using Sloan Digital Sky Survey (SDSS) and SuperCOSMOS data. For the south cap halo, the archive of the SuperCOSMOS photographic photometry sky survey is used. The coincident source rate between SuperCOSMOS data in B J band from 16.5 to 20.5 mag and SDSS data is about 92 per cent, in a common sky area in the south. While that in the R F band is about 85 per cent from 16.5 to 19.5 mag. Transformed to the SuperCOSMOS system and downgraded to the limiting magnitudes of SuperCOSMOS, the star counts in the North Galactic Cap from SDSS show up to an 16.9±6.3 per cent asymmetric ratio (defined as relative fluctuations over the rotational symmetry structure) in the B J band, and up to 13.5 ± 6.7 per cent asymmetric ratio in the R F band. From SuperCOSMOS Bj and R F bands, the structure of the Southern Galactic hemisphere does not show the same obvious asymmetric structures as the northern sky does in both the original and downgraded SDSS star counts. An axisymmetric halo model with n = 2.8 and q = 0.7 can fit the projected number density from SuperCOSMOS fairly well, with an average error of about 9.17 per cent. By careful analysis of the difference of star counts between the downgraded SDSS northern halo data and SuperCOSMOS southern halo data, it is shown that no asymmetry can be detected in the South Galactic Cap at the accuracy of SuperCOSMOS, and the Virgo overdensity is likely a foreign component in the Galactic halo.
119233618
The K giant stars from the LAMOST survey data I: identification, metallicity, and distance
We present a support vector machine classifier to identify the K giant stars from the LAMOST survey directly using their spectral line features. The completeness of the identification is about 75% for tests based on LAMOST stellar parameters. The contamination in the identified K giant sample is lower than 2.5%. Applying the classification method to about two million LAMOST spectra observed during the pilot survey and the first year survey, we select 298,036Kgiant candidates. The metallicities of the sample are also estimated with an uncertainty of 0.13 similar to 0.29 dex based on the equivalent widths of Mgb and iron lines. A Bayesian method is then developed to estimate the posterior probability of the distance for the K giant stars, based on the estimated metallicity and 2MASS photometry. The synthetic isochrone-based distance estimates have been calibrated using 7 globular clusters with a wide range of metallicities. The uncertainty of the estimated distance modulus at K = 11 mag, which is the median brightness of the K giant sample, is about 0.6 mag, corresponding to similar to 30% in distance. As a scientific verification case, the trailing arm of the Sagittarius stream is clearly identified with the selected K giant sample. Moreover, at about 80 kpc from the Sun, we use our K giant stars to confirm a detection of stream members near the apo-center of the trailing tail. These rediscoveries of the features of the Sagittarius stream illustrate the potential of the LAMOST survey for detecting substructures in the halo of the Milky Way.