狮子座流星雨1999年照相观测的分析

对1999年11月19日拍摄的两张狮子座流星胶片进行了分析研究照相观测比目观测记录了更多的定量信息计算了流星在胶片上显露时必须满足的运动角速度条件,求出了流星起始点仰角、流星结束点与辐射点的角距离、流星运动的角速度以及流星路径的弧长等并且得出流星在大气中的烧蚀时间仅0 65秒左右,即烧蚀的路径长约40 50公里通过在扫描仪上得到的黑白图像的处理,求得两颗流星的照相星等分别为-10.3 ± 0.2和-4.8±0.2.由此可以得到它们的质量和电子线密度.给出的处理方法,也可用于其他流星的照相观测资料处理.并且,对流星观测使用的照相镜头也进行了讨论.     

GRBs search results with the ARGO-YBJ experiment operated in scaler mode

The ARGO-YBJ experiment is almost completely installed at the YangBaJing Cosmic Ray Laboratory (4300 m a.s.l., Tibet, P.R. China). The lower energy limit of the detector (E∼1 GeV) is reached with the scaler mode, i.e., recording the single particle rate at fixed time intervals. In this technique, due to its high altitude location and large area (∼6700 m²), this experiment is the most sensitive among all present and past ground-based detectors. In the energy range under investigation, signals due to local (e.g. solar GLEs) and cosmological (e.g. GRBs) phenomena are expected as significant enhancements of the counting rate over the background. Results on the search for GRBs in coincidence with satellite detections are presented. For the ARGO-YBJ Collaboration.     

HIGH SPATIAL AND TEMPORAL RESOLUTION OPTICAL SEARCH FOR EVIDENCE OF METEOROID FRAGMENTATION

A digital image intensified CCD camera with an electronically gated image intensifier was used to produce very short duration images of meteors. The observational system employed a 0.40 m F/4.5 Newtonian telescope to obtain high spatial resolution. A second intensified CCD camera was used to yield height information using parallax. At a typical meteor height one pixel (for the vertically oriented system) corresponded to about 1.1 m. A sampling of 59 mainly sporadic meteors was analyzed. There is clear variability from meteor to meteor, with many meteors (nearly 50%) showing only a small amount of wake, while some meteors (approximately 20%) have the off segments completely filled in.     

Measurements of attenuation and absorption lengths with the KASCADE experiment

The attenuation of the electron shower size beyond the shower maximum is studied with the KASCADE extensive air shower (EAS) experiment in the primary energy range of about 10¹⁴–10¹⁶ eV. Attenuation and absorption lengths are determined by applying different approaches, including the method of constant intensity, the decrease of the flux of EASs with increasing zenith angle, and its variation with ground pressure. We observe a significant dependence of the results on the applied method. The determined values of the attenuation length ranges from 175 to 196 g/cm² and of the absorption length from 100 to 120 g/cm². The origin of these differences is discussed emphasizing the influence of intrinsic shower fluctuations.     

ON THE FUTURE PROSPECTS OF METEOR DETECTIONS (INVITED REVIEW)

The successful application of modern observing techniques for Leonid storm observations show that meteor (shower) detections will have a bright future if the field will pursue difficult but important questions. How to forecast a satellite threatening meteor storm? What happens to the organic matter in meteors and can this be an important source of prebiotic molecules? What range of variations in composition and morphology exists among cometary grains and what does this tell us about the origin of the solar system? What long-period comets approach Earth orbit and can meteoroid streams provide early warning for giant impacts? What are the sources of interstellar and interplanetary grains? Just to mention a few. To answer these questions will need new technologies and facilities, some of which are being developed for other use. This may include NASA’s Stratospheric Observatory For Infrared and sub-millimeter Astronomy (SOFIA). In addition, big-science space missions can drive the field if meteor detections are an integral part. Special events, such as meteor outbursts and the “artificial meteor” from the reentry of sample return capsules from interplanetary space, can mobilize observing and theoretical efforts. These and other future opportunities are briefly discussed.     

OH and O2 airglow emissions during the 1998 leonid outburst and the 2002 leonid storm

In order to enhance our understanding of the possible influence of meteor ablation on the enrichment in OH and O₂ of the lower thermosphere we studied intense Leonid meteor activity by using the SATI (Spectral Airglow Temperature Imager) interferometer of the Instituto de Astrofísica de Andalucía. We measured the emission rate and rotational temperature of OH and O₂ airglow emission layers during two observation periods of high meteoric activity: the 1998 Leonid outburst and the 2002 Leonid storm. The results show that there is not a clear relation of O₂ and OH airglow emission and rotational temperature with meteoric activity.     

Power Fluctuations in Meteor Head Echoes Observed with the EISCAT VHF Radar

We present observations and preliminary results from a meteor experiment carried out with the 224 MHz EISCAT VHF radar in Tromsø, Norway, which was run for 6 h on November 26, 2003. The data set contains echoes with peculiar pulsations in received power in the frequency range 20–200 Hz, limited by instrumental parameters. The process causing the echo power pulsations has not yet been identified. Plasma effects are the most likely cause, a possible mechanism is for instance asymmetrical dust grains in rotation causing a modulation of the ionization rate.     

Searching for tau neutrinos with Cherenkov telescopes

Cherenkov telescopes have the capability of detecting high energy tau neutrinos in the energy range of 1–1000 PeV by searching for very inclined showers. If a tau lepton, produced by a tau neutrino, escapes from the Earth or a mountain, it will decay and initiate a shower in the air which can be detected by an air shower fluorescence or Cherenkov telescope. In this paper, we present detailed Monte Carlo simulations of corresponding event rates for the VERITAS and two proposed Cherenkov Telescope Array sites: Meteor Crater and Yavapai Ranch, which use representative AGN neutrino flux models and take into account topographic conditions of the detector sites. The calculated neutrino sensitivities depend on the observation time and the shape of the energy spectrum, but in some cases are comparable or even better than corresponding neutrino sensitivities of the IceCube detector. For VERITAS and the considered Cherenkov Telescope Array sites the expected neutrino sensitivities are up to factor 3 higher than for the MAGIC site because of the presence of surrounding mountains.