The first results of observations of lunar occultations in different spectral ranges at the 6-m telescope of the SAO RAS

Observations by the method of lunar occultations at the 6-m telescope of the SAO RAS reach a resolution limit better than 1mas.We have devised a new method of observation,which allows obtaining the curves of lunar occultations simultaneously in different ranges of the visible part of the spectrum,and conducted the first observations using amodified optical system.In January 2019,applying the newmethod,the magnitude differences of the components of the binary star HD 36524 in the R and I bands were measured,which were 1.5 and 1.3mag,respectively,in good agreement with values calculated from the Gaia mission.According to the obtained data,it was determined that with this method it is possible to reach a signal-to-noise ratio of about 5–10 for stars of 10th magnitude.We discuss the applicability of the proposed optical scheme for the study of binary stars.

An algorithm to resolve γ-rays from charged cosmic rays with DAMPE

The DArk Matter Particle Explorer（DAMPE）,also known as Wukong in China,which was launched on 2015 December 17,is a new high energy cosmic ray and γ-ray satellite-borne observatory.One of the main scientific goals of DAMPE is to observe Ge V-Te V high energy γ-rays with accurate energy,angular and time resolution,to indirectly search for dark matter particles and for the study of high energy astrophysics. Due to the comparatively higher fluxes of charged cosmic rays with respect to γ-rays,it is challenging to identify γ-rays with sufficiently high efficiency,minimizing the amount of charged cosmic ray contamination. In this work we present a method to identify γ-rays in DAMPE data based on Monte Carlo simulations,using the powerful electromagnetic/hadronic shower discrimination provided by the calorimeter and the veto detection of charged particles provided by the plastic scintillation detector. Monte Carlo simulations show that after this selection the number of electrons and protons that contaminate the selected γ-ray events at～10 Ge V amounts to less than 1% of the selected sample.Finally,we use flight data to verify the effectiveness of the method by highlighting known γ-ray sources in the sky and by reconstructing preliminary light curves of the Geminga pulsar.

Photometric Calibration of the Lunar-based Ultraviolet Telescope for Its First Six Months of Operation on the Lunar Surface

We describe the photometric calibration of the Lunar-based Ultraviolet Telescope（LUT）, the first robotic astronomical telescope working on the lunar surface, for its first six months of operation on the lunar surface. Two spectral datasets（set A and B） from near-ultraviolet（NUV） to the optical band were constructed with 44 International Ultraviolet Explorer（IUE） standards, because of the LUT＇s relatively wide wavelength coverage. Set A was obtained by extrapolating the IUE NUV spectra（λ 〈 3200 ） to the optical band based upon the theoretical spectra of stellar atmosphere models. Set B was composed of theoretical spectra from 2000 to 8000 extracted from the same model grid. In total, seven standards have been observed in15 observational runs until May 2014. The calibration results show that the photometric performance of LUT is highly stable in its first six months of operation. The magnitude zero points obtained from the two spectral datasets are also consistent with each other, i.e., zp = 17.54 ± 0.09 mag（set A） and zp = 17.52 ± 0.07 mag（set B）.

Modeling the rail surface unevenness of a high-precision radio telescope

This study proposed a coarse-fine mixed model for describing the rail surface unevenness of an ultra-large fully steerable radio telescope （Qi Tai Telescope） with a diameter of 110 meters. The rail surface unevenness includes information on error arising from two different scales, i.e., the long-period- short-change and the short-period-long-change. Consequently, in this study an idea of a mixed model was proposed, in which trigonometric and fractal functions were, respectively, used to describe infor- mation on error from two scales. Key parameters were determined by using the least squares method and the wavelet transform method, and finally, a specific mathematical expression of the model was obtained by optimization. To validate the effectiveness of the new modeling method, the mixed model was then used to describe the rails of the Green Bank Telescope, the Large Millimeter Telescope, and a radio telescope in Miyun, Beijing. A comparative study revealed that the maximum error was less than 15 %, thus the result was superior to those of existing modeling methods.