The one-meter telescope at Weihai Observatory of Shandong University is an f/8 Cassegrain telescope. Three sets of filters, including Johnson-Cousins UBVRI, Sloan Digital Sky Survey u ′ g ′ r ′ i ′ z ′ and Strömgren uvby, are installed in a dual layer filterwheel. The photometric system and the CCD camera are introduced in this paper, followed by detailed analysis of their performances, and determination of the relevant parameters, including gain, readout noise, dark current and linearity of the CCD camera. In addition, the characteristics of the site astro-climate condition, including typical seeing, clear nights statistics, and average sky brightness were studied systematically based on data gathered from Sep. 2007 to Aug. 2013, and were reported in this work. Photometric calibrations were done using 8 nights Landolt standard star observations, which yielded transformation coefficients, photometry precision and system throughput. The limiting magnitudes were simulated using the derived calibration parameters and classic observation conditions at WHO.

We present a model atom for C i-C ii-C iii-C iv using the most up-to-date atomic data and evaluated the non-local thermodynamic equilibrium (NLTE) line formation in classical 1D atmospheric models of O-B-type stars. Our models predict the emission lines of C ii 9903Å and 18 535Å to appear at effective temperature T eff ≥ 17 500 K, those of C ii 6151Å and 6461Å to appear at T eff > 25 000 K, and those of C iii 5695, 6728-44, 9701-17Å to appear at T eff ≥ 35 000 K (log g=4.0). Emission occurs in the lines of minority species, where the photoionization-recombination mechanism provides a depopulation of the lower levels to a greater extent than the upper levels. For C ii 9903 and 18 535Å, the upper levels are mainly populated from C iii reservoir through the Rydberg states. For C iii 5695 and 6728-44Å, the lower levels are depopulated due to photon losses in UV transitions at 885, 1308, and 1426-28Å which become optically thin in the photosphere.We analysed the lines of C i, C ii, C iii, and C iv for twenty-two O-B-type stars with temperature range between 15 800 ≤ T eff ≤ 38 000 K. Abundances from emission lines of C i, C ii and C iii are in agreement with those from absorption ones for most of the stars. We obtained log ǫ C =8.36±0.08 from twenty B-type stars, that is in line with the present-day Cosmic Abundance Standard. The obtained carbon abundances in 15 Mon and HD 42088 from emission and absorption lines are 8.27±0.11 and 8.31±0.11, respectively. ). Several model atoms of carbon were constructed and several independent codes were used to perform the analyses.Carbon lines in the visible spectral region can be measured over a wide range of effective temperatures up to 55 000 K. In the low-resolution spectroscopy, the strongest features in the metal line spectra are demanded for study. In the case of carbon, the C ii 4267 and C iii 4647Å lines are strong in B-type stars, and C iii 5695 and C iv 5801, 5811Å in O-type stars. These lines can be used as abundance indicators even in low-resolution spectroscopy. It should be noticed that the C iii 5695Å line can be a good gravity indicator, since it strongly depends on luminosity classes (and surface gravity), that was pointed out in the spectroscopic atlas of O-B stars of Walborn (1980) and theoretical analyses of Carneiro et al. (2018). However, these lines are highly sensitive not only to the choice of stellar atmospheric parameters but also to the NLTE effects. For example, Lyubimkov et al. (2013) found that for stars with T eff between 20 000 and 24 000 K the C ii 4267Å line to give lower log ǫ C values, and the underestimation amounts to 0.20-0.70 dex. A tendency of the 4267Å line to yield lower values of log ǫ C for B stars has been noted in earlier studies, e.g. presented a solution to the long-standing discrepancy between NLTE analyses of the C ii 4267 and 6578/82Å multiplets in six slowly-rotating early B-type dwarfs and giants, which cover a wide parameter range. Their comprehensive NLTE model atom of C ii/ iii/ iv was constructed with critically selected a...

In this paper, a total of about 28000 images in $V$ and $R$ band obtained on 161 nights using the one-meter optical telescope at Weihai Observatory (WHO) of Shandong University since 2008 to 2012 have been processed to measure the sky brightness. It provides us with an unprecedented database, which can be used to study the variation of the sky brightness with the sky position, the moonlight contribution, and the twilight sky brightness. The darkest sky brightness is about 19.0 and 18.6 $mag$ $arcsec^{-2}$ in $V$ and $R$ band, respectively. An obvious darkening trend is found at the first half of the night at WHO, and the variation rate is much larger in summer than that in other seasons. The sky brightness variation depends more on the azimuth than on the altitude of the telescope pointing for WHO. Our results indicate that the sky brightness at WHO is seriously influenced by the urban light.Comment: 15pages, 8 figure

During October 2019 and March 2020, the luminous red supergiant Betelgeuse demonstrated an unusually deep minimum of its brightness. It became fainter by more than one magnitude and this is the most significant dimming observed in the recent decades. While the reason for the dimming is debated, pre-phase of supernova explosion, obscuring dust, or changes in the photosphere of the star were suggested scenarios. Here, we present spectroscopic studies of Betelgeuse using high-resolution and high signal-to-noise ratio near-infrared spectra obtained at Weihai Observatory on four epochs in 2020 covering the phases of during and after dimming. We show that the dimming episode is caused by the dropping of its effective temperature by at least 170 K on 2020 January 31, that can be attributed to the emergence of a large dark spot on the surface of the star.

In optical observations of moving targets, field stars can be trailed when the telescope tracks at the speed of the targets. When these trailed sources are relatively long, faint, or distorted, the popular source extraction techniques, such as thresholding and profile fitting, tend to fail. We present a new source extraction strategy based on the template matching method. We described the pipeline of template matching in detail and tested its performances compared with thresholding on 9 × 4320 synthetic images and 349 real images. The indicators, including recall, position extraction error, and flux extraction error, are analyzed and given. The results show that template matching can obtain higher recalls and smaller position and flux extraction errors for trailed sources.