This paper presents the history and observational records of Nagashima Astronomical Observatory established in 1949 at Nagashima Aiseien, a national sanatorium for Hansen’s disease in Japan. The observatory was a part of the meteorological observatory of the sanatorium, and the observers, who were also Hansen’s disease patients, conducted regular sunspot observations and occasional stellar occultations. The observatory also provided residents and staff of the sanatorium with opportunities to enjoy watching stars. Two astronomers outside the sanatorium deeply committed to the foundation and observations at the Nagashima Observatory: Issei Yamamoto, the first director of Kyoto University’s Kwasan Observatory, and Minoru Honda, known for his discoveries of comets and novas. The records of sunspot and occultation observations were sent to Yamamoto as well as to the Tokyo Astronomical Observatory (Today’s National Astronomical Observatory of Japan) . The significance and uniqueness of the astronomical observations at Nagashima Observatory are discussed from the perspectives of amateur astronomy and the history of Hansen’s disease sanatoria.

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The astronomy laboratory of the School of Science and Engineering, Tokyo Denki University is newly established in April 2021. Since this is the first laboratory to work on astronomy at our university, we have been conducting management while exploring the direction of research and education style. Here, we present the current status of our activities and then discuss education by using astronomy at universities.

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Two Geminid meteor head echoes were detected simultaneously at three points on December 13, 2021, by installing amateur radio receivers within approximately 20 km east from the transmitting station that was continuously transmitting at 10W. The meteor echo of the VHF ham wave was received using the USB format, and the waveform was imaged after frequency analysis. The transmission wave of the meteor head echo is reflected at the head portion of the meteor. The Doppler frequency was confirmed by subjecting the meteoroid to Doppler effect according to its observed velocity. These two meteors have been successfully observed at multiple points optically by the network of meteor researchers in Japan, and several meteor optical path parameters, such as entry angles into the atmosphere and observed velocity, have been published. The authors analyzed the Doppler frequency of the meteor head echoes and the time at which the meteor head reached the point where the meteor path and transmitted waves were orthogonal (f0 point) by using the free FFT software. The radio meteor paths and observed velocities which were derived from the radio observation data were in good agreement with the published optical meteor path specifications. These findings indicate that this meteor radio observation method can serve as a substitute for the optical meteor observation method during daytime or bad weather conditions. If we install observation devices in several locations throughout Japan, we will be able to find several meteorites falling on our country during daytime or bad weather conditions, which have been overlooked to date.

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A systematic way of data reduction for the NIC polarimetry mode has been devised and implemented to an open software called NICpolpy in the programming language python (tested on version 3.8–3.10 as of writing). On top of the classical methods, including vertical pattern removal, a new way of diagonal pattern (Fourier pattern) removal has been implemented. Each image undergoes four reduction steps, resulting in “level 1” to “level 4” products, as well as nightly calibration frames. A simple tutorial and in-depth descriptions are provided, as well as the descriptions of algorithms. The dome flat frames (taken on UT 2020-06-03) were analyzed, and the pixel positions vulnerable to flat error were found. Using the dark and flat frames, the detector parameters, gain factor (the conversion factor), and readout noise are also updated. We found gain factor and readout noise are likely constants over pixel or “quadrant”.

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We present development of a new data reduction and analysis pipeline for Nishiharima Infrared Camera on 2 m Nayuta telescope. The new pipeline includes fundamental reduction procedures, as well as miscellaneous utilities to prepare the calibration frames such as dark and flatfield. We improved the subtraction procedures of the detectorspecific background patterns. These together improves the resulting photometric precision by a factor of ∼ 2, when using the newly obtained flat frames. We also find that the photometric precision can further be improved by introducing “ubercalibration”, resulting in the rms photometric errors of Δmag ∼ 0.02−0.03 for 14−15 mag (AB) in H-band, under the very best condition.

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Dependence of Nayuta’s pointing errors on the telescope orientation has been analyzed using images obtained with NIC from 2014 to 2022. Maps of the pointing errors on the azimuth–elevation plane have been developed. It has been confirmed that pointing correction based on the maps reduces the pointing errors from 46′′ ± 19′′ to 15′′ ± 8′′. The pointing correction presented here will enhance the time efficiency of observations and make the automation easier.

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Donati comet (1858) was observed at Tsuchimikado, Tenmongata and Hazama observatories in Japan. Their daily observational records were found to give us numerical data of apparent positions of the comet and permit us to get equatorial coordinates of daily positions of the comet. Intercomparison among the three observatories records results in the followings. (1) Japanese technological arts of the astronomical observation did not attained the technical levels in Western observatories yet, (2) the obtained accuracies of the equatorial coordinates of the comet was within ±2 degrees, (3) Tsuchimikado is superior to the other two in the viewpoint of observational accuracy, and (4) Tenmongata and Hazama equatorial coordinates show systematic offsets, which we can see only in the short time-spans of observation records at the two observatories. The three observatories had common knowledge of astronomical position measurements and utilized the similar instruments both in the position measurements and the time reckoning. The difference of accuracies of measurements can be due to the setting accuracies of instruments, the robustness of the instruments and the human errors of the naked-eye observers.

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The secular variation in the interval of outbursts in the following six Z Cam-type dwarf novae (including the subtype IW And-type) is investigated: Z Cam, RX And, AH Her, HL CMa, SY Cnc, andWWCet. An analysis using the O − C diagram shows that the interval of outbursts is not steady in one system. The outburst properties before standstill are the decrease in outburst interval, enhancement of the magnitude in quiescence, and disappearance of the long outburst. Meanwhile, several objects have at least two typical intervals of outbursts. These characteristics are difficult to be explained only by the variation in mass transfer from the secondary.

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In the early universe, the formation process of supermassive blackholes in quasars is still in debate. Our group focuses on the light variation of quasars and discuss this problem. We continuously observe high-z quasars in J, H, and Ks bands with Nayuta/NIC since 2019. Here we report 2022 data for three quasars, PSO338+29 (redshift z = 6.66), ULAS J1120+0641 (redshift z = 7.09) and ULAS J1342+0928 (redshift z = 7.54). We also report J, Ks bands magnitude of ULAS J1342+0928 observed with Subaru/SWIMS in 2022. PSO338+29 shows a ∼ 2 σ level light variation in the J band. ULAS J1342+0928 shows a sign of ∼ 102 days periodic variation in the J band. At redshift z ∼ 7, the C IV emission line comes into the J band. Hence, we discuss the relation between periodic motion of BLR (Broad Line Region) to this variability period. The orbital period of BLR is ∼ 104 days. We conclude that the BLR motion is not responsible to this periodic variability. It is important to reduce the magnitude uncertainty for the variability research. We have examined the magnitude uncertainties when adopting different numbers of dithering points and ubercalibration. However, any significant reduction of the uncertainties was not observed.

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For many years, photometric and spectroscopic observations of Be stars (γ-type variable stars in Cassiopeia) have been carried out, but the mechanism of the formation and extinction of the circumstellar disk is still unclear. Therefore, from September 2018 to March 2020, we performed spectroscopic monitoring observations of several Be stars using the Small Aperture Telescope + Low Dispersion Spectrograph at the School Observatory. From the obtained spectra, we calculated the hydrogen emission line equivalent widths and Balmer decrement (Hα / Hβ), and investigated the time variability and so on. As a result, we identified several sources with significant variations in the Balmer decrement. To explain this phenomenon, we hypothesized that the disk is ringed by the tidal force of Be’s companion star as it passes the perihelion point.

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