A synthetic spectrum-fitting analysis was applied to the resonance Ca ii line at 3933.68 Å for a large sample of 122 A-type main-sequence stars (7000 ≲ Teff ≲ 10000 K) in a wide range of projected rotational velocity (10 ≲ vsini ≲ 300 km s−1), with an aim of investigating the behaviors of Ca abundances ([Ca/H]39) determined from this strong Ca ii 3934 line, especially in context of (i) how they are related with the Am phenomenon (often seen in slow rotators) and (ii) whether they are consistent with the Ca abundances ([Ca/H]61) previously derived by the author from the weaker Ca i 6162 line. It was confirmed that Ca line strengths in Am stars tend to be weaker and associated abundances are lower compared to non-Am stars at the same Teff, indicating a deficiency of Ca in the photosphere of Am stars. However, an appreciable fraction of cool Am stars (Teff ≲ 8000 K) were found to show extraordinarily anomalous Ca ii 3934 line feature (i.e., unusually broad for its considerable weakness) which is hard to explain. Regarding the comparison between [Ca/H]39 and [Ca/H]61, while both are roughly consistent with each other for hotter stars (Teff ≳ 8000 K), the former tends to be lower (by up to −1 dex or even more) than the latter for cooler A stars (Teff ≲ 8000 K) including those “weak broad K line” objects, This fact suggests that some special mechanism reducing the strength of Ca ii 3934 line is involved at Teff ≲ 8000 K where [Ca/H]39 would be no more reliable. Whereas atomic diffusion causing the deficit of Ca in the photosphere as a result of element segregation in the deeper radiative envelope may be regarded as a promising explanation because it seems to fit in the qualitative trend of [Ca/H]61 in A-type stars, the well-known feature of considerably weak Ca ii K line in classical Am stars should not necessarily be attributed to only this element diffusion scenario, for which some unknown weakening mechanism specific to this resonance line may independently be operative.

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Accurate comparison of photometric data acquired by different telescopes and instruments requires the transformation of the magnitudes to the same photometric system. In this paper, I derived color transformation coefficients to convert the magnitudes observed with the Nishiharima Infrared Camera (NIC) equipped on the Cassegrain focus of the Nayuta telescope to the Two Micron All Sky Survey (2MASS) system, which has become the de facto standard system in the near-infrared. I was able to derive the color transformation coefficients using sources with a wide range of colors since the sample contains very red sources affected by strong interstellar extinction in the Galactic plane. As a result, the conversion coefficients are small, and it is confirmed that the NIC and 2MASS photometric systems are similar.

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Recent observations suggest the presence of supermassive black holes at the centers of many galaxies. The existence of intermediate-mass black holes (IMBHs) in globular clusters has also been predicted. We focus on gravitational lensing as a new way to explore these entities. It is known that the mass distribution of a self-gravitating system such as a globular cluster changes greatly depending on the presence or absence of a central massive object. After considering possible mass distributions for a globular cluster belonging to the Milky Way galaxy, we estimate that the effect on the separation angle of gravitational lensing due to an IMBH would be of milliarcsecond order.

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The resonance hypothesis for the cause of the decreasing event in the pulsation amplitude of the Cepheid component of Polaris is proposed. If Polaris is at the center of the 2:1 resonance between the first and the fourth overtone modes, we can estimate the mass and luminosity from the results of the linear nonadiabatic pulsation models using resonance conditions. The estimated stellar parameters from the resonance hypothesis are within the possible parameter range.

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Starting with our investigation of the telescope settled in the Elementary School Attached to Kyoto Women’s University (hereafter Kyojo telescope), we examine the development history of Japanese astronomy during Taisho and Showa era. For the history of astronomy, studying people behind published papers and works is as important as studying those papers. In this paper, with the results of the Kyojo telescope investigation, we try to reconstruct the history of Japanese astronomy from the viewpoint of Kyoto Women’s University and discuss the potential of this kind of study in multiple perspectives.

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