The new detection of blue straggler stars in 50 open clusters using Gaia DR3

The particularly abundant presence of blue straggler stars (BSS) in Galactic open clusters offers favorable conditions for detailed studies on the statistical properties and the origin of the blue straggler population. With the help of Gaia DR3, the number of identified open clusters continuously increases, and the determination of star cluster members is more reliable. We performed a more thorough search for BSS in newly found open clusters based on Gaia data. We implemented a uniform membership determination for over one thousand newly identified open clusters with larger sky coverage based on the astrometric and photometric data from Gaia DR3. The membership probabilities of stars were assigned by the pyUPMASK algorithm. Then we estimated the physical parameters of these clusters by isochrone fitting on their CMDs and picked out BSS in the specific region of these CMDs. We identified 138 BSS that had not been reported before in 50 open clusters. Compared with recent catalogs that present more than 1500 BSS in 339 open clusters, our new catalog increased the number of BSS in Galactic open clusters by about 10%, and the number of open clusters with BSS by nearly 17%. In the future, more accurate abundance measurements are anticipated to better probe the origin of BSS in open clusters.Comment: 9 pages, 10 figures, 2 tables. Published in A&

The role of tidal interactions in the formation of slowly rotating early-type stars in young star clusters

The split main sequences found in the colour-magnitude diagrams of star clusters younger than ~600 Myr are suggested to be caused by the dichotomy of stellar rotation rates of upper main-sequence stars. Tidal interactions have been suggested as a possible explanation of the dichotomy of the stellar rotation rates. This hypothesis proposes that the slow rotation rates of stars along the split main sequences are caused by tidal interactions in binaries. To test this scenario, we measured the variations in the radial velocities of slowly rotating stars along the split main sequence of the young Galactic cluster NGC 2422 (~90 Myr) using spectra obtained at multiple epochs with the Canada-France-Hawai'i Telescope. Our results show that most slowly rotating stars are not radial-velocity variables. Using the theory of dynamical tides, we find that the binary separations necessary to fully or partially synchronise our spectroscopic targets, on time-scales shorter than the cluster age, predict much larger radial velocity variations across multiple-epoch observations, or a much larger radial velocity dispersion at a single epoch, than the observed values. This indicates that tidal interactions are not the dominant mechanism to form slowly rotating stars along the split main sequences. As the observations of the rotation velocity distribution among B- and A-type stars in binaries of larger separations hint at a much stronger effect of braking with age, we discuss the consequences of relaxing the constraints of the dynamical tides theory.Comment: 14 pages, 10 figures, 2 tables, accepted for publication in MNRA

The new detection of blue straggler stars in 50 open clusters using Gaia DR3

The particularly abundant presence of blue straggler stars (BSS) in Galactic open clusters offers favorable conditions for detailed studies on the statistical properties and the origin of the blue straggler population. With the assistance of Gaia DR3, the number of identified open clusters is continuously increasing, and the determination of star cluster members has become more reliable. We conducted a comprehensive and thorough search for BSS in newly discovered open clusters by employing a uniform membership determination method for over one thousand newly identified open clusters with broader sky coverage, utilizing Gaia DR3's astrometric and photometric data. The membership probabilities of stars were assigned using the pyUPMASK algorithm. Then, we estimated the physical parameters of these clusters through isochrone fitting on their color-magnitude diagrams (CMDs) and identified BSS within specific regions of these CMDs. As a result, we identified 138 BSS that had not been previously reported in 50 open clusters. In comparison to the latest catalogs, which document a total of approximately 1500 BSS in 339 open clusters, our new catalog increased the number of BSS in Galactic open clusters by roughly 10%, and the number of open clusters with BSS by nearly 17%. In the future, more accurate abundance measurements are anticipated to better elucidate the formation pathways of BSS in open clusters

Open Cluster of Solar Neighborhood (OCSN)

We systematically searched for open clusters in the solar neighborhood within 500 pc using pyUPMASK and HDBSCAN clustering algorithms based on Gaia DR3. Taking into consideration that the physical size for most open clusters is less than 50 pc, we adopted a slicing approach for different distance shells and identified 324 neighboring open clusters, including 223 reported open clusters and 101 newly discovered open clusters (named as OCSN, Open Cluster of Solar Neighborhood). Our discovery has increased the number of open clusters in the solar neighborhood by about 45%. In this work, larger spatial extents and more member stars were attained for our cluster sample. We performed membership determination with the pyUPMASK algorithm and then derived the mean position, proper motion, radial velocity, parallax and structural parameters for each cluster. Through isochrone fitting we obtained ages, distance modulus and reddening parameters for the clusters. The cluster catalog and the list of member stars with membership probabilities greater than 0.5 have been made publicly available. For our hunted OC samples, more detailed analyses are needed to further investigate their properties, such as the mass function and the dynamical states. Especially more spectroscopic data for the member stars will be of prime importance to determine the dynamical and chemical evolution of these clusters

Introducing preparation before class and Japanese native speakers into group work activity : The conversation class of Japanese major students in China

本研究では、中国の大学における会話授業の改善を目指して、日本語専攻会話授業に事前課題と日本語母語話者の参加を導入したグループワークによる内容重視の会話授業の実践を行った。そこからデータを収集し、学習者が今回の新たなデザインに対してどのような受け止めを形成しているかを検討することで、会話教育のあり方について提言することを目的とする。学習者の受け止めは修正版グラウンデッド・セオリー・アプローチを援用して探った。分析の結果、学習者はこれまで受けてきた会話授業と対照しながら、今回の会話授業に対する肯定的な評価をしていたことが分かった。Aiming to improve the conversation class of Japanese major students at universities in China, I conducted a content-based practical study of introducing preparation before class and Japanese native speakers into group work activity. By examining the data collected form the practical study I intend to provide recommendations for conversation classes. The data was analyzed by the Modified Grounded Theory Approach (M-GTA). The findings showed that the learners found this experience positive