分类： 天文学 >> 天文学 提交时间： 2023-02-19
Ruobing Dong
Hauyu Baobab Liu
Nicolas Cuello
Christophe Pinte
Peter Abraham
Eduard Vorobyov
Jun Hashimoto
Agnes Kospal
Eugene Chiang
Michihiro Takami
Lei Chen
Michael Dunham
Misato Fukagawa
Joel Green
Yasuhiro Hasegawa
Thomas Henning
Yaroslav Pavlyuchenkov
Tae-Soo Pyo
Motohide Tamura
摘要： Close encounters between young stellar objects in star forming clusters are expected to dramatically perturb circumstellar disks. Such events are witnessed in numerical simulations of star formation, but few direct observations of ongoing encounters have been made. Here we report sub-0".1 resolution Atacama Large Millimeter Array (ALMA) and Jansky Very Large Array (JVLA) observations towards the million year old binary protostar Z CMa in dust continuum and molecular line emission. A point source ~4700 au from the binary has been discovered at both millimeter and centimeter wavelengths. It is located along the extension of a ~2000 au streamer structure previously found in scattered light imaging, whose counterpart in dust and gas emission is also newly identified. Comparison with simulations shows signposts of a rare flyby event in action. Z CMa is a "double burster", as both binary components undergo accretion outbursts, which may be facilitated by perturbations to the host disk by flybys.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Michihiro Takami
Hans Moritz Guenther
P. Christian Schneider
Tracy L. Beck
Jennifer L. Karr
Youichi Ohyama
Roberto Galvan-Madrid
Taichi Uyama
Marc White
Konstantin Grankin
Deirdre Coffey
Chun-Fan Liu
Misato Fukagawa
Nadine Manset
Wen-Ping Chen
Tae-Soo Pyo
Hsien Shang
Thomas P. Ray
Masaaki Otsuka
Mei-Yin Chou
摘要： We present Gemini-NIFS, VLT-SINFONI and Keck-OSIRIS observations of near-infrared [Fe II] emission associated with the well-studied jets from three active T Tauri stars; RW Aur A, RY Tau and DG Tau taken from 2012-2021. We primarily covered the redshifted jet from RW Aur A, and the blueshifted jets from RY Tau and DG Tau, to investigate long-term time variabilities potentially related to the activities of mass accretion and/or the stellar magnetic fields. All of these jets consist of several moving knots with tangential velocities of 70-240 km s-1, ejected from the star with different velocities and at irregular time intervals. Via comparison with literature, we identify significant differences in tangential velocities for the DG Tau jet between 1985-2008 and 2008-2021. The sizes of the individual knots appear to increase with time, and in turn, their peak brightnesses in the 1.644-micron emission decreased up to a factor of ~30 during the epochs of our observations. A variety of the decay timescales measured in the [Fe II] 1.644 micron emission can be attributed to different pre-shock conditions if the moving knots are unresolved shocks. However, our data do not exclude the possibility that these knots are due to non-uniform density/temperature distributions with another heating mechanism, or in some cases due to stationary shocks without proper motions. Spatially resolved observations of these knots with significantly higher angular resolutions are necessary to better understand their physical nature.
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