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
Cheng-Han Hsieh
Héctor G. Arce
Zhi-Yun Li
Michael Dunham
Stella Offner
Ian W. Stephens
Amelia Stutz
Tom Megeath
Shuo Kong
Adele Plunkett
John J. Tobin
Yichen Zhang
Diego Mardones
Jaime E. Pineda
Thomas Stanke
John Carpenter
摘要： We present Atacama Large Millimeter/submillimeter Array observations of the $\sim$10 kAU environment surrounding 21 protostars in the Orion A molecular cloud tracing outflows. Our sample is composed of Class 0 to flat-spectrum protostars, spanning the full $\sim$1 Myr lifetime. We derive the angular distribution of outflow momentum and energy profiles and obtain the first two-dimensional instantaneous mass, momentum, and energy ejection rate maps using our new approach: the Pixel Flux-tracing Technique (PFT). Our results indicate that by the end of the protostellar phase, outflows will remove $\sim$2 to 4 M$_\odot$ from the surrounding $\sim$1 M$_\odot$ low-mass core. These high values indicate that outflows remove a significant amount of gas from their parent cores and continuous core accretion from larger scales is needed to replenish core material for star formation. This poses serious challenges to the concept of ``cores as well-defined mass reservoirs", and hence to the simplified core-to-star conversion prescriptions. Furthermore, we show that cavity opening angles, and momentum and energy distributions all increase with the protostar evolutionary stage. This is clear evidence that even garden-variety protostellar outflows: (a) effectively inject energy and momentum into their environments on $10$ kAU scales, and (b) significantly disrupt their natal cores, ejecting a large fraction of the mass that would have otherwise fed the nascent star. Our results support the conclusion that protostellar outflows have a direct impact on how stars get their mass, and that the natal sites of individual low-mass star formation are far more dynamic than commonly accepted theoretical paradigms.
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