ALMA image of AFGL5142. Image credit: ALMA (ESO/NAOJ/NRAO)
Massive star formation is a complex process which is not yet fully understood. Studies of massive star forming regions usually involve observations of outflows and jets in order to understand the feedback mechanisms acting against accretion. These phenomena can be observed using multi-epoch VLBI, revealing their kinematics at very high precision. However, this technique is under the assumption that masers co-propagate with the shock surfaces.
3D water maser velocities in AFGL5142 taken using VERA in 2015
AFGL5142 is a massive star forming region with multiple outflows on multiple scales, with the primary object, MM1 with a mass of
\(6.5~\mathrm{M}_{\odot}\) hosting rare double bowshocks observed using VERA in 2015 via water masers (Burns et al., 2017). However, when the kinematics are extrapolated and compared with new observations, the masers do not move as far as expected (Rosli et al., 2023). This suggests that the discrepencies may exist between the motions of the masers and the motions of the bowshocks, either due to relative motions of the shock and the maser cloudlets, supersonic turbulence, or on an extreme, the deceleration of the shock itself. Nonetheless, this result underlines the importance of both short- and long-term monitoring of masers to understand the true kinematics of the bowshocks at different scales.
Evolution of protostellar bowshocks in AFGL5142-MM1
References
Trigonometric distance and proper motions of H2O maser bowshocks in AFGL 5142
R. A. Burns, T. Handa, H. Imai, T. Nagayama, T. Omodaka, ...
Monthly Notices of the Royal Astronomical Society, Jan 2017
Multi-epoch very long baseline interferometry (VLBI) observations
measure three-dimensional water maser motions in protostellar outflows,
enabling analysis of inclination and velocity. However, these analyses
assume that water masers and shock surfaces within outflows are
co-propagating. We compare VLBI data on maser-traced bow shocks in the
high-mass protostar AFGL 5142-MM1, from seven epochs of archival data
from the VLBI Exploration of Radio Astrometry (VERA), obtained from 2014
April to 2015 May, and our newly conducted data from the KVN and VERA
Array (KaVA), obtained in 2016 March. We find an inconsistency between
the expected displacement of the bow shocks and the motions of
individual masers. The separation between two opposing bow shocks in
AFGL 5142-MM1 was determined to be \(337.17
\pm 0.07~\mathrm{mas}\) in the KaVA data, which is less than an
expected value of \(342.1 \pm
0.7~\mathrm{mas}\) based on extrapolation of the proper motions
of individual maser features measured by VERA. Our measurements imply
that the bow shock propagates at a velocity of \(24 \pm 3~\mathrm{km}~\mathrm{s}^{-1}\),
while the individual masing gas clumps move at an average velocity of
\(55 \pm
5~\mathrm{km}~\mathrm{s}^{-1}\); that is, the water masers are
moving in the outflow direction at double the speed at which the bow
shocks are propagating. Our results emphasize that investigations of
individual maser features are best approached using short-term
high-cadence VLBI monitoring, while long-term monitoring on timescales
comparable to the lifetimes of maser features is better suited to
tracing the overall evolution of shock surfaces. Observers should be
aware that masers and shock surfaces can move relative to each other,
and that this can affect the interpretation of protostellar
outflows.
@article{Rosli2023,title={Limits of water maser kinematics: Insights from the high-mass protostar {AFGL 5142-MM1}},volume={527},issn={1365-2966},url={http://dx.doi.org/10.1093/mnras/stad3767},doi={10.1093/mnras/stad3767},number={4},journal={Monthly Notices of the Royal Astronomical Society},publisher={Oxford University Press (OUP)},author={Rosli, Zulfazli and Burns, Ross A. and Nazri, Affan Adly and Sugiyama, Koichiro and Hirota, Tomoya and Kim, Kee-Tae and Yonekura, Yoshinori and Tie, Liu and Orosz, Gabor and Chibueze, James Okwe and Sobolev, Andrey M and Kang, Ji Hyun and Lee, Chang Won and Hwang, Jihye and Mohammad, Hafieduddin and Hashim, Norsiah and Abidin, Zamri Zainal},year={2023},month=dec,pages={10031-10037},}
