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.
Water masers and their 3D 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 \(6.5\,\text{M}_{\odot}\) 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.
I worked on data analysis of the data involving parametric fitting, error calculations, and confidence intervals as well as data visualization.
Evolution of protostellar bowshocks in AFGL5142-MM1.
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 ± 0.07 mas in the KaVA data, which is less than an expected value of 342.1 ± 0.7 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 ± 3 km s-1, while the individual masing gas clumps move at an average velocity of 55 ± 5 km 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},google_scholar_id={u5HHmVD_uO8C},}
