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There are more than a dozen protoplanetary disks that have spiral arms, and the formation mechanism for these arms is under debate (Dong et al. 2018). Two leading mechanisms, (1) companion-driven and (2) graviational instatbility induction, can create spirals. "Missing Planets" refers to the phenomenon that no planetary drivers have been confirmed in spiral arm systems (Brittain et al. 2020). Using multi-epoch observations, we can discern the leading mechanisms by measuring the motion of the spirals.
1. Mathematical foundation
1. Mathematical foundation
Formation mechanism of spiral arms in protoplanetary disks (Ren et al. 2020, ApJL). See AAS Nova feature here.
Technical highlight: by developing a method which involves polynomial fitting with dummy varaibles, we tested the formation mechanism of the MWC 758 spiral arms using a precise measurement of their rotation pattern speeds.
Scientific highlight: our measurement rules out one leading formation mechanism -- gravitational instability -- for the first time, which in turn supports the hypothesis that a hidden planet is responsbile for driving the spirals. We also observe shadowing effects at a global scale.
Project timescale: 2019 March to 2020 July.
MWC 758 Driver Orbit
2. Application using 1 year data
2. Application using 1 year data
Together with a great undergrad Chengyan Xie (Xiamen University '22), Motion measurement of spiral arm motion for the SAO 206462 system (Xie, Ren et al. 2021, ApJL).
Technical highlight: separation of 1 year suffices in distinguishing leading formation mechanisms for spiral arm motion.
Scientific highlight: a 3σ evidence that there might be two planets driving the arms.
Project timescale: 2020 August to 2020 December.
Advising highlight: Chengyan's admission to top Astro PhD programs (e.g, U Arizona).
SAO 206462 Driver Orbit(s)
3. Stellar flyby history of spiral systems
3. Stellar flyby history of spiral systems
Together with an excellent undergrad Linling Shuai (Xiamen University '23), we traced back the historical locations for stars surrounding spiral arm hosts (Shuai, Ren et al. 2022; ApJS). By doing so, we can investigate the formation mechanism of spirals: are they driven by close-in flybys in the recent past?
Technical highlight: Using Gaia Data Release 3 (DR3), we developed an analytical mathematical framework to track the relative location of stars. In comparison with prior studies using Monte Carlo Markov Chain simulations, we reduced the calculation cost by 4–5 orders of magnitude!
Scientific highlight: none of the standalone systems are caused by flybys (caveat: non-detection from Gaia DR3).
Project timescale: 2021 summer to 2022 fall.
Advising highlight: (1) Publication charge waiver by AAS Journals. (2) Linling's admission to top Astro PhD programs (e.g, U Michigan, U Florida).
4. Surveying all spiral arm systems
4. Surveying all spiral arm systems
The SAFFRON (Spiral Arm Formation from mOtion aNalysis) project surveys all known spiral systems. The VLT/SPHERE program led by me was approved in 2023 spring.
Technical highlight: By observing all known spiral systems again with a ~5 year separation from their previous observation, we can quantify spiral motion, discern formation mechanism, and pinpoint hidden planetary locations.
Scientific highlight: _________.
Project timescale: 2023 Apr to 202_ ____.
More updates to come.
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