Searching for Rotating Disks in Young Protostellar Systems in Orion

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Speaker : Bin-Yeh Wu (NTU)

Supervisor : Chin-Fei Lee (ASIAA)

2026/08/31

Evolutionary stages of star formation

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https://doi.org/10.6084/m9.figshare.654555

Class 0 protostellar system

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• The surrounding material falls toward the center, feeding the protostar

arXiv:0907.3265v1 [astro-ph.SR]

• A rotating accretion disk is expected to form

• Excess angular momentum removed by jets and outflows

Targets

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ALMA project ID 2022.1.01437.S (PI : Somnath Dutta)

Angular resolution : 0.02arcsec

Band : 7 (wavelength ~ 0.87mm)

G206

G209

https://www.deepskycolors.com/product/orion-head-to-toes/

The Orion molecular cloud complex

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Herschel (250 μm)

Herschel (160 μm)

ALMA (band 7 continuum)

ALMA (band 7 continuum)

G206

G209

G206

G209

Uniform weighting

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Res. 0.013’’ × 0.011’’

= 5.2 au × 4.4 au

Res. 0.015’’ × 0.013’’

= 6 au × 5.2 au

Res. 0.015’’ × 0.012’’

= 6 au × 4.8 au

Res. 0.017’’ × 0.014’’

= 6.8 au × 5.6 au

G206

G206

G209

G209

G206

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• Disk-like structure

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• Size ≈ 40~50 au

G209

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• Size ≈ 50~60 au

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• Two spots with strong emission separated by ≈ 10 au

Two possibilities:

1. Binary system
2. One disk with two sides being brighter

How to determine?

Molecular emissions

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Goals:

1. Pinpoint the centers of the structures
2. Determine the orientations of the systems
3. Look for potential rotations

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G206

CO jet & outflow

SiO jet

SO outflow

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G206 - center

• The origin of the jet is the center of the disk continuum emission.

Moment 0 map of SiO jet

• The direction of the outflow is roughly perpendicular to the disk plane

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G206 - orientation

Moment 1 map of CO jet & outflow

Moment 1 map of SiO jet

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G206 – inclination angle

Moment 0 map of SiO jet

PV diagram along the jet

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G206 – inclination angle

PV diagram along the jet

Relative velocity : up to 70 km/s

Inclination angle given : 10°

• Deprojected velocity : up to 400 km/s

Typical protostellar jet velocity from previous studies :

100 ~ 200 km/s

• The inclination angle may be larger, around 20° ~ 40°

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G209

CO outflow

SiO jet

SO outflow

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G209 - center

• Weak emission

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• Difficult to pinpoint the center

Moment 8 map of SiO jet

Moment 8 map of SO outflow

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G209 - orientation

Moment 1 map of CO outflow

Summary

G206.93-16.61W2

• Disk-like structure with jets and outflows
• Inclination angle likely larger than previously estimated

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Thank you for listening!

Future work

• Search for other emission lines to locate the central region of G209

G209.55-19.68S1

• Candidate binary system (separation ~10 au)

• Evidence for binary system in G209

• Evidence of disk rotation

Backup slides

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Evolutionary stages of star formation

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Bianchi et al. 2019

Other information on the targets

The properties are from Dutta et al. (2020) and the proposal of ALMA project ID 2022.1.01437.S

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Information from the project proposal

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System velocity:

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G206.93-16.61W2 : 5km/s

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G209.55-19.68S1 : 10km/s

Sidelobes

• Comes from a non complete coverage of the uv plane

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https://science.nrao.edu/opportunities/courses/casa-caltech-winter2012/Isella_Radio_Interferometry_Basics_Caltech2012.pdf

https://www.sciencedirect.com/science/chapter/monograph/pii/B9780123705884500634

FFT / IFFT

Image cleaning

• CASA tclean

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https://casadocs.readthedocs.io/en/stable/api/tt/casatasks.imaging.tclean.html

Image cleaning

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https://events.asiaa.sinica.edu.tw/workshop/20250213/download/alma_imaging_SJLin.pdf

Continuum subtraction

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Original data set

Continuum subtracted data set

CASA uvcontsub

CASA tclean

CASA tclean

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G206 – rotation?

Moment 0 map of SiO jet

PV diagram across the jet

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G206 – rotation?

Moment 0 map of SiO jet

PV diagram across the jet