Clouds To Discs 2021

How do high-mass stars get their mass?
Brinary stars as a probe


Adam Ginsburg

Assistant Professor
Department of Astronomy
University of Florida, Gainesville

  • Postdoc: Allison Towner
  • PhD: Desmond Jeff, Theo Richardson, Alyssa Bulatek, Nazar Budaiev
  • REU: Justin Otter, Danielle Bovie, Josh Machado, Sydney Petz
  • Undergrad: Madeline Hall, Michael Fero, Derod Deal, Parker Ormonde, Aden Dawson, Helen Radomski, Brice Tingle, Oketa Basha, Morgan Himes
Slides available at https://keflavich.github.io/talks/CloudsToDiscs2021.html

How does accretion end?

A star accretes gas from its surroundings.
Its final mass is set when this process stops.
What stops mass buildup?
  • Gas runs out (exhaustion)
  • Star is ejected from its reservoir (core)
  • Gas is blown out (evacuation, feedback)
  • Another steals it (theft, fragmentation-induced starvation)

The role of disks

HMYSOs have disks.
How & when does mass get from disk to star?
  • Mostly during the "stage 0" phase (Bourke talk)
  • Largely through bursts?
    Accretion bursts are an important mode to move gas from disk to star.
  • They are driven by:
    • Asymmetric (non-axisymmetric) accretion flows
    • Dynamical interactions
    • Disk instabilities? (Elbakyan poster)
    • Smooth accretion? (Oudmaijer talk)

W51 e2e & north: non-axisymmetric accretion flows

Ongoing mass accretion, Menv > M*
Outflows imply disks, but no rotation is seen.
Inflow is coming from several directions.
Goddi+ 2020

CS v=0 J=1-0 and v=0 J=2-1 masers trace the disk?

Ginsburg+ 2019

CS maser conditions

van der Walt+ 2020
  • Top: CS J=1-0, Bottom: CS J=2-1
  • Red: Consistent w/W51e2e observations
  • Masers do not coexist; require different specific CS column
    (N2-1=1015.6, N1-01016.1 cm-2)
  • Require high abundance (XCS > 10-5)
  • Hot (300-500 K), moderate-density (n~105 cm-3): Disk surface? Or outflow cavity wall?
Goddi+ 2020

non-Axisymmetric Accretion

The outflow (& disk) around W51 North changed direction by ~50 deg in < 100 years.

0.25-0.5 M⊙ accreted in ~100 years.

Zooming in: W51-IRS2

Zooming in: W51-IRS2

Zooming in: W51-IRS2

At high stellar densities,
close encounters are frequent

N*OMC = 1.6 x 105 pc-3
N*ONC = 0.6 x 105 pc-3
Otter+ 2021: arXiv 2109.14592

How dense are cluster-forming regions?

OMC1 is denser than the ONC

N*OMC(Otter+ 2021) = 1.6 x 105 pc-3
N*ONC(Otter+ 2021) = 0.6 x 105 pc-3
N*ONC(Hillenbrand+ 1998) = 0.2 x 105 pc-3

Many new disks in the OMC

Otter+, resubmitted
FOV: 0.07 pc (16000 AU)
72 YSOs
One "hot core"

Disk Gallery

Dynamical ends to accretion

Bally+ 2017
Farias+ 2018

The BN/I/x interaction is the poster case of accretion ended by dynamical interaction.

Orion Source I
a disk around a 15 M⊙ YSO

Material with vesc < vejected was lost.

vejected = 11.5 km/s = vesc(200 AU)

Disk is oriented along the direction of motion: probably re-oriented in ejection

Mdisk ~ 0.02 - 2 M⊙ << M*
(Plambeck+ 2016)

SrcI is leaving the hot core
Image: Ginsburg, NRAO
Left: Tanaka+ 2020, pair of NaCl-bearing disks.
Right: G17, Maud+ 2020

Temperature?

Temperature?

A contrived model

Observing the Keplerian rotation profile of a disk is the most direct way to measure a protostar's mass

(we can only see the disk, not the star itself)

How can we measure masses of HMYSOs?

Brinary disks

The SrcI disk has gas-phase salt (NaCl, KCl) and water (H2O).
So it's brine.
(blame Adam Leroy for this term)
IRAS16547A/B (Tanaka+ 2020) have (unresolved) salt water disks

Brine lines measure dynamical mass


NaCl v=1 J=18-17 Stack of v=[0,1] Ju=18,17

15 M⊙ 30 M⊙ 40 M⊙

What have we learned about brinaries?

  • Somewhat rare?: 4 known so far, ~10 examined
    • Y: SrcI, G17, IRAS16547, NGC6334I?
      • Ginsburg+ 2019, Maud+ in prep, Tanaka+ 2020
    • N: I16523, I18089, G11, G5, W33, NGC6334IN
      • Sanhueza, Olguin, Ginsburg+ in prep
  • Coincide w/line-poor sources
    • Not hot cores; little mass reservoir?
  • Trace reasonably symmetric disks (in the two well-resolved cases)

Compare: G17 vs W33

Hot (ionizing) photosphere. Circular disk.
Molecule rich, kinematically messy & extended

Summary

  • Ejection and dynamical interaction are important in HMSF. Bold, moderately supported claim: More important than disk-mediated accretion
    • Ejection ends accretion [SrcI]
    • Dynamical interaction, non-axisymmetry triggers bursts
  • Brinary disks exist around HMYSOs
    • Brine lines are good for kinematic mass measurements
      (NaCl, KCl have low-frequency transitions accessible to ngVLA)
    • They may show up at the end of accretion
    • Still too few to draw firm conclusions
      • More to be found!