Lee Hartmann, University of Michigan

Andi Burkert, John Tobin, Marina Kounkel, Fred Adams

ONC: kinematics etc.

large-scale AV map

Rowles & Froebrich 2009

Orion A/B

3

Non-linear acceleration vs. position in filaments

(Bonnell et al 1992)- “edge effect” in ~ 1 dimension

make concentrations (clusters) at ends

acce

lera

tion

Evidence for large-scale gravity; focusing in elongated clouds causes clusters to form preferentially at ends

(Bonnell; Burkert & LH, “focal points”)

Pipe (Lombardi)

NGC 2264 (Sung+)

Perseus (Rebull)

Orion A/B

13CO, Bally et al.

Orion A (Hartmann & Burkert 2007); elliptical sheet, smooth density gradient, ~ 2 Myr evolution

cluster

Short radius of curvature results in extra mass

concentrations assemble cluster

gas/stars

Carpenter + 2001

1 pc

1 pc HH98,

e ~ 0.3

RV

1pc/2 km/s ~ 0.5 Myr

(2GM/R)1/2 ~ 3 km/s (4000 M☉/4 pc)1/2

fixed gas potential; N body

spherical, subvirial elongated, subvirial, major axis

elongated, subvirial, 30o

elongated, virial, 30o

Megeath et al.

caustic? why only one side?

asymmetry of mass distribution?

histogram = *

13CO

Jones & Walker 88 1D FWHM (proper motion)

ONC

Foreground contamination?

Briceno et al.

What accounts for the stellar/13CO velocity offset?

stellar motions? stars moving away from us too extincted for optical study?

<

problem? velocity widths already seem to be ≥ Jones/Walker p.m. dispersion

What accounts for the stellar/13CO velocity offset?

evaporation/blowout of dense gas?

<

works for ONC/1977(?), but what about OMC 2/3?

What accounts for the stellar/13CO velocity offset?

gravitational collapse + dissipation

to make narrow filament?

<

OMC 2/3?

crazy idea; “some stars left behind?”

1st generation less redshifted (running into denser gas)?

later generation?

need to understand time evolution of region

NGC 2264 – Kounkel, Tobin et al. in prep

?

kinematics:

not equilibrium – constraint on timescales?

gravity is important, but details uncertain

need to understand time evolution of region

histogram = *

13CO

foreground 1a pop?

27 Orion A 13CO; Bally et al. 1987

Velocity fields not particularly random

30 pc

(G x 105 M(sun)/15 pc)1/2 ~ 5 km/s

how do you avoid gravitationally-generated motion??

factor in efficiency; pre-existing cloud structure?

ages of ONC stars??

Heitsch

Vazquez-S.

Simulations of cloud flow with gravity show accelerating collapse

Orion Nebula regionMegeath et al. 2012

T Tauri stars

Protostars: collapse down

to extremely dense filament Pgrav >> P(ISM)