Planet Formation through Radio Eyes

A. Meredith HughesWesleyan University

Kevin Flaherty (Wesleyan), Amy Steele (Wesleyan), Jesse Lieman-Sifry (Wesleyan), David Wilner (CfA), Sean Andrews (CfA), John Carpenter (Caltech), Angelo Ricarte (Yale), Margaret Pan (GSFC), Hilke Schlichting (MIT), and others…

Star and Planet Formation Overview

cloud grav. collapseprotostar

+ disk + envelope + outflow

PMS star+ disk

MS star+ debris disk+ planets?

Adapted from Shu et al. 1987

Animation: JPL, M. Roessler

Circumstellar Disk EvolutionProtoplanetary

Pre-MS stars

Gas-rich

Primordial dust

Debris_____

Main sequence

No (or very little) gas

Dust must be replenished

planets?

Some Questions:When and why do disks disperse?

What can disks tell us about planet properties?

AU Mic, Liu et al. 2004HH 30, Burrows et al. 1996

ALMA Observatory

50 12-meter telescopes at 16,500 ft altitude in the Atacama Desert of northern Chile

Person, for scale

The Bird’s-Eye View

1. Disk Dissipation

When and why do primordial disks disperse?

What can disks tell us about planet properties?

2. Resolving Debris Disk Structure

1. Disk Dissipation

When and why do primordial disks disperse?

The standard story

Then what is this?

Dust looks like a debris disk… But still has lots of molecular gas!

Lots of gas/dust left over from SF

Gas/dust disappear (~10Myr)

Debris dust only

Background: Gas in Debris Disks

Zuckerman et al. (1995)Roberge et al. (2000)

Kospal et al. (2013) Moor et al. (2013)

Resolved Observations

Hughes et al. (2008)

Dent et al. (2014)

Continuum CO

HD 21997

β Pictoris

The Mystery of Gas-Rich Debris Disks

Is the gas primordial (Peter Pan disks) or second-generation (evaporating comets)?

• Gas/Dust morphology: Are they in the same place?• Gas mass/lifetime: How does it compare to age of star?• Gas chemistry: Is it more similar to a disk or a comet?• Frequency: Are we seeing something common or unusual?

ALMA Observations of 49 Ceti

Jesse Lieman-Sifry

ALMA Observations of 49 Ceti

ALMA Observations of 49 Ceti

ALMA Observations of 49 Ceti

This… …became this…

…which is not symmetric

The Mystery of Gas-Rich Debris Disks

Gas/Dust morphology: Are they in the same place?

49 Ceti: Essentially. Both gas and dust fill disk, with concentration @ 100 AUβ Pic: Essentially. Both gas and dust exhibit concentration on one limb

HD 21997: No. Gas fills disk while dust is concentrated in a ring

Gas mass/lifetime: How does it compare to age of star?

All: Lifetime MUCH SHORTER than age of star (of order kyr)

Gas chemistry: Is it more similar to a disk or a comet?

We’ve only seen CO so far (upper limit on HCN from 49 Cet w/ALMA)From optical lines, 49 Cet and β Pic may be volatile-rich

Frequency: Are these disks common or unusual?

Free molecular gas with every ALMA-observed A star debris disk!(No CO around F-type HD 107146 or M-type AU Mic)

Summary

49 Ceti is an interesting debris disk in its own right. ALMA data dominated by smooth, extended flux component. Steeply rising Σ surrounded by slowly decreasing Σ. 90AU is special (gas+dust).

Evidence leans towards second-generation gas, but primordial not ruled out. HD 21997 is unusual in mismatched gas/dust morphology. Need to evaporate lots of big comets for a long time.

2. Resolving Debris Disk Structure

What can disks tell us about planet properties?

Debris DisksFomalhautKalas et al. (2005)

Weinberger et al. (1999)

AU MicFitzgerald et al. (2007)

HR 4796ASchneider et al. (1999)

Heap et al. (2000)β Pictoris

Debris DisksIf debris disks were primordial, they wouldn’t be there

dust ≤10 Myr

Debris disks look different at different wavelengths

70 m; Su et al. (2005) 350 m; Marsh et al. (2006) 850 m; Holland et al. (2006)

At least 15% of nearby main-sequence stars have debris disks

(Habing et al. 2001, Rieke et al. 2005, Trilling et al. 2008, Hillenbrand et al. 2008)

Debris Disks and Millimeter Interferometry

Wyatt (2006)

Why Millimeter?

• Few stellar radiation effects• Good for tracing parent

planetesimal belts and resonances

Why Interferometry?

• Can resolve distant sources• Particularly good at picking

out clumps and rings

Our Solar System ~4.4Gyr ago?

Uniform sample of debris disks spatially resolved using mm-wave interferometrySample: young Solar analogues from FEPS

Steele et al. in prep

Courtesy Amy SteeleGrain size Mdisk Mbelt β Rin ΔR PA inclination

ResultsParameter HD 377 HD 8907 HD 61005 HD 104860 HD 107146

Rin (AU) 40 50 60 120 60

ΔR (AU) <70 <10 <10 <13 109

a (μm) 28 1.9 1.2 1.6 1.6

β 0.9 1.1 0.4 0.5 0.7

MD (M) 0.0063 0.0039 0.0063 0.0019 0.0032

Axisymmetric? Y Y Y Y Y

Courtesy Amy Steele

Results – Axisymmetry

Courtesy Amy Steele

Conclusions

• Most radii are similar to the Kuiper belt

• Grain sizes are comparable to the blowout grain size 1-3x larger than the BB radius

• Only one disk has a resolved width

• No detected asymmetriesRicci et al. (2014)

Vertical height of edge-on debris disks has been measured before, but only at optical wavelengths, where it is puffed up by starlight.

Scale height at mm wavelengths directly measures the total mass of perturbing bodies in the disk.

Ongoing: Vertical structure of edge-on debris disks

Based on Pan & Schlichting (2012)

Based on Thebault (2009)

Summary

Debris disks with molecular gas inform deadline for giant planet formation. Second-generation evaporating comets are likely, but

Peter Pan (primordial material) is still a possibility!

Young Solar analogs w/bright debris look mostly like Kuiper belts. Debris disk dust is not actually very clumpy, despite planets! Edge-on debris disks measure total mass.