The Legacy of Beta PictorisThe Legacy of Beta Pictoris

Dave KoernerNorthern Arizona University

Early Images Contributed to a “Two-Culture” Early Images Contributed to a “Two-Culture”

Divide in Circumstellar Disk ResearchDivide in Circumstellar Disk Research

HL Tauri HL Tauri o age ~ few x 105 yr.o size ~ 1000 AUo mass ~ 0.1 M

Beta PictorisBeta Pictoriso age ~ 107- 108 yr ?o radius ~ 1000 AUo mass < 0.000001 M?

Two Cultures Two Cultures (circa C.P. Snow’s comment on humanities/sciences)(circa C.P. Snow’s comment on humanities/sciences)

Protostellar or Protoplanetary Accretion Disks • Young, Pre-Main-Sequence• Typically associated with Molecular Clouds • Resolved disk observations initially at long wavelengths

“Debris Disks” • Initially categorized as main sequence• Typical examples located in the solar neighborhood• In β Pic’s case, initially studied more often at optical wavelengths

Two Cultures Merging Two Cultures Merging or “Third Culture” Forming? or “Third Culture” Forming?

(a la Brockman)(a la Brockman)

Protostellar or Protoplanetary Accretion Disks • Isolated cTTs found nearby (e.g., TW Hya)• Spitzer “missing link” studies of wTTs in clouds• Resolved Optical Images obtained

“Debris Disks” • Some Nearby debris disks identified as young (t < 107 yr)• Images at thermal infrared, sub-mm, and mm wavelengths

Beta Pictoris as a “Young” Debris Disk (eventually)

Lanz et al. 1995 - “Underluminous” and either pre-main-sequence or older than 0.3 Gyr.

Crifo et al. 1997 - “Back to ZAMS” w/larger hipparcos distance, age still uncertain

Barrado y Navascues et al. 1998 – Enter Moving Groups w/200 Myr age

Barrado y Navascues et al. 1999 – Oops wrong moving group; age really 20 Myr

A Protocometary Cloud around HR 4796A?

JURA, MALKAN, WHITE, TELESCO, PINA, AND FISHER (1995)ApJ 505, 897

We report both ROSAT observations and ground-based 10.8 μm imaging of the wide binary HR 4796, which consists of a main-sequence A-type star with a large amount of circumstellar dust, HR 4796A, and, at a separation of 7.’’7, a pre-main-sequence M-type companion, HR 4796B. From the ROSAT data, we find that the X-ray emission is centered on HR 4796B, with LX/Lbol 3 × 10-4. The 10.8 μm flux, which arises from HR 4796A, displays an excess over the photospheric emission of 0.08 ± 0.02 Jy, a result consistent with the previous characterization of the emission from the circumstellar dust in the wavelength range 12 μm < λ <100 μm as a 110 K blackbody.

The Hipparcos data can be used to argue that the three main-sequence A-type stars in the Bright Star Catalogue with LIR/Lbol > 10-3 (HR 4796A, β Pic, and 49 Cet) all have low luminosities for their colors. We argue that approximately 20% of all A-type stars pass through an early phase where they possess an amount of circumstellar dust comparable to that found around HR 4796A or β Pic

… Beta Pic as one of three young debris disks

What What isis a “Young” Debris Disk? a “Young” Debris Disk?(is “Young Debris Disk” an oxymoron?)(is “Young Debris Disk” an oxymoron?)

•The “young three” have ages within range of many T Tauri stars

•Are these truly “debris” disks or evolved remnant protostellar disks?

•Viscous accretion disks are likely to have a large component of dust grains that arise from secondary collisions – are these “debris” disks too?

•In practice, does “debris disk” really mean optically thin dust disks with little gas?

MWC 480Mannings, Koerner, & Sargent 1997, Nature, 388, 555

What is Younger than a “Young What is Younger than a “Young Debris Disk?”Debris Disk?”

Disk around a Herbig Ae young F StarDisk around a Herbig Ae young F Star

Dust CO(21) Velocity Structure

MWC 480MWC 480

Maps of CO(2-1) emission Maps of CO(2-1) emission at different velocitiesat different velocities

as observedas observed

Keplerian disk modelKeplerian disk model

Mannings, Koerner & Mannings, Koerner & Sargent 1997Sargent 1997

CO (2-1) CO (2-1) spectrumspectrum

OVRO Survey of CO(2-1) Emission OVRO Survey of CO(2-1) Emission from from ClassicalClassical T Tauri Stars T Tauri Stars

(Also See Surveys w/PdBI)

ββ Pic is not a Herbig Ae StarPic is not a Herbig Ae StarSo what is it?So what is it?

Herbig Ae, Be stars analagous to cTTs with EW(Hα) > 10 Å

wTTs are pre-main sequence with EW(Hα) < 10 Å

Conjecture: “Young Debris Disks” are around A-type stars analagous to wTTs or “post T Tauri Stars” These also show dynamic signatures of planetary formation

A Warp in the Disk around A Warp in the Disk around Pictoris Pictoris

Burrows et al. 1995; Heap et al. 2000

ββ Pictoris Pictoris :Deconvolved :Deconvolved ImagedImaged25 Iterations of Richardson-Lucy (1974) Deconvolution

Wahhaj et al. (2003)

HST Imaging of Outer DiskHST Imaging of Outer Diskaround around Pictoris Pictoris

•HST observations by Kalas & Larwood (2000)

•Outer rings can be produced by simulations of a stellar flyby

•However, this mechanism cannot easily produce inner rings

Modeling the Properties of the Modeling the Properties of the HR4796A Ring SystemHR4796A Ring System

=24.5 mKeck/MIRLIN

Unconvolved Model Convolved Model Data

=1.6 m(HST/NICMOS;Schneider et al 1999)

Wahhaj et al. (2005)

Wahhaj et al.(2005)

Profiles of mid-infared emissionProfiles of mid-infared emissionfrom HR 4796Afrom HR 4796A

•Outer Ring models fit to disk ansae in images•Stellar photospheric flux added •Model convolved with PSF

Conclusion: All three images show substantial excess in an

unresolved region interior to the outer ring

Wahhaj et al. (2005)

Spectral Energy Distribution for Spectral Energy Distribution for HR 4796AHR 4796A

Zodiacal dust contributes negligibly to total SED, and cannot bededuced without high resolution imaging results (e.g., Li & Lunine 2003)

HR 4796A: HR 4796A: HIRES MODELHIRES MODEL

49 Cet49 Cet:: Keck/MIRLIN ImagesKeck/MIRLIN ImagesArcseconds

AU

Young DD Properties from Thermal IR ImagesYoung DD Properties from Thermal IR ImagesSignatures of Planet Formation?Signatures of Planet Formation?

• Beta Pic – Inner evacuated region and rings (Wahhaj et al. 2003) Amorphous and crystalline sillicate emission inside ~20 AU only => small grains inside, larger grains outside? (Weinberger et al. 2003); Inner “planetesimal belts” w/differing grain sizes (Okamoto et al. 2004)

• HR 4796A – Inner hole (Jayawardhana et al. 1998; Koerner et al. 1998) “Pericenter Glow” (Telesco et al. 2000); Two-part outer ring - narrow large-grain ring surrounded by broader small-grain ring - (Wahhaj et al. 2005)

•49 Cet - Inner evacuated region. Small grains between 30 and 60 AU; larger grains in outer disk - (Wahhaj et al. 2005)

(See poster by Wahhaj et al)

Where are the Where are the ββ Pic-like disks Pic-like disks around wTTs?around wTTs?

C2d C2d SpitzerSpitzer Legacy Project Legacy ProjectDisks around wTTsDisks around wTTs

•MIPS/IRAC Mapping of nearby star-forming clouds (Lupus, Ophiuchus, Chamaelaeon, Serpens, Perseus)

- Cieza et al. 2005 – 20% of known selected wTTs on clouds have 24 micron excess. These are systematically younger than the general wTTs sample

•Pointed MIPS/IRAC Observations of ROSAT-selected wTTs within 6 degrees of closest clouds

- Padgett et al. 2005 – Less than 10 percent of ROSAT-selected objects show excess

Conclusion: Stars w LIR/Lbol > 10-3 and ages less than 20 MYr constitute a transitional class from emission-line stars w/disks to those with optically thin disks and more advanced planet formation

Things We’d STILL Like to Know•What is the dissipation time scale for molecular gas?

•What kinds of bodies are responsible for disk features that require gravitational influence for persistence?

•Timescale for the “Young Debris Disk” phase?

•Frequency of stars that go through such a phase

Planetary RingsPlanetary Rings

The Nearest Debris Disk The Nearest Debris Disk (Zodiacal Dust)(Zodiacal Dust)

Moon