1. The Legacy of Beta Pictoris
Dave Koerner
Northern Arizona University

2. Early Images Contributed to a “Two-Culture” Divide in Circumstellar Disk Research
HL Tauri
age ~ few x 105 yr.
size ~ AU
mass ~ 0.1 M
Beta Pictoris
age ~ yr ?
radius ~ AU
mass < M?

3. Two Cultures (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

4. Two Cultures Merging or “Third Culture” Forming? (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

5. Beta Pictoris as a “Young” Debris Disk (eventually)
Lanz et al “Underluminous” and either pre-main-sequence or older than 0.3 Gyr.
Crifo et al “Back to ZAMS” w/larger hipparcos distance, age still uncertain
Barrado y Navascues et al – Enter Moving Groups w/200 Myr age
Barrado y Navascues et al – Oops wrong moving group; age really 20 Myr

6. Beta Pic as one of three young debris disks
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 × 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

7. What is a “Young” Debris Disk? (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?

8. What is Younger than a “Young Debris Disk
What is Younger than a “Young Debris Disk?” Disk around a Herbig Ae young F Star
Dust
CO(21)
Velocity
Structure
MWC 480
Mannings, Koerner, & Sargent 1997, Nature, 388, 555

9. Mannings, Koerner & Sargent 1997
MWC 480
Maps of CO(2-1) emission at different velocities
as observed
Keplerian disk model
Mannings, Koerner & Sargent 1997
CO (2-1)
spectrum

10. OVRO Survey of CO(2-1) Emission from Classical T Tauri Stars
(Also See Surveys w/PdBI)

11. β Pic is not a Herbig Ae Star 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

12. A Warp in the Disk around  Pictoris
Burrows et al. 1995; Heap et al. 2000

13. β Pictoris :Deconvolved Imaged
Wahhaj et al. (2003)
β Pictoris :Deconvolved Imaged
25 Iterations of Richardson-Lucy (1974) Deconvolution
To better study the disk features, we deconcolved the 18 image using a RL algorithm.
Limiting super res to a fac of two….

14. HST Imaging of Outer Disk around  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

15. Modeling the Properties of the HR4796A Ring System
Keck/MIRLIN
Unconvolved Model
Convolved Model
Data
=1.6 m
(HST/NICMOS;
Schneider et al 1999)
Wahhaj
et al. (2005)

16. Profiles of mid-infared emission from 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)

17. Spectral Energy Distribution for HR 4796A
Zodiacal dust contributes negligibly to total SED, and cannot be
deduced without high resolution imaging results (e.g., Li & Lunine 2003)
Wahhaj et al. (2005)

18. HR 4796A: HIRES MODEL

19. 49 Cet: Keck/MIRLIN Images
Arcseconds AU

20. Young DD Properties from Thermal IR Images Signatures of Planet Formation?
Beta Pic – Inner evacuated region and rings (Wahhaj et al ) 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)

21. Where are the β Pic-like disks around wTTs?

22. C2d Spitzer Legacy Project Disks around wTTs
MIPS/IRAC Mapping of nearby star-forming clouds (Lupus, Ophiuchus, Chamaelaeon, Serpens, Perseus)
- Cieza et al – 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 – Less than 10 percent of ROSAT-selected objects show excess

23. Things We’d STILL Like to Know
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

24. Planetary Rings

25. The Nearest Debris Disk (Zodiacal Dust)
Moon