1. Debris Disk Studies with CCAT
D. Dowell, J. Carpenter, H. Yorke
Jet Propulsion Laboratory/Caltech
2006 October 27

2. Debris Disks with the CCAT
Debris disks, a.k.a. “Vega phenomenon”, a.k.a. “extra-zodiacal dust”:
solid particles surrounding main sequence stars, especially youngish ones ( Myr), after the gas has been absorbed into giant planets or expelled
product of collisional grinding of planetesimals in Kuiper belts
probably episodic in nature
tracer of orbital dynamics (analogous to Saturn’s rings)
CCAT niches
high-quality images of statistical sample of nearby disk systems
surveys for undiscovered cold disks (T < 40 K) around nearby stars
important data points on spectral energy distribution
characteristics of particles  evolutionary clues?
much better measurement of mass than is possible with scattered light images
unbiased surveys for disks in stellar clusters
b Pictoris: debris disk discovery image
Smith & Terrile (1984)
Saturn’s rings: result of the interaction of moons and dust

3. CCAT fills an important role at 2-100″ scales for nearby disks.
Fomalhaut (d = 8 pc) with 10 m telescope at left
Debris in an eccentric orbit maintained by a planet (Marsh et al. 2005)
Can use super-resolution techniques to “beat” diffraction by a factor of ~2 at l = 350 mm where signal-to-noise is high  2’’ resolution for CCAT at l = 200 and 350 mm
~20 resolution elements (15 AU) across sources such as this
Marsh et al. (2005)

4. Debris disks trace the underlying distribution of planets.
The distribution of dust indicates where planets are and what their mass is. Theoretical simulations:
We are currently in a situation where better images are needed to identify disk structures in more than a handful of sources.
The nearby debris disk systems to be imaged with CCAT are the ones which have the best chance for direct detection of both the dust and the planets (the latter with other facilities).
Ozernoy et al. (2000)
Wilner et al. (2002)

5. CCAT can image a statistical sample
While only 8 debris disks have resolved structure with existing ~10 m telescopes (most at d < 10 pc), we would expect to resolve 50 with a 25 m telescope.
In fact, we can already catalog nearly this many known debris disks to d = 30 pc:
UPDATE THIS TALLY?

6. Effect of larger telescope aperture
Going to 25 m aperture is like bringing source 2.5× closer.
(Vega at 8 pc; Marsh et al. 2006)
Ring structure can be studied in detail.
Source at 29 pc with 10 m telescope
Central clearing? Asymmetry?

7. CCAT has plenty of sensitivity to image nearby resolved debris disks
With CSO and JCMT, it has been possible to image structures down to:
30 mJy/9” beam at 350 mm  5 mJy/CCAT beam, requiring only a few minutes to detect with CCAT
5 mJy/15” beam at 850 um  2 mJy/CCAT beam, requiring only a few minutes to detect with CCAT
Due to telescope surface quality and transmissive atmosphere, CCAT will have a sensitivity advantage, too – not just an angular resolution advantage.

8. Interferometers like ALMA are likely to miss a lot of the dust
Wilner et al. (2002)
IRAM 1.3 mm
J. Greaves, W. Holland
JCMT/SCUBA 850 mm
INTERFEROMETERS SHOULD EXCEL AT THE PATTERN ROTATION EXPERIMENTS
Comparison of single dish image (left) and interferometer image (right) of the same source with existing ground-based technology.
ALMA will make large steps in sensitivity and fidelity compared to present-day interferometers, but may still specialize in small angular scales.
CCAT and ALMA maps will jointly identify all major dust structures in these sources.

9. Importance of Multiple Wavelengths
l = 200 mm capability allows measurement of dust temperature in cooler systems
Since debris disk grains are large, there are emissivity effects as well through the submillimeter.
Interpreted as two orbital populations with different grain size (Marsh et al. 2006)
Vega at 850 mm
(Greaves & Holland)
Vega at 350 mm
(Marsh et al. 2006)

10. CCAT can discover colder disks too faint for Spitzer to have detected
Explores outer Kuiper belts (>100 AU) around solar-like stars that are difficult to detect by other means
Quantifies debris around lower-luminosity stars
d = 50 pc
30 minute integrations, except Spitzer shorter/typical
Herschel confusion noise dominated (15 mJy)

11. Removing Pollution of Submillimeter Galaxies
Parts of the disks, or background galaxies?
CCAT will be good at identifying background sources through their intensity profile, color, and presence/absence of redshifted emission lines.
b Pic at 850 mm
(Holland et al. 1998)
e Eri at 850 mm
(Greaves et al. 2005)
h Crv at 850 mm
(Wyatt et al. 2005)

12. Gas Emission
Dust debris disks around main sequence stars – especially older ones – have been cleared of CO by photodissociation, so they are not easy targets for submillimeter spectroscopy.
However, there are some detections (see Dent et al for recent summary), and due to the importance of getting dynamical information, deeper searches should be made with CCAT, including new molecular species.

13. Unbiased Surveys of Open Clusters for Debris Disks Are Challenging
M47:
d = 450 pc,
100 Myr
Gorlova et al. (2004) – attempt at this with Spitzer
7 dust-excess candidates at 24 mm (T > 50 K)
NONE at 70 mm

14. With very large detector arrays, CCAT can survey stellar clusters efficiently.
Can survey 1°×1° clusters to 4s = 0.2 mJy depth at 350 mm in 200 hr, assuming filled 20′×20′ field of view
Confusion noise from background galaxies plays a role, and <25 m telescopes are insufficient at this wavelength.
Can detect at 5s:
e Eri-like debris disks to 130 pc (e.g., Pleiades, 100 Myr)
2× e Eri disks to 180 pc (M44 = Beehive, 700 Myr)
Fomalhaut-like disks to 500 pc (e.g., NGC 752, 1100 Myr)
Only a weak temperature bias in submillimeter (flux  T)
CCAT can:
derive debris disk lifetime from detection statistics
provide target list for ALMA

15. Flow from Science to Technical Requirements
First-light debris disk science with CCAT:
Images of disks around nearby stars
25 m aperture plus operation at 200 mm and 350 mm
(Provides 2″ angular resolution in part of spectrum complementary to Herschel at 60 mm, initial ALMA bands, and even larger mm telescopes.)
>30% aperture efficiency
(Disks are faint, and image fidelity is key.)
Background-limited/high quantum efficiency detectors with at least 2′×2′ field of view.
(Disks are faint and extended.)
Nyquist sampled focal plane
(No compromise in angular resolution; 3× reduction in time to map extended disks compared to 2l/D feedhorn arrays.)
Longer-term debris disk science with CCAT:
Efficient surveying for unknown debris disks in Galactic open clusters.
Entire focal plane filled with detectors
As large an aperture as possible to reduce confusion noise