Debris Disk Studies with CCAT

1. Debris Disk Studies with CCAT D. Dowell, J. Carpenter, H. Yorke 2005 October 11

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 (10-100 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 roleat 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:

6. Effect of larger telescope aperture Going to 25 m aperture is like bringing source 2.5× closer. (Vega at 8 pc) 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 • 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. Wilner et al. (2002)

9. 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)

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

11. 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

12. 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