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Submillimeter Observations of Debris Disks

Submillimeter Observations of Debris Disks. Wayne Holland UK Astronomy Technology Centre, Royal Observatory Edinburgh With Jane Greaves, Mark Wyatt, Bill Dent and a cast of many…. Observing Debris Disks. Debris disks must be cold (e.g. Pluto temperature)  so observe at long wavelengths.

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Submillimeter Observations of Debris Disks

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  1. Submillimeter Observations of Debris Disks Wayne Holland UK Astronomy Technology Centre, Royal Observatory Edinburgh With Jane Greaves, Mark Wyatt, Bill Dent and a cast of many…

  2. Observing Debris Disks Debris disks must be cold (e.g. Pluto temperature)  so observe at long wavelengths Large submillimetre telescope (JCMT) and sensitive camera (SCUBA)  can attain sub-mJy noise levels but it takes a long time… Thus can detect < 1 Lunar-mass of dust around stars within ~10pc

  3. Submillimeter Observations • Submm observations pick up the thermal emission from cold dust grains • Sensitive to large scales (10’s to 100’s AU) so can probe Solar System-sized regions • Signal is optically thin (so traces mass) • Stellar photosphere signal is very weak so minimal calibration errors

  4. Vega Debris Disk • 25 hours of integration time; peak flux is 16 mJy at 850μm • Two peaks seen in an otherwise face-on disk structure • Clumps can be explained by migration of a Neptune mass planet • Possible “spiral-arm” type structure? Size of Pluto’s orbit

  5. Diversity of Disks (to same physical scale) τ Ceti ε Eridani Vega Fomalhaut β Pictoris

  6. Key Results • Submillimeter observations have revealed: • Disk structures that are 1–3 times the size of the Solar System • Disk masses that are tiny – up to several tens of lunar masses – trace the more massive comet population • Dust grains that are a few microns up to centimetres (or more) in size

  7. Evidence for Planets? • Two kinds of evidence • Inner holes in most of the disks • dust is ejected by the planets • Structure within the dust belts • if due to planets, ‘clumps’ should be associated with particular resonances • could pinpoint the planet position, in advance of imaging missions!

  8. Limitations… • Observing with 8–15’’ beams limits us to nearby stars... but it’s the only way to detect outer bounds of planetary systems • finding mostly large examples! • only one is as small as the Sun’s Kuiper Belt, with r ~ 50AU • Observations are sensitive to mJy fluxes... but still need to observe for tens of hours to get deep images • especially at 450μm…

  9. New Generation Arrays Array module SCUBA-2 is a new generation imaging array for the JCMT • Disk observations will take minutes instead of many hours… • SCUBA-2 will be capable of detecting many more disks • Due on the telescope in less than a year… SCUBA-2 in the lab

  10. SCUBA-2 Debris Disk Survey Survey aims: • The aim of the survey is to perform an unbiased search of 500 nearby main sequence stars for disk emission at 850μm Survey logistics : • The survey has been awarded 400 hours of JCMT time from late-2006 for ~2 years

  11. SCUBA-2 Debris Disk Survey Scientific goals: • To determine unbiased statistics on the incidence of debris disks around nearby stars • To constrain disk masses and temperatures for far-IR detections (e.g. ISO, Spitzer) Grey body fit at 55K

  12. SCUBA-2 Debris Disk Survey Scientific goals (cont): • To discover numerous disks too cold to be detected in the far-IR • To be the basis of source lists for future observing campaigns (e.g. using ALMA and JWST) • To provide limits on the presence of dust that are vital to future planets detection missions (e.g. Darwin/TPF)

  13. SCUBA-2 Debris Disk Survey Survey plan: • 500 stars comprising 100 nearest observable stars from JCMT in spectral types A, F, G, K and M • All stars will be imaged at 850μm to the confusion limit (~0.7 mJy) • Unbiased surveys so far show that detection rates increase sharply with lower flux limits as we probe into the mass function • Disks with significant structure will be targets for further deep imaging at 450μm

  14. SCUBA-2 Debris Disk Survey Selection criteria: • Unbiased sample for each spectral type so can distinguish between detection rates of 5,10, 25 and 50% when dataset is subdivided • Stellar type with 100 stars of A, F, G, K, and M • Stellar age arises naturally, with 150 stars < 1 GYr and 350 stars 1–10 Gyr • Stellar multiplicity arises naturally, with one-third of stars having a companion • Presence of a planetary system, with ~20 samples having one or more planets from radial velocity estimates

  15. Summary • Debris disks so far imaged have been very diverse in size, morphology and properties • There is growing evidence that planets (or planetary systems) have played a major role in shaping the disk structure • Large unbiased surveys are about to revolutionise this field of astronomy by substantially extending the number of known disks

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