The JCMT Debris Disk Legacy Survey:

the (long) Calm before the Storm

Brenda MatthewsHerzberg Institute of Astrophysics

Known Debris Disks

•Discovered by their thermal emission by IRAS, which remains the only large, unbiased survey of nearby stars for thermal emission longward of 12 m– 15% of stars seen to have far infrared emission (Backman & Paresce 1993)

•Approximately 200 debris disk candidates have been identified based on their thermal emission– But optical images are scarce Pictoris remained the only optically imaged debris disk for years

Known Debris Disks

Known Debris Disks

•Discovered by their thermal emission by IRAS, which remains the only large, unbiased survey of nearby stars for thermal emission longward of 12 m– 15% of stars seen to have far infrared emission (Backman & Paresce 1993)

•Approximately 200 debris disk candidates have been identified based on their thermal emission– But optical images are scarce Pictoris remained the only optically imaged debris disk for years

Known Debris Disks

•Submm emission from JCMT has been pivotal in follow-up studies of these disks– imaging with SCUBA has mapped/discovered 7 of 10 resolved disks (Holland et al. 1998)

A SCUBA Gallery

The disks are shown to the same physical scale, i.e. as if all at one distance; actual distances are 3 to 18 pc.

Ceti Eridani Vega Fomalhaut Corvi

G8V K2V A0V A3V F2V10 Gyr 0.85 Gyr ~0.4 Gyr 0.3 Gyr ~ 1 Gyr

0.5 micron 2.2 micron 10-20 micron 850 micron

Pic

AU Mic

Vega

Fomalhaut

Eridani

HR 4796A

HD 141569

Pre-1998

First Resolved Images

http://astron.berkeley.edu/~kalas/disksite/pages/

Advantages of the Submillimetre

•Any star can be observed (star’s flux is negligible at submm wavelengths)

•Best method to measure the mass of the disk

•Only means to search for very cold disks (Teff < 40 K)

•Only reliable radii determinations are for the few disks which have submm detections (e.g. Sheret, Dent & Wyatt 2004)

•SED modeling essential for unresolved sources

--- primary star fit71 +/- 15 AU

___ primary + secondary star fit110 +/- 21 AU6.7''Resolved image will be difficult from ground

Current Picture

•Small submm surveys have detected disks at a rate of 5-25%

•ISO, Spitzer surveys have targeted ~100 stars•The emerging picture is that the fraction of stars with detectable disks is a function of – Stellar age (Spangler et al. 2001)– Spectral type (Habing et al. 2001)– Wavelength (Laureijs et al. 2002)– Presence of known giant planets (Beichman et al. 2005)

•Nature of these dependencies remains to be quantified

SCUBA-2 SCUBA-2 SCUBA-2 SCUBA-2

•TES array camera for JCMT (5100 pixels per wavelength)

•FOV – 8 arcmin x 8 arcmin •Excellent SURVEY instrument

– 100 x faster at mapping an area to same depth as SCUBA

– 3-5x more sensitive at 850 micron

•Debris Disk survey is one of seven distilled from a multinational meeting of partner countries

•Goal to provide a legacy of the JCMT which will outlive the telescope

The JCMT Debris Disk Survey

•First completely unbiased survey since IRAS•Sufficient size (500 stars) to provide a statistically relevant sample to discriminate between detection rates even in sub-samples of the data– Including nearby companions in the field (i.e., extended binaries), an additional 125 stars will be surveyed

•Driven by deep 850 m imaging to the confusion limit – 45 minutes per field to 0.7 mJy/beam

•Allocated 390 hours with 90% completion in 2 years from survey start

Science Goals of the Survey

1.determine unbiased statistics on the incidence of disks around nearby stars;

2.constrain disk masses and temperatures for far-IR detections (e.g., IRAS, ISO, Spitzer);

3.discover numerous disks too cold to detect in the far-IR;

4.be the basis of source lists for future observing campaigns using e.g., ALMA and JWST;

5.provide limits on the presence of dust that are vital to future missions like Darwin/TPF.

The Sample

•Survey is unbiased – No star is rejected based on its intrinsic properties

– Deep 850 micron imaging to the confusion limit

•500 stars (+ companions in field = 625 stars)– 100 nearest stars (visible to JCMT) in each of A, F, G, K and M spectral types

– Requires different volumes for each of the sub-samples

– Extend to 42, 24, 20, 15 and 10 pc respectively

•At median distance of 15 pc, the 3σ limit corresponds to 0.002 Earth masses of dust – i.e., Eridani, Greaves et al. 2004

Sample Details

•Sample size chosen so that we can distinguish between detection rates of 5,10, 25 and 50% when the dataset is divided into these subcategories:

– Stellar type (100 stars in A, F, G, K, and M)

– Stellar age (150 < 1 Gyr and 350 > 1 Gyr)• Boundary is the end of the heavy bombardment phase in the solar system

– Presence of a planetary system• 20 are currently known in the sample

– Binarity

current

SCUBA-2

Legacy value of the survey

•Definitive and comprehensive database on debris disks that is accessible to all future researchers

•Answers to key scientific questions on the place of debris disks in our picture of evolving planetary systems

•A target list for future high-resolution studies (e.g. with ALMA, or sooner) and alerts for systems that may be unsuitable for planet search missions

e.g. AU Mic Debris Disk

• Mdust ~ 0.011

Mearth (3.3x less

than Pic)

• 40 K dust

• Dust depleted

within

17 AU (planet?)

IRAS

JCMT

Spitzer

0.41'' x 0.25 ''

0.90'' x 0.75 ''

2.2'' x 1.4 ''

Can we resolve the AU Mic disk?

Survey Outcome

•At least 50 new disk candidates (assuming 10% detection rate)

•+ 50 submm detections of sources known from IRAS, ISO or Spitzer (assuming 50% far-IR detections are bright enough at submm wavelengths)

•Measurement of disk rate as a function of spectral type, age, binarity

Data Products

•Archived data of all 500 fields •Fully sampled images of all detected disks•Catalogue of fluxes and limits•Plots of all spectral energy distributions•Disk parameters

– including dust temperatures, masses, spectral indices, and characteristic disk radii

– results from systematic modelling of the masses and sizes of colliding planetesimals, and masses and locations for perturbing planets (where the disk structure is well-resolved).

Data Products

Ancillary Data:

•Background source catalogue – Used for extragalactic science– Provides a sample of high-z objects with nearby bright guide star for followup

•Flux list for nearby star photospheric fluxes where no disk is detected– stellar science, testing atmospheric models at very long wavelengths

Timeline

•SCUBA-2 science first light is delayed – Oct/Nov 2007

•Surveys start date: 07B? (or 08A)•330 hours to be observed over a 2-year survey period– Small allocation held back for 450 micron followup

•Only legacy survey fully allocated for 90% completion in 2 years– Complementary observations with Herschel Space Observatory (launch 2008)

•Source identification is in progress– Elimination of K-giants is the most important issue

Where do I sign up?

•Data are available to survey members only for the proprietary period (1 year after the completion of the survey’s final data acquisition)

•Survey membership open to members of JCMT partner countries until observing starts– Canada, UK, The Netherlands– Hawaii has opted out of Legacy surveys– Others can join if they bring a substantial contribution to the survey (i.e., complementary data)

Survey Members*

Bill DentJane GreavesWayne HollandRob IvisonGlenn WhiteMark WyattJeremy Yates

Pierre BastienJames Di FrancescoMark HalpernRay JayawardhanaDoug JohnstoneJJ KavelaarsBrenda Matthews

Carsten DominikIgnas Snellan

Harold ButnerPer FribergTim JennessGerald SchievenMing Zhu

Chas Beichman

Survey Coordinators

Benevolent Dictator

* As of summer 2006