Transcript JCMT Debris Disks Survey - Physics and Astronomy

The JCMT Debris Disk
Legacy Survey:
the (long) Calm before the Storm
Brenda Matthews
Herzberg 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 followup studies of these disks
– imaging with SCUBA has mapped/discovered 7 of 10
resolved disks (Holland et al. 1998)
A SCUBA Gallery
 Ceti
G8V
10 Gyr
 Eridani
K2V
0.85 Gyr
Vega
A0V
~0.4 Gyr
Fomalhaut
A3V
0.3 Gyr
 Corvi
F2V
~ 1 Gyr
The disks are shown to the same physical scale, i.e. as if all at one
distance; actual distances are 3 to 18 pc.
0.5 micron
2.2 micron
10-20 micron 850 micron
 Pic
AU Mic
Vega
Pre-1998
First Resolved Images
Fomalhaut
 Eridani
HR 4796A
HD 141569
http://astron.berkeley.edu/~kalas/disksite/pages/
Advantages of the Submillimetre
--- primary star fit
71 +/- 15 AU
• Any star can be observed (star’s flux is negligible at
___ primary + secondary
submm wavelengths)
star fit
+/-disk
21 AU
• Best method to measure the mass110
of the
6.7''
Resolved
image< 40
willK)
be
• Only means to search for very cold
disks (T
eff
difficult from ground
• 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
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
current
• 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
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
IRAS
• Mdust ~ 0.011 Mearth
(3.3x less than  Pic)
• 40 K dust
Spitzer
• Dust depleted within
17 AU (planet?)
JCMT
Can we resolve the AU Mic disk?
2.2'' x 1.4 ''
0.90'' x 0.75 ''
0.41'' x 0.25 ''
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 wellresolved).
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*
Benevolent Dictator
Survey Coordinators
Bill Dent
Jane Greaves
Wayne Holland
Rob Ivison
Glenn White
Mark Wyatt
Jeremy Yates
Pierre Bastien
James Di Francesco
Mark Halpern
Ray Jayawardhana
Doug Johnstone
JJ Kavelaars
Brenda Matthews
Chas Beichman
* As of summer 2006
Carsten Dominik
Ignas Snellan
Harold Butner
Per Friberg
Tim Jenness
Gerald Schieven
Ming Zhu