Transcript JCMT Sciences on Debris Disks and other brief

JCMT:
Debris Discs and
Miscellaneous
Sciences
Doug Johnstone:
Former Associate Director JCMT,
NRC Herzberg, Univ. Victoria
Wind Speeds on
Venus by
Sandor et al 2012
- HARP: 16 element 350 GHz
heterodyne array
The JCMT has observed:
• Atmospheres of many planets
•
Venus, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto
• Chemistry (SO, SO2, CO, etc)
• detection of CO in Neptune’s atmosphere (1993)
• Temperatures, Phase Variations (day/night)
Planetary Atmospheres
Left: HCN 4-3 map of Hale-Bopp
Right: HCN line profile fit with an
outgassing model in which the rate of
day to night emission is 3:1
Comets
SCUBA-2 – 20 sq. degree map of Galactic Centre (Staff
Time Project)
Also have CO 3-2 over much of the region.
Analysing reltative strength of dust emission versus CO
Galactic Centre
Galactic Plane Survey using
SCUBA-2
45 sq. degrees in total over
Six 5 by 1.5 degree strips
5 x deeper than ATLASGAL
Galactic Plane
Debris Disks
with the JCMT
UKT-14
A historical perspective leading to the motivation behind the
“SCUBA-2 Observations of Nearby Stars Survey” (SONS)
Evidence for a disk?
• Infrared emission from a star
brighter than the photosphere (e.g.
70K excess for Fomalhaut)
Fomalhaut
70K far-IR
excess
Observables
Optical
– scattered light
(Hubble)
Far-IR
– dust emission
(Herschel/PACS)
Submm
– dust emission
(JCMT/SCUBA-2
and ALMA)
Debris disks and planets
• Structure provides indirect
information on the architecture (and
evolution) of a possible planetary
system
Kuiper Belt
• Structure also can be used to
predict and identify perturbers,
such as planets
Fomalhaut system
Debris disks with the JCMT
• “Pioneering” work was carried out using the single-pixel UKT14
photometer in the early 1990s
Vega
Fomalhaut
Zuckerman & Becklin, 1993 (ApJ 414, 793)
• Point-by-point photometry suggested extended structures – proved
to be very accurate!
SCUBA observations (1998-2005)
• The revolutionary
SCUBA camera was
finally able to produce
images of these faint
structures at submm
wavelengths
β Pictoris
Fomalhaut
• Provided some of the first
images of these cold belts of
dust – not to mention a
number of high profile papers!
Vega
Holland et al., 1998 (Nature 392, 788)
ε Eridani – a close Solar analog?
• Famous face-on dust ring
with a central cavity
• Observed ring is very like
our Kuiper Belt in size and
mass
• Star is of a similar age to
our Sun – could we be
seeing a young analog to
our Solar System?
• Bright peaks could indicate
dust perturbed by one or
more planets
Size of Pluto’s orbit
Greaves et al., 1998 (ApJ 506L, 133)
Dynamical modeling
Planet migration in the Vega system?
Offset clump structure implies the system hosts a
Neptune mass planet which has migrated from 40 to
65 AU over 55 Myr.
Wyatt, 2003 (ApJ 598, 1321)
The clumpy disk of ε Eridani
Most likely explanation is the clumps are caused by
dust (caused by collisions between planetesimals)
trapped in resonance with a planet of Neptune mass.
Greaves et al., 2005 (ApJ 619, 187)
The asymmetric Fomalhaut disk
Modelling suggests the asymmetry, seen in the SCUBA
450µm image, is caused by a clump embedded in a
smooth ring. The clump could be trapped in resonance
with a planet at ~100 AU from the star.
Holland et al., 2003 (ApJ 582, 1141)
Motivation for SONS
• SCUBA became synonymous with debris disk
studies providing some of the first images of these
structures
• The observations were a struggle as the disks
(outside of the “Big 6”) are faint, requiring lengthy
observing times
• Nevertheless, SCUBA and the JCMT produced a
number of high profile papers, often with
photometric measurements of disk flux rather
than images
Fomalhaut (450µm)
τ Ceti (850µm)
• The main motivation behind the “SCUBA-2
Observations of Nearby Stars” survey was to
greatly increase the number of imaged disks at
submm wavelengths
η Corvi (850µm)
Introduction to SONS
Searching for debris signatures in the form of excess dust
emission at 850µm around 115 nearby stars:
• Image new (cold) debris disks  discovery potential
• Provide direct dust masses uniquely constrained at long
wavelengths  dust mass evolution
• Add to the far-IR/submm spectrum to constrain the dust
size distribution  insights on dust origin
• Resolve disk structures around the nearest systems 
distribution of grains; constraints on possible planetary
system
SONS survey
• Survey: Awarded 270 hrs of band 2 and 3 weather (135 hrs in
each band)
• Target selection: Biased survey based on disk detections
from IRAS/Spitzer/Herschel with predicted 850µm fluxes > 3 mJy
• Strategy: Aiming to reach an RMS noise level of < 1.4
mJy/beam at 850µm
• Aims: To image as many disks as possible - very nearby disks
can be extended up to a few arc-minutes
• Serendipity: Survey of a larger field area (e.g. for high-z
galaxies)
SONS status
• Time allocation: SONS is now 100% complete – the first
JCMT Legacy Survey to achieve this milestone
• Source list: Exactly 100 stars have been observed
• Image depth: Mean depth is 1.37 mJy/beam at 850µm (c.f.
revised goal of 1.4), although ~1/3 of the sample (34 stars) are
higher than 1.4
• Detection rate: 48 out of 100 stars (48%) have detected
peaks at or near the star (the offset ones could be background
objects…)
• Publications: First-look paper has been published (Panić et
al., 2013) with many more in preparation
Gallery of disks
HD 170773
HD 127821
HD 107146
Bar represents 500
AU at the distance
of the star
Characterising the disks
● Model fits to the photosphere and
far-IR excess combining with data
from shorter wavelengths  dust
temperature
● Example of γ Tri shows that a single
70K dust temperature is adequate
suggesting the dust is NOT spread
over a wide range of radii
Dust mass evolution
Dust masses for circumstellar disks for low-mass stars (0.2 – 3.3 MSun) as a function of stellar age (from Panić et
al. 2013 – with 8 SONS detections in bold). One aim of SONS is to address the issue of when the transition from
the protoplanetary to debris stage occurs (around 10 Myrs) and how the disk mass subsequently evolves.
450µm results
● Somewhat surprisingly, a number of disks have also been detected (and
imaged) at 450µm, such as HR 4796 (shown below)
850µm
● This has been a real bonus
as the primarily wavelength
has been 850µm (band 2/3
weather conditions)
● The 450µm data nicely help
to constrain the SED and hence
the dust grain size distribution
● 33% of the SONS sample have
detected peaks at, or close to, the
star at 450µm
450µm
Future survey options
SONS has been a great success and the current consortium would
welcome collaborations with EACOA astronomers in either extending the
current survey or starting a new one…
What would the survey look like? Some options include:
• It could expand the source list (perhaps be more unbiased like the
original proposal)
• It could go deeper than the existing survey (the average RMS at
850µm is slightly more than twice the confusion limit), which would be
beneficial for a significant number of stars in the current sample
• Would a 450µm survey have any merit?
• Should we target a more specific set of stars e.g. binaries, cold disk
candidates (like Algol, which was detected in SONS)?
Summary
• JCMT has a strong heritage of carrying out observations of debris
disks – particularly in the earlier days with SCUBA
• SONS has already produced spectacular results - more than doubling
the number of imaged disks at long submm wavelengths
• SONS will help to address key scientific questions on the place of
debris disks in the picture of evolving planetary systems
• SONS provides a target list for high angular resolution studies with (for
example) ALMA and eventually JWST and other future missions
• There are a number of possible options to continue with debris disks
surveys using SCUBA-2 and the JCMT
• The SONS consortium would warmly welcome new ideas and
collaborations with EACOA astronomers (several of our group have
already worked with astronomers such as Motohide Tamura in the past)
JCMT:
Debris Discs and
Miscellaneous
Sciences
Doug Johnstone:
Former Associate Director JCMT,
NRC Herzberg, Univ. Victoria