Doug Johnstone: Former Associate Director JCMT,NRC Herzberg, Univ. Victoria

JCMT:Debris Discs and Miscellaneous

Sciences

Planetary Atmospheres

Wind Speeds on Venus bySandor 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)

Comets

Left: HCN 4-3 map of Hale-BoppRight: HCN line profile fit with an outgassing model in which the rate of day to night emission is 3:1

Galactic Centre

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 Plane

Galactic Plane Survey using SCUBA-2

45 sq. degrees in total overSix 5 by 1.5 degree strips

5 x deeper than ATLASGAL

Debris Disks with the JCMT

A historical perspective leading to the motivation behind the “SCUBA-2 Observations of Nearby Stars Survey”

(SONS)

UKT-14

Evidence for a disk? Observables

Optical – scattered light (Hubble)

Far-IR – dust emission (Herschel/PACS)

Submm – dust emission (JCMT/SCUBA-2 and ALMA)

• Infrared emission from a star brighter than the photosphere (e.g. 70K excess for Fomalhaut)

Fomalhaut

70K far-IR excess

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

Zuckerman & Becklin, 1993 (ApJ 414, 793)

• Point-by-point photometry suggested extended structures – proved to be very accurate!

Vega

Fomalhaut

SCUBA observations (1998-2005)

Fomalhaut β Pictoris

Vega

Holland et al., 1998 (Nature 392, 788)

• The revolutionary SCUBA camera was finally able to produce images of these faint structures at submm wavelengths

• Provided some of the first images of these cold belts of dust – not to mention a number of high profile papers!

ε Eridani – a close Solar analog?

Size of Pluto’s orbit

Greaves et al., 1998 (ApJ 506L, 133)

• 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

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)

Greaves et al., 2005 (ApJ 619, 187)

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.

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

• The main motivation behind the “SCUBA-2 Observations of Nearby Stars” survey was to greatly increase the number of imaged disks at submm wavelengths

Fomalhaut (450µm)

τ Ceti (850µm)

η Corvi (850µm)

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

Introduction to SONS

• 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 survey

• 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

SONS status

Gallery of disksHD 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)

● 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

450µm850µm

● 33% of the SONS sample have detected peaks at, or close to, the star at 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)?

• 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)

Summary

Doug Johnstone: Former Associate Director JCMT,NRC Herzberg, Univ. Victoria

JCMT:Debris Discs and Miscellaneous

Sciences