U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 1

William Forrest (U of Rochester)

Kyoung Hee Kim, Dan Watson, Ben Sargent (U. of R.) and IRS_Disks Team

Full Accretion Disk by Robert Hurt (Spitzer Science Center)

Spitzer-IRS spectra of transitional disks in the Chamaeleon Cloud

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 2

Transitional disks, and why they are important

Transitional disks: protoplanetary disks with central clearings or radial gaps.

Clearings and gaps (and details of their structure) can be revealed by the wavelength dependence of infrared excess.

In ~1-2 Myr-old objects, such clearings are most easily explained by giant-planetary formation (e.g. Forrest et al 2004, d’Alessio et al. 2005, Calvet et al. 2005).

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 3

IRS/Spitzer Spitzer Space Telescope Launched on 25 Aug. 2003 Three scientific instruments :

• Infrared Spectrograph (IRS) (Houck et al., 2004)

• Infrared Array Camera (IRAC)• Multiband Imaging Photometer (MIPS)

• IRS (Infrared Spectrograph)

▫ Composed of four modules

- λ/Δλ ~ 64-128 (SL, LL), λ/Δλ ~ 600 (SH, LH)

▫ Sensitive in 5-40 μm wavelength rangeClockwise from the top:

IRS, IRAC, MIPS

▫ Suitable for looking at faint IR sources including protostars and protoplanetary disks

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 4

88 YSOs in Chamaeleon I & II dark cloud observed during Campaign 20, 21, and 22. IRS staring mode, SL-LL, SL-SH-LH S13 pipeline, BCD Data (flatfielded, stray-light corrected, dark current subtracted) Bad pixel fixing Extraction of spectra using SMART (Sky subtraction, RSRF calibration) (Higdon et al., 2004) 7 Transitional Disks candidates

Observation & Data Reduction

Sz 18

CHXR 30

UX Cha

Sz 27

Ced 110 IRS2

CS Cha

CHX 22

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 5

IRS spectra of Transitional Disks with central clearings in Cha I

Extinction corrected with Av/τ(9.7μm) = 18.5 and the opacity from Draine(2003) for Rv=3.1

Kurucz photospheric models fit to J, H, K NIR photometry

Cha Class II median spectrum

(normalized at H band)

IRS spectrum

10 μm silicate feature

20 μm silicate feature

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 6

photosphere subtracted from the IRS spectrum best BB temperature chosen to fit the dust continuum

Dust opacity ~ equal at 13 and 30 m Twall (wall temperature)

Rhole (radius of hole) from the radiative equilibrium

• Assuming a black, insulating wall facing the star (no free parameters!)

(test against CoKu Tau/4, DM Tau)

Radius of central clearings

44holewall

LR

T

  Sz 18CHX

22CS Cha

Ced110 IRS 2 Sz27 UX Cha

CHXR 30

CoKu Tau/4

DM Tau

Rhole (AU) 10.1 25 23 124 19 13 5 9.3 4.2

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 7

Check on Derived Hole Radius

 Sz 18 CHX 22

CS Cha

Ced110 IRS 2 Sz27 UX Cha

CHXR 30

CoKu Tau/4

DM Tau

Rhole (AU) 10 25 23 124 19 13 5 9.3 4.2

Superheated Silicates 5.5 >24 10 n.a. 7.8 n.a. 2.1

Assumed

10 3.0

RealModel 10 3

Toy model: Subtract optically thick “continuum” fit to 5-8 m

From 10-20 m color temperature, calculate dust temperature Calculate radius to reach this temperature Dust is ‘superheated’, absorbs at short wavelengths better than it emits Scale using 10 AU for CoKu Tau/4

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 8

Upper mass limit of small dust gains in the holeMust be considerably less than the optically thin, upper layers of

Classical (Class II) T Tauri stars. Use same toy model:

• From 10-20 m color T, calculate average dust T, <T>• Observed flux is

• Size of region: maximum optical depth (10 m) = 0.1

2

dustdustM

F B T B Td

FM Tau IP Tau

GG Tau A

GG Tau B

FN Tau

V 410 Anon 13

CY Tau

Mdust/MMoon

4 10-3 2 10-

3

5 10-3 0.3 10-

3

8 10-3 0.1 10-3 0.3 10-3

R(AU) 3 2 3.3 0.9 4 0.6 0.8 Mdust (trans.)/Mdust (opt. thick) ≤ 10-5

Can be done by giant-planet formation in < 105 yr (Quillen et al. 2004, Varniere et al., 2006). Can’t be done by radiative means, in the age of the objects.

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 9

Transitional disks frequency

Transitional disks in the Taurus-Aurigae cloud• 151 objects observed, 85 objects are classified as

Class II YSOs, 3 transitional disks, two of which (CoKu Tau/4, DM Tau) have central clearings

• Frequency = 2/85 ~ 0.02 Transitional disks in the Chamaeleon cloud

• 88 objects observed, 65 objects are classified as Class II YSOs, 7 transitional disks with central clearings

• Frequency = 7/65 ~ 0.11 More evolved YSOs in Cha I cloud than Tau-Aur cloud region?

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 10

Transitional disks trend : Teff vs. Rhole

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 11

Conclusion & Future Work

Seven protoplanetary disks in Cha I with sharp-edged central clearingsUpper limit to mass of small dust grains in central clearing typically 10-3 lunar mass. Planetary formation in first ~1-3 Myr still best explanation for these structures. Higher frequency of the transitional disks with central clearing in Chamaeleon cloud than in Taurus-Aurigae cloud more advanced state of evolution for Cha I ?

Need to work on detail models to get more accurate Rhole and the upper mass limits of small dust grains inside the central clearing region and to understand the central dust clearing mechanism in holes. Need to search Cha I IRS spectra for transitional disks with radial gaps (like Taurus/Auriga’s GM Aur) Similar survey of the Ophiuchus cloud on the way.

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 12

References (selected)

D’Alessio et al., 2005, ApJ, 621, 461 Forrest et al., 2004, ApJ, 154, 443 Calvet et al., 2005, ApJ, 630, L185

U. Western Ontario Protoplanetary Disk Workshop, 19 May 2006 13

IRS/Spitzer Spitzer Space Telescope Launched on 25 Aug. 2003 Three scientific instruments :

• Infrared Spectrograph (IRS) (Houck et al., 2004)

• Infrared Array Camera (IRAC)• Multiband Imaging Photometer (MIPS)

• IRS (Infrared Spectrograph)

▫ Composed of four modules

- λ/Δλ ~ 64-128 (SL, LL), λ/Δλ ~ 600 (SH, LH)

▫ Sensitive in 5-40 μm wavelength rangeClockwise from the top:

IRS, IRAC, MIPS

▫ Suitable for looking at faint IR sources including protostars and protoplanetary disks