U. Western Ontario Protoplanetary Disk Workshop, 19 May 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 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 IRS/Spitzer Spitzer Space Telescope  Launched on 25 Aug  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 ~ (SL, LL), λ/Δλ ~ 600 (SH, LH) ▫ Sensitive in 5-40 μm wavelength range Clockwise 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  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 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  photosphere subtracted from the IRS spectrum  best BB temperature chosen to fit the dust continuum  Dust opacity ~ equal at 13 and 30  m  T wall (wall temperature)  R hole (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 Sz 18 CHX 22 CS Cha Ced110 IRS 2Sz27UX Cha CHXR 30 CoKu Tau/4 DM Tau R hole (AU)

U. Western Ontario Protoplanetary Disk Workshop, 19 May Check on Derived Hole Radius Sz 18 CHX 22 CS Cha Ced110 IRS 2Sz27UX Cha CHXR 30 CoKu Tau/4 DM Tau R hole (AU) Superheated Silicates 5.5>2410n.a.7.8n.a.2.1 Assumed Real Model103  Toy model: Subtract optically thick “continuum” fit to 5-8  m From  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 Upper mass limit of small dust gains in the hole Must be considerably less than the optically thin, upper layers of Classical (Class II) T Tauri stars.  Use same toy model: From  m color T, calculate average dust T, Observed flux is Size of region: maximum optical depth (10  m) = 0.1 FM TauIP TauGG Tau A GG Tau B FN Tau V 410 Anon 13 CY Tau M dust /M Moon R(AU)  M dust (trans.)/M dust (opt. thick) ≤  Can be done by giant-planet formation in < 10 5 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 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 Transitional disks trend : T eff vs. R hole

U. Western Ontario Protoplanetary Disk Workshop, 19 May Conclusion & Future Work  Seven protoplanetary disks in Cha I with sharp-edged central clearings  Upper limit to mass of small dust grains in central clearing typically 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 R hole 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 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 IRS/Spitzer Spitzer Space Telescope  Launched on 25 Aug  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 ~ (SL, LL), λ/Δλ ~ 600 (SH, LH) ▫ Sensitive in 5-40 μm wavelength range Clockwise from the top: IRS, IRAC, MIPS ▫ Suitable for looking at faint IR sources including protostars and protoplanetary disks