Marginally Resolved Disks with Spitzer Bryden, Stapelfeldt, Tanner, Werner (JPL) Beichman (MSC) Rieke, Trilling, Stansberry, Su, & the MIPS instrument team (Arizona) SIM/TPF Science Team (Berkeley, ROE, etc.)

“Dirty Dozen” Targets Star nameSpectral TypeDistance (pc)Notes Alpha CrBA023Ecl binary; P=17d, G type Beta LeoA313Most likely to be extended after Fab4 Beta UmaA124 Delta VelA025Ecl binary, P=45d, A type Eta TelA048 Gamma TriA136 Gamma OphA029 Sigma BooF216JCMT detection? Tau3 EriA426 Tau CetG83.5Solar type Zeta LepA321Evidence for hot dust Best targets identified based on expected angular size: (Select targets with potential 70 micron source diameter > 10”)

Results No identification of extended emission for any of the Dirty Dozen

Conclusion Spitzer is too small a telescope to resolve anything but the most fabulous disks The End Results No identification of extended emission for any of the Dirty Dozen

MIPS Photometric Survey at 24 and 70  m Spectral types range from M2 to F0. (Also Stansberry/Gautier sample down to M9) No excess detections below K0. Distances ~10-20 pc (MIPS FWHM = 17”) 130 FGK stars (MIPS GTO) 85 SIM/TPF stars (Beichman GO1) Spectral Type

24 μm Flux Histogram (observed / expected stellar flux) Only 2 out of 153 stars have 24 μm excess A detection rate of 1 ± 1% at 24 μm

70 μm Flux Histogram (observed / expected stellar flux) Many stars have 70μm emission much greater than expected from the stellar photosphere alone. A detection rate of 14 ± 3% at 70 μm

Identifying extended emission No single method is completely robust; a combination of strategies is considered: - Measure FWHM with Gaussian fit (idp3) or Airy ring fit (idl) in 1-D or 2-D. Only works for high SNR data. - Visual inspection of frames for offset emission due to background galaxies or close binaries. 24um frames are also inspected. Does not give a quantitative measure of extension. - Subtraction of normal-star PSF, centered on the 24um centroid position. Only the core of the PSF is fit, such that excess wings are not subtracted off. The significance level of the remaining nearby emission is calculated, based on the noise level within the overall field. - Use a broader PSF for colder sources

Extended Emission v.s. IR Excess Among the 215 observed sources, those with significantly extended emission also have IR excess. The correlation of extension with flux or SNR is relatively weak.

Stellar PSF subtracted from cool sources Longer effective wavelength within the MIPS band results in somewhat larger FWHM

PSF-subtracted Images High SNR emission around IR excess sources, much broader than PSF

Summary Despite fine scale imaging, no resolved A star disks Rules out small grains / low emissivities Better success around FGK stars; smaller particles? 5 stars with solid evidence for extended emission Several more possibly resolved Broader PSF for stars with IR excess confirms that the emission is much cooler than stellar Follow-up with 1) IRS to model warm emission, particularly the grain sizes needed to fit silicate features 2) sub-mm to constrain cold emission 3) MIPS 70um fine scale for better resolution 4) HST-ACS for press release images