Marginally Resolved Diskswith 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 name Spectral Type Distance (pc) Notes

Alpha CrB A0 23 Ecl binary; P=17d, G type

Beta Leo A3 13 Most likely to be extended after Fab4

Beta Uma A1 24

Delta Vel A0 25 Ecl binary, P=45d, A type

Eta Tel A0 48

Gamma Tri A1 36

Gamma Oph A0 29

Sigma Boo F2 16 JCMT detection?

Tau3 Eri A4 26

Tau Cet G8 3.5 Solar type

Zeta Lep A3 21 Evidence 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)

24 μm Flux Histogram(observed / expected stellar flux)

Only 2 out of 153 stars have 24 μm excess

A detection rate of1 ± 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 of14 ± 3% at 70 μm

Identifying extended emissionNo 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 subtractedfrom 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