Spitzer Space Telescope MIPS photometry of the active centaur 60558 Echeclus

1. Spitzer Space Telescope MIPS photometry ofthe active centaur 60558 Echeclus Bauer, J. M., Choi, Y-J., Weissman, P. R. (JPL), Stansberry, J. A. (Univ. of Arizona), Fernandez, Y. R. (Univ. Central Florida), & Roe, H. G. (California Institute of Technology)

2. New Discovery of activity • Choi & Weissman reported observations of a formerly inactive Centaur, 2000EC98 (now 1784P/Echeclus, Choi et al. 2006 IAU Circular No. 8656, 2) which indicated the presence of a strong coma (preceding talk): • Previously inactive surface, un-obscured by coma (Rousselot et al. 2005) • Studied extensively at optical through IR wavelengths • We applied for SST DDT to observe Echeclus using the Multi-band Imaging Photometer (MIPS) at 24 and 70 m: • If inactive: observe a surface altered by recent, strong outbursting & compare with previous observations by SST • If active: characterize the coma wrt dust characteristics and, if possible, image the nucleus through the coma • to see how quickly and profoundly centaurs & their surfaces are altered by activity, and characterize the onset, persistence and amount of activity

3. Simultaneous Optical Imaging • Images obtained in B, V, R and I bands from TMO throughout the nights of Feb 24 & 25 (UT) • Several images also obtained in RI-band from Palomar 200-inch on Feb 24-26. • Separation btw Echeclus and coma peak ~6 arcsec = 55000 km 06 Feb 24 06 Feb 25 N E 2 arcmin (R-band images)

4. Optical imaging Highlights • V-R & R-I colors: ~0.6 (coma+nucleus) for 4arcsec ap., ~ 0.48 for 40 arcsec (coma bluer than nucleus) • R-band Afp values ~104 [cm] • Qdust~70 kg/s(p~0.05, ~1g/cm3, dgr~1m, vej~50m/s) • Coma extent = 1 arcmin (550000 km), beyond which point the signal drops quickly

5. Recap: comparison with some other active Centaurs • Chiron: V-R~0.4 (), Qdust~ 4 kg/s (Meech et al. 1990) • SW1: V-R~0.55 (Bauer et al. 2003a), Qdust~50 kg/s (Stansberry et al. 2004) • 166P/NEAT: V-R~0.9, Qdust~5kg/s (Bauer et al. 2003b) Stansberry et al. 04 Bauer et al. 03

6. SST MIPS Observations overview • Observations taken near 11UT on the 24th (shadow) & 25th of Feb, 2006. • R=12.97 AU, =12.62 AU, =3.0 • MIPS 70 & 24 m modes were used • Shadow observations were taken before to avoid dust trail contamination • Shadow observations also contained Echeclus. N E • At 24 m, able to resolve separate coma peak & nucleus components 24 m, Feb24 ~ 6 arcmin

7. 24 m Imaging • “ad hoc” removal of signal of nucleus. • Within a 5 arcsec aperture, nucleus accounts for ~ 20% of signal at 24 m. • SBP of 24 m coma show similar shape as optical • Coma extends out to ~60 arcsec, then drops off…

8. SST MIPS Observations (continued) Feb 25 Feb 24 N • 70 m resolution ~7 arcsec (not able to separate components in images) • Clear coma visible in both nights 70m images ~2 arcmin across (as in optical & 24 m) • 70 m shadow image contains only a small portion of the coma E 3 arcmin

9. SST Photometry • Comparative scaling yields consistent results with “ad hoc” nucleus signal removal (~ 20-30% of total), within 2X resolution apertures at 24 & 70m • Signal scaling yields dust production estimates of ~100-300 kg/s (vej~50 m/s)

10. Summary • Simultaneous Ground-based optical & SST MIPS 24 & 70 m observations were successfully conducted on Feb 24 & 25, 2006 • Both nucleus and coma were apparent in optical and IR data sets (except 70 m, where resolution too poor to individually resolve) • Separation btw nucleus & coma brightness peak ~6 arcsec (55000 km) • Coma extended out ~ 1 arcmin in optical and IR bands • In both IR bands, coma accounts for ~70-80% of signal • Optical and IR dust production estimates agree (??), which, owing to the grain-size sensitivity at different , is puzzling. All estimates exceed production estimates of other Centaur-Comets.