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 (comanucleus) for 4arcsec
  ap., 0.48 for 40 arcsec (coma bluer than
  nucleus)
• R-band Afp values 104 cm
• Qdust70 kg/s (p0.05, ?1g/cm3, dgr1?m,
  vej50m/s)

• Coma extent 1 arcmin (550000 km), beyond which
  point the signal drops quickly

5
Recap comparison with some other active Centaurs

• Chiron V-R0.4 (?), Qdust 4 kg/s (Meech et al.
  1990)
• SW1 V-R0.55 (Bauer et al. 2003a), Qdust50 kg/s
  (Stansberry et al. 2004)
• 166P/NEAT V-R0.9, Qdust5kg/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.
• R12.97 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 24
Feb 25

• 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

N
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 (vej50 m/s)

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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.