Transcript Spitzer Space Telescope MIPS photometry of the active centaur

Spitzer Space Telescope MIPS photometry of
the 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)
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
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)
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
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
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.
• At 24 m, able to resolve
separate coma peak &
nucleus components
N
E
24 m, Feb24
~ 6 arcmin
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…
SST MIPS Observations (continued)
Feb 25
Feb 24
• 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
3 arcmin
N
E
SST Photometry
SST data set
Flux
Comments
Feb, 2006
24m
30 (+/- 0.3) mJy
~5 arcsec ap
Feb, 2006
70m
90 (+/- 4) mJy
~15 arcsec ap
Cruikshank/Rieke GTO
24 m
5 (+/- 0.2) mJy
No coma, R=14.1,
=13.7 [AU]
Cruikshank/Rieke GTO
70 m
16 (+/- 4) mJy
No coma, “
• 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)
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 CentaurComets.