5 th SECCHI Consortium Meeting Orsay, France SECCHI Observations of Comets and Minor Planets Karl Battams (NRL)

Overview ● SOHO Recap  Current comet status  Comet highlight ● SECCHI – Early Results  HI-2, HI-1 and COR-2  The COR-2 Kreutz comet problem... ● Prospects For SECCHI Comets  Science discovery potential  New object discovery potential ● Some Highlights For This Coming Year

SOHO – History's Greatest Comet Discoverer! ● To date, SOHO has discovered 1,273 previously unknown comets  1,069 Kreutz  30 Marsden  29 Kracht  73 Meyer  72 Non-group (including 3 “Kracht II”; several “pairs”) ● SOHO has discovered three well-populated comet groups

SOHO Observations of Known Objects ● Asteroids  Ceres and Vesta ● Pleasant surprises  Several of Jupiter's moons! ● Comets  Over a dozen comets (Machholz (twice), Kudo- Fujikawa, NEAT, Bradfield, McNaught, ASAS...)

Some SOHO Comet Highlights ● Nearly 1,300 new discoveries!! ● Link between comet Machholz and the Marsden and Kracht groups (and two meteor showers... and an asteroid...)  Wealth of information on the dynamics and evolution of old comets ● “Clusters” of comets just hours apart  Information regarding pre-perihelion fragmentation of comets ● CME striking the tail of comet NEAT  Information on solar wind, comet dust tails and CME-comet interactions

SECCHI – Early Results: HI-2 Observations ● Stars  Apparent limiting magnitude: ~m11 ● Too many stars! ● Comets and Minor Planets:  Comet C/2006 M4 (SWAN) (m9.6)  Tail of comet C/2006 P1 (McNaught) ● And later, all of it!  Asteroid 15 Eunomia (m10.1)

SECCHI – Early Results: HI-2 Observations ● Other Objects:  M31 (Andromeda)  M16, M17, M22, M25, M28...  Milky Way  LMC, SMC  Many more!

SECCHI – Early Results: HI-1 Observations ● Stars:  Apparent limiting magnitude: almost m14?  m12 stars certainly visible Image courtesy of A.Watson, SOHO comet hunter (Australia) using “Starry Night” software

● Minor Planets:  (15) Eunomia  (10) Hygiea  (532) Herculina  (8) Flora  (1) Ceres  (29) Amphitrite  (349) Dembowska  (6) Hebe  (14) Irene  (95) Arethusa (m13.3!)  (219) Thusnelda ● And that's just in the HI-1 A data! SECCHI – Early Results: HI-1 Observations

● Comets:  C/2006 M4 (SWAN) at m9.6  Spectacular C/2006 P1 (McNaught) at m-5.5! ● High-resolution images of dust tail and striae  Five SOHO-discovered Kreutz- group comets ● Visible prior to their LASCO C3 appearance! ● HI-1 more sensitive than LASCO C3 SECCHI – Early Results: HI-1 Observations

SECCHI – Early Results: COR-2 Observations ● Apparent limiting magnitude: at least m11  Lots of stars ● Observed comets:  Surprisingly few!  Over 40 “SOHO” Kreutz have passed through COR-2 ● We have seen just four of them  What's the problem? ● Exposure times? Bandpass? Polarization?

● SECCHI: A salt-free diet?  Kreutz comets show up well in the sodium-D line (589.0nm, 589.6nm) ● LASCO C3 (Clear) bandpass: nm ● LASCO C2 (Orange) bandpass: nm ● SECCHI COR-2 bandpass: nm ● SECCHI HI-1 bandpass: nm  Sodium-D not visible in COR-2 or HI-1!  But... ● HI-1 is more sensitive to Kreutz than LASCO C3 SECCHI – Early Results: COR-2 Observations

● So why so few COR-2 Kreutz comets?  Polarized images? ● Kreutz still show in LASCO C2 polarized images, though are noticeably fainter  Exposure time? ● LASCO C2 exposures are quadrupled for polarized C2 images (to 100 secs) ● Answer:  Probably both (but I think longer exposures would really help...) SECCHI – Early Results: COR-2 Observations

Scientific Potential ● Discoveries of new comet populations would add to what is known from SOHO of the end life of a comet ● HI observations of “SOHO” comets will extend light curves to much greater distances ● Greatly improved orbit determinations ● Detailed images of comet tails (e.g. McNaught) lead to better understanding of solar wind / comet interaction ● Possible CME-comet interactions ● First 3-D reconstruction of comets

SECCHI Object Discovery Prospects ● HI-2  Discoveries extremely infrequent ● Other surveys have it covered ● HI-1  Discoveries very likely and relatively frequent ● COR-2  Could still surprise us... ● COR-1  Very unlikely to make new discoveries due to limited field of view

Some Highlights For This Year... ● Comet 2P/Encke  Mag 6, will pass from HI-1A into HI-1B (also LASCO C3) (late April) ● Comet 96P/Machholz  Mag 8 (very approx), LASCO C3 (faint) and HI-1B (early April) ● C/1999 R1 = C/2002 R5 (SOHO)  Predicted 3rd perihelion passage (~September)  Mag 6; LASCO C2, C3 and (hopefully) HI-1B ● Many more asteroids...