Kreutz group comets and SOHO

Information about the latest comet discoveries is available from SOHO/LASCO Comet observations page. To mark SOHO-100 ESA issued a Press release and there was more news for SOHO-1500. There is more information and images at NASA hotshots.

Realtime images are available at a number of locations, including:

  • C3 images
  • C2 images
  • Real-time fits images
  • Black and white current C3 image
  • Comets currently visible in SWAN
  • SWAN images

    Images from the Solar Maximum Mission, which ran from 1980 to 1989, albeit with a gap when it was out of action. It discovered 10 Kreutz group comets.

    Karl Battams provides the following information about SOHO data

    There are 3 data streams -- realtime, QL and LZ. The realtime and QL are essentially the same, with the QL just being a slightly more time-ordered version. The LZ is the refined, final version of the data. The realtime is available within a very short time of SOHO transmitting the data to us. The QL data is (here at least) processed the following day. The LZ data (here) is anywhere from two to five weeks behind.

    The complete set of the realtime (rt) data (fits files) can be found in where YYMMDD is obviously the date and c? the camera.

    If you want QL or LZ (Level-0) then you need to download that from either the soho site: (only the most recent ~16 months of data) or from our LASCO site:

    On the latter, you'll see it states the date of the most recent LZ data that has been included in the database. Any data you request that is later than this date will be QL. Any data prior to that date will be LZ.

    The fits files for every half hour are in the ftp://lasco6... directory (above). The c3 cadence is usually 30 mins, the c2 cadence usually 20mins, though at the moment were are getting an increased data-rate for c2 until the EIT bakeout is over.

    There is nearly always going to be a delay of 3 to 5 weeks in getting the astrometry done on the comets. This is because the astrometry, if done *correctly*, should only be done with "LZ" (level-0) data -- the near-realtime stuff is "QL" (QuickLook), which I'm sure you have all noticed can often contain many missing images or missing blocks. The LZ data fixes (nearly) all of those gaps, and so is what should be used for astrometry measurements. The LZ data is typically 3 to 5 weeks behind the QL -- it depends on when I process it.

    SOHO was launched on 1995 December 2. It experienced a malfunction on 1998 June 25 and contact with it was lost. It was located by radar on July 29, communication was established in early August and it resumed pointing at the Sun in mid September. The LASCO cameras were reactivated in October but further problems were encountered and the spacecraft did not return to action until February 1999. Further control problems were encountered from time to time during the winter of 1999/2000.

    There are three LASCO (Large Angle Spectroscopic Coronographs) on the SOHO spacecraft, which orbits the sun at the earth's L1 Lagrangian point, 1.5 million km ahead of the earth. C1 had a field from 1.1 to 3 solar radii, but did not survive one of the shutdowns, C2 from 1.5 to 6 (giving an ecliptic width of 1.6 degrees and a radius of 2.1 degrees on movie loops) with a resolution of 11.4" and C3 from 3.5 to 30 (an ecliptic width of 7.8 degrees and a radius of 8.3 degrees) with a resolution of 56". The C2 coronagraph has an effective aperture of 20mm at f18 with ICQ wavelength code a and C3 8mm at f9 with ICQ code K. Most objects are discovered in the real time data, but some are still being found in the archival data. Sometimes real time data is not available and is published after a short time delay.

    There is also the all sky SWAN (Solar Wind ANisotropies) which measures Lyman alpha ultraviolet radiation. This has also discovered some comets and 2002 O6 shows that it can be used for real-time discovery. Although it does cover virtually the entire sky, there is a small area which is shadowed by the spacecraft and it is this area which now remains as virtually the only place where it is worth amateurs searching for comets. For northern hemisphere observers the band is roughly 8 degrees wide, north of the ecliptic, in the evening sky, running out perhaps 50 degrees from the Sun. The latest comet movies show several comets, including 2001 Q4, 2002 T7 and 2004 F4.

    A recently launched USAF satellite named Coriolis has a CME imager called SMEI (Solar Mass Ejection Imager) on board. This only has a 1 degree resolution, but may be able to detect comets.

    A new spacecraft mission commenced on 2006 October 25 with the launch of STEREO. This features a pair of Sun-orbiting NASA spacecraft called STEREO (Solar TErrestrial RElations Observatory). One STEREO spacecraft orbits slightly further from the Sun than the Earth and lags behind the Earth at a rate of 22 degrees / year. The other STEREO spacecraft orbits slightly closer to the Sun than the Earth and advances ahead of the Earth at a rate of 22 degrees / year.

    Each STEREO spacecraft carries the Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument. SECCHI includes the COR1 and COR2 coronagraphs that are similar to C2 and C3 respectively but with higher resolution and more frequent image rates.

    Karl Battams provides the following information on the imagers:

    COR1: Internally occulted coronagraph (similar to LASCO C2) will image from 1.1 - 3.0 Rsun with 2048x2048 pixel CCDs, and a resolution of 7.5 arcsec/pixel (C2 has a 23.8 arcsec/pixel resolution and 1024x1024 CCDs). Bandpass is 650-660 nm.

    COR2: Externally occulted coronagraph (like C3, except you won't see the pylon for COR2 like you do for C3) will image from 2.0 - 15Rsun with 2048x2048 pixel CCDs, and a resolution of 15 arcsec/pixel. (LASCO C3 has 1024x1024 CCDs with 56arcsec resolution). Bandpass is 650-750 nm.

    HELIOSPHERIC IMAGER ("HI"): Two externally occulted coronagraphs with the occulter at the edge of the field (not the center, like COR1/2, C1/2). These will allow us to follow CME's as they head out from the Sun, towards the Earth. They are as follows: HI-1: 2048x2048 CCDs, 35 arcsec/pix resolution. Will image along the ecliptic from 3.28-23.28 degrees (that's roughly 12 - 92 Rsun) HI-2: 2048x2048 CCDs, 240 arcsec/pix resolution. Will image along the ecliptic from 18.36-88.36 degrees (roughly 73 - 318 Rsun)

    Things to note are as follows. 1) COR1/2 images will be polarized on-board and will usually be taken as +90/0/-90 -degree triplets. 2) There will be *very little* full-resolution realtime data as there is with SOHO now. Most data will be dumped in one large load, once per day. 3) No one is sure on limiting magnitudes yet, but I think the COR's are hoped to be m10 - m12, and the HI's m10 - m14. We really don't know until we start imaging in space (and I'm not certain I have remembered the numbers correctly...). 4) There will NOT be a SWAN-like instrument on STEREO. 5) STEREO has a larger bandwidth available to it than SOHO... this means LOTS more data...

    Rainer Kracht has a an excellent page for comets seen with the STEREO instruments.

    SOHO has discovered over 1700 comets (mostly with LASCO), of which the majority are all members of the Kreutz group of sungrazing comets. So far, some 15% are not Kreutz group sungrazers and only 4% are not members of the other three groups. Further background information on the SOHO comets can be found at the LASCO Comet site. If you look at the archive of LASCO real-time movies, you will see two bright sungrazers in the C2 field at the same time at Christmas 1996. The LASCO images are downloaded every half an hour and you can view the Latest images or use the real-time JAVA movie player.

    Long intervals without comets being discovered from SOHO include 45 days, between December 21, 2001, when Mike Boschat found a fairly bright (though stellar-looking) comet in C3 that also became visible in C2, and February 6, 2002, when Maik Meyer found fainter and diffuse C3 comet. Another long gap was between August 4 and September 6 2006

    Solar Maximum Mission

    Doug Biesecker provides the following information: The SMM Coronagraph obtained images of the corona in white light and halpha from March through September of 1980 before suffering an electronics failure that rendered it inoperative. The instrument was repaired by the Challenger Space Shuttle (STS-41C) in April 1984 and obtained images between June 1984 and November 1989 when it re-entered the Earth's atmosphere. The SMM coronagraph obtained ~240,000 images of the corona during its operation. The SMM C/P recorded quadrants of the sun (north-east-south-west) in a square field-of-view extending around the entire corona between 1.6 and 4.1 solar radii and out to 6.0 solar radii along the diagonals (corresponding to the solar equator). Images were obtained at a spatial resolution of 12 arcseconds in the wideband 'green' filter (500 to 535 nm). Three polaroid filters were used for polarization analysis of the observed radiation. Between 1980 and December 1986, many of the orbital data sequences included images taken in the neutral line of hydrogen known as halpha (654.3 to 658.3 nm).

    Images from the Solar Maximum Mission. It discovered 10 Kreutz group comets.

    SOHO Comet Hunters

  • Michal Kusiak
    Published by Jonathan Shanklin. Jon Shanklin -