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About Comet Bradfield LASCO/C3 Images |
1. Around 05:00 UT (01:00 EDT) today, the reformatter at the Naval Research Laboratory (NRL, the home institution of the Principal Investigator for LASCO), the piece of software that takes the 1's and 0's from the LASCO coronagraphs and makes them into images, broke down. I don't know why, and normally it wouldn't make a difference, because we use images on the SOHO Website that are reformatted, with different software, by NRL machines here at NASA Goddard, in the SOHO Experimenters' Operations Facility (EOF). In an effort to try to prevent overexposure (and thus "pixel bleeding," or the appearance of a line across the bright nucleus of the comet when it dumps too many photons into one or more pixels of the CCD detector), the LASCO Team had decreased the exposure time. The software here then produced very poor images, so the SOHO Website folks decided to go with the images produced at NRL instead.
2. Sometime soon after 05:37 UT (01:37 EDT), the electronics box (the LEB) that runs LASCO and EIT, the EUV telescope on SOHO, started dropping "normal" images from its plan, and only taking images that involve the rotation of a mechanism (the polarizer wheel on LASCO and the sector wheel on EIT). This happens once or twice a year. We don't know why, but we've always been able to restore the instruments to normal operations by rebooting the LEB. Unfortunately, that we missed almost all the C3 images for the day, the ones that contain the comet.
In the last hour, Mr. Kevin Schenk of the LASCO/EIT ops team at Goddard, having abandoned his weekend plans on the first really nice weekend day this spring in Maryland to stay around in case of need, came to the EOF and commanded LASCO: he stopped the then-current plan and load a new one, optimized the exposure times, and got things generally going right again.
Mr. Schenk also managed to get in touch with one of the NRL folks, who also came in to work and got their reformatter started again. I'm looking at a black and white representation of the latest LASCO C3 image at:
http://lasco-www.nrl.navy.mil/java/lastC3.html ,
taken at 22:54 UT. (In case the image has updated between the time I send this and the time you receive it, I'm attaching a copy.) Mr. Schenk found that the shortest C3 exposure time that still shows the solar corona is still too long, and, as you can see in the image, we have pixel bleeding in the comet nucleus. I suspect these images will appear in the normal, colorized format on the SOHO Website soon.
By the way, if you use that link to the black-and-white images, don't be surprised to see a smaller image some of the time --- the LASCO team is also taking shorter exposure, subfield images of comet at much reduced exposure times. The images are the wrong size for display on the SOHO Website, and don't show the solar corona well, but they will be used to put together detailed movies of the comet's passage across the C3 field of view, and comet scientists will be able to use them for research purposed. To my knowledge, such subfield images are the only LASCO images that don't normally get displayed on the SOHO Website.
Sorry for the inconvenience,
Joe Gurman
US project scientist for SOHO