JOP011: SUNGRAZING COMET STUDY Authors: C. St.Cyr, P. Lamy, D. Biesecker, R. Howard, D. Michels (LASCO), J. Raymond (UVCS), J. Gurman, R. Catura (EIT) Progress: Revised Submission (this work) Objective: To study the interaction of the solar atmosphere with a sungrazing comet. Conditions Necessary to Run: This is a target-of-opportunity program. This is not a "comet search" JOP. This program requires the pre-perihelion discovery of a sungrazing comet. For members of the Kreutz family of comets such a discovery could occur several days before perihelion (SWAN or LASCO C3) or several hours before perihelion (LASCO C3 or C2). It is also possible that a groundbased observer could discover a Kreutz comet many days or weeks before perihelion. Scientific Case: The appearance of a sungrazing comet offers the opportunity to study the interaction between coronal plasma and the dust and ions released by the comet. For example, one might expect the transient deposition of (initially cooler) cometary material into the Sun's atmosphere to produce a significant effect on the tenuous corona. But only one of the 16 members of the Kreutz family discovered between 1979-1989 by the Solwind and SMM coronagraphs produced any lasting effect on coronal brightness. None of the three sungrazers discovered by LASCO produced a significant coronal response. What can we learn about the comets? The structure of the cometary ionosphere, the plasma temperature, and other parameters under such extreme conditions are not known, but UVCS observations of the EUV spectra of a sungrazer would provide unique data toward understanding the solar wind-comet interaction. Pointing and Target Selection: To be defined when target appears. But the Kreutz group appears to be the only active family of sungrazers at this time. The orbital elements of this family are well-known, so we will know the projected path through the corona for any newly discovered member. The location of perihelion (presumed to be at the photosphere) will be more difficult to predict. For at least one of the three sungrazers discovered by LASCO, discovery was more than 12 hours before perihelion. This allowed the EOF operations team to respond with a higher cadence of C2 and C3 images. Observing Details: LASCO/EIT -- The first three LASCO sungrazer discoveries were all extremely faint objects. We suspect that none of these three would have been detected by the Solwind or SMM coronagraphs. Therefore, we would propose only minor modifications to the regularly scheduled observations (ie., only the additional C3 sequences listed below) to the discovery of the next faint member. But if a significantly brighter sungrazer is discovered, then we propose to implement the full sequences described below. We can have a prepared response for LASCO/EIT to such a discovery, with a likely response time being about four hours following the comet discovery. Because the orbital path of the Kreutz members is well-defined, on any given day-of-year a single apparent altitude measurement from LASCO C3 (or SWAN) will give us our first estimate of t0, the time of perihelion. We divide the LASCO/EIT response into time intervals identified by (t-t0): (~36 hours) > (t-t0) > (~6 hours) corresponding to ~30R>d>~8R Nominal Synoptic Program for LASCO and EIT Additional C3 sequences: Full spatial resolution, partial field IR, Blue, Red, and Orange filters Blue full-field polarization sequence [2x2] Red full-field polarization sequence [2x2] **Clear exposure before-and-after any color or polarization sequence** (~6 hours) > (t-t0) > (~3 hours) Reduced Synoptic Program for LASCO and EIT Additional C3 sequences: Full spatial resolution, partial field IR, Blue, Red, and Orange filters Orange full-field polarization sequence [2x2] Blue full-field polarization sequence [2x2] Red full-field polarization sequence [2x2] **Clear exposure before-and-after any color or polarization sequence** Additional C2 sequences: Full spatial resolution, partial field Blue and Red filters Orange full-field polarization sequence [2x2] Blue full-field polarization sequence [2x2] Red full-field polarization sequence [2x2] **Orange exposure before-and-after any color or polarization sequence** (~3 hours) > (t-t0) > (~1.5 hours) Suspend Synoptic Program C2 sequences: Full spatial resolution, partial field Blue and Red filters Orange full-field polarization sequence [2x2] Blue full-field polarization sequence [2x2] Red full-field polarization sequence [2x2] **Orange exposure before-and-after any color or polarization sequence** C1 sequences: H-alpha on/off full-field LEB-binned FeX on/off full-field LEB-binned FeXIV on/off full-field LEB-binned Na on/off full-field LEB-binned EIT sequences: 195 and 304 full-field [2x2] (t-t0) < (~1.5 hours) Suspend Synoptic Program C3 sequence: Single Full-field Clear [2x2] C2 sequence: Single Full-field Orange [2x2] C1 sequences: H-alpha on/off full-field LEB-binned FeX on/off full-field LEB-binned FeXIV on/off full-field LEB-binned Na on/off full-field LEB-binned EIT sequences: 195 and 304 full-field [2x2] For post-perihelion schedule we will invert the pre-perihelion observational sequences. ========================================================================== In the context of this JOP, someone from the other instrument teams should provide details for their observations: SUMER -- Predefined Observing Program #15, but the trajectory of a Kreutz comet will be different than that of a stellar target. This may be moot because of the pointing difficulty. UVCS -- To be defined by John Raymond. SWAN -- No interest in participation as of November 1995. Groundbased -- After the fact, we will check with the MLSO observers for any 10830, H-alpha, or coronameter data. -- end of JOP --