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HINODE Operation Plan (HOP)

accepted on


 HOP No.

 HOP title

HOP 0242

Hinode observations for Comet ISON

plan term


@ @


 name : McCauley @  e-mail : pmccauley[at]cfa.harvard.edu

contact person in HINODE team

 name : Reeves @  e-mail : kreeves[at]cfa.harvard.edu

 abstract of observational proposal
Comet ISON will reach perihelion on November 28, coming to within 1.7 solar radii of the photosphere. If ISON survives its closet approach, it is likely to reach negative magnitudes and become the brightest comet since Ikeya-Seki in 1965. However, whether it will survive perihelion is very difficult to predict. ISONfs nucleus is estimated to be 5 km in diameter, 5-10 times larger than Comet Lovejoyfs, which survived a much closer perihelion (0.2 R_s) in 2011. ISON also appears to be a dynamically young comet, fresh from the Oort cloud. This may suggest a lower bulk density than that of Lovejoy, which was a fragment of a much larger sungrazing comet, and mean that ISON will be more susceptible to fragmentation by tidal forces within the Sunfs Roche limit. As long as it survives to within 30 minutes of perihelion, it can be observed by XRT.

ISONfs trajectory will be accessible to XRT for about 55 minutes surrounding perihelion, from 11/28 18:12 to 19:07 UT. It will pass too far from the limb to be observed by SOT and may be observable to EIS for around 20 minutes. XRT will detect emission from the comet if the density of material lost from the nucleus combined with the coronal density is sufficient to generate O VII, which is what XRT is thought to have observed for Comet Lovejoy. Such observations would be useful to both the study of the comet and of the coronal environment. They can be used in combination with AIA observations to determine the density of the cometary material and to probe ionization timescales in the corona, since a detection would represent neutral material being fully ionized to coronal charge states.

 request to SOT
None, see telemetry note in Remarks.

 request to XRT
Field-of-view: 1024x1536 pixels
CCD Center: 512, 768
Binning: 2
Cadence: 12 sec
Filter: Al-mesh
Exposure: 8 sec, fixed (no AEC)
No flare response (important so that FOV doesnft change)
Do not stop observations for SAAs
Synoptic images (Al-mesh, G-band, and VLS closed G-band) should be taken at the start of the observing period for alignment and calibration.
   A Dark image with matching FOV should also be taken at the start of the observing period.

An XOB has already been created for test purposes (#19DF), but the CO must edit it for use. The Al-mesh exposure time should be changed to 8-sec and the loop count should be increased to ensure that observations donft stop. Otherwise, the existing XOB should be fine but the CO should verify.

 request to EIS
EIS can off-point by 890ff from the Hinode pointing using its coarse mirror movement. ISONfs trajectory is within this range for 24 minutes from 18:26 to 18:50 UT. The minimum distance from the proposed Hinode pointing is 818ff at 18:38 UT, 6 minutes before perihelion.

There are several Oxygen lines that would be observable: O VI (171 A), O V (193), O III (263), and O IV (279). Fe VIII, Fe IX, Si VII, and Si VIII may also be observable.

A detection of the Ne III line at 251.14 A would also be very exciting, as it may be the first confirmed detection and would be relevant to cometary formation models.

Other species may also be detectable – itfs not known what exactly there is to see. If possible, binned exposures covering the full spectral range and unbinned exposures focues on the Oxygen lines would be best.

The 40 arcsec slot configuration should be used in a single pointing centered on the trajectory at 18:38 UT (-1679 ef, -529.3ff). This will maximize the likelihood of detecting the cometfs tail. A raster slit scan is not advisable because of the small time window available, uncertainties in the timing of the comet trajectory, and uncertainties in the direction the cometfs tail will take (which depends on the magnetic field configuration).

 other participating instruments

Timing/Pointing info:

Hinode pointing: (-930, -200) arcsec

Observing period: 11/28 18:00 to 19:20

A plot of ISONfs trajectory with the Hinode and XRT pointing info can be found here:



This XRT plan requires a very high data rate, which may exceed 2/3 of XRTfs typical 2-day allowance. Due to the CCD bakeout that will be performed during the previous plan, XRT will not require much of its telemetry allocation for the Tuesday plan. We request that 1.2 GBits of XRTfs Tuesday telemetry be given to SOT in exchange for XRT receiving 1.2 GBits of SOTfs telemetry on the Thursday plan.

Patrick McCauley, Support Scientist
(617) 495 - 7121
Solar & Stellar X-Ray Group
Harvard-Smithsonian Center for Astrophysics

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