We are also interested, if the Hinode rate allows it, to get observations with EIS and XRT every 10 or 20 minutes of the same field of view. This will help to follow the upper chromosphere (He 256A) and corona (FeXV 284A) with EIS during the formation of the photospheric network in the quiet Sun.
Date: Tue, 21 Aug 2012 15:23:21 -0700
From: Ted Tarbell <email@example.com>
I had an action item from the last meeting to find out if the ToO HOP 217 (48 hour continuous SOT observation of quiet sun, tracking through disk center) could use an on-disk coronal hole near disk center as its target. If so, then the EIS team was very interested in using the opportunity for CH evolution studies, some time after EUV eclipse season ends.
The answer is affirmative as long as it is reasonably close to disk center, as stated by Thierry Roudier in the following reply:
"Regarding the quiet sun area , I would like the location to be not too far to the disk centre ( to avoid the projection effects). But, I think you can get the best compromise to include part of a coronal hole if it is possible , in order to have EIS observations."
This is not a quantitative answer to how close is close enough, but also remember that the EIS slit is much longer than the SOT FOV (218x109 arcsec). If the top of the SOT FOV just grazed disk center, the bottom would be at theta = 6.5 degrees, and the bottom of an EIS slit }256 arcsec long centered on SOT would be at 15 degrees. The projection effect at this angle in SOT is very tiny (mu > 0.99), and another 5 or 10 degrees N or S should not be a problem. As an example, pointing SOT at the top of the CH that passed central meridian on August 15, and timing the observation so central meridian came in the center of the interval, would have worked for both instruments, I think: