Observing with IRCAM at Leuschner

Marshall Perrin, Adam Leroy, and Jason Wright

With the Leuschner 30" newly collimated, it was high time to get down and dirty and do some observin'. And so Marshall, Adam, Jason and Don headed out into the (luckily, clear) May night.  Dick Treffers met us at Leuschner to get us started, and managed to save the day with a manual override when the dome refused to open. Due to some troubles with the cooling system, the detector was pretty hot (~ 110 K) and thus the image quality wasn't the best, but we did what we could.


First task was to check the pointing.  This turned out to be pretty darn good - everything we looked at showed up in the CCD field of view basically on the first try.  At first things were a bit off center, probably due to the new collimation, but after some offseting and a TX ZERO LAST command, we were all set. There were a few oddities - at one point it seemed as though a star had shifted from one part of the field of view to another during a series of ON/OFF pointings. However, we tested this again by writing a script to slew ON/OFF by a degree a number of times, and the star ended up in basically the same position every time, modulo seeing fluctuations.


The following two images show the difference between 5 seconds vs. 2 minutes on some star in Bootes. Note both the blurring due to seeing, as well as the chip flaws that become apparent: the crack between rows 128 and 129 where the individual component quarters abut, and the dark region in the upper left. That region showed up on several of our images, though the stretch here was used intentionally to bring it out. Both of these images are POST sky frame subtraction, though no CR rejection was done.

We found the best focus for the instrument was around 590 mils, give or take a couple. It was actually somewhat hard to quickly determine the best focus, since the seeing conditions were changing pretty rapidly. The best we saw was a FWHM of about 3.5, but more typically it was around 4.5-5 arcsec, for 5 second integrations.

There is a visible astigmatism when not in focus; inside of focus you get elliptical blobs at a 45 degree angle, and outside of focus you get elliptical blobls at a 135 degree angle. (Or was it the other way around?) Even at the optimum focus, things aren't *quite* perfect, but rather a point source appears about 10% wider in one direction than the other. Some of that might have been seeing, though; more careful measurements are needed to pin this down.

Double Stars

We could easily split the double star Bootes Mu-2. This frame has had CRs rejected as well as the sky subtracted, cleaning it up substantially. Probably a fair number of these "CRs" are really hot pixels due to the high chip temp, but the effect was the same so QZAP in IDL killed 'em off.


We next turned our sights on the globular cluster M3. We observed M3 in both the J and K bands. The image here is a two-color composite, with 5s K in red and 20s J in cyan. The K band image is noticably sharper than the J, due most likely to the shorter exposure time, which was necessary in order to prevent the detector from saturating at the higher count rates for K band.


Our last and best target was the famous Whirlpool galaxy M51. Well, turns out we missed it and only got its smaller companion galaxy NGC 5195. At the time of observations, we thought we had shots of the cores of each galaxy, but we were somewhat confused and upon later reflection it became clear that we hadn't shifted the telescope nearly enough to get both cores. This would be a fun observing project to do-over again right once IRCAM is back up; the two galaxies are 270 arcsec apart, just barely within IRCAM's 280 arcsec field of view, so it ought to be possible to get both on one frame. Now, without any further ado, here are our two  images, which were each built up by adding 7 20sec exposures less 7 20 second sky frames. Both of these images have had CRs removed and are displayed with a highly stretched linear scale; the reason it looks like there's still a fair amount of garbage present is that the color table is scaled way down in order to bring out the still-quite-faint features of the galaxy. We probably would have done better with a good deal more exposure time. .

And, courtesy of Kitt Peak, I found some context for the above, proving to my own satisfaction that we really were looking in the right place; you already saw up at the top of this page an overlay of our observations over the KPNO image, visible also below; Click here for the original image. This image, which I found just by doing a google search on M51, turned out to be far more useful than the amazingly poor and low-signal images I was able to get from 2MASS... Note particularly the two small clusters visible to the left of NGC5195, and also how well the galaxy's shape in IR tracks the visible. Image scale is 1 arcsec/pixel, 10% smaller than the above. The dust lane linking the two galaxies is not visible at all, which is somewhat surprising, but then again we're not down in the thermal IR where the dust is presumably radiating.