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2013_09_2425

Weather:

Clear and cool – almost perfect night.  Seeing is not quite as good as last night but close – and I think transparency may be better.  Low 50F, fairly low humidity but dew will be strong by sunrise, no wind.  Seeing around 2.0 arcseconds.

UPDATE:  3:10am – a few clouds.  Getting worse – out at 3:50am.

Rig #1:  Spectra of Nova Del (=v339 Del) – and guider focusing issues return.

More frustration focusing the guide camera.  It seemed that everything last night was in good order – so of course I tried to improve things.  I rotated the main camera so that the spectrum is as horizontal as possible.  And since the guide camera seemed to be moving around a bit I tried focusing it on the slit using daylight to illuminate the field.  I got the slit as focused as I could – the fwhm was around 3 pixels.  Usually in order to get the best focus I simply get maximize the maximum value in the psf, then move the star onto the slit and turn on the guider.   The normal location of the slit center was near the center of the image; last night at x=160, y=103.  Tonight, after focusing the slit earlier in the day, it seemed the location of the slit in the camera had moved to around y=125.  And when I used Altair to peak up the focus by taking a series of 10-second spectra the resulting image seen in the guider was decidedly not right.  Basically it looked like an arc.  But I figured what the hey – it was sharp in the main camera so off to Nova Del.  The first spectrum was certainly sharp – measured by taking a vertical cut through the profile, but the overall level was down by almost a factor of two from the previous night.   I’d seen that before and really have no clue how it happens except that I knew the only thing that had changed was the guide camera positioning.  I tried a few simple things but just decided to get what I could.  Finally, once Nova Del moved out of range (behind the maple tree!) I went to Alpheratz to work on getting things aligned again.  I think the guide camera is too loose in the holder and so moves around a bit.  And it can get out of alignment – the camera’s chip can become non-coplanar with the image “plane”.  Once I got it moved so that the slit was back to y=107, and where the image looked round when located near the slit and x=160 (near chip center) I went to Alpheratz and ran a sequence of spectra tweaking focus on the telescope until, with the star on the slit at x=155, y=107, the peak intensity was maximized and the FWHM of a vertical cut through the spectrum was minimized.  I then found a nearby 6th-mag star and looked at the image in the guider and it was what I am used to – a fairly tight “spot” with no artifacts other than the ghost image just below the main image – and the ghost image slightly out of focus.  Taking an image of the 6th mag star the FWHM of a cut through the spectrum was 3 pixels, which is great.

I’m going to see if I can find something to “shim” the guide camera in it’s holder.  It sits about 1 or 2 mm off of the “shoulder” of the guide camera port.  Something that would keep it square and less easy to move if bumped.  Perhaps a 1.25-inch gasket of some sort?

Flat Fields

Last night I attempted to get flats for each of the micrometer settings, but in the middle of the first flat image the bulb blew out.  Interestingly, when it did it left emission lines.  Might be fun to see what they were.  Anyway, bought a couple of new bulbs today and am running sequences of flats for all three settings.

Rig #2: OT J004527.52+503213.8  (=new CV in Cas)

Another night of images of this very interesting newly-discovered CV in Cassiopeia.  Joe Patterson thinks this may be a WZ Sge type – based on it’s huge brightness increase of at least 7 magnitudes.  The star is exhibiting huge superhumps (see last night’s log).

 

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