One of the challenges of observing in the near-IR / optical is field identification. In the case of the Apache Point Observatory 3.5m, the "raw" pointing - i.e., if you enter a coordinate and press "slew" - is usually good to within ~1 arcminute. However, once you're on the target field, it's up to you as the observer to identify the exact location within the 5x5' field to observe. This proves quite challenging in crowded fields, especially with rotation. It is far more difficult, though, in sparse fields when your target is a faint emission line feature - there will be no corresponding light in your guider image. But you still want ~arcsecond pointing accuracy. I think this can be achieved by using the astrometry.net source recognition and field identification tools, but highly constrained to be within ~10' of the target field. The WCS coordinates would then be applied to the guider image, and the target location identified and translated into a telescope pointing offset. This technique is probably not needed for most spectroscopic observations (e.g., of bright point sources). However, for slit-scan-mapping or observations of faint point sources, this approach provides the opportunity to do fast-switching with a bright calibration star so that telluric correction can be provided on a short (~5-10 minute) timescale, as is needed for truly accurate calibration.
Research Idea: Stacking Finders
Idea: Stack all of the finders from spectroscopic observations. Finder images tend to be on lower-quality CCDs with no filter, but they frequently produce very deep observations. For example, the open K-band finder on TripleSpec (though it's technically not a CCD).
In order to stack them, you would need to mask out the bad pixels (already done) and compute astrometic solutions for the CCD. Un-warping the images will take some work, but there should be plenty of information available from thousands of observations of different fields to make this computation nearly ideal. Similarly, it should be possible to calibrate different pixels on the imager based on response to 2MASS standards.
Applications? Very deep imaging of spectroscopic targets. Short- and long-term variability (typical finder cadence is ~a few seconds). Deep imaging around stars and galaxies of interest - probably far deeper than you could get with classical observing requests.
This project should be achievable by a motivated undergraduate, but I think the tools for astrometric solutions need to be in place first. Astrometry.net is a great tool for this, but I think operates on spatial scales that are too large. Once basic astrometric solutions are available (e.g., pointing center for the image), I think IRAF tools could be automated to compute the complete solution, which would then be applied to all images.
Calibration might end up being the most challenging component, since there is variable atmospheric emission (absorption) that is not filtered by the finder. Depending on the application, though, large calibration errors may be acceptable. i.e., for deep nebular observations, morphology will be more important than absolute brightness, since the line responsible for the brightness cannot be directly determined. Whereas, for variability, calibration is important, but it can be computed directly from other stars in the field.
Last month's observations in L111
Mapped sources: SH 2-156 [no high resolution observations; covered by 1.2m CO 1-0 survey] SH 2-157 Yancy CS 5-4, CO, 13CO 1-0, CS 2-1, HCN & SCUBA too.... IRAS 23151 (two pointings) Unmapped: BFS 18 = IRAS 23042+6000 = IRCO 859 Wu et al mapped this in CO 2-1 and detected no outflows. They used the NRAO 12m with a heterodyne array with very high Tsys ~700-1100K.
Observing 10/20
I don't have a better place to post this one, so here it is:
My automated fitter (Gaussfitting Cube Collapser) has come a long way. I now adaptively choose to fit 1, 2, or 3 Gaussian components to output to a data cube. The purpose of that code is primarily to find a two-dimensional way to display information about the 3D structure, specifically about the presence/absence of outflows. Outflows will inevitably be confused with multiple velocity components, but they are also likely to be convolved with them.
Observing run summary
3 nights of worse than grade 4 weather (tau ~.4, i.e. the atmosphere is nearly opaque) have given me a few interesting results. 1. Non-detections of CS 5-4 in a few bright BGPS cores. My best guess is that the pointing was off, though, because I definitely got down to a noise level around 50mK. 2. Lots of CO 2-1 mapping, 13CO/C18O too. That means I can now use this plot: http://dustem.astro.umd.edu/pdrt/co3221web.html to try to measure the incident flux. 3. I can't do homework at the summit. Maybe it's just that I can't do stellar structures homework, but I really am not processing this stuff well. Damn. 4. Running at altitude uphill is really, really hard. All the running I've been doing the past N months has not even come close to preparing me. Need to correct that... 5. "I am inappropriate." I probably violate a bunch of those rules... the important ones... 6. gotta get back to the mountains. Really. Seriously. OMFG. 7. ARGH those papers need writing! Lots of it! For the next observing run, need the following: 1. Pre-prepared A3 rasters 2. Larger selection of summit music 3. Better sleep schedule preparation 4. More caffeinated drinks per night 5. Cloud cannons.
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