From: Milton Aupperle <milton@outcastsoft.com>

Date: April 23, 2011 1:17:41 PM MDT

To: Astro_IIDC@yahoogroups.com

Subject: Re: [Astro_IIDC] Re: Spectroscopy

Hi Darryl;

On 23-Apr-11, at 12:31 PM, Stanford, Darryl wrote:

-------- Snipped for Brevity.

Terrance and Milton,

Our observatory is using students, in a special projects class, to help take dozens of spectra of the eclipsing binary epsilon Aurigae, using an off-the-shelf Meade 8”, an SBIG SGS spectrograph and CCDSoft.  We have taken darks but have not needed to take flats in any of our spectra.  We are also beginning to make our own spectral catalog to use in my labs.   We are in an urban environment in San Mateo and find that light pollution is not a problem, even with the glow of San Francisco city lights 25 miles away and parking lot lights on campus.  The spectral quality has been sufficiently good, such that students have presented several posters at recent AAS meetings.   The point that I am making is that small telescopes can do amazing work in spectroscopy, as part of a community college curriculum.

If your not taking Flats,  are you calibrating your profiles / curves for the camera with a known star spectral profile? Or are you just using Raw curves for your program work?

I'm just trying to figure out what people are likely to do, so that I'm not spending too much time adding features people won't use anyhow. Adding in the absolute calibration stuff is a considerable amount of work (i.e. smoothing curves, re-sampling curves to a common base values, setting up file formats, managing file curves etc.) over the basic features.

Flats may or may not be needed, depending on your optical system, though they are recommended by other peoples work flow. With my ATRC8 scope, I have at most 0.7% brightness difference across the 1384 x 1036 2/3" Grasshopper CCD FOV (I measure these things). You get bigger difference for changing elevation and star air masses than that. With the C8 and a Focal reducer at F5.7, my variance was was much higher across the field.

But if you have any "donuts" (i.e. dust on the CCD, dust on your filters etc.) , you do want to make sure those get corrected out or they affect your spectral curve. If your optical system produces an evenly illuminated field, then a single set of flats to remove dust donuts for the camera and filters would do the job fine. Your likely not going to be doing log sqrt curve stretches on spectra or it screws up your absolute spectral curves.

One feature that likely would be includes is subtracting the spectral continuum curve out , which just leaves you with a roughly horizontal lines that has spiked and dips for emission or absorption lines.

On a related note, if people who are not doing Astronomical imaging but are doing some sort of spectral work in a different field (microscopy for example), I'd like to hear from you people too - either on list or directly at support@outcastsoft.com.

Thanks in advance..

Milton J. Aupperle