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Hi Robin,
Are you able to share if much has been added to the second book (Spectroscopy for Amateur Astronomers) compared to the on-line version, or is it essentially just a very nicely bound copy of the original material?
Paul
Nice work Andrew. I spent some time revisiting IRAF recently with help from a colleague and have all but decided to give up on the idea. Life is just too short 😉
By the way, are there details somewhere on the design and construction of your echelle?
Paul
I could be wrong, but I think they’ve been gradually replacing sodium and/or mercury vapour street lighting with some other fluorescent variant over the last few years (not LED as far as I know). No doubt to save money, not light pollution.
Speaking of LED, I’ve just replaced a number of old ceiling mounted halogen interior down lights with LED versions due to some safety concerns with the old technology in my house. As my backyard observatory is very near our living room I’ve wondered if I’m seeing the effects of this appear in my background (must dig out some old files to check).
Ernst – I’ll happily email you that FITs file.
Paul
Hi Nick,
As you’ve probably noticed, Atik have removed the MaxIM drivers from their installer and recommend using an ASCOM driver instead.
However, you might try to get the Titan working using the original MaxIM plugin (https://www.atik-cameras.com/downloads/). You need to manually download the files and copy them into the MaxIM folder as documented.
Try setting it up as camera 1 (ie, pretend you only have one camera – the Atik Titan). If that works, then it should also connect as camera 2 (the guide camera in MaxIM).
Paul
… Always use AOD for reference spectra processing.
Use AOD on target spectra only if reference spectra taken at a different time / altitude.
Do not use AOD on target spectra if reference spectra taken at same time / altitude as target.
Edit: Apologies, it was late. What I mean’t to say, and what I think is correct:
If AOD is enabled when processing reference spectra, ensure AOD is also enabled when processing target if using this “AOD corrected” reference.
Do not enable AOD when processing target spectra if reference spectra (taken adjacent to target) has not been AOD corrected.
If reference spectra has been AOD corrected (ie, it is IR only) then target spectra that it is applied to needs to be second order corrected using AOD.
Thanks Andy,
Yes, these discussions have got me thinking again because of the pro-am stuff that I’ve been involved in where using AOD was mandated simply because of the cadence requirements of rapidly changing features and the inability to acquire sufficient reference spectra often enough as the target moved through different altitudes. As Robin has mentioned, it’s also a usual technique used by professionals.
However, I’ve never been totally at home with its implementation in ISIS – having witnessed some weird effects that could only be corrected with bizarre AOD values. So, more often than not, I revert to the standard practice of obtaining nearby reference star spectra to correct for instrument response and extinction – particularly when taking just an hour’s worth of spectra or so. The problem it seems, at least for me, is when to use one vs another, and applying some consistency to spectral processing (which seems more important).
Thanks for the contributions to this interesting dissection. Response and extinction correction in spectroscopy (and photometry for that matter) seem to be recurring themes, so there’s obviously some merit in all of this banter.
Paul
Hi Robin,
The question remains, should we be using AOD as a matter of course when we process our reference star before dividing it by an atmosphere corrected standard such as Miles?
This regardless of whether we use AOD or not in our target spectrum processing (yes if reference was taken at another time / altitude, no if taken at the same time / altitude).
Paul
Hi John,
I’m referring to the step, in ISIS, where a Miles (or other) standard, is applied to the reference. Assuming the Miles reference is atmosphere corrected, shouldn’t our standard also be corrected before it is divided by the Miles?
Paul
Edit: Or to put it another way, as I understand it, the sequence in ISIS is:
Creation of IR:
1. Process the IR spectra with AOD configured and enabled.
2. Create an IR curve of the processed spectra using a published reference and the continuum shaping tools in ISIS.Processing target spectra:
1. Enable the AOD function (assuming you have a web connection and have correctly specified object name).
2. Specify the atmosphere corrected IR curve (from above).ISIS will then remove the atmospheric effects before applying the IR correction.
The alternative method is to take reference spectra of a nearby star at every run. If a target and reference star are very close together then they will be equally affected by any atmospheric effects (attenuation, pollution) and as one is divided by the other those effects are self cancelling. The IR is processed as above (ie, with AOD enabled in order to correctly compare to a published reference) and then applied to the target with AOD disabled during processing.
Hi Andy, all,
The response tool in ISIS divides the spectrum of our processed standard star by a Miles (or other) standard to create a response profile – which is then smoothed before applying to our target spectra during processing.
Assuming the database standard has been corrected for atmosphere, shouldn’t we be doing the same (ie, invoking ‘auto atmosphere’ with an AOD value) when we pre-process our standard star? Otherwise, how does ISIS correctly correlate the atmosphere corrected Miles standard with our non-atmosphere corrected calibration star.
What am I missing?
Paul
Hi Andrew,
I’ve emailed you a link to a dropbox location with some zipped up Lhires2400 data of HD54879 (a current project). The target is on the faint side, so it may provide some worthy test material. Lots of Tellurics to play with too. 😉
Also in the folder are zipped archives of bias, darks and flats (but only one variety I’m afraid).
Looking forward to your results,
Paul
Yes, I believe so Robin. In fact that’s exactly what I did for the aforementioned high cadence campaigns (gam2 Vel, zet Pup). I created a response correction, initially processing the reference star with AOD enabled. At the time I assumed it was necessary in order to compare to the (presumably corrected) published references when creating the IR profile.
I must confess though, I’m no expert. Bernard H., provided much of the guidance during my initiation into these campaigns, having spent many more hours (years !) working with both the ISIS and the pros in question. I’m still [mostly] confused about how to use this feature, particularly when it comes to determining the correction value. As such I’ve reverted to back the conventional method of correction using a nearby standard for each session and leave AOD switched off.
I do recall seeing some analysis (again, from Bernard) that showed only minor – almost insignificant – variations between the two methods – supporting the consistency of the ‘one IR’ method.
Cheers,
Paul
Hi John,
Apologies for the lack of a useful Buil link, but you may also want to take a look at the AOD function in ISIS if you’re correcting your spectra using references taken at different altitudes, times and varying atmospheric conditions. I’ve used it for pro-am collaborations where high cadence spectra were required – in some cases using the same IR correction curve over several months. In recent times I’ve become less sure of the AOD tool (lacking the time to dig into the detail of aerosol theory among other things).
Also – for the benefit of other newcomers, make sure you scale your miles comparison spectrum to the same range as your processed spectra when comparing the two. This appears to be the case with your plots John, but I just thought I’d mention it for others. In ISIS this is the “Normalize” button on the “Profile” page. The values applied to a comparison should match the ones you used for processing your spectra (specified on the “Settings” page) otherwise you’ll usually see a big offset.
Cheers from the southern colony,
Paul
Hi Jack,
Essentially, you store all of your bias, dark and flat fields in a single location, and then use the Set Calibration dialog in MaxIM DL to manage your calibration files and, optionally, create masters. There are a number of options available in the dialog (feel free to ask specific questions) but little house keeping is required once your library is ‘up and running’ in MaxIM. There’s also a ‘calibration wizard’, but I’ve not used it.
Also, check out the MaxIM help topics under the Help menu. There’s a whole section on image calibration and the use of calibration groups in the ‘Processing Images’ section.
Paul
Steve,
I don’t think it likes dates that are in the past. Try setting the second box to today’s date and see what happens.
Cheers,
Paul
Hi Steve,
I recently compiled a database for TheSkyX based on data extracted using VizieR. Attached is the text file (uploaded as a .doc as per forum requirements) which includes name, coordinates and spectral type. I haven’t checked for accuracy, but I have no reason to believe there are any major errors.
Cheers,
Paul
Hi Kate,
It sounds suspiciously like your wavelength solution is the culprit. Can you you elaborate on how you’ve performed the calibration (this is an Alpy, right?). If there was a way to share your spectral and calibration images I’d be happy to take a look in ISIS.
In the mean time, I created a guide some time ago on using ISIS’ calibration assistant that may, or may not, be useful to you:
http://jazzistentialism.com/blog/wp-content/uploads/2016/10/alpy-600-mixed.pdf
Cheers,
Paul
