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Hi Kevin,
I think the “type wrong” is Brian Skiffs comment against the reference. G8III and K0III are very close but your K0III reference (and your own confirming spectrum of course !) is missing from Brian’s catalogue so it could be worth letting him know so he can add it.
Here’s another oddity currently under investigation (BD-1 2458 referenced as G0v in the literature but clearly much hotter from a preliminary spectrum). Even visually the colour looks obviously wrong for the catalogued classification so it is not clear what is going on here.
https://stargazerslounge.com/topic/289163-s617-triple-star-work-to-do/
Robin
It sounds like the prnu map which ISIS uses. For ISIS this is generated separately, illuminating the sensor disconnected from the instrument
http://www.astrosurf.com/buil/isis/eshel/reduction/echelle.htm
Cheers
Robin
Hi Andrew,
Ok it would need to be observations going forward then. I can take two sets of flats in future for anything that might be suitable. Probably best not to depend on me short term though as I am back to the ALPY 200 supernova hunting setup currently which is not the most typical of applications.
Cheers
Robin
Hi Andrew,
Are the low and high ADU flats conventional imaging or spectroscopic flats? The reason I ask is my individual ALPY spectroscopic flats for example can typically range from a few hundred to a few tens of thousand ADU even within the flat due to the instrument response and lamp spectrum. If they are conventional imaging flats I could perhaps take a few of these to supplement my test data set of MILES stars posted on here for you to test.
Cheers
Robin
I have had IRAF sitting installed on a spare laptop running Linux Ubuntu for some time, waiting for me to pluck up enough courage to dive in and start using it. This could be the spur I need. I must admit I find the prospect rather daunting though. It is a long time since I used command line programs!
Thinking about it though, I guess in planetary imaging where focal ratios are invariably very high it is not so much of a problem
Robin
This look pretty good value as a couple of decent wedge prism eg from Edmund Optics alone would be close to this figure. This arrangement though would generate astigmatism placed in a converging beam wouldn’t it? Shouldn’t there ideally be some form of collimator ?
Robin
Hi Alun,
The ALPY600 is an impressive tool for measuring active galaxy redshifts. For example Etienne Bertrand has found it is possible to get down to mag 15-16 on active galaxy and QSO with a C8 scope. You might be interested in his growing collection that he has been reporting on the ARAS forum here.
http://www.spectro-aras.com/forum/viewforum.php?f=6
His latest ( QSO 1247+267 at z=2 and V mag 16) is here
http://www.spectro-aras.com/forum/viewtopic.php?f=6&t=1663&p=7726
Cheers
Robin
Also some additional comments here which might be useful where a change to 256 colours was needed
http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=1660
Robin
Hi Peter,
The shape of your spectrum looks different from the one in the library because your spectrum is not corrected for the response of your instrument or the absorption of the atmosphere. You can see an example of this for the Star Analyser in the VSpec tutorial lesson 5 here
http://www.astrosurf.com/vdesnoux/tutorial5.html
You can also see the same process in my BAA Workshop presentations
http://www.threehillsobservatory.co.uk/astro/spectroscopy_10.htm
Cheers
Robin
You should try keeping a flip top dry! The moisture condenses on the inside of the open roof and can even rain down on the gear when you close it up. I run a dehumidifier 24/7 (with a tubular heater when it is below freezing), though apart from after I close up, it never seems to be running when I go back to it. The observatory volume is very small though!
http://www.threehillsobservatory.co.uk/astro/observatory/observatory_C11_LHIRES_feb_2010.jpg
Hi Andrew,
Yes the effect of atmospheric dispersion (particularly if combined with CA) is well known in amateur spectra too eg
http://www.astrosurf.com/buil/dispersion/atmo.htm
but that does not seem to explain this case where the results were ok when the seeing was better, unless the target was also higher in the sky or the location was such that the parallactic angle fortuitously aligned better with the slit
Cheers
Robin
Hi David,
I am not sure I follow this. I can understand how the wavelength dependency of the Airy disc size due to diffraction could potentially cause this effect in a diffraction limited situation but in your setup I would expect this to small compared with the slit width and the seeing. Also the atmospheric effects which affect seeing and atmospheric dispersion are due to refraction, so wouldn’t they reduce with increasing wavelength? Comparing the star FWHM from photometric B and I band measurements could be interesting. Do you know if that this affect on seeing is seen there ?
Robin
Hi Tony,
I forgot about that. In fact it was me who asked for it !
http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=516#p1829
It was added in v5.1.3
http://www.astrosurf.com/buil/isis/new/release.html
Cheers
Robin
I am wondering if using the AOD technique to do a second order extinction correction coupled with our standard reference star technique as a first order correction might be useful, reducing the need to chose the reference star precisely at the same elevation as the target. ie The MILES star need not then be at the same elevation, as the effect of the difference in air mass is calculated separately using a typical AOD.
Robin
Hi Paul,
Yes it is described in part 4 of the link I posted above.
http://www.astrosurf.com/buil/calibration2/absolute_calibration_en.htm
It seems to be what the pro I talked to was suggesting too. ie separating out the instrument response (which is presumed stable so measured infrequently) and extinction (measured on the night and adjusted for air mass using the AOD)
Cheers
Robin
Hi Andrew,
Yes I agree, this is an area which definitely needs more consideration. Even Pro-Am campaigns are rarely specified beyond a SNR figure and in most cases I suspect these sort of systematic errors are much greater than the stochastic ones that SNR estimates, and much harder to quantify. These problems are not confined to amateur observations and databases either. For example the continuum of the ELODIE Vega spectrum originally incorporated into ISIS and which has probably used to correct hundreds of spectra in BeSS, is significantly in error.
http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=1369#p6205
and the Indo-US library spectra sometimes suggested as reference stars have a completely synthetic continuum based on Pickles
http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=1582
Cheers
Robin
Hi Tony,
I have only a couple in BeSS (I also have a few BeSS candidate spectra but those stars are not in BeSS yet)
They are also in the BAA database so you can pick them up there. Note that the V361 Per spectrum there is as I submitted it to BeSS but the BD+55521 is the version outputted by BeSS so has extra fields in the header which BeSS adds.
They are both very noisy but my excuse is they are high resolution spectra at mag 10 so a bit of a challenge.
Cheers
Robin
Hi Tony,
I need to think about doing it that way as I think ISIS normally does some internal rescaling rather than outputting in ADU counts so the final spectra may not subtract correctly. (you would need to test this) What I was proposing is to produce a single pre processed spectrum image manually with the dark, flat correction and the sky image subtracted already, ready for processing in ISIS without any further dark, flat bias correction or background subtraction to produce the spectrum profile but ISIS may then complain if it is not given any master dark or bias frames.
It seems this might not be as straightforward in ISIS as I thought. Perhaps putting the question on ARAS might be a better bet. Francois Teyssier there would know how to do it in practise.
Cheers
Robin
