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Hi Matt and welcome to the BAA !
Sorry I did not get back to you on the stargazer’s lounge thread about your latest spectrum of S617b. This one is much less noisy and as you say now seems to match much better with what would be expected for a G0v star. I am not sure why it looked so much bluer than its companion in your image though. (It is hotter (compared with the late G/early K companion) but not as much as the image colour difference might suggest) Overlaying your latest spectrum of the b component over the spectrum of the a component or A comparison of B-V for the two stars should clarify the colour difference.
Precise spectral classification is a bit limited with the Star Analyser as the resolution is not really high enough (you really need around 10A resolution or higher to do this) It is not so bad at showing the difference between hot eg A stars and cool M stars but in the middle temperature range say mid F to mid K, you get hundreds of metal lines which merge at Star Analyser resolution. You can get an idea from the shape of the spectrum continuum but interstellar extinction can distort this so you have to be careful. Spectral classification is all about what lines appear and how strong they are so matching the details in the spectrum with the Pickles library can help decide what type as star is. I suggest overlaying the Pickles spectra on your spectra looking for matches in the features and general shape.
Cheers
Robin
I was able to get just 10 mins on this object with the modified ALPY 200 before the clouds rolled in last night. This is a bright target for this setup though so it was enough to get a decent low resolution spectrum (R~130). Here is my spectrum overlaid on the confirming spectrum from 14th May posted on TNS.
The Supernova identification program SNID confirms from my spectrum it is a type IIP near maximum light. There have been some significant changes in the spectrum over the past 3 days which is expected.
The blue shifted absorption component of the H alpha P Cygni profile is clear now in my spectrum and can be used to estimate the explosion velocity (~11600km/s)
Cheers
Robin
There is also a lot of background information and amateur spectra at all resolutions on VV Cep posted on the ARAS forum over the past few years.
http://www.spectro-aras.com/forum/viewforum.php?f=19
Cheers
Robin
I was clouded out by the time it got dark enough/cleared the tree line so no spectrum from here. The confirming spectrum (type IIP) on TNS is fairly featureless with a blue continuum at the moment and a small hump at H alpha.
https://wis-tns.weizmann.ac.il/object/2017eaw
This should grow into a nice strong P Cygni line profile over the next couple of weeks though.
Robin
Hi Andrew, Andy
I come across this format from time to time and it would be nice to be able to convert multispec format spectra to single orders. Storing them in the database in multispec would probably not be a good idea unless they can be output as separate orders as none of the usual amateur fits reading programs can handle them as far as I know.
I have used a very long winded approach involving dismantling the multispec files and importing them into Excel but Otmar Stahl, the professional on the German VdS spectroscopy forum, kindly converted some to separate orders for me a few years back using an IRAF script I believe. You could ask on there or if you get no joy I can try contacting him and see if he would share the script.
Cheers
Robin
Hi Tony,
Except for a mismatch in the strength of the lines, probably due to a mismatch in resolution, the disparity at the blue end does not look that obvious to me from here. What does the fractional error look like if you divide one by the other and smooth the result?
I (and others) have also found getting a good flux calibration below 4000A tough. Most of the sources of error were probably been covered in this thread.
https://britastro.org/node/9700
and Chrisitan Buil’s site covers chromatic aberration, atmospheric absorption and the effect of position on the slit
http://www.astrosurf.com/buil/dispersion/atmo.htm
I suspect the best (though time consuming) solution when after highest accuracy in the continuum shape at the blue end is to use a spectrophotometric technique using a very wide photometric slit to determine the shape of the continuum and combine that with the resolution of a narrow slit spectrum eg
http://www.astrosurf.com/buil/calibration2/absolute_calibration_en.htm
David found using a wider slit gave better results, though the reason for the improvement was not clear in this case
https://britastro.org/node/9199
Cheers
Robin
Hi Tony,
These look really good, particularly below 4000A where i had trouble getting a perfect fit. What reference star did you use to calculate the instrument response ? Did you use the same one for all the targets?
Cheers
Robin
Hi Peter,
You are getting there. The Hydrogen Balmer lines in Denebola in particular are nice and clear.
There’s no Methane in Sirius but the Hydrogen Balmer lines are visible. The H2O telluric line marked should be at an absorption line. The most obvious telluric line is the broad O2 band at ~7620, off the edge of your plot but very clear in the image you posted on “Cloudy Nights” and “StargazersLounge” forums. The other humps and bumps are from the camera’s 3 colour filters. (Monochrome cameras are better in this respect for spectroscopy)
Cheers
Robin
Hi Paul,
Yes, The way I understand it is if you are using the AOD function in ISIS to calculate and correct for atmospheric extinction then the resulting instrument response just takes into account the instrument (ie not the “IR+extinction” commonly calculated using a nearby reference star.) You are therefore correcting your spectrum in two stages, instrument response and atmospheric extinction. (I understand this is the usual technique used by professionals who know their instrument response and therefore just correct for the atmosphere for that particular observation) You can see an example of the procedure here.
http://www.astrosurf.com/buil/atmosphere/annexe.htm
EDIT: linked from
http://www.astrosurf.com/buil/atmosphere/transmission.htm
Cheers
Robin
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
