S617 and a question on how to proceed

[Matthew Jenkins]

Hi All,

First post as a new BAA member :). I recently took a StarAnalyser spectrum of the double star S617 in Leo, as well as a colour image and posted on SGL, where Robin kindly commented and pointed out that the spectrum for the secondary star in the system didn’t look right compared with the Vizier catalog for the single spectrum recorded there for that star.

https://stargazerslounge.com/topic/289163-s617-triple-star-work-to-do/?page=1

I did a subsequent SA200 followup spectrum for just that secondary which did resemble it more, but wondered how to use this as a project to practice some spectral work/photometry. I am planning on a LHiresIII next year as I am certainly hooked, but wondered if a B-V reading and other types of observations would help me in my classification project?

Thanks

Matt

[Robin Leadbeater]

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

[Andy Wilson]

Hi Matt,

First of all welcome to the BAA 🙂

Robin has already given you some excellent advice on spectral typing so I won’t bother adding any more.

I own an Lhires III and I find it an excellent spectrograph. It took me several months of practice to get to know it well and tweak its performance, but I was able to get good spectra of bright stars very quickly. While a star analyser is great to start off with, as well as always being a good tool for fainter targets, there are some things that will be easier with the Lhires III. For example wavelength calibration, flat fielding and simply having a slit removes the potential problem of nearby stars contaminating a slitless spectrum. Though of course you do need a good mount to be able to position the star onto the slit and to hold it there accurately.

Best wishes,

Andy

[Matthew Jenkins]

Thanks both. I will give what you suggest a go and get learning!

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