A tale of inconsistently catalogued spectral type

[Kevin Gurney]

In my efforts to capture some main sequence stars as a starting project, I  recently targetted HD120787. In Deep Sky Planner 7.0, this was given as G3V. I was disappointed and puzzled when, even after several attempts at instrument response correction, it didn’t look much like such a beast. I then dug down a bit using Simbad and Vizier with some interesting results… In the simple Simbad search, it also lists this star as of type G3V. However, looking at other catalogues it cites K0. I followed up one of the papers on Simbad (Willmarth et al., Astro. J., 2016) who note that “Takeda et al. (2008) …. determined its effective temperature  and gravity, which correspond to a K0 III”

So, attached, is my spectrum alongside relevant Pickles references (there is apparently no G3V a such, so G2V sufficed). I was pleased to see a close match to the K0III !

So moral is – don’t believe what the catalogues say! 🙂

Kevin

Attachments:

1. 

   hd_120787_compare.png
   

[Andy Wilson]

Hi Kevin,

That is a nice looking spectrum and an interesting story to go with it. A good example that you can get unexpected results with spectroscopy and by digging around in the literature lots of useful and interesting information can be found.

You are getting some great results with your ALPY.

Cheers,

Andy

[Dr Andrew Smith]

I think it is quite common for there to be several “options” for the spectral class. It seems that it is as much art as science to the process. The VizeirR access to Catalogue of Stellar Spectral Classifications (Skiff, 2009-2016) is where I always go.

Regards Andrew

[Kevin Gurney]

Thanks for the link Andrew – looks handy..

However, in this instance, the entry is intriguing… One catalogue gives G8III and another, G3V, but with a remark ‘type wrong’: I can vouch for that 🙂

cheers

Kevin

[Robin Leadbeater]

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

[Author]

Posts