Hello to those of you who are spectroscopists.
I am planning on observing a most strange star called GP Orionis, or the VSX calls it 000-BCS-326, next week.
I have been going through the spectral classes down through history starting as far back as 1943 up to 1988.
The range of spectral classes is quite long - ranging from S pec, M2, N6, SC, C pec, C8, C8-SC, SC8, SC7 to C.
The star GP Orionis is a variable star and its magnitude has been estimated by some observers here on AAVSO.
And I will be following their example when I'm free to do so.
On the VSX here on AAVSO the spectroscopist(s) have issued the following spectral class for GP Orionis: C8,0J (SC) ea.
I fully realise that SC stars are extremely rare in our galaxy. They seem to be a combination of both S-class and C class stars.
I don't know what the letter J stands for. Can someone help?
I would be delighted if one or more spectroscopists could check out GP Ori with their spectroscopes - especially as northern Orion is now in a good position in our skies.
Thank you for reading.
Clear skies from Aubrey (Gath)
Looks as though this did not get a response, and I have just noticed it. Your project is probably finished for the season, but perhaps there is some broader value in explaining things. The date range you give for the various sources of the spectral types matches what's listed in the 'B/mk' file in VizieR, which I maintain. B-)
The carbon stars have been subject to a variety of classifications schemes over the years, and as more details were recognized in the spectra, the nomenclature was adjusted to suit as the importance of various features were gradually understood. The spectrum of GP Ori evidently _does_ change to some degree, though the appearance of the spectra can vary depending on the spectral resolution. The modest variation is evident in that it was recognized early-on as having the ZrO bands that define the S class (i.e. they had to be strong), but then at other times these were absent, and it appeared to be an ordinary carbon star. The paper by Kennan & Boeshaar (1980ApJS...43..379K), which more-or-less defines the classification scheme for S and SC stars (Keenan is the 'K' of the MK system), specifically indicates only marginal ZrO and carbon bands (strength zero in their scheme). To look at the details, you'll probably want to dig out that paper (it is a very good one!).
The 'J' classification has to do with isotope ratios of C^12 and C^13 in the compound carbon molecules.
Some example spectra of all types are shown in Richard Gray's atlas at the NED site:
https://ned.ipac.caltech.edu/level5/Gray/frames.html
For the gory details and historical background, you'll have to find the book by Gray & Corbally:
https://press.princeton.edu/books/paperback/9780691125114/stellar-spectral-classification
\Brian
It ended up being covered on Cloudy Nights (with references to Brian's superb catalogue and G&C)
https://www.cloudynights.com/topic/815151-gp-orionis-mystery/
Cheers
Robin
Thanks, Robin, for the link to the 'cloudynights' discussion. The various contributors ought to prepare a summary for JAAVSO or the BAA journal with new photometry and spectra!
There is, by the way, a recent paper on astro-ph digging out new S-type stars from LAMOST spectra:
https://arxiv.org/abs/2204.06200
...which I have not examined yet.
\Brian