Orion Sword variables spectral types

     Another one not quite VSX related.  I am presently going over the classic Parenago catalogue of stars in the Orion Sword region.  Much of the Orion literature uses these numbers to identify stars (especially pre-GAIA etc).  There is a rough catalogue of the 3000 entries available in machine-readable form from VizieR, but it shows only approximate coordinates for the stars, and little else from the original 500-page monograph.  Only maybe half of the stars have accurate coordinates in SIMBAD.  I am working from a very good list made some 15 years ago by star-chart expert Mati Morel in Australia.  Anyway, as part of the revision, I am having a look at LAMOST spectra for stars that appear there.  (The LAMOST DR4 spectra are available through VizieR.)  This shows that many of the spectral types in VSX (harvested from the literature) are wrong.  VSX indeed copies the literature faithfully, but often the types were estimated in the blue part of the spectrum, traditionally from about 3800A to 5000A.  However, the spectra of later-type stars, typically early-M variables of the T Tauri type, are veiled by what is assumed to be hot gas surrounding the stars (in the accretion disc etc) that ends up making the blue spectra look like an earlier class.  George Herbig and others recognized this even 60 years ago, so this is not new.

     The LAMOST spectra run from about 3700A out to 9000A, thus covering the entire visible and far-red region.  Some of the spectra are faulty in various ways, but usually they are suitable for classification if the signal-to-noise is adequate.  The veiling is much weaker in the far-red, and in the professional literature nowadays the classifying of late-type stars is done from the TiO bands in the far-red.  An example is V500 Ori, which was classified in a 1983 paper by Merle Walker from a blue spectrum as K2:Ve (1983ApJ...271..642W), which is what VSX shows.  The LAMOST spectrum in the blue is consistent with this.  However, the star shows strong TiO bands in the far-red, so it is not a K star.  My estimate is M2/3Ve (i.e. a somewhat uncertain temperature type between M2 and M3).  There is emission in the Balmer lines and CaII H&K in the violet (the latter certainly not from the overlying nebulosity).

     Among ordinary stars one would normally conclude that divergent spectral types in the blue-violet and far-red indicate a spectroscopic binary with hotter/cooler components.  But I have so far seen only one such obvious to me in the Parenago list.  This is V374 Ori, which VSX shows as GCVS variable-type 'IN', and only H-alpha emission reported in the spectrum (from Guillermo Haro's early H-alpha survey in the early 1950s).  The star has been recently identified as a cv, and the LAMOST spectrum shows the unmistakable very broad Balmer lines of a white dwarf in the blue (with sharp emission cores), and the TiO bands of an M1 dwarf in the far-red.  Wow!  Interestingly, the GAIA parallax places the cv at the distance of the Orion Nebula (380 pc).  The system cannot be as young as this implies, and must be unrelated but at a similar distance.

     I'm getting close to the end of the work, which I'll supply to Sebastian and others --- hopefully to end up at VizieR so that it can become generally available.

\Brian