Plate 12: Strong Helium Stars in the Orion Association

Star Index

Plate 12: Strong Helium Stars in the Orion Association

There are three stars in the Orion Association whose spectra contain exceedingly strong lines of He I; they are: (1) HR 1890 = HD 37017, (2) HR 1851 = δ Ori (ft) and (3) HR 1932 = σ Ori E. Their V magnitudes (Crawford–Lesh) are 6.57, 6.86 and 6.66, respectively, and their B–V colors are almost identical. Two of these stars are illustrated below, together with HR 1891 (B2.5V), a neighbor to HR 1890. Nine members of the 23P0–n3D series of He I are marked above HR 1890. The higher members of this series appear to be systematically weaker in HR 1851 than in HR 1890.

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