11. In the MK system, a luminosity class is added to the spectral class using Roman numerals. 12. The luminosity class cannot be determined clearly, although it has been suggested to be a supergiant. 13. The MK classification assigned each star a spectral type based on the Harvard classification and a luminosity class . 14. Classification is complex and difficult with small differences between luminosity classes and a continuous range of intermediate forms. 15. It is a dwarf ( luminosity class V ) red ( spectral class M1 ) variable by rotation. 16. The supergiant luminosity classes are due to very low surface gravities on pulsating low-mass and rarefied stars. 17. With a stellar classification of G8 IV, the luminosity class of IV indicates this is a subgiant star. 18. The luminosity class sub-type Vz is defined uniquely for O stars, specifically types O3 to O8. 19. It forms a pair with a star of type B9 with an unknown luminosity class separated by 0.28 arcseconds. 20. This star has a stellar classification of G5, making it a G-type star with an undetermined luminosity class .
