1. Adam F., Lada C., Shu F., Astrophys. J. 312, 788 (1987);
2. André P., Montmerle T., ibid. 420, 837 (1994);
3. ; review by
4. Shu F., Adams F., Lizano S., Annu. Rev. Astron. Astrophys. 25, 23 (1987).
5. The HR diagram is a plot of stellar luminosity versus temperature. The effective temperature ( T eff ) of a star is equivalent to its spectral type which can be determined from the appearance and strength of absorption lines in the spectrum of the star. The sequence of spectral types OBAFGKM runs from massive hot O stars to low-mass cold M stars. The position on the vertical axis in the HR diagram is given as luminosity Class from I for supergiants (large surface very luminous) to VI for small subdwarfs. Each spectral type is subdivided by arabic numbers for example a G2.5V star (such as 16 Cyg) is slightly colder than our sun (type G2V = 5780 K effective surface temperature). See Fig. 1 for an HR diagram.