ABSTRACT
We have seen in the previous chapter how the interpretation of data associated with visual binaries and astrometric techniques have enhanced knowledge of stellar physics. In this chapter we concentrate on the application of the parallel, but rather separate, techniques of stellar spectroscopy to stars in relatively close proximity. The role of spectral lines is prominent in this context. Although this is a big subject of study in its own right, well beyond the compass of this book, it will be taken as understood that the distribution of radiation with wavelength in the light coming from stars consists of a smoothly varying continuum, interrupted here and there by sudden and short variations of flux – lines – that can be above or below the continuum level, but usually the latter for our context. In some (‘cool’) stars, groups of lines are so plentiful and close together that they appear as bands: formations associated with the properties of atoms bonded together as molecules, rather than single atoms or ions of a particular element. There are also places in the spectrum where the entire continuum changes suddenly: spectral discontinuities, the most familiar of which is probably the Balmer discontinuity at 364.6 nm, in the near ultra-violet. But it is the properties of spectral lines – in particular their positions and shapes – that are most relevant to the themes of this book.
