Spectroscopic parallax

To apply this method, one must measure the apparent magnitude of the star and know the spectral type of the star. The spectral type can be determined by observing the star's spectrum. If the star lies on the main sequence, as determined by its luminosity class, the spectral type of the star provides a good estimate of the star's absolute magnitude. Knowing the apparent magnitude (m) and absolute magnitude (M) of the star, one can calculate the distance (d, in parsecs) of the star using m - M = 5 \log (d/10) (see distance modulus). The true distance to the star may be different than the one calculated due to interstellar extinction. While the method of trigonometric parallax provides accurate distances without underlying astrophysical assumptions, it is limited to distances of less than 500-1000 parsecs by current technology. Within the volume measurable by trigonometry are numerous main sequence stars that can be used to calibrate the relationship between absolute magnitude and spectral type.

The method ultimately derives from the spectroscopic studies of sunspots and stars by Walter Sydney Adams and Ernst Arnold Kohlschütter.

The method is an important step on the cosmic distance ladder.

References

References

1. (2017). "An introduction to modern astrophysics".
2. (18 September 2007). "Biographical Encyclopedia of Astronomers". Springer Science & Business Media.
3. (2013-05-14). "Stellar Distances".
4. (14 September 2016). "Horizons: Exploring the Universe". Cengage Learning.