Spectroscopic parallax
Encyclopedia
Spectroscopic parallax is an astronomical method for measuring the distances to stars. Despite its name, it does not rely on the apparent change in the position of the star (see parallax
). This technique can be applied to any main sequence
star for which a spectrum
can be recorded. The method depends on the star being sufficiently bright to provide a measurable spectrum, which currently limits its range to about 10,000 parsec
s.
To apply this method, one must measure the apparent magnitude
of the star and know the spectral type of the star. If the star lies on the main sequence, 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) of the star using
(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 absolute magnitude - spectral type relationship.
The method ultimately derives from the spectroscopic studies of sunspots and stars by Walter Sydney Adams
and Ernst Arnold Kohlschütter.
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...
). This technique can be applied to any main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...
star for which a spectrum
Astronomical spectroscopy
Astronomical spectroscopy is the technique of spectroscopy used in astronomy. The object of study is the spectrum of electromagnetic radiation, including visible light, which radiates from stars and other celestial objects...
can be recorded. The method depends on the star being sufficiently bright to provide a measurable spectrum, which currently limits its range to about 10,000 parsec
Parsec
The parsec is a unit of length used in astronomy. It is about 3.26 light-years, or just under 31 trillion kilometres ....
s.
To apply this method, one must measure the apparent magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
of the star and know the spectral type of the star. If the star lies on the main sequence, the spectral type of the star provides a good estimate of the star's absolute magnitude
Absolute magnitude
Absolute magnitude is the measure of a celestial object's intrinsic brightness. it is also the apparent magnitude a star would have if it were 32.6 light years away from Earth...
. Knowing the apparent magnitude (m) and absolute magnitude (M) of the star, one can calculate the distance (d) of the star using
(see distance modulusDistance modulus
-Definition:The distance modulus \mu=m-M is the difference between the apparent magnitude m and the absolute magnitude M of an astronomical object...
). 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 absolute magnitude - spectral type relationship.
The method ultimately derives from the spectroscopic studies of sunspots and stars by Walter Sydney Adams
Walter Sydney Adams
Walter Sydney Adams was an American astronomer.-Life and work:He was born in Antioch, Syria to missionary parents, and was brought to the U.S. in 1885 He graduated from Dartmouth College in 1898, then continued his education in Germany...
and Ernst Arnold Kohlschütter.
See also
- Photometric parallax methodPhotometric parallax methodThe photometric parallax method is a method of data analysis used in astronomy that uses the colours and apparent brightnesses of stars to infer their distances...
- Dynamical parallaxDynamical ParallaxIn astronomy, the distance to a visual binary star may be estimated from the masses of its two components, the size of their orbit, and the period of their revolution around one another...