Spectroscopic parallax

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Spectroscopic parallax is an astronomical method for measuring the distances to stars. Despite its name, it does not rely on the geometric parallax effect. 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 as of 2013 limits its range to about 10,000 parsecs. [1]

Parallax difference in the apparent position of an object viewed along two different lines of sight

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. Due to foreshortening, nearby objects show a larger parallax than farther objects when observed from different positions, so parallax can be used to determine distances.

Main sequence A continuous band of stars that appears on plots of stellar color versus brightness

In astronomy, 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. Stars on this band are known as main-sequence stars or dwarf stars. These are the most numerous true stars in the universe, and include the Earth's Sun.

Astronomical spectroscopy science of temporal, spatial, and spectral distributions of radiation

Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the spectrum of electromagnetic radiation, including visible light and radio, which radiates from stars and other celestial objects. A stellar spectrum can reveal many properties of stars, such as their chemical composition, temperature, density, mass, distance, luminosity, and relative motion using Doppler shift measurements. Spectroscopy is also used to study the physical properties of many other types of celestial objects such as planets, nebulae, galaxies, and active galactic nuclei.

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 (see distance modulus). The true distance to the star may be different than the one calculated due to interstellar extinction. [2]

Apparent magnitude measure of brightness for celestial objects

Apparent magnitude is a measure of the relative brightness of a star or other astronomical object as seen by an observer. An object's apparent magnitude depends on its intrinsic luminosity, its distance from the observer, and any extinction of the object's light by interstellar dust along the line of sight to the observer.

Absolute magnitude is a measure of the luminosity of a celestial object, on an inverse logarithmic astronomical magnitude scale. An object's absolute magnitude is defined to be equal to the apparent magnitude that the object would have if it were viewed from a distance of exactly 10.0 parsecs, without extinction of its light due to absorption by interstellar matter and cosmic dust. By hypothetically placing all objects at a standard reference distance from the observer, their luminosities can be directly compared on a magnitude scale.

The distance modulus is a way of expressing distances that is often used in astronomy. It describes distances on a logarithmic scale based on the astronomical magnitude system.

The method ultimately derives from the spectroscopic studies of sunspots and stars by Walter Sydney Adams and Ernst Arnold Kohlschütter. [3]

Walter Sydney Adams American astronomer

Walter Sydney Adams was an American astronomer.

See also

The 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. It was used by the Sloan Digital Sky Survey to discover the Virgo super star cluster.

In 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 orbit about one another. A dynamical parallax is an (annual) parallax which is computed from such an estimated distance.

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Rigel star in the constellation Orion

Rigel, designated β Orionis, is generally the seventh-brightest star in the night sky and the brightest star in the constellation of Orion. Its brightness varies slightly, and it is occasionally outshone by Betelgeuse, itself a semi-regular variable star. Rigel looks blue-white to the naked eye, contrasting with orange-red Betelgeuse. Although appearing as a single star to the naked eye, Rigel is actually a multiple star system composed of at least four stars: Rigel A, Rigel Ba, Rigel Bb, and Rigel C.

Luminosity total amount of energy emitted by an object per unit time

In astronomy, luminosity is the total amount of energy emitted per unit of time by a star, galaxy, or other astronomical object. As a term for energy emitted per unit time, luminosity is synonymous with power.

A visual binary is a gravitationally bound system that can be resolved into two stars. These stars are estimated, via Kepler's 3rd law, to have periods ranging from a number of years to thousands of years. A visual binary consists of two stars, usually of a different brightness. Because of this, the brighter star is called the primary and the fainter one is called the companion. If the primary is too bright, relative to the companion, this can cause a glare making it difficult to resolve the two components. However, it is possible to resolve the system if observations of the brighter star show it to wobble about a centre of mass. In general, a visual binary can be resolved into two stars with a telescope if their centres are separated by a value greater than or equal to one arcsecond, but with modern professional telescopes, interferometry, or space-based equipment, stars can be resolved at closer distances.

Stellar parallax apparent shift of position of a nearby star against the background of distant objects during Earths orbital period

Stellar parallax is the apparent shift of position of any nearby star against the background of distant objects. Created by the different orbital positions of Earth, the extremely small observed shift is largest at time intervals of about six months, when Earth arrives at exactly opposite sides of the Sun in its orbit, giving a baseline distance of about two astronomical units between observations. The parallax itself is considered to be half of this maximum, about equivalent to the observational shift that would occur due to the different positions of Earth and the Sun, a baseline of one astronomical unit (AU).

Cosmic distance ladder succession of methods by which astronomers determine the distances to celestial objects

The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. A real direct distance measurement of an astronomical object is possible only for those objects that are "close enough" to Earth. The techniques for determining distances to more distant objects are all based on various measured correlations between methods that work at close distances and methods that work at larger distances. Several methods rely on a standard candle, which is an astronomical object that has a known luminosity.

Magnitude (astronomy) logarithmic measure of the brightness of a celestial object, in astronomy

In astronomy, magnitude is a unitless measure of the brightness of an object in a defined passband, often in the visible or infrared spectrum, but sometimes across all wavelengths. An imprecise but systematic determination of the magnitude of objects was introduced in ancient times by Hipparchus.

Alpha Tucanae star in the constellation Tucana

Alpha Tucanae is a binary star system in the southern circumpolar constellation of Tucana. With an apparent visual magnitude of 2.86, it can be seen with the naked eye from the southern hemisphere. Using parallax measurements, the distance to this system can be estimated as 200 light-years. A cool star with a surface temperature of 4300 K, it is 424 times as luminous as the sun and 37 times its diameter. It is 2.5 to 3 times as massive. It is unclear what stage of evolution the star is in.

VV Cephei binary star in the constellation Cepheus

VV Cephei, also known as HD 208816, is an eclipsing binary star system located in the constellation Cepheus, approximately 5,000 light years from Earth. It is both a B[e] star and shell star.

HD 895 is a multiple star system in the constellation Andromeda. Its apparent magnitude is 6.277, so it can be seen by the naked eye under very favourable conditions. Based on parallax measured by Hipparcos, the system is located around 54 parsecs (180 ly) away, and it's made of two different spectroscopic binary pairs.

HD 153261 is the Henry Draper Catalogue designation for a star in the southern constellation of Ara. It has an apparent visual magnitude of 6.137, placing it near the threshold of naked eye visibility. According to the Bortle Dark-Sky Scale, it can be viewed from dark suburban or rural skies. Based upon an annual parallax shift of just 2.32 mas, it is located at a distance of around 1,400 light-years from Earth.

Hertzsprung–Russell diagram A scatter plot of stars showing the relationship between the stars absolute magnitudes or luminosities versus their stellar classifications

The Hertzsprung–Russell diagram, abbreviated as H–R diagram, HR diagram or HRD, is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their stellar classifications or effective temperatures. More simply, it plots each star on a graph plotting the star's brightness against its temperature (color).

HD 108063 is a star that lies approximately 176 light-years away in the constellation of Centaurus. The star is not particularly noteworthy with exception to its enormously high heavy element content.

66 Eridani is a binary star in the constellation of Eridanus. The combined apparent magnitude of the system is 5.12 on average. Parallax measurements by Hipparcos put the system at some 309 light-years away.

36 Tauri is a binary star in the constellation of Taurus. Parallax measurements made by the Hipparcos spacecraft put it at a distance of over 1,000 light years from Earth. The combined apparent magnitude of the system is about 5.5, meaning it can barely be seen with the naked eye, according to the Bortle scale.

DS Andromedae

DS Andromedae is an eclipsing binary star in the constellation Andromeda and a member of the open cluster NGC 752. Its maximum apparent visual magnitude is 10.44, but drops down to 10.93 during the main eclipse and to 10.71 during the secondary one.

BB Phoenicis is a variable star in the constellation of Phoenix. It has an average visual apparent magnitude of 6.17, being visible to the naked eye with excellent viewing conditions. From parallax measurements by the Gaia spacecraft, it is located at a distance of 448 light-years from Earth. Its absolute magnitude is calculated at 0.6.

References

  1. ↑ "Stellar Distances". European Space Agency . 2013-05-14. Retrieved 2014-09-23.
  2. ↑ Michael A. Seeds; Dana Backman (14 September 2016). Horizons: Exploring the Universe. Cengage Learning. pp. 152–. ISBN   978-1-337-51578-8.
  3. ↑ Virginia Trimble; Thomas R. Williams; Katherine Bracher; Richard Jarrell; Jordan D. Marché; F. Jamil Ragep (18 September 2007). Biographical Encyclopedia of Astronomers. Springer Science & Business Media. pp. 648–. ISBN   978-0-387-30400-7.
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