17.3 The Spectra of Stars (and Brown Dwarfs)
4 min read•june 12, 2024
Stellar spectra reveal a star's secrets through its light. Temperature plays a crucial role, determining which appear. Cooler stars show more lines, while hotter stars have fewer. This pattern helps astronomers classify stars into spectral types.
From the hottest to the coolest Y-type , each has unique characteristics. These classifications help us understand a star's composition, temperature, and evolutionary stage. blur the line between stars and planets, adding complexity to our cosmic understanding.
Stellar Spectra and Classification
Temperature effects on absorption lines
Top images from around the web for Temperature effects on absorption lines
The Spectra of Stars (and Brown Dwarfs) | Astronomy View original
Is this image relevant?
The Spectra of Stars (and Brown Dwarfs) | Astronomy View original
Is this image relevant?
17.4 Using Spectra to Measure Stellar Radius, Composition, and Motion | Astronomy View original
Is this image relevant?
The Spectra of Stars (and Brown Dwarfs) | Astronomy View original
Is this image relevant?
The Spectra of Stars (and Brown Dwarfs) | Astronomy View original
Is this image relevant?
1 of 3
Top images from around the web for Temperature effects on absorption lines
The Spectra of Stars (and Brown Dwarfs) | Astronomy View original
Is this image relevant?
The Spectra of Stars (and Brown Dwarfs) | Astronomy View original
Is this image relevant?
17.4 Using Spectra to Measure Stellar Radius, Composition, and Motion | Astronomy View original
Is this image relevant?
The Spectra of Stars (and Brown Dwarfs) | Astronomy View original
Is this image relevant?
The Spectra of Stars (and Brown Dwarfs) | Astronomy View original
Is this image relevant?
1 of 3
- Surface temperature of a star determines the appearance of absorption lines in its spectrum
- Atoms in the star's outer layers absorb specific wavelengths of light forming absorption lines
- Strength and presence of absorption lines vary with temperature
- Cooler stars like have more absorption lines in the visible spectrum
- Lower temperatures allow atoms to remain in lower energy states resulting in more absorption
- Hotter stars like have fewer absorption lines in the visible spectrum
- Higher temperatures excite atoms to higher energy states reducing the number of atoms available for absorption
- The strongest absorption lines correspond to the most abundant elements in the
- lines prominent in stars with temperatures around 10,000 K (spectral type A)
- lines strong in stars with temperatures around 6,000 K (spectral type G)
Characteristics of spectral classes
- Stars are assigned based on surface temperatures and spectral features
- Classes arranged in decreasing temperature order: O, B, A, F, G, K, M, L, T, Y
- O-type stars are the hottest with surface temperatures exceeding 30,000 K
- Appear blue with few visible spectrum absorption lines
- Prominent lines include ionized (He II) and highly ionized metals
- have surface temperatures between 10,000-30,000 K
- Appear blue-white with strong hydrogen and neutral helium (He I) lines
- have surface temperatures between 7,500-10,000 K
- Appear white with the strongest hydrogen among all classes
- have surface temperatures between 6,000-7,500 K
- Appear yellow-white with weaker hydrogen lines and more prominent calcium (Ca II) lines
- like our Sun have surface temperatures between 5,000-6,000 K
- Appear yellow with strong calcium (Ca II) and many metal lines
- have surface temperatures between 3,500-5,000 K
- Appear orange with strong metal lines and weak hydrogen lines
- are the coolest main-sequence stars with surface temperatures below 3,500 K
- Appear red with strong molecular bands like in their spectra
- are cool, low-mass stars and brown dwarfs with temperatures between 1,300-2,500 K
- Spectra dominated by metal hydride bands and alkali metal lines
- are cool brown dwarfs with temperatures between 700-1,300 K
- Spectra dominated by absorption bands
- are the coolest known brown dwarfs with temperatures below 700 K
- Spectra characterized by absorption features
Brown dwarfs vs planets
- Brown dwarfs and planets distinguished by mass and ability to sustain fusion reactions
- Brown dwarfs have masses between ~13-80
- Massive enough to fuse (heavy hydrogen) in their cores
- Not massive enough to sustain regular hydrogen fusion
- fusion provides temporary energy but once depleted, brown dwarf cools and contracts
- Planets have masses below the deuterium-burning limit (~13 Jupiter masses)
- Insufficient mass to sustain any type of core fusion reaction
- Form through accretion of material in a protoplanetary disk around a young star
- Boundary between the most massive planets and least massive brown dwarfs is unclear
- Objects with masses close to 13 Jupiter masses may be called "" or ""
- Brown dwarfs and planets have overlapping temperature ranges
- Coolest brown dwarfs (Y-type) have temperatures comparable to some planetary atmospheres
- Distinguishing them requires mass measurements or observations of their formation environments
Radiation and Stellar Spectra
- Stars emit , a of electromagnetic radiation
- relates a star's surface temperature to the peak wavelength of its emission
- The stellar atmosphere, a layer of gases surrounding the star, affects the observed spectrum
- of the atmosphere determines which wavelengths of light can escape
- of atoms in hot stellar atmospheres influences spectral features
- Stellar spectra consist of a with superimposed absorption or
- Absorption lines form when cooler outer layers absorb specific wavelengths
- Emission lines can appear in certain conditions, such as in very hot or active stars
Key Terms to Review (45)
A-type stars: A-type stars are a class of main-sequence stars that have surface temperatures ranging from 7,500 to 10,000 Kelvin, making them appear blue-white in color. They are characterized by their strong hydrogen absorption lines in their spectra, which is a defining feature of this stellar classification.
Absorption Lines: Absorption lines are dark lines that appear in the spectrum of a star or other celestial object, representing wavelengths of light that have been absorbed by atoms or molecules in the object's atmosphere. These lines provide valuable information about the chemical composition and physical properties of the object.
Ammonia: Ammonia is a colorless, pungent gas that is composed of one nitrogen atom and three hydrogen atoms. It is a key compound in the study of astronomy, particularly in the context of the atmospheres of the giant planets and the spectra of stars and brown dwarfs.
B-type Stars: B-type stars are a class of hot, luminous stars that are characterized by their blue-white appearance and high surface temperatures. These stars are an important component of the stellar population and play a significant role in the study of stellar spectra and the evolution of stars.
Balmer lines: Balmer lines are a series of spectral line emissions of hydrogen that occur when an electron transitions from a higher energy level (n > 2) to the n=2 energy level. They are prominent in astronomical spectroscopy and are used to identify and analyze stars' compositions and properties.
Balmer Lines: Balmer lines are a series of spectral lines in the visible region of the electromagnetic spectrum that are produced by the transitions of hydrogen atoms from higher energy levels to the second energy level. These lines are named after the Swiss physicist Johann Balmer, who discovered the mathematical formula that describes this pattern of spectral lines.
Blackbody Radiation: Blackbody radiation is the thermal electromagnetic radiation emitted by a perfect absorber and emitter of radiation, known as a blackbody. It is a fundamental concept in understanding the relationship between the temperature of an object and the spectrum of radiation it emits, which is crucial in various fields of astronomy, including the study of the electromagnetic spectrum, spectroscopy, and the formation of spectral lines.
Blue Giants: Blue giants are a class of extremely luminous, hot, and massive stars that appear blue in color due to their high surface temperatures. These stars are among the most massive and energetic objects in the universe, producing copious amounts of ultraviolet radiation and stellar winds.
Brown dwarfs: Brown dwarfs are celestial objects that are too large to be planets but not massive enough to sustain hydrogen fusion in their cores like true stars. They occupy the mass range between the heaviest gas giant planets and the lightest stars.
Brown Dwarfs: Brown dwarfs are substellar objects that are too large to be considered planets, yet not massive enough to sustain the nuclear fusion reactions that power stars. They occupy the mass range between the heaviest gas giant planets and the lightest stars, bridging the gap between these two celestial bodies.
Calcium: Calcium is a chemical element that is essential for the proper functioning of the human body. It is a key component of bones and teeth, and also plays important roles in muscle contraction, nerve function, and blood clotting.
Cannon: Annie Jump Cannon was an American astronomer who significantly contributed to the development of stellar classification. She cataloged over 350,000 stars and developed the Harvard Classification Scheme.
Continuous spectrum: A continuous spectrum is a range of emitted radiation that contains all wavelengths within a specific range. It appears as a smooth gradient of colors without any gaps or lines.
Continuous Spectrum: A continuous spectrum is a type of electromagnetic spectrum that consists of a continuous range of wavelengths or frequencies, without any distinct gaps or lines. It is often associated with the emission or absorption of light by hot, dense objects, such as stars or the Sun.
Deuterium: Deuterium is an isotope of hydrogen with one proton and one neutron in its nucleus. It is also known as heavy hydrogen due to its greater mass compared to protium, the most common hydrogen isotope.
Deuterium: Deuterium, also known as heavy hydrogen, is a stable isotope of hydrogen with one proton and one neutron in the nucleus, compared to the more common hydrogen isotope which has only one proton. Deuterium plays a significant role in the context of mass, energy, and the theory of relativity, the spectra of stars and brown dwarfs, as well as the beginning of the universe.
Emission Lines: Emission lines are distinct, narrow bands of light observed in the spectrum of an object, such as a star or a gas cloud. These lines are produced when electrons in atoms or molecules transition from higher energy levels to lower energy levels, emitting photons with specific wavelengths in the process.
F-type Stars: F-type stars are a class of main-sequence stars that have surface temperatures ranging from 6,000 to 7,500 Kelvin, making them appear yellowish-white in color. These stars are more luminous and hotter than our Sun, which is a G-type star, but cooler and less luminous than the hotter, bluer A-type and B-type stars.
Fleming: Fleming was a pioneering astronomer known for her groundbreaking work in stellar spectroscopy. She made significant contributions to the classification of stars based on their spectral characteristics.
Fraunhofer: Fraunhofer lines are dark absorption lines in the solar spectrum, named after the German physicist Joseph von Fraunhofer. They result from specific wavelengths of light being absorbed by elements in the Sun's atmosphere.
G-type Stars: G-type stars, also known as yellow dwarfs, are a class of main-sequence stars that are similar to our Sun in terms of size, temperature, and luminosity. These stars are characterized by their yellow-white color and are the most common type of stars in the Milky Way galaxy.
Helium: Helium is a colorless, odorless, and inert gas that is the second most abundant element in the universe, after hydrogen. It is a crucial component in various scientific and technological applications, as well as in the understanding of the universe and the evolution of stars and planets.
Huggins: William Huggins was a pioneering astronomer who used spectroscopy to analyze the composition of stars and nebulae. His work laid the foundation for understanding stellar spectra and chemical makeup in astronomy.
Hydrogen: Hydrogen is the simplest and most abundant element in the universe, consisting of a single proton and electron. It is a key component in the formation and composition of many astronomical objects and phenomena, playing a crucial role in the study of the very small, the formation of spectral lines, the atmospheres of the giant planets, the spectra of stars, the interstellar medium, and the fundamental makeup of the universe.
Ionization: Ionization is the process in which an atom or molecule loses or gains electrons, resulting in the formation of ions. This often occurs due to high energy photons interacting with atoms or molecules.
Ionization: Ionization is the process by which an atom or molecule loses or gains one or more electrons, resulting in the formation of an ion. This process is fundamental to understanding the formation of spectral lines, the spectra of stars and brown dwarfs, the composition of interstellar gas, the behavior of cosmic rays, and the nature of interstellar matter around the Sun.
Jupiter Masses: Jupiter masses is a unit of measurement used to express the mass of celestial objects, particularly exoplanets and brown dwarfs, in relation to the mass of the planet Jupiter. It provides a convenient way to compare the masses of these objects to the largest planet in our solar system.
K-type Stars: K-type stars, also known as orange dwarfs, are a class of main-sequence stars that are slightly cooler and less massive than our Sun. They have a surface temperature range of 3,700 to 5,200 Kelvin and are characterized by their distinctive orange hue, which is a result of their relatively low surface temperatures compared to other stellar classes.
L-type Objects: L-type objects are a class of brown dwarfs, which are substellar objects that are not massive enough to sustain hydrogen fusion in their cores, but are too large to be considered planets. L-type objects are characterized by their distinct spectral features, which provide insights into their atmospheric composition and physical properties.
M-type stars: M-type stars, also known as red dwarfs, are the most common and longest-lived type of stars in the universe. They are characterized by their low surface temperatures, small sizes, and low luminosities compared to other stellar classifications.
Metal Hydrides: Metal hydrides are chemical compounds formed by the combination of a metal and hydrogen. They have unique properties that make them useful in various applications, particularly in the context of stellar spectra and the study of brown dwarfs.
Methane: Methane is a colorless, odorless, and flammable gas that is the simplest alkane hydrocarbon. It is a major component of natural gas and is also produced through the anaerobic decomposition of organic matter, making it an important player in the context of Earth's atmosphere, the exploration of other planets, and the spectra of celestial bodies.
O-type stars: O-type stars are the hottest, most luminous, and most massive stars in the universe. They are characterized by their extremely high surface temperatures, which can reach up to 50,000 Kelvin, and their intense blue-white color. O-type stars play a crucial role in the evolution of galaxies and the formation of other stellar objects.
Opacity: Opacity is a measure of the degree to which a material or substance obstructs the transmission of light or other forms of electromagnetic radiation. It is a critical concept in various fields, including astrophysics, where it plays a vital role in understanding the behavior and properties of celestial bodies and their environments.
Red Dwarfs: Red dwarfs are the most common type of star in the universe, characterized by their small size, low mass, and cool surface temperatures. These stars are the focus of topics 17.3 The Spectra of Stars (and Brown Dwarfs) and 18.1 A Stellar Census, as their unique properties and abundance provide valuable insights into the composition and evolution of the cosmos.
Spectral class: A spectral class is a classification of stars based on their spectral characteristics, particularly the absorption lines present in their spectra. These classes are primarily determined by a star's surface temperature and are categorized using the letters O, B, A, F, G, K, and M.
Spectral Classes: Spectral classes are a way to categorize stars based on their surface temperature, which is determined by analyzing the absorption lines in their spectra. This classification system provides valuable insights into the physical properties and evolutionary stage of different types of stars.
Spectral Classification: Spectral classification is a scheme used to categorize stars based on their observed spectral characteristics, which are directly related to their surface temperature and chemical composition. This classification system is a fundamental tool in the study of stellar properties and evolution.
Stellar Atmosphere: The stellar atmosphere is the outermost layer of a star, surrounding the star's core and extending outward. It is the region where the star's radiation escapes into space, and it plays a crucial role in determining the observed properties and spectra of stars.
Sub-brown Dwarfs: Sub-brown dwarfs are celestial objects that fall in the mass range between the heaviest planets and the lightest stars. They are not massive enough to sustain nuclear fusion in their cores, like normal stars, but are also too large to be considered true planets. This unique classification places sub-brown dwarfs in a distinct category between the two better-known types of stellar objects.
Super-Jupiters: Super-Jupiters are a class of exoplanets that are significantly larger than the planet Jupiter in our own solar system. These massive gas giant planets orbit their host stars at relatively close distances, often much closer than Jupiter's orbit around the Sun.
T-type objects: T-type objects, also known as T dwarfs, are a class of brown dwarfs that have effective temperatures between approximately 1,300 and 2,200 Kelvin. These objects are characterized by their distinct spectral features, which differentiate them from other types of brown dwarfs and low-mass stars.
Titanium Oxide: Titanium oxide, also known as titanium dioxide, is a naturally occurring mineral compound composed of titanium and oxygen. It is a white, crystalline solid that is widely used in various industries and applications due to its unique properties.
Wien's Displacement Law: Wien's Displacement Law is a fundamental principle in astrophysics that describes the relationship between the temperature of a blackbody and the wavelength at which it emits the most radiation. It is a crucial concept in understanding the electromagnetic spectrum, spectroscopy in astronomy, and the spectra of stars and brown dwarfs.
Y-type objects: Y-type objects are a class of brown dwarfs that exhibit very low surface temperatures, typically less than 500 Kelvin. These objects are the coolest known substellar bodies, bridging the gap between the coolest stars and the warmest gas giant planets.