Carbon star
Encyclopedia
A carbon star is a late-type star
similar to a red giant
(or occasionally to a red dwarf
) whose atmosphere contains more carbon
than oxygen
; the two elements combine in the upper layers of the star, forming carbon monoxide
, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds, giving the star a "soot
y" atmosphere and a strikingly red appearance.
In normal stars (such as the Sun
), the atmosphere is richer in oxygen than carbon. Ordinary stars not exhibiting the characteristics of carbon stars, but that are cool enough to form carbon monoxide, are therefore called oxygen stars.
Carbon stars have quite distinctive spectral characteristics
, and they were first recognized by their spectra by Angelo Secchi
in the 1860s, a pioneering time in astronomical spectroscopy
.
In the classical carbon stars, those belonging to the modern spectral types
C-R and C-N, the abundance of carbon is thought to be a product of helium fusion
, specifically the triple-alpha process
within a star, which giants reach near the end of their lives in the Asymptotic Giant Branch
(AGB). These fusion products have been brought to the stellar surface by episodes of convection
(the so-called third dredge-up
) after the carbon and other products were made. Normally this kind of AGB carbon star fuses hydrogen in a hydrogen burning shell, but in episodes separated by 104-105 years, the star transforms to burning helium in a shell, while the hydrogen fusion temporarily ceases. In this phase, the star's luminosity rises, and material from the interior of the star (notably carbon) moves up. Since the luminosity rises, the star expands so that the helium fusion ceases, and the hydrogen shell burning restarts. During these shell helium flashes, the mass loss from the star is significant, and after many shell helium flashes, an AGB star is transformed into a hot white dwarf
and its atmosphere becomes material for a planetary nebula
.
The non-classical kinds of carbon stars, belonging to the types C-J and C-H, are believed to be binary star
s, where one star is observed to be a giant star (or occasionally a red dwarf
) and the other a white dwarf
. The star presently observed to be a giant star accreted carbon-rich material when it was still a main sequence
star from its companion (that is, the star that is now the white dwarf) when the latter was still a classical carbon star. That phase of stellar evolution
is relatively brief, and most such stars ultimately end up as white dwarfs. We are now seeing these systems a comparatively long time after the mass transfer
event, so the extra carbon observed in the present red giant was not produced within that star. This scenario is also accepted as the origin of the barium star
s, which are also characterized as having strong spectral features of carbon molecules and of barium (an s-process element
). Sometimes the stars whose excess carbon came from this mass transfer are called "extrinsic" carbon stars to distinguish them from the "intrinsic" AGB stars which produce the carbon internally. Many of these extrinsic carbon stars are not luminous or cool enough to have made their own carbon, which was a puzzle until their binary nature was discovered.
The enigmatic hydrogen deficient carbon stars (HdC), belonging to the spectral class C-Hd, seems to have some relation to R Coronae Borealis variable
s (RCB), but aren't variable themselves and lack a certain infrared
radiation typical for RCB:s. Only five HdC:s are known, and none is known to be binary, so the relation to the non-classical carbon stars is not known.
Other less convincing theories, such as CNO cycle
unbalancing and Core Helium Flash
have also been proposed as mechanisms for carbon enrichment in the atmospheres of smaller carbon stars.
), C3 and SiC2. Carbon is formed in the core and circulated into its upper layers, dramatically changing the layers' composition. Other elements formed through helium fusion and the s-process are also "dredged up" in this way, including lithium
and barium
.
When astronomers developed the spectral classification of the carbon stars, they had considerable difficulty when trying to correlate the spectra to the stars' effective temperatures. The trouble was with all the atmospheric carbon hiding the absorption lines normally used as temperature indicators for the stars.
erected the Secchi class IV for the carbon stars, which in the late 1890s were reclassified as N class stars.
, was determined to be C54, where 5 refers to temperature dependent features, and 4 to the strength of the C2 Swan bands in the spectrum. (C54 is very often alternatively written C5,4). This Morgan-Keenan C system classification replaced the older R-N classifications from 1960-1993.
A new revised Morgan-Keenan classification was published in 1993 by Philip Keenan, defining the classes: C-N, C-R and C-H. Later the classes C-J and C-Hd were added. This constitutes the established classification system used today :
s of the long period variable
types.
to the light of the stars, amateur astronomers making magnitude
estimates of red variable star
s, especially carbon stars, have to know how to deal with the Purkinje effect
in order not to underestimate the magnitude of the observed star.
, as much as half (or more) of the total mass of a carbon star may be lost by way of powerful stellar wind
s. The star's remnants, carbon-rich "dust" similar to graphite
, therefore become part of the interstellar dust
. This dust is believed to be a significant factor in providing the raw materials
for the creation of subsequent generations of stars and their planetary systems. The material surrounding a carbon star may blanket it to the extent that the dust absorbs all visible light.
Specimens:
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
similar to a red giant
Red giant
A red giant is a luminous giant star of low or intermediate mass in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius immense and the surface temperature low, somewhere from 5,000 K and lower...
(or occasionally to a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
) whose atmosphere contains more carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
than oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
; the two elements combine in the upper layers of the star, forming carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
, which consumes all the oxygen in the atmosphere, leaving carbon atoms free to form other carbon compounds, giving the star a "soot
Soot
Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres,...
y" atmosphere and a strikingly red appearance.
In normal stars (such as the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
), the atmosphere is richer in oxygen than carbon. Ordinary stars not exhibiting the characteristics of carbon stars, but that are cool enough to form carbon monoxide, are therefore called oxygen stars.
Carbon stars have quite distinctive spectral characteristics
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
, and they were first recognized by their spectra by Angelo Secchi
Angelo Secchi
-External links:...
in the 1860s, a pioneering time in astronomical spectroscopy
Spectroscopy
Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative...
.
Astrophysical mechanisms
Carbon stars are explained by more than one astrophysical mechanism. McClure distinguishes between classical carbon stars, and other non-classical ones that are less massive.In the classical carbon stars, those belonging to the modern spectral types
Stellar classification
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
C-R and C-N, the abundance of carbon is thought to be a product of helium fusion
Helium fusion
Helium fusion is a kind of nuclear fusion, with the nuclei involved being helium.The fusion of helium-4 nuclei is known as the triple-alpha process, because fusion of just two helium nuclei only produces beryllium-8, which is unstable and breaks back down to two helium nuclei with a half-life of...
, specifically the triple-alpha process
Triple-alpha process
The triple alpha process is a set of nuclear fusion reactions by which three helium-4 nuclei are transformed into carbon.Older stars start to accumulate helium produced by the proton–proton chain reaction and the carbon–nitrogen–oxygen cycle in their cores...
within a star, which giants reach near the end of their lives in the Asymptotic Giant Branch
Asymptotic Giant Branch
The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass stars. This is a period of stellar evolution undertaken by all low to intermediate mass stars late in their lives....
(AGB). These fusion products have been brought to the stellar surface by episodes of convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
(the so-called third dredge-up
Dredge-up
Dredge-up refers to a period in the evolution of a star where a surface convection zone extends down to the layers where material has undergone nuclear fusion...
) after the carbon and other products were made. Normally this kind of AGB carbon star fuses hydrogen in a hydrogen burning shell, but in episodes separated by 104-105 years, the star transforms to burning helium in a shell, while the hydrogen fusion temporarily ceases. In this phase, the star's luminosity rises, and material from the interior of the star (notably carbon) moves up. Since the luminosity rises, the star expands so that the helium fusion ceases, and the hydrogen shell burning restarts. During these shell helium flashes, the mass loss from the star is significant, and after many shell helium flashes, an AGB star is transformed into a hot white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
and its atmosphere becomes material for a planetary nebula
Planetary nebula
A planetary nebula is an emission nebula consisting of an expanding glowing shell of ionized gas ejected during the asymptotic giant branch phase of certain types of stars late in their life...
.
The non-classical kinds of carbon stars, belonging to the types C-J and C-H, are believed to be binary star
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...
s, where one star is observed to be a giant star (or occasionally a red dwarf
Red dwarf
According to the Hertzsprung-Russell diagram, a red dwarf star is a small and relatively cool star, of the main sequence, either late K or M spectral type....
) and the other a white dwarf
White dwarf
A white dwarf, also called a degenerate dwarf, is a small star composed mostly of electron-degenerate matter. They are very dense; a white dwarf's mass is comparable to that of the Sun and its volume is comparable to that of the Earth. Its faint luminosity comes from the emission of stored...
. The star presently observed to be a giant star accreted carbon-rich material when it was still a 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 from its companion (that is, the star that is now the white dwarf) when the latter was still a classical carbon star. That phase of stellar evolution
Stellar evolution
Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years to trillions of years .Stellar evolution is not studied by observing the life of a single...
is relatively brief, and most such stars ultimately end up as white dwarfs. We are now seeing these systems a comparatively long time after the mass transfer
Mass transfer
Mass transfer is the net movement of mass from one location, usually meaning a stream, phase, fraction or component, to another. Mass transfer occurs in many processes, such as absorption, evaporation, adsorption, drying, precipitation, membrane filtration, and distillation. Mass transfer is used...
event, so the extra carbon observed in the present red giant was not produced within that star. This scenario is also accepted as the origin of the barium star
Barium star
Barium stars are G to K class giants, whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4nm. Barium stars also show enhanced spectral features of carbon, the bands of the molecules CH, CN and C2...
s, which are also characterized as having strong spectral features of carbon molecules and of barium (an s-process element
S-process
The S-process or slow-neutron-capture-process is a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars. Under these conditions the rate of neutron capture by atomic nuclei is slow relative to the rate of radioactive beta-minus decay...
). Sometimes the stars whose excess carbon came from this mass transfer are called "extrinsic" carbon stars to distinguish them from the "intrinsic" AGB stars which produce the carbon internally. Many of these extrinsic carbon stars are not luminous or cool enough to have made their own carbon, which was a puzzle until their binary nature was discovered.
The enigmatic hydrogen deficient carbon stars (HdC), belonging to the spectral class C-Hd, seems to have some relation to R Coronae Borealis variable
R Coronae Borealis variable
A R Coronae Borealis variable is an eruptive variable star that varies in luminosity in two modes, one low amplitude pulsation , and one irregular unpredictably sudden fading by 1 to 9 magnitudes...
s (RCB), but aren't variable themselves and lack a certain infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
radiation typical for RCB:s. Only five HdC:s are known, and none is known to be binary, so the relation to the non-classical carbon stars is not known.
Other less convincing theories, such as CNO cycle
CNO cycle
The CNO cycle is one of two sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton–proton chain. Unlike the proton–proton chain reaction, the CNO cycle is a catalytic cycle. Theoretical models show that the CNO cycle is the dominant source of energy in stars...
unbalancing and Core Helium Flash
Helium flash
A helium flash is the runaway fusion of helium in the core of low mass stars of less than about 2.25 solar masses and greater than about 0.5 solar mass, or on the surface of an accreting white dwarf star. They may also occur in the outer layers of larger stars in shell flashes...
have also been proposed as mechanisms for carbon enrichment in the atmospheres of smaller carbon stars.
Carbon star spectra
By definition carbon stars have dominant spectral Swan bands from the molecule C2. Many other carbon compounds may be present at high levels, such as CH, CN (cyanogenCyanogen
Cyanogen is the chemical compound with the formula 2. It is a colorless, toxic gas with a pungent odor.The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups — analogous to diatomic halogen molecules, such as Cl2, but far less oxidizing...
), C3 and SiC2. Carbon is formed in the core and circulated into its upper layers, dramatically changing the layers' composition. Other elements formed through helium fusion and the s-process are also "dredged up" in this way, including lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...
and barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
.
When astronomers developed the spectral classification of the carbon stars, they had considerable difficulty when trying to correlate the spectra to the stars' effective temperatures. The trouble was with all the atmospheric carbon hiding the absorption lines normally used as temperature indicators for the stars.
Secchi
Carbon stars were discovered already in the 1860s when spectral classification pioneer Pater Angelo SecchiAngelo Secchi
-External links:...
erected the Secchi class IV for the carbon stars, which in the late 1890s were reclassified as N class stars.
Harvard
Using this new Harvard classification, the N class was later enhanced by an R class for less deeply red stars sharing the characteristic carbon bands of the spectrum. Later correlation of this R to N scheme with conventional spectra, showed that the R-N sequence approximately run in parallel with c:a G7 to M10 with regards to star temperature.| MK-type | R0 | R3 | R5 | R8 | Na | Nb |
| giant equiv. | G7-G8 | K1-K2 | ~K2-K3 | K5-M0 | ~M2-M3 | M3-M4 |
| Teff | 4300 | 3900 | ~3700 | 3450 |
Morgan-Keenan C system
The later N classes correspond less well to the counterparting M types, because the Harvard classification was only partially based on temperature, but also carbon abundance; so it soon became clear that this kind of carbon star classification was incomplete. Instead a new dual number star class C was erected so to deal with temperature and carbon abundance. Such a spectrum measured for Y Canum VenaticorumLa Superba
La Superba is a star in the constellation Canes Venatici, well-known for its strikingly red appearance.- Physical characteristics :...
, was determined to be C54, where 5 refers to temperature dependent features, and 4 to the strength of the C2 Swan bands in the spectrum. (C54 is very often alternatively written C5,4). This Morgan-Keenan C system classification replaced the older R-N classifications from 1960-1993.
| MK-type | C0 | C1 | C2 | C3 | C4 | C5 | C6 | C7 |
| giant equiv. | G4-G6 | G7-G8 | G9-K0 | K1-K2 | K3-K4 | K5-M0 | M1-M2 | M3-M4 |
| Teff | 4500 | 4300 | 4100 | 3900 | 3650 | 3450 |
The Revised Morgan-Keenan system
The two-dimensional Morgan-Keenan C classification failed to fulfill the creators' expectations:- it failed to correlate to temperature measurements based on infrared,
- originally being two-dimensional it was soon enhanced by suffixes, CH, CN, j and other features making it impractical for en-masse analyses of foreign galaxies' carbon star populations,
- and it gradually occurred that the old R and N stars actually were two distinct types of carbon stars, having real astrophysical significance.
A new revised Morgan-Keenan classification was published in 1993 by Philip Keenan, defining the classes: C-N, C-R and C-H. Later the classes C-J and C-Hd were added. This constitutes the established classification system used today :
| class | spectrum | population Metallicity In astronomy and physical cosmology, the metallicity of an object is the proportion of its matter made up of chemical elements other than hydrogen and helium... |
MV | theory | temperature range (K) |
example(s) | # known |
|---|---|---|---|---|---|---|---|
| classical carbon stars | |||||||
| C-R: | the old Harvard class R reborn: are still visible at the blue end of the spectrum, strong isotopic bands, no enhanced Ba Barium Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with... line |
medium disc pop I | 0 | red giants? | 5100-2800 | S Cam | ~25 |
| C-N: | the old Harvard class N reborn: heavy diffuse blue absorption, sometimes invisible in blue, s-process elements enhanced over solar abundance, weak isotopic bands | thin disc pop I | -2.2 | AGB Asymptotic Giant Branch The asymptotic giant branch is the region of the Hertzsprung-Russell diagram populated by evolving low to medium-mass stars. This is a period of stellar evolution undertaken by all low to intermediate mass stars late in their lives.... |
3100-2600 | R Lep R Leporis R Leporis , sometimes called Hind's Crimson Star, is a well-known variable star in the constellation Lepus, near its border with Eridanus. It is designated "R" in the chart to the right.... |
~90 |
| non-classical carbon stars | |||||||
| C-J: | very strong isotopic bands of C2 and CN | unknown | unknown | unknown | 3900-2800 | Y CVn La Superba La Superba is a star in the constellation Canes Venatici, well-known for its strikingly red appearance.- Physical characteristics :... |
~20 |
| C-H: | very strong CH absorption | halo pop II | -1.8 | bright giants, mass transfer (all C-H:s are binary ) | 5000-4100 | V Ari, TT CVn | ~20 |
| C-Hd: | hydrogen lines and CH bands weak or absent | thin disc pop I | -3.5 | unknown | ? | HD 137613 | ~7 |
Other qualities
Most classical carbon stars are variable starVariable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
s of the long period variable
Long period variable
A long period variable is a type of variable star in which variations in brightness occur over long timescales of months or years. Long period variables are giant stars and brighter, from spectral class F and redwards, but most are red giants and AGB giants, meaning spectral class M, S or C...
types.
Observing carbon stars
Due to the insensitivity of night vision to red and a slow adaption of the red sensitive eye rodsRod cell
Rod cells, or rods, are photoreceptor cells in the retina of the eye that can function in less intense light than can the other type of visual photoreceptor, cone cells. Named for their cylindrical shape, rods are concentrated at the outer edges of the retina and are used in peripheral vision. On...
to the light of the stars, amateur astronomers making 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...
estimates of red variable star
Variable star
A star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
s, especially carbon stars, have to know how to deal with the Purkinje effect
Purkinje effect
The Purkinje effect is the tendency for the peak luminance sensitivity of the human eye to shift toward the blue end of the color spectrum at low illumination levels.This effect introduces a difference in color contrast under different levels of...
in order not to underestimate the magnitude of the observed star.
Interstellar carbon sowers
Owing to its low surface gravityGravitation
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their mass. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped...
, as much as half (or more) of the total mass of a carbon star may be lost by way of powerful stellar wind
Stellar wind
A stellar wind is a flow of neutral or charged gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric.Different types of stars have...
s. The star's remnants, carbon-rich "dust" similar to graphite
Graphite
The mineral graphite is one of the allotropes of carbon. It was named by Abraham Gottlob Werner in 1789 from the Ancient Greek γράφω , "to draw/write", for its use in pencils, where it is commonly called lead . Unlike diamond , graphite is an electrical conductor, a semimetal...
, therefore become part of the interstellar dust
Cosmic dust
Cosmic dust is a type of dust composed of particles in space which are a few molecules to 0.1 µm in size. Cosmic dust can be further distinguished by its astronomical location; for example: intergalactic dust, interstellar dust, interplanetary dust and circumplanetary dust .In our own Solar...
. This dust is believed to be a significant factor in providing the raw materials
Molecular cloud
A molecular cloud, sometimes called a stellar nursery if star formation is occurring within, is a type of interstellar cloud whose density and size permits the formation of molecules, most commonly molecular hydrogen ....
for the creation of subsequent generations of stars and their planetary systems. The material surrounding a carbon star may blanket it to the extent that the dust absorbs all visible light.
See also
- Barium starBarium starBarium stars are G to K class giants, whose spectra indicate an overabundance of s-process elements by the presence of singly ionized barium, Ba II, at λ 455.4nm. Barium stars also show enhanced spectral features of carbon, the bands of the molecules CH, CN and C2...
s - S-type starS-type starA star with spectral type S is a late-type giant star whose spectrum displays bands from zirconium oxide in addition to titanium oxide which is characteristically exhibited by K and M class giant stars...
s - Technetium starTechnetium starA technetium star, or more properly a Tc-rich star, is a star whose stellar spectrum contains absorption lines of the light radioactive metal technetium. The most stable isotope of technetium is 98Tc with a half-life of 4.2 million years, which is too short a time to allow the metal to be material...
s - Marc AaronsonMarc AaronsonMarc Aaronson was an American astronomer.-Education:Aaronson was educated at the California Institute of Technology, where he received a BSc in 1972. He completed his Ph.D. in 1977 at Harvard University with a dissertation on the near-infrared aperture photometry of galaxies...
: an AmericaUnited StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
n astronomerAstronomyAstronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
and noted researcher of carbon stars
Specimens:
- R LeporisR LeporisR Leporis , sometimes called Hind's Crimson Star, is a well-known variable star in the constellation Lepus, near its border with Eridanus. It is designated "R" in the chart to the right....
, Hind's Crimson Star: an example of a carbon star - IRC +10216IRC +10216IRC +10216 or CW Leonis is a well-studied carbon star that is embedded in a thick dust envelope. It was first discovered in 1969 by a group of astronomers led by Eric Becklin, based upon infrared observations made with the Caltech Infrared Telescope at Mount Wilson Observatory. Its energy is...
, CW Leonis: the most studied carbon star, and also the brightest star in the sky at N-band - La SuperbaLa SuperbaLa Superba is a star in the constellation Canes Venatici, well-known for its strikingly red appearance.- Physical characteristics :...
, Y Canum Venaticorum: one of the brighter carbon stars
External links
- McClure's paper on the carbon and related stars
- List of 110 carbon stars. Includes HD numberHenry Draper CatalogueThe Henry Draper Catalogue is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension , published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the...
; secondary identification for most; position in right ascensionRight ascensionRight ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
and declinationDeclinationIn astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
; magnitudeApparent magnitudeThe 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...
; spectrumStellar classificationIn astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure...
; magnitude range (for variable starVariable starA star is classified as variable if its apparent magnitude as seen from Earth changes over time, whether the changes are due to variations in the star's actual luminosity, or to variations in the amount of the star's light that is blocked from reaching Earth...
s); period (of variability cycle).