In
astronomy, 'stellar classification' is a classification of
stars based initially on
photospheric temperature and its associated
spectral characteristics, and subsequently refined in terms of other characteristics. Stellar temperatures can be classified by using
Wien's displacement law, but this poses difficulties for distant stars.
Stellar spectroscopy offers a way to classify stars according to their
absorption lines; particular absorption lines can be observed only for a certain range of temperatures because only in that range are the involved
atomic energy levels populated. An early scheme (from the 19th century) ranked stars from ''A'' to ''Q'', which is the origin of the currently used spectral classes.
Secchi classes
Pioneering stellar spectroscopy Pater
Angelo Secchi created and consolidated the 'Secchi classes' during 1863–1867, they were:
★ 'Class I:' white and blue stars with broad heavy
hydrogen lines and
metallic lines, (modern class A)
★ 'Class II:' yellow stars – hydrogen less strong, but evident metallic lines, (modern classes G and K)
★ 'Class III:' orange stars with complex band spectra, (modern class M)
★ 'Class IV:' red stars with significant
carbon bands and lines (
carbon stars),
★ 'Class V:'
emission lines (f.ex. Be, Bf etc).
This classification was superseded by the Harvard classification in the late 1890s, which is discussed in the remainder of this article.
[1]
Harvard spectral classification
'Harvard' one-dimensional (temperature) classification scheme (based on hydrogen Balmer line strengths) was developed in
Harvard College Observatory at about 1912 by
Annie Jump Cannon and
Edward C. Pickering.
[2] The common classes are normally listed from hottest to coldest (with mass, radius and luminosity compared to the Sun) and are given in the following table.
| Class | Temperature | Conventional color | Apparent color[3] | Mass | Radius | Luminosity | Hydrogen lines | % of all MSSs |
|---|
| O | 30,000–60,000 K | blue | blue | 60 | 15 | 1,400,000 | Weak | ~0.00003% |
|---|
| B | 10,000–30,000 K | blue white | blue white to white | 18 | 7 | 20,000 | Medium | 0.13% |
|---|
| A | 7,500–10,000 K | white | white | 3.1 | 2.1 | 80 | Strong | 0.6% |
|---|
| F | 6,000–7,500 K | yellowish white | white | 1.7 | 1.3 | 6 | Medium | 3% |
|---|
| G | 5,000–6,000 K | yellow | yellow | 1.1 | 1.1 | 1.2 | Weak | 8% |
|---|
| K | 3,500–5,000 K | orange | yellow orange | 0.8 | 0.9 | 0.4 | Very weak | 13% |
|---|
| M | 2,000–3,500 K | red | orange red | 0.3 | 0.4 | 0.04 | Very weak | >78% |
|---|
The sizes listed for each class are appropriate only for stars on the
main sequence portion of their lives and so are not appropriate for
red giants. A popular
mnemonic for remembering the order is "'O'h 'B'e 'A' 'F'ine 'G'irl, 'K'iss 'M'e" (there are
many variants of this mnemonic). The
Hertzsprung-Russell diagram relates stellar classification with
absolute magnitude,
luminosity, and surface
temperature.
The reason for the odd arrangement of letters is historical. When people first started taking
spectra of stars, they noticed that stars had very different
hydrogen spectral lines strengths, and so they classified stars based on the strength of the hydrogen
Balmer series lines from A (strongest) to Q (weakest). Other lines of neutral and ionized species then came into play (H and K lines of
calcium,
sodium D lines, etc). Later it was found that some of the classes were actually duplicates and those classes were removed. It was only much later that it was discovered that the strength of the hydrogen line was connected with the surface
temperature of the star. The basic work was done by the "girls" of
Harvard College Observatory, primarily Annie J. Cannon,
Henrietta Swan Leavitt and
Antonia Maury, based on the work of
Williamina Fleming. In the 1920s, the Indian physicist
Megh Nad Saha derived a theory of ionization by extending well-known ideas in physical chemistry pertaining to the dissociation of molecules to the ionization of atoms. First applied to the solar chromosphere, he then applied it to stellar spectra.
[4] The Harvard astronomer
Cecilia Helena Payne (later to become
Cecilia Payne-Gaposchkin) then demonstrated that the OBAFGKM spectral sequence is actually a sequence in temperature.
[5]
Spectral classes are further subdivided by
Arabic numerals (0–9). For example, A0 denotes the hottest stars in the A class and A9 denotes the coolest ones. Because the classification sequence predates our understanding that it is a temperature sequence, the precise values of these digits depend upon (largely subjective) estimates of the strengths of absorption features in stellar spectra. As a result, the subclasses are not evenly divided into any sort of mathematically representable intervals. The Sun is classified as G2.
O, B, and A spectra are sometimes misleadingly called "early spectra", while K and M stars are said to have "late spectra". This stems from an early 20th century theory, now obsolete, that stars start their lives as very hot "early type" stars, and then gradually cool down, thereby evolving into "late type" stars. We now know that this theory is entirely wrong (see:
stellar evolution).
Conventional and apparent colors
The ''Conventional color'' descriptions are traditional in astronomy, and represent colors ''relative to
Vega'', a star that is perceived as white under naked eye observational conditions, but which magnified appears as blue. The ''Apparent color''
[6] descriptions is what the observer would see if trying to describe the stars under a dark sky without aid to the eye, or with binoculars. The table colors used, are D65 standard colors, which are what you would see if the star light would be magnified to be filling non-dazzlingly bright areas.
[7] Most stars in the sky, except the brightest ones, appear white or blueish white to the unaided eye because they are too dim for color vision to work.
Our Sun itself is white. It is sometimes called a yellow star (spectroscopically, relative to Vega), and may appear yellow or red (viewed through the atmosphere), or appear white (viewed when too bright for the eye to see any color). Astronomy images often use a variety of exaggerated colors (partially founded in faint light conditions observations, partially in conventions). But the Sun's own intrinsic color is white (aside from sunspots), with no trace of color, and closely approximates a
black body of 5780
K (see
color temperature). This is a natural consequence of the evolution of our optical senses: the response curve that maximizes the overall efficiency against solar illumination will by definition perceive the Sun as white.
Yerkes spectral classification
The 'Yerkes spectral classification', also called the 'MKK' system from the authors' initials, is a system of stellar spectral classification introduced in 1943 by
William Wilson Morgan,
Phillip C. Keenan and
Edith Kellman from
Yerkes Observatory [8].
This classification is based on
spectral lines sensitive to stellar surface gravity which is related to luminosity, as opposed to the Harvard classification which is based on surface temperature.
Later, in 1953, after some revisions of list of standard stars and classification criteria, the scheme was named 'MK' (by William Wilson Morgan and Phillip C. Keenan initials).
[9]
Since the radius of a
giant star is much larger than a
dwarf star while their masses are roughly comparable, the gravity and thus the gas density and pressure on the surface of a giant star are much lower than for a dwarf.
These differences manifest themselves in the form of ''luminosity effects'' which affect both the width and the intensity of spectral lines which can then be measured. Denser stars with higher surface gravity will exhibit greater ''pressure broadening'' of spectral lines.
A number of different luminosity classes are distinguished:
★ 'I'
supergiants
★
★ 'Ia-0' (
hypergiants or extremely luminous
supergiants (later addition), Example:
Eta Carinae (spectrum-peculiar)
★
★ 'Ia' (luminous supergiants), Example:
Deneb (spectrum is A2Ia)
★
★ 'Iab' (intermediate luminous supergiants)
★
★ 'Ib' (less luminous supergiants), Example:
Betelgeuse (spectrum is M2Ib)
★ 'II'
bright giants
★
★ 'IIa', Example:
β Scuti (HD 173764) (spectrum is G4 IIa)
★
★ 'IIab' Example: HR 8752 (spectrum is G0Iab:)
★
★ 'IIb', Example: HR 6902 (spectrum is G9 IIb)
★ 'III' normal
giants
★
★ 'IIIa', Example:
ρ Persei (spectrum is M4 IIIa)
★
★ 'IIIab' Example: δ Reticuli (spectrum is M2 IIIab)
★
★ 'IIIb', Example: Pollux (spectrum is K2 IIIb)
★ 'IV'
subgiants
★
★ 'IVa', Example:
ε Reticuli (spectrum is K1-2 IVa-III)
★
★ 'IVb', Example: HR 672 A (spectrum is G0.5 IVb)
★ 'V'
main sequence stars (dwarfs)
★
★ 'Va', Example: AD Leonis (spectrum M4Vae)
★
★ 'Vb', Example: 85 Pegasi A (spectrum G5 Vb)
★ 'VI'
subdwarfs (rarely used)
★ 'VII'
white dwarfs (rarely used)
Marginal cases are allowed; for instance a star classified as Ia0-Ia would be a very luminous supergiant, verging on hypergiant. Examples are below. The spectral type of the star are not a factor.
| Marginal Symbols | Example | Explanation |
|---|
| - | G2 'I-II' | The star is between super giant and bright giant. |
|---|
| + | O9.5 'Ia+' | The star is a hypergiant star. |
|---|
| / | M2 'IV/V' | The star is either a subgiant or a dwarf star. |
|---|
Spectral types
The following illustration represents star classes with the colors very close to those actually perceived by the human eye. The relative sizes are for
main sequence or "dwarf" stars.
The Morgan-Keenan spectral classification
Class O
Class 'O' stars are very hot and very luminous, being bluish in color; in fact, most of their output is in the
ultraviolet range. These are the rarest of all main sequence stars, constituting as few as 1 in 3,000,000 in the solar neighborhood (''Note:'' these abundancies are based on a census of stars brighter than absolute magnitude 16; lowering this limit will render earlier types even rarer while generally adding only to the M class).
[10] O-stars shine with a power over a million times our Sun's output. These stars have dominant lines of absorption and sometimes emission for
He II lines, prominent ionized (
Si IV,
O III,
N III, and
C III) and neutral
helium lines, strengthening from O5 to O9, and prominent hydrogen
Balmer lines, although not as strong as in later types. Because they are so huge, class O stars burn through their hydrogen fuel very quickly, and are the first stars to leave the
main sequence. Recent observations by the
Spitzer Space Telescope indicate that planetary formation does not occur around other stars in the vicinity of an O class star due to the
photo evaporation effect.
[11]
:'Examples:'
Zeta Puppis,
Lambda Orionis,
Delta Orionis
Class B
Class 'B' stars are extremely luminous and blue. Their spectra have neutral helium, which are most prominent at the B2 subclass, and moderate hydrogen lines. Ionized metal lines include
Mg II and
Si II. As
O and B stars are so powerful, they only live for a very short time, and thus they do not stray far from the area in which they were formed. These stars tend to cluster together in what are called
OB associations, which are associated with giant
molecular clouds. The Orion OB1 association occupies a large portion of a
spiral arm of our
galaxy and contains many of the brighter stars of the
constellation Orion. They constitute about 1 in 800 main sequence stars in the solar neighborhood
—rare, but much more common than those of class O.
:'Examples:'
Rigel,
Spica, the brighter
Pleiades
Class A
Class 'A' stars are amongst the more common naked eye stars, and are white or bluish-white. They have strong hydrogen lines, at a maximum by A0, and also lines of ionized metals (
Fe II,
Mg II,
Si II) at a maximum at A5. The presence of
Ca II lines is notably strengthening by this point. They comprise about 1 in 160 of the main sequence stars in the solar neighborhood.
:'Examples:'
Vega,
Sirius,
Deneb
Class F
Class 'F' stars are still quite powerful but they tend to be
main sequence stars. These stars have strengthening ''H'' and ''K'' lines of
Ca II. Neutral metals (
Fe I,
Cr I) beginning to gain on ionized metal lines by late F. Their spectra is characterized by the weaker hydrogen lines and ionized metals, their color is white with a slight tinge of yellow. These represent about 1 in 32 of the main sequence stars in the solar neighborhood.
:'Examples:'
Canopus,
Procyon
Class G
The most important class G star to humanity: our
Sun. The dark area visible northwest of the South pole is a large
sunspot.
Class 'G' stars are probably the best known, if only for the reason that our
Sun is of this class. Most notable are the ''H'' and ''K'' lines of
Ca II, which are most prominent at G2. They have even weaker hydrogen lines than F, but along with the ionized metals, they have neutral metals. There is a prominent spike in the G band of CH molecules. G is host to the "Yellow Evolutionary Void".
[12] Supergiant stars often swing between O or B (blue) and K or M (red). While they do this, they do not stay for long in the G classification as this is an extremely unstable place for a supergiant to be. G stars represent about 1 in 13 of the main sequence stars in the solar neighborhood.
:'Examples:'
Sun,
Alpha Centauri A,
Capella,
Tau Ceti
Class K
Class 'K' are orangish stars which are slightly cooler than our Sun. Some K stars are
giants and
supergiants, such as
Arcturus, while others, like
Alpha Centauri B, are main sequence stars. They have extremely weak hydrogen lines, if they are present at all, and mostly neutral metals (
Mn I,
Fe I,
Si I). By late K, molecular bands of
titanium oxide become present. These make up 1 in 8 of the main sequence stars in the solar neighborhood.
:'Examples:'
Alpha Centauri B,
Epsilon Eridani,
Arcturus,
Aldebaran
Class M
Class 'M' is by far the most common class. At least 80% of the main sequence stars in the solar neighborhood are
red dwarfs (see the note under
Class O),
such as
Proxima Centauri. M is also host to most giants and some supergiants such as
Antares and
Betelgeuse, as well as
Mira variables. The late-M group holds hotter
brown dwarfs that are above the L spectrum. This is usually in the range of M6.5 to M9.5. The spectrum of an M star shows lines belonging to
molecules and all neutral metals but hydrogen lines are usually absent.
Titanium oxide can be strong in M stars, usually dominating by about M5.
Vanadium oxide bands become present by late M.
:'Example:'
Betelgeuse (
supergiant)
:'Examples:'
Proxima Centauri,
Barnard's star,
Gliese 581 (red dwarf)
:'Example:' LEHPM 2-59
[13] (subdwarf)
:'Examples:'
Teide 1 (field brown dwarf), GSC 08047-00232 B
[14] (companion brown dwarf)
Extended spectral types
A number of new spectral types have been taken into use from newly discovered types of stars.
Hot blue emission star classes
Spectra of some very hot and bluish stars exhibit marked emission lines from carbon or nitrogen, or sometimes oxygen.
Class W: Wolf-Rayet
Main articles: Wolf-Rayet stars
Artist's impression of a Wolf-Rayet star
Class 'W' or 'WR' represents the superluminous Wolf-Rayet stars, notably unusual since they have mostly helium in their atmospheres instead of hydrogen. They are thought to be dying supergiants with their hydrogen layer blown away by hot
stellar winds caused by their high temperatures, thereby directly exposing their hot helium shell. Class W is subdivided into subclasses 'WC' ('WCE' early-type, 'WCL' late-type), 'WN' ('WNE' early-type, 'WNL' late-type), and 'WO' according to the dominance of carbon, nitrogen, or oxygen emission in their spectra (and outer layers).
★ W: Up to 70,000 K
:'Example:'
Gamma Velorum A (WC)
:'Example:'
WR124 (WN)
:'Example:'
WR93B (WO)
Classes OC, ON, BC, BN: Wolf-Rayet related O and B stars
Intermediary between the genuine Wolf-Rayet's and ordinary hot stars of classes O and early B, there are OC, ON, BC and BN stars. They seem to constitute a short continuum from the Wolf-Rayet's into the ordinary OB:s.
:'Example:' HD 152249 (OC)
:'Example:' HD 105056 (ON)
:'Example:' HD 2905 (BC)
:'Example:' HD 163181 (BN)
The "class" OB
Main articles: OB star
In lists of spectra, the ''"spectrum OB"'' may occur. This is in fact not a spectrum, but a marker which means that ''"the spectrum of this star is unknown, but it belongs to an
OB association, so probably either a class 'O' or class 'B' star, or perhaps a fairly hot class 'A' star."''
Cool red and brown dwarf classes
The novel spectral types L and T were created to classify infrared spectra of cool stars and
brown dwarfs very faint in visual light. Y spectral type was later created.
Class L
Artists vision of an L-dwarf
Class 'L', dwarfs get their designation because they are cooler than M stars and 'L' is the remaining letter alphabetically closest to 'M'. 'L' does not mean lithium dwarf; a large fraction of these stars do not have
lithium in their spectra. Some of these objects are of substellar mass (do not support fusion) and some are not, so collectively this class of objects should be referred to as "L dwarfs", not "L stars." They are a very dark red in color and brightest in
infrared. Their
gas is cool enough to allow
metal hydrides and
alkali metals to be prominent in their spectra.
[15][16] Due to low gravities in giant stars, TiO- and VO-bearing condensates never form. Thus, larger L-type stars can never form in an isolated environment. It may be possible for these L-type supergiants to form through stellar collisions, however, an example of which is
V838 Monocerotis.
★ L: 1,300–2,000 K — Dwarfs (some stellar, some substellar) with
metal hydrides and
alkali metals prominent in their spectra.
:'Example:' VW Hyi
:'Example:' 2MASSW J0746425+2000321 binary
[17]
::Component 'A' is an L Dwarf Star
::Component 'B' is an L Brown Dwarf
:'Example:'
V838 Monocerotis (supergiants)
Class T: methane dwarfs
Artists vision of a T-dwarf
Class 'T' stars are very young and low density stars often found in the
interstellar clouds they were born in. These are stars barely big enough to be stars and others that are
substellar, being of the
brown dwarf variety. They are black, emitting little or no
visible light but being strongest in
infrared. Their surface temperature is a stark contrast to the fifty thousand kelvins or more for Class O stars, being merely up to 1,000 K. Complex molecules can form, evidenced by the strong
methane lines in their spectra.
★ T: ~770-1,000 K - Cooler
brown dwarfs with
methane in the spectrum
:'Examples:'
SIMP 0136 (the brightest T dwarf discovered)
[18]
:'Examples:'
Epsilon Indi Ba & Epsilon Indi Bb
Class T and L could be more common than all the other classes combined, if recent research is accurate. From studying the number of
proplyds (protoplanetary discs, clumps of gas in
nebulae from which stars and solar systems are formed) then the number of stars in the
galaxy should be several
orders of magnitude higher than what we know about. It is theorized that these proplyds are in a race with each other. The first one to form will become a
proto-star, which are very violent objects and will disrupt other proplyds in the vicinity, stripping them of their gas. The victim proplyds will then probably go on to become main sequence stars or brown dwarf stars of the L and T classes, but quite invisible to us. Since they live so long, these smaller stars will accumulate over time.
Class Y
Class 'Y' stars are expected to be much cooler than T-dwarfs. None have been found as of yet, but they have been modelled.
[19]
★ Y: < 700 K - Ultra-cool dwarfs are
brown dwarfs that are cooler than T-dwarfs, (theoretical)
:'Examples:'
ULAS J0034-00 (status is suspected)
[20]
Carbon related late giant star classes
Carbon related stars are stars whose spectra indicate production of carbon by helium
triple-alpha fusion. With increased carbon abundance, and some parallel
s-process heavy element production, the spectra of these stars are becoming increasingly deviant from the usual late spectral classes G, K and M. The giants among those stars are presumed to produce this carbon themselves, but not too few of this class of stars are believed to be double stars whose odd atmosphere once was transferred from a former carbon star companion that is now a white dwarf.
Class C: carbon stars
Main articles: Carbon star
Originally classified as 'R' and 'N' stars, these are also known as 'carbon stars'. These are red giants, near the end of their lives, in which there is an excess of carbon in the atmosphere. The old R and N classes ran parallel to the normal classification system from roughly mid G to late M. These have more recently been remapped into a unified carbon classifier 'C', with N0 starting at roughly C6. Another subset of cool carbon stars are the 'J'-type stars, which are characterized by the strong presence of molecules of
13CN in addition to those of
12CN.
[21] A few dwarf (that is, main sequence) carbon stars are known, but the overwhelming majority of known carbon stars are giants or supergiants.
★ C: Carbon stars, e.g. ''R CMi''
★
★ C-R: Formerly a class on its own representing the carbon star equivalent of late G to early K stars. Example: S Camelopardalis
★
★ C-N: Formerly a class on its own representing the carbon star equivalent of late K to M stars. Example:
R Leporis
★
★ C-J: A subtype of cool C stars with a high content of
13C. Example:
Y Canum Venaticorum
★
★ C-H: Population II analogues of the C-R stars. Examples: V Ari, TT CVn
[22]
★
★ C-Hd: Hydrogen-Deficient Carbon Stars, similar to late G supergiants with CH and C
2 bands added. Example: HD 137613
Class S
Class 'S' stars have
zirconium oxide lines in addition to (or, rarely, instead of) those of
titanium oxide, and are in between the Class M stars and the carbon stars.
[23] S stars have excess amounts of
zirconium and other elements produced by the
s-process, and have their carbon and oxygen abundances closer to equal than is the case for M stars. The latter condition results in both
carbon and
oxygen being locked up almost entirely in
carbon monoxide molecules. For stars cool enough for carbon monoxide to form that molecule tends to "eat up" all of whichever element is less abundant, resulting in "leftover oxygen" (which becomes available to form titanium oxide) in stars of normal composition, "leftover carbon" (which becomes available to form the
diatomic carbon molecules) in carbon stars, and "leftover nothing" in the S stars. The relation between these stars and the ordinary M stars indicates a continuum of carbon abundance. Like carbon stars, nearly all known S stars are giants or supergiants.
:'Examples:' ''S Ursae Majoris'', ''HR 1105''
Classes MS and SC: intermediary carbon related classes
In between the M class and the S class, border cases are named MS stars. In a similar way border cases between the S class and the C-N class are named SC or CS. The sequence M → MS → S → SC → C-N is believed to be a sequence of increased carbon abundance with age for
carbon stars in the
asymptotic giant branch.
:'Examples:' R Serpentis, ST Monocerotis (MS)
:'Examples:' CY Cygni, BH Crucis (SC)
White dwarf classifications
Main articles: White dwarf
The class 'D' is the modern classification used for white dwarfs, low-mass stars that are no longer undergoing
nuclear fusion and have shrunk to planetary size, slowly cooling down. Class D is further divided into classes DA, DB, DC, DO, DZ, and DQ. The letters are not related to the letters used in the classification of true stars, but instead indicate the composition of the white dwarf's outer layer or "atmosphere".
★ 'Examples:'
Sirius B (DA2),
Van Maanen's star (DZ7)
★ 'Examples:'
Procyon B (DQZ)
The white dwarf classes are as follows:
★ 'DA': a hydrogen-rich "atmosphere" or outer layer, indicated by strong Balmer hydrogen spectral lines.
★ 'DB': a neutral helium-rich "atmosphere" or outer layer, indicated by neutral helium spectral lines, (
He I lines).
★ 'DO': an ionized helium-rich "atmosphere" or outer layer, indicated by ionized helium spectral lines, (
He II lines).
★ 'DC': no strong spectral lines indicating one of the above categories.
★ 'DQ': a carbon-rich "atmosphere" or outer layer, indicated by atomic or molecular carbon lines.
★ 'DZ': a 'metal'-rich "atmosphere" or outer layer, indicated by magnesium, calcium, and/or iron lines, (
Ca I, Ca II H and K,
Mg I,
Fe I,
Na I).
★ 'DX': spectral lines are insufficiently clear to classify into one of the above categories.
All class D stars use the same sequence from 1 to 9, with 1 indicating a temperature above 37,500
K and 9 indicating a temperature below 5,500 K. (The number is by definition equal to
Teff = 50,400 K.)
[24]
'Extended white dwarf class'
★ 'DAB': a hydrogen- and neutral helium-rich white dwarf
★ 'DAO': a hydrogen- and ionized helium-rich white dwarf
★ 'DAZ': a hydrogen-rich cool metallic white dwarf
★ 'DBZ': a helium-rich cool metallic white dwarf
★ 'DAV' or 'zz Ceti': a hydrogen-rich
pulsating white dwarf
★ 'DBV' or 'V777 Her': a helium-rich pulsating white dwarf
★ 'DOV' or '
PG 1159': a helium-rich pulsating white dwarf
Non-stellar spectral types: Class P & Q
Finally, the classes 'P' and 'Q' are occasionally used for certain non-stellar objects. Type P objects are
planetary nebulae and type Q objects are
novae.
Spectral peculiarities
Additional nomenclature, in the form of lower-case letters, can follow the spectral type to indicate peculiar features of the spectrum.
[25]
| Code | Spectral peculiarities for stars |
|---|
| : | Bleeding and/or uncertain spectral value |
|---|
| … | Undescribed spectral peculiarities exist |
|---|
| ! | Special peculiarity |
|---|
| comp | Composite spectrum |
|---|
| e | Emission lines present |
|---|
| [e] | "Forbidden" emission lines present |
|---|
| er | "Reversed" center of emission lines weaker than edges |
|---|
| ep | Emission lines with peculiarity |
|---|
| eq | Emission lines with ^P-Cygni//gr 304.446667, 38.032944^ profile |
|---|
| ev | Spectral emission that exhibits variability |
|---|
| f | NIII and HeII emission |
|---|
| f+ | Si IV emission additional to HeII and NIII emission |
|---|
f
★ | NIV emission stronger than NIII emission |
|---|
| (f) | Weak emission lines of He |
|---|
| ((f)) | No emission of He |
|---|
| He wk | Weak He lines |
|---|
| k | Spectra with interstellar absorption features |
|---|
| m | Enhanced metal features |
|---|
| n | Broad ("nebulous") absorption due to spinning |
|---|
| nn | Very broad absorption features due to spinning very fast |
|---|
| neb | A nebula's spectrum mixed in |
|---|
| p | Peculiar spectrum, strong spectral lines due to metal |
|---|
| pq | Peculiar spectrum, similar to the spectra of novae |
|---|
| q | Red & blue shifts line present |
|---|
| s | Narrowly "sharp" absorption lines |
|---|
| ss | Very narrow lines |
|---|
| sh | Shell star |
|---|
| v | Variable spectral feature (also "var") |
|---|
| w | Weak lines (also "wl" & "wk") |
|---|
| d Del | Type A and F giants with weak calcium H and K lines, as in prototype ^delta Delphini//gr 310.8647916, 15.074694^ |
|---|
| d Sct | Type A and F stars with spectra similar to that of short-period variable ^delta Scuti//gr 280.568417, -9.0525556^ |
|---|
| Code | If spectrum shows enhanced metal features |
|---|
| Ba | Abnormally strong Barium |
|---|
| Ca | Abnormally strong Calcium |
|---|
| Cr | Abnormally strong Chromium |
|---|
| Eu | Abnormally strong Europium |
|---|
| He | Abnormally strong Helium |
|---|
| Hg | Abnormally strong Mercury |
|---|
| Mn | Abnormally strong Manganese |
|---|
| Si | Abnormally strong Silicon |
|---|
| Sr | Abnormally strong Strontium |
|---|
| Code | Spectral peculiarities for white dwarfs |
|---|
| P | Magnetic white dwarf with detectable polarization |
|---|
| E | Emission lines present |
|---|
| H | Magnetic white dwarf without detectable polarization |
|---|
| V | Variable |
|---|
| PEC | Spetral peculiarities exist |
|---|
For example,
Epsilon Ursae Majoris is listed as spectral type A0pCr, indicating general classification A0 with an unspecified peculiarity and strong emission lines of the element
chromium. There are several common classes of chemically
peculiar stars, where the spectral lines of a number of elements appear abnormally strong.
Photometric classification
Stars can also be classified using photometric data from any
photometric system. For example, we can calibrate
color index diagrams UB, BV in the
UBV system according to
spectral and
luminosity classes. Nevertheless, this callibration is not straightforward, because many effects are superimposed in such diagrams:
metallicity,
interstellar reddening,
binary and
multiple stars.
The more colors and more narrow passbands in photometric systems we use, the more precisely we can derive a star's class (and, hence, physical parameters). The best are, of course, spectral measurements, but we not always have enough time to get qualitative spectra with high
signal-to-noise ratio.
See also
★
Stellar evolution
★
Stellar associations
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Metallicity
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Astrograph
References
1. Classification of Stellar Spectra: Some History
2. Cannon, Annie Jump; Pickering, Edward Charles (1912), Annals of the Astronomical Observatory of Harvard College; vol. 56, no. 4, Cambridge, Mass.: The Observatory
3. The Guinness book of astronomy facts & feats, Patrick Moore, 1992, 0-900424-76-1
4. Saha, M. N.; ''On a Physical Theory of Stellar Spectra'', Proceedings of the Royal Society of London, Series A, Volume 99, Issue 697 (May 1921), pp. 135–153
5. Payne, C. H.; ''Stellar Atmospheres; A Contribution to the Observational Study of High Temperature in the Reversing Layers of Stars'', Ph. D. Thesis, Radcliffe College, 1925
6. Möremöre
7.
What color are the stars? Charity, Mitchell
8. Morgan, William Wilson; Keenan, Philip Childs; Kellman, Edith (1943), "An atlas of stellar spectra, with an outline of spectral classification", Chicago, Ill., The University of Chicago press
9. SPECTRAL CLASSIFICATION, , William Wilson Morgan, Phillip C. Keenan, Annual Reviews of Astronomy and Astrophysics,
10. LeDrew, G.; ''The Real Starry Sky'', Journal of the Royal Astronomical Society of Canada, Vol. 95, No. 1 (whole No. 686, February 2001), pp. 32–33
11. Planets Prefer Safe Neighborhoods
12. ''Checking the yellow evolutionary void. Three evolutionary critical Hypergiants: HD 33579, HR 8752 & IRC +10420''
13. Optical Spectroscopy of 2MASS Color-Selected Ultracool Subdwarfs, Adam J. Burgasser et al., 2006
14. Astrometric and Spectroscopic Confirmation of a Brown Dwarf Companion to GSC 08047-00232, G. Chauvin et al., 2004
15. Dwarfs Cooler than M: the Ddefinition of Spectral Type L Using Discovery from the 2-µ ALL-SKY Survey (2MASS), , J. Davy, Kirkpatrick ''et al'', Astrophysical Journal,
16. New Spectral Types L and T, , J. Davy, Kirkpatrick, Annual Reviews of Astronomy and Astrophysics,
17. Ultra-cool Diminutive Star Weighs In
18. Discovery of the brightest T dwarf in the northern hemisphere, 2007
19. Y-Spectral class for Ultra-Cool Dwarfs, N.R.Deacon and N.C.Hambly, 2006
20. Discovery Narrows the Gap Between Planets and Brown Dwarfs, 2007
21. Bouigue, R. 1954, Annales d'Astrophysique, Vol. 17, p.104
22. Spectral Atlas of Carbon Stars (Barnbaum+ 1996)
23. Keenan, P. C. 1954 Astrophysical Journal, vol. 120, p.484
24. White Dwarf (wd) Stars
25. SkyTonight: The Spectral Types of Stars
External links
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www.twcac.org/Tutorials/spectral_classes.htm
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Libraries of stellar spectra, D. Montes, UCM
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Webfooted Astronomer
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The rate of period change in pulsating DB white dwarf stars, A. H. Corsico, L. G. Althaus, has the DAV, DBV, & DOV explanation.
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The Close DAO+dM Binary RE J0720-318: A Stratified White Dwarf with a Thin H Layer and a Possible Circumbinary Disk DAO type White Dwarf.
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The Spatial Distribution and Kinematics of Cool Metallic Line White Dwarfs, has DAZ and DBZ spectrums
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A K-Band Spectral Atlas of Wolf-Rayet Stars, has WC, WN, and WO spectrums
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Properties of the WO Wolf-Rayet stars, has WO spectrum ranging from WO1 to WO5
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Spectral Types for Hipparcos Catalogue Entries
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[1], has the luminous subclasses.
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Discovery of a Very Young Field L Dwarf, 2MASS J01415823-4633574, J. Davy Kirkpatrick et al.
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