Stellar Classification System (old)

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**The Stellar Classification System** was created by the **Interstellar Association for Research and Progress** **(IASPR)** as a way to officially categorize different astronomical objects observed in **The Silky Way**. It is split into three groups: **Stars**, **Stellar Remnants**, and **Exotic Objects**.

Note: Feel free to add your star to the examples section, with a link.

## Stars

Stars are mainly classified by their spectrum and their luminosity.

### Spectral Classification

In the spectral classification system, stars are classified by their emission spectrum. From lowest (red colored) to highest (blue colored), classification groups follow this order: Y, T, L, M, K, G, F, A, B, O, W, P, I with subtypes from 9 to 0. Hotter stars have lower numbers, but only within the same spectral group (examples: M1 is cooler than G8 and K1 is hotter than K5).

Also, some M, most L, and all T and Y are brown dwarfs.

* Y Dwarfs, the coldest and dullest of the brown dwarfs, have atmospheres composed largely of water and ammonia, possibly existing in the form of ice clouds. Due to the time it takes for brown dwarfs to cool to the Y stage, Y dwarfs are very rare, but more and more will form as the universe ages. These Y dwarfs have effective temperatures lower than 600 K, some of them are even at room temperature! They would be violet in appearance.
* T Dwarfs are composed, unlike their hotter cousins, largely of methane (CH4) and, like L dwarfs, have large amounts of alkali metals, although, unlike L dwarfs, they lack substantial amounts of metal hydrides. They typically range in effective temperature from 600 K to 1400 K, and visually would appear magenta.
* L Dwarfs are composed largely of the same materials as M dwarfs, but with significantly higher amounts of metal hydrides (FeH, CrH, MgH, CaH) and alkali metals (Na I, K I, Cs I and Rb I). They may also have quantities of lithium in their composition. They have effective temperatures between 1400 K and 2500 K. They would be a dull red in appearance.
* M Class objects can be either stars or young brown dwarfs.
	+ M Class Brown Dwarfs are the youngest and hottest of the brown dwarfs and occupy the late stage of the M spectrum (M6.5 or later). They are composed largely of the same materials as sunspots: carbon monoxide, molecular hydrogen and water vapor. The presence of lithium in their composition is often used as a test to differentiate them from M stars. They have effective temperatures (surface temperatures) greater than about 2500 K. Visually, an M dwarf would have a bright red appearance, similar to M stars (red dwarfs).
	+ M class stars are generally red and dim and usually invisible to the naked eye from afar. They live for hundreds of billions, even trillions of years and have extremely close in habitable zones (often under 0.05 AU). Their emission spectrums peak in the infrared and red part of the electromagnetic spectrum, which is why they are often called Red Dwarfs. They also often behave unpredictably during the first billion years of their lives, changing their brightness by a factor of two in only a few minutes. They are also usually, but not always, flare stars. This means that life around M dwarfs have to adapt to constant changes in brightness and large amounts of solar activity, especially if the star is young. Nevertheless, life still managed to get a foothold in red dwarf solar systems.
* K class stars are smaller than the Sun, and more orange in color, which is why they are often nicknamed "orange dwarfs". Most K stars are not bright enough to be seen with the naked eye from the Sun. Small K stars can live up to 50 billion years, and larger K (main sequence) stars may host planets that are not tidally locked. K stars have emission spectrums that peak in the orange and yellow areas of the electromagnetic spectrum, depending on the type of K star. These stars also emit less ionizing radiation than the Sun, making these stars some of the best candidates for life as we know it.
* G class stars are generally the same size as the sun, although most of them are smaller (the sun is a G2 star, which is relatively large for a G-type). These stars are also generally referred to as yellow dwarf stars, although the spectrum they emit is white. G-type emission spectrums generally peak in the green portion of the electromagnetic spectrum. Late G-types are some of the best stars for hosting life (similar to Early K-types), as they emit relatively low levels of ionizing radiation and remain in the main sequence for a long time (up to 20 billion years, 10 billion for the Sun).
* F class stars are often referred to as yellow-white stars, although they emit white (and slightly blue for larger F types) light in reality. These stars emit more (and harsher) light than the Sun, with the emission spectrum peaking in the blue (and violet for larger stars) range of light and with a significant fraction of the spectrum being composed of UV rays. These stars also live for less time than the Sun: about 3-7 billion years. However, F-type stars are still manageable in terms of UV and lifespan, so these stars are still good possibilities for hosting life.

* A class stars are bluish-white in color, and they are the most abundant stars that are visible to the naked eye from the Verda System (and most other populated systems). These stars typically live for 1-4 billion years, barely enough time for life to get started in some cases. The emission spectrum given by these stars also peak firmly in ultraviolet light. Despite the large amount of radiation and short lifespans, Terallan scientists think life may have a chance of surviving around small A-type star, as they have (barely) tolerable UV emission and lifespans. After all, life usually finds a way. *Usually.*

Sidenote: A class stars used to be used as the baseline for "white" color stars. This role is now taken by F-class stars.

* B class stars are a pretty blue color, and live for a ridiculously short 100 million to 1 billion years. They also emit a deadly amount of radiation, as the emission spectrum is almost entirely UV and violet light. Needless to say, life probably has a hard time surviving around stars like these. Some Terallan scientists remain optimistic though.

* O class stars are staggeringly large, usually exceeding 16 solar masses. They have luminosities sometimes millions of times more than the Sun, and live for less than 100 million years. Most planet forming materials probably get stripped away into deep space by intense solar winds. Even if planetary formation was possible, they most likely wouldn't have enough time to fully grow into true planets. For this reason, many scientists think planets around O-type stars are short-lived and rare. Plus, there are too many harmful X-rays and UV rays being emitted from these stars. Therefore, virtually no scientists from any planet believe O-type stars are capable of supporting life (unless of course, they are counting stars that formed as M-type and slowly became O-type, which would be *great.*)

* W class stars are Wolf-Rayet stars. They're extremely luminous and massive stars that are releasing tremendous amounts of energy. The average mass of Wolf-Rayet stars is around 25 solar masses, but the most massive Wolf-Rayet stars can exceed 100 solar masses! These stars mostly live only 500 thousand years. At the end of their lives, W class stars mostly explode in Ib or Ic type supernovas. They actually evolve from stars with masses of that of the O-class stars, and are the final stage of their lives.

* P class stars are the largest, most dangerous stars in the universe. They live for an absolutely ludicrously short time period of 3000000 years. This means that they can only be found in stellar nurseries, and absolutely no one thinks that they can support life, considering that they don't even live long enough to form planets. P class stars are also likely the first to be targeted for starlifting to avoid them going supernova, and killing everyone within 300 light years (yes, their supernovae are that powerful.) Note: P class stars have a very small metallicity, smaller than that of the O class star. This is one of the reason why P class stars are so hot.
* I class stars are the ultimate toppers of the universe. They are so rare only 1 out of 1.3 TRILLION (1,300,000,000,000) stars are I-type. They are so rare they aren't mentioned in the textbooks, but they are in fact, larger, hotter and brighter than even P class stars. What's ironic is that they normally start their lives as oversized P-type stars. They consist of an evolved P-type star that has passed the red hypergiant phase, and into the yellow hypergiant/ LBV stage. But they also have a compact star at their center, commonly a neutron star or a black hole. The neutron star/black hole can eat the star from inside, not allowing for formed-via-nuclear-fusion complex elements to form and so prolonging the life of the star. The neutron star and black hole than blasts radiation out so much it the star balloons in size and brightness and temperature, so much they rank in the largest stars in the universe. The radiation jets of the compact star inside the I class star come out through the surface, bringing so much material with them they can last for several hundred lightyears before finally calming down and forming a sphere of mass and energy around the star, measuring 100 lighryears in radius, at least. Then, the solar wind of the star becomes so powerful I class stars can easily create extremely active starburst nebulas, just like Aesin and the Apple Nebula.

Their incredible rareness means that in the Silky Way, there is only 1 I class star, which is Aesin. Aesin is visible in Teralla's night sky, and is one of the brightest stars in the Terallan night sky, despite being over 10,000 lightyears away. It is so bright in Teralla's night sky because of its 39,512,324-solar-luminosity luminosity. Its mass is 421.52 Solar masses, which makes it the most massive star in the Silky way itself. Its size is 844.302 Solar Radii and its temperature is a staggering 74,592 Kelvin, which is extremely hot for a star. That makes it able to build the biggest star factory in the galaxy, the infamous Apple Nebula, 620 lightyears wide, 570 lightyears tall and 654 lightyears deep. This is the second largest independent structure in the Silky Way, beaten by the Kerillis Nebula.

In short, I class stars are worse than even P class stars, but are so rare they aren't mentioned a lot in textbooks.

The average stats of an I class star:

Mass: 200 - 800 SM

Radius: 200 - 5000 SR

Temperature: 60000 - 300000 K

Luminosity: 20 Million to 66 Trillion

Lifetime: 1 yoctosecond to 4 million years

### Luminosity Classification

Luminosity Classifications, otherwise known as the Yark stellar classification system, is a system that is tacked on to the end of a spectral classification, based solely on luminosity. The classes are denoted with Adelphan numerals for some reason, probably to distinguish them from the ordinary numbers of the spectral classification.

* 0: Hypergiants or ridiculously luminous supergiants
* I: Supergiants
	+ Ia: Luminous supergiants
	+ Ib: Intermediate-size luminous supergiants
	+ Ic: less luminous supergiants
* II: Bright Giants
* III: Ordinary Giants
* IV: Subgiants
* V: Main Sequence
* VI: Subdwarfs
* B: Brown Dwarfs

### Notation Examples

Verda A: M4.5 V

Kerillis: P9 V

Kegåsis: M1.2 0

Aesin: I6.9

Anhooie: F6.5 V

Verda B: M7.6 VI

Vernarca A: WN2

### Spectral Peculiarities

Additional nomenclature, in the form of lower-case letters, can follow the spectral type to indicate peculiar features of the spectrum.

### Snacchi Classes

During the 1860s and 1870s, pioneering stellar spectroscopist Angelo Snacchi created the *Snacchi classes* in order to classify observed spectra. By 1866, he had developed three classes of stellar spectra, shown in the table below.

In the late 100s AFO, this was later superseded by the above classification.

 Snacchi Class I (Erian Subtype)
 Snacchi Class II
 Snacchi Class III
 Snacchi Class IV
 Snacchi Class V
Emission-line stars, such as Gamma Cassis and Sheliakon, which are in modern class Be. In 1891, Ed Piccqueris proposed that class V should correspond to the modern class O (which then included Wolf-Rayet stars) and stars within planetary nebulae.

### Dapper System

In the 30s AFO, the astronomer Ed C. Piccqueris began to make a survey of stellar spectra at the Harvard College Observatory, using the objective-prism method. A first result of this work was the *Dapper Catalogue of Stellar Spectra*, published in 34. William Flam classified most of the spectra in this catalogue.

The catalogue used a scheme in which the previously used Snacchi classes (I to V) were subdivided into more specific classes, given letters from A to P. Also, the letter Q was used for stars not fitting into any other class.

Classes carried through into the Yark system are in **BOLD DAMMIT**.

### Mount Vera Classes

A luminosity classification known as the Mount Vera system was used to distinguish between stars of different luminosities. This notation system is still sometimes seen on modern spectra.

 d
 sg
 g
 c

### Extended Spectral Types

A number of new spectral types have been taken into use from newly discovered types of stars.

#### Extensions of Class W

Once included as type O stars, the Wolf-Rayet stars of class W or WR are noted for spectra without hydrogen lines. Instead their spectra are dominated by broad emission lines of highly ionized helium, nitrogen, carbon, and sometimes oxygen. They are thought to mostly be dying supergiants with their hydrogen layers blown away by stellar winds, thereby directly exposing their hot helium shells. Class W is further divided into subclasses according to the relative strength of nitrogen and carbon emission lines in their spectra (and outer layers).

The W spectral range is listed below.

* WN – spectrum dominated by N III-V and He I-II lines
	+ WNE (WN2 to WN5 with some WN6) – hotter or "early"
	+ WNL (WN7 to WN9 with some WN6) – cooler or "late"
	+ Extended WN classes WN10 and WN11 sometimes used for the Ofpe/WN9 stars
	+ h tag used (e.g. WN9h) for WR with hydrogen emission and ha (e.g. WN6ha) for both hydrogen emission and absorption
* WN/C – WN stars plus strong C IV lines, intermediate between WN and WC stars
* WC – spectrum with strong C II-IV lines
	+ WCE (WC4 to WC6) – hotter or "early"
	+ WCL (WC7 to WC9) – cooler or "late"
* WO (WO1 to WO4) – strong O VI lines, extremely rare

Although the central stars of most planetary nebulae (CSPNe) show O type spectra, around 10% are hydrogen-deficient and show WR spectra. These are low-mass stars and to distinguish them from the massive Wolf-Rayet stars, their spectra are enclosed in square brackets: e.g. [WC]. Most of these show [WC] spectra, some [WO], and very rarely [WN].

### Peculiar Brown Dwarfs

Young brown dwarfs have low surface gravities because they have larger radii and lower masses compared to the field stars of similar spectral type. These sources are marked by a letter beta (β) for intermediate surface gravity and gamma (γ) for low surface gravity. Indication for low surface gravity are weak CaH, K I and Na I lines, as well as strong VO line. Alpha (α) stands for normal surface gravity and is usually dropped. Sometimes an extremely low surface gravity is denoted by a delta (δ). The suffix "pec" stands for peculiar. The peculiar suffix is still used for other features that are unusual and summarizes different properties, indicative of low surface gravity, subdwarfs and unresolved binaries. The prefix sd stands for subdwarf and only includes cool subdwarfs. This prefix indicates a low metallicity and kinematic properties that are more similar to halo stars than to disk stars. Subdwarfs appear bluer than disk objects. The red suffix describes objects with red color, but an older age. This is not interpreted as low surface gravity, but as a high dust content. The blue suffix describes objects with blue near-infrared colors that cannot be explained with low metallicity. Some are explained as L+T binaries, others are not binaries, such as Yakto and are explained with thin and/or large-grained clouds.

 sd
 β
 γ
 red
 blue

### White Dwarf Classifications

The class D (for Degenerate) 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 spectral types DA, DB, DC, DO, DQ, DX, and DZ. The letters are not related to the letters used in the classification of other stars, but instead indicate the composition of the white dwarf's visible outer layer or atmosphere.

The white dwarf types are as follows:

* DA – a hydrogen-rich atmosphere or outer layer, indicated by strong Balmer hydrogen spectral lines.
* DB – a helium-rich atmosphere, indicated by neutral helium, He I, spectral lines.
* DO – a helium-rich atmosphere, indicated by ionized helium, He II, spectral lines.
* DQ – a carbon-rich atmosphere, indicated by atomic or molecular carbon lines.
* DZ – a metal-rich atmosphere, indicated by metal spectral lines (a merger of the obsolete white dwarf spectral types, DG, DK, and DM).
* DC – no strong spectral lines indicating one of the above categories.
* DX – spectral lines are insufficiently clear to classify into one of the above categories.

The type is followed by a number giving the white dwarf's surface temperature. This number is a rounded form of 50400/*T*eff, where *T*eff is the effective surface temperature, measured in kelvins. Originally, this number was rounded to one of the digits 1 through 9, but more recently fractional values have started to be used, as well as values below 1 and above 9.

Two or more of the type letters may be used to indicate a white dwarf that displays more than one of the spectral features above.

#### Extended White Dwarf Spectral Types

* DAB – a hydrogen- and helium-rich white dwarf displaying neutral helium lines.
* DAO – a hydrogen- and helium-rich white dwarf displaying ionized helium lines.
* DAZ – a hydrogen-rich metallic white dwarf.
* DBZ – a helium-rich metallic white dwarf.

A different set of spectral peculiarity symbols are used for white dwarfs than for other types of stars:

 E
 H
 V
 PEC

### Non-stellar Spectral Types

Finally, the classes **R** and **S**, left over from the Dapper system, are occasionally used for certain non-stellar objects. Type R objects are stars within planetary nebulae and type S objects are novae.

## Stellar Remnants

* Z class stellar remnants are black holes, which have an escape velocity equal or greater than the speed of light. They come in 4 different subtypes, based on mass.
	+ Za class black holes are Stellar Mass Black Holes, which are very common and form from the supernova of a high-mass star.
	+ Zb class black holes are Intermediate Mass Black Holes, which form from mergers of stellar mass black holes. They are most common near the center of the galaxy.
	+ Zc class black holes are Supermassive Black Holes, which form from gravitational collapse of clouds of gas in the centers of galaxies.
	+ Zd class black holes are ULTRAMASSIVE BLACKHOLES, found at the centers of quasars and very big galaxies. they are very rare.
	+ Zy class black holes are artificial kugelblitz black holes, often used as batteries by advanced civilizations.
	+ Zx class black holes are primordial black holes, which formed in the big bang in ridiculous numbers and are the mass of planets.

* Q class stellar remnantsare known by the less convoluted name neutron stars. These are the hot, dense remains of supermassive stars that weren't quite massive enough to form black holes. Neutron stars are made primarily of neutrons, hence the name. They have some subclasses, most of which are actually under "Exotic Objects"
	+ Q\* class stellar remnants are pulsars, which used to be under Q class, but this was replaced when someone figured out that pulsars were basically neutron stars.
	+ Q^ class stellar remnants are magnetars. These stars spin very fast and have a gigantic magnetic field. They are pretty uncommon.

* D class stellar remnants are White Dwarfs. They are the remains of small stars under 9 solar masses, and are under 1.4 solar masses.
	+ D; class stellar remnants are Black Dwarfs, which are the cooled remains of white dwarfs. The universe is not old enough for these to have formed. They are under 150 K.
	+ D\* class stellar remnants are Grey dwarfs, which are a sort of intermediate stage between white dwarfs and black dwarfs. They are generally under 600 K.

## Exotic Objects™

* X class objects are Wormholes, which are common across the galaxy, and allow long-distance interstellar travel. We have not yet found any which exit the galaxy. *Yet.* The Creator is hypothesized to be a member of X class.

* J class objects are artificial megastructures, which are common around populated systems.
* Qƣ class objects are Quark Stars, a subclass of neutron star. They are rather exotic, so I put them under Exotic Objects.
	+ Qȹ class objects are Strange Stars, another subclass of neutron star. These are quark stars, but their interiors have been converted into Strange Matter, an exotic type of matter that is exotic.
* Qe class objects are Electroweak stars, which have conditions so extreme that the electromagnetic and weak forces unify. They have a core approximately twice the mass of earth, and the size of your average Rellisian Apple.
* Qp class objects are Preon Stars, which have a core so extreme that even quarks disassemble themselves into Preons, their constituents.

* H class objects are Iron Stars, which are former white dwarfs that are so old that quantum tunneling has turned the entire thing into Iron.

## Examples

Here, edit the page to plug in examples of each star type.

### Stars

#### **M class:**

* Yakto (M9.5 B)

* Verda A (M4.5 V)

* Klein (M9 VI!e)

* Dar A (M7 V)
* Verda B (M7.6 VI)