Post by Dazo on Aug 25, 2004 1:56:12 GMT -5
What I should have done in the first place, look on the net. Here's some stellar descriptions amongst other things that may interest you or help you when designing a world.
Contents
I- STAR CLASS
II-RED DWARVES
III-NEW STAR TYPES
IV-R,N,S TYPES
V-LUMINOSITY
VI-TEMPERATURE
VII-BROWN DWARVES
VIII- SKY COLOUR
IX-WORLD CONCEPTS
X-STARPORTS
XI-PEOPLE AND PLANTS
I) STAR CLASS
II) RED DWARVES
III) NEW STAR TYPES
IV) R,N,S TYPE STARS
V) LUMINOSITY
VI) TEMPERATURE
Contents
I- STAR CLASS
II-RED DWARVES
III-NEW STAR TYPES
IV-R,N,S TYPES
V-LUMINOSITY
VI-TEMPERATURE
VII-BROWN DWARVES
VIII- SKY COLOUR
IX-WORLD CONCEPTS
X-STARPORTS
XI-PEOPLE AND PLANTS
I) STAR CLASS
Class O stars are very hot and very luminous, being strongly blue in colour. Naos (in Puppis) shines with a power close to a million times solar. These stars have prominent ionized and neutral helium lines and only weak hydrogen lines. Class O stars emit most of their radiation in ultra-violet.
Class B stars are again extremely luminous, Rigel (in Orion) is a prominent B class blue supergiant. Their spectra have neutral helium and moderate hydrogen lines. As O and B stars are so powerful, they live for a very short time. They do not stray far from the area in which they were formed as they don't have the time. They therefore tend to cluster together in what we call OB1 associations, which are associated with giant molecular clouds. The Orion OB1 association is an entire spiral arm of our Galaxy (brighter stars make the spiral arms look brighter, there aren't more stars there) and contains all of the constellation of Orion.
Class A stars are amongst the more common naked eye stars. Deneb in Cygnus is another star of formidable power, while Sirius is also an A class star, but not nearly as powerful. As with all class A stars, they are white. Many white dwarves are also A. They have strong hydrogen lines and also ionized metals.
Class F stars are still quite powerful but they tend to be main sequence stars, such as Fomalhaut in Pisces Australis. Their spectra is characterized by the weaker hydrogen lines and ionized metals, their colour is white with a slight tinge of yellow.
Class G stars are probably the most well known if only for the reason that our Sun is of this class. They have even weaker hydrogen lines than F but along with the ionized metals, they have neutral metals. G is host to the "Yellow Evolutionary Void". 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.
Class K are orange stars which are slightly cooler than our Sun. Some K stars are giants and supergiants, such as Antares 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.
Class M is by far the most common class if we go by the number of stars. All our red dwarves go in here and they are plentiful; more than 90% of stars are red dwarfs, such as Proxima Centauri. M is also host to most giants and some supergiants such as Arcturus and Betelgeuse, as well as Mira variables. The spectrum of an M star shows lines belonging to molecules and neutral metals but hydrogen is usually absent. Titanium oxide can be strong in M stars.
Class B stars are again extremely luminous, Rigel (in Orion) is a prominent B class blue supergiant. Their spectra have neutral helium and moderate hydrogen lines. As O and B stars are so powerful, they live for a very short time. They do not stray far from the area in which they were formed as they don't have the time. They therefore tend to cluster together in what we call OB1 associations, which are associated with giant molecular clouds. The Orion OB1 association is an entire spiral arm of our Galaxy (brighter stars make the spiral arms look brighter, there aren't more stars there) and contains all of the constellation of Orion.
Class A stars are amongst the more common naked eye stars. Deneb in Cygnus is another star of formidable power, while Sirius is also an A class star, but not nearly as powerful. As with all class A stars, they are white. Many white dwarves are also A. They have strong hydrogen lines and also ionized metals.
Class F stars are still quite powerful but they tend to be main sequence stars, such as Fomalhaut in Pisces Australis. Their spectra is characterized by the weaker hydrogen lines and ionized metals, their colour is white with a slight tinge of yellow.
Class G stars are probably the most well known if only for the reason that our Sun is of this class. They have even weaker hydrogen lines than F but along with the ionized metals, they have neutral metals. G is host to the "Yellow Evolutionary Void". 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.
Class K are orange stars which are slightly cooler than our Sun. Some K stars are giants and supergiants, such as Antares 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.
Class M is by far the most common class if we go by the number of stars. All our red dwarves go in here and they are plentiful; more than 90% of stars are red dwarfs, such as Proxima Centauri. M is also host to most giants and some supergiants such as Arcturus and Betelgeuse, as well as Mira variables. The spectrum of an M star shows lines belonging to molecules and neutral metals but hydrogen is usually absent. Titanium oxide can be strong in M stars.
II) RED DWARVES
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. They comprise the vast majority of stars and have a diameter and mass of less than one-third that of the Sun (down to 0.08 solar masses, which are Brown dwarves) and a surface temperature of less than 3,500 K. They emit little light, sometimes as little as 1/10,000th that of the sun. Due to the slow rate at which they burn hydrogen, red dwarves have an enormous estimated lifespan; estimates range from tens of billions up to trillions of years. Red dwarves never initiate helium fusion and so cannot become red giants; the stars slowly contract and heat up until all the hydrogen is consumed. In any event, there has not been sufficient time since the big bang for red dwarfs to evolve off the main sequence.
III) NEW STAR TYPES
The new class L are stars that are a very dark red in colour; they are brightest in infra red. Their gas is cool enough to allow metal hydrides and alkali metals to be prominent in the spectrum.
Right at the bottom of the scale is T. 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 degrees or more for O stars, being a cool 700 degrees Celsius. Complex molecules can form, evidenced by the strong methane lines in their spectra.
T and L could be more common than all the other classes combined, if recent research is accurate. From studying the number of propylids (clumps of gas in nebulae from which stars are formed) then the number of stars in the galaxy should be several orders of magnitude higher than what we know about. It's theorised that these propylids 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 propylids in the vicinity, stripping them of their gas. The victim propylids 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 (no star below 0.8 solar masses has ever died in the history of the galaxy) then these smaller stars will accumulate over time.
Right at the bottom of the scale is T. 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 degrees or more for O stars, being a cool 700 degrees Celsius. Complex molecules can form, evidenced by the strong methane lines in their spectra.
T and L could be more common than all the other classes combined, if recent research is accurate. From studying the number of propylids (clumps of gas in nebulae from which stars are formed) then the number of stars in the galaxy should be several orders of magnitude higher than what we know about. It's theorised that these propylids 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 propylids in the vicinity, stripping them of their gas. The victim propylids 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 (no star below 0.8 solar masses has ever died in the history of the galaxy) then these smaller stars will accumulate over time.
IV) R,N,S TYPE STARS
Also occasionally used are the stellar classifications R, N and S. R and N stars are carbon stars (that is, giants) which run 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. S stars have ZrO lines rather than TiO, and are in between the M stars and the carbon stars. S stars have carbon and oxygen abundances are almost exactly equal, and both elements are locked up almost entirely in CO molecules. For stars cool enough for CO to form that molecule tends to "eat up" all of whichever element is less abundant, resulting in "leftover oxygen" on the normal main sequence, "leftover carbon" on the C sequence, and "leftover nothing" on the S sequence.
V) LUMINOSITY
A star's full spectral classification often also includes a 'luminosity class', a Roman numeral from I to VII indicating the star's luminosity, which correlates with its mass. The luminosity class is simply appended to the spectral class. So, for example, the Sun's full spectral classification, including its luminosity class, is G2V. The seven luminosity classes are listed below.
I Supergiants: extremely massive and luminous stars, usually nearing the end of their lifespan. They are subclassified as Ia or Ib, with Ia representing the most luminous stars of all. Examples include Rigel (B8Ia), Betelgeuse (M2Ib) and Antares (M1Ib).
II Bright Giants: a relatively uncommon group of giant stars that are particularly luminous, and can be a thousand times more so than the Sun, or more. Examples include Adara (B2II), Sargas (F1II) and Kraz (G5II).
III Normal Giants: the giant stars in this category are typically a hundred times more luminous than Earth's Sun, and considerably more massive. Examples of this populous group include Arcturus (K2III), Agena (B1III) and Aldebaran (K5III).
IV Subgiants: though still far more massive and luminous than the Sun, subgiants fall short of the true giants. Examples include Acrux (B0.5IV), Shaula (B1.5IV) and Miaplacidus (A2IV).
V Dwarfs: a very numerous class of main sequence stars, whose mass and luminosity is generally comparable with that of the Sun. Examples include Sirius (A0V), Alpha Centauri (G2V) and Vega (A0V).
VI & VII These classes designate subdwarfs and white dwarfs, respectively. They are not now in common use, but are included here for completeness.
I Supergiants: extremely massive and luminous stars, usually nearing the end of their lifespan. They are subclassified as Ia or Ib, with Ia representing the most luminous stars of all. Examples include Rigel (B8Ia), Betelgeuse (M2Ib) and Antares (M1Ib).
II Bright Giants: a relatively uncommon group of giant stars that are particularly luminous, and can be a thousand times more so than the Sun, or more. Examples include Adara (B2II), Sargas (F1II) and Kraz (G5II).
III Normal Giants: the giant stars in this category are typically a hundred times more luminous than Earth's Sun, and considerably more massive. Examples of this populous group include Arcturus (K2III), Agena (B1III) and Aldebaran (K5III).
IV Subgiants: though still far more massive and luminous than the Sun, subgiants fall short of the true giants. Examples include Acrux (B0.5IV), Shaula (B1.5IV) and Miaplacidus (A2IV).
V Dwarfs: a very numerous class of main sequence stars, whose mass and luminosity is generally comparable with that of the Sun. Examples include Sirius (A0V), Alpha Centauri (G2V) and Vega (A0V).
VI & VII These classes designate subdwarfs and white dwarfs, respectively. They are not now in common use, but are included here for completeness.
VI) TEMPERATURE
O: 30,000 - 60,000 K Blue stars
B: 10,000 - 30,000 K Blue-white stars
A: 7,500 - 10,000 K White stars
F: 6,000 - 7,500 K Yellow-white stars
G: 5,000 - 6,000 K Yellow stars (like the Sun)
K: 3,500 - 5,000K Yellow-orange stars
M: < 3,500 K Red stars
B: 10,000 - 30,000 K Blue-white stars
A: 7,500 - 10,000 K White stars
F: 6,000 - 7,500 K Yellow-white stars
G: 5,000 - 6,000 K Yellow stars (like the Sun)
K: 3,500 - 5,000K Yellow-orange stars
M: < 3,500 K Red stars
