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Disc of debris around an F-type star, HD 181327. [1] An F-type main-sequence star (F V) is a main-sequence, hydrogen-fusing star of spectral type F and luminosity class V. These stars have from 1.0 to 1.4 times the mass of the Sun and surface temperatures between 6,000 and 7,600 K. [2] Tables VII and VIII.
where M and L are the mass and luminosity of the star, respectively, is a solar mass, is the solar luminosity and is the star's estimated main-sequence lifetime. Although more massive stars have more fuel to burn and might intuitively be expected to last longer, they also radiate a proportionately greater amount with increased mass.
Frost crystals may be invisible (black), clear (translucent), or, if a mass of frost crystals scatters light in all directions, the coating of frost appears white. Types of frost include crystalline frost (hoar frost or radiation frost) from deposition of water vapor from air of low humidity, white frost in humid conditions, window frost on ...
Marginal cases are allowed; for example, a star may be either a supergiant or a bright giant, or may be in between the subgiant and main-sequence classifications. In these cases, two special symbols are used: A slash (/) means that a star is either one class or the other. A dash (-) means that the star is in between the two classes.
This white dwarf started its life as a star about twice the sun's mass, living a lifespan of perhaps 1.2 billion years before entering its death throes. Many white dwarfs have a debris disk ...
ζ Ophiuchi is an O9.5 main sequence star, the brightest in the sky at 3rd magnitude. υ Orionis is a main sequence star of spectral type O9.7, although it has sometimes been given the spectral type B0V; Plaskett's star, a massive binary consisting of two O-class stars in orbit around each other and also one of the most massive binaries known.
A heavy coating of hoar frost, called white frost, is very similar in appearance to soft rime, but the formation process is different; it happens when there is no fog, but very high levels of air relative humidity (above 90%) and temperatures below −8 °C (18 °F). Soft rime formations appear as narrow white icy needles and scales.
Dwarf nova HT Cas seen in outburst (mag ~13.4) on November 2, 2010A dwarf nova (pl. novae), or U Geminorum variable, is one of several types of cataclysmic variable star, consisting of a close binary star system in which one of the components is a white dwarf that accretes matter from its companion.