Classes of stars

The radiation coming from a black body is continuous in wavelength but dispersing the radiation from a star reveals absorption lines, which can be identified clearly 

The spectral features observed by astronomers have led to the classification of stars into seven broad classes outlined in Table 4.1, together with their surface temperatures. The highest-temperature class, class O, contains may ionised atoms in the spectrum whereas the older stars in class M have a much lower temperature and many more elements present in the spectrum of the star. Observation of a large number of the stars has lead to extensive stellar catalogues, recently extended by the increased sensitivity of the Hubble Space Telescope. Making sense of this vast quantity of information is difficult but in the early 19th century two astronomers 

Spectral type Surface temperature (K) Spectral features 

G 5 500 H absorption weakening with increasing non-ionised heavy elements 

M 3 000 Many heavy element spectra and simple molecules 

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Two classes of stars are presently suggested, IM-AGB stars and RGB stars slightly more massive than the present turn-off mass ([12]). Both are able to provide the ON and NeNa cycles in H burning (in shell in RGB stars and at the base of the convective envelope in AGB) and a mechanism to bring to the surface and then eject the matter, polluting other stars. 

Variable stars are so called because the luminosity of the star varies intrinsically and is not due to the passage of an eclipsing star. One such class of stars is the... 

Sketch the HR diagram and identify the four major classes of stars. A star with radius 7 x 109 m has a surface temperature of 10000 K. Plot its position on the HR diagram and indicate a birth line for this star. 

Sub-mm galaxies are another class of star-forming galaxies at typical redshifts around 2 found using the SCUBA detector5 and pin-pointed from their radio... 

T Tauri stars very young, low-mass stars, less than 10 million years old and under 3 solar-masses, that are still undergoing gravitational contraction. T Tauri stars represent an intermediate stage between a protostar and a low-mass main-sequence star like the Sun. The prototype for this class of stars is T Tau. 

Asymmetric stars are a special class of stars that is characterized by an asymmetry factor compared to the classical symmetric structures described previously. The following parameters have been considered as asymmetry factors ... 

Poly (amidoamine) dendrimers (PAMAM) are new interesting class of star polymers. They have mono dispersive, well defined and developed three-dimensional structures comprising functional groups at high concentration. In its core they have amidic groups. Structurally modified PAMAM dendrimers with 1,8-naphthalimide derivatives are fluorescent dendrimers and they can be applied as effective and selective sensors for different metal cations and protons in organic solvents. This property can be nansferred to other polymer matrixes (for example textiles). 

M Class Star The most common class of stars. These are red dwarf stars and are relatively small and cool. 

Asymmetric stars consist of a special class of star stmaures with molecular weight, functional group, or topological asymmetry" (Figure 4). 

Table 6.5. Spectral features characterizing different classes of stars...

Special (and somewhat rare) classes of stars have much higher abundances of the lanthanides in their atmospheres than does the sun, evidence of unusual stellar processes. On the whole, most stellar matter appears to have relative abundances of heavy elements similar to those of the sun (e.g.. Unsold, 1969). This suggests that statistical aspects have overcome the contributions of individual stars to the overall evolution of interstellar gas composition. Alternatively, current ideas about the origin of matter may be incorrect the universe... 

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