--- Related Arguments ---
Many of the sub-arguments under this page CMDs like: "Interstellar Reddening", "Spectroscopy & Photometry" and "The Two Color Diagram" are each other connected.
Particularly under command "Interstellar Reddening" the follwing sub-arguments plays a fundamental role in the Two Color Diagram ussage.
- (1) "Interstellar Reddening Evidence"
- (2) "O Type Stars Reddening Line Determination"
- (3) "The Ratio of Total to Selective Absorption"
- (4) "The Slope of the Reddening Line"
--- Related Arguments ---
Many of the sub-arguments under this page CMDs like: "Interstellar Reddening", "Spectroscopy & Photometry" and "The Two Color Diagram" are each other connected.
--- Related Arguments ---
Many of the sub-arguments under this page CMDs like: "Interstellar Reddening", "Spectroscopy & Photometry" and "The Two Color Diagram" are each other connected.
Fundamental Spectroscopy & Photometry
Star light is the total sum of energy
of many wavelengths. When this light is spread out to display spectrum, it supplies
us various and important astrophysical information depending upon the presence
or absence of certain wavelengths. Spectral classification started in the second
half of the nineteenth century and from that time, various and important developments
have been bring on it. The two most important systems in spectral classification,
are the Harvard and the Yerkes. Classification of stars is based on patterns
gradation of spectral lines and it is independent from theoretical considerations.
The Harvard classification sequence is characterized by the rise or decline
in the strength of the hydrogen lines throughout its extension. Lines of other
chemical elements could become prominent or less at different stages of the
sequence [ Ionized helium lines appear toward hotter end sequence - O type stars
- while bands of chemical compounds appear toward cooler end sequence - K, M,
R, S stars -]. First Harvard classification scheme, divided spectra into classes
defined by capital letters arranged in alphabetical order and successive revisions
rearranged the order of the groups to produce this final order sequence: O,B,A,F,G,K,M
and sub groups W,R,N. Subsequently the system was complemented with subdivision
denoted by range number 0 to 9 providing thus, a kind of decimal class intervals.
While Harvard system is based on objective prism spectra the Yerkes system is
based on slit spectrograms obtained with a prismatic spectrograph. The advantage
of Yerkes solution - slit spectrograms over objective prism spectrogram.
+s - is due to the fact that the definition of spectra is independent by the
quality of images. Yerkes solution therefore gives much higher quality material
in resolution and contrast. Yerkes system is a development of Harvard classification
and its main difference from Harvard is represented by the introduction of a
second parameter related to the luminosity of the stars (distinction from dwarfs,
giants and supergiants). More on spectroscopy classification and related arguments
under the following links.
© 2006 - Valter Arnò.