One of the standard candle methodologies

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Discussion Overview

The discussion revolves around the methodology of using standard candles in astronomy, specifically focusing on how the width of spectral lines can indicate whether a star is a main sequence star. Participants express confusion regarding the relationship between spectral line widths and star classification.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions the meaning of spectral line width and its relevance to determining if a star is a main sequence star, specifically asking if it refers to absorption lines.
  • Another participant clarifies that spectral lines can be absorption or emission lines, noting that in this context, it is likely an absorption line, but expresses uncertainty about how the width relates to star classification.
  • A third participant provides an overview of the Morgan-Keenan classification system, explaining how spectral types and luminosity classes are determined by the width of absorption lines, suggesting that this is a measure of the star's size and luminosity.
  • Links to external resources are shared for further reading on stellar classification and the structure of spectral lines.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the specific relationship between spectral line width and main sequence classification, with some expressing confusion and others providing information that may not fully clarify the issue.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the definitions of spectral lines and the specifics of the classification system. The relationship between spectral line width and star classification remains unresolved.

Who May Find This Useful

This discussion may be of interest to those studying stellar classification, astrophysics, or anyone seeking to understand the methodologies used in determining star properties through spectral analysis.

ehabmozart
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In one of the standard candle methodologies, it is given in my book that by looking at the EM spectrum , we can know the temp. of the star by wien's law... To this point, everything's fine... now, the next sentence is FROM THE WIDTH OF THE SPECTRAL LINES, YOU CAN DETERMINE WHETHER OR NOT IT IS A MAIN SEQUENCE STAR... This part is completely confusing.. I understand nothing and don't know what do they mean by this. What is the width of spectral line. DO they mean the absobtion lines and how would that determine whether it is a main sequence star or NOT? I really need help, so whoever can contribute with a fine answer, i am so thankful to him/her. Thanks!
 
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The spectral line can be either an absorption or emission line depending of what you are looking for. In this case it is an absorption line. As for how the width tells you if it's a main sequence star or not, I don't know.
 
“In the current star classification system, the Morgan-Keenan system, the spectrum letter is enhanced by a number from 0 to 9 indicating tenths of the range between two star classes, so that A5 is five tenths between A0 and F0, but A2 is two tenths of the full range from A0 to F0. Lower numbered stars in the same class are hotter. Another dimension that is included in the Morgan-Keenan system is the luminosity class expressed by the Roman numbers I, II, III, IV and V, expressing the width of certain absorption lines in the star's spectrum. It has been shown that this feature is a general measure of the size of the star, and thus of the total luminosity output from the star. Class I are generally called supergiants, class III simply giants and class V either dwarfs or more properly main-sequence stars. For example, our Sun has the spectral type G2V, which might be interpreted as "a 'yellow' two tenths towards 'orange' main-sequence star". The apparently brightest star Sirius has type A1V.”:
http://en.wikipedia.org/wiki/Stellar_classification

Hertzsprung-Russell Diagrams and Structure of Spectral Lines:
http://web.njit.edu/~gary/321/Lecture6.html

Classification of stars using Spectral line widths:
http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.shtml
 

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