One of the standard candle methodologies

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In summary, in the Morgan-Keenan star classification system, the width of certain absorption lines in a star's spectrum is used to determine its luminosity class and size, with lower numbered stars in the same class being hotter. This is a general measure of the star's size and total luminosity output, with class I being supergiants, class III being giants, and class V being main-sequence stars. The width of the spectral lines can also help determine the star's temperature using Wien's law. However, the classification system may be confusing for some and further explanation may be needed.
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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.
 
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“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
 
  • #5


I can provide an explanation for the method of using standard candles to determine the temperature and spectral lines of a star.

Firstly, it is important to understand that stars emit a wide range of electromagnetic (EM) radiation, including visible light. This radiation can be analyzed using a spectrograph, which separates the different wavelengths of light and creates a spectrum.

Wien's law states that the peak wavelength of a blackbody radiation spectrum is inversely proportional to the temperature of the object. This means that by measuring the peak wavelength of a star's spectrum, we can calculate its temperature. This is the first part of the methodology mentioned – using the EM spectrum to determine the temperature of a star.

The next part of the methodology involves looking at the width of the spectral lines in the star's spectrum. Spectral lines are dark or bright lines in a spectrum that correspond to specific wavelengths of light. These lines are caused by the absorption or emission of light by different elements in the star's atmosphere.

The width of these spectral lines can provide information about the physical properties of the star. For example, main sequence stars (like our sun) have relatively narrow spectral lines, while giant stars have broader lines. This is because giant stars have a larger and more turbulent atmosphere, causing the spectral lines to be broader.

Therefore, by analyzing the width of the spectral lines in a star's spectrum, we can determine whether it is a main sequence star or not. This is because main sequence stars have a specific temperature and composition that results in narrow spectral lines.

I hope this explanation helps to clarify the methodology of using standard candles to determine the temperature and spectral lines of stars. If you have any further questions, please feel free to ask.
 

What is a standard candle methodology?

A standard candle methodology is a scientific technique used to measure distances in the universe by comparing the intrinsic brightness of celestial objects, such as stars or galaxies, to their observed brightness.

How does the standard candle methodology work?

The standard candle methodology works by using the known intrinsic brightness of a celestial object, which is determined through other methods such as parallax or spectroscopy, and comparing it to its observed brightness. By knowing the intrinsic brightness and comparing it to the observed brightness, the distance to the object can be calculated.

What are some examples of standard candles?

Some examples of standard candles include Cepheid variables, Type Ia supernovae, and the Tully-Fisher relation for galaxies. These objects have well-known intrinsic brightnesses that can be used to calculate distances to other objects.

What are the advantages of using standard candles?

One of the main advantages of using standard candles is that they provide a reliable and consistent way to measure distances in the universe. They also allow for the measurement of distances to objects that are too far away for other methods to be effective.

Are there any limitations to the standard candle methodology?

Yes, there are limitations to the standard candle methodology. One limitation is that it relies on the assumption that all objects of the same type have the same intrinsic brightness, which may not always be the case. Additionally, the accuracy of the distance measurement can be affected by factors such as dust, which can obscure the observed brightness of an object.

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