Globular cluster luminosity function

Xiv ReprintIn summary, astronomers use various techniques such as parallax, classical Cepheid variable stars, and Type 1a supernovae to measure cosmological distances. However, the Globular Cluster Luminosity Function, while a useful tool, is not as accurate as other methods due to potential systematic errors. More research is needed to calibrate its zero-point and improve its accuracy.
  • #1
John Titor
6
0
So I was interested in how astronomers measure the distances to other stars, galaxies, etc and I found this pdf about the subject http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1992PASP..104..599J&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf [Broken]
It seems to be a good source but I still don't understand exactly how it is done, and don't have a high level of math understanding yet. I'm mostly interested in the globular cluster luminosity function, and the steps taken to actually get a distance to another galaxy etc. I understand a little bit about it but there is quite a bit such as the math that I don't understand. Can anyone help and explain this to someone who doesn't know much about the subject? Thank you.
 
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  • #2
John Titor said:
So I was interested in how astronomers measure the distances to other stars, galaxies, etc and I found this pdf about the subject http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1992PASP..104..599J&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf[/URL]
It seems to be a good source but I still don't understand exactly how it is done, and don't have a high level of math understanding yet. I'm mostly interested in the globular cluster luminosity function, and the steps taken to actually get a distance to another galaxy etc. I understand a little bit about it but there is quite a bit such as the math that I don't understand. Can anyone help and explain this to someone who doesn't know much about the subject? Thank you.[/QUOTE]
It is a good source, but a bit out-dated with regard to Type 1a SNe. There are several techniques used by astronomers to determine cosmological distances, some more accurate than others.

[INDENT]d = 1/p[/INDENT]

Where:
[INDENT]p = The angle between the sun and Earth's position in relationship to the star, measured in arcseconds
d = The distance in parsecs[/INDENT]

Parallax is without a doubt the most accurate means of measuring cosmological distances, but measuring the parallax of objects further than ~1,000 light years is extremely difficult. The star is measured in relationship to the surrounding stars, and then six months later, when the Earth is as far from when the original measurements were taken as possible, the relationship to the surrounding stars is measured again. Parallax is measured in arcseconds

Out to approximately a million parsecs, classical Cepheid variable stars can be used to determine cosmological distances. All classical Cepheid variable stars have a direct correlation between their rate of pulsation and their absolute magnitude. Once the absolute magnitude is known, the distance can be calculated using the apparent magnitude.

[INDENT]d = 10[SUP]((m - M)+5) / 5[/SUP][/INDENT]

Where:
[INDENT]M = Bolometric absolute magnitude;
m = Bolometric apparent magnitude;
d = Distance in parsecs.[/INDENT]

At cosmological distances beyond one megaparsec Type 1a SNe can be used. However, care must be taken to ensure that it is not a Type 1ax SNe because they have a dimmer absolute magnitude, or a super-Chandrasekhar Type 1a SNe which have a brighter absolute magnitude. All Type 1a SNe have an absolute magnitude of -19.3.

See also:
[URL]http://www.nature.com/nature/journal/v443/n7109/full/nature05103.html[/URL] - Nature 443, 308-311 (21 September 2006) | doi:10.1038/nature05103; Received 7 April 2006; Accepted 18 July 2006 [I](paid subscription)[/I] - [URL='http://arxiv.org/pdf/astro-ph/0609616v1.pdf']arXiv Reprint[/URL]
[URL='http://iopscience.iop.org/0004-637X/767/1/57/']Type 1ax Supernovae: A New Class of Stellar Explosion[/URL] - The Astrophysical Journal Volume 767 Number 1, 2013 March 25 [I](free issue)[/I]

Lastly, and the least accurate of all the methods used, is red shift. A spectrum of the object is taken and the amount of the object's light that has shifted into the infrared part of the spectrum indicates how far away the object must be.
 
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  • #3
Thank you for the response though there wasn't much about GCLF it was helpful
 
  • #4
John Titor said:
Thank you for the response though there wasn't much about GCLF it was helpful
The Globular Cluster Luminosity Function is based upon the premise that old (metal-poor) globular clusters exhibit a universal shape in luminosity that can be characterized by some number that can be used as a "standard candle." However, the systematic error inherent in the GCLF method makes it less accurate than measuring Surface Brightness Fluctuations, Planetary Nebula Luminosity Function, or classical Cepheid variable distance indicators. It has also been suggested that super-Chandrasekhar Type 1a SNe are more likely in globular clusters due to the integrated flux density of pulsars. The use of the GCLF to determine cosmological distances hinges on accurate and relevant calibration of the zero-point of the GCLF turnover and shape.

Sources:
Globular cluster luminosity function as distance indicator - Astrophysics & Space Science (September 2012), Volume 341, Issue 1, pp 195-206 (paid subscription) - arXiv free reprint
Dynamical friction in constant density cores: a failure of the Chandrasekhar formula - Monthly Notices of the Royal Astronomical Society (2006) 373 (4): 1451-1460, published December 21, 2006 (free issue)
 

1. What is a globular cluster luminosity function?

A globular cluster luminosity function is a graph that shows the number of stars in a globular cluster at different magnitudes (brightness). It is used to study the distribution and properties of stars within the cluster, such as their ages and evolution.

2. How is a globular cluster luminosity function created?

A globular cluster luminosity function is created by counting the number of stars in a globular cluster at different magnitudes. This data is then plotted on a graph, with the number of stars on the y-axis and magnitude on the x-axis.

3. What can we learn from a globular cluster luminosity function?

A globular cluster luminosity function can tell us about the age and evolution of stars within the cluster. It can also provide insight into the formation and structure of the cluster itself.

4. How are globular cluster luminosity functions used in research?

Globular cluster luminosity functions are used in research to study the properties and evolution of stars within globular clusters. They can also be compared to other clusters or models to gain a better understanding of stellar populations.

5. Are all globular cluster luminosity functions the same?

No, globular cluster luminosity functions can vary depending on the age, size, and composition of the cluster. Some clusters may have a larger number of low-mass stars, while others may have a higher proportion of high-mass stars. This can result in different shapes and distributions on the luminosity function graph.

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