Globular cluster luminosity function

[John Titor]

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
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.

 

[|Glitch|]

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.

 

[John Titor]

Thank you for the response though there wasn't much about GCLF it was helpful

 

[|Glitch|]

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)