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Crowded Field Photometry and Luminosity Function Analysis as Probes of Galactic Evolution

Snel, Ralph LU (1998)
Abstract
Crowded field photometry is a powerful method to investigate stellar evolutionary processes in astrophysically interesting regions such as nearby external galaxies and globular cluster cores. While detectors are approaching the physical limits for photon detection, data analysis methods for crowded stellar fields are not yet equally sophisticated.



In order to obtain high accuracy of measurements and optimally extract astrophysically relevant information from observational data, it is essential to have thorough understanding of the processes affecting photometric accuracy, and knowledge of the theoretical limits of the information extraction. This thesis discusses data analysis methods for crowded stellar fields, as well... (More)
Crowded field photometry is a powerful method to investigate stellar evolutionary processes in astrophysically interesting regions such as nearby external galaxies and globular cluster cores. While detectors are approaching the physical limits for photon detection, data analysis methods for crowded stellar fields are not yet equally sophisticated.



In order to obtain high accuracy of measurements and optimally extract astrophysically relevant information from observational data, it is essential to have thorough understanding of the processes affecting photometric accuracy, and knowledge of the theoretical limits of the information extraction. This thesis discusses data analysis methods for crowded stellar fields, as well as theoretical and practical limits to the accuracy of measurements in CCD based crowded field observations.



Conventional crowded field photometry is discussed, with emphasis on detection and measurement of sources in the presence of known and unknown nearby stars. Special attention is given to the stellar luminosity function. A method is presented to derive the luminosity function of stars beyond the observational limit of individually detectable stars. This method uses the histogram of an observed image of a crowded field, and compares this with the histogram of a simulated image, determined with a model luminosity function, an instrument model, and detailed knowledge of the noise in the image. Similarity of histograms is interpreted as similarity of the true and model luminosity functions. An application of this method to a Hubble Space Telescope image of the Large Magellanic Cloud Bar is presented.



Completeness of detection of stars in crowded fields, normally determined through artificial star experiments, can be derived from prior assumptions concerning the luminosity function. Three detection algorithms are tested using simulated and observed images, and the results are compared with the theoretically determined completeness of detection.



With proper knowledge of the instrument, noise sources, and data analysis methods, it is possible to retrieve additional relevant information from the data, plan instrument configurations and observing strategies, and recognise possible areas of improvement in data analysis methods. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Dr Grosbøl, Preben, European Southern Observatory
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Astronomy, observational, Methods: data analysis, statistical - Techniques: photometric - Stars: luminosity function, imaging, evolution - Galaxies: stellar content, mass function, space research, cosmic chemistry, Astronomi, rymdvetenskap, kosmisk kemi, Fysicumarkivet A:1998:Snel
pages
88 pages
publisher
Lund Observatory, Lund University
defense location
Fysiska Institutionen, sal B, Sölvegatan 14
defense date
1998-02-14 10:00
external identifiers
  • Other:ISRN: LUNFD6/(NFAS 1018)/1-88/(1998)
language
English
LU publication?
yes
id
e2a1ab17-4f9f-4d09-9a62-13050cef10bf (old id 38366)
date added to LUP
2007-08-01 11:58:11
date last changed
2016-09-19 08:45:07
@misc{e2a1ab17-4f9f-4d09-9a62-13050cef10bf,
  abstract     = {Crowded field photometry is a powerful method to investigate stellar evolutionary processes in astrophysically interesting regions such as nearby external galaxies and globular cluster cores. While detectors are approaching the physical limits for photon detection, data analysis methods for crowded stellar fields are not yet equally sophisticated.<br/><br>
<br/><br>
In order to obtain high accuracy of measurements and optimally extract astrophysically relevant information from observational data, it is essential to have thorough understanding of the processes affecting photometric accuracy, and knowledge of the theoretical limits of the information extraction. This thesis discusses data analysis methods for crowded stellar fields, as well as theoretical and practical limits to the accuracy of measurements in CCD based crowded field observations.<br/><br>
<br/><br>
Conventional crowded field photometry is discussed, with emphasis on detection and measurement of sources in the presence of known and unknown nearby stars. Special attention is given to the stellar luminosity function. A method is presented to derive the luminosity function of stars beyond the observational limit of individually detectable stars. This method uses the histogram of an observed image of a crowded field, and compares this with the histogram of a simulated image, determined with a model luminosity function, an instrument model, and detailed knowledge of the noise in the image. Similarity of histograms is interpreted as similarity of the true and model luminosity functions. An application of this method to a Hubble Space Telescope image of the Large Magellanic Cloud Bar is presented.<br/><br>
<br/><br>
Completeness of detection of stars in crowded fields, normally determined through artificial star experiments, can be derived from prior assumptions concerning the luminosity function. Three detection algorithms are tested using simulated and observed images, and the results are compared with the theoretically determined completeness of detection.<br/><br>
<br/><br>
With proper knowledge of the instrument, noise sources, and data analysis methods, it is possible to retrieve additional relevant information from the data, plan instrument configurations and observing strategies, and recognise possible areas of improvement in data analysis methods.},
  author       = {Snel, Ralph},
  keyword      = {Astronomy,observational,Methods: data analysis,statistical - Techniques: photometric - Stars: luminosity function,imaging,evolution - Galaxies: stellar content,mass function,space research,cosmic chemistry,Astronomi,rymdvetenskap,kosmisk kemi,Fysicumarkivet A:1998:Snel},
  language     = {eng},
  pages        = {88},
  publisher    = {ARRAY(0x8f1ef90)},
  title        = {Crowded Field Photometry and Luminosity Function Analysis as Probes of Galactic Evolution},
  year         = {1998},
}