EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 130/ 1 Article

Free access article

Issue Astron. Astrophys. Suppl. Ser.
Volume 130, Number 1, May_II 1998
Page(s) 173 - 182
DOI http://dx.doi.org/10.1051/aas:1998219

DOI: 10.1051/aas:1998219

Astron. Astrophys. Suppl. Ser. 130, 173-182

The $\vec{t}$ system; a new system for estimating the total magnitudes of galaxies

C. Ke-shih Young1 - N. Metcalfe2 - Jin Zhu1 - Hong Wu1 - Jian-sheng Chen1

Send offprint request: C.K. Young - c.young1@physics.oxford.ac.uk


1 - Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100080, China
2 - Department of Physics, University of Durham, South Road, Durham DH1 3LE, UK

Received September 26; accepted November 12, 1997

Abstract:

We present a new, but simple, procedure for estimating the total magnitudes of galaxies. This procedure involves the out-focusing of digital galaxy images numerically, the fitting of the resulting surface-brightness profiles with a single generalised profile model and the extrapolation of the fitted profiles to infinite radial distances. This new system, which we denote t, differs fundamentally from the T system (of the Reference Catalog of Bright Galaxies series) in that: (1) it enables a galaxy's luminosity profile to be extrapolated without the need for any prior morphological classification, and (2) it is applicable to images of widely different spatial resolutions (including unresolved ones) because it takes into account systematic effects due to differential image resolution. It also differs fundamentally from the Kron system in that: (1) it can be derived directly from surface photometry without the need to go back to the plate scans or CCD frames (unless the surface photometry is of high resolution and/or the galaxies being measured are very bright), and (2) it can cope with merged images (provided they are separable by image-segmentation software). Through worked examples, we demonstrate the stability of t-system total magnitudes with respect to morphological type, the seeing conditions at the time of observation, degree of smoothing and limiting isophote. We also compare and contrast the new system with both the T system and the Kron system, and investigate the advantages and limitations of each of the three systems.

Key words: methods: data analysis -- galaxies: fundamental parameters -- galaxies: photometry


Copyright The European Southern Observatory (ESO)

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.
  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.