Guide to NED Diameter Search Results

(Latest Revision: 8 May 2009)

This page displays results from searches for diameter data for an individual object. These diameter data are distinct from NED's "Basic Data" because they are not only referenced, but accompanied by detailed qualifiers. Within NED, each measurement (single data point) along with its descriptors is called a "Diameter Data Frame" or a "Diameter Data Point".

The diameter data returned by your search will be presented as an HTML table (default), HTML preformatted text, ASCII text (tab-separated or bar-separated), or in XML (VOTable) format. The HTML output is formatted for easy reading by eye on your computer screen, while the ASCII and XML output is appropriate for parsing by computer scripts or programs. The ASCII and XML tables are preceded by a header line showing the data contents of each column.

The top section of this page displays a summary table of NED's diameter data frames for a given object. There are two parts of the summary table: The first displays the diameters as published, the second displays the diameters in NED's homogenized units.

Published units:
  • A sequential data-point number applicable to this list only.
  • The frequency or wavelength at which the data apply (in common astronomical jargon, e.g. "Optical", "21-cm"). Also in this cell, the reference code for the source of the diameter. This is linked to NED's Reference database so that you may retrieve the full reference or abstract easily.
  • The major axis (2a) as published. If this is a radius, the value in the column will be flagged with the letter "a" in parentheses: "(a)".
  • The major axis units, as published.
  • The minor axis (2b), as published. This will also be a radius if the major axis is flagged as a radius.
  • The minor axis units, as published.
  • The axis ratio, as published: it may be b/a, a/b or log a/b; all are appropriately flagged.
  • The major axis uncertainty, as published.
  • The ellipticity as published.
  • The eccentricity as published.
  • The position angle as published (in deg.): The equinox is also given in brackets. When the equinox is followed by an asterisk, no equinox was published, and the value given is assumed by NED (cf. comment in the Detailed Information.)
Homogenized units:
  • The reference level in common astronomical jargon.
  • The frequency in standard units (Hz).
  • The major axis in arcseconds.
  • The major axis uncertainty.
  • The axis ratio b/a.
  • The ellipticity, (1 - b/a), calculated as needed from the axis ratio.
  • The eccentricity, [(a/b)2 - 1]/[(a/b)2 + 1], calculated as needed.
  • cos-1(b/a), also calculated as needed. This is representative of the inclination of the galaxy to the line of sight, in degrees.
  • The position angle in degrees for equinox J2000.

More extensive data for any measurement in the list may be seen by clicking on the sequential number for that measurement, or by scrolling down the page to the measurement of interest.

The second part of this page displays the data associated with the diameter data frame for the object you selected. These data include:

  • Reference code: The literature source for the present diameter data frame, in NED's standard 19-byte code (click on the highlighted reference code to display the full reference).
  • Frequency targeted: The target of the observations in frequency domain in astronomical jargon. Typical entries could be "B", "r(Thuan-Gunn)", "5 keV continuum", "IRAS 12 micron", "^12^CO(1-0)", "H{alpha}", etc.
  • Major Axis (2a): The major axis, first as published (diameter or radius), then in arcseconds.
  • Uncertainty: Uncertainty for the major axis, first as published, then in arcseconds.
  • Minor Axis (2b): First, as published, the minor axis (axis ratio b/a or a/b, log(a/b), or ellipticity), then transformed as needed, the minor axis in arcseconds.
  • Axis Ratio: First as published (b/a, a/b or log(a/b)) then b/a.
  • Uncertainty: Uncertainty on the axis ratio.
  • Ellipticity: First as published, then calculated as needed.
  • Uncertainty: Uncertainty on the ellipticity.
  • Eccentricity: First as published, then calculated as needed.
  • Uncertainty: Uncertainty on the eccentricity.
  • cos-1(b/a): Inverse cosine, in degrees, of the axis ratio; this is a rough indicator of the galaxy's inclination to the line of sight.
  • Position Angle (Equinox): The major axis position angle, first as published, then in degrees, from north through east, for equinox J2000.0.
  • Uncertainty: Uncertainty on the Position Angle, first as published, then in degrees.
  • Significance: The type of uncertainty reported in the original publication; e.g. "rms uncertainty", "90% confidence", "no unc. reported", etc.
  • Diameter Reference Level: This field specifies the reference level, with units, for the diameters. For an optical diameter, this might be an isophote (surface brightness); for a radio diameter, it might be a half-peak level; etc. More generally, it might specify the reference level as a fraction of a peak value, the percentage of the light included, a step ratio "folding" scale length, etc.
  • Frequency: This is the frequency or wavelength of observation first as given in the paper, or as the established standard indicates for continuum observations, then translated as needed in Hz.
  • Frequency Mode: The method(s) by which the data were collected, reduced, or derived, in relation to the frequency or wavelength; e.g. "broad-band measurement", "flux integrated over line", "absorption lines measured", "color-corrected", etc.
  • Measurement Mode:
    • Detector type: The observing instrumentation.
    • Fitting technique: The observing technique.
    • Measured quantity: The part of the object measured.
    • Qualifiers: Comments regarding the measurement mode.
  • Coordinates Targeted: The object's coordinates and equinox, as published.
  • Qualifiers: Self-explanatory notes pertaining to
    • The history of the data (e.g. "from new raw data", "transformed from previously published data", etc.).
    • Adjustments to the data (e.g. "corrected for contaminating sources").
    • Changes introduced by NED (e.g. "obvious typo corrected", "correction published in errata", etc.).
    • Values modified by NED (e.g. "Diameter modified from published value", "Uncertainty modified from published value", etc.).
  • *: (Optional) This line exists only if an asterisk follows the equinox given with the Position Angle in the Summary Table ("No epoch/equinox published. The value given is assumed by NED").
  • NED Comment: Other information about the data.

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