Using the NED, you can search via frequency range corresponding to the selected pass band filter. I'm a beginner here and don't really understand. Here's the quote:

NOTES: Objects with observations in the frequency range corresponding to the selected passband filter will be returned. For example, selection of Spitzer MIPS 24 µm will also return objects with photometry from IRAS 25 µm because these filters overlap. This feature permits the location of objects with photometry in the selected region of the spectrum, while cutting across multiple surveys, detectors and filters that have been cross-correlated by NED. A future upgrade will include an option to restrict the search to only the selected passband filter.

There are then a list of 'passbands', all the way up to gamma. What is this actually mean? The amount of radiation given off by a celestial body?

I'm looking at the categories I'm more familiar with:

Helio. Radial Velocity
Major Diameter (arcmin)
Minor Diameter (arcmin)
Magnitude and Filter

And I'm not sure where this radiation fits in. Is it

Spectral Energy Distribution (SED) 

? Could someone explain the following terms to me if this is the case:

  • Observed Passband
  • Uncertainty Units
  • Freq (Hz)
  • Mode Aperture/Qualifiers
  • Reference Code No.

Wnad what about published and homogenised variables? Are homogenised variables the avarage of all observations?


2 Answers 2


Take for instance radio, when listening to radio you gather static on the frequency. A passband filters the static which in turn provides a clearer signal. Objects radiate in multiple frequencies/wavelengths, for instance heat/thermal (infrared) and visible. Not all object radiate in a range of frequencies, humans for example can be seen well in infrared and visible, but our skin and circulatory system are opaque in x-ray and radio. Spitzer MIPS 24µm is the wavelength corresponding to mid-infrared (between 3µm-50µm).

What the statement is saying, is multiple imaging sources have been used for the same frequency. When choosing the Spitzer MIPS 24µm result, it additionally includes results from other imaging sources such as the IRAS 25µm result. It does this because the filters of the passband overlap and return the same result, as a result the process is changing where it only displays the result of the filter you choose.

All radiation is apart of the electromagnetic spectrum, spectral energy distribution is a way to present the data results as a plot, in turn that can be used to identify the source of the radiation.

The observed passband, is just stating which frequencies are being filtered, such as perhaps within a small range. For example, a Quasar is a highly active radio source typically found in the center of young galaxies. In correlation, you can determine what kind of stellar objects you would expect given a certain range of frequencies or the observed passband.

Frequency is the simple measure of how frequent something happens, for example if you flash a torch once a second, the time between each flash is 1 second long, the frequency 1Hz. If you flash a second torch twice a second, the time between each flash is a 1/2 second long, the frequency is 2Hz. More relevant in physics, is the correlation between wavelength, frequency and photon energy. Waves oscillate and light acts as waves, and the frequency between each wave correlates to how fast the wave is moving and what wavelength the radiation is.

Homogenized results are just a collection of results which are made to fit a pattern, sometimes to better represent the data (this may be filtering results in a database to exclude results outside a range of study). Published results on the other hand are raw results which include a full spectrum of the data. I am unsure about the mode aperture, this may refer to the sensitivity and correlate to how much interference/static is captured with the wave. Best if someone else can explain this.


Ashley's comments are all fine. I'll add that homogenisation just means that where you have results from different instruments at the same frequency, they have been averaged in some way.

The reference code refers to something like this 1995MNRAS.273..559J

That can be used to look up the paper referred to at somewhere like the NASA ADS catalogue.

Can you add a sample of the output you are looking at: uncertainty would usually mean it indicates an "error bar" on the flux or magnitude in question - i.e. what is the estimated uncertainty in the measurement. The units are probably just referring to whether this is quoted in magnitudes or Janskys right?


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