UVOT Tool for Simulating Observations with Point Sources

A web based form that will aid you in planning observations by giving estimates of count rates and signal to noise ratios for given exposure times.

** Please note that this tool may not work in all browsers.**
(It has been tested in Firefox and Safari 3.1.2, 4.0.4 and 5.0.2)

Values in this tool have been updated to correspond to CalDB release 20070627.
4th Feb 2010: The background count rate has been adjusted to better match measurements as described in
Breeveld et al. 2010 (MNRAS, 406, 1687-1700, (2010))
20th Oct 2010: The UV count rates have changed slightly with updated effective area curves, as in the CalDB
(to be released by end of 2010).

Observational Details Form

Right Ascension of source (h,m,s):
Declination of source (deg,arcmin,arcsec):
Epoch of given coordinates:
Spectral type of source:
Red shift of the GRB (z):
Visual magnitude of source (mv):
Exposure time for each filter (in seconds):
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Information about the UVOT Tool

Above is a tool to aid in simulating observations of point sources using the UVOT. On submission the results will return:

  1. A list of observer inputs.
  2. The calculated count rate of the source. (NOTE: If a &gamma -Ray Burst is the chosen spectral type, the count rates are not adjusted for redshift. The redshift is only used to determine the position of the Lyman break).
  3. The assumed background count rate. This is calculated from the combination of zodiacal light, diffuse galactic light, and the average dark count rate of the detector; and therefore depends upon the position of the source.
  4. The expected signal to noise of the source.
  5. The filter in which the Lyman break may be observed if a &gamma -Ray Burst is chosen for the spectral type.
  6. Maximum visual magnitude in each filter.
  7. Minimum visual magnitude in each filter.
  8. Visual magnitude warnings.
  9. Notes on calculations.

The input required from the observer to complete these calculations are as follows:

  1. Right Ascension of the source (units in hours mins, and secs).*
  2. Declination of the source (units in degrees, arcmins and arcsecs).*
  3. The epoch for the right assention and declination coordinates. The choices given are 2000 or 1950
  4. Spectral type of source. The choices include GRB, B0, A0, G0, G2, K0, M0 and white dwarf. If your source type does not appear on the list then please use the closest source type available.
  5. If the source is GRB, the index &beta, where F&nu ~ &nu(-&beta). The choice of &beta is 0.5 or 1.0.
  6. Red Shift of the &gamma -Ray Burst (leave this as 0.0 if a &gamma -Ray Burst is not being considered). This is only used to determine the position of the Lyman break using &lambda &le 91.2(1+z) nm (Bloom et al. 1997). The count rates are not adjusted for redshift.
  7. Visual magnitude (mv) of source, in order to calculate the expected count rate.
  8. The filters required for the observation.
  9. The exposure time required for each filter.

On submission of this data in the Observational Details Form , a new web page will be open containing the calculated results.

*Right Ascension and Declination are required for sky maps of the diffuse galactic background (Lienert, 1998) and zodiacal light background (Levasseur-Regourd & Dumont, 1980). These maps are combined with the average dark count rate of the instrument to produce a total sky background count rate for the signal-to-noise calculation.

Avoiding Errors on Submitting the Form

Here is a list of possible errors that might occur, and how they can be avoided.
  1. Entering a space (` ') anywhere in a text entry field, whether it is before, after, or in the middle of a number, will produce a "Bad Request" error message, so avoid using spaces.
  2. Commas (,) within numbers eg. ten thousand written as `10,000', will result in a "NaN" response in the results, so avoid using commas.
  3. If a filter is not selected, then the results will not be printed on the results page.
  4. If you require more than one filter, click on the filter and drag the mouse, or use < crtl> click to select the required filters.


Leinert, C. et al., 1998, Astr. & Astrophys. Suppl., 127, 1.
Levasseur-Regourd, A. C., & Dumont, R., 1980, Astr. & Astrophys., 84, 277.
Bloom, J. S., 1997, Mon. Not. R. astr. Soc., 292, 55.

Questions about this UVOT tool should be addressed to email address.
Last Updated by A. A. Breeveld on October 20th 2010