- 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 220.127.116.11 and Safari 3.1.2, 4.0.4 and 5.0.2)
Values in this tool have been updated to correspond to CalDB release
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
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:
- A list of observer inputs.
- 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).
- 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 expected signal to noise of the source.
- The filter in which the Lyman break may be observed if a &gamma -Ray
Burst is chosen for the spectral type.
- Maximum visual magnitude in each filter.
- Minimum visual magnitude in each filter.
- Visual magnitude warnings.
- Notes on calculations.
The input required from the observer to complete these calculations are as
- Right Ascension of the source (units in hours mins, and
- Declination of the source (units in degrees, arcmins and arcsecs).*
- The epoch for the right assention and declination coordinates. The
choices given are 2000 or 1950
- 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.
- If the source is GRB, the index &beta, where F&nu ~ &nu(-&beta). The choice of &beta is 0.5 or 1.0.
- 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.
- Visual magnitude (mv) of source, in order to calculate
the expected count rate.
- The filters required for the observation.
- 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
- 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.
- Commas (,) within numbers eg. ten thousand written as `10,000', will
result in a "NaN" response in the results, so avoid using commas.
- If a filter is not selected, then the results will not be printed on the
- 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,
Levasseur-Regourd, A. C., & Dumont, R., 1980, Astr. & Astrophys.,
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