OM Tool for Planning Observations with Point Sources

Information about the OM Tool

Below is a tool to aid in planning observations of point sources using the Optical Monitor. On submission the results will return:

1. A list of observer inputs.
2. The correct filter order.
3. The calculated count rate of the source.
4. 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.
5. The expected signal to noise of the source.
6. The exposure time available per filter once the overheads have been taken into account, assuming that the UVW2 filter requires twice as much time as the optical filters.
   NOTE: If Image mode or Fast mode are chosen, there are 5 exposures per filter.
7. Maximum visual magnitude in each filter.
8. Minimum visual magnitude in each filter.
9. Exposure time and visual magnitude warnings, if the calculated values do not lie within the recomended limits set out in the XMM-Newton Users' Handbook .
10. Notes on calculations.

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

1. Right Assention 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 B0, A0, G0, G2, K0, M0, and white dwarf stars. If your source type does not appear on the list then please use the closest source type available.
5. Visual magnitude (m_v) of source, in order to calculate the expected count rate.
6. The filters required for the observation. The use of the following filters are recommended from the XMM-Newton Users' Handbook :
   • UVM2 (first choice)
   • UVW1 (second choice)
   • U (third choice)
   The number of filters that can be used is dependant on the total observation time available to the observer, therefore the number of filters may need to be reduced from this recommended number.
7. Total observation time available for the observation. Field Acquisition (FAQ) time needs to be removed from the total observation time before submitting the form. The FAQ = 298 seconds. All other overhead times are taken into account in the calculations so you do not need to subtracted these times.
8. Default mode required for observation. Your choices include:
   • Image mode
   • Fast mode
   • Full-frame high resolution imaging mode - WARNING due to high overheads this mode is not recommended in the XMM-Newton Users' Handbook .
   • Full-frame low resolution imaging mode
   • User defined mode - assumes one exposure per filter, exposure time contraints are the same as the Image mode, and window sizes do not exceed the limits set down in the XMM-Newton Users' Handbook .
   A full account of each of these modes can be found in the XMM-Newton Users' Handbook .

Currently this tool does not give any warnings about other bright sources that are in close proximity to the coordinates submitted. Maximum and minimum magnitudes are output to demonstrate the magnitude range allowed in the Field of View of the Optical Monitor, for the planned observation.

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

1. If the Total Exposure time is small, a "NaN" response is produced in the `Signal to Noise' count results. To solve this problem the Total Exposure time must be greater than 6657 seconds.
2. 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.
3. Comma's (,) within numbers eg. ten thousand written as `10,000', will result in a "NaN" response in the results, so avoid using comma's.

References