RA & Dec of the desired target can be specified either in decimal degrees (DD.DD) or in "HH MM SS.S" and "DD MM SS.S" format. All internal operations are done in degrees. For RA, a floating point number indicates that you are giving your input in decimal degrees. An integer number will be taken as HH MM SS.S. For instance, 4 is taken as 4 hours but 4. is taken as 4 degrees.
The rest of parameters are optional, if you do not enter any of them the Visibility Checker will provide defaults, as indicated for each parameter below.
An optional Target Name can be entered which could be the name of the source or some other identifier. Default is "Target".
If you select this entry option (Default) you can provide the revolution range for which the visibility should be computed.
Enter the first and last revolutions for which you would like the visibility computed.
The default for these entries is the approximate revolution range covered by AO7 (revolutions 1537-1720). The minimum and maximum values
used in this version are revolutions 1380 - 1740.
If you leave these fields empty or you use an out of range value, the tool will use the deafults (AO7).
Note: The tool internally uses revolutions for all computations.
The terms revolution and orbit are used interchangeable by the tool.
Instead of a revolution range you may select a range of dates. If you select this option you may provide the date range for which
the visibility should be computed. Enter the first and last dates for which you
would like the visibility computed.
The format is 'free' for the dates but we recommend to use the forms YYYY-MM-DD
or YYYY MM DD (or even DD Month YYYY).
The default for these entries is the approximate date range covered by AO7 (2008-05-01 to 2009-05-01, corresponding to the above AO7 revolutions).
The minimum and maximum values used in this version are dates 2007-06-22 and 2009-06-10.
If you leave these fields empty or you use an out of range value, the tool will use the AO7 defaults.
You can find out the equivalence between date and revolution number by using the orbit calculator.
Minimum and Maximum visibility
A time is specified for the minimum length that a target is required to be visible.
For example, if 10000 seconds are requested, the tool will return information about those revolutions in the specified range which are visible for at least this time.
Default and minimum is 5000 secs. The maximum visibility that can be achieved in this version is below 130 Ks, and therefore the maximum rounded visibility (see below
) that can be obtained is 130Ks.
Any value outside the range (5 - 130 Ks) is changed by the tool to the appropriate within range value.
Note on visibility duration
The tool constraints the output visibility according to several factors:
The XMM-Newton radiation model predicting when the radiation levels will allow XMM-Newton to execute scientific observations.
This radiation model has been developed using the XMM-Newton Radiation Monitor data and predicts future behaviour taking
into account the orbit evolution.
To see more details about the model, refer
XMM-Newton Radiation Monitor Details page.
- The eclipse periods where special operations are required (thus giving less room for science).
- The nominal (altitude based) time when scientific observations may start or have to be finished.
A plot (pdf)
with the factors that constraint the start of the scientific window is provided for AO7 (and as used in the visibility calculations).
For the end of the science window the factor that dominates is radiation and is the constraint that is taken into account.
The final combination of all these factors is represented for AO7 in the following PDF file
Bin corners visible
This version of the Visibility Checker uses a finer bin geometry than previous versions. The size of a bin is now 2x2 degrees (as oppossed to the previous 10x10 degrees bin size in previous releases).
The visibility tool imposes that for a target to be visible, all corners of the corresponding bin must be visible.
Visibility checker output
The output of the tool is provided in a new Browser window (titled "Vischecker Output") in the form of tables.
It consists of the following components:
- one table containing the submitted parameters to the tool (RA, Dec and minimum duration) and some default internal values.
- one table with the ranges, first the selected range (if dates were selected the entered dates will be displayed as given, if orbits were
selected then the corrected orbits will be displayed) and then the corresponding used values (always corrected to be the within range).
- one table with the results, as follows:
- the revolution number when the target is visible (for at least the minimum
- the starting time and date when the target is visible,
- the total time that the target could be visible in this revolution,
- the time and date when the target becomes not visible,
- the phase in the revolution when the target becomes visible (0 = perigee, 0.5 = apogee),
- the phase in the revolution when the target becomes not visible,
- the rounded visibility: the total observation duration requested
in the HRPS by potential proposers should not exceed the rounded
- the angle to the Sun,
- the mean astronomical position angle of the instruments during the
visible period . The visibility checker uses a nominal roll angle of 0°.
This position angle can be used in conjunction with SciSim to check the orientation of the source,
especially for RGS observations.
If the tool fails to yield a successful answer these are some of the common problems.
The target may not be visible in the specified orbit range for the minimum requested duration. Try a shorter duration time or a different orbit range.
- The target might be visible in the specified orbit range (based on astronomical constraints -DBOB-) for the minimum
requested duration but after further constraints are applied, e.g.: radiation model, the final duration is below the minimum or the requested