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IFU_PA_REQUEST allows the catalogue provider to specify a rotation angle (position angle) of the LIFU, if this is required. Any dithering requested for the field is applied to the rotated LIFU frame. If a specific PA value is not requested, then the following defaults are applied: IFU_PA=0° (for declinations lower than 28.7°) and IFU_PA=180° (for declinations higher than 28.7°). Note that the requested IFU_PA could be changed by the IFU workflow software if a suitable guiding star cannot be found at the requested PA. Below it's a plot which shows how the PA is changed to find a suitable guiding star (from the requested PA marked as a blue cross to the final PA marked as a black cross).
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IMPORTANT: During the IFU observation preparation using the IFU workflow software, an analysis is performed on putative LIFU pointings to determine if a rotation is required and provides the optimal value IFU_PA should take. Rotation is generally used in cases where the default or requested PA results in no viable guide stars falling within the autoguider field of view, or when the rotation during an exposure is likely to exceed the angular limits of the rotator. This means that it's not always possible that the IFU workflow software can provide the IFU_PA_REQUEST value in the catalogue. The table below shows the allowed IFU_PA_REQUEST (=PA in the table) ranges PIs can safely apply for. Maximum value of PA is |
180º so if requesting PA=300º, then enter -60º. |
The table below shows the allowed values for the PA depending on minimum elevation requested in the OB and the target’s declination. Following are plots showing two cases, for better understanding of the PA ranges in the table.
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Aladin overlays of the LIFU footprints
Aladin overlays can be useful for preparing your observations. To use the Aladin overlays below, follow these instructions:
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