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Phoenix OT Details
After the queue for a given semester is consolidated, PIs
of approved proposals are sent a "Phase II skeleton", imported
into the Observing Tool (OT) so that individual observations can be
The Observing Constraints and Target coordinates are automatically imported
from the Phase I proposal. By selecting the Target tree branch and clicking on the
Image button at the top of the page, the observer can access the Position
Editor, which allows for interactively selecting WFS guide stars and defining
the Position Angle of the slit (see below).
The Phoenix Component: The
instrument configuration is defined here. The example below is for
an observation in M band (4.9 µm), using the
default exposure time of 30sec x 4 coadds at each offset (nod) position.
The Filter and Focal Plane Mask pull-down menus allow for choosing the
appropriate order sorting filter and desired slit width. By default,
the K4308 filter and the 0.34 arcsec slit are shown. The grating angle can be
selected by inputting
either the central wavelength (in air microns, µm) or wavenumber (in vacuum wavenumbers, /cm)
The conversion is automatic between them. The default position angle for
the Phoenix slit is 90 degrees (slit oriented E-W).
The Position Editor output for the observation above would look like:
The Sequence Iterator: The image to the right corresponds to a zoom into the science FOV in the position editor and shows the offset pattern corresponding to a standard ABBA nod sequence along the slit, with 5 arcsec separation between the two positions. Unlike the facility instruments (GMOS, T-ReCS, etc.), the Phoenix OT does not contain an instrument iterator, and therefore each grating setting has to be defined as a separate observation.
The above example was constructed to result in a 64 min
exposure on-source, consisting of 8 ABBA sequences (4 x 120sec each).
This is achieved by selecting the Sequence branch, and adding
under it (from the Iterator menu to the left) first a Repeat, then an
Offset layer: The actual offset (nod) pattern is defined
by selecting the Offset branch, then adding four offset steps, 5 arcsec
apart centered on the base position. The p-q coordinate system is fixed
on the focal plane of the instrument and actually rotates with the PA
selected in the "static" configuration. For Phoenix, the "q" axis is always
oriented along the slit.
The last step in defining the observations is to add an "Observe",
so the resulting sequence would look like this:
This example shows the telescope and instrument configuration
blocks, then the first three steps of the actual observing sequence.
When observing extended objects, or emission lines from nebulae,
it may be necessary to offset to a clear patch of sky. The example below
is for a K band observation, 30 min on target (no coadds), centered on
the H2 2.12 µm emission line, with the slit oriented along an arbitrary PA
and a large offset to sky.
The exposures are taken using one single ABBA sequence,
but with the sky unguided (PWFS-2 set to "freeze" for the two sky positions).
Note that with such a large offset, the guide star selected for the target
cannot be used for the sky position (if a guided exposure was necessary)
and would actually vignette the field if the WFS was left following.