This page describes some random notes for Observers and
Instrument Scientists to bear in mind regarding operation of
NIRSPEC on AO nights.
Summary
Normal operating practice requires that the Keck domes be closed
whenever the sun is above the Mauna Kea horizon. However, this
does not allow adequate time or sky flux for taking sky flats
with the AO system, due to the very small plate scales. Hence,
the following modified dome opening policies apply for all AO
nights:
- In order to permit the acquisition of suitable twilight
flats, observers may request that the dome be opened 15
minutes prior to sunset.
- If and only if the dome was not opened early due to
problems with equipment or weather, then observers
may request that the dome remain open until 15 minutes
past sunrise. It is not permissible to both open early and
close late. It is also not optional for observers to
choose to close late instead of opening early. This
restriction is imposed for the health and safety of the
summit staff, so that they will not be expected to stay
late on the mountain except when absolutely necessary. A
late close is permitted only when an equipment
fault or bad weather prevents opening early.
- As with non-AO NIRSPEC observing, select the Enable
Nighttime Mode option from the pulldown menu
labelled NIRSPEC Control Menu. Note
that in AO mode you will not get a NIRSPEC
Rotator GUI window --- the AO system handles field
rotation.
- Start Netscape.
- Select the bookmark AO WUI Simple Session
Manager to launch the AO session manager.
- From the session manager page, select Observer
Tools to get the observer tools menu.
- Click on the options Astronomer Screen and
Observer AO Status Screen to launch new Netscape
windows running these tools.
- This window allows control of telescope offsets and rotator
modes.
- Note the important colored button at the upper right which
indicates the status of the AO system:
- red means loops are not
closed and exposures should not be taken;
- yellow means loops
are closed but PRC matrix is still updating so
science exposures can be started, albeit with a small
degradation in image quality;
- green means loops are
closed and it's OK to begin or continue working;
full corrections are being applied to obtain best
possible image quality.
- Note that when Guider Eavesdrop is launched, you
will be viewing the ACAM guider rather than the
usual NIRSPEC PXL guider.
- ACAM field of view: 2 x 2 arcmin (approximately)
- ACAM scale: 0.125 arcsec/pixel
- NOTE: There is a "ghost" reflection in the acquisition
camera optics, such that two images are seen of every object,
and the images are offset vertically. The image of the target
that is closest to the center (upper of the two?) is the
"real" image.
- All normally-used NIRSPEC controls for doing telescope
offsets will work properly when the AO system is operating and
the loops are closed, including:
- the snapi and box9 options from
XNIRSPEC
- the various options for slit nodding on the
EFS (nod 2m nod 4,
ABBA, etc.)
- the Move Telescope and Center Slit on
Gaussian features from the SCAM
QuickLook tool
- the NIRSPECAO Slit Nod widget
- Note that when the AO loops are open, you must not
use these tools mentioned above to make offsets --- they will
hang while waiting for the AO loops to close following the
move. In this case, use only the entry boxes for RA/DEC or
Instrument X/Y offsets on the
Astronomer Screen to move the telescope.
- FACSUM will correctly report on the AO rotator
mode and the AO rotator position angle.
- When the AO rotator is at SKYPA=0°
according to FACSUM, the
columns of SCAM are at a position angle of
90° as projected onto the sky. This corresponds to an
angle of 92° as seen on the Astronomer
Screen.
- NIRSPEC keywords relating to position angles:
- SCAMPA gives the PA of SCAM columns as
projected onto the sky.
- SLITANG related to the difference between
the position angle of SCAM and that of the current slit.
- Commanding the AO Rotator:
- Astronomer Screen allows positioning of
the rotator and selection of modes (vertical,
stationary, position angle).
- Use the command slitpa_ao from any
waimea command line to set the position angle
of the current slit. Note that the rotator must be in
PA mode for this to work!
- Using the NIRSPEC Rotator to set PA. This feature is
useful only when a particular slit PA is required, but the
spectroscopic target is far enough from the guide star that
the AO rotator angle is dictated by the needs of the AO
system. In that case, follow these steps:
- Set the AO rotator PA to the angle needed to lock on the
guide star and acquire the science target.
- Proceed to acquire the science target as usual.
- On the science field, with the loops closed, take a SCAM
image.
- From that image, measure the number of degrees you want
the sky to rotate to put your objects correctly on
the slit. Sign conventions (at least when looking South) are:
- Positive if you want the sky to rotate CCW.
- Negative if you want the sky to rotate CW.
- In any window with a waimea prompt, enter the
command:
where [degrees] is the number of degrees you want the
sky to rotate.
- Take another SCAM image to verify alignment. Proceed with
observing as usual when alignment is satisfactory.
- To restore the default rotator and DCS settings, enter the
command:
Using the argument "default" should reset the image rotator to
its init position and restore the standard value of INSTANGL.
Please note that there is a modest loss of setup efficiency in
this mode. When the NIRSPEC rotator is at any angle other
than its default position, all moves, no matter how
small, require opening and reclosing the AO loops. When the
NIRSPEC rotator is at its default position, moves of less than
0.2 arcsec made with the "NIRSPEC/AO Slit Nod" widget do not
require opening the AO loops, thus saving time.
- Observers should be aware that differential refraction is
a much more serious concern with AO observing than non-AO,
because the target can move out of the slit within just a
couple of minutes. Henry Roe (UCB) has put together an
excellent synopsis
of the consideration for differential refraction and AO.
- In many cases, observers should consider minimizing slit
losses by using vertical angle mode on the AO
rotator. This mode can be selected from the Astronomer
Screen. See Henry Roe's writeup on slit losses for further details.
- Observers should monitor position of the object relative
to the slit by taking frequent SCAM images. One can read
out test images from SCAM continuously by typing this
command at a waimea prompt:
goibuf2 -1
- Anecdotal evidence suggests that using non-sidereal tracking
rates with AO on does not work.
- Instead, turn off non-sidereal tracking and simply allow
the AO system to lock onto the moving target.
Symptoms of an AO software server crash are that the AO WUI
screens no longer update. Usually the OA will notice this before
the astronomer because of the many more windows that the OA must
monitor. Take these steps after the OA has restarted the AO server:
- Kill any existing Astronomer Screen or
Observer AO Status Screen windows by using the
Quit option from the title bar.
- Do a Shift + Reload in the Netscape
window running the AO WUI Simple Session Manager to
restart the Java code.
- Restart the Astronomer Screen and Observer
AO Status Screen as described above.
- There are two intensity settings for the NIRSPEC's
internal flat lamp: low and high. These settings can only be
changed by a manual movement of a toggle switch on the top of
the NIRSPEC Calibration Unit (which is attached to the front
of NIRSPEC). Thus, to change this switch a summit technician
must go into the AO enclosure and change the switch by hand.
Changing this setting during the night is easy, but may
takes of order 10 minutes depending on how far the telescope has
to slew to allow personnel access to the AO enclosure.
- The Lamps Only mode of the EFS sets exposure
times for flat lamp spectra assuming that the lamp is set to
the low intensity setting for low resolution (non-echelle)
modes and the high intensity setting for high resolution
(echelle) modes.
- With the lamp switch set to high intensity, flat lamp
spectra in low-resolution mode will saturate in even the
shortest available integration times (0.25 seconds in CDS
readout). Thus the lamp MUST be set to low intensity
for low-resolution spectroscopy.
- Practical Suggestions:
- If you are only taking spectra in low-resolution
mode, or only high-resolution mode, have the lamp intensity
switch set accordingly and
take your calibrations with the Lamps Only mode of
the EFS.
- If you are taking a mix of low-resolution and
high-resolution spectra, you'll have to find the compromise
that best fits your programme until we can make the switch remote
controllable. Some possibilities are:
- Arrange your programme to separate the low-resolution and
high-resolution spectroscopy into as few parts of the night
as possible, and endure the down-time that results from
having a summit technician or OA change the switch for you
when you finish sections of your programme. If you elect to do
this, be sure to discuss it beforehand with your
supporting Instrument Scientist and the OA, to make sure that
the summit personnel on duty are familiar with the switch and
how to change it.
- Leave the lamp in its low intensity setting all night long
and make your own script to take longer exposure
lamp spectra when in echelle
mode. If echelle mode is only a small part of your programme
this may be your best option. To make your own script;
set up the EFS in Lamps Only as if you
were going to take a lamp sequence (that is, in Lamps
Only mode select your filter, grating settings, etc.)
but do NOT click GO. Go to the EFS
File menu and select Save Configuration
As..., enter a filename to save this lamps-only setup in
a script, then edit the script to change the exposure time for
the flat lamp spectrum to a more reasonable value.
Experiment with
test images to find the best value for your purposes. Then
you can take your lamp sequences by running this script
from the command line in a window with a
waimea prompt. Ask your supporting Instrument
Scientist for help if you have any questions about this
process.
- Do Not Use Setups From Non-AO Runs on AO Nights,
and vice versa! If one reads a non-AO EFS script
into the EFS and runs it without changing the filter
selected, then filter wheel 1 could be changed from the AO
pupil stop to the open or thin blocker positions.
Subsequent on-sky images will be way out of focus, making it
appear as if the light path is blocked. Issue the following
command from a waimea window to return the pupil
to its proper position:
set_ao_pupil
Re-selecting
the filter from NIRSPEC or EFS may
also restore the AO stop.
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Last modified: Thu Aug 23 19:52:07 HST
