Working with WEAVE

WEAVE

WEAVE (WHT Enhanced Area Velocity Explorer) is a new multi-object survey spectrograph for the 4.2-m William Herschel Telescope (WHT) at the Observatorio del Roque de los Muchachos, on La Palma in the Canary Islands. It will allow astronomers to take optical spectra of up to ~1000 targets over a two-degree field of view in a single exposure (MOS), or to carry out integral-field spectroscopy using 20 deployable mini integral-field units (mIFUs) or one large fixed integral-field unit (LIFU). WEAVE's fibre-fed spectrograph comprises two arms, one optimised for the blue and one for the red, and offers two possible spectroscopic resolutions, 5000 and 20,000.

On September 11 2020, ING celebrated WEAVE PFC first light, after images of Vega were obtained with the acquisition camera. WEAVE construction is funded by STFC, NOVA, NWO, ING, IAC, MINECO, INAF, INSU, Observatoire de Paris, île de France, INAOE, Lund Observatory, Uppsala University, AIP, MPIA, University of Pennsylvania, and Konkoly Observatory.

At the moment (September 2020) the optical performance of the PFC mounted at the WHT's Prime Focus is being verified on-sky using the ING's Shack-Hartmann (SH).

Startup

TCS:

USER> STATION WEAVE
USER> INSTRUMENT WEAVE
USER> AGSELECT MOS
USER> CAL LAST
USER> FOCUS -1.40 (Sep 2020)

On the TCS it will show that the optical configuration is "Prime (Nasmyth flat not stowed)" (NASMYTH DRIVE SIDE SET would be lit, GRACE). Should you have to move the Nasmyth flat (M3), please check that the telescope is at zenith and the petals are closed. Then press the NASMYTH DRIVE SIDE (GRACE) button.

Filling the cryostat:

The cryostat will last about 9-10 hours between refills. It is at prime focus so it is necesary to park the telescope at AP2. The detector may be filled with the telescope at Elevation 9 degrees (AP2) without opening the barrier. It can be filled from the left side of the positioner.

VERY IMPORTANT
As a safety precaution, the cryostat should always be filled at ROT MOUNT 150. Otherwise the LN2 will pour out during the refill. Also, the dome should be closed and the dome lights should be ON.

(1) From the TCS:

USER>PARK ZEN
USER>ROT MOUNT 150

(2) Wait until the telescope is stopped and change to ENGINEERING mode:

USER>ENG

(3) Bring the telescope to AP2 by clicking on AP2 in the TCS display, located at R1 (the rack number 1, left-hand side from the TO workstation).
(4) Lock the telescope in EL and in AZ with the two interlock keys on the main control panel. (Make an entry in the logbook).
(5) From the gallery, place the dewar and the ladder in place on the left side of the positioner.
(6) Fill the detector.
(7) Remove and lay down the ladder. Separate the dewar from the positioner.
(8) Unlock the telescope in the control room. (Write down the time of filling and sign off in the logbook).
(9) Move the telescope back to park zenith by clicking on ZP in the TCS display, located at R1 (the rack number 1, left-hand side from the TO workstation).

Initialisation of the FTUs:

At the beginning of the night, the FTUs need to be initialised ("Home All" button in the PLC GUI, WEAVE FTUs menu). In order to do that, the telescope has to be at EL = 60deg (Zenith Distance 30) and in ENGINEERING mode. Otherwise it would probably initialised the FTUs and then change their values to a (random) value taken from the TCS. The mirror petals should be closed as well.

Movement of target using XY HANDSET keys:

SHAcqTV

       +------+
       |      |
       |      |
       | <--  |
       |      |
+------+------+------+
|   |  |      |  ^   |
|   |  |      |  |   |
|   |  | -->  |  |   | 
|   v  |      |  |   |
+------+------+------+

SH - TEK2

       +------+
       |   |   |
       |   |   |
       |   |   |
       |   v   |
+------+------+------+
|      |   ^  |      |
|      |   |  |      |
| <--  |   |  | -->  | 
|      |   |  |      |
+------+------+------+

TWFC1

       +------+
       |      |
       |      |
       | <--  |
       |      |
+------+------+------+
|   |  |      |  ^   |
|   |  |      |  |   |
|   |  | -->  |  |   | 
|   v  |      |  |   |
+------+------+------+

Notes

The Operations team have confirmed it’s not possible (at least, at the moment) to do the PRIME FOCUS ROTATOR (WEAVE) ZEROSET if it doesn’t need to be done.
In case it’s in red, then you have to make sure it’s in positive values (if you’re not sure, then take the rotator to the positive limit) and then click on ZEROSET in the TCS panel. It will leave the rotator close to zero but in negative values (at around -1.4), and that’s fine.

Should you need to unscrew the panels in the positioner (black cube at prime), an Allen key M5 is required.

There are three PLC GUI WEAVE menus of interest for the current tests:
WEAVE WRS (WEAVE Rotator System) - Normally not used during normal operations.
WEAVE FTUs - Useful for the initialisation at the beginning of the night.
WEAVE WCS (WEAVE Corrector System) - Useful in order to report ADC problems.