WHT quality-control tests pending

Below is a list of on-sky WHT quality-control tests which are currently pending. They are in broad priority order (most urgent first), but the order in which they are best carried out will depend on the observing conditions, how much time is available etc. E.g. if the seeing is 0.5 arcsec, give preference to tests needing exceptional seeing.

See the WHT quality-control pages for more information on each topic.

FWHM of top-end sky-brightness monitor
Aim: to check the pointing and response FWHM of the sky-brightness monitor (it reads out every few sec).
Method: point at moon, then at elevations 5, 10, 15, 20, 25, 30 deg higher than moon. Point back to moon and repeat for -5 ... -30 deg (or as low as possible). Repeat, for positive and negative steps in azimuth. At each pointing, note the sky brightness recorded by the WHT top-end sky-brightness monitor (second column, labelled 'Teles mags', not the column labelled 'Zenith Mags') and mail the results to crb.
Time required: 0.5 hour.
Conditions required: moon at elevation >~ 20 deg, no cloud.
Instrument required: none.
Calibration exposures for sky-brightness meter
Aim: check of photometric calibration of the new top-end sky-brightness meter:
http://icsdev.ing.iac.es:8081/SQM/
to keep an eye on any photometric drift. Last measurement was November 2012.
Method: take ~ 100-sec exposures of the twilight-free sky (if saturating, reduce exposure time), <~ 45 deg from the zenith, >~ 30 deg from the galactic plane, and >~ 20 deg away from the ecliptic (see chart on control-room wall for plot of these in RA, Dec), through each of Sloan r, g and, if possible (only if already mounted in the wheels) through non-Sloan broad-band filters at similar wavelengths, e.g. Bessell or Harris (doesn't matter which) V and R. Take also an unsaturated image of a Landolt standard through each of the filters used. Mail the file numbers to crb.
Time required: 0.5 hour.
Conditions required: no twilight, no cloud, any seeing, any sky brightness, any dust.
Instrument required: ACAM imaging
ISIS focus / astigmatism tests
Aim: check consistency of red/blue-arm focus; checking on-sky for astigmatism
Method: see Marie's document linked ('Discretionary tasks') from the ISIS main page.
Time required: 1 hour.
Conditions required: seeing <~ 0.6 arcsec, no cloud or thin cloud, any sky brightness.
Instrument required: ISIS
Check PSF delivered by ACAM, as a function of radius
Aim: measure any degradation of PSF with radius in the field.
Method: focus ACAM through a red filter (preferably Sloan R, but any red filter is OK), point to globular cluster (e.g. M13, RA ~ 17) (NB may be too crowded for focusing) or Milky Way, take short exposure. Repeat in U and Z bands.
Time required: 20 mins
Conditions required: seeing <~0.5 arcsec
Instrument required: ACAM
Spectrophotometric standards
Aim: to update the information about spectrophotometric standards on the ING web pages.
Method: see Javier's web page for details.
Time required: several hours (but can be done bit by bit).
Conditions required: seeing <~ 2 arcsec, any sky brightness, non-photometric for the imaging, and no more than thin cloud for the spectroscopy.
Instrument required: ACAM imaging and spectroscopy
Characterise NAOMI NGS AO performance
Aim: fill in gaps in our current performance matrix = PSF as a function of mag, seeing, band, radius from guide star.
Method: obtain open-loop and closed-loop (AO-corrected) exposures of stars for each of the areas of parameter space listed below. For the near-IR data, 5-point dithers are required. The individual exposures should be at least 7 sec in duration.
(1) Radius = 0, i.e. measuring PSF at guide star:
```
The following permutations are required:

Seeing ~ 1.0 arcsec, guide-star mag 8, 10, 12, 14, for each
of H (INGRID) and R (OASIS) bands.

Seeing ~ 0.5 arcsec, guide star mag 10, 12, 13, 14, for 
R band
```
(2) Radius > 0, using star pairs, from:
http://catserver.ing.iac.es/aotools/pairfind.html
with the guide star of specified mag on-axis, and the other star lying a specified number of arcsec away:
```
The following permutations are required:

Any seeing <~ 0.8 arcsec; 
for guide star mag <= 9; for each of star separations 5, 10 and 20
arcsec, in each of H and R bands.
If there's time, repeat for J and I bands as well 
```
Time required: ~ 1 night
Conditions required: seeing <1.0 arcsec
Instrument required: NAOMI/INGRID, OASIS (not GLAS)
Measure OASIS and INGRID zeropoints
Aim: measure OASIS and INGRID throughputs.
Method: (1) With OASIS in imaging mode, obtain unsaturated images of 2 different Landolt standards through each of the MR454, MR591, MR661, MR735, MR875 filters, slow readout, binned 4*4.
(2) With INGRID, obtain unsaturated images of an IR standard star in each of Z J H K bands.
(3) With OASIS in spectroscopic mode, 22-mm enlarger, obtain spectrum of spectrophotometric standard in MR454, MR591, MR735, MR875 modes.
(1) has higher priority than (2), which has higher priority than (3).
Time required: 30 mins
Conditions required: photometric, any seeing, any sky brightness
Instrument required: NAOMI/OASIS
Measure zeropoint for any instrument for which you are specialist
Aim: measure the instrument zeropoints (mags in each band for 1 detected photon/sec for imaging, 1 detected photon/sec/A for spectroscopy) at regular intervals.
Method: obtain unsaturated images of imaging or spectrophotometric standards (ideally more than one, e.g. three) through the relevant filters. Avoid exposures shorter than ~ 2 sec (could be affected by shutter timing). Avoid very low elevations (i.e. high airmass). The counts/sec can be measured from the raw images - no flat-fielding needed.
Time required: typically ~ 30 mins
Conditions required: photometric, any seeing, any sky brightness.
Instrument required: any

Done, no longer required (but might be needed again one day):

Scattered moonlight in ACAM vs radius from moon, with 380-mm baffle
Aim: to check the effectiveness of a 380-mm diameter baffling ring installed in the below-Nasmyth turret 15/2/12 or 25/2/12, and to check for any vignetting of guide stars (i.e. at large radius in the focal plane).
Method (start with the baffle in):
(1) Set up ACAM for imaging in r band, bin 4*4, readout speed = fast.
(2) Ask the OSA to point the telescope at the moon.
(3) Ask the OSA to point the telescope successively dEl = 4, 6, 8, 12, 14, 20, 24, 30, 40, 50... deg from the moon in elevation (ideally higher than the moon, until the zenith is reached, but lower elevation than the moon is also useful), at the same azimuth as the moon, and take a 1-sec exposure at each position. Record the value of dEL for each run.
(4) Point the telescope well away from the moon, so that no moonlight falls on any part of the telescope structure, and take another 1-sec exposure. If there is any cloud around, try to pick an area of sky with no cloud.
(5) Image a series of guide stars on the Cass autoguider (the aim is to monitor any large-radius vignetting by the baffle), recording for each one the RA, Dec, mag, r, theta, seeing (on autoguider), exposure time (on autoguider, probably ~ 1 sec), S:N (on autoguider) and the run number. Do 4 guide stars at one sky PA (any PA), then rotate by 180 deg and do 4 more. With these 8 stars, sample a range of r (goes from 0 to 40000) and theta. Sampling r is particularly important, to help see at what radius any vignetting sets in.
Ask the OSA to remove the 380-mm baffle, and repeat (1) - (5) above.
Mail the dEl and run numbers for steps (3) - (5) to crb.
Time required: ~ 3 hours (including 0.5 hour to remove baffle).
Conditions required: reasonably clear, any seeing, moon > 20 deg above horizon.
Instrument required: ACAM imaging.
ISIS zeropoint
Aim: measure ISIS throughput.
Method: see Marie's document ('Discretionary tasks') linked from the main ISIS page.

Time required: 1 hour.
Conditions required: photometric, any seeing, any sky brightness.
Instrument required: ISIS
Cassegrain wobble
Aim: investigate Cassegrain oscillations (period few 10s sec)
Method: see the recipe provided by Cecilia
Time required: 2 hours.
Conditions required: seeing <~ 2 arcsec, any transparency or sky brightness
Instrument required: ACAM, ISIS, ISIS slit-viewing camera
Cass pointing test (carried out by telescope operator), using ~ 70 - 100 stars.
Aim: improve Cass pointing rms (should be <~ 1.5 arcsec).
Method: see pointing-test instructions on a separate page.
Time required: 2 - 3 hours.
Conditions required: any, as long as seeing is <~2.5 arcsec
Instrument required: any imager (including acquisition camera) allowing stars to be acquired rapidly at rotator centre.
Check pointing rms
Aim: compare actual Cass pointing rms (which has been unusually good over the last 3 months) with CALIBRATE rms.
Method: determine rotator centre on detector of your choice, carry out the usual 7-star CALIBRATE, then point at ~ 20 stars scattered over the sky in azimuth and elevation, and measure for each the AZ, EL offset required to bring it to the rotator centre. Mail results to crb.
Time required: 0.5 hours.
Conditions required: seeing <~ 2.5 arcsec, any transparency, any sky brightness.
Instrument required: any
Check field distortion for ACAM
Aim: check the field distortion (i.e. the scale in arcsec/pixel as a function of position in the field), only measured once since commissioning.
Method: find a pair of stars separated by between 20 and 50 arcsec (i.e. point pretty much anywhere on the sky), take R-band exposure ~ 10 sec (to average out seeing), check neither star saturated. Offset telescope to each of a grid of positions +- 1, 2, 3, 3.5 arcmin along each axis, take 10-sec exposure at each point (include offset in title of run. Mail file numbers to crb.
Time required: ~ 0.5 hour.
Conditions required: seeing <~ 1.5 arcsec, any moon
Instrument required: ACAM, imaging mode
Measure focus offsets for new Sloan filters in ACAM
Aim: measure more accurate focus offsets between the Sloan filters.
Method: point the telescope anywhere on the sky at high elevation (for good seeing). Use focusrun (keep all the images) to determine the best focus in Sloan r (use exposures of at least 7 sec when doing a focus run). Record the telescope focus and the filter-specific offset (shown on the ACAM gui) and the offset as recorded on the TCS info page (DF). Repeat the test for each of the new Sloan filters u g i z, and record the TCS focus, focus offset and DF, and anything unusual about the best-focus image (e.g. elongated, or not otherwise consistent with seeing). Highest priority (after r) are u and z (for which we have two measurements so far, but not in very good agreement).
Mail results (best-focus values for each filter) to crb, ldp.
Time required: 2 hours.
Conditions required: seeing <~ 1 arcsec
Instrument required: ACAM
Measure stability of ACAM focus offset imaging vs spectroscopy
Aim: check the change in telescope focus required when switching between imaging (Sloan r) and spectroscopy modes. Usually, it's 0.22 mm, but on at least two occasions, it's been measured as 0.11 mm. We need to explore whether the change depends on telescope position (flop, flexure).
Method: point anywhere on the sky at high elevation (for good seeing). Set rotator mount PA near 0 deg. Determine the best focus in Sloan r, using focusrun (keep all the exposures), and a wavelength region corresponding roughly to Sloan r, i.e. ~ 6200 A, which lies at y(unwindowed) ~ 2120 or y(standard window) ~ 1320. Record the telescope focus and the filter-specific offset (shown on the ACAM gui) and the offset as recorded on the TCS info page (DF). Switch to spectroscopic mode, record the filter offest on the TCS info page, acquire on the 1-arcsec slit a star anywhere in the field, determine best spectroscopic focus, and record the offset between imaging and spectroscopic focus. Only rotator mount PA = 0 is required. Repeat (determine best imaging and spectroscopic focus) at elevation 40 deg, at each of rotator mount PAs near 0, 90, 180 and 270 deg, and record the telescope focus and offset between imaging and spectroscopic focus at each. Mail results to crb, ldp.
Time required: 1 - 2 hours.
Conditions required: seeing <~ 1 arcsec
Instrument required: ACAM
Test image quality delivered by filter #60 in ACAM
Aim: measure image PSF delivered by ACAM through filter #60, which has 'lots of internal speckles', but is a possible substitute for filter #58 (bad PSF) for a service programme. However, it may also degrade the transmitted wavefront, so we need to measure the PSF.
Method: install filter #60 in the wheel, do a focus run, find best focus and take an image. Take an image through the Sloan r filter (use nominal ACAM imaging focus). Mail run numbers to crb.
Time required: 0.3 hours.
Conditions required: seeing <~ 1.5 arcsec.
Instrument required: ACAM imaging.
Measure telescope focus vs elevation at Nasmyth
Aim: determine whether there is any change of telescope focus with elevation. For Casssegrain focus, the telescope-control software includes a correction. For Nasmyth, it doesn't, which doesn't sound right.
Method:
The NAOMI DM needs to have been flattened, and NAOMI set up for imaging on the AG7 camera in the red (NAOMI dichroic #3). Do standard focus runs at each of elevations 20 30 40 ... 90 deg.
Mail results (best focus vs elevation) to crb.
Time required: 1 - 2 hours.
Conditions required: seeing <~ 1 arcsec
Instrument required: NAOMI/AG7
Measure colour terms for ACAM filters
Aim: Determine relations between observed counts, star mag and star colour for different filters. Method: Take short exposures of two Landolt standard-star fields (with at least 3 standard stars visible on ACAM) in each of Sloan u g r i z, old Sloan filters g1 g2 r i and Bessell U B I Z.
Time required: 1 - 2 hours
Conditions required: photometric, seeing < 2.5 arcsec, any moon
Instrument required: ACAM
Sensitivity of Cass TV in the red
Aim: discover why bright, but very red, objects are invisible on the Cass acquisition TV, inconsistent with the predicted throughput of the optics/CCD out to ~ 1 micron.
Method:
(1) Take z, i, r... images of the very red object with ACAM (coordinates available from crb), and deduce at what wavelength it vanishes.
(2) Do the tests suggested by Neil (you'll need help from the OSA):
"To check the optics in the focal reducer barrel, you can move the slide to the OUT position and get an image of the central 1 arcmin of the slit area. Then the light passes through the "relay lens" only, reflected from the slit. You can even eliminate the slit by looking at the field in "direct tv" view, i.e off the back of the Acqcomp mirror. Of course for this test you may have find out which point on ACAM corresponds to the slit centre and then acquire the mystery star on ACAM. This is just to ensure the mystery object is within the smaller field of view, hopefully in the middle."
Record the image numbers from both ACAM and Cass TV.
Mail a report to crb, nom.
Time required: 1 hour.
Conditions required: any
Instrument required: ACAM, Cass TV
Check ACAM narrow-band filter focus offsets
Method: Point the telescope anywhere on the sky at high elevation (for good seeing). Use focusrun (keep all the images) to determine the best focus in Sloan r (use exposures of at least 7 sec when doing a focus run). Record the telescope focus and the filter-specific offset (shown on the ACAM gui) and the offset as recorded on the TCS info page (DF). Repeat the test without filters in the beam (i.e. clear) and then for each of the Halpha filters: #61 63 65 66 69 71 72 73 74, and record the TCS focus, focus offset and DF, and anything unusual about the best-focus image (e.g. elongated, or not otherwise consistent with seeing). Mail results to srix, crb.
Time required: 2 hours.
Conditions required: seeing <~ 1 arcsec
Instrument required: ACAM
Check blind-offset accuracy, over distances up to 20 arcmin, using ~ 10 - 20 stars pairs listed in Janet Sinclair's technical note (copy in the green binder of miscellaneous star lists on the control desk).
Method: Go to one star of pair, record x,y on detector, blind-offset to second star, record offset which TO needs to make in azimuth and elevation to restore restore to same coordinates. Dan has already taken some measurements, but more are useful.
Time required: up to 1 hour.
Conditions required: any, as long as seeing is <~1.5 arcsec
Instrument required: imager (including acquisition camera)
Check image FWHM at Cass does not depend on telescope elevation (following the re-insertion of a loose top-end locking pin Dec 2007).
Method: Determine best telescope focus using aux-port, at elevations ~ 90, 60, 40, 20 deg.
Time required: ~ 1 hour
Conditions required: any, as long as seeing is < 1 arcsec
Instrument required: aux port (or any Cass imager)
Check zenith distance for vignetting: ZD at which (1) the upper edge of (unlowered) lower dome shutter starts to vignette the telescope, and (2) (lower priority) the telescope is completely vignetted. This information is required before we can safely operate GLAS with the proposed new ZD limit = 67 deg.
Method: observe stars at successively greater ZD (probably easiest to pick these near the meridian, i.e. RA = ST), with the telescope out of focus, to give a view of the primary mirror.
Time required: 0.5 hours
Conditions required: any
Instrument required: acqusition camera in TV mode
Check scale and distortion on Cass TV camera in ISIS slit-view mode, required for the new ISIS acquisition tool being written by Craige.
Method: (1) Acquire star roughly at centre of slit, record x and y.
(2) Offset star to each of a series of 8 positions on a square 3 x 3 grid centred at the above, separation between positions = 10 arcsec, recording x and y at each position.
(3) Repeat (2) for positions on a 3 x 3 grid with separations 1 arcmin. The aim is to determine the scale near the centre of the TV, and to get some idea how much the scale varies across the field.
Time required: 1 hour.
Conditions required: any, as long as seeing is <~2 arcsec
Instrument required: Cass TV camera viewing ISIS slit
Check atmopsheric dispersion observed by ACAM
Method: focus ACAM through a red filter, point to a star at elevation ~ 20 deg, obtain images in U and B bands.
Time required: 10 mins
Conditions required: any, as long as seeing is < 1 arcsec, can be done in twilight
Instrument required: ACAM
Characterise wings of stellar PSF in normal seeing
Method: point to bright star V ~ 5, insert R filter, take exposures of 1, 10, 100 sec.
Time required: 20 mins
Conditions required: any, as long as seeing is <~1.5 arcsec
Instrument required: ACAM
Template lines for the above sections...
Aim:
Method: details... Mail results to crb...
Time required: ? hours.
Conditions required: seeing <~ ? arcsec
Instrument required: ?

Last Updated: 25 January 2013

Chris Benn crb@ing.iac.es