We have written this document for observers wishing to perform CCD imaging at the 84-cm telescope of the OAN-SPM.
Our first purpose is to provide information on the performance of the equipment to allow observers to plan their observations and to check that the equipment is functioning normally. We present the characteristics of the telescope, the guider, the filter wheel, the filters, the focal reducers, and the CCDs along with typical stellar count rates, sky brightnesses, and transformations.
Our second purpose is to provide a guide to the operation of the telescope, guider, filter wheel, and CCD. We reference existing documentation, provide check-lists for common tasks and for trouble-shooting common problems, document previously undocumented quirks and foibles, and give advice on how best to use the equipment.
This document is intended to be a guide, not a complete reference manual. Further details on various subsystems used in CCD imaging at the 84-cm telescope are given in the manuals below. Please read them before your observing run.
We have benefited greatly from discussion with many astronomers and technicians at the OAN-SPM, especially Joaquín Bohigas, Almudena Bullejos, Hector Castañeda, Carlos Chavarria, Benjamín García, Olga Kuhn, Steve Lawrence, Beto López, José Luis Ochoa, and Salvador Zazueta. We are especially grateful to Almudena Bullejos and Hector Castañeda for correcting the Spanish version of this manual.
Please contact us if you encounter a new problem, find a solution to an existing problem, have a suggestion for an improvement to the telescope or instrument, or have comments on this document.
This section will contain news of changes to the equipment, so you can quickly determine what has changed since the last time you used the equipment.
Manuals on the individual components used in CCD imaging at the 84-cm telescope include:
Sources of information with some relevance to CCD imaging at the 84-cm telescope include:
Other sources of information on particular aspects of CCD imaging include:
In this section we briefly characterize the observing environment, telescope, guider, CCDs, focal reducers, and filters and provide information on their typical performance.
The door to the 84-cm dome can be difficult to open. Try pulling on the cable. Should that fail, (gently) kick or hit the door while pulling on the cable. It should then open easily.
The telescope, guider, CCD, and filter wheel are controlled from the dome floor; you will be working outside at night on a mountain top. Except in the height of summer, warm clothes, including thermal underwear, a hat, and gloves, are essential. You can borrow a quilted jacket and pants from the OAN headquarters in Ensenada.
A flashlight and batteries can be obtained from the observatory supervisor. However, we have found that the observatory flashlights are unreliable, and recommend purchasing a more reliable one (such as an AA-size "Mini Maglite" flashlight). Flashlights are used more frequently at the 84-cm telescope than elsewhere on the mountain, and we have found that a pair of AA batteries lasts about two nights. We recommend obtaining spare batteries.
You should not assume that all of the reference documentation you might need will be available on hand or online (documentation goes missing and internet connections can be lost for significant periods). Therefore, we recommend that you bring with you paper copies of manuals for the equipment as well as coordinates and finding charts for your objects and standards.
The telescope is a Ritchey-Chrétien with an 84-cm primary mirror. It delivers a roughly f/15 beam to a Cassegrain focus. The telescope often suffers from significant astigmatism.
The dome does not rotate automatically. For this reason, you should frequently check that the dome is not oculting the telescope.
The filter wheel allows the CCD to be rotated under computer control; the manual filter holder does not permit the CCD to be rotated.
The telescope has an equatorial mount and can point to declinations between +80 and -45 degrees and hour angles between +5 and -5 hours. If the telescope is not perfectly balanced, it can have problems pointing at the northern and southern extremes of declination.
The pointing accuracy is about 3 arcmin over the whole sky, about 1 arcmin along the equator (e.g., moving between Landolt standard fields), and a few arcsec over small distances.
Typical delivered image quality is 1.5 to 2.5 arcsec.
The telescope is located at a longitude of +115° 27' 58", a latitude of +31° 02" 42", and an altitude of 2790 meters (9150 feet).
The guider hardware consists of an intensified CCD camera and an inclined plane mirror. The camera is mounted on a carriage (which provides control of the focus and moves the field in right ascension) and the plane mirror swivels (which moves the field in declination).
The instantaneous field of the guider camera is about 45 arcsec. The guider can guide on stars at least as faint as 12 mag. The guider camera can move within a field of roughly 40 arcmin in right ascension and 25 arcmin in declination. However, a ghost image is thrown onto the science CCD if the guider camera is used in the northern half of its field (see below). This ghost image is a annulus.
Guide stars can be selected automatically from the GSC (HST Guide Star Catalog). However, for this to work reliably, the coordinates of the telescope must be known to an accuracy of about 10 arcsec; these can be obtained from the console if the telescope is pointing to this accuracy.
There is a filter wheel ("La Ruca") and two manual filter holders ("La Cubeta Cuadrada" and "La Cubeta Cilindrica").
La Ruca has a pair of focal reducers, optimized for the blue and red, that may be inserted in the beam. La Cubeta Cuadrada has a single focal reducer that may be inserted in the beam; La Cubeta Cilindrica does not. This is the principal difference between the two filter holders. As the two filter holders are so similar, we will refer to both as "La Cubeta" except when when we need to distinguish between them.
La Ruca has space for eight filters and allows the CCD to be rotated. Changing sets of filters takes several minutes.
La Cubeta allows an unlimited number of filters to be used, but changing manually from one filter to another takes about a minute. Furthermore, dust can be deposited on the filters during manual filter changes, leading to problems with flat fields.
La Ruca and La Cubeta are shared with the 1.5-m telescope. Therefore, you should clearly specify your requirements on your proposal for telescope time.
The filters are described in detail in "Filtros para Imagen Directa" by Joaquín Bohigas. There are two sets of Johnson-Cousins UBVRI filters, a set of Strømgren uvby filters, a set of Thuan-Gunn uvgriz filters, and several sets of galactic (zero-redshift) and extra-galactic (redshifted) narrow-band filters. The filters vary considerably in quality.
There are two sets of UBVRI filters. They are similar, except the "U2" filter is preferred over the "U" filter as it has a higher transmission (71% at the peak versus 45%) and is wider (680 Å versus 500 Å). The BVR filters are parfocal, but the U/U2 and I/I2 filters are not.
In the galactic narrow-band sets, the "II 6563" H-alpha filter from set II is preferred over the "I 6563" filter from set I as it has a higher transmission (66% versus 38%).
Filters are shared with the 1.5-m and 2.1-m telescopes. Therefore, you should clearly specify your requirements on your proposal for telescope time.
La Cubeta Cilindrica does not have a focal reducer.
La Cubeta Cuadrada has a focal reducer that can be placed in the beam. Neither its transmission nor its parfocality are well characterized.
La Ruca has two focal reducers that can be placed in the beam. One is optimized for use in the red and the other optimized for use in the blue.
| CCD | Without focal reducer | La Cubeta Cuadrada | La Ruca (blue) | La Ruca (red) | ||
| Demagnification | 1.00x | 1.65x | 1.58x | 1.67x | ||
| Pixel size (arcsec) | SITe 1k | 0.425 | 0.701 | 0.672 | 0.710 | |
| Thomson 2k | 0.248 | 0.409 | 0.392 | 0.414 | ||
| CCD size (arcmin) | SITe 1k | 7.2 | 12.0 | 11.6 | 11.6 | |
| Thomson 2k | 8.5 | 13.5 | 13.5 | 13.5 | ||
| Field diameter at a transmission of 80% (arcmin) | 9.7 | ??? | ??? | |||
| Field diameter at a transmission of 50% (arcmin) | 13.4 | ??? | ??? |
Note that the focal reducers have fields at 50% transmission that are larger than the SITe 1k CCD.
There are two CCDs available at the 84-cm telescope: the SITe 1k CCD and the Thomson 2k CCD.
| SITe 1k | Thomson 2k | |
| Format | 1k x 1k | 2k x 2k |
| Physical size (mm) | 25 | 29 |
| Pixel size (micron) | 24 | 14 |
| Pixel size (arcsec) | 0.425 | 0.248 |
| Field (arcmin) | 7.2 | 8.5 |
| Vignetted by guider? | no | yes |
| Orientation (PMIS) | N left E down | N up E right |
| Orientation (FITS) | N left E up | N down E right |
| Temperature (C) | -80 | -90 |
| Dewar hold time (hr) | 6-8 | 9-12 |
The guider mirror has a circular aperture roughly 9.3 arcmin in diameter; vignetting beyond this is sudden and severe. Thus, the Thomson 2k CCD suffers from vignetting, but the SITe 1k CCD does not.
The orientations given are the default orientations (with the dewar fill tubes to the north). La Ruca allows the CCD to be rotated under computer control; La Cubeta does not permit the CCD to be rotated. Note that the PMIS program on the CCD control computer displays pixel (1,1) in the upper left corner rather than the conventional lower left corner.
The SITe 1k CCD is cosmetically excellent. The Thomson 2k has two very hot pixels in adjacent columns near the center which ruin up to about 15 adjacent columns in long exposures.
The CCD temperatures are displayed on the CCD controller. They should not vary by more than a few tenths of a degree, otherwise the response of the CCD can change, as can the spatial and wavelength variation of the response.
The dewar hold times depend upon the degree of vacuum. We recommend filling every 6 hours (for the SITe 1K CCD) or 9 hours (for the Thomson 2k CCD). The mechanical engineer will fill in the morning and the telescope operator from the 1.5-m or the 2.1-m will fill in the afternoon, if asked.
| Binning | SITe 1k | Thomson 2k | |
| Dark current (e/hr/pixel) | 1x1 | 20 | 2.0 |
| Full well (e) | 1x1 | 300k | 120k |
| Read rate (kHz) | 200 | 40 | |
| Read time (s) | 1x1 | 5 | 84 |
| 2x2 | 1 | 21 | |
| 4x4 | 1 | 5 | |
| ADC bits | 16 | 16 | |
| Gain (e) (1/4) | 5.0/1.3 | 2.0/0.5 | |
| Read noise (e) (1/4) | 1x1 | 18.5/8.1 | 8.5/6.9 |
| 2x2 | 18.5/10.4 | 9.3/7.5 | |
| 4x4 | 11.0/8.8 | ||
| Bias level (1/4) | 1x1 | 515.4/489.7 | 396.6/429.0 |
| 2x2 | 547.4/501.9 | 400.8/440.4 | |
| 4x4 | 409.0/470.6 | ||
| Non-linearity | <0.45% | <0.58% |
Each CCD can be read with one of two gains. The low-gain mode (mode 1) roughly matches the dynamic range of the analog-to-digital converter (ADC) to the full well of a single pixel. The high-gain mode (mode 4) gives lower read noise.
The read noise depends on the degree of binning because the CCDs suffer from spurious charge (especially the SITe 1k).
The CCDs have up to 48 columns of overscan. The CCD amplifiers appear to suffer from moderate amplifier hysteresis, so the first few columns of the overscan region can be contaminated by the exposed region. We recommend only using the last half of the overscan region to determine the bias level.
The CCD biases appear to be relatively stable, varying by about 1 DN (data number = analog-to-digital unit) during the night. Note that the bias levels given in the table were measured in a section in the centre of the CCD.
Given the relatively poor seeing at the 84-cm, it is often worthwhile to bin the CCDs to reduce the read times, effective read noise, and the sizes of the images. Of course, this reduces the bright limit of the ADC.
The SITE 1k and Thomson 2k CCDs suffer from a small residual image. That is, if a deep exposure is taken, a tiny fraction of the charge is lost during parallel charge transfer and is released over the course of a few minutes. This is not a serious problem, as the amount of charge lost is so small. However, it can be noticed if a very shallow exposure follows immediately after a very long exposure. This can happen, for instance, when mixing narrow-band and broad-band imaging.
| SITe 1k | Thomson 2k | |
| 3400 Å | 26% | 15% |
| 3600 Å | 31% | 15% |
| 3800 Å | 35% | 22% |
| 4000 Å | 38% | 37% |
| 4500 Å | 43% | 55% |
| 5000 Å | 67% | 64% |
| 5500 Å | 71% | 64% |
| 6000 Å | 73% | 63% |
| 6500 Å | 73% | 60% |
| 7000 Å | 72% | 54% |
| 7500 Å | 65% | 42% |
| 8000 Å | 52% | 31% |
| 8500 Å | 47% | 23% |
| 8500 Å | 32% | 15% |
| 9500 Å | 18% | 8% |
| 10000 Å | 12% | 4% |
The CCDs have the following strengths and weaknesses:
Our preference for both broad-band and narrow-band imaging is the SITe 1k CCD, then the Thomson 2k CCD.
Whichever CCD you select, consider binning, especially for narrow-band imaging.
The shutter is an iris with a travel time of about 10 milliseconds. This leads to "shutter shading" in short exposures. For example, the actual exposure varies by about 20 milliseconds or 2% between the center and the edge of the field in a nominal 1 second exposure. We recommend exposures of 3 seconds or longer whenever possible.
The CCDs suffer from significant light leaks. The dome should be kept dark and the computer monitors should be covered with black cloth during exposures.
The CCDs have the following typical zero-points, extinction terms, and transformations with the UBVRI filters (without the focal reducers):
| CCD | Filter | stdcol | C0 | C1 | C2 | C3 |
| SITe 1k | U | U-B | -5.00 | -0.43 | ??? | ??? |
| U2 | U-B | -4.07 | -0.43 | +0.08 | -0.04 | |
| B | B-V | -2.71 | -0.19 | +0.11 | ||
| V | B-V | -2.18 | -0.13 | -0.01 | ||
| R | R-I | -1.99 | -0.06 | +0.05 | ||
| I | R-I | -2.26 | -0.03 | +0.12 | ||
| Thomson 2k | U | U-B | -5.62 | -0.43 | ??? | ??? |
| U2 | U-B | -4.58 | -0.43 | ??? | ??? | |
| B | B-V | -2.61 | -0.19 | ??? | ||
| V | B-V | -2.25 | -0.13 | ??? | ||
| R | R-I | -2.09 | -0.06 | ??? | ||
| I | R-I | -2.63 | -0.03 | ??? |
Here, we use
stdmag = instmag + C0 + C1 X + C2 stdcol + C3 stdcol^2
where stdmag and stdcol are the standard magnitude and color, X is the air-mass, and the instrumental magnitude instmag is given by
instmag = -2.5 log electrons/second + 25
Note that the instrumental magnitude is given here in terms of the count rate in electrons, not DN or ADU.
From these transformations we obtain the following count rates in electron/second from a star with magnitude 0, color 0, and air-mass 1 (without the focal reducers):
| SITe 1k | Thomson 2k | |
| U | 6.76e7 | 3.79e7 |
| U2 | 1.56e8 | 9.93e7 |
| B/B2 | 6.91e8 | 7.59e8 |
| V/V2 | 1.19e9 | 1.12e9 |
| R/R2 | 1.52e9 | 1.38e9 |
| I/I2 | 1.21e9 | 8.61e8 |
The accompanying tables give typical values for the sky brightness at the zenith during dark time and bright time (3 hours from the full moon) in mag arcsec^-2 and in electron/second/pixel (with 1x1 binning and without the focal reducers).
| Sky | mag/arcsec^2 | SITe 1k | Thomson 2k | |
| U | dark | 20.8 | 5.8e-2 | 1.1e-2 |
| bright | 17.8 | 9.3e-1 | 1.8e-1 | |
| U2 | dark | 20.8 | 1.3e-1 | 2.9e-1 |
| bright | 17.8 | 2.1e+0 | 4.6e-1 | |
| B/B2 | dark | 21.8 | 2.4e-1 | 8.9e-2 |
| bright | 18.3 | 6.0e+0 | 2.2e+0 | |
| V/V2 | dark | 21.0 | 8.6e-1 | 2.7e-1 |
| bright | 18.3 | 1.0e+1 | 3.3e+0 | |
| R/R2 | dark | 20.4 | 1.9e+0 | 5.9e-1 |
| bright | 18.2 | 1.4e+1 | 4.5e+0 | |
| I/I2 | dark | 18.7 | 7.2e+0 | 1.8e+0 |
| bright | 17.8 | 1.7e+1 | 4.0e+0 |
The sky brightness during bright time is relatively constant, but rises rapidly within 15° of the moon.
In the Stromgren filters, the CCDs have the following typical count rates in electron/second from a star with magnitude 0, color 0, and air-mass 1 (without the focal reducers):
| SITe 1k | Thomson 2k | |
| u | 3.88e7 | 1.89e7 |
| v | 9.76e7 | 1.10e8 |
| b | 2.39e8 | 2.40e8 |
| y | 2.49e8 | 2.30e8 |
| beta-n | 5.53e7 | 3.17e7 |
| beta-w | 2.47e8 | 1.68e8 |
The accompanying tables gives estimated values for the sky brightness at the zenith during dark time and bright time (3 hours from the full moon) in mag arcsec^-2 and in electron/second/pixel (with 1x1 binning and without the focal reducers).
| Sky | mag/arcsec^2 | SITe 1k | Thomson 2k | |
| u | dark | 20.8 | 3.4e-2 | 5.6e-3 |
| bright | 17.8 | 5.3e-1 | 8.8e-2 | |
| v | dark | 21.8 | 3.4e-2 | 1.3e-2 |
| bright | 18.3 | 8.4e-1 | 3.2e-1 | |
| b | dark | 21.6 | 9.9e-2 | 3.4e-2 |
| bright | 18.3 | 2.1e+0 | 7.1e-1 | |
| y | dark | 21.0 | 1.8e-1 | 5.6e-2 |
| bright | 18.3 | 2.2e+0 | 6.8e-1 | |
| beta-n | dark | 21.6 | 2.3e-2 | 4.5e-3 |
| bright | 18.3 | 4.8e-1 | 9.3e-2 | |
| beta-w | dark | 21.6 | 1.0e-1 | 2.4e-2 |
| bright | 18.3 | 2.1e+0 | 4.9e-1 |
The sky brightness during bright time is relatively constant, but rises rapidly within one hour of the moon.
In the commonest narrow-band filters, the CCDs have the following typical count rates in electron/second from a star with magnitude 0, color 0, and air-mass 1 (without the focal reducers):
| SITe 1k | Thomson 2k | |
| II 3727 | 2.27e7 | 9.61e6 |
| II 4363 | 6.44e6 | 8.37e6 |
| II 4861 | 7.92e7 | 7.94e7 |
| II 5007 | 9.32e7 | 9.17e7 |
| II 6300 | 1.36e7 | 1.38e7 |
| II 6563 | 1.16e7 | 9.90e6 |
| II 6730 | 1.16e8 | 1.05e8 |
These correspond to the following rates in electron/second from an emission line centered in the filter with a flux of 1 erg/second/cm^2 and air-mass 1 (without the focal reducers):
| SITe 1k | Thomson 2k | |
| II 3727 | 7.7e13 | 3.3e13 |
| II 4363 | 1.2e14 | 1.5e14 |
| II 4861 | 3.5e14 | 3.5e14 |
| II 5007 | 3.9e14 | 3.9e14 |
| II 6300 | 4.9e14 | 5.1e14 |
| II 6563 | 4.9e14 | 4.2e14 |
| II 6730 | 7.0e14 | 6.3e14 |
The accompanying tables gives estimated values for the sky brightness at the zenith during bright time in mag arcsec^-2 and in electron/second/pixel (with 1x1 binning and without the focal reducers).
| mag/arcsec^2 | SITe 1k | Thomson 2k | |
| II 3737 | ??? | ??? | ??? |
| II 4363 | ??? | ??? | ??? |
| II 4861 | ??? | ??? | ??? |
| II 5007 | ??? | ??? | ??? |
| II 6300 | ??? | ??? | ??? |
| II 6563 | ??? | 0.051 | 0.044 |
| II 6570 | ??? | 0.46 | 0.39 |
| E6607 | ??? | 0.43 | 0.36 |
| II 6730 | ??? | ??? | ??? |
Twilight flats seem to work well. Peak-to-peak errors of 2% in magnitudes and 0.5% in color have been measured by Watson, García, & García (2000, unpublished).
Twilight flats in broad-band filters can be taken from about 10 minutes after sunset to about 25 minutes after sunset. Twilight flats in narrow-band filters can be taken from sunset to about 15 minutes after sunset.
It is unlikely that all eight filters in La Ruca can be calibrated in a single twilight. Obtaining flats in three filters is easy and, with practice and a bit of luck, obtaining flats in all five UBVRI filters is not impossible. The slowness of changing filters with La Cubeta makes it more difficult to obtain flats in many filters.
It's important not to track while taking flat fields. Use the
QUITA_GUIADO command at the telescope console.
Take flats to the east in the evening and the west in the morning to avoid problems with polarized light.
The facilities for taking dome flats are primitive. There is a white spot on the dome, but there are no means to illuminate it evenly.
Because of shutter shading, flats should be taken with exposures of at least 3 seconds.
We have no information of whether flat fields change significantly as the CCD is rotated, but we would not be surprised if this were the case.
The CCDs suffer from significant light leaks. Biases (and darks) must be taken at night and with the computer monitors covered with black cloth.
In this chapter we provide information on the operation of the telescope console, guider, La Ruca, focal reducers, and CCD.
Our intent is not to provide a tutorial; first-time users should request the assistance of a telescope operator and a resident astronomer in their observing proposal. Instead, we provide check-lists so that tasks are carried out correctly. Thus, we will say "Open the shutter", but we will not describe the location of the switch. Please also read the separate manuals for these components.
The decision to open or close the telescope is entirely at the discretion of the telescope operators. Reasons include but are not limited to rain or snow, threat of rain or snow, wind, humidity, and smoke. Do not argue. Do not complain. Do not pester.
If rain or snow is likely, the telescope should be covered with a tarpaulin.
Observers deal with several computers: the CCD control computer; the filter wheel and guider control computer; the telescope console computer; and the Sun and Linux workstations. The first three are located in the dome and the last two on the second floor.
The observing account is "observa". The passwords change with time and may well be different on the PCs and the workstation, but they should be written on the white board on the telescope floor.
The telescope is switched on by the three switches on the console cabinet.
The telescope console computer is located in the cabinet, but its
keyboard is outside of the cabinet on the table. After it boots, log in
as root (although it beggars belief, there is no password), and start
the console program with the consola command.
The telescope is assumed to be at the zenith when it is turned on, but
nevertheless the telescope coordinates will have errors typically larger
than the field of the CCD but smaller than the field of the finder. You
must go to a bright star (selected from the "Posiciones Medias"
section of the almanac), center the star first in the finder and then on
the CCD, and then correct the coordinates by issuing the CORR
command at the telescope console. (The positions for the almanac for
year YYYY have an epoch of YYYY.5.)
The telescope is switched off by placing it at the zenith with the
CENIT command, stopping the console program with the SALIR
command, stopping the console computer with the halt, and turning
off the three switches on the console cabinet.
There is no "panic button", but in an emergency, the telescope can be stopped by switching off the three power switches on the console cabinet. Unfortunately, the telescope will be completely lost if you do this.
The following are the most useful telescope console commands (capitals are required):
AR HH MM SS
DEC DD MM SS
DEC 00 -10 23.
EPOCA YYYY.Y
ACT
CORR
AR_OF SS
DEC_OF SS
+A -A
+D -D
QUITA_GUIADO
PON_GUIADO
AH HH MM SS
FIJODEC DD MM SS
LEN_AR X
LEN_DEC X
CENIT
SALIR
The switch on the back of the hand paddle selects normal and rapid ("R") motions. It is much better to pulse the hand paddle than to hold the switches down continuously.
The telescope does not point especially well over the whole sky. Errors
of up to three or four minutes are possible. Therefore, after a large
slew, you may need to find a bright star in the "Posiciones Medias"
section of the almanac and correct the telescope coordinates by issuing
the CORR command. (The positions for the almanac for year YYYY
have an epoch of YYYY.5.)
Furthermore, if your object is well centered in the CCD, it is worthwhile to correct the telescope coordinates before moving after a long exposure.
If the telescope is completely lost (normally because the console program was stopped with the telescope other than at the zenith):
SALIR command.
halt command.
The guider is described in detail in "Guiador del Telescopio de 84 cm del OAN - Manual de Usuario" by Salvador Zazueta & Joaquín Bohigas.
The guider uses an intensified CCD camera which can be degraded and damaged by excessive saturation (from too much light combined with too much gain). Therefore, you should increase gain only slowly and not use the intensifier while there is light in the dome or while the sun is up.
| SITe 1k | Thomson 2k | |
| No focal reducer | -16 | |
| La Cubeta Cuadrada | -116 | |
| La Ruca (blue) | -116 | |
| La Ruca (red) | -116 |
CORR command) whenever its position is known.
CAJA=size in the guider window and pressing "Manda".
Here, size is the size of the centroid box in pixels. The default
is 30 pixels.
LEN_AR 0.1 and LEN_DEC
0.01.
La Ruca is described in detail in "Rueda de Filtros La Ruca - Manual de Usuario" by Salvador Zazueta & Joaquín Bohigas.
Ask the mechanical engineer to install the filters you require. Ideally, you will inform him of your needs prior to your arrival at the observatory. La Ruca holds eight filters.
To initialize La Ruca at the start of your run:
MUEVE PASOS REDUCTOR 6997 in the command line field.
Most of the problems we have encountered with La Ruca stem from improper initialization. Therefore, we recommend removing the cover from the filter wheel and spending five minutes exercising and checking the filter wheel movement. Take care to replace the filter wheel cover with the large retaining screws to the bottom, otherwise the filter wheel may jam.
Furthermore, we recommend leaving La Ruca powered up between nights.
La Ruca also controls the rotation of the CCD. The CCD should be rotated so that the fill tubes are on the north side of the dewar; appropriate rotations are given in the table. Note that the rotations can change by 30 degrees, depending upon exactly how the CCD has been attached.
| SITe 1k | Thomson 2k | |
| Angle | +17 | +75 |
The filter program allows the filters to be labelled. The filter labels must not contain spaces.
La Cubeta Cilindrica does not have a focal reducer.
La Cubeta Cuadrada has a focal reducer that may be placed in the beam. It is operated manually by the rod above the filter; when the rod is out, the focal reducer is out of the beam.
La Ruca has two focal reducers that may be placed in the beam. One optimized for use in the red and the for use in the blue. To control the slide that holds the focal reducers, it is necessary to open a terminal window to La Ruca (Comunicacion/Abre un terminal?) and issue the following commands (capitals are required):
MUEVE PASOS REDUCTOR 0
MUEVE PASOS REDUCTOR 6997
MUEVE PASOS REDUCTOR 13934
It is a good idea to specifically move the focal reducer to the clear aperture position if you do not wish to use a focal reducer, even though this should be its default position when La Ruca is turned on.
The telescope and guider focus change when using the focal reducers.
| La Cubeta Cuadrada | La Ruca (blue) | La Ruca (red) | ||
| Change in guider focus | approx -100 | approx -100 | approx -100 | |
The operation of the CCDs is described in the manual "Macros for the PMIS CCD System" by Alan Watson and Michael Richer.
There is no need to run the ESPIA program (which formerly was used to copy images across the network), as images are now transfered much more quickly from the CCD control computer to the Linux workstation.
To fill the CCD, the telescope has to be moved to -30 degrees by issuing:
AH 00 00 00 FIJODEC -30 0 0
If the dewar is taking too long to fill, check that there is pressure and nitrogen in the tank. If the tank is very light, it is empty. In that case, ask the telescope operator at the 1.5-m o 2.1-m to fill it for you.
AH 00 00 00 FIJODEC -30 0 0
AH -03 00 00 FIJODEC 0 0 0Take your flat fields.
AR HH MM SS DEC DD MM SS EPOCA YYYY.Y ACTFind the star in the finder telescope. Center it in the finder telescope with the paddle. On the rear of the paddle is a switch to change between fast ("R") and slow motions. Pulse the switches rather than holding them down.
CORR command to update the coordinates.
Note: there is a new telescope control program, so this section is currently out of date.
HA 00 00 00 FIJODEC -30 0 0 ACT QUITA_GUIADOWait for the telescope to stop moving before issuing the
QUITA_GUIADO command.
CENIT
SALIR
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The internal surfaces in the guider and La Ruca cast ghost images in the form of arcs onto the field of the CCD. The pattern of these ghost arcs changes as the field is moved.
If necessary the ghost arcs can probably be removed by taking images at several different positions and combining the images with rejection of outliers.
When the guider camera is used in the north of the guider field, an annular ghost is cast into the field of the CCD.
Both the SITe 1k and Thomson 2k CCDs suffer from residual bulk images.
This chapter contains lists of problems and possible solutions.
len 0.3.
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