We have written this document for observers wishing to perform CCD imaging at the 1.5-m 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 1.5-m 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, Leonel Gutierrez, 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 1.5-m telescope include:
Sources of information with some relevance to CCD imaging at the 1.5-m 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 1.5-m telescope is operated from a warm room. Recently, the dome has been automated. Nevertheless, it is wise to enter the dome on occasion. Except in the height of summer, warm clothes, including thermal underwear, a hat, and gloves, are recommended. 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). 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 1.5-m primary mirror. It delivers a roughly f/13.5 beam to a Cassegrain focus. The edge of the primary is out of figure, and so the telescope is stopped down at the secondary to about 1.32 meters. The telescope often suffers from significant astigmatism.
Recently, automatic dome rotation has been installed. Nonetheless, it is prudent to occasionally check that the dome is not occulting the telescope.
The telescope is equipped with two finder telescopes. The finder with the smaller field of view has a video camera attached. This camera is viewed and controlled from the control room.
There are two routes from the warm room to the telescope: through the old control room and by the outside walkway. To minimize heat leaks into the dome, which can degrade the seeing, we recommend using the outside walkway.
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 +59° 40' and -40° 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 telescope has a reputation for pointing inconsistently, sometimes badly and sometimes well. The best that can be expected 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, although often the pointing is worse. Recently, the pointing map has been refined, but it is too early to tell whether there is a significant improvement.
Typical delivered image quality is 1.0 to 1.5 arcsec.
The telescope is located at a longitude of +115° 28' 00", a latitude of +31° 02' 43", 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 78 x 135 arcsec (ra x dec). The guider can guide on stars at least as faint as 13 mag. The guider camera can move within a field of roughly 40 arcmin in right ascension and 25 arcmin in declination.
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 15 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.
When a focal reducer is used, it is impossible to focus the guider. Thus, images with the focal reducer must be taken unguided.
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 is the default filter wheel at the 1.5-m telescope, but La Cubeta is shared with the 84-cm telescope. Should you require La Cubeta, you should clearly specify this 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 84-cm and 2.1-m telescopes. Therefore, you should clearly specify your requirements on your proposal for telescope time.
When a focal reducer is used, it is impossible to focus the guider. Thus, images with the focal reducer must be taken unguided.
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 (azul) | La Ruca (rojo)
| ||
| Demagnification | 1.00x | 1.65x | 1.58x | 1.67x
| ||
| Size of pixel (arcsec) | SITe1 1k | 0.274 | 0.452 | 0.432 | 0.458
| |
| Thomson 2k | 0.160 | 0.264 | 0.253 | 0.267
| ||
| Size of CCD (arcmin) | SITe1 1k | 4.7 | 7.7 | 7.4 | 7.8
| |
| Thomson 2k | 5.5 | 9.0 | 8.6 | 9.1
| ||
| Field diameter at 80% transmission (arcmin) | ??? | 8.2 | 8.4
| |||
| Field diameter at 50% transmission (arcmin) | ??? | 9.1 | 9.6
|
have fields at 50% transmission that 1k CCD.
There are two CCDs available at the 1.5-m telescope: the SITe1 1k CCD and the Thomson 2k CCD. There is an unofficial programme of CCD calibration every fall. The most recent CCD characteristics will always be found from the links in the CCD section of "Noticias recientes del OAN" on the observatory web page.
| SITe1 1k | Thomson 2k
| |
| Format | 1k x 1k | 2k x 2k
|
| Physical size (mm) | 25 | 29
|
| Pixel size (micron) | 24 | 14
|
| Pixel size (arcsec) | 0.274 | 0.160
|
| Field (arcmin) | 4.7 | 5.5
|
| Vignetted by guider? |
| |
| Orientation (image display) | N left E down | N up E right |
| Orientation (FITS, IRAF) | N left E up | N down E right |
| Temperature (C) | -80 | -90
|
| Dewar hold time (hr) | 6-8 | 9-12
|
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 CCD control program displays pixel (1,1) in the upper left corner rather than the conventional lower left corner.
The SITe1 1k CCD is cosmetically excellent. The Thomson 2k has two very hot pixels in adjacent columns near the center that ruin up to about 15 adjacent columns in long exposures.
The CCD temperatures are displayed on the CCD controller, located on the north-west side of the mirror cell. 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 SITe1 1k CCD) or 9 hours (for the Thomson 2k CCD). The mechanical engineer should fill at mid-day and the telescope operator should fill at the beginning and end of the night, though this should be checked if there is only one telescope operator on duty.
| Binning | SITe1 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 SITe1 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 small pixels at the 1.5-m, 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 SITe1 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.
The following quantum efficiency values come from the manufacturer's specifications.
| SITe1 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 during exposures.
The photometric zero points are routinely measured during the CCD calibration campaigns and the latest values for these will also be found from the links in the CCD section of "Noticias recientes del OAN" on the observatory web page.
The CCDs had the zero-points with the UBVRI filters (without the focal reducers) shown in the following table in the fall of 2001. These count rates in electron/second are for a star with magnitude and colour of 0 mag. at an airmass of 1. The values for the SITe1 1k were measured, while those for Thomson 2k are based upon the count rates measured for both CCDs in the fall of 2000 and the more recent measurements for the SITe1 1k. (Both reports are available from the CCD section at "Noticias recientes del OAN" on the observatory web page.)
| SITe1 1k | Thomson 2k
| |
| U | 2.25e8 | 1.3e8
|
| U2 | 5.33e8 | 3.7e8
|
| B/B2 | 2.05e9 | 2.3e9
|
| V/V2 | 3.45e9 | 3.1e9
|
| R/R2 | 4.19e9 | 3.6e9
|
| I/I2 | 3.20e9 | 2.3e9
|
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). These values are based upon the measurements obtained in the fall of 2000 and corrected for the increase in sensitivity measured for the zero points in the fall of 2001.
| Sky | mag/arcsec^2 | SITe1 1k | Thomson 2k
| |
| U | dark | 20.8 | 0.081 | 0.016
|
| bright | 17.8 | 1.3 | 0.26
| |
| U2 | dark | 20.8 | 0.19 | 0.047
|
| bright | 17.8 | 3.0 | 0.73
| |
| B/B2 | dark | 21.8 | 0.29 | 0.11
|
| bright | 18.3 | 7.4 | 2.72
| |
| V/V2 | dark | 21.0 | 1.0 | 0.32
|
| bright | 18.3 | 12.3 | 3.8
| |
| R/R2 | dark | 20.4 | 2.2 | 0.64
|
| bright | 18.2 | 17.0 | 4.8
| |
| I/I2 | dark | 18.7 | 8.0 | 2.0
|
| bright | 17.8 | 18.5 | 4.4
|
The sky brightness during bright time is relatively constant, but rises rapidly within 15 degrees of the moon.
In the Stromgren filters, the CCDs had the following typical count rates in electron/second from a star with magnitude 0, color 0, and air-mass 1 (without the focal reducers) in the fall of 2000. The current performance should account for the increase in sensitivity measured in the fall of 2001 (see the reports in the CCD section at "Noticias recientes del OAN" on the observatory web page).
| SITe1 1k | Thomson 2k
| |
| u | 3.00e7 | 1.46e7
|
| v | 1.34e8 | 1.51e8
|
| b | 3.76e8 | 4.31e8
|
| y | 4.90e8 | 4.52e8
|
| beta-n | 5.80e7 | 5.59e7
|
| beta-w | 3.10e8 | 2.94e8
|
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). These count rates should also be corrected for the increase in sensitivity measured in the fall of 2001 (see the reports in the CCD section at "Noticias recientes del OAN" on the observatory web page).
| Sky | mag/arcsec^2 | SITe1 1k | Thomson 2k
| |
| u | dark | 20.8 | 1.1e-2 | 1.8e-3
|
| bright | 17.8 | 1.7e-1 | 2.8e-2
| |
| v | dark | 21.8 | 1.9e-2 | 7.4e-3
|
| bright | 18.3 | 4.8e-1 | 1.9e-1
| |
| b | dark | 21.6 | 6.5e-2 | 2.5e-2
|
| bright | 18.3 | 1.4e+0 | 5.3e-1
| |
| y | dark | 21.0 | 1.5e-1 | 4.6e-2
|
| bright | 18.3 | 1.8e+0 | 5.5e-1
| |
| beta-n | dark | 21.6 | 1.0e-1 | 3.3e-2
|
| bright | 18.3 | 2.1e-1 | 6.8e-2
| |
| beta-w | dark | 21.6 | 5.3e-2 | 1.7e-2
|
| bright | 18.3 | 1.1e+0 | 3.6e-1
|
The sky brightness during bright time is relatively constant, but rises rapidly within 15° 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). These count rates should also be corrected for the increased sensitivity measured in the fall of 2001 (see the reports in the CCD section at "Noticias recientes del OAN" on the observatory web page).
| SITe1 1k | Thomson 2k
| |
| II 3727 | 1.98e7 | 9.94e6
|
| II 4363 | 1.05e7 | 1.33e7
|
| II 4861 | 1.49e8 | 1.43e8
|
| II 5007 | 1.82e8 | 1.72e8
|
| II 6300 | 3.16e7 | 2.85e7
|
| II 6563 | 2.60e7 | 2.08e7
|
| II 6730 | 2.73e8 | 2.25e8
|
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). These count rates should also be corrected for the increased sensitivity measured in the fall of 2001 (see the reports in the CCD section at "Noticias recientes del OAN" on the observatory web page).
| SITe1 1k | Thomson 2k | |
| II 3727 | 6.70e13 | 3.38e13
|
| II 4363 | 1.87e14 | 2.37e14
|
| II 4861 | 6.63e14 | 6.36e14
|
| II 5007 | 7.70e14 | 7.28e14
|
| II 6300 | 1.13e15 | 1.02e15
|
| II 6563 | 1.09e15 | 8.75e14
|
| II 6730 | 1.65e15 | 1.36e15
|
The accompanying tables gives estimated values for the sky brightness at the zenith during dark time in mag arcsec^-2 and in electron/second/pixel (with 1x1 binning and without the focal reducers). These count rates should also be corrected for the increased sensitivity measured in the fall of 2001 (see the reports in the CCD section at "Noticias recientes del OAN" on the observatory web page).
| Sky | mag/arcsec^2 | SITe1 1k | Thomson 2k
| |
| II 3737 | dark | ??? | ??? | ???
|
| bright | ??? | ??? | ???
| |
| II 4363 | dark | ??? | ??? | ???
|
| bright | ??? | ??? | ???
| |
| II 4861 | dark | ??? | ??? | ???
|
| bright | ??? | ??? | ???
| |
| II 5007 | dark | ??? | ??? | ???
|
| bright | ??? | ??? | ???
| |
| II 6300 | dark | ??? | ??? | ???
|
| bright | ??? | ??? | ???
| |
| II 6563 | dark | ??? | ??? | ???
|
| bright | ??? | 0.12 | 0.092
| |
| II 6570 | dark | ??? | ??? | ???
|
| bright | ??? | 1.02 | 0.82
| |
| E6607 | dark | ??? | ??? | ???
|
| bright | ??? | 0.95 | 0.76
| |
| II 6730 | dark | ??? | ??? | ???
|
| bright | ??? | ??? | ???
|
Twilight flats seem to work well.
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 (see the telescope console sections).
Take flats to the east in the evening and to 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.
In this chapter we provide information on the operation of the telescope console, dome, finder, guider, filter wheel, focal reducers, and CCD. Although all observing operations may now be accomplished without leaving the control room, many components must be started from within the dome (opening the dome, the telescope shutters, and the finder covers; powering up the guider; filling the CCD dewar).
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, snow blowing off the trees, 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 primarily with two computers: the telescope console
computer and the Linux workstation agua.
The telescope console computer is located in the console cabinet. One may control the telescope from this computer, but this is now normally done with the Linux workstation.
The Linux workstation agua serves as the interface to all
observing operations: the dome control, the telescope console, the
secondary mirror focus, the finder camera, the CCD, the filter
wheel, and the guider. The workstation agua has an
Instrumentos folder on the that contains the icons that
start the various instrument control programs. The Paquetes
Astronomia folder on the desktop contains the icon that starts up
IRAF and an image display (ds9, SAOtng, Ximtool). By default,
images are stored in agua:/home/observa/imagenes, though
this can be easily modified. Given the number of components
controlled from the Linux workstation, we recommend using several
desktops to conveniently display their program windows.
There is a second Linux workstation (beta) in the observing
room to which the instrument control programs may be exported
(telescope console, dome, CCD, guider, secondary). This
workstation also has the same Paquetes Astronomia folder as
does agua. On beta, the images are also found in
/home/observa/imagenes by default.
The observing account is "observa" on all computers. The passwords will be indicated in the observing room.
The telescope is switched on by the three switches on the console cabinet.
The telescope movement is controlled via the telescope console computer, which is located in the console cabinet. There are two interfaces to the console computer. The first is the command line interface that starts automatically when the telescope is switched on. The second is the graphical interface that runs on the Linux workstation. These interfaces are discussed in the following two subsections.
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 (see below).
(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 (see below) and turning off the three switches on the console cabinet.
There is a "panic button" on the front of the lower telescope support (that is, the north side of the southern telescope support). Also, in an emergency, the telescope can be stopped by switching off the three power switches on the console cabinet. Regardless, when stopped in either manner, the telescope will be completely lost.
The graphical console interface is started by clicking once on the
consola nueva icon found in the Instrumentos folder
on the Linux computer's desktop. In the event that this icon is
missing, the graphical interface may be started by issuing
/home/observa/bin/consola.new at the command prompt in any
terminal window.
The graphical interface opens three windows: the telescope console window, a object catalogue, and the dome control window (described in the section following focus control).
The default catalogue (/home/observa/default.cat) contains
only very bright stars. It is also possible to load an object
list with the coordinates for your objects. See the default
catalogue for the file format. To move the telescope to a
catalogue object, select the object and then click on the
MUEVE TELESCOPIO button.
In most cases, the user will interact primarily with the telescope console window. This window is divided into three vertical panes.
MOVS RELATIVOS). There are two boxes in which offsets (in
arcseconds) may be typed, one for each of right ascension and
declination. Below these are buttons for each direction (north,
south, east, west). The largest offset that may be entered is 60".
EDITAR COORDENADAS button opens a window
in which object coordinates and epoch are entered. To move the
telescope to these coordinates, accounting for precession and the
pointing map, click MUEVE TELESCOPIO (PRECESA, ETC). Should
you not want to correct for precession or the telescope pointing
map (probably a poor idea), click MUEVE SIN CORRECCIONES.
Note that if the declination is between 0° and -1°, the negative
sign must precede the first non-zero number, e.g., -0° 14' 57"
would be entered as 0 -14 57. It is necessary to close the
coordinates window, in order to interact with other components of
the console interface, by clicking on CIERRA ESTA VENTANA.
POSICIONES FIJAS button opens a menu from which
fixed telescope positions may be selected. Currently, the only
fixed positions defined are the zenith (CENIT) and the
position for filling the dewar (PONER LONA).
INSTRUCCIONES MAS USADAS button opens a menu with
several useful options:
CORRIGE CENIT informs the console that the telescope
is at the zenith and resets the coordinates appropriately. Be
careful not to select this button by mistake!
CORRIGE COORDENADAS sets the current telescope
coordinates to the coordinates most recently entered at the
coordinates window or selected from the object catalogue.
DESACTIVA GUIADO deactivates telescope guiding.
ACTIVA GUIADO activates telescope guiding.
INSTRUCCIONES EN LINEA opens a command line window at
which console commands may be typed (always in uppercase). The
most useful of these are
AH hh mm ss.s: Set the hour angle. The
telescope guiding is deactivated.
FIJODEC dd mm ss: Set the declination. The
telescope guiding is deactivated. Note that if the declination is
between 0° and -1°, the negative sign must precede the first
non-zero number, e.g., -0° 14' 57" would be entered as 0 -14
57.
LEE_RELOJ: Force the console computer to set its
time.
Mover Telescopio button. All object
coordinates entered using the EDITAR COORDENADAS window are
stored here for future use. Selecting an object from this list
and pressing the Mover Telescopio button sends the
telescope to the object position. The console program may be left
running even though the telescope control computer is turned off,
so object coordinates in this list may be used over several
nights. Unfortunately, this catalogue cannot be saved as an
object list for future use.
INFO UTIL) lists the object hour
angle, airmass, and azimuth as well as the universal and sidereal
times and the julian date.
Most of the preceeding operations may also be accomplished from the console computer in the console cabinet. The following are the most useful telescope console commands:
ar HH MM SS
dec DD MM SS
dec 00 -10 23.
epoca YYYY.Y
act
cenit
ah HH MM SS
fijo_dec DD MM SS
fijo_dec 00 -10 23.
nguia
len X
len 1.0
(the default) for adjusting the field of the CCD. Use len 0.3
when guiding.
<Alt-Fn-i>
There are two hand paddles - one in the dome and one at the observing station. Both have switches to permit rapid motions, though all motions are slow by default. On the paddle in the dome, rapid motions are activated by pressing the button on the back of the paddle while simultaneously pressing one of the directional buttons on the front of the paddle. On the paddle at the observing station, rapid motions are activated by pressing the small, red button on the paddle while simultaneously moving the joystick. The command line program on the console computer indicates whether the telescope motions are slow or rapid. 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 (INSTRUCCIONES MAS USADAS/CORRIGE
COORDENADAS with the graphical interface, the corr command
with the command line interface). (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):
The telescope focus can be controlled with either the Linux workstation or the hand paddles. We recommend that the Linux workstation be used, as movements with the hand paddle are very coarse.
To start the telescope focus control program on the Linux
workstation, click once on the Secundario icon in the
Instrumentos folder on the Linux workstation desktop. If
the icon is not present, the focus control program may be started
by issuing /usr/local/bin/foco_15 from any terminal window.
The telescope focus depends on the position of the telescope, see "El foco del telescopio de 1.5m". The focus changes because the support structure for the secondary mirror deforms as the telescope is elevated towards the zenith, requiring the secondary mirror to be raised as the zenith distance decreases. Recently, the program that controls the secondary mirror has been modified to correct this systematic effect automatically. This correction is implemented as an option. To use it, click the button at the bottom of the focus control program's window. Note that this option should only be activated after the telescope has been focused. Even with this option, we recommend checking the focus if the image quality is important, though the automatic focus control should be sufficient for standard star fields and the like. For additional details, see "La calidad de imagen del 1.5m".
It is best to always focus by raising the secondary, which corresponds to decreasing the focus read out by pressing the "Dn" button.
Rough values of the telescope focus are:
| SITe1 1k | Thomson 2k
| |
| No focal reducer | 730 |
|
| La Cubeta Cuadrada |
| |
| La Ruca (blue) | 2400 |
|
| La Ruca (red) | 3020 |
|
The differences will undoubtedly be more stable than the absolute values.
The automatic dome control program starts when the telescope's
graphical console interface starts. Occasionally, the program
window freezes. Should this happen, there is also a cupula
icon in the Instrumentos folder that may be used to restart
the control programe. The program itself is located at
home/observa/bin/cupula_uis.
The dome control program positions the dome so that it is very close to the east side of the telescope, sometimes alarmingly so, though it never appears to occult the telescope. In this way, the dome movement is minimized while the telescope tracks an object.
By default, dome control is active when the control program is running, though there is a button to turn this off. While the dome program is running, it is still possible to move the dome using either of the hand paddles. This is not recommended, since the control program will immediately return the dome so that it does not occult the telescope once the manual dome movement is released, possibly severely jarring the dome. The control program does not rotate the dome when the telescope is sent to one of its fixed positions (zenith, filling).
The telescope finder video camera is controlled using the
Buscador icon in the Instrumentos folder. The
program itself is located at /home/observa/buscador. Note
that the danes computer must be up and running for this
video camera to be used. (This computer is located in the hallway
between the control room and the dome. If it is not running, ask
the electronics technician to start it.)
The program window has a slider bar for changing the camera gain and a box where the integration time is specified. The default gain is 1.0 and the default integration time is 100 ms. These values are sufficient to easily see 6 mag stars. There are buttons to start and stop the integrations and another button to close the program.
To see the signal from the video camera, turn on the large video monitor in the control room and press the "LINE A" button. (This same monitor receives the guider video signal.)
The guider is described in detail in "Guiador del Telescopio de 150 cm del OAN - Manual de Usuario" by Salvador Zazueta & Joaquín Bohigas (though this is now somewhat out of date).
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.
agua
that is also used for the finder video camera.) Press the "LINE
B" button. If all is well, a variety of system messages will
appear on the camera monitor. If not, the guider control computer
("PC DE LA CAMARA DEL GUIADOR", on the telescope mirror cell)
probably did not boot properly. In this case, it will perhaps
beep repeatedly. Pressing the reset button (indicated) should
reboot the control computer and resolve the problem. If not,
contact the electronics technician.
guiador icon in the Instrumentos
folder on the Linux workstation desktop. The program may be
started manually by issuing cd /home/observa/guiador2 and
./guiador150 in any terminal window. This will present a
control panel with buttons labelled "GUIADOR", "GSC", and
"CAMARA", each of which opens its own subprogramme window.
| SITe1 1k | Thomson 2k | |
| No focal reducer | 2100 | |
| La Cubeta Cuadrada | cannot be focused | cannot
be focused |
| La Ruca (blue) | cannot be focused |
cannot be focused |
| La Ruca (red) | cannot be focused | cannot be focused
|
| FACTOR DE BINNING | 2
|
| TAM. CAJA GUIADO | 60
|
| VALOR KP | 10
|
| ZONA MUERTA | 0.7
|
mount /cd-r in any xterm window.
len
0.5.
len 1.0.
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:
Instrumentos folder
on the Linux workstation (agua) desktop. The programme is located
at /usr/local/bin/ruca. If there is communication with La
Ruca, the control program will open after a five second delay. If
not, a window will eventually state that communication has failed.
The interface is rather intuitive.
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.
| SITe1 1k | Thomson 2k
| |
| Angle | +39 | +75
|
The control program allows the filters to be labelled and saved in
a file. First, edit the filter labels ("Archivos/Edita
filtros"), then save them to a file ("Archivos/Grabar filtros en
archivo"). This file can then be loaded at a later time if
necessary via "Archivos/Cargar filtros". The filter labels
should not contain spaces. By default, the files containing the
filter labels are stored in the directory
agua:/home/observa/archivos_filtros.
When a focal reducer is used, it is impossible to focus the guider. Thus, images with the focal reducer must be taken unguided.
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 other for use in the blue. 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 focus changes when using the focal reducers.
| La Cubeta Cuadrada | La Ruca (blue) | La Ruca (red)
| ||
| Change in guider focus | cannot be focused | cannot be focused | cannot be focused
| |
| Change in telescope focus | +1710 | +2440
|
The CCD is now controlled using a Linux-based program, not PMIS.
To start the CCD control program, click on the CCDS-OAN
icon in the Instrumentos folder on the Linux workstation
(agua) desktop.
When the program starts
Continue.
To fill the CCD, the telescope has to be moved to -30 degrees, e.g., by issuing
ah 00 00 00 (if the telescope is not on the meridian) fijo_dec -30 0 0
at the telescope console computer (command line interface) or
selecting POSICIONES FIJAS/PONER LONA from the graphical
interface.
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 your telescope operator (or the telescope operator at the 2.1-m if you are without one) to fill it for you.
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.
Both the SITe1 1k and Thomson 2k CCDs suffer from residual bulk images.
This chapter contains lists of problems and possible solutions.
len 0.3.