Preparation for observing (Are you ready?)Turn on power to appropriate equipmentChip binning (resolution, sensitivity, and saturation)
Finding objects and framing/centering images
Finished for the evening? (Do you have all the sky observations that are needed?)
Turn off power to appropriate equipment
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What is your observing program for the evening? Are you ready to observe if the weather is actually clear?Here is a brief list of the information you will probably need:
program nameobject names or field names
coordinates for objects or fields
You really will need these! SSUO currently uses 2000.0 coordinates (equinox and epoch 2000.0, Julian epoch). Coordinates from other equinoxes and epochs will not work..The SSUO Epoch telescope normally points to within 1-3 arcminutes. Thus, you will need coordinates accurate to 1 second of time of right ascension, and 1 arcminute of declination.
If your coordinates are not accurate to 1 second of time in RA and 1 arcminute of declination, or if your equinox and epoch are not 2000.0 you will not find your objects.
finding charts
You really will need these! Without a finder chart chart you will not know for sure where the telescope is pointing. The SSUO Epoch telescope with the ST-7 CCD camera has a field of view of approximately 20 arcminutes. With no filter (clear) images reach 12th magnitude for 1 second exposures, and 14th magnitude for 10 second exposures. JPEG images produced by the SIMBAD system for the Palomar survey images generally reach to 18th magnitude.filters for which you will obtain images
estimated exposure times
Ideally, you should be able to write a tentative script for which objects you will observe, and in which order you will observe them. Your script should include objects, coordinates, filters, and exposure times.
Of course, you need to be prepared to improvise and adjust your plans as needed.
It is occasionally the goal of an observing run simply to obtain a pleasing image, or to evaluate possible exposure times for use at a leter time.
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But before you open the observatory, call the campus police ( 4-2143). Do not use the emergency phone number unless there is a police emergency. It is a requirement for using the observatory that we advise the police that we are at the observatory. The police dispatcher may ask for your names and may ask for an estimate of how long you will be at the observatory.Open the roof as soon as possible to allow the telescope and the interior of the building to cool to the ambiant air temperature.
Obviously, make sure you know how to open the observatory safely and without injury to yourself or to others. Make sure you know how and will be able to close the observatory and secure all locks.
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Turn on power to appropriate equipment
The details can change here as new equipment is introduced and as old equipment is replaced. Make sure you have a current understanding of the POWER-ON and POWER-OFF sequences. In general, you will need to provide power to whatever telescope you will be using, plus whatever computers will be needed. Whenever possible, power is provided using power strips for related instrument groupings.Power to the drive motors for the Epoch telescope (rocker switch on Epoch telescope pier) should not be truned on until the telescope control software (Servostar) is ready to be launched. After the rocker switch is turned on, the telescope begins to track at the established drive rate. If the telescope drives without the control software being engaged, the telescope will lose synchronization with the sky. This can make it impossible to acquire objects. The start-up sequence for the telescope should be... (1) launch the Servostar software, (2) turn-on power to the telescope drive motors by using the rocker switch on the telescope pier. (as of October 2001)
The power protocols vary for computers depending on the season.
During the winter we generally retain power to the computer systems. This helps to keep moisture from the computer systems. It has also been found that some hard drives become slugish in the winter and may fail to boot if the temperature drops too low. Keeping the power on keeps the computer systems at an ideal operating temperature. During the winter computer systems will not generally need to be turned on.
During the summer the daytime temperatures will exceed safe operating temperatures if the computers are kept on. Thus, during the summer power to all equipment is truned off. During the summer computer systems will need to be turned on.
Computer monitors are always turned off regardless of the season. Thus, you should always expect that you will need to turn on any computer monitor you need to use.
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Launch appropriate software
The details can change as new software systems and new software software versions are utilized. In particular, the camera control software should be launched, and the telescope control software should be launched.As of October 2001, the camera control software CCDSoft should be launched on the camera control computer, and the telescope control software Servostar should be launched on the telescope control computer. However, the rocker switch on the Epoch telescope pier should be turned on immediately prior to launching Servostar. If the rocker switch is not on, Servostar will encounter an error when it fails to find a telescope. If this occurs, the telescope computer may hang and may need to be rebooted. If the rocker switch on the telescope pier is turned on long before Servostar is launched, the telescope will continuously move away from synchronization with the sky. If this occurs, the telescope should be initialized from within Servostar before trying to acquire an object. In general, the cautious observer may decide to always initialize the telescope before trying to acquire any object.
However, to minimize these problems, the start-up sequence for the telescope should be... (1) turn-on power to the telescope drive motors by using the rocker switch on the telescope pier, (2) launch the Servostar software, (as of October 2001)
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Start the camera cooling
Use the camera control software to start the camera cooling as soon as possible. It generally takes 15-20 minutes for the camera to reach its operating temperature. The set-point temperature should be set as low as possible. The lower the temperature, the lower will be the dark current, and the more reliable will be the dark current correction. However, temperature stability is always more important than the actual temperature value. The cooling mechanism should be capable of stable operation at about 30 degrees Centigrade below the ambient temperature. Ideally, the power utilized by the cooling system should be in the range of 80-90% of maximum. Setting the temperature is normally a balance between desiring to get the temperature as low as possible, and making sure the cooling system does not burn out by running at maximum power for too long. The camera will always run at 100%, or maximum power, during the initial first 15-20 minutes while the camera is cooling.During cooler weather at SSUO we should be able to run the camera at -20oC. During warmer weather we may be forced to operate at -15oC or even warmer.
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Specify observers names
Use the camera control software to specify the names of the observers. This information is part of the information that is automatically written into the image headers when images are saved. This information in the FITS header becomes a permanent part of the saved images. Since the software normally remembers settings from the last time it was used, you should check this to make sure your images are not saved under someone else's name.Custom information along with comments may also be included in the FITS headers. To learn more about what type of information is included, and how to add custom information, consult the SSUO FITS Resources Page.
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Saving images
Use the camera control software to create a directory in which you will save tonight's images. All images should be saved in the directory (folder) IMAGES. This directory is one of the high level directories on the C: drive on the camera control computer. Images are saved in a separate folder for each night the observatory is used. Our standard directory naming system is to use a text string consisting of a six numeral string that corresponds to the local date. For example, if you were observing on October 8 in the year 2001 you would name your directory for that night as 011008. There must be no spaces or special characters such as under_scores in the directory names. Note that the first two digits represent the year, the second two digits represent the month (01-12), and the last two digits represent the day of the month (01-31). Yes, the sequence is year, month, day. These directory names must always be comprised of 6 digits.
If there is some question about what time you may actually start saving images, always use the first date of the double date that represents the possible observing night. For example, October 8 is actually the first date of the double date that represents that night (October 8/9). Our current standard requires that you use the first date of the double date for the SAVE directory (October 8) even if you do not start saving images until after midnight (which would technically be October 9).
Currently, observers are free to create arbitrary sub-directories within the main image directories for each night. The only restrictions are that the data is destined to be archived on a UNIX system so directory names may not contain spaces (blanks) and should not contain special characters that are unacceptable to a UNIX file system. Under scores ( _ ) and dashes ( - ) are fine, dots ( . ) should be avoided in directory names.
File names for images should be meaningful. File names may not contain spaces (blanks). A file name should identify a key object or program objective in some succinct manner. Including a filter as part of a file name can be helpful. This can be helpful in identifying related images at the file system level.
Our current camera control software, CCDSoft, can provide automatic file naming when used in conjunction with The Sky. However, since it is currently not possible to link the Epoch telescope directly to The Sky software, this capability may not be practical or convenient. The file names generated automatically are extremely long and include a date, RA and DEC coordinates, a filter designation, and even possibly an object name.
Software is being developed at SSUO to generate an observing log or catalog for all CCD images in a specified directory. Such a catalog should make it possible to keep track of images that are obtained.
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Chip temperature
The cooler the temperature of the chip, the lower will be the noise in the image. As a very general rule, for each one degree Centigrade drop in temperature, the dark current seems to decrease by about a factor of six. It is normally possible to run the chip at SSUO at a temperature of around -20 oC. During the summer it may only be possible to get the chip down to -15 oC, while during the colder months temperatures below -20 may be possible. It is probably more important that the chip temperature remain constant during an observing run, than that the chip reaches the lowest temperature possible on a given night.
In addition to the chip temperature, the control software will display the power being utilized by the thermoelectric cooling unit. During an observing run the power reading should be below 90% of maximum. When the cooling system is started, the power will always be at 100%, but will automatically drop as the chip reaches an equilibrium temperature. If the power display does not decrease from 100% after opperating for ten minutes or so, the temperature set point should be increased.
The cooling system for the camera should be started as soon as possible when you arrive at the observatory. After uncovering the telescope and the camera, the switch on the power strip at the base of the telescope will provide power to the telescope motors and to the CCD camera. Whenever the camera has power you should hear the cooling fan in the camera. However, the cooling system is not started until it is specifically turned on using the camera control software (CCDSoft).
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Chip binning (resolution, sensitivity, and saturation)
The ST7 CCD camera can provide on-chip binning where several adjacent pixels are combined before (actually during) the readout process. When the data is binned the resulting image will be smaller since it will contain fewer pixels. A binned image will have lower resolution than an un-binned image. However, a binned image will effectively have more sensitivity since more electrons (more photons) will be combined to produce one pixel in the resulting image. Shorter exposure times will be required to produce comparable results for binned images with respect to un-binned images. For finding and verifying fields it can be more efficient to use the detector in one of the binned modes. However, science observations are normally obtained using un-binned images. If you change the binning during setup operations, make sure to return to appropriate binning before commencing a science run.
For the ST7 chip the available binning modes are...
high-res
1 x 1
un-binned image, highest resolution, lowest sensitivity, normal science observations
medium-res
2 x 2
each pixel contains 4 original pixels, sensitivity 4X greater than 1 x 1, medium size image, good for public viewing events
low-res
3 x 3
each pixel contains 9 original pixels, sensitivity 9X greater than 1 x 1, smallest images, good for looking for faintest objects
For the individual pixels for the ST7 saturation is reached for pixel data values of about 20000 ADUs. At saturation pixel data values do not increase even when more photons strike the pixel. Under some circumstances the pixels begin to bleed into adjacent pixels. This is termed blooming. Our ST7 has an anti-blooming system (anti-bloomong gate, ABG) to prevent the appearance of this phenomenon. Saturation for the ST7 is a consequence of the rather modest full well capacity for the Kodak chip used in this camera. This means that objects in an image will become saturated for values of about 20000, rather than near 65000 as would be expected for a 16-bit data system.
Binned images (either 2x2 or 3x3) will not saturate until data values of 65000 are reached. For binned images it is the data system (specifically the 16-bit analogue-to-digital-converter, ADC) that sets the saturation levels for ST7 images.
Image focus
Image focus should be checked while the telescope is being synchronized with the sky. The images seen for bright stars should appear focused. However, the bright images used for synchronizing are normally bright and saturated. Sometimes fainter stars can be seen in the vicinity of the bright stars used for synchronizing, and these stars should appear focused. Of course, star images are focused when they are small and sharp. Sometimes poor seeing can make star images appear soft and mushy.
Our experience with the Epoch telescope and ST7 camera system suggests that focus tends to be quite stable for many months at a time. This is ture even for rather large ranges in temperature. You should not expect to need to adjust the focus for this system. If you feel that a focus adjustmnent may be needed you should attempt to seek the advice of one of the more experienced observers or the Observatory Director. Any focus changes should be reported in the observatory log. If you feel the focus might need changing you should report this in the observatory log.
Finding objects and framing/centering images
Finding objects and verifying fields should probably be accomplished using binned images. This makes the system more sensitive and provides faster download times since the images are smaller. To further increase sensitivity, filters should probably not be used during field verificastion. Use the CLEAR position on the filter wheel.
For reference, without a filter, images of 5 to 10 seconds generally reach to about 10th magnitude. This means, for example, that exposures of under 10 seconds will record virtually any object in the NGC calatog. Unfiltered exposures of one minute (60 seconds) should surely record objects as faint as 12th magnitude.
Once you have verified the field, to frame or center the image for your purposes you should use continuous automatic imaging to download and refresh images as rapidly as possible. The focus mode for the camera control in CCDSoft is ideal for this purpose. To speed up this process decrease the exposure time to the point where you can just see the brightest stars in the field.
After you have verified your field and centered your objects, remember to return binning, filters, and exposure times to the settings you will need.
Dark frame subtraction
The standard procedure at SSUO is to automatically take a dark frame whenever an image is taken and then perform a dark subtract at the telescope. Thus, the images you should see will always have been dark subtracted.
If you are taking a sequence of images over a short period of time to be stacked and combined, or used for time series observation of motion or brightness variation, it is probably reasonable to obtain a single dark frame to be used for the entire sequence.
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Finished for the evening? (Do you have all the sky observations that are needed?)
Are you really finished?
Do you need to observe another object? Do you need an additional observation of an object you have already observed? Remember, just one point or one observation is never really convincing.
However, also remember if your object is getting ready to set the noise will be getting worse, the sky background will be getting worse, and you may not have enough time to get the observations you need.
Do you need to observe any standards?
Is it still clear? Remember, we are climatically challenged at SSUO, and it may not be clear tomorrow or the next time you are scheduled to observe.
Of course, you also need to consider that if you need to take flat field frames (you probably do!) it may take an additional half-hour after you close the observatory roof.
And yes, I also know you probably have that 8 AM class tomorrow morning.
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Return telescope to home position
Use the telescope control software (Servostar). When you EXIT this software the telescope is automatically returned to the HOME position. The telescope should be horizontal and pointing south directly toward the flat field screen on the south wall. You can use the rocker switch on the telescope pier to turn off power to the telescope drive motors. The software should quit and you should be left is DOS mode. You can probably turn off the monitor to the telescope control computer at this time.
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Close the observatory roof. Make sure all telescopes are in their stow positions. It is best to push from the middle of the roof sections from the outside. Slow and steady is best. Some final strong-arm adjustment to the roof sections is often required before the roof sections can be locked together. Lock the roof sections. Place the four wedges under the wheels of the roof sections.
If you have calibrations such as flat fields to obtain you should not waste any time. Once the roof is closed the temperature in the observatory will start to increase. This will make the camera cooling system work harder. The more time that elapses, the greater the chance that some property of the CCD camera may change.
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It is standard practice to take flat field frames at the end of an observing run. This insures that you will have flat fields that accurately represent the status of the entire instrument (telescope, filters, detector) at the time of your observations. This includes variable factors such as temperature and humidity, and can properly account for any possible unknown changes that the system may have experienced. Separate sets of flat fields are needed for each filter used (including the CLEAR position). Four or five flats for each filter are probably adequate.
As part of the shut-down procedures, the camera cooling should be turned off using the camera control software (CCDSoft) as soon as the camera is no longer needed for the night (after taking flat fields or any other calibration data). When the cooling system is turned off, the power to the system is slowly decreased automatically to prevent the chip from receiving a thermal shock. You should never quit the camera control software (CCDSoft) without first turning off the cooling to the chip. Note that the camera fan will continue to run after the cooling system is truned off.
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You have saved all your data, right? Do you know where your data has been saved? Have you checked? Will the observatory data be archived? Do you know where the data will be archived? Do you know how to retrieve archived data? Do you need to make a copy of your data and take it with you?
You are not finished at the observatory until you complete an observatory log entry. The log is maintained using an Excel spreadsheet on the Macintosh computer. Fill in the available comumns, including the time you are leaving the observatory. Make sure to include any special circumstances or phenomena you may have observed. Be sure to note any problems with equipment or software. This is how things get fixed!
Save the log file and quit Excel. Turn off the monitor for this computer.
One of the last parts of the shut-down procedure should be to turn off power to the camera and the Epoch telescope. This accomplished by using the switch on the power strip at the base of the Epoch telescope. You should hear the camera fan stop when this switch is truned off. At this point it is safe to cover the telescope and the CCD camera.
All computer monitors should always be turned off. It is normal practice to leave all computers running continuously during the academic year. During the summer season when daytime temperatures can reach 100o F inside the observatory it is essential to turn off all computers to keep them from over heating.
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No, you are not really done until you have analyzed your data. It is normally not convenient to analyze your data at the observatory, but I just had to put this here as a reminder. Take your data to Darwin Hall (or some other place with a good network connection) and archive the data. Take your data home or to Darwin Hall and analyze what you have obtained. Compare with similar data. Compare with the same data at different times.
If you do not analyze your data it is like you have wasted the time and energy you have spent at the observatory.
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Make sure everything is off that should be off. Turn off the lights. (Take one last look and listen.) Lock the door.
Have a safe trip home!
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