1) Plan on arriving at the observatory ~30-40 minutes before you want to observe your first target. There should be a graphical observing plan for the night and a list of the RA/Dec values of each star (if not, phone ACL).
2) Ensure the CCD PC in the warmroom is shutdown. In the dome, connect the CCD cable to the CCD unit on the telescope; be gentle with the connector and snug the screws. Never plug the cable in when the PC is powered up -- you will damage the CCD! Also plug in the filterwheel control cable and its power transformer (find on the shelf at the back of the control room).
3) Boot up the CCD PC. Check the clock (lower-right corner of screen) to ensure that it is within a minute or so of the correct local day and time. If it is off by more than 1-2 minutes, double click on the clock and set it correctly (the UT and HJD are computed from this clock and are stored in the image headers; we can't do variable star photometry if it is incorrect!).
4) Enter MaxIm_DL by clicking on the "Shortcut to MaxIm_DL" icon on the left side of the screen. Initialize the CCD camera.
5) Set the camera temperature to keep the CCD cooled to a constant temp -- it may take a few minutes to stabilize.
6) Start a paper log of the night's observing (blank pages available on the shelf). Now is a good time to go outside and look at the sky from horizon to horizon and document the sky conditions and dome temperature. Also record the Universal Time (UT), Local Sidereal Time (ST), and Local Time (LT) at the beginning of the night. A sample log sheet is included in the back of the folder.
7) Partially start up the telescope: turn on drives and remove the dust covers. Do not yet turn on the autodome or open the dome slit (we want to control the amount of light in the dome). Slide the eyepiece to the extreme right, out of the light path to the CCD, and set the telescope focus to the CCD default value of 2382 units.
8) Before opening the dome, with the dome lights OFF, take 10 bias frames.
9) Take dome flats:
10) Finish opening the telescope as usual, following the "Telescope Observing Procedures for CCD" sheet. Check that the UT on the TCS is correct (+/- a few minute or so). Be sure that the autodome is working (check that the telescope is pointing out the slit; in cold temperatures it can "stick").
11) If there are no/few clouds outside and the moon isn't too large/bright (sky brightness is uniform), take twilight sky flats. Each flat must have:
12) Zero-Point and Focus the telescope.
13) Pick a cluster from your observing list, locate its finder chart, and observe the cluster :
14) Repeat 13 until dawn, you are tired, you are out of clusters, or it clouds up. Go outside periodically (every hour?) to check & record the sky conditions, etc.
15) If Andy asked you to (rare), take dark sky flats. This can be done at any time during the night, and need not be complete or sequential (any frames you can get is a help!). It can be done using any/all of the filters you are using that night. Point the telescope near the zenith to minimize light pollution effects. Ideally, each flat should have:
16) When you have finished all your on-sky observations, slide the eyepiece back to the center (7.5 on the scale) and set the telescope focus back to 2420 (visual; a courtesy to our StarGaze Staff).
17) With the dome lights OFF, take 10 more bias frames (see Step 8). You can take dome flats now too, instead of or in addition to before you begin observing.
18) Close up the telescope as usual.
19) Warm the CCD to dome temperature and shut down the CCD (from setup tab). You can probably take the bias frames (see Step 8/17) while the CCD is warming, if you are quick! You can also transfer the night's data to baade using SFTP.
20) Exit MaxIm_DL (File/Close), and shutdown the CCD PC (fans in the dome should turn off). Unplug the filter wheel cables and the CCD cable from the CCD unit (this minimizes danger of damage from lightning strikes). Never unplug the cable when the PC is powered (CCD fans running) -- you will damage the CCD!
21) Peek back in the dome before you leave: are the lights and CCD fans off? Lock up and get some sleep!
Note: Here is a page for troubleshooting Telescop, CCD & PC problems. Instructions for observing field RR Lyrae stars (our older research program).
Updated 2009 May 20 -- ACL
1) On the Shelf on the cabinets to the left of the door, there should be a current Observing Plan plot, which should look something like this. If there is not, call Andy Layden to get one.
2) Hint: While observing, after you finish the observation sequence for a cluster, place a mark on the plot at the ST. In the event that you deviate from your plan (lose time to clouds or equipment failure) you can revise your plan "on the fly". Just revert to the Rule in Red ("In general, ...") above.
Updated 2009 Feb 28 -- ACL
Note: In order to send and receive information from the camera, or to make the filter wheel turn, there must be links established to these devices.
1) If it did not appear already, bring up the CCD control window "MaxIm CCD" by clicking on the button icon on the toolbar (8th from the left). Select the Setup tab.
2) The three boxes along the left of the window should read:
If these do not appear, choose them correctly from the drag-down menus (see Troubleshooting). When all is OK, click Restart to initialize the camera.
3) In the "MaxIm CCD" window, select the Settings tab. In the "Auto Calibration" field, click the None radio button (you do NOT want the Simple Auto-dark radio button, as you may have used in Astr 309). We will take bias images and use dark images to remove those signatures during the processing step.
Updated 2009 Mar 02 -- ACL
Note: In general, CCD's perform best, producing the lowest noise, when they are cooled well below freezing (0C). We also want to keep the CCD at a constant temperature all night, so its noise and sensitivity characteristics stay constant, otherwise the bias and flat frames you take at the beginning of the night won't properly correct the images you take later at a different temperature (especially true for dark frames).
Our CCD camera has an automatic temperature control which makes it pretty easy to set and forget, but it is important to set it correctly at the beginning of the night. The camera assembly contains a thermoelectric cooler that can drive the CCD temperature down to about 30C below the ambient air temperature in the dome. The CCD performance seems best if we can keep it at -15C or below.
1) In the dome, check the ambient air temperature in Celsius (let's call this Tdome) using the thermometer on the desk. We will set the CCD temperature 28C below this value:
2) Select the Setup tab in the "MaxIm CCD" window, and click the Cooler On box. Enter your value for Tset into the box labeled New (C) and click the Set button.
3) The message "Cooling Down" should appear in the box at the bottom of the window, and the temperature in the Actual box should change in the direction of Setpoint. It may take a few minutes for Actual and Setpoint to match. Don't take any images until they match. Note: only rarely will the values in Actual and Setpoint match exactly -- usually Actual shifts around within 1-2C of the Setpoint value -- this is normal.
4) At the end of the night, you should allow the CCD to warm up to dome temperature before turning off the CCD. Do this by selecting the Setup tab in the "MaxIm CCD" window, and clicking the Go to Ambient box. You will see the Actual value change away from Setpoint, and the message in the box will say "Cooler Regulating". It may take a few minutes to warm up, so be patient. When the temperature stabilizes, click the Shutdown button to turn off the CCD. While it is warming, you can:
Updated 2002 Jun 07 -- ACL
Definition: A "bias" or "zero" frame measures the amount of signal, or charge, that was placed on the CCD before the image was taken. It has zero exposure time, and received no light. In addition to determining and correcting for the mean level of this signal, the bias can also be used to correct the object images for any pattern in this signal which is constant in time (often referred to as "fixed-pattern noise").
Why a bias? The CCD automatically puts a background level of counts on the chip. Imagine if there was no bias applied. If you took a frame with a very short exposure time or in very dark conditions, the counts due to the sky background would be about 0. However, there is noise associated with reading out the chip, so some pixels would want to have negative counts. Since the chip only records integer counts between 0 and 16384 (2^14 -- we have a 14-bit chip), these pixels would get the value 0, and the statistics of the sky noise would be corrupted. Putting a bias on the chip ensures that all pixels will have a positive value, and the statistics will be computed correctly.
1) Be sure all light sources are OFF in the dome, including the eyepiece reticle lights. The dome slit should be closed, and the dome as dark as possible. The covers should be on the telescope.
2) In the "MaxIm CCD" control window, select the Expose tab and
3) The image will read out and appear on the screen. For the first bias image you take, check the number of counts -- slide the pointer around the image and note the (X,Y,Counts) readout just below the image. You should see around 500 counts, depending on CCD temperature. This is the usual bias level for our chip. If it is much different, please report it to Andy Layden.
4) Save the image to disk by clicking the 3rd button from left on the toolbar (diskette icon). You will want to create a new directory for each night's data.
5) Take a second bias frame using the Expose button. Save it.
4) Repeat Step 5 eight more times, giving 10 bias frames in the sequence.
Updated 2002 Mar 07 -- ACL
Definition: Flat field images (or "flats") measure the relative sensitivity of each pixel. If we observe a uniformly bright source (a "flat" source like the clear night sky), the pixels with lower sensitivities will record lower numbers of counts. As part of the "image processing" procedure, we will later correct for the pixel-to-pixel sensitivity variations by DIVIDING each object (star/cluster) frame by a combined flat frame, thus increasing the measured counts in the pixels we know to be under-sensitive to the intensity level they should have. The pixel sensitivities may depend on the color of the light they are seeing, so we must take flats through each filter we will use that night.
Why Dome Flats? We can not always observe the clear sky with enough counts to map out the pixel-to-pixel sensitivity variations (it may be cloudy, a bright moon, or too long a wait till dawn or dusk to warrant staying awake; in the past, we have relied on twilight sky flats on clear, moonless nights to give us lots of counts). Dome flats allow us to use bright lighting and therefore get lots of counts to develop a precise map of the pixel to pixel sensitivity on small scales (say, 1-30 pix) across the CCD (see Dark Sky Flats for more).
Goals: We need to get 8 or more flats through each filter you will be observing with to reject "cosmic rays" that appear on the individual images. An ideal exposure would have ~6000 counts in each image, though any exposure with 200 to 8000 is worth saving.
1) With the dome closed, set up the red lamp facing the South dome wall and turn it on; try to illuminate the wall as uniformly as possible (minimize shadows).
2) Point the telescope toward the South dome wall where the light is shining (dome pointed home).
3) Slide the visual eyepiece all the way to the right and tighten the thumbscrew (lest it obscure the CCD!). Set the telescope focus to the default CCD value (2382 units).
4) Take dome flats; at least 8 in each filter you will be using that night. Each flat should have:
To take a 1 sec test exposure: select the Expose tab on the "MaxIm CCD" window,
5) Save each file according to the naming convention, e.g. dflatI01.fit, dflatI02.fit, ... dflatV01.fit, dflatV02.fit, etc.
6) Turn off the red lamp and/or white dome lights and procede with telescope startup and observing.
Updated 2009 Mar 03 -- ACL
Twilight Sky Flats can be taken at dusk (evening) or dawn (morning). Doing them at BOTH is preferable, if you can manage to stay awake in the morning! The procedures for the two are subtly different, so explicit instructions for dusk flats and dawn flats are given separately. After that, there is some wisdom on when to start taking your sky flats.
Note: Sky flats are best taken when the sky is perfectly clear, so the sky is uniformly bright. Uniform clouds are ok, but you should try to get more images per filter (10 or more, if possible) to help average out any non-uniformities due to the clouds. A bright moon within ~60 degrees on the sky of where you are pointing may make the sky background non-uniform (especially as the scattered sunlight fades).
Goals: ideally, we would like 5 or more images in each filter you will be using that night. An ideal exposure would have 6000 ± 2000 counts in each image, though any sky flat with 2000 to 10000 is worth saving. All of the images must have exposure times longer than 10 sec. It is also important to move the telescope between images, so any stars change position on the chip from one image to the next (we can remove them during image processing).
Definition: Sky flats measure the relative sensitivity of each pixel. Assuming the sky is uniformly bright, the pixels with lower sensitivities will have lower numbers of counts. As part of the image processing procedure, we will later correct for the pixel-to-pixel sensitivity variations by DIVIDING each object (cluster) frame by a combined sky flat frame, thus increasing the measured counts in the pixels we know to be under-sensitive to where it should be. The pixel sensitivities may depend on the color of the light they are seeing, so we must take flats through each filter we will use that night. We need to get 5 or more flats per filter to reject "cosmic rays" and star images that appear on the individual frames. We move the telescope between images so the stars do not appear in the same (X,Y) location on the chip, and thus create an erroneous "divet" in the combined flat field image.
Why the 10 second Rule? One should never take sky flat or object (star) exposures shorter than 10 sec with our CCD. The shutter in front of the CCD takes a finite amount of time to open and close. Tests show that for exposure times less than 10 sec, this "shutter delay time" results in a true exposure time that is different from the requested time by more than ~1%. What's more, the shutter is an iris (like in your 35mm camera), so the center opens before and closes after the corners, resulting in extra exposure in the center relative to the corners. In theory, one can map out this effect (create a "shutter correction image") and apply the correction to all your images, but it is a pain. Easier to just avoid the short exposures altogether!
1) If you are taking dusk flats, point the telescope about 1.5 hours East of the Zenith. The dome should rotate so the slit is facing East, away from the setting Sun (if there is a bright moon nearby, shift the telescope North so there is >60 degrees angle between the moon and where the telescope is pointed ... >90 deg is better still).
2) Be sure the telescope tracking and autodome are ON. Be sure the telescope focus is set to the default value for CCD observing (2382 units) and the eyepiece is all the way to the right.
3) Take a 0.1 sec test exposure: select the Expose tab on the "MaxIm CCD" window,
Once the image has read out and appeared on the screen, move the cursor around near the image center (brightest region) and see roughly how many counts there are using the (X,Y,Counts) readout at lower-left. A well-exposed skyflat has between 5000 and 7000 counts, though any flat with 2000 to 10000 is worth saving. If the image is good, save it to disk.
4) If the image is saturated (all pixels uniformly 16383), you will have to wait a while and try again when the sky is darker (maybe 5 minutes). If this image is not saturated, but has more or less than the optimal number of counts, estimate your next exposure time with
though remember that while you are doing this, the sky is getting fainter outside. Experience will enable you to guess a "seat of the pants" correction to your computed exposure time.
5) Take another test image with your improved exposure time estimate. When your exposure times finally get longer than 10 sec, start saving the images to disk.
6) After each good sky flat, move the telescope East with the handpaddle by an arcmin or more. This is to ensure that star images don't land atop each other.
7) Keep taking and saving skyflats until the exposure times are longer than 200 sec. The rule of skyflats is, "the more the better." Besides, you can't begin taking good star images until the sky has darkened, so you might as well be taking sky flats!
1) Dawn comes on quickly and can surprise you. Check the time of morning twilight on the RRLyr shelf, and set an alarm (mental or mechanical) to alert you. You will probably want to start morning sky flats about 30 min after astronomical twilight. Another warning is that the sky level in your star images will start rising. You want sky flats with about 6000 counts, so when the sky background in your images reaches the following value (where T_star is the exposure time of your star image), you would switch over to sky flats:
2) Point the telescope about 1.5 hours West of the Zenith. The dome should rotate so the slit is facing West, away from the rising Sun). The telescope tracking and autodome should still be ON, and the eyepiece and focus as you had them while observing stars. If there is a bright moon nearby, shift the telescope North so the angle between the moon and where the telescope is pointing is >60 degrees ... >90 deg if possible).
3) From you last star image, calculate the exposure time needed to give you 7000 counts in your skyflat using the following equation, where Counts_star is the number of sky counts in your star image:
Let's say you estimate it to be 150 sec. Take an exposure (Expose tab on "MaxIm CCD" window):
Once the image has read out and appeared on the screen, move the cursor around near the image center (brightest region) and see roughly how many counts there are using the (X,Y,Counts) readout at lower-left. A well-exposed skyflat has between 5000 and 7000 counts, though any sky flat with 2000 to 10000 is worth saving. If the image is good, save it to disk.
5) If the image was saturated (all pixels uniformly 16383), you cut your exposure time a lot (maybe a factor of 5). If the image was not saturated, compute your next exposure length as in Step 3, though remember that while you are doing this, the sky is getting brighter outside. Experience will enable you to guess a "seat of the pants" correction to your computed exposure time.
6) After each good sky flat, move the telescope East with the handpaddle (about an arcmin is good). This is to ensure that star images don't land atop each other.
7) Take another image with your updated exposure time. When your exposure times finally get shorter than 10 sec, you can stop (again, "the more sky flats, the better").
This depends on whether you are taking dawn or dusk sky flats, and what filters you are using. The following are vary rough estimates for when you should start taking 1 sec test exposures. Of course, only flats with exposure times longer than 10 sec should be used, but starting with 1 sec test exposures allows you to increase exposure times gradually.
Dusk Sky Flats:
Dawn Sky Flats:
Updated 2010 Sep 14 -- ACL
Dark Sky Flats can be taken at any time and can be used to fill gaps between globular cluster observations. In general, only take them if Andy has requested them (they are usually much less useful than skyflats and we only take them if we are short on good skyflats).
Note: Dark sky flats should be taken when the sky is perfectly clear and there is no moon in the sky, so the sky is uniformly bright. Pointing the telescope near the zenith should minimize the amount of direct artificial light entering the tube, and hopefully the sources of artificial light are more or less evenly distributed around the horizon (azimuthally) so the sky at the zenith is subject to a uniform light pollution.
Goals: ideally, we would like 5 or more images in each filter you will be using that night. An ideal exposure would have ~2000 counts in each image, though any exposure with 500 to 4000 is worth saving. All of the images must have exposure times longer than 10 sec. It is also important to move the telescope (offset >60 arcsec) between images, so any stars change position on the chip from one image to the next. In practice, any dark sky images you can get will be useful; we will combine ones from different nights as needed. Over the course of a few nights (weeks, months?), we need to get >5 or flats in each filter to reject "cosmic rays" and star images that appear on the individual frames. We move the telescope between images so the stars do not appear in the same (X,Y) location on the CCD, and thus create an erroneous "divot" in the combined flat field image.
Dark Sky and Dome Flats: We can get dome flats every night to measure small scale (pixel-to-pixel) differernces in sensitivity due to moving dust rings, temperature sensitivity, etc. But uneven illumination of the dome wall will leave large scale (100s of pix and more) variations in the count levels that are spurious. Meanwhile, dark sky flats will generally have few counts (noisy, "grainy" appearance), though they should be evenly illuminated. We will combine the daily dome flats with dark sky flats (heavily "smoothed" to remove the noise) during the processing step to make a combined flat that should have the best of both and the worst of neither. More details on that in the Image Processing Cookbook.
Why the 10 second Rule? One should never take sky flat or object (star/cluster) exposures shorter than 10 sec with our CCD. The shutter in front of the CCD takes a finite amount of time to open and close. Tests show that for exposure times less than 10 sec, this "shutter delay time" results in a true exposure time that is different from the requested time by more than ~1%. What's more, the shutter is an iris (like in your 35mm camera), so the center opens before and closes after the corners, resulting in extra exposure in the center relative to the corners. In theory, one can map out this effect (create a "shutter correction image") and apply the correction to all your images, but it is a pain. Easier to just avoid the short exposures altogether! (Note: we didn't set the 10s limit on the dome flats because we know there are large-scale non-uniformities in the illumination; we will "flatten" both the central bump due to the shutter and any bright or faint regions from the non-uniform illumination using the smoothed dark sky flats).
1) Go outside and confirm that the sky is clear and that the moon is down. Point the telescope at/near the Zenith.
2) Be sure the telescope tracking and autodome are ON; the telescope should be pointing out the slit with no obstruction along either edge (sight down the tube to be sure).
3) Take a 50 sec test exposure: select the Expose tab on the "MaxIm CCD" window,
Once the image has read out and appeared on the screen, move the cursor around near the image center (brightest region) and see roughly how many counts there are using the (X,Y,Counts) readout at lower-left. A well-exposed skyflat has ~2000 counts, though anything between 500 and 4000 counts is worth keeping .
4) If the image has more or less than the optimal number of counts, estimate your next exposure time with
though exposure times longer than 500 sec should be avoided (that is, if t_next > 500 sec, use 500 sec and we will be happy with however many counts we get!).
5) Save the images to disk if they are suitable (if none are, send Andy an email with what you tried, and I'll make suggestions).
6) After each good sky flat, move the telescope East with the handpaddle by 60 arcsec or more. This is to ensure that star images don't land atop each other.
7) Get as many skyflats as you reasonably can, in both V and I filters, but observing the globulars near the meridian should be your top priority.
Updated 2009 Mar 02 -- ACL
General: We will determine the best telescope focus by obtaining a sequence of short exposures of a bright star, stepping the focus slightly from one exposure to the next. MaxIm has a handy tool which allows us to determine which focus setting gives the narrowest, roundest images, with the highest peak intensity, i.e., the best focus. We then set the telescope focus to that value. You can read more about this procedure in the MaxIm CCD Manual (pp.4-3 to 4-5).
NOTE: the focus is set using the buttons on the handpaddle (not with the keyboard).
1) Rough zero-point check:
2) Point the telescope at a Focus Star near the zenith (RA = ~ST). Pick a star from this list of candidates. Find your focus star on the image (see Focus Star Finder Charts in the binder containing hardcopy manuals).
3) Refine the telescope position ("zero-point") so objects are centered on the CCD:
4) Set a starting focus -- generally, we start 5 units below the default focus: 2382-5=2377. Use the focus buttons on the handpaddle to rive the focus 10-15 units below this value, then approach the starting value from below. There may be some "backlash" in the focus screws, so always approach focus from below.
5) Using a piece of scrap paper, scrawl a "focus table" on it. For each focus image you take, record the focus value, the Full-Width Half-Maximum (FWHM) values in X and Y, the Maximum Counts, and comments on appearance.
6) Select the Focus tab on the "MaxIm CCD" window, and
this will take one 12 sec exposure and write it to the screen, then pause. Why 12 sec exposures?
7) Find your focus star on the image (see Focus Star Finder Charts if needed).
8) Select the Inspect tab on the "MaxIm CCD" window. You see a 3-D picture of what the star's "profile" looks like, along with measurements of the FWHM in X and Y (the width of the star image in the X and Y direction), and Maximum (the number of counts at the peak of the profile -- if it is 16383, the star is saturated and you need to use a shorter exposure time, or chose a fainter star). Write these in your focus table.
9) Increase the telescope focus (using the handpaddel button) by about one unit (to 2378 in our example) and hit Start Focus to take a new exposure at this focus setting. Carefully record the focus value and results associated with each image in your focus table -- it is easy to forget!
10) Repeat Step 8. If all goes well, you will see that the first exposures in your sequence had low, broad profiles and few counts at peak, but as the focus increased, the images got taller and narrower. At some point, the images began to broaden and flatten again. This means that you passed through best focus, and it is time to stop your sequence. Look back to decide at which focus setting you got the tallest/narrowest profiles. This is your final focus value -- record it and the dome temperature on your observing log.
11) Set the telescope focus to the final value, but drive the focus 10-15 units below this value and approach it from below to avoid "backlash" effects. You are now ready to observe variable stars.
12) If your subsequent variable star images look out of focus (stars are elongated or "mini-doughnuts"), you may need to refocus (the telescope focus can change if the dome temperature changes a lot, or if you make a large slew across the sky that causes the mirror to shift in its mounting). If you still can't get good focus, check the Trouble Shooting page.
Updated 2010 June 18 -- ACL
Note: In most cases, we will obtain several frames of the same cluster, at slightly different positions on the chip and in different filters, to create an "observation sequence". For example, if your observing plan calls for observing the cluster "NGC 1234 " at ST = 10:30, you would obtain bunch of V and I images of the cluster in close succession, and we would refer to these as a "sequence". In general, we observe each globular cluster only one time each night (though you may redo a sequence if you think the seeing or sky brightness conditions have improved; keep both sequences of images).
1) Chose a cluster to observe (see your Observation Plan plot) and get out its finder chart.
2) Point the telescope to the cluster's coordinates. They may be preset in the telescopes coordinate table -- if not, feel free to place them there. Center the cluster using the telescope offset command. If the seeing looks bad (blurry stars, FWHM values > ~3 pixels) you may want to do a focus sequence to verify/improve the focus. We want the best possible seeing to minimize the effects of crowding on our stellar photometry; focus sometimes changes when you cross the meridian, or when the temperature changes.
3) On the finder chart, there are instructions on how to take an observation sequence for this particular cluster. For example, you might see:
4) Take the first observation -- in the Expose tab in "MaxIm CCD" window:
5) Check the sky level; if it is bright (>6000 counts), you may want to shorten the exposure times and take more exposures through each filter (or, dawn may be coming on, or you may be pointed near a bright moon... check in the dome if the sky level seems odd).
6) Save the image to disk (floppy disk icon). Here is a description of our naming convention -- please follow it carefully, as it avoids accidentally overwriting your data, and facilitates data reduction later! e.g. N1234_1v1.fit, N1234_1v2.fit, ..., etc.
7) Go to Step 4 and take the next 3 frames in the sequence, inspecting and saving each. Move the telescope by the offset amounts listed on the cluster finder chart (e.g., 0" E and 20" N) using the OFFSET command on the telescope PC (TCS).
8) Record comments in your paper log : Cluster, UT/Local Time, Sidereal Time, CCD Temperature, Exposure/Filters, Comments (e.g., moon & sky conditions, problems, errors in file naming, etc). You might do one line in the log for each IIVV group, giving you 4 lines in the log for each cluster.
Image Anomalies: sometimes something goes wrong, and your images look funny. Here is a nice web page devoted to describing anomalous images, identifying what went wrong, and how it can be corrected. Please inform Andy Layden if you cannot correct the problem.
Updated 2009 Mar 02 -- ACL
Note: It is important to follow this naming convention. Otherwise, it is easy to accidentally give your new image the same name as an older one -- the older one will be written over and lost forever. Also, type carefully -- typos can have the same result.
1) Nightly directories: Each night should have a separate directory with the format YYYYmmmDD. If you start observing on July 27, 20002, you would call your directory "2002jul27". Each directory should be placed in "C: CCD Images\".
2) Bias frames: Say you take 10 in the evening and 10 more in the morning. Call the evening ones:
bias01.fit, bias02.fit, ..., bias10.fit,
and call the morning ones
bias11.fit, bias12.fit, ..., bias19.fit.
The ".fit" stands for Flexible Image Transport and defines the format the image was saved with (kind of like .gif or .jpeg but different). Always save all images as .fit format!
3) Flats: The name should contain the prefix "tsflat" (for twilight sky), "dsflat" (for dark sky),or "dflat" (for dome), it should contain the filter (V or I), and a unique number (so it doesn't overwrite an existing file). For example, for sky and dome flats, respectively:
tsflatV01, tsflatV02, ..., tsflatV12, tsflatI01, ..., tsflatI08. dflatV01, dflatV02, ..., dflatV12, dflatI01, ..., dflatI08.
4) Object/Target: The first part of each filename will be the 6-character name on the finder chart (our Unix workstations will not accept blank spaces in file names; underscores, "_" are better for dividing up names). For example, the cluster "NGC 1234" would be "N1234_". Keep the capitalization.
In most cluster observing seequences, we take 4 groups, each with short-I, long-I, long-V and short-V exposures. The following example should keep things organized and ensure each image gets a unique name (so it doesn't overwrite another image!) that can go seamlessly into our semi-automated image processing "pipeline". For example:
N1234_3v1
Another example shows the file names for an entire sequence of frames in one night's observtion of "NGC 9876":
N9876_1i1, N9876_1i2, N9876_1v2, N9876_1v1. {group 1}
Offset the telescope,
N9876_2v1, N9876_2v2, N9876_2i2, N9876_2i1. {group 2}
Offset the telescope,
N9876_3i1, N9876_3i2, N9876_3v2, N9876_3v1. {group 3}
Offset the telescope,
N9876_4v1, N9876_4v2, N9876_4i2, N9876_4i1. {group 4}
You have completed the sequence for this cluster on this night.
If you repeat a cluster (maybe the seeing got better or the sky background got darker), keep the images from the original sequence, and "jog" the group numbers for the new sequence by 4 (1=>5, 2=>6, 3=>7, 4=>8) so the new sequence is saved with unique filenames. We'll decide which sequence to use in the processing or photometry stages.
Updated 2009 May 20 -- ACL
Chose the star from this list which is nearest to the zenith (ie, has the RA closest to the current ST).
Star# |
RA (2000) |
Dec (2000) |
V |
|
1 |
00 00 10.71 |
+41 19 29.2 |
9.18 |
|
2 |
01 59 28.58 |
+41 13 44.3 |
8.77 |
|
3 |
03 58 55.33 |
+41 15 4.1 |
9.16 |
|
4 |
06 01 2.65 |
+41 18 4.5 |
9.38 |
|
5 |
07 59 1.25 |
+41 28 43.2 |
9.29 |
|
6 |
09 57 30.04 |
+41 11 39.0 |
8.93 |
|
7 |
11 57 24.44 |
+40 55 24.3 |
9.22 |
|
8 |
13 59 47.76 |
+41 20 59.9 |
9.58 |
|
9 |
16 01 18.50 |
+41 24 30.7 |
9.47 |
|
10 |
17 57 38.78 |
+41 13 10.7 |
9.01 |
|
11 |
19 59 28.45 |
+41 12 11.7 |
8.98 |
|
12 |
21 59 42.29 |
+41 34 24.9 |
9.35 |
A Finder Chart for each Focus Star is available in the "CCD Photometry" binder in the control room.
Updated 1999 June 09 --ACL
These data were taken during focusing the telescope one night. Your numbers and choice of best focus will be different!
|
Focus Value |
FWHM X |
FWHM Y |
Max |
Comment |
|
2377 |
19.8 |
17.4 |
890 |
doughnut! |
|
2378 |
13.1 |
11.0 |
1832 |
smaller donut |
|
2379 |
8.3 |
7.4 |
6711 |
broad, low star |
|
2380 |
4.2 |
4.0 |
12491 |
getting good |
|
2381 |
3.7 |
3.6 |
14432 |
good |
|
2382 |
3.2 |
3.3 |
15323 |
best focus? <<-- YES, smallest FWHM and largest Max (narrow, tall star profile is best). |
|
2383 |
3.6 |
3.9 |
13983 |
lower and broader, worse |
|
2384 |
3.9 |
4.2 |
12821 |
worse |
|
2385 |
7.1 |
8.3 |
6104 |
very broad, low ... way past best focus, stop! |
Updated 1999 June 09 --ACL