Occasionally -- maybe
every few weeks on average -- the dome will start
rotating at its slow speed for no reason, often
during an observation. I call it the dome's
"fugue state", after a psychiatric condition marked by aimless
amnesia. This is almost certainly caused by a
software bug in the TCS. It has always snapped out of it eventually.
In the meantime, you can keep observing using the following procedure:
If this fails after several attempts, then stop observing, turn
off the track and drives switches, and shut down the
TCS computer using the procedure in the lightning shutdown (i.e.,
orderly shutdown, stopping the program first). Turn the computer
back on, let it come back up, and the problem should be cleared.
- Go into the computer room and push the yellow button at the
bottom of the leftmost rack. This disables computer control of the dome.
- Look at the TCS display and note the Azimuth reading (far
right of the display, near the top).
- Take a flashlight and go into the dome. Using the switch
on the dome control box, rotate the dome
manually into position so the telescope is looking out. The dome
azimuth is indicated by the red reflective tape markers every 10 degrees,
and there's a fiducial red tape marking the center of the slit.
The center of the dome coincides with the telescope's optical axis,
so the correct dome setting is simply the azimuth.
- Continue observing for 10-20 minutes. Depending on where you
are in the sky, you may have to tweak the dome a bit.
- After a decent time interval, press the yellow button again to
re-enable computer control. If the condition has cleared, the
dome will re-center to where it thinks it should be.
If the dome just continues
to rotate, turn it off, re-center manually, and wait a while longer.
- After all this it's likely that the dome has lost track of
where it is, so that even if it's not rotating, you may need to
re-set the dome position. You can do this by estimating the dome
azimuth from the tape marks and setting it using the pull-down
menu called by the pink Setup box in the xtcs window.
Just be sure not to reset the RA and dec encoders by mistake.
(You may need to tune up the dome azimuth slightly at the
end of the night to get the dome closed; the electrical contact box
is connected when the dome is at 320 degrees.)
Note that the procedure above can keep you going even in the event
of a more serious failure of the autodome system, as long as you
can still rotate the dome manually.
- take sky flats?
- See the earlier
discussion under Opening for
details. If you've written down the exposure data on previous mornings
and evenings, it should be possible to get a fairly good exposure the
- slew to zenith.
- An easy way to do this enter coordinates
RA = sidereal time + 1 minute
into the xtcs window, and slew.
Dec = 31 57 12
Epoch = now (in decimal years)
- reset instrument rotator to 0 degrees if needed.
- If you've rotated the instrument and it's in some funny
you should set it back to zero, at least on your last night. Remember
that the mirror covers must be open to rotate the instrument!!
- close mirror covers (do not move
rotator with mirror cover
- You should ideally be near the zenith to close the mirror
though in an emergency you should just go ahead. To do this, flip the
silver switch on the black panel down. You'll hear the four of them
crash down, hopefully in order.
- set accurately to zenith; track off, drives off.
- It's worthwhile to get the telescope dead straight up,
you know exactly where it is if there's some kind of problem (e.g. a
lightning shutdown). You can easily combine this step with the
slew-to-zenith step, by simply slewing to a point a little
east of the zenith, allowing the telescope to track in, and
flipping the track switch off when the telescope reaches
about 3 seconds west. Then turn the drives switch off,
and the telescope will rebound almost exactly to the meridian.
- all other switches down. Dome goes home.
- hit red STOP button on TCS black box.
- dome lights on.
- close instrument dark hatch.
- close dome.
- if dome did not return to contacts, hit the yellow button and tweak
- dropout must close before main shutter
- Note that the main shutter takes a while to close, so you
can get it
started first, and then hold down the dropout close button until it
slams shut. If you need it, the yellow auto-dome enable switch
(discussed earlier) is in the computer room at the bottom of the
- If there's a problem getting power to the dome - for
example, if the
rotation fails and you can't get it on the contacts - there is an
emergency cable which can be connected. See the full manual for
details.. Note that plugging in the cable with the dome on
contacts will cause a short, so don't do that!!
- top off instrument dewar
- Doing this as the dome is closing is a good habit. Don't
mark the time on the whiteboard. See earlier cautions on filling
upward-looking dewars and not filling warm dewars.
- close louvers and garage door
- verify dome fully closed
- back up the night's data
- If you lose the data, your work, and the telescope time,
It should be sufficient to copy the data to another computer (e.g. a
or, if you're using the 8k you may want to put it on tape.
- The Linux rsync command is your
friend here. For example,
if you're using one of the Owl-controlled detectors, you might copy
your data onto agung by making your own directory, cd-ing into it, and
typing something like
rsync -azvt /data/mdmarc1/mydir/night1 .
This will make a copy of "night1" in your current directory. If
"night1" already exists, it will copy only new files or files that have
- There's a nice DVD-burning utility on Agung that you can
use to make copies of your data. Sometimes it even works!
- If you're using the 8k, be sure to back up on tape as
you go along. Observers sometimes get into trouble by leaving their
to the last day. Not only does this leave you vulnerable to disk or
computer failure, it can cause problems if you underestimate the time
required, leading to collisions with the next observer. Back up every
night, and be sure that your plans for writing tapes the last morning
the run are realistic.
- check mirror air conditioning computer; adjust if needed
- Once the mirror petals are closed, the air conditioner
will try to
cool the mirror to a settable temperature, because the seeing goes bad
in a hurry if the mirror is more than 1 degree C or so warmer than
ambient. The mirror has a long thermal time constant (like 12 hours),
and the air conditioner is not particularly effective at cooling the
mirror, so if you want to adjust the temperature for the next night,
better do it now.
- How to decide on a temperature? The A/C control program
feature which displays the history of the ambient temperature, the
mirror temperature, and the temperature set point for the last 3 days
so. Detailed weather forecasts are available on the web; the National
Weather Service Tucson office (http://www.wrh.noaa.gov/Tucson/twc.html)
has a terrific site which includes very technical details of the
forecast. If humidity could be an issue, you'll want to be careful not
to overcool the mirror.
- record any messages for staff (e.g., filter changes) on
- If you have any requests which will require timely action
by the staff, please be certain to write them out legibly on the
whiteboard. You cannot expect to wake up at 3 PM, saunter out of bed,
and tell the staff to drop whatever they're doing and swap out all your
filters. In this, and everything else, try to think ahead, both to
assure that your requests can be handled and to minimize the strain on
our very small staff. Be sure to also alert the staff in your
nightly observing report (next item).
- Fill out the Observer's
Nightly Report Form.
- MDM requires that all observers fill out a brief report
of the night's activities. To make this as painless as possible, a
simple web form has been created that is accessed from the mountain web server..
Even if you did not observe, you should fill out a report saying why.
Nightly observing reports are stored on the mountaintop
server, and emailed to a short list of recipients that includes the
observatory directory, mountain superintendant, and the MDM consortium
representatives from each member institution. Report data are used to
track how much observing time is lost to weather, problems, etc., as
well as to keep a permanent record of activities.
If you encountered any problems at all, even
ones you fixed yourself (i.e., not common mistakes but real problems
that required you take some special action to continue working), also
fill out a Trouble
Report Form. There is no such thing as a "minor" trouble
report. Often a big problem starts as lots of little problems or quirky
annoyances. If we can see a pattern develop in the trouble logs, we
might be able to head off bigger problems later. Remember, the run you
save could be your own!
Some problems occur when using the data-acquisition
software or other computer systems. It will greatly help diagnosis and
solution of a problem if you can include the verbatim
text of any error messages printed when the problem occurred.
- go to bed!
- Your program may call for instantaneous data reduction -
bring a collaborator or automate it so you can get enough sleep. It's
important not to get too tired!
the end of your run ...
- Plan to depart as soon as practicable; keep staff
- Accomodations at the Obsevatory are very limited, and the
observer should noit have to work around you as they set up and settle
in. Accordingly, observers are required to leave the mountain as soon
as they can, ideally by the early afternoon of the day after their last
run. Please keep the staff informed of your plans. If you intend to
sleep for a while after your final night, be sure the staff knows when
you intend to get up and leave, or they have no idea what to tell the
next observer about bedroom availability and so on. The
instant-departure rule can be relaxed when there is a very good reason
(e.g., packing up a complicated user instrument at the end of a run),
but exceptions must be cleared with all concerned!
- Pay your Kitt Peak meal bill, if you have one
(ideally on the afternoon of the last business day before your departure.)
- If you've taken any meals up at the Kitt Peak cafeteria,
you're to pay for them before you leave. This is at the main office of
the Admin building up top. If it's after hours or the
weekend, you can go to the admin building and fill out a form with a
credit card number -- they'll charge you and send you a receipt. But
you have to remember to do this!
- Pay your room usage and/or vehicle usage fees.
- MDM levies a
$40/night usage charge to help cover the Observatory's budget.
We are also recharging observers $50 if they
transport themselves to and from the mountain in an observatory vehicle
-- this should just cover the actual expense, and is much less than the
cost of a rental car. In any case, make arrangements with the staff
to pay these fees, and get a receipt to claim the expense. A PayPal
account is available for these fees. Checks are accepted, but
you'll get a handwritten receipt that university cashiers may
regard with suspicion.
- Check with staff about whether to fill dewar.
- Sometimes the staff may want the dewar to run low because
it makes it more convenient for them to change the instruments.
- Make arrangements to get off mountain if needed
- If you're using the Kitt Peak shuttle you'll have to
reserve a spot; the schedules are kept in the Admin building up top.
MDM pays an annual fee so that observers may use the shuttle; we are
not charged by the passenger, so go right ahead. MDM users may not
drive Kitt Peak vehicles, so you can only use the 'U-drive' schedule
options when someone else is driving.
- If you're using an MDM vehicle to get off the mountain,
you'll have to arrange it ahead of time with the staff. Be sure to give
the staff plenty of advance notice!
- If you're driving yourself off the mountain, be very
careful in this case not to overextend yourself to the point where
you're really sleepy while driving. Falling asleep at the wheel is one
of the most important causes of fatal crashes -- don't put yourself in
a position where this is a danger.
- Be sure all your data are properly backed up.
- Standard operating procedure is for the staff to simply
your data from the observatory computers as soon as you're gone (though
if you ask real nice they can sometimes be persuaded to leave your data
alone until you verify your tape is legible at home). It's therefore a
good idea to write more than one copy of your data. There are many
possibilities for this -- tapes (for 8k data), transferring the data to
a laptop, writing
a DVD, bringing your own USB-pluggable disk drive, etc. The observatory
internet service is now fast enough that modest-size
data sets (e.g., single-chip detectors) can be shipped home, but given
that the phone lines can sometimes go down you shouldn't depend on this
exclusively! It's a good idea to leave a backup at the observatory in
case something gets wrecked on the way home.
- Be sure to allow sufficient time to back up your data.
plan any backups carefully so that you're finished early enough to
allow the staff to start instrument changes when they arrive at 8 AM.
As noted earlier, you should be backing up your data as you go along
- Tidy up control room
- Gather up all your charts, scratch paper, whatever, and
leave a neat workspace for the next observer.
- Throw away uneaten food and wash your dishes
- There's a tiny refrigerator and larder in the
kitchenette -- space
is very limited, so don't leave behind anything which could go bad. Who
knows when that half-eaten sandwich was parked there, anyway? There are
vermin (verpersons?) at the observatory, so you should never let dishes
pile up, but if you have, better get 'em now.
- Strip your bed
- Stuff your used linens and towels into one of your
pillowcases and leave by linen closet.
- Leave your bedroom tidy
- There's no chambermaid. Behave accordingly.
- Be certain: bedroom windows closed, heater and lights
off, no water leaks
- As noted earlier, water and electrical power are
on the mountain. No one else is going to check your room to be sure
you've turned things off, so be especially careful that you do. Be
absolutely sure that (a) the heater is off and (b) the toilet isn't
- Look around to be sure you haven't forgotten anything.
for New Observers ...
I trained as an observer at Lick in the 1970s. At that time
observers were walked through procedures by seasoned staff observers.
This certainly got the job done - we learned the equipment - but in the
long run, the most important lessons we learned from this were not
which buttons to push, or how to develop plates. They were instead
lessons about the experience of observing, and the attitude to bring to
the telescope. As an old curmudgeon I think some of these lessons have
atrophied over the intervening years, as overworked faculty pack
students off to observe with minimal preparation. Here's a distillation
of some of that acculturation, as refined through many hundreds of
nights of observing experience since then, most of them at MDM.
- Telescope time is precious, and using a large telescope
privilege. You should feel a strong obligation to use your time
- Accordingly, it's important to be efficient. This means
thought to your procedures. It also means having a well-thought-out and
well-prepared program. I remember one famously efficient observer who
was said to have spent three nights of large telescope time efficiently
observing the wrong list of objects - he'd grabbed the "already
observed" list instead of the "to be observed" list, and hey, galaxies
all look alike!
- Be careful with the equipment. It's expensive stuff and
carelessness is not an option. Leave everything in good working order.
Report problems completely and carefully so that they may be fixed.
Leave the control room in better order than you found it. And when
conditions become dangerous to the telescope (blowing dust, too-high
humidity, etc.), close immediately!
- Work very hard, but try to take care of yourself. If you
sleep-deprived, you're liable to make really dangerous errors.
- Most primary programs require excellent conditions. What
conditions are usable, but mediocre? What if the seeing is 2 arcsec
instead of 0.7 arcsec? What if you require photometric conditions but
there are high clouds? This happens a lot - have a backup program! If
you can't think of one yourself, ask around your department and
collaborators - someone else is sure to need something.
- You should take a workmanlike attitude toward your data.
should be in focus and centered. Spectra should be in focus and
properly calibrated - and they should be of the object you intended!
Take a few moments to get things right.
- On the other hand, better is the enemy of good. I
meticulous student who hardly ever took data because the conditions
never perfect enough for his high standards - he had the most wonderful
dome flats, though. I actually witnessed a memorable scene in which an
instrumentally-minded investigator spent most of a beautiful night
fine-tuning equipment endlessly as the stars wheeled overhead and a
roomful of European collaborators flown in for the occasion became
increasingly exasperated. Telescope time is precious. Use it.
- Even though you should feel a strong obligation to use
well, you'll be more efficient in the long run if you don't hurry.
Hurrying leads to really big mistakes, like that poor guy observing the
- Finally, have the discipline to avoid excessive
the TV, the stereo, and so on. Sometimes observing gets boring
and it's fine to let part of your mind do something else, but it's
important to stay on task. Observing is like a dance in time,
and it either happens or it's gone -- pay attention!
This little blurb isn't complete but might help get you
started. A description of the many improvements wrought by the
August 2005 upgrade is given here .
By now (2012), 2005 is a long time ago, so the machines described here
are pretty old. New machines have been purchased and will be installed during
2012, so the details in this writeup are likely to go obsolete fairly quickly.
There are two main computers at each telescope. At the
Hiltner and agung run
the K windowing environment,
and have been set up to have a common look and feel which will be
familiar to most observers. The
window system has four desktops available - there's a little
cartoon in one corner showing them all.
- This is the main Observing Workstation where the observer
logs in for most things. It is a Linux box.
- This is an identical PC running Linux configured as a
Data Reduction Workstation. It offers a second console and
allows you to run tasks without any possibility of interfering with
In addition, there are specialty machines for the instruments;
the facility CCDs are run by mdmarc1, and the Ohio
State instruments (OSMOS, CCDS, and TIFKAM)
that are run by
Prospero have their own machines. Refer to the
individual instrument manuals for details.
On all machines you login to a visitor account named obs24m.
Logging onto hiltner as obs24m
puts you into the
directory /lhome/obs24m. The data all go to
under /data, where the next item in the path is
the machine name (e.g., hiltner or mdmarc1), followed by the user
name (obs24m), followed by whatever you want to put there. The /data
directories are transparently visible to all themachines.
The telescope and the MIS (Multiple Instrument System, used for
everything except the MDM 8K camera) are controlled from windows on hiltner.
There's one window called xtcs, which
runs the telescope control system, and another called xmis,
which runs the MIS. These controls are thoughtfully designed and should
be fairly intuitive. The
web-based manual has sample displays of these windows, in
The facility MDM CCDs (Echelle, Charlotte, Templeton, etc.) are
(since 2011 September) run by a program called Owl, which
runs on the mdmarc1 machine. Here is a
Note that you can run everything from hiltner's
terminal - just ssh to the other machines as you wish.
It's probably a good idea to use agung for any
heavy reduction, to keep hiltner free for observing.
the Telescope Works
official manual contains a lot of detailed information on
the workings of the telescope. Here's a short overview which may be helpful
but which is necessarily very general. (Note also the
gotchas listed elsewhere, all of
which are known telescope bugs.)
The telescope is generally configured as an f/7.5
Ritchey-Chrï¿½tien - an f/13.5 secondary
has not been used in decades. It has an
equatorial fork mount, built by DFM engineering in the early 80s. The
drives are unusual in that they do not have worm gears - rather, the
telescope is driven by large steel wheels with smaller driving wheels
pressed up against them.
The Telescope Control System, or TCS, is a PC containing a
of custom hardware. In particular, it contains counters that listen to
and interpret the pulses from encoders, and boards that issue signals
to the power electronics "muscle boxes". These in turn send power to
the stepper motors which run almost everything. The TCS dates from
1995, when the original custom computer which came with the telescope
was retired. Because of limitations of the multitasking software
available for PCs at the time, the operating system of the TCS PC is
OS/2, which will be unfamilar to almost everyone; luckily, observers
should never have to interact with the OS (except if they need to turn
it off for a lightning shutdown, but this is straightforward).
The user interface for computer control of the telescope is
through a program on hiltner called xtcs. This is fairly
easy to use
-- to slew, just enter the coordinates and hit `send' and `go'. As
noted earlier, this can be made more efficient by putting your target
list in a file ahead of time and calling the objects by name. The xtcs
window also allows users to reset the encoders, adjust
track rates, and so on. It may be helpful to keep in mind that xtcs
is only a user interface -- the actions are mostly
occurring in the separate TCS computer.
When the TCS computer program is running normally, the TCS computer's
monitor displays the status of the telescope. It's designed to be
similar to the old TCS monitor, so the comprehensive
manual in the
control room gives a fairly good idea of its function. I'd recommend
that you peruse the monitor display carefully on your first day -
be looking at it a lot, so you'll want to understand what you're
In practice, the telescope points to about 30 arcsec rms.
This figure can change depending on how recently the pointing
errors have been mapped and modeled; the position as displayed has been
corrected using a model of the telescope errors. The position displayed
is also corrected for refraction, nutation, aberration, and precession,
so it should approximate the mean coordinates for the specified
The model (and the corrections) are handled correctly when the
coordinates are reset using a known star. The telescope readouts
tend to drift during the night, mostly in declination. It is
a good practice to update the pointing from time to time, when
you are (a) near the zenith and (b) are quite sure that you
know exactly where you're pointing. Whenever you update
pointing, be sure to check that the new correct
coordinates are displayed. If you mis-set the coordinates
and move off target, you are totally lost, and
will need to execute the rather
lengthy lost-pointing procedure
Note that the telescope has some pointing limits. It can't
extremely close to the horizon, or various hard and soft limits are
triggered (see the comprehensive
manual for where these limits are and
how to back out of them if you get into them). The RA is limited to
+/-6 hours to avoid cable wrap problems. Observing under the pole is
not really supported, though I hear it's been done.
There are manual control paddles to move the telescope.
directional buttons NSEW, and two buttons labeled SET and SLEW. The
actions of these buttons are quite standard. Holding a directional
button down moves the telescope very slowly in GUIDE rate (typically
or two arcsec per second of time - the guide rate can be adjusted with
the xtcs window). Holding down the SET button
results in a
much faster rate, about 1 arcmin per second. Finally, the SLEW rate is
full-speed, around 1 degree per second, used for major repositioning of
the telescope. If you need to slew manually, you must keep an eye on
the telescope to be sure you know what it's up to.
lost pointing. Occasionally the telescope may lose pointing
failures may be responsible; more frequently, it's due to pilot error
(updating pointing carelessly and then slewing away before the error is
detected). There's only one way to reliably set pointing from scratch,
and that's to slew to the zenith and reset the encoders. Follow
instructions exactly and pointing will be restored. The whole
procedure takes 10-15 min at the most, if you try to improvise you'll
waste much more time than that, so don't.
- Turn off the TRACK switch (on black TCS switch panel).
- Get a working flashlight, and go out in the dome, turning
on the red dome lights as you go. There's a telescope hand paddle out
in the dome, it's usually hanging near the southwest side of the polar
axis. Get it.
- Look at the telescope. Figure out which way you should
move it to point at the zenith (east or west? north or south?). Then,
using the paddle, manually slew the telescope to near the zenith. Keep
looking at the telescope as you slew to be sure you're moving the right
direction and not driving toward the horizon!!
- Go back in the control room. If you have another
observer leave them in the dome.
- Within a few degrees of the zenith, tiltmeters mounted on
the telescope will read how far off the zenith you are. The readouts
are on a rack in the computer room. Move the telescope with the control
room handpaddle to set the tiltmeters to
the current zenith reading, which is close
to zero in both axes. The current zenith reading is usually on a
post-it note stuck to the glass between the console room and the computer
room. If you can't find this, set to (X = 0.00,Y = 0.00), but expect to search
rather widely for the bright star (when you get to step 14, below).
- In the xtcs window, set the TCS
Equinox to the current epoch, within half a year or so, e.g.
- Find the Sidereal Time display on
the TCS monitor. Note the time and write down the sidereal time 1 or 2
minutes in the future, to allow time for typing and so on.
- Type the coordinates of the zenith into the appropriate
fields in the xtcs window on hiltner; they are
RA = sidereal time (the one which you just wrote down).
Dec = 31 57 12
Equinox = right now (decimal year)
- SEND the coordinates to the TCS.
- Pull down the setup menu in the xtcs
window, and note the set RA and dec encoders
item. Watch the sidereal time readout on the tcs. At the moment the
sidereal time matches the sidereal time you've set up, let your finger
off the mouse button to reset the encoders.
- Verify that the hour angle is reading within a couple of
seconds of time of zero, and that the dec is within one arcminute of 31
57 12 in the present-epoch coordinates.
- Turn the TRACK switch back on.
- The xtcs window has a button
labeled Get Coords; click on this and select Nearest
Bright from the pull-down menu. This will load the Yale
Bright Star catalog entry nearest the zenith.
- Slew to this bright star. Since all the bright stars are
around 6th or brighter this should be a huge
unmistakable star. (It's a common mistake to set up on the wrong star.
Don't be fooled by cheap imitations, this sucker will be bright!)
The zenith tilt meters are not necessarily accurate enough to get the
star in the field of view (which for some instruments is very tiny,
like 90 arcsec), so you will probably need to scan the telescope back
and forth a little bit in order to find it. Note
that the best way to pick up the bright star will be
instrument-dependent, and requires a little thought on your part; here
are some suggestions:
- With the MIS: In xmis, find the pink "Preset" menu button
for the guide probe position, and pull down "center". This will put
the upward-looking probe in the center of the field. Set the FLI
camera on continuous, short exposures, and move the telescope around
to look for the bright star. Don't forget
to move the probe away fom the center when you're done, since it
will block your science instrument there.
- Retrocam: Put in the retrocam and take a quick shot. It's accurately
boresighted with the telescope and shows a much bigger field of view than the
- With OSMOS: Take an image (probably binned pretty heavily to minimize
read time) and the very bright star should be obvious.
- Use the directional buttons on the telescope handpaddle
to put the bright star near the center of the field of view of your
- With the telescope pointing right at the star, go to the
pink "Setup" menu in xtcs and pull down the "set RA/dec encoders" item.
This should reset the telescope position to that of the bright star.
- Before moving away, make absolutely certain
that the coordinates have set correctly on the TCS; look at the
original coordinates of the star (recall it again in xtcs) and verify
carefully that you have reset the coordinates correctly. Be aware of
the coordinate "epoch" (more properly equinox); if the telescope
"epoch" is not 2000, click on the "TCS Equinox" button in the xtcs
window and adjust the telescope's display to 2000 (this affects the
display, but not the actual position), and then the telescope should
agree with the star's catalogued position. If you've used any offset
commands in centering the star, be aware of the following insidious way to make a mistake :
the set RA/dec encoders command sets the
encoders to the values in the Next Object field.
But, if you send offset commands to the TCS, this over-writes
the Next Object values, so when you set, it will be to the
wrong coordinates. The cure is to use the Send Coords
button in xtcs to reset the Next Object field to
the correct coordinates before setting the encoders. Bottom
line: don't move away until you're certain you have it right.
- Select another bright star nearby and slew to it to
double-check. You can do this by slewing randomly by 10 degrees in any
direction and doing "Nearest Bright" again.
- Don't forget to turn off the red lights if you turned
- If you've put the MIS guide probe in the center of the
field, better withdraw it to where it's not blocking the beam.
That's the procedure. I hope it's worked for you!
Here are a few more aspects of the telescope you'll want to
The focus control: The telescope is
focused by holding down the IN and OUT buttons on the
paddle. This moves the focus rather slowly. If you also hold down the
SET button, the focus moves much more quickly. The focus numbers are
arbitrary and their zero point varies widely - your numbers from the
last run mean nothing. Focus numbers tend to decrease as the
temperature goes down.
The Instrument Rotator: There is an
instrument rotator at the back of the telescope. It has its
own encoder, which is not particulary reliable these days; you can set
the encoder using xtcs. There are various
pieces of tape
marking different position angles. Note the following about the
What's the "slit angle"? :
On this last, note that there's a little quantity called the "slit
angle" displayed on the TCS, in the upper right-hand corner. The story
behind this is as follows. If
you do slit spectroscopy away from the zenith, your data suffer from
atmospheric dispersion - the star is smeared into a little spectrum in
direction perpendicular to the horizon. You can capture all the
wavelengths in the slit by orienting the slit perpendicular to the
horizon. (The importance of doing this was all emphasized in
paper by Alex Filippenko very early in his career.)
The position angle of an arc connecting a given point to the
zenith is called the parallactic angle, because
(anti)parallel to the direction of topocentric parallax displacements.
With the rotator angle at zero, the MDM spectrographs are
oriented with their slits north-south, so that they're on the
parallactic angle for any object crossing the meridian. Once you're far
away from the meridian, you want to rotate the slit to the parallactic
angle, but keep the rotator angle within +/-90 degrees. Because the
slit is indifferent to 180-degree rotations, but the rotator isn't, the
"slit angle" is the rotator angle which, for the present position of
telescope, will put the slit on the parallactic angle and keep the
rotator within its travel. For instance, if the parallactic angle is
-150 degrees, the "slit angle" will be +30 degrees. It's
to interpret the "slit angle" as an actual readout of the rotator
position. The rotator position readout is the "Rotator Angle",
displayed near the middle of the TCS monitor about 1/3 of the way from
- You must have the mirror covers
open to rotate the instrument. The mirror covers bear upon a moving
part of the instrument rotator! Metal shavings and paint flakes don't
do much good for the mirror!
- The rotator paddle is in the dome. Be sure to turn the
speed all the way down before turning the rotator on or reversing
- While rotating the instrument, use a flashlight to watch
carefully for any cables which might be hanging up. It's a helluva
thing to have a cable catch on some critical switch or knob, pull it,
and then get ripped out ... ruins your whole night.
- To avoid problems with cable hangup, the rotator angle
should be kept within +/-90 degrees.
- In 2011, he rotator controls were reworked, and much improved,
to enable the very fine control needed by OSMOS in multiple
object mode. A GUI on Hiltner allows you to execute very fine
moves, but only if they're smaller than one degree. Gross
rotations must still be done in the dome because they must
be monitored carefully for cable snags and the like.
intend to track an object over a large range of hour angle, you
will want to check out the Parallactic... button on JSkyCalc24mGS.
This computes the optimal rotator setting over a range of time
for your object and gives a graph showing how
badly you do if you're off on either side. The "cross-slit
refraction factor" given there is a "badness parameter",
computed as the
tangent of the zenith distance times the sine
of the mismatch of the slit away from the parallactic angle.
How much effect this has depends on a host of factors, but it
you keep the absolute value less than 0.5 or so you should
have minimal effects with most setups.
All the commonly used instruments except
the MDM 8k camera are
mounted on an adapter called the MIS (Multiple Instrument System). This
provides a number of commonly-needed utilities. Some useful diagrams
can be found in the
There are three parts to the MIS. Working downward from the
The MIS is operated using the xmis program on hiltner.
This issues commands to the MIS controller box. (As of this
writing, we are on the verge of replacing these almst 30-year-old
boxes with modern units; the change should be almost transparent to the
user, except that the GUI will look somewhat different.)
The controls are fairly straightforward to operate. There are a
number of preset positions for the guide stage (slit, center, etc). You
can also type in an X or Y coordinate for the guide stage and hit
return to send them; an indicator blinks red while the stage is moving, then
stops blinking and shows the new position when it gets there. You can
also get relative steps using the "Delta X" or "Delta Y" fields. Other
buttons or menus allow you to turn comparison lamps on or off, move the
RETROCAM prism in or out, and so on.
- The finder unit:
- This is a gold-anodized box about two feet square and 10
inches deep. It contains a prism that can slide in and out of the beam to feed
an Apogee CCD camera called RETROCAM, so called
because it was retrofitted to the MIS by Chris Morgan of OSU. The finder unit also
houses a set of comparison lamps - an incandescent flat bulb,
and Ne, Hg, Ar, and Xe discharge lamps - for calibrating spectra. The prism that
feeds the RETROCAM also diverts the comparison lamp
light downward to the instrument, and the optics are arranged so that
they provide an approximate f/7.5 beam to match the telescope. Note
that you can either see comparison lamps or the sky, but not both at
the same time, as they call for different positions of the RETROCAM
prism. To summarize:
- RETROCAM out: The main science instrument sees the sky.
- RETROCAM in: The main science instrument is blocked.
Comparison lamp light gets to the science instrument, and RETROCAM
can see the sky.
- The guider unit:
- This is about 5 inches deep; it bolts to the back of the
unit. It has a pickoff mirror which feeds optics leading to a
CCD camera. The pickoff mirror (which I'll call the guide
probe can be moved around on a precision XY stage.
The camera fed from this mirror is used
for offset guiding; one acquires a guide star by moving the guide probe,
and then starts the autoguider to keep the telescope locked in
position. The guide camera has a fairly
small field (about one arcminute). The CCDS, Mark III, and
Modspec spectrographs use a separate CCD camera to view the
slit, so one can see the slit and
offset-guide at the same time. OSMOS does not use a
slit-viewer; you acquire targets by taking direct images
with the disperser and slit out of the beam.
- The filter wheel:
- The "Buckeye" filter wheel (built at Ohio State
and Ohio University) is used only for direct imaging.
It has 12 positions and takes 4-inch filters. A
limited number of 2-inch inserts are
available for mounting smaller filters. The Buckeye
filter wheel has been very reliable and positions filters with
One can also move the
guide probe using the JSkyCalc24mGS program.
Read on for details.
There are a number of things to be aware of when using the
- The JSkyCalc24mGS program running
on agung makes it almost
criminally easy to pre-select guide stars for your target, using the
recent and very accurate UCAC3 star catalog as a database.
full explanation is given a little later in the document.
This is highly recommended, even if you're working at low latitude
where guide stars are plentiful, since the software flags
in which the guide probe might obscure the field center (see the next
item on the list). Also, pre-setting the guide star can
greatly expedite field acquisition and centering; JSkyCalc24mGS
actually makes it possible to do this with a mouse click.
There is also a
newer, very complete manual that describes these guide-probe
centering tricks in detail.
- It's important to note that there's nothing to
from blocking the telescope beam with the guide probe. You must
keep the guide probe away from the science field!
The JSkyCalc24mGS program indicates rough boundaries for the
"safe" positions, but if you have a big detector and you choose
a star close to the boundary, you may see some shadowing at the
edge of your field.
- The guide probe camera needs to be focused so that when
the telescope is in focus, the guide probe is also. The guide probe focus
is controlled by a rocker switch on a little aluminum box a couple
inches square. If you run all the way to the end of the focus travel,
and the stars is out of focus, try guiding anyway -- Maxim DL does
an amazing job on truly terrible images. The guider
focus sometimes slips; if this happens, try slipping it back
by changing the telescope position. If you happen to be using
Modspec or Mark III, it is theoretically possible to
adjust the guide stage by hand -- have the staff show you
how to do this -- but with the Buckeye filter wheel and
OSMOS, the relevant port is covered and it can't be done.
- If the guide probe is driven past the end of its travel,
track of where it is. I've also seen it lose track when it gets close
to the end of its travel in Y, say at 10000 or greater.
In any case, it takes only a minute or so to reset the coordinates, by
selecting Origin in xmis.
This drives the probes back to
its zero position and resets the counters.
- The guide probe travel is larger than the unvignetted
field of the telescope. The outer red circle in the JSkyCalc24mGS
diagram shows this.
- Easy pre-selection of guide stars!
The program JSkyCalc24mGS is available on
on agung and hiltner. This is a 2.4-meter specific version of JSkyCalc
that lets you select guide stars for your target, and is also aware of where the telescope
is pointing. Users report that it is a great convenience. The program
has its own help facilities; for instructions as to how
to start it, see
the short document
linked here, or for a more comprehensive view refer to
recent and detailed manual.
target acquisition using the guide probe.
The guider XY stage is very accurate, and so is the UCAC3 catalog
used in JSkyCalc24mGS (positions are even updated for
proper motion). Therefore centering the preselected
guide star in the appropriate location on the guide camera should put you
very close to your target, provided of course that you're
setting on the right star! This can save enormous amounts of time. To
develop this procedure, start with a target you can set up accurately.
Select a guide star using the program (described immediately above), set up the
guide probe at the XY coordinates predicted by the program
(JSkyCalc24mGS lets you push the guide probe directly), aim the
telescope accurately at your target, and note where the guide star
lands on the guide camera. If you keep the
fiducial guide position in the same place as you set up on new
fields, and center the (correct!) guide star in the box, you should be
within a few arcseconds of the target. Be
careful of the a HUGE GOTCHA
here, explained a
little farther up: the guide probe can lose track of where it
is when it is
driven to Y-values greater than about 10000. It does
this silently -- no error message is printed, and it all
looks fine, but the numbers are all wrong. Just reset the probe
coordinates by sending the probe to the present "Origin" if this
happens. Also, you'll want to be sure you know the rotator angle
As noted earlier,
recent and detailed manual explains all this more comprehensively.
- You should almost never need to "hunt and peck" for guide stars,
but if you you need to for some reason, here's how to do it.
(The units used here for X-Y are the default, raw counts; you can
make them arcsec or mm instead.)
and so on, raster scanning until you have a guide star.
In principle you can scan across the low Y range and up the far side of
X without vignetting the chip, but this is seldom necessary. The field
maps produced by the skycalc tool give an idea
of the useful field.
- Center up on the object
- Be sure guide camera is on and updating.
- set the guide probe to X = 0, Y = 2000
- set Delta-Y to 1000
- repeatedly hit carriage return and watch the camera
output to look for guide stars
- stop when Y = 10000; if you drive beyond that, the
guider will silently lose track of its
- At the top of the Y travel, set X = 1000 and Delta-Y
= -1000, then step back down ...
Guiding and acquisition cameras
In order to do science, you obviously need to find targets
and keep the telescope pointed at them accurately as they
track across the sky. The telescope position readouts
are nowhere near accurate enough to do this -- you need to
be able to acquire and guide on targets. This requires
the use of sensitive cameras.
For decades, we used an image-tube based system for this,
but by 2009 these were aging and their shortcomings
were becoming too much to bear. They have been replaced
by small, self-contained CCD systems. These are as follows;
- For offset guiding, we use Finger Lakes
Instrument (FLI) cameras. These are run by the commercial
software package Maxim DL, which puts out guide
signals that our telescopes can use. Essentially
all users use this system.
- For slit viewing with Modspec and Mark III, we
use a more sensitive and versatile camera built by
Andor. This can read up to 8 frames per second,
and integrate for many seconds to see very faint object
on the slit. They look at the slit through a side port
in the MIS built by Dr. Yorke Brown; this has high
throughput because of the short, simple optical path.
Because every observer needs to know how to autoguide
new observers should be sure to
READ THE MANUAL that describes how to do this.
Mark III and Modspec users will also want read the
manual for the Andor cameras. The Andors were
originally used for guiding as well as slit viewing,
but that function has been retired; in that manual,
skip right to the part about the Solis software.
Note that CCDS has
its own slit-viewing camera, an
SBIG. The Andor cameras are much better than this,
but as of this writing the slit-viewer on CCDS has not been
mated to an Andor.
CCDCOM is gone!
About Owl ...
Until mid-2011, the
facility MDM CCDs, which are workhorse direct imagers
and the only detectors that work
on the Mark III and Modspec spectrographs, were run by
a program called CCDCOM. (The Ohio State
CCDS, and TIFKAM are run using an entirely separate progam called
Prospero). CCDCOM was tied to old Sun Sparcstation computers
that were unmaintainable, so over the summer of 2011 we
shipped the controllers and detectors to Bob Leach at
Astronomical Research Cameras (ARC) in San Diego. As this
is being written, one detector has been converted to
run with ARC Gen III controllers and is in routine use;
the others should follow before too long. The change is
not reversible -- the old controllers and computers could
not be revived even if we wanted to.
At present (and probably indefinitely), the new system is
controlled using ARC's in-house software, called Owl.
Manual for Owl explains the details. Be sure to have
a look at this if you're intending to use a facility
CCD. Even if you're familiar with the old commands, be advised
that this is completely different.
At present the system is a little primitive, but it does get
the job done and it is not especially difficult to use.
It does at least capture the telescope and MIS configuration
information and populate the FITS header keywords automatically.
As of this writing there is only one automated script written for
Owl, a multiple-exposure "step-and-shoot" script for
focusing direct images. There is, unfortunately, no easy
way to generate observing scripts "on the fly", but one
can at least take a series of identical exposures without
time should I start?
OK, so the weather's great -- low humidity, photometrically
clear, and the wind is a gentle zephyr. So you can open. But
when should you plan to start observing? Here are a few remarks on that.
It obviously depends on what time it gets dark.
Java skycalc, and its 2.4 m version
both have a "Nightly Almanac" button, which pops up a
window with the information you want.
If you can do it, it's a good idea to open the dome maybe 15-20 minutes
before sunset so you can have your dewar topped off and ready to go by
the time the sun actually sets (that way you can enjoy the sunset and
see the green flash). There are constructive uses for twilight time.
If you're doing direct imaging in the optical, sky flats can start
in the U band shortly after sunset, within 5 minutes or so, and the
window of opportunity for well-exposed sky flats is pretty short.
Bright stars can be found almost in bright twilight to verify telescope
pointing. Certain kinds of spectroscopic standards can
be done in quite a bright sky -- e.g. 10-th magnitude flux standards
should be do-able within 20 minutes after sunset. The limiting factor
will be when the sky saturates the guide camera in a very short
A word about the
python-based skycalc GUI ...
There's an older python-based
which was the prototype of the Java version and resembles it closely.
The python version has several useful tools not implemented in JSkyCalc24mGS. These include:
- A powerful program for grabbing DSS images and making finding charts from them
- A facility for keeping track of electronic finding charts (e.g. jpg or png
images) and displaying them (this requires some setup).
- An ephemeris predictor that will print a table of, for example, expected
geocentric eclipse times for a variable star.
You have (at least) two ways to get at this program:
- On Agung's (or Hill's) console, it's installed in the
launch menu (the red hat in the lower left).
But -- you'll have to scoot over to agung to consult it.
- To lanch it on hiltner, click on the little terminal icon
in the lower
left to get a terminal. Into this terminal type the following:
and it should fire right up. The "disp" means it has the planetarium
display implemented; the ".py" indicates that it's in the Python