Observing

Introduction

• A list of Telescope Commands
• Image acquisition with the Apogee CCD
• ds9 image processing software
• Are you LOST?

Opening up Telescope

openup

Watch the terminal as the script executes, to see what telescope commands are issued.
What's Up?
To find the Local
Sidereal Time:
lst

To find a bright
star, for example:

bright ra=12:22 dec=33 faint=4

 Will find the brightest star no fainter than 4th order magnitude,
centered around the ra and dec specified. (see link above for details
on using bright)

Pointing the telescope
To point, for example, to alpha Lyrae, type the following:
tx point ra=18:36:56.2 dec=38:47:01 epoch=2000


 To point the telescope without moving the dome, include the keyword
'nodome' after the coordinates.


Offsetting Telescope
To move the telescope a small amount - say .01 degree North:
tx offset dec=.01

IR Camera Status
To see whether the *IR* camera has cooled down type the following:
tx ccd_status

You should get a reply similar to the following:

done ccd_status nrow=256 ncol=256 readtime=1.0 tchip=91.5
t77=68.4
tfil=149.0 topt=150.3 name=picnic darktime=76515.0 gain=1 seq=Fowler
pixel=40.0
rot=0

Which returns, among other things, the name of the sequence being
used
at the moment as well as the various Dewar temperatures.

Telescope Status
tx slit          - tells whether the slit is open
tx temps         - tells the current weather conditions
tx tel_status    - returns values of telescope limits

Focusing
To move the secondary to a focus position of, for example, 515 mils,
type the following:
tx move_sec mils=515

Using the command without specifying the number of mils will return
the current position. Currently, for the new Apogee visible CCD, focus
is at about 515 mils.

Setting Flip Mirror
Before taking a picture make sure that the flip
mirror
is
in the proper position.
tx flip put=12    #for ircam
tx flip put=237   #for SETI counter 
tx flip put=328    #for Apogee 47p CCD

If the power has gone off, or the servers restarted recently, the flip
mirror will need to be homed, first.


Setting the IR Camera Filters
The filters are discussed here.
To install the Kshort filter type the line:

tx filter name=Kshort

Taking a picture with the Apogee CCD
You need to run startapogee as user ay120 or thirty, from their home
directory.
Please see 

Dome Centering
The dome does not
follow the telescope during tracking. It only adjusts
when the point command is used. Therefore if you are observing
for
a long period of time on one target the dome may mask the telescope. To
adjust the dome so the telescope is looking out type:

tx dome center

Tracking
Track is not
automatically turned on, ,unless you use the 'openup' script to start
up the telescope. However, if you have tracking on, the telescope does
NOT check for a limit condition as it tracks.
PLEASE endeavor to remember to TURN TRACK OFF when leaving the
telescope
running for any length of time. Track is also turned off when using the
'closedown' script.

Lost?
For the latest pointing
information 
see pointing writeup.
If you can't find a star it may be because you have a pointing
error.
First check that:


  

It is clear (the weather cloud sensor is not reliable; check satellite
images online)

  

Ths slit is open!

  

The dome has been homed and is centered

  

The mirror cover is open

  

The secondary has been homed and is close to the correct focus
(mils=995 for
Apogee CCD)

  

The flip mirror has been homed, if needed, and is at the correct angle

  

IRCAM: The filter wheel has been homed and the correct filter has been
selected

  

IRCAM: The chip temperature is nominal (70 - 90 K for IRCAM)

  

The exposure has not saturated on the sky


If the above list checks out o.k., then check your offsets with tx zero and se if they match the
values seen here.

When all that fails, offset the telescope small amounts to seek your
star - if you believe the weather to be good.



Don't forget, you can, and should, email me at bresloff@astron.berkeley.edu with
unusual problems.   

Closing down
DON'T FORGET TO SHUT DOWN THE OBSERVATORY AT THE END
OF YOUR OBSERVING SESSION! To shutdown
the
observatory for the night type:
closedown

Pipes
Commands can be strung together if you wish: For example:
#To to point to a bright star near the meridian
    bright ra=`lst` dec=30 | dopoint

#To take a picture , subtract a premade dark frame and display it
    qimage time=5 outfile=- | sub - dark | tv -

Scripts
Below is an example script written in C-shell and using image
processing
programs from XVista.
#!/bin/csh
#script to generate a flat by jogging the telescope around
#between exposures then computing the median
#and writing the file 'flat.fts'
set i=0
rm F?.fts       
while ($i<5)
        qimage time=10 outfile=F$i
        tx offset ha=.02 cos
        @ i++
end
median F?.fts outfile=flat

Troubleshooting
To display the telescope command as they are executed open a separate
window
and type
show log .
If you forget the command options type the command with the keyword
help.
e.g. tx point help.

If you forget all command names type tx help.

To see whether the slit is open type: tx slit.

To see whether the mirror is open type: tx mirror.

To see whether the telescope is tracking: tx track. It
should
reply tx track ha=.004175 dec=0.00000. If ha=0.00000
type tx track on.

If dome is stuck try moving it slightly to the left then to the
right.
For example if the present azimuth is 250 degrees try

tx dome put=260
tx dome put=240
If you believe the dome is mispointing you can rehome it by:
tx dome home     <-- this may take over a minute
tx dome center
If server is truly hung it can be
restart but this is a time consuming procedure and you should quit if it has to
be done often.

Time
The ntp protocal is used to set the time on fast and crystalize. 
If you are suspicious of the clock settings type on fast:
ntptrace 
ntptrace crystalize

the offsets should be small (less than a second). If not, call it
quits.
If images are strange on IRCAM, check the chip temperature by
typing:
tx ccd_status
It
should tchip less than 100 K. If not there is a problem with the
refrigerator
(serious).

If the telescope secondary runs away try the following procedure as
a fix.

tx move_sec home         <--- this may take up to two minutes 
tx move_sec mils=570     <--- this will take over one minute


If you are getting the message tx power off when you don't want
it, you may have hit a telescope limit. To extricate yourself first find
out where the telescope is pointing.
  tx where
If the hour angle (ha=) is large then the telescope is at the West limit
and you should move East.
 tx power on
 tx offset ha=-10
 tx where
Similar procedures will work if you are stuck at the North, South, or East
limit. If the Altitude is too low the only way you are allowed to go (offset)
is North.


[ IRCam Index |
Leuschner
Index ]


Last updated on 2002 October 4, C Bresloff