Poster 10.02 at the AAS Meeting Jan. 1995
(Automatic Radio-Linked Telescope)
An Imaging Observatory
A. William Neely
Adjunct Professor of Research Astronomy
Western New Mexico University
Silver City, NM
The NF/ Observatory was founded in late 1986 to develop an
automated and flexible telescope system for astronomical study. It
was designed to be reliable, cost-effective, and easy to upgrade.
The site has an extremely dark sky at 1768 meters on a ranch 40 km
outside Silver City, NM. The telescope is a .44 meter F4.5
reflector with a fork mount. Since the site is remote and
unmanned, a 440 MHz radio data link was established to perform data
and command transfer to Silver City. A phone modem is available
as a backup, but it is a long distance call.
The mission of the observatory has evolved with time. We started
with a plan for an automated supernova search. Relatively slow
slew rates and long exposure times for our aperture size, limited
that application. When a Craf-Cassini CCD became available from
JPL, scientific grade images were possible, and we re-directed the
project. The observatory is currently a fully automatic CCD
Imaging facility. The nightly observation list is determined in
advance and compiled in the ATIS (automatic telescope instruction
set) format. The ATIS file can be updated by radio, as needed, to
modify the target list. A direct Internet link is in development.
Current projects include:
A. BL Lac objects for Hubble Space Telescope,
Looking at the Hydrogen Alpha Forest
Hydrogen Cloud study (Recent Observation on
Hubble June 5, 1994.)
J. Stocke - U of CO Principal Investigator
B. Asteroid lightcurves and pole orientations
1. Minor Planet Bulletin (5 recent
C. Ground Optical Observations of the (LMXB)
Sco-X1, to correlate with the X-Ray
observations of the CGRO -B. MacNamara - NMSU
D. Image data base for Supernova search in lesser
Bill Wren - McDonald Observatory
E. Mira survey for correlation with a VLBA survey
of molecular products.
Kevin Marvel - NMSU
F. Nova Survey in M31
G. Light Curves for all Supernova's > 14 mag
(currently imaging 1994ae)
Sixteen articles have been published in conjunction with the
observatory's activities, including two student papers from Western
New Mexico University.
When SN 1993J appeared, the telescope was engaged in imaging all
the Messier objects, and the telescope fortuitously imaged the SN
only a few hours after shock outbreak, and a day before discovery.
A complete data set for the first 400 days was recently
II. SYSTEM DESCRIPTION
The system (see block diagram) is run by four computers linked by
447.5 MHz transceivers and packet modems. Although not all of the
radios and computers are state-of-the-art, they are high quality
and reasonably priced. There are three computers at the telescope
site, one controlling the telescope and dome direction, another
controlling the CCD camera, filters, and observatory housekeeping,
and the third computer controlling communications and dome power.
A fourth is located in town and performs communications, data
reduction and image processing.
PROBLEMS AND SOLUTIONS
The communication between the 'warm room' and dome are accomplished
via a long coax cable ethernet. Lightning is a common problem and
ethernet boards are expensive. Although fiber optic would be the
best solution, Lou Boyd suggested a simple 'fast diode' protection
circuit that has done the job.
The mouse-proofing was one of the most difficult of the challenges.
The observatory is located at the edge of a large open field and in
spite of the efforts of a specially-installed security cat, the
field mice were persistent in building nests in the computer and
shorting it out with conductive liquids. The problem was solved by
installing tight-fitting sheet metal over all openings.
The telescope drive motors are controlled by a custom-built
interface attached to the parallel printer port. The dome and
shutter motors are also controlled by this interface. We used the
printer port because it has both output (8 bits parallel TTL data
loaded by a strobe signal) and input (4 TTL status bits). We also
knew that sooner or later we would have to replace the computer,
and that a standard parallel printer port should be available on
any system we are likely to use in the future. The tracking
computer is clocked at a sidereal rate using a simple software
Most of the software is written in C, except the motor drivers and
camera drivers, which are written in assembly. The assembly
routines are 'real-time' routines and during the camera readout,
the interrupts must be turned off. This is easily accomplished in
the software. The observatory clock is another problem in a remote
installation. Since we have changed mother-boards on all the
computers a few times, the clocks are not always accurate. A few
years ago we could adjust the clock oscillator, but that isn't
possible on the newer boards. A short software routine to add or
subtract time at intervals, provided the fix.
B. TELESCOPE AND DOME DRIVE
The equatorial fork mount uses a main bearing from a 1965 3/4-Ton
Ford Truck rear ene RA drive uses a 16-inch Mathis worm
drive reduction gear coupled with a timing belt to a Vexta
PH265M-31 stepper motor available from Oriental Motors. The timing
belt provides a two-to-one reduction in addition to eliminating the
vibration noise transmitted to the optics. The gear lash
(especially in DEC) and vibration continues to be a problem. Some
of the vibration at low temperatures was reduced using a low
temperature grease, developed for arctic conditions.
The stepper motor provides 0.6 oz/in of torque and has 400 steps
per revolution. A Rifa 3690 decoder and 3771 driver pair provides
an additional 16 microsteps giving a single step resolution of .2
arc-seconds. The DEC axis is a similar system using a 12-inch worm
drive gear producing .35 arc-seconds per step. Software ramp
functions can slew either axis at greater than 3 degrees per second
using full steps.
Considerable effort was expended to provide correction factors for
precession, refraction, mount alignment error, and mount
fabrication error. The fabrication error ( the DEC optical axis is
not quite perpendicular to the RA axis) correction was derived
from the coordinate transform formula. The mount is aligned within
2 arc-minutes of the pole. Corrections are also added to the
apparent position for this error. After each slewing procedure, a
nearby 'navigation star' is picked from a database, and the
telescope is recalibrated.
We decided on a dome rather than a roll-off roof because of high
average winds at the site. With proper observing quadrants, picked
by software and depending on weather telemetry, we can increase our
observing time. The dome is 11 feet in diameter and resembles a
short Quonset hut sitting on a octagon. The geometry allowed easier
and more reliable weatherproofing in addition to providing more
interior space than the traditional spherical dome.
The dome has a .70 meter aperture and can be turned through 360
degrees. It rests on a circular track on miniature railroad type
wheels. A 1/20 hp motor with a reduction gear walks the dome
around a fixed bicycle chain at 1 rpm. A light interrupter wheel
sends information back to the interface board.
The shutter uses another 1/20 hp motor with a reduction gear
connected to a live shaft with sprocket gears on either side of the
shutter, to walk the shutter open or closed along fixed chains.
Making sure the dome shutter closes in a weather or system problem
was an early priority. The shutter has a 'dead-man' switch, which
requires a signal from the main computer every 20 seconds, or the
shutter will close. The warm room computer is always checking on
shutter status also.
The heart of the CCD camera is an evaluation CCD from JPL. The
chip was made by Ford-JPL for the CRAF-Cassini Mission. The
mission has since undergone changes, and out CCD was dropped from
the flight list. The CCD is a 1024x1024 pixel format, with a floor
noise of 5 electrons. It is insensitive in U and B, but has a 50%
quantum efficiency in red. The electronics are similar to the HST
wide field camera. We laid out the board for photo-resist and
produced the circuit boards ourselves. Since the boards are at
most two layer, we suffer from more noise than a multi-layered,
but expensive, board would offer. The total signal chain and chip
noise is 25 electrons.
The camera is cooled to about -45C with thermocouple. There is a
temperature sensor on the cold-finger to monitor cooling. The
thermocouple runs wide open all the time. If the temperature drops
below a set point, a small resistive heat source on the cold finger
stabilizes the temperature. The set point and dark fields are
re-done at intervals through the night.
D. RADIO COMMUNICATIONS
We elected to use a frequency of 447.5 MHz in the 70-cm amateur
band to transmit data between the two sites. This band allows us
to remotely turn on or off the computer systems at the telescope,
to send the observing schedule to the telescope computers and to
receive digital picture data back from the CCD camera. The radios
are retired commercial Motorola MOCOM 70 units that we have
modified to operate at the 447.5 MHz frequency by replacing the
crystals and re-tuning the transmitter and receiver. The radios
are all solid-state units made in the early seventies and cost
us $10.00 apiece. Three of antennas used with this system are
highly directional Yagi-Uda beams that minimize the chance of
interference to or from other services. The Observatory uses a
donated and modified 'satellite dish' which offers a gain of 18 db.
The design painted on the dish is taken from a 900 year old Mimbres
Indian bowl which probably depicts the famous 1068 apparition of
We have other radio links to the internet operating at a high baud
rate and will eventually upgrade the main link. We want to
integrate the observatory into the internet gradually. We are
starting with a web home page. Since the observatory operates
independently, the current 9600 baud rate is sufficient. Most of
the data is stored on a potable hard disk, which is changed once a
week. Critical images can be transferred over the link in about 12
E. WEATHER STATION
Automatic weather sensing is critical for an automatic observatory.
Moisture is the biggest enemy. The moisture sensor is a simple
grid with a comparitor sensing resistance changes. This works well
for rain and usually for snow. It also is very sensitive to dew,
so an independent dew point sensor, hasn't been needed.
Windspeed and direction are important in our ridgetop location.
The sensor are standard, and used to select acceptable azimuths in
A ambient temperature is needed to predict the holding temperature
of the CCD.
A cloud sensor rounds out the weather station. It consists of two
plates, separated by a thermocouple. In cloudy conditions the two
plates are the same temperature, but on a clear night, the top
plate gets cold. This differential produces a small voltage in
the thermocouple, which is amplified and measured with a A to D
converter. The observatory waits for acceptable skies before
opening the dome, then will close the dome if navigation stars
aren't found and the sensor indicates clouds. About 4 months were
required to calibrate this system, and we are continuing to monitor
this sensor. The biggest problem is with the low voltages present.
We use a contact enhancer to help the cable contacts.
F. CALIBRATION PROCEDURES
We go through a standard calibration procedure each night. After
the warm-room computer turns on the power at the dome, the dome
computers wait till sunset and calibrate the telescope. If clouds
aren't present, the dome shutter opens and the observatory waits
till a specific sun angle. At that time the telescope points to
the zenith and starts to take twilight flats for all filters. Bias
and then later darks are also taken. Anyone who has taken twilight
flat knows that timing is everything. Sky brightness changes
rapidly, so the 'window' for a successful calibration run is small.
The automated system just described always gets its flats unless it
Focusing the camera is not trivial. The mechanics are controlled
by a stepper motor with a light-interrupter for a zero-point. The
last focus position is stored in the startup file.
A suitable navigation star is chosen for focusing. The Full-Width-
Quarter-Max is determined for the current position. The current
position is then bracketed on both sides, production a chat of
positions and values. Finally, a curve is fitted to the data,
reveling the optimum focus. This is very repeatable. 'Quarter-
Max' is used rather than 'Half-Max' because it 'blows-up' faster
with out-of-focus images.
The focusing is repeated at intervals through the night.
G. DATA ANALYSIS
As can be seen by the bar chart of monthly observations, we are
current taking five to six hundred images per month. The actual
number depends on the weather and target. We can expect to be
collecting photons on the CCD for greater that 6 hours on a clear
All images, flats, darks and bias frames are in FITS format. The
images are flat fielded, with dark and bias subtracted at the dome
during the night. Photometry is done in town later using PCVISTA,
written by Michael Richmond. We would like to acquire a
workstation do use IRAF to analyze the data, and will be writing a
grant proposal soon.
Several of our current projects are analyzed 'off campus' at the
location of the principal investigator. We use an exabyte tape
drive to send these images through the mail. Images that are more
time-critical are loaded onto the internet and can be FTP'd by an
IV. FUTURE DIRECTIONS
The observatory software is very reliable after many years of
Our major goal at this point is to upgrade our optics. Our main
current limitations involve the optics and mount. Our newtonian
focus is difficult to balance, and leads to an image jitter in
certain parts of the sky. We also have a fair amount of
astigmatism in the mirror, making gausian fits to our photometry
difficult. We would also like to increase the aperture size to
expand our range of targets.
The optimal mirror would be a 28 inch F6 system. However, any high
quality mirror 24 inches or greater (but less than 1 meter) would
justify a new dome etc. We plan a new raised dome, to reduce ground
distortion. A direct contact drive to eliminate gear lash will
eliminate lash. We would consider a consortium, with sharing of
telescope time if a suitable mirror became available. The
combination of dark clear skies, proven automatic imaging software
and a new mirror and mount would lead to an even greater scientific
We are planning an addition to the World Wide Web homepage, which
will feature the current image (binned to 128x128 pixels). It will
also have information about the observatory and include a updated
file of the most recent telescope instructions. The homepage can
be reached at http://www.wnmu.edu.
We hope to upgrade our computer capability with a workstation.
This will add flexibility in data analysis. Although we were able
to get a good series of images on supernovae 1994d and 1994i, we
were unable to analyze the images because of the limitations of
PCVISTA. IRAF could have filled the bill but we can't run it on
our present hardware.
1. B. Neely and F. Treasure, "The Automatic Radio-Linked Telescope
(ARLT) at the NF/ Observatory", Remote Access Automatic Telescopes,
D. Hayes and R. Genet ed., Fairborn Press 1989.
2. B. Neely and F. Treasure, "Progress on the Automatic
Radio-Linked Telescope (ARLT) at the NF/ Observatory - A CCD
Primer", Advances on Robotic Telescopes, M. A. Seeds and John L.
Richards ed., Fairborn Press 1991.
3. B. Neely and D. Epand, "A Proposal for an ATIS Command Set
Extension for CCD Cameras", IAPPP Communications No. 45 p92-103
Sep.- Nov. 1991.
4. B. Neely, "CCD Photometry of Asteroid 16 Psyche", The Minor
Planet Bulletin, Vol. 19, Number 4 p28 Oct.- Nov. 1992.
5. B. Neely, "CCD Photometry of Asteroid 487 Venetia", The Minor
Planet Bulletin, Vol. 19 Number 4 p 31-32 Oct.- Nov. 1992.
6. A. W. Neely, "CCD Photometry of Asteroid 441 Bathilde", The
Minor Planet Bulletin, Vol. 20, Number 3 p 21-22 July - Sept. 1993.
7. A. W. Neely, "Pre-discovery photometry of 1993j", IAU circ.
5740, April 1, 1993.
8. A. Porter, A. W. Neely,"Reddening of 1993j", IAU circ. 5742,
April 2, 1993.
9. A. W. Neely, "Continued photometry on 1993j", IAU circ. 5847,
August 18, 1993.
10. A. W. Neely, Jim Janesick, " A CCD Anti-Blooming technique for
Use in Photometry" PASP 105: 1330-1333, 1993 Nov.
11. L.J. Boyd, A. W. Neely, et al "Automatic Telescope Instruction
Set 1993", IAPPP No 52, pp 23-81, Summer 1993.
12. A. W. Neely, "Flare of 3C279", IAU circ. 5911, December 20,
13. A. W. Neely, M. Harvanek, J. Stocke, Brightening of 3C279, IAU
circ. 5978, April 23, 1994.
14. E. Richmond, A. W. Neely, "CCD Photometry of 9 Metis", The
Minor Planet Bulletin, Vol. 21, Number 3 p 23-24 July - Sept. 1993.
15. E. Richmond, A. W. Neely, "CCD Photometry of 480 Hansa", The
Minor Planet Bulletin, Vol. 21, Number 4 p 37-38 Oct.- Dec. 1994.
16. A. W. Neely, "VRI Photometry of Supernova 1993j", IAPPP No. 56,
p448-55, Summer 1994.
17. A. W. Neely, "The ARLT (Automatic Radio-Linked Telescope); An Imaging Observatory, IAPPP No. 58,
p 51-59, Winter, 1995.
18 . Robert Brown, A. W. Neely, "CCD Photometry of 16 Psyche", The Minor Planet Bulletin.
19. S. J. Bus, S. Xu, R. P. Binzel, A. William Neely, Robert W.
Brown, "Rotationally Resolved Spectra of Asteroid 16 Psyche",
submitted to Icarus.
Rt. 15 Box 760
San Lorenzo, NM 88041