Hereford Arizona Observatory (HAO)
Tour of HAO
HAO#2, illuminated by a full moon.
Links Internal to this Web Page
Extinction (broadband spectrum)
for All Bands
Flat Field Performance
Clear Sky Statistics
Directions to HAO
Tour of HAO
The HAO consists of two telescopes in two separate observatory
structures: HAO#1 and HAO#2. But let's start the tour with this south-looking
view of my house from near the driveway entrance.
Notice HAO#1 behind and to the left of my house. Looking
This view, looking west, shows both dome observatories.
HAO#1 (foreground) houses the Celestron 11-inch (CPC-1100) telescope
and HAO#2 houses the Meade 14-inch (LX-200GPS). Both are controlled using
Both domes are 8-foot diameter ExploraDomes. They are
motorized for azimuth movement only (no shutter motors). This picture
was taken before completion of HAO#2, and shows one of the two trenches
open with conduit in position. One conduit is for AC power and another
is for control cables. The left end of the house is my office (control
Looking inside HAO#2 which houses a Meade 14-inch LX200GPS on an equatorial
wedge. Note the sophisticated RA balance tool, secured by duct tape.
Dome flats are made by closing the dome shutter and pointing the telescope
to zenith for a view of a painted area on the inside of the moveable dome
shutter. When observing this white area is not viewable.
The optical backend consists of a wireless focuser, focal reducer
lens, a 10-position filter wheel and a ST-10XME CCD. The dome material
is polyethelene, which is transparent to the wireless focuser frequency.
More information is given in the "Hardware Specifications" section.
The HAO#2 dome is moved in azimuth by a motor/gear that
I modified to achieve 4 times better azimuth resolution. The original
design used a shaft painted white and black (total of 2 sectors) that
were viewed by an optical sensor; I moved the optical senor for a down-looking
view of an 8 sector black and white pattern. The quantization interval
is 4 degrees, and this provides reliable slaving of the dome to the telescope
azimuth with no occasions of dome slit obstruction.
HAO#1 houses a Celestron 11-inch CPC-1100 telescope. It employs a wireless
focuser, focal reducer, a 5-slot filter wheel and SBIG ST-8XE CCD. Note
the sophisticated Dec balance weight, held in place by bungie cord.
The control room has dedicated computers for the M14 (right)
and C11 (left). Each computer commands the telescope, focuser, CCD,
etc using serial and USB cables or wireless units. Communication with
the CCD cameras employs 100-foot ethernet cables and pairs of USB boosters
(Icron). Each computer has a dual DVI video card for display on two LCD
monitors. In this view both telescopes are observing the same object,
as seen by their respective left panel displays. The right displays are
usually used for display of TheSky/Six which assists in positioning the
main chip FOV so that the autoguider chip has a sufficiently bright guide
star. The M14 station includes a wireless audio/video camera display; this
provides audible and visual feedback of M14 movements.
M14 (in HAO#2)
Meade LX200 GPS, a 14-inch Schmidt-Cassegrain telescope
on an equatorial mount (Meade Super Wedge).
CCD: SBIG ST-10XME (KAF 3200E main chip, TC-237 autoguide
chip next to main chip). The main chip has a 2184 x 1472 array of 6.8-micron
pixels (physical size is 14.9 x 10.0 mm). Gain is 1.3 electrons/ADU
(unbinned). Read noise = 8.8 photoelectrons. Full well capacity is
External 10-position filter wheel for 1.25-inch threaded filters.
The CFW contains the following filters: B (Astrodon), V (Schuler), Rc
(Schuler), g' (Astrodon), r' (Astrodon), i' (Astrodon), z' (Astrodon), NIR
(Astrodon) and CBB (clear with blue-blocking, Astrodon).
FOV with Optec 0.5x focal reducer: 26.9 x 18.1 'arc. Image
scale = 0.74 "arc/pixel (unbinned). EFL = 1896 mm, f/5.33.
C11 (in HAO#1)
Celestron CPC 1100, a 11-inch Schmidt-Cassegrain telescope
on an equatorial mount (wedge).
CCD: SBIG ST-8XE (KAF 1602E main chip, TC-237A autoguide
chip next to main chip). The main chip has a 1530 x 1024 array of 9
micron pixels (physical size is 13.8 x 9.2 mm). Gain is 2.7 electrons/ADU
(measured). Full well capacity is 100,000 electrons.
External filter wheel: 5-position, 1.25-inch threaded filters.
At the present time the filters in use are CCB (clear with blue-blocking,
Schuler), NIR (near infra-red, turnon at 720 nm), V, Rc and Ic (Custom
Scientific Johnson-Cousin photometric filters).
FOV: 21.9 x 14.6 'arc. Image scale = 0.86 "arc/pixel. EFL
= 2158 mm, f/9.32 (with a focal reducer ahead of the CFW).
Filter Passband Shapes
Here are some useful filter passband shape plots.
SBIG's "pretty picture" B, G and R filter passbands.
My site altitude is 4670 feet, which determines the average Rayleigh scattering
spectrum. The other extinction components, which are weakly or not correlated
with altitude, are aerosols, water vapor and (stratospheric) ozone. Here
are some atmospheric extinction measurements with model fits for a sampling
of seasons, showing the range of variability of zenith extinction at the various
System Throughput for
The "counts" produced by a star (also called ADU intensity) depends upon
more than just exposure time and telescope aperture; it is also affected
by the star's spectral energy distribution (SED), CCD response (relaive Quantum
Efficiency), the filter transmission function, atmospheric extinction (and
air mass) and telescope optics (corrector plate and focal reducer transmissions).
In planning an observing session it is helpful to know the expected SNR
of a particular star for each of the filter bands. The following figure
shows expected SNR versus filter band for my Meade 14-inch telescope system
(M14) for the following assumptions: exposure time = 15 seconds, air
mass = 1.3 (typical atmospheric extinction), V-mag = 12.0, B-V = 0.2 (blue
star) and 1.4 (red star).
If the target is a red star the highest SNR is acheved by using a r'-band
filter. If it's blue, the g' filter is best. Notice the low throughout for
the u'-band filter; for a red and blue stars the u'-band SNRs, relative
to the V-band SNR, are 1/550 and 1/26. In other words, observing with a
u'-filter incurs a penalty that ranges from 3.5 to 6.9 magnitudes (for blue
and red stars).
Flat Field Performance
Since my observing involves bands that extend to the shjort and ong wavelength
extremes, u' and z', it is important to use a focal reducer (FR) that has
an anti-reflection coating that is wide-band. The Optec 0.5x FR has multi-layers
to achieve this purpose, and it also is designed to correct for optical
imperfections in the model of Meade telescope that I use (LX200GPS, sold
in 2004). The following image shows flat fields for three conficurations:
top row is without a FR, middle row is with a Celestron f/0.63 FR (showing
presence of reflections that are worst at u' and z'), bottom row is with
the Optec 0.5x FR (showing minimal to no reflections):
Why does it matter to minimize reflections in flat fields? Because reflections
add a component to the flat field that does not relate to the losses of
starlight at the CCD pixel location. During a long observing session small
pointing drifts require correction for each star's transmission loss corresponding
to each pixel location, and if an incorrect flat field is used the calibrated
star flux will be in error, causing ratios of star fluxes to exhibit errors
that vary during the observing session. If absolutely no drift occurred,
and no image rotation was present, even though star flux ratios would have
errors they would remain fixed during the observing session and would therefore
not contribute to a target's light curve shape. However, for an all-sky
observing session no errors in star flux ratios can be tolerated.
Looking south at mountains that are at 4.0 deg elevation on
the meridian (vertical red line). The star Canopus (declination -52.7
deg) is transiting. Stars at declination -53 deg can be observed for
more than an hour either side of transit, although the air mass would
be ~ 10 for most of that time. Observations with the NIR filter
would be subject to an extinction of 0.75 magnitude at this air mass.
Mexico is 7 miles in this direction, so this sky is quite dark.
Clear Sky Statistics
There's a "clear sky band" in the USA extending from Yuma, AZ toward northern
California. Although Yuma is the "sunshine city" it is also a low altitude
and hot place. The small black cross east of Yuma is Hereford, at an altitude
of 4670 feet, which accounts for the almost ideal weather. Summer afternoon's
are ~ 7 F cooler compared with Tucson, and the winter nights are below freezing
less than half the time. We get snow once or twice each winter and it usually
melts in a few hours.
The following graph summarizes my first year living in Hereford, AZ. Note
that we have a monsoon that typically starts July 7 and lasts until mid-September.
We have a second "rainy season" (very mild) in February. May and June are
the clearest months.
"Possible starshine" is defined as nightime conditions that are either
clear or scattered clouds (<10% coverage).
Directions to HAO
The HAO is located at West Longitude 110:14:16 and North
Latitude +31:27:08, at an altitude of 4670 feet. As the following
map shows the HAO is ~80 miles southeast of Tucson, 7 miles from the
Note that a street name has been changed from Janice to "Edward
This picture was taken (for Google) just after a wind-shipped wildfire went
through my neighborhood, buring one of my fields (lower-center) and burning
parts of properties on all four sides of me. Luckily, my house and observatories
Related External Links
Amateur Exoplanet Archive
for Amateurs, book by Bruce L. Gary (free PDF download)
Gary. This site opened: 2009.06.14. Last Update: 2012.03.17.