Hereford Arizona Observatory
Tour of HAO
HAO#2, illuminated by a full moon.
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Throughput for All Bands
Capability with Meade 14" HyperStar (magnitude &
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 buried cables.
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 room).
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
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
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,
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 filter
for All Bands
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 short and long
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 configurations: 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):
Flat fields with no focal reducer (top row), a
standard focal reducer (middle row) and a higher quality Optec
focal reducer designed for use with this model telescope (and
having multi-layer anti-reflection lens coatings).
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.
Under average conditions my Meade 14-inch telescope in prime focus
configuration with a HyperStar and SBIG ST-10XME/CFW10 (31%
blockage) can be used to obtain useful measurements described by the
Magnitude/wavelength observation capabilities using the
Meade 14" telescope in prime focus configuration (HyperStar, SBIG
The SA-100 is a transmission grating with ~ 55% of light in the
first-order spectrum (25% in the zero-order straight-through path).
It has an advertized resolution of 1% (hence the "100" in the
product name). Anything brighter than the SA-100 curve can be
"measured;" thus, bright asteroids (e.g., Ceres and Vesta) can
produce spectra extending from ~ 380 nm to 1050 nm, whereas fainter
asteroids will have a more limited wavelength coverage. The 20.7
V-mag point is for 2 or 3 hours of median combined images,
unfiltered (effective wavelength ~ 650 nm). The "LC (unfiltered)"
symbol corresponds to seeing the asteroid image in each 30-second
exposure; this allows easy "moving target" photometry using MaxIm
DL. An extra ~0.3 magnitude is achievable if the asteroid is moving
slow enough to permit combining several images in order to "see" the
asteroid at the beginning and end of the observing session for
specifying "moving target" photometry.
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 Mexican
Note that a street name has been changed from Janice to "Edward V
Google Earth image of my property, showing two domes. HAO#2 is the
main telescope (14-inch Meade); the other dome is my "backup"
observatory (because Meade's need frequent repairs), containing a
reliable Celestron 11-inch telescope.
Related External Links
Observing for Amateurs, book by Bruce L. Gary (free PDF
WebMaster: B. Gary. This site opened: 2009.06.14. Last Update: 2014.09.27. BGary web sites