Hereford Arizona Observatory (HAO)

HAO#2, illuminated by a full moon.
Links Internal to this Web Page
    Tour of HAO
    Hardware Specifications
    Filter Passbands
    Extinction (broadband spectrum)
    System Throughput for All Bands
    Flat Field Performance
    Horizon
    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 south-south-west.

 
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 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.

Hardware Specifications

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 77,000 electrons.
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.

Extinction

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 bands.

 

 

System Throughput 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 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.

Horizon


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 Mexican border.

 



 
Note that a street name has been changed from Janice to "Edward V St." 

  
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
 
All-sky procedure  
  Astrophotos  
  Amateur Exoplanet Archive (AXA)  
  Exoplanet Observing for Amateurs, book by Bruce L. Gary (free PDF download)
  Resume

WebMaster: B. Gary.  This site opened:  2009.06.14 Last Update:  2013.11.26.