The DEdicated MONitor of EXotransits (DEMONEX) is a low cost, small aperture telescope assembled from commercially available parts.

It is a 0.5 meter (20 inch) Meade RCX400 located at the Winer Observatory in Sonoita AZ, and equipped with an Orion 80mm ED and ST402-ME as a guider, an FLI Precision Digital Focuser, an FLI 7 position CFW-5-7 filter wheel, and FLI Proline CCD3041. From data acquisition to reduction, it is fully automated through TheSky6, CCDSoft, TPoint, VBScripts, and IDL. While all transits are observed in the sloan z' band to reduce the effects of limb darkening, it has g'r'i'z'VRI and clear filters available for auxillary science.

DEMONEX Pictures: On Trailer | M42 | At Winer

DEMONEX Movies: Disassembly | Assembly | DEMONEX Fail


A transit occurs when a planet passes in front of its star, as seen from Earth. The pictures to the right illustrate what is happening, and why it is so difficult to detect an Earth-like planet around a Sun-like star. However, since these stars are so far away, we cannot resolve the planets themselves; the only thing we can see is the total light from the star and how it changes as the planet passes in front.

From the shape of the lightcurve, we can derive the mass and radius of the star, the radius and inclination of the planet, and how far the planet is from its star -- this information is unmatched with any other observational technique.

A "Hot Jupiter", HD189733b, transiting across its parent star (to scale). How earth would appear to a distant observer if it transited the Sun (relative sizes to scale).


  1. Improve on discovery light curves of known primary transits
    • So uncertainty in lightcurves dominated by stellar models
    • Better constrain planetary physics/composition
    • Search for Transit Timing Variations (TTVs)
    • Provide a homogeneous sample from which to compare planets
  2. Observe secondary transits
    • Measure the albedo of planets
    • Determine the atmospheric composition of exoplanets
    • Constrain the energy Budget
  3. Systematically search planets discovered via Radial Velocity for transits
  4. Follow up of KELT candidates
  5. Observe outside of expected transit window for additional transits

CCD Characteristics & Parameters

Focuser and Filter Wheel

Because adjusting the focus from the corrector plate will introduce systematic flat field errors, we've purchased an FLI Precision Digital Focuser. It will be adjusted automatically according to the ambient temperature based on a lookup table.

Our FLI CFW-5-7 filter wheel has 7 positions, populated with g'r'i'z'VRI filters. Alternatively, a clear filter is available. To the right is the combined throughput of g'r'i'z with the CCD QE.


Observing Efficiency

Observable transits from Winer Observatory from 1/1/2008 to 12/31/2010. Shorter tick marks indicate a secondary transit. Observable is defined as less than 2.5 airmasses with the sun less than -18 degrees below the horizon, and 15 degrees from the moon during the entire duration of the transit.

Fraction of nights at Winer that have an observable transit as of February 2008, smoothed over 90 days. Candidates are radial velocity detected planets that could be observed to transit. The rollover image is the same plot, but only using the planets known as of May 2007. This gives you an idea of how rapidly this field is growing.

Documentation & Information

Current Status

Set up and working at Winer Observatory.

Last revised: May 10, 2008 [jde/osu]