Observing Exoplanet Transits with Limited Amateur Equipment

In May 2007, after obtaining a DMK firewire camera, I had the idea to observe exoplanet transits with my limited equipment (see below). After reading papers, some test and calculations, I came to the conclusion that this could indeed be possible with the brightest transit stars and the deepest minima. I chose HD 189733 for this purpose and developed IDL code for the light curve analysis. My first observation was on 2007-06-07. And it was a success! I could not quite believe it - but subsequent observations confirmed the reliability of my methodology. Unfortunately, the weather here prevents me from observing exoplanet transits more often...

This is the equiment used:

  • Takahashi FS 60C
  • DMK 31AF03.AS

So all it took was a 6 cm refractor and an uncooled 8-bit camera. I even did not have any guide control. But, some sophisticated data analysis revealed the dimming of the host star HD 189733.

For details, have a look at this PDF of a presentation I gave at the ESOP 2008 conference.

Informative publications on exoplanets

Gary, B., 2007: "Exoplanet observing for Amateurs", e-book. Gives a good introduction into the matter. However, does not consider the possibility of using equipment as limited as mine.

Perryman, M.A.C., 2000: "Review: Extra-Solar Planets". Rep. Prog. Phys., 63, 1209-1272. A nice overview on exoplanets in general, and possible advanced detection techniques.

Mandel, K. and E. Agol, 2002: "Analytic Light Curves for Planetary Transit Searches". Astrophys. J. , 580, L171-L175. A more technical, though, highly interesting paper on transit light curve models.

Pál, A., 2008: "Properties of analytic transit light curve models". Mon. Not. R. Astron. Soc. 390, 1, 281-288. Another technical paper describing advantages of using the Levenberg-Marquardt algorithm for transit light curve fitting.

Exoplanet databases

The Extrasolar Planets Encyclopaedia. An interactive catalog.

Exoplanet transit time predictions provided by Transitsearch.

 

IDL code for transit light curve fitting

Transit light curve modeling by Eric Agol (also in Python and Fortran).

Levenberg-Marquardt fitting algorithm by Craig Marquardt.

My Observations of HD 189733b Transits

The times given are all in UTC and mark the predicted start, center, and end of the transit.

2007-06-07/08

Predicted transit times: 22:20, 23:15, 00:10 UTC.

The weather did not seem to be favourable first, as many clouds moved in in the evening. So I went to a beer garden with a friend. However, it started to clear up later and there was too little time left to set up all the equipment and catch the transit from it's beginning. So when, finally, everything was ready it was already 23:07 UTC - almost center transit.

The next day I started analysing the data and it quickly became clear that it had all worked! I was so excited! The night was very warm with temperatures between +18 °C and +20 °C. This caused a lot of noise on the uncooled sensor and resulted in large scatter of the data points.

20070607

2007-10-16

Predicted transit times: 19:50, 20:45, 21:40 UTC.

Only after a long wait came the next opportunity to record a transit of HD 189733b.

I had everything going in time for the beginning of the transit. However, from time to time thin clouds moved through... I still continued and obtained quite a nice light curve in the end. The temperature was around +14 °C and the noise much reduced compared to my first transit in June.

The thick black dots are five minute averages, while the plus signs mark the original data. The solid line (upper plot) is the fitted transit light curve using the Levenberg-Marquardt algorithm and Eric Agol's transit light curve models.

 20071016

2008-09-26/27

Predicted transit times: 22:11, 23:06, 00:01 UTC.

One year later the next chance to record a transit opened up. Only, thin cirrus clouds moved through. This time, however, I performed the observation from a darker site about 30 km south of Hannover and not from the suburb where I live. The night was colder than during the previous observations (+4 °C to +6 °C). This helped reducing the sensor noise while the cirrus clouds ultimately caused a larger scatter of the data points.

20080926

2008-10-25

Predicted transit times: 18:22, 19:17, 20:12 UTC.

Only about a monthafter my last observation, the next opportunity occurred. However, I had to drive more than 200 km to a location near Bad Hersfeld to have clear skies.

I was able to record a complete transit, again. So the drive was worth it. Again, temperature was around +6 °C.

20081025