HD 189733 transit

On June 11 (UT) I was in Arizona and used a 3" refractor mounted on my 18" remote telescope in New Mexico Skies to try to get the exoplanet transit of HD 189733 near M27.

I am glad to report that the observation was successfully and both the ingress and egress was definitely detected and recorded. But there was a very interesting observation.

When planning the observation, I visited www.transitsearch.org for HD 189733's transit window timing (http://www.ucolick.org/~laugh/HD189733_b.transits.txt). The mid point should be around JD 2453897.89 or June 11 09:18 UT.

As a double check, I visited Beglium amateur Tonny Vanmunster 's web page. Ron Bissinger (California) had observed HD 189733b transit successfully in 2005 Oct. 10 and recorded the transit midpoint at JD 2453653.79 <http://users.skynet.be/fa079980/non_cv_2005
/images/exoplanet_HD189733_bissinger.gif) >

Since the period of HD 189733b was calculated to be 2.219 d (+/- 0.0005). My observation happened to be exactly 110 cycles after Ron Bissinger's Oct. 10, 2005 detection.

The math is as below:

JD 2453653.79 + 2.219 * 110 = JD 2453897.88, which agree with the prediction time given by www.transitsearch.org to within 15 minutes!

So I schedulled my observation to begin exactly 1 hr before transit and 1 hr after. The fact that I almost have missed the ingress really surprised me. There are two conclusions:

1. The actual period is a bit shorter than the stated 2.219d obtained by radial velocity calculation. It should be more like 2.2186d [ (2453897.84-2453653.79) / 110 ]

2. If such a well known exoplanet's transit center time could be off by 1 hr after just 110 cycles. Imagine how much it could be off for other exoplanets candidates like HD 188753 which has no previous detection? I won't be surprised that it could be off by as much as 5, 6 hrs.