June 6, 2007
From AAVSO Alert Notice 350:
Dr. Greg Laughlin (UC Santa Cruz/Lick Observatory & Transitsearch.org) has requested help in observing GJ 436 to look for transits of previously detected and undetected extrasolar planets.
Geir Klingenberg (KGE) observed a transit on May 31, 2007.Full report and details here (updated!) [broken link] . This observation has been confirmed by Dr. Laughlin.
Charts & Additional Info:
Since we are looking for extremely small transit depths, please use ensemble techniques if your software permits. Use the set of 8 comparison stars for the field as your ensemble.
If you use the standard comparison and check scheme, the best stars look like two stars in the grouping just NNW of the target:
V V-B V-Rc Rc-Ic V-Ic
These are about as close in color as possible to the target, but there will still be systematic differences between observers if data is not transformed. Beware that the 11.370 star has a fainter companion about 15arcsec to the NW - try to use an aperture small enough to exclude this companion.
GJ436 is near 11th magnitude, so exposures will be relatively long in comparison to some of the other transiting targets. Scintillation will not be as important. If you can do two filters, it is strongly advised to do so in order that your data can be transformed. Choosing B and V would be your best choice, as B is less influenced by molecular lines and, since GJ436 is fainter in the blue, will enable longer exposures so that scintillation is even less important. Remember that exoplanet transits are 'grey', meaning there is little advantage for any specific bandpass in maximizing transit depth. Instead, use filters to: standardize your observations; cut down the amount of light so that you can use longer exposures; and to remove the influence of spectral features like molecular absorption lines that will plague unfiltered measurements.
We will provide instructions as to how to determine your transformation coefficients in the near future.
Our first data set, from Bill Goff (GFB)
We will post light curves as data comes in.