XO-1b was already in transit at the start of observations. ( Predicted ingress @ 01:33 UT reported at transitsearch.org ). Observations were commenced at 21:34 local time 20060608 (01:34 UT 20060609). Atmospheric conditions were hazy with occasional major cloud. Lunar phase was 89%. The dome and telescope dewshield mitigated the adverse effects of indirect moonlight effectively. Thin clouds impaired early observations as well as post egress beyond 4.8hrs UT. The blue dots represent individual 30 sec data points. The average sigma for the data is 0.0057.Obvious outliers were found to have a direct correlation with passing clouds and noticeable degradation of the photometry.10 individual data points were averaged to produce the larger solid red dots corresponding to a time interval of roughly 7.5 min for each datum. Predicted egress was at 04:43 as listed at transitsearch.org. My estimate is in the neighborhood of ~04:36UT based on rough analysis of my light curve. The observatory pc clock is updated once/minute from the USNO's time server and I am sure that the time of mid exposure is being recorded properly in the image fits header. Perhaps another body is perturbing XO-1b or maybe the times listed at transitsearch are off ? Bruce Gary of Hereford, AZ notes that the published transitsearch times for mid transit are offset 6 minutes from the schedule he derived from the data listed in table 3 of the McCullough, et al article, A Transiting Planet of a Sun-like Star . Using this info mid transit is ~ 03:02UT instead of 03:08. Note the asymmetry in the curve, namely that the maximum depth appears to occur just after mid transit.Why?
Details:
Observations were conducted from my suburban backyard observatory located in Knoxville, TN. Instrumentation used was a 0.36m Meade SCT with an Optec TCF-s focuser mounted on an Astrophysics AP1200 GTO mount with an SBIG ST10XME/CFW-8a CCD binned 2x2. An Agos universal focal reducer was used inline producing an effective focal length of 2261mm (f/6.37) with the current spacing. The resulting image scale is 1.24 arcsec/pixel with a fov of 15.2 x 22.5 arcmin. CCD operating temp was set to -20C, operating with water cooling assist. 30sec exposures were utilized with a Schuler Rs photometric filter. The scope was autofocused with Focusmax then the temperature compensation feature was enabled in Maxim, automatically maintaining correct focus position for the Optec TCF-s for the duration of the observing run. The mount was allowed to track the object past the meridian so a flip was not required. The exposures were autoguided with the ST10 camera's self guiding TC-237 ccd. This allowed the star centroids to be maintained to within 1.5 pixels over the length of the observing run. Calibration flats were acquired at dusk. Dark and Bias frames were acquired at a later time at the same operating temp and integration time as light frames. Master calibration frames consist of 10 flats median combined, 40 bias median combined, and 40 darks sigma clipped combined. Image data was acquired unattended with observatory automation via ACP v 4.2. Maxim DL/CCD 4.53 was utilized for data acquistion, reduction and ensemle differential photometry. To aid in this task I used R band comp star magnitudes determined by Bruce Gary. These are listed on his excellent XO-1 webpage. These results from Maxim were found to be consistent with the results above generated with AIP4Win version 2. Data manipulation and charting were performed with MS Excel 2003.This represents my most successful observation of an XO-1 transit to date. I am pleasantly surprised to find that even in the presence of a bright moon and hazy, humid conditions that I can still produce differential photometry with the required precision to detect a planetary body orbiting another star ~ 400LY away. Just think this transit occurred during the time that Galileo first made his observations with a telescope!
mlfleenor"at"charter.net