XO-1

XO-1
AXA Light Curves & Finder Charts & All-Sky Photometry Results
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    Comments
    Basic data
    LC only (not included in plots)
    TTV
    Transit Table & Parameter Plots
    Transit LCs - Amateur
    Transit LCs - Professional
    OOT LCs
    All-sky photometry
    Finder images
    Refrences

Comments

Mid-transit times exhibit a sinusoidal variation with a peak-to-peak amplitude of 2.20 +/- 0.61 minutes. If this is real it would imply the presence of another exoplanet in the system, XO-1c. Since the period of these variations is close to a year (339 days) no one will believe this "signal" until it is confirmed by an independent analysis. One-year "signals" in astronomy are notorious for being wrong! I can't see how my JD to HJD for this object could be wrong when no other exoplanet shows a one-year sinusoidal variation.

Professional astronomers like to use only professionally observed data, which means their coverage is limited to only a few days. This might be a handicap in concluding that no TTV variations are present.

Basic data - Updated 2009.08.16

    RA = 16:02:11.6, Decl = +28:10:11
    Season = May 26
    B = 11.85 ± 0.025, V = 11.19 ± 0.035, Rc = 10.81 ± 0.030, Ic = 10.43 ± 0.040, B-V = 0.66 ± 0.05 (B. Gary, all-sky)
    HJDo = 3808.9170 & P = 3.941534 day (discovery paper)
    HJDo = 3887.74679 & P = 3.941534 (27) day (Schneider listing in Extrasolar Planets Encyclopaedia, based on Wilson et al, 2006)
    HJDo = 3887.74733 & P = 3.94150279 (??) day (AXA sinusoidal data fit, below)
    Depth = 23.21 ± 0.15 mmag (mostly BVRIC-band)
    Length = 2.910 ± 0.015 hr (mostly BVRIC-band)
    Fp (fraction of time in partial transit) = 0.26 ± 0.01
    F2 (relative depth at contact #2) = 0.80 ± 0.02

TTV - Updated 2009.08.16

Plot of all mid-transit measurements, amateur and professional, versus expected HJD using the ephemeris given in the upper-left had corner. The sinusoidal model has been fit to the data using chi-squared minimization. The peak-to-peak amplitude is 2.20 +/- 0.61 minutes (based on chi-square procedures). This is a 3.6-sigma "detection" - meaning that it verges on being significant. (Note: data that depart from the fit by more than 3.1 times the SE are rejected; this is based on the expectation of Gaussian error function and when only 81 points are present there is only a 15% probability that a true datum will be rejected when using this outlier rejection criterion.)

This TTV plot is suggestive of a second planet in a resonant orbit that perturbs XO-1b's orbital motion. I am reluctant to interpret this data as constituting a "second planet" detection because my "eyeball" doesn't believe it. The amplitude is 3.6 times its formal SE. This illustrates what a search for another exoplanet would involve. In fact, the main message of this plot is that amateur data must be in groups of 6 to10 at the approximate same date in order for the median value of the group to be "useful." Every group has outliers, and the outliers have undue influence when they are not accompanied by other measurements at about the same date to reveal that they are outliers. It's too bad that observations in 2007 weren't coordinated with this in mind. If only groups of data are considered there are just 3 TTV values in this plot (one in 2006 and two in 2008) that can be relied upon for a TTV anomaly search. Another "problem" with the sinusoid solution in this plot is that the preiodicity is very close to one year. I'm confident that the JD to HJD conversion was done correctly, nevertheless, it is always prudent to be wary of any anomaly with a one year periodicity. In 2009 the sinusoidal model will be put to a definitive test I hope. (Symbol descriptions are available from the webmaster.)

Transit Parameters - Updated 2009.08.16