Mid-transit times exhibit a sinusoidal variation with a
peak-to-peak amplitude of 1.5 +/- 0.7 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 (350 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. I currently don't believe there's
evidence in this data set for supporting the presence of a real TTV.
Professional astronomer Burke et al (2010) have a preprint
that doesn't find convincing evidence for a sinusoidal variation.
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 = 3887.7474 & P = 3.9415038 (72) day (AXA sinusoidal data fit, below, v20110312)
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 1.54 +/- 0.72 minutes (based on chi-square procedures). This is a 2.1-sigma "detection" - meaning that it probably is not significant.
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
Light Curves by Amateurs
100622-xo1-C11(Ic)-pro Note the correlated "brightening" above the model fit at 5.5 UT for simultaneously observed LCs using two telescopes.
Clouds ruined this observing session.
Many images had XO-1 saturated so the depth is uncertain and the data are noisy.
0404GBL Depth is lower than the others because that's the case for i'-band compared with shorter wavelengths. Some autoguiding problems made for noisy data early on.
8405gary High air mass ruined the early data and clouds affected the post-egress data.
7921gary Wind, clouds and lightning degraded data & forced early closure.
6424heal Junk Bond Observatory 32-inch allowed B-band observing. Depth was greater, as expected.
6406vanV Depth sortof deep. "Low frequency" variations.
6314gary This LC was used to establish HJDo for the discovery paper ephemeris.
6306gary 2006.03.06. UT mid ~12.88 (i.e., 11.40 + 1.48).
5705gary 2005.07.05. UT mid ~03.74 +/- 0.10.
5701gary There were lots of problems with this data: clouds, poor tracking,too-short exposure times, etc.
Light Curves - Professional
6520holR (this data downloaded from NStED)
Out-of-Transit (OOT) Light
In spite of cirrus clouds, with losses up to ~1/2 magnitude, the LC is featureless at the 1 mmag level.
I have a couple dozen OOT observing sessions from May, 2006 that I'll add to this section when time permits.
Estimated SEs are 0.025, 0.035, 0.030, 0.040 magnitude,
based on RMS residuals of fit to three
Landolt star regions (N = 29, 35, 18, 14).
Note: The star to the upper-right of star #3 in the above
image is continuosuly variable ("contact binary"). Don't use it for reference.
RA/DE = 16:02:07.7,+28:14:45 (GSC 2041:1416). Two other stars to the
upper-right of this FOV are also variables (see next image).
Warning: Stars #3, #10 and #14 are variables.
Detailed description of Spring, 2006 observations of XO-1
McCullough et al, 2006 link
Wilson et al, 2006 link
Machalek et al, 2008 link
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