Comments

Mid-transit times exhibit a sinusoidal variation with a peak-to-peak amplitude of 2.02 +/- 0.63 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 astronomer Burke et al (2010) have a preprint (http://fr.arxiv.org/abs/1004.4252) 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 = 3887.74733 & 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 1.28 +/- 0.39 minutes (based on chi-square procedures). This is a 3.3-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

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.

100622-XO1-M14(i')-pro  

100618-XO1-M14(cbb)-sys  

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.

9927GBL

9818SG22

9814SG2

9512NWP

9714LC2

9714WPK

9612SG21

9608SG21

9604AA2

9531GJ2

9527GJ2

9524GBL1

9520NWP

9516GBL

9512GBL

9508GBL

9430GBL

9318GJ2

9302GBL1

9226GBL1

8630mndz

8630srdc

8615roeV

8611HD2

8611roeV

8607futR

8607futV

8607futB

8603gary

8603futR

8530futR
 

8413haar 


8405gary  High air mass ruined the early data and clouds affected the post-egress data.

8328gary 
   

8109gary

 
7921gary  Wind, clouds and lightning degraded data & forced early closure.

7704futR 
 

7506greg 

7424gary

 

7216gary   

6826HVP1

6624OJ2

6617vanm 

6612OJ2

6613vanm 

6601futV
 


6601futR

6601gary

6424heal  Junk Bond Observatory 32-inch allowed B-band observing. Depth was greater, as expected.

6406vanR  

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).

5712vanC

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

More coming

6528holz

6520holR (this data downloaded from NStED)

Out-of-Transit (OOT) Light Curves

8701gary

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.
 
 

All-Sky Photometry

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).

Finder Charts

Detailed description of Spring, 2006 observations of XO-1

References

McCullough et al, 2006 link
Wilson et al, 2006 link
Machalek et al, 2008 link

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