We report on observations of transit events of the transiting planets XO-1b and TrES-1 with the AIU Jena telescope in Großschwabhausen. Based on our (IR) photometry (in March 2007) and available transit timings (SuperWASP, XO and TLC-project-data) we improved the orbital period of XO-1b (P = 3.941497 ± 0.000006) and TrES-1 (P = 3.0300737 ± 0.000006), respectively. The new ephemeris for the both systems are presente

Broeg, C.

Eisenbeiss, T.

Hohle, M.

Koeltzsch, A.

Koppenhoefer, J.

Mugrauer, M.

Neuhäuser, R.

Raetz, S.

Roell, T.

Schmidt, T. O. B.

Seifahrt, A.

Vaňko, M.

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Transiting PlanetsProceedings IAU Symposium No. 253, 2008Fre´de´ric Pont, Dimitar Sasselov & Matthews Holman, eds.c© 2009 International Astronomical Uniondoi:10.1017/S1743921308026872Transit observation at the observatory inGroßschwabhausen: XO-1b and TrES-1M. Vanˇko1, S. Raetz1, M. Mugrauer1, T. O. B. Schmidt1, T. Roell1,T. Eisenbeiss1, M. Hohle1, A. Seifahrt1,2, A. Koeltzsch1, C. Broeg1,3,J. Koppenhoefer4 and R. Neuha¨user11Astrophysikalisches Institute und Universita¨ts-Sternwarte,Schillerga¨ßchen 2-3, 07745 Jena, Germanyemail: vanko@astro.uni-jena.de2 Institut fu¨r Astrophysik, Georg-August-Universita¨t,Friedrich-Hund-Platz 1, 37077, Go¨ttingen, Germany3Space Research and Planetary Sciences, Physikalishes Institute, University of Bern,Sidlerstraße 5, 3012 Bern, Switzerland4Max-Planck Institute of Extraterrestrial Physics,Giessenbachstraße, 85748 Garching, GermanyAbstract. We report on observations of transit events of the transiting planets XO-1b and TrES-1 with the AIU Jena telescope in Großschwabhausen. Based on our (IR) photometry (in March2007) and available transit timings (SuperWASP, XO and TLC-project-data) we improved theorbital period of XO-1b (P = 3.941497 ± 0.000006 ) and TrES-1 (P = 3.0300737 ± 0.000006),respectively. The new ephemeris for the both systems are presented.1. IntroductionIn this paper we present observations of two known transiting planets, XO-1b andTrES- 1. The observations were carried out with the AIU Jena telescope at the observa-tory in Großschwabhausen on March 2007. We have used the 25cm Cassegrain telescopeinstalled at the tube of the 0.9m telescope. The R and I-band images were obtained withthe Cassegrain-Telescope-Kamera (CTK) a CCD-camera with 37.7’x37.7’ ﬁeld of viewand 1024x1024 pixels. (Mugrauer et al. (2008), in preperation).For both systems, XO-1b and TrES-1, we have observed one transit event in I-band andR-band, respectively. The data were reduced by standard IRAF procedures. For dataanalysis we have used IRAF task chphot, written by Ch. Broeg and based on the stan-dard IRAF routine phot (Broeg et al. 2005). We have then corrected data from systematiceﬀects using the “Sys-Rem” detrending algorithm (Tamuz et al. (2005)) as implementedby Johannes Koppenhoefer. The main aim of our investigation is to improve orbital pe-riods of these transiting planets as well as to discuss possible changes of orbital periodsbased on their O-C diagrams. For this purpose we collected all available transit times foreach transiting system using SuperWASP, XO and TLC-project data.2. XO-1bWe have observed the transit of the exoplanet XO-1b on March 11th 2007. Accordingto the ephemeris provided by McCullough et al. (2006): Tc(E) = (2453808.9170 + E ·3.941534)d, this transit corresponds to epoch 92. During observation we have performed161 I-band exposures. Our mean photometric accuracy is 0.008 mag. Due to the variableobservational conditions, the photometric accuracy at the beginning of the night was a440at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921308026872Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 30 May 2017 at 17:18:38, subject to the Cambridge Core terms of use, availableTransit observation of XO-1b and TrES-1 441bit worse then at the end. For data analysis we have used aperture photometry on allavailable images. To get as good as possible transiting light curve, we have used only themost stable comparison stars in the ﬁeld. After the ﬁrst run of the artiﬁcial-comparison-star-algorithm we have rejected 168 comparison stars. After repetition of the algorithmFigure 1. (left plot) Relative I-band photometry of XO-1b. (right plot) Transit timing residualsfor XO-1b. The dashed line shows the ephemeris given by McCullough et al. (2006). The bestﬁt (dotted line) is representing by the updated ephemeris.we have rejected other faint stars with low S/N and stars suspected of variability. Withthe remaining 28 most stable stars we calculated the artiﬁcial CS. In the resulting lightcurves we have used Sys-Rem. The algorithm works without any prior knowledge of theeﬀects. The number of eﬀects that should be removed from the light curves is selectableand can be set as a parameter. Using Sys-Rem with two eﬀects the transit itself isdisappearing from the light curve. Thus we have used only one eﬀect.To determine the time of the center transit we have used the ﬁt based on the systemparameters of Holman et al. (2006). With the help of the χ2-test, we have determinedthe time of the midtransit as follows: Tc(HJD) = (2454171.53188± 0.00130)d.The ﬁnal time series is plotted in Fig. 1 (left plot). Except of our transit, observedat the observatory in Großschwabhausen, we found 16 other transit times for XO-1bin the literature. We have used the ephemeris of McCullough et al. (2006) to compute“Observed minus Calculated” (O-C) residuals for all 17 transit times. Figure 1 (rightplot) shows the diﬀerences between the oberved and predicted times of midtransit as afunction of epoch. The dashed line represents the ephemeris given by McCullough et al.(2006). We found a negative trend in this (O-C) diagram. For an exact determination ofthe orbital period we set the transit time with the smallest uncertainties as T0 . In thiscase we have used the transit with epoch 20, according to the ephemeris of McCulloughet al. (2006). Hence, the transit time for the epoch 0 is Tc(HJD) = (2453887.74679 ±0.00015)d. Therefore we plotted the midtransit times over the epoch and did a linear ﬁtwith ﬁxed T0 . We got the best χ2 with an orbital period of P = (3.941497 ± 0.000006)days. Within the error bars almost 70% of the points are consistent with our calculatedperiod. The remaining measurements are less than 1-σ from the new “zero” line (solidline in Fig. 1 - right plot). The resulting ephemeris which is in a good agreement withour observation is: Tc(HJD) = (2453887.74679 + E · 3.941497)d.3. TrES-1The other observation at the observatory in Großschwabhausen was performed onMarch 15th 2007. We observed one transit of TrES-1 with the same 24.5cm Cassegraintelescope. The light curve consists of 88 R-band images with 60s exposures.at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921308026872Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 30 May 2017 at 17:18:38, subject to the Cambridge Core terms of use, available442 M. Vanˇko et al.Figure 2. (left plot) Relative R-band photometry of TrES-1. (right plot) Transit timing residualsfor TrES-1. The dashed line shows the ephemeris given by Winn et al. (2007). The data pointsare consistent with the constant period.Unfortunately, our observation was aborted too early and the last part of the lightcurve is missing. This transit corresponds to epoch 326 of the ephemeris given by Winnet al.(2007): Tc(E) = (2453186.80603+E ·3.0300737)d. In this case our mean photometricaccuracy is 0.009 mag. The data reduction and analysis was carried out in the same wayas in the case of XO-1b. For calculation of the artiﬁcial comparison stars, we have used34 most stable stars with a good S/N. As we did not have light from out of transit whichallow us to ﬁnd the systematic eﬀect, the Sys-Rem was not used. The determination ofthe transit center was done in the same way as in the case of XO-1b. After normalizationwe did a ﬁt of the light curve using the system parameters by Winn et al. (2007). Usingthe theoretical light curve and the χ2-test, it was possible to estimate the center of thetransit even without the egress. The minimal value of χ2 corresponds with the followingmidtransit time: Tc(HJD) = (2454174.60958± 0.00150)d.The resulting light curve is shown in the Fig. 3 (left plot). For TrES-1 we found 15midtransit times in the literature. The transit of epoch 40.5 (forced e = 0) according tothe ephemeris given by Winn et al. (2007) is even a secondary transit observed by Char-bonneau et al. (2005). With all 16 available transit times we determined the transit andsecondary-eclipse timing residuals for TrES-1. The calculated times (using the ephemerisof Winn et al. (2007)) have been subtracted from the observed times. The resulting (O-C)diagram is shown in the Fig. 2 (right plot). The point lie on the horizontal line. It meansthat data are consistent with a constant period which conﬁrmes the ephemeris given byWinn et al. (2007).ReferencesBroeg, Ch., Fernndez, M., & Neuha¨user, R. 2005, AN, 326, 134Charbonneau, D., et al. 2005, ApJ, 626, 523Holman, M. J., et al. 2007 ApJ, 664, 1185McCullough, P. R., et al. 2008, ApJ, 648, 1228Mugrauer, M., et al. 2008, AN, in preperationTamuz, O., Mazeh, T., & Zucker, S. 2005, MNRAS, 356, 1466Winn, J. N., Holman, M. J., & Roussanova, A. 2007, ApJ, 657, 1098at https:/www.cambridge.org/core/terms. https://doi.org/10.1017/S1743921308026872Downloaded from https:/www.cambridge.org/core. University of Basel Library, on 30 May 2017 at 17:18:38, subject to the Cambridge Core terms of use, available

Transit observation at the observatory in Großschwabhausen: XO-1b and TrES-1

Transit observation at the observatory in Großschwabhausen: XO-1b and TrES-1

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