arXiv:1010.1173v2 [astro-ph.EP] 10 Jan 2011 oe hc eepeiul dnie yBuh ta.(2005 al. et Bouchy by identified previously were which modes nuprms ii f4 of limit est and upper transits an during photom variations both profile considering line spectral study and detailed a out Cameron carried Collier (2010) work. velocity radial precise hampers this o not was it but candidate (2006), planet al. transiting et a Christian as reported first mai was o b fast-rotating WASP-33 that main-sequen intermediate-mass case a an uncommon studying on of an possibility transits WASP-3 represents showing , . planet A5 late-type date, giant sequence or to gas solar-type confirmed a orbiting b, been them have of most transiting 100 Over Introduction 1. ssfraslrlk lnths star, host planet solar-like a et a asteroseismic (Silvotti first for the method performed ysis (2005) timing al. the et Bazot wh using 2007). type), discovered (sdB Pegasi was V391 exoplanets host planet as known its such few stars, on a pulsating only pulsations, orbiting are radial there However, cases 2010). special (Schuh in and sations, eaieyln ielpemyb xlie eas h host T the (2010). because 15082, explained al. (HD be et may Cameron lapse Collier time of long relatively study the until hr rsne vdneo o-ailplain ntest the in pulsations suggested non-radial of evidence presented thors ela diinlosrain rmteEolntTransit Exoplanet the Montsec http: from ETD, robotic as observations (hereafter 2008), additional Database fully al. (Colom´e et as OAdM professional well – the Observatory Astronomical and Observatory equator. t stellar that the and to motion relative retrograde inclined in is star orbit the orbits b WASP-33 that dct.Tepeec falrepae ls oasa a cau may star a peri- to close and planet amplitude e large tidal their a analyse of presence to oscillat The and odicity. photometric WASP-33, for star evidence the first on the provide to us low oebr1 2018 1, November srnm Astrophysics & Astronomy eew s bevtostkna h mtu Montcabrer amateur the at taken observations use we Here e words. Key iesre aata ilpri h dnicto ftes the of identification with the star motion host permit exoplanet orbital will planet that the data time-series with commensurability possible a rudafeunyo 1ccd cyc detail 21 The of mmag. frequency 1 a and about around of fitting semi-amplitude Proper a Observatory. with Astronomical variations Montsec the at 1 the 2 eevd¡date¿ Received erpr h icvr fpooercoclain nteh the in oscillations photometric of discovery the report We ff csta r epnil o utproi o-ailpul non-radial multiperiodic for responsible are that ects ntttd iece elEpi(SCIE) apsUB F UAB, Campus (CSIC-IEEC), l’Espai Ci`encies de de Institut e-mail: bevtr otarr C Montcabrer, Observatori R γ adi ohtastadoto-rni hssfo h 0.3- the from phases out-of-transit and transit both in band o-yevraiiy utemr,te lofound also they Furthermore, variability. Dor-type V hreoiect [email protected],[email protected] [email protected], [email protected], = tr:vrals et ct tr:oclain (inclu oscillations Stars: - Scuti delta variables: Stars: 8 . )i atrttr( rotator fast a is 3) AP3:Tefirst The WASP-33: / cetd¡date¿ Accepted . M 1 δ J c aiblt n eyitrsigcniaet erhf search to candidate interesting very a and variability Sct aucitn.ms no. manuscript o h lnt nadto,teau- the addition, In planet. the for / // am ams 4 arl,San e-mail: Spain, Cabrils, 24, Balmes, Jaume var2.astro.cz − 1 hc stpclof typical is which , .Herrero E. µ ffi v re oeln 3p- 43 modelling Arae, ilyanucda an as announced cially sin i / = T) hs al- These ETD). 1 6kms 86 ..Morales J.C. , L te othe to etter δ ablished ff − ct-yevral tr.A cuaesuyo h oe sp power the of study accurate An stars. variable Scuti-type estar. ce r the ers 1 rand ar s tro h xpae AP3 H 58) h aawr o were data The 15082). (HD b WASP-33 exoplanet the of star ost δ and ) gicn rqece.Teefidnsmk AP3 h first the WASP-33 make findings These frequencies. ignificant anal- tal. et ABSTRACT ions etry star star ose ihafco f2,btti ean ob ofimdwt addit with confirmed be to remains this but 26, of factor a with by he he ct xpae otstar host exoplanet Scuti daayi fteproormyed tutr fsignific of structure a yields periodogram the of analysis ed se n- ). l. 3 usqetrmvlo h rni inlrvasselrph stellar reveals signal transit the of removal subsequent eecp n h otarrOsraoyadte08mtel 0.8-m the and Observatory Montcabrer the and telescope m - cla eC`nis or 5prl,2 l 89 Bellater 08193 pl, 2a parell, C5 Ci`encies, Torre de acultat 1 igplain)-Tcnqe:photometric Techniques: - pulsations) ding .Ribas I. , Spebr2 n 8 00 a bandfo AMand OAdM from obtained 2k and Ritchey-Chr´etienPL4240 telescope was 80-cm condition robotic 2010) fully photometric on a 28, with good Photometry and very Spain. 21 with Barcelona, (September of nights suburbs additional whic the two 213, in code Center located Planet is Minor the with observatory vate e,wriga 1.03 a sys- from at optics adaptive working AO-8 obtained an tem, with camera telesco ST8-XME were Schmidt-Cassegrain and SBIG 0.3-m a a 7 and dataset using September 20, 26, October our and August 14 2010 in on Observatory observations Montcabrer first The photometry and Observations 2. star. host exoplanet transiting known a in served AP3 stefis aewhere case first the a is et WASP-33 disc (Christensen-Dalsgaard exoplan simultaneously oscillations its solar-like the of ered characterize analysis to an through used HAT-P-7 host were data Kepler Recently, sso ahtast AP3 transit anal b parameter WASP-33 a transit. and each diagrams of some ysis including ETD, the at able t seemed dataset photometric gest. first the furthe to that order oscillations in photom phases the orbital follow-up several at the so obtained whereas was incomplete try 2010), them defini al. of Th the et most Cameron improving curves, available. (Collier light of as existing aim the stars, the of with tion comparison observed im- four was the transit or on photomet- first three performed the was using increase photometry to ages, Aperture images Johnson the precision. the defocusing ric in by out and carried band was above described photometry l htmtydtst sdi hssuyaelse nTabl in listed are study this analysi in our used in datasets used were photometry 2010) 2010) All 26, 11, (August (September Hormuth Lopresti F. C. 2010), and 23, (August Hose K. from E diinlrcn rni htmtyo AP3 savail- is WASP-33 of photometry transit recent Additional [email protected] ditor 1 n .Naves R. and , × kcmr ihapaesaeo 0.36 of scale plate a with camera 2k rsa-lntinteractions. star-planet or ′′ e ie cl.Ti sa mtu pri- amateur an is This scale. pixel per 2 δ c ustoshv enob- been have pulsations Sct R bn htmti data photometric -band crmreveals ectrum n signals ant ′′ tie in btained otometric a Spain, ra, transiting

c e ie.All pixel. per escope S 2018 ESO ional .2010). l. study r sug- o FLI a 1. e ov- far pe e- et s. R h e s - - 2 E.Herrero1 et al.: WASP-33: The first δ Scuti exoplanet host star

Table 1. Photometric datasets used in this work. Montcabrer -0.01 Observatory and OAdM data were specially acquired during 0 the course of this work. The rest of the photometry is public (O-C) at the ETD. In transit observations, the photometric root mean 0.01 square (rms) residual per measurement and the transit time de- -0.01 viation (TTD) with respect to the mid-transit ephemeris given in Collier Cameron et al. (2010) are calculated from the fits repre- 0 sented in Fig. 2. R (mag)

Author/ Transit / rms TTD ∆ 0.01 Observatory Date Out of tr. (mmag) (min) K. Hose 23/08/2010 T 3.7 4.10 ± 1.31 Montcabrer 26/08/2010a T 2.8 9.76 ± 1.01 0.02 F. Hormuth 26/08/2010b T 2.7 3.18 ± 0.86 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 Montcabrer 07/09/2010 OOT 3.1 Phase C. Lopresti 11/09/2010 T 3.9 −1.66 ± 1.62 Montcabrer 14/09/2010 OOT 2.3 Fig. 1. Best fit to the overall R-band transit photometry phase- OAdM 21/09/2010 OOT 1.6 folded (grey symbols) and binned in steps of 0.001 in phase OAdM 28/09/2010 T 2.1 2.83 ± 0.50 (black symbols) for better visualization. The top panel shows the Montcabrer 20/10/2010 T 1.8 7.55 ± 0.86 residuals of this fit. Error bars are computed as the mean value error of each bin. Table 2. Transit parameters fitted using JKTEBOP. The transit depth was computed from the fit. The error bars are 1-σ uncer- To better determine the characteristic period of the observed tainties. pulsations, we carried out individual fits to each transit by leav- ing the inclination and transit time as free parameters and fixing Parameter Value the relative radii of the star and the planet according to the global r + r 0.309 ± 0.007 1 2 result. This was done to minimize the possible effects of transit r2/r1 0.1066 ± 0.0008 i (◦) 85.8 ± 2.0 time variations caused by unknown third bodies in the system ff T0 − 2450000 5431.8879 ± 0.0003 on the residuals and the e ect of trend corrections on the transit rms (mmag) 3.44 depth. We find that the inclination of each individual fit is well Depth (mmag) 14.3 ± 0.2 within the uncertainty of that determined for the combination of the transits. In Table 1 the transit time deviations of each transit are also listed, however, their scarcity and possible systematics The root mean square (rms) residuals given in the third column, caused by the pulsation precludes us of drawing any conclusions even though they are affected by the pulsations, give an idea of about the presence of additional planets in the system. the precision of the photometry from each observatory. As already shown,the residuals of the transit fits show a clear oscillation pattern that is also present in the out-of-transit pho- tometry obtained for WASP-33. The presence of oscillations dur- 3. Data analysis and discussion ing the entire , including out-of-transit phases as shown in Fig. 3, rules out the possibility of the “bumps” seen in The transit photometry datasets were analysed with the transit as being caused by the effect of the gravity darkening in a JKTEBOP code (Southworth et al. 2004a,b), which is based on rapidly rotating star such as WASP-33 (Barnes 2009). Thus, we the EBOP code written by Paul B. Etzel (Popper & Etzel 1981). combined the residuals from the transit fits and the out-of-transit Each transit light curve was corrected for a slight trend us- light curves in a single curve to better determinethe period of the ing low-order polynomials. Preliminary fits were run with the oscillations. Figure 4 shows the results of running a periodogram JKTEBOP by solving for the sum of the radii relative to the or- on these data with the PERIOD04 code (Lenz & Breger 2005, bital semi-major axis (star + planet; r1 +r2), ratio of radii (r2/r1), http://www.univie.ac.at/tops/period04/) that is based on the dis- inclination, and time of transit. This was done before combining crete Fourier transform algorithm. A main peak around a fre- all transits by including a shift to normalize their out-of-transit quency of 21 d−1 is clearly present in this figure, corresponding level, so that consistent parameters were obtained for all the tran- to a period of about 68 min. However, a close inspection of this sits. The period was fixed to that given in Collier Cameron et al. peak reveals that it is composed of several other peaks that are (2010), Porb = 1.2198669 d. To properly weigh the observa- an imprint of the window function associated to our data. The tions from different authors, we performed a running average second structure around 6 d−1, which is similar to the typical of the residuals from a preliminary fit in bins of 20 minutes, length of the individual photometric series, is probably spurious selecting as individual error for each point the standard devi- and may be related to the detrending and the flux-shift of the ation of its bin. The best fit to the overall transit photometry different light curves. is shown in Fig. 1 and the associated parameters are given in To better analyse the structure of this peak, we fitted the the- Table 2. All parameters are consistent within the uncertainties oretical transit light curve to the original data by adding a si- with those in Collier Cameron et al. (2010). A pulsation trend is nusoidal modulation of the light of the system, thus perform- clearly present on the residuals of this fit, and as Fig. 2 illus- ing a phase dispersion minimization algorithm (Stellingwerf trates, it is already apparent to the eye that all the curves (some 1978). The minimization of this parametric fit was performed by of them separated by almost 60 d) show “bumps” that always ap- means of a Levenberg-Marquardt algorithm (Press et al. 1992). pear at the similar orbital phases (note, e.g., the phases just after Because of the degeneracy on the solutions, we fitted the ampli- the egress). tude of the modulation and tested a grid of frequency and phase E. Herrero1 et al.: WASP-33: The first δ Scuti exoplanet host star 3

-0.015 1 0 0.8 (O-C) 0.015 0.6 -0.015

Power 0.4 0

(O-C) 0.2 0.015 -0.015 0 -10 -5 0 5 10 0 1 (O-C)

0.015 ) -0.015 2 0.8 0 0.6 (O-C) 0.015 0.4

-0.015 Power (mmag 0.2 0 0 (O-C) 0.015 0 5 10 15 20 25 30 35 40 -1 -1 -0.015 P (days ) 0 (O-C) 0.015 Fig. 4. Periodogram of the transit residuals and out-of-eclipse phases of WASP-33 using PERIOD04 code. Top panel displays the window function. 0 23/08/2010

0.02 step process in which we performed the analysis assuming an 26/08/2010a initial constant arbitrary value of the standard deviation σ=1 for each data point. The best-fitting solution was then used to cal- 0.04 26/08/2010b culate a new value for σ as the local value of the rms residual (computed as the running average of the residuals in bins of 20

R (mag) 0.06 minutes), and a final fit was run with weights set accordingly. ∆ 2 11/09/2010 As can be seen in Fig. 5, the lowest χ is found for a pulsa- tion with a semi-amplitude of 0.98±0.05 mmag and a frequency −1 0.08 of 21.004±0.004 d at a phase difference with the mid-transit ◦ 28/09/2010 time of 264±12 (at reference from Table 2). This corre- sponds to a period of P = 68.56 ± 0.02 min. Figure 6 shows the 0.1 overall residuals and the out-of-eclipse photometry phase-folded 20/10/2010 according to this best-fitting period. As a result of the separation between observing nights, the main feature in Fig. 5 is composed 0.12 of many equidistant peaks with similar χ2. Interestingly, the pe- -0.1 -0.05 0 0.05 0.1 riodogram peak with lower resulting rms differs from the one Phase above as it occurs for a pulsation of about 0.86 mmag in semi- Fig. 2. R-band transit photometry of WASP-33. The solid line is amplitude with frequency of 21.311±0.004 d−1 corresponding the best fit to each curve with the relative radii of the star and the to a pulsation period of 67.57 ± 0.02 min. This illustrates the planet fixed to those found in the global fit using the JKTEBOP relatively strong impact of the weighing scheme because the code. The residuals are shown in the upper panels in the same signal is weak and our time series is relatively short. The lat- order as transits are displayed. See Table 1 for reference. ter frequency is especially interesting as is happens to be com- mensurable with the planet’s orbital motion with a factor of Phase 25.997±0.005. 0.25 0.3 0.35 0.4 0.01 Line-profile tomography in Collier Cameron et al. (2010) 0.005 provided strong evidence for non-radial pulsations in WASP-33 with a period around one , similar to those usually found 0 in γ Dor stars. Moreover, the authors point out the possibil- R (mag)

∆ ity that the retrograde orbiting planet could be tidally induc- -0.005 ing them. Both the period of the photometric oscillations pre- -0.01 0.45 0.5 0.55 0.6 0.65 sented here and the stellar propertiesfrom Collier Cameron et al. HJD (+2455461.0) (2010) (Teff = 7400 ± 200 K, log g = 4.3 ± 0.2) locate WASP- 33 well within the δ Sct instability strip. Handler & Shobbrook Fig. 3. Out-of-transit photometry of WASP-33 obtained from (2002) present a discussion on the different properties of δ Sct OAdM on 21 September, 2010. and γ Dor pulsators. Using the formalism there it can be shown that the pulsation constant of WASP-33 (log QWASP−33 = −1.45) perfectly corresponds to the δ Sct domain. The power spectrum difference values. A key element to consider is the weighing of of δ Sct pulsators is usually very rich, as illustrated by the 75+ each data point. At the high precision of our photometry, photon frequencies identified for FG Vir (Breger et al. 2005), but as- noise is not a good measure of the uncertainty of the measure- teroseismic modelling is especially difficult for fast rotators as ment because systematic effects in the form of correlated noise WASP-33. Given this evidence, a different scenario consider- dominate (e.g., Pont et al. 2006). Therefore, we applied a two- ing that WASP-33 belongs to the relatively rare class of hybrid 4 E.Herrero1 et al.: WASP-33: The first δ Scuti exoplanet host star

P /P orb As seen above, the periodogram is still not defined suffi- 24 25 26 27 28 ciently well to assess the true pulsation spectrum of WASP- 1 33. However, given the potential interest, we find it appropri- 0.8 0.6 ate to briefly address here the possibility of the coupling be- 0.4 tween the pulsation and the orbit. If the pulsation frequency of −1 A (mmag) 0.2 21.311±0.004 d turned out to be real, this could suggest the 0 existence of some kind of star-planet interactions that lead to a 2.75 high-order commensurability of 26 between the pulsation and orbital periods. Very few cases are known to date of a δ Sct 2.7 variable belonging to a close binary system (Willems & Claret 2.65 2005). The best described candidate for tidally-induced oscilla- rms (mmag) tions is HD 209295, which simultaneously presents γ Dor and 1.7 δ Sct-type pulsations, and which was photometrically found to 1.65

2 show several p-modes directly related to the orbital motion of 1.6 χ 1.55 its companion (Handler et al. 2002). This poses the tantalizing 1.5 possibility of a similar situation occurring in WASP-33, which 19 19.5 20 20.5 21 21.5 22 22.5 23 23.5 will certainly be much clearer when additional photometry is -1 -1 P (days ) acquired and puts constraints on the δ Sct frequency spectrum. Fig. 5. Results from the Levenberg-Marquardtalgorithm method displaying the structure of the main periodogrampeak. Both am- 4. Conclusions plitude and χ2 give best fits for 21.00 d−1, while the rms is mini- −1 High-precision R-band photometry has allowed us to present mized for a pulsation of frequency 21.31 d , which is commen- the discovery of photometric oscillations in WASP-33, thus be- surable with the planet’s orbital period. coming the first transiting planet host with δ Sct pulsations. These oscillations have a period of about 68 minutes and a semi- amplitude of 1 mmag. The frequency spectrum of WASP-33 is 0.004 still not well defined because the size and significance of the peaks depends on the scheme used to weigh the data. In a par- 0.002 ticular weighing criterion, the most significant period comes out to be commensurable with the orbital period at a factor of 26. 0 If this association is assumed to be physically relevant, the mul- R (mag) ∆ tiplicity hints at the existence of planet-star interactions. In any -0.002 case, gaining insight into the nature of WASP-33 will necessarily require the collection of additional data (possibly multi-colour) -0.004 with longer time baseline and to carry out pulsation and dy- -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 namical modelling. The WASP-33 system now represents a new Pulsation phase benchmark in the world of exoplanets that can provide valuable Fig. 6. Residuals of the transit fits and out-of-eclipse photometry information on stellar pulsations (through, e.g., transit surface of WASP-33 phase-folded according to the period of the pulsa- mapping), on the tidal interactions between planets and stars, tion found in this work, i.e., 68.56±0.02min, (grey symbols) and and on the dynamical evolution of planetary systems. 0.01 phase binning (black symbols). The solid curve is the best Acknowledgements. We thank G. Handler, P. J. Amado and C. Jordi for useful fit sinusoidal modulation with an amplitude of 0.98 mmag. discussions. The referee, M. Bazot, is thanked for insightful comments that led to the improvement of the paper. Data were partially obtained by J. Martin with the Joan Or´oTelescope (TJO) of the Montsec Astronomical Observatory (OAdM), which is owned by the Consorci del Montsec and operated by the Institute for pulsators, showing simultaneous δ Sct and γ Dor oscillations Space Studies of Catalonia (IEEC). This research has made use of the Exoplanet (Handler et al. 2002; Handler 2009), may be possible. Transit Database (http://var.astro.cz/ETD). One scenario that should be explored in spite of all the ev- idence is the possibility that the photometric variations are el- References lipsoidal in nature and are not caused by pulsations. Indeed, the tidal bulge travels particularly fast over the stellar surface, be- Barnes, J. W. 2009, ApJ, 705, 683 cause the orbital motion of the planet is retrograde with respect Bazot, M., Vauclair, S., Bouchy, F., & Santos, N. C. 2005, A&A, 440, 615 Bouchy, F. and Bazot, M. and Santos, N. C. and Vauclair, S. and Sosnowska, D. to the stellar rotation. Note that there is an indeterminacy in the 2005, A&A, 440, 609 stellar rotation velocity because it is not a given assumption that Breger, M., Lenz, P., Antoci, V., et al. 2005, A&A, 435, 955 the inclination of the stellar spin axis corresponds to the planet’s Collier Cameron, A. 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