Funding: UGJ acknowledges funding from the Novo Nordisk Foundation Interdisciplinary Synergy Programme grant no. NNF19OC0057374 and from the European Union H2020-MSCA-ITN-2019 under Grant no. 860470 (CHAMELEON). NP’s work was supported by Fundação para a Ciência e a Tecnologia (FCT) through the research grants UIDB/04434/2020 and UIDP/04434/2020. PLP was partly funded by Programa de Iniciación en Investigación-Universidad de Antofagasta, INI-17-03.TRAPPIST-1 is an ultra-cool dwarf that hosts seven known transiting planets. We present photometry of the system obtained using three telescopes at ESO La Silla (the Danish 1.54-m telescope and the 2.2-m MPI telescope) and Paranal (Unit Telescope 1 of the Very Large Telescope). We obtained 18 light curves from the Danish telescope, eight from the 2.2-m and four from the VLT. From these we measure 25 times of mid-transit for four of the planets (b, c, f, g). These light curves and times of mid-transit will be useful in determining the masses and radii of the planets, which show variations in their transit times due to gravitational interactions.PostprintPeer reviewe

Bozza, V.

Burgdorf, M. J.

Dominik, M.

Figuera Jaimes, R.

Haikala, L. K.

Henning, Th.

Hinse, T. C.

Hundertmark, M.

Jørgensen, U. G.

Longa-Peña, P.

Mancini, L.

Rabus, M.

Rahvar, S.

Sajadian, S.

Skottfelt, J.

Snodgrass, C.

Southworth, John

English

Funding: UGJ acknowledges funding from the Novo Nordisk Foundation Interdisciplinary Synergy Programme grant no. NNF19OC0057374 and from the European Union H2020-MSCA-ITN-2019 under Grant no. 860470 (CHAMELEON). NP’s work was supported by Fundação para a Ciência e a Tecnologia (FCT) through the research grants UIDB/04434/2020 and UIDP/04434/2020. PLP was partly funded by Programa de Iniciación en Investigación-Universidad de Antofagasta, INI-17-03.TRAPPIST-1 is an ultra-cool dwarf that hosts seven known transiting planets. We present photometry of the system obtained using three telescopes at ESO La Silla (the Danish 1.54-m telescope and the 2.2-m MPI telescope) and Paranal (Unit Telescope 1 of the Very Large Telescope). We obtained 18 light curves from the Danish telescope, eight from the 2.2-m and four from the VLT. From these we measure 25 times of mid-transit for four of the planets (b, c, f, g). These light curves and times of mid-transit will be useful in determining the masses and radii of the planets, which show variations in their transit times due to gravitational interactions.Peer reviewe

St Andrews Research Repository

arXiv:2207.05874v1  [astro-ph.EP]  12 Jul 20222022 Aug J. Southworth et al. 1VLT, GROND AND DANISH TELESCOPE OBSERVATIONS OFTRANSITS IN THE TRAPPIST-1 SYSTEMBy John Southworth1, L. Mancini,2,3,4 M. Dominik,5 U. G. Jørgensen6,V. Bozza7,8, M. J. Burgdorf 9, R. Figuera Jaimes10, L. K. Haikala11,Th. Henning3, T. C. Hinse12,13, M. Hundertmark14, P. Longa-Peña15,M. Rabus16, S. Rahvar17, S. Sajadian18, J. Skottfelt19 and C. Snodgrass201. Astrophysics Group, Keele University, Staffordshire, UK2. University of Rome “Tor Vergata”, Rome, Italy3. Max Planck Institute for Astronomy, Heidelberg, Germany4. INAF — Turin Astrophysical Observatory, Pino Torinese, Italy5. University of St Andrews, St Andrews, UK6. Centre for ExoLife Sciences, Niels Bohr Institute, Copenhagen, Denmark7. Università di Salerno, Fisciano, Italy8. Istituto Nazionale di Fisica Nucleare, Sezione di Napoli, Napoli, Italy9. Universität Hamburg, Hamburg, Germany10. Universidad San Sebastian, Valdivia, Chile11. Universidad de Atacama, Copiapo, Chile12. Nicolaus Copernicus University, Toruń, Poland13. Chungnam National University, Daejeon, South Korea14. Zentrum für Astronomie der Universität Heidelberg, Germany15. Centro de Astronomı́a, Universidad de Antofagasta, Chile16. Universidad Católica de la Sant́ısima Concepción, Concepción, Chile17. Department of Physics, Sharif University of Technology, Tehran, Iran18. Department of Physics, Isfahan University of Technology, Isfahan, Iran19. The Open University, Milton Keynes, UK20. University of Edinburgh, Royal Observatory, Edinburgh, UKTRAPPIST-1 is an ultra-cool dwarf that hosts seven known tran-siting planets. We present photometry of the system obtained usingthree telescopes at ESO La Silla (the Danish 1.54 m telescope andthe 2.2 m MPI telescope) and Paranal (Unit Telescope 1 of theVery Large Telescope). We obtained 18 light curves from the Dan-ish telescope, eight from the 2.2 m and four from the VLT. Fromthese we measure 25 times of mid-transit for four of the planets (b,c, f, g). These light curves and times of mid-transit will be usefulin determining the masses and radii of the planets, which showvariations in their transit times due to gravitational interactions.IntroductionTRAPPIST-1 is an ultra-cool dwarf of mass 0.089± 0.006 M⊙, radius 0.121±0.003 R⊙, and effective temperature 2516± 41 K1. Two transiting planets werefound in this system by Gillon et al.2, based on photometry from the 0.6-mTRAPPIST telescope3. A further five transiting planets were found by Gillon2 Transit timing measures for TRAPPIST-1 Vol.et al.4 and Luger et al.5 from observations with the Spitzer and K2 satellitesaugmented by ground-based data.Based on analysis of transit light curves, the radii of the planets have beenfound to range from 0.76 R⊕ to 1.13 R⊕ and their orbital periods from 1.5 d to18.8 d 6–8. All seven planets are in orbital resonances with each other7–9, causingdynamical interactions between the planets which depend on their masses andorbital characteristics. This has allowed measurement of their masses, whichrange from 0.33 M⊕ to 1.37 M⊕7,8, from analysis of transit timing variations(e.g. Refs.10,11).TRAPPIST-1 remains the lowest-mass stellar object known to host a transitingplanet∗, so the system is an important one for further study. Aside from massand radius measurements, it is an important tracer of tidal effects13–15, theformation and interior structure of rocky planets16–19, and the characterisation ofatmospheres via transmission spectroscopy20–23. TRAPPIST-1 is a high-prioritytarget for observations with the James Webb Space Telescope24–28.The faintness of the TRAPPIST-1 system (V = 18.8, I = 14.0) and the lowplanet masses means that it is difficult to measure the masses of the planetsusing high-precision spectroscopic radial velocities. Therefore measurements ofthe times of mid-transit for these planets are crucial for improving measurementsof their masses, and thus densities and surface gravities. In this work we presentextensive photometry of transits of TRAPPIST-1 obtained in the 2017 and 2018observing seasons using three telescopes.Observations with the Danish telescopeA total of 18 light curves of TRAPPIST-1 were obtained in 2017 June–Augustusing the 1.54m Danish Telescope at ESO La Silla, Chile, equipped with theDFOSC imager. The data were obtained whilst the telescope was being operatedby the MiNDSTEp Consortium29 in the context of the transit project runningas a side project in this consortium30,31. A Cousins I filter was used for allobservations of TRAPPIST-1, which is an extremely red star. A total of 13transits were detected, with others lost to poor weather or the shifting of thetransit outside the observing interval due to dynamical effects.Data reduction was performed using the defot pipeline30,32, which uses anIDL implementation of the daophot aperture photometry routine33. The ob-servations were taken in focus and were debiassed and flat-fielded. Differentialphotometry versus multiple comparison stars was obtained by optimising theweights of the comparison stars simultaneously with a low-order polynomial tominimise the scatter around zero differential magnitude outside transit.An observing log is given in Table I. The light curves are shown in Fig. 1. Thetimestamps have been placed on the BJD(TDB) timescale using routines fromEastman et al.34. The times written into the FITS files were manually checkedduring the observation of the majority of the transits to confirm their reliability.∗Based on data obtained from the Transiting Extrasolar Planet Catalogue (TEPCat12 athttps://www.astro.keele.ac.uk/jkt/tepcat/) on 2022/05/11.2022AugJ.Southworthetal.3Table I: Log of the observations from the Danish telescope. Nobs is the number of observations, Texp is the exposure time, Tdead is the deadtime between exposures, ‘Moon illum.’ is the fractional illumination of the Moon at the midpoint of the transit, and Npoly is the order of thepolynomial fitted to normalise the light curve to zero differential magnitude. The aperture radii refer to the target aperture, inner sky andouter sky, respectively.Telescope Planet(s) Date of Start End Filter Nobs Texp Tdead Airmass Moon Aperture Npoly Scatterfirst obs (UT) (UT) (s) (s) illum. radii (px) (mmag)Danish c 2017/06/10 08:13 10:30 I 74 100 12 1.32 → 1.10 0.876 9 14 30 1 2.9Danish b 2017/06/13 06:31 08:24 I 63 100 8 1.96 → 1.25 0.992 8 12 30 1 2.9Danish b 2017/06/19 07:02 09:15 I 72 100 11 1.50 → 1.12 0.301 8 13 30 1 1.9Danish e ∗ 2017/06/30 08:00 10:09 I 67 100 16 1.15 → 1.10 → 1.13 0.432 9 13 30 2.8Danish f 2017/07/22 05:21 08:58 I 116 100 11 1.50 → 1.12 0.019 7 12 25 1 2.1Danish c 2017/07/26 08:25 10:28 I 67 100 12 1.13 → 1.51 0.117 8 12 25 1 1.8Danish g 2017/07/27 06:27 10.01 I 98 100 13 1.13 → 1.10 → 1.44 0.187 6 12 25 1 2.6Danish h ∗ 2017/07/28 04:50 08:52 I 92 200–100 12 1.38 → 1.10 → 1.22 0.272 7 13 25 3.7Danish c, d ∗ 2017/07/31 04:25 07:32 I 88 200–100 6 1.44 → 1.10 0.561 4 8 20 6.0Danish c, b 2017/08/17 03:51 08:27 I 103 100 25 1.49 → 1.10 → 1.17 0.258 8 12 25 1 2.2Danish e ∗ 2017/08/18 02:36 04:50 I 69 100 25 1.72 → 1.14 0.170 6 10 20 3.1Danish b 2017/08/20 05:32 07:25 I 68 100 8 1.10 → 1.21 0.030 9 13 25 1 2.6Danish b ∗ 2017/08/23 06:34 09:12 I 86 100 11 1.13 → 1.77 0.030 6 11 25 8.2Danish e ∗ 2017/08/24 04:55 07:14 I 84 100 16 1.11 → 1.10 → 1.25 0.075 5 8 20 40.1Danish b 2017/08/26 05:59 09:05 I 98 100 13 1.11 → 1.80 0.224 9 13 25 1 2.4Danish c 2017/09/15 05:19 07:27 I 66 100 13 1.15 → 1.64 0.279 9 13 25 2 2.4Danish b 2017/09/20 23:29 01:17 I 51 100 11 2.42 → 1.37 0.008 8 13 25 1 2.5Danish b 2017/09/23 23:58 01:44 I 57 100 13 1.83 → 1.23 0.149 8 12 25 1 1.9∗ transit not detected due to observing conditions or dynamical effects.4 Transit timing measures for TRAPPIST-1 Vol.Observations with the MPI 2.2 m telescopeTRAPPIST-1 was observed on four night using the MPI 2.2 m telescope atESO La Silla. The GROND imager35 was used to obtain observations simultane-ously in seven passbands, approximating the Gunn g, r, i and z and near-infraredJ , H and K filters. The g and r bands suffer from a high scatter due to thefaintness of the target. Conversely, the J , H and K bands do not yield goodlight curves because the target is much brighter than the available comparisonstars. We therefore present light curves from only the i and z bands here.We encountered a problem with the presence of transient bad pixels in ther and z bands caused by a bug in the CCD controller software. These badpixels comprise approximately 0.5% of the pixels in an image and cause thepixel count rate to be either the bias level or unusually high. Left uncorrected,the bad pixels significantly increase the scatter in the light curves. Fortunately,the bad pixels occurred randomly in each image. We were therefore able to findthem by comparing each pixel value in two successive images to detect thosethat differed by more than a manually-chosen threshold. The count rates inthe affected pixels were then replaced by the means of the count rates in thesurrounding eight pixels.Aside from the bad-pixel correction, the data were reduced using the defotpipeline as described above. The observing log is given in Table II and the dataare plotted in Fig. 2.Observations with the VLTTwo transits of TRAPPIST-1 b and two more of TRAPPIST-1 c were observedusing the Very Large Telescope (VLT) Unit Telescope 1 (UT1) equipped withthe FORS2 imager36. The data were obtained through either a zspecial filter witha central wavelength of 916 nm and a full-width at half maximum of 18 nm, ora night-sky suppression filter with a central wavelength of 813 nm and a full-width at half maximum of 13 nm. These observations were obtained in order tosearch for a variation in radius with wavelength indicative of the presence of aplanetary atmosphere, as tentatively found for GJ 113237, but this test couldnot be performed due to the scatter of the observations plus complications withthe scheduling of these time-critical observations in service mode.The data were reduced using the defot pipeline as described above. Theobserving log is given in Table II and the data are plotted in Fig. 3. These datahave a relatively large scatter because all comparison stars had significantlylower count rates than the target star.Transit timing measurementsEach light curve was modelled individually using version 38 of the jktebop†code38,39. We fitted for the sum of the fractional radii (rA + rb where rA =RAa,rb =Rba, RA is the radius of the star, Rb is the radius of the planet in question,†http://www.astro.keele.ac.uk/jkt/codes/jktebop.html2022AugJ.Southworthetal.5Table II: Log of the observations from the MPI 2.2 m telescope and the VLT. Other comments are as in Table I.Telescope Planet(s) Date of Start End Filter Nobs Texp Tdead Airmass Moon Aperture Npoly Scatterfirst obs (UT) (UT) (s) (s) illum. radii (px) (mmag)GROND c 2017/06/10 07:49 10:37 i 80 90 25 1.40 → 1.10 0.876 15 22 40 2 2.4GROND c 2017/06/10 07:49 10:37 z 77 90 25 1.40 → 1.10 0.876 20 28 50 2 1.6GROND b 2017/08/02 03:01 04:49 i 54 90 25 2.17 → 1.31 0.747 27 35 60 2 8.6GROND b 2017/08/02 03:01 04:49 z 55 90 25 2.17 → 1.31 0.747 34 40 70 2 2.7GROND b 2017/10/06 01:17 04:30 i 105 60–80 27 1.19 → 1.10 → 1.21 0.997 14 23 50 2 3.1GROND b 2017/10/06 01:17 04:30 z 108 60–80 27 1.19 → 1.10 → 1.21 0.997 18 28 60 1 2.6GROND f 2017/10/13 01:41 05:45 i 119 80 31 1.11 → 1.10 → 1.70 0.429 16 25 50 2 3.1GROND f 2017/10/13 01:41 05:45 z 118 80 31 1.11 → 1.10 → 1.70 0.429 20 30 55 2 2.7VLT c 2017/11/05 02:23 04:29 zspecial 192 12–8 26 1.18 → 1.77 0.980 10 15 35 1 3.1VLT c 2018/09/06 05:45 07:52 zspecial 230 10–6 26 1.13 → 1.55 0.167 11 20 40 1 2.4VLT b 2018/09/11 02:13 04:17 815 / 13 145 25 26 1.31 → 1.09 0.028 12 20 40 1 2.3VLT b 2018/11/14 23:56 01:54 zspecial 195 25–6 25 1.10 → 1.21 0.447 10 30 40 1 2.86 Transit timing measures for TRAPPIST-1 Vol.and a is the semimajor axis of the relative orbit), their ratio (k = rbrA) and thetime of transit mid-point. We fixed the orbital periods and inclinations to thevalues measured by Gillon et al.4. Limb darkening was accounted for using thequadratic law with coefficients fixed at u = 0.25 and v = 0.60.The light curve from the Danish telescope on the night of 2017/08/17 con-tains two transits, the first by planet c and the second by planet b. These weremodelled separately after removing the data for the other transit from the lightcurve before fitting.Four of our transit observations were obtained simultaneously in the i and zpassbands using GROND. This provides an opportunity to check if the two lightcurves from each night yield timings in mutual agreement. We calculated thelevel of agreement to be 1.5σ for the night of 2017/06/10, 0.3σ for 2017/08/02,0.8σ for 2017/10/06 and 2.9σ for 2017/10/13. This agreement is acceptable butsuggests that the errorbars of our timing measurements may be slightly toosmall.The resulting transit times are given in Table III. The reduced light curveswill be made available at the Centre de Données astronomiques de Strasbourg‡.Because all planets in the TRAPPIST-1 system show complex transit timingvariations caused by gravitational interactions, and because good ephemeridesare available from elsewhere (Refs.4,6,8), we have not performed any analysis onthe transit timings in the current work. They are instead presented here so theymay be used in future studies of this system.AcknowledgementsThis paper was based on data collected by MiNDSTEp with the Danish 1.54mtelescope at the ESO La Silla Observatory. This paper was also based on observa-tions collected using the Gamma Ray Burst Optical and Near-Infrared Detector(GROND) instrument at the MPG 2.2 m telescope located at ESO La Silla,Chile, under programs 099.A-9030(A) and 0100.A-9004(A). GROND was builtby the high-energy group of MPE in collaboration with the LSW Tautenburgand ESO, and is operated as a PI-instrument at the MPG 2.2 m telescope. Thispaper was also based on observations collected at the European Southern Ob-servatory under ESO programme 0100.C-0716(C). The following resources wereused in the course of this work: the NASA Astrophysics Data System; the SIM-BAD database operated at CDS, Strasbourg, France; and the arχiv scientificpaper preprint service operated by Cornell University.UGJ acknowledges funding from the Novo Nordisk Foundation InterdisciplinarySynergy Programme grant no. NNF19OC0057374 and from the European UnionH2020-MSCA-ITN-2019 under Grant no. 860470 (CHAMELEON).NP’s work was supported by Fundação para a Ciência e a Tecnologia (FCT)through the research grants UIDB/04434/2020 and UIDP/04434/2020.PLP was partly funded by Programa de Iniciación en Investigación-Universidadde Antofagasta, INI-17-03.‡http://cdsweb.u-strasbg.fr/2022 Aug J. Southworth et al. 7Table III: Times of mid-transit measured for the planets in the TRAPPIST-1 system.Telescope Filter Planet Time of mid-transit (BJD/TDB)GROND i c 2457914.90035 ± 0.00039GROND z c 2457914.89956 ± 0.00034Danish I c 2457914.90084 ± 0.00047Danish I b 2457917.80266 ± 0.00049Danish I b 2457923.84702 ± 0.00042Danish I f 2457956.80753 ± 0.00054Danish I c 2457960.91366 ± 0.00036Danish I g 2457961.82616 ± 0.00067GROND i b 2457967.66265 ± 0.00098GROND z b 2457967.66231 ± 0.00042Danish I c 2457982.70928 ± 0.00051Danish I b 2457982.77099 ± 0.00039Danish I b 2457985.79287 ± 0.00042Danish I b 2457991.83630 ± 0.00032Danish I c 2458011.77209 ± 0.00046Danish I b 2458017.52100 ± 0.00039Danish I b 2458020.54178 ± 0.00030GROND i b 2458032.63003 ± 0.00044GROND z b 2458032.62955 ± 0.00038GROND i f 2458039.65854 ± 0.00064GROND z f 2458039.66100 ± 0.00057VLT zspecial c 2458062.62830 ± 0.00031VLT zspecial c 2458367.77302 ± 0.00023VLT 815 / 13 b 2458372.61662 ± 0.00027VLT zspecial b 2458437.54799 ± 0.00028References(1) V. Van Grootel et al., ApJ, 853, 30, 2018.(2) M. Gillon et al., Nature, 533, 221, 2016.(3) E. Jehin et al., The Messenger, 145, 2, 2011.(4) M. Gillon et al., Nature, 542, 456, 2017.(5) R. Luger et al., Nature Astronomy, 1, 0129, 2017.(6) L. Delrez et al., MNRAS, 475, 3577, 2018.(7) S. L. Grimm et al., A&A, 613, A68, 2018.(8) E. Agol et al., Planetary Sciences Journal, 2, 1, 2021.(9) J. Teyssandier, A. S. Libert & E. Agol, A&A, 658, A170, 2022.(10) M. J. Holman & N. W. Murray, Science, 307, 1288, 2005.(11) E. Agol et al., MNRAS, 359, 567, 2005.(12) J. Southworth, MNRAS, 417, 2166, 2011.(13) H. C. F. C. Hay & I. Matsuyama, ApJ, 875, 22, 2019.(14) R. Brasser, A. C. Barr & V. Dobos, MNRAS, 487, 34, 2019.(15) E. Bolmont et al., A&A, 644, A165, 2020.(16) G. A. L. Coleman et al., A&A, 631, A7, 2019.(17) M. Turbet et al., A&A, 638, A41, 2020.(18) R. Burn et al., A&A, 656, A72, 2021.(19) S. N. Raymond et al., Nature Astronomy, 6, 80, 2022.8 Transit timing measures for TRAPPIST-1 Vol.(20) E. 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Southworth, A&A, 557, A119, 2013.2022 Aug J. Southworth et al. 9Figure 1: Plot of the light curves of TRAPPIST-1 from the Danish Telescope. Eachpanel shows one light curve on the same scale (0.16 d and 0.05mag). The data areshown using open circles and the jktebop best fits using solid lines. For clarity, theerrorbars are not plotted. The designation(s) of the planet(s) transiting are shown atthe top-right of each panel.10 Transit timing measures for TRAPPIST-1 Vol.Figure 2: Plot of the light curves of TRAPPIST-1 from the MPI 2.2 m telescope. Thedata are shown using open circles and the jktebop best fits using solid lines. Panelson the same row show data from the same transit.2022 Aug J. Southworth et al. 11Figure 3: Plot of the light curves of TRAPPIST-1 from the VLT. The data are shownusing open circles and the jktebop best fits using solid lines.

VLT, GROND and Danish telescope observations of transits in the TRAPPIST-1 system

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VLT, GROND and Danish telescope observations of transits in the TRAPPIST-1 system

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