Hint of an exocomet transit in the CHEOPS light curve of HD 172555

F. Kiefer*, V. Van Grootel, A. Lecavelier Des Etangs, G.M. Szabó, A. Brandeker, C. Broeg, A. Collier Cameron, A. Deline, G. Olofsson, T.G. Wilson, S.G. Sousa, D. Gandolfi, G. Hébrard, Y. Alibert, R. Alonso, G. Anglada, T. Bárczy, D. Barrado, S.C.C. Barros, W. BaumjohannM. Beck, T. Beck, W. Benz, N. Billot, X. Bonfils, J. Cabrera, S. Charnoz, S. Csizmadia, M.B. Davies, M. Deleuil, L. Delrez, O.D.S. Demangeon, B.-O. Demory, D. Ehrenreich, A. Erikson, A. Fortier, L. Fossati, M. Fridlund, M. Gillon, M. Güdel, K. Heng, S. Hoyer, K.G. Isaak, L.L. Kiss, J. Laskar, M. Lendl, C. Lovis, D. Magrin, P.F.L. Maxted, M. Munari, V. Nascimbeni, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, D. Piazza, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, F. Ratti, H. Rauer, C. Reimers, I. Ribas, N.C. Santos, G. Scandariato, D. Ségransan, A.E. Simon, A.M.S. Smith, M. Steller, N. Thomas, S. Udry, I. Walter, N.A. Walton

*Corresponding author for this work

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HD 172555 is a young (∼20 Myr) A7V star surrounded by a 10 au wide debris disk suspected to be replenished partly by collisions between large planetesimals. Small evaporating transiting bodies, that is exocomets, have also been detected in this system by spectroscopy. After β Pictoris, this is another example of a system possibly witnessing a phase of the heavy bombardment of planetesimals. In such a system, small bodies trace dynamical evolution processes. We aim to constrain their dust content by using transit photometry. We performed a 2-day-long photometric monitoring of HD 172555 with the CHEOPS space telescope in order to detect shallow transits of exocomets with a typical expected duration of a few hours. The large oscillations in the light curve indicate that HD 172555 is a δ Scuti pulsating star. After removing those dominating oscillations, we found a hint of a transient absorption. If fitted with an exocomet transit model, it would correspond to an evaporating body passing near the star at a distance of 6.8±1.4R∗ (or 0.05±0.01 au) with a radius of 2.5 km. These properties are comparable to those of the exocomets already found in this system using spectroscopy, as well as those found in the β Pic system. The nuclei of the Solar System's Jupiter family comets, with radii of 2-6 km, are also comparable in size. This is the first piece of evidence of an exocomet photometric transit detection in the young system of HD 172555.
Original languageEnglish
Article numberA25
Number of pages12
JournalAstronomy and Astrophysics
Early online date1 Mar 2023
Publication statusPublished - 1 Mar 2023


  • Circumstellar matter
  • Comets: general
  • Stars: individual: HD 172555
  • Stars: variables: δ Scuti
  • Techniques: photometric


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