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The Tess-Keck Survey. Ii. An Ultra-Short-Period Rocky Planet And Its Siblings Transiting The Galactic Thick-Disk Star Toi-561, L. M. Weiss, F. Dai, D. Huber, J. M. Brewer, K. A. Collins, D. R. Ciardi, E. C. Matthews, C. Ziegler, S. B. Howell, N. M. Batalha, I. J. M. Crossfield, C. Dressing, B. Fulton, A. W. Howard, H. Isaacson, S. R. Kane, E. A. Petigura, P. Robertson, A. Roy, R. A. Rubenzahl, J. D. Twicken, Z. R. Claytor, K. G. Stassun, M. G. Macdougall, A. Chontos, S. Giacalone, P. A. Dalba, T. Mocnik, M. L. Hill, C. Beard, J. M. Akana Murphy, L. J. Rosenthal, A. Behmard, J. Van Zandt, J. Lubin, M. R. Kosiarek, M. B. Lund, J. L. Christiansen, R. A. Matson, C. A. Beichman, J. E. Schlieder, E. J. Gonzales, C. Briceño, N. Law, A. W. Mann, K. I. Collins, P. Evans, A. Fukui, Eric L.N. Jensen, F. Murgas, N. Narita, E. Palle, H. Parviainen, R. P. Schwarz, T.-G. Tan, J. S. Acton, P. Eigmüller, J. Jenkins, G. Ricker, S. Seager, J. N. Winn

Physics & Astronomy Faculty Works

We report the discovery of TOI-561, a multiplanet system in the galactic thick disk that contains a rocky, ultra-short-period planet. This bright (V = 10.2) star hosts three small transiting planets identified in photometry from the NASA TESS mission: TOI-561 b (TOI-561.02, P = 0.44 days, Rp = 1.45 ± 0.11 R⊕), c (TOI-561.01, P = 10.8 days, Rp = 2.90 ± 0.13 R⊕), and d (TOI-561.03, P = 16.3 days, Rp = 2.32 ± 0.16 R⊕). The star is chemically ([Fe/H] = −0.41 ± 0.05, [α/Fe] = +0.23 ± 0.05) and kinematically consistent with the galactic thick-disk population, making …