Ten new, ultracompact triply eclipsing triple star systems

¹ HUN–REN–SZTE Stellar Astrophysics Research Group, H-6500 Baja, Szegedi út, Kt. 766, Hungary
² Baja Astronomical Observatory of University of Szeged, H-6500 Baja, Szegedi út, Kt. 766, Hungary
³ Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, H-1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary
⁴ Department of Physics, Kavli Institute for Astrophysics and Space Research, M.I.T., Cambridge, MA 02139, USA
⁵ Department of Experimental Physics, University of Szeged, H-6720 Szeged, Dóm tér 9, Hungary
⁶ Amateur Astronomer, Glendale, AZ 85308, USA
⁷ Amateur Astronomer, Missouri City, Texas 77459, USA
⁸ NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
⁹ SETI Institute, 189 Bernardo Avenue, Suite 200, Mountain View, CA 94043, USA
¹⁰ Citizen Scientist, c/o Zooniverse, Dept, of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
¹¹ Brorfelde Observatory, Observator Gyldenkernes Vej 7, DK-4340 Tølløse, Denmark
¹² National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby, Denmark
¹³ Amateur Astronomer, 7507 52nd Place NE, Marysville, WA 98270, USA
¹⁴ Astronomical Institute, Slovak Academy of Sciences, 05960 Tatranská Lomnica, Slovakia
¹⁵ ELTE Gothard Astrophysical Observatory, Szent Imre herceg u. 112, H-9700 Szombathely, Hungary

^⋆ Corresponding authors: borko@bajaobs.hu; sar@mit.edu

Received: 22 August 2025
Accepted: 1 October 2025

Abstract

Aims. We have identified more than a hundred close triply eclipsing hierarchical triple star systems from data taken with the space telescope TESS. Many of them have outer periods less than, or close to, 100 days, and hence we call them ‘ultracompact hierarchical triples’. These systems are noteworthy in that we can potentially determine their dynamical and astrophysical parameters with a high precision, in many cases even without radial velocity data. In the present paper, we report the comprehensive study of ten new ultracompact triply eclipsing triple star systems, located in the northern ecliptic hemisphere, taken from this larger sample: TICs 198581208, 265274458, 283846096, 337993842, 351404069, 378270875, 403792414, 403916758, 405789362, and 461500036.

Methods. Most of the data for this study come from TESS observations, but we obtained supplemental ground-based photometric measurements for two of the systems. The eclipse timing variation curves extracted from the TESS and the ground-based follow-up data, the photometric light curves, and the spectral energy distribution were combined in a complex photodynamical analysis to yield the stellar and orbital parameters of all ten systems.

Results. The outer periods are in the range of 46.8–101.4 days. We found third-body-forced, rapid apsidal motion in four systems. Moreover, TIC 403916758 was found to be a double twin triple (i.e. both the inner and the outer mass ratios are close to unity). All of the systems are substantially flat, with mutual inclination angles of ≲5°. Finally, we have taken the results for the ten systems in the present paper and combined them with the system parameters for more than 30 other compact triples that we have reported on in previous work, in order to examine some of the global properties of these systems on a statistical basis.