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Alexander Mustill. Profile picture.

Alexander Mustill


Alexander Mustill. Profile picture.

The HD 93963 A transiting system: A 1.04 d super-Earth and a 3.65 d sub-Neptune discovered by TESS and CHEOPS


  • L. M. Serrano
  • A. J. Mustill
  • M. B. Davies
  • N. Walton

Summary, in English

We present the discovery of two small planets transiting HD 93963A (TOI-1797), a GOV star (M* = 1.109 ± 0.043M, R* = 1.043 ± 0.009 R)
in a visual binary system. We combined TESS and CHEOPS space-borne
photometry with MuSCAT 2 ground-based photometry, ‘Alopeke and PHARO
high-resolution imaging, TRES and FIES reconnaissance spectroscopy, and
SOPHIE radial velocity measurements. We validated and spectroscopically
confirmed the outer transiting planet HD 93963 A c, a sub-Neptune with
an orbital period of Pc ≈ 3.65 d that was reported to
be a TESS object of interest (TOI) shortly after the release of Sector
22 data. HD 93963 A c has amass of Mc = 19.2 ± 4.1 M and a radius of Rc = 3.228 ± 0.059 R, implying a mean density of ρc = 3.1 ± 0.7 g cm-3.
The inner object, HD 93963 A b, is a validated 1.04 d ultra-short
period (USP) transiting super-Earth that we discovered in the TESS light
curve and that was not listed as a TOI, owing to the low significance
of its signal (TESS signal-to-noise ratio ≈6.7, TESS + CHEOPS combined
transit depth Db = 141.5−8.3+8.5
ppm). We intensively monitored the star with CHEOPS by performing nine
transit observations to confirm the presence of the inner planet and
validate the system. HD 93963 A b is the first small (Rb = 1.35 ± 0.042 R)
USP planet discovered and validated by TESS and CHEOPS. Unlike planet
c, HD 93963 Ab is not significantly detected in our radial velocities (Mb = 7.8 ± 3.2 M).
The two planets are on either side of the radius valley, implying that
they could have undergone completely different evolution processes. We
also discovered a linear trend in our Doppler measurements, suggesting
the possible presence of a long-period outer planet. With a V-band
magnitude of 9.2, HD 93963 A is among the brightest stars known to host
a USP planet, making it one of the most favourable targets for precise
mass measurement via Doppler spectroscopy and an important laboratory to
test formation, evolution, and migration models of planetary systems
hosting ultra-short period planets.


  • Lund Observatory - Has been reorganised
  • Mathematics (Faculty of Sciences)
  • LUNARC, Centre for Scientific and Technical Computing at Lund University

Publishing year





Astronomy and Astrophysics



Document type

Journal article


EDP Sciences


  • Astronomy, Astrophysics and Cosmology


  • planets and satellites: detection
  • planets and satellites: fundamental parameters
  • instrumentation: photometers
  • instrumentation: spectrographs
  • methods: data analysis
  • Astrophysics - Earth and Planetary Astrophysics




  • ISSN: 1432-0746