Abstract
We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data with TESS and CHEOPS
photometry, and a new set of 62 HARPS-N radial velocities (RVs). Our
joint analysis confirms the presence of four transiting planets, namely
TOI-561 b (P = 0.45 d, R = 1.42 R⊕, M = 2.0 M⊕), c (P = 10.78 d, R = 2.91 R⊕, M = 5.4 M⊕), d (P = 25.7 d, R = 2.82 R⊕, M = 13.2 M⊕) and e (P = 77 d, R = 2.55 R⊕, M = 12.6 R⊕).
Moreover, we identify an additional, long-period signal (>450 d) in
the RVs, which could be due to either an external planetary companion or
to stellar magnetic activity. The precise masses and radii obtained for
the four planets allowed us to conduct interior structure and
atmospheric escape modelling. TOI-561 b is confirmed to be the lowest
density (ρb = 3.8 ± 0.5 g cm−3) ultra-short period
(USP) planet known to date, and the low metallicity of the host star
makes it consistent with the general bulk density-stellar metallicity
trend. According to our interior structure modelling, planet b has
basically no gas envelope, and it could host a certain amount of water.
In contrast, TOI-561 c, d, and e likely retained an H/He envelope, in
addition to a possibly large water layer. The inferred planetary
compositions suggest different atmospheric evolutionary paths, with
planets b and c having experienced significant gas loss, and planets d
and e showing an atmospheric content consistent with the original one.
The uniqueness of the USP planet, the presence of the long-period planet
TOI-561 e, and the complex architecture make this system an appealing
target for follow-up studies
| Original language | English |
|---|---|
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 511 |
| Issue number | 3 |
| Pages (from-to) | 4551–4571 |
| Number of pages | 21 |
| ISSN | 0035-8711 |
| DOIs | |
| Publication status | Published - 2022 |