The young HD 73583 (TOI-560) planetary system: two 10-M⊕ mini-Neptunes transiting a 500-Myr-old, bright, and active K dwarf

Abstract

We present the discovery and characterisation of two transiting planets observed by TESS in the light curves of the young and bright (V = 9.67) star HD73583 (TOI-560). We perform an intensive spectroscopic and photometric space- and ground-based follow-up in order to confirm and characterise the system. We found that HD73583 is a young (∼500 Myr) active star with a rotational period of 12.08 ± 0.11 d, and a mass and radius of 0.73 ± 0.02 M⊙ and 0.65 ± 0.02 R⊙, respectively. HD 73583 b (Pb =$6.3980420 _{ - 0.0000062 } ^ { + 0.0000067 }$ d) has a mass and radius of $10.2 _{ - 3.1 } ^ { + 3.4 }$ M⊕ and 2.79 ± 0.10 R⊕, respectively, that gives a density of $2.58 _{ - 0.81 } ^ { + 0.95 }$ g cm−3. HD 73583 c (Pc=$18.87974 _{ - 0.00074 } ^ { + 0.00086 }$ d) has a mass and radius of $9.7 _{ - 1.7 } ^ { + 1.8 }$ M⊕ and $2.39 _{ - 0.09 } ^ { + 0.10 }$ R⊕, respectively, this translates to a density of $3.88 _{ - 0.80 } ^ { + 0.91 }$ g cm−3. Both planets are consistent with worlds made of a solid core surrounded by a volatile envelope. Because of their youth and host star brightness, they both are excellent candidates to perform transmission spectroscopy studies. We expect on-going atmospheric mass-loss for both planets caused by stellar irradiation. We estimate that the detection of evaporating signatures on H and He would be challenging, but doable with present and future instruments.

TOI 560: Two Transiting Planets Orbiting a K Dwarf Validated with iSHELL, PFS, and HIRES RVs

“…Our analyses arrived at similar conclusions to Barragán et al (2022) for the youth of the TOI 560 system, primarily supported by our common analysis of the archival SuperWASP light curve to identify the stellar-rotation period. Our detections of the RV semiamplitudes are consistent to within the uncertainties of TOI 560 b and c with the work presented in Barragán et al (2022). Our analysis also included the PFS and HIRES RVs, but not the HARPS and CORALIE RVs, and a joint chromatic RV analysis combining these data sets with our iSHELL RVs may be warranted with continued future RV monitoring of this system to further constrain the masses and confirm the mild eccentricities from the RV data alone.…”

“…During the preparation of this manuscript, additional papers were written presenting an independent HARPS RV analysis of this system in Barragán et al (2022) as well as transit spectroscopy in Zhang et al (2022). Our analyses arrived at similar conclusions to Barragán et al (2022) for the youth of the TOI 560 system, primarily supported by our common analysis of the archival SuperWASP light curve to identify the stellar-rotation period. Our detections of the RV semiamplitudes are consistent to within the uncertainties of TOI 560 b and c with the work presented in Barragán et al (2022).…”

“…Differentiating our two works, we had evidence for a moderate eccentricity orbit for planet b from the Spitzer light-curve photoeccentric effect, and therefore we proceeded our analysis with an eccentric model, whereas in Barragán et al (2022), they assumed a circular-orbit model. Barragán et al (2022) also presented a more detailed investigation of the suitably of the planets for atmospheric characterization and the search for hydrogen and helium escape, the latter of which a repeated detection of helium escape is reported in Zhang et al (2022).…”

Generalized Peas in a Pod: Extending Intra-system Mass Uniformity to Non-TTV Systems via the Gini Index

“…We note that our initial query is agnostic to any newly confirmed systems discovered by the Transiting Exoplanet Survey Satellite that are not yet present in the NASA Exoplanet Archive. HD 73583 (Barragán et al 2022) and HD 63935 (Scarsdale et al 2021) are two such non-TTV systems that similarly abide by our restrictions and are therefore also considered for our analysis. The resulting final sample thus consists of 17 close-in, compact, non-TTV systems containing a total of 42 planets.…”

Non-detection of He I in the Atmosphere of GJ 1214b with Keck/NIRSPEC, at a Time of Minimal Telluric Contamination

“…The smallest planets with helium detections so far have been TOI 560.01 (Zhang et al 2022), with a radius of 2.84 R ⊕ , and GJ 1214b (Orell-Miquel et al 2022), with a radius of 2.74 R ⊕ . Among all of the sub-Neptunes observed at 10830 Å, the TOI 560 system is one of the most favorable targets because of its young (500 Myr) and chromospherically active K4 host star (Barragán et al 2022). For TOI 560.01, Zhang et al (2022) measured an excess absorption of 0.68% in the core of the helium triplet at mid-transit.…”