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Register a new userA hot mini-Neptune in the radius valley orbiting solar analogue HD 110113
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We report the discovery of HD 110113 b (TOI-755.01), a transiting mini-Neptune exoplanet on a 2.5-day orbit around the solar-analogue HD 110113 (Teff = 5730K). Using TESS photometry and HARPS radial velocities gathered by the NCORES program, we find HD 110113 b has a radius of $2.05pm0.12$ $R_oplus$ and a mass of $4.55pm0.62$ $M_oplus$. The resulting density of $2.90^{+0.75}_{-0.59}$ g cm^{-3} is significantly lower than would be expected from a pure-rock world; therefore, HD 110113 b must be a mini-Neptune with a significant volatile atmosphere. The high incident flux places it within the so-called radius valley; however, HD 110113 b was able to hold onto a substantial (0.1-1%) H-He atmosphere over its $sim4$ Gyr lifetime. Through a novel simultaneous gaussian process fit to multiple activity indicators, we were also able to fit for the strong stellar rotation signal with period $20.8pm1.2$ d from the RVs and confirm an additional non-transiting planet with a mass of $10.5pm1.2$ $M_oplus$ and a period of $6.744^{+0.008}_{-0.009}$ d.
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We report on the validation of two planets orbiting the nearby (36pc) M2 dwarf TOI-1266 observed by the TESS mission. The inner planet is sub-Neptune-sized ($R=2.46 pm 0.08 R_oplus$) with an orbital period of 10.9 days. The outer planet has a radius of $1.67_{-0.11}^{+0.09} R_oplus$ and resides in the exoplanet Radius Valley---the transition region between rocky and gaseous planets. With an orbital period of 18.8 days, the outer planet receives an insolation flux of 2.4 times that of Earth, similar to the insolation of Venus. Using precision near-infrared radial velocities with the Habitable-zone Planet Finder Spectrograph, we place upper mass limits of $15.9 M_oplus$ and $6.4 M_oplus$ at 95% confidence for the inner and outer planet, respectively. A more precise mass constraint of planet c, achievable with current RV instruments given the host star brightness (V=12.9, J=9.7), will yield further insights into the dominant processes sculpting the exoplanet Radius Valley.
As exoplanetary science matures into its third decade, we are increasingly offered the possibility of pre existing, archival observations for newly detected candidates. This is particularly poignant for the TESS mission, whose survey spans bright, nearby dwarf stars in both hemispheres, which are precisely the types of sources targeted by previous radial velocity (RV) surveys. On this basis, we investigated whether any of the TESS Objects of Interest (TOIs) coincided with such observations, from which we find 18 single planet candidate systems. Of these, one exhibits an RV signature that has the correct period and phase matching the transiting planetary candidate with a false alarm probability of less than 1 percent. After further checks, we exploit this fact to validate HD 183579b (TOI-1055b). This planet is less than 4 Earth Radii and has better than 33 percent planetary mass measurements, thus advancing the TESS primary objective of finding 50 such worlds. We find that this planet is amongst the most accessible small transiting planets for atmospheric characterization. Our work highlights that the efforts to confirm and even precisely measure the masses of new transiting planet candidates need not always depend on acquiring new observations - that in some instances these tasks can be completed with existing data.
We detect Lyman $alpha$ absorption from the escaping atmosphere of HD 63433c, a $R=2.67 R_oplus$, $P=20.5$ d mini Neptune orbiting a young (440 Myr) solar analogue in the Ursa Major Moving Group. Using HST/STIS, we measure a transit depth of $11.1 pm 1.5$% in the blue wing and $8 pm 3$% in the red. This signal is unlikely to be due to stellar variability, but should be confirmed by an upcoming second visit with HST. We do not detect Lyman $alpha$ absorption from the inner planet, a smaller $R=2.15 R_oplus$ mini Neptune on a 7.1 d orbit. We use Keck/NIRSPEC to place an upper limit of 0.5% on helium absorption for both planets. We measure the host stars X-ray spectrum and FUV flux with XMM-Newton, and model the outflow from both planets using a 3D hydrodynamic code. This model provides a reasonable match to the light curve in the blue wing of the Lyman $alpha$ line and the helium non-detection for planet c, although it does not explain the tentative red wing absorption or reproduce the excess absorption spectrum in detail. Its predictions of strong Lyman $alpha$ and helium absorption from b are ruled out by the observations. This model predicts a much shorter mass loss timescale for planet b, suggesting that b and c are fundamentally different: while the latter still retains its hydrogen/helium envelope, the former has likely lost its primordial atmosphere.
About one out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultra-short-period planet (Sanchis-ojeda et al. 2014; Winn et al. 2018). All of the previously known ultra-short-period planets are either hot Jupiters, with sizes above 10 Earth radii (Re), or apparently rocky planets smaller than 2 Re. Such lack of planets of intermediate size (the hot Neptune desert) has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. Here, we report the discovery of an ultra-short-period planet with a radius of 4.6 Re and a mass of 29 Me, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite (Ricker et al. 2015) revealed transits of the bright Sun-like star starname, every 0.79 days. The planets mean density is similar to that of Neptune, and according to thermal evolution models, it has a H/He-rich envelope constituting 9.0^(+2.7)_(-2.9)% of the total mass. With an equilibrium temperature around 2000 K, it is unclear how this ultra-hot Neptune managed to retain such an envelope. Follow-up observations of the planets atmosphere to better understand its origin and physical nature will be facilitated by the stars brightness (Vmag=9.8).
We report the discovery and characterization of a transiting warm sub-Neptune planet around the nearby bright ($V=8.75$ mag, $K=7.15$ mag) solar twin HD 183579, delivered by the Transiting Exoplanet Survey Satellite (TESS). The host star is located $56.8pm0.1$ pc away with a radius of $R_{ast}=0.97pm0.02 R_{odot}$ and a mass of $M_{ast}=1.03pm0.05 M_{odot}$. We confirm the planetary nature by combining space and ground-based photometry, spectroscopy, and imaging. We find that HD 183579b (TOI-1055b) has a radius of $R_{p}=3.53pm0.13 R_{oplus}$ on a $17.47$ day orbit with a mass of $M_{p}=11.2pm5.4 M_{oplus}$ ($3sigma$ mass upper limit of $27.4 M_{oplus}$). HD 183579b is the fifth brightest known sub-Neptune planet system in the sky, making it an excellent target for future studies of the interior structure and atmospheric properties. By performing a line-by-line differential analysis using the high resolution and signal-to-noise ratio HARPS spectra, we find that HD 183579 joins the typical solar twin sample, without a statistically significant refractory element depletion.
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