9 research outputs found
A dense mini-Neptune orbiting the bright young star HD 18599
© 2022 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This is the accepted manuscript version of an article which has been published in final form at https://doi.org/10.1093/mnras/stac2845Very little is known about the young planet population because the detection of small planets orbiting young stars is obscured by the effects of stellar activity and fast rotation which mask planets within radial velocity and transit data sets. The few planets that have been discovered in young clusters generally orbit stars too faint for any detailed follow-up analysis. Here we present the characterization of a new mini-Neptune planet orbiting the bright (V=9) and nearby K2 dwarf star, HD 18599. The planet candidate was originally detected in TESS light curves from Sectors 2, 3, 29, and 30, with an orbital period of 4.138~days. We then used HARPS and FEROS radial velocities, to find the companion mass to be 25.54.6~M. When we combine this with the measured radius from TESS, of 2.700.05~R, we find a high planetary density of 7.11.4~g cm. The planet exists on the edge of the Neptune Desert and is the first young planet (300 Myr) of its type to inhabit this region. Structure models argue for a bulk composition to consist of 23% HO and 77% Rock and Iron. Future follow-up with large ground- and space-based telescopes can enable us to begin to understand in detail the characteristics of young Neptunes in the galaxy.Peer reviewe
A dense mini-Neptune orbiting the bright young star HD 18599
Very little is known about the young planet population because the detection of small planets orbiting young stars is obscured by the effects of stellar activity and fast rotation which mask planets within radial velocity and transit data sets. The few planets that have been discovered in young clusters generally orbit stars too faint for any detailed follow-up analysis. Here we present the characterization of a new mini-Neptune planet orbiting the bright (V=9) and nearby K2 dwarf star, HD 18599. The planet candidate was originally detected in TESS light curves from Sectors 2, 3, 29, and 30, with an orbital period of 4.138 days. We then used HARPS and FEROS radial velocities, to find the companion mass to be 25.5±4.6 M⊕. When we combine this with the measured radius from TESS of 2.70±0.05 R⊕, we find a high planetary density of 7.1±1.4 g cm-3. The planet exists on the edge of the Neptune Desert and is the first young planet (300 Myr) of its type to inhabit this region. Structure models argue for a bulk composition to consist of 23 per cent H2O and 77 per cent Rock and Iron. Future follow-up with large ground- and space-based telescopes can enable us to begin to understand in detail the characteristics of young Neptunes in the galaxy
The Magellan-TESS Survey I: Survey Description and Mid-Survey Results
One of the most significant revelations from Kepler is that roughly one-third
of Sun-like stars host planets which orbit their stars within 100 days and are
between the size of Earth and Neptune. How do these super-Earth and sub-Neptune
planets form, what are they made of, and do they represent a continuous
population or naturally divide into separate groups? Measuring their masses and
thus bulk densities can help address these questions of their origin and
composition. To that end, we began the Magellan-TESS Survey (MTS), which uses
Magellan II/PFS to obtain radial velocity (RV) masses of 30 transiting
exoplanets discovered by TESS and develops an analysis framework that connects
observed planet distributions to underlying populations. In the past, RV
measurements of small planets have been challenging to obtain due to the
faintness and low RV semi-amplitudes of most Kepler systems, and challenging to
interpret due to the potential biases in the existing ensemble of small planet
masses from non-algorithmic decisions for target selection and observation
plans. The MTS attempts to minimize these biases by focusing on bright TESS
targets and employing a quantitative selection function and multi-year
observing strategy. In this paper, we (1) describe the motivation and survey
strategy behind the MTS, (2) present our first catalog of planet mass and
density constraints for 25 TESS Objects of Interest (TOIs; 20 in our population
analysis sample, five that are members of the same systems), and (3) employ a
hierarchical Bayesian model to produce preliminary constraints on the
mass-radius (M-R) relation. We find qualitative agreement with prior
mass-radius relations but some quantitative differences (abridged). The the
results of this work can inform more detailed studies of individual systems and
offer a framework that can be applied to future RV surveys with the goal of
population inferences.Comment: 101 pages (39 of main text and references, the rest an appendix of
figures and tables). Submitted to AAS Journal
An ultrahot Neptune in the Neptune desert
About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R⊕), or apparently rocky planets smaller than 2 R⊕. 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 ultrashort-period planet with a radius of 4.6 R⊕ and a mass of 29 M⊕, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. The planet’s 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 2,000 K, it is unclear how this ‘ultrahot Neptune’ managed to retain such an envelope. Follow-up observations of the planet’s atmosphere to better understand its origin and physical nature will be facilitated by the star’s brightness (V_(mag) = 9.8)
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An ultrahot Neptune in the Neptune desert
About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet1,2. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R⊕), or apparently rocky planets smaller than 2 R⊕. 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 ultrashort-period planet with a radius of 4.6 R⊕ and a mass of 29 M⊕, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite3 revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. The planet’s 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 2,000 K, it is unclear how this ‘ultrahot Neptune’ managed to retain such an envelope. Follow-up observations of the planet’s atmosphere to better understand its origin and physical nature will be facilitated by the star’s brightness (Vmag = 9.8).<br