LAMOST telescope reveals that Neptunian cousins of hot Jupiters are mostly single offspring of stars that are rich in heavy elements

Abstract

We discover a population of short-period, Neptune-size planets sharing key similarities with hot Jupiters: both populations are preferentially hosted by metal-rich stars, and both are preferentially found in Kepler systems with single transiting planets. We use accurate LAMOST DR4 stellar parameters for main-sequence stars to study the distributions of short-period 1d < P < 10d Kepler planets as a function of host star metallicity. The radius distribution of planets around metal-rich stars is more "puffed up" as compared to that around metal-poor hosts. In two period-radius regimes, planets preferentially reside around metal-rich stars, while there are hardly any planets around metal-poor stars. One is the well-known hot Jupiters, and the other is a population of Neptune-size planets (2 R_Earth <~ R_p <~ 6 R_Earth), dubbed as "Hoptunes". Also like hot Jupiters, Hoptunes occur more frequently in systems with single transiting planets though the fraction of Hoptunes occurring in multiples is larger than that of hot Jupiters. About 1% of solar-type stars host "Hoptunes", and the frequencies of Hoptunes and hot Jupiters increase with consistent trends as a function of [Fe/H]. In the planet radius distribution, hot Jupiters and Hoptunes are separated by a "valley" at approximately Saturn size (in the range of 6 R_Earth <~ R_p <~ 10 R_Earth), and this "hot-Saturn valley" represents approximately an order-of-magnitude decrease in planet frequency compared to hot Jupiters and Hoptunes. The empirical "kinship" between Hoptunes and hot Jupiters suggests likely common processes (migration and/or formation) responsible for their existence.

Published in PNAS. Title modified and text slightly adjusted according to PNAS style. Two ancillary files: 1) Table S1 (hoptune_tableS1.csv) with planetary and stellar parameters of the sample; 2) Table S2 (hoptune_tableS2.csv) with stellar parameters of 32556 LAMOST-Kepler targets from LAMOST DR3

References in corpus (12)

• Atmospheric Escape from Hot Jupiters
• Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation
• Three regimes of extrasolar planets inferred from host star metallicities
• Planetary Candidates Observed by Kepler VI: Planet Sample from Q1-Q16 (47 Months)
• Kepler constraints on planets near hot Jupiters
• A Study of the Shortest-Period Planets Found With Kepler
• Exoplanet Orbital Eccentricities Derived From LAMOST-Kepler Analysis
• The LAMOST Stellar Parameter Pipeline at Peking University --- LSP3
• Activity indicators and stellar parameters of the Kepler targets. An application of the ROTFIT pipeline to LAMOST-Kepler stellar spectra
• A Super-Solar Metallicity For Stars With Hot Rocky Exoplanets
• The metallicity distribution and hot Jupiter rate of the Kepler field: Hectochelle High-resolution spectroscopy for 776 Kepler target stars
• LAMOST observations in the Kepler field. Analysis of the stellar parameters measured with the LASP based on the low-resolution spectra

Cited by in corpus (36)

• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• Overview of the LAMOST survey in the first decade
• Heavy metal rules. I. Exoplanet incidence and metallicity
• The Habitable-zone Planet Finder Reveals A High Mass and a Low Obliquity for the Young Neptune K2-25b
• A Tale of Planet Formation: From Dust to Planets
• Phase II of the LAMOST-Kepler/K2 survey. I. Time series of medium-resolution spectroscopic observations
• A Joint Mass-Radius-Period Distribution of Exoplanets
• Evolution of the Exoplanet Size Distribution: Forming Large Super-Earths Over Billions of Years
• A significant mutual inclination between the planets within the $\pi$ Mensae system
• Mutual Orbital Inclinations Between Cold Jupiters and Inner Super-Earths
• TKS X: Confirmation of TOI-1444b and a Comparative Analysis of the Ultra-short-period Planets with Hot Neptunes
• Zodiacal Exoplanets in Time. X. The Orbit and Atmosphere of the Young "Neptune Desert"-Dwelling Planet K2-100b
• Overview of the LAMOST-$Kepler$ project
• TKS III: A Stellar Obliquity Measurement of TOI-1726 c
• Planets Across Space and Time (PAST). III. Morphology of the Planetary Radius Valley as a Function of Stellar Age and Metallicity in the Galactic Context Revealed by the LAMOST-Gaia-Kepler Sample
• An Increase in Small-planet Occurrence with Metallicity for Late-type Dwarf Stars in the Kepler Field and Its Implications for Planet Formation
• LAMOST Observations in 15 \textit{K}2 Campaigns: I. Low resolution spectra from LAMOST DR6
• Evidence for Primordial Alignment: Insights from Stellar Obliquity Measurements for Compact Sub-Saturn Systems
• TOI-4010: A System of Three Large Short-Period Planets With a Massive Long-Period Companion
• Super-Earths and sub-Neptunes are Insensitive to Stellar Metallicity
• Which stars can form planets: Planetesimal formation at low metallicities
• A Spectroscopic Analysis of the California-Kepler Survey Sample: II. Correlations of Stellar Metallicities with Planetary Architectures
• The sub-Jovian desert of exoplanets: parameter dependent boundaries and implications on planet formation
• HATS-37Ab and HATS-38b: Two Transiting Hot Neptunes in the Desert
• Hot planets around cool stars -- two short-period mini-Neptunes transiting the late K-dwarf TOI-1260
• TOI-954 b and K2-329 b: Short-Period Saturn-Mass Planets that Test whether Irradiation Leads to Inflation
• Sub-Jovian desert of exoplanets at its boundaries. Parameter dependence along the main sequence
• Planetary Orbit Eccentricity Trends (POET). I. The Eccentricity-Metallicity Trend for Small Planets Revealed by the LAMOST-Gaia-Kepler Sample
• TOI-5108 b and TOI 5786 b: Two transiting sub-Saturns detected and characterized with TESS, MaHPS and SOPHIE
• A Spectroscopic Analysis of a Sample of K2 Planet-Host Stars: Stellar Parameters, Metallicities and Planetary Radii
• The Hot-Neptune Initiative (HONEI) I. Two hot sub-Neptunes on a close-in, eccentric orbit (TOI-5800 b) and a farther-out, circular orbit (TOI-5817 b)
• Detecting and Monitoring Tidal Dissipation of Hot Jupiters in the Era of SiTian
• The young planetary system K2-25: constraints on companions and starspots
• The New Generation Planetary Population Synthesis (NGPPS) VIII. Impact of host star metallicity on planet occurrence rates, orbital periods, eccentricities, and radius valley morphology
• Chemical Abundances Shape History (CASH). I. A Link between Giant Planets Orbital Periods and Host Stellar C/O Ratios