Properties and Occurrence Rates for Kepler Exoplanet Candidates as a Function of Host Star Metallicity from the DR25 Catalog

Abstract

Correlations between the occurrence rate of exoplanets and their host star properties provide important clues about the planet formation processes. We studied the dependence of the observed properties of exoplanets (radius, mass, and orbital period) as a function of their host star metallicity. We analyzed the planetary radii and orbital periods of over 2800 Kepler candidates from the latest Kepler data release DR25 (Q1-Q17) with revised planetary radii based on Gaia DR2 as a function of host star metallicity (from the Q1-Q17 (DR25) stellar and planet catalog). With a much larger sample and improved radius measurements, we are able to reconfirm previous results in the literature. We show that the average metallicity of the host star increases as the radius of the planet increases. We demonstrate this by first calculating the average host star metallicity for different radius bins and then supplementing these results by calculating the occurrence rate as a function of planetary radius and host star metallicity. We find a similar trend between host star metallicity and planet mass: the average host star metallicity increases with increasing planet mass. This trend, however, reverses for masses > 4.0 M J : host star metallicity drops with increasing planetary mass. We further examined the correlation between the host star metallicity and the orbital period of the planet. We find that for planets with orbital periods less than 10 days, the average metallicity of the host star is higher than that for planets with periods greater than 10 days.

A Statistical Search for Star–Planet Interaction in the Ultraviolet Using GALEX

“…Although we have removed all known planet hosting stars from our control sample, stars with yet undetected planets could still contaminate the sample. However, from Figure 1, we see that the predominant spectral type of the control sample is F-G-K type stars, for which the occurrence rate of hot Jupiters which are responsible for causing SPI-induced activity enhancement is as low as 0.7 hot Jupiters per 100 stars (This value has been obtained based on the treatment in Narang et al (2018) and is similar to what is presented in Hsu et al (2019)). This is not high enough to alter the total distribution of our control sample and hence our general conclusion will remain unaffected even if such a contamination is present.…”

Investigating the planet–metallicity correlation for hot Jupiters

“…A number of studies examine the relationship between metallicity of a host star and the orbital period of different planet types in the system, including giant planets. The result of Narang et al (2018) finds no difference in metallicity with orbital period for giant planets. Adibekyan et al (2013) find that, from ∼ 10 M ⊕ to ∼ 4 M J , planets in metalpoor systems have longer periods than those in metal-rich systems.…”

“…Their transiting sample has an average orbital period of 11 days, whereas the average for their RV sample is 1202 days. Unfortunately, the average of the transit sample in Adibekyan (2019) is a little over the 10 day threshold that defines a short period giant planet in Narang et al (2018), therefore making the two incomparable.…”

Not gone with the wind: Planet occurrence is independent of stellar galactocentric velocity

“…When we first saw the apparent difference in planet host and field star velocities, we considered that we may be indirectly picking up on the relation between stellar metallicity and planet occurrence rate. The relation posits that planets are more common around metal-rich stars (Wang & Fischer 2015), though the relation is strongest for Jupiter-mass plan-ets and short-period planets (planets with periods shorter than 10 days) (Mulders et al 2016;Petigura et al 2018;Narang et al 2018). We thought we might be picking up on this relation because metal-poor stars are more common in the thick disk of the Milky Way, where stellar motion is also higher.…”