Diversities and similarities exhibited by multi-planetary systems and their architectures: II. Radii of singles and multis

Abstract

The discovered planets in apparent single-planet systems (singles) and those in systems with multiple detected planets (multis) exhibit a rich diversity of physical and orbital properties. We investigate the differences and similarities between 1730 singles and 1522 multis in a catalogue of confirmed transiting planets orbiting main-sequence stars with spectral classes ranging from late-M to late-F. After we removed the hot Jupiters, the planet types and their fractional numbers were similar for the multis and singles hosted by FGK-type stars. Furthermore, the median radii of both the singles and the multis increase with host star temperature already from late- to early-type M dwarfs and further up to F stars. Our analyses show that the singles are larger on average than the multis in our F, G, K, and M samples. However, after we excluded the hot Jupiters, the radius distributions of the singles and multis orbiting FGK stars are statistically indistinguishable, particularly at $R < 4\, R_\oplus$. In the FGK sample, we also identified an unexpected and significant overabundance of multis, compared to singles, at radii of $\approx1.4-1.6\, R_\oplus$. For the early- and late-type M samples, our work indicates that the multis are smaller on average than the singles and that the radius distributions of the multis and singles are different, except for the planets with $R < 4\, R_\oplus$ hosted by early-type M dwarfs. Nevertheless, these results for the two M samples are inconclusive because the sample sizes of 167 and 101 planets are limited. In conclusion, our analyses reveal that the singles and multis, excluding the hot Jupiters, orbiting FGK stars are overall consistent with originating from the same underlying population based on their planet types and radii. This interpretation is, however, not applicable within the region of the overabundance of multis identified in this work.

Figures (9)

• Figure 1: Boxplots showing the radius distributions of all the singles (magenta) and multis (blue) examined in this work, divided into five samples based on the spectral type of the host star. Each box includes the data between the 0.25th and 0.75th quantiles, while the whiskers extend to the 5th and 95th percentiles. The median and mean radii of both the multis and singles increase as the host star temperature increases. The number of planets in each sample is indicated next to the host star type.
• Figure 2: Three main planet samples, divided into singles (magenta) and multis, for which the colours indicate the observed planet multiplicity in the system. The corresponding number of planets is written in white font. M0-2 and M3-9 hosts represent early- and late-type M stars, respectively. The FGK sample contains all the planets in Table \ref{['tab:all_stypes']} that orbit F, G, and K-type stars.
• Figure 3: Singles and multis orbiting the FGK host stars in our catalogue, divided into six different planet types as indicated in the figure legend and Table \ref{['tab:pct_pltypes']}. Upper panel: Entire FGK sample, including hot Jupiters, of which only 1% are multis. Lower panel: FGK sample after removing the hot Jupiters. The singles and multis now have similar fractional numbers of the remaining five planet types.
• Figure 4: Singles and multis in the early-type (upper panel) and late-type (lower panel) M sample, divided into five different planet types as listed in the figure legend and Table \ref{['tab:pct_pltypes']}. The middle column displays the distribution of the singles after removing the hot Jupiters.
• Figure 5: Percentages (purple line) and binomial uncertainties (magenta region) of the planets that are singles as a function of planet radius (Sect. \ref{['sect:pct_singles']}). These percentages are computed as a function of the mean of the planet radii in each consecutive bin comprising 100 singles in the FGK sample (panel a), 20 singles in the early-type M sample (panel b), and 15 singles in the late-type M sample (panel c). The sharp decline for the FGK sample occurs in the region of the multis overabundance at $R \approx1.4-1.6\, R_\oplus$.