System Architectures by Spectral Type

System Architectures by Spectral Type

System Architecture by Spectral Type

Planetary Systems Detected by Radial Velocity Observations
Within 200 Parsecs

 

Star
Mass
(M
SOL)

Star
Spectral
Type

Median
Star
[Fe/H]

Number
of
Stars

Number
of
Planets

Hot
Jupiter
Systems

Hot
Neptune/Earth
Systems

Median
Planet
 Mass
(M
JUP)

Median
Planet
S/A

Median
Planet
Eccentricity

0.24 – 0.50

M

+0.04

8

13

0

63%

0.05

0.07

0.12

0.70 – 0.89

K, G

-0.01

39

48

26%

13%

0.63

0.20

0.12

0.90 – 1.19

K, G, F

+0.17

110

135

15%

5%

1.62

1.19

0.23

1.20 – 1.45

F*

+0.20

50

57

30%

2%

1.98

0.83

0.28

1.70 – 2.70

A**

-0.10

14

14

0

0

3.70

1.45

0.14

* Main-sequence F stars are mixed with subgiants (K2 IV-F6 IV) and giants (K III) representing evolved phases of F stars. Also included are several host stars identified as G dwarfs on the main sequence; some are probably misidentified subgiants.

** These are so-called “retired A stars” (see Johnson et al. 2007, 2008), meaning stars in the mass range of spectral type A (1.6-3.0 MSOL) that have evolved off the main sequence into the giant or subgiant phase. Their current spectral types range from K1 IV to G0 III.

 

Column 1 indicates the stellar mass range in units of Solar mass (MSOL). Column 2 indicates the spectral types included in the corresponding mass range. Column 3 lists the median metallicity for each mass range. Column 4 lists the number of exoplanetary host stars in each mass range. Column 5 lists the total number of exoplanets in each stellar mass range. Column 6 lists the percentage of systems containing at least one gas giant planet (minimum mass 0.2 MJUP) with a semimajor axis smaller than 0.1 astronomical unit (AU). Column 7 lists the percentage of systems containing at least one planet less massive than 0.2 MJUP with a semimajor axis smaller than 0.1 AU. Column 8 lists the median planet mass in units of Jupiter mass (MJUP). Column 9 lists the median planet semimajor axis in AU. Column 10 lists the median eccentricity of all planetary orbits in the stellar mass range.

 

Sources: Data on all stars of mass 0.7-1.45 MSOL follow the Extrasolar Planets Encyclopaedia, retrieved 15 May 2009. Data on all M dwarf stars follow Planets of Red Dwarfs; data on all “retired A stars” follow Planets & Debris Around A-type Stars.

 

This table presents basic statistical data on all well-constrained exoplanetary systems located within 200 parsecs of the Earth, as of June 2009. The breakdown by stellar mass is intended to mirror the distribution of host stars by spectral type (but see discussion, below).

 

trends

These simple statistics imply several interesting trends:

§           Both planet mass and planet semimajor axis increase along with stellar mass.

§           The frequently noted association between enhanced stellar metallicity and planet formation seems to hold only for stars in the mass range of spectral types G and F.

§           Hot Jupiters are typical evolutionary outcomes of F, G, and K stars, but not of lower-mass or higher-mass stars.

§           Orbital eccentricities increase with host star mass from type M through type F, but planets orbiting within a few AU of A stars have relatively circular orbits, like planets around M dwarfs. This trend becomes even clearer when we note that the maximum eccentricity so far observed among M dwarf planets is 0.38, while the maximum eccentricity among “retired A star” planets is 0.4. These moderate values contrast with the maximum eccentricities of planets orbiting F, G, and K stars within the 200 parsec sample: 0.85, 0.97, and 0.75, respectively.

 

sample selection

System data are presented by mass instead of by spectral type because these two parameters only partly coincide. The correspondence between mass and spectrum is most exact for M dwarfs and retired A stars, which lie at either extreme of the range. In this table, all stars 0.24-0.5 Msol are early M dwarfs, and all stars 1.7-2.7 MSOL are evolved A stars.

The correspondence is less exact, and the overlap is more extensive, among so-called “Sun-like” stars. In this group, the sample of stars 0.70-0.89 MSOL is the most homogeneous, with 82% K dwarfs and 18% G dwarfs.

Stars in the range of 0.90-1.19 MSOL are more diverse, with about 75% representing main-sequence G dwarfs (G0-G8) and another 10% representing subgiants and giants that probably originated as G dwarfs. An additional 15% are main-sequence stars of types K0 and K1 (at 1.0 MSOL or less) and F8 (above 1.0 MSOL).

The most diverse group comprises the 50 host stars in the range of 1.20-1.45 MSOL. Among them, 18 are main-sequence F stars (F5-F8); another 18 are subgiant stars (F6 IV-K2 IV) that likely represent the evolved phases of late F or early G-type stars; 11 are G stars (G0-G8), purportedly on the main sequence but probably, in at least some cases, misidentified subgiants; and 3 are red giants (K III), again representing the evolutionary outcomes of F-type stars.

 

limitations

More or less uncertainty applies to every parameter of interest, and data have been derived from various sources that may lack methodological consistency. Further, data on planetary systems orbiting the most massive and least massive host stars suffer from sampling limitations due to small numbers. Finally, no statistical tests of significance have been applied to any of these results, given my near-total ignorance of classical and modern statistical methods. Therefore, the values presented here are suggestive rather than authoritative. (Hey, this ain’t peer-reviewed literature, it’s self-publication on the Internet.)

 

Last update: June 2009

 

 

Works Cited

Johnson JA, Fischer D, Marcy GW, Wright JT, Driscoll P, Butler RP, Hekker S, Reffert S, Vogt SS. (2007) Retired A stars and their companions: Exoplanets orbiting three intermediate-mass subgiants. Astrophysical Journal, 665: 785-793. Abstract.

Johnson JA, Marcy GW, Fischer DA, Wright JT, Reffert S, Kregenow JM, Williams PKG, Peek KMG. (2008) Retired A stars and their companions II: Jovian planets orbiting Kappa Coronae Borealis and HD 167042. Astrophysical Journal, 675: 784-789. Abstract.

 

 

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All text is copyright Raymond Harris 2006-2009