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On the Nature of Small Planets around the Coolest Kepler Stars

Gaidos, Eric LU ; Fischer, Debra A.; Mann, Andrew W. and Lepine, Sebastien (2012) In Astrophysical Journal 746(1).
Abstract
We constrain the densities of Earth-to Neptune-size planets around very cool (T-e = 3660-4660 K) Kepler stars by comparing 1202 Keck/HIRES radial velocity measurements of 150 nearby stars to a model based on Kepler candidate planet radii and a power-law mass-radius relation. Our analysis is based on the presumption that the planet populations around the two sets of stars are the same. The model can reproduce the observed distribution of radial velocity variation over a range of parameter values, but, for the expected level of Doppler systematic error, the highest Kolmogorov-Smirnov probabilities occur for a power-law index alpha approximate to 4, indicating that rocky-metal planets dominate the planet population in this size range. A... (More)
We constrain the densities of Earth-to Neptune-size planets around very cool (T-e = 3660-4660 K) Kepler stars by comparing 1202 Keck/HIRES radial velocity measurements of 150 nearby stars to a model based on Kepler candidate planet radii and a power-law mass-radius relation. Our analysis is based on the presumption that the planet populations around the two sets of stars are the same. The model can reproduce the observed distribution of radial velocity variation over a range of parameter values, but, for the expected level of Doppler systematic error, the highest Kolmogorov-Smirnov probabilities occur for a power-law index alpha approximate to 4, indicating that rocky-metal planets dominate the planet population in this size range. A single population of gas-rich, low-density planets with alpha = 2 is ruled out unless our Doppler errors are >= 5 m s(-1), i.e., much larger than expected based on observations and stellar chromospheric emission. If small planets are a mix of gamma rocky planets (alpha = 3.85) and 1 - gamma gas-rich planets (alpha= 2), then gamma > 0.5 unless Doppler errors are >= 4 m s(-1). Our comparison also suggests that Kepler's detection efficiency relative to ideal calculations is less than unity. One possible source of incompleteness is target stars that are misclassified subgiants or giants, for which the transits of small planets would be impossible to detect. Our results are robust to systematic effects, and plausible errors in the estimated radii of Kepler stars have only moderate impact. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
astrobiology, planetary systems, techniques: radial velocities
in
Astrophysical Journal
volume
746
issue
1
publisher
University of Chicago Press
external identifiers
  • wos:000302861300036
  • scopus:84856286138
ISSN
0004-637X
DOI
10.1088/0004-637X/746/1/36
language
English
LU publication?
yes
id
f97a678b-b875-4bc3-9a06-954a2ac08f6b (old id 2570692)
date added to LUP
2012-06-01 14:31:49
date last changed
2017-07-30 04:15:18
@article{f97a678b-b875-4bc3-9a06-954a2ac08f6b,
  abstract     = {We constrain the densities of Earth-to Neptune-size planets around very cool (T-e = 3660-4660 K) Kepler stars by comparing 1202 Keck/HIRES radial velocity measurements of 150 nearby stars to a model based on Kepler candidate planet radii and a power-law mass-radius relation. Our analysis is based on the presumption that the planet populations around the two sets of stars are the same. The model can reproduce the observed distribution of radial velocity variation over a range of parameter values, but, for the expected level of Doppler systematic error, the highest Kolmogorov-Smirnov probabilities occur for a power-law index alpha approximate to 4, indicating that rocky-metal planets dominate the planet population in this size range. A single population of gas-rich, low-density planets with alpha = 2 is ruled out unless our Doppler errors are >= 5 m s(-1), i.e., much larger than expected based on observations and stellar chromospheric emission. If small planets are a mix of gamma rocky planets (alpha = 3.85) and 1 - gamma gas-rich planets (alpha= 2), then gamma > 0.5 unless Doppler errors are >= 4 m s(-1). Our comparison also suggests that Kepler's detection efficiency relative to ideal calculations is less than unity. One possible source of incompleteness is target stars that are misclassified subgiants or giants, for which the transits of small planets would be impossible to detect. Our results are robust to systematic effects, and plausible errors in the estimated radii of Kepler stars have only moderate impact.},
  author       = {Gaidos, Eric and Fischer, Debra A. and Mann, Andrew W. and Lepine, Sebastien},
  issn         = {0004-637X},
  keyword      = {astrobiology,planetary systems,techniques: radial velocities},
  language     = {eng},
  number       = {1},
  publisher    = {University of Chicago Press},
  series       = {Astrophysical Journal},
  title        = {On the Nature of Small Planets around the Coolest Kepler Stars},
  url          = {http://dx.doi.org/10.1088/0004-637X/746/1/36},
  volume       = {746},
  year         = {2012},
}