On the Nature of Small Planets around the Coolest Kepler Stars
(2012) In Astrophysical Journal 746(1). Abstract
 We constrain the densities of Earthto Neptunesize planets around very cool (Te = 36604660 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 powerlaw massradius 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 KolmogorovSmirnov probabilities occur for a powerlaw index alpha approximate to 4, indicating that rockymetal planets dominate the planet population in this size range. A... (More)
 We constrain the densities of Earthto Neptunesize planets around very cool (Te = 36604660 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 powerlaw massradius 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 KolmogorovSmirnov probabilities occur for a powerlaw index alpha approximate to 4, indicating that rockymetal planets dominate the planet population in this size range. A single population of gasrich, lowdensity 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 gasrich 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)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/record/2570692
 author
 Gaidos, Eric ^{LU} ; Fischer, Debra A.; Mann, Andrew W. and Lepine, Sebastien
 organization
 publishing date
 2012
 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
 0004637X
 DOI
 10.1088/0004637X/746/1/36
 language
 English
 LU publication?
 yes
 id
 f97a678bb8754bc39a06954a2ac08f6b (old id 2570692)
 date added to LUP
 20120601 14:31:49
 date last changed
 20180107 07:48:43
@article{f97a678bb8754bc39a06954a2ac08f6b, abstract = {We constrain the densities of Earthto Neptunesize planets around very cool (Te = 36604660 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 powerlaw massradius 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 KolmogorovSmirnov probabilities occur for a powerlaw index alpha approximate to 4, indicating that rockymetal planets dominate the planet population in this size range. A single population of gasrich, lowdensity 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 gasrich 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 = {0004637X}, 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/10.1088/0004637X/746/1/36}, volume = {746}, year = {2012}, }