Download The same frequency of planets inside and outside open

The same frequency of planets
inside and outside open clusters
of stars
S. Meibom, G. Torres, F. Fessin et al.
Nature 499, 55–58 (04 July 2013)
Background
and the punchline 
• Most stars and planets formed in star clusters.
• Richer and denser clusters survive (1000-10000 per
cubic parsec). 95% fall apart.
• Survived clusters are hostile environment for planets.
• Statistics support that too. More than 800 planets in Sun
like stars (usually Neptine size or smaller)
• Only 4 planets in clusters.
• Discovery of 2 sub-Neptune planets in a billion year old
open cluster NGC 6811 (Meibom et al. 2013)
Details
• Before Kepler, the surveys were less sensitive.
• Difficult to detect smaller planets.
• 4 planets in star clusters, all jupiter like
• A jupiter in epsilon-tau in Hyades (Sato et al. 2007)
• A jupiter in TYC 5409-2156-1 in NGC 2423 (Lovis and Mayor
2007).
• Theory: most Sun like stars did not posses disk massive enough
to form gas giant planets.
• Two jupiters in Beehive cluster (Prasepe, Quimm et al. 2012) in
Sun like stars.
Doppler Shift method
Problem
Transit of planets
NASA’s Kepler mission
Kepler Discoveries
Discovery of Planets in
NGC6811
• NGC 6811- Open cluster in constellation of Cygnus
• At 3600 light years away with size 13’ (14-20ly
across)
• Age is more than a billion year.
• At birth must have consisted more than 6000 stars
including 8 O-type and 125 B type stars
• Hosts many mid F to early K stars.
Discovery of Planets in
NGC6811
• Survey of 377 stars
• Found planets in Kepler-66 and Kepler-67.
Kepler-66 and Kepler-67 are
indeed part of NGC 6811.
• Common Space motion of stars in NGC 6811.
• NGC6811 members radial velocity peak 7.7+/-0.8
km/s with 5 year of monitoring.
• Kepler-66 and Kepler-67 7.8+/-0.2 and 8.2+/0.2km/s based on 7-8 measurements.
The colour–magnitude and colour–period diagrams for
NGC6811.
S Meibom et al. Nature 000, 1-4 (2013) doi:10.1038/nature12279
Transit light curves.
S Meibom et al. Nature 000, 1-4 (2013) doi:10.1038/nature12279
Properties of planets in
NGC6811
Validation
• Rule out false positives. No presence of nearby
object in the analysis of centroid motion and high
resolution imaging.
• Low precision radial velocities with Keck and MMT
rule out star or brown dwarf.
• High precision Doppler spectroscopy not possible
because stars very faint (15.3 and 16.4).
• BLENDER technique used to discard false positive.
BLENDER
• Simulate large number of foreground background scenarios.
• Use constraints from centroid motion, high resolution
imaging and high resolution spectroscopy, color of the star,
mass of the star etc.
• Found that false positives resulting from eclipsing binaries
placed at distanced much farther away from cluster.
• Large planet also ruled out.
• Two false positive chances only 0.2%. One false positive
chances 7.7%.
Distribution of planetary properties.
S Meibom et al. Nature 000, 1-4 (2013) doi:10.1038/nature12279
Significance
• Cluster is placid environment for planet formation,
especially old cluster like NGC 6811.
• As cluster ages it dissolves away 90% of stars in
first few tens of million years.
• This means NGC6811 must be initially dense
cluster i.e. even more hostile environment.
• Planet formation is robust 
Radial Velocity Method
Kepler’s Field of View
Statistics
• Lower limit to frequency of detectable neptunes in
this cluster=1/377 =2.7E-3
• Frequency of detectable neptunes in field stars by
Kepler: 6.6E-3 ((985-66)/138253)).
• Clusters should have at least 40% detectable
neptunes.
• Mass of the planets was constrained based on the
model, as to this size planet can have what kind of
composition <10-15 earth.