HW 2 Question 1 (Jocelyn)



Evidence of an upper bound on the masses of planets and its implications for giant planet formation


Kevin C. Schlaufman


The current existence of 10 M_jup objects orbiting nearby stars and floating freely in star-forming regions have confused many in the astronomical community. It is currently impossible to determine the origin of these objects and has come down to two working theories: formation through core accretion similar to giant gas planets or formation through gravitational instability similar to stars. Due to many unknowns about these objects, it has made it difficult to determine a clear upper limit for planets. However the differences between formation of core accretion or gravitation instability can be separated statistically. Giant planets equal to the mass of Jupiter prefer to orbit metal rich host stars, these indicative of formation through core accretion. While formations through gravitational instability occurs with equal efficiency regardless of gas-phase metallicity. From these observations, the maximum mass at which planets no longer prefer orbits metal rich host stars can be used to separate massive planets from brown dwarfs.  As well as give a rough mass of the largest planets that can be formed through core accretion. 

Schlaufman states that this transition area from large celestial object orbiting metal rich stars to metal poor stars occurs somewhere between 4 M_jup ≤ M ≤ 10 M_jup. From here he suggests that M ≤ 10 M_jup form throughcore accretion while object with M ≥ 10 M_Jup form through gravitational instability.  Schlaufman targets system where the minimum mass of the secondary has been inferred using the Doppler method and has an inclination close to 90˚ due to the observed transit. This provides 2 key advantages. First, having a minimum mass inferred for the secondary using the Doppler measurement give a closer secondary mass because of the observed transit ensuring that inclination is close to 90˚. Second, having observations using both the Doppler and transit method guarantees that the secondary is real. After using the NASA Exoplanet Archive to find test subjects, Schlaufman was able to have a combined sample size of 146 giant planets, brown dwarfs and low mass stars. Once complying the sample, Schlaufman used two methods to analyze it. First, he used the clustering algorithm to show the relationship between the mass of the bodies and the metallicity of the host star. Examining the graph, there is a clear distinction between the two objects. 

Second, he used the theoretical prediction of Mordasini, that massive objects formed by core accretion should only happen in the most metal rich primaries. From that theory, he created a plot of the median metallicity as a function of the secondary mass. This graph shows that the moving median metallicity begins to decrease as the secondary mass increase, showing the shift of preference from metal rich to metal poor. The boundary of second graph is near the 10 M_Jup.

From the graphs, it seems that celestial objects with a mass less than 10 M_Jup are more likely to orbit metal rich solar type dwarf stars while objects with a mass greater than 10 M_jup do not orbit metal rich stars. This preference of orbiting metal rich host stars is thought to be a property of planet formation through core accretion. While orbiting metal poor host stars is a property of planet formed through gravitational instability. The data shows that it is very rare for giant planets to form from core accretion and that these objects should not be considered as planet but rather something else all together.

Comments

  1. UnknownFebruary 27, 2018 at 12:28 AM

    Very nicely organized by an overall abstract in the beginning to summarizing till a conclusion at the end.

    ReplyDelete

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