Browsing by Subject "Planetary systems"
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Item Doppler tomographic observations of exoplanetary transits(2013-08) Johnson, Marshall Caleb; Dodson-Robinson, Sarah E.Transiting planet candidates around rapidly rotating stars, a number of which have been found by the Kepler mission, are not amenable to follow-up via the usual radial velocity techniques due to their rotationally broadened stellar lines. An alternative method is Doppler tomography. In this method, the distortions of the stellar spectral lines due to subtracted light during the transit are spectroscopically resolved. This allows us to not only validate the transiting planet candidate but also to obtain the spin-orbit misalignment for the system. The spin-orbit misalignment is a powerful statistical tracer of the migration histories of planets. I discuss our project to perform Doppler tomographic observations of Kepler candidates and other transiting planets using the facilities at McDonald Observatory. I present our first transit detection, that of Kepler-13 b, and discuss some other recent results.Item Silicon and oxygen abundances in planet-host stars(2010-12) Brugamyer, Erik John; Dodson-Robinson, Sarah E.; Komatsu, EiichiroThe positive correlation between planet detection rate and host star iron abundance lends strong support to the core accretion theory of planet formation. However, iron is not the most significant mass contributor to the cores of giant planets. Since giant planet cores grow from silicate grains with icy mantles, the likelihood of gas giant formation should depend heavily on the oxygen and silicon abundance of the planet formation environment. Here we compare the silicon and oxygen abundances of a set of 60 planet hosts and a control sample of 60 metal-rich stars without giant planets. We find a 99% probability that planet detection rate depends on the silicon abundance of the host star, over and above the observed planet-metallicity correlation. Due to our large error bars on oxygen abundances, we do not yet observe any correlation between oxygen abundance and planet detection rate. We predict that a correlation between planet occurrence and oxygen abundance should emerge when we can measure [O/Fe] at 0.05 dex precision. Since up to 20% of the carbon in the universe may be in refractory grains, we also predict that planet detection rate should correlate positively with host star carbon abundance for any population of planets formed by core accretion.Item Spin-orbit misalignments, planet candidate validation, and nodal precession via Doppler tomography(2016-08) Johnson, Marshall Caleb; Cochran, William D.; Collier Cameron, Andrew; Endl, Michael; Robinson, Edward L; Sneden, ChrisTransiting planets around intermediate-mass stars (1.5 MSun < M* < 2.5MSun , or 6500 K < Teff < 10000 K on the main sequence) occupy a largely unexplored part of parameter space; these stars tend to rotate rapidly, and thus are unsuitable for the precise radial velocity observations that are typically used to follow up and confirm transiting planet candidates. In this dissertation I demonstrate the use of Doppler tomography, where I spectroscopically resolve the perturbation to the rotationally broadened stellar line profile during the transit due to the Rossiter-McLaughlin effect, to confirm transiting planet candidates around rapidly-rotating stars and to measure the (mis)alignment of the planetary orbit with respect to the stellar rotation. The demographics of planets around intermediate-mass stars are important for constraining models of planet formation as a function of stellar mass, while the distribution of spin-orbit misalignments of transiting planets is a powerful statistical tracer of planet migration processes. Using Doppler tomography, I show that the hot Jupiter Kepler-13 Ab has a misaligned but prograde orbit; I improve upon the precision of the misalignment measurement for the hot Jupiter WASP-79 b, which has a nearly polar orbit; and I measure an aligned orbit for the warm Jupiter Kepler-448 b, and two degenerate solutions (both prograde) for the hot Jupiter HAT-P-41 b. I also analyze observations of several Kepler planet candidates–KOI-366.01, KOI-368.01, and KOI-972.01–in an attempt to validate them as bona fide planets. Unfortunately, due to small planetary radii and/or limited amounts of data, I am able to achieve only a ∼ 2σ detection of KOI-368.01, and am unable to detect KOI-366.01 or KOI-972.01. I also analyze two epochs of Doppler tomographic observations of the highly inclined hot Jupiter WASP-33 b taken six years apart, and show that the path of the transit across the stellar disk has changed between the two epochs due to nodal precession of the planetary orbit. This allows me to measure the precession rate, and constrain the stellar gravitational quadrupole moment J2. Overall, I show that Doppler tomography is an effective tool for confirming and characterizing transiting planets around rapidly-rotating stars, where typical methods have difficulty.