Author ORCID Identifier
Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
The open clusters IC 2602 and IC 2391 are important benchmarks for testing early star and planet evolution theories, both structural and dynamical, because they are the nearest open clusters with ages of ∼50 Myr. Because accurate membership lists are vital to age-determination of clusters and placing observational constraints on theories, we refine membership lists for these clusters. We identify 529 new candidate members (801 in total, including known members) using Gaia DR2 data and we confirm membership for 26 of these based on spectra obtained with the CHIRON spectrograph. We identify new binaries, measure signatures of youth (lithium, Hα), and determine effective temperatures, metallicities, surface gravities, as well as radial velocities and vsini values for these new members.
A major challenge to detecting planets via radial velocity (RV) measurements in these clusters is stellar jitter that can mask or even mimic planetary RVs. However, the amplitude of stellar jitter in the age range of 10-100 Myr remains largely unknown. To address this, we monitor the radial velocity of 29 slower rotating (vsini < 30 km/s), Sun-like (FGK), bona-fide members of IC 2602, IC 2391, and the ∼45 Myr moving group Tucana-Horologium (Tuc-Hor). By fitting possible orbits, we find two stars that show RV variations similar to that expected for hot Jupiter companions. However, line bisector analyses reveal that the observed RV variations are most likely caused by stellar jitter. We measure the dispersion of RVs for 29 stars to be 168 m/s for IC 2602, 225 m/s for IC 2391, and 311 m/s for Tuc-Hor. Overall, the stellar jitter at ∼50 Myr is 237 m/s. This is similar to the semi-amplitude produced by a 2 Jupiter-mass planet on a 3-day orbit or a 3 Jupiter-mass planet on a 10-day orbit. Our survey complements NASA’s TESS and Kepler K2 missions by helping to confirm or reject candidate planets in RV follow-up. Our survey also complements field studies in older open clusters, helping us to map out the evolution of stellar jitter and planetary systems as a function of age and strongly constraining competing theories of planet formation and migration.
Nisak, Azmain, "Confirming New Suns and Searching for New Planets in IC 2602 and IC 2391." Dissertation, Georgia State University, 2022.
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