1,721,404 research outputs found
ARE TIDAL EFFECTS RESPONSIBLE FOR EXOPLANETARY SPIN–ORBIT ALIGNMENT?
No full textThe obliquities of planet-hosting stars are clues about the formation of planetary systems. Previous observations led to the hypothesis that for close-in giant planets, spin–orbit alignment is enforced by tidal interactions. Here, we examine two problems with this hypothesis. First, Mazeh and coworkers recently used a new technique—based on the amplitude of starspot-induced photometric variability—to conclude that spin–orbit alignment is common even for relatively long-period planets, which would not be expected if tides were responsible. We re-examine the data and find a statistically significant correlation between photometric variability and planetary orbital period that is qualitatively consistent with tidal interactions. However it is still difficult to explain quantitatively, as it would require tides to be effective for periods as long as tens of days. Second, Rogers and Lin argued against a particular theory for tidal re-alignment by showing that initially retrograde systems would fail to be re-aligned, in contradiction with the observed prevalence of prograde systems. We investigate a simple model that overcomes this problem by taking into account the dissipation of inertial waves and the equilibrium tide, as well as magnetic braking. We identify a region of parameter space where re-alignment can be achieved, but it only works for close-in giant planets, and requires some fine tuning. Thus, while we find both problems to be more nuanced than they first appeared, the tidal model still has serious shortcomings.United States. National Aeronautics and Space Administration. Origins Program t (grant NNX11AG85G
The Geometry of Planetary Systems: An Exploration of the Obliquities of Kepler Planet-Hosting Stars
No full textAs new exoplanetary systems have been discovered, it has become clear that our Solar System’s architecture is not the only possible result of planetary system formation, and, in fact, may not be the dominant architecture for systems with otherwise similar characteristics. One key difference is the angle between the stellar axis of rotation and the orbital axis of the planet(s) around a star: the stellar obliquity. Stellar obliquities ranging from 0◦ to 180◦ have been observed. This is different than what might be expected based upon the Sun, which is aligned with the planets to within 6◦. The exoplanetary systems whose obliquities have been previously measured tend to be those with giant close-in planets, because the signals in those cases are larger and easier to detect. As a result, very few investigations have been done into the obliquities of Kepler planet-hosting stars. Using a new control sample of stars and data from the California-Kepler Survey, we seek to fill in this gap in understanding and investigate the obliquity distribution of Kepler planet hosts. We analyzed the observed distribution of projected rotation velocity (v sin i) of the planet hosts and the control stars, finding that the hosts have typical inclinations of 60◦ to 70◦, corresponding to minimum obliquities of 20◦ to 30◦. These results suggest that planet-hosts were misaligned with the protoplanetary disk or later misaligned by dynamical heating
The Geometry of Planetary Systems: An Exploration of the Obliquities of Kepler Planet-Hosting Stars
No full textAs new exoplanetary systems have been discovered, it has become clear that our Solar System’s architecture is not the only possible result of planetary system formation, and, in fact, may not be the dominant architecture for systems with otherwise similar characteristics. One key difference is the angle between the stellar axis of rotation and the orbital axis of the planet(s) around a star: the stellar obliquity. Stellar obliquities ranging from 0◦ to 180◦ have been observed. This is different than what might be expected based upon the Sun, which is aligned with the planets to within 6◦. The exoplanetary systems whose obliquities have been previously measured tend to be those with giant close-in planets, because the signals in those cases are larger and easier to detect. As a result, very few investigations have been done into the obliquities of Kepler planet-hosting stars. Using a new control sample of stars and data from the California-Kepler Survey, we seek to fill in this gap in understanding and investigate the obliquity distribution of Kepler planet hosts. We analyzed the observed distribution of projected rotation velocity (v sin i) of the planet hosts and the control stars, finding that the hosts have typical inclinations of 60◦ to 70◦, corresponding to minimum obliquities of 20◦ to 30◦. These results suggest that planet-hosts were misaligned with the protoplanetary disk or later misaligned by dynamical heating
The Geometry of Planetary Systems: An Exploration of the Obliquities of Kepler Planet-Hosting Stars
No full textA Preliminary Analysis of GDR3 Metallicities for Exoplanet Hosts
No full textThere are long-established correlations between exoplanet properties and the metallicities of their host stars. For example, gas giants have a higher occurrence rate around stars with higher metallicities. With the release of Gaia DR3 (GDR3), we now have access to a massive new sample of metallicities derived from Gaia's photometric BP/RP and RVS instruments to investigate these trends further. However, these metallicity values must be validated against the literature before any widespread use. I start by cross-matching GDR3 against the NASA Exoplanet Archive and the TESS TOI Catalog, isolating GDR3's data on exoplanet and exoplanet candidate host stars. After applying recommended calibrations to GDR3's spectroscopic and photometric metallicity data, I compared the host star metallicity in GDR3 to the metallicities in LAMOST DR8 and GALAH DR3. Both photometric and spectroscopic metallicities correlated well with literature values. However, the photometric metallicity showed evidence of systematic errors. Next, I demonstrate that GDR3's metallicities are consistent with LAMOST metallicities across all magnitude ranges. Nevertheless, correlation with GALAH decreases for dimmer stars in almost all cases. Reflecting this trend, Gaia correlation with GALAH is shown to be best for the largest, hottest stars in the subset. Finally, I show that GDR3's photometric and spectroscopic metallicities show evidence of the well-established correlation between gas giants' occurrence and host star metallicity. I also present evidence for a potential correlation between planet multiplicity and host star metallicity. However, a more robust statistical study is needed to verify this trend
The TESS Grand Unified Hot Jupiter Survey
No full textHot Jupiters – gas giant planets that orbit their stars once every few days – were a surprising discovery at the dawn of the exoplanet era. The existence of these massive planets so close to their host stars contradicted previous theories of planet formation, and their origins remain unclear. Even though hundreds of hot Jupiters have now been found, the sample was drawn from a diverse collection of ground-based surveys with heterogeneous selection biases, making it difficult to draw statistical inferences about this population.This dissertation presents the TESS Grand Unified Hot Jupiter Survey – our effort to leverage NASA’s Transiting Exoplanet Survey Satellite (TESS) to expand the statistical sample of hot Jupiters by an order of magnitude. By uniformly searching the sky for transiting exoplanets, TESS allows us to unify the past three decades of ground-based planet searches with new discoveries, thereby assembling a homogeneous catalog of 400 transiting hot Jupiters orbiting FGK stars brighter than G ≤ 12.5. Chapter 2 contains our initial forecasts and feasibility study for this survey, where we found that ≈ 50% of hot Jupiters around such a sample of stars remained to be discovered. Chapters 3 through 5 describe the discovery of 60 new giant planets from our survey, based on follow-up photometric, imaging, and spectroscopic data. These observations are key to confirming the planet candidates from TESS and eliminating false positives. We highlight the first statistical findings to emerge from our survey in Chapter 6, where we show that the orbital period distribution of hot Jupiters does not depend the metallicity of their host stars.
Looking forward, we present an update on the current status of the survey in Chapter 7, including new planet confirmations, a list of false positives, and a preliminary magnitude-limited catalog of hot Jupiters. Finally, in Chapter 8, we provide a glimpse at the demographic results from the full sample, including a 4-σ detection of the “period pile-up” at ≈ 3 days, and quantifying how hot Jupiter occurrence rates depend on stellar metallicity. These are the first clues toward understanding the enigmatic origins of hot Jupiters
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Origins and Fates of Close-In Giant Planets
No full textThe exoplanet census has revealed a diversity of worlds far beyond that of the solar system. This work aims to advance our empirical understanding of the evolutionary processes responsible for this diversity.
Chapters 2 and 3 focus on the final tidal inspirals of hot Jupiters. Using transit timing measurements from NASA's Transiting Exoplanet Survey Satellite (TESS), we found that the apparent orbital period of the hot Jupiter WASP-4b is slowly shrinking. Care was warranted however before claiming a detection of tidal orbital decay. In our case, we showed that the data were best explained through a Doppler-like effect caused by an outer planet or brown dwarf; future searches for tidal orbital decay will need to account for similar effects.
Chapters 4 through 7 are oriented around the discovery of young short-period giant planets. While thousands of planets have been discovered, most are between one and ten billion years old. These chapters introduce a Cluster Difference Imaging Photometric Survey that uses TESS to find planets around stars in coeval groups younger than one billion years. Most of the targeted stars are in open clusters that are poorly resolved by TESS, so we built our own difference-imaging data reduction pipeline (Chapter 4).
Three results based on the data products are highlighted. First, PTFO 8-8695b, a 10 Myr (million-year) old candidate hot Jupiter whose planetary status has been debated for nearly a decade, is not a planet (Chapter 5). The rejection of PTFO 8-8695b implies that the existence of sub-100 Myr old hot Jupiters is an open question. Second, based on TESS transits and ground-based follow-up, the 40 Myr old Saturn-sized TOI 837b is likely a planet (Chapter 6). Its size (8.6 Earth radii) and orbital period (8.3 days) are consistent with a Neptune-mass planet whose rocky core is enveloped by a primordial atmosphere of hydrogen and helium. Finally, based on Gaia kinematics and TESS rotation periods, the open cluster NGC 2516 (150 Myr old) has a halo of stars that spans 500 parsecs tip-to-tip (Chapter 7). This supports a new Gaia-enabled paradigm wherein the halos of open clusters are often more populous than their cores. There are significant implications for upcoming planet searches around young stars
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