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Open Access Publications from the University of California

Scholarly Works (10 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2022)

This thesis is part of larger survey conducted using the OSIRIS IFU on the W. M. Keck Telescope to directly image exoplanets. I begin this publication with an overview of direct detection and characterization of exoplanets, the current key scientific questions plaguing the field such as the formation of these objects and how they are distinct from low-mass brown dwarfs, and my contributions using OSIRIS. OSIRIS is an ideal instrument for this type of imaging; an integral field spectrograph (IFU) allows us to distinguish scattered starlight and speckle artifacts from the planet itself. OSIRIS observations of directly imaged planets have greatly improved our understanding of their atmospheres, hinted at formation pathways, and, with sufficient SNR, can reveal individual molecular lines.

The three substellar companions were observed, spectrally extracted, and atmospherically characterized with OSIRIS in K-band (~2.2 um) -- kappa And b, VHS 1256 b, and HD 284149 b. The R~4,000 spectra were analyzed via a forward modeling framework with custom PHOENIX atmosphere models and Husser et al. 2013 models. This framework allowed for the derivation of effective temperatures, surface gravities, metallicities, and carbon and oxygen abundances. In particular, the C/O ratio was derived for each source as a possible formation tracer diagnostic.

Finally, this thesis analyzed the C/O ratio formation tracer. Directly imaged planets remain a mystery for the two main formation pathways--core accretion/pebble accretion. It was believed an elevated C/O ratio would point towards formation via core accretion, and a stellar C/O ratio would insinuate formation through gravitational instability. The C/O ratios of the planets in this thesis, as well as the C/O ratios from other works show that all directly imaged planets have stellar C/O. A small fraction of transit/eclipse planets also have derived C/O ratios, thus they were compared to the directly imaged planet C/O ratios against various system parameters. A trend was revealed between companion mass and the C/O ratio, which showed that there may be two distinct populations of exoplanets with possible different formation mechanisms. This thesis expresses a need for new formation diagnostics, a more in depth study into why the directly imaged planet population have the same C/O ratios, and more analyses that span across the different exoplanet populations.

    Cover page: Moderate Resolution Spectroscopy of Directly Imaged Exoplanets
    • Article
    UC San Diego Previously Published Works (2023)
    We present the kinematic anaylsis of $246$ stars within $4^\prime$ from the center of Orion Nebula Cluster (ONC), the closest massive star cluster with active star formation across the full mass range, which provides valuable insights in the the formation and evolution of star cluster on an individual-star basis. High-precision radial velocities and surface temperatures are retrieved from spectra acquired by the NIRSPEC instrument used with adaptive optics (NIRSPAO) on the Keck II 10-m telescope. A three-dimensional kinematic map is then constructed by combining with the proper motions previously measured by the Hubble Space Telescope (HST) ACS/WFPC2/WFC3IR and Keck II NIRC2. The measured root-mean-squared velocity dispersion is $2.26\pm0.08~\mathrm{km}\,\mathrm{s}^{-1}$, significantly higher than the virial equilibrium's requirement of $1.73~\mathrm{km}\,\mathrm{s}^{-1}$, suggesting that the ONC core is supervirial, consistent with previous findings. Energy equipartition is not detected in the cluster. Most notably, the velocity of each star relative to its neighbors is found to be negatively correlated with stellar mass. Low-mass stars moving faster than their surrounding stars in a supervirial cluster suggests that the initial masses of forming stars may be related to their initial kinematic states. Additionally, a clockwise rotation preference is detected. A weak sign of inverse mass segregation is also identified among stars excluding the Trapezium stars, though it could be a sample bias. Finally, this study reports the discovery of four new candidate spectroscopic binary systems.
      Cover page: The 3D Kinematics of the Orion Nebula Cluster II: Mass-dependent Kinematics of the Inner ClusterCreative Commons 'BY-NC' version 4.0 license
      • Article
      • Peer Reviewed
      UCLA Previously Published Works (2016)
      We present the discovery of a brown dwarf companion to the debris disk host star HR 2562. This object, discovered with the Gemini Planet Imager (GPI), has a projected separation of 20.3 ± 0.3 au (0.″618 ± 0. ″004) from the star. With the high astrometric precision afforded by GPI, we have confirmed, to more than 5?, the common proper motion of HR 2562B with the star, with only a month-long time baseline between observations. Spectral data in the J-, H-, and K-bands show a morphological similarity to L/T transition objects. We assign a spectral type of L7 ± 3 to HR 2562Band derive a luminosity of log(Lbol/L⊙) = -4.62 ± 0.12, corresponding to a mass of 30 ± 15 MJup from evolutionary models at an estimated age of the system of 300-900 Myr. Although the uncertainty in the age of the host star is significant, the spectra and photometry exhibit several indications of youth for HR 2562B. The source has a position angle that is consistent with an orbit in the same plane as the debris disk recently resolved with Herschel. Additionally, it appears to be interior to the debris disk. Though the extent of the inner hole is currently too uncertain to place limits on the mass of HR 2562B, future observations of the disk with higher spatial resolution may be able to provide mass constraints. This is the first brown-dwarf-mass object found to reside in the inner hole of a debris disk, offering the opportunity to search for evidence of formation above the deuterium burning limit in a circumstellar disk.
        Cover page: DISCOVERY OF A SUBSTELLAR COMPANION TO THE NEARBY DEBRIS DISK HOST HR 2562
        • Article
        • Peer Reviewed
        UCLA Previously Published Works (2017)
        We present new observations of the low-mass companion to HD 984 taken with the Gemini Planet Imager (GPI) as a part of the GPI Exoplanet Survey campaign. Images of HD 984 B were obtained in the J (1.12-1.3 μm) and H (1.50-1.80 μm) bands. Combined with archival epochs from 2012 and 2014, we fit the first orbit to the companion to find an 18 au (70-year) orbit with a 68% confidence interval between 14 and 28 au, an eccentricity of 0.18 with a 68% confidence interval between 0.05 and 0.47, and an inclination of 119°with a 68% confidence interval between 114°and 125°. To address the considerable spectral covariance in both spectra, we present a method of splitting the spectra into low and high frequencies to analyze the spectral structure at different spatial frequencies with the proper spectral noise correlation. Using the split spectra, we compare them to known spectral types using field brown dwarf and low-mass star spectra and find a best-fit match of a field gravity M6.5 ±1.5 spectral type with a corresponding temperature of K. Photometry of the companion yields a luminosity of log(Lbol/L⊙)=2.88 ± 0.07 dex with DUSTY models. Mass estimates, again from DUSTY models, find an age-dependent mass of 34 ±1 to 95 ±4 M Jup. These results are consistent with previous measurements of the object.
          Cover page: Integral Field Spectroscopy of the Low-mass Companion HD 984 B with the Gemini Planet Imager
          • Article
          • Peer Reviewed
          UCLA Previously Published Works (2015)
          We present new Gemini Planet Imager observations of the young exoplanet 51 Eridani b that provide further evidence that the companion is physically associated with 51 Eridani. Combining this new astrometric measurement with those reported in the literature, we significantly reduce the posterior probability that 51 Eridani b is an unbound foreground or background T-dwarf in a chance alignment with 51 Eridani to 2 × 10-7, an order of magnitude lower than previously reported. If 51 Eridani b is indeed a bound object, then we have detected orbital motion of the planet between the discovery epoch and the latest epoch. By implementing a computationally efficient Monte Carlo technique, preliminary constraints are placed on the orbital parameters of the system. The current set of astrometric measurements suggest an orbital semimajor axis of AU, corresponding to a period of years (assuming a mass of 1.75 Mo for the central star), and an inclination of deg. The remaining orbital elements are only marginally constrained by the current measurements. These preliminary values suggest an orbit that does not share the same inclination as the orbit of the distant M-dwarf binary, GJ 3305, which is a wide physically bound companion to 51 Eridani.
            Cover page: ASTROMETRIC CONFIRMATION AND PRELIMINARY ORBITAL PARAMETERS OF THE YOUNG EXOPLANET 51 ERIDANI b WITH THE GEMINI PLANET IMAGER
            • Article
            • Peer Reviewed
            UCLA Previously Published Works (2017)
              Cover page: Integral Field Spectroscopy of the Low-mass Companion HD 984 B with the Gemini Planet Imager
              • Article
              • Peer Reviewed
              UCLA Previously Published Works (2016)
              We present new spatially resolved astrometry and photometry from the Gemini Planet Imager of the inner binary of the young multiple star system V343 Normae, which is a member of the β Pictoris (β Pic) moving group. V343 Normae comprises a K0 and mid-M star in a ∼4.5 year orbit (AaAb) and a wide 10″ M5 companion (B). By combining these data with archival astrometry and radial velocities we fit the orbit and measure individual masses for both components of MAa = 1.10 ± 0.10 M⊙ and MAb = 0.290 ± 0.018 M⊙. Comparing to theoretical isochrones, we find good agreement for the measured masses and JHK band magnitudes of the two components consistent with the age of the β Pic moving group. We derive a model-dependent age for the β Pic moving group of 26 ±3 Myr by combining our results for V343 Normae with literature measurements for GJ 3305, which is another group member with resolved binary components and dynamical masses.
                Cover page: DYNAMICAL MASS MEASUREMENT OF THE YOUNG SPECTROSCOPIC BINARY V343 NORMAE AaAb RESOLVED WITH THE GEMINI PLANET IMAGER
                • Article
                • Peer Reviewed
                UCLA Previously Published Works (2018)
                The Gemini Planet Imager Exoplanet Survey (GPIES) is a multiyear direct imaging survey of 600 stars to discover and characterize young Jovian exoplanets and their environments. We have developed an automated data architecture to process and index all data related to the survey uniformly. An automated and flexible data processing framework, which we term the Data Cruncher, combines multiple data reduction pipelines (DRPs) together to process all spectroscopic, polarimetric, and calibration data taken with GPIES. With no human intervention, fully reduced and calibrated data products are available less than an hour after the data are taken to expedite follow up on potential objects of interest. The Data Cruncher can run on a supercomputer to reprocess all GPIES data in a single day as improvements are made to our DRPs. A backend MySQL database indexes all files, which are synced to the cloud, and a front-end web server allows for easy browsing of all files associated with GPIES. To help observers, quicklook displays show reduced data as they are processed in real time, and chatbots on Slack post observing information as well as reduced data products. Together, the GPIES automated data processing architecture reduces our workload, provides real-Time data reduction, optimizes our observing strategy, and maintains a homogeneously reduced dataset to study planet occurrence and instrument performance.
                  Cover page: Automated data processing architecture for the Gemini Planet Imager Exoplanet Survey
                  • Article
                  • Peer Reviewed
                  UCLA Previously Published Works (2016)
                  A principal scientific goal of the Gemini Planet Imager (GPI) is obtaining milliarcsecond astrometry to constrain exoplanet orbits. However, astrometry of directly imaged exoplanets is subject to biases, systematic errors, and speckle noise. Here, we describe an analytical procedure to forward model the signal of an exoplanet that accounts for both the observing strategy (angular and spectral differential imaging) and the data reduction method (Karhunen-Loève Image Projection algorithm). We use this forward model to measure the position of an exoplanet in a Bayesian framework employing Gaussian processes and Markov-chain Monte Carlo to account for correlated noise. In the case of GPI data on β Pic b, this technique, which we call Bayesian KLIP-FM Astrometry (BKA), outperforms previous techniques and yields 1σ errors at or below the one milliarcsecond level. We validate BKA by fitting a Keplerian orbit to 12 GPI observations along with previous astrometry from other instruments. The statistical properties of the residuals confirm that BKA is accurate and correctly estimates astrometric errors. Our constraints on the orbit of β Pic b firmly rule out the possibility of a transit of the planet at 10-σ significance. However, we confirm that the Hill sphere of β Pic b will transit, giving us a rare chance to probe the circumplanetary environment of a young, evolving exoplanet. We provide an ephemeris for photometric monitoring of the Hill sphere transit event, which will begin at the start of April in 2017 and finish at the end of January in 2018.
                    Cover page: THE ORBIT AND TRANSIT PROSPECTS FOR β PICTORIS b CONSTRAINED WITH ONE MILLIARCSECOND ASTROMETRY
                    • Article
                    • Peer Reviewed
                    UC Santa Cruz Previously Published Works (2024)
                      Cover page: Innovations and advances in instrumentation at the W. M. Keck Observatory, vol. IIICreative Commons 'BY-NC-SA' version 4.0 license
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