ORCID Profile
0000-0002-9936-6285
Current Organisation
University of California, San Diego
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Publisher: American Astronomical Society
Date: 03-06-2019
Publisher: American Astronomical Society
Date: 2022
Abstract: While the Milky Way nuclear star cluster (MW NSC) has been studied extensively, how it formed is uncertain. Studies have shown it contains a solar and supersolar metallicity population that may have formed in situ, along with a subsolar-metallicity population that may have formed via mergers of globular clusters and dwarf galaxies. Stellar abundance measurements are critical to differentiate between formation scenarios. We present new measurements of [M/H] and α -element abundances [ α /Fe] of two subsolar-metallicity stars in the Galactic center. These observations were taken with the adaptive-optics-assisted high-resolution ( R = 24,000) spectrograph NIRSPEC in the K band (1.8–2.6 micron). These are the first α -element abundance measurements of subsolar-metallicity stars in the MW NSC. We measure [M/H] = − 0.59 ± 0.11, [ α /Fe] = 0.05 ± 0.15 and [M/H] = − 0.81 ± 0.12, [ α /Fe] = 0.15 ± 0.16 for the two stars at the Galactic center the uncertainties are dominated by systematic uncertainties in the spectral templates. The stars have an [ α /Fe] in between the [ α /Fe] of globular clusters and dwarf galaxies at similar [M/H] values. Their abundances are very different than the bulk of the stars in the nuclear star cluster. These results indicate that the subsolar-metallicity population in the MW NSC likely originated from infalling dwarf galaxies or globular clusters and are unlikely to have formed in situ.
Publisher: American Astronomical Society
Date: 02-08-2023
Abstract: The carbon-to-oxygen (C/O) ratio in an exoplanet atmosphere has been suggested as a potential diagnostic of planet formation. Now that a number of exoplanets have measured C/O ratios, it is possible to examine this diagnostic at a population level. Here, we present an analysis of currently measured C/O ratios of directly imaged and transit/eclipse planets. First, we derive atmospheric parameters for the substellar companion HD 284149 AB b using data taken with the OSIRIS integral field spectrograph at the W.M. Keck Observatory and report two non-detections from our ongoing imaging spectroscopy survey with Keck/OSIRIS. We find an effective temperature of T eff = 2502 K, with a range of 2291–2624 K, log g = 4.52 , with a range of 4.38–4.91, and [M/H] = 0.37, with a range of 0.10–0.55. We derive a C/O of 0.59 − 0.30 + 0.15 for HD 284149 AB b. We add this measurement to the list of C/O ratios for directly imaged planets and compare them with those from a s le of transit/eclipse planets. We also derive the first dynamical mass estimate for HD 284149 AB b, finding a mass of ∼28 M Jup . There is a trend in C/O ratio with companion mass ( M Jup ), with a break seen around 4 M Jup . We run a Kolmogorov–Smirnov and an Anderson–Darling test on planets above and below this mass boundary, and find that they are two distinct populations. This could be additional evidence of two distinct populations possibly having two different formation pathways, with companion mass as an indicator of most likely formation scenario.
Publisher: American Astronomical Society
Date: 02-2022
Abstract: The kinematics and dynamics of stellar and substellar populations within young, still-forming clusters provide valuable information for constraining theories of formation mechanisms. Using Keck II NIRSPEC+AO data, we have measured radial velocities for 56 low-mass sources within 4′ of the core of the Orion Nebula Cluster (ONC). We also remeasure radial velocities for 172 sources observed with SDSS/APOGEE. These data are combined with proper motions measured using HST ACS/WFPC2/WFC3IR and Keck II NIRC2, creating a s le of 135 sources with all three velocity components. The velocities measured are consistent with a normal distribution in all three components. We measure intrinsic velocity dispersions of ( σ v α , σ v δ , σ v r ) = (1.64 ± 0.12, 2.03 ± 0.13, 2.56 − 0.17 + 0.16 ) km s −1 . Our computed intrinsic velocity dispersion profiles are consistent with the dynamical equilibrium models from Da Rio et al. (2014) in the tangential direction but not in the line-of-sight direction, possibly indicating that the core of the ONC is not yet virialized, and may require a nonspherical potential to explain the observed velocity dispersion profiles. We also observe a slight elongation along the north–south direction following the filament, which has been well studied in previous literature, and an elongation in the line-of-sight to tangential velocity direction. These 3D kinematics will help in the development of realistic models of the formation and early evolution of massive clusters.
Publisher: American Astronomical Society
Date: 28-02-2018
Publisher: American Astronomical Society
Date: 03-05-2010
Publisher: American Astronomical Society
Date: 11-02-2019
Location: United States of America
No related grants have been discovered for Quinn Konopacky.