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Joseph Y. Tang

Publications and source records attributed to Joseph Y. Tang.

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An early look at how gas giants shape small planet bulk compositions

Gas giants may shape the reservoir of solids and gas in the inner disk in which the small planets assemble. To test this possibility, we collect a sample of 43 exoplanetary systems containing 68 inner small planets (ISP) with both measured masses (1-20 M$_{\oplus}$) and radii (1-4 R$_{\oplus}$). After correcting for heterogeneous individual system sensitivities to distant gas giants, we calculate the gas giant occurrence rate in ISP systems P(GG$|$ISP) as a function of inner small planet density, envelope mass fraction (EMF), and core mass. While we find no significant difference between P(GG$|$ISP) given high/low small planet density, EMF, or core mass, we see hints of a trend when only looking at the metal-rich systems. Despite the substantial limitations due to small sample sizes, we find that gas giants in metal-rich systems are preferentially found with lower density planets with similar core masses. We find consistent hints of trends using larger samples of inner planets with measured radii divided across the radius valley or with measured masses divided across 10 $M_\oplus$. Our result is consistent with more metal-enriched disks catalyzing rapid core assembly and kickstarting the gas accretion early, while the muted difference in the outer giant occurrence rate with respect to core mass may indicate contamination by post-formation photoevaporation.

astro-ph.EP

The Kinematically Hot, Extremely Metal-Poor C-19 Stellar Stream in DESI DR2

Stellar streams are the result of a host galaxy's gravitational potential tidally disrupting satellite dwarf galaxies and globular clusters (GCs), causing them to grow leading and trailing tidal tails. The C-19 stellar stream is an extremely metal-poor stellar population, showing chemical abundance patterns characteristic of a globular cluster. However, its large velocity dispersion is difficult to reconcile with a conventional, purely baryonic, disrupting-GC progenitor. Current techniques for stream characterization are primarily applied to Gaia DR3, relying heavily on proper motion measurements. Using the Dark Energy Spectroscopic Instrument (DESI), which provides radial velocities and metallicites for over 10 million stars reaching significantly fainter magnitudes than comparable surveys, we employ a mixture model approach to jointly characterize stream populations in proper motions, radial velocities, and metallicities against a Milky Way halo background. By applying this framework to the C-19 stellar stream, we identify a total of 47 spectroscopically confirmed member stars, of which 41 are newly identified and only 6 were previously reported in the literature. In this work, we measure a velocity dispersion of $7.8^{+1.5}_{-1.3}$ km s$^{-1}$ and a mean metallicity of [Fe/H] = $-3.36^{+0.12}_{-0.10}$. We further identify a novel 'spur' feature within the stream. We conclude that our measurements are in line with previous works identifying C-19 as a 'hot', metal-poor stream. In forthcoming work, we will apply this approach to many more streams in the DESI footprint, enabling population-level comparisons with predictions from simulations.

astro-ph.GA