Caeley Pittman | Searcharxiv

arXiv2026

Indications of Rapid Dust Formation in the Inner Region of a Protoplanetary Disk

We report a significant increase in mid-infrared emission $\leq10$ $\mu$m in a transitional disk. The 2024 JWST/MIRI observation of the disk around CVSO 1942 reveals flux increase by a factor of two at $\lambda\leq10$ $\mu$m, compared to the near photospheric flux level observed with Spitzer/IRS in 2005. No significant change in flux at $\gtrsim15$ $\mu$m is detected in the spectra. Comparing the MIRI/MRS spectrum and NEOWISE photometry, we found that this $\leq10$ $\mu$m flux increase occurs on a timescale of 2 weeks and is consistent with the presence of warm (1,400 K), optically thick, large ($\gtrsim1$ $\mu$m) dust grains near the dust sublimation radius. We propose that this rapid dust appearance may indicate in situ dust formation, possibly from planetesimal collisions in the inner disk.

astro-ph.EP↗

arXiv2024

A Model of the C IV $\lambda\lambda$ 1548, 1550 Doublet Line in T Tauri Stars

The C IV doublet in the UV has long been associated with accretion in T Tauri stars. However, it is still unclear where and how the lines are formed. Here, we present a new C IV line model based on the currently available accretion shock and accretion flow models. We assume axisymmetric, dipolar accretion flows with different energy fluxes and calculate the properties of the accretion shock. We use Cloudy to obtain the carbon level populations and calculate the emerging line profiles assuming a plane-parallel geometry near the shock. Our model generally reproduces the intensities and shapes of the C IV emission lines observed from T Tauri stars. We find that the narrow component is optically thin and originates in the postshock, while the broad component is optically thick and emerges from the preshock. We apply our model to seven T Tauri stars from the Hubble Ultraviolet Legacy Library of Young Stars as Essential Standards Director's Discretionary program (ULLYSES), for which consistently determined accretion shock properties are available. We can reproduce the observations of four stars, finding that the accretion flows are carbon-depleted. We also find that the chromospheric emission accounts for less than 10 percent of the observed C IV line flux in accreting T Tauri stars. This work paves the way toward a better understanding of hot line formation and provides a potential probe of abundances in the inner disk.

astro-ph.SR↗