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

TL;DR

The study targets rapid inner-disk dust evolution in CVSO 1942 by comparing a 2024 JWST/MIRI spectrum with archival Spitzer/IRS data and NEOWISE photometry, revealing a mid-infrared flux increase by a factor of ~2 at $λ \,\leq\, 10\,\mu$m over a timescale of $\lesssim$2 weeks. The excess is well modeled by warm (≈1400 K), optically thick dust near the sublimation radius, with an emitting area of about $A \approx 1.93\times10^{23}$ cm$^2$ and a minimum dust mass $M_d \gtrsim 9.7\times10^{20}$ g (≈$4.9\times10^{-13}$ M$_{\odot}$), while the 10 μm silicate feature remains unchanged. The authors argue for rapid in situ dust formation, possibly from planetesimal collisions, as the most plausible mechanism, with alternative explanations such as accretion bursts or drifting dust clumps disfavored by the data. This provides evidence for active dust production at the inner disk edge and hints at the late stages of disk evolution toward a debris-disk-like state, underscoring the need for multi-timescale monitoring. Absent longer-term data, the exact triggering process remains uncertain but is consistent with in situ events in a low-accretion, transitional disk system.

Abstract

We report a significant increase in mid-infrared emission $\leq10$ $μ$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 $λ\leq10$ $μ$m, compared to the near photospheric flux level observed with Spitzer/IRS in 2005. No significant change in flux at $\gtrsim15$ $μ$m is detected in the spectra. Comparing the MIRI/MRS spectrum and NEOWISE photometry, we found that this $\leq10$ $μ$m flux increase occurs on a timescale of 2 weeks and is consistent with the presence of warm (1,400 K), optically thick, large ($\gtrsim1$ $μ$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.

Figures (4)

• Figure 1: Infrared Spectral Variability of CVSO 1942. The blue, orange, and red lines are observations from JWST/MIRI (2024), Spitzer/IRS-LowRes (2005), and Spitzer/IRS-HiRes (2008), respectively. The best fit to the IRS-LowRes spectrum is shown as a black dashed line, which represents the combination of the photosphere (gray dotted line), the optically thin dust (brown solid line), and the outer wall (green solid line), as described in espaillat2012. By adding a blackbody component with T=1400 K (pink solid line) to the 2008 Spitzer model, we can fit the JWST/MIRI observation. The purple and red vertical bars denote the range of observations with WISE W1 and W2, shown in Fig. \ref{['fig:wise']}.
• Figure 2: Left: The light curve of CVSO 1942 from the ALLWISE (2010-2011) and NEOWISE (2014-2024) survey. The photosphere has been subtracted. The horizontal lines indicate the levels extrapolated by the models that fit the 2008 Spitzer observation (dashed lines) and the 2024 JWST observation (solid lines). The horizontal dotted lines show the photospheric level, and the vertical dashed line shows the date of the JWST observation, which was 2 weeks after the last NEOWISE observation. The data points are binned to 7-days. Right: The zoom-in, unbinned light curve of the star around the JWST observation.
• Figure 3: Optical light curves of CVSO 1942. Top/middle: The photometry from ZTF DR23 in the g and r bands. The data points are subtracted by the median magnitudes (shown in dashed lines). Vertical lines mark the observation dates of TESS, Magellan/MIKE (2020), JWST/MIRI, and WIYN/NEID. Bottom: The TESS light curve. The optical light curve is periodic with a period of 4.688 days.
• Figure 4: H$\alpha$ profiles of CVSO 1942 across 15 years. The blue lines represent the observations, the red lines represent the average magnetospheric model, and the gray lines represent the top 100 best-fit models. The orange lines are the average chromospheric models, and the black lines are the average total models.