Dust and Water in V883 Ori: Relics of a Retreating Snowline

Abstract

V883 Ori is an FU-Orionis-type outburst system characterized by a shoulder at 50-70 au in its ALMA band 6 and 7 intensity profiles. Previously, this feature was attributed to dust pile-up from pebble disintegration at the water snowline. However, recent multi-wavelength observations show continuity in the spectral index across the expected snowline region, disfavoring abrupt changes in grain properties. Moreover, extended water emission is detected beyond 80 au, pointing to a snowline further out. This Letter aims to explain both features with a model in which the snowline is receding. We construct a 2D disk model that solves the cooling and subsequent vapor recondensation during the post-outburst dimming phase. Our results show that both the intensity shoulder and the extended water emission are natural relics of a retreating snowline: the shoulder arises from excess surface density generated by vapor recondensation at the moving condensation front, while the outer water vapor reservoir persists due to the long recondensation timescales of $10^{2}-10^{3}$ yr at the disk atmosphere. As V883 Ori continues to fade, we predict that the intensity shoulder will migrate inward by an observationally significant amount of 10 au over about 25 years.

Figures (7)

• Figure 1: Evolution of the bolometric luminosity of V883 Ori during the outburst dimming phase. The symbols denote measurements from different studies, with horizontal bars showing the time range of adopted data. The blue band represents the adopted luminosity curve, which carries an uncertainty of ${\sim}40~\mathrm{yrs}$ due to the uncertainties in estimating $L_{\mathrm{bol}}$.
• Figure 2: Time evolution of the surface density profiles of the best-fit model. Silicate surface density remains constant with time. The thick line denotes the best-fit $t^{\prime}=121$ yr.
• Figure 3: Comparison of the synthetic intensity profiles with ALMA continuum. Crosses show ALMA data adopted from HougeEtal2024, spaced according to the beam sizes; shaded regions indicate the rms error. Solid lines represent the best-fit retreating snowline model, while dotted lines correspond to the best-fit static model. Enhanced emission towards the inner regions arises likely from intense viscous heating AlarconEtal2024, which is not accounted for in the model.
• Figure 4: Average column density of H$_{2}^{18}$O at 80-120 au under different condensation rate ($f_{\mathrm{cond}}$). The vertical grey band indicates the time range when observing the intensity shoulder. The dashed black line denotes the average column density derived from ALMA band 5 data by TobinEtal2023 with $1\sigma$ uncertainty shaded in grey. Dotted grey line denotes the best-fit value in static snowline model.
• Figure 5: Disk temperature, vapor condensation timescale ($t_{\mathrm{cond}}$) and number density of water ($n_{\mathrm{H_{2}\mathrm{O}}}$) during the outburst dimming phase of the best-fit model. Here $t^{\prime}=t-t_{\mathrm{beg}}$ is the time lapse since the bolometric luminosity started to decline. The value of $L_{\mathrm{bol}}$ corresponding to this time is labeled. In the top row, the range of 140-150 K is shaded in white to highlight the snowline region. At $t^{\prime}=121~\mathrm{yr}$ -- the present epoch -- the emission surfaces ($\tau_{\mathrm{mm}}=2/3$) of ALMA band 5, 6 and 7 and disk photosphere (see Sect. \ref{['sec:t_relax']}) are plotted along with the temperature contour. In the middle row, the region where no condensation occurs is plotted in white. In the bottom row, two lines denoting ice(vapor)-to-gas ratio of $10^{-3}$ are indicated to highlight the snowline region.