Tracing the water snowline in low-mass young stellar objects (YSOs) is important because dust grain growth is promoted and the chemical composition varies at the water snowline, which influences planet formation and its properties. In protostellar envelopes, the water snowline can be estimated as a function of luminosity using a relation derived from radiative transfer models, and these predictions are consistent with observations. However, accurately estimating the water snowline in protoplanetary disks requires new relations that account for the disk structure. We present the relations between luminosity and water snowline using the dust continuum radiative transfer models with various density structures. We adopt two-dimensional density structures for an envelope-only model (Model E), an envelope+disk+cavity model (Model E+D), and a protoplanetary disk model (Model PPD). The relations between the water snowline, where Tdust = 100 K, and the total luminosity, ranging 0.1–1,000 L⊙, are well fitted by a power-law relation, Rsnow = a × (L/L⊙)p au. The factor a decreases with increasing disk density, while the power index p has values around 0.5 in all models. As the disk becomes denser, the water snowline forms at smaller radii even at the same luminosity, since dense dust hinders photon propagation. We also explore the effect of viscous heating on the water snowline. In Model PPD with viscous heating, the water snowline shifts outward by a few au up to 15 au, increasing the factor a and decreasing the power index p. In Model E+D with lower disk mass, the effect of viscous heating is negligible, indicating that the disk mass controls the effect. The discrepancy between our models and direct observations provides insights into the recent outburst event and the presence of a disk structure in low-mass YSOs.

Introduction
Radiative Transfer Model
    Model E: Envelope-Only
        Density Structure
        Dust Property
        Energy Source
    Model E+D: Envelope + Disk + Cavity
        Density Structure
        Dust Property
        Energy Source
    Model PPD: Protoplanetary Disk
        Density Structure
        Dust Property
        Energy Source
Result
Discussion
    The Effect of Disk Structure in Class 0 Stage
    The Effect of Viscous Heating
    An Indicator of Burst Events in YSOs
Conclusion
Acknowledgments
References

• Young-Jun Kim(Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea)
• Jeong-Eun Lee(Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea, SNU Astronomy Research Center, Seoul National University, Seoul 08826, Republic of Korea) Corresponding author
• Giseon Baek(Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea, Research Institute of Basic Sciences, Seoul National University, Seoul 08826, Republic of Korea)
• Seokho Lee(Korea Astronomy and Space Science Institute, Daejeon 34055, Republic of Korea)