We compare mass-loss rates of OH/IR stars obtained from radio observations with those derived from the dust radiative transfer models and IR observations. We collect radio observational data of OH maser and CO line emission sources for a sample of 1533 OH/IR stars listed in Suh & Kwon (2011). For 1259 OH maser, 76 CO(J=1-0), and 55 CO(J=2-1) emission sources, we compile data of the expansion velocity and mass-loss rate. We use a dust radiative transfer model for the dust shell to calculate the mass-loss rate as well as the IR color indices. The observed mass-loss rates are in the range predicted by the theoretical dust shell models corresponding to M = 10-8M⊙/yr - 10-4M⊙/yr. We find that the dust model using a simple mixture of amorphous silicate and amorphous Al2O3 (20% by mass) grains can explain the observations fairly well. The results indicate that the dust radiative transfer models for IR observations generally agree with the radio observations. For high mass-loss rate OH/IR stars, the mass-loss rates obtained from radio observations are underestimated compared to the mass-loss rates derived from the dust shell models. This could be because photon momentum transfer to the gas shell is not possible for the physical condition of high mass-loss rates. Alternative explanations could be the e®ects of di®erent dust-to-gas ratios and/or a superwind.

ABSTRACT
1. INTRODUCTION
2. SAMPLE STARS
    2.1 Comparison of Expansion Velocities
    2.2 The IRAS and 2MASS Data
3. THEORETICAL DUST SHELL MODELS
    3.1 Dust Shell Model Parameters
4. COMPARISON OF THE THEORETICAL MODELS WITH THE OBSERVATIONS
    4.1 Vexp - Color Diagrams
    4.2 M - Color Diagrams
    4.3 M - Period Diagram
5. SUMMARY
REFERENCES

• KYUNG-WON SUH(Department of Astronomy and Space Science, Chungbuk National University) Corresponding Author
• YOUNG-JOO KWON(Department of Astronomy and Space Science, Chungbuk National University)