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The alignment of dust grains with the ambient magnetic field producespolarization of starlight as well as thermal dust emission. Using the archivalSOFIA/HAWC+ polarimetric data observed toward $\rho$ Ophiuchus (Oph) A cloudhosted by a B association star at 89 $\mu$m and 154 $\mu$m, we find that thefractional polarization of thermal dust emission first increases with the graintemperature and then decreases once the grain temperature exceeds $\simeq$25-32 K. The latter trend differs from the prediction of the popular RAdiativeTorques (RATs) alignment theory which implies a monotonic increase of thepolarization fraction with the grain temperature. We perform numerical modelingof polarized dust emission for the $\rho$ Oph-A cloud and calculate the degreeof dust polarization by simultaneously considering the dust grain alignment androtational disruption by RATs. Our modeling results could successfullyreproduce both the rising and declining trends of the observational data.Moreover, we show that the alignment of only silicate grains or a mixture ofsilicate-carbon grains within a composite structure can reproduce theobservational trends, assuming that all dust grains follow a power-law sizedistribution. Although there are a number of simplifications and limitations toour modeling, our results suggest grains in $\rho$ Oph-A cloud have a compositestructure, and the grain size distribution has steeper slope than the standardsize distribution for the interstellar medium. Combination of SOFIA/HAWC+ datawith JCMT observations 450 $\mu$m and 850 $\mu$m would be useful to test theproposed scenario based on grain alignment and disruption by RATs.

Understanding polarized dust emission from $\rho$ Ophiuchi A in light of grain alignment and disruption by radiative torques