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Radial velocity (RV) observations of an exoplanet system giving a value ofM_T sin(i) condition (ie. give information about) not only the planet's truemass M_T but also the value of sin(i) for that system (where i is the orbitalinclination angle). Thus the value of sin(i) for a system with any particularobserved value of M_T sin(i) cannot be assumed to be drawn randomly from adistribution corresponding to an isotropic i distribution, i.e. the presumptiveprior distribution . Rather, the posterior distribution from which it is drawndepends on the intrinsic distribution of M_T for the exoplanet population beingstudied. We give a simple Bayesian derivation of this relationship and apply itto several "toy models" for the (currently unknown) intrinsic distribution ofM_T. The results show that the effect can be an important one. For example,even for simple power-law distributions of M_T, the median value of sin(i) inan observed RV sample can vary between 0.860 and 0.023 (as compared to the0.866 value for an isotropic i distribution) for indices (alpha) of thepower-law in the range between -2 and +1, respectively. Over the same range ofindicies, the 95% confidence interval on M_T varies from 1.002-4.566 (alpha =-2) to 1.13-94.34 (alpha = +1) times larger than M_T sin(i) due to sin(i)uncertainty alone. Our qualitative conclusion is that RV studies of exoplanets,both individual objects and statistical samples, should regard the sin(i)factor as more than a "numerical constant of order unity" with simple and wellunderstood statistical properties. We argue that reports of M_T sin(i)determinations should be accompanied by a statement of the correspondingconfidence bounds on M_T at, say, the 95% level based on an explicitly statedassumed form of the true M_T distribution in order to more accurately reflectthe mass uncertainties associated with RV studies.

The Posterior Distribution of sin(i) for Exoplanets with M_T sin(i) Determined from Radial Velocity Data