  We characterized the effects of telluric absorption lines on the radial
velocity (RV) precision of stellar spectra taken through an iodine cell. To
isolate the effects induced by telluric contamination from other stellar,
instrumental, or numerical systematic RV noise, we extracted RVs from simulated
iodine calibrated spectra of three RV standard stars regularly observed by
Keck/HIRES. We add in water absorption lines according to measured precipitable
water vapor (PWV) contents over a one-year period. We concluded that telluric
contamination introduces additional RV noise and spurious periodic signals on
the level of 10-20 cm/s, consistent with similar previous studies. Our findings
show that forward modeling the telluric lines effectively recovers the RV
precision and accuracy, with no prior knowledge of the PWV needed. Such a
recovery is less effective when the water absorption lines are relatively deep
in the stellar template used in the forward modeling. Overall, telluric
contamination plays an insignificant role for typical iodine-calibrated RV
programs aiming at ~1-2 m/s, but we recommend adding modeling of telluric lines
and taking stellar template observations on nights with low humidity for
programs aiming to achieve sub-m/s precision.
