Err... > sfr = StarFormationRate(pf, star_mass=sm, star_creation_time=ct, > volume=dd.volume('mpc')) You might need to make sure that 'sm' and 'ct' are arrays when you pass them in. I don't remember, so I'd just do it to be careful! -- Stephen Skory s at skory.us http://stephenskory.com/ 510.621.3687 (google voice)