It is important to explore the diversity of characteristics of low-mass , low-density planets to understand the nature and evolution of this class of planets .
We present a homogeneous analysis of 12 new and 9 previously published broadband photometric observations of the Uranus-sized extrasolar planet GJ 3470b , which belongs to the growing sample of sub-Jovian bodies orbiting M dwarfs .
The consistency of our analysis explains some of the discrepancies between previously published results and provides updated constraints on the planetary parameters .
Our data are also consistent with previous transit observations of this system .
The physical properties of the transiting system can only be constrained as well as the host star is characterized , so we provide new spectroscopic measurements of GJ 3470 from 0.33 to 2.42 \mu m to aid our analysis .
We find R _ { \star } = 0.48 \pm 0.04 R _ { \odot } , M _ { \star } = 0.51 \pm 0.06 M _ { \odot } , and T _ { eff } = 3652 \pm 50 K for GJ 3470 , along with a rotation period of 20.70 \pm { 0.15 } d and an R-band amplitude of 0.01 mag , which is small enough that current transit measurements should not be strongly affected by stellar variability .
However , to report definitively whether stellar activity has a significant effect on the light curves , this requires future multi-wavelength , multi-epoch studies of GJ 3470 .
We also present the most precise orbital ephemeris for this system : T _ { o } = 2455983.70472 \pm 0.00021 BJD _ { TDB } , P = 3.3366487 ^ { +0.0000043 } _ { -0.0000033 } d , and we see no evidence for transit timing variations greater than 1 minute .
Our reported planet to star radius ratio is 0.07642 \pm 0.00037 .
The physical parameters of this planet are R _ { p } = 3.88 \pm 0.32 R _ { \oplus } , and M _ { p } = 13.73 \pm 1.61 M _ { \oplus } .
Because of our revised stellar parameters , the planetary radius we present is smaller than previously reported values .
We also perform a second analysis of the transmission spectrum of the entire ensemble of transit observations to date , supporting the existence of a H _ { 2 } dominated atmosphere exhibiting a strong Rayleigh scattering slope .