  We made photometric and spectroscopic observations of the rapidly pulsating
subdwarf B star EC 09582-1137 with the aim of determining the target's
fundamental structural parameters from asteroseismology. The new data comprise
~ 30 hours of fast time-series photometry obtained with SUSI2 at the NTT on La
Silla, Chile, as well as 1 hour of low-resolution spectroscopy gathered with
EMMI, also mounted on the NTT. From the photometry we detected 5 independent
harmonic oscillations in the 135-170 s period range with amplitudes up to 0.5%
of the mean brightness of the star. In addition, we extracted two periodicities
interpreted as components of a rotationally split multiplet that indicate a
rotation period of the order of 2-5 days. We also recovered the first harmonic
of the dominant pulsation, albeit at an amplitude below the imposed 4-sigma
detection threshold. The spectroscopic observations led to the following
estimates of the atmospheric parameters of EC 09582-1137: Teff = 34,806+-233 K,
log g = 5.80+-0.04, and log[N(He)/N(H)] = - 1.68+-0.06.
  Using the observed oscillations as input, we searched in model parameter
space for unique solutions that present a good fit to the data. Under the
assumption that the two dominant observed periodicities correspond to radial or
dipole modes, we were able to isolate a well-constrained optimal model that
agrees with the atmospheric parameters derived from spectroscopy. The inferred
structural parameters of EC 09582-1137 are Teff = 34,806 K (from spectroscopy),
log g = 5.788+-0.004, M = 0.485+-0.011 M_solar, log(M_env/M_star) = -
4.39+-0.10, R = 0.147+-0.002 R_solar, and L = 28.6+-1.7 L_solar. We
additionally derive the absolute magnitude M_V = 4.44+-0.05 and the distance d
= 1460+-66 pc.
