SIMBAD references

We obtained coordinated broadband optical photometry and hard X-ray data on the AM Her objects VV Pup, V834 Cen, and EF Eri. The X-ray data were obtained using the Proportional Counter Array detectors of the Rossi X-Ray Timing Explorer, and the optical data were obtained using the 1 m telescope of the Cerro Tololo Inter-American Observatory. During our observations, VV Pup and V834 Cen were in their high optical luminosity states with average m_V∼17 and 15.1, respectively. EF Eri was in a very low state at the time of our observation: m_V>17.7. VV Pup and V834 Cen had average 2-10 keV X-ray fluxes of 1.7x10^–12 and 2.13x10^–11 ergs.cm^–2.s^–1, respectively. EF Eri was not detected in X-rays. The X-ray spectrum of V834 Cen was adequately modeled using an absorbed bremsstrahlung continuum with a Gaussian emission line. The best-fit model had continuum temperature kT_X=11.8±1.0 keV and absorption column n_H=(1.03±0.39)x10²² cm^–2. The Gaussian emission line had line center energy E=6.7±0.1 keV and equivalent width EW=0.64 keV. VV Pup was too faint to produce reliable spectral fits. The 2-10 keV flux for VV Pup quoted above was based on the best-fit spectral model. Holding kT_X fixed in the fitting process yielded roughly the same flux for kT_X=0.5-30 keV.

We detected ∼1 Hz optical quasi-periodic oscillations (QPOs) with amplitude ∼2.2% from VV Pup and ∼1% from V834 Cen. We did not detect optical QPOs over the range 0.2-1 Hz from EF Eri at a 90% confidence upper limit of 4.5%. The QPO properties are consistent with those found in the literature. None of the targets showed X-ray QPO activity. However, only V834 Cen yielded a meaningful upper limit: ∼14% at the 90% confidence level over 0.2-1.2 Hz.