Chandra Observations of a Young Embedded Magnetic B Star in the ρ Ophiuchus Cloud

This paper reports on an analysis of two Chandra X-ray observations of the young magnetic B star ρ Ophiuchus S1. X-ray emission from the star was detected in both observations. The average flux was almost the same in both, but during each observation the flux showed significant time variations by a factor of two on timescales of 20–40 ks. Each spectrum could be fit by either an absorbed power-law model with a photon index of ∼ 3 or a thin-thermal plasma model with a temperature of ∼ 2 keV and an extremely low metal abundance (< ∼ 0.1 solar). The spectrum of the first observation has a weak-line feature at about 6.8 keV, which might correspond to highly ionized iron Kα. In contrast, the spectrum of the second observation apparently shows a weak edge absorption component at E ∼ 4 keV. The continuum emission and log(LX/Lbol)∼−6 are similar to those of young intermediate-mass stars (Herbig Ae/Be stars), although the presence of a strong magnetic field (inferred from the detection of non-thermal radio emission) has drawn an analogy between ρ Ophiuchus S1 and magnetic chemically peculiar (MCP) stars. If the X-ray emission is thermal, the small abundances that we derived might be related to the inverse first-ionization potential (FIP) effect, though there is no significant trend as a function of FIP from our model fits. If the emission is non-thermal, it might be produced by high-energy electrons in the magnetosphere.