The Astrophysical Plasmadynamic Explorer (APEX): a high-resolution spectroscopic observatory

Abstract

<i>EUVE</i> and the <i>ROSAT WFC</i> have left a tremendous legacy in astrophysics at EUV wavelengths. More recently, <i>Chandra</i> and <i>XMM-Newton</i> have demonstrated at X-ray wavelengths the power of high-resolution astronomical spectroscopy, which allows the identification of weak emission lines, the measurement of Doppler shifts and line profiles, and the detection of narrow absorption features. This leads to a thorough understanding of the density, temperature, abundance, magnetic, and dynamic structure of astrophysical plasmas. However, the termination of the <i>EUVE</i> mission has left a gap in spectral coverage at crucial EUV wavelengths (~100-300 &angst;), where hot (10⁵ - 10⁸ K) plasmas radiate most strongly and produce critical spectral diagnostics. <i>CHIPS</i> will fill this hole only partially as it is optimized for diffuse emission and has only moderate resolution (R~150). For discrete sources, we have successfully flown a follow-on instrument to the EUVE spectrometer (A_eff ~ 1 cm², R ~ 400), the high-resolution spectrometer <i>J-PEX</i> (A_eff ~ 3 cm², R ~ 3000). Here we build on the <i>J-PEX</i> prototype and present a strawman design for an orbiting spectroscopic observatory, <i>APEX</i>, a SMEX-class instrument containing a suite of 8 spectrometers that together achieve both high effective area (A_eff > 10 cm²) and high spectral resolution (R ~ 10,000) over the range 100-300 &angst;. We also discuss alternate configurations for shorter and longer wavelengths.