The Astrophysical Plasmadynamic Explorer (APEX): A High Resolution Spectroscopic Observatory

EUVE and the ROSAT WFC have left a tremendous legacy in astrophysics at EUV wavelengths. More recently, Chandra and XMM-Newton 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 EUVE mission has left a gap in spectral coverage at crucial EUV wavelengths (~100-300 a), where hot (10 5 - 10 8 K) plasmas radiate most strongly and produce critical spectral diagnostics. CHIPS 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 cm 2 , R ~ 400), the high-resolution spectrometer J-PEX (A eff ~ 3 cm 2 , R ~ 3000). Here we build on the J-PEX prototype and present a strawman design for an orbiting spectroscopic observatory, APEX , a SMEX-class instrument containing a suite of 8 spectrometers that together achieve both high effective area (A eff > 10 cm 2 ) and high spectral resolution (R ~ 10,000) over the range 100-300 a. We also discuss alternate configurations for shorter and longer wavelengths.