... alone.¹

Jeremy Drake is preparing the in-flight calibration target list and exposure times. One critical instrumental calibration issue that may drive exposure times is line response function, which will require very high signal-to-noise in emission line features throughout the spectral bands.

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... thin.²

Spectral observations from EUVE have shown that optical depth effects are indeed negligible for most spectral lines; while EUVE cannot rule out the possibility of non-negligible optical depth in the few strongest X-ray lines, these lines will be easily observed and compared to other lines from the same ions. The question of whether stellar coronae are in ionization equilibrium remains to be determined; however, we have no evidence to date requiring us to give up this assumption. Even solar flares are observed to be only marginally out of equilibrium, and we expect the dominant emission from these sources to be from confined plasma. Furthermore, the line spectra themselves provide an excellent test for equilibrium: to compare temperatures derived from relative ionization state populations with temperature-sensitive line ratios. Should unexpected difficulties in unraveling the atomic physics from the astrophysics occur, the observations will provide critical feedback for setting priorities for controlled experiments in the laboratory.

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... EUVE.³

Andrea Dupree as head of the EUVE Science Advisory Board (which is to begin directing operations, time allocation and budget of the EUVE satellite now outsourced to U. C. Berkeley) has expressed great interest in coordinating with the AXAF calibration measurements.

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