Observations of 1s2-1s np and 1s-np lines in RESIK soft X-ray spectra

RESIK is the X-ray bent crystal spectrometer on the CORONAS-F satellite. Between 2002 and 2003, RESIK collected numerous spectra of active regions and flares in the wavelength range from 3.37 to 6.09 Å. This range includes many strong emission lines due to transitions 1s2-1s np and 1s-np, in He-like and H-like ions, respectively; the n = 2 and 3 lines are routinely observed for Si, S and Ar ions. For some flares RESIK has observed enhanced emission in spectral features coinciding with lines due to transitions for n up to 9 or 10. Identifications of these features, not previously observed in astrophysical spectra, are presented in this paper. Their observed intensities are compared with those from theory.