2 Observations

The spectrum of Procyon was obtained during 70.4 ksec (on November 8, 1999) by the High Resolution Camera (HRC-S) and the LETGS on board Chandra. The HRC-S contains three flat detectors, each 10 cm long. LETGS consists of 180 grating modules. The LETGS spectrum covers the range from 5 to 175 Å. The LETGS spectra were summed over the +1 and -1 orders and contain also the higher orders. The higher orders are fitted in the model calculations, but can be neglected for Procyon. The curve of the effective area as a function of wavelength is complicated because of the presence of absorption edges (e.g., around 42 Å) and gaps between 62-65 Å and 52-56 Å (+1 and -1 order, respectively) due to the gaps between the detector plates. We use the SRON values (based on calibration by van der Meer et al. 2002), which agree within about 5-10% with the CXC values, as given in the Chandra LETGS Calibration Review of 31 Oct. 2001. The wavelength resolution is $\Delta\lambda\sim0.06$ Å (FWHM). The wavelength uncertainty in the calibration is a few mÅ below 30 Å and about 0.020 Å in the region above 30 Å. The spectra are background subtracted. The statistical errors in the line fluxes include errors from the background. For further instrumental details see also Brinkman et al. (2000).

Later (on October 22, 2000), the spectrum of Procyon was observed by XMM-Newton using the RGS and EPIC-MOS. The total observing time was $\approx$107 ksec; however, due to large solar flare activity at the end of the observation, we removed 16.7 ksec of data, leaving a total of 90.5 ksec of "good'' data. In XMM-Newton three telescopes focus X-rays onto three EPIC cameras (two MOS and one pn). About half of the photons in the beams of two telescopes (Turner et al. 2001) are diffracted by sets of reflecting gratings and are then focussed onto the RGS detectors. The RGS spectral resolution is $\Delta\lambda\sim0.07$ Å, with a maximum effective area of about 140 cm² around 15 Å. The wavelength uncertainty is 7-8 mÅ. The first spectral order has been selected by means of the energy resolution of the individual CCDs. For further details see den Herder et al. (2001).

The data were processed by the XMM-Newton SAS using the calibration of February 2001. The RGS cover the range from 5 to 37 Å. The EPIC spectra, which have a lower resolution but higher sensitivity, are used to constrain the high-temperature part of Procyon's EM distribution. Because of the high resolution of the grating spectrometers we will focus on the spectra from these instruments. In Fig. 1, we show the RGS spectra together with an extract of the LETGS spectrum covering the wavelength range from 10 to 37 Å. No notable features are observed below 10 Å in the LETGS and RGS spectra. However, the EPIC-MOS detects the H- and He-like lines of Mg. The remaining part of the LETGS spectrum is shown in Fig. 2. From Fig. 1 the gaps in the two RGS spectra due to CCD failure of CCD 7 (RGS1) and 4 (RGS2) are obvious.