2 Observations and data reduction

The data presented here were obtained during the commissioning and the calibration phases of XMM-Newton, and as part of the Guaranteed Time of Reflection Grating Spectrometer Team. We present results based on the "quiescent'' X-ray spectra of the five targets. With the exception of HR 1099, their light curves showed no evidence for rapid flux variations as typical of flares; they were either constant or slowly varying within 25%. The binary HR 1099 displayed a strong flare at the end of the observation (Audard et al. 2001a); we have selected only the low-level pre-flare emission in this paper. Note that the HR 1099 and Capella data, previously published (Audard et al. 2001a,b), have been reanalyzed with a more recent and more accurate calibration. Table 2 gives the observation log for the five RS CVn binaries. We used only observations for which both EPIC and RGS observed our targets simultaneously (except for Capella).

 

 

Table 1: Properties of the targets; spectral types and orbital periods from Strassmeier et al. (1993), distances from Perryman et al. (1997).

Target	Spectral Type	$P_{\rm orb}$ (d)	d (pc)
HR 1099	K1 IV+G5 IV-V	2.84	28.97
UX Ari	K0 IV+G5 V	6.44	50.23
$\lambda$ And	G8 IV-III	20.52	25.81
VY Ari	K3-4 IV-V	13.20	43.99
Capella	G0 III+G8 III	104.02	12.94

   

Table 2: Observation log of the data presented in this paper. The revolution number and the observation identification number are given after the object's name. Dates are given in yyyy-mm-ddThh:mm:ss format. The exposures (in ksec) are corrected for deadtime.

INSTRUMENT	FILTER	MODE	DATE-OBS (UT)	DATE-END (UT)	Exposure
HR 1099, rev 36, obsid 0117890901
MOS2$\dots$	MEDIUM	FULL FRAME	2000-02-18T14:26:07	2000-02-19T05:29:01a	40.3
RGS1$\dots$	NONE	SPEC+Q	2000-02-18T13:24:45	2000-02-19T05:25:41a	43.9
RGS2$\dots$	NONE	SPEC+Q	2000-02-18T13:24:45	2000-02-19T05:25:41a	43.9
UX Ari, rev 218, obsid 0111390301
MOS2$\dots$	MEDIUM	SMALL WINDOW	2001-02-15T19:39:30	2001-02-16T03:51:34	28.5
RGS1$\dots$	NONE	SPEC+Q	2001-02-15T19:30:54	2001-02-16T04:08:30	30.9
RGS2$\dots$	NONE	SPEC+Q	2001-02-15T19:30:54	2001-02-16T04:08:30	30.9
$\lambda$ And, rev 208, obsid 0099320101
MOS2$\dots$	THICK	SMALL WINDOW	2001-01-26T20:10:05	2001-01-27T04:08:49	27.7
RGS1$\dots$	NONE	SPEC+Q	2001-01-26T19:21:29	2001-01-27T04:15:45	31.8
RGS2$\dots$	NONE	SPEC+Q	2001-01-26T19:21:29	2001-01-27T04:15:45	31.8
VY Ari, rev 217, obsid 0111490401
MOS2$\dots$	MEDIUM	SMALL WINDOW	2001-02-13T19:33:30	2001-02-14T04:43:04	31.8
RGS1$\dots$	NONE	SPEC+Q	2001-02-13T19:24:54	2001-02-14T04:50:50	33.8
RGS2$\dots$	NONE	SPEC+Q	2001-02-13T19:24:54	2001-02-14T04:50:50	33.8
Capella, rev 54, obsid 0121920101
RGS1$\dots$	NONE	SPECTROSCOPY	2000-03-25T11:36:33	2000-03-26T02:54:09b	52.9
RGS2$\dots$	NONE	SPECTROSCOPY	2000-03-25T11:36:33	2000-03-26T02:54:09b	52.9

a Quiescent data before 2000-02-19T01:46:40 UT only were used.
b Data from 00:30 to 00:50 UT on 2000 March 26 discarded due to attitude problems.

The XMM-Newton Observatory (Jansen et al. 2001) carries three Wolter-type I X-ray telescopes which allow for simultaneous observations by five different detectors: two MOS-type (Turner et al. 2001) and one pn-type (Strüder et al. 2001) European Photon Imaging Cameras (EPIC), and two Reflection Grating Spectrometers (RGS; den Herder et al. 2001). An optical telescope, the Optical Monitor (OM; Mason et al. 2001), observes simultaneously as well. The EPIC instruments are sensitive from 0.1 to 15 keV, with a higher spectral resolution in the MOS than in the pn, although the sensitivity of the latter is higher. The RGS provide spectra at high resolution ( ${E/\Delta E} = 100{-}500$FWHM) in the soft X-ray range from 6 to 38 Å (0.3-2.1 keV; effective area $A_{\rm eff} \approx 140$ cm² around 15 Å) and are optimized for the detection of H-like and He-like transitions of abundant elements (C, N, O, Ne, Mg, Si) and of a number of L-shell Fe transitions.

The XMM-Newton Science Analysis System (SAS) has been used to reduce the data, in conjunction with calibration files (June 2001). We used standard processing performed by the RGS metatask rgsproc and the EPIC MOS task emchain. The HR 1099 and Capella data were provided to us as part of the calibration phase; such data can be analyzed with the SAS in the same way as archival data. One of the main purposes of this analysis being the determination of coronal abundances, we have decided to give a larger weight to the high-resolution RGS data than to the EPIC data. Therefore, data from only one EPIC MOS have been used (MOS2 for practical reasons). It gives us access to the H-like and He-like transitions of Si, S, Ar, and Ca, and to the Fe K-shell transitions at 6.7 keV. The high-temperature component of the thermal bremsstrahlung continuum is also better constrained by the EPIC data. However, we did not use the full MOS spectrum in our fits, but only its information at energies above $\approx$1.33 keV (see below in Sect. 3.1 for more details). With the exception of HR 1099, EPIC MOS2 data were taken in the small window mode. In this mode, only the inner $100\times100$ pixels of the central CCD work (whereas the other 6 outer CCDs work nominally), with a smaller integration time, thus bright objects suffer less from pile-up. The disadvantage of this mode is that its window size is too small to extract a background region from the central CCD; therefore, we selected a source-free region on an outer CCD. No time-screening was applied since the background contamination due to solar flares was low during these observations.

We used the EPIC MOS instrument team response matrices (m2_medv9q19t5r5_all_15.rsp and m2_thickv9q19t5r5_all_15.rsp for the medium and thick filters, respectively). For VY Ari, UX Ari, and $\lambda$ And, we extracted the source data from a circle as large as the small window mode could allow ($\approx$1000 detector pixels = 50 $^{\prime\prime}$). Despite the brightness of the targets, the operating mode allowed us to obtain spectra with negligible pile-up for these stars. Indeed, the difference between spectra extracted with photon pattern 0 only and with patterns 0-12 (the default) proved to be insignificant. We additionally constructed images, divided the pixel values by the average exposure time, and multiplied it by the frame integration time to get units of counts per pixel per frame. We then confirmed that there were very few pixels with more than 0.01 counts per pixel per frame, a practical limit above which pile-up begins to be important (Jean Ballet, private communication). For HR 1099, despite the off-axis pointing (the source lies on CCD 6 on MOS2 and in CCD gaps for MOS1 and pn), the brightness of the source and the full frame mode produced severe pile-up; therefore, we used an annulus extraction region with inner and outer radii of 300 and 1800 detector pixels, respectively, to remove the piled-up central part of the XMM-Newton Point Spread Function (PSF). We used circular extraction regions on other CCD chips to obtain background information. Note that the sources were much brighter than the background, thus the former dominate the spectral features (except at the highest energies - typically above 8 keV - and possibly below 0.15 keV - but we always cut data below 1.33 keV, see Sect. 3.1). We did not apply corrections for vignetting, since the latter essentially has no influence on the contamination by soft protons (J. Ballet, private communication). Furthermore, the background spectra are consistent with the internal MOS detector background, thus the contribution by the vignetted cosmic X-ray background is negligible. Even if some correction factor should need to be applied, it would range between 20-30% and thus would essentially reduce slightly the high temperature component, however within the temperature uncertainties and with no essential influence on the abundances. For Capella, no EPIC data could be used due to severe optical contamination and pile-up.

For the RGS data reduction, we extracted the first order net spectra from a spatial cut including 90% of the cross-dispersion PSF (xpsfincl=90 in rgsproc) and an energy cut including 95% of the pulse-height distribution (pdistincl=95). The background spectra were extracted above and below the source spectra, by excluding 95% of the source's cross-dispersion PSF (xpsfexcl=95). The RGS matrices were created by rgsrmfgen 0.41 (except for VY Ari for which we used rgsrmfgen 0.44; the differences between the two versions are negligible and have virtually no impact), with 6000 energy bins and correcting for the background subtraction, and for the spatial and pulse-height cuts.