Author name code: mewe ADS astronomy entries on 2022-09-14 author:"Mewe, Rolf" ------------------------------------------------------------------------ Title: XMM-Newton Studies of the Wolf-Rayet Colliding-Wind Binaries WR 25 (WN6h+O4f) and WR 11 (WC8+O7.5III) Authors: van der Hucht, K. A.; Raassen, A. J. J.; Mewe, R.; Antokhin, I. I.; Rauw, G.; Vreux, J. -M.; Schild, H.; Schmutz, W. Bibcode: 2007ASPC..367..159V Altcode: We report the analysis of high- and medium-resolution X-ray spectra of the Wolf-Rayet (WR) objects WR25 (HD93162, WN6h+O4f) and WR11 (γ2 Velorum, WC8+O7.5III, P =78.53 d), obtained with the reflection grating spectrometers (rgs) and the european photon imaging cameras (epicmos and <small>PN</small>) <small>CCD</small> spectrometers on board the XMM-Newton satellite. Title: XMM-Newton observations of β Centauri (B1 III): The temperature structure in the hot plasma and the photosphere-wind connection Authors: Raassen, A. J. J.; Cassinelli, J. P.; Miller, N. A.; Mewe, R.; Tepedelenlioǧlu, E. Bibcode: 2005A&A...437..599R Altcode: We present XMM-Newton observations of the B giant β Centauri (B1 III). The spectra are rich of spectral lines from a wide range of ionization stages which indicate temperatures in the range ~0.1-0.6 keV. Simultaneous fits to the rgs, epic-mos, and epic-pn spectra yield three plasma temperatures (0.1, 0.2, and 0.6 keV), emission measures, and elemental abundances which are quite close to solar values. These temperatures are confirmed by DEM modeling. According to the derived models the intrinsic source X-ray luminosity in the energy range 0.3-10 keV is Lx = 10 × 1030 erg s-1 at a distance of 161 pc. An analysis of the X-ray light curve suggests that the photospheric variability does not have much of an effect on the properties of the X-ray luminosity. The sensitivity of the He-like forbidden and intercombination lines to a strong ultraviolet stellar radiation field is used to constrain the radial distances at which the lines of Ne ix, O vii, and N vi originate. Title: Rolf Mewe: a career devoted to X-ray spectroscopy Authors: Kaastra, Jelle S.; Mewe, Rolf Bibcode: 2005AIPC..774....1K Altcode: An overview of the life and work of Rolf Mewe (1935-2004) as an X-ray spectroscopist is given. He was one of the pioneers in the field of X-ray spectroscopy. His work illustrates nicely how this field developed from the early days up to the present high-resolution era. His plasma emission codes, developed by him and collaborators over several decades, is one of the most widely used. His thorough knowledge of the field, as well as his ability and enthousiasm to cooperate with many colleagues, made his career a succes. He will be missed by all of us for his work and personality. Title: Relationship between X-ray and ultraviolet emission of flares from dMe stars observed by XMM-Newton Authors: Mitra-Kraev, U.; Harra, L. K.; Güdel, M.; Audard, M.; Branduardi-Raymont, G.; Kay, H. R. M.; Mewe, R.; Raassen, A. J. J.; van Driel-Gesztelyi, L. Bibcode: 2005A&A...431..679M Altcode: 2004astro.ph.10592M We present simultaneous ultraviolet and X-ray observations of the dMe-type flaring stars AT Mic, AU Mic, EV Lac, UV Cet and YZ CMi obtained with the XMM-Newton observatory. During 40 h of simultaneous observation we identify 13 flares which occurred in both wave bands. For the first time, a correlation between X-ray and ultraviolet flux for stellar flares has been observed. We find power-law relationships between these two wavelength bands for the flare luminosity increase, as well as for flare energies, with power-law exponents between 1 and 2. We also observe a correlation between the ultraviolet flare energy and the X-ray luminosity increase, which is in agreement with the Neupert effect and demonstrates that chromospheric evaporation is taking place. Title: New Results on X-ray Models and Atomic Data Authors: Kaastra, Jelle S.; Mewe, Rolf; Raassen, Ton Bibcode: 2005HiA....13..648K Altcode: We discuss the most recent developments of the spectral analysis package SPEX. We report on the progress made in updating the atomic data that are used in the spectroscopic code. We also present a set of spectral models that are used for the analysis of high-resolution X-ray spectra of photo-ionized plasmas such as occur in active galactic nuclei. These models include absorption line spectroscopy of photoionized layers. The importance and diagnostic power of innershell transitions is shown. We illustrate our results with several examples of observed spectra obtained with the XMM-Newton and Chandra grating spectrometers. Title: X-ray/UV campaign on the Mrk 279 outflow: Density diagnostics in Active Galactic Nuclei using O V K-shell absorption lines Authors: Kaastra, J. S.; Raassen, A. J. J.; Mewe, R.; Arav, N.; Behar, E.; Costantini, E.; Gabel, J. R.; Kriss, G. A.; Proga, D.; Sako, M.; Steenbrugge, K. C. Bibcode: 2004A&A...428...57K Altcode: 2004astro.ph..6199K One of the main problems in modeling the ionised outflows in Active Galactic Nuclei is the unknown distance of the outflowing wind to the central source. Only if the density is known this distance can be determined through the ionisation parameter. Here we study density diagnostics based upon O V transitions. O V is known to have metastable levels that are density dependent. We study the population of those levels under photoionisation equilibrium conditions and determine for which parameter range they can have a significant population. We find that resonance line trapping plays an important role in reducing the critical densities above which the metastable population becomes important. We investigate the K-shell absorption lines from these metastable levels. Provided that there is a sufficient population of the metastable levels, the corresponding K-shell absorption lines are detectable and are well separated from the main absorption line originating from the ground state. We then present the Chandra LETGS spectrum of the Seyfert 1 galaxy Mrk 279 that may show for the first time the presence of these metastable level absorption lines. A firm identification is not yet possible due to both uncertainties in the observed wavelength of the strongest line as well as uncertainties in the predicted wavelength. If the line is indeed due to absorption from O V, then we deduce a distance to the central source of one light week to a few light months, depending upon the importance of additional heating processes. Title: Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary γ2 Velorum observations at high and low state. XMM-Newton observations at high and low state Authors: Schild, H.; Güdel, M.; Mewe, R.; Schmutz, W.; Raassen, A. J. J.; Audard, M.; Dumm, T.; van der Hucht, K. A.; Leutenegger, M. A.; Skinner, S. L. Bibcode: 2004A&A...422..177S Altcode: 2004astro.ph..4610S We present XMM-Newton observations of γ2 Velorum (WR 11, WC8+O7.5III, P = 78.53 d), a nearby Wolf-Rayet binary system, at its X-ray high and low states. At high state, emission from a hot collisional plasma dominates from about 1 to 8 keV. At low state, photons between 1 and 4 keV are absorbed. The hot plasma is identified with the shock zone between the winds of the primary Wolf-Rayet star and the secondary O giant. The absorption at low state is interpreted as photoelectric absorption in the Wolf-Rayet wind. This absorption allows us to measure the absorbing column density and to derive a mass loss rate .M = 8 × 10-6 M yr-1 for the WC8 star. This mass loss rate, in conjunction with a previous Wolf-Rayet wind model, provides evidence for a clumped WR wind. A clumping factor of 16 is required. The X-ray spectra below 1 keV (12 Å) show no absorption and are essentially similar in both states. There is a rather clear separation in that emission from a plasma hotter than 5 MK is heavily absorbed in low state while the cooler plasma is not. This cool plasma must come from a much more extended region than the hot material. The Neon abundance in the X-ray emitting material is 2.5 times the solar value. The unexpected detection of C V (25.3 Å) and C VI (31.6 Å) radiative recombination continua at both phases indicates the presence of a cool (∼40 000 K) recombination region located far out in the binary system.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: XMM-Newton X-ray observations of γ2 Velorum (WC8 + O7.5III) Authors: Raassen, A. J. J.; Mewe, R.; van der Hucht, K. A.; Schmutz, W.; Schild, H.; Dumm, T.; Güdel, M.; Audard, M.; Leutenegger, M. A.; Skinner, S. L. Bibcode: 2004NuPhS.132..697R Altcode: The spectrum of the binary system γ2 Velorum (WC8 + O7.5III) has been observed with RGS and EPIC-MOS aboard XMM-Newton. The system shows a 'high state' when the O-star is between the Wolf-Rayet star and the observer (near periastron) and a 'low state' when most of the spectrum is absorbed by the dense stellar wind of the Wolf-Rayet star (near apastron). The spectrum has been model-led by a 4-T plasma, using SPEX. The absorption affects the hot temperature component (kT = 1.5 keV) that is formed by the collision of the Wolf-Rayet wind and the O-star wind, and the second hot component (kT = 0.65 keV) for which the origin is still unclear. Part of the spectrum is not sensitive to the absorption by the stellar wind. This concerns a low-temperature component (kT = 0.23 keV) and features that are produced by plasma that has been photoionized by X-ray radiation from the hot component. In the RGS spectrum features of Radiative Recombination Continua (RRC) of C VI and C V of this photoionized plasma are detected. Title: X-ray Emission from Young Stars in Suburban Orion Authors: Briggs, K.; Güdel, M.; Audard, M.; Smith, K.; Mewe, R.; den Boggende, T. Bibcode: 2004IAUS..219..228B Altcode: 2003IAUS..219E.234B The Orion Nebula region is the richest site in the sky for study of X-ray emission from pre-main sequence stars harbouring almost a thousand sources in its heart around the O-stars of the Trapezium alone. However not all stars are born within such an environment and the effect of environment on the coronal properties of PMS stars is not well-studied. We present detailed analysis of an XMM-Newton observation of a region on the outskirts of the Orion Nebula 40 arcmin to the north containing over 200 sources and compare coronal properties of this less-dense PMS population to those of the high-density Trapezium cluster. Title: Coronae of Cool Stars Authors: Audard, M.; Drake, S. A.; Güdel, M.; Mewe, R.; Pallavicini, R.; Simon, T.; Singh, K. P.; Skinner, S. L.; White, N. Bibcode: 2004IAUS..219..243A Altcode: 2003IAUS..219E.188A; 2003astro.ph.10032A We present preliminary results of grating observations of YY Mensae and V824 Arae by Chandra and XMM-Newton. Spectral features are presented in the context of the emission measure distributions, the coronal abundances, and plasma electron densities. In particular, we observe a coronal N/C enhancement in YY Men believed to reflect the photospheric composition (CN cycle). Finally, we interpret line broadening in YY Men as Doppler thermal broadening in its very hot corona. Title: Density diagnostics in AGN using O V K-shell absorption lines Authors: Kaastra, J. S.; Raassen, A. J. J.; Mewe, R.; Mrk 279 Team Bibcode: 2004cosp...35.3022K Altcode: 2004cosp.meet.3022K One of the main problems in modeling AGN outflows is the unknown distance of the outflowing wind. Only if the density is known this distance can be determined. Here we study density diagnostics based upon O V ions. O V is known to have metastable levels that are density dependent. We study the population of those levels under photo-ionization equilibrium conditions and determine for which parameter range they can have a significant population. We then investigate the K-shell absorption lines from these metastable levels. Provided that there is a sufficient population of the metastable levels, the corresponding K-shell absorption lines are detectable and are well separated from the main absorption line originating from the ground state. We present Chandra LETGS spectra of the Seyfert 1 galaxy Mrk 279 that may show for the first time the presence of these metastable level absorption lines, and discuss the physical implications. Title: Coronal X-Ray Spectroscopy of Solar Analogs Authors: Telleschi, A.; Güdel, M.; Arzner, K.; Briggs, K.; Audard, M.; Ness, J. -U.; Mewe, R.; Raassen, A. J.; Skinner, S. L.; Cuntz, M.; Saar, S. Bibcode: 2004IAUS..219..930T Altcode: 2003IAUS..219E.203T We present an X-ray study of a series of solar-mass main-sequence stars with different ages based on data from XMM-Newton and Chandra. This investigation aims at a closer understanding of the physical mechanisms of heating and mass transport in magnetically active stars. All targets are proxies of the Sun that essentially differ only in their rotation periods and hence in the efficiency of the magnetic dynamo. We present a spectral analysis that constrains the average elemental composition and the thermal structure of the coronae at different stages of their evolution. Further we use the He-like line triplets to derive characteristic coronal densities and investigate the time variability in the X-ray light curves. We discuss implications for models related to heating physics and coronal structure. Title: The X-ray spectra of the flaring and quiescent states of AT Microscopii observed by XMM-Newton Authors: Raassen, A. J. J.; Mewe, R.; Audard, M.; Güdel, M. Bibcode: 2003A&A...411..509R Altcode: 2003astro.ph..9383R The X-ray spectrum of the late-type M-dwarf binary AT Mic (dM4.5e+dM4.5e) is observed in the wavelength range 1-40 Å by means of RGS and EPIC-MOS on board XMM-Newton. During the exposure a flare occured. We have performed a 3-temperature fit and a DEM-modeling to the flaring and quiescent part of the spectrum. We report the coronal temperature distribution, emission measures, and abundances of the flaring and quiescent state of this bright X-ray source. The temperature range stretches from about 1 to 60 MK. The total volume emission measure in this temperature interval is ~ 12.2 x 1051 cm-3 for the quiescent state and ~ 19.5 x 1051 cm-3 for the flare state. This difference is due to the contribution of the hot temperature component. The high-resolution spectrum of AT Mic, obtained by RGS, is dominated by the H- and He-like transitions of C, N, O, and Ne and by Fe XVII lines, produced by the plasma with temperatures from 1 to 10 MK. The EPIC-MOS spectrum below 10 Å shows H- and He-like Ne, Si and the iron K-shell transitions. They are produced by the hot component (30 MK). The iron K-shell is more prominent in the flare state. The abundance pattern in the quiescent state of AT Mic shows the depletion of low-FIP elements relative to high-FIP elements, indicating the presence of an I(nverse)FIP effect in this active star. In the flare state, however, some flattening of this IFIP effect is present.

Based on observations obtained with XMM-Newton, an ESA scienc mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: X-Ray-Extreme-Ultraviolet Simultaneous Observations of NGC 5548: Fast Extreme-Ultraviolet Dip without X-Ray Variation Authors: Haba, Y.; Kunieda, H.; Misaki, K.; Terashima, Y.; Kaastra, J. S.; Mewe, R.; Fabian, A. C.; Iwasawa, K. Bibcode: 2003ApJ...599..949H Altcode: The bright Seyfert 1 galaxy NGC 5548 was monitored in X-rays by ASCA for 9 days and in EUV by EUVE for 12 days continuously in 1996. The periods of X-ray observations were really simultaneously covered by EUV observations. The 0.1-10 keV combined continuum of X-ray and EUV is well presented by a simple power law with a photon index Γ=1.78 plus the Wien part of a disk blackbody with kT=17 eV. On long timescales of days, the variability of the EUV flux is in good accordance with that of the X-rays. Furthermore, there is a clear positive correlation between Γ and the 2-10 keV flux. These results are consistent with the scenario that the X-rays are produced by inverse Compton scattering of soft photons in hot electron clouds. On the other hand, focusing on the short-term variability, we found that the EUV flux shows 20,000 s variability with 40% amplitude with neither X-ray flux nor spectral changes when the source is at its maximum flux state. This seems to conflict with the ordinary framework of the inverse Compton model. To explain such fast variability of the EUV flux accompanied by no X-ray change, we suggest that the EUV emission consists of two components; relatively stable disk emission and a variable component that is dominant at EUV flares. Title: AD Leonis: Flares observed by XMM-Newton and Chandra Authors: van den Besselaar, E. J. M.; Raassen, A. J. J.; Mewe, R.; van der Meer, R. L. J.; Güdel, M.; Audard, M. Bibcode: 2003A&A...411..587V Altcode: 2003astro.ph..9315V; 2003astro.ph..9315B The M-dwarf AD Leonis has been observed with the Reflection Grating Spectrometers and the European Photon Imaging Camera aboard XMM-Newton and also with the Low Energy Transmission Grating Spectrometer aboard the Chandra X-ray Observatory. In the observation taken with XMM-Newton five large flares produced by AD Leo were identified and only one in the observation taken with Chandra. A quiescent level to the lightcurves is difficult to define, since several smaller flares mutually overlap each other. However, we defined a quasi-steady state outside of obvious flares or flare decays. The spectra from the flare state and the quasi-steady state are analysed separately. From these spectra the temperature structure was derived with a multi-temperature model and with a differential emission measure model. The multi-temperature model was also used to determine the relative abundances of \element{C}, \element{N}, \element{O}, \element{Ne}, \element{Mg}, \element{Si}, \element{S}, and \element{Fe}. \element{He}-like ions, such as O Vii and Ne Ix, produce line triplets which are used to determine or constrain the electron temperature and electron density of the corresponding ion. During the flare state a higher emission measure at the hottest temperature is found for both XMM-Newton and Chandra observations. The derived abundances suggest the presence of an inverse First Ionization Potential effect in the corona of AD Leo. Title: Improved Line Ratio Calculations for He-like Ions Authors: Mewe, R.; Porquet, D.; Raassen, A. J. J.; Kaastra, J. S.; Dubau, J.; Ness, J. -U. Bibcode: 2003csss...12.1123M Altcode: Helium-like density and temperature diagnostics, since more than three decades applied to the Sun, have now become a powerful tool in the analysis of the high-resolution Chandra and XMM-Newton X-ray spectra. Therefore, we have revisited the calculation of the ratios R=f/i and G=(f+i)/r of the resonance r (1s2 1S0 - 1s2p 1P1), intercombination i (1s2 1S0 - 1s2p 3P2,1), and forbidden f (1s2 1{S}0 - 1s2s 3{S}1) ``triplet'' lines of the He-like ions ion{C}{5}, ion{N}{6}, ion{O}{7}, ion{Ne}{9}, ion{Mg}{11}, and ion{Si}{13}, taking into account all relevant processes and improved atomic data. The first calculations have been done for optically thin plasmas in collisional ionization equilibrium (e.g., stellar coronae). The influence of an external radiation field on the depopulation of the upper level of f is considered which can be important for hot OB or F stars (e.g., ζ Puppis, Procyon, and Algol). In preparation are updated calculations for photo-ionized and hybrid plasmas (e.g., warm absorber in AGNs), and for transient ionization plasmas (young SNRs). Title: Influence of UV Radiation Fields on Density Diagnostics with He-like Triplets Authors: Ness, J. -U.; Mewe, R.; Schmitt, J. H. M. M.; Raassen, A. J. J. Bibcode: 2003csss...12..265N Altcode: Spectroscopic density diagnostics based on He-like triplets are routinely used to investigate the solar corona. With the new instrumentation onboard Chandra and XMM this method of analysis can also be applied to stellar coronae. In collision-dominated plasmas the forbidden line f (1s2s 3S1 rightarrow 1s2 1S0), disappears at high densities, and the intercombination line i (1s2p 3P2,1 rightarrow 1s21S0) increases at higher densities at the expense of the forbidden line. Therefore, the ratio f/i is used as a sensitive indicator of electron density. However, depopulation of the forbidden line compared to the intercombination line, is not always an indicator for high densities, it might also indicate that the depopulation of the forbidden line level (1s2s 3S1 rightarrow 1s2p 3P2,1) is due to a UV radiation field instead of the collisions in a high-density plasma. We illustrate this effect with IUE measurements of Capella, Procyon, Algol and α Cen A and α Cen B and a simulation showing the trend of the radiation fields when regarding stars with different surface temperatures. Focusing on the triplets of C V, N VI, O VII and Ne IX, we show that the radiation fields can have significant influence on the density analysis of the low-Z He-like ions of C, N and O. We present Chandra LETGS measurements and calculate the densities accounting for the measured radiation fields and neglecting them. The sources of the UV radiation are assumed to be the respective stellar surfaces, but in the case of Algol the radiation is supplied by the companion B star. A detailed investigation of whether the observed part of Algol's corona is actually illuminated by the radiation field of the B star, is necessary. Title: A Systematic Spectroscopic X-Ray Study of Stellar Coronae with XMM-Newton: Early Results Authors: Güdel, M.; Audard, M.; Smith, K. W.; Sres, A.; Escoda, C.; Wehrli, R.; Guinan, E. F.; Ribas, I.; Beasley, A. J.; Mewe, R.; Raassen, A. J.; Behar, E.; Magee, H. Bibcode: 2003csss...12..303G Altcode: 2001astro.ph..9267G We have been conducting a comprehensive survey of stellar coronae with the XMM-Newton Reflection Grating Spectrometers during the commissioning, calibration, verification, and guaranteed time phases of the mission, accompanied by simultaneous observations with the EPIC cameras and, for several targets, with the radio VLA and/or the VLBA. The principal aim of this project is threefold: i) To understand stellar coronal structure and composition by studying systematics in the coronae of stars with widely different levels of magnetic activity; ii) to investigate heating and particle acceleration physics during flares, their role in the overall coronal energy budget, and their possible role in the quiescent stellar emission; iii) to probe stellar coronal evolution by studying solar analogs of different ages. We report early results from this project. Title: Temperature Determination and Emission Measure Modeling of the Coronae of α Centauri and Procyon Authors: Raassen, A. J. J.; Kaastra, J. S.; van der Meer, R. L. J.; Mewe, R.; Audard, M.; Güdel, M.; Ness, J. -U.; Behar, E. Bibcode: 2003csss...12..313R Altcode: We have obtained the spectra of the coronae of α Centauri and Procyon using the Reflection Grating Spectrometer (RGS) on board XMM-Newton and the Low Energy Transmission Grating Spectrometer (LETGS) on board Chandra. From measured line fluxes of H- and He-like lines of Carbon, Nitrogen and Oxygen and of strong lines of Fe IX and Fe X temperature estimates and emission measures EM have been obtained. For all three stars (Procyon, α Cen (G2V),

and α Cen (K1V)) the temperatures are in the regime of 1-2 MK. The emission measure for Procyon is about 1× 1050 cm-3 and for both components of α Cen about 8 × 1048 cm-3. Global fits to the total spectrum using SPEX show significant temperature components around 1 and 2 MK. Self-consistent continuous emission measures have been constructed. The α Cen (K1V) is somewhat hotter than its G2V companion. Title: A Study of the Coronal Plasma in RS CVn Binary Systems Authors: Audard, M.; Güdel, A.; Sres, A.; Mewe, R.; Raassen, A. J. J.; Behar, E.; Foley, C. R.; van der Meer, R. L. J. Bibcode: 2003csss...12..293A Altcode: XMM-Newton has been performing comprehensive studies of X-ray bright RS CVn binaries in its Calibration and Guaranteed Time programs. We present results from ongoing investigations in the context of a systematic study of coronal emission from RS CVns. We concentrate in this paper on coronal abundances and investigate the abundance pattern in RS CVn binaries as a function of activity and average temperature. A transition from an Inverse First Ionization Potential (FIP) effect towards an absence of a clear trend is found in intermediately active RS CVn systems. This scheme corresponds well into the long-term evolution from an IFIP to a FIP effect found in solar analogs. We further study variations in the elemental abundances during a large flare. Title: High-resolution XMM-Newton X-ray spectra of τ SCORPII Authors: Mewe, R.; Raassen, A. J. J.; Cassinelli, J. P.; van der Hucht, K. A.; Miller, N. A.; Güdel, M. Bibcode: 2003AdSpR..32.1167M Altcode: The first high-resolution X-ray spectra of the B0.2V star τ Scorpii obtained during 22.5ks on Aug. 20, 2001 with the RGS GRATING and the EPIC-MOS CCD spectrometers on board XMM-Newton exhibit bright emission lines of the H- and He-like ions of C, N, O, Ne, Mg, and Si, as well as Fe XVII and Fe XVIII lines. The emission line and continuum spectra have been simultaneously fitted. We obtain four temperatures: 1.6, 5.2, 8.2, and ≳20 MK, emission measures and abundances. The nitrogen lines are relatively strong: The N/O abundance ratio is ∼3x solar. No indication of a solar-type "FIP effect" was found for the other elements. The temperatures are confirmed by DEM modeling. According to the derived models Lx (0.3-10 keV) = 3.2 × 1031 ergs -1 at a distance of 132 pc. The He-like forbidden and intercombination line ratios of N,O,Ne, and Mg are determined by the strong stellar UV radiation field and yield upper limits to the radial distances at which these lines originate. The soft (≲ 8 MK) component probably originates from shocks low in the wind that are produced by the common mechanism of radiation line-driven instabilities, consistent with the observed emission line profiles that are much narrower (≲ 500 km/s) than the broad lines (up to 1500 km/s) observed high up in the wind of ζ Puppis. The hot (∼ 20-40 MK) component is explained by a model involving dense clumps embedded in a wind that approaches high relative velocities (∼ 1400 - 1700 km/s) and the interaction produces strong shocks Title: XMM-Newton high-resolution x-ray spectroscopy of the Wolf-Rayet object WR25 (WN6HA+04F) Authors: Raassen, A. J. J.; van der Hucht, K. A.; Mewe, R.; Antokhin, I.; Rauw, G.; Vreux, J. -M.; Schmutz, W.; Güdel, M. Bibcode: 2003AdSpR..32.1161R Altcode: We report the analysis of the X-ray spectrum of the Wolf-Rayet star WR 25, observed by RGS and EPIC-MOS on board XMM-Newton. Temperatures up to 40 MK have been determined. Strong absorption, exceeding the value due to the Inter Stellar Medium (ISM) has been detected and assigned to the dense stellar wind. Title: AD Leonis, (dM3:l5V): Analysis of the x-ray spectrum Authors: van den Besselaar, E. J. M.; Raassen, A. J. J.; Mewe, R.; van der Meer, R. L. J.; Güdel, M.; Audard, M. Bibcode: 2003AdSpR..32.1155V Altcode: We report the analysis of the X-ray spectrum of AD Leo (dM3.5 V), observed by RGS and EPIC-MOS on board XMM-Newton and by LETGS on board Chandra. From the lightcurve the presence of flaring states and a quiescent part is noticed. Temperatures up to 20 MIA have been determined. A significant increase of the emission measure (EM) at high temperatures is determined for the flaring state. An indication for an Inverse First Ionization Potential (IFIP) effect has been found. Title: An XMM-Newton observation of the flare star AU MIC Authors: Magee, H. R. M.; Güdel, M.; Audard, M.; Mewe, R. Bibcode: 2003AdSpR..32.1149M Altcode: Preliminary results from an XMM- Newton observation of the active flare star AU Mic are presented. During the observation six flares were observed, along with numerous smaller-scale events. Coronal densities have been obtained using the density-sensitive He-like line triplet of O VII, for both the full observation and the final four flares. High background levels were seen for the initial 20 ks of the observation during the time when the first two flares were observed. The average density during the course of the whole observation was found to be at the low-density limit of the O VII triplet i.e 1×10 9 cm -3. However, in the case of flares four and five, O VII line ratios appear to indicate the density has increased to 2.0×10 10 and 1.0-1.6×10 10cm -3. Title: Are stellar coronae optically thin in X-rays?. A systematic investigation of opacity effects Authors: Ness, J. -U.; Schmitt, J. H. M. M.; Audard, M.; Güdel, M.; Mewe, R. Bibcode: 2003A&A...407..347N Altcode: 2003astro.ph..6308N The relevance of resonant scattering in the solar corona has always been discussed controversially. Ratios of emission lines from identical ions but different oscillator strengths have been used in order to estimate damping of resonance lines due to possible resonant scattering, i.e., absorption by photo-excitation and re-emission out of the line of sight. The analysis of stellar spectra in analogy to previous works for the Sun is possible now with XMM-Newton and Chandra grating spectra and requires this issue to be considered again. In this work we present a sample of 45 X-ray spectra obtained for 26 stellar coronae with the RGS on board XMM-Newton and the LETGS and HETGS on board Chandra. We use ratios of the Fe XVII lines at 15.27 Å and 16.78 Å lines to the resonance line at 15.03 Å as well as the He-like f/r ratio of O VII and Ne IX to measure optical depth effects and compare them with ratios obtained from optically thin plasma atomic databases such as MEKAL, Chianti, and APEC. From the Fe XVII line ratios we find no convincing proof for resonance line scattering. Optical depths are basically identical for all kinds of stellar coronae and we conclude that identical optical depths are more probable when effects from resonant scattering are generally negligible. The 15.27/15.03 Åratio shows a regular trend suggesting blending of the 15.27 Åline by a cooler Fe line, possibly Fe XVI. The He-like f/r ratios for O and Ne show no indication for significant damping of the resonance lines. We mainly attribute deviations from the atomic databases to still uncertain emissivities which do not agree well with laboratory measurements and which come out with differing results when accounting for one or the other side effect. We attribute the discrepancies in the solar data to geometrical effects from observing individual emitting regions in the solar corona but only overall emission for stellar coronae including photons eventually scattered into the line of sight. Title: X-ray Emission from Pre-main Sequence Stars in the Orion Star-forming Region Authors: Briggs, K. R.; Güdel, M.; Audard, M.; Smith, K.; Mewe, R.; den Boggende, T. Bibcode: 2003ANS...324....9B Altcode: 2003ANS...324c...9B; 2003ANS...324..B03B No abstract at ADS Title: XMM-Newton high-resolution X-ray spectroscopy of the Wolf-Rayet object WR 25 in the Carina OB1 association Authors: Raassen, A. J. J.; van der Hucht, K. A.; Mewe, R.; Antokhin, I. I.; Rauw, G.; Vreux, J. -M.; Schmutz, W.; Güdel, M. Bibcode: 2003A&A...402..653R Altcode: We report the analysis of the first high-resolution X-ray spectra of the Wolf-Rayet (WR) object WR 25 (HD 93162, WN6ha+O4f) obtained with the Reflection Grating Spectrometers (RGS) and the European Photon Imaging Cameras (EPIC-MOS and PN) CCD spectrometers on board the XMM-Newton satellite. The spectrum exhibits bright emission lines of the H- and He-like ions of Ne, Mg, Si and S, as well as Fe XVII i to Fe XX and Fe XXV lines. Line fluxes have been measured. The RGS and EPIC spectra have been simultaneously fitted to obtain self-consistent temperatures, emission measures, and elemental abundances. Strong absorption by the dense WR stellar wind and the interstellar medium (ISM) is observed equivalent to NH = 7 x 1021 cm-2. Multi-temperature (DEM) fitting yields two dominant components around temperatures of 7.0 and 32 MK, respectively. The XMM intrinsic (i.e. unabsorbed, corrected for the stellar wind absorption and the absorption of ISM) X-ray luminosity of WR 25 is Lx(0.5-10 keV) = 1.3 x 1034 erg s-1, and Lx(0.5-10 keV) = 0.85 x 1034 erg s-1, (when correcting for the ISM only) assuming d=3.24 kpc. The obtained chemical abundances are subsolar, except for S. This may be real, but could equally well be due to a weak coupling to the continuum, which is strongly influenced by the absorption column density and the subtracted background. The expected high N-abundance, as observed in the optical wavelength region, could not be confirmed due to the strong wind absorption, blocking out its spectral signature. The presence of the Fe XXV emission-line complex at ~ 6.7 keV is argued as being indicative for colliding winds inside a WR+O binary system.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: Tomography of a stellar X-ray corona: alpha Coronae Borealis Authors: Güdel, M.; Arzner, K.; Audard, M.; Mewe, R. Bibcode: 2003A&A...403..155G Altcode: We interpret the X-ray light curve obtained by XMM-Newton during a total X-ray eclipse in the nearby binary star alpha Coronae Borealis. This system consists of a G5 V main-sequence star orbiting an X-ray dark A0 star. The secondary G star is a young, active solar analog with an age of a few 100 Myr. As the primary A star eclipses active regions on the X-ray bright companion, the light curve drops in consecutive steps to zero; as individual active regions reappear during egress, the flux rises in similar steps. The ingress and egress light curves are combined to reconstruct the 2D distribution of X-ray brightness on and around the G star. Three different methods are applied, and variations due to statistical noise and uncertainties in the binary system parameters are discussed. Although the solutions are non-unique, all reconstructions reveal a similar distribution of X-ray bright regions and large areas with little flux. We present plausible estimates of (lower limits to) the electron densities in the bright regions, obtaining characteristic values between 109-3x 1010 cm-3.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: Chandra-LETGS X-ray observation of alpha Centauri: A nearby (G2V + K1V) binary system Authors: Raassen, A. J. J.; Ness, J. -U.; Mewe, R.; van der Meer, R. L. J.; Burwitz, V.; Kaastra, J. S. Bibcode: 2003A&A...400..671R Altcode: A Chandra LETGS X-ray observation of alpha Centauri with an exposure time of 81.5 ks is presented with the two components (K1V and G2V) spectrally resolved for the first time. We use the emission lines from the individual spectra to determine plasma temperatures and find similar temperatures as for the Sun with higher temperatures for the K1V star than for the G2V star. Global fitting techniques are used in order to construct an emission measure distribution for each star and we find emission measure distributions consistent with what is found from the line ratios. A two-temperature model is used in order to derive abundances normalized to iron and relative to solar photosheric values. For both stars we find a FIP effect with a slight but not significant tendency of a stronger FIP effect for the K1V component. Title: The Hot Corona of the Giant YY Mensae with Chandra and XMM-Newton Authors: Audard, M.; Güdel, M.; Skinner, S. L.; Pallavicini, R.; Drake, S. A.; Mewe, R. Bibcode: 2003HEAD....7.1202A Altcode: 2003BAAS...35..616A We present Chandra and XMM-Newton high-resolution X-ray spectra of the rapidly rotating giant YY Mensae. It belongs to the class of ``FK Com stars'', i.e. single cool giant stars with projected equatorial velocities measured up to 110 km/s. Chandra and XMM-Newton provide excellent high-resolution X-ray spectra to study the properties of this extreme coronal source. The X-ray spectrum is dominated by a strong continuum component with bright emission lines, mostly from H-like transitions and highly ionized Fe lines (up to Fe XXV), indicative of a very high coronal temperature (≈ 3 keV). The Chandra High-Energy Transmission Grating Spectrometer data are ideal to study at very high resolution this hot coronal source. The Reflection Grating Spectrometer onboard XMM-Newton however provides better information on the cool coronal plasma, and on the carbon and nitrogen abundances. Although no obvious flare was detected in the light curves, YY Men's X-ray luminosity varied by a factor of two between the Chandra and XMM-Newton observations (log LX ≈ 32.16 - 32.42). We derive the coronal emission measure distribution, elemental abundances, and density estimates.

We acknowledge support by SAO grant GO2-3016X. Title: Performance and results of the reflection grating spectrometers onboard XMM-Newton Authors: den Herder, Jan-Willem W.; Brinkman, A. C.; Kahn, Steven M.; Branduardi-Raymont, Graziella; Audard, M.; Behar, E.; Blustin, A.; den Boggende, Antonius J. F.; Cottam, Jean; Erd, Christian; Gabriel, Carlos; Guedel, Manuel; van der Heyden, K.; Kaastra, Jelle S.; Kinkhabwala, A.; Leutenegger, Maurice A.; Mewe, Rolf; Paerels, Frits B. S.; Raassen, A. J. J.; Peterson, J. R.; Pollock, A.; Rasmussen, Andrew P.; Sako, M.; Santos-Lleo, M.; Steenbrugge, K.; Tamura, T.; de Vries, Cor P. Bibcode: 2003SPIE.4851..196D Altcode: XMM-Newton was launched in December 1999 and science operations started in March 2000. Following two years of very successful operations, a report on the instrument performance and a selection of exciting new results are presented. Behind two of the three telescopes of XMM-Newton Reflection Grating Spectrometers (RGS) are placed. Each spectrometer consists of an array of reflection gratings and a set of back illuminated CCDs. They cover the wavelength band between 6 and 38 Angstromwith a resolution varying between 100 and 600 (E/DE) and a maximum effective area of 140 cm2 for the two spectrometers combined. The selected wavelength band covers the K-shell transitions of C, N, O, Ne, Mg and Si as well as the L- and M-shell transitions of Fe. After a short introduction to the instrument design, the in-orbit performance is given. This includes the line spread function, the wavelength scale and the effective area including their stability during the more than 2 years of operations. Following this a number of key scientific results are briefly addressed, illustrating the power of the RGS instrument in combination with the other instruments on-board of XMM-Newton as well as the wealth of information which is obtained as the RGS instruments operate continuously. Title: A study of coronal abundances in RS CVn binaries% Authors: Audard, M.; Güdel, M.; Sres, A.; Raassen, A. J. J.; Mewe, R. Bibcode: 2003A&A...398.1137A Altcode: 2001astro.ph..9268A We present XMM-Newton data of several RS CVn binary systems. High-resolution X-ray spectra obtained with the Reflection Grating Spectrometers have been interpreted simultaneously with the European Photon Imaging Camera spectra. Highly active stars show a depletion of elements with a low first ionization potential (FIP) relative to high-FIP elements, whereas intermediately active binaries show either no FIP bias or a possible solar-like FIP effect. We find that the low-FIP abundance ratios to oxygen vary with the coronal average temperature whereas the ratios for high-FIP elements stay constant. Since we observe that the absolute Fe (low-FIP) abundance increases with decreasing activity, this suggests that the abundances of elements with low FIP vary with the coronal activity level. Compared with laboratory measurements of the intensity ratios of the Fe Xvii lambda lambda 15.01 and 15.26 Å lines, the coronal plasmas are in the optically thin regime.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: New Results on X-Ray Models and Atomic Data Authors: Kaastra, Jelle S.; Mewe, Rolf; Raassen, Ton Bibcode: 2003IAUJD..17E..24K Altcode: We discuss the most recent developments of the spectral analysis package SPEX. We report on the progress made in updating the atomic data that are used in the spectroscopic code. We also present a set of spectral models that are used for the analysis of high-resolution X-ray spectra of photo-ionized plasmas such as occur in active galactic nuclei. These models include absorption line spectroscopy of photoionized layers. The importance and diagnostic power of innershell transitions is shown. We illustrate our results with several examples of observed spectra obtained with the XMM-Newton and Chandra grating spectrometers. Title: High-resolution X-ray spectroscopy of tau Scorpii (B0.2V) with XMM-Newton Authors: Mewe, R.; Raassen, A. J. J.; Cassinelli, J. P.; van der Hucht, K. A.; Miller, N. A.; Güdel, M. Bibcode: 2003A&A...398..203M Altcode: We report the analysis of the first high-resolution X-ray spectrum of the B0.2V star tau Scorpii obtained with the Reflection Grating Spectrometers (RGS) and the EPIC-MOS CCD spectrometers on board XMM-Newton. The spectrum exhibits bright emission lines of the H- and He-like ions of C, N, O, Ne, Mg, and Si, as well as Fe XVII & Fe XVIII lines. Line fluxes have been determined. Simultaneous fits to the RGS and EPIC spectra were used to obtain four plasma temperatures, emission measures, and the overall elemental abundances. This multi-temperature fitting yielded temperatures of 1.6, 5.2, 8.2, and ga 20 MK. These temperatures are confirmed by DEM modelling. The nitrogen lines are relatively strong: the N/O abundance ratio is about 3x solar. No indication of a solar-type ``FIP effect'' was found for the other elements. According to the derived models the X-ray luminosity in the energy range 0.3-10 keV is Lx = 3.2 x 1031 erg s-1 at a distance of 132 pc. The sensitivity of the He-like forbidden and intercombination lines to a strong ultraviolet radiation field is used to derive upper limits to the radial distances at which lines of Mg XI, Ne IX, O VII, and N VI originate. The results suggest that the soft X-rays (la 8 MK) originate from shocks low in the wind that are produced by the common mechanism of radiation line-driven instabilities. This is consistent with the observed emission line profiles that are much narrower (la 500 km s-1) than the broad lines (up to 1500 km s-1) observed high up in the wind of zeta Puppis. The hot ( ~ 20-40 MK) component may be explained by a model involving dense clumps embedded in a wind which sweeps past them at high relative velocity ( ~ 1400-1700 km s-1). Such an interaction would produce the strong shocks required.

Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: High-resolution X-ray spectroscopy of late-type stars with CHANDRA Authors: Mewe, R.; Raassen, A. J. J.; Kaastra, J. S.; van der Meer, R. L. J.; Brinkman, A. C. Bibcode: 2003AdSpR..32.2059M Altcode: We have analyzed high-resolution (Δλ ≅ 0.06 Å) X-ray spectra in the region 6-180 Å of the coronae of the cool stars Capella, Procyon, and α Centauri. These stars were observed with the the CHANDRA Low Energy Transmission Grating Spectrometer (LETGS) between Sep. and Dec. 1999. Temperatures are derived from line ratios of helium-like lines and long-wavelength iron lines. Electron densities are obtained for the relatively cooler (few MK) and more tenuous (⪅ 10 11 cm -3) plasma components from the forbidden to intercombination line ratios in the helium-like triplets of O, N, and C and for the hotter (⪆ 5 MK) and denser (⪆ 10 12 cm -3) components (such as occur in Capella) from the helium-like triplets of Mg and Si and the ratios of Fe XIX-Fe XXII 2ℓ-2ℓ' lines above 90 Å. The implications of these results for the coronal structure are discussed. Title: Emission measure modeling and abundance determination of Procyon by means of a variety of instruments on board Chandra and XMM-Newton Authors: Raassen, A. J. J.; Audard, M.; Mewe, R.; Güdel, M.; van der Meer, R. L. J.; Behar, E. Bibcode: 2002ASPC..277..573R Altcode: 2002sccx.conf..573R No abstract at ADS Title: High Resolution X-ray Spectroscopy with XMM-Newton of Hot Stars: Tau Scorpii Authors: Raassen, T.; Mewe, R.; Cassinelli, J. P.; van der Hucht, K. A.; Miller, N. A.; Guedel, M. Bibcode: 2002hrxs.confE..32R Altcode: The spectra of the B0.2V star Tau Scorpii, observed with RGS and EPIC-MOS on board XMM-Newton, are simultaneously fitted to obtain self-consistent temperatures, emission measures, and elemental abundances. The nitrogen lines are relatively very strong: the N/O abundance ratio is about 3 times solar. Multi-temperature fitting yields 4 components at temperatures of 1.6, 5.2, 8.2, and >~ 20 MK which are confirmed by DEM modeling. The X-ray luminosity (0.3-10 keV) is 3.2e31 erg/s at d=132 pc. The sensitivity of the He-like forbidden and intercombination lines to a strong UV stellar radiation field yields upper limits to the radial distances at which the He-like lines of Mg, Ne, O, and N originate. The results suggest that the soft X-rays (<~ 8 MK) originate from shocks low in the wind produced by the common mechanism of radiation line-driven instabilities. This is consistent with the observed emission line profiles that are much narrower (<~ 500 km/s) than the broad lines (up to 1500 km/s) observed high up in the wind of Zeta Puppis. The hot (~ 20-40 MK) component may be explained by a model involving dense clumps embedded in a wind which is approaching at high relative velocity (~ 1400-1700 km/s) and the interaction produces strong shocks. Title: Emission measure modeling and abundance determination of α Centauri and Procyon Authors: Raassen, A. J. J.; Mewe, R.; Ness, J. -U. Bibcode: 2002ASPC..277..567R Altcode: 2002sccx.conf..567R No abstract at ADS Title: Chandra and XMM-Newton X-Ray Spectroscopy of the Hot Corona of YY Mensae Authors: Audard, M.; Güdel, M.; Skinner, S. L.; Pallavicini, R.; Drake, S. A.; Mewe, R. Bibcode: 2002AAS...201.3307A Altcode: 2002BAAS...34.1156A We present Chandra and XMM-Newton X-ray spectra of the rapidly rotating K giant YY Mensae (d = 290 pc). YY Men is a member of a loosely-defined class of rapidly rotating single cool giant stars (``FK Com stars''), whose outstanding property is a projected equatorial velocity measured up to 110 km/s, in contrast with the expected maximum of 6 km/s for giants. One of the leading theories to explain the extreme properties of FK Com stars suggests that they were formed by coalescence of a contact binary when one of the components entered into the giant stage. Previous observations have shown that its corona displays plasma with a very hot temperature of about 3 keV, with probably no or very little plasma at temperatures below 1 keV. The new X-ray observatories now provide excellent high-resolution X-ray spectra to study the coronal properties of this extreme coronal source. The X-ray spectrum is dominated by a strong continuum and by bright emission lines, mostly from H-like transitions and Fe XXIV lines. Thanks to its wavelength range and its sensitivity, the Reflection Grating Spectrometer onboard XMM-Newton provides important information on the presence of cool coronal plasma, mostly seen at wavelengths between 20 and 40 Å. Simultaneous EPIC CCD spectra also constrain the high-temperature component of the emission measure distribution. The Chandra High-Energy Transmission Grating Spectrometer data are ideal to study at very high resolution the short wavelength range of this hot coronal source. We derive the coronal emission measure distribution, elemental abundances, and density estimates. We acknowledge support by SAO grant GO2-3016X. Title: Coronal density diagnostics with Helium-like triplets: Chandra-LETG observations of Algol, Capella, Procyon, ∈ Eri, α Cen A&B, and UX Ari Authors: Ness, J. -U.; Mewe, R.; Schmitt, J. H. M. M.; Raassen, A. J. J.; van der Meer, R. L. J.; Burwitz, V.; Predehl, P.; Brinkman, A. C. Bibcode: 2002ASPC..277..127N Altcode: 2002sccx.conf..127N No abstract at ADS Title: A Study of the Coronal Plasma in RS CVn binary systems: HR 1099 and co. Authors: Audard, M.; Güdel, M.; Sres, A.; Mewe, R.; Raassen, A. J. J.; Behar, E.; Foley, C. R.; van der Meer, R. L. J. Bibcode: 2002ASPC..277...65A Altcode: 2001astro.ph..9264A; 2002sccx.conf...65A XMM-Newton has been performing comprehensive studies of X-ray luminous RS CVn binary systems in its calibration and guaranteed time programs. We present results from ongoing investigations in the context of a systematic study of coronal emission from RS CVns. We concentrate here on coronal abundances and investigate the abundance pattern in RS CVn binaries as a function of activity and average temperature. We find a transition from an Inverse First Ionization Potential (FIP) effect towards an absence of a clear trend (no FIP) in intermediately active RS CVn systems. This scheme fits well into the long-term evolution from an IFIP to a FIP effect found in solar analogs. We further study variations in the elemental abundances during a large flare. Title: XMM-Newton Probes the Solar Past: Coronal Abundances of Solar Analogs at Different Ages Authors: Güdel, M.; Audard, M.; Sres, A.; Wehrli, R.; Behar, E.; Mewe, R.; Raassen, A. J. J.; Magee, H. R. M. Bibcode: 2002ASPC..277..497G Altcode: 2002sccx.conf..497G; 2001astro.ph..9265G We present an X-ray spectral analysis of four solar analogs with different ages and magnetic activity levels. We find largely different coronal compositions. The most active stars tend to show an ``Inverse First Ionization Potential'' (IFIP) effect, i.e., elements with low FIP are underabundant. Less active stars tend to the opposite effect, with relative overabundances of low-FIP elements. Equivalent Chandra results are presented that support these results. Title: Influence of radiation fields on the density diagnostics Chandra-LETGS observations of Algol and Procyon Authors: Ness, J. -U.; Mewe, R.; Schmitt, J. H. M. M.; Raassen, A. J. J. Bibcode: 2002ASPC..277..545N Altcode: 2002sccx.conf..545N No abstract at ADS Title: Coronal density diagnostics with Helium-like triplets: CHANDRA-LETGS observations of Algol, Capella, Procyon, epsilon Eri, alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR 1099 Authors: Ness, J. -U.; Schmitt, J. H. M. M.; Burwitz, V.; Mewe, R.; Raassen, A. J. J.; van der Meer, R. L. J.; Predehl, P.; Brinkman, A. C. Bibcode: 2002A&A...394..911N Altcode: 2002astro.ph..9033N We present an analysis of ten cool stars (Algol, Capella, Procyon, epsilon Eri, alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR 1099) observed with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory. This sample contains all cools stars observed with the LETGS presently available to us with integration times sufficiently long to warrant a meaningful spectral analysis. Our sample comprises inactive, moderately active, and hyperactive stars and samples the bulk part of activity levels encountered in coronal X-ray sources. We use the LETGS spectra to carry out density and temperature diagnostics with an emphasis on the H-like and the He-like ions. We find a correlation between line flux ratios of the Lyalpha and He-like resonance lines with the mean X-ray surface flux. We determine densities using the He-like triplets. For all stars we find no significant deviations from the low-density limit for the ions of Ne, Mg, and Si, while the measured line ratios for the ions of C, N, and O do show evidence for departures from the low-density limit in the active stars, but not in the inactive stars. Best measurements can be made for the O VII triplet where we find significant deviations from the low-density limit for the stars Algol, Procyon, YY Gem, epsilon Eri, and HR 1099. We discuss the influence of radiation fields on the interpretation of the He-like triplet line ratios in the low-Z ions, which is relevant for Algol, and the influence of dielectronic satellite lines, which is relevant for Procyon. For the active stars YY Gem, epsilon Eri, and HR 1099 the low f/i ratios can unambiguously be attributed to high densties in the range 1-3*E10 cm-3 at O VII temperatures. We find our LETGS spectra to be an extremely useful tool for plasma diagnostics of stellar coronae. Title: Emission Lines of Fe VII-Fe X in the Extreme Ultraviolet Region, 60-140 Å Authors: Lepson, J. K.; Beiersdorfer, P.; Brown, G. V.; Liedahl, D. A.; Utter, S. B.; Brickhouse, N. S.; Dupree, A. K.; Kaastra, J. S.; Mewe, R.; Kahn, S. M. Bibcode: 2002ApJ...578..648L Altcode: We report on emission spectra of iron in the extreme ultraviolet recorded at an electron density of ~5×1011 cm-3 at the Lawrence Livermore electron beam ion trap EBIT-II. We present a summary of observed emission lines, including wavelengths and emission intensities. We also illustrate our technique for isolating pure charge states of the desired ion and present spectra of pure Fe VII-Fe X. Our measurements add a large number of newly identified lines to existing line lists in the extreme-ultraviolet region, 60-140 Å. While many of these lines are quite weak, they add up to a significant flux that can seriously affect interpretations of global fitting models, especially when applied to stars with material at the appropriate temperatures, such as Procyon, α Cen, and the Sun. Title: High-Resolution X-ray imaging and spectroscopy of N 103B Authors: van der Heyden, K. J.; Behar, E.; Vink, J.; Rasmussen, A. P.; Kaastra, J. S.; Bleeker, J. A. M.; Kahn, S. M.; Mewe, R. Bibcode: 2002A&A...392..955V Altcode: The X-ray emission from the young supernova remnant (SNR) N 103B is measured and analysed using the high-resolution cameras and spectrometers on board XMM-Newton and Chandra. The spectrum from the entire remnant is reproduced very well with three plasma components of kTe = 0.55, 0.65, and 3.5 keV, corresponding roughly to line emission by the O-K, Fe-L, and Fe-K species, respectively. Narrow band images reveal different morphologies for each component. The kTe = 0.65 keV component, which dominates the emission measure (4.5*E65 m-3), is in ionisation equilibrium. This provides a lower limit of 1200 yrs to the age of the remnant, which is in agreement with the previously assumed age of the remnant (1500 yrs). Based on the measured energy of the Fe-K feature at 6.5 keV, the hot (3.5 keV) component is found to be recently shocked ( ~ 200 yrs) and still ionising. The high elemental abundances of O and Ne and the low abundance of Fe could imply that N 103B originated from a type II supernova (SN) rather than a type Ia SN as previously thought. Title: Detection of the Neupert Effect in the Corona of an RS Canum Venaticorum Binary System by XMM-Newton and the Very Large Array Authors: Güdel, Manuel; Audard, Marc; Smith, Kester W.; Behar, Ehud; Beasley, Anthony J.; Mewe, Rolf Bibcode: 2002ApJ...577..371G Altcode: 2002astro.ph..6080G The RS CVn-type binary σ Geminorum was observed during a large, long-duration flare simultaneously with XMM-Newton and the Very Large Array. The light curves show a characteristic time dependence that is compatible with the Neupert effect observed in solar flares: the time derivative of the X-ray light curve resembles the radio light curve. This observation can be interpreted in terms of a standard flare scenario in which accelerated coronal electrons reach the chromosphere, where they heat the cool plasma and induce chromospheric evaporation. Such a scenario can hold only if the amount of energy in the fast electrons is sufficient to explain the X-ray radiative losses. We present a plausibility analysis that supports the chromospheric evaporation model. Title: High-resolution X-ray spectroscopy of Procyon by Chandra and XMM-Newton Authors: Raassen, A. J. J.; Mewe, R.; Audard, M.; Güdel, M.; Behar, E.; Kaastra, J. S.; van der Meer, R. L. J.; Foley, C. R.; Ness, J. -U. Bibcode: 2002A&A...389..228R Altcode: 2002astro.ph..4385R We report the analysis of the high-resolution soft X-ray spectrum of the nearby F-type star Procyon in the wavelength range from 5 to 175 Å obtained with the Low Energy Transmission Grating Spectrometer (LETGS) on board Chandra and with the Reflection Grating Spectrometers (RGS) and the EPIC-MOS CCD spectrometers on board XMM-Newton. Line fluxes have been measured separately for the RGS and LETGS. Spectra have been fitted globally to obtain self-consistent temperatures, emission measures, and abundances. The total volume emission measure is ~ 4.1 x 1050 cm-3 with a peak between 1 and 3 MK. No indications for a dominant hot component (T ~> 4 MK) were found. We present additional evidence for the lack of a solar-type FIP-effect, confirming earlier EUVE results. Title: Low-Energy X-Ray Emission from the Abell 2199 Cluster of Galaxies Authors: Kaastra, Jelle S.; Lieu, Richard; Bleeker, Johan A. M.; Mewe, Rolf; Colafrancesco, Sergio Bibcode: 2002ApJ...574L...1K Altcode: 2002astro.ph..6235K In a recent Letter, Berghöfer & Bowyer rediscussed the analysis of BeppoSAX LECS data of the cluster of galaxies Abell 2199 as presented by Kaastra et al., in particular the detection of a soft X-ray excess. Berghöfer & Bowyer stated that their analysis method is better suited and does not show evidence of a soft X-ray excess. Here we find it necessary to publish a rebuttal because it can be demonstrated that the method used by Berghöfer & Bowyer is oversimplified, leading to an erroneous result. As a consequence, their statement that our initial analysis is incorrect is invalid, and the detection of a soft X-ray excess in A2199 is still confirmed. Title: Chandra LETGS observation of the active binary Algol Authors: Ness, J. -U.; Schmitt, J. H. M. M.; Burwitz, V.; Mewe, R.; Predehl, P. Bibcode: 2002A&A...387.1032N Altcode: 2002astro.ph..3431N A high-resolution spectrum obtained with the low-energy transmission grating onboard the Chandra observatory is presented and analyzed. Our analysis indicates very hot plasma with temperatures up to T~ 15-20 MK from the continuum and from ratios of hydrogen-like and helium-like ions of Si, Mg, and Ne. In addition lower temperature material is present since O VII and N VI are detected. Two methods for density diagnostics are applied. The He-like triplets from N VII to Si XIII are used and densities around 1011 cm-3 are found for the low temperature ions. Taking the UV radiation field from the B star companion into account, we find that the low-Z ions can be affected by the radiation field quite strongly, such that densities of 3x 1010 cm-3 are also possible, but only assuming that the emitting plasma is immersed in the radiation field. For the high temperature He-like ions only low density limits are found. Using ratios of Fe XXI lines produced at similar temperatures are sensitive to lower densities but again yield only low density limits. We thus conclude that the hot plasma has densities below 1012 cm-3. Assuming a constant pressure corona we show that the characteristic loop sizes must be small compared to the stellar radius and that filling factors below 0.1 are unlikely. Title: X-ray powerful diagnostics for highly-ionized plasmas: He-like ions Authors: Porquet, D.; Mewe, R.; Kaastra, J. S.; Dubau, J.; Raassen, A. J. J. Bibcode: 2002astro.ph..4119P Altcode: The calculations of the ratios of the Helium-like ion X-ray lines from C V to Si XIII are revisited in order to apply the results to density, temperature and ionization process diagnostics of data from high-resolution spectroscopy of the new generation of X-ray satellites: Chandra and XMM-Newton. Comparing to earlier computations, Porquet & Dubau (2000), the best experimental values are used for radiative transition probabilities. The influence of an external radiation field (photo-excitation), the contribution from unresolved dielectronic satellite lines and the optical depth are taken into account. These diagnostics could be applied to collision-dominated plasmas (e.g., stellar coronae), photo-ionized plasmas (e.g., ``Warm Absorber'' in AGNs), and transient plasmas (e.g., SNRs). Title: Evidence for a Heated Gas Bubble inside the ``Cooling Flow'' Region of MKW 3s Authors: Mazzotta, P.; Kaastra, J. S.; Paerels, F. B.; Ferrigno, C.; Colafrancesco, S.; Mewe, R.; Forman, W. R. Bibcode: 2002ApJ...567L..37M Altcode: 2001astro.ph..7557M We report on the deep Chandra observation of the central r=200 kpc region of the cluster of galaxies MKW 3s, which was previously identified as a moderate cooling flow cluster. The Chandra image reveals two striking features-a 100 kpc long and 21 kpc wide filament, extending from the center to the southwest, and a nearly circular, 50 kpc diameter depression 90 kpc south of the X-ray peak. The temperature map shows that the filamentary structure is colder while the surface brightness depression is hotter than the average cluster temperature at any radius. The hot and the cold regions indicate that both cooling and heating processes are taking place in the center of MKW 3s. We argue that the surface brightness depression is produced by a heated, low-density gas bubble along the line of sight. We suggest that the heated bubble is produced by short-lived nuclear outbursts from the central galaxy. Title: X-ray diagnostics for photo-ionized plasmas: He-like triplets Authors: Porquet, D.; Mewe, R.; Kaastra, J. S.; Dubau, J. Bibcode: 2002xsac.conf..285P Altcode: The calculations of the ratios of the Helium-like ion X-ray lines from ion{C}{v} to ion{Si}{xiii} are revisited in order to apply the results to density, temperature and ionization process diagnostics of data from high-resolution spectroscopy of the new generation of X-ray satellites: Chandra and XMM-Newton. These diagnostics could be applied to collision-dominated plasmas (e.g. stellar coronae), photo-ionized plasmas (e.g, AGNs), and transient plasmas (e.g., SNRs). Here we will present improved calculations which could be dedicated to the detailed study of the physical parameters of the totally or partially photo-ionized plasmas in Active Galactic Nuclei, the so-called ``Warm Absorber''. Indeed the Warm Absorber is an important component of the environment of Supermassive Black Holes in these powerful objects. Title: XMM-newton high-resolution x-ray - spectroscopy of wr 25 Authors: Raassen, A.; van der Hucht, K.; Mewe, R.; Antokhin, I.; Guedel, M.; Schmutz, W. Bibcode: 2002cosp...34E1592R Altcode: 2002cosp.meetE1592R We report the analysis of the first high-resolution X-ray spectra of the WN6ha star WR 25 (HD 93162) obtained with the reflection grating spectrometers (rgs) and the european photon imaging cameras (epic- mos and -pn) ccd spectrometers on board XMM-Newton. The spec- trum exhibits bright emission lines of the H- and He-like ions of Ne, Mg, Si and S, as well as lines of Fe xvii to Fe xx and Fe xxv. Line fluxes have been determined. The rgs and epic spectra have been simultane- ously fitted to obtain self-consistent temperatures, emission measures, and elemental abundances. Multi-temperature fitting yields two dom- inant components around temperatures of 7 and 30 MK, respectively. An interstellar absorption value, related to the optically thick wind of the WR star is obtaines as NH in the range 3-6 1021 cm-2 . The pres- ence of the Fe xxv emission-line complex at6.7 keV is argued as being indicative for colliding winds inside the WR+O binary system. Title: The x-ray spectrum of ad leo (M3.5 V) Authors: Raassen, A.; van den Besselaar, E.; Mewe, R.; Audard, M.; Guedel, M. Bibcode: 2002cosp...34E1589R Altcode: 2002cosp.meetE1589R The X-ray spectrum of the M3.5V star AD Leo at a distance of 4.7 pc has been observed with RGS and EPIC on board XMM-Newton. The spectrum is dominated by H-, and He-like transitions of C, N, O, Ne, Mg, and Si and by many Fe XVII lines. The Fe K-shell transitions around 6.7 keV are also present in the EPIC-MOS spectrum. Individual lines fluxes have been measured. The spectra have been fitted simultaneously using SPEX in combination with MEKAL applying a multi-temperature fit as well as a self-consistent DEM-Modeling. Temperatures between 3 and 20 MK have been established. Abundances have been determined to monitor FIP or IFIP effects. Title: XMM-Newton observations of eclipsing binary systems Authors: Guedel, M.; Audard, M.; Mewe, R. Bibcode: 2002cosp...34E2542G Altcode: 2002cosp.meetE2542G XMM-Newton and Chandra are providing access to eclipsing binaries at unprecedented sensitivity that allows for the reconstruction of the distribution of coronal material around one or both of the stellar components. Here, we present results from XMM-Newton observations, including the binaries AR Lac and alpha CrB. Of primary interest are i) the distribution of coronal emission measure as a function of stellar latitude, ii) the degree of inhomogeneity in the surface distribution of coronal material, iii) the differences in the surface distribution for different hardness bands (e.g., implying a vertical temperature structure), and iv) the radial extent of significant coronal X-ray emission, indicating the extent of magnetic fields that carry significant X-ray emission measure. Title: High-resolution x-ray spectroscopy of scorpii (B0.2. V) by xmm-newton Authors: Mewe, R.; Raassen, A.; Cassinelli, J.; van der Hucht, K.; Miller, N.; Guedel, M. Bibcode: 2002cosp...34E1593M Altcode: 2002cosp.meetE1593M We report the analysis of the first high-resolution X-ray spectrum of the B0.2 V starScorpii obtained with the Reflection Grating Spec- trometers (rgs) and the epic-mos ccd spectrometers on board XMM- Newton. The spectrum exhibits bright emission lines of the H- and He-like ions of C to Si, as well as Fe xvii &xviii lines. Line fluxes have been determined. The nitrogen lines are relatively strong: the N/O ratio is about 3× solar. The rgs and epic spectra have been simultaneously fitted to obtain self-consistent temperatures, emission measures, and ele- mental abundances. Except for nitrogen, the abundances are near solar. Multi-temperature fitting yields four components at temperatures of 1.6, 5.2, 8.2, and >20 MK. The sensitivity of the He-like forbidden and inter-combination lines to a strong ultraviolet radiation field is used to derive upper limits to the radial distances at which lines of Mg xi, Ne ix, O vii, and N vi originate. The results suggest that the soft (< 10 MK) X-raysoriginate from shocks low in the wind that are produced by the com- mon mechanism of radiation line-driven instabilities. This is consistent with the observed emission line profiles that are much narrower (< 500km/s) than the broad lines (< 1500 km/s) observed high up in the windofPuppis. The hot ( 20-40 MK) component may be explained by a model with dense clumps embedded in the wind which approach high relative velocities ( 1600 km/s) and therefore produce such hot shocks. Title: Line ratios for helium-like ions: Applications to collision-dominated plasmas Authors: Porquet, D.; Mewe, R.; Dubau, J.; Raassen, A. J. J.; Kaastra, J. S. Bibcode: 2001A&A...376.1113P Altcode: 2001astro.ph..7329P The line ratios R and G of the three main lines of He-like ions (triplet: resonance, intercombination, forbidden lines) are calculated for C V, N Vi, O Vii, Ne Ix, Mg Xi, and Si Xiii. These ratios can be used to derive electron density n_e and temperature T_e of hot late-type stellar coronae and O, B stars from high-resolution spectra obtained with Chandra (LETGS, HETGS) and XMM-Newton (RGS). All excitation and radiative processes between the levels and the effect of upper-level cascades from collisional electronic excitation and from dielectronic and radiative recombination have been considered. When possible the best experimental values for radiative transition probabilities are used. For the higher-Z ions (i.e. Ne Ix, Mg Xi, Si Xiii) possible contributions from blended dielectronic satellite lines to each line of the triplets were included in the calculations of the line ratios R and G for four specific spectral resolutions: RGS, LETGS, HETGS-MEG, HETGS-HEG. The influence of an external stellar radiation field on the coupling of the 23S (upper level of the forbidden line) and 23P levels (upper levels of the intercombination lines) is taken into account. This process is mainly important for the lower-Z ions (i.e. C V, N Vi, O Vii) at moderate radiation temperature (T_rad). These improved calculations were done for plasmas in collisional ionization equilibrium, but will be later extended to photo-ionized plasmas and to transient ionization plasmas. The values for R and G are given in extensive tables, for a large range of parameters, which could be used directly to compare to the observations. Tables 4 to 69 and A.1 to A.6 are only available in electronic form at the CDS via anonymous ftp to\ cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/376/1113 Title: VizieR Online Data Catalog: Line ratios for helium-like ions (Porquet+, 2001) Authors: Porquet, D.; Mewe, R.; Dubau, J.; Raassen, A. J. J.; Kaastra, J. S. Bibcode: 2001yCat..33761113P Altcode: The tables include data concerning six He-like ions: wavelengths, transition probabilities, wavelengths at which the radiation temperatures should be determined. Line ratios (G and R, see definition in table 1 below) for six He-like ions from Tables 3 to 69 for various parameters: density (ne), temperature (Te), dilution factor (W), radiation temperature (Trad), and spectral resolution. Atomic data (appendix A) concerning the unresolved satellite lines are displayed (from Tables A1 to A6). (4 data files). Title: The coronal FeXXI lambda 1354.094 line in AB Doradus Authors: Vilhu, O.; Muhli, P.; Mewe, R.; Hakala, P. Bibcode: 2001A&A...375..492V Altcode: 2001astro.ph..5475V The active late-type star AB Doradus was observed in February 1996 with the Goddard High Resolution Spectrograph of the Hubble Space Telescope using the low resolution G140L grating. The observations covered one half of the star's rotation cycle (P = 0.514 d) with 11.5 min time resolution. The strong coronal FeXXI lambda 1354.094 line formed at 107 K was analysed and its emission measure (EM) derived. This EM is much higher than that derived from recent XMM-Newton observations (Güdel et al. 2001), and earlier EXOSAT (Collier Cameron et al. 1988) and ASCA/EUVE (Mewe et al. 1996) data, as well, requiring a variability by a factor of 5. The physical reason for the variability remains unknown, since (outside flares) the observed broad band variability of AB Dor is much smaller. Based on observations with the NASA/ESA Hubble Space telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under the NASA contract NAS 5-26555. Title: V857 Centauri Authors: in 't Zand, J. J. M.; Mewe, R.; Heise, J. Bibcode: 2001IAUC.7693....3I Altcode: 2001IAUC.7693C...1I J. J. M. in 't Zand, Astronomical Institute, Utrecht University, and Space Research Organization Netherlands (SRON), Utrecht; R. Mewe and J. Heise, SRON, write: "Analysis of archival data from the Wide Field Cameras on BeppoSAX has revealed an energetic x-ray flare from a position consistent with that of V857 Cen = Gliese 431, a dM4.5e star (V = 11.5) at a distance of 10.5 pc that was seen to flare once before in the optical (Doyle et al. 1990, A.Ap. Suppl. 86, 403). The x-ray flare occurred on May 28.739 UT, had a rise time of 1 to 3 min, and lasted at least 12 min. After a data gap from 12 to 88 min after the onset, the flare was over. The peak luminosity is 3 x 10**31 erg s**-1 cm**-2 (2-28 keV), and the fluence at least 2 x 10**34 ergs. The spectral shape is consistent with thermal bremsstrahlung at 11 +/- 4 keV. This is the only flare detected from Gl 431 above 1 x 10**31 erg s**-1 cm**-2 in 1 month of net exposure time over the past five years." Title: CHANDRA-LETGS X-ray observations of Capella. Temperature, density and abundance diagnostics Authors: Mewe, R.; Raassen, A. J. J.; Drake, J. J.; Kaastra, J. S.; van der Meer, R. L. J.; Porquet, D. Bibcode: 2001A&A...368..888M Altcode: We report an analysis of the X-ray spectrum of Capella from 6 to 175 Å obtained with the Low Energy Transmission Grating Spectrometer (LETGS) on board of the X-ray space observatory CHANDRA. Many emission line features appear that can be resolved much better as compared to former instruments (EUVE and ASCA). Coronal electron densities (ne) and temperatures (T) of brightly emitting regions are constrained by an analysis of ratios of density- and temperature-sensitive lines of helium-like ions and highly ionized iron atoms. Lines emitted by e.g., O VII & VIII, Mg X-XII, Si XII-XIV, Fe IX, X & XV-XXIII are used to derive T. Line ratios in the helium-like triplets of C V, N VI, O VII, Mg XI, and Si XIII yield T in the range 0.5-10 MK, and ne in the range 109-1013 cm-3. The Fe IX/X ratio yields T =~ 0.9 MK, while lines from Fe XVIII to XXII give T ~ 6-10 MK. Flux ratios of Fe XX-XXII lines indicate for the electron densities an upper limit in the range ne <~ (2-5) 1012 cm-3. From line ratios of Fe XVII and Fe XVIII we derive constraints on the optical depth tau of ~ 1-1.5. An emission measure distribution is derived from Fe line intensities. Results for element abundances (relative to Fe) from a 4-T model are: O and Ne/Fe about solar, N, Mg and Si/Fe ~ 2x solar. The results for T and ne are described in terms of quasi-static coronal loop models and it is shown that the X-ray emission originates from compact structures much smaller than the stellar radii. Title: Helium-like triplet density diagnostics. Applications to CHANDRA-LETGS X-ray observations of Capella and Procyon Authors: Ness, J. -U.; Mewe, R.; Schmitt, J. H. M. M.; Raassen, A. J. J.; Porquet, D.; Kaastra, J. S.; van der Meer, R. L. J.; Burwitz, V.; Predehl, P. Bibcode: 2001A&A...367..282N Altcode: 2000astro.ph.12223N Electron density diagnostics based on the triplets of helium-like C v, N vi, and O vii are applied to the X-ray spectra of Capella and Procyon measured with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory. New theoretical models for the calculation of the line ratios between the forbidden (f), intercombination (i), and the resonance (r) lines of the helium-like triplets are used. The (logarithmic) electron densities (in cgs units) derived from the f/i ratios for Capella are <9.38 cm-3 for O vii (2sigma upper limit) (f/i=4.0+/- 0.25), 9.86+/-0.12 cm-3 for N vi (f/i=1.78+/- 0.25), and 9.42+/- 0.21 cm-3 for C v (f/i=1.48+/- 0.34), while for Procyon we obtain 9.28+0.4-9.28 cm-3 for O vii (f/i=3.28+/- 0.3), 9.96+/- 0.23 cm-3 for N vi (f/i=1.33+/- 0.28), and <8.92 cm-3 for C v (f/i=0.48+/- 0.12). These densities are quite typical of densities found in the solar active regions, and also pressures and temperatures in Procyon's and Capella's corona at a level of T ~ 106 K are quite similar. We find no evidence for densities as high as measured in solar flares. Comparison of our Capella and Procyon measurements with the Sun shows little difference in the physical properties of the layers producing the C v, N vi, and O vii emission. Assuming the X-ray emitting plasma to be confined in magnetic loops, we obtain typical loop length scales of {L_Capella} >= 8 {L_Procyon} from the loop scaling laws, implying that the magnetic structures in Procyon and Capella are quite different. The total mean surface fluxes emitted in the helium- and hydrogen-like ions are quite similar for Capella and Procyon, but exceed typical solar values by one order of magnitude. We thus conclude that Procyon's and Capella's coronal filling factors are larger than corresponding solar values. Title: The XMM-Newton view of stellar coronae: High-resolution X-ray spectroscopy of Capella Authors: Audard, M.; Behar, E.; Güdel, M.; Raassen, A. J. J.; Porquet, D.; Mewe, R.; Foley, C. R.; Bromage, G. E. Bibcode: 2001A&A...365L.329A Altcode: We present the high-resolution RGS X-ray spectrum of the stellar binary Capella observed by the XMM-Newton satellite. A multi-thermal approach has first been applied to fit the data and derive elemental abundances. Using the latter, the emission measure distribution has been reconstructed using a Chebychev polynomial fit. Its shape is found to display a sharp peak around 7 MK, consistent with previous EUVE and ASCA results. A smaller but significant amount of emission measure is required around 1.8 MK in order to explain the O Vii He-like triplet and the C Vi Lyalpha line. We have applied the temperature diagnostics of dielectronic recombination satellite lines to the He-like O Vii triplet to constrain the cool plasma temperature, and have obtained a lower limit consistent with the global reconstruction of the emission measure distribution. We have used line ratios from the forbidden, intercombination, and resonance lines of the O Vii triplet to derive an average density for the cool coronal plasma (ne <1 1010 cm-3). Implications for the coronal structure of Capella are discussed. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: The XMM-Newton view of stellar coronae: Flare heating in the coronae of HR 1099 Authors: Audard, M.; Güdel, M.; Mewe, R. Bibcode: 2001A&A...365L.318A Altcode: The RS CVn system HR 1099 was observed by XMM-Newton for a time span of 25 days during the commissioning phase. Rotational modulation in the RGS light curve has been detected with maximum flux when the active K1 IV star is in front. Following a quiescent phase of emission, the rise and peak of a large flare were observed. Time-dependent spectroscopy has been performed to derive elemental abundances and their variations during the various stages of the flare. Emission measure distributions have been reconstructed. Two different components are detected: a very hot plasma (up to 100 MK) that evolves rapidly, and a stable quiescent plasma. Low first-ionization-potential elemental (such as Fe and Si) abundances increase significantly during the flare, while the abundance of the high-FIP element Ne stays constant at the quiescent value. We report direct detection of a flux increase in the Fe Xxiv X-ray lines during a stellar flare. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: High resolution X-ray spectroscopy of zeta Puppis with the XMM-Newton reflection grating spectrometer Authors: Kahn, S. M.; Leutenegger, M. A.; Cottam, J.; Rauw, G.; Vreux, J. -M.; den Boggende, A. J. F.; Mewe, R.; Güdel, M. Bibcode: 2001A&A...365L.312K Altcode: 2000astro.ph.11026K We present the first high resolution X-ray spectrum of the bright O4Ief supergiant star zeta Puppis, obtained with the Reflection Grating Spectrometer on-board XMM-Newton. The spectrum exhibits bright emission lines of hydrogen-like and helium-like ions of nitrogen, oxygen, neon, magnesium, and silicon, as well as neon-like ions of iron. The lines are all significantly resolved, with characteristic velocity widths of order 1000-1500 km s-1. The nitrogen lines are especially strong, and indicate that the shocked gas in the wind is mixed with CNO-burned material, as has been previously inferred for the atmosphere of this star from ultraviolet spectra. We find that the forbidden to intercombination line ratios within the helium-like triplets are anomalously low for N VI, O VII, and Ne IX. While this is sometimes indicative of high electron density, we show that in this case, it is instead caused by the intense ultraviolet radiation field of the star. We use this interpretation to derive constraints on the location of the X-ray emitting shocks within the wind that are consistent with current theoretical models for this system. Title: Stellar Coronae with XMM-Newton RGS I. Coronal Structure Authors: Güdel, M.; Audard, M.; den Boggende, A. J.; Brinkman, A. C.; den Herder, J. W.; Kaastra, J. S.; Mewe, R.; Raassen, A. J. J.; de Vries, C.; Behar, E.; Cottam, J.; Kahn, S. M.; Paerels, F. B. S.; Peterson, J. M.; Rasmussen, A. P.; Sako, M.; Branduardi-Raymont, G.; Sakelliou, I.; Erd, C. Bibcode: 2001ASPC..234...73G Altcode: 2000astro.ph.11573G; 2001xras.conf...73G First results from high-resolution coronal spectroscopy with the {\it XMM-Newton} Reflection Grating Spectrometers (RGS) are reviewed. Five stellar systems (HR 1099, Capella, Procyon, YY Gem, AB Dor) have been observed. The emphasis of the present paper is on overall coronal structure. Elemental abundances in {\it active stars} are found to be `anomalous' in the sense that they tend to increase with increasing First Ionization Potential (FIP - i.e., signifying an inverse FIP effect). Coronal densities are measured at levels of a few times $10^{10}$ cm$^{-3}$ for cooler plasma, although there are indications for very high densities in the hotter plasma components. Title: XMM-Newton RGS observations of MCG -6-30-15 and Mrk 766: evidence for emission lines from a relativistic accretion disk Authors: Branduardi-Raymont, G.; Page, M. J.; Sakelliou, I.; Zane, S.; den Boggende, A. J.; Brinkman, A. C.; den Herder, J. W.; Kaastra, J. S.; Mewe, R.; de Vries, C.; Behar, E.; Cottam, J.; Kahn, S. M.; Paerels, F. B.; Peterson, J.; Rasmussen, A.; Sako, M.; Audard, A. M.; Güdel, M.; Kuster, M.; Wilms, J.; Erd, C. Bibcode: 2001ASPC..234..477B Altcode: 2001xras.conf..477B No abstract at ADS Title: Helium-like ions as powerful X-ray plasma diagnostics Authors: Porquet, D.; Mewe, R.; Raassen, A. J. J.; Kaastra, J. S.; Dubau, J. Bibcode: 2001ASPC..234..121P Altcode: 2000astro.ph.12218P; 2001xras.conf..121P We revisited the calculations of the ratios of the Helium-like ion ``triplet'' (resonance, intercombination, and forbidden lines) for Z=6 to 14 (C V, N VI, O VII, Ne IX, Mg XI, Si XIII) in order to provide temperature, density and ionization diagnostics for the new high-resolution spectroscopic data of Chandra and XMM-Newton. Comparing to earlier computations, collisional rates are updated and the best experimental values for radiative transition probabilities are used. The influence of an external radiation field (photo-excitation) and the contribution from unresolved dielectronic satellite lines to the line ratios are discussed. Collision-dominated plasmas (e.g. stellar coronae), photo-ionized plasmas (e.g. AGNs) or transient plasmas (e.g. SNRs) are considered. Title: Stellar Coronae with XMM-Newton RGS II. X-ray Variability Authors: Audard, M.; Güdel, M.; den Boggende, A. J.; Brinkman, A. C.; den Herder, J. W.; Kaastra, J. S.; Mewe, R.; Raassen, A. J. J.; de Vries, C.; Behar, E.; Cottam, J.; Kahn, S. M.; Paerels, F. B. S.; Peterson, J. M.; Rasmussen, A. P.; Sako, M.; Branduardi-Raymont, G.; Sakelliou, I.; Erd, C. Bibcode: 2001ASPC..234...79A Altcode: 2000astro.ph.11574A; 2001xras.conf...79A First results from high-resolution coronal spectroscopy of flares with the Reflection Grating Spectrometers on board the \textit{XMM-Newton} satellite are reviewed. Rotational modulation in the X-ray light curve of HR 1099 is discussed. Results from time-dependent spectroscopy of flares in the active stars HR 1099, AB Dor, YY Gem are also presented. Variations in the shape of the emission measure distributions, in the abundances and in the average density of the cool plasma are discussed. Title: X-ray spectroscopy of clusters of galaxies with XMM Authors: Kaastra, J. S.; den Boggende, A. J.; Brinkman, A. C.; Ferrigno, C.; den Herder, J. W.; Mewe, R.; Tamura, T.; de Vries, C.; Cottam, J.; Kahn, S. M.; Paerels, F. B. S.; Peterson, J. M.; Rasmussen, A. P.; Branduardi-Raymont, G.; Sakelliou, I.; Audard, M.; Güdel, M.; Erd, C. Bibcode: 2001ASPC..234..351K Altcode: 2001xras.conf..351K No abstract at ADS Title: First light measurements with the XMM-Newton reflection grating spectrometers: Evidence for an inverse first ionisation potential effect and anomalous Ne abundance in the Coronae of HR 1099 Authors: Brinkman, A. C.; Behar, E.; Güdel, M.; Audard, M.; den Boggende, A. J. F.; Branduardi-Raymont, G.; Cottam, J.; Erd, C.; den Herder, J. W.; Jansen, F.; Kaastra, J. S.; Kahn, S. M.; Mewe, R.; Paerels, F. B. S.; Peterson, J. R.; Rasmussen, A. P.; Sakelliou, I.; de Vries, C. Bibcode: 2001A&A...365L.324B Altcode: 2000astro.ph.11018B The RS CVn binary system HR 1099 was extensively observed by the XMM-Newton observatory in February 2000 as its first-light target. A total of 570 ks of exposure time was accumulated with the Reflection Grating Spectrometers (RGS). The integrated X-ray spectrum between 5-35 Å is of unprecedented quality and shows numerous features attributed to transitions of the elements C, N, O, Ne, Mg, Si, S, Fe, and Ni. We perform an in-depth study of the elemental composition of the average corona of this system, and find that the elemental abundances strongly depend on the first ionisation potential (FIP) of the elements. But different from the solar coronal case, we find an inverse FIP effect, i.e., the abundances (relative to oxygen) increase with increasing FIP. Possible scenarios, e.g., selective enrichment due to Ne-rich flare-like events, are discussed. Title: The Reflection Grating Spectrometer on board XMM-Newton Authors: den Herder, J. W.; Brinkman, A. C.; Kahn, S. M.; Branduardi-Raymont, G.; Thomsen, K.; Aarts, H.; Audard, M.; Bixler, J. V.; den Boggende, A. J.; Cottam, J.; Decker, T.; Dubbeldam, L.; Erd, C.; Goulooze, H.; Güdel, M.; Guttridge, P.; Hailey, C. J.; Janabi, K. Al; Kaastra, J. S.; de Korte, P. A. J.; van Leeuwen, B. J.; Mauche, C.; McCalden, A. J.; Mewe, R.; Naber, A.; Paerels, F. B.; Peterson, J. R.; Rasmussen, A. P.; Rees, K.; Sakelliou, I.; Sako, M.; Spodek, J.; Stern, M.; Tamura, T.; Tandy, J.; de Vries, C. P.; Welch, S.; Zehnder, A. Bibcode: 2001A&A...365L...7D Altcode: The ESA X-ray Multi Mirror mission, XMM-Newton, carries two identical Reflection Grating Spectrometers (RGS) behind two of its three nested sets of Wolter I type mirrors. The instrument allows high-resolution (E/Delta E = 100 to 500) measurements in the soft X-ray range (6 to 38 Å, or 2.1 to 0.3 keV) with a maximum effective area of about 140 cm2 at 15 Å. Its design is optimized for the detection of the K-shell transitions of carbon, nitrogen, oxygen, neon, magnesium, and silicon, as well as the L shell transitions of iron. The present paper gives a full description of the design of the RGS and its operational modes. We also review details of the calibrations and in-orbit performance including the line spread function, the wavelength calibration, the effective area, and the instrumental background. Title: The Ups and Downs of AD Leo (CD-ROM Directory: contribs/guedel3) Authors: Güdel, M.; Audard, M.; Guinan, E. F.; Mewe, R.; Drake, J. J.; Alekseev, I. Y. Bibcode: 2001ASPC..223.1085G Altcode: 2001csss...11.1085G No abstract at ADS Title: The XMM-Newton view of stellar coronae: X-ray spectroscopy of the corona of AB Doradus Authors: Güdel, M.; Audard, M.; Briggs, K.; Haberl, F.; Magee, H.; Maggio, A.; Mewe, R.; Pallavicini, R.; Pye, J. Bibcode: 2001A&A...365L.336G Altcode: We report results of deep X-ray observations of AB Doradus obtained with the XMM-Newton observatory during its Performance Verification phase. The main objective of the analysis is a study of the spectral variability of coronal plasma in a very active star, including investigations of the variable thermal structure, abundance variations, and possible density changes during flares. AB Dor revealed both quiescent and flaring emission. The RGS spectra show flux changes in lines of highly ionized Fe during the flares, and an increase of the continuum. Elemental abundances increase in the early flare phases, by a factor of three. The quiescent abundances are lower than corresponding solar photospheric values, and tend to increase with increasing first ionization potential, contrary to the behavior in the solar corona. High-resolution spectra show an average density of the cool plasma of ~3 1010 cm-3; this value does not change during the flares. We analyse and model the temporal behavior of heating and cooling, and present model results for one of the flares. We find that magnetic loops with a semilength of the order of 2.5 1010 cm ~ 0.3 R_star are involved. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: The XMM-Newton view of stellar coronae: Coronal structure in the Castor X-ray triplet Authors: Güdel, M.; Audard, M.; Magee, H.; Franciosini, E.; Grosso, N.; Cordova, F. A.; Pallavicini, R.; Mewe, R. Bibcode: 2001A&A...365L.344G Altcode: We present results of a comprehensive X-ray investigation of the multiple stellar system Castor AB + YY Gem. The observations were obtained with the XMM-Newton observatory. We report the first spatially separated detection and identification of both Castor A and B as frequently flaring X-ray sources. Spectral modeling of the YY Gem and Castor coronal sources indicates a broad plasma distribution between 2-15 MK. Elemental abundances are found to be below solar photospheric values, with the abundance of Ne being highest ( ~ 0.7 times solar photospheric). The abundances increase during a large flare, most notably for Fe. The O Vii He-like line triplet indicates average coronal densities of the cooler plasma of a few times 1010 cm-3 for YY Gem and Castor. The YY Gem light curve shows three deep eclipses, indicating that the coronae of both binary components are similarly active and are relatively compact. A 3-D light curve inversion shows that coronal active regions follow density scale heights compatible with spectroscopically measured temperatures. The dominant densities also agree with spectroscopic values. Most active regions are located between +/- 50 degrees latitude, in agreement with findings from previous Doppler imaging. We also report the tentative detection of line broadening due to orbital motion. Based on observations obtained with {\it XMM-Newton}, an ESA science mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). Title: Stellar Coronae with XMM-Newton RGS Authors: Audard, M.; Güdel, M.; Mewe, R.; Raassen, A. J. J.; Behar, E. Bibcode: 2001aax..proc...19A Altcode: First results from high-resolution coronal spectroscopy with the Reflection Grating Spectrometers on board the XMM-Newton satellite are reviewed. This paper is structured in two sections: The first section presents results in the context of coronal structure of active stars, while the second discusses X-ray variability in these stars. Title: In-flight calibration of the XMM-Newton reflection grating spectrometers Authors: Erd, Christian; Audard, M.; den Boggende, Antonius J.; Branduardi-Raymont, Graziella; Brinkman, A. C.; Cottam, Jean; Dubbeldam, Luc; Guedel, Manuel; den Herder, Jan-Willem; Kaastra, Jelle S.; Kahn, Steven M.; Mewe, Rolf; Paerels, Frits B.; Peterson, John R.; Rasmussen, Andrew P.; Sakelliou, Irini; Spodek, Joshua; Thomsen, Knud; de Vries, Cor P.; Zehnder, Alex Bibcode: 2000SPIE.4140...13E Altcode: The activities during the instrument calibrations are summarized and first data are presented. The main instrument features, the line-spread function and the effective area, are discussed and the status of the in-flight calibrations is summarized. Title: AD Leo from X-Rays to Radio: Are Flares Responsible for the Heating of Stellar Coronae? Authors: Guedel, M.; Audard, M.; Guinan, E. F.; Drake, J. J.; Kashyap, V. L.; Mewe, R.; Alekseev, I. Y. Bibcode: 2000astro.ph.11572G Altcode: In spring 1999, a long coordinated observing campaign was performed on the flare star AD Leo, including {\it EUVE}, {\it BeppoSAX}, the {\it VLA}, and optical telescopes. The campaign covered a total of 44 days. We obtained high-quality light curves displaying ongoing variability on various timescales, raising interesting questions on the role of flare-like events for coronal heating. We performed Kolmogorov-Smirnov tests to compare the observations with a large set of simulated light curves composed of statistical flares that are distributed in energy as a power law of the form ${\rm d}N/{\rm d}E \propto E^{-\alpha}$ with selectable index $\alpha$. We find best-fit $\alpha$ values slightly above a value of 2, indicating that the extension of the flare population toward small energies could be important for the generation of the overall X-ray emission. Title: Coronal Plasmas Modeling and the MEKAL Code Authors: Kaastra, Jelle S.; Mewe, Rolf Bibcode: 2000adnx.conf..161K Altcode: An overview is given of the current status of the spectral code development that takes place at SRON Utrecht. Title: The Magellanic Cloud Supernova Remnant Sample as Observed by XMM/Newton RGS. Authors: Rasmussen, A.; Behar, E.; Cottam, J.; Kahn, S. M.; Paerels, F. B. S.; Peterson, J. R.; Sako, M.; Bleeker, J. A. M.; den Boggende, A. J.; Brinkman, A. C.; den Herder, J. W.; van der Heyden, K. J.; Kaastra, J. S.; Mewe, R.; Tamura, T.; de Vries, C. P.; Branduardi-Raymont, G.; Sakelliou, I.; Audard, M.; Guedel, M.; Erd, C. Bibcode: 2000HEAD....5.4003R Altcode: 2000BAAS...32R1252R We present the currently available sample of high resolution, soft X--Ray spectra of the Magellanic Cloud supernova remnants observed as part of the RGS guaranteed time observation program. The RGS is uniqely suited to provide high quality spectra even for moderately (Δ θ ~ 1') extended sources, and thus yields the most detailed X--Ray spectra of entire SNRs. The current sample which will be presented include N132D (of the LMC) and 1E0102-72.3 (of the SMC), and possibly others. The spectra clearly betray the explosion event type, abundances, ionization balance and nonequilibrium state of the X--Ray emissive medium. Additional diagnostics provided by the resolved line complexes and spectral serieses will be discussed. Title: High Resolution Spectroscopy of the Nuclear Region of NGC1068 with XMM-Newton/RGS Authors: Paerels, F.; Audard, M.; Behar, E.; Branduardi-Raymont, G.; Brinkman, A. C.; Cottam, J.; den Boggende, A.; den Herder, J. -W.; de Vries, C.; Ferrigno, C.; Guedel, M.; Kaastra, J.; Kahn, S. M.; Mewe, R.; Peterson, J.; Rasmussen, A.; Sakelliou, I.; Sako, M.; Tamura, T.; van der Heyden, K. Bibcode: 2000HEAD....5.0105P Altcode: 2000BAAS...32.1181P The soft X-ray spectrum of the innermost regions (r < 30 arcsec) of NGC1068 as observed with the Reflection Grating Spectrometer on XMM/Newton displays a wealth of discrete features. Preliminary analysis of the spectrum indicates that the emission is completely dominated by recombination in cool, X-ray photoionized gas, with a possible contribution from emission following photoexcitation by the obscured central continuum source. We briefly discuss constraints on the properties of the emission line region derived from the spectroscopic analysis. Title: X-ray Spectroscopy of Clusters of Galaxies with XMM-Newton Authors: Peterson, J. R.; Audard, M.; Behar, E.; den Boggende, A. J.; Brinkman, A. C.; Branduardi-Raymont, G.; Cottam, J.; Erd, C.; Ferringo, C.; Guedel, M.; den Herder, J. W.; Jernigan, J. G.; Kaastra, J. S.; Kahn, S. M.; Mewe, R.; Paerels, F. B. S.; Rasmussen, A. P.; Sako, M.; Tamura, T.; Sakelliou, I.; Thomsen, K.; de Vries, C. Bibcode: 2000HEAD....5.1322P Altcode: 2000BAAS...32.1201P We present high-resolution X-ray spectra with the Reflection Grating Spectrometer (RGS) and medium-resolution X-ray spectra and images with the European Photon Imaging Camera (EPIC) of clusters of galaxies. The RGS has the unique ability to produce high-resolution spectra of moderately extended objects. This has enabled detailed spectroscopy of compact and luminous clusters of galaxies. We present the first spectra of a selection of clusters that have been observed with the XMM-Newton. Through spatially-resolved spectroscopy, we constrain the temperature and density structure of the X-ray emitting gas. We make elemental abundance determinations and emission line optical depth measurements. We relate the measurements to cooling-flow models, discuss the dark matter fraction of clusters, and address the origin of the intergalactic medium. Title: Modeling of Non Equilibrium Ionizing Plasmas: Applications and Comparison with Supernova Remnant Observations by the RGS spectrometer Authors: Behar, E.; Rasmussen, A.; Cottam, J.; Kahn, S. M.; Paerels, F. B. S.; Peterson, J. R.; Sako, M.; Brinkman, A. C.; den Boggende, A. J. F.; den Herder, J. W.; de Vries, C. P.; Ferrigno, C.; Kaastra, J. S.; Mewe, R.; Tamura, T.; van der Heyden, K. J.; Branduardi-Raymont, G.; Sakelliou, I.; Audard, M.; Gudel, M.; Erd, C. Bibcode: 2000HEAD....5.4004B Altcode: 2000BAAS...32.1252B Shocked plasmas of young supernova remnants (SNRs) are in a transient (but very long) phase of being ionized. In these remnants, the temperature is high compared with the charge states present in the plasma. Consequently, the standard single-ion collisional plasma models are inadequate for analyzing SNR spectra. We have developed a non equilibrium ionization model that includes two or more successive charge states. All of the spontaneous and electron-impact atomic processes are incorporated in the model, including radiative recombination, autoionization, and inner-shell ionization, some of which can be of vast importance in SNR plasmas. Based on the HULLAC atomic code, the model is highly versatile and can basically run for any desired highly ionized species. Synthetic spectra are calculated for various plasma conditions and compared with RGS spectra of several SNRs in the Magellanic Clouds, namely 1E0102-72.3, N132D, N49, and 0519-69.0. Title: Stellar Coronal Spectroscopy with the XMM-Newton RGS Authors: Guedel, M.; Audard, M.; Behar, E.; Cottam, J.; Kahn, S. M.; Paerels, F. B. S.; Peterson, J. M.; Rasmussen, A. P.; Branduardi-Raymont, G.; Sakelliou, I.; den Boggende, A. J.; Brinkman, A. C.; den Herder, J. W.; Kaastra, J. S.; Mewe, R.; Tamura, T.; de Vries, C.; Erd, C.; XMM Collaboration Bibcode: 2000HEAD....5.4503G Altcode: 2000BAAS...32Q1266G High resolution X-ray spectroscopy opens new windows to the study of the structuring and energetics of stellar coronae. XMM-Newton has obtained excellent spectra of several stellar coronal sources (e.g., HR1099, Capella, YY Gem, and AB Dor) with its two Reflection Grating Spectrometers (RGS). These sources represent coronae of various activity levels, comprising a wide range of plasma temperatures. Several flares were observed in the course of the observations for which time-resolved RGS spectroscopy will be presented. The RGS spectra offer important diagnostics to probe properties of the coronal plasma. The large number of detected lines from various elements offer the possibility to determine emission measure distributions between approximately 1-20 MK. He-like triplets further provide information on electron densities at various temperatures. Coronal elemental abundances are found to vary between quiescent and flare states. Abundance anomalies may shed light on the coronal heating mechanism. We discuss implications from spectral modeling on coronal structuring, including the size of coronal structures, the abundance stratification, and possible optical depth effects. We complement this information with geometric modeling obtained from stellar eclipses and rotational modulation. Implications for the coronal heating scenario are discussed. Title: High-Resolution X-Ray Spectroscopy of the Late-Type binary system α Centauri with the LETGS on Chandra Authors: van der Meer, R. L. J.; Brinkman, A. C.; Kaastra, J. S.; Mewe, R.; Raassen, A. J. J. Bibcode: 2000HEAD....5.4204V Altcode: 2000BAAS...32.1255V We have analyzed high-resolution (Δ λ ~= 0.06 Å) X-ray spectra in the wavelength region from 5 - 175 Å of the coronae of the nearby binary α Centauri (G2V + K1V). This binary system, which is separated by 16'', was observed with the Chandra LETG/HRC-S spectrometer at 25 December 1999. The dispersion axis was positioned nearly perpendicularly to the axis of the binary, resulting in two separated spectra. It is the first time that the X-ray spectra of the two binary components could be studied separately and simultaneously. The spectra of both components look much alike and have comparable fluxes. This is in contrast with earlier ROSAT observations where a flux ratio of 1:2 was found. The emission measures peak at slightly diffent temperatures around 1-3 MK. He-like ions of O, N, and C, emitting temperature- and density-dependent resonance, forbidden and intercombination lines, have been observed in the lower wavelength region (λ < 45 Å). Si-lines have been observed in the wavelength region around 50 Å in a variety of ionization stages (Si X - Si XII), while at long wavelengths the spectrum is dominated by the Fe IX (171.1 Å) and Fe X (174.5 Å). These lines are known from previous EUVE observations. Using the SPEX90 code, developed at SRON, multi-temperature fits of the entire spectrum, have been made. Title: A Chandra HETG Observation of the Active Binary Algol: Flaring and Quiescent Spectra Authors: Drake, S. A.; White, N. E.; Guedel, M.; Kaastra, J. S.; Mewe, R.; Simon, T.; Singh, K. P. Bibcode: 2000HEAD....5.4208D Altcode: 2000BAAS...32Q1256D On April 1st 2000, we obtained a 52 kilosecond HETG/ACIS-S spectrum of the protypical evolved binary Algol. This active binary has an orbital period of 2.87 days, and contains a primary B8V star, and a secondary K2 IV star which is filling its Roche lobe and rotating in synchronism with the orbital period. The observation commenced during secondary eclipse, and, as the secondary came into view, it was evident that a large flare was in process. The durations of the `rising' and declining phases of this flare were about 5 and 7 ks, respectively, although the former timescale almost certainly is the eclipse modulation timescale and not the actual true flare rise time. We compare and contrast the flare spectrum, and derived quantities such as the DEM, coronal densities, and metal abundances, with the observed spectrum and inferred parameters of the corona during the last 30 ksec of the observation when the system was essentially quiescent. We also discuss evidence for kinematical effects such as line broadening due to turbulence, Doppler shifts, and the orbital motion of the secondary. This research was supported by NASA through funding obtained from the Chandra General Observer Project, Cycle 1. Title: XMM-Newton Observation of the Complex Absorbing Medium in IRAS 13349+2438 Authors: Sako, M.; Audard, M.; Behar, E.; den Boggende, A. J.; Boller, Th.; Branduardi-Raymont, G.; Brinkman, A. C.; Cottam, J.; Erd, C.; Ferringo, C.; Guedel, M.; den Herder, J. W.; Kaastra, J. S.; Kahn, S. M.; Lagostina, A.; Mewe, R.; Paerels, F. B. S.; Peterson, J. R.; Pierre, M.; Puchnarewicz, E. M.; Rasmussen, A. P.; Tamura, T.; Sakelliou, I.; Thomsen, K.; de Vries, C. Bibcode: 2000HEAD....5.0203S Altcode: 2000BAAS...32.1182S The luminous infrared-selected quasar IRAS 13349+2438 was observed with XMM-Newton as part of the performance verification program. The spectrum obtained by the RGS exhibits broad and narrow absorption lines from highly ionized elements including hydrogen- and helium-like nitrogen, oxygen, and neon, and several iron L ions. Also shown in the spectrum is the first detection of an "unresolved transition array" of iron in a much cooler medium. We present a preliminary analysis of the RGS spectrum and discuss the structure and dynamics of the complex absorbing medium surrounding the active nucleus. Title: High-Resolution X-Ray Spectroscopy of Zeta Puppis and Eta Carinae with the RGS on XMM Authors: Leutenegger, M. A.; Audard, M.; Behar, E.; den Boggende, A. J.; Brinkman, A. C.; Branduardi-Raymont, G.; Cottam, J.; Erd, C.; Ferringo, C.; Guedel, M.; den Herder, J. W.; Kaastra, J. S.; Kahn, S. M.; McGee, J.; Mewe, R.; Paerels, F. B. S.; Pallavicini, R.; Peterson, J. R.; Rasmussen, A. P.; Raux, G.; Sako, M.; Tamura, T.; Sakelliou, I.; Thomsen, K.; de Vries, C. Bibcode: 2000HEAD....5.4201L Altcode: 2000BAAS...32.1254L We present high-resolution X-ray spectra of massive stars Zeta Puppis and Eta Carinae obtained with the Reflection Grating Spectrometer (RGS) onboard the XMM/Newton observatory. The spectrum of Zeta Puppis has many emission lines, including bright, broad hydrogenic and helium-like lines from oxygen and nitrogen. Analysis of these lines indicates a plasma density of at least 1010 {cm}-3. The spectrum of Eta Carinae is dominated by the bright hydrogenic nitrogen line. We will present the analysis of the spectra and discuss implications. Title: Description and performance of the reflection grating spectrometer on board of XMM-Newton Authors: den Herder, Jan-Willem; den Boggende, Antonius J.; Branduardi-Raymont, Graziella; Brinkman, Bert C.; Cottam, Jean; Dubbeldam, Luc; Erd, Christian; Guedel, Manuel; Kaastra, Jelle S.; Kahn, Steven M.; Mewe, Rolf; Paerels, Frits B.; Rasmussen, Andrew P.; Sakelliou, Irini; Spodek, Joshua; Thomsen, Knud; de Vries, Cor Bibcode: 2000SPIE.4012..102D Altcode: The ESA X-ray Multi Mirror mission, XMM-Newton, carries two identical Reflection Grating Spectrometers behind two of its three nested sets of Wolter I type mirrors. The instrument allows high-resolution (E/(Delta) E equals 100 to 500) measurements in the soft X-ray range (6 to 38 A or 2.1 to 0.3 keV) with a maximum effective area of about 150 cm2 at 15 A. The satellite was successfully launched on December 10, 1999, from Guyana Space Center. Following the launch the instrument commissioning was started early in 2000. First results for the Reflection Grating Spectrometers are presented concentrating on instrumental parameters such as resolution, instrument background and CCD performance. The instrument performance is illustrated by first results from HR 1099, a non-eclipsing RS CVn binary. Title: Description and performance of the low-energy transmission grating spectrometer on board Chandra Authors: Brinkman, Bert C.; Gunsing, Theo; Kaastra, Jelle S.; van der Meer, Rob; Mewe, Rolf; Paerels, Frits B.; Raassen, Ton; van Rooijen, Jan; Braeuninger, Heinrich W.; Burwitz, Vadim; Hartner, Gisela D.; Kettenring, Guenther; Predehl, Peter; Drake, Jeremy J.; Johnson, C. Olivia; Kenter, Almus T.; Kraft, Ralph P.; Murray, Stephen S.; Ratzlaff, Peter W.; Wargelin, Bradford J. Bibcode: 2000SPIE.4012...81B Altcode: The Chandra spacecraft has been launched successfully on July 23, 1999. The payload consists of a high resolution X- ray telescope, two imaging detector systems in the focal plane and two transmission gratings. Each one of the two gratings can be put in the beam behind the telescope and the grating spectrometers are optimized for high and low energy, respectively. The Low Energy Transmission Grating Spectrometer consists of three parts: the high-resolution telescope, the transmission grating array and the detector, to read-out the spectral image. Title: An X-ray and optical study of the cluster A33 Authors: Colafrancesco, S.; Mullis, C. R.; Wolter, A.; Gioia, I. M.; Maccacaro, T.; Antonelli, A.; Fiore, F.; Kaastra, J.; Mewe, R.; Rephaeli, Y.; Fusco-Femiano, R.; Antonuccio-Delogu, V.; Matteucci, F.; Mazzotta, P. Bibcode: 2000A&AS..144..187C Altcode: 2000astro.ph..2224C We report the first detailed X-ray and optical observations of the medium-distant cluster A33 obtained with the Beppo-SAX satellite and with the UH 2.2 m and Keck II telescopes at Mauna Kea. The information deduced from X-ray and optical imaging and spectroscopic data allowed us to identify the X-ray source 1SAXJ0027.2-1930 as the X-ray counterpart of the A33 cluster. The faint, F_{2-10 keV} ~ 2.4 10-13 erg s-1 cm-2, X-ray source 1SAXJ0027.2-1930, ~ 2 arcmin away from the optical position of the cluster as given in the Abell catalogue, is identified with the central region of A33. Based on six cluster galaxy redshifts, we determine the redshift of A33, z=0.2409; this is lower than the value derived by \cite[Leir & Van Den Bergh (1977)]{lei77}. The source X-ray luminosity, L_{2-10 keV} = 7.7 1043 erg s-1 cm-2, and intracluster gas temperature, T = 2.9 keV, make this cluster interesting for cosmological studies of the cluster L_X-T relation at intermediate redshifts. Two other X-ray sources in the A33 field are identified. An AGN at z=0.2274, and an M-type star, whose emissions are blended to form an extended X-ray emission ~ 4 arcmin north of the A33 cluster. A third possibly point-like X-ray source detected ~ 3 arcmin north-west of A33 lies close to a spiral galaxy at z=0.2863 and to an elliptical galaxy at the same redshift as the cluster. Title: High Resolution Spectroscopy of EXO 0748-67 with the RGS on XMM Authors: Cottam, J.; den Boggende, A. J.; Branduardi-Raymont, G.; Brinkman, A. C.; Erd, C.; Guedel, M.; den Herder, J. W.; Jansen, F.; Kaastra, J.; Kahn, S. M.; Mewe, R.; Paerels, F.; Rasmussen, A.; Sakelliou, I.; Sako, M.; de Vries, C. P. Bibcode: 2000AAS...196.3418C Altcode: 2000BAAS...32..726C The high-resolution spectrum of EXO 0748-67 obtained by the Reflection Grating Spectrometer on XMM-Newton shows bright hydrogenic and helium-like oxygen lines forming in an extended photoionized region surrounding the central neutron star. Analysis of the helium triplet line ratios for both oxygen and neon indicate a plasma density of at least 1013cm-3. The light curves show frequent bursting activity during which the continuum flux increases by as much as a factor of 10 and the equivalent width of the line emission drops significantly. We will present the details of the data as well as the integrated physical model derived from the spectroscopic diagnostics. Title: The active binary star II Pegasi with it BeppoSAX Authors: Covino, S.; Tagliaferri, G.; Pallavicini, R.; Mewe, R.; Poretti, E. Bibcode: 2000A&A...355..681C Altcode: 1999astro.ph.11352C II Peg is an ideal target to study stellar activity and flares, since intense and long lasting flares have been frequently detected from this system at all wavelengths. We report here about a BeppoSAX observation of II Peg. We followed the system for ~ 19 hours on December 5 and 6 1997 with BeppoSAX and the X-ray light curve resembles the typical behavior of a decay phase of a long-lasting flare. The spectral analysis shows that the II Peg X-ray spectrum is described by a two-temperature components, with the two dominant temperatures centered in the range of 9-11 and 24-26 MK. The derived coronal metal abundance is low ( Z ~ 0.2 Z_sun) compared to recent determinations of the photospheric abundance (Z ~ 0.6 Z_sun). Some possible explanations for this phenomenology are reviewed. As for most other stellar coronal sources observed with BeppoSAX, we find that in order to fit the BeppoSAX spectra an interstellar column density about a factor ten higher than previously determined is required. Title: First Light Measurements of Capella with the Low-Energy Transmission Grating Spectrometer aboard the Chandra X-Ray Observatory Authors: Brinkman, A. C.; Gunsing, C. J. T.; Kaastra, J. S.; van der Meer, R. L. J.; Mewe, R.; Paerels, F.; Raassen, A. J. J.; van Rooijen, J. J.; Bräuninger, H.; Burkert, W.; Burwitz, V.; Hartner, G.; Predehl, P.; Ness, J. -U.; Schmitt, J. H. M. M.; Drake, J. J.; Johnson, O.; Juda, M.; Kashyap, V.; Murray, S. S.; Pease, D.; Ratzlaff, P.; Wargelin, B. J. Bibcode: 2000ApJ...530L.111B Altcode: 2000astro.ph..1034B We present the first X-ray spectrum obtained by the Low-Energy Transmission Grating Spectrometer (LETGS) aboard the Chandra X-Ray Observatory. The spectrum is of Capella and covers a wavelength range of 5-175 Å (2.5-0.07 keV). The measured wavelength resolution, which is in good agreement with ground calibration, is Δλ~=0.06 Å (FWHM). Although in-flight calibration of the LETGS is in progress, the high spectral resolution and unique wavelength coverage of the LETGS are well demonstrated by the results from Capella, a coronal source rich in spectral emission lines. While the primary purpose of this Letter is to demonstrate the spectroscopic potential of the LETGS, we also briefly present some preliminary astrophysical results. We discuss plasma parameters derived from line ratios in narrow spectral bands, such as the electron density diagnostics of the He-like triplets of carbon, nitrogen, and oxygen, as well as resonance scattering of the strong Fe XVII line at 15.014 Å. Title: X-ray absorption lines in the Seyfert 1 galaxy NGC 5548 discovered with Chandra-LETGS Authors: Kaastra, J. S.; Mewe, R.; Liedahl, D. A.; Komossa, S.; Brinkman, A. C. Bibcode: 2000A&A...354L..83K Altcode: 2000astro.ph..2345K We present for the first time a high-resolution X-ray spectrum of a Seyfert galaxy. The Chandra-LETGS spectrum of NGC 5548 shows strong, narrow absorption lines from highly ionised species (the H-like and He-like ions of C, N, O, Ne, Na, Mg, Si, as well as Fe Xiv - Fe Xxi). The lines are blueshifted by a few hundred km/s. The corresponding continuum absorption edges are weak or absent. The absorbing medium can be modelled by an outflowing, thin and warm shell in photoionization equilibrium. The absorption lines are similar to lower ionization absorption lines observed in the UV, although these UV lines originate from a different location or phase of the absorbing medium. Redshifted with respect to the absorption lines, emission from the O Viii Lyalpha line as well as the O Vii triplet is visible. The flux of these lines is consistent with emission from the absorbing medium. The O Vii triplet intensity ratios demonstrate that photoionization dominates and yield an upper limit to the electron density of 7x 1016 m-3. Title: Preliminary Results of the Low Energy Transmission Grating Spectrometer on board Chandra Authors: Brinkman, A.; Gunsing, T.; Kaastra, J.; van der Meer, R.; Mewe, R.; Paerels, F.; van Rooijen, J.; Brauninger, H.; Burwitz, V.; Hartner, G.; Kettenring, G.; Predehl, P.; Dewey, D.; Marshall, H.; Chappell, J.; Drake, J.; Johnson, O.; Kenter, A.; Kraft, R.; Meehan, G.; Murray, S.; Ratzlaff, P.; Wargelin, B.; Zombeck, M. Bibcode: 1999AAS...195.9605B Altcode: 1999BAAS...31.1515B The Chandra spacecraft was launched successfully on July 23,1999.The payload consists of a high resolution X-ray telescope,two imaging detector systems in the focal plane and two transmission gratings.Each one of the two gratings can be put in the X-ray beam behind the telescope.The Low Energy Transmission Grating Spectrometer ( LETGS) will be described and in-flight calibration measurements will be discussed.In addition data from LETG GTO observations taken between the date of abstract submission and the conference date will be presented. We are grateful to many individuals who contributed over the years to build and calibrate the instruments and prepared the data analysis software.These include the hardware teams and their subcontractors in Europe,the project scientst and his team,the Chandra Science Center team and many industrial contracter teams. Title: A. Thorne, U. Litzen and S. Johansson, Spectrophysics Principles and Applications Authors: Mewe, R. Bibcode: 1999SSRv...90..525M Altcode: No abstract at ADS Title: Benchmarking the MEKAL spectral code with solar X-ray spectra Authors: Phillips, K. J. H.; Mewe, R.; Harra-Murnion, L. K.; Kaastra, J. S.; Beiersdorfer, P.; Brown, G. V.; Liedahl, D. A. Bibcode: 1999A&AS..138..381P Altcode: With the likelihood that high-resolution soft X-ray spectra of non-solar astronomical sources will soon become available, it is desirable to examine the accuracy of spectral synthesis codes. In this paper, a benchmark study of the MEKAL code, extensively used in the past for spectra from EUVE, ASCA, SAX, and other spacecraft, is presented using high-resolution solar flare X-ray spectra obtained with the Bragg Flat Crystal Spectrometer (FCS) on SMM. Lines in the range 5-20 Ä are used to adjust the wavelengths in the MEKAL code. Many of the lines are due to Fe ions, and arise from 3-2 transitions for spectra obtained during the decay phase of one of the flares, while others arise from higher-excitation (4-2, 5-2 etc.) transitions for spectra obtained near the peak of a second flare. Laboratory measurements of the wavelengths of these lines were also used to confirm the SMM values as well as published identifications from the HULLAC atomic code. The adjustments needed were up to 35 mÄ for line wavelengths above 13 Ä but much less at shorter wavelengths. Some of these adjustments will be perceptible for spectra from the forthcoming XMM and Chandra spacecraft. Appendices A and B are only available in electronic form at the http://www.edpsciences.com Title: High- and Low-Energy Nonthermal X-Ray Emission from the Abell 2199 Cluster of Galaxies Authors: Kaastra, Jelle S.; Lieu, Richard; Mittaz, Jonathan P. D.; Bleeker, Johan A. M.; Mewe, Rolf; Colafrancesco, Sergio; Lockman, Felix J. Bibcode: 1999ApJ...519L.119K Altcode: 1999astro.ph..5209K We report the detection of both soft and hard excess X-ray emission in the cluster of galaxies A2199, based upon spatially resolved spectroscopy with data from the BeppoSAX, Extreme Ultraviolet Explorer, and ROSAT missions. The excess emission is visible at radii larger than 300 kpc and increases in strength relative to the isothermal component. The total 0.1-100 keV luminosity of this component is 15% of the cluster luminosity, but it dominates the cluster luminosity at high and low energies. We argue that the most plausible interpretation of the excess emission is an inverse Compton interaction between the cosmic microwave background and relativistic electrons in the cluster. The observed spatial distribution of the nonthermal component implies that there is a large halo of cosmic-ray electrons between 0.5 and 1.5 Mpc surrounding the cluster core. The prominent existence of this component has cosmological implications, since it is significantly changing our picture of clusters' particle acceleration history, dynamics between the thermal and relativistic media, and total mass budgets. Title: V. S. Lebedev and I. L. Beigman, Physics of Highly Excited Atoms and Ions Authors: Mewe, R. Bibcode: 1999SSRv...89..689M Altcode: This book contains a comprehensive description of the basic principles of the theoretical spectroscopy and experimental spectroscopic diagnostics of Rydberg atoms and ions, i.e., atoms in highly excited states with a very large principal quantum number (n≫1). Rydberg atoms are characterized by a number of peculiar physical properties as compared to atoms in the ground or a low excited state. They have a very small ionization potential (∝1/n2), the highly excited electron has a small orbital velocity (∝1/n), the radius (∝n2) is very large, the excited electron has a long orbital period (∝n3), and the radiation lifetime is very long (∝n3-5). At the same time the R. atom is very sensitive to perturbations from external fields in collisions with charged and neutral targets. In recent years, R. atoms have been observed in laboratory and cosmic conditions for n up to ∼1000, which means that the size amounts to about 0.1 mm, ∼106 times that of an atom in the ground state. The scope of this monograph is to familiarize the reader with today's approaches and methods for describing isolated R. atoms and ions, radiative transitions between highly excited states, and photoionization and photorecombination processes. The authors present a number of efficient methods for describing the structure and properties of R. atoms and calculating processes of collisions with neutral and charged particles as well as spectral-line broadening and shift of Rydberg atomic series in gases, cool and hot plasmas in laboratories and in astrophysical sources. Particular attention is paid to a comparison of theoretical results with available experimental data. The book contains 9 chapters. Chapter 1 gives an introduction to the basic properties of R. atoms (ions), Chapter 2 is devoted to an account of general methods describing an isolated Rydberg atom. Chapter 3 is focussed on the recent achievements in calculations of form factors and dipole matrix elements of different types of bound-bound and bound-free radiative transitions. Chapter 4 concentrates on the formulation of basic theoretical methods and physical approaches to collisions involving R. atoms. Chapters 5 to 8 contain a systematic description of major directions and modern techniques in the collision theory of R. atoms and ions with atoms, molecules, electrons, and ions. Finally, Chapter 9 deals with the spectral-line broadening and shift of R. atomic series induced by collisions with neutral and charged particles. A subject index of four pages and 250 references are given. This monograph will be a basic tool and reference for all scientists working in the fields of plasma physics, spectroscopy, physics of electronic and atomic collisions, as well as astrophysics, radio astronomy, and space physics. Title: On the perspectives of using XMM to study fundamental parameters of early-type stars Authors: Rauw, G.; van der Hucht, K. A.; Mewe, R.; Güdel, M.; Vreux, J. -M.; Gosset, E.; Schmutz, W.; Stevens, I. R. Bibcode: 1999IAUS..193...90R Altcode: No abstract at ADS Title: Benchmarking the MEKAL Spectral Synthesis Code with High Resolution Solar X-ray Spectra Authors: Phillips, K. J. H.; Harra-Murnion, L. K.; Mewe, R.; Kaastra, J. Bibcode: 1999ASPC..158..235P Altcode: 1999ssa..conf..235P No abstract at ADS Title: Atomic Physics of Hot Plasmas Authors: Mewe, R. Bibcode: 1999LNP...520..109M Altcode: 1999xrsa.conf..109M Introduction X-Ray Spectral Modeling of Hot Plasmas Radiation Processes and Plasma Models Spectral Modeling of Optically Thin Plasmas General scheme Spectral fitting with SPEX Coronal Model Deviations from the coronal CIE model approximation Ionization and Recombination in a Coronal Plasma Ionization Balance Accuracy of atomic physics for the ionization balance Update of the ionization balance by improved calculations for - the rate coefficients Rate Coefficients for Ionization Collisional ionization Rate Coefficients for Recombination Radiative recombination; the Milne equation Dielectronic recombination Formation of X-Ray Spectra in a Coronal Plasma Line Radiation Excitation processes Radiative transitions Continuum Radiation Diagnostics of Plasma Parameters Electron Temperature Elemental Abundances Ionization Balance in NEI Electron Density Differential Emission Measure Diagnostics of Satellite Lines Dielectronic recombination (DR) satellite intensity Inner-shell excitation (IE) Inner-shell ionization (II) Diagnostics Comparison of Calculated Spectra and Accuracy Summary Title: Spatially resolved spectroscopy of the cluster of galaxies A 2199 Authors: Kaastra, J. S.; Bleeker, J. A. M.; Mewe, R. Bibcode: 1999NuPhS..69..567K Altcode: The X-ray spectrum of the bright cD cluster of galaxies A 2199 is studied using all instruments of BeppoSAX. Spatially resolved spectroscopy with the MECS instrument shows the presence of spectral hardening in the outer parts of the cluster. The presence of a hard tail is also confirmed by the simultaneous PDS observations. Our analysis shows that the hard component cannot be due to a population of point sources like AGN but corresponds to a diffuse non-thermal component. We also discuss the presence of resonance scattering in this cluster. Title: A BeppoSAX/LECS X-ray observation of alpha Centauri Authors: Mewe, R.; Guedel, M.; Favata, F.; Kaastra, J. S. Bibcode: 1998A&A...340..216M Altcode: We present the X-ray spectrum of the nearby binary alpha Cen AB (G2V + K1V) that has been obtained from observations with the low-energy concentrator (LECS) onboard the BeppoSAX X-ray astronomy satellite. SAX combines, in contrast to previous satellites, simultaneous coverage of the 0.1-10 keV energy range with sufficient spectral resolution to determine emission measure distributions and elemental abundances of soft coronal sources. The analysis of the spectrum using the SPEX plasma emission code shows a two-temperature structure of the corona which is confirmed by a differential emission measure analysis. It reveals a soft ( ~ 0.1 keV) component as detected previously by \hboxEUVE and ROSAT and a hard ( ~ 0.5 keV) component comparable to that seen by EINSTEIN, \hboxEUVE, and ASCA. The derived coronal Fe abundance of 0.7 +/- 0.3 (relative to solar photospheric) is consistent with the solar photospheric abundance but marginally (3hbox {\sigma^2 CrB}ma) different from the value of the metal-rich photosphere of alpha Cen. The abundance ratios Mg/Fe and Si/Fe are consistent (within 1hbox {\sigma^2 CrB}ma) with solar photospheric and coronal values, whereas the O/Fe ratio (3+/- 2) appears too high but the uncertainty is large. The X-ray flux in the 0.1-2.4 keV band is comparable to the average of previous observations with other instruments and to that derived from the ASCA observations if the different passbands of the instruments are taken into account. The two-temperature structure is reminiscent of recently determined emission measure distributions of the solar corona; the hotter component may be evidence for flare heating. Title: Alpha Centauri: coronal temperature structure and abundances from ASCA observations Authors: Mewe, R.; Drake, S. A.; Kaastra, J. S.; Schrijver, C. J.; Drake, J. J.; Guedel, M.; Schmitt, J. H. M. M.; Singh, K. P.; White, N. E. Bibcode: 1998A&A...339..545M Altcode: We have analyzed the X-ray spectrum of the nearby binary alpha Cen AB (G2V + K1V) that has been obtained from observations with ASCA. The coronal temperature structure and abundances have been derived from multi-temperature fitting and confirmed by a differential emission measure analysis. The corona as seen by ASCA is essentially isothermal with a temperature around 0.3 keV, consistent with the evolutionary picture of coronae of aging solar-type stars. A comparison between the measurements from various instruments indicates a source variability in the coronal flux (which precludes the joint fitting of data from different instruments taken at different epochs) and temperature structure consistent with that discovered in a series of ROSAT observations. The elemental abundances agree with solar photospheric abundances for Ne, Si, and Fe at 1hbox {\sigma^2 CrB}ma level, while O appears to be underabundant by a factor of about 3 relative to solar photospheric values, and Mg overabundant by a factor of a few. The abundance ratios with respect to Fe are better determined: [O/Fe] = 0.4+/-0.14 (x solar, etc.), [Mg/Fe] = 4+/-1, [Ne/Fe] = 1+/-0.3, and [Si/Fe] = 6+/-4. Title: High Resolution Spectroscopy with XMM Authors: Paerels, Frits; Brinkman, A. C.; den Herder, J. W.; de Vries, C.; den Boggende, A. J. F.; Mewe, R.; Kaastra, J.; Kahn, Steven M.; Rasmussen, Andrew P.; Decker, Todd; Stern, Marcela; Cottam, Jean; Spodek, Joshua; Branduardi-Raymont, Graziella; Guedel, Manuel; Liedahl, Duane A.; Erd, Christian Bibcode: 1998sxmm.confE...9P Altcode: No abstract at ADS Title: Assembling the Pieces of the Puzzle: A Nearby, Rapidly Rotating Young Sun in 47 Cas? Authors: Gudel, Manuel; Guinan, Edward F.; Etzel, Paul B.; Mewe, Rolf; Kaastra, Jelle S.; Skinner, Stephen L. Bibcode: 1998ASPC..154.1247G Altcode: 1998csss...10.1247G 47 Cas (F0 V, 33 pc distance) has been observed in a number of campaigns to study its luminous radio and X-ray corona and its strong chromospheric line emission. The {\it Hipparcos} satellite has detected orbital motion of the F star, indicating that it possesses a companion of about one solar mass, which is most likely a G star. In addition, radio data indicate that a third stellar component is also present at a separation of about 2.5". The young age of this system and its high X-ray flux make it conceivable that the G star companion is an ultra-fast rotator of the type seen in the Pleiades cluster. Title: Modelling of hot optically thin plasmas Authors: Mewe, R. Bibcode: 1998PhST...77...97M Altcode: No abstract at ADS Title: Using high resolution solar X-ray spectra to benchmark the MEKAL spectral synthesis code Authors: Phillips, K. J. H.; Mewe, R.; Harra-Murnion, L. K.; Kaastra, J. Bibcode: 1998sxmm.confE..34P Altcode: No abstract at ADS Title: Spectral Catalogue of the Intermediate Ionization States of Iron in the Extreme Ultraviolet Authors: Beiersdorfer, P.; Utter, S. B.; Brown, G. V.; Liedahl, D. A.; Mauche, C. W.; Kahn, S. M.; Brickhouse, N. S.; Dupree, A. K.; Mewe, R.; Kaastra, J. S. Bibcode: 1998lss..work...89B Altcode: No abstract at ADS Title: The Reflection Grating Spectrometer onboard XMM Authors: Brinkman, A.; Aarts, H.; den Boggende, A.; Bootsma, T.; Dubbeldam, L.; den Herder, J.; Kaastra, J.; de Korte, P.; van Leeuwen, B.; Mewe, R.; Paerels, F.; de Vries, C.; Cottam, J.; Decker, T.; Kahn, S.; Rasmussen, A.; Spodek, J.; Branduardi-Raymont, G.; Guttridge, P.; Thomsen, K.; Zehnder, A.; Guedel, M. Bibcode: 1998sxmm.confE...2B Altcode: No abstract at ADS Title: X-Ray Spectroscopy Diagnostics with XMM and AXAF: Prospects and Challenges Authors: Gudel, Manuel; Mewe, Rolf Bibcode: 1998ASPC..154.1051G Altcode: 1998csss...10.1051G We present simulations of the expected performance of the XMM Reflection Grating Spectrometer, the AXAF Low Energy Grating Spectrometer, and the XMM European Photon Imaging Camera. We discuss quality and limitations of diagnostics of temperatures, emission measures, emission measure distributions, velocity fields, and electron densities. Although the presented simulations are idealized, they nevertheless show that a number of physical phenomena in stellar coronae are within reach of the instrumental capabilities. Title: X-Ray Spectroscopy with XMM: A New Powerful Tool to Determine Fundamental Parameters of Early-type Stars Authors: Mewe, R.; Rauw, G.; van der Hucht, K. A.; Vreux, J. -M.; Gosset, E.; Guedel, M.; Schmutz, W.; Stevens, I. R.; Kahn, S. Bibcode: 1998sxmm.confE..69M Altcode: No abstract at ADS Title: X-ray Spectroscopy Diagnostics with XMM: New Prospects for the Physics of Thermal, Optically Thin Plasmas Authors: Güdel, M.; Mewe, R. Bibcode: 1998sxmm.confE..10G Altcode: No abstract at ADS Title: EUV spectroscopy of cool stars. III. Interpretation of EUVE spectra in terms of quasi-static loops. Authors: van den Oord, G. H. J.; Schrijver, C. J.; Camphens, M.; Mewe, R.; Kaastra, J. S. Bibcode: 1997A&A...326.1090V Altcode: We discuss the limitations of coronal spectroscopy to derive physical parameters of stellar magnetic loops. We distinguish between the intrinsic non-uniqueness of emitted spectra for models of quasi-static coronal loops, and the supplemental ambiguity introduced by both instrumental effects and spectral line formation. We demonstrate that the spectrum emitted by loops with constant cross-sections is the same for a large range of values of the conductive flux at the base when the apex temperature is fixed. Because it is impossible to estimate the conductive flux at the base from observations, it is also impossible to determine the volume heating rate and the loop length uniquely. For geometrically expanding (tapered) loops, the emitted spectrum depends on the expansion and on the conductive flux at the base, and there is a trade off between them without significant changes in the spectrum. We show that loop length and heating rate can only be derived if the density is known, but that even then a large intrinsic uncertainty remains for these loop parameters. We conclude that there is no unambiguous relationship between loop parameters and emitted spectra: modeling the spectra as the sum of spectra from discrete loops cannot result in a unique determination of coronal structure. Based on spectra observed with the Extreme Ultra Violet Explorer (EUVE) we find that quasi-static loop models allow adequate modeling of stellar coronal spectra. We show that coronal loops on active cool stars must expand with height. The minimum required areal expansion between base and apex is not very large, lying between 2 and 5. For three stars (α Cen, Capella and ξ UMa) the observations suggest the presence of two distinct, dominant loop populations, while for χ^1^ Ori a single population, characterized by a single apex temperature, suffices. The high electron densities (10^12^-10^13^cm^-3^) for coronal components on Capella and ξ UMa require abnormally large heating rates. It is likely that these high densities are related to a multitude of small volumes that are temporarily excited. Title: A SAX/LECS X-ray observation of the active binary Capella. Authors: Favata, F.; Mewe, R.; Brickhouse, N. S.; Pallavicini, R.; Micela, G.; Dupree, A. K. Bibcode: 1997A&A...324L..37F Altcode: 1997astro.ph..7061F We present a SAX/LECS X-ray observation of the active binary Capella, the first coronal source observed in the SAX Guest Investigator program. The analysis of this observation, performed using the mekal plasma emission code, shows that the LECS spectrum is well fit by a two-component optically-thin plasma model. A differential emission measure (DEM) obtained by direct inversion of the X-ray spectrum shows no additional features in addition to the double-peaked structure implied by the direct two-temperature analysis. Such a simple temperature stratification is however not compatible with the EUVE emission from the same object, which is well represented by a more complex DEM, with a power-law-like tail toward the low temperatures. At the same time, the EUVE-derived DEM predicts well the softer part of the Capella LECS spectrum, but it fails to correctly reproduce the higher energy part of the Capella LECS spectrum. Possible causes for this discrepancy are discussed. The coronal metallicity derived from the SAX observation is compatible both with the EUVE-derived metallicity as well as with the photospheric metallicity of Capella, thus showing no evidence for coronal under-abundances. Title: A Determination of the Coronal Emission Measure Distribution in the Young Solar Analog EK Draconis from ASCA/EUVE Spectra Authors: Güdel, Manuel; Guinan, Edward F.; Mewe, Rolf; Kaastra, Jelle S.; Skinner, Stephen L. Bibcode: 1997ApJ...479..416G Altcode: We present the results of a coronal differential emission measure (DEM) analysis of the nearby analog of the young Sun, EK Draconis, using data obtained with the ASCA and EUVE satellites. Various methods (including a CLEAN algorithm, a polynomial fit, a direct inversion method, a genetic algorithm, and a multitemperature fit) have been applied to reconstruct the DEM between 0.1 and 100 MK. The spectra from the four ASCA detectors and the two spectra from the short-wavelength and the medium-wavelength detectors of EUVE were subject jointly to the algorithms, taking into account both emission lines and continua. All methods converge to a DEM distribution that is essentially bimodal: we find two significant peaks near 7 MK and near 18 MK with a deep minimum around 10 MK. Little plasma is found at temperatures below 3-4 MK, despite EUVE's sensitivity to this temperature regime. We argue that the DEM distribution seen in EK Dra is induced by the properties of the radiative cooling function of a thermal, optically thin plasma. From an elemental abundance analysis, an Fe abundance of 0.83 times the corresponding solar photospheric abundance is found, and an abundance of Mg of 1.69 times the solar photospheric abundance, which may indicate for this specific element a first ionization potential effect similar to that found in the solar corona. Title: ASCA and EUVE observations of II Pegasi: flaring and quiescent coronal emission. Authors: Mewe, R.; Kaastra, J. S.; van den Oord, G. H. J.; Vink, J.; Tawara, Y. Bibcode: 1997A&A...320..147M Altcode: We have analyzed X-ray and EUV spectra of both the quiescent and flaring state of II Peg, obtained from observations with ASCA and EUVE. Coronal temperature structure and abundances have been derived from multi-temperature and differential emission measure (DEM) analyses of the spectra. The abundances are non-solar; in the case of ASCA for most elements (O, Ne, Mg, Si, S, Ar, Ca, Ni) we obtain abundances that are consistent with about 1/2-1/5 of the solar photospheric abundances of Anders and Grevesse (1989, Geochim. Cosmochim. Acta 53, 197), but the Fe abundance is even lower, i.e. 0.1xSolar. The multi-T and DEM fitting analysis shows that the quiescent EUVE and ASCA spectra can be described by two temperature components: 4 and 10MK (EUVE), 10 and 20MK (ASCA). The two flares detected by EUVE and ASCA show peak temperatures of 20 and >35MK, respectively. The latter flare has a total energy (0.1-10keV) of 2.7x10^34^erg, a peak luminosity of 2.6x10^30^erg/s. There is evidence for an increase of a factor ~4 of the iron abundance during the rise phase of the flare. Application of a cooling model yields a loop height of about 8x10^10^cm and a plasma density of 8x10^10^cm^-3^. Title: BY Draconis Authors: Mewe, R.; Heise, J.; Muller, J. M.; Coletta, A.; D'Andreta, G.; di Ciolo, L.; Spoliti, G.; Ricci, R.; Giommi, P.; Piro, L. Bibcode: 1997IAUC.6551....2M Altcode: 1997IAUC.6551R...1M R. Mewe and J. Heise, Space Research Organization of the Netherlands (SRON); J. M. Muller, SRON and BeppoSAX, Rome; A. Coletta, G. D'Andreta, L. Di Ciolo, G. Spoliti, R. Ricci, and P. Giommi, BeppoSAX, Rome; and L. Piro, Istituto Astrofisica Spaziale, Frascati, report: "For 50 min (during an entire orbit of BeppoSAX) during Jan. 23.863-23.898 UT, the Wide Field Camera 2 (WFC2) onboard BeppoSax detected a transient x-ray source that was not seen over 10 hr during immediately-preceding observations of the same field. The source is located at R.A. = 18h33m.4, Decl. = +51 46' (equinox 2000.0; error radius 10'), which is 6 deg from the center of the WFC2 image. Initially, the source flux was 40 mCrab (8.5 WFC2 counts/s) in the energy band 2-9 keV, decreasing to 14 mCrab towards the end of the observation. At higher energies (up to 28 keV), no flux was found during the entire observation. In the next orbit, the 2-9-keV flux had fallen below the sensitivity limit (over one orbit) of about 10 mCrab. We have identified the source with the dM0e flare star BY Dra (distance 15.6 pc). No other sources with a flux > 10 mCrab are present in x-ray catalogues within 3 deg of the source. We conclude that a giant stellar flare was detected in x-rays with a remarkably short decay time. The expected countrates for typical M dwarf flare stars like BY Dra are of the order of 0.3-1 WFC2 counts/s (during flare), but the measured countrate (corresponding to an x-ray luminosity of about 2 x 10E31 erg/s) is exceptionally high -- comparable to the strongest flare ever seen with the ROSAT PSPC detector." Title: The Reflection Grating Spectrometer (rgs) On-Board the X-Ray Multi-Mirror (xmm) Mission Authors: Branduardi-Raymont, G.; Aarts, H. J. M.; den Boggende, P. A. J.; Brinkman, A. C.; Dubbeldam, L.; den Herder, J. M.; Kaastra, J. S.; de Korte, P. A. J.; Mewe, R.; Hailey, C. J.; Kahn, S. M.; Paerels, F.; Bixler, J.; Thomsen, K.; Zehnder, A. Bibcode: 1997xisc.conf..625B Altcode: No abstract at ADS Title: Abundances and Flares in the ASCA Observation of the Young k0 Star AB Doradus Authors: White, S. M.; Pallavicini, R.; Mewe, R.; Kaastra, J. S.; Lim, J. Bibcode: 1997xisc.conf..573W Altcode: No abstract at ADS Title: X-ray Spectroscopy of Stellar Coronae: History - Present - Future Authors: Mewe, Rolf Bibcode: 1996SoPh..169..335M Altcode: Since in 1948 X-rays were detected from the solar corona, stellar coronae were among the first predicted non-solar X-ray sources. However, because of their relatively low X-ray luminosity, the first non-solar stellar corona was not detected in X-rays until 1974 - twelve years after the discovery of the first non-solar X-ray source. After the 1980s, with the advent of sensitive X-ray imaging instruments on board the EINSTEIN, EXOSAT, and later the ROSAT observatories, the study of stellar coronae has become a vastly growing field of research. These X-ray observations have demonstrated that X-ray emitting coronae are a common feature among stars on the cool side of the Hertzsprung-Russell diagram, with the probable exception of single very cool giant and supergiant stars and A-type dwarfs. The instruments on board these satellites provided for the first time a taste of what can be achieved with X-ray spectroscopy and with the advent of the EUVE (1992) and ASCA (1993), detailed spectroscopy of stellar coronae in the EUV and X-ray regimes got off to a real start. The observations have permitted the identification of coronal material at different temperatures whose existence relates to a range of possible magnetic loop structures in the hot outer atmospheres of stars. The higher spectral resolution of the next generation of spectrometers on board NASA's AXAF (1998), ESA's XMM (1999), and the Japanese ASTRO-E (2000) will improve the determination of coronal temperature structure, abundances, and densities from which loop geometries can be derived and will enable velocity diagnostics. This paper reviews our present knowledge of observational stellar X-ray spectroscopy up to EUVE and ASCA and briefly discusses the perspectives for coronal diagnostics offered by AXAF, XMM, and ASTRO-E. Title: Simultaneous EUVE & ASCA observations of AB Doradus: temperature structure and abundances of the quiescent corona. Authors: Mewe, R.; Kaastra, J. S.; White, S. M.; Pallavicini, R. Bibcode: 1996A&A...315..170M Altcode: We have analyzed EUV and X-ray spectra of the non-flaring state of AB Dor, obtained from simultaneous observations with EUVE and ASCA. The coronal temperature structure and the coronal elemental abundances have been derived by jointly fitting the spectra, including lines and continuum. We have applied a multi-temperature fitting method and we have found that an optically thin plasma model with solar abundances (relative to hydrogen) does not yield a good fit. A 4-T fit allowing the abundances of the more important elements (Fe, S, Si, Mg, Ne, and O) plus four other less important abundances (N, Ar, Ca, and Ni) to vary improves the fit markedly. This results in values of the first 6 abundances relative to solar photospheric values that are significantly (a factor 2-3) below solar except for Ne, which is solar, while most of the remaining four abundances are consistent both with solar and reduced abundances. In the course of the 4-T fitting we have determined a best-fit value for the interstellar hydrogen column density of N_H_=(2.0+/-0.5)10^18^cm^-2^. We have applied four differential emission measure (DEM) distribution analysis techniques, viz.: (i) regularization method, (ii) polynomial method, (iii) clean algorithm, and (iv) genetic algorithm. The four different methods all yield a qualitatively similar DEM, showing two maxima in the temperature intervals 5-8MK and 20-30MK. Our analysis demonstrates the great value of simultaneous ASCA and EUVE observations in determining the fundamental parameters of stellar coronae. Title: Reflection Grating Spectrometer on board XMM Authors: Brinkman, Albert C.; Aarts, Henry J.; den Boggende, Antonius J.; Bootsma, T. M.; Dubbeldam, Luc; den Herder, Jan-Willem; Kaastra, J. S.; de Korte, Piet A.; van Leeuwen, B. J.; Mewe, R.; van Zwet, E. J.; Decker, Todd A.; Hailey, Charles J.; Kahn, Steven M.; Paerels, Frits B.; Pratuch, Steven M.; Rasmussen, A.; Branduardi-Raymont, G.; Guttridge, P.; Bixler, Jay V.; Thomsen, K.; Zehnder, A.; Erd, Christian Bibcode: 1996SPIE.2808..463B Altcode: The x-ray multi-mirror (XMM) mission is the second of four cornerstone projects of the ESA long-term program for space science, Horizon 2000. The payload comprises three co- aligned high-throughput, imaging telescopes with a FOV of 30 arcmin and spatial resolution less than 20 arcsec. Imaging CCD-detectors (EPIC) are placed in the focus of each telescope. Behind two of the three telescopes, about half the x-ray light is utilized by the reflection grating spectrometer (RGS). The x-ray instruments are co-aligned and measure simultaneously with an optical monitor (OM). The RGS instruments achieve high spectral resolution and high efficiency in the combined first and second order of diffraction in the wavelength range between 5 and 35 angstrom. The design incorporates an array of reflection gratings placed in the converging beam at the exit from the x-ray telescope. The grating stack diffracts the x-rays to an array of dedicated charge-coupled device (CCD) detectors offset from the telescope focal plane. The cooling of the CCDs is provided through a passive radiator. The design and performance of the instrument are described below. Title: Emission measure analysis methods: the corona of AR Lacertae revisited. Authors: Kaastra, J. S.; Mewe, R.; Liedahl, D. A.; Singh, K. P.; White, N. E.; Drake, S. A. Bibcode: 1996A&A...314..547K Altcode: A simultaneous ROSAT/ASCA observation of the RS CVn binary AR Lac has been re-analysed using updated calculations for the plasma emission. Several analysis methods are applied that serve to reconstruct the emission measure distribution of AR Lac. In particular we describe the regularisation method, a Chebyshev polynomial method, a clean algorithm, a genetic algorithm and a method based upon broadened discrete temperature components. We confirm earlier results that the abundances are non-solar; for most elements (O, Mg, Si, S, Ar, Ca and Fe), we find abundances that are consistent with 1/3 of the solar photospheric abundances. The abundances of Ne (0.7) and Ni (1.1) are somewhat larger. The emission measure analysis shows that there are at least two and probably three temperature components: a cool, intermediate and hot component at temperatures of 0.6, 1 and 2.4keV, respectively. The cool component is rather narrow (less than 50% relative width) and there is no significant emission below 0.3keV down to our detection limit at about 0.03keV. The intermediate and hot component may be separate structures, but could also be the dominant features of a more continuous emission measure distribution between 1-4keV. High-temperature emission above 5keV is limited to at most 5% of the total Title: High resolution X-ray spectroscopy with the low energy transmission grating of AXAF. Authors: Brinkman, A. C.; van Baren, C.; Gunsing, C. J. T.; Kaastra, J. S.; Kamperman, T. M.; van der Meij, Z. N.; Mewe, R.; Valkenburg, C.; Brauninger, H.; Kettenring, G.; Lochbihler, H.; Predehl, P. Bibcode: 1996rftu.proc..677B Altcode: The Advanced X-ray Astrophysics Facility (AXAF) is the third in the series of great observatories in the NASA programme after the Hubble Space Telescope and the Gamma Ray Observatory, and will be launched in a highly eccentric orbit, in 1998. The AXAF payload contains a Wolter-type I high resolution mirror assembly (HRMA) two insertable grating systems, the high energy transmission grating (HETG) and the low energy transmission grating (LETG) and two imaging detector systems. The LETG is being developed in a collaborative effort between SRON and MPE. Title: X-ray spectroscopy with the Reflection Grating Spectrometer on-board of XMM. Authors: Brinkman, A. C.; Aarts, H. J. M.; den Boggende, A. J. F.; Dubbeldam, L.; den Herder, J. W.; Kaastra, J. S.; de Korte, P. A. J.; Mewe, R.; Hailey, C. J.; Kahn, S. M.; Paerels, F.; Branduardi-Raymont, G.; Bixler, J.; Thomsen, K.; Zehnder, A. Bibcode: 1996rftu.proc..675B Altcode: The X-ray Multi-Mirror (XMM) mission is the second of the four cornerstone projects of the ESA long-term programme for space science, Horizon 2000. The payload comprises three co-aligned high-throughput, imaging telescopes with a FOV of 30' and spatial resolution <20″ Imaging CCD-detectors (EPIC) are placed in the focus of each telescope (with total effective area ≡4000 cm2 at 1.5 keV). Behind two of the three telescopes, about half of the X-ray light is utilized by the Reflection Grating Spectrometer (RGS) (with maximum total effective area in first order of ≍200 cm2 at 12 Å for both modules). The instruments are co-aligned and measure simultaneously with an optical monitor (1800-10000 Å, limiting magnitude 24m5, spatial resolution 1″ FOV 8'). It is envisaged that the observatory is launched near the end of the 20th century in a deep eccentric orbit allowing for sensitive, long uninterrupted observations of a large variety of astrophysical sources. XMM offers the possibility to perform broadband (0.1-10 keV) imaging spectroscopy with a resolving power E/ΔE ≅ 5-60 with the EPIC, combined with high resolution (Δλ 0.04 Å, or E/Δ 150-800 in 1st order) spectroscopy between 5-35 Å with the RGS. Compared to the ASCA-SIS, the EPIC has the same spectral resolution, but more than 10 times larger effective area and spatial resolution, covering a wider energy range, while the RGS has comparable effective area, but at least 10 times more spectral resolution. Title: DEM Analyses with the Utrecht Codes Authors: Mewe, R.; van den Oord, G. H. J.; Schrijver, C. J.; Kaastra, J. S. Bibcode: 1996aeu..conf..553M Altcode: 1996IAUCo.152..553M No abstract at ADS Title: X-ray diagnostics of supernova remnants. Authors: Kaastra, J. S.; Bleeker, J. A. M.; Mewe, R. Bibcode: 1996uxsa.conf...15K Altcode: 1996uxsa.coll...15K The authors discuss recent developments in studies of the X-ray emission of supernova remnants (SNRs). The young SNR Cas A is used as an example to illustrate several aspects of the problems encountered in this field of research. Topics included are multi-temperature structure, non-equilibrium ionization, uncertainties in the atomic data, pre-shock heating, temperature equilibration, spectral morphology, mass motion and resonance scattering. Title: SPEX: a new code for spectral analysis of X & UV spectra. Authors: Kaastra, J. S.; Mewe, R.; Nieuwenhuijzen, H. Bibcode: 1996uxsa.conf..411K Altcode: 1996uxsa.coll..411K An overview is given of the software package SPEX that has been developed at the Space Research Organization of the Netherlands (SRON) for complex modelling of hot astrophysical plasmas. An example of a spectral simulation is presented. Title: Line Emission from Warm Material in NGC 5548 Authors: Kaastra, J. S.; Mewe, R.; Roos, N. Bibcode: 1996aeu..conf...51K Altcode: 1996IAUCo.152...51K No abstract at ADS Title: The corona of AB Dor: temperatures and abundances determined with ASCA and EUVE Authors: Mewe, R.; Kaastra, J. S.; White, S. M.; Pallavicini, R. Bibcode: 1996ASPC..109..273M Altcode: 1996csss....9..273M No abstract at ADS Title: EUV spectroscopy and coronal loop models Authors: van den Oord, G. H. J.; Schrijver, C. J.; Mewe, R.; Kaastra, J. S. Bibcode: 1996ASPC..109..231V Altcode: 1996csss....9..231V No abstract at ADS Title: XMM: spectroscopic capabilities. Authors: Mewe, R.; Kaastra, J. S.; Bleeker, J. A. M. Bibcode: 1996uxsa.conf..229M Altcode: 1996uxsa.coll..229M The ESA X-ray Multi-Mirror (XMM) mission comprises three high-throughput (≡4000 cm2 at 1.5 keV), imaging telescopes. The payload comprises three elements: a CCD imaging camera (EPIC), a reflection grating spectrometer (RGS), and an optical monitor. Spectral simulations for sources such as stellar coronae, clusters of galaxies, and supernova remnants illustrate the spectroscopic capabilities of the RGS and the EPIC. Title: Spectroscopic EUVE Observations of the Active Star AB Doradus Authors: Rucinski, Slavek M.; Mewe, Rolf; Kaastra, Jelle S.; Vilhu, Osmi; White, Stephen M. Bibcode: 1996aeu..conf..159R Altcode: 1996IAUCo.152..159R No abstract at ADS Title: Are Some Stellar Coronae Optically Thick? Authors: Schrijver, C. J.; van den Oord, G. H. J.; Mewe, R.; Kaastra, J. S. Bibcode: 1996aeu..conf..121S Altcode: 1996IAUCo.152..121S No abstract at ADS Title: An analysis of the ASCA spectra of the active giants Beta CET and Capella using the new MEKAL coronal plasma code Authors: Drake, S. A.; Singh, K. P.; White, N. E.; Mewe, R.; Kaastra, J. S. Bibcode: 1996ASPC..109..263D Altcode: 1996csss....9..263D No abstract at ADS Title: Is the optical depth of stellar coronae really negligible? Authors: Schrijver, C. J.; Mewe, R.; Kaastra, J. S.; van den Oord, G. H. J.; Bruls, J. H. M. J. Bibcode: 1996ASPC..109..289S Altcode: 1996csss....9..289S No abstract at ADS Title: Algol: A joint analysis of the EUVE and ASCA Spectra Authors: Singh, K. P.; White, N. E.; Drake, S. A.; Mewe, R.; Kaastra, J. S. Bibcode: 1995AAS...187.6004S Altcode: 1995BAAS...27.1371S Algol is a semi-detached stellar binary in which an active late-type star fills its Roche-Lobe and accretion onto an early-type companion takes place. Recent medium resolution X-ray and high resolution extreme ultra-violet (EUV) spectral observations of Algol have independently indicated that the elemental abundances in the hot corona of the active star in Algol are depleted with respect to the solar photospheric abundances. We present a joint analysis of the EUV and X-ray spectra of Algol. The non-simultaneously observed EUV and X-ray spectra were obtained from the EUVE and ASCA archives. The spectra were fitted jointly with the plasma emission models assuming (a) discrete emission components with different temperatures, and (b) different continuous emission measure (CEM) models, in particular the power-law type and Chebyshev Polynomial type. We demonstrate that both ASCA and EUVE data can be best-fitted with a common plasma emission model. We will discuss the implications of the different emission measure models on the derivation of the elemental abundances in the corona of the active star in Algol, and compare our results with the previous analyses. Title: EUV spectroscopy of cool stars. II. Coronal structure of selected cool stars observed with the EUVE. Authors: Schrijver, C. J.; Mewe, R.; van den Oord, G. H. J.; Kaastra, J. S. Bibcode: 1995A&A...302..438S Altcode: We analyze the coronal EUV spectra of seven cool stars, solar-like single stars and components of RS CVn-like binaries, as observed with the Spectrometers of the Extreme Ultraviolet Explorer (EUVE). The observations cover the wavelength range of 60A up to 800A with a resolution of λ/{DELTA}λ=~160-320. The data constrain the coronal temperature structure between several hundred thousand Kelvin up to roughly 10 million Kelvin through a differential emission measure analysis. The resulting differential emission measure distributions show distinct features from source to source, but the common properties are a) a relatively weak emission from coronal plasma below about 1MK, b) a dominant component somewhere between 2MK and about 10MK, often peaking at solar-like coronal temperatures of 2 to 4MK, and c) in all cases but χ^1^ Ori a very hot component in the formal solution with a temperature exceeding several tens of million of Kelvin. This hot tail in the differential emission measure distribution may reflect, as discussed in this paper, one or several of the following sources or processes: a real hot component, a reduced coronal abundance of heavy elements, or scattering in some of the strongest coronal lines with subsequent photon destruction upon impact on the lower, dense atmosphere. Coronal electron densities of brightly emitting regions are constrained by an analysis of ratios of density-sensitive iron lines. Strengths of Fe XIX-Fe XXII lines (corresponding to a temperature range of T=6-11MK) for α Aur, AU Mic (of which the spectrum is dominated by a large flare), ξ UMa, and σ Gem suggest typical electron densities in the range n_e_~10^12^-10^13^cm^-3^. Cooler Fe X and Fe XII-Fe XIV lines (T=1-2MK) in the case of α CMi suggest n_e_~10^9^-10^10^cm^-3^. In general, the electron densities of the hot 5-15MK components are some three orders of magnitude larger than typical of the solar-like component around 2MK; the volume filling factors of the hot components are therefore expected to be substantially smaller than those of the cooler component. Title: Optical depth effects in the X-ray emission from supernova remnants Authors: Kaastra, J. S.; Mewe, R. Bibcode: 1995A&A...302L..13K Altcode: We study the effects of resonance scattering in the X-ray spectra of supernova remnants. We show the importance of these effects using the ASCA X-ray spectrum of Cas A as an example. In particular the abundances derived in the common optically thin approximation can be off by a factor of 2 in the case of oxygen. Also in other supernova remnants similar effects are expected to be important. With future high-resolution missions like AXAF and XMM it is necessary to incorporate resonance scattering in the spectral analysis tools. Title: EUVE observations of NGC 5548. Authors: Kaastra, J. S.; Roos, N.; Mewe, R. Bibcode: 1995A&A...300...25K Altcode: EUVE observations of the Seyfert 1 galaxy NGC 5548 show the presence of line emission features identified as a Ne VII/Ne VIII blend at 88A and Si VII emission at 70A. The lines show significant broadening (FWHM 3800km/s) placing the emitting region at the same distance as the inner broad-line region. A fit to a thermal plasma yields a temperature of 6x10^5^K. The lines are possibly variable on a time scale of weeks. The line emission can be attributed to the warm absorbing material discovered before from oxygen and Fe absorption features, which then at a distance of ~3x10^14^m is near pressure equilibrium with the hot medium confining also the broad-line clouds. The material should have a low spatial filling factor. The plasma is probably closer to collisional ionisation equilibrium than to photo-ionisation equilibrium. Extra heat supply of the order of 10 % of the total AGN luminosity is required to sustain the high temperature. Title: Spectroscopic EUVE Observations of the Active Star AB Doradus Authors: Rucinski, Slavek M.; Mewe, Rolf; Kaastra, Jelle S.; Vilhu, Osmi; White, Stephen M. Bibcode: 1995ApJ...449..900R Altcode: We present observations of the pre-main-sequence, rapidly rotating (0.515 day) late-type star, AB Doradus (HD 36705), made by the Extreme Ultraviolet Explorer (EUVE) satellite. A spectrum from 80 to 700 Å with a resolution Δλ ≍ 0.5-2 Å was accumulated between 1993 November 4-11, with an effective exposure time of about 40 hours. No obvious EUV flares were detected during the observation. The data constrain the coronal temperature structure between several 104 K up to roughly 2 × 107 K through a differential emission measure analysis using the optically thin MEKA plasma model. The resulting differential emission measure (DEM) distribution shows: (1) dominant emission from plasma between about 2 × 106 and 2 × 107 K, which may show a substructure with two components around 3 × 106 and 107 K; (2) very little emission from plasma between 105 and 2 × 106 K; and (3) emission from plasma below about 105 K. If solar photospheric abundances are assumed, then the formal DEM solution also requires the presence of a strong high-temperature component (above about 3 × 107 K) in order to explain the strong continuum emission below about 150 Å. We believe that this component of the solution is not physical: it is not present in the solution if we assume lower iron abundance, or if there is significant resonance scattering in some of the stronger (mainly iron) spectral lines with subsequent photon absorption in the lower, dense atmosphere. Finally, the DEM analysis gives a best-fit value for the interstellar hydrogen column density of NH = (2.4±0.5) × 1018 cm-2. Title: Book reviews Authors: Mewe, R.; de Jager, Cornelis; Kleczek, J.; Icke, Vincent; van Bueren, H. G.; Jones, C.; Schatzman, E.; Meynet, G.; van der Kruit, P. C.; van der Hucht, K. A.; Raadu, M. A.; Sterken, C. Bibcode: 1995SSRv...72..679M Altcode: No abstract at ADS Title: EUV spectroscopy of cool stars. I. The corona of α Centauri observed with EUVE. R Authors: Mewe, R.; Kaastra, J. S.; Schrijver, C. J.; van den Oord, G. H. J.; Alkemade, F. J. M. Bibcode: 1995A&A...296..477M Altcode: We perform an emission measure analysis of spectra of the coronae of the cool star binary α Cen (A: HD 128620 (G2 V) + B: HD 128621 (K1 V)) as observed with the Spectrometers of the Extreme UltraViolet Explorer (EUVE). These observations, covering the wavelength range of 60A up to 800A with a resolution of λ/{DELTA}λ=~160-320, constrain the coronal temperature structure between about 10^5^K up to roughly 10MK, while some additional line and continuum information is available to extend that coverage from several tens of thousands of Kelvin up to several tens of millions of Kelvin, although the solution is poorly constrained in the extended range. We performed a re-calibration of the wavelength scale for each of the three instrumental pass bands by comparing the model list of emission lines with the spectra of α Cen and eight other cool stars. The high signal-to-noise ratio of the α Cen spectrum yielded indications for a Lorentzian rather than a Gaussian line profile for the MW passband. The observed spectrum was decomposed into a linear combination of spectra emitted by isothermal plasmas in thermal equilibrium, using the SPEX plasma emission code developed in Utrecht. The resulting differential emission measure distribution shows: a) emission from plasma below ~5MK with a broad peak around ~3MK and with a tail extending down to about 0.5MK, b) very little emission from plasma between 0.1MK and 0.5MK, c) emission from plasma below 0.1MK, and d) possibly a hot component exceeding several tens of million of Kelvin which, however, may (in part) have another origin than a hot coronal plasma component. We propose that the hot component may be an artifact of the corona being close to unit optical thickness for resonant scattering in the strongest spectral lines, so that part of the line photons can be destroyed by being scattered towards the stellar surface while the plasma remains optically thin for continuum photons. Diagnostics for the electron density n_e_, using Fe X, XII, XIII, and XIV lines, yields values in the range 2-20x10^8^cm^-3^ at T=1-2MK. Title: The optical thickness of stellar coronae in the EUV lines. Authors: Schrijver, C. J.; van den Oord, G. H. J.; Mewe, R. Bibcode: 1994A&A...289L..23S Altcode: Stellar coronae are commonly assumed to be optically thin. Recent spectroscopic observations in the EUV, however, lead us to question the validity of this approximation for strong lines. We argue that scattering may significantly affect the strongest coronal lines in coronae composed of magnetic loops, possibly embedded in a hot stellar wind. Even if the average number of scatterings per photon in some coronal lines is only of order unity, the relative line strenghts and the line-to-continuum ratio can be significantly affected in non-symmetric inhomogeneous atmospheres: photons in weak lines and in the optically thin continuum escape without any scattering, but strong lines can be weakened or enhanced depending on the balance between outward traveling line photons that are scattered back toward the stellar surface (if not lost by branching), there destroyed by absorption, and downward traveling line photons that are scattered upward and escape. We draw attention to the fact that line scattering due to the non-negligible optical thickness in strong coronal lines can have severe implications for differential emission measure models and for abundance and density determinations, while it may serve as a diagnostic for the existence of tenuous hot winds. Title: Book Review: Solar photo rates for planetary atmospheres and atmospheric pollutants / Kluwer, 1992 Authors: Heubner, W. F.; Mewe, R. Bibcode: 1994SSRv...69..211H Altcode: No abstract at ADS Title: EUVE Spectroscopy of XI UMa; sigma Gem; and Chi {1} ORI Authors: Mewe, R.; Schrijver, C. J.; Kaastra, J. S.; Alkemade, F. J. M.; Haisch, B. M. Bibcode: 1994ASPC...64...41M Altcode: 1994csss....8...41M No abstract at ADS Title: EUVE observations of NGC 5548. Authors: Kaastra, J. S.; Mewe, R.; Heise, J.; Alkemade, F. J. M.; Schrijver, C. J.; Carone, T. Bibcode: 1994IAUS..159..325K Altcode: No abstract at ADS Title: New Calculations of Fe Spectra in High-Temperature Plasmas Authors: Liedahl, D.; Osterheld, A.; Mewe, R.; Kaastra, J. Bibcode: 1994nhxr.conf..629L Altcode: No abstract at ADS Title: VizieR Online Data Catalog: Fluorescence for Be to Zn (Kaastra+ 1993) Authors: Kaastra, J. S.; Mewe, R. Bibcode: 1993yCat..40970443K Altcode: The basic physical processes responsible for X-ray emission from thin plasmas are considered. Collisional ionization or photoionization of inner shells of neutral atoms and ions leads to the creation of a vacancy in one of the inner shells of the ion or atom, which is filled by a cascade of radiative (fluorescent) and nonradiative (Auger) transitions. The net result is the ejection of several electrons and photons, leaving the atom in a multiply ionized state. In this paper, the distribution of the number of emitted photons and electrons after the creation of a hole in an inner shell of an atom or ion is calculated for all ions from H to Zn. The method consists of two stages: the calculation of transition rates for a given electron configuration, and calculation of probabilities of the several cascade sequences using these transition rates. (2 data files). Title: Book reviews Authors: Rutten, R. J.; Mewe, R.; Houziaux, L.; Cheng, Chung-Chieh; van der Klis, M.; Sylwester, Janusz; Tajima, T.; Kresák, Ľ.; Minarik, S.; de Jager, Cornelis; van der Kruit, P. C. Bibcode: 1993SSRv...65..181R Altcode: No abstract at ADS Title: GOME instrument simulation Authors: Kamperman, Th. M.; Goede, A. P. H.; Gunsing, C. J. Th.; Mewe, R.; Nieuwenhuijzen, H.; Slijkhuis, S.; de Vries, J.; Spurr, R. J. D.; Burrows, J. P.; Chance, K. V. Bibcode: 1993SPIE.1715..562K Altcode: The paper presents a detailed software simulation package for the Global Ozone Monitoring Experiment (GOME) instrument which will fly on ERS-2 in 1994. The GOME instrument is a nadir-viewing spectrometer designed for measurements of ozone and related trace gases such as NO, NO2, ClO, BrO, OClO, HCHO, SO2, O2/O4, and H2O. Examples are presented of input and output spectra and signal-to-noise calculations for normal viewing mode (nadir observations) and for sun and moon calibration mode. The GOME instrument simulating program can be used for a variety of purposes during instrument development, such as tests and calibrations, and tests of the so-called Zero-to-One processing step. The scheme could be adapted to other optical instruments. Title: X-ray spectroscopy with the XSPECT/SODART telescopes on SRG. Authors: Schnopper, H. W.; Budtz-Jørgensen, C.; Christensen, F. E.; Mewe, R.; Nørgaard-Nielsen, H. U.; Westergaard, N. J. Bibcode: 1993uxrs.conf..483S Altcode: 1993uxsa.conf..483S The XSPECT/SODART X-ray telescopes and their associated focal plane instrumentation will be launched on board the Russian X-ray mission Spectrum Röntgen-Gamma (SRG). The authors first present the main properties of the instruments and then present simulations of some of the scientific questions which can be addressed by the observing program. XSPECT/SODART consists of two, high-throughput telescopes. In the focal plane of each one, there are high- and low energy imaging proportional counters. One telescope also has an array of silicon detectors and the other a polarimeter. An imaging, objective spectrometer consisting of three different kinds of Bragg crystals and two different multilayers is mounted in front of one of the telescopes. The broad bands of the imaging X-ray detectors collectively cover the energy rangy from 0.2 to 25 keV. The objective spectrometer samples this range around the emission and absorption features from, among others, the cosmically important ions of Fe, S, Si and O. An optical/UV monitor, co-aligned with the X-ray telescopes and consisting of three separate telescopes, will support the X-ray observations and provide aspect information. Title: Book-Review - Basic Space Science Authors: Haubold, H. J.; Khanna, R. K.; Mewe, R. Bibcode: 1993SSRv...65..183H Altcode: No abstract at ADS Title: Stellar Coronal X-ray Spectroscopy Authors: Mewe, R. Bibcode: 1993ASSL..183..225M Altcode: 1993pssc.symp..225M No abstract at ADS Title: X-ray emission from thin plasmas. I - Multiple Auger ionisation and fluorescence processes for Be to Zn Authors: Kaastra, J. S.; Mewe, R. Bibcode: 1993A&AS...97..443K Altcode: The basic physical processes responsible for X-ray emission from thin plasmas are considered. Collisional ionization or photoionization of inner shells of neutral atoms and ions leads to the creation of a vacancy in one of the inner shells of the ion or atom, which is filled by a cascade of radiative (fluorescent) and nonradiative (Auger) transitions. The net result is the ejection of several electrons and photons, leaving the atom in a multiply ionized state. In this paper, the distribution of the number of emitted photons and electrons after the creation of a hole in an inner shell of an atom or ion is calculated for all ions from H to Zn. The method consists of two stages: the calculation of transition rates for a given electron configuration, and calculation of probabilities of the several cascade sequences using these transition rates. Title: Multiple Auger ionisation and fluorescence processes for Be to Zn. Authors: Kaastra, J. S.; Mewe, R. Bibcode: 1993uxrs.conf..134K Altcode: 1993uxsa.conf..134K No abstract at ADS Title: Book-Review - Handbook of Space Astronomy and Astrophysics Authors: Zombeck, M. V.; Mewe, R. Bibcode: 1992SSRv...59..207Z Altcode: No abstract at ADS Title: X-ray spectroscopy of solar & stellar coronae. Authors: Mewe, R. Bibcode: 1992MmSAI..63..681M Altcode: Results of broadband and medium-resolution spectral X-ray observations obtained with the spectrometers aboard Einstein and Exosat are presented, showing that these spectra make it possible to identify coronal gas at different temperatures associated with various possible loop structures. Simulations are presented of spectra of the NASA's Advanced X-ray Astrophysics Facility and the ESA's X-ray Multimirror Mission, which demonstrate the capabilities of these future instruments for the diagnosing plasma parameters such as temperature, density, and velocity. Title: Book reviews Authors: Icke, V.; Wakker, K. F.; Journet, A.; van der Kruit, P. C.; Nieuwenhuijzen, H.; Mewe, R. Bibcode: 1992SSRv...59..205I Altcode: No abstract at ADS Title: Modelling of high-temperature plasmas (review) Authors: Mewe, R. Bibcode: 1992sccw.conf...33M Altcode: No abstract at ADS Title: The AXAF Low-Energy Transmission Grating Spectrometer / LETGS / Diagnostic Capabilities for the Study of Stellar Coronae Authors: Mewe, R.; Lemen, J. R.; Schrijver, C. J. Bibcode: 1991Ap&SS.182...35M Altcode: We study the diagnostic capabilities of the high-resolution, Low-Energy Transmission Grating Spectrometer, LETGS, of NASA's planned Advanced X-ray Astrophysics Facility, AXAF, for optically thin stellar coronae. Spectra are simulated on the basis of isothermal and source loop models and are analyzed with particular emphasis on the extraction of the differential emission measure distribution. The AXAF-LETGS is shown to be particularly sensitive for plasma at temperatures between 0.5 and 15 MK. Emission from temperatures in excess of 20 MK can be observed, but the lack of strong spectral lines hampers accurate temperature determinations. We simulate spectra of close binaries to demonstrate the observability of the Doppler effects associated with orbital motions. We present lists of spectral lines that can be used for density diagnostics, and we simulate and compare various spectra at different electron densities. Title: Solar and stellar coronal loops Authors: Mewe, R. Bibcode: 1991AdSpR..11a.127M Altcode: 1991AdSpR..11..127M X-ray and EUV pictures from space experiments (e.g. SKYLAB) have revealed that the corona of the Sun consists of a variety of discrete structures - involving a range of timescales - which appear to outline the magnetic field lines emerging from the convection zone below the photosphere. Among the brightest regions in X-rays and EUV are those in which the field lines close back to the surface and which confine the hot emitting plasma in loop structures. Simple scaling laws have been developed for the static model of a single magnetic loop relating average loop temperature, pressure and length and these have been applied more or less successfully to solar observations. For many other cool stars with convective envelopes X rays have been detected from hot plasmas with temperatures ranging from ~0.5 to ~30 MK. The strong correlation between X-ray luminosity and stellar rotational velocity suggests a surface magnetic activity associated with an internal dynamo such as has been assumed for the Sun. The detailed spatial structure of stellar coronae is not yet known, although by analogy with the Sun it is widely assumed that stellar coronae - both quiescent and flaring - are heated by magnetohydrodynamic processes, with much of the plasma confined in loop-like structures connecting opposite magnetic polarities in the photosphere. In this paper I consider a few results from solar and stellar X-ray observations that constrain basic properties of magnetic loops. Title: X-ray Lines in Stellar Coronae Authors: Mewe, R. Bibcode: 1991LNP...385...13M Altcode: 1991ildx.conf...13M Because the emission line spectra and continua from optically thin plasmas are fairly well known, high-resolution X-ray spectroscopy has its most obvious application in the measurement of optically thin sources such as the coronae of stars. In particular X-ray observations with the EINSTEIN observatory have demonstrated that soft X-ray emitting coronae are a common feature among stars on the cool side of the Hertzsprung-Russell diagram, with the probable exception of single very cool giant and supergiant stars and A-type dwarfs. Observations with the spectrometers aboard EINSTEIN and EXOSAT have shown that data of even modest spectral resolution (/= 10-100 permit the identification of coronal material at different temperatures whose existence may relate to a range of possible magnetic loop structures in the outer atmospheres of these stars. The improved spectral resolution of the next generation of spectrometers aboard XMM and AXAF is needed to fully resolve the temperature structure of stellar coronae and to enable density and velocity diagnostics. In this paper spectral results from EINSTEIN and EXOSAT are discussed. A few simulations of high-resolution re L, K, and 2s-2p spectra with AXAF, XMM, and several detectors such as calorimeter and Nb-junction are shown to demonstrate the capabilities for plasma diagnostics. Title: X-ray spectroscopy of stellar coronae Authors: Mewe, R. Bibcode: 1991A&ARv...3..127M Altcode: From the early discovery in 1948 of X-rays from the Solar corona, X-ray spectroscopy has proven to be an invaluable tool in studying hot astrophysical and laboratory plasmas. Because the emission line spectra and continua from optically thin plasmas are fairly well known, high-resolution X-ray spectroscopy has its most obvious application in the measurement of optically thin sources such as the coronae of stars. In particular X-ray observations with the EINSTEIN observatory have demonstrated that soft X-ray emitting coronae are a common feature among stars on the cool side of the Hertzsprung-Russell diagram, with the probable exception of single very cool giant and supergiant stars and A-type dwarfs. Observations with the spectrometers aboard EINSTEIN and EXOSAT have shown that data of even modest spectral resolution ( α/ Δα = 10 100) permit the identification of coronal material at different temperatures whose existence may relate to a range of possible magnetic loop structures in the hot outer atmospheres of these stars. The higher spectral resolution of the next generation of spectrometers aboard NASA's AXAF and ESA's XMM will allow to fully resolve the coronal temperature structure and to enable velocity diagnostics and the determination of coronal densities, from which the loop geometry (i.e. surface filling factors and loop lengths) can be derived. In this paper various diagnostic techniques are reviewed and the spectral results from EINSTEIN and EXOSAT are discussed. A number of spectral simulations for AXAF and XMM, especially high-resolution iron K-shell, L-shell, and 2s-2p spectra in the wavelength regions around 1.9 Å, 10 Å, and 100 Å, respectively, are shown to demonstrate the capabilities for temperature, density, and velocity diagnostics. Finally, iron K-shell spectra are simulated for various types of detectors such as microcalorimeter, Nb-junction, and CCD. Title: Book Review: The sun: an introduction / Springer-Verlag Authors: Mewe, R.; Švestka, Z.; Mewe, R. Bibcode: 1990SoPh..126..411M Altcode: 1990SoPh..126..411S No abstract at ADS Title: Ionization of Hot Plasmas Authors: Mewe, R. Bibcode: 1990ASIC..305...39M Altcode: 1990pphc.conf...39M The processes of ionization and recombination in hot (T ⪆ 105K) astrophysical plasmas are considered, emphasizing the case of optically thin plasmas. A detailed comparison among different computations is made for the coronal model. The emergent radiation spectra are treated as a function of electron temperature. The effects of optical depth, photoionization, high densities, time variations, electromagnetic fields, and non-Maxwellian electron energy distributions are briefly discussed. Title: Temperatures of coronae of cool stars, derived from EXOSAT observations Authors: Mewe, R.; Lemen, J. R.; Schrijver, C. J. Bibcode: 1990AdSpR..10b.129M Altcode: 1990AdSpR..10..129M We observed the late-type stars Capella, σ2 CrB, λ And, AD Leo, GL494, GL569 and Procyon with different combinations of three instruments aboard EXOSAT : the low-energy channel multiplier array (LE), the medium-energy proportional counters (ME), and the transmission grating spectrometer (TGS). We derive crude temperature information on the coronae of these stars from the photometric data, using one- and two-temperature models of optically thin, thermal plasmas. We compare the results with 2-T fits and differential emission measure analyses of three grating observations and with simulations for mixtures of two plasma components with varying emission measure ratios. But for Procyon, all sources have a strong, hot component between 10 and 25 MK. The TGS spectra of Capella and σ2 CrB reveal a cooler component with comparable emission measure around 5 MK. The emission from the corona of Procyon is dominated by a very cool (0.6 MK) component, with an additional contribution from a 2-3 MK component. Title: High-resolution X-ray spectroscopy in astrophysics Authors: Mewe, R. Bibcode: 1990asos.conf...67M Altcode: No abstract at ADS Title: Simulations of High-Resolution X-Ray Spectra of Active Galactic Nuclei / AGN Authors: Kaastra, J. S.; Mewe, R.; Brinkman, A. C. Bibcode: 1989ESASP.296..951K Altcode: 1989ttxa.symp..951K The improvements in spectral resolution and sensitivity in soft X-rays detection by NASA's Advanced X-ray Astrophysics Facility (AXAF) and ESA's X-ray Multi-Mirror Mission (XMM) are underlined. Spectral simulations with 0.05A resolution are performed to investigate the diagnostic capabilities of the XMM reflection grating spectrometer for Active Galactic Nuclei (AGN) spectra. Observations of resolved emission lines and absorption edges in soft X-rays allow a better interpretation of the origins of the different spectral components. Title: Book reviews Authors: Hovenier, J. W.; Ne'Eman, Yuval; Kleczek, J.; Vn Nes, P.; Somogyi, A. J.; Mewe, R.; Klos, Z.; Bertaux, J. L.; van Beek, H. F.; 't Hooft, G. Bibcode: 1989SSRv...51..229H Altcode: No abstract at ADS Title: Magnetic structure in cool stars. XVI. Emissions from the outer atmospheres of M-type dwarfs. Authors: Rutten, R. G. M.; Schrijver, C. J.; Zwaan, C.; Duncan, D. K.; Mewe, R. Bibcode: 1989A&A...219..239R Altcode: Consideration is given to emission from the outer atmospheres of M-type dwarfs in several spectral lines originating from the chromosphere, the transition-region, and the soft X-ray emission from the corona. It is shown that M-type dwarfs systematically deviate from relations between flux densities in soft X-rays and chromospheric and transition-region emission lines. The quantitative relation between the equivalent width of H-alpha and the Ca II, H, and K emission index is determined. It is suggested that the emission in the Balmer spectrum may result from back heating by coronal soft X-rays. Title: Coronal Activity in F-, G-, and K-Type Stars. III. The Coronal Differential Emission Measure Distribution of Capella, sigma 2 Coronae Borealis, and Procyon Authors: Lemen, J. R.; Mewe, R.; Schrijver, C. J.; Fludra, A. Bibcode: 1989ApJ...341..474L Altcode: EXOSAT soft X-ray spectra of three binary systems of cool stars are analyzed: Capella (G6 III + F9 III), Sigma-squared CrB (F8 V + G1 V), and Procyon (F5 IV-V + DF). The EXOSAT transmission grating spectrometer permits the study of individual spectral lines and line complexes between 10 and 200 A with approximately 3 A resolution. First it is demonstrated that the spectra can be described reasonably well by a two-temperature model corona. Then the assumption that only two temperatures exist in the stellar coronas is relaxed and differential emission measure distributions are derived from the three spectra. The results from the multithermal modeling are consistent with those of the two-temperature models: emission from the coronas of each of the three stars is dominated by plasma in two relative narrow temperature intervals. These intervals are centered on 5 MK and 25 MK in the cases of Capella and Sigma-squared CrB, and 0.6 MK and 3 MK in the case of Procyon. The implications of the results for the structure of stellar coronas are briefly discussed. Title: Coronal Activity in F-, G-, and K-Type Stars. IV. Evidence for Expanding Loop Geometries in Stellar Coronae Authors: Schrijver, C. J.; Lemen, J. R.; Mewe, R. Bibcode: 1989ApJ...341..484S Altcode: A detailed analysis is presented of X-ray spectra of Capella and of Sigma2 CrB. The spectra of both stars are compatible with coronae consisting of two different ensembles of static loops with different maximum temperatures and ratios of the cross sectional areas at the loop top and at the footpoint. The cool (5 MK) loop components in both stars show evidence of relatively strong expansion with height. The hot (30 MK) components appear to expand much less. Title: The X-ray flare and the quiescent emission from Algol as detected by EXOSAT. Authors: van den Oord, G. H. J.; Mewe, R. Bibcode: 1989A&A...213..245V Altcode: The Algol system was observed on August 18/19,1983 with different combinations of three instruments aboard EXOSAT: the low-energy channel multiplier array, the medium-energy proportional counters, and the transmission grating spectrometer. The X-ray flare observed on August 19 was analyzed and the decay phase was studied. It is shown that during this phase the flare cools quasistatically according to the scaling laws and analytical expressions for the time-evolution of the relevant physical quantities are presented. Title: Book-Review - Fundamental Astronomy Authors: Karttunen, H.; Korger, P.; Oja, H.; Poutanen, M.; Doner, K. J.; Mewe, R. Bibcode: 1989SSRv...51..232K Altcode: No abstract at ADS Title: A study of the decay phase of an X-ray flare on Algol. Authors: Mewe, R.; van den Oord, G. H. J.; Jakimiec, J. Bibcode: 1989sasf.confP.123M Altcode: 1988sasf.conf..123M; 1989IAUCo.104P.123M The authors have re-analyzed the X-ray flare on Algol which was observed with EXOSAT (White et al., 1986). The common practice of estimating loop volume and length from the decay time of the flare is discussed extensively. The authors show that during the decay phase of the flare both scaling laws for coronal loops are valid. This implies a unique determination of loop volume and length and allows a check whether additional heating occurs in the decay phase of a flare. Title: An EXOSAT observation of an X-ray flare and quiescent emission from the RS CVn binary sigma2 CrB. Authors: van den Oord, G. H. J.; Mewe, R.; Brinkman, A. C. Bibcode: 1988A&A...205..181V Altcode: The RS CVn binary sigma2 Coronae Borealis was observed with medium-energy and low-energy detectors and the transmission grating spectrometer aboard EXOSAT, and a strong X-ray flare rising within about five minutes and lasting more than two hours was detected. The temperature rises steeply within three minutes from 19 MK to a value well above 70 MK, while the emission measure attains a maximum of 6 x 10 to the 53rd/cu cm five minutes later. The e-folding time is about half an hour. The flare volume and density are estimated and, on the basis of the short rise time of the flare, can be classified as a compact flare. The flare energy requirements are discussed, and it is found that current-driven turbulence can produce such fast heating. An equivalent-circuit description is presented. Title: Intercomparison of flare observations with two SMM spectrometers: BCS and HXIS Authors: Jakimiec, J.; Prés, P.; Fludra, A.; Bentley, R. D.; Lemen, J. R.; Mewe, R.; Schrijver, J.; Sylwester, J. Bibcode: 1988AdSpR...8k.231J Altcode: 1988AdSpR...8..231J The temperature diagnostics of hot flare plasma, obtained from two Solar Maximum Mission instruments (HXIS and BCS), is compared. A good general agreement between the HXIS and BCS-Fe temperature scales has been found. However, for the growth phase of some flares a systematic difference, THXIS>TFe, has been found, which is not likely to be due to the typical non-thermal electron beams. Possible explanation of this effect is briefly discussed. Title: Ionisation Rate Coefficients Authors: Mewe, R. Bibcode: 1988als..conf..141M Altcode: No abstract at ADS Title: Satellite Lines as a Diagnostic Authors: Mewe, R. Bibcode: 1988als..conf..167M Altcode: No abstract at ADS Title: Recombination Rate Coefficients Authors: Mewe, R. Bibcode: 1988als..conf..155M Altcode: No abstract at ADS Title: Ionisation Balance in Low Density Plasmas Steady State and Transient Case Authors: Mewe, R. Bibcode: 1988als..conf..129M Altcode: No abstract at ADS Title: The 67-min X-ray period of EX Hydrae observed with the EINSTEIN Observatory. Authors: Heise, J.; Mewe, R.; Kruszewski, A.; Chlebowski, T. Bibcode: 1987A&A...183...73H Altcode: The cataclysmic variable EX Hydrae has been observed in X-rays with the high resolution imager (HRI), IPC, and monitor proportional counter (MPC) of the Einstein observatory on two occasions. The X-ray spectra indicate multiple spectral components. A constant hard X-ray flux is found in the high-energy channels of the MPC. In the lower energy channels of the MPC and in the IPC a variable softer component is observed with a period of 67 min. The modulation is approximately in phase with the stable 67-min modulation in the optical brightness. The IPC X-ray spectrum changes slightly with the 67 min phase. The X-ray observations of EX Hya, recently interpreted as an intermediate polar, exhibit many features characteristic of AM Her-type stars. The constant hard X-ray source, e.g., is expected from an AM Her-type star with suitable orientation of the magnetic axis with respect to the inclination angle. The AM Her-type X-ray properties of EX Hya and the possible absence of a standard accretion disk in the system are discussed. Title: Low Energy X-Ray Transmission Grating Spectrometer for AXAF Authors: Brinkman, A. C.; van Rooijen, J. J.; Bleeker, J. A. M.; Dijkstra, J. H.; Heise, J.; de Korte, P. A. J.; Mewe, R.; Paerels, F. Bibcode: 1987ApL&C..26...73B Altcode: 1987ApL....26...73B The proposed grating spectrometer for the Advanced X-ray Astrophysics Facility (AXAF) covers the wavelength region between 2 and 140 Å. The wavelength resolution Δλ = 0.05 Å. The effective sensitive area as a function of wavelength is discussed. To illustrate the expected performance of the spectrometer some simulated spectra of a few interesting astrophysical objects are presented. Title: Evidence for Expanding Loop Geometries in Stellar Coronae Authors: Mewe, R.; Lemen, J. R.; Schrijver, C. J.; Fludra, A. Bibcode: 1987LNP...291...60M Altcode: 1987csss....5...60M; 1987LNP87.291...60M No abstract at ADS Title: Variation in Calcium Abundance during Flares Authors: Sylwester, J.; Lemen, J. R.; Mewe, R.; Bentley, R. D.; Sylwester, B. Bibcode: 1987sman.work..123S Altcode: The authors discuss the variation of the line-to-continuum ratio throughout the entire flare including the temperature rise phase. Title: High-Temperature Plasma Diagnostics of Solar Flares and Comparison with Model Calculations Authors: Jakimiec, J.; Sylwester, B.; Sylwester, J.; Lemen, J. R.; Mewe, R.; Bentley, R. D.; Peres, G.; Serio, S.; Schrijver, J. Bibcode: 1987sman.work...91J Altcode: The present state of flare diagnostics from X-ray spectra is briefly outlined. The authors discuss how improved diagnostic results can be used in flare heating process investigations. Title: A Large X-ray Flare on σ2 Coronae Borealis Observed with EXOSAT Authors: van den Oord, G. H. J.; Mewe, R.; Brinkman, A. C. Bibcode: 1987LNP...291..494V Altcode: 1987LNP87.291..494V; 1987csss....5..494V We report the observation of a compact flare on σ2 Coronae Borealis. The energy requirements for the flare are discussed and we find that current-driven turbulence can produce heating fast enough. During the initial phase of the flare classical transport theory is not applicable. Title: A two-component model for the corona of lambda Andromedae. Authors: Mewe, R.; Schrijver, C. J. Bibcode: 1986A&A...169..178M Altcode: The binary Lambda Andromedae (HD 222107) was studied with the low-energy (LE) and medium-energy (ME) X-ray detectors of Exosat on December 5, 1983 and on January 8, 1984, half a rotation period later. The ME data for the observations are compatible with emission from a plasma with a temperature of about 20 MK. If the strong variability in the hard X-ray flux is interpreted as due to rotational modulation the scale height of the hot plasma should be significantly smaller than the stellar radius. If the ME data are interpreted in terms of a model for quasi-static loops, the footpoints of these loops cover at most a few percent of the stellar surface, and the pressure of the hot plasma may exceed about 25 dyn/sq cm. The LE data require an additional, weaker contribution by a cooler component that does not vary significantly with time. A later observation of the object on August 6, 1984 shows no significant change in the two plasma components as inferred from the observations on January 8, 1984, when the same hemisphere of the primary star was observed. Title: Calculated X-radiation from optically thin plasmas. VI - Improved calculations for continuum emission and approximation formulae for nonrelativistic average Gaunt actors. Authors: Mewe, R.; Lemen, J. R.; van den Oord, G. H. J. Bibcode: 1986A&AS...65..511M Altcode: The continuum spectrum of an optically thin plasma whose electrons have a Maxwellian energy distribution is calculated for the wavelength range 1 - 1000 Å and temperature range 0.01 - 100 MK. The effect of recombination to excited states on the free-bound emission is taken into account. Simple analytic approximations to the total free-free, free-bound and two-photon Gaunt factors are presented for various wavelength and temperature intervals covering the whole considered range. A simple computer routine for calculating the continuum emission with the aid of this approximation is given. Title: Investigation of flare heating based on X-ray observations Authors: Jakimiec, J.; Sylwester, B.; Sylwester, J.; Mewe, R.; Peres, G.; Serio, S.; Schrijver, J. Bibcode: 1986CoSka..15..123J Altcode: Using X-ray data recorded by the Solar Maximum Mission Hard X-ray Imaging Spectrometer the authors have investigated flare evolution in a (Tm, N)-diagram, where Tm is the maximum temperature and N is the mean density in the flare volume. This flare diagnostics allows one to show that most large flares achieve a quasi-steady-state during their decay, which means that the cooling is then so slow that a flare evolves along the line of steady-state loops in the (Tm, N)-diagram. The diagnostics allows one to determine the time evolution of the flare heating function, which gives the rate of thermal energy release, per unit volume. Title: X-Ray Emission of λ Andromedae: Correlation with Spot Activity Authors: Mewe, R.; Schrijver, C. J. Bibcode: 1986LNP...254..297M Altcode: 1986csss....4..297M No abstract at ADS Title: Differential emission measure distributions of Capella and σ2 CrB Authors: Mewe, R.; Schrijver, C. J.; Lemen, J. R.; Bentley, R. D. Bibcode: 1986AdSpR...6h.133M Altcode: 1986AdSpR...6..133M The active late-type stars Capella (α Aur G6III+F9III) and σ2 CrB (F6V+GV) (X-ray candidate emitters underlined) were observed with the EXOSAT Transmission Grating Spectrometer (TGS) in the region 10-200 Å. We have made an analysis of the differential emission measure (DEM) distribution. The derived DEM peaks between 3 and 7 MK and above 10 MK. The results disagree with models for static loops as developed by Rosner, Tucker and Vaiana [1, hereafter referred to as RTV]: the contrast in emission between the maximal and lower temperatures in the loop is larger than predicted by the RTV model. Other models which predict DEM distributions falling off more steeply towards lower temperatures are briefly discussed: e.g. quasi-static loops with varying cross-sectional area or dynamic loops with strong downward flows. Title: Investigation of flare heating based on X-ray observations Authors: Jakiemiec, J.; Sylwester, B.; Sylwester, J.; Mewe, R.; Peres, G.; Serio, S.; Schrijver, J. Bibcode: 1986AdSpR...6f.237J Altcode: 1986AdSpR...6..237J Using X-ray data recorded by the Solar Maximum Mission Hard X-ray Imaging Spectrometer we have investigated flare evolution in a (Tm, N)-diagram, where Tm is the maximum temperature and N is the mean density in the flare volume. It is important that the behaviour of a flare in such a diagram does not depend significantly on details of the flare geometry and therefore can be effectively compared with simplified model calculations of flare loops. This flare diagnostics allows us to show that most large flares achieve a quasi-steady-state during their decay, which means that the cooling is then so slow that a flare evolves along the line of steady-state loops in the (Tm, N)-diagram. The diagnostics allows us to determine the time evolution of the flare heating function, EH(t), which gives the rate of thermal energy release, per unit volume. For the flares which achieve the quasi-steady-state branch it gives a new valuable method of estimation of the electron density in the flare loops. Title: X-Ray Spectroscopy of Capella and σ2 Coronae Borealis Authors: Schrijver, C. J.; Mewe, R. Bibcode: 1986LNP...254..300S Altcode: 1986csss....4..300S No abstract at ADS Title: Solar X-ray spectrum simulations for flaring loop models with emphasis on transient ionization effects during the impulsive phase Authors: Mewe, R.; Lemen, J. R.; Peres, G.; Schrijver, J.; Serio, S. Bibcode: 1985A&A...152..229M Altcode: X-ray spectra are simulated for observations with the Bent Crystal Spectrometer (BCS) on the Solar Maximum Mission (SMM) spacecraft (around 1.9 A and 3 A) using results of a time-dependent numerical code for a dynamic flaring loop model. The spectra are integrated over the whole loop and fully take into account the effects of deviations from ionization equilibrium and Doppler shifts resulting from plasma movements. The effect of transient ionization on the spectra emitted during the initial impulsive phase is emphasized. In all the cases considered a strong depletion (relative to the continuum) of high-ionization spectral lines takes place during about the first minute of the flare for electron densities below about 10 to the 11th/cu cm. A preliminary comparison to observations made with the BCS show some indications for such effects in a few strong flares, but more sensitive instruments will be needed in the future to exploit such transient ionization effects as a possible valid density diagnostic for hot solar flares. Title: Calculated X-Radiation from Optically Thin Plasmas - Part Five Authors: Mewe, R.; Gronenschild, E. H. B. M.; van den Oord, G. H. J. Bibcode: 1985A&AS...62..197M Altcode: 2009A&A...500..301M The spectral line list in a previously developed computer code has been updated and extended with many new lines up to 300 A. These lines comprise: H- and He-like n = 1-2 lines, together with their satellites which are produced by innershell transitions: 2l-nl-prime (n = 3, 4) transitions in Fe XVII-XXIV (10-17 A); 2s-2p lines in Fe XVIII-XXIII and Ni XX-XXV (90-140 A); 3l-nl-prime (n = 3, 4) transitions in Fe VIII-XVI and Ni X-XIV (50-200 A), and many lines from Li to Ne isoelectronic sequences of elements C to Ca (20-300 A). Intensities of 2131 spectral lines are tabulated over the temperature range 3 x 10 to the 4th - 10 to the 9th K. Title: The Bright Pre-main Sequence Variable HR5999 Authors: The, P. S.; Tjun-A-Djie, H. R. E.; Brown, A.; Catala, C.; Doazan, V.; Linsky, J.; Mewe, R.; Praderie, F.; Talavera, A.; Zwaan, C. Bibcode: 1985IrAJ...17...79T Altcode: A meeting to review the reduced coordinated observations by EXOSAT, IUE and ground-based instruments of the bright and variable Herbig A7e star HR 5999 is summarized. The attempt was to delineate the relationship between the various observable quantities of its atmosphere (colors, emission-line fluxes, wind velocities, etc.) in order to develop a dynamical model of the extended atmosphere. The observations were made around September 11, 1983. Title: Low Energy Transmission Grating Spectrometer (LETGS) for AXAF Authors: Brinkman, A. C.; van Rooijen, J. J.; Bleeker, J. A. M.; Dijkstra, J. H.; Heise, J.; Mewe, R.; Paerels, F.; de Korte, P. A. J. Bibcode: 1985BAAS...17Q.865B Altcode: 1985BAAS...17..865B No abstract at ADS Title: Dispersive X-ray spectroscopy with transmission gratings. Authors: Paerels, F.; Bleeker, J. A. M.; Brinkman, A. C.; Dijkstra, J. H.; Mewe, R.; Schrijver, C. J. Bibcode: 1985ESASP.239..205P Altcode: 1985cxrs.work..205P The possibilities for plasma diagnostics with high throughput grating spectrometers are illustrated by presenting spectra of a coronal X-ray source (Capella), a Seyfert Galaxy (NGC 4151) and a BL Lac object (PKS 2155-304). Einstein and EXOSAT spectra are contrasted with computer-simulated AXAF or XMM spectra, to illustrate the increase of insight expected from grating spectroscopy with these instruments. Title: Spectral variability of scorpius X-1, as observed with EXOSAT Authors: Brinkman, A. C.; Mewe, R.; Langerwerf, T.; Heise, J.; Peacock, A.; White, N. Bibcode: 1985SSRv...40..201B Altcode: EXOSAT measurements of Sco X-1 have been carried out with the 500 l/mm and 1000 l/mm grating spectrometers and simultaneously with the gas scintillation proportional counter (GSPC) on two occasions in August 1983. The first observing period, part of the instrument performance verification phase, on August 7 and 8, 1983, lasted for about twenty two hours and showed the source flaring during the first six hours. During the second observing period, August 29 and 30, 1983, the source was again active during part of the time. The lightcurves of the spectrometers and the GSPC show some correlation during the flaring activity. The grating spectra show clear emission features between 12 and 20 Å, which vary with time. When fitting the observed spectra to a thermal bremsstrahlungs model (exponential with gaunt factor) together with absorption by neutral matter, a reduced abundance of oxygen in the absorbing matter with respect to Solar is required. Title: Spectral and temporal studies of various late-type stars Authors: Brinkman, A. C.; Gronenschild, E. H. B. M.; Mewe, R.; McHardy, I.; Pye, J. P. Bibcode: 1985AdSpR...5c..65B Altcode: 1985AdSpR...5Q..65B The RS CVn stars Capella and σ2 CrB have been measured with EXOSAT in soft and medium X-rays for about 24 hours each and the less active late-type star Procyon for about 6.5 hours. In addition, the RS CVn star γ. And was twice observed about one month apart for a total of about 7 hours, with the ME and the LE in the photometer mode only. All three RS CVn stars were detected with the ME-detector. The star σ2 CrB showed a flare both in LE and ME with a rise time of about twelve minutes and a decay time of three hours. The active late-type stars σ2 CrB and Capella show in the spectral region between 90 and 140 A lines from Fe XVIII to Fe XXIII, which can be resolved with the moderate resolution (Δγ ~ 5 A) of the spectrometer. These lines are indicative of the presence of hot (~ 10 MK) plasma like that in a Solar flare. In contrast, the spectrum of the cooler corona of the star Procyon does not show the hot Fe XXII and Fe XXIII lines but instead a blend at 175 A of Fe IX, X and XI lines that are formed in a typically quiet corona of a temperature around 1.5 MK. From the spectral intensities and the additional results of the simultaneous multi-color photometry coronal temperatures and emission measures are derived. There are indications in the spectra that the emission should be interpreted in terms of differential emission measure distribution models. Title: Coronal activity in F-, G- and K-type stars. II. Coronal structure and rotation. Authors: Schrijver, C. J.; Mewe, R.; Walter, F. M. Bibcode: 1984A&A...138..258S Altcode: Einstein Observatory soft X-ray spectra for a sample of 34 late-type stars are analyzed in order to determine coronal temperatures and emission features per unit area at the stellar surface. No obvious relation between coronal temperature and (B-V) color index could be found. Coronal temperature is dependent on stellar luminosity class. The data are discussed in terms of a model for static magnetic loops, and indications are found for a variety of coronae in which the sizes of the dominating loops range from more compact than loops in solar-active regions to loops that are comparable to the pressure scale height (or even greater). Despite observed structural differences, a single, strict relation holds between X-ray surface flux density and the Ca II H + K excess flux density of these stars. Coronal activity and structure are noted to be related to the stellar rotation rate. Title: Variation in observed coronal calcium abundance of X-ray flare plasmas Authors: Sylwester, J.; Lemen, J. R.; Mewe, R. Bibcode: 1984Natur.310..665S Altcode: Variations in chemical composition during solar flares have been inferred from elemental abundance changes in cosmic ray fluxes, but have so far not been detected spectroscopically. We present here the first spectroscopic evidence for the variation of the coronal calcium abundance in high-temperature solar flare plasmas. The analysed data consist of the high-resolution X-ray flare spectra (λ /Δλ ~ 4,000) observed with the Bent Crystal Spectrometer (BCS) on board the Solar Maximum Mission (SMM) satellite and described in detail by Acton et al.1. The observed abundance variation has important consequences for the analysis and interpretation of XUV and X-ray spectra. Title: Chromospheric and Coronal Activity of K-Type Giant Stars in Binaries Authors: Mewe, R. Bibcode: 1984iue..prop.2055M Altcode: No abstract at ADS Title: Book reviews Authors: van der Hucht, K. A.; Pedersen, A.; Kesák, Ľ.; Zwaan, C.; Fárník, F.; Kovalevsky, J.; van Beek, H. F.; Mewe, R.; Page, D. E.; van Genderen, A. M.; Koch-Miramond, L.; de Jager, C.; Ooms, G.; Pedersen, Arne; de Jager, C.; Hultqvist, Bengt; Waters, R.; Schrijver, J. Bibcode: 1984SSRv...38..179V Altcode: No abstract at ADS Title: A Multiwavelength Study of a Double Impulsive Flare Authors: Strong, K. T.; Benz, A. O.; Dennis, B. R.; Leibacher, J. W.; Mewe, R.; Poland, A. I.; Schrijver, J.; Simnett, G.; Smith, J. B., Jr.; Sylwester, J. Bibcode: 1984SoPh...91..325S Altcode: Extensive data from the Solar Maximum Mission (SMM) and ground-based observatories are presented for two flares; the first occurred at 12:48 UT on 31 August, 1980 and the second just 3 min later. They were both compact events located in the same part of the active region. The first flare appeared as a typical X-ray flare: the CaXIX X-ray lines were broadened (≡ 190±40 km s-1) and blue shifted (≡ 60±20 km s-1) during the impulsive phase, and there was a delay of about 30 s between the hard and soft X-ray maxima. The relative brightness of the two flares was different depending on the spectral region being used to observe them, the first being the brighter at microwave and hard X-ray wavelengths but fainter in soft X-rays. The second flare showed no significant mass motions, and the impulsive and gradual phases were almost simultaneous. The physical characteristics of the two flares are derived and compared. The main difference between them was in the pre-flare state of the coronal plasma at the flare site: before the first flare it was relatively cool (3 × 106 K) and tenuous (4 × 109 cm-3), but owing to the residual effects of the first flare the coronal plasma was hotter (5 × 106 K) and more dense (3 × 1011 cm-3) at the onset of the second flare. We are led to believe from these data that the plasma filling the flaring loops absorbed most of the energy released during the impulsive phase of the second flare, so that only a fraction of the energy could reach the chromosphere to produce mass motions and turbulence. Title: Variation in the Observed Coronal Calcium Abundance for Various X-Ray Flare Plasmas Authors: Lemen, J. R.; Sylwester, J.; Mewe, R. Bibcode: 1984BAAS...16..545L Altcode: No abstract at ADS Title: Book reviews Authors: Ooms, O.; van der Woerd, Hans; Lamers, Henny J. G. L. M.; Kleczek, Josip; Kovalevsky, J.; Gathier, R.; Jarzebowski, T.; Swings, J. P.; van der Hucht, K. A.; Namba, O.; Mewe, R.; Lynden-Bell, D.; Kuijpers, Jan; van der Klis, M.; de Hoop, D.; Wittenberg, H.; Iwanowska, W.; Thé, P. S.; Schrijver, J.; Pottasch, S. R. Bibcode: 1984SSRv...37..399O Altcode: No abstract at ADS Title: Book reviews Authors: Fárník, František; Mewe, R. Bibcode: 1984SoPh...91..193F Altcode: No abstract at ADS Title: Book-Review - Compendium in Astronomy Authors: Mariopoulos, E. G.; Pheocaris, P. S.; Mavrides, G. N.; Mewe, R. Bibcode: 1984SSRv...37..403M Altcode: No abstract at ADS Title: Differential emission measure analysis of hot-flare plasma from solar-maximum mission X-ray data Authors: Jakimiec, J.; Sylwester, J.; Lemen, J. R.; Mewe, R.; Bentley, R. D.; Fludra, A.; Schrijver, J.; Sylwester, B. Bibcode: 1984AdSpR...4g.203J Altcode: 1984AdSpR...4..203J We have investigated differential emission measure (DEM) distribution of hot flare plasma (T>10 MK) using SMM X-ray data from Bent Crystal Spectrometer (BCS) and Hard X-ray Imaging Spectrometer (HXIS). We have found that the analysis provide a very sensitive test of consistency of observational data coming from different instruments or different channels of the same instrument. This has allowed to eliminate some systematic differences contained in the analysed data.

Typical examples of the DEM distribution are discussed. It is stressed that these improvements in the multitemperature flare diagnostics are very important for the discussion of flare energetics. Title: Coronal Structure and Rotation in Late-type Stars Authors: Schrijver, C. J.; Mewe, R.; Walter, F. M. Bibcode: 1984LNP...193..166S Altcode: 1984csss....3..166S No abstract at ADS Title: The high resolution soft X-ray spectrum of AM Herculis. Authors: Heise, J.; Kruszewski, A.; Chlebowski, T.; Mewe, R.; Kahn, S.; Seward, F. D. Bibcode: 1984PhST....7..115H Altcode: 1984PhyS....7..115H The authors present a high resolution (λ/Δλ = 80) soft X-ray spectrum (44 - 95 Å) of the magnetic white dwarf binary AM Her obtained with the Objective Grating Spectrometer on board the Einstein Observatory. Black body fits to the continuum strongly limit the range of allowable parameters and indicate a "color" temperature in the soft X-ray range between 40 and 55 eV. Title: Book-Review - Supernova Remnants and Their X-Ray Emission Authors: Danziger, J.; Gorenstein, P.; Mewe, R. Bibcode: 1984SSRv...38..181D Altcode: No abstract at ADS Title: Soft X-Ray Spectroscopy with EXOSAT (invited Paper) Authors: Mewe, R. Bibcode: 1984uxsa.coll...59M Altcode: 1984uxsa.conf...59M; 1984IAUCo..86...59M No abstract at ADS Title: Hot optically thin plasmas in astrophysics. Authors: Mewe, R. Bibcode: 1984PhST....7....5M Altcode: 1984PhyS....7....5M The study of hot thin plasmas in astrophysics is reviewed with particular reference to X-ray spectroscopy and the modeling of spectra to derive important information on the physical properties of the emitting regions. Some of the methods are discussed by which spectral line intensities can be related to the temperature and density structure and the elemental abundances of the source through the processes of electron impact excitation and ionization, and radiative and dielectronic recombination. Various applications to sources such as stellar coronae, supernova remnants, hot component of the interstellar medium and intracluster gas are discussed. Title: Book-Review - Solar and Stellar Magnetic Fields - Origins and Coronal Effects Authors: Stenflo, J. O.; Mewe, R. Bibcode: 1984SoPh...91..193S Altcode: No abstract at ADS Title: X-ray spectrum simulations for flaring loop models - Transient ionization effects during the impulsive phase Authors: Mewe, R. Bibcode: 1984MmSAI..55..763M Altcode: X-ray spectra were simulated for observations with the bent crystal spectrometer (BCS) on the Solar Maximum Mission spacecraft using results of a time-dependent one-dimensional numerical code for a dynamic flaring loop model. It turns out that in all cases considered during about the first minute of the flare a strong depletion (relative to the continuum) of high-ionization spectral lines takes place at electron densities below about 1011cm-3. A preliminary comparison to observations with the BCS shows some indications for such effects in a few strong flares, but clearly more sensitive instruments will be needed in future to exploit such transient ionization effects as valid density diagnostics for hot solar flares. Title: Variation of the Observed Coronal Calcium Abundance for Various X-Ray Flare Plasmas (short Abstract) Authors: Sylwester, J.; Lemen, J. R.; Mewe, R. Bibcode: 1984uxsa.coll...21S Altcode: 1984uxsa.conf...21S; 1984IAUCo..86...21S No abstract at ADS Title: Time variation of the differential emission measure of hot flare plasma. Authors: Jakimiec, J.; Mewe, R.; Schrijver, J.; Sylwester, J.; Sylwester, B. Bibcode: 1983PDHO....5..127J Altcode: 1984PDHO....5..127J The authors have investigated details of the time evolution of the flare differential emission measure (DEM) distribution in the temperature range 10 - 50 MK using high-resolution X-ray spectra recorded by the Bent Crystal Spectrometer aboard the Solar Maximum Mission satellite. It has been found that for big flares the local maximum in the DEM distribution is systematically broader during the phase of flare increase than during the phase of decay. It is shown that this systematic effect is a result of development of a hot "wing" of the DEM local maximum during flare increase and its disappearance during flare decay. Title: SMM flat crystal spectrometer data analysis of 7 April 1980 flare. Authors: Sylwester, B.; Sylwester, J.; Jakimiec, J.; Mewe, R.; Bentley, R. D. Bibcode: 1983PDHO....5...85S Altcode: 1984PDHO....5...85S The authors have analysed soft X-ray images of the 1B/M4 flare of 7 April 1980 recorded by Flat Crystal Spectrometer aboard Solar Maximum Mission satellite. The X-ray flare consisted of two patches about 1 arcmin apart. A comparison with magnetograms and white light images indicates that the two soft X-ray patches originate from two different loops or systems of loops. For two selected resolution elements of the X-ray pictures a detailed differential emission measure analysis has been carried out and time evolution of the mean electron density and thermal energy content has been investigated. Title: Coronal activity in F-, G-, and K-type stars - Empirical relations between stellar parameters Authors: Mewe, R.; Schrijver, C. J.; Gronenschild, E. H. B. M.; Zwaan, C. Bibcode: 1983IAUS..102..205M Altcode: For a sample of 58 late type stars the authors analyse the relations between the soft X-ray flux density Fx, the Ca II H and K line-core flux density FH+K, and parameters determining the global stellar structure. By analysing the soft X-ray spectra from 15 stars the authors determine the coronal temperatures T and specific emission measures per unit area ζ. They discuss the dependence of T on B-V, Fx and stellar radius R. The diagram of the specific emission measure ζ against the temperature T is interpreted in terms of a coronal model consisting of static loops. Also, a search for time variations in the X-ray flux has been performed. Title: Book reviews Authors: de Jager, C.; Sehnal, L.; Kleczek, Josip; Vanysek, V.; Quenby, J. J.; van Duinen, R. J.; van Gent, R. H.; Kaastra, J. S.; Ringeard, G.; Mewe, R.; Stiller, H.; Wäsch, R.; Wenzel, K. -P.; Vrijer, A.; Ceplecha, Z.; Hellings, P.; Houziaux, L. Bibcode: 1982SSRv...31..453D Altcode: No abstract at ADS Title: X-ray spectrum of Capella and its relation to coronal structure and ultraviolet emission. Authors: Mewe, R.; Gronenschild, E. H. B. M.; Westergaard, N. J.; Heise, J.; Seward, F. D.; Chlebowski, T.; Kuin, N. P. M.; Brinkman, A. C.; Dijkstra, J. H.; Schnopper, H. W. Bibcode: 1982ApJ...260..233M Altcode: The binary system Capella has been observed on 1979 March 15 and on 1980 March 15-17, with the objective grating spectrometer on board the Einstein Observatory. The spectrum measured with the 1000 1/mm grating covers the range 5-30 A with a resolution less than 1 A. The spectra show evidence for a bimodal temperature distribution of emission measure in an optically thin plasma with one component about 5,000,000 K and the other one about 10,000,000 K. Spectral features can be identified with line emissions from O VIII, Fe XVII, Fe XVIII, Fe XXIV, and Ne X ions. Good spectral fits have been obtained assuming standard cosmic abundances. The data are interpreted in terms of emission from hot static coronal loops rather similar to the magnetic arch structures found on the sun. It is shown that the conditions for such a model can exist on Capella. Typical values of loop base pressure and half-length are derived for both temperature components and discussed in relation to UV observations. Title: Einstein Observations of Late-Type Stars of Different Calcium-II Activity Authors: Mewe, R. Bibcode: 1982Obs...102..109M Altcode: No abstract at ADS Title: Calibration and efficiency of the Einstein objective grating spectrometer Authors: Seward, F. D.; Chlebowski, T.; Delvaille, J. P.; Henry, J. P.; Kahn, S. M.; van Speybroeck, L.; Dijkstra, J. H.; Brinkman, A. C.; Heise, J.; Mewe, R.; Schrijver, J. Bibcode: 1982ApOpt..21.2012S Altcode: The Einstein Observatory, a large satellite dedicated to X-ray astronomy, carried the first large X-ray telescope to be placed in orbit and an objective grating spectrometer with two sets of gratings. This paper lists prelaunch calibration results and describes the derivation of spectrometer efficiency and resolution. Several calibration spectra are shown, and theoretical grating parameters are derived from the calibration results. Title: The effects of non-equilibrium ionization on the X-ray emission of supernova remnants Authors: Gronenschild, E. H. B. M.; Mewe, R. Bibcode: 1982A&AS...48..305G Altcode: It is shown that nonequilibrium conditions of the ionization balance in a supernova remnant strongly affect the emergent X-ray spectrum. The continuum emission is enhanced by two-photon decay radiation mainly due to oxygen for wavelengths larger than about 20 A, whereas it is suppressed by the lack of recombination radiation of bare nuclei below about 10 A. The line emission is significantly intensified especially for wavelengths larger than about 10 A where transitions in helium-like and lower ions are dominant. The strength of individual lines departs sometimes by orders of magnitude from the equilibrium prediction even for older remnants, while the soft X-ray luminosity is larger by more than a factor of 10 than in the case where the ionization balance immediately follows the temperature changes. It is shown that a multitemperature component spectrum emerges quite naturally owing to nonequilibrium ionization. Title: Book Review: Invitation of Physics Authors: Pasachoff, J. M.; Kutner, M.; Mewe, R. Bibcode: 1982SSRv...31..457P Altcode: No abstract at ADS Title: Coronal activity in F-, G-, and K-type stars; relations between parameters characterizing stellar structures and X-ray emission Authors: Schrijver, C. J.; Mewe, R.; Zwaan, C. Bibcode: 1982AdSpR...2i.243S Altcode: 1982AdSpR...2..243S A sample of 52 stars containing dwarfs and giants is subjected to a multidimensional factor analysis. The parameters used are the soft X-ray flux at the stellar surface Fx, the Ca II H+K line-core flux FH+K, the stellar radius and mass. We find a high correlation between Fx and the Ca II H+K excess flux ΔFH+K obtained by subtracting an observational lower-limit flux from FH+K. We conclude that the lower-limit Ca II flux is uncorrelated with the stellar X-ray emission. The common-factor analysis shows that, for the present sample, Fx depends only on ΔFH+K, and not on the stellar radius or mass. All stars included in our analysis follow the relation Fx ~ Δ1.4H+K over almost four decades in Fx. Title: Transient Ionization Conditions in Solar Flares. Analysis of High-Resolution X-Ray Spectra. Authors: Schrijver, J.; Mewe, R.; Sylwester, J.; Strong, K. T.; Bentley, R. D. Bibcode: 1982uxsa.collQ...4S Altcode: 1982IAUCo..73Q...4S No abstract at ADS Title: Book Review: X-Ray Astronomy Authors: Giacconi, R.; Mewe, R. Bibcode: 1982SSRv...31..457G Altcode: No abstract at ADS Title: Variability of soft X-ray emission of EX Hydrae observed with Einstein Observatory Authors: Kruszewski, A.; Mewe, R.; Heise, J.; van Dijk, W.; Chlebowski, T.; Bakker, R. Bibcode: 1982ASSL...98..457K Altcode: 1982bmst.proc..457K; 1982IAUCo..69..457K The cataclysmic variable star EX Hydrae has been observed with the High Resolution Imager (HRI) and the Imaging Proportional Counter (IPC) onboard the Einstein Observatory. The X-ray position is coincident within 3 arcsec of the optical position as measured on Schmidt survey plates. During a 15 1/2 hour observation with IPC a search has been made for a modulation of the X-ray flux. Strong evidence for a 67 min period (one of two known optical periods) has been found in the energy range 0.1-3.5 keV with the IPC. The time dependence of modulations is used to discuss a model and evolutionary status of this close binary system. Title: Calculated X-radiation from optically thin plasmas. IV - Atomic data and rate coefficients for spectra in the range 1-270 A. Authors: Mewe, R.; Gronenschild, E. H. B. M. Bibcode: 1981A&AS...45...11M Altcode: Rate coefficients of ionization, recombination, and excitation, used in recent computations of the soft X-ray (1-270 A) spectra of transient optically thin plasmas are discussed in detail. A total of 870 spectral lines containing about 100 satellites to resonance lines in hydrogen- and helium-like ions is considered. These satellite lines are produced by innershell excitation, dielectronic recombination, and innershell ionization, processes that can be extremely sensitive to nonequilibrium effects in the ionization balance. The elements that are included in the calculations are H, He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Fe, and Ni. Some resulting spectra are shown graphically, and the intensities of the emission lines of a stationary plasma are tabulated over the temperature range 10 to the 5th - 10 to the 8th K. The effects on the emergent X-ray spectrum and on the satellite line formation processes deriving from deviations from the ionization equilibrium are illustrated for the model of a transient plasma in which the electron temperature strongly increases with a jump. Title: Results from an extensive Einstein stellar survey. Authors: Vaiana, G. S.; Cassinelli, J. P.; Fabbiano, G.; Giacconi, R.; Golub, L.; Gorenstein, P.; Haisch, B. M.; Harnden, F. R., Jr.; Johnson, H. M.; Linsky, J. L.; Maxson, C. W.; Mewe, R.; Rosner, R.; Seward, F.; Topka, K.; Zwaan, C. Bibcode: 1981ApJ...245..163V Altcode: The preliminary results of the Einstein Observatory stellar X-ray survey are presented. To date, 143 soft X-ray sources have been identified with stellar counterparts, leaving no doubt that stars in general constitute a pervasive class of low-luminosity galactic X-ray sources. Stars along the entire main sequence, of all luminosity classes, pre-main sequence stars as well as very evolved stars have been detected. Early type OB stars have X-ray luminosities in the range 10 to the 31st to 10 to the 34th ergs/s; late type stars show a somewhat lower range of X-ray emission levels, from 10 to the 26th to 10 to the 31st ergs/s. Late type main-sequence stars show little dependence of X-ray emission levels upon stellar effective temperature; similarly, the observations suggest weak, if any, dependence of X-ray luminosity upon effective gravity. Instead, the data show a broad range of emission levels (about three orders of magnitude) throughout the main sequence later than F0. Title: Variability of Soft X-Ray Emission of Ex-Hydrae Observed with Einstein Observatory Authors: Kruszewski, A.; Mewe, R.; Heise, J.; Chlebowski, T.; van Dijk, W.; Bakker, R. Bibcode: 1981SSRv...30..221K Altcode: The cataclysmic variable EX Hydrae has been observed in X-rays with Einstein Observatory. A 67 min periodic X-ray modulation has been found in the energy range. 1 2 keV, whereas the source is approximately constant above 2 keV. The modulation is approx. in phase with the stable 47 min modulation in the optical brightness. The X-ray spectrum changes slightly with the 67 min phase but is consistent with a two component model with constant temperature only changing in relative intensity. Quasi-simultaneous optical observations were also obtained and used to extend the time base of the optical modulation. The result is indicative of a decrease in the 67 min period on a time scale of 3 106 yr. The implications for the hypothesis of a non-uniform rotating white dwarf as the origin of the 67 min optical and X-ray modulation are discussed. Title: Coronal Activity an F-Type G-Type and K-Type Stars Authors: Mewe, R.; Schrijver, C. J.; Zwaan, C. Bibcode: 1981SSRv...30..191M Altcode: Soft X-ray (0.3 3.5 keV) observations with the Imaging Proportional Counter (IPC) onboard Einstein Observatory are presented for a sample of some 20 cool stars of luminosity classes III V. The results are compared with the Ca II H and K emission, which had served as a selection criterion. The specific X-ray flux FX is an increasing function of the specific Ca II H and K line-core flux FH+K. This correlation can be considerably improved by replacing FH+K by the excess flux (ΔFH+K) above a certain lower limit which varies with B-V. This relation holds with little scatter over the two decades in FX in our sample. The FX-ΔFH+K relation shows no significant dependence on spectral type or luminosity class, it suits close binaries as well as single stars. However, the coronal X-ray temperature Tc strongly depends on the luminosity class: Tc≈ 3 106 K for dwarfs and ≈ 107 K for giants. The results are interpreted in the framework of magnetic activity. The X-ray emission and the excess Ca II H and K flux are attributed to magnetic structure in the corona and chromosphere, the magnetic features emerging from the stellar convective envelope, where they are generated by dynamo action. Title: X-Ray Spectroscopic Investigation of the Coronal Structure of Capella Authors: Gronenschild, E. H. B. M.; Mewe, R.; Westergaard, N. J.; Heise, J.; Seward, F. D.; Chlebowski, T.; Kuin, N. P. M.; Brinkman, A. C.; Dijkstra, J. H.; Schnopper, H. W. Bibcode: 1981SSRv...30..185G Altcode: The binary system Capella (G6 III + F9 III) has been observed on 1979 March 15 and on 1980 March 15 17 with the Objective Grating Spectrometer (OGS) onboard the Einstein Observatory. The spectrum measured with the 1000 l/mm grating covers the range 5 30 Å with a resolution < 1 Å. The spectra show evidence for a bimodal temperature distribution of emission measure in an optically thin plasma with one component ∼ 5 million degrees and the other one ∼10 million degrees. Spectral features can be identified with line emissions from O VIII, Fe XVII, Fe XVIII, Fe XXIV, and Ne X ions. Good spectral fits have been obtained assuming standard cosmic abundances. The data are interpreted in terms of emission from hot static coronal loops rather similar to the magnetic arch structures found on the Sun. It is shown that the conditions required by this model exist on Capella. Mean values of loop parameters are derived for both temperature components. Title: Multi-Temperature Analysis of Solar X-Ray Line Emission Authors: Sylwester, J.; Schrijver, J.; Mewe, R. Bibcode: 1980SoPh...67..285S Altcode: In this paper we propose and test a new method of multitemperature analysis of solar X-ray spectra. The method, which is based on a technique developed by Withbroe (1975), is designed to be used in the interpretation of spectra, to be measured by the X-Ray Polychromator on the Solar Maximum Mission. Various tests of the method on simulated temperature models establish its usefulness, generality, and stability. The possibilities of deriving the relative element abundances are analysed. The results of the present paper extend the possibility of the multitemperature analysis of X-ray spectra as compared with the results of Craig and Brown (1976a, b) and Craig (1977). Title: Analysis of X-ray line spectra from a transient plasma under solar flare conditions. I - General outline Authors: Mewe, R.; Schrijver, J. Bibcode: 1980A&A....87..261M Altcode: Complex iron and calcium spectra were computed as a function of time in the wavelength region (1.7 to 3.2 A) observable by the bent crystal spectrometer of the X-ray polychromator in the NASA Solar Maximum Mission. The computations were done on the basis of simple models with temperature-time courses considered as representative of the impulsive and gradual phases of solar flares. Results illustrate changes in the spectra with time and temperature. Title: Heliumlike ion line intensities. IV - Z-dependence of collision strengths for N = 2 - N = 1 transitions in helium- and hydrogenlike ions Authors: Mewe, R.; Schrijver, J.; Sylwester, J. Bibcode: 1980A&A....87...55M Altcode: In earlier work a semi-empirical fit to the electron-excitation collision strengths was obtained for the n = 1 to n = 2 transitions in H- and He-like ions of nuclear charge Z ≳ 14. This work is here extended to incorporate the effects of scaling with Z by a comparison with more recent theoretical data for low Z. Title: Analysis of X-ray line spectra from a transient plasma under solar flare conditions. II - Rate coefficients. III - Diagnostics for measuring electron temperature and density Authors: Mewe, R.; Schrijver, J.; Sylwester, J. Bibcode: 1980A&AS...40..323M Altcode: The rate coefficients for ionization, recombination, excitation, etc., needed for the calculations of high-resolution X-ray line spectra in the wavelength range 1.7-3.2 Å from highly ionized iron and calcium atoms have been presented. Title: Analysis of X-Ray Line Spectra from a Transient Plasma Under Solar Flare Conditions - Part Three - Diagnostics for Measuring Electron Temperature and Density Authors: Sylwester, J.; Mewe, R.; Schrijver, J. Bibcode: 1980A&AS...40..335S Altcode: In this paper, the third in a series dealing with plasmas out of equilibrium we present quantitative methods of analysis of non-stationary flare plasma parameters. The method is designed to be used for the interpretation of the SMM XRP Bent Crystal Spectrometer spectra. Our analysis is based on measurements of 11 specific lines in the 1.77-3.3 Å range. Using the proposed method we are able to derive information about temperature, density, emission measure, and other related parameters of the flare plasma. It is shown that the measurements, to be made by XRP can give detailed information on these parameters and their time evolution. The method is then tested on some artificial flares, and proves to be useful and accurate. Title: Chromospheric and Coronal Activity in F-Type G-Type and K-Type Stars Authors: Mewe, R.; Zwaan, C. Bibcode: 1980SAOSR.389..123M Altcode: 1980csss....1..123M No abstract at ADS Title: Measurements of weak X-ray sources by ANS. Authors: Brinkman, A. C.; den Boggende, A. J. F.; Heise, J.; Mewe, R.; Gronenschild, E. H. B. M.; Schrijver, J.; Parsignault, D.; Grindlay, J. Bibcode: 1980A&A....81..185B Altcode: Data from the Astronomical Netherlands Satellite (ANS) on intensity and in some cases on spectrum and position are reported for 22 weak X-ray sources selected from the 3 U-catalog (Giacconi et al., 1974). Five of them are extragalactic, the remaining 17 presumably galactic due to their location close to the galactic plane. The data includes ANS observing periods and measured intensities, and for some stars, three sigma upper limits of intensity, or spectral parameters derived by a least squares fitting technique using power law and thermal spectrum models. Measurements of intensity of two supernova remnants, Cas A and Tycho, are also presented. Title: Preliminary Results of OGS X-Ray Observations of Capella Authors: Mewe, R.; Gronenschild, E. H. B. M.; Brinkman, A. C.; Dijkstra, J. H.; Schrijver, J.; Heise, J.; Seward, F. D.; Schnopper, H. W.; Delvaille, J. P. Bibcode: 1980SAOSR.389..107M Altcode: 1980csss....1..107M No abstract at ADS Title: The nature of the secondaries in some single-line spectroscopic binaries from X-ray observations. Authors: den Boggende, A. J. F.; Lamers, H. J. G. L. M.; Mewe, R. Bibcode: 1979A&A....80....1D Altcode: The paper presents the results of a search for X-ray emission in the energy regions 0.16-0.284 keV and 1-3.5 keV from a number of single line spectroscopic binaries. In the soft X-ray channel two of the program objects, HR 976 and Pi(5) Ori, gave fluxes corresponding to about 10 to the 30 and 10 to the 32 erg per s, respectively. For the other objects upper limits corresponding to 10 to the 31 - 10 to the 33 erg per s, depending on the object, are reported. On the basis of a stellar wind accretion model, these upper limits are converted into upper limits of mass loss rates of the primary components in the case of the secondary being a normal as well as a compact companion. These values are compared with the known mass loss rates for stars of the same type. From this comparison, the presence of a compact secondary could be excluded in BD+57 deg 2611. Title: Minimum-flux coronal models for hydrogen and helium white dwarf atmospheres. Authors: Lampton, M.; Mewe, R. Bibcode: 1979A&A....78..104L Altcode: Families of zero-mass-loss coronal models based on the minimum-flux prescription of Hearn (1975), in which bound-bound, bound-free, and free-free radiative processes with their differing emissivity vs. temperature laws are included, have been computed. These models are applied to the case of white-dwarf envelopes of pure hydrogen or helium, and the results are expressed as relationships between the required total energy flux, the coronal base pressure, and its temperature. The soft X-ray detection of Sirius by the ANS group is discussed. If all the X-ray flux is ascribed to a minimum-flux hydrogen corona surrounding the white dwarf Sirius B, it must have a temperature of 1.6 + or -0.3 million K and a base pressure of 110,000 + or - 40,000 dyne/sq cm. The surface energy flux needed to heat such a corona is (9 + or - 5) x 10 to the 10th erg/sq cm per sec. Title: Stellar coronae—Evidence for their existence from X- and UV observations Authors: Mewe, R. Bibcode: 1979SSRv...24..101M Altcode: Stellar coronae were among the first predicted X-ray sources. Because of their relatively low X-ray luminosities, however, they have been discovered only during the last few years. In the present paper the current state of stellar coronal X- and UV observations has been reviewed, including some preliminary observational results from the HEAO-1 and IUE satellites, but still without any result from the recently launched X-ray satellite HEAO-2. Late 1978 about two dozens of stellar soft X-ray sources have been detected, e.g., normal stars like the Sun (e.g., α Cen), very active stars (RS CVn systems), and possibly a corona around an intermediately hot white dwarf (Sirius B). The observational results of various objects have been discussed and compared with X-ray luminosity predictions based on minimum-flux coronal models. Title: Book review Authors: Mewe, R. Bibcode: 1979SoPh...62..221M Altcode: 1979SoPh...62..221. No abstract at ADS Title: ANS: evidence for soft X-ray emission from the binary HR 976. Authors: den Boggende, A. J. F.; Mewe, R. Bibcode: 1979xras.proc..193D Altcode: Observations of the region around the single-lined spectroscopic binary HR 976 are reported which were made with the soft (0.16-0.284 keV) and medium-energy (1-8 keV) X-ray detectors aboard ANS. A mass of 1.7 solar masses and a radius of 1.56 solar radii are derived for the Am primary star, and a distance of 53 pc is adopted. A soft X-ray luminosity of (2 + or - 1) x 10 to the 30th erg/s is obtained, along with a 3-sigma upper limit of 1.3 x 10 to the 31st erg/s for the range from 1 to 3.5 keV. The possibility of X-ray emission from a corona around the Am primary is investigated on the basis of the minimum-flux model. It is shown that the soft X-ray observations are consistent with a minimum-flux corona having a temperature of 2 to 3 million K, a base pressure of 5 to 20 dyne/sq cm, and a mechanical flux of 100 million to 1 billion erg/sq cm-sec. Title: A Short-lived Transient X-ray Source at High Galactic Latitude Authors: Schrijver, J.; Brinkman, A. C.; Heise, J.; den Boggende, A. J. F.; Gronenschild, E. H. B. M.; Mewe, R.; Grindlay, J. E.; Parsignault, D. R. Bibcode: 1978A&A....69L...1S Altcode: ABSTRACT A transient X-ray source at galactic latitude S1o, with a duration between 12 5 and 1.5 hour, has been detected by the medium and hard X-ray detectors on board ANS. The source, AN50208+07, was not seen in other observations made in the same region of the sky, nor was it present in sky surveys made by other satellites. No obvious candidates for identification are present in the pcsitional error box. Keywords: X-rays - transient sources. Title: Heliumlike ion line intensities. III. Results. Authors: Mewe, R.; Schrijver, J. Bibcode: 1978A&AS...33..311M Altcode: Line intensities of resonance, forbidden, and intercombination transitions have been deduced from population densities computed for all levels with principal quantum number n = 2 in several heliumlike ions from C V to Ni XXVII as a function of electron temperature and density, external radiation field, and proton and alpha-particle densities. The excitation and deexcitation mechanisms considered in the calculations are identified. Plots are presented which: (1) give the solution for steady-state ionization equilibrium as a function of reduced electron temperature in terms of relative ion densities; (2) show some intensity ratios for the limiting case of zero electron density; (3) give the composite rate coefficients, including those involving cascade effects from higher levels; (4) illustrate the effect of processes connecting the upper levels of forbidden and intercombination lines on the intensity ratio of these lines as a function of the reduced electron density and the blackbody temperature of the external radiation field; and (5) give the dependence of the forbidden/intercombination line intensity ratio on the blackbody temperature of the external radiation field. Title: On the low energy X-ray absorption of the Coma, Virgo and Perseus clusters. Authors: Brinkman, A. C.; den Boggende, A. J. F.; Gronenschild, E. H. B. M.; Heise, J.; Mewe, R.; Schrijver, J. Bibcode: 1978A&A....68..281B Altcode: X-ray data from the soft and medium energy X-ray experiments (0.15-8 keV) on board ANS for the Coma, Perseus and Virgo Clusters are presented. The derived spectral parameters above 2 keV are in general agreement with the Uhuru, Ariel V and OSO-8 data. Due to the availability of a low-energy channel around 0.25 keV, further limits on the low energy absorption have been determined. Title: A soft X-ray source in the vicinity of the Am star HR 976. Authors: den Boggende, A. J. F.; Mewe, R.; Heise, J.; Brinkman, A. C.; Gronenschild, E. H. B. M.; Schrijver, J. Bibcode: 1978A&A....67L..29D Altcode: SUMMARY A region of 34' in diameter around the position of BR976 (= BD20210) was observed with the soft and medium energy X-ray instrument on-board ANS. A 3.Sa signal in the 0.16-0.284 kev interval and an upper limit in the 1-3.5 keV interval was obtained. Tentatively identifying this X-ray source with HR976 (at a distance of about 53 pc) yields an X-ray luminosity of 2.0 (I 1) 1030 erg/s (0.16-0.284 keV) and a 3a-upper limit < 1.3 1031 erg/s (1-3.5 kev). Various X-ray emission mechanisms are considered. If the observations are explained as emission from a corona around the primary of BR976, minimum-f lux calculations indicate coronal temperatures in the range (2-3) 106 K. The energy flux to heat such a corona would be in the range (1-10) l0 erg/cm2.s. Key words: X-rays - Am stars - spectroscopic binaries. Title: Calculated X-radiation from optically thin plasmas. III. Abundance effects on continuum emission. Authors: Gronenschild, E. H. B. M.; Mewe, R. Bibcode: 1978A&AS...32..283G Altcode: The continuum spectrum (wavelength range 1-1000 A, temperature range 100,000 to 10 million deg K) of an optically thin stationary plasma has been calculated. Abundance effects on the free-free, free-bound and two-photon emission have been investigated. Individual effective gaunt factors for both low- and high-density plasmas have been computed for the elements H, C, N, O, Ne, Mg, Si, S, Ca, Fe and Ni, respectively. Title: Evidence of X-ray emission from W44. Authors: Gronenschild, E. H. B. M.; Mewe, R.; Heise, J.; den Boggende, A. J. F.; Schrijver, J.; Brinkman, A. C. Bibcode: 1978A&A....65L...9G Altcode: The Astronomical Netherlands Satellite (ANS) has provided X-ray observations around the supernova remnant W44. X-ray emission with an observed intensity of 8 x 10 to the -11th power erg/sq cm/s (i.e., 1.03-3.5 keV) has been detected from a region which overlaps the radio source. Spectral fits to the pulse-height data and the application of the shock-wave model for the evolution of the signal-to-noise ratio suggest that W44 is the X-ray source. Title: Heliumlike Ion Line Intensities. II Non-stationary Plasmas Authors: Mewe, R.; Schrijver, J. Bibcode: 1978A&A....65..115M Altcode: Summary. The ratio R of the forbidden to intercombination line intensities and the ratio G of the forbidden plus intercombination to resonance line intensities of heliumlike ions have been evaluated as a function of time for two models of time-varying plasmas representative of solar flares. The following effects of processes populating the upper line levels besides direct collisional excitation from the ground state have been fully considered: cascades following collisional excitation of higher levels or radiative and dielectronic recombination, collisional innershell ionization of the lithiumlike ion. In the models considered, it is assumed that the electron density is constant (=10 or 1010 ) and that the electron temperature increases from an initial value % either with a steep jump to a constant high value T1 or a rise linear with time in 60 5 to a maximum value T1 and drops thereafter with an e-folding time of 600 s (% = 20 z4 K, T1 = 3500 Z3 K, Zis nuclear charge number), conditions typical for solar flares. Results for ions of silicon (Z =14) and iron (Z =26) are presented and discussed. By scaling the time inversely as the density the results can be applied also to hot transient laboratory plasmas like those produced in Tokamak, vacuum spark, theta pinch, and laser focus. Key words: heliumlike ions - non-stationary plasmas - line excitation - X-ray spectroscopy Title: Helium-like ion line intensities. I. Stationary plasmas. Authors: Mewe, R.; Schrijver, J. Bibcode: 1978A&A....65...99M Altcode: Consideration is given to heliumlike ion line intensities for both stationary and nonstationary plasmas. For stationary plasmas the population densities of all levels having principal quantum number two in heliumlike ions (CV to Ni XXVII) are studied. Attention is given to several excitation mechanisms and de-excitation mechanisms. For nonstationary plasmas the ratios of forbidden intercombination line intensities and forbidden plus intercombination to resonance line intensities are studied for models representing solar flares. The effects of processes populating the upper line levels are discussed, such as direct collisional excitation of higher levels, radiative recombination, and dielectronic recombination. Results are presented for silicon and iron ions. The study is also applicable to hot transient laboratory plasmas. Title: Detection of both soft and hard X-ray emission from SS Cygni with ANS. Authors: Heise, J.; Mewe, R.; Brinkman, A. C.; Gronenschild, E. H. B. M.; den Boggende, A. J. F.; Schrijver, J.; Parsignault, D. R.; Grindlay, J. E. Bibcode: 1978A&A....63L...1H Altcode: The dwarf nova SS Cygni was observed twice with the X-ray instruments aboard the Astronomical Netherlands Satellite ANS. A soft (0.16-0.284 keV) and a hard (1-7 keV) X-ray signal were detected while SS Cygni was in its quiescent optical state. The discovery of hard X-ray emission suggests that SS Cygni is a source similar to the AM Her/3U 1809+50 system. Title: X-ray observations with the Astronomical Netherlands Satellite ANS Authors: Heise, J.; Brinkman, A. C.; Mewe, R.; den Boggende, A. J. F.; Gronenschild, E. H. B. M.; Schrijver, J. Bibcode: 1978pans.proc..774H Altcode: Data obtained by the Astronomical Netherlands Satellite are reported and discussed. The satellite carries a soft X-ray telescope (0.2-0.28 keV), a medium X-ray proportional counter (0.4-7 keV), a hard X-ray proportional counter (1.4-30 keV), and an ultraviolet spectrophotometer in 5 bands of approximately 100 A between 1500-3300 A. Topics discussed include star coronas, dwarf novas, flare stars, and compact stars (in particular Cyg X-1). Title: ANS: X-rays from the direction of the Orion Nebula (M42). Authors: den Boggende, A. J. F.; Mewe, R.; Gronenschild, E. H. B. M.; Heise, J.; Grindlay, J. E. Bibcode: 1978A&A....62....1D Altcode: It is found that X-ray emission of 3U 0527-05, measured by the Astronomical Netherlands Satellite, comes from the direction of the Orion Nebula M42 ( NGC 1976). The mean flux at earth is 1.0 (plus or minus 4) x 10 to the -10th (1.3-7 keV) or 1.5 (plus or minus 0.3) x 10 to the -10th (1-8 keV) erg/sq cm and the corresponding intrinsic X-ray luminosity is about 3.8 (plus or minus 0.8) x 10 to the 33rd erg/s (1-8 keV), assuming a distance to the nebula of 460 pc and a hydrogen column density of less that 3 x 10 to the 21st atoms/sq cm. None of the candidate objects proposed earlier as a possible X-ray source - Theta(2) Ori A, Theta(1) Ori B BM Ori and Theta(1) Ori C - show clear evidence for emitting X-rays. The observed X-ray signal may be explained, however, as emission from coronas around T Tauri stars within the nebula. Title: Oscillator strength interpolation formulae for transitions to the ground state within isoelectronic sequences of hydrogen through aluminum. Authors: Mewe, R. Bibcode: 1977A&A....59..275M Altcode: Summary. Absorption oscillator strengths of electric dipole transitions to the ground state in H- to Al-like atoms or ions are approximated within a -i isoelectronic sequence by semi-empirical non-relativistic 1/Z expansions with no more than three terms. These simple analytic expressions are appropriate for the use in subroutines of programs computing XUV line intensities from hot optically thin plasmas. Key words: oscillator strengths atomic physics XUV-radiation Title: The corona around the white dwarf Sirius B determined from X-ray measurements. Authors: Hearn, A. G.; Mewe, R. Bibcode: 1976A&A....50..319H Altcode: Summary. The X-ray measurements from Sirius are explained as emission from a corona around the white dwarf Sirius B. Minimum flux calculations suggest that the corona has a temperature of 3.3 106 0K and a base pressure of 1.3 10 dyn . The energy needed to heat the corona is estimated at 8 1011 erg 1 This is consistent with the acoustic flux calculated with the assumption that Sirius B has a helium convection zone. This would mean that the hydrogen rich envelope is very thin and perhaps supports the suggestion that it is formed by accretion. Key words: stellar coronae X-rays white dwarfs Title: A Search for Soft X-Ray Radiation from Pulsars with the Astronomical Netherlands Satellite Authors: Schrijver, J.; Heise, J.; Brinkman, A. C.; Gronenschild, E. H. B. M.; Mewe, R.; den Boggende, A. J. F. Bibcode: 1976Ap&SS..42..205S Altcode: We present the results of a search for X-ray emission in the energy range 0.2 0.28 keV and 1 7 keV from a number of radio pulsars, including Crab, Vela and the binary pulsar PSR 1913+16, using the soft X-ray experiment aboard ANS. Except for the Crab no pulsed flux has been found. From the Vela pulsar we have detected continuous flux in agreement with earlier observations. Upper limits are given. Title: Interpretation of X-ray Observations with ANS on Sirius Authors: Mewe, R. Bibcode: 1976BAAS....8..454M Altcode: No abstract at ADS Title: ANS Observations of Cygnus X-1 Authors: Parsignault, D. R.; Epstein, A.; Grindlay, J.; Schreier, E.; Schnopper, H.; Gursky, H.; Tanaka, Y.; Brinkman, A. C.; Heise, J.; Schrijver, J.; Mewe, R.; Gronenschild, E.; den Boggende, A. Bibcode: 1976Ap&SS..42..175P Altcode: Cygnus X-1 was observed from 3 November until 9 November, 1974, using the hard X-ray (1 28 keV) and soft X-ray (1 8 keV) experiment on board the Astronomical Netherlands Satellite. On three occasions, on 4 and 5 November, the X-ray spectrum was observed to be harder, while the flux intensity in the 1 7 keV ranges decreased by ∼50% from its quiescent value. These events occurred near and following the time of superior conjunction of the likely optical counterpart HDE 226 868. These events appear to be the same as previously reported absorption dips and reveal this phenomenon to be more complex than had been believed. A systematic study of the X-ray spectral variations in these energy bands, on a time scale of 64 seconds over the period of the spectroscopic binary, is presented. Title: A Search for Soft X-Ray Emission from Stellar Sources Authors: Mewe, R.; Heise, J.; Gronenschild, E. H. B. M.; Brinkman, A. C.; Schrijver, J.; den Boggende, A. J. F. Bibcode: 1976Ap&SS..42..217M Altcode: With the soft X-ray detector (∼0.2 0.284 keV) aboard the Astronomical Netherlands Satellite (ANS) we have searched for X-ray emission from hot star coronae and peculiar stars. On Sirius (α CMa) and Capella (α Aur) X-ray emission has been measured at 6σ and 5σ level, respectively, above background. In all other cases the search revealed no evidence for soft X-ray emission. Upper limits to the luminosities of about 25 star coronae (main-sequence stars, (sub)giants, and supergiants) and of 4 peculiar stars (λ Sco, β Lyr, P Cyg, and η Car) have been obtained. Title: Spectral and Intensity Variations in Cygnus X-3 by the Astronomical Netherlands Satellite Authors: Brinkman, A. C.; Heise, J.; Mewe, R.; den Boggende, A. J. F.; Schrijver, J.; Gronenschild, E.; Tanaka, Y.; Parsignault, D. R.; Grindlay, J.; Schreier, E.; Schnopper, H.; Gursky, H. Bibcode: 1976Ap&SS..42..201B Altcode: Measurements obtained with the Utrecht (1 8 keV) and Cambridge (1 28 keV) instruments on board the Astronomical Netherlands Satellite are discussed. Particularly, the 4.8 hr period is investigated. Title: Preliminary X-ray Map of the Cygnus Loop by ANS Authors: Gronenschild, E. H. B. M.; Mewe, R.; Heise, J.; Brinkman, A. C.; den Boggende, A. J. F.; Schryver, J. Bibcode: 1976BAAS....8Q.449G Altcode: No abstract at ADS Title: ANS: preliminary X-ray brightness map of the Cygnus Loop. Authors: Gronenschild, E. H. B. M.; Mewe, R.; Heise, J.; Brinkman, A. C.; den Boggende, A. J. F.; Schrijver, J. Bibcode: 1976A&A....49..153G Altcode: With the X-ray detectors on the Astronomical Netherlands Satellite (ANS) the Cygnus Loop has been observed in a sequence of nearly 200 pointings. A preliminary brightness map in the energy band 0.16-0.284 keV is presented. Provisional data of photon energy fluxes and electron temperatures are given for the bright regions in the north and northeast filaments and for the central region. Title: Book reviews Authors: de Jager, C.; van Rensbergen, Walter; Kuperus, M.; Falthammar, Carl-Gunne; Mewe, R.; Reunen, G. C. M.; Bruzek, A.; Swanenburg, B. N.; Kleczek, J.; Millman, Peter M.; Vesseur, H. J. A.; Pacini, F.; Monfils, A. Bibcode: 1976SSRv...18..541D Altcode: No abstract at ADS Title: Measurements of A 0620-00 with ANS. Authors: Brinkman, A. C.; Heise, J.; den Boggende, A. J. F.; Mewe, R.; Gronenschild, E.; Schrijver, H. Bibcode: 1976NASSP.389..349B Altcode: 1976NASSP.589..349B No abstract at ADS Title: Observations of Cygnus X-3 by ANS. Authors: Brinkman, A. C.; Heise, J.; den Boggende, A. J. F.; Mewe, R.; Gronenschild, E.; Schrijver, H. Bibcode: 1976NASSP.389..241B Altcode: 1976NASSP.589..241B No abstract at ADS Title: ANS ontdekte röntgenstraling van Sirius. Authors: Mewe, R. Bibcode: 1976Zenit...3..328M Altcode: No abstract at ADS Title: Results of observations with the Utrecht X-ray experiment on the ANS (Astronomical Netherlands Satellite). Authors: Mewe, R. Bibcode: 1976NTNA...42..126M Altcode: No abstract at ADS Title: Evidence for X-ray emission from flare stars observed by ANS. Authors: Heise, J.; Brinkman, A. C.; Schrijver, J.; Mewe, R.; Gronenschild, E. H. B. M.; den Boggende, A. J. F.; Grindlay, J. Bibcode: 1975ApJ...202L..73H Altcode: Observations that detected the first X-ray emission from flare stars are described. An X-ray flare was detected from YZ CMi at 0.28 keV and approximately 1-7 keV, although no optical or radio coverage was available. During a very large optical flare from UV Ceti, X-ray emission at (only) 0.28 keV was detected. Upper limits for X-ray emission from several small optical flares of UV Ceti are presented. Implications for X-ray flare models, the diffuse X-ray background, and low-energy cosmic-ray flux are mentioned. Title: Detection of X-ray emission from stellar coronae with ANS. Authors: Mewe, R.; Heise, J.; Gronenschild, E. H. B. M.; Brinkman, A. C.; Schrijver, J.; den Boggende, A. J. F. Bibcode: 1975ApJ...202L..67M Altcode: The soft X-ray detector aboard the Astronomical Netherlands Satellite (ANS) has been used to search for soft X-ray emission in the range 0.2 to 0.284 keV from hot stellar coronae. X-ray emission has been detected from Capella (alpha Aur) and Sirius (alpha CMa). For 26 other stars (main sequence, subgiants, giants, and supergiants) upper limits to the X-ray luminosity have been obtained. The physical conditions of a corona needed to explain the observations are discussed. Title: Computed n=2 Level Populations in Helium-Like Ions from C V to NI XXVII Authors: Mewe, R.; Schrijver, J. Bibcode: 1975Ap&SS..38..345M Altcode: 1975IAUCo..27..345M The population densities of all levels with principal quantum numbern=2 in a number of helium-like ions with nuclear charge numberZ, in the range 6 to 28 have been evaluated as a function of various parameters, i.e., electron temperature,T e, electron density,N e, radiation temperature,T r, dilution factor,W, and of the state of ionization. The spectral line fluxes from all possible radiative transitions from these levels have been calculated for an optically thin plasma. The effects of cascades following collisional excitation of higher levels or radiative and dielectronic recombination have been computed in detail. Innershell ionization of the lithium-like ion to form the helium-like ion in a 23 S or 21 S state has been considered. It can have a strong influence on the forbidden line intensity in a non-equilibrium plasma. Collisional and radiative coupling of levels of the same multiplicity (e.g. 23 S 1 and 23 P 2,1,0) have been considered as a function ofT e, Ne orT r, W, respectively. The computations were performed both for stationary and time-varying plasmas. In the latter case strong departures from a stationary ionization equilibrium can significantly alter the line fluxes. A few examples of the results are shown and discussed. Title: Calculated Solar X-Radiation. II: Spectrum between 61 and 220 &Aring 383 Authors: Mewe, R. Bibcode: 1975SoPh...44..383M Altcode: Earlier calculations on the solar X-ray spectrum between 1 and 61 å have now been extended by the addition of the intensities of about 90 spectral lines up to 220 å from ions of the elements O, Ne, Mg, Si, S, Fe, and Ni for electron temperatures between 105 and 1.5 × 107K. The continuum emission has been calculated in the temperature range 105-108K for the wavelength region 40-220 å. Title: Soft X rays from Sirius Authors: Mewe, R.; Heise, J.; Gronenschild, E. H. B. M.; Brinkman, A. C.; Schrijver, J.; den Boggende, A. J. F. Bibcode: 1975Natur.256..711M Altcode: ON April 3, 4 and 5, 1975 the star Sirius (α CMa) was observed with the soft X-ray detector aboard the Astronomical Netherlands Satellite (ANS). The instrument consists of a parabolic collecting mirror which has at its focus a proportional counter with a 3.6-µm polypropylene window. It responds to X rays in the photon energy range 0.284-~ 0.2 keV. The projected area is 144 cm2 which, allowing for reflectivity, counter efficiency and so on, leads to a sensitive area of about 25 cm2 at the carbon absorption edge (0.284 keV). The field of view is 34' FWHM circular. Further instrumental details are given in refs 1ndash;3. Title: X-ray observations of CYG X-1 with ANS Authors: Heise, J.; Mewe, R.; Brinkman, A. C.; den Boggende, A.; Schrijver, J.; Gronenschild, E.; Parsignault, D.; Grindlay, J.; Schreier, E.; Schnopper, H. Bibcode: 1975Natur.256..107H Altcode: The equipment, method and results of the measurements performed with soft and hard X-ray detectors of the Space Research Laboratory in Utrecht and the Center for Astrophysics in Cambridge, Mass., are described. Cyg X-1 underwent an upward transition in its intensity, that seems to be the inverse of the downward transition seen by Uhuru in April 1971. The bulk of the increase, as observed by the Astronomical Netherlands Satellite instruments, from May 1 to May 8, 1975, occurs at low energy: between 1 and 2 keV, the intensity increased by a factor of 10 over the November 1974 intensity, while above 8 keV there is no significant change. The data suggest that Cyg X-1 has reverted to its high state. Title: Cygnus X-1. Authors: Wu, C. C.; Wesselius, P. R.; van Duinen, R. J.; de Boer, K. S.; Aalders, J. W. G.; Heise, J.; Brinkman, A. C.; Mewe, R.; Schrijver, J.; den Boggende, A. G. F.; Gronenschild, E.; Hjellming, R. M.; Gibson, D. M.; Owen, F. N.; Bolton, C. T. Bibcode: 1975IAUC.2779....1W Altcode: No abstract at ADS Title: X-ray sources. Authors: Gursky, H.; Grindlay, J.; Schnopper, H.; Schreier, E.; Parsignault, D.; Brinkman, A. C.; Heise, J.; Schrijver, J.; Mewe, R.; Gronenschild, E.; den Boggende, A.; Chevalier, C.; Ilovaisky, S. A. Bibcode: 1975IAUC.2778....1G Altcode: No abstract at ADS Title: X-ray flare from YZ Canis Minoris. Authors: Heise, J.; Brinkman, A. C.; Schrijver, J.; Mewe, R.; Groneschild, E.; den Boggende, A.; Grindlay, J.; Schnopper, H.; Schreier, E.; Gursky, H.; Parsignault, D. Bibcode: 1974IAUC.2731....1H Altcode: No abstract at ADS Title: Calculations on the Solar Spectrum from 1 TO 60 Å Authors: Mewe, R. Bibcode: 1972SSRv...13..666M Altcode: 1972IAUCo..14..666M No abstract at ADS Title: Interpolation Formulae for the Electron Impact Excitation of Ions in the H-, He-, Li-, and Ne- Sequences Authors: Mewe, R. Bibcode: 1972A&A....20..215M Altcode: Summary. The cross sections for electron impact excitation from the ground state of H-, He-, Li-, and Nelike ions are approximated by interpolation formulae with four parameters that can be integrated analytically over a maxwellian electron velocity distribution to give the corresponding rate coefficients. The formulae are fitted to the available theoretical and observational data about excitation cross sections and rate coefficients. Key words: cross section - atomic physics - solar corona - X-ray radiation Title: Calculated Solar X-Radiation from 1 to 60 Å Authors: Mewe, R. Bibcode: 1972SoPh...22..459M Altcode: The fluxes of about 230 spectral lines in the range 1-60 Å from coronal ions of C, N, O, Ne, Na, Mg, Al, Si, S, Ar, K, Ca, Ti, Cr, Mn, Fe, and Ni are computed for a range of electron temperature from 105 to 109 K. The relative ion abundances are derived from Jordan's ionization equilibrium calculations. The continuum emission is derived from computations of Landini and Monsignori Fossi with a correction for the free-free emission. Title: Note on the Helium-Like Ion Line Emission in Solar Plasmas Authors: Mewe, R. Bibcode: 1972SoPh...22..114M Altcode: An analysis is presented of the rate coefficients occurring in the Gabriel-Jordan theory on the relative intensities of the forbidden, intercombination, and resonance lines of helium-like ions in a steady-state plasma. Simple expressions are given to show the dependence on atomic number and electron temperature. The influence of proton collisions on the excitation 23S→23P is estimated and deviations from the theory under non-equilibrium conditions are briefly discussed. Title: Book reviews Authors: Veldkamp, J.; Kovalevesky, J.; Plaut, L.; Bondi, H.; Mewe, R.; de Jager, C. Bibcode: 1969SSRv....9..872V Altcode: No abstract at ADS