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Author name code: mewe
ADS astronomy entries on 2022-09-14
author:"Mewe, Rolf"
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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.
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
(γ<SUP>2</SUP> 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.
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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.
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 L<SUB>x</SUB> = 10 × 10<SUP>30</SUP> erg s<SUP>-1</SUP> 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.
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Title: Rolf Mewe: a career devoted to X-ray spectroscopy
Authors: Kaastra, Jelle S.; Mewe, Rolf
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.
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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.
2005A&A...431..679M Altcode: 2004astro.ph.10592M
We present simultaneous ultraviolet and X-ray observations of
the dMe-type flaring stars <ASTROBJ>AT Mic</ASTROBJ>, <ASTROBJ>AU
Mic</ASTROBJ>, <ASTROBJ>EV Lac</ASTROBJ>, <ASTROBJ>UV Cet</ASTROBJ>
and <ASTROBJ>YZ CMi</ASTROBJ> 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.
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Title: New Results on X-ray Models and Atomic Data
Authors: Kaastra, Jelle S.; Mewe, Rolf; Raassen, Ton
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.
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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.
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.
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Title: Wind clumping and the wind-wind collision zone in the
Wolf-Rayet binary γ<SUP>2</SUP> 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.
2004A&A...422..177S Altcode: 2004astro.ph..4610S
We present XMM-Newton observations of γ<SUP>2</SUP> 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<SUP>-6</SUP> M<SUB>⊙</SUB> yr<SUP>-1</SUP>
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. <P />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).
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Title: XMM-Newton X-ray observations of γ<SUP>2</SUP> 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.
2004NuPhS.132..697R Altcode:
The spectrum of the binary system γ<SUP>2</SUP> 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.
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Title: X-ray Emission from Young Stars in Suburban Orion
Authors: Briggs, K.; Güdel, M.; Audard, M.; Smith, K.; Mewe, R.;
den Boggende, T.
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.
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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.
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.
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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
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.
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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.
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.
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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.
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 10<SUP>51</SUP> cm<SUP>-3</SUP>
for the quiescent state and ~ 19.5 x 10<SUP>51</SUP> cm<SUP>-3</SUP>
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. <P />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).
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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.
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.
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Title: <ASTROBJ>AD Leonis</ASTROBJ>: 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.
2003A&A...411..587V Altcode: 2003astro.ph..9315V; 2003astro.ph..9315B
The M-dwarf <ASTROBJ>AD Leonis</ASTROBJ> 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 <ASTROBJ>AD
Leo</ASTROBJ> 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 <ASTROBJ>AD Leo</ASTROBJ>.
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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.
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 (1s<SUP>2</SUP>
<SUP>1</SUP>S<SUB>0</SUB> - 1s2p <SUP>1</SUP>P<SUB>1</SUB>),
intercombination i (1s<SUP>2</SUP> <SUP>1</SUP>S<SUB>0</SUB> -
1s2p <SUP>3</SUP>P<SUB>2,1</SUB>), and forbidden f (1s<SUP>2</SUP>
<SUP>1</SUP>{S}<SUB>0</SUB> - 1s2s <SUP>3</SUP>{S}<SUB>1</SUB>)
“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).
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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.
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 <SUP>3</SUP>S<SUB>1</SUB> rightarrow
1s<SUP>2</SUP> <SUP>1</SUP>S<SUB>0</SUB>), disappears at high densities,
and the intercombination line i (1s2p <SUP>3</SUP>P<SUB>2,1</SUB>
rightarrow 1s<SUP>2</SUP>1<SUP>S</SUP><SUB>0</SUB>) 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
<SUP>3</SUP>S<SUB>1</SUB> rightarrow 1s2p <SUP>3</SUP>P<SUB>2,1</SUB>)
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.
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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.
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.
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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.
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), <P />and α Cen (K1V)) the temperatures
are in the regime of 1-2 MK. The emission measure for Procyon is about
1× 10<SUP>50</SUP> cm<SUP>-3</SUP> and for both components of α Cen
about 8 × 10<SUP>48</SUP> cm<SUP>-3</SUP>. 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.
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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.
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.
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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.
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 L<SUB>x</SUB> (0.3-10 keV) = 3.2 × 1031 ergs <SUP>-1</SUP>
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
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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.
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.
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.
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 <SUP>9</SUP>
cm <SUP>-3</SUP>. However, in the case of flares four and five, O VII
line ratios appear to indicate the density has increased to 2.0×10
<SUP>10</SUP> and 1.0-1.6×10 <SUP>10</SUP>cm <SUP>-3</SUP>.
---------------------------------------------------------
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.
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.
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.
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 N<SUB>H</SUB> =
7 x 10<SUP>21</SUP> cm<SUP>-2</SUP>. 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 L<SUB>x</SUB>(0.5-10 keV) = 1.3 x 10<SUP>34</SUP> erg
s<SUP>-1</SUP>, and L<SUB>x</SUB>(0.5-10 keV) = 0.85 x 10<SUP>34</SUP>
erg s<SUP>-1</SUP>, (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. <P
/>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: <ASTROBJ>alpha Coronae
Borealis</ASTROBJ>
Authors: Güdel, M.; Arzner, K.; Audard, M.; Mewe, R.
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 <ASTROBJ>alpha Coronae
Borealis</ASTROBJ>. 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 10<SUP>9</SUP>-3x
10<SUP>10</SUP> cm<SUP>-3</SUP>. <P />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.
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.
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 L<SUB>X</SUB> ≈ 32.16 - 32.42). We derive the
coronal emission measure distribution, elemental abundances, and
density estimates. <P />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.
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 cm<SUP>2</SUP> 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.
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. <P />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
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.
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 L<SUB>x</SUB> =
3.2 x 10<SUP>31</SUP> erg s<SUP>-1</SUP> 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<SUP>-1</SUP>) than the broad lines (up to 1500 km s<SUP>-1</SUP>)
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<SUP>-1</SUP>). Such an interaction would produce the strong shocks
required. <P />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.
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 <SUP>11</SUP> cm <SUP>-3</SUP>) 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 <SUP>12</SUP>
cm <SUP>-3</SUP>) 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.
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.
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.
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.
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.
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.
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.
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.
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.
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 Ly<SUB>alpha</SUB>
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*E<SUP>10</SUP>
cm<SUP>-3</SUP> 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.
2002ApJ...578..648L Altcode:
We report on emission spectra of iron in the extreme ultraviolet
recorded at an electron density of ~5×10<SUP>11</SUP> cm<SUP>-3</SUP>
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.
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 kT<SUB>e</SUB> = 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
kT<SUB>e</SUB> = 0.65 keV component, which dominates the emission
measure (4.5*E<SUP>65</SUP> m<SUP>-3</SUP>), 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
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.
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 10<SUP>50</SUP> cm<SUP>-3</SUP> 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
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.
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 10<SUP>11</SUP> cm<SUP>-3</SUP> 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 10<SUP>10</SUP> cm<SUP>-3</SUP> 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 10<SUP>12</SUP>
cm<SUP>-3</SUP>. 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.
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.
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.
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.
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.
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.
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.
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.
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
2<SUP>3</SUP>S (upper level of the forbidden line) and 2<SUP>3</SUP>P
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.
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 (n<SUB>e</SUB>), temperature (T<SUB>e</SUB>),
dilution factor (W), radiation temperature (T<SUB>rad</SUB>), 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.
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 10<SUP>7</SUP> 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.
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.
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 (n<SUB>e</SUB>)
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 n<SUB>e</SUB> in the range 10<SUP>9</SUP>-10<SUP>13</SUP>
cm<SUP>-3</SUP>. 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
n<SUB>e</SUB> <~ (2-5) 10<SUP>12</SUP> cm<SUP>-3</SUP>. 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 n<SUB>e</SUB> 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.
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<SUP>-3</SUP> for O vii (2sigma upper limit) (f/i=4.0+/- 0.25),
9.86+/-0.12 cm<SUP>-3</SUP> for N vi (f/i=1.78+/- 0.25), and 9.42+/-
0.21 cm<SUP>-3</SUP> for C v (f/i=1.48+/- 0.34), while for Procyon we
obtain 9.28<SUP>+0.4</SUP><SUB>-9.28</SUB> cm<SUP>-3</SUP> for O vii
(f/i=3.28+/- 0.3), 9.96+/- 0.23 cm<SUP>-3</SUP> for N vi (f/i=1.33+/-
0.28), and <8.92 cm<SUP>-3</SUP> 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 ~ 10<SUP>6</SUP> 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.
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 (n<SUB>e</SUB>
<1 10<SUP>10</SUP> cm<SUP>-3</SUP>). 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.
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.
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<SUP>-1</SUP>. 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.
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.
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.
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.
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.
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.
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.
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
cm<SUP>2</SUP> 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.
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 <ASTROBJ>AB Doradus</ASTROBJ>
Authors: Güdel, M.; Audard, M.; Briggs, K.; Haberl, F.; Magee, H.;
Maggio, A.; Mewe, R.; Pallavicini, R.; Pye, J.
2001A&A...365L.336G Altcode:
We report results of deep X-ray observations of <ASTROBJ>AB
Doradus</ASTROBJ> 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. <ASTROBJ>AB Dor</ASTROBJ> 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 10<SUP>10</SUP>
cm<SUP>-3</SUP>; 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 10<SUP>10</SUP> 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 <ASTROBJ>Castor</ASTROBJ> X-ray triplet
Authors: Güdel, M.; Audard, M.; Magee, H.; Franciosini, E.; Grosso,
N.; Cordova, F. A.; Pallavicini, R.; Mewe, R.
2001A&A...365L.344G Altcode:
We present results of a comprehensive X-ray investigation of the
multiple stellar system <ASTROBJ>Castor</ASTROBJ> AB + <ASTROBJ>YY
Gem</ASTROBJ>. The observations were obtained with the XMM-Newton
observatory. We report the first spatially separated detection
and identification of both <ASTROBJ>Castor</ASTROBJ> A and B as
frequently flaring X-ray sources. Spectral modeling of the <ASTROBJ>YY
Gem</ASTROBJ> and <ASTROBJ>Castor</ASTROBJ> 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 10<SUP>10</SUP> cm<SUP>-3</SUP> for <ASTROBJ>YY Gem</ASTROBJ>
and <ASTROBJ>Castor</ASTROBJ>. The <ASTROBJ>YY Gem</ASTROBJ> 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.
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
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.
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
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.
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<SUP>'</SUP>) 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.
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.
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.
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
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.
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<SUP>”</SUP>, 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.
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.
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.
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 10<SUP>10</SUP> {cm}<SUP>-3</SUP>. 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
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 cm<SUP>2</SUP> 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.
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.
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<SUP>-13</SUP>
erg s<SUP>-1</SUP> cm<SUP>-2</SUP>, 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 10<SUP>43</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP>,
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.
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 10<SUP>13</SUP>cm<SUP>-3</SUP>. 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.
2000A&A...355..681C Altcode: 1999astro.ph.11352C
<ASTROBJ>II Peg</ASTROBJ> 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 <ASTROBJ>II Peg</ASTROBJ>. 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 <ASTROBJ>II
Peg</ASTROBJ> 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.
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.
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 10<SUP>16</SUP>
m<SUP>-3</SUP>.
---------------------------------------------------------
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.
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.
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.
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.
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.
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/n<SUP>2</SUP>), the highly
excited electron has a small orbital velocity (∝1/n), the radius
(∝n<SUP>2</SUP>) is very large, the excited electron has a long
orbital period (∝n<SUP>3</SUP>), and the radiation lifetime is
very long (∝n<SUP>3-5</SUP>). 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, ∼10<SUP>6</SUP>
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.
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.
1999ASPC..158..235P Altcode: 1999ssa..conf..235P
No abstract at ADS
---------------------------------------------------------
Title: Atomic Physics of Hot Plasmas
Authors: Mewe, R.
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.
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.
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.
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
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
1997xisc.conf..573W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray Spectroscopy of Stellar Coronae: History - Present
- Future
Authors: Mewe, Rolf
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.
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
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.
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.
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.
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 cm<SUP>2</SUP> 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 cm<SUP>2</SUP> at 12 Å for both
modules). The instruments are co-aligned and measure simultaneously with
an optical monitor (1800-10000 Å, limiting magnitude 24<SUP>m</SUP>5,
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.
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.
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.
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.
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.
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.
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.
1996uxsa.conf..229M Altcode: 1996uxsa.coll..229M
The ESA X-ray Multi-Mirror (XMM) mission comprises three high-throughput
(≡4000 cm<SUP>2</SUP> 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.
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.
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.
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.
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.
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.
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.
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.
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.
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 10<SUP>4</SUP> K
up to roughly 2 × 10<SUP>7</SUP> 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 × 10<SUP>6</SUP> and 2
× 10<SUP>7</SUP> K, which may show a substructure with two components
around 3 × 10<SUP>6</SUP> and 10<SUP>7</SUP> K; (2) very little
emission from plasma between 10<SUP>5</SUP> and 2 × 10<SUP>6</SUP> K;
and (3) emission from plasma below about 10<SUP>5</SUP> 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 × 10<SUP>7</SUP> 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 N<SUB>H</SUB> = (2.4±0.5) × 10<SUP>18</SUP>
cm<SUP>-2</SUP>.
---------------------------------------------------------
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1993SSRv...65..183H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar Coronal X-ray Spectroscopy
Authors: Mewe, R.
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.
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.
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.
1992SSRv...59..207Z Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray spectroscopy of solar & stellar coronae.
Authors: Mewe, R.
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.
1992SSRv...59..205I Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modelling of high-temperature plasmas (review)
Authors: Mewe, R.
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.
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.
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.
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.
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.
1990SoPh..126..411M Altcode: 1990SoPh..126..411S
No abstract at ADS
---------------------------------------------------------
Title: Ionization of Hot Plasmas
Authors: Mewe, R.
1990ASIC..305...39M Altcode: 1990pphc.conf...39M
The processes of ionization and recombination in hot (T ⪆
10<SUP>5</SUP>K) 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.
1990AdSpR..10b.129M Altcode: 1990AdSpR..10..129M
We observed the late-type stars Capella, σ<SUP>2</SUP> 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 σ<SUP>2</SUP> 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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, T<SUB>HXIS</SUB>>T<SUB>Fe</SUB>, 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.
1988als..conf..141M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Satellite Lines as a Diagnostic
Authors: Mewe, R.
1988als..conf..167M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Recombination Rate Coefficients
Authors: Mewe, R.
1988als..conf..155M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ionisation Balance in Low Density Plasmas Steady State and
Transient Case
Authors: Mewe, R.
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.
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.
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.
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.
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.
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 σ<SUP>2</SUP> Coronae Borealis Observed
with EXOSAT
Authors: van den Oord, G. H. J.; Mewe, R.; Brinkman, A. C.
1987LNP...291..494V Altcode: 1987LNP87.291..494V; 1987csss....5..494V
We report the observation of a compact flare on σ<SUP>2</SUP>
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.
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.
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.
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 (T<SUB>m</SUB>, N)-diagram, where T<SUB>m</SUB> 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 (T<SUB>m</SUB>, 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.
1986LNP...254..297M Altcode: 1986csss....4..297M
No abstract at ADS
---------------------------------------------------------
Title: Differential emission measure distributions of Capella and
σ<SUP>2</SUP> CrB
Authors: Mewe, R.; Schrijver, C. J.; Lemen, J. R.; Bentley, R. D.
1986AdSpR...6h.133M Altcode: 1986AdSpR...6..133M
The active late-type stars Capella (α Aur G6III+F9III) and
σ<SUP>2</SUP> 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.
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
(T<SUB>m</SUB>, N)-diagram, where T<SUB>m</SUB> 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 (T<SUB>m</SUB>, N)-diagram. The diagnostics
allows us to determine the time evolution of the flare heating function,
E<SUB>H</SUB>(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 σ<SUP>2</SUP> Coronae
Borealis
Authors: Schrijver, C. J.; Mewe, R.
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.
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.
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.
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.
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.
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.
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.
1985AdSpR...5c..65B Altcode: 1985AdSpR...5Q..65B
The RS CVn stars Capella and σ<SUP>2</SUP> 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 σ<SUP>2</SUP> 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 σ<SUP>2</SUP> 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.
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.
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.<SUP>1</SUP>. 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.
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.
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.
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<SUP>-1</SUP>) and blue shifted (≡
60±20 km s<SUP>-1</SUP>) 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 ×
10<SUP>6</SUP> K) and tenuous (4 × 10<SUP>9</SUP> cm<SUP>-3</SUP>),
but owing to the residual effects of the first flare the coronal plasma
was hotter (5 × 10<SUP>6</SUP> K) and more dense (3 × 10<SUP>11</SUP>
cm<SUP>-3</SUP>) 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.
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.
1984SSRv...37..399O Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book reviews
Authors: Fárník, František; Mewe, R.
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.
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.
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. <P />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.
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.
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.
1984SSRv...38..181D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Soft X-Ray Spectroscopy with EXOSAT (invited Paper)
Authors: Mewe, R.
1984uxsa.coll...59M Altcode: 1984uxsa.conf...59M; 1984IAUCo..86...59M
No abstract at ADS
---------------------------------------------------------
Title: Hot optically thin plasmas in astrophysics.
Authors: Mewe, R.
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.
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.
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 10<SUP>11</SUP>cm<SUP>-3</SUP>. 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.
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.
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.
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.
1983IAUS..102..205M Altcode:
For a sample of 58 late type stars the authors analyse the relations
between the soft X-ray flux density F<SUB>x</SUB>, the Ca II H and
K line-core flux density F<SUB>H+K</SUB>, 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, F<SUB>x</SUB> 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.
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.
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.
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.
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.
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.
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.
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 F<SUB>x</SUB>, the Ca II H+K
line-core flux F<SUB>H+K</SUB>, the stellar radius and mass. We find
a high correlation between F<SUB>x</SUB> and the Ca II H+K excess flux
ΔF<SUB>H+K</SUB> obtained by subtracting an observational lower-limit
flux from F<SUB>H+K</SUB>. 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, F<SUB>x</SUB> depends
only on ΔF<SUB>H+K</SUB>, and not on the stellar radius or mass. All
stars included in our analysis follow the relation F<SUB>x</SUB>
~ Δ<SUP>1.4</SUP><SUB>H+K</SUB> over almost four decades in
F<SUB>x</SUB>.
---------------------------------------------------------
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.
1982uxsa.collQ...4S Altcode: 1982IAUCo..73Q...4S
No abstract at ADS
---------------------------------------------------------
Title: Book Review: X-Ray Astronomy
Authors: Giacconi, R.; Mewe, R.
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.
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.
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.
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.
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
10<SUP>6</SUP> 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.
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 F<SUB>X</SUB> is an
increasing function of the specific Ca II H and K line-core flux
F<SUB>H+K</SUB>. This correlation can be considerably improved by
replacing F<SUB>H+K</SUB> by the excess flux (ΔF<SUB>H+K</SUB>)
above a certain lower limit which varies with B-V. This relation
holds with little scatter over the two decades in F<SUB>X</SUB> in
our sample. The F<SUB>X</SUB>-ΔF<SUB>H+K</SUB> 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 T<SUB>c</SUB> strongly depends on the luminosity class:
T<SUB>c</SUB>≈ 3 10<SUP>6</SUP> K for dwarfs and ≈ 10<SUP>7</SUP>
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
1976NASSP.389..241B Altcode: 1976NASSP.589..241B
No abstract at ADS
---------------------------------------------------------
Title: ANS ontdekte röntgenstraling van Sirius.
Authors: Mewe, R.
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.
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.
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.
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.
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 <SUB>e</SUB>, electron density,N
<SUB>e</SUB>, radiation temperature,T <SUB>r</SUB>, 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 2<SUP>3</SUP>
S or 2<SUP>1</SUP> 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. 2<SUP>3</SUP> S <SUB>1</SUB> and 2<SUP>3</SUP> P
<SUB>2,1,0</SUB>) have been considered as a function ofT <SUB>e</SUB>,
N<SUB>e</SUB> orT <SUB>r</SUB>, 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.
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 10<SUP>5</SUP> and 1.5
× 10<SUP>7</SUP>K. The continuum emission has been calculated in the
temperature range 10<SUP>5</SUP>-10<SUP>8</SUP>K 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.
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 cm<SUP>2</SUP> which, allowing
for reflectivity, counter efficiency and so on, leads to a sensitive
area of about 25 cm<SUP>2</SUP> 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.
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.
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.
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.
1974IAUC.2731....1H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Calculations on the Solar Spectrum from 1 TO 60 Å
Authors: Mewe, R.
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.
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.
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
10<SUP>5</SUP> to 10<SUP>9</SUP> 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.
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 2<SUP>3</SUP>S→2<SUP>3</SUP>P
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.
1969SSRv....9..872V Altcode:
No abstract at ADS
