A&A 400, 671-678 (2003)
DOI: 10.1051/0004-6361:20021899
A. J. J. Raassen1,2 - J.-U. Ness3 - R. Mewe1 - R. L. J. van der Meer1 - V. Burwitz4 - J. S. Kaastra1
1 - SRON National Institute for Space Research,
Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2 -
Astronomical Institute "Anton Pannekoek'', Kruislaan 403,
1098 SJ Amsterdam, The Netherlands
3 -
Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
4 -
Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
Received 7 October 2002 / Accepted 23 December 2002
Abstract
A Chandra LETGS X-ray observation of
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.
Key words: stars: individual:
Centauri - stars: coronae - stars: late-type - stars: activity - X-rays: stars
Late-type F-M stars with photospheric temperatures between 4000 and 7000 K show hot outer atmospheres (coronae) (Schmitt 1997) with temperatures around 1-10 MK. Due to the high temperature these plasmas emit X-ray radiation. This steep rise of the temperature above the stellar surface by 3 orders of magnitude is - after decades of investigations - still a puzzling problem and not well understood. The solar corona shows rich details on structures, mass motions, abundance patterns, loops and flares. These phenomena are driven by magnetic activity.
From studies by, e.g., Güdel et al. (1997a,b) of a series of solar-type stars of
different ages with ROSAT, EUVE, and ASCA,
it is established that the relatively old, non-flaring Sun has a rather inactive
corona with temperatures in the range 1-3 MK, while the more active (and
younger) G dwarfs like EK Dra have coronae with both 5 and
10 MK
plasmas. The latter temperature is reached in the solar corona only during
short flares.
However, many of the stellar objects,
regularly observed by X-ray satellites belong to the more abundant low-mass
stars (M and K dwarfs)
with high X-ray luminosities and flares and therefore very high magnetic
activity. This magnetic activity has been found to be correlated with the
rotational velocity on the stellar surface (e.g., Pallavicini et al.
1981; Güdel et al. 1997b) and a dynamo process is the most plausible
source of magnetic field generation in these stars.
![]() |
Figure 1:
The spectra of the binary system ![]() |
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The components A and B of the binary
Centauri (HD 128620;1) are slightly older than the Sun
and are therefore expected to have a coronal activity comparable to the solar
corona (cf. e.g., Güdel et al. 1997b).
The binary system
Centauri is the nearest stellar system at a distance
of 1.34 pc. It consists of a 1.1
G2V star with a radius of 1.24
and a 0.9
K1V star with a radius of
0.84
(e.g., Flannery & Ayres 1978). The orbit of the binary system
is wide (semi-major axis 23.5 AU = 17.5
), with a period of
80.1 years (Flannery & Ayres 1978).
The rotational periods of A and B are 29 and 42 days (Hallam et al. 1991; Saar & Osten 1997)
and the corresponding rotational velocities
and
km s-1, respectively
(Saar & Osten 1997). According to the X-ray luminosity-velocity relations given by Pallavicini
et al. (1981) and Güdel et al. (1997b) the velocities characterize the corona
Cen as
rather inactive (like the solar corona).
The system has been studied in X-rays in the past, e.g, by Einstein (Golub et al. 1982), EUVE
(Drake et al. 1997, Mewe et al. 1995b), ASCA (Mewe et al. 1998a),
BeppoSAX (Mewe et al. 1998b), and ROSAT (Schmitt 1997 and 1998). Though the ROSAT and
Einstein HRI
detectors have separated the two components to measure fluxes, spectra of the two individual
stars could never be obtained separately.
After the launch of Chandra and XMM-Newton the Centauri binary system can be studied in more detail in the X-ray region.
The spectra of the G2V and K1V star were obtained (on December 25 1999) with an exposure time of 81.5 ks
by the Low Energy Transmission Grating ( LETG) in combination with the High Resolution Camera ( HRC-S)
on board Chandra. During that observation the two stars were separated by 16
on the sky.
The dispersion axis was positioned nearly perpendicular to the axis of the binary, resulting in two separated spectra.
This offers the possibility to study the differences and similarities between the two stars in detail.
To obtain the spectra from the Chandra data we used the standard CXC pipeline
products, later updated with the standard CIAO reduction: CIAO 2.2 with the
science threads for LETG/HRC-S observations. We then used our own software
based on FTOOLS routines to separate the two spectra.
We used the standard 'bow-tie-shaped'
extraction box for the spectrum of each star. The width of the extration box
at the longest wavelength is less than 10
.
Since the spectra had a separation of 16
,
the extraction boxes do not
overlap. To avoid having the spectrum of the other star in the background, we
used a background box of 30
on only one side of the star (opposite of
the other component). This lowers the statistics of the background, but the
background box is still sufficiently large.
For the analysis the spectra of the +1 and -1 order were summed.
The spectra are background-subtracted.
For the effective area we have used the values as calibrated in flight at SRON
(van der Meer et al. 2003), which agree within about 5-10% with the values, as given in
the Chandra LETGS Calibration Review
of 31 Oct. 2001.
Figure 1 shows the spectra of
Cen G2V (top) and K1V (bottom) obtained by LETGS in the
range from 10 to 180 Å.
The effective area calibration at long wavelength is based on the
spectra of HZ43 and Sirius B.
The error on the effective area at 170-175 Å is about 10-15%.
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Figure 2:
Spectra of ![]() |
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ion | ![]() |
G2V/K1V | ![]() |
Fe IX | 171.075 | 1.54 | 0.71 |
Fe X | 174.534 | 1.04 | 0.95 |
Fe XI | 89.185 | 0.43 | 1.3 |
Fe XI | 86.772 | 0.55 | 1.3 |
C V(r) | 40.268 | 1.71 | 0.93 |
C VI(r) | 33.736 | 0.99 | 1.4 |
N VI(r) | 28.787 | 1.04 | 1.4 |
N VII(r) | 24.781 | 0.50 | 2.1 |
O VII(r) | 21.602 | 0.77 | 2.1 |
O VIII(r) | 18.969 | 0.51 | 3.3 |
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|||
![]() | 4700 | 4100 | ||
lines | ratio | T(MK) | ratio | T(MK) |
O VII(i+f)/O VII(r) | 1.00(0.17) | 1.5(0.5) | 1.07(0.16) | 1.5(0.5) |
O VII(r)/O VIII(r) | 3.11(0.68) | 1.8(0.1) | 2.06(0.34) | 2.0(0.1) |
N VI(r)/N VII(r) | 2.40(1.13) | 1.3(0.2) | 1.15(0.46) | 1.5(0.2) |
C V(r)/C VI(r) | 0.64(0.12) | 1.1(0.1) | 0.37(0.09) | 1.3(0.1) |
lines | ratio | densityb | ratio | densityb |
O VII(f/i) | 3.7(1.1) | <1010 | 6.8(2.4) | - |
N VI(f/i) | 4.0(2.0) | <
![]() | 2.9(2.3) | <
![]() |
C V(f/i) | 2.7(1.0) | <2
![]() | 3.8(1.7) |
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Figure 3: The ratio between the line fluxes of the G2V star and the K1V star compared to the temperature of optimal line formation for five silicon ions and three iron ions. |
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In Fig. 1 we recognize the dominant Fe IX and Fe X lines between 170 and 175 Å (which are even more prominent when corrections for the relatively low effective area are made) and strong H-like and He-like lines of C, N, and O in the wavelength region below 40 Å. The latter are better seen in Fig. 2 covering the wavelength range from 10 to 45 Å. From Fig. 1 we notice that the intensity of the "cool'' Fe IX line relative to the "hot'' O VIII line at 18.969 Å is higher for the G2V star (top panel) than for the K1V star. A similar temperature behaviour is seen from Fig. 2 with respect to the "cool'' C V and C VI lines which are higher relative to the "hotter'' O VII and O VIII lines in the spectrum of the G2V star than in the spectrum of the K1V star. This trend is shown in Table 1. In that table we give the calculated line flux ratios between G2V and K1V, together with the optimal line formation temperature. In the lower temperature regime the lines are stronger in the spectrum of the G2V star than in the spectrum of the K1V star, while for "hotter'' lines the lines in the G2V star have lower fluxes than those in the K1V star. This trend is illustrated in Fig. 3 in which the line flux ratios (G2V/K1V) of a number of Si-ions and Fe-ions are shown relative to the temperature of optimum line formation. It is seen that the line flux ratio between the G2V and the K1V star is decreasing with the temperature. The shift between the silicon and iron ratios reflects the abundance difference between the two stars (see also Table 3). Table 1 shows that flux ratios from other elements (C, N, O) are in line with the Si-ratios.
A second temperature indication for the two stars is obtained from line flux ratios between the "cooler'' He-like lines of C V, N VI, and O VII and the "hotter'' H-like resonance lines of C VI, N VII, and O VIII.
In addition, the three O VII lines themselves are density- and temperature-dependent. The "triplet'' consists of
the
-
resonance line (r), the
-
intercombination line (i),
and the
forbidden
line (f). The
level is metastable and can only decay to
the ground by means of a forbidden magnetic
dipole transition. However, the level will be depopulated by electron
collisions at higher densities in favour of the
level. This results
in a decrease of the forbidden line and an increase of the intercombination line. Therefore the value
R = f/i is an adequate
diagnostic tool to constrain the density. The sum of the intercombination line and the forbidden line relative to the resonance line,
G = (i+f)/r is a temperature indicator. Results of this comparison of the temperatures of the G2V and the K1V star
are given in Table 2, showing
higher ratios for the "cooler'' (He-like) ions in the G2V star. For completeness the density-sensitive He-like (f/i) lines ratios
have been inserted in Table 2. The values agree with Ness et al. (2002). For density diagnostics we refer to that paper.
The analysis of the individual line fluxes of the two stars leads to the conclusion that the corona of the K1V star is hotter
than that of the G2V star.
Multi-T fitting | ||
Parameter | K1V | G2V |
log ![]() |
17.95 | 17.95 |
T1 [MK] | 1.17(2) | 1.10(2) |
T2 [MK] | 2.19(3) | 2.00(5) |
EM1 [1049 cm-3] | 1.01(11) | 1.08(10) |
EM2 [1049 cm-3] | 1.87(17) | 1.11(8) |
![]() |
2.88(19) | 2.09(13) |
Lx [1027 ergs](0.07-2.5 keV) | 2.4(3) | 2.3(3) |
Lx [1027 ergs](0.1-2.4 keV) | 1.9 | 1.6 |
Lx [1027 ergs](0.15-4 keV) | 1.6 | 0.87 |
C/Fe 11.26 eV | 0.44(9) | 0.58(9) |
N/Fe 14.53 eV | 0.30(12) | 0.46(11) |
O/Fe 13.62 eVc | 0.23(4) | 0.30(5) |
Ne/Fe 21.56 eVc | 0.38(13) | 0.37(13) |
Mg/Fe 7.65e Vc | 1.12(14) | 1.01(21) |
Si/Fe 8.15 eVc | 0.86(12) | 1.18(16) |
Fe/Fe 7.87 eV | 1 | 1 |
Ni/Fe 7.64 eV | 1.67(26) | 1.55(20) |
Fe/Hc | 1.43(9) | 1.36(16) |
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6130/4484 | 5887/4453 |
![]() |
Figure 4:
Abundances relative to iron for the G2V star (top) and K1V star (bottom) of ![]() |
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From Table 3 and Fig. 4 we notice the relatively high abundances for the elements with a low First Ionization Potential,
indicating a FIP effect. This FIP effect was first observed in the solar
corona (e.g., Feldman et al. 1992). For hot active stars also
an inverse FIP effect is observed (Güdel et al. 2003).
This confirms the work by Drake et al. (1997), based on EUVE observations of
the
Cen ensemble. The low value of oxygen also appears in Fig. 7 of Drake et al. (1997) and might be due to
deficiences of the used solar oxygen abundance. Allende Prieto & Lambert (2001) have found a lower solar photospheric
oxygen abundance value of
(instead of
)
bringing the oxygen value in line with nitrogen
and carbon.
The abundance ratios from ASCA observations (Mewe et al. 1998), reduced by a factor 1.48
because they use
(instead of 7.51), are within the statistical errors comparable to our values
(cf. Table 3).
Comparing the abundance values in Table 3 (especially those of Ne (high FIP) and Mg and Ni (low FIP)) some indication is found
for a stronger FIP effect in the K1V star than in the G2V star. However, this indication is not very significant in view of the
uncertainties.
![]() |
Figure 5:
DEM modeling of the G2V star (thin line) and
the K1V star (thick line) of ![]() ![]() |
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To show the connectivity of the different temperature components obtained in the multi-temperature fitting, we applied
a differential emission measure (DEM) model of the coronae of the K1V and the G2V stars of
Cen,
using the various inversion techniques offered by SPEX (see Kaastra et al. 1996b). We applied the abundances
obtained in the multi-temperature fit of Table 3. Figure 5 shows the EM based on the polynomial method of order 10.
The temperatures range from 0.9 up to 3.5 MK for the G2V and the K1V star.
From this figure it is clear that the G2V star (thin line) has a lower emission measure volume at the higher
coronal temperature than the K1V star (thick line).
In Table A.2 the measured line fluxes of a number of selected lines have been compared with the model fluxes obtained from the DEM-modeling and abundances given in Table 3. Taking into account the uncertainties in the atomic data (20-50%) the flux values are in good agreement with each other. From this table we notice that the modeled fluxes for the H-like ions (C VI, N VII and O VIII) are higher than the measured line fluxes, while those for the He-like ions (C V, N VI, and O VII) are lower. This might indicate a systematic error in atomic data or the wrong assumption that the elemental abundances has to be coupled for all temperature bins. The latter might imply that the He-like lines are formed in inactive regions of the corona and the H-like lines in active regions, resulting in higher abundances for He-like ions compared to H-like ions.
The coronal spectra of the two components of
Centauri (K1V and G2V)
are analyzed separately for the first time. Both LETGS spectra are full with
emission lines, but no significant continuum emission can be measured. We use
the strongest emission lines in order to derive temperatures and to constrain densities
for each component. In addition we construct self-consistent emission measure
distributions for the stars in order to derive elemental abundances. This is
done using global fitting of multi-T models with a combination of SPEX and
MEKAL databases.
We use the He-like f/i ratio of oxygen, nitrogen, and carbon in order to
constrain the plasma densities. For the G2V star we find low density
limits with all the ions. They are all consistent the low density limit
found for carbon, indicating the density below
cm-3.
For the K1V star the intercombination line of oxygen is not detected and
the low density limit is measured with nitrogen, which is, again,
consistent with the measurement of carbon, indicating a density range of
cm-3. We point out the the carbon f/i ratio measures
at the lowest densities, but has the highest low density value of f/i of
all the ions. Therefore the intercombination line is very weak and very
long exposure times are necessary in order to better constrain the
densities measured with the carbon f/i ratio.
Plasma temperatures are measured using line flux ratios of H-like and He-like lines of oxygen, nitrogen, and carbon. We find temperatures between 1 and 2 MK with a slight but not significant tendency that the K1V star is hotter than the G2V star (Table 2). However, this tendency is much clearer when comparing line flux ratios of the same lines for the two stars. We find that the lines formed at lower temperatures (Fe IX, Fe X, C V, N VI, Si VIII, Si IX, and Si X) are stronger in the G2V star, while the "hotter'' lines of Fe XI, N VII, O VII, O VIII, Si XI, and Si XII are stronger in the K1V star. From these measurements we conclude that in the G2V star the emission measure distribution peaks at lower temperatures than in the K1V star. The emission measure distributions derived from the DEM modeling are consistent with this trend and we conclude that they can be used for further analysis expecting results consistent with our analysis from individual lines. We calculated the abundances relative to iron for the two stars and find a FIP effect for both stars. Some indication for a stronger FIP effect in the corona of the K1V star than in the G2V star may be present. However, the errors for these measurements are dominated by systematic effects such as misplacements in wavelength or a lack of lines in the databases, so that the given statistical errors are not fully representative.
Acknowledgements
The National Institute for Space Research (SRON) is financially supported by NWO. We are grateful to the Chandra team, that is responsible for the on board calibration of the LETGS. We like to thank the referee for useful comments.
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Line IDa | |||
![]() | fluxb | ![]() | fluxb | ![]() | Ion |
13.439 (18) | 0.09 (4) | 13.462 (11) | 0.06 (3) | 13.447 | Ne IX |
- | - | 13.658 (11) | 0.02 (3) | 13.700 | Ne IX |
15.011 (17) | 0.14 (5) | 15.027 (12) | 0.15 (4) | 15.013 | Fe XVII |
15.220 (15) | 0.12 (4) | 15.243 (13) | 0.10 (4) | 15.260 | Fe XVII |
15.991 (27) | 0.08 (3) | 15.991 (12) | 0.05 (3) | 16.007 | O VIII |
16.780 (56) | 0.13 (4) | 16.781 (11) | 0.08 (4) | 16.775 | Fe XVII |
17.040 (14) | 0.12 (3) | 17.075 (9) | 0.11 (4) | 17.051 | Fe XVII |
17.093 (14) | 0.19 (4) | 17.115 (9) | 0.06 (3) | 17.100 | Fe XVII |
18.630 (10) | 0.10 (4) | 18.638 (12) | 0.10 (4) | 18.627 | O VII |
18.974 (5) | 0.53 (7) | 18.968 (5) | 0.27 (5) | 18.969 | O VIII |
20.875 (11) | 0.14 (5) | - | - | 20.910 | N VII |
21.606 (4) | 1.09 (11) | 21.601 (4) | 0.84 (10) | 21.602 | O VII |
21.808 (9) | 0.15 (5) | 21.812 (9) | 0.18 (5) | 21.804 | O VII |
22.098 (4) | 1.02 (11) | 22.095 (5) | 0.66 (9) | 22.101 | O VII |
24.787 (9) | 0.20 (6) | 24.795 (11) | 0.10 (4) | 24.781 | N VII |
28.444 (18) | 0.11 (4) | 28.482 (10) | 0.10 (4) | 28.466 | C VI |
28.799 (51) | 0.23 (6) | 28.782 (9) | 0.24 (6) | 28.787 | N VI |
29.101 (12) | 0.07 (4) | 29.085 (11) | 0.07 (3) | 29.084 | N VI |
29.533 (9) | 0.20 (6) | 29.539 (10) | 0.28 (7) | 29.534 | N VI |
33.520 (12) | 0.21 (6) | 33.520 (10) | 0.13 (5) | 33.515 | Si XI |
33.739 (5) | 1.22 (11) | 33.742 (4) | 1.21 (11) | 33.736 | C VI |
- | - | 35.000 (9) | 0.18 (6) | 34.973 | C V |
35.600 (9) | 0.25 (7) | 35.587 (8) | 0.21 (6) | 35.576 | Ca XI |
35.697 (7) | 0.38 (8) | 35.660 (12) | 0.18 (6) | 35.665 | S XIII |
40.264 (11) | 0.45 (10) | 40.244 (8) | 0.77 (12) | 40.268 | C V |
- | - | 40.414 (13) | 0.08 (4) | - | |
- | - | 40.634 (12) | 0.15 (6) | - | |
40.704(15) | 0.13 (5) | 40.749 (15) | 0.25 (8) | 40.731 | C V |
40.872 (11) | 0.37 (11) | - | - | - | |
41.456 (48) | 0.49 (11) | 41.461 (12) | 0.68 (11) | 41.472 | C V |
43.668 (11) | 0.18 (5) | - | - | - | |
43.760 (5) | 0.51 (7) | 43.748 (7) | 0.43 (6) | 43.763 | Si XI |
43.915 (8) | 0.14 (5) | 43.900 (10) | 0.13 (4) | - | |
44.046 (8) | 0.31 (6) | 44.042 (10) | 0.19 (5) | 44.050 | Mg X |
44.020 | Si XII | ||||
44.164 (6) | 0.52 (7) | 44.155 (6) | 0.41 (5) | 44.165 | Si XII |
44.244 (12) | 0.20 (5) | 44.211 (6) | 0.26 (5) | 44.215 | Si IX |
45.511 (8) | 0.19 (5) | 45.518 (9) | 0.16 (4) | 45.519 | Si XII |
45.691 (9) | 0.27 (5) | 45.692 (8) | 0.21 (5) | 45.692 | Si XII |
46.278 (12) | 0.19(5) | 46.287 (9) | 0.21 (5) | 46.300 | Si XI |
46.401 (8) | 0.22 (5) | 46.393 (8) | 0.40 (7) | 46.401 | Si XI |
47.238 (10) | 0.15 (4) | - | - | 47.231 | Mg X |
47.640 (15) | 0.18 (5) | 47.645 (11) | 0.16 (4) | 47.655 | S X |
47.802 (12) | 0.20 (5) | 47.837 (10) | 0.13 (4) | 47.791 | S X |
47.931 (12) | 0.14 (4) | - | - | 47.905 | S X |
49.201 (5) | 0.94 (8) | 49.204 (6) | 0.80 (8) | 49.222 | Si XI |
49.691 (11) | 0.13 (4) | - | - | 49.701 | Si X |
50.324 (7) | 0.37 (8) | 50.321 (9) | 0.31 (6) | 50.333 | Si X |
50.513 (6) | 0.89 (12) | 50.515 (6) | 0.99 (10) | 50.524 | Si X |
50.682 (5) | 0.78 (10) | 50.679 (6) | 0.91 (11) | 50.691 | Si X |
52.314 (6) | 0.68 (11) | 52.331 (11) | 0.34 (7) | 52.296 | Si XI |
52.876 (10) | 0.27 (8) | 52.915 (10) | 0.34 (7) | 52.911 | Fe XV |
54.723 (9) | 0.35 (8) | - | - | 54.728 | Fe XVI |
- | - | 55.091 (19) | 0.32 (7) | 55.096 | Si X |
55.060 | Mg IX |
|
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![]() |
Line IDa | |||
![]() | fluxb | ![]() | fluxb | ![]() | Ion |
55.331 (7) | 0.55(10) | 55.301 (8) | 0.80 (11) | 55.305 | Si IX |
55.393 (7) | 0.90 (12) | 55.380 (8) | 1.22 (14) | 55.356 | Si IX |
- | - | - | - | 55.401 | Si IX |
56.920 (12) | 0.28 (7) | 56.949 (9) | 0.46 (8) | - | |
57.202 (8) | 0.43 (9) | 57.182 (9) | 0.38 (7) | - | |
57.365 (10) | 0.32 (7) | 57.359 (9) | 0.42 (7) | - | |
57.869 (7) | 0.65 (9) | 57.873 (6) | 0.85 (9) | 57.876 | Mg X |
58.891 (11) | 0.17 (5) | 58.876 (11) | 0.24 (6) | - | |
58.956 (12) | 0.37 (7) | 58.928 (11) | 0.32 (7) | 58.963 | Fe XIV |
59.121 (10) | 0.23 (6) | 59.160(11) | 0.21(5) | 59.153 | Mg VIII |
59.391 (7) | 0.46 (9) | 59.394 (9) | 0.29 (6) | - | |
59.596 (10) | 0.16 (5) | 59.596 (12) | 0.15 (4) | - | |
60.800 (12) | 0.33 (8) | - | - | - | |
60.981 (11) | 0.39 (10) | 61.011(11) | 0.88(11) | 61.019 | Si VIII |
61.069 (7) | 0.85 (12) | 61.067(11) | 1.04(12) | 61.070 | Si VIII |
61.638 (10) | 0.59 (12) | 61.686 (11) | 0.57 (11) | 61.649 | Si IX |
61.925 (28) | 0.54 (11) | 61.918 (10) | 0.93 (13) | 61.914 | Si VIII |
63.163 (11) | 0.19 (5) | 63.129 | 0.24 | 63.152 | Mg X |
63.294 (6) | 0.97 (11) | 63.280 (8) | 0.85 (12) | 63.295 | Mg X |
- | - | 63.894(12) | 0.43(10) | 63.903 | Si VIII |
65.667 (12) | 0.39 (8) | 65.675 (10) | 0.38 (9) | 65.672 | Mg X |
65.812 (13) | 0.15 (6) | 65.826 (9) | 0.53(9) | 65.822 | Ne VIII |
65.867 (12) | 0.59 (9) | 65.847 | Mg X | ||
67.166 (11) | 0.40 (6) | 67.156 (12) | 0.29 (6) | 67.135 | Mg IX |
67.245 (10) | 0.46 (7) | 67.246 (10) | 0.57 (9) | 67.239 | Mg IX |
67.347 (10) | 0.50 (7) | 67.365 (9) | 0.34 (6) | 67.382 | Ne VIII |
69.672 (5) | 1.45 (12) | 69.661 (7) | 1.46 (11) | 69.632 | Si VIII |
70.039 (9) | 0.55 (8) | 70.036 (9) | 0.44 (7) | 70.054 | Fe XV |
71.924 (7) | 0.68 (10) | 71.918 (29) | 0.51 (7) | 71.901 | Mg IX |
72.041 (10) | 0.30 (6) | 72.029 (25) | 0.39 (7) | 72.027 | Mg IX |
72.318 (28) | 0.55 (9) | 72.322(20) | 0.71(10) | 72.312 | Mg IX |
73.481 (7) | 0.71 (11) | 73.479 (12) | 0.37 (6) | 73.470 | Ne VIII |
- | - | 74.379 (11) | 0.35 (6) | - | |
74.865 (7) | 0.55 (10) | 74.878 (7) | 0.76 (10) | 74.858 | Mg VIII |
75.060 (6) | 0.69 (11) | 75.050 (6) | 1.13 (12) | 75.034 | Mg VIII |
75.905 (14) | 0.36 (8) | - | - | - | |
76.033 (6) | 1.01 (11) | 76.042 (10) | 0.40 (7) | 76.022 | Fe XIV |
76.143 (10) | 0.68 (11) | 76.158 (11) | 0.30 (6) | 76.152 | Fe XIV |
76.117 | Fe XIII | ||||
76.688 (12) | 0.32 (8) | - | - | - | |
76.877 (7) | 0.69 (11) | 76.877 (9) | 0.44 (7) | - | |
76.991 (10) | 0.35 (8) | - | - | - | |
77.373 (11) | 0.29 (7) | - | - | 77.393 | Ni XI |
77.518 (10) | 0.30 (7) | - | - | - | |
77.756 (7) | 0.66 (10) | 77.751 (9) | 0.66 (9) | 77.737 | Mg IX |
- | - | 77.872 (14) | 0.44 (8) | 77.865 | Fe X |
78.738 (9) | 0.40 (8) | 78.762 (10) | 0.38 (7) | 78.744 | Ni XI |
79.482 (9) | 0.50 (9) | 79.479 (10) | 0.36 (7) | 79.488 | Fe XII |
82.430 (8) | 0.57 (9) | 82.423 (12) | 0.32 (7) | 82.430 | Fe IX |
82.660 (7) | 0.83 (11) | 82.665 (30) | 0.62 (9) | 82.598 | Mg VIII |
- | - | 82.804 (30) | 0.37 (7) | 82.822 | Mg VIII |
83.204 (9) | 0.42 (8) | - | - | - |
![]() |
![]() |
Line IDa | |||
![]() | fluxb | ![]() | fluxb | ![]() | Ion |
83.386 (10) | 0.37 (7) | 83.342 (30) | 0.40 (7) | 83.358 | Si VI |
- | - | 83.443 (30) | 0.41 (7) | 83.457 | Fe IX |
- | - | 83.571 (30) | 0.52 (9) | 83.587 | Mg VII |
- | - | 83.959 (30) | 0.44 (8) | 83.959 | Mg VII |
- | - | 84.054 (30) | 0.60 (9) | 84.025 | Mg VII |
85.444 (8) | 0.66 (11) | 85.448 (12) | 0.26 (7) | 85.461 | Fe XIII |
86.758 (8) | 0.55 (9) | 86.767 (18) | 0.30 (7) | 86.772 | Fe XI |
- | - | 88.094 (10) | 0.19 (5) | 88.092 | Ne VIII |
88.936 (7) | 0.60 (9) | 88.930 (8) | 0.64 (11) | 88.952 | Mg VI |
89.170 (10) | 0.59 (9) | 89.144 (12) | 0.25 (8) | 89.185 | Fe XI |
90.189 (10) | 0.43 (9) | 90.201 (10) | 0.42 (10) | - | |
90.707 (10) | 0.35 (8) | - | - | 90.708 | Mg VII |
90.995 (9) | 0.44 (9) | - | - | 91.009 | Fe XIV |
91.563 (10) | 0.30 (7) | 91.529 (12) | 0.36 (9) | 91.527 | Ni X |
91.789 (11) | 0.60 (10) | 91.817 (12) | 0.54 (11) | 91.790 | Ni X |
92.186 (9) | 0.48 (9) | 92.148 (12) | 0.30 (10) | 92.123 | Mg VIII |
94.000 (7) | 1.26 (13) | 94.012 (7) | 1.10 (13) | 94.012 | Fe X |
- | - | 95.359 (12) | 0.37 (10) | 95.338 | Fe X |
- | - | 95.440 (10) | 0.52 (11) | 95.421 | Mg VI |
95.856 (11) | 0.35 (8) | - | - | - | |
95.992 (8) | 0.58 (10) | 95.997 (8) | 0.89 (11) | 96.022 | Si VI |
96.101 (8) | 0.69 (11) | 96.100 (9) | 0.21 (6) | 96.122 | Fe X |
98.093 (9) | 0.36 (10) | 98.120 (10) | 0.79 (15) | 98.115 | Ne VIII |
98.242 (48) | 0.49 (11) | 98.262 (14) | 0.40 (11) | 98.260 | Ne VIII |
- | - | 98.495 (12) | 0.83 (18) | - | |
- | - | 100.005 (10) | 0.40 (10) | - | |
100.567 (6) | 0.95 (13) | 100.561 (7) | 1.06 (15) | 100.597 | Mg VIII |
- | - | 102.765 (13) | 0.62 (14) | - | |
103.039 (22) | 0.53 (27) | 103.063 (10) | 0.65 (12) | 103.085 | Ne VIII |
103.262 (43) | 0.49 (28) | 103.280 (11) | 0.41 (12) | - | |
103.567 (19) | 0.68 (29) | 103.537 (8) | 0.78 (12) | 103.566 | Fe IX |
103.926 (40) | 0.53 (29) | 103.904 (12) | 0.49 (12) | - | |
- | - | 104.856 (11) | 0.72 (14) | 104.813 | O VI |
105.183 (11) | 0.56 (10) | 105.197 (9) | 1.06 (16) | 105.208 | Fe IX |
108.420 (46) | 0.88 (12) | - | - | - | |
- | - | 116.675 (11) | 0.38 (9) | 116.693 | Ne VII |
- | - | 122.482 (10) | 0.71 (13) | 122.49 | Ne VI |
129.818 (13) | 1.42 (22) | - | - | 129.871 | O VIc |
142.378 (11) | 1.42 (18) | - | - | - | |
146.095 (12) | 1.38 (18) | - | - | - | |
148.339 (6) | 6.05 (44) | 148.332 (6) | 6.54 (46) | 148.402 | Ni XI |
- | - | 150.046 (11) | 2.19 (23) | 150.089 | O VI |
- | - | 150.099 | 1.38 | 150.124 | O VI |
- | - | 150.332 (14) | 1.26 (18) | - | |
152.110 (39) | 5.40 (44) | 152.120 (11) | 3.66 (34) | 152.153 | Ni XII |
154.131 (10) | 2.36 (28) | 154.158 (17) | 1.03 (15) | 154.175 | Ni XII |
157.596 (12) | 1.87 (25) | - | - | - | |
157.730 (9) | 3.24 (35) | 157.709 (12) | 1.96 (23) | 157.730 | Ni XIII |
- | - | 157.972 (30) | 1.31 (30) | - | |
171.089 (4) | 51.8 (25) | 171.093 (4) | 71.7 (29) | 171.075 | Fe IX |
174.535 (6) | 50.3 (43) | 174.537 (5) | 52.2 (43) | 174.534 | Fe X |
Table A.2. Comparison of model and observed fluxes from LETGS for the
Cen K1V and G2V star.
![]() |
![]() |
Line IDa | |||
fluxb | fluxc | fluxb | fluxc | ![]() | Ion |
0.41 | 0.45 (10) | 0.56 | 0.77 (12) | 40.268 | C V |
0.03 | 0.13 (5) | 0.04 | 0.25 (8) | 40.731 | C V |
0.37 | 0.49 (11) | 0.51 | 0.68 (11) | 41.472 | C V |
0.11 | 0.14 | 41.480 | Ar IX | ||
0.12 | 0.11 (4) | 0.10 | 0.10 (4) | 28.466 | C VI |
1.25 | 1.22 (11) | 1.23 | 1.21 (11) | 33.736 | C VI |
0.16 | 0.23 (6) | 0.17 | 0.24 (6) | 28.787 | N VI |
0.02 | 0.07 (4) | 0.03 | 0.07 (3) | 29.084 | N VI |
0.12 | 0.20 (6) | 0.14 | 0.28 (7) | 29.534 | N VI |
0.20 | 0.20 (6) | 0.16 | 0.10 (4) | 24.781 | N VII |
0.10 | 0.10 (4) | 0.08 | 0.10 (4) | 18.627 | O VII |
0.92 | 1.09 (11) | 0.78 | 0.84 (10) | 21.602 | O VII |
0.16 | 0.15 (5) | 0.14 | 0.18 (5) | 21.804 | O VII |
0.63 | 1.02 (11) | 0.56 | 0.66 (9) | 22.101 | O VII |
0.05 | 0.08 (3) | 0.03 | 0.05 (3) | 16.007 | O VIII |
0.59 | 0.53 (7) | 0.36 | 0.27 (5) | 18.969 | O VIII |
0.07 | 0.09 (4) | 0.03 | 0.06 (3) | 13.447 | Ne IX |
0.30 | 0.55 (10) | 0.47 | 0.76 (10) | 74.858 | Mg VIII |
0.27 | 0.25 | 74.843 | Fe XIII | ||
0.35 | 0.69 (11) | 0.55 | 1.13 (12) | 75.034 | Mg VIII |
0.18 | 0.40 (6) | 0.21 | 0.29 (6) | 67.135 | Mg IX |
0.55 | 0.30 (6) | 0.72 | 0.39 (7) | 72.027 | Mg IX |
0.40 | 0.55 (9) | 0.51 | 0.71 | 72.311 | Mg IX |
0.19 | 0.21 | 72.310 | Fe IX | ||
0.90 | 1.24 (16) | 1.45 | 1.92 (25) | 61.019 | Si VIII |
61.070 | Si VIII | ||||
0.22 | 0.20 (5) | 0.19 | 0.26 (5) | 44.215 | Si IX |
0.27 | 0.55(10) | 0.35 | 0.80 (11) | 55.305 | Si IX |
1.64 | 0.90 (12) | 2.15 | 1.22 (14) | 55.356 | Si IX |
- | - | - | - | 55.401 | Si IX |
0.73 | 0.89 (12) | 0.83 | 0.99 (10) | 50.524 | Si X |
0.73 | 0.78 (10) | 0.83 | 0.91 (11) | 50.691 | Si X |
0.40 | 0.51 (7) | 0.40 | 0.43 (6) | 43.763 | Si XI |
0.33 | 0.68 (11) | 0.37 | 0.34 (7) | 52.296 | Si XI |
0.23 | 0.31 (6) | 0.20 | 0.19 (5) | 44.020 | Si XII |
0.22 | 0.18 | 44.050 | Mg X | ||
0.47 | 0.52 (7) | 0.41 | 0.41 (5) | 44.165 | Si XII |
51.1 | 51.8 (25) | 80.6 | 71.7 (29) | 171.075 | Fe IX |
39.8 | 50.3 (43) | 52.7 | 52.2 (43) | 174.534 | Fe X |
0.16 | 0.68 (11) | 0.12 | 0.30 (6) | 76.117 | Fe XIII |
0.12 | 0.11 | 76.152 | Fe XIV | ||
0.45 | 1.01 (11) | 0.40 | 0.40 (7) | 76.022 | Fe XIV |
0.25 | 0.14 (5) | 0.10 | 0.15 (4) | 15.013 | Fe XVII |
0.15 | 0.13 (4) | 0.06 | 0.08 (4) | 16.775 | Fe XVII |
0.18 | 0.12 (3) | 0.07 | 0.11 (4) | 17.051 | Fe XVII |
0.14 | 0.19 (4) | 0.06 | 0.06 (3) | 17.100 | Fe XVII |
6.55 | 6.05 (44) | 5.85 | 6.54 (46) | 148.402 | Ni XI |
2.61 | 5.40 (44) | 2.25 | 3.66 (34) | 152.153 | Ni XII |
1.43 | 2.36 (28) | 1.32 | 1.03 (15) | 154.175 | Ni XII |
3.69 | 3.24 (35) | 2.30 | 1.96 (23) | 157.730 | Ni XIII |
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