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5.6 Putting it all together: The XUV Sun in time

The above subsections provide the input for a comprehensive model of the spectral evolution of the “Sun in Time” in the wavelength band that is relevant for ionization of and chemical reactions in planetary atmospheres and circumstellar disks, namely the 1–1700 Å (≈ 0.007–10 keV) FUV/EUV/X-ray (“XUV”) range. The results are summarized in Tables 4 and 5 compiled using data from Ribas et al. (2005Jump To The Next Citation Point) (for the UV-EUV range) and Telleschi et al. (2005Jump To The Next Citation Point) (for the X-ray range). The table also contains data referring to the classical T Tauri star TW Hya, to be discussed in Section 6, and solar data (see Ribas et al. 2005Jump To The Next Citation Point for references).2 The line fluxes given in Table 4 are normalized to a distance of 1 AU and have also been normalized to the radius our Sun had at the age of the respective star. Note that the Lyα line fluxes were corrected for interstellar H i and D i absorption, i.e., they represent the pure stellar contribution.

Ribas et al. (2005Jump To The Next Citation Point) constructed band-integrated irradiances for the spectral ranges 1–20 Å (X-rays), 20–100 Å (soft X-rays and EUV), 100–360 Å (EUV), and 920–1180 Å (FUV). For the wavelength range of 1180–1700 Å, only line fluxes are provided because of increasing contributions from the photospheric continuum.

All integrated irradiances correlate tightly with the stellar rotation period or age, suggesting a rapid decay of activity at all atmospheric levels in concert. The relations are excellently represented by power laws, as illustrated in Figure 19View Imagea. The power-law fits to the fluxes of the form

F = αtβ9 (17 )

(α and β being constants) are given in Table 5. Note that the inaccessible spectral range of 360–920 Å (strongly absorbed by interstellar gas) has been interpolated between adjacent spectral ranges, assuming a decay law with β = –1.


Table 4: Integrated fluxes (in units of erg cm–2 s–1) of strong emission features normalized to a distance of 1 AU and the radius of a one solar mass star. UV and EUV fluxes of 1 π UMa and 1 χ Ori have been averaged. Data for solar analogs are from Telleschi et al. (2005Jump To The Next Citation Point) and Ribas et al. (2005Jump To The Next Citation Point), and for TW Hya from Herczeg et al. (2002Jump To The Next Citation Point), Herczeg et al. (2004Jump To The Next Citation Point), Kastner et al. (2002Jump To The Next Citation Point), and Stelzer and Schmitt (2004Jump To The Next Citation Point); the radius of TW Hya is 1R ⊙ and its distance is 56 pc, see Herczeg et al. (2004Jump To The Next Citation Point). Fluxes of TW Hya have not been corrected for (small) photoabsorption and extinction.
λ Ion log Tmax 0.01 Gyr
____________ 0.1 Gyr ____________
___________ 0.3 Gyr ___________
 0.65 Gyr 1.6 Gyr 4.56 Gyr 6.7 Gyr
(Å) TW Hya 47 Cas EK Dra π1 UMa χ1 Ori κ1 Cet β Com Sun β Hyi
1.85 Fe xxv 7.84 – 2.57±0.63 1.29±0.45 – – – – – –
4.72 S xvi 7.41 – 1.87±0.29 – – – – – – –
10.62 Fe xxiv 7.27 <1.4 2.52±2.10 1.70±1.06 – – – – – –
6.18 Si xiv 7.21 1.2±0.8 4.62±0.87 2.00±0.38 – – – – – –
5.04 S xv 7.18 – 3.72±0.67 1.08±0.20 – – – – – –
11.74 Fe xxiii 7.18 <1.7 5.50±0.72 3.48±0.45 – – – – – –
12.29 Fe xxi 7.04 – 6.72±1.43 4.20±0.94 0.39±0.12 0.21±0.07 0.33±0.05 – – –
6.65 Si xiii 7.01 2.3±1.1 7.33±2.65 3.32±0.44 0.21±0.04 0.14±0.02 0.19±0.03 0.02±0.00 – –
8.42 Mg xii 7.01 0.9±0.6 8.70±0.48 3.46±0.51 0.11±0.03 0.07±0.02 0.19±0.03 0.01±0.01 – –
12.83 Fe xx 6.98 <5.1 8.73±0.03 4.59±0.96 0.27±0.06 0.14±0.06 0.24±0.05 – – –
13.52 Fe xix 6.92 – 8.32±1.41 3.64±1.08 0.46±0.07 0.18±0.09 0.22±0.07 0.02±0.02 – –
14.20 Fe xviii 6.84 1.6±1.3 10.52±0.67 6.57±0.50 0.65±0.09 0.54±0.04 0.57±0.04 0.04±0.02 – –
9.17 Mg xi 6.81 – 11.30±0.40 5.32±0.43 0.41±0.04 0.30±0.02 0.45±0.03 0.04±0.01 – –
12.13 Ne x 6.76 16.1±1.7 17.69±1.25 5.30±0.69 – – – – – –
15.01 Fe xvii 6.72 <31.6 16.89±0.69 12.02±0.52 1.96±0.09 1.62±0.05 1.50±0.06 0.21±0.02 – –
16.78 Fe xvii 6.71 2.4±1.6 7.86±0.66 4.78±0.48 0.99±0.09 0.78±0.06 0.86±0.05 0.12±0.02 – –
13.45 Ne ix 6.59 24.1±2.3 10.08±1.51 2.78±1.15 0.25±0.13 0.32±0.08 0.36±0.10 – – –
13.70 Ne ix 6.59 6.8±1.7 – – 0.16±0.06 0.19±0.04 0.24±0.04 – – –
18.97 O viii 6.48 42.4±3.9 23.03±0.63 9.25±0.36 1.05±0.05 0.89±0.03 1.02±0.29 0.15±0.01 0.029 –
335 Fe xvi 6.35 – – 36.6
9.7
2.6 – – –
361 Fe xvi 6.35 – – 15.7
6.6
1.6 – 0.016 –
21.60 O vii 6.33 21.3±2.6 3.53±0.74 1.44±0.42 0.38±0.05 0.28±0.04 0.37±0.05 0.07±0.02 0.063 –
22.10 O vii 6.32 0.5±0.7 1.55±0.37 1.25±0.37 0.27±0.05 0.20±0.04 0.22±0.04 0.08±0.02 0.041 –
24.77 N vii 6.32 12.6±2.4 2.45±0.33 1.03±0.17 0.07±0.03 0.05±0.01 0.09±0.02 0.01±0.01 0.009 –
284 Fe xv 6.30 – – 22.0
5.0
2.4 – 0.025 –
284 Fe xv 6.30 – – 22.0
5.0
2.4 – 0.025 –
33.73 C vi 6.13 6.1±1.1 2.01±0.27 0.96±0.16 0.08±0.03 0.09±0.02 0.12±0.02 0.03±0.01 0.016 –
610&625 Mg x 6.08 – – –
–
– – 0.028 –
1032 O vi 5.42 41.3 – 3.1
0.75
0.43 0.16 0.050 0.048
1038 O vi 5.42 20.0 – 1.5
0.38
0.21 0.074 0.025 0.022
630 O v 5.26 – – –
–
– – 0.037 –
789 O iv 5.05 – – –
–
– – 0.017 –
1550 C iv 5.00 378.0 – 9.1
2.21
1.02 0.40 0.146 0.082
834 O ii 4.80 – – –
–
– – 0.015 –
304 He ii 4.75 – – 44.3
8.3
2.3 – 0.260 –
1640 He ii 4.75 180.0 – 6.0
0.99
0.56 – 0.040 –
1400 Si iv 4.75 14.6 – 4.3
1.59
0.77 0.28 0.083 0.097
977 C iii 4.68 58.6 – 5.0
1.22
0.59 0.30 0.150 0.124
1176 C iii 4.68 55.9 – 3.4
0.73
0.37 0.15 0.053 0.046
1206 Si iii 4.40 – – –
1.12
0.75 – 0.095 –
584 He i 4.25 – – –
–
– – 0.032 –
1335 C ii 4.25 45.2 – 4.7
1.52
0.95 0.36 0.188 0.155
1304 O i 3.85 126.4 – 4.3
1.18
0.60 0.45 0.143 0.163
1657 C i 3.85 29.2 – 4.1
0.97
0.78 0.47 0.202 0.210
1026 H i 3.84 – – –
3.1
0.80