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42 Manuel Güdel Consequently, the average stellar X-ray spectrum indicates more hot plasma (Schrijver et al., 1984; Maggio et al., 1994; Güdel et al., 1997b; Preibisch, 1997; Orlando et al., 2000; Peres et al., 2000). • Increased magnetic activity leads to more numerous interactions between adjacent magnetic field structures at the chromospheric level (Cuntz et al., 1999) and therefore at the coronal level, owing to higher magnetic filling factors in the photosphere (Section 4.2.6). The heating efficiency thus increases. Specifically, a higher rate of large flares is expected. Flares produce hot, dense plasma and therefore increase both the X-ray luminosity and the average coronal temperature of a star (Güdel et al., 1997b). • Jordan et al. (1987) and Jordan and Montesinos (1991) described an emission measure (EM)- T relation based on arguments of a minimum energy loss configuration of the corona, assuming a fixed ratio between radiative losses and the coronal conductive loss. A relation including the stellar gravity g was suggested, of the form EM ∝ T 3 g , (16) which fits to a sample of observations with T taken from single-T fits to stellar coronal spectra. Equation (16) holds because coronal heating directly relates to the production rate of magnetic fields, and the magnetic pressure is assumed to scale with the thermal coronal pressure. 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 ˚A (≈ 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. (2005) (for the UV-EUV range) and Telleschi et al. (2005) (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. 2005 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. (2005) constructed band-integrated irradiances for the spectral ranges 1 – 20 ˚A (X-rays), 20 – 100 ˚A (soft X-rays and EUV), 100 – 360 ˚A (EUV), and 920 – 1180 ˚A (FUV). For the wavelength range of 1180 – 1700 ˚A, 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 19a. The power-law fits to the fluxes of the form F = αt β 9 2 The line fluxes of O viii, O vii, N vii, and C vi were determined from a model spectrum synthesized in the XSPEC software (Arnaud, 1996) using the vapec model (Smith et al., 2001). The model is based on an isothermal plasma with a temperature of 2 MK normalized such that the 0.1 – 10 keV luminosity is 2 × 10 27 erg s −1 . The low-FIP element abundances were set to values four times higher than standard photospheric abundances, while the high-FIP element abundances were photospheric; the S abundance was set to an intermediate value of 2× the photospheric value. Living Reviews in Solar Physics http://www.livingreviews.org/lrsp-2007-3 (17)
The Sun in Time: Activity and Environment 43 (α and β being constants) are given in Table 5. Note that the inaccessible spectral range of 360 – 920 ˚A (strongly absorbed by interstellar gas) has been interpolated between adjacent spectral ranges, assuming a decay law with β = −1. Living Reviews in Solar Physics http://www.livingreviews.org/lrsp-2007-3
Page 1 and 2: Living Rev. Solar Phys., 4, (2007),
Page 3 and 4: Contents 1 Introduction 7 2 What is
Page 5: List of Tables 1 Symbols and units
Page 8 and 9: 8 Manuel Güdel The discovery of ex
Page 10 and 11: 10 Manuel Güdel 2 What is a Solar-
Page 12 and 13: 12 Manuel Güdel 3 The Sun in Time
Page 14 and 15: 14 Manuel Güdel Guinan, 1994a; Dor
Page 16 and 17: 16 Manuel Güdel 4 The Solar Magnet
Page 18 and 19: 18 Manuel Güdel 4.1.2 Polar spots
Page 20 and 21: 20 Manuel Güdel structure”; furt
Page 22 and 23: 22 Manuel Güdel Because the X-ray
Page 24 and 25: 24 Manuel Güdel Flux density at bo
Page 26 and 27: 26 Manuel Güdel Figure 7: Left (a)
Page 28 and 29: 28 Manuel Güdel detection until re
Page 30 and 31: 30 Manuel Güdel stellar winds and
Page 32 and 33: 32 Manuel Güdel Figure 11: Relatio
Page 34 and 35: 34 Manuel Güdel 5.4 The far-ultrav
Page 36 and 37: 36 Manuel Güdel X-ray luminosity (
Page 38 and 39: 38 Manuel Güdel Flux density at 1
Page 40 and 41: 40 Manuel Güdel count rate (cts s
Page 44 and 45: 44 Manuel Güdel Table 4: Integrate
Page 46 and 47: Relative flux (Sun=1) 46 Manuel Gü
Page 48 and 49: 48 Manuel Güdel Flux at 1 AU (erg
Page 50 and 51: 50 Manuel Güdel Figure 22: Correla
Page 52 and 53: 52 Manuel Güdel a concept also pro
Page 54 and 55: 54 Manuel Güdel • This latter co
Page 56 and 57: 56 Manuel Güdel entire observed X-
Page 58 and 59: 58 Manuel Güdel 5.9.2 The composit
Page 60 and 61: 60 Manuel Güdel Abundance 1.0 0.1
Page 62 and 63: 62 Manuel Güdel 6.2.2 New features
Page 64 and 65: 64 Manuel Güdel Figure 30: Summary
Page 66 and 67: 66 Manuel Güdel among the stars co
Page 68 and 69: 68 Manuel Güdel et al. (2005), and
Page 70 and 71: 70 Manuel Güdel same time, related
Page 72 and 73: 72 Manuel Güdel active stars, incl
Page 74 and 75: 74 Manuel Güdel magnetized; such w
Page 76 and 77: 76 Manuel Güdel low viscous heatin
Page 78 and 79: 78 Manuel Güdel all isotopic anoma
Page 80 and 81: 80 Manuel Güdel 7 The Solar System
Page 82 and 83: 82 Manuel Güdel of life, and life
Page 84 and 85: 84 Manuel Güdel 7.1.3 Cosmic rays
Page 86 and 87: 86 Manuel Güdel H2O + hν → OH +
Page 88 and 89: 88 Manuel Güdel Here, v0 = (2kTexo
Page 90 and 91: 90 Manuel Güdel Figure 41: Modeled
Page 92 and 93:
92 Manuel Güdel Figure 42: Modeled
Page 94 and 95:
94 Manuel Güdel (Section 5.6), one
Page 96 and 97:
96 Manuel Güdel 8 Summary and Conc
Page 98 and 99:
98 Manuel Güdel Solar magnetic act
Page 100 and 101:
100 Manuel Güdel References Acuña
Page 102 and 103:
102 Manuel Güdel Balbus, S.A., Haw
Page 104 and 105:
104 Manuel Güdel Calvet, N., Muzer
Page 106 and 107:
106 Manuel Güdel Curiel, S., Rodr
Page 108 and 109:
108 Manuel Güdel Favata, F., Micel
Page 110 and 111:
110 Manuel Güdel Gagne, M., Cailla
Page 112 and 113:
112 Manuel Güdel Güdel, M., 1997,
Page 114 and 115:
114 Manuel Güdel workshop held at
Page 116 and 117:
116 Manuel Güdel Holman, G.D., Ben
Page 118 and 119:
118 Manuel Güdel Johns-Krull, C.M.
Page 120 and 121:
120 Manuel Güdel König, B., Guent
Page 122 and 123:
122 Manuel Güdel Maggio, A., Peres
Page 124 and 125:
124 Manuel Güdel Mitra-Kraev, U.,
Page 126 and 127:
126 Manuel Güdel Parnell, C.E., Ju
Page 128 and 129:
128 Manuel Güdel Proceedings for a
Page 130 and 131:
130 Manuel Güdel Schmitt, J.H.M.M.
Page 132 and 133:
132 Manuel Güdel Smith, K., Pestal
Page 134 and 135:
134 Manuel Güdel Telleschi, A., G
Page 136 and 137:
136 Manuel Güdel Weber, E.J., Davi
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