1. Proxima (TRAPPIST1) Exreme Events
Cosmic rays across
scales and disciplines
April 13, 2018
EGU Cosmic rays and their interaction with astrospheres
Andrei Sadovski, Alexey Struminsky, Maria Zharikova
Space Research Institute (IKI), Moscow, Russian Federation
SCR Tabataba-Vakili et al. (2015) consirdered an influence of stellar cosmic rays (SCR) на on atmospheres of exoplanets assuming that their spectra are similar to spectra Solar CR at 1 AU with scaling of distance to exoplanets as a square of radius.
Atri (2016) consirdered an influence of SCR using spectra of well known solar proton events - hard (SPE56), soft (SPE72), medium (SPE89).
The GOAL – to estimate fluxes of GCR and SCR near exoplanets in a habitable zone of stars of different spectral classes using solar-stellar analogies and simple models elaborated for the Sun and the heliosphere at the beginning of space era – solar wind(Parker, 1958), GCR modulation(Parker, 1958), stellar CR (Hayakava,1969).
GCR.
Grießmeier et al.(2015) considered the dependence of the Galactic cosmic rays (GCR) induced radiation dose on the strength of the planetary magnetic field and its atmospheric depth. GCR modulation was not considered! Scherer et al. (2002) demonstrated by quantitative modeling that a change of the interstellar medium surrounding the heliosphere triggers significant changes of planetary environments caused by enhanced fluxes of neutral atoms as well as by the increased cosmic ray fluxes. Cohen et al. (2012) showed that the GCR flux near the Archean Earth (for the early Sun) would has greatly reduced than is the case today is mainly due to the shorter solar rotation period and tighter winding of the Parker spiral. Sadovski et al.(2018) considered radiation conditions close to Proxima b. They should be determined by stellar CR since there are no GCR due to GCR modulation by the stellar wind.
Stellar wind and astrosphere
Stellar Cosmic Rays
Maximal possible temperature of the quite corona corresponds to the critical point at the photosphere.
fNp – proton production per second,
f – frequency of stellar flares
Stellar wind and GCR modulation
- Proxima Centauri ( TRAPPIST 1)
Other astrospheres
Rotation period 83 (3) days
average stellar magnetic field 600 G, no magnetic field maps
Wind velosity ( ) km/s
First turn of the Parer spiral 23 (1-2) AU
Wind density ( ) см-3
Radius of the astrosphere ( ) AU.
sp. class
L*/Ls
M*/Ms
R*/Rs
H AU
B0B G
Emax/(αβ) TeV
Tcor К Lx
Erg/s V
Km/s n
cm^-3
Mass rate
g/s
R ast-sph AU O5
7.9E5 60 14
746
710 69
1.733e+07
4.550e+32
4.942e+03
2.900e-03
4.327e+15
4.815e+04 B0
5.2E4 16
7.4
185
693 36
8.745e+06
2.193e+31
3.216e+03
8.196e-03
4.895e+14
1.306e+04 B5
830 7
3.9
26.4
870 24
7.260e+06
6.025e+30
2.468e+03
2.409e-01
2.248e+14
7.755e+03 A0 54 3
2.4
10.6
925 15
5.056e+06
1.045e+30
1.933e+03
5.352e-01
6.309e+13
3.636e+03 A5 2
1.7
3.3
970 11
4.758e+06
5.988e+29
1.640e+03
5.089e+00
4.931e+13
2.961e+03 F0
6.5
1.8
1.5
2.1
1147 12
4.854e+06
5.662e+29
1.562e+03
1.363e+01
5.093e+13
2.937e+03 F5
3.2
1.4
1.6
1122
4.334e+06
3.554e+29
1.420e+03
1.946e+01
3.840e+13
2.432e+03 G0
1.05
1.1
1195 9
3.861e+06
1.864e+29
1.306e+03
2.763e+01
2.370e+13
1.832e+03 G5
0.8
0.92
0.73
1338
8.5
4.045e+06
1.835e+29
1.300e+03
5.187e+01
2.342e+13
1.817e+03 K0
0.4
0.78
0.85
0.64
1468
8.7
3.712e+06
1.255e+29
1.209e+03
6.851e+01
1.840e+13
1.553e+03 K5
0.15
0.69
0.72
0.38
1480
3.876e+06
1.237e+29
1.143e+03
2.224e+02
1.992e+13
1.572e+03 M0
0.08
0.51
0.6
0.24
1527
6.4
3.438e+06
6.775e+28
1.009e+03
4.365e+02
1.377e+13
1.227e+03 M5
0.01
0.2
0.27
2125
4.0
2.996e+06
1.884e+28
8.741e+02
1.645e+03
4.994e+12
6.879e+02 M8
0.001
0.1
0.11
0.02
3352
0.5
3.677e+06
1.571e+28
8.453e+02
2.315e+04
4.248e+12
6.239e+02
Stellar wind velocity and density estimates within the Parker model, radius of astrosphere for maximal coronal temperature.
Values of stellar wind velocity differ by several times but observed values of stellar magnetic field may differ by one-two orders in comparison with corresponding solar values.
To estimate GCR modulation in some point in the astrosphere we need know stellar magnetic field and rotation period, parameters of local interstellar medium
PROXIMA b
Trappist 1 d
Trappist 1 f
GCR would be absent up to about 1 TeV due to stellar wind modulation
Proxima (TRAPPIST1) Exreme Events
Conclusions
Stellar and galactic cosmic rays (SCR and GCR) are important factors of space weather determining radiation conditions near e[oplanets.
GCR spectrum and its variations near exoplanets are detemined by modulation processes in astrospheres – stellar wind parameters and local conditions of the interstellar medium.
As a result of modulation GCR would be practically absent near exoplanets of stars with strong magnetic field. Radiation conditions would be determined by SCR – stellar activity, energy distribution of flares (frequency), orbit parameters of exoplanets.