The origin of superflares on G-type dwarfs of different ages

Size: px

Start display at page:

Download "The origin of superflares on G-type dwarfs of different ages"

Moris Powers
5 years ago
Views:

Pushkov Institute of Terrestrial Magnetism,

Russian Academy of Sciences, Troitsk, Moscow,

1 The origin of superflares on G-type dwarfs of different ages Moisey Livshits, Maria Katsova Pushkov Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation of the Russian Academy of Sciences, Troitsk, Moscow, RUSSIA Sternberg State Astronomical Sternberg State Astronomical Institute, Lomonosov Moscow State University, Moscow, RUSSIA. April 2015

2 Outline Introduction: Kepler s era -- Baby Sun and Young Sun What one can conclude about the origin of superflares in frameworks of gas-dynamic response of the chromosphere to an impulsive heating: on the area of the optical continuum source and the evaluation of the flux of accelerated electrons? Consequences in the case of hard electron spectrum: a - the microwave radiation of superflares b - lithium production during impulsive flares Magnetic fields of G-stars and maximal flare energies Concluding remark

Flares on red dwarfs and the Sun and problem of superflares Impulsive stellar flares and

particular, the gasdynamic response of the chromosphere to heating by accelerated

The explosive evaporation leads to the upward motion of the hot gas and downward motion

GAS-DYNAMIC MODELLING: N.Kostyuk, S.Pikelner, 1974-1975, Sov. Astron. M. Livshits, O.

3 Flares on red dwarfs and the Sun and problem of superflares Impulsive stellar flares and superflares Solar flares: E = 10 ^32 ergs The scenario of impulsive flares, in particular, the gasdynamic response of the chromosphere to heating by accelerated electrons is well-studied. The explosive evaporation leads to the upward motion of the hot gas and downward motion of the low-t condensation. The coronal loop fills up gradually with the hot plasma. GAS-DYNAMIC MODELLING: N.Kostyuk, S.Pikelner, , Sov. Astron. M. Livshits, O.Badalyan, A.Kosovichev and M.Katsova, 1981, Solar Phys. 73, 269 M.Katsova, ABoiko A.Boiko, M.Livshits, 1997 A & A, 321, 549 G. Fisher et al. ApJ, more than 100 papers + RADYN

Flares on red dwarfs and the Sun and problem of superflares An area of superflares observed

cm^2 (solar flares in 1972, June 15, 1991) Now it is confirmed by current data about the

4 Flares on red dwarfs and the Sun and problem of superflares An area of superflares observed in V - band October 24, :08:46 UT The area of white-light solar flare is 3x10^16 cm^2 (solar flares in 1972, June 15, 1991) Now it is confirmed by current data about the area of the brightest footpoints in the G-band of the WL flare continuum (Krucker et al. 2011). E_ flare = σt^4 S Δt, for Δt = 300 s The flare with the total energy E = 10^34 ergs and Δt = 30 min covers the area S = 10^19 cm^2 that is the maximal area of Hα ribbons of solar flares

5 ***** 40 -years investigations of the explosive evaporaton showed that downward moving low-t condensation is the basic source of the optical continuum emission of the hydrogen plasma. The energy of the accelerated electron beam, injected into the chromosphere, can not exceed 3 x erg cm -2 s -1. This value is limited due to the appearance of the return electric current and is the low limit of the energy of particles accelerated in the pulse and injected gradually from the coronal part of loops into the chromosphere over all flare area.

6 Evaluation of the accelerated electron fluxes for flares registered with the Kepler mission The optical observations of superflares with E = erg give information about the total number of electrons with E> 20 kev N electron s -1. This injection is about of 100 times more than in X1 flares on the Sun and this process lasts 30 min. It requires exceptionally effective acceleration of particles

Superflares with the total energies 10^33 10^34 ergs as an analog of the solar events with effective

the white-light ht image Protons are accelerated up to energies of a few hundreds MeV in the low source

2000 with the effective particle acceleration with Solar Cosmic Rays 10:19 -- 10:28 UT time of γ-burst

7 Superflares with the total energies 10^33 10^34 ergs as an analog of the solar events with effective particle acceleration Isophotes of the hard X-rays against emission at 195 А The 195 A emission against the white-light ht image Protons are accelerated up to energies of a few hundreds MeV in the low source adjacent to the umbra of the spot WHERE AND WHEN ARE SOLAR COSMIC RAYS ACCELERATED MOST EFFICIENTLY? LIVSHITS M.A., BELOV A.V Astron.Reports 48, 665 Time profile of the 171 A emission in the source I The flare on with the effective particle acceleration with Solar Cosmic Rays 10: :28 UT time of γ-burst S l YY M JA h d SW d YD S l Ph (2001) See also: Y.Yan, M.J.Ashwanden, S.Wang, and Y.Deng, Solar Phys. 204, 29 (2001). The region where particles are accelerated is at h = ± km

8 On a Model of the Optical Continuum Source of Superflares The first source is a region of the main acceleration (I); this is a single or a few very low-lying loops located above the polarity inversion line (PIL) crossing the big spot. The system of coronal loops begins to form above the PIL over the entire active region, and some of footpoints of loops in this post-eruptive arcade are sources of the enhanced X-ray radiation (II). The coronal loop, which connects the region of the main particle acceleration with another ribbon, is often a source of strong microwave radiation, because many particles of relativistic energies are captured therein. The footpoint of this loop (III) is also bright in the hard X- ray and γ-ranges. The X-ray sources I, II, and III were observed both in this flare and in subsequent large events and looked like inhomogeneities at kev-images of ribbons. It is seen in many powerful events, for example, on 28. October 2003, and even in the flare on 6. December 2006 located near the limb in not quite convinient i conditions for observations (Krucker et al. 2011).

9 Flare on January 20, 2005 S N RHESSI Red kev Blue kev This conclusion was confirmed by V.V. Grechnev, V.G. Kurt, I.M. Chertok, A.M. Uralov, H. Nakajima, A.T. Altyntsev, AV A.V. Belov, B.Yu.Y YuYushkov ushkov, SN S.N. Kuznetsov, LK L.K. Kashapova, N.S. Meshalkina, N.P. Prestage The January 20, 2005 big solar flare and its relation to Solar Energetic Particles, Solar Phys. 2008

10 Flare on January 20, 2005 The microwave burst at the maximum of the big impulsive flare reaches almost 10^5 sfu. This is the gyrosynchrotron radiation of electrons with energies of about 1 MeV.

11 Flare on 28. October 2003 Using the code for computation of the gyrosynchrotron radiation (Fleishman and Kuznetsov, 2014, Nita et al., 2014), we have calculated the spectrum of the microwave radiation of the accelerated electrons with the single slope γ = The magnetic field in the corona was reconstructed from the MDO/SOHO charts. The microwave emission arose in the loop of the length of 2 x cm and the width of 3 x 10 9 cm. The magnetic field strength in the loop top was 175 G. In this case it is impossible to achieve the consent between the observed and the calculated spectrum. The maximal microwave flux reaches 10 5 sfu at GHz for both these flares.

Extrapolation of Microwave Soft X-ray Relationship The IZMIRAN data base for observations in 1976 2006 with different radio telescopes shows than this maximal flux I 35 at this frequency depends

12 Extrapolation of Microwave Soft X-ray Relationship The IZMIRAN data base for observations in with different radio telescopes shows than this maximal flux I 35 at this frequency depends weakly from the soft X-ray flux, I R, for faint flares, while the I 35 value is proportional to I 1.5 R for the flares with the particle acceleration (Belov A., 2015). If we adopt the total energy of the largest solar flares as much as erg and use the same law for variations of the microwave emission in the form of I 35 is proportional to the total flare energy E 1.5 tot, then we obtain that the microwave flux of flares with E = erg at the distance of 1 AU is about 10 8 sfu. This means that such a flare on a star at a distance of 100 pc will produce the microwave flux above 2 mjy.

13 The Lithium Production by Spallation Reactions during Stellar Flares The appearance of a large amount of Li and its diffusion over the surface during some big solar flares The theoretical estimate - M. Livshits, Sol. Phys. 173/2, 377 (1997); Ramaty, R. et al., 2000, ApJ. 534, L207 ( 6 Li/ 7 Li ratio) Observations: # 4B Solar Flare on 9 March 1989 (W. Livingston et al. (1997); # Li I line enhancement during the big flare on a late-type star - D. Montes, L.W. Ramsey, A & A, 340, L5 (1998), see also Ramaty et al. (2000). Chromospheric activity and lithium line variations in the spectra of the spotted star LQ Hydrae - M. Flores Soriano, K. G. Strassmeier, M. Weber A&A 575, A57 (2015). Because sporadic flares of moderate intensity were also detected at the same hemisphere in the hydrogen and helium lines, authors supposed that these Li atoms are produced during flares.

14 The Magnetic Fields on Late-Type Stars - I ksi Boo A (HD A, G8V, P=6.1 day) Plachinda and Tarasova (2000) 61 Cyg A (HD , K5V, P=6.2 day) T. N. Tarasova, S. I. Plachinda, and V. V. Rumyantsev. Astron. Reports, V. 45 (2001) Maximal strengths of the magnetic field in stellar spots Maximal strengths of the magnetic field in stellar spots are the same as those on the Sun. Review of results of previous observations of stellar magnetic fields see in Reiners A., Observations of Cool Star Magnetic Fields, Living Rev. Solar Phys., 8, (2012)

The Magnetic Fields on Late-Type Stars - II A Bcool magnetic snapshot survey of solar-type stars S. C. Marsden, et al. + the Bcool Collaboration, arxiv 1311.3374 (2013) ksi Boo A, B_l = +18.

15 The Magnetic Fields on Late-Type Stars - II A Bcool magnetic snapshot survey of solar-type stars S. C. Marsden, et al. + the Bcool Collaboration, arxiv (2013) ksi Boo A, B_l = G, > 100 measurements) Spectropolarimetry, around линий, 170 stars, the mean longitudinal field is measured on 67 stars (including > 20 G type dwarfs) Recent spectropolarimetric observations show that the general character of the magnetic fields of slow rotating G stars is similar to the solar one: there are poles of the magnetic dipole at high latitudes and strong local fields in the equatorial zone. These observations o s give the mean Stars in red have Teff < 5000 longitudinal field. K, those in orange have 5000 K > Teff > 6000 K For G-type stars B_l = 4.72 ±0.53 G. and those in yellow have Teff > 6000 K

16 The Magnetic Fields of G-type Dwarfs - the Young Suns x 10 d <P_rot < 20 days We chose young Suns from stars monitored by the Bcool collaboration taking into account our knowledge about indices of the chromospheric and coronal activity. # The mean value of B_l is around 5 G as it is obtained by Marsden et al. (2013) in Bcool collaboration. # For these young Suns the mean magnetic field age relation does exist, while it is weak for baby-suns. # Comparison with the present day-sun: the averaged over the Carrington rotation the magnetic fields of the Sun as a stars at high activity level (for example, in 1980), B_l =0.5 G. THUS, THE MAGNETIC FIELD OF THE YOUNG SUNS IS 10 TIMES STRONGER THAN THAT IN THE PRESENT EPOCH AND THIS IS NOT DUE TO LARGE SPOTTEDNESS *** *** *** *** *** *** Zeeman Doppler Imaging results indicate, apparently, a presence of the large-scale toroidal component of the magnetic field in young Suns. P. Petit et al. (2008) Toroidal vs. poloidal magnetic fields in Sun-like stars: a rotation threshold

17 The Maximal Flare Energy on the Young Sun We have analyzed new observations of magnetic fields on G stars with the rotation periods > 7 days. The mean longitudinal magnetic field is 10 times stronger than that t on the Sun at the maximum of the cycle. This allows us to estimate the maximal energy of flares on these G stars to be not more than ergs. Livshits, M.A., Rudenko, G.V., Katsova, M.M., Myshyakov, I.I.: I 2015, Adv. Space Res. 55(3), 920.

18 Maximal flare energies HMI/SDO -- SP-SOT/Hinode Background Вz Arrows : Horizontal field In regions where Вz< 200 G Black arrows from + to White arrows from to + Bz > 1000 G Box The quite Sun region corresponding to 2 σ 0.5 arcsec arcsec J. K. Thalmann et al astro-ph, 12 apr 2013

Estimate of the Maximal Possible Flare Energy in a Given Active Region Ef = E Epot = R/8π ((Bt,pot )^2 - (Bt)^2)) ds

The tangential components of the observed Bt and potential Bt,pot fields under condition that Bn = Bn,pot in each point

) For calculation of the free energy one use here observations and the calculated values of the potential field on the

19 Estimate of the Maximal Possible Flare Energy in a Given Active Region Ef = E Epot = R/8π ((Bt,pot )^2 - (Bt)^2)) ds the free energy arriving from the photosphere into the corona of AR. The tangential components of the observed Bt and potential Bt,pot fields under condition that Bn = Bn,pot in each point (Livshits, Rudenko, Katsova, 2015, Adv. Sp. Res.) For calculation of the free energy one use here observations and the calculated values of the potential field on the photosphere without t extrapolation ti NLFFF. We have applied one of NLFFF extrapolation algorithms and the virial theorem to data of vector magnetic field of solar AR. Maximal Possible Flare Energy of gy G dwarfs is also close to ergs.

20 Superflares with E > 10^34 erg As for flares of the higher energies, from erg to erg, there is evidence for occurrence of these events on the stars of the larger radius than R. This correlation is revealed by Balona (2015). If the radius of the G star increases, then the character of activity, including flares, changes significantly.

21 Concluding remark The detection of the flare microwave source and the emission in the Li resonant line could demonstrate how effective can be particle acceleration on the stars in the lower part of the main sequence.

22 Abstract Moisey Livshits (IZMIRAN, Russia), Maria Katsova (Sternberg State Astronomical Institute, Moscow State University, Russia), The origin of superflares on G-type dwarfs of different ages We discuss new observations of superflares on G stars discovered in optics with the Kepler mission. The origin of superflares is associated with effective particles acceleration on these stars that are slightly younger than the contemporary Sun. With a limited electron flux, penetrating into the chromosphere the explosive evaporation should lead to generation of the optical continuum covering the area of about cm 2. Such an area is typical to H α -ribbons of powerful solar flares and it is by 2 orders of magnitudes greater than that of white-light flares on the Sun. We propose that model of the optical continuum source consisting of the blue and red continua. We discuss two consequences of this model in the case of the hard spectrum of accelerated particles. Firstly, even in flares with E=10 34 erg, that can occur on the young Sun, a microwave source should arise, and its flux at 35 GHz is about of 7 mjn at the distance of 100 pc can be registered, for instance, with VLA (Very Large Array). Secondly, one can attempt to detect of flare-produced lithium that arises in the course of spallation reactions. The positive results of these observations will be evidence for extreme effective acceleration of particles in stellar atmospheres. See also Solar Physics DOI /s

23 Thank you for attention!

Flare Energy Release in the Low Atmosphere

Flare Energy Release in the Low Atmosphere Alexander G. Kosovichev, Viacheslav M. Sadykov New Jersey Institute of Technology Ivan N. Sharykin, Ivan V. Zimovets Space Research Institute RAS Santiago Vargas