An evolution of the magnetic fields of massive stars. A.F. Kholtygin. Saint-Petersburg University, Russia. Tartu Observatory December 15, 2015

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1 An evolution of the magnetic fields of massive stars A.F. Kholtygin Saint-Petersburg University, Russia Tartu Observatory December 15, 2015

2 LPV and Magnetic field Line profiles in spectra of massive stars are changing on time scales from minutes to days. LPV amplitude varies from fractions of a percent to tens of percent. In some cases, even the line type is changed. In the profiles of absorption lines the emission components are often detected. In some cases the lines can be vary to purely emission ones. Coherent LPV of NII and C II in the spectrum of weakly magnetic star Leo controlled by magnetic field (Kholtygin et al. 2007)

3 Sources of the magnetic field data Aims: To investigate statistically whether magnetic fields in massive stars are ubiquitous or appear only in stars with a specific spectral classification, certain ages, or in a special environment. Telescopes and Spectrographs VLT, 8-m Antu m ESO FORS2+HARPS, NOT O star observations with FORS and HARPS: MAGORI and O PROJECTS Results for O stars: In stars > 100 spectra. Magnetic field at 3 level was detected for 14 O stars, including two Of?p stars. 26% 21% 24% 30% Hubrig et al. (2011, 2013)

4 Project MIMES: Magnetism in Massive Stars Head of the Project: Gregg Wade, Canada 5/5 for two Of?p stars (HD и CPD ) magnetic fields have been detected by MAGORI group Magnetism_in_Massive_Stars.html

5 Magnetic field distribution for O stars f 0 ), ( ) ( N N f obs 0 0 A f The number of data is small ~ stars

6 Magnetic field distribution for A stars: first glance Magnetic field distribution for (empty) and A (filled) symbols accordingly. Power approximation is shown with a dashed line. Pentagons mark data in the region < 300 G. Is the gap at < 0.3 kg (magnetic desert) real? Probably not!

7 Magnetic field distribution for A stars: the second view Changing paradigm: Log-normal distribution instead of power law We use only data from ychkov (2009) catalog There is NO of the magnetic desert

8 From Magnetic Fields to Magnetic fluxes Net magnetic fluxes of massive stars F R 2 * 2 0 r sin d d r F 4 R 2 *

9 Magnetic pseudo-flux distribution for massive O stars WR stars, pulsars and magnetars Magnetars WR stars (upper limit) Millisecond pulsars Normal pulsars Massive O stars

10 The general scheme of the massive stars and their magnetic field evolution 0.5 kg 10-6 G G Stages of evolution, about which we know the typical values of the magnetic field are marked

11 Magnetic field generation for massive stars Protostellar cloud 0.01 pc & 10-6 G 3-5 R 10 4 G White dwarfs km & G Neutron stars Dynamo action lack Holes 12 km & G F П R 4R 2 const 1 2 R

12 Our new population synthesis code We create an ensemble of massive stars on the main sequence in order to obtain mass, age, radius distributions of these stars based on the AMUSE platform Initial distribution of magnetic fluxes Magnetic flux evolution Magnetic flux and rms magnetic field d is the dissipation parameter. i =t/ MS Also we introduce a threshold value of the magnetic field min ~ 300 G (Auriere et al. 2007) as an optional parameter. Dissipation parameter derived from observations is about 0.1 In that case a magnetic field distribution would be highly asymmetric. Observational data is incomplete, more data is needed f 1 = N magn /N nomagn (at ZAMS) f 2 = N magn /N nomagn (at the present time)

13 Common distribution function for A stars f 1 = 30% f 2 =10% It means that 2/3 of A are nonmagnetic at ZAMS

14 Distribution function for O stars

15 Evolution of the magnetic fields and magnetic fluxes for stars with masses in the interval [3,4] solar masses А) MF measurements ) Model Landstreet et al. (2007)

16 What happens before ZAMS Toy model of the magnetic field and magnetic flux generation by dynamo-action All stars have the equal initial magnetic flux F 0 Magnetic field is generated during the N cycles fin = 0 * 1 * 2 * N i is the uniformly distributed random variable in an interval [a,b] Magnetic flux F i = 4R i2 i, R i is the stellar radius at the cycle i, F fin = F 0 * 1 * 2 * N, where i+1 = i*( i+1 / i )*(R i+1 /R i ) 2 F 0 = 0 * 4R 0 2 Parameters of the model: 0 (or F 0 ), R 0, a, b, N

17 A stars F fin F Parameters of the model: logf 0 =1.5*10 24 G*cm 2, a=1.0, b=1.85, N=20

18 F fin O stars 3 F Parameters of the model: logf 0 =8.8*10 24 G*cm 2, a=1.0, b=2.00, N=20

19 Magnetic fields of WR stars Short history 1999, 2 Vel (WR11) Eversberg et al. < 280 Гс 2002, 2 Vel Chesneau & Moffat. No results 2006, WR6, St-Louis et al. < 25 Гс 2011, Kholtygin et al. WR 135 < 200 Гс WR 136 < 50 Гс 2013 WR 6 de la Chevrotière et al. < 100 Гс 2014 de la Chevrotière et al. WR 134 ~ 200 Гс WR 137 ~ 130 Гс WR 138 ~ 80 Гс HeII4686 WN4 ММО Our group investigations 6-meter telescope MSS + polarization analyzer WR 135: 23 spectra (2009) WR136: 62 spectra (2009_2010) Indirect evidence of the magnetic field AT V =1600 км/с V cor sini= км/с R cor =12 R * V*sini =14070 км/с surf =20 kg The observed spectrum (solid blue line) in a comparison with a model spectrum without rotation (black dotted line) and the rotation (red dotted line, Shenar et al. A & A 562, A118, 2014). The observed line profiles can be explained by the assumption of the existence of the corotation region up to 12 R *

20 Stochastic LPV for WR 136 The dynamical LPV for HeII5411 star WR 136 on 25 July dv / dt =500 km / s / day (Kholtygin et al. 2011)

21 Smooth time variation (smtvs) spectra for HeII5411 line HeII5411 Top: smoothed TVS spectrum of left-polarized component of HeII5411 line (TVSL spectrum) for WR136, obtained in 2009; Middle: the same as that on the right panel, but for the right-polarized component profiles (TVSR spectrum); ottom: the average profile of the line HeII5411 (Kholtygin et al. 2011).

22 smtvs for HeII5411 Stokes parameter V SmTVS of the Stokes parameter V for the WR 136 (6-meter telescope July 25th, 2010)

23 The characteristic times of the magnetic field evolution A Alfven frequency rotation frequency raithwaite and Cantiello, MNRAS (2013)) i) High E, high H ii) High E, low H evol «MS iii) Low E, low H evol» MS Helicity H= A 2 L Cantiello et al. (2009))

24 Local solar magnetic fields, prominences and loops ancja_s%c5%82oneczna_trace.jpg

25 Conclusions 1. The magnetic desert for OA does not exist. 2. We create a model which can describe the real distribution of massive star magnetic fields 3. Initial fraction (at ZAMS) of magnetic O stars can be in the range from 30% to 90% 4. The question remains why only a small fraction of O stars are magnetic remains unanswered 5. The connection between LPV and Magnetic field have to be invetigated 6. It is not clear yet, if the magnetic field presents in WR stars?