Dichroic absorption by circumstellar dust as a possible polarigenic mechanism of RW Aur A and RY Tau Boris Safonov, Alexandr Dodin, Sergei Lamzin SAI MSU St. Petersburg, October 2019 Safonov B. Dichroic absorption in YSO
UX Ori variables Grinin, 1991 Polarization rises during fading. Explanation: the contribution of scattered light increases. Safonov B. Dichroic absorption in YSO
UX Ori variables Grinin, 1991 Polarization rises during fading. Explanation: the contribution of scattered light increases. Exceptions: RW Aur A and RY Tau. Safonov B. Dichroic absorption in YSO
Polarization of RW Aur A 35 pre 2010 30 2011-2012 2015-2018 25 20 p, % 15 10 5 0 150 100 PA 50 disc 0 10 11 12 13 14 15 10 11 12 13 14 15 9 10 11 12 13 14 15 V R c I c 1) Polarization rises during fading 2) Plane of polarization is almost perpendicular to jet (parallel to disc). Safonov B. Dichroic absorption in YSO
Polarization of RW Aur A 35 pre 2010 30 2011-2012 2015-2018 25 20 p, % 15 10 5 0 150 100 PA 50 disc 0 10 11 12 13 14 15 10 11 12 13 14 15 9 10 11 12 13 14 15 V R c I c Consider a specific date: 22-10-2016. Magnitude is R c = 10 . 1 (by 0 . 7 m fainter than pre-eclipse state). Total polarization 5%. Safonov B. Dichroic absorption in YSO
Resolving the polarized flux Differential Speckle Polarimetry: image in polarized flux at diffraction limited resolution (50 mas = 7 au @ 140 pc) Safonov+ 2019. polarized ✁ ux There is polarized structure shifted towards blue jet. PSF Safonov B. Dichroic absorption in YSO
Resolving the polarized flux Differential Speckle Polarimetry: image in polarized flux at diffraction limited resolution (50 mas = 7 au @ 140 pc) Safonov+ 2019. polarized fl ux There is polarized structure shifted towards blue jet. jet wind II PSF Ib Ia protoplanetary disk Its geometry qualitatively conforms to dusty wind hypothesis Dodin+ 2019. Safonov B. Dichroic absorption in YSO
Resolving the polarized flux Differential Speckle Polarimetry: image in polarized flux at diffraction limited resolution (50 mas = 7 au @ 140 pc) Safonov+ 2019. polarized fl ux There is polarized structure shifted towards blue jet. Summary of observational data for 2016-10-22: Magnitude is by 0 . 7 m , Total polarization is 5%, PSF The geometry of resolved polarized flux. Safonov B. Dichroic absorption in YSO
Model: disc log10 of density polarized flux, model − 5 polarized flux, obs − x 10 x 10 − 18 1.5 14 12 15 − 19 0.1 10 1 z, a.u. 8 10 − 20 0 6 0.5 4 5 − 21 − 0.1 2 0 − 22 0 0 5 10 15 − 0.1 0 0.1 − 0.1 0 0.1 r, a.u. arcsec arcsec Radiation transfer modeling: MC3D, Wolf, S., 2003. First approximation: thin disc ρ ( r , z ) = ρ 0 ( r / R ⋆ ) − α exp − z 2 / 2 h 2 ( r ) � � , (1) h ( r ) = h 0 ( r / R 0 ) β , (2) α = 2 . 3 , β = 1 . 2 , h 0 = 2.5 au, R 0 = 50 au, M = 10 − 4 M ⊙ . Safonov B. Dichroic absorption in YSO
Model: disc log10 of density polarized flux, model − 5 polarized flux, obs − x 10 x 10 − 18 1.5 14 12 15 − 19 0.1 10 1 z, a.u. 8 10 − 20 0 6 0.5 4 5 − 21 − 0.1 2 0 − 22 0 0 5 10 15 − 0.1 0 0.1 − 0.1 0 0.1 r, a.u. arcsec arcsec Resolved structure is not observable (too faint). Total polarization is too small: 0.7% (perpendicular to disc). Magnitude drop is − 0 . 05 m . Safonov B. Dichroic absorption in YSO
Model: disc log10 of density polarized flux, model − 5 polarized flux, obs − x 10 x 10 − 18 1.5 14 12 15 − 19 0.1 10 1 z, a.u. 8 10 − 20 0 6 0.5 4 5 − 21 − 0.1 2 0 − 22 0 0 5 10 15 − 0.1 0 0.1 − 0.1 0 0.1 r, a.u. arcsec arcsec Resolved structure is not observable (too faint). Total polarization is too small: 0.7% (perpendicular to disc). Magnitude drop is − 0 . 05 m . Common protoplanetary disc is thin and poorly illuminated → it scatters little light → . Safonov B. Dichroic absorption in YSO
Model: thick disc log10 of density polarized flux, model − 3 polarized flux, obs x 10 x 10 − − 18 3 1.5 2.5 15 − 19 0.1 2 1 z, a.u. 10 − 20 1.5 0 1 0.5 5 − 21 − 0.1 0.5 0 − 22 0 0 0 5 10 15 − 0.1 0 0.1 − 0.1 0 0.1 r, a.u. arcsec arcsec Resolved structure is reproduced. Total polarization is reproduced: 6%. Magnitude drop is 2 . 4 m — more than observed. Safonov B. Dichroic absorption in YSO
Model: cone wind log10 of density polarized flux, model − 4 polarized flux, obs − x 10 x 10 − 18 1.5 5 15 − 19 0.1 4 1 z, a.u. 10 − 20 3 0 2 0.5 5 − 21 − 0.1 1 0 − 22 0 0 0 5 10 15 − 0.1 0 0.1 − 0.1 0 0.1 r, a.u. arcsec arcsec Extended structure is reproduced. Total polarization: 0.8%, less than observed. Magnitude drop is reproduced: 0 . 7 m . Safonov B. Dichroic absorption in YSO
Cone wind + polarized star 5.9% log10 of density polarized flux, model − 3 polarized flux, obs − x 10 x 10 − 18 3 1.5 2.5 15 − 19 0.1 2 1 z, a.u. 10 − 20 1.5 0 1 0.5 5 − 21 − 0.1 0.5 0 − 22 0 0 5 10 15 − 0.1 0 0.1 − 0.1 0 0.1 r, a.u. arcsec arcsec Extended structure is reproduced ( χ 2 r = 1 . 1 ). Total polarization is reproduced: 5%. Magnitude drop is reproduced: 0 . 7 m . Safonov B. Dichroic absorption in YSO
RY Tau Safonov B. Dichroic absorption in YSO
RY Tau ALMA 3 mm, Harrison+ 2019. Oudmaijer+ 2001. V-band polarimetry. Disc, infalling envelope, wind, jet. UX Ori variability, timescale 1 h – 1 yr. Sometimes quite chaotic. Safonov B. Dichroic absorption in YSO
RY Tau: DSP Takami+ 2013ApJ...772..145T Differential Speckle Polarimetry, I Subaru/HiCIAO band. (AO+coronagraph), H band Dashed circle corresponds to coronagraphic mask of HiCIAO. N 0.2 0 E -0.2 0.2 0 -0.2 arcsec Safonov B. Dichroic absorption in YSO
RY Tau: multiple epochs 05−09−2017 −4 02−12−2017 −4 06−03−2018 −4 x 10 x 10 x 10 0.2 12 0.2 12 0.2 12 10 10 10 0.1 0.1 0.1 8 8 8 0 0 0 6 6 6 −0.1 −0.1 −0.1 4 4 4 −0.2 −0.2 −0.2 2 2 2 14−10−2018 −4 25−11−2018 −3 03−12−2018 −4 x 10 x 10 x 10 2.5 0.2 6 0.2 0.2 6 5 2 5 0.1 0.1 0.1 4 4 1.5 0 0 0 3 3 1 −0.1 −0.1 −0.1 2 2 0.5 −0.2 1 −0.2 −0.2 1 0.2 0.1 0.0 −0.1 −0.2 0.2 0.1 0.0 −0.1 −0.2 0.2 0.1 0.0 −0.1 −0.2 arcsec arcsec arcsec Two components of polarized flux distribution: Extended constant. Interstellar polarization substracted (I band): P=2.39%, χ = 26 ◦ , Petrov+ 1999. Point–like variable. Safonov B. Dichroic absorption in YSO
RY Tau: two epochs Apporximate data for 2018 Dec 3 by the data for 2018 Nov 25: 1) Add a point-like polarized source: q s , u s , ∆ RA , ∆ dec . 2) Change the brightness of the star by γ . Band I c : 2018 Dec 3: original (I c =8.5 ± 0.2) 2018 Dec 3: modified (I c =8.8 ± 0.2) 2018 Nov 25: original (I c =9.1 ± 0.2) 0.2 0.2 0.2 0.1 0.1 0.1 arcsec 0 0 0 −0.1 −0.1 −0.1 −0.2 −0.2 −0.2 0.2 0.1 0.0 −0.1 −0.2 −0.2 0 0.2 0.2 0.1 0.0 −0.1 −0.2 χ 2 band q s , % u s , % ∆ RA , mas ∆ dec , mas γ r 2 . 9 ± 0 . 1 2 . 0 ± 0 . 2 2 ± 2 2 ± 2 0 . 75 ± 0 . 06 1.8 I c Safonov B. Dichroic absorption in YSO
Conclusions The resolved polarimetric data for RW Aur A are difficult to explain by scattering only. Additional polarized flux can be generated by dichroic absorption by aligned circumstellar dust. RY Tau circumstellar nebula consists of stable extended component and variable uresolved point–like component (size less than 50 mas) co-located with the star (<4 mas displacement). Point–like component is probably direct stellar radiation polarized by aligned dust. Safonov B. Dichroic absorption in YSO
Conclusions The resolved polarimetric data for RW Aur A are difficult to explain by scattering only. Additional polarized flux can be generated by dichroic absorption by aligned circumstellar dust. RY Tau circumstellar nebula consists of stable extended component and variable uresolved point–like component (size less than 50 mas) co-located with the star (<4 mas displacement). Point–like component is probably direct stellar radiation polarized by aligned dust. Thank you Supported by RNF (17-12-01241) Safonov B. Dichroic absorption in YSO
Alignment mechanisms r que alignment magnetic fi eld alignment r � ✂ ✄ � ☎ ✄ ✆ ✝ ☎ ✞ ✝ r : st ✝ r : st r ized ✞ ♦ ✟ ✝ r ✆ � r ✄ ✟ ❛ ♥ ✠ ✞ ✡ � r ✄ ☛ ✝ ✂ ✞ ♦ ✟ ✝ r ✆ � r ✄ ✟ ✠ ✞ ✡ � magnetic fi eld radiation radiation Safonov B. Dichroic absorption in YSO
Alignment mechanisms Polarization along the disc equator is consistent with torodial magnetic field. observer magnetic fi eld polarization disc equator Safonov B. Dichroic absorption in YSO
Alignment timescales precession timescale 15 z, a.u. 10 0 10 gas dumping time radiation t, year magnetic 5 10 -5 0 0 5 10 15 r, a.u. Tazaki+ (2017) 10 -10 10 -3 10 -2 10 -1 10 0 10 1 dust size, mkm Gas density: 5 × 10 − 19 g · cm − 3 . Gas temperature: 220 K. Average wavelength: 0 . 65 µ m. Radiation energy density: 2 . 7 × 10 − 5 erg · cm − 3 . Magnetic field strength: 5 mG. smaller timescale wins Safonov B. Dichroic absorption in YSO
Recommend
More recommend
