Dichroic absorption by circumstellar dust as a possible polarigenic - - PowerPoint PPT Presentation

Dichroic absorption by circumstellar dust as a possible polarigenic mechanism

• f 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

• f scattered light increases.

Safonov B. Dichroic absorption in YSO

UX Ori variables

Grinin, 1991 Polarization rises during fading. Explanation: the contribution

• f scattered light increases.

Exceptions: RW Aur A and RY Tau.

Safonov B. Dichroic absorption in YSO

Polarization of RW Aur A

p, %

5 10 15 20 25 30 35

pre 2010 2011-2012 2015-2018

V

10 11 12 13 14 15

PA

disc

50 100 150 Rc 10 11 12 13 14 15 Ic 9 10 11 12 13 14 15

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

p, %

5 10 15 20 25 30 35

pre 2010 2011-2012 2015-2018

V

10 11 12 13 14 15

PA

disc

50 100 150 Rc 10 11 12 13 14 15 Ic 9 10 11 12 13 14 15

Consider a specific date: 22-10-2016. Magnitude is Rc = 10.1 (by 0.7m 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

PSF

There is polarized structure shifted towards blue jet.

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 flux PSF

There is polarized structure shifted towards blue jet.

Ia Ib II

protoplanetary disk wind jet

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 flux PSF

There is polarized structure shifted towards blue jet. Summary of observational data for 2016-10-22: Magnitude is by 0.7m, Total polarization is 5%, The geometry of resolved polarized flux.

Safonov B. Dichroic absorption in YSO

Model: disc

r, a.u. z, a.u. log10 of density 5 10 15 5 10 15 −22 −21 −20 −19 −18 −0.1 0.1 polarized flux, model arcsec 2 4 6 8 10 12 14 x 10

−5

−0.1 0.1 −0.1 0.1 arcsec polarized flux, obs 0.5 1 1.5 x 10

−

Radiation transfer modeling: MC3D, Wolf, S., 2003. First approximation: thin disc ρ(r, z) = ρ0(r/R⋆)−α exp

• −z2/2h2(r)
• ,

(1) h(r) = h0(r/R0)β, (2) α = 2.3, β = 1.2, h0 = 2.5 au, R0 = 50 au, M = 10−4M⊙.

Safonov B. Dichroic absorption in YSO

Model: disc

r, a.u. z, a.u. log10 of density 5 10 15 5 10 15 −22 −21 −20 −19 −18 −0.1 0.1 polarized flux, model arcsec 2 4 6 8 10 12 14 x 10

−5

−0.1 0.1 −0.1 0.1 arcsec polarized flux, obs 0.5 1 1.5 x 10

−

Resolved structure is not observable (too faint). Total polarization is too small: 0.7% (perpendicular to disc). Magnitude drop is −0.05m.

Safonov B. Dichroic absorption in YSO

Model: disc

r, a.u. z, a.u. log10 of density 5 10 15 5 10 15 −22 −21 −20 −19 −18 −0.1 0.1 polarized flux, model arcsec 2 4 6 8 10 12 14 x 10

−5

−0.1 0.1 −0.1 0.1 arcsec polarized flux, obs 0.5 1 1.5 x 10

−

Resolved structure is not observable (too faint). Total polarization is too small: 0.7% (perpendicular to disc). Magnitude drop is −0.05m. Common protoplanetary disc is thin and poorly illuminated → it scatters little light →.

Safonov B. Dichroic absorption in YSO

Model: thick disc

r, a.u. z, a.u. log10 of density 5 10 15 5 10 15 −22 −21 −20 −19 −18 −0.1 0.1 polarized flux, model arcsec 0.5 1 1.5 2 2.5 3 x 10

−3

−0.1 0.1 −0.1 0.1 arcsec polarized flux, obs 0.5 1 1.5 x 10

−

Resolved structure is reproduced. Total polarization is reproduced: 6%. Magnitude drop is 2.4m — more than observed.

Safonov B. Dichroic absorption in YSO

Model: cone wind

r, a.u. z, a.u. log10 of density 5 10 15 5 10 15 −22 −21 −20 −19 −18 −0.1 0.1 polarized flux, model arcsec 1 2 3 4 5 x 10

−4

−0.1 0.1 −0.1 0.1 arcsec polarized flux, obs 0.5 1 1.5 x 10

−

Extended structure is reproduced. Total polarization: 0.8%, less than observed. Magnitude drop is reproduced: 0.7m.

Safonov B. Dichroic absorption in YSO

Cone wind + polarized star 5.9%

r, a.u. z, a.u. log10 of density 5 10 15 5 10 15 −22 −21 −20 −19 −18 −0.1 0.1 polarized flux, model arcsec 0.5 1 1.5 2 2.5 3 x 10

−3

−0.1 0.1 −0.1 0.1 arcsec polarized flux, obs 0.5 1 1.5 x 10

−

Extended structure is reproduced (χ2

r = 1.1).

Total polarization is reproduced: 5%. Magnitude drop is reproduced: 0.7m.

Safonov B. Dichroic absorption in YSO

RY Tau

Safonov B. Dichroic absorption in YSO

RY Tau

ALMA 3 mm, Harrison+ 2019. Disc, infalling envelope, wind, jet. UX Ori variability, timescale 1 h – 1 yr. Sometimes quite chaotic. Oudmaijer+ 2001. V-band polarimetry.

Safonov B. Dichroic absorption in YSO

RY Tau: DSP

Takami+ 2013ApJ...772..145T Subaru/HiCIAO (AO+coronagraph), H band Differential Speckle Polarimetry, I band. Dashed circle corresponds to coronagraphic mask of HiCIAO.

N E

arcsec

0.2

• 0.2
• 0.2

0.2 Safonov B. Dichroic absorption in YSO

14−10−2018 arcsec 0.2 0.1 0.0 −0.1 −0.2 −0.2 −0.1 0.1 0.2 1 2 3 4 5 6 x 10

−4

25−11−2018 arcsec 0.2 0.1 0.0 −0.1 −0.2 −0.2 −0.1 0.1 0.2 0.5 1 1.5 2 2.5 x 10

−3

03−12−2018 arcsec 0.2 0.1 0.0 −0.1 −0.2 −0.2 −0.1 0.1 0.2 1 2 3 4 5 6 x 10

−4

05−09−2017 −0.2 −0.1 0.1 0.2 2 4 6 8 10 12 x 10

−4

02−12−2017 −0.2 −0.1 0.1 0.2 2 4 6 8 10 12 x 10

−4

06−03−2018 −0.2 −0.1 0.1 0.2 2 4 6 8 10 12 x 10

−4

RY Tau: multiple epochs

Two components of polarized flux distribution: Extended constant. Point–like variable.

Safonov B. Dichroic absorption in YSO

Interstellar polarization substracted (I band): P=2.39%, χ = 26◦, Petrov+ 1999.

arcsec 2018 Dec 3: original (Ic=8.5±0.2) 0.2 0.1 0.0 −0.1 −0.2 −0.2 −0.1 0.1 0.2 2018 Dec 3: modified (Ic=8.8±0.2) −0.2 0.2 −0.2 −0.1 0.1 0.2 2018 Nov 25: original (Ic=9.1±0.2) 0.2 0.1 0.0 −0.1 −0.2 −0.2 −0.1 0.1 0.2

RY Tau: two epochs

Apporximate data for 2018 Dec 3 by the data for 2018 Nov 25: 1) Add a point-like polarized source: qs, us, ∆RA, ∆dec. 2) Change the brightness of the star by γ. Band Ic:

band qs, % us, % ∆RA, mas ∆dec, mas γ χ2

r

Ic 2.9 ± 0.1 2.0 ± 0.2 2 ± 2 2 ± 2 0.75 ± 0.06 1.8

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

radiation radiation magnetic fi eld

• ☎

• r

• r ✄

magnetic fi eld alignment

• r

• rized

Alignment mechanisms

Safonov B. Dichroic absorption in YSO

• bserver

disc equator magnetic fi eld polarization

Alignment mechanisms

Polarization along the disc equator is consistent with torodial magnetic field.

Safonov B. Dichroic absorption in YSO

Alignment timescales

r, a.u. z, a.u. 5 10 15 5 10 15

Tazaki+ (2017)

dust size, mkm

10 -3 10 -2 10 -1 10 0 10 1

t, year

10 -10 10 -5 10 0

precession timescale

gas dumping time radiation magnetic

Gas density: 5 × 10−19 g·cm−3. Gas temperature: 220 K. Average wavelength: 0.65 µm. Radiation energy density: 2.7 × 10−5 erg·cm−3. Magnetic field strength: 5 mG. smaller timescale wins

Safonov B. Dichroic absorption in YSO

RW Aur A: 22-10-2016

5200 5600 6000 6400 6800 7200 7600 8000 14 13 12 11 10 V

Soon after recovery from deep eclipse. Dense wind just passed line of sight and should be visible.

Safonov B. Dichroic absorption in YSO

RW Aur A SED

MC RT modeling.

λ, µm

10 -1 10 0 10 1 10 2 10 3

Fλ, erg s -1 cm -2 µm -1

10 -13 10 -12 10 -11 10 -10 10 -9 10 -8

SED of RW Aur A

thin disc cone wind thick disc pre-eclipse obs

Safonov B. Dichroic absorption in YSO

Disty disc wind

Gressel+, 2015: Dust can be entrained from the disc by the slow ( 10 km/s) disc wind (Owen et al., 2011; Hutchinson et al., 2016), or possibly by magnetospheric wind.

Safonov B. Dichroic absorption in YSO