Akimasa Kataoka (NAOJ fellow, NAOJ)

Transcription

1 Investigating planet formation by FIR and sub-mm polarization observations of protoplanetary disks The Astrophysical Journal Letters, 844:L5 (5pp), 2017 July 20 ALMA Band 7 (870 µm) essential. The wavelength dependence of the polarization fraction is not strong in the case of the grain alignment, while it is strong in the case of the self-scattering because the scattering-induced polarization is efficient only when the maximum grain size is around l 2p where λ is the wavelengths (Kataoka et al. 2015). To obtain the wavelength-dependent polarimetric images, we observe the HL Tau disk with the Atacama Large Millimeter/ submillimeter Array (ALMA) using Band 3. HL Tau is a young star in the Taurus molecular cloud with a distance of 140 pc (Rebull et al. 2004). The circumstellar disk is around in 100 au scale (Kwon et al. 2011). The disk has several ring and gap structures with tens of au scales (ALMA Partnership et al. 2015). The observed band corresponds to wavelengths of 3.1 mm, which is sufficiently longer than the previous CARMA polarimetric observations at 1.3 mm (Stephens et al. 2014). ALMA Band 3 (3.1 mm) HL Tau Kataoka et al. 2. Observations Stephens et al Kataoka et al HL Tau was observed by ALMA on 2016 October 12, during its Cycle 4 operation ( S, PI: A. Kataoka). Scattering Alignment The antenna configuration was C40-6, and 41 antennas were operating. The correlator (Kataoka processed et al. four 2015) spectral windows (Tazaki et al. 2015) centered at 90.5, 92.5, 102.5, and GHz with a bandwidth of 1.75 GHz each. The bandpass, amplitude, and phase were calibrated by observations of J , J , and J , respectively, and the polarization calibration was performed by observations of J The raw data were reduced T. by the Muto EA-ARC (Kogakuin staff. U.), M. Momose, T. Tsukagoshi (Ibaraki U.), H.Nagai (NAOJ), M. Fukagawa (Nagoya U.), We H. Shibai further(osaka performu.), thet. iterative Hanawa CLEAN (Chiba deconvolution U.), K. Murakawa (Osaka-S.), Kees Dullemond, Adriana Pohl (Heidelberg) Akimasa Kataoka (NAOJ fellow, NAOJ)

2 Millimeter Polarization Old and new theories for explaining millimeter-wave polarization 1. Alignment with magnetic fields 2. Self-scattering of thermal dust emission Kataoka et al Alignment with radiation fields Testing the theory with ALMA polarization observations HD morphology of pol. vectors HL Tau - wavelength dependence Kataoka et al AU

3 Dust is big in disks 0.1μm 1mm 1m 1km km κ abs,sca [cm 2 /g] dust opacity a max =1 µm, κ abs a max =1 µm, κ sca a max =100 µm, κ abs a max =100 µm, κ sca λ [µm] scattering > absorption

4 Light source of scattering IR scattered light example (face-on, PI) Infrared disk radio scattered light (self-scattering) Pohl et al millimeter?

5 self-scattering in an inclined disk polarization reversal in the large grain case, which yields an intrinsic (or face-on) polarization direction in the radial (as opposed to azimuthal) direction and an inclination-induced polarization along the major (rather than minor) axis. The interplay between the intrinsic and inclination-induced polarization leads to polarization directions in the region of high polarized intensity (the most easily observable part) completely different from those observed in HL thermal dust emission of the disc closer to the observer (the right half) brighter. The polarization fraction is, however, higher on the far side (especially towards the outer part of the disc) because the polarization degree of the scattered light is higher for backward scattering than for forward scattering (see Fig. 6). The most striking difference between this case and the Rayleigh scattering case shown in Fig. 5 lies in the polarization direction. The difference comes from the polarization vector (disk, edge-on view) Figure 7. Scattering-induced polarization by large grains. As in Fig. 5, plotted are the polarized intensity (colour map) and polarization vectors (line segments, with length proportional to the polarization fraction). Note the strong asymmetry with respect to the major axis in both the polarized intensity and the polarization vectors. The polarization along the major axis in the central region is due to polarization reversal, which may be a robust indicator of scattering by large, mm/cm-sized, grains. The near side of the disc is on the right. thermal dust emission i=45 Yang, Li, et al See also Kataoka et al. 2016a

6 Conditions of dust grains for polarization For efficient scattering (grain size) >~ λ For efficient polarization (grain size) <~ λ There is a grain size which contributes most to the polarized emission P P 90 λ=870 µm (ALMA Band 7) Maximum grain size [cm] grain size [cm] P ω Albedo If (grain size) ~ λ/2π, the polarized emission due to dust scattering is the strongest

7 Grain size constraints by polarization Expected polarization degree (scalable) 0.87 mm (Band 7) 0.34 mm (Band 10) 3.1 mm (Band 3) 7 mm (Band 1) Maximum grain size [cm] Kataoka, et al., 2015 Multi-wave polarization constraints on the grain size

8 HL Tau - continuum The Astrophysical Journal Letters, 808:L3 (10pp), ALMA2015 Partnership July 20 et al. ALMA Partnership, 2015

9 HL Tau pol. - prediction λ=870µm i = 47 (ALMA Partnership 2015) The polarization vectors are parallel to the minor axis Kataoka, et al., 2016a (see also Yang et al. 2016)

10 Polarization mechanisms alignment with B-fields self-scattering alignment with radiation AASTEX wavelength-dependentpolarization AU 100 AU self-scattering alignment with radiation Kataoka, et al., 2017 Figure 2. Comparison of the polarization images between = 1.3 mm(carma Stephens et al. 2014) and = 3.1 mm

11 Total polarization fraction 100 AU 100 AU integrating weak polarization 0.5% <0.1% We can extract the self-scattering components

12 HL Tau polarization The maximum grain size is ~ 70 µm Kataoka, et al., 2017

13 What can we do at MIR? MIR Scattered Light (sub-)mm a b d c Distance in AU 1 Turbulent Mixing (radial or vertical) 2 Vertical Settling 3 Radial Drift 4 a) Sticking b) Bouncing c) Fragmentation with mass transfer d) Fragmentation mm 3.0 mm ALMA VLTI/MATISSE 10 µm 2 µm µm EELT JWST/MIRI Fig. 1. Illustration of the structure, grain evolution processes and observational constraints for protoplanetary disks. On Akimasa Kataoka (NAOJ fellow)

14 Current understandings 1µm 10µm 100µm 1mm scattering of photons of central star Alignment with B-field? Alignment with rad-fields scattering (?) scattering Astrophysical Journal, 832:18 (9pp), 2016 November 20 Li et al. main-sequence The stars of 2 4 Me) at the distance of 144 pc circumstellar disk HD : gas, dust and planets acting in concert? 5 Warf et al. 2003). At 4 ± 1 Myr old, this source still shows 7 1 ence of significant accretion ( 10 Me yr ; DeWarf l. 2003; Tang et al. 2012). AB Aur is surrounded by a minent disk, with mid-ir and 1.3 mm dust emission cted out to 280 au and CO line emission detected out to 0 au from the star (Mariñas et al. 2006; Tang et al. 2012). oth CO and near-ir scattered-light images, the disk is rich morphological features such as spiral arms and gaps, gesting a dynamical disk environment and, perhaps, oing planet formation (Piétu et al. 2005; Hashimoto. 2011; Tang et al. 2012). Previous observations at various elengths gave a fairly consistent disk inclination of 27 ere 0 corresponds to pole-on), with the major axis of the oriented at a position angle (P.A.) of 70 (measured E m N) (Piétu et al. 2005; Tang et al. 2012; Rodríguez. 2014). H-band (1.6 μm) polarization of the AB Aur disk been imaged by Hashimoto et al. (2011), showing a clear rosymmetric pattern indicative of scattering, as expected at e short IR wavelengths. he paper is organized as follows. Section 2 describes our acquisition and reduction, with results presented in ion 3. Disk models are presented in Section 4. The Figure 1. Polarization map of the AB Aur protoplanetary disk at 10.3 μm. Displayed in logarithmic color is the totalscale intensity of the disk, superimposed by Q r 2 ications 1. of our are discussed in Section 5, with our image Figure Left:study J-band azimuthally polarized intensity Q in forimage better visualization. Right: white contours of polarized intensities at 20, 40, 80, 160, 320, and 640 mjy ngs summarized in Section 6. 2Each image pixel is multiplied with the square of its distance n linear scale with annotations for the gap and ring structures. arcsec. Each polarization vector is derived from an aperture of 3 3 pixels the original image. Polarization only plotted where the signal-toto the star, r2, to compensate for the stellar illumination in drop-o with radius. Allvectors flux are scales are normalized to half of the noise (S/N) is higher than 150 in by the the total intensity image, North yielding is a up, East brightest pixel along the inner ring. The region masked by the ratio coronagraph is indicated gray circle. maximum uncertainty in the degree of polarization (p) of 1%. Near the disk 2. OBSERVATIONS AND DATA REDUCTION points towards left. center, where the highest S/N is reached, the typical uncertainty in p is 0.1%. The angular resolution of the observation is 0 35, as shown in the bottom-left We observed AB Aur on 2015 February 6 UT using the corner. The upper-left sketch shows the projected spin axis (thick line) and m band dual-beam polarimetry mode of CanariCam. We Pohl, et al., 2017 Li, et al., 2016 Akimasa Kataoka AASTEX AAST wavelength-dependent polarization polarization EX wavelength-dependent 100 AU Kataoka, et al., AU Figure 2. Figure Comparison 2. Comparison of the polarization of the polarization images between images between = 1.3 mm = (CARMA 1.3 mm (CARMA Stephens Stephens et al. 2014) et al. and 2014)= and 3.1 (ALMA, (ALMA, this observation). this observation). The ALMA Theimage ALMA is image smoothed is smoothed to have the to have samethe beam same sizebeam of CARMA size of CARMA where thewhere beamthe siz with 0.56 the with PA ofthe 79.5 PAdegrees. of 79.5 The degrees. colorthe scale color represents scale represents the polarized the polarized intensity intensity while thewhile grey contours the grey conto repre the continuum the continuum emission.emission. The levelsthe of the levels grey of contours the grey contours are (3, 6, 12, are 24, (3, 48, 6, 12, 96)24, 48, 96) II where = 2.1 mjy/beam for the CAR for I where I = 2.1 mjy/beam data and fellow) data 34.9 mjy/beam ALMA data. ALMA data. I = and I = 34.9 mjy/beam (NAOJ

15 Science: scattering is efficient at MIR? Porous Compact

16 Case study: HL Tau meter variation along changing bheight. The thinner models are preferred by both of our millimeter wavelength images, based on the posterior n disk models cannot explain the mid-infrared fluxes (Figure 3). ED overlaid with models of various bheight values. The solid line is the case of bheight = 1.5 and the dashed lines are cases of bheight = 0.1, 0.2, m the bottom. The two stars indicate our data points 700 and 120 mjy at λ = 1.3 and 2.7 mm, respectively. ~ 50 Jy at 100 micron by both of our millimeter wavelength images from CARMA, they cannot explain the mid-infrared fluxes. In contrast, the bheight = 1.5 case recovers the SED reasonably well over midinfrared to millimeter wavelengths and fits the two CARMA images. The bump of the model SEDs in near-infrared regime is = 1.5 case, which is closest to and does e the data points, is presented by a solid line. gular points are data from Men shchikov et al. olid stars mark our values at λ = 1.3 mm and lthough the thinner disk models are preferred ght 1% polarization: 500 mjy 4 0.1% polarization 50 mjy

17 Conclusions We have observed polarization of HL Tau with ALMA 3.1 mm polarization vectors are dominated by explained by the grain alignment, while 1.3 mm pol. vectors by the self-scattering. The maximum grain size is constrained to be ~70 µm (Kataoka et al. 2016a ApJ, Kataoka et al ApJL) Possible science goals of MIR polarimetry of protoplanetary disks HL Tau Detection of MIR polarization of HL Tau -> porous dust aggregates Non-detection of MIR polarization of HL Tau -> compact dust aggregates Other disks If scattering is observed, it would represents disks with small grains - may be young. This is complementary with ALMA observations. If we can detect polarization due to alignment of grains with B-fields, this would be the unique way to study the magnetic fields in disks

18 Dust opacity of protoplanetary disks Grain size is ~ millimeter (or larger) Testi et al. 2014