Spectropolarimetry Bag Lunch Seminar - Dec 2003 Outline 1.Background 2.Applications a)Studying the transition from AGB to post-AGB; b)Probing the structure of Herbig Ae/Be stars; c)Seyfert galaxies.

1 – Background Spectropolarimetry –Simultaneous measurement of the four stokes parameters, as a function of wavelength: I( )  Intensity Q( ) & U( )  linear polarization: P = (Q 2 +U 2 ) 1/2 V( )  circular polarization How to measure polarization: AnaliserBeam displacer ( /2 waveplate) (calcite) Detector E O Light beam

1 – Background (cont.) Example: PBO –Modified Boller and Chivens small telescope spectrograph Detector Wollaston Prism Rotating waveplate Grating Camera Glan Prism Colimator Difficulties –Polarization optics have to be achromatic –Measurement require much more photons: observation must be made for at least 4 positions of the waveplate polarization do not follow Poisson statistics  statistical errors for Q, U and V larger than for I

1 – Background (cont.) Typical resolution –In general, largely confined to low spectral resolution (R = ) –Most studies concentrate on the continuum –Studies of polarimetric line profiles are scarce (or used to be…) expect for greatly broadened lines (QSOs, Seyfert, SNe)

2 – Applications a) Transition from AGB to PN From the AGB to the PN phase, the circumstellar envelope goes from nearly spherical to aspherical, presenting a wide range of morphologies When and how the transition starts? Trammell et al  investigated 31 stars believed to be undergoing the early phases of the transition 24 were intrinsically polarized  evidence that aspherical structure appears very early in the transition

2 – Applications: a) AGB to PN (cont.) IRAS (post-AGB) Lack of features in the lines Polarization raises to the blue. 10%! PA change of ~ 70 deg

2 – Applications: a) AGB to PN (cont.) How to get a PA flip? Ingredients: –Bipolar geometry (two components) –Absorption (  < 1) Net pol: IRAS –PA flip of 70 deg  indication that the symmetry axis of the two components differ (e.g. clumpy media)

2 – Applications: a) AGB to PN (cont.) IRC H  is less polarized

2 – Applications: a) AGB to PN (cont.) Line Depolarization P Stellar photosfere P Line emitting regiion  Many other line effects alter the polarization… ContinuumLine scattering region

2 – Applications b) Circumstellar Structure of Ae/Be Stars Ae/Be stars are pre-main sequence stars of intermediate mass Most of them are intrisecally polarized in the continuum Spectropolarimetry of emission lines gives the possibility of probing the circumstellar structure near the star Vink et al  Studied H  in 22 Herbig Ae/Bes 15 out of 22 objects show clear line effects  indication that the geometry near the star is not spherical

2 – Applications: b) Ae/Be stars

Spectropolarimetric expectations  No line effect

2 – Applications: b) Ae/Be stars Spectropolarimetric expectations  depolarization

2 – Applications: b) Ae/Be stars Spectropolarimetric expectations  rotating disk

2 – Applications: b) Ae/Be stars Example: no line effect  IL Cep

2 – Applications: b) Ae/Be stars Example: depolarization  BD

2 – Applications: b) Ae/Be stars Example: loop  CQ Tau

2 – Applications c) Seyfert Galaxies Seyfert galaxies are named for Carl K. Seyfert who in 1943, described them as their central regions having peculiar spectra with notable emission lines. They are spiral galaxies and account for about 10% of all galaxies (Ho et al. 1997) Two types, depending on the line profiles: –Type I: very broad lines  gas velocities over 1000 km/s –Type II: much narrower lines SU theory  same type of object  observational differences arise from differing viewing angles They are one class of AGN galaxies  broad emission lines which is evidence of highly excited gas

2 – Applications: c) Seyfert Galaxies Type I Seyfert Type II Seyfert Jet of Radio Emission Dusty Torus Broad Line Clouds Narrow Line Clouds

2 – Applications: c) Seyfert Galaxies Antonucci & Miller 1985  spectropolarimetry of NGC 1068 Seyfert II profile in total flux Seyfert I profile in polarized flux!

2 – Applications: c) Seyfert Galaxies Type I Seyfert Type II Seyfert Jet of Radio Emission Dusty Torus Broad Line Clouds Narrow Line Clouds

2 – Applications: c) Seyfert Galaxies Watanabe et al polarizing mechanisms: –Electron scattering –Dust scattering –Dichroic absorption 2 polarizing sources –Electron scattering in the jets (optical) –Dust scattering in the torus (optical) –Dichroic absorption (NIR)