1 / 22

Spectropolarimetry

Spectropolarimetry. Bag Lunch Seminar - Dec 2003. Outline Background Applications Studying the transition from AGB to post-AGB; Probing the structure of Herbig Ae/Be stars; Seyfert galaxies. How to measure polarization:. Detector. Analiser. Beam displacer. E. Light beam. O.

kesler
Download Presentation

Spectropolarimetry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. How to measure polarization: Detector Analiser Beam displacer E Light beam O (calcite) (/2 waveplate) 1 – Background • Spectropolarimetry • Simultaneous measurement of the four stokes parameters, as a function of wavelength: I() Intensity Q() & U() linear polarization: P = (Q2+U2)1/2 V()  circular polarization

  3. Glan Prism Grating Camera Rotating waveplate Wollaston Prism Detector Colimator 1 – Background (cont.) • Example: HPOL @ PBO • Modified Boller and Chivens small telescope spectrograph • 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

  4. 1 – Background (cont.) • Typical resolution • In general, largely confined to low spectral resolution (R = 500-2000) • 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)

  5. 2 – Applications • From the AGB to the PN phase, the circumstellar envelope goes from nearly spherical to aspherical, presenting a wide range of morphologies a) Transition from AGB to PN • When and how the transition starts? • Trammell et al. 1994  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

  6. Polarization raises to the blue. 10%! Lack of features in the lines PA change of ~ 70 deg 2 – Applications: a) AGB to PN (cont.) • IRAS 08005-2356 (post-AGB)

  7. Net pol: Net pol: Net pol: 2 – Applications: a) AGB to PN (cont.) • How to get a PA flip? Ingredients: • Bipolar geometry (two components) • Absorption ( < 1) • IRAS 08005-2356 • PA flip of 70 deg indication that the symmetry axis of the two components differ (e.g. clumpy media)

  8. H is less polarized 2 – Applications: a) AGB to PN (cont.) • IRC+10420

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

  10. 2 – Applications • Ae/Be stars are pre-main sequence stars of intermediate mass b) Circumstellar Structure of Ae/Be Stars • Spectropolarimetry of emission lines gives the possibility of probing the circumstellar structure near the star • Vink et al. 2002  Studied H in 22 Herbig Ae/Bes • Most of them are intrisecally polarized in the continuum • 15 out of 22 objects show clear line effects  indication that the geometry near the star is not spherical

  11. 2 – Applications: b) Ae/Be stars

  12. 2 – Applications: b) Ae/Be stars Spectropolarimetric expectations No line effect

  13. 2 – Applications: b) Ae/Be stars Spectropolarimetric expectations depolarization

  14. 2 – Applications: b) Ae/Be stars Spectropolarimetric expectations  rotating disk

  15. 2 – Applications: b) Ae/Be stars Example: no line effect  IL Cep

  16. 2 – Applications: b) Ae/Be stars Example: depolarization  BD+40 4124

  17. 2 – Applications: b) Ae/Be stars Example: loop  CQ Tau

  18. 2 – Applications • Seyfert galaxies are named for Carl K. Seyfert who in 1943, described them as their central regions having peculiar spectra with notable emission lines. c) Seyfert Galaxies • They are spiral galaxies and account for about 10% of all galaxies (Ho et al. 1997) • They are one class of AGN galaxies broad emission lines which is evidence of highly excited gas • 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

  19. 2 – Applications: c) Seyfert Galaxies Jet of Radio Emission Broad Line Clouds Type II Seyfert Dusty Torus Type I Seyfert Narrow Line Clouds

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

  21. 2 – Applications: c) Seyfert Galaxies Jet of Radio Emission Broad Line Clouds Type II Seyfert Dusty Torus Type I Seyfert Narrow Line Clouds

  22. 2 – Applications:c) Seyfert Galaxies Watanabe et al. 2003 • 3 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)

More Related