Observations of the Vela pulsar region with the Chandra X-ray observatory have revealed the fine structure of its synchrotron pulsar-wind nebula (PWN). Deep radio observations have also shown a large, highly polarized (~70%) radio nebula located further away from the pulsar. However, no firm optical detection of the Vela PWN has been reported yet. The detection of the extended emission in previous observations was hindered by the presence of a bright background due to SNR filaments and field stars. Since the degree of polarization in the optical should be similar to that observed in radio, we propose to use the ACS/WFC imaging polarimetry to detect the highly polarized optical emission from the Vela PWN. By subtracting the images obtained with different polarizers we will eliminate the very weakly polarized background component and preserve the strongly polarized PWN emission. Polarimetry will allow us to determine the magnetic field structure inside the PWN. This approach has been successfully tested with ASC/WFC polarimetry of the Crab PWN. Detection of the optical nebula, combined with the radio and X-ray data, will establish the properties of the relativistic pulsar wind, including its energetics, magnetic field structure, spatial evolution and interaction with the ambient medium.

The purpose of this proposal is to obtain polarization observations of the Vela synchrotron nebula in 5 visits with ACS/WFC. First visit consists of 4 orbits. During one of the orbits a CR-SPLIT image is obtained with F550M, an almost line-free continuum filter. This exposure will provide an image of the total intensity from the synchrotron nebula, with little contamination from emission-line filaments. The other three orbits obtain CR-SPLIT F606W images crossed with POL0V, POL60V, and POL120V. The "WFC1-2K" aperture is used with F550M, while the "WFC" aperture is used with F606W+POL0V, F606W+POL60V and F606W+POL120V. This should put the object at the same place on the WFC [reference pixel (3096,1024)] for all the four exposures. The remaining visits (2nd through the 5th) consist of 3 orbits each, with polarizing filters only (i.e. no imaging with F550M). The only special requirement is that the position and orientation be the same for each of the three polarizer images taken during each visit, which is needed to extract most reliable polarization information. We intentionally choose to point at RA=08 35 20.86, DEC=-45 10 44.90, i.e. 10'' south of the Vela pulsar since optical synchrotron emission is expected to be brighter in this direction. We also request to schedule the visits as close to each other as possible since having similar Roll Angle values for all visits would simplify the analysis of the polarimetric data and provide more accurate results. HOT STARS 12 false 0.0 0.0 0.0 false false false false false false SUPPORTED ISM JET SNR WIND Our target is an extended source, hence pointing accuracy of ~1 arcsec is sufficient. We intentionally point 10'' south of the Vela pulsar. The target coordinates are based on HST images. We request that the position and orientation of the target be the same for each of the three polarizer images taken during each visit. We also request to schedule the visits as close to each other as possible since having similar Roll Angle values for all visits would simplify the analysis of the polarimetric data and provide more accurate results. V=27 mag arcsec^-2 J2000 08 35 20.0000 -45 11 14.00 J2000 ACS/WFC Imaging No Yes F606W ACS/WFC Imaging No No F550M The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12240 :visit-id "01" :proposal-version -1 :trans-version "20100505" :date "02-Jul-2010 17:22:12.0" :trans-errors '(:WARNINGS 6 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 4 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 561952 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12240 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12240 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3058 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12240 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3168 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12240 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3168 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12240 :visit-id "01" :orbit-number 4 :pcs-time 222 :si-vis-utilization 3168 :al-overhead-at-end 0 :internal-dur-at-end 346 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) false 4 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12240 :visit-id "02" :proposal-version -1 :trans-version "20100505" :date "02-Jul-2010 17:22:05.0" :trans-errors '(:WARNINGS 4 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 421472 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12240 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12240 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3058 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12240 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3168 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12240 :visit-id "02" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3168 :al-overhead-at-end 0 :internal-dur-at-end 192 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) false 3 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12240 :visit-id "03" :proposal-version -1 :trans-version "20100505" :date "02-Jul-2010 17:21:59.0" :trans-errors '(:WARNINGS 4 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 421472 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12240 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12240 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3058 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12240 :visit-id "03" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3168 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12240 :visit-id "03" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3168 :al-overhead-at-end 0 :internal-dur-at-end 192 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) false 3 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12240 :visit-id "04" :proposal-version -1 :trans-version "20100505" :date "02-Jul-2010 17:21:53.0" :trans-errors '(:WARNINGS 4 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 421472 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12240 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12240 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3058 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12240 :visit-id "04" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3168 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12240 :visit-id "04" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3168 :al-overhead-at-end 0 :internal-dur-at-end 192 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3391 :pcs-gap 0 ) false 3 0 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. 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