| Instrument | |
| Instrument Name: | The Extreme Polarimeter (ExPo) |
| Telescope: | William Herschel Telescope (WHT) La Palma |
| Telescope Aperture: | 4.2 m |
| Telescope Port: | Nasmyth (visiting port) |
| Status: | Operational |
| Commissioning Date: | 01.10.2008 |
| Polarimetry: | |
| Polarimetry Type: | Beam-exchange |
| Stokes Parameters: | I Q U |
| Wavelength Range: | |
| Modulator Type: | (FLC) Ferro-electric Liquid Crystal |
| Modulator Type Other: | |
| Modulation Frequency: | 35 Hz |
| Analyzer Type: | Polarizing beamsplitter cube |
| Analyzer Type Other: | |
| Sensitivity: | 0.0001 |
| Accuracy Zero Point: | |
| Accuracy Scaling: | |
| Imaging: | Yes |
| Wavelength Range: | 500-900 nm |
| Field of View: | 12'' x 12'' |
| Resolution: | Seeing-limited |
| Pixel Scale: | 80 mas |
| Pixel Dimensions: | 200 x 200 |
| Sensor Type: | EMCCD (Andor iXon) |
| Limiting Magnitude: | 14 |
| Coronograph: | Yes |
| Coronograph Type: | Lyot |
| Coronograph IWA: | ~1'' |
| Adaptive Optics: | No |
| DM, Number of Actuators: | |
| DM Type: | |
| WFS Type: | |
| WFS Update frequency: | |
| Strehl: | |
| Limiting Magnitude: | |
| Spectroscopy: | No |
| Sampling: | |
| Wavelength Range: | |
| Spectral Resolution: | |
| Limiting Magnitude: | |
| Instrument Image: | 513a0aa456722-fig1.pdf |
| Instrument Image Caption: | The ExPo instrument as installed at the Nasmyth visiting instrument focus of the William Herschel Telescope. |
| Instrument Reference Paper: | Rodenhuis et al. 2012 (Proc. SPIE) http://adsabs.harvard.edu/abs/2012SPIE.8446E..9IR |
| Known Issues: | |
| Instrument Contact: | Michiel Rodenhuis (rodenhuis@strw.leidenuinv.nl) |
| Instrument Website: | |
| Planned Upgrades: | Adaptive optics system, Spectro-polarimetric IFU |
| Science | |
| Science Description: | Scattering polarization from dust in circumstellar environments: Protoplanetry disks, debris disks, dust envelopes around evolved stars. |
| Target Types: | Herbig Ae/Be, Post-AGB, Solar System |
| Sample Image/Result: | 513f2fd11daf1--fig2.eps |
| Sample image Caption: | ExPo linear polarization image of T Tauri. Image measures 12 x 12 arcseconds across. The degree of linear polarization is shown on a logarithmic (red-yellow-white) intensity scale between 10^-2 and 10^-4. Blue vectors trace the polarization direction. |
| Sample Science Papers: | http://adsabs.harvard.edu/abs/2012A%26A...543A..70C http://adsabs.harvard.edu/abs/2012A%26A...539A..56J http://adsabs.harvard.edu/abs/2011ASPC..448...15J |
| Remarks: | |