RINGO was removed from the LT on 23rd June 2009 and returned to the UK for an upgrade. The new instrument (RINGO2) has been deployed to the telescope now. See the RINGO2 link on the left for details. The info presented here is for historical use only.
Introduction
RINGO is an an optical polarimeter, using a novel design first used by David Clarke (Glasgow) where a polaroid is rotated rapidly at 500rpm in the beam of the telescope, creating a time variable signal if the source is polarized. This time variable signal is converted into a spatial signal by a small angle wedge prism rotating with the polaroid. This signal is recorded on a thermoelectrically cooled CCD. The end result is that each source is imaged as a small ring, with the polarization signal mapped out twice around its circumference.
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(click on image for bigger picture) |
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This image shows the basic RINGO setup before the CCD camera is attached on top of the centre metal box which contains the polariser and prism. The optical axis runs up through the centre hole, perpendicular to the plane of the table (the blue disc in the hole is a dust cap). The polariser/prism setup is connected by a belt to the motor bearing at left in the blue enclosure. The box at right contains the power supply and speed controls. |
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This image shows the completed RINGO setup complete with CCD camera now on top of the rotator assembly that contains the polariser and prism. The black plate underneath is the mounting plate for the telescope. |
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This is the result of a test run last year when the known polarised star BD +64 106 was imaged with RINGO. |
Specifications & Current Performance
| Time Resolution | Measures polarization on timescale of ~10s |
| Wavelength Range at FWHM | 460-720nm |
| Filter | 3mm Schott GG475 + 2mm KG3 cemented together |
| Polarizer | Meadowlark Precision linear polarizer: |
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| Deviating element | CVI Laser Optics 1.5 degree BK7 wedge prism |
| Polarizer/deviator rotation speed | 500 rpm |
| Camera | Apogee ALTA E42: |
| CCD | AIMO E2V CCD42-40: back illuminated, midband coated. |
| Operating temperature | -10° C |
| Quantum efficiency | > 80% |
| Dark current | ~ 1 electron/pixel/second |
| Pixel scale | 0.27"/pixel (binned 2x2) |
| Readout time | < 10s (binned 2x2) |
Filter Set
RINGO uses a hybrid "V+R" filter, consisting of a 3mm Schott GG475 filter cemented to a 2mm KG3 filter. The resulting bandpass curve is shown below, compared to Bessell V and R filters.
Standards are spaced approximately every few hours of RA.
| Name | J2000 |
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RA |
DEC |
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| BDp64_106 | 00:57:36.71 |
+64° 51' 26.5" |
| BDp59_389 | 02:02:42.06 |
+60° 15' 26.5" |
| PG0231+051 | 02:33:41.00 |
+05° 18' 40.0" |
| HD25443 | 04:06:08.07 |
+62° 06' 07.0" |
| GD319 | 12:50:04.49 |
+55° 06' 02.5" |
| BDp33_2642 | 15:51:59.86 |
+32° 56' 54.8" |
| HD155197 | 17:10:15.60 |
-04° 50' 03.0" |
| HILT_960 | 20:23:28.44 |
+39° 20' 56.1" |
| VICYG12 | 20:32:40.98 |
+41° 14' 26.2" |
| BDp28_4211 | 21:51:11.07 |
+28° 51' 51.8" |
| 2331+055A | 23:33:48.00 |
+05° 46' 10.7" |
Sensitivity
Sensitivity curves for the instrument in dark and bright conditions are shown below (click on graph for bigger version).
Saturation
In order to avoid saturation, the following are the maximum exposure times allowed for a given target brightness:
MAGNITUDE |
MAXIMUM |
5 |
1 |
6 |
1 |
7 |
2 |
8 |
5 |
9 |
10 |
10 |
30 |
11 |
60 |
12 |
120 |
Pipeline
RINGO data are dark subtracted and flat-fielded before being distributed to the user.
Error codes are identical those defined in the RATCam pipeline description.
For the subsequent stages of data reduction, please contact Iain Steele or Robert Smith for advice.
Data which predate the availabilty of the automated pipeline (i.e., prior to March 2007) are only available as raw data. They are not loaded into the main data archive but may be downloaded from Unloaded Data.
