Electronographic polarimetry: the Durham polarimeter

Scarrott, S. M.; Warren-Smith, R. F.; Pallister, W. S.; Axon, D. J.; Bingham, R. G.

doi:10.1093/mnras/204.4.1163

Cited by 43 publications

(27 citation statements)

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“…The Cassegrain focal plane of the telescope coincides with a mask containing 18 parallel sets of positionable slit jaws, which in simple spectroscopy allow multi-object spectroscopy of up to 18 objects simultaneously. For spectropolarimetry every second pair of slit jaws is masked to prevent beam overlapping in the camera (following the scheme proposed by Scarrott et al 1983), so up to nine slits can be used at once. For most observations only a single slit was used, normally (but not always) centred on the optical axis of the telescope and of the spectrograph collimator ("fast" mode), but a number of spectropolarimetric observations using the multi-slit capability were carried out for studies of clustered objects (e.g.…”

Section: Instrument and Instrument Settingsmentioning

confidence: 99%

The FORS1 catalogue of stellar magnetic field measurements

Bagnulo

Fossati

Landstreet

et al. 2015

A&A

114

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Context. The FORS1 instrument on the ESO Very Large Telescope was used to obtain low-resolution circular polarised spectra of nearly a thousand different stars, with the aim of measuring their mean longitudinal magnetic fields. Magnetic fields were measured by different authors, and using different methods and software tools. Aims. A catalogue of FORS1 magnetic measurements would provide a valuable resource with which to better understand the strengths and limitations of this instrument and of similar low-dispersion, Cassegrain spectropolarimeters. However, FORS1 data reduction has been carried out by a number of different groups using a variety of reduction and analysis techniques. Our understanding of the instrument and our data reduction techniques have both improved over time. A full re-analysis of FORS1 archive data using a consistent and fully documented algorithm would optimise the accuracy and usefulness of a catalogue of field measurements. Methods. Based on the ESO FORS pipeline, we have developed a semi-automatic procedure for magnetic field determinations, which includes self-consistent checks for field detection reliability. We have applied our procedure to the full content of circular spectropolarimetric measurements of the FORS1 archive. Results. We have produced a catalogue of spectro-polarimetric observations and magnetic field measurements for ∼1400 observations of ∼850 different objects. The spectral type of each object has been approximately classified. We have also been able to test different methods for data reduction is a systematic way. The resulting catalogue has been used to produce an estimator for an upper limit to the uncertainty in a field strength measurement of an early type star as a function of the signal-to-noise ratio of the observation. Conclusions. While FORS1 is not necessarily an optimal instrument for the discovery of weak magnetic fields, it is very useful for the systematic study of larger fields, such as those found in Ap/Bp stars and in white dwarfs.

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Section: Instrument and Instrument Settingsmentioning

confidence: 99%

The FORS1 catalogue of stellar magnetic field measurements

Bagnulo

Fossati

Landstreet

et al. 2015

A&A

114

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“…Quite a good amount of work has been done in this area over the last two decades. The Durham University group with their imaging polarimeter sometimes cover a field angle up to 1 arcmin (Scarrott et al 1983(Scarrott et al , 1991. Similarly, astronomers from MPIK, Germany have used their polarimeter to cover field angles as large as 1 arcmin (Röser 1981;Röser & Meisenheimer 1986;Schlötelburg et al 1988).…”

Section: Introductionmentioning

confidence: 99%

Instrumental polarization caused by telescope optics during wide field imaging

Sen

Kakati

1997

Astron. Astrophys. Suppl. Ser.

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Abstract. When astronomical observations are made for a celestial object, with non -zero field angle (wrt telescope axis), the beam of parallel rays from the celestial object strikes the telescope mirror obliquely. Each unpolarized ray of light when it strikes the metal coated mirror surface gets polarized due to reflection. On the contrary, when the field angle is zero, these reflected rays for a field star, combine together to produce an instrumental polarization effect. A 100% linearly polarized star when observed even at zero field angle, exhibits depolarization due to the above effect. A detailed procedure has been worked out here to estimate such polarization effects at the prime and Cassegrain focii, considering the case for linear polarizations only.Also to find the typical values of such polarization, a 2.3 m telescope having beam sizes f/3.23 and f/13 at the prime and Cassegrain focii, has been considered. The instrumental polarization values as calculated at these two focii are 0.000092 and 0.016104% at the field angles 300 and 90 arcsec, respectively. Furthermore, a 100% polarized star when observed at the above two focii will appear to be 99.9999 and 99.9983% polarized respectively due to depolarization.

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“…The scattering pattern indicates that much of the region is illuminated by sources in the central Trapezium Cluster, principally Θ1 and Θ2 Orionis. b) A schematic illustration of a two-channel polarimeter design, from Scarrott et al (1983) the northern hemisphere observations of Hiltner, Hall and others. This resulted in maps of the projected Galactic B-field ( Fig.…”

Section: Early Polarimetric Workmentioning

confidence: 99%

“…CCD detectors began to be used regularly for optical polarimetry from the early 1980s (e.g. Scarrott et al 1983) and advances in infrared detector technology also allowed imaging polarimetry up to 5 um using InSb arrays. The first common-user infrared camera was IRCAM, commissioned on the UK Infrared Telescope in 1986 (McClean et al 1986), which was later fitted with a Wollaston prism and waveplate system in 1995 to allow imaging and spectropolarimetry between 1 and 5 μm.…”

Section: Imaging Polarimetrymentioning

confidence: 99%

Imaging polarimetry as a diagnostic tool

Gledhill¹

2008

Proc. IAU

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Abstract. Some of the earliest polarimetric measurements made in astronomy were concerned with the polarization of the interstellar medium resulting from dust grains aligned in the Galactic magnetic field. More than 50 years later, polarimetry continues to be an important diagnostic of field structure on size scales ranging from planetary to galactic. The use of both linear and circular polarimetry at optical and infrared wavelengths can provide additional insights into the nature of dust particles, their alignment in magnetic fields and the field topology. Given the science benefits that polarimetry offers it is perhaps surprising that the continued existence of polarimetric facilities on current and next generation large telescopes needs to be ensured.

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Electronographic polarimetry: the Durham polarimeter

Cited by 43 publications

References 0 publications

The FORS1 catalogue of stellar magnetic field measurements

The FORS1 catalogue of stellar magnetic field measurements

Instrumental polarization caused by telescope optics during wide field imaging

Imaging polarimetry as a diagnostic tool

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