Instruments / Polarimeters

Dual-channel photoelectric polarimeters POLSHAKH

The POLSHAKH complex consists of two dual-channel photoelectric polarimeters designed for high-precision polarimetric observations of astrophysical objects.

One instrument is installed at the 2.6-m ZTSh telescope of the Crimean Astrophysical Observatory, and the other at the 2-m RCC telescope of the Terskol Peak Observatory.

The instruments are based on a dual-channel detection scheme allowing simultaneous measurements of orthogonal polarization components. This improves measurement stability against atmospheric transparency variations and changing observing conditions.

The polarimeters operate in broadband photometric filters and allow the use of specialized narrowband filters.

Optical scheme

The optical scheme includes phase plates, field and collimating optics, a Wollaston prism, filter units, and independent detection channels. The dual-channel scheme enables simultaneous registration of orthogonally polarized components.

Fig. 1 — Optical scheme of the dual-channel polarimeter POLSHAKH.

1 — Telescope focus
2 — Field lens
3 — Half-wave phase plate (polarization modulator)
4 — Neutral density filter
5 — Wollaston prism
6 — Collimator
7 — Camera lens
8 — Beam splitter
9 — Interference filters
10 — Fabry lens
11 — Photomultiplier
12 — Fold mirrors
13 — Detector channels

Polarization elements

The polarization performance of the instrument is determined by the characteristics of the phase plates. The figures below show the spectral dependences of phase shift for λ/4 and λ/2 plates.

Spectral phase shift of λ/4 plates.

Spectral phase shift of λ/2 plates.

Spectral characteristics

The polarimeters include a set of exchangeable optical elements, including broadband photometric filters and specialized filters. Their transmission curves define the working spectral range and observing modes of the instruments.

Transmission of neutral filters.

Broadband filter transmission curves.

Spectral transmission in the short-wavelength channel.

Optical path configuration

The optical path includes a phase plate, field lens, Wollaston prism, collimator, filter unit, and photoelectric detectors. The modular layout allows the configuration to be adapted to different observing programmes.

Optical path of the POLSHAKH instrument.

Use of these data in the database

Observations obtained with these instruments are included in the database catalogue.

A significant part of the dataset consists of new polarimetric measurements of near-Earth asteroids obtained at the Crimean Astrophysical Observatory and the Terskol Peak Observatory.

Reference