| Issue |
A&A
Volume 708, April 2026
|
|
|---|---|---|
| Article Number | A30 | |
| Number of page(s) | 16 | |
| Section | Astronomical instrumentation | |
| DOI | https://doi.org/10.1051/0004-6361/202558243 | |
| Published online | 26 March 2026 | |
Polarimetric and spectropolarimetric observations with FoReRo2: Instrument overview and standard star monitoring★
1
Institute of Astronomy and National Astronomical Observatory, Bulgarian Academy of Sciences,
72 Tsarigradsko Chaussée Blvd.,
1784
Sofia,
Bulgaria
2
Armagh Observatory and Planetarium,
College Hill,
Armagh
BT61 9DG,
Northern Ireland,
UK
★★ Corresponding authors: This email address is being protected from spambots. You need JavaScript enabled to view it.
; This email address is being protected from spambots. You need JavaScript enabled to view it.
Received:
24
November
2025
Accepted:
1
February
2026
Abstract
In this paper, we present a description and characterisation of the 2-Channel Focal Reducer Rozhen (FoReRo2), with an emphasis on its polarimetric and spectropolarimetric observation modes. FoReRo2 is a multimode instrument mounted at the Ritchey-Chrétien (RC) focus of the 2-meter Ritchey-Chrétien-Coude (RCC) telescope at the Bulgarian National Astronomical Observatory (BNAO) - Rozhen. The primary targets of this instrument include novae, Be/X-ray binaries, symbiotic stars, asteroids, and comets. Standard stars with a high degree of polarisation are an essential part of the polarimetric observations. In our sample, HD 204827 shows shortterm variability in the position angle (PA), making it unsuitable for calibration. HD 183143 displays intrinsic polarisation variability, but remains stable in terms of the PA. For the first time, we present a statistical study of the K and λmax parameters of Serkowski’s law, including the mean value, standard deviation, and distribution. To demonstrate FoReRo2's polarimetric capabilities, we present several examples. The recurrent nova RS Oph shows the variability of Serkowski’s K parameter, which is due to dust formation within the first few days after the 2021 outburst. These examples also include the imaging polarimetry of comet C/2019 Y4 (ATLAS) and spectropolarimetric observations of the symbiotic star Z And.
Key words: standards / instrumentation: polarimeters / techniques: polarimetric / binaries: symbiotic / comets: individual: C/2019 Y4 (ATLAS)
Based on data collected with the 2-m RCC telescope at Rozhen National Astronomical Observatory.
© The Authors 2026
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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