A1 Refereed original research article in a scientific journal
Characterization of High-polarization Stars and Blazars with DIPOL-1 at Sierra Nevada Observatory
Authors: Otero-Santos, J.; Piirola, V.; Escudero Pedrosa, J.; Agudo, I.; Morcuende, D.; Sota, A.; Casanova, V.,; Aceituno, F. J.; Santos-Sanz, P.
Publisher: Institute of Physics Publishing
Publication year: 2024
Journal: The Astronomical Journal
Journal name in source: ASTRONOMICAL JOURNAL
Article number: 137
Volume: 167
Issue: 3
ISSN: 0004-6256
eISSN: 1538-3881
DOI: https://doi.org/10.3847/1538-3881/ad250d
Web address : https://iopscience.iop.org/article/10.3847/1538-3881/ad250d
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/387523154
Preprint address: https://arxiv.org/abs/2312.05312
We report here the performance and first results of the new multiband optical polarimeter DIPOL-1, installed at the Sierra Nevada Observatory 90 cm T90 telescope (SNO, Granada, Spain). DIPOL-1 is equipped with a plane parallel calcite plate and λ/2 retarder for modulating the intensity of two perpendicularly polarized beams, and a high readout speed CMOS camera that allows for fast, time-dense coverage. We characterize the performance of this instrument through a series of tests on zero- and high-polarization standard stars. The instrumental polarization in the Nasmyth focus was well determined, with a very stable contribution of 4.0806% ± 0.0014% in the optical R band. For bright high-polarization standards (mR < 8) we reach precisions <0.02% in polarization degree and 0
1 in polarization angle for exposures of 2–4 min. The polarization properties of these stars have been constrained, providing more recent results also about possible variability for future studies of some of the most used calibrators. Moreover, we have tested the capability of observing much fainter objects, in particular through blazar observations, where we reach a precision of <0.5%−0.6% and <05 for faint targets (mR ∼ 16.5) with exposures of ∼1 hr. For brighter targets (mR ∼ 14.5−15), we can aim for time-dense observations with errors <0.2%−0.4% and <1°−15 in 5–20 min. We have successfully performed a first campaign with DIPOL-1, detecting significant polarized emission of several blazars, with special attention to the highest ever polarization degree measured from blazar 3C 345 at ∼32%.
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Funding information in the publication:
Based on observations made at the Sierra Nevada Observatory, operated by the Instituto de Astrofísica de Andalucía (IAA-CSIC). We thank all SNO staff for their excellent work and support during the installation of the instrument. In particular the support from Francisco Hernández, David Pérez, and José Luis de la Rosa was essential. We also thank the Direction of the IAA-CSIC for the support of the installation, testing, and commissioning projects of the DIPOL-1 polarimeter at SNO. The IAA-CSIC team acknowledges financial support from the Severo Ochoa grant CEX2021-001131-S funded by the MCIN/AEI/10.13039/501100011033, through grants PID2019-107847RB-C44 and PID2022-139117NB-C44. DIPOL-1 polarimeters have been built in cooperation between the University of Turku, Finland, and the Kiepenheuer Institut für Sonnenphysik, Germany, with the support by the Leibniz Association grant SAW-2011-KIS-7 and ERC Advanced grant Hot-Mol ERC-2011-AdG-291659. P.S.-S. acknowledges financial support from the Spanish I+D+i project PID2022-139555NB-I00 funded by MCIN/AEI/10.13039/5011000110033. We thank the referee for her/his thorough review of the manuscript and helpful comments.
