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The interest in polarimetric and spectropolarimetric observations increased in the last few years. In this poster, we report polarimetric and spectropolarimetric observations of standard stars with a low and high degree of linear polarisation obtained with the 2-Channel-Focal-Reducer Rozhen (FoReRo2) attached to the 2m Ritchey–Chrétien-Coudé (RCC) telescope of the Rozhen National Astronomical Observatory (NAO) located in Rhodope mountains, Bulgaria., Acknowledgements This work was partially supported by the Bulgarian National Science Fund of the Ministry of Education and Science under grants: KΠ-06-M58/1 - "Spectral and spectropolarimetric characteristics of the interstellar medium" КП-06-Н28/2 08.12.2018, "Binary stars with compact object" KP-06-Russia/2-2020, "An investigation of binary systems with a compact object using Doppler tomography" KΠ-06-H58/3 "Environments of exoplantes: the role of coronal mass ejections and superflares" D01-383/2020, "RACIO (Regional Astronomical Center for Research and Education"

About one star in four will end its life as a magnetic white dwarf. Although magnetism is a very common feature in degenerate stars, we still do not know much about its origin and evolution. Our volume-limited spectropolarimetric survey of white dwarfs reveals statistical characteristics that may help to understand it., Published in The Messenger vol. 186, pp. 14-18, March 2022.

We identify a small group of low mass ultra fast rotating (UFR) stars which have rotation periods less than 0.3 days and show low levels of flaring activity in their TESS lightcurves. Given the rotation-activity relation, faster rotating stars should display higher levels of activity. We do not find any evidence that the lack of activity is related to age or rotational velocities and conclude it is most likely to be a result of the magnetic configurations of the star. In this talk, we will discuss the further analysis of these UFRs using TESS data from Cycles 1-3, NOT spectra and FORS2 spectropolarimetric observations. Overall, we compare the flare rates between the TESS Cycle lightcurves while investigating any long term variability. The NOT spectra is used to investigate radial velocity variations ruling out potential short duration binaries. We also bring in the spectropolarimetric data to determine an estimate on the magnetic field strength of our targets. If these objects do possess a strong magnetic field then why do they not show more flares? Also, If they do not possess a strong field then how can such rapidly rotating stars not show evidence for a magnetic field?, {"references":["Doyle L., Ramsay G., Doyle J. G., Wu K., (2019), MNRAS, 489, 437 – 445","Doyle L., Ramsay G., Doyle J. G., Wu K., Scullion E., (2018), MNRAS, 480 (2), 2153 – 2164","Günther et al. (2020), AJ, 159, 60","Ramsay G., Doyle J.G.,Doyle L., (2020), MNRAS,497 (2), 2320-2326"]}

Replacing the unused ADC by a polarizing filter would transform the VST into the first large polarimetric optical survey telescope, without affecting the current capabilities of the VST+OmegaCAM system. Scientific cases include: mapping the Milky-Way and Magellanic clouds magnetic fields, surveys of quasar polarization, identification and variability of polarized brown dwarfs, polarimetric characterization and mapping of solar-system objects (incl. the moon, comets, and asteroids), detection of polarized signal around the L4 and L5 Lagrange points, a census of magnetic white dwarfs and Herbig Ae/Be stars, etc. The design of the VST limits the technical implementation for the polarimetric unit to a single-beam system: therefore, we will develop data-driven calibration methods to achieve a sub-percent polarimetric accuracy. The proposed implementation is of low cost and requires no major development, as polarizing filters of the needed size are readily available. In particular, it does not require major modification neither of VST, nor of OmegaCAM. In fact, the currently offered capabilities of the VST+OmegaCAM are preserved as the polarizing filter can be removed from the optical beam. Would this project be accepted, efforts will be needed on the design of the polarimeter unit to optimize accuracy and execution times, on the design of the calibration plan, and on the extension of the data reduction pipeline to extract the polarization signals.

All known Galactic Of?p stars have been shown to host strong, organized, magnetic fields. Recently, five Of?p stars have been discovered in the Magellanic Clouds. They posses photometric \citep{Naze} and spectroscopic \citep{Walborn} variability compatible with the Oblique Rotator Model (ORM). However, their magnetic fields have yet to be directly detected. We have developed an algorithm allowing for the synthesis of photometric observables based on the Analytic Dynamical Magnetosphere (ADM) model of \citet{Owocki}. We apply our model to OGLE photometry in order to constrain their magnetic geometries and surface dipole strengths. We predict that the field strengths for some of these candidate extra-Galactic magnetic stars may be within the detection limits of the FORS2 instrument., 5 pages, 2 figures

"We will discuss several sources of non-photon noise that may prevent the current polarimetric instrumentation from reaching the accuracy needed in various astronomical applications, from the detection of weak magnetic fields to the characterisation of (exo) planetary atmospheres and the search of extra-terrestrial life. Lessons learnt today will help to improve the design of future instrumentation.", Content of this collection: presentation slides, Q&A transcript.

The meeting “Polarization of Planetary Systems”, sponsored by the EU-COST Ac- tion, brought together experts in the study of polarization from the celestial bodies of our solar system and extra-solar planets. Among the main themes under discussion, particular emphasis was given to the diagnostic power offered by the study of the atmospheric properties of planetary systems in the search for life features., Il Colle di Galileo, Vol 3, No 1 (2014)

International audience

Recently announced magnetic models for four SPB and �� Cep stars, along with magnetic detections for two additional stars, have potentially doubled the number of known magnetic SPB and ��Cep stars (see Grunhut et al., these proceedings). We have reanalyzed the published data and re-reduced archival low resolution spectropolarimetry collected with the FORS1/2 instruments at VLT on which the models were based, and compare them with high resolution data from the ESPaDOnS spectropolarimeter at CFHT, investigating previously noted inconsistencies between results from the two instruments., 5 pages, 4 figures, StarPol: Stellar Polarimetry from Birth to Death

International audience

International audience

International audience

International audience; The Plutino 28978 Ixion, one of the largest objects in the Kuiper Belt, is measured by R filter photometry and linear polarimetry over the phase angle range as well as by BVRI colours and visible spectroscopy. Ixion is a medium red object with spectral slope of 17.7%/100 nm (400-900 nm). While its opposition phase curve surge (0.2 mag/deg) is within the typical range found for other solar system objects, it displays unusually high negative polarization (min. -1.3%). Comparison with model spectra and numerical modeling of the opposition brightening and polarization effects suggest an areal mixture of absorbing (dark) and icy (bright) compounds on its surface: the mixing ratio is about 6:1 for dark and bright material of 0.21 and 0.79 single-scattering albedo and of 250 and 33 dimensionless mean free path (length multiplied by wave number), respectively.