Linear spectropolarimetry of polarimetric standard stars with VLT/FORS2

Cikota, Aleksandar; Patat, F.; Cikota, Stefan; Faran, T.

doi:10.1093/mnras/stw2545

Cited by 47 publications

(72 citation statements)

References 11 publications

(33 reference statements)

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“…The halfwave retarder plate was positioned at four angles of 0 • , 22.5 • , 45 • , and 67.5 • per sequence. The ordinary and extraordinary beams were extracted using standard procedures in IRAF (as described in Cikota et al 2017a). Wavelength calibration was achieved using He-Ne-Ar arc lamp exposures.…”

Section: Instruments and Observationsmentioning

confidence: 99%

Linear spectropolarimetry of 35 Type Ia supernovae with VLT/FORS: an analysis of the Si ii line polarization

Cikota

Patat

Wang

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Spectropolarimetry enables us to measure the geometry and chemical structure of the ejecta in supernova explosions, which is fundamental for the understanding of their explosion mechanism(s) and progenitor systems. We collected archival data of 35 Type Ia Supernovae (SNe Ia), observed with FORS on the Very Large Telescope at 127 epochs in total. We examined the polarization of the Si ii λ6355Å line (p Si ii ) as a function of time which is seen to peak at a range of various polarization degrees and epochs relative to maximum brightness. We reproduced the ∆m 15 -p Si ii relationship identified in a previous study, and show that subluminous and transitional objects display polarization values below the ∆m 15 -p Si ii relationship for normal SNe Ia. We found a statistically significant linear relationship between the polarization of the Si ii λ6355Å line before maximum brightness and the Si ii line velocity and suggest that this, along with the ∆m 15 -p Si ii relationship, may be explained in the context of a delayed-detonation model. In contrast, we compared our observations to numerical predictions in the ∆m 15 -v Si ii plane and found a dichotomy in the polarization properties between Chandrasekhar and sub-Chandrasekhar mass explosions, which supports the possibility of two distinct explosion mechanisms. A subsample of SNe display evolution of loops in the q-u plane that suggests a more complex Si structure with depth. This insight, which could not be gleaned from total flux spectra, presents a new constraint on explosion models. Finally, we compared our statistical sample of the Si ii polarization to quantitative predictions of the polarization levels for the double-detonation, delayed-detonation, and violent-merger models.

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Section: Instruments and Observationsmentioning

confidence: 99%

Linear spectropolarimetry of 35 Type Ia supernovae with VLT/FORS: an analysis of the Si ii line polarization

Cikota

Patat

Wang

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…where λ must be expressed in Å. Cikota et al (2017) derived Eqs. (8) from observations taken with the instrument position angle χ set to zero (i.e.…”

Section: Correction For the Chromatism (Wavelength Dependence) Of Thementioning

confidence: 99%

“…Numerical simulations performed by Cikota et al (2017, presentation at the ESO Calibration Workshop) suggested that this short-timescale variability could be linked to an inaccurate setting of the retarder waveplate.…”

Section: Inconsistencies Between Consecutive Observationsmentioning

confidence: 99%

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Large Interstellar Polarisation Survey (LIPS)

Bagnulo¹,

Cox²,

Cikota³

et al. 2017

A&A

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Polarimetric studies of light transmitted through interstellar clouds may give constraints on the properties of the interstellar dust grains. Traditionally, broadband linear polarisation (BBLP) measurements have been considered an important diagnostic tool for the study of the interstellar dust, while comparatively less attention has been paid to spectropolarimetric measurements. However, spectropolarimetry may offer stronger constraints than BBLP, for example by revealing narrowband features, and by allowing us to distinguish the contribution of dust from the contribution of interstellar gas. Therefore, we have decided to carry out a Large Interstellar Polarisation Survey (LIPS) using spectropolarimetric facilities in both hemispheres. Here we present the results obtained in the Southern Hemisphere with the FORS2 instrument of the ESO Very Large Telescope. Our spectra cover the wavelength range 380-950 nm at a spectral resolving power of about 880. We have produced a publicly available catalogue of 127 linear polarisation spectra of 101 targets. We also provide the Serkowski-curve parameters, as well as the wavelength gradient of the polarisation position angle for the interstellar polarisation along 76 different lines of sight. In agreement with previous literature, we found that the best-fit parameters of the Serkowski-curve are not independent of each other. However, the relationships that we obtained are not always consistent with what has been found in previous studies.

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“…Skalidis et al (2018); (3)Cikota et al (2017); (4)Turnshek et al (1990); (5)Berdyugin & Teerikorpi (2002) …”

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confidence: 99%

RoboPol: a four-channel optical imaging polarimeter

Ramaprakash

Rajarshi

Das

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present the design and performance of RoboPol, a four-channel optical polarimeter operating at the Skinakas Observatory in Crete, Greece. RoboPol is capable of measuring both relative linear Stokes parameters q and u (and the total intensity I) in one sky exposure. Though primarily used to measure the polarization of point sources in the R-band, the instrument features additional filters (B, V and I), enabling multi-wavelength imaging polarimetry over a large field of view (13.6 ′ × 13.6 ′ ). We demonstrate the accuracy and stability of the instrument throughout its five years of operation. Best performance is achieved within the central region of the field of view and in the R band. For such measurements the systematic uncertainty is below 0.1% in fractional linear polarization, p (0.05% maximum likelihood). Throughout all observing seasons the instrumental polarization varies within 0.1% in p and within ∼1 • in polarization angle.

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Linear spectropolarimetry of polarimetric standard stars with VLT/FORS2

Cited by 47 publications

References 11 publications

Linear spectropolarimetry of 35 Type Ia supernovae with VLT/FORS: an analysis of the Si ii line polarization

Linear spectropolarimetry of 35 Type Ia supernovae with VLT/FORS: an analysis of the Si ii line polarization

Large Interstellar Polarisation Survey (LIPS)

RoboPol: a four-channel optical imaging polarimeter

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