PlanetPol: A Very High Sensitivity Polarimeter

Hough, J. H.; Lucas, P. W.; Bailey, Jeremy; Tamura, Motohide; Hirst, Edwin; Harrison, D.; Bartholomew‐Biggs, M. C.

doi:10.1086/507955

Cited by 122 publications

(121 citation statements)

References 30 publications

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“…The observations were carried out from 27 April 2005 to 8 May 2005 with a new high-sensitivity astronomical polarimeter PlanetPol, which achieves fractional polarization sensitivities better than 10 −6 with an absolute accuracy of about 1% (Hough et al, 2006). The polarimeter was mounted on the William Herschel Telescope located on the island of La Palma at an altitude of 2340 m. The measurements extended over a broad band of wavelengths from 590 to 1000 nm and were of polarized flux from four nearby stars which normally show little polarization.…”

Section: Polarimetry Observationsmentioning

confidence: 99%

Alignment of atmospheric mineral dust due to electric field

et al. 2007

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Abstract. Optical polarimetry observations on La Palma, Canary Islands, during a Saharan dust episode show dichroic extinction indicating the presence of vertically aligned particles in the atmosphere. Modelling of the extinction together with particle orientation indicates that the alignment could have been due to an electric field of the order of 2 kV/m. Two alternative mechanisms for the origin of the field are examined: the effect of reduced atmospheric conductivity and charging of the dust layer, the latter effect being a more likely candidate. It is concluded that partial alignment may be a common feature of Saharan dust layers. The modelling indicates that the alignment can significantly alter dust optical depth. This "Venetian blind effect" may have decreased optical thickness in the vertical direction by as much as 10% for the case reported here. It is also possible that the alignment and the electric field modify dust transport.

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Section: Polarimetry Observationsmentioning

confidence: 99%

Alignment of atmospheric mineral dust due to electric field

et al. 2007

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“…As projects grow in scope and complexity, real error analysis and tradeoff studies are becoming essential as exemplified by the VLT and E-ELT codes under development (de Juan Ovelar et al 2011. Even axially symmetric telescope beams require calibration of instrumental polarization from the instrument optics and nonuniformities in coatings (Hough et al 2006;Bailey et al 2010Bailey et al , 2008Wiktorowicz & Matthews 2008) In the solar community, several instruments have included very fast polarimetric modulation to overcome many of these common instrument issues to achieve 0.001% differential precision polarimetry. Modulators include liquid crystals (LCs), piezo-elastic modulators (PEMs), rapidly rotating components and other techniques (Gandorfer 1999;Elmore et al 1992;Skumanich et al 1997;Gandorfer et al 2004;Lin et al 2004).…”

Section: Spectropolarimetric Instruments Errors and Suppression Tecmentioning

confidence: 99%

“…Modulation can be chromatically balanced, tuned or optimized for various observing cases (Povel 1995;Gisler et al 2003;Tomczyk et al 2010;de Wijn et al 2010de Wijn et al , 2011Snik et al 2009;López Ariste & Semel 2011;Nagaraju et al 2007). At modulation rates faster than 1kHz most instrument effects and even atmospheric seeing fluctuations can be suppressed (Keller et al 1994;Stenflo 2007;Hough et al 2006;Hanaoka 2004;Rodenhuis et al 2012;Xu et al 2006). Night-time modulation frequencies are usually much slower and fixed at the exposure time so that detector read noise does not dominate.…”

Section: Spectropolarimetric Instruments Errors and Suppression Tecmentioning

confidence: 99%

Calibrating and stabilizing spectropolarimeters with charge shuffling and daytime sky measurements

Harrington

Kuhn

Nevin

2015

A&A

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Well-calibrated spectropolarimetry studies at resolutions of R > 10 000 with signal-to-noise ratios (S/Ns) better than 0.01% across individual line profiles, are becoming common with larger aperture telescopes. Spectropolarimetric studies require high S/N observations and are often limited by instrument systematic errors. As an example, fiber-fed spectropolarimeters combined with advanced line-combination algorithms can reach statistical error limits of 0.001% in measurements of spectral line profiles referenced to the continuum. Calibration of such observations is often required both for cross-talk and for continuum polarization. This is not straightforward since telescope cross-talk errors are rarely less than ∼1%. In solar instruments like the Daniel K. Inouye Solar Telescope (DKIST), much more stringent calibration is required and the telescope optical design contains substantial intrinsic polarization artifacts. This paper describes some generally useful techniques we have applied to the HiVIS spectropolarimeter at the 3.7 m AEOS Telescope on Haleakala. HiVIS now yields accurate polarized spectral line profiles that are shot-noise limited to 0.01% S/N levels at our full spectral resolution of 10 000 at spectral sampling of ∼100 000. We show line profiles with absolute spectropolarimetric calibration for cross-talk and continuum polarization in a system with polarization cross-talk levels of essentially 100%. In these data the continuum polarization can be recovered to one percent accuracy because of synchronized charge-shuffling model now working with our CCD detector. These techniques can be applied to other spectropolarimeters on other telescopes for both night and daytime applications such as DKIST, TMT, and ELT which have folded non-axially symmetric foci.

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“…These results can be achieved thanks to radial velocity measurements, orbital brightness modulations, gravitational microlensing, direct imaging, astrometry, and polarimetry. The later is probably one of the most delicate methods since the anticipated white light polarization degree (about 10 −5 , Carciofi & Magalhães 2005;Kostogryz et al 2014;Kopparla et al 2016) resulting from scattering of stellar photons onto the atmospheric layers of Hot frederic.marin@astro.unistra.fr 1 In December 2016, 2695 planets out of a total of 3547 have been discovered by transit techniques, see http://exoplanet.eu/ Jupiters is expected to be just about detectable given the current limits of current optical, broad-band, stellar polarimeters (Schmid et al 2005;Hough et al 2006;Wiktorowicz 2009). Berdyugina et al (2008Berdyugina et al ( , 2011 reported to have successfully achieved a B-band polarimetric detection of HD 189733b and found a peak polarization of 2×10 −4 (i.e.…”

Section: Introductionmentioning

confidence: 99%

Computation of the Transmitted and Polarized Scattered Fluxes by the Exoplanet HD 189733b in X-Rays

Marin

Grosso

2017

ApJ

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Thousands of exoplanets have been detected, but only one exoplanetary transit was potentially observed in X-rays from HD 189733A. What makes the detection of exoplanets so difficult in this band? To answer this question, we run Monte-Carlo radiative transfer simulations to estimate the amount of X-ray flux reprocessed by HD 189733b Despite its extended evaporating-atmosphere, we find that the X-ray absorption radius of HD 189733b at 0.7 keV, the mean energy of the photons detected in the 0.25-2 keV energy band by XMM-Newton, is ∼1.01 times the planetary radius for an atmosphere of atomic Hydrogen and Helium (including ions), and produces a maximum depth of ∼2.1% at ∼±46 min from the center of the planetary transit on the geometrically thick and optically thin corona. We compute numerically in the 0.25-2 keV energy band that this maximum depth is only of ∼1.6% at ∼±47 min from the transit center, and little sensitive to the metal abundance assuming that adding metals in the atmosphere would not dramatically change the density-temperature profile. Regarding a direct detection of HD 189733b in X-rays, we find that the amount of flux reprocessed by the exoplanetary atmosphere varies with the orbital phase, spanning between 3-5 orders of magnitude fainter than the flux of the primary star. Additionally, the degree of linear polarization emerging from HD 189733b is <0.003%, with maximums detected near planetary greatest elongations. This implies that both the modulation of the X-ray flux with the orbital phase and the scattered-induced continuum polarization cannot be observed with current X-ray facilities.

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PlanetPol: A Very High Sensitivity Polarimeter

Cited by 122 publications

References 30 publications

Alignment of atmospheric mineral dust due to electric field

Alignment of atmospheric mineral dust due to electric field

Calibrating and stabilizing spectropolarimeters with charge shuffling and daytime sky measurements

Computation of the Transmitted and Polarized Scattered Fluxes by the Exoplanet HD 189733b in X-Rays

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