The Hubble Space Telescope Northern-Hemisphere grid of stellar polarimetric standards

Schmidt, Gary D.; Elston, R.; Lupie, O. L.

doi:10.1086/116341

Cited by 345 publications

(379 citation statements)

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“…The polarization values are similar to values obtained in previous publications Turnshek et al 1990;Schmidt et al 1992). Position angles are not completely defined after calculations.…”

Section: Standard Starssupporting

confidence: 89%

Polarimetric observations of comet 67P/Churyumov-Gerasimenko during its 2008–2009 apparition

Hadamcik

Sen²,

Levasseur-Regourd

et al. 2010

A&A

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Context. Remote observations of the light scattered by comet 67P/Churyumov-Gerasimenko dust coma are of major importance for determining the physical properties of the particles and prepare the rendezvous with the ESA/Rosetta spacecraft in 2014. Aims. Light scattering and especially linear polarization observations allow comparison between different coma regions and different comets, including comets that have been studied by space probes. Our aim is to retrieve physical properties of the dust particles and to characterize their evolution around perihelion passage. Results. The decrease in intensity as a function of the distance to nucleus in log-log scale is on average close to −1, although important variations with values down to −1.5 are noticed, in agreement with previous observations in 1982−83 and 1995−96. The intensity along the tailward direction decreases with a slope between −1.2 two months before perihelion (2009 February 28) to −1.0 two months after perihelion, and the decrease is more pronounced in the sunward direction. Before perihelion, aperture polarization values are comparable to polarization values measured on other comets at similar phase angles. The sharp decrease in intensity and the feature in the tailward direction, without any difference in polarization in the coma before perihelion, could suggest the presence of large dark particles. The post-perihelion increase in intensity and in polarization suggests that an outburst has occurred. The freshly ejected dust polarizes more the scattered light and is more sensitive to the solar radiation pressure, suggesting small micron-or submicron-sized grains. Conclusions. Polarization and intensity variations in the coma of 67P/Churyumov-Gerasimenko are reminiscent of those noticed for some comets such as comet 81P/Wild 2 and comet 9P/Tempel 1. The presence of rather large particles can thus be suggested before and just after perihelion and the ejection of post-perihelion smaller grains, eventually in fluffy aggregates. A strong seasonal effect related to the obliquity of the comet suggests that the different grains originate in different hemispheres of the nucleus.

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“…The polarization values are similar to values obtained in previous publications Turnshek et al 1990;Schmidt et al 1992). Position angles are not completely defined after calculations.…”

Section: Standard Starssupporting

confidence: 89%

Polarimetric observations of comet 67P/Churyumov-Gerasimenko during its 2008–2009 apparition

Hadamcik

Sen²,

Levasseur-Regourd

et al. 2010

A&A

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“…The zero point of v was calibrated with the polarized standard star BD ϩ59Њ389 (Schmidt, Elston, & Lupie 1992). For the unpolarized standard star HD 14069, we found across the entire p ≤ 0.1% optical spectrum.…”

mentioning

confidence: 89%

Optical Spectropolarimetry of the GRB 020813 Afterglow

Barth

Sari

Cohen

et al. 2003

The Astrophysical Journal

105

111

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The optical afterglow of gamma-ray burst GRB 020813 was observed for 3 hr with the LRIS spectropolarimeter at the Keck I telescope, beginning 4.7 hr after the burst was detected by the HETE-2. The spectrum reveals numerous metal absorption lines that we identify with two systems at and . We also detect z p 1.223 z p 1.255 an [O ii] l3727 emission line at , and we identify this galaxy as the likely host of the GRB. After a z p 1.255 correction for Galactic interstellar polarization, the optical afterglow has a linear polarization of 1.8%-2.4% during 4.7-7.9 hr after the burst. A measurement of on the following night by Covino et p p 0.80% ‫ע‬ 0.16% al. demonstrates significant polarization variability over the next 14 hr. The lack of strong variability in the position angle of linear polarization indicates that the magnetic field in the jet is likely to be globally ordered rather than composed of a number of randomly oriented cells. Within the framework of afterglow models with collimated flows, the relatively low observed polarization suggests that the magnetic field components perpendicular and parallel to the shock front are only different by about 20%.

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“…We followed our standard RINGO reduction procedure in which flux traces for all objects on all nights were extracted within annuli with inner (8 arcsec) and outer (14 arcsec) radii sufficient to ensure that seeing variations do not influence the extracted fluxes. The traces were then sky subtracted by the normalized flux inside the inner trace radius and 10 divided through by an average of the traces from routinely obtained zero-polarization standards 29 to remove the known 2.7% instrumental polarization. The resulting flux traces for a sample of objects and the GRB are presented in Figure 2.…”

mentioning

confidence: 99%

Ten per cent polarized optical emission from GRB 090102

Steele

Mundell

Smith

et al. 2009

Nature

154

182

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The nature of the jets and the role of magnetic fields in gamma-ray bursts (GRB) remains unclear 1, 2 . In a baryon-dominated jet only weak, tangled fields generated in situ through shocks would be present 3 . In an alternative model, jets are threaded with large scale magnetic fields that originate at the central engine and which accelerate and collimate the jets 4 . The way to distinguish between the models is to measure the degree of polarization in early-time emission, however previous claims of γ-ray polarization have been controversial 5-8 . Here we report that the early optical emission from GRB 090102 was polarized at the level of P = 10 ± 1%, indicating the presence of large-scale fields originating in the expanding fireball. If the degree of polarization and its position angle were variable on timescales shorter than our 60-s exposure, then the peak polarization may have been larger than 10 per cent.The standard GRB fireball model 3 comprises an initial compact emitting region, expanding relativistically, in which internal shocks dissipate the bulk energy, converting kinetic to radiated energy, the so-called prompt emission. As the shell of the relativistically expanding fireball collides with the surrounding circumburst medium, a forward shock is produced, which propagates outwards through the external medium and results in the long-lived afterglow whose emission is detectable from X-ray to optical, infrared and, in some cases, radio wavelengths. Interaction of 1

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The Hubble Space Telescope Northern-Hemisphere grid of stellar polarimetric standards

Cited by 345 publications

References 0 publications

Polarimetric observations of comet 67P/Churyumov-Gerasimenko during its 2008–2009 apparition

Polarimetric observations of comet 67P/Churyumov-Gerasimenko during its 2008–2009 apparition

Optical Spectropolarimetry of the GRB 020813 Afterglow

Ten per cent polarized optical emission from GRB 090102

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