Ultraviolet interstellar polarization observed with the Hubble Space Telescope

We show that a coupling between chameleon-like scalar fields and photons induces linear and circular polarization in the light from astrophysical sources. In this context chameleon-like scalar fields includes those of the Olive-Pospelov (OP) model, which describes a varying fine structure constant. We determine the form of this polarization numerically and give analytic expressions in two useful limits. By comparing the predicted signal with current observations we are able to improve the constraints on the chameleon-photon coupling and the coupling in the OP model by over two orders of magnitude. It is argued that, if observed, the distinctive form of the chameleon induced circular polarization would represent a smoking gun for the presence of a chameleon. We also report a tentative statistical detection of a chameleon-like scalar field from observations of starlight polarization in our galaxy.

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“…[71]. In this case, we have only undertaken a preliminary analysis of the data, postponing a full reanalysis to a later work.…”

Section: A Starlight Polarizationmentioning

confidence: 99%

Detecting chameleons: The astronomical polarization produced by chameleonlike scalar fields

2009

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“…For average lines of sight through the ISM, maximum linear polarization, p max , occurs at max 1 0.55 m, but a substantial range is observed within individual clouds (e.g., 0.4 Ͻ max Ͻ 0.6 in Taurus; 0.6 Ͻ max Ͻ 0.8 in Ophiuchus; Whittet et al 1992). In general, equation (1) is an excellent representation of the polarization as a function of wavelength from short optical wavelengths to the near-infrared, but recent ultraviolet observations have shown the existence of enhanced short-wavelength polarization in cases in which max Ͻ 0.53 m (Clayton et al 1992(Clayton et al , 1995Wolff, Clayton, & Meade 1993;Somerville et al 1994). However, in essentially every case, p() declines smoothly to shorter wavelength.…”

Section: The Spm Hypothesismentioning

confidence: 99%

A Point in Favor of the Superparamagnetic Grain Hypothesis

Goodman

Whittet

1995

The Astrophysical Journal

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If the GEMS (glass with embedded metal and sulfides) particles recently identified by meteoriticists are indeed examples of interstellar silicate grains, then the spacing of the embedded ''superparamagnetic'' (SPM) inclusions in GEMS particles appears consistent with the theory of superparamagnetic grain alignment first proposed by Jones & Spitzer. Using an SPM hypothesis, Mathis has shown that the observed wavelength dependence of the polarization of background starlight is readily explained if grains smaller than about 0.09 m in size have no SPM inclusions.Martin has already noted that the bulk properties of GEMS particles are consistent with the SPM hypothesis, as well as with the notion that GEMS particles are interstellar grains. In this Letter we make the single point that the spatial frequency (10.1 m) of the SPM inclusions implied by the GEMS particles for interstellar grains is tantalizingly close to the Mathis value needed to explain the observed wavelength dependence of polarization.

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“…Therefore, we find that space craft jitter does not produce polarization greater than 1%. Interstellar polarization is seen to peak in the optical and then falls rapidly in the UV (Clayton et al 1992;Somerville et al 1994), therefore we do not expect interstellar polarization to be significant in our targets.…”

Section: Observationsmentioning

confidence: 77%

Below the Lyman Edge: UV Polarimetry of Quasars

Koratkar¹,

Goodrich²,

Antonucci³

1997

International Astronomical Union Colloquium

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Abstract.The Lyman edge at 912A is an important diagnostic region for studying quasi-stellar objects (QSOs). In particular, it reveals a great deal about the physical conditions within the atmospheres of accretion disks, a ubiquitous component of QSO theories. Observations of the Lyman edge regions of QSOs have shown scant evidence for the predicted features -few QSOs show the broad, partial Lyman edges expected to be common according to most theories. The FOS in its polarimetry mode has been instrumental in studying the Lyman edge region in QSOs. One of the most exciting discoveries is that the polarization rises, not at wavelengths longward of the Lyman edge, but at wavelengths well below it! Here we present the status of polarimetry observations at the Lyman edge and discuss their implications to accretions disks.

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Ultraviolet interstellar polarization observed with the Hubble Space Telescope

Cited by 28 publications

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Detecting chameleons: The astronomical polarization produced by chameleonlike scalar fields

Detecting chameleons: The astronomical polarization produced by chameleonlike scalar fields

A Point in Favor of the Superparamagnetic Grain Hypothesis

Below the Lyman Edge: UV Polarimetry of Quasars

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