Polarization Of Emission Lines Research Articles

Record-breaking polarization from the interacting superluminous supernova 2017hcc

ABSTRACT We present multi-epoch spectropolarimetry of Type IIn supernova SN2017hcc, 16–391 d after explosion. Continuum polarization up to 6 per cent is observed during the first epoch, making SN 2017hcc the most intrinsically polarized SN ever reported at visible wavelengths. During the first 29 d, when the polarization is strongest, the continuum polarization exhibits wavelength dependence that rises toward the blue, then becomes wavelength independent by day 45. The polarization drops rapidly during the first month, even as the flux is still climbing to peak brightness. None the less, unusually high polarization is maintained until day 68, at which point the polarization declines to levels comparable to those of previous well-studied SNe IIn. Only minor changes in position angle (PA) are measured throughout the evolution. The blue slope of the polarized continuum and polarized line emission during the first month suggests that an aspherical distribution of dust grains in pre-shock circumstellar material (CSM) is echoing the SN IIn spectrum and strongly influencing the polarization, while the subsequent decline during the wavelength-independent phase appears consistent with electron scattering near the SN/CSM interface. The persistence of the PA between these two phases suggests that the pre-existing CSM responsible for the dust scattering at early times is part of the same geometric structure as the electron-scattering region that dominates the polarization at later times. SN 2017hcc appears to be yet another, but more extreme, case of aspherical yet well-ordered CSM in Type IIn SNe, possibly resulting from pre-SN mass-loss shaped by a binary progenitor system.

Thomson Scattering above Solar Active Regions and an Ad Hoc Polarization Correction Method for the Emissive Corona

Thomson-scattered photospheric light is the dominant constituent of the lower solar corona’s spectral continuum viewed off-limb at optical wavelengths. Known as the K-corona, it is also linearly polarized. We investigate the possibility of using the a priori polarized characteristics of the K-corona, together with polarized emission lines, to measure and correct instrument-induced polarized crosstalk. First we derive the Stokes parameters of the Thomson scattering of unpolarized light in an irreducible spherical tensor formalism. This allows forward synthesis of the Thomson-scattered signal for the more complex scenario that includes symmetry-breaking features in the incident radiation field, which could limit the accuracy of our proposed technique. For this, we make use of an advanced 3D radiative magnetohydrodynamic coronal model. Together with synthesized polarized signals in the Fe xiii 10746 Å emission line, we find that an ad hoc correction of telescope- and instrument-induced polarization crosstalk is possible under the assumption of a nondepolarizing optical system.

Surface acoustic wave modulation of single photon emission from GaN/InGaN nanowire quantum dots

On-chip quantum information processing requires controllable quantum light sources that can be operated on-demand at high-speeds and with the possibility of in-situ control of the photon emission wavelength and its optical polarization properties. Here, we report on the dynamic control of the optical emission from core-shell GaN/InGaN nanowire (NW) heterostructures using radio frequency surface acoustic waves (SAWs). The SAWs are excited on the surface of a piezoelectric lithium niobate crystal equipped with a SAW delay line onto which the NWs were mechanically transferred. Luminescent quantum dot (QD)-like exciton localization centers induced by compositional fluctuations within the InGaN nanoshell were identified using stroboscopic micro-photoluminescence (micro-PL) spectroscopy. They exhibit narrow and almost fully linearly polarized emission lines in the micro-PL spectra and a pronounced anti-bunching signature of single photon emission in the photon correlation experiments. When the nanowire is perturbed by the propagating SAW, the embedded QD is periodically strained and its excitonic transitions are modulated by the acousto-mechanical coupling, giving rise to a spectral fine-tuning within a ~1.5 meV bandwidth at the acoustic frequency of ~330 MHz. This outcome can be further combined with spectral detection filtering for temporal control of the emitted photons. The effect of the SAW piezoelectric field on the QD charge population and on the optical polarization degree is also observed. The advantage of the acousto-optoelectric over other control schemes is that it allows in-situ manipulation of the optical emission properties over a wide frequency range (up to GHz frequencies).

DISCOVERY OF POLARIZED LINE EMISSION IN SN 1006

Laming (1990) predicted that the narrow Balmer line core of the ~3000 km/s shock in the SN 1006 remnant would be significantly polarized due to electron and proton impact polarization. Here, based on deep spectrally resolved polarimetry obtained with the European Southern Observatory (ESO)'s Very Large Telescope (VLT), we report the discovery of polarized line emission of polarization degree approx 1.3 percent with position angle orthogonal to the SNR filament. Correcting for an unpolarized broad line component, the implied narrow line polarization is approx 2.0 percent, close to the predictions of Laming (1990). The predicted polarization is primarily sensitive to shock velocity and post-shock temperature equilibration. By measuring polarization for the SN1006 remnant, we validate and enable a new diagnostic that has important applications in a wide variety of astrophysical situations, such as shocks, intense radiation fields, high energy particle streams and conductive interfaces.

Motional Stark Effect measurements of the local magnetic field in high temperature fusion plasmas

The utilization of the Motional Stark Effect (MSE) experienced by the neutral hydrogen or deuterium injected into magnetically confined high temperature plasmas is a well established technique to infer the internal magnetic field distribution of fusion experiments. In their rest frame, the neutral atoms experience a Lorentz electric field, EL = v × B, which results in a characteristic line splitting and polarized line emission. The different properties of the Stark multiplet allow inferring, both the magnetic field strength and the orientation of the magnetic field vector. Besides recording the full MSE spectrum, several types of polarimeters have been developed to measure the polarization direction of the Stark line emission. To test physics models of the magnetic field distribution and dynamics, the accuracy requirements are quite demanding. In view of these requirements, the capabilities and issues of the different techniques are discussed, including the influence of the Zeeman Effect and the sensitivity to radial electric fields. A newly developed Imaging MSE system, which has been tested on the ASDEX Upgrade tokamak, is presented. The sensitivity allows to resolve sawtooth oscillations.A shorter version of this contribution is due to be published in PoS at: 1st EPS conference on Plasma Diagnostics

Orthogonally polarized dual-wavelength Nd:YLiF4 laser

This Letter proposes a method to balance the gain and loss of the orthogonally polarized emissions of dual wavelengths in a solid laser cavity. By adjusting the tilt angle of the uncoated glass plate inserted into the cavity, the gain and loss of the orthogonally polarized emission lines with small intervals can be balanced to equalize the oscillation thresholds of the orthogonally polarized dual wavelengths. We select the birefringent crystal Nd:LiYF (Nd:YLF) as the gain media, and theoretically analyze the simultaneous oscillation conditions of dual wavelengths with π- and σ-polarized emissions from a four-level transition (F3/24→I11/24 and F3/24→I13/24) in Nd3+. A simple linear cavity structure is adopted in the experiment, and stable CW orthogonally polarized dual-wavelength laser outputs of 1047, and 1053, 1321, and 1313 nm are obtained.

POLARIZATION DIAGNOSTICS FOR COOL CORE CLUSTER EMISSION LINES

The nature of the interaction between low-excitation gas filaments at ~10^4 K, seen in optical line emission, and diffuse X-ray emitting coronal gas at ~10^7 K in the centers of galaxy clusters remains a puzzle. The presence of a strong, empirical correlation between the two gas phases is indicative of a fundamental relationship between them, though as yet of undetermined cause. The cooler filaments, originally thought to have condensed from the hot gas, could also arise from a merger or the disturbance of cool circumnuclear gas by nuclear activity. Here, we have searched for intrinsic line emission polarization in cool core galaxy clusters as a diagnostic of fundamental transport processes. Drawing on developments in solar astrophysics, direct energetic particle impact induced polarization holds the promise to definitively determine the role of collisional processes such as thermal conduction in the ISM physics of galaxy clusters, while providing insight into other highly anisotropic excitation mechanisms such as shocks, intense radiation fields and suprathermal particles. Under certain physical conditions, theoretical calculations predict of order ten percent polarization. Our observations of the filaments in four nearby cool core clusters place stringent upper limits (<0.1%) on the presence of emission line polarization, requiring that if thermal conduction is operative, the thermal gradients are not in the saturated regime. This limit is consistent with theoretical models of the thermal structure of filament interfaces.

Off-axis irradiation and the polarization of broad emission lines in active galactic nuclei

The stokes Monte Carlo radiative transfer code has been extended to model the velocity dependence of the polarization of emission lines. We use stokes to present improved modeling of the velocity-dependent polarization of broad emission lines in active galactic nuclei. We confirm that off-axis continuum emission can produce observed velocity dependencies of both the degree and position angle of polarization. The characteristic features are a dip in the percentage polarization and an S-shaped swing in the position angle of the polarization across the line profile. Some differences between our stokes results and previous modeling of polarization due to off-axis emission are noted. In particular we find that the presence of an offset between the maximum in line flux and the dip in the percentage of polarization or the central velocity of the swing in position angle does not necessarily imply that the scattering material is moving radially. Our model is an alternative scenario to the equatorial scattering disk described by Smith et al. (2005). We discuss strategies to discriminate between both interpretations and to constrain their relative contributions to the observed velocity-resolved line and polarization.

The linear polarization of emission lines from EIE and DR of highly charged tungsten ions

Cross sections for electron impact excitation and capture to individual magnetic sublevels of Cu-like to Ge-like tungsten ions have been calculated, by using MCDF method. Furthermore, these cross sections are employed in calculating the polarization of the corresponding 5f→3d lines. We compare the polarization of the lines formed by EIE with that of the same lines but formed by DR. It is found the differences are very large.

Growth and micro‐luminescence from diluted magnetic quantum dots

AbstractCdTe quantum dots containing magnetic Mn‐ions are grown by molecular beam epitaxy. The Mn content is varied by changing the growth conditions from about 3% to 0.04%. The presence of the magnetic impurities inside the quantum dots results in the giant Zeeman splitting of excitonic levels. Direct insight into magnetic properties of these structures is obtained by the micro‐photoluminescence at an external magnetic field. A careful analysis of the spectral position, the shape and the polarization of emission lines from individual quantum dots reveals a paramagnetic character of Mn ions and provides with a tool to obtain information about the average Mn concentration and the approximate number of Mn‐ions inside dots. Quantum dots with the number of Mn ions of the order of 100 are found in the sample with Mn content of 3% and with only 1 or 0 Mn ions in the sample with 0.04% (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

SPECTROPOLARIMETRIC EVIDENCE FOR RADIATIVELY INEFFICIENT ACCRETION IN AN OPTICALLY DULL ACTIVE GALAXY

We present Subaru/FOCAS spectropolarimetry of two active galaxies in the Cosmic Evolution Survey. These objects were selected to be optically dull, with the bright X-ray emission of an AGN but missing optical emission lines in our previous spectroscopy. Our new observations show that one target has very weak emission lines consistent with an optically dull AGN, while the other object has strong emission lines typical of a host-diluted Type 2 Seyfert galaxy. In neither source do we observe polarized emission lines, with 3-sigma upper limits of P_BLR < 2%. This means that the missing broad emission lines (and weaker narrow emission lines) are not due to simple anisotropic obscuration, e.g., by the canonical AGN torus. The weak-lined optically dull AGN exhibits a blue polarized continuum with P = 0.78 +/- 0.07% at 4400 A < lambda_rest < 7200 A (P = 1.37 +/- 0.16% at 4400 A < lambda_rest < 5050 A). The wavelength dependence of this polarized flux is similar to that of an unobscured AGN continuum and represents the intrinsic AGN emission, either as synchrotron emission or the outer part of an accretion disk reflected by a clumpy dust scatterer. Because this intrinsic AGN emission lacks emission lines, this source is likely to have a radiatively inefficient accretion flow.

Spectropolarimetry of the Superwind Filaments of the Starburst Galaxy M 82: Kinematics of Dust Outflow

Spectropolarimetry results for the starburst galaxy M 82 are presented. The optical emission lines of the filaments in the energetic outflow (``superwind'') from the nuclear starburst region of M 82 are substantially polarized. The H$\alpha$ polarization degrees and angles measured by our study are consistent with previous narrowband imaging polarimetry data. The polarized emission lines are redshifted with respect to the emission lines in the total light and systemic motion of the galaxy. The emission line intensity ratios [N II]$/$H$\alpha$ and [S II]$/$H$\alpha$ in the polarized light are similar to those of the nuclear star-forming region. In addition, the electron density $N_{\rm e}$ derived from the [S II]$\lambda$6731$/\lambda$6717 line ratio of the polarized light is $\sim\ $600–1000 cm$^{-3}$ at a distance of more than 1 kpc from the nucleus, whereas the $N_{\rm e}$ derived from the total light are less than 300 cm$^{-3}$. These facts strongly suggest that the emission from the nuclear starburst of M 82 is scattered by dust grains entrained and transported outward by the superwind. A simple hollow biconical outflow model shows that the velocity of the outflowing dust grains, $v_{\rm d}$, ranges from 100 to 200 km s$^{-1}$ near the nucleus, decreases monotonically with the distance from the nucleus, and reaches $\sim\ $10 km s$^{-1}$ at around 1 kpc. The motion of the dust is substantially slower than that of both ionized gas ($v_{{\rm H}\alpha}$$\sim\ $ 600 km s$^{-1}$) and molecular gas ($v_{\rm CO}$$\sim\ $ 200 km s$^{-1}$) at the same distance from the nucleus of M 82. This indicates that dust grains in the superwind are kinematically decoupled from both gas components at large radii. Since the dust velocity $v_{\rm d}$ is much less than the escape velocity of M 82 ($v_{\rm esc}$$\approx$ 170 km s$^{-1}$ at 1.5 kpc from the nucleus), most of the dust entrained by the superwind cannot escape to intergalactic space, and may fall back into the galaxy disk if there is no additional acceleration mechanism (such as radiation pressure).

VERY LARGE TELESCOPE SPECTROPOLARIMETRY OF BROAD ABSORPTION LINE QSOs

We present spectropolarimetry of 19 confirmed and 4 possible bright, southern broad absorption line (BAL) quasars from the European Southern Observatory (ESO) Very Large Telescope (VLT). A wide range of redshifts is covered in the sample (from 0.9 to 3.4), and both low- and hi-ionization quasars are represented, as well as radio-loud and radio-quiet BALQSOs. We continue to confirm previously established spectropolarimetric properties of BALQSOs, including the generally rising continuum polarization with shorter wavelengths and comparatively large fraction with high broad-band polarization (6 of 19 with polarizations >2%). Emission lines are polarized less than or similar to the continuum, except in a few unusual cases, and absorption troughs tend to have higher polarizations. A search for correlations between polarization properties has been done, identifying 2 significant or marginally significant correlations. These are an increase in continuum polarization with decreasing optical luminosity (increasing absolute B magnitude) and decreasing \ion{C}{4} emission-line polarization with increased continuum polarization.

ON THE SCATTERING ENHANCEMENT OF N V λ1240 EMISSION LINE OF QUASI-STELLAR OBJECTS

The Nv emission line of active galactic nuclei shows peculiar behavior in the line--continuum correlation, which may be indicative of an extra line component in addition to that from the normal broad emission line region. In this paper, we investigate possible contribution to the Nv emission via resonant scattering of both continuum and Ly alpha in a broad absorption line (BAL) outflow, by performing the Sobolev Monte Carlo simulations. The contribution is dependent on the covering factor, optical depth and velocity profile of the outflow, as well as the equivalent width (EW) of Ly alpha. Adopting model parameters constrained by observations, we find that the measured Nv EW in the spectra of non-BAL quasi-stellar objects (QSOs) could have been enhanced by a factor of 1.82~2.73 on average, while there is only moderate absorption of Ly alpha along the BAL outflow direction. Our model can produce a relatively narrow scattering line profile. About 80% of the total scattered flux falls within the central +-4500km/s. We find that the resonant scattering can produce a prominent polarized emission line around Nv. Both the broad excess emission and the unusually large polarized flux observed around Nv in BAL QSOs are considered as strong evidence for the scattering enhancement. Future spectropolarimetric observations and spectroscopic monitoring of luminous QSOs may offer crucial tests for this interpretation, and provide useful information on the physical and geometrical properties of QSO outflows. We argue that the scattering offers a promising and robust process for producing the peculiar behavior of Nv emission compared to the other processes proposed previously.

Optical transitions of positively charged excitons and biexcitons in single InAs quantum dots

We investigate fine structures observed in the optical transitions of positively charged excitons and biexcitons in single quantum dots. We show that double charged biexciton XX2+ emits into a hot double charged exciton X2+∗ at first, and then relaxes into charged excitons X2+ or X+ states via phonon scattering or Auger process respectively. XX2+ gives rise to two elliptically polarized emission lines due to the mixing of two lower-levels in the final state. X2+ causes two optical transitions with different polarizations, i.e., a linearly polarized emission with a fine structure splitting of 45 μeV and a circularly polarized emission with twofold degeneracy.

Magnetooptical properties of a single CdMnSe/CdMgSe quantum well

The spectra of photoluminescence and reflectance in magnetic fields up to 7 T are studied for a 3.8 nm semimagnetic CdMnSe quantum well confined by two CdMgSe barriers. A noticeable magnetic shift in the σ+-polarized emission line of the heavy exciton to low energies and a decrease in the halfwidth of the line by more than one-half are detected with increasing magnetic field. It is established that a localized magnetic polaron is formed, with the polaron energy of 19.8 meV determined from the change in the degree of circular polarization in magnetic field. A σ−-polarized emission line is observed in magnetic fields ranging from 0.4 to 2 T. This line can be interpreted as being produced by the complex of two electrons, with oppositely directed spins, and a heavy hole, i.e., by the trion X− or the exciton localized at a donor, D0X. The binding energy of such complex is 10 meV.

Polarized hydrogen emission lines in Mira stars: a mystery behind the shock

AbstractWe present a full spectropolarimetric study (in the Stokes parameters I, Q, U and V) on omicron Ceti (the prototype of Mira stars), and focus on the strong polarization detected in Balmer emission lines. This study is made with observations from NARVAL instrument at TBL (Telescope Bernard Lyot) in Pic du Midi Observatory, France.

Observations of the Goldreich-Kylafis effect in star-forming regions with XPOL at the IRAM 30 m telescope

Context. The Goldreich-Kylafis (GK) effect causes certain molecular line emission to be weakly linearly polarized, e.g., in the presence of a magnetic field. Compared to polarized dust emission, the GK effect potentially yields additional information along the line of sight through its dependence on velocity in the line profile. Aims. Our goal was to detect polarized molecular line emission toward the DR21(OH), W3OH/H2O, G34.3+0.2, and UYSO 1 dense molecular cloud cores in transitions of rare CO isotopologues and CS. The feasibility of such observations had to be established by studying the influence of polarized sidelobes, e.g., in the presence of extended emission in the surroundings of compact sources. Methods. The observations were carried out with the IRAM 30 m telescope employing the correlation polarimeter XPOL and using two orthogonally polarized receivers. We produced beam maps to investigate instrumental polarization. Results. While a polarized signal is found in nearly all transitions toward all sources, its degree of polarization in only one case surpasses the polarization that can be expected from instrumental effects. It is shown that any emission in the polarized sidelobes of the system can produce instrumental polarization, even if the source is unpolarized. Tentative evidence of astronomically polarized line emission with pL 1.5% was found in the CS(2-1) line toward G34.3+0.2.

Polarized emission from GaN/AlN quantum dots: Single-dot spectroscopy and symmetry-based theory

We report micro-photoluminescence studies of single GaN/AlN quantum dots grown along the (0001) crystal axis by molecular beam epitaxy on Si(111) substrates. The emission lines exhibit a linear polarization along the growth plane, but with varying magnitudes of the polarization degree and with principal polarization axes that do not necessarily correspond to crystallographic directions. Moreover, we could not observe any splitting of polarized emission lines, at least within the spectral resolution of our setup (1 meV). We propose a model based on the joint effects of electron-hole exchange interaction and in-plane anisotropy of strain and/or quantum dot shape, in order to explain the quantitative differences between our observations and those previously reported on, e.g. CdTe- or InAs-based quantum dots.

Polarization in aurorae: A new dimension for space environments studies

The polarization of emission lines is a noteworthy observational parameter in astronomy. However, it has never been detected without ambiguity in planetary upper atmospheres. Theoretical considerations have suggested that the polarization of the thermospheric oxygen red line (630 nm) could exist in the polar cap region. We present here its first successful measurement at Svalbard in January 2007, during active geophysical conditions. We assign its origin and variability to complementary effects between permanent low‐energy electron precipitation and sporadic auroral events. Implications in physics, geophysics and planetary science are foreseen. In physics, it raises the question of the polarization of a forbidden transition by electron impact which is still unknown. In geophysics, it provides a new parameter to constrain the thermospheric models. In planetary science, it makes it possible to derive the local configuration of the magnetic fields. It therefore opens new perspectives for future space missions towards other planets