Near-infrared Polarimetry Research Articles

Quantitative grain size estimation on airless bodies from the negative polarization branch

Context. Sunlight scattered from the surface of an airless body is generally partially polarized, and the corresponding polarization state includes information about the scattering surface, such as albedo, surface grain sizes, composition, and taxonomic types. Most polarimetric studies on airless bodies thus far have focused on optical wavelengths (λ ≲ 1 µm). Aims. We conducted polarimetry of two large airless bodies, the Dawn mission targets (1) Ceres and (4) Vesta, in the near-infrared region. We further investigated the change in the polarimetric phase curves over the wavelengths expected from previous works. Methods. We used the Nishiharima Infrared Camera (NIC) installed at the Nishi-Harima Astronomical Observatory (NHAO) to observe these objects at multiple geometric configurations in the J, H, and Ks bands (λ ~ 1.2–2.3 µm). Results. Polarimetric parameters were determined and compared with previously reported experimental results. In particular, Vesta exhibits a characteristic change in the negative polarization branch as the wavelength increases to the Ks band, which we interpret as an indication of the dominant existence of D ~ 10–20 µm particles. Our approach is supported by empirical reasoning and coincides well with an independent, theory-driven approach based on thermal modeling. Conclusions. This work demonstrates how near-infrared polarimetry can be utilized to quantitatively determine the particle size of airless objects. This finding will have important implications for asteroid taxonomy and regolith evolution.

Exploring the Magnetic Field Geometry in NGC 891 with SOFIA/HAWC+

Stratospheric Observatory For Infrared Astronomy/High-resolution Airborne Wideband Camera-plus 154 μm Far-Infrared polarimetry observations of the well-studied edge-on galaxy NGC 891 are analyzed and compared to simple disk models with ordered (planar) and turbulent magnetic fields. The overall low magnitude and the narrow dispersion of fractional polarization observed in the disk require significant turbulence and a large number of turbulent decorrelation cells along the line of sight through the plane. Higher surface brightness regions along the major axis to either side of the nucleus show a further reduction in polarization and are consistent with a view tangent to a spiral feature in our disk models. The nucleus also has a similar low polarization, and this is inconsistent with our model spiral galaxy where the ordered magnetic field component would be nearly perpendicular to the line of sight through the nucleus on an edge-on view. A model with a barred spiral morphology with a magnetic field geometry derived from radio synchrotron observations of face-on barred spirals fits the data much better. There is clear evidence for a vertical field extending into the halo from one location in the disk coincident with a polarization null point seen in near-infrared polarimetry, probably due to a blowout caused by star formation. Although our observations were capable of detecting a vertical magnetic field geometry elsewhere in the halo, no clear signature was found. A reduced polarization due to a mix of planar and vertical fields in the dusty regions of the halo best explains our observations, but unusually significant turbulence cannot be ruled out.

The Increasingly Strange Polarimetric Behavior of the Barbarian Asteroids

Polarization phase-curve measurements provide a unique constraint on the surface properties of asteroids that are complementary to those from photometry and spectroscopy and have led to the identification of the “Barbarian” asteroids as a class of objects with highly unusual surfaces. We present new near-infrared polarimetric observations of six Barbarian asteroids obtained with the WIRC+Pol instrument on the Palomar Hale telescope. We find a dramatic change in polarimetric behavior from visible to near-infrared for these objects, including a change in the polarimetric inversion angle that is tied to the index of refraction of the surface material. Our observations support a two-phase surface composition consisting of high albedo and high index of refraction inclusions with a small optical size scale embedded in a dark matrix material more closely related to C-complex asteroids. These results are consistent with the interpretation that the Barbarians are remnants of a population of primitive bodies that formed shortly after calcium-aluminum-rich inclusion (CAIs). Near-infrared polarimetry provides a direct test of the constituent grains of asteroid surfaces.

Near-infrared Polarimetry and H2 Emission toward Massive Young Stars: Discovery of a Bipolar Outflow Associated to S235 e2s3

We present a near-infrared H-band polarimetric study toward the S235 e2s3 protostar, obtained using the POLICAN instrument on the 2.1 m OAGH telescope. The images reveal a bipolar outflow with a total length of about 0.5 pc. The outflow nebulosity presents a high degree of linear polarization (∼80%) and reveals a centrosymmetric pattern with the polarization position angles. The polarization characteristics suggest their origin to be single scattering associated with dust in the outflow. Using multiwavelength archival data, we performed spectral energy distribution (SED) fitting based on radiative transfer models of turbulent core accretion theory. The best-fit SED model indicated that the protostar has a mass of 6.8 ± 1.2 M ⊙, with a disk accretion rate of 3.6 ± 1.2 × 10−4 M ⊙ yr−1 and a total bolometric luminosity of 9.63 ± 2.1 × 103 L ⊙. Narrowband H2 (2.12 μm) observations show shocked emission along the bipolar lobes tracing the jet’s interaction with the surrounding medium. The estimated H2 luminosity of the outflow is , which matched the known power-law correlation with the source bolometric luminosity, similar to other high-mass outflows. The orientation of the bipolar outflow was found to be parallel to the local magnetic field direction. The overall results assert the fact that the S235 e2s3 source is a massive young star driving a highly collimated bipolar outflow through disk accretion.

Near-infrared Polarization from Unresolved Disks around Brown Dwarfs and Young Stellar Objects

Abstract Wide-field near-infrared (NIR) polarimetry was used to examine disk systems around two brown dwarfs (BDs) and two young stellar objects (YSOs) embedded in the Heiles Cloud 2 (HCl2) dark molecular cloud in Taurus as well as numerous stars located behind HCl2. Inclined disks exhibit intrinsic NIR polarization due to scattering of photospheric light, which is detectable even for unresolved systems. After removing polarization contributions from magnetically aligned dust in HCl2 determined from the background star information, significant intrinsic polarization was detected from the disk systems of one BD (ITG 17) and both YSOs (ITG 15, ITG 25), but not from the other BD (2M0444). The ITG 17 BD shows good agreement of the disk orientation inferred from the NIR and from published Atacama Large Millimeter/submillieter Array dust continuum imaging. ITG 17 was also found to reside in a 5200 au wide binary (or hierarchical quad star system) with the ITG 15 YSO disk system. The inferred disk orientations from the NIR for ITG 15 and ITG 17 are parallel to each other and perpendicular to the local magnetic field direction. The multiplicity of the system and the large BD disk nature could have resulted from formation in an environment characterized by misalignment of the magnetic field and the protostellar disks.

Polarimetric signature of the oceans as detected by near-infrared Earthshine observations

Context.The discovery of an extrasolar planet with an ocean has crucial importance in the search for life beyond Earth. The polarimetric detection of specularly reflected light from a smooth liquid surface is anticipated theoretically, though the polarimetric signature of Earth’s oceans has not yet been conclusively detected in disk-integrated planetary light.Aims.We aim to detect and measure the polarimetric signature of the Earth’s oceans.Methods.We conducted near-infrared polarimetry for lunar Earthshine and collected data on 32 nights with a variety of ocean fractions in the Earthshine-contributing region.Results.A clear positive correlation was revealed between the polarization degree and ocean fraction. We found hourly variations in polarization in accordance with rotational transition of the ocean fraction. The ratios of the variation to the typical polarization degree were as large as ~0.2–1.4.Conclusions.Our observations provide plausible evidence of the polarimetric signature attributed to Earth’s oceans. Near-infrared polarimetry may be considered a prospective technique in the search for exoplanetary oceans.

Monolithic Full-Stokes Near-Infrared Polarimetry with Chiral Plasmonic Metasurface Integrated Graphene-Silicon Photodetector.

The ability to detect the full-Stokes polarization of light is vital for a variety of applications that often require complex and bulky optical systems. Here, we report an on-chip polarimeter comprising four metasurface-integrated graphene-silicon photodetectors. The geometric chirality and anisotropy of the metasurfaces result in circular and linear polarization-resolved photoresponses, from which the full-Stokes parameters, including the intensity, orientation, and ellipticity of arbitrarily polarized incident infrared light (1550 nm), can be obtained. The design presents an ultracompact architecture while excluding the standard bulky optical components and structural redundancy. Computational extraction of full-Stokes parameters from mutual information among four detectors eliminates the need for a large absorption contrast between different polarization states. Our monolithic plasmonic metasurface integrated polarimeter is ideal for a variety of polarization-based applications including biological sensing, quantum information processing, and polarization photography.

High-resolution Near-infrared Polarimetry and Submillimeter Imaging of FS Tau A: Possible Streamers in Misaligned Circumbinary Disk System

Abstract We analyzed the young (2.8 Myr-old) binary system FS Tau A using near-infrared (H-band) high-contrast polarimetry data from Subaru/HiCIAO and submillimeter CO (J = 2–1) line emission data from Atacama Large Millimeter/submillimeter Array (ALMA). Both the near-infrared and submillimeter observations reveal several clear structures extending to ∼240 au from the stars. Based on these observations at different wavelengths, we report the following discoveries. One arm-like structure detected in the near-infrared band initially extends from the south of the binary with a subsequent turn to the northeast, corresponding to two bar-like structures detected in ALMA observations with an local standard of rest kinematic (LSRK) velocity of 1.19–5.64 km s−1. Another feature detected in the near-infrared band extends initially from the north of the binary, relating to an arm-like structure detected in ALMA observations with an LSRK velocity of 8.17–16.43 km s−1. From their shapes and velocities, we suggest that these structures can mostly be explained by two streamers that connect the outer circumbinary disk and the central binary components. These discoveries will be helpful for understanding the evolution of streamers and circumstellar disks in young binary systems.

Polarimetry of relativistic tidal disruption event Swift J2058+0516

ABSTRACT A small fraction of candidate tidal disruption events (TDEs) show evidence of powerful relativistic jets, which are particularly pronounced at radio wavelengths, and likely contribute non-thermal emission at a wide range of wavelengths. A non-thermal emission component can be diagnosed using linear polarimetry, even when the total received light is dominated by emission from an accretion disc or disc outflow. In this paper, we present Very Large Telescope (VLT) measurements of the linear polarization of the optical light of jetted TDE Swift J2058+0516. This is the second jetted TDE studied in this manner, after Swift J1644+57. We find evidence of non-zero optical linear polarization, $P_{V}\sim 8{{\, \rm per\, cent}}$, a level very similar to the near-infrared polarimetry of Swift J1644+57. These detections provide an independent test of the emission mechanisms of the multiwavelength emission of jetted TDEs.

Magnetic fields in Bok globules: multi-wavelength polarimetry as tracer across large spatial scales

Context. The role of magnetic fields in the process of star formation is a matter of continuous debate. Clear observational proof of the general influence of magnetic fields on the early phase of cloud collapse is still pending. In an earlier study on Bok globules with simple structures, we find strong indications of dominant magnetic fields across large spatial scales. Aims. The aim of this study is to test the magnetic field influence across Bok globules with more complex density structures. Methods. We apply near-infrared polarimetry to trace the magnetic field structure on scales of 104–105 au (~0.05–0.5pc) in selected Bok globules. The combination of these measurements with archival data in the optical and sub-mm wavelength range allows us to characterize the magnetic field on scales of 103–106 au (~0.005–5pc). Results. We present polarimetric data in the near-infrared wavelength range for the three Bok globules CB34, CB56, and [OMK2002]18, combined with archival polarimetric data in the optical wavelength range for CB34 and CB56, and in the submillimeter wavelength range for CB34 and [OMK2002]18. We find a strong polarization signal (P ≥ 2%) in the near-infrared for all three globules. For CB34, we detect a connection between the structure on scales of 104–105 au (~0.05–0.5pc) to 105–106 au (~0.5–5pc). For CB56, we trace aligned polarization segments in both the near-infrared and optical data, suggesting a connection of the magnetic field structure across the whole globule. In the case of [OMK2002]18, we find ordered polarization structures on scales of 104–105 au (~0.05–0.5pc). Conclusions. We find strongly aligned polarization segments on large scales which indicate dominant magnetic fields across Bok globules with complex density structures. To reconcile our findings in globules, the lowest mass clouds known, and the results on intermediate (e.g. Taurus) and more massive (e.g. Orion) clouds, we postulate a mass-dependent role of magnetic fields, whereby magnetic fields appear to be dominant on low and high mass but rather subdominant on intermediate mass clouds.

Magnetic field structures in star-forming regions revealed by imaging polarimetry at multi-wavelengths

AbstractMagnetic fields are ubiquitous in various scales of astronomical objects, and they are considered as playing significant roles from star to galaxy formations. However, the role of the magnetic fields in star forming regions is less well understood because conventional optical polarimetry is hampered by heavy extinction by dust. We have been conducting extensive near-infrared polarization survey of various star-forming regions from low- and intermediate-mass to high-mass star-forming regions, using IRSF/SIRPOL in South Africa. Not only linear but also circular polarizations have been measured for more than a dozen of regions. Both linear and circular polarimetric observations at near-infrared wavelengths are useful tools to study the magnetic fields in star forming regions, although infrared circular polarimetry has been less explored so far. In this presentation, we summarize our results of the near-infrared polarization survey of star forming regions and its comparison with recent submillimeter polarimetry results. Such multi-wavelength approaches can be extended to the polarimetry using ALMA, SPICA in future, and others. We also present our recent results of the first near-infrared imaging polarimetry of young stellar objects in the Circinus molecular cloud, which has been less studied but a very intriguing cluster containing numerous signs of active low-mass star formation.

Near-infrared Polarimetry of the Outflow Source AFGL 6366S: Detection of Circular Polarization

Abstract We have carried out near-infrared circular and linear imaging polarimetry of the AFGL 6366S region. There is one large infrared reflection nebula associated with the AFGL 6366S cluster and one small infrared reflection nebula associated with AFGL 6366S NE. Prominent and extended polarized nebulosities over the AFGL 6366S cluster field are found to be composed of several components and local nebula peaks, and those nebulosities are illuminated by at least three sources, which is roughly consistent with a previous study. However, the detailed linear polarization patterns and their degrees differ from the earlier study. The brightest regions of the nebulae are illuminated by the IRAS/WISE source. In addition, we report the first detection of circular polarization (CP) in the reflection nebula associated with AFGL 6366S. The CP is as large as approximately 4% in the K s band, and the maximum CP extent is approximately 0.45 pc, which is comparable to that for the largest CP regions known to date, such as Orion and Mon R2, although the CP degrees are much smaller. The CP pattern is mostly quadrupolar, and its morphology resembles the shape of the C18O dense core. Therefore, the CP region is probably illuminated by the IRAS/WISE source and its polarization is amplified by the dichroic absorption of the dense core associated with the cluster. This is the ninth source whose degrees of CPs are measured to be greater than 3%, suggesting that large and extended infrared CP regions are common among mid- to high-mass young stellar objects.

First Near-infrared Imaging Polarimetry of Young Stellar Objects in the Circinus Molecular Cloud

First Near-infrared Imaging Polarimetry of Young Stellar Objects in the Circinus Molecular Cloud

Optical and Near-infrared Polarimetry of Non-periodic Comet C/2013 US10 (Catalina)

Abstract We present an optical and near-infrared (hereafter NIR) polarimetric study of a comet C/2013 US10 (Catalina) observed on UT 2015 December 17–18 at phase angles of α = 52.°1–53.°1. Additionally, we obtained an optical spectrum and multi-band images to examine the influence of gas emission. We find that the observed optical signals are significantly influenced by gas emission; that is, the gas-to-total intensity ratio varies from 5 to 30% in the R C and 3%–18% in the I C bands, depending on the position in the coma. We derive the “gas-free dust polarization degrees” of 13.8% ± 1.0% in the R C and 12.5% ± 1.1% in the I C bands and a gray polarimetric color, i.e., −8.7% ± 9.9% μm−1 in optical and 1.6% ± 0.9% μm−1 in NIR. The increments of polarization obtained from the gas correction show that the polarimetric properties of the dust in this low-polarization comet are not different from those in high-polarization comets. In this process, the cometocentric distance dependence of polarization has disappeared. We also find that the R C-band polarization degree of the southeast dust tail, which consists of large dust particles (100 μm–1 mm), is similar to that in the outer coma where small and large ones are mixed. Our study confirms that the dichotomy of cometary polarization does not result from the difference of dust properties, but from depolarizing gas contamination. This conclusion can provide a strong support for similarity in origin of comets.

Distortion of Magnetic Fields in a Starless Core: Near-infrared Polarimetry of FeSt 1–457

Abstract Magnetic fields are believed to play an important role in controlling the stability and contraction of the dense condensations of gas and dust that lead to the formation of stars and planetary systems. In the present study, the magnetic field of FeSt 1–457, a cold starless molecular cloud core, was mapped on the basis of the polarized near-infrared light from 185 background stars after being dichroically absorbed by dust aligned with the magnetic field in the core. A distinct “hourglass-shaped” magnetic field was identified in the region of the core, and was interpreted as the first evidence of a magnetic field structure distorted by mass condensation in a starless core. The steep curvature of the magnetic field lines obtained in the present study indicates that the distortion was mainly created during the formation phase of the dense core. The derived mass-to-magnetic flux ratio indicates that the core is in a magnetically supercritical state. However, the stability of the core can be considered to be in a nearly critical state if the additional contributions from the thermal and turbulent support are included. Further diffusion of the magnetic field and/or turbulent dissipation would cause the onset of the dynamical collapse of the core. The geometrical relationship between the direction of the magnetic field lines and the elongation of the core was found to be in good agreement with theoretical predictions for the formation of Sun-like stars under the influence of a magnetic field.

Near-infrared polarimetry of the GG Tauri A binary system

A high angular resolution near-infrared image that shows the intensity of polarization for the GG Tau A binary system was obtained with the Subaru Telescope. The image shows a circumbinary disk scattering the light from the central binary. The azimuthal profile of the intensity of polarization for the circumbinary disk is roughly reproduced by a simple disk model with the Henyey-Greenstein phase function and the Rayleigh function, indicating there are small dust grains at the surface of the disk. Combined with a previous observation of the circumbinary disk, our image indicates that the gap structure in the circumbinary disk orbits counterclockwise, but material in the disk orbits clockwise. We propose that there is a shadow caused by material located between the central binary and the circumbinary disk. The separations and position angles of the stellar components of the binary in the past 20 yr are consistent with the binary orbit with a = 33.4 AU and e = 0.34.

YOUNG STELLAR OBJECT SEARCH TOWARD THE BOUNDARY OF THE CENTRAL MOLECULAR ZONE WITH NEAR-INFRARED POLARIMETRY

We have carried out near-infrared polarimetry toward the boundary of the Central Molecular Zone, in the field of (-1.4 deg $\lesssim l \lesssim$ -0.3 deg and 1.0 deg $\lesssim l \lesssim$ 2.9 deg, $|b|\lesssim$ 0.1 deg), using the near-infrared polarimetric camera SIRPOL on the 1.4 m Infrared Survey Facility telescope. We have selected 112 intrinsically polarized sources on the basis of the estimate of interstellar polarization on Stokes $Q/I-U/I$ planes. The selected sources are brighter than $K_S=14.5$ mag and have polarimetric uncertainty $\delta P<1\,%$. Ten of these distinctive polarized sources are fit well with spectral energy distributions of young stellar objects when using the photometry in the archive of the Spitzer Space Telescope mid-infrared data. However, many sources have spectral energy distributions of normal stars suffering heavy interstellar extinction; these might be stars behind dark clouds. Due to the small number of distinctive polarized sources and candidates of young stellar object, we cannot judge if there is a decline of them outside the Central Molecular Zone. Many of massive candidates of young stellar object in the literature have only small intrinsic polarization. This might suggest that their masses are 4-15 M$_{{\rm sun}}$, whose intrinsic polarization has been expected to be small.

Large-scale magnetic fields in Bok globules

Context: The role of magnetic fields in the star formation process is a contentious matter of debate. In particular, no clear observational proof exists of a general influence by magnetic fields during the initial collapse of molecular clouds. Aims: Our aim is to examine magnetic fields and their influence on a wide range of spatial scales in low-mass star-forming regions. Method: We trace the large-scale magnetic field structure on scales of 10^3-10^5 AU in the local environment of Bok globules through optical and near-infrared polarimetry and combine these measurements with existing submillimeter measurements, thereby characterizing the small-scale magnetic field structure on scales of 10^2-10^3 AU. Results: For the first time, we present polarimetric observations in the optical and near-infrared of the three Bok globules B335, CB68, and CB54, combined with archival observations in the submillimeter and the optical. We find a significant polarization signal (P>=2%, P/sigma(P)>3) in the optical and near-infrared for all three globules. Additionally, we detect a connection between the structure on scales of 10^2-10^3 AU to 10^3-10^4 AU for both B335 and CB68. Furthermore, for CB54, we trace ordered polarization vectors on scales of ~10^5 AU. We determine a magnetic field orientation that is aligned with the CO outflow in the case of CB54, but nearly perpendicular to the CO outflow for CB68. For B335 we find a change in the magnetic field oriented toward the outflow direction, from the inner core to the outer regions. Conclusion: We find strongly aligned polarization vectors that indicate dominant magnetic fields on a wide range of spatial scales.

New insights into the study of magnetic field in the clumpy torus of AGN using near-infrared polarimetry

We present J, H and Kn imaging polarimetry of IC5063. NIR polarimetry observations may advance our understanding of the mechanisms of polarisation and hence magnetic field strength in the torus of AGN. In these proceedings we summarize the polarisation results of the central 1.2″ aperture (~263 pc) of IC5063. We present a simple polarising model to account for various mechanisms of polarisation in the central regions of IC5063. The model is consistent with dichroic absorption from diffuse stellar emission through dust in the nuclear bulge and electron scattering as dominant mechanisms of polarisation at J and H. Dichroic absorption from aligned dust grains within the torus of IC5063 is dominant at Kn with a visual extinction of Av = 48±2 mag by the torus. Through the use of various components to the central engine of IC5063, we estimated the intrinsic polarisation from dichroic absorption to be . The dust grain alignment mechanism is assumed to be produced by paramagnetic relaxation. In this case, the intrinsic polarisation, , and the visual extinction by the torus, Av, are related with the magnetic field strength. The magnetic field strength is estimated to be in the range of 12–128 mG, for the physical conditions and environments of the gas and dust in the NIR emitting regions of the torus of IC5063.

Estimations of the magnetic field strength in the torus of IC 5063 using near-infrared polarimetry

An optically and geometrically thick torus obscures the central engine of Active Galactic Nuclei (AGN) from some lines of sight. From a magnetohydrodynamical framework, the torus can be considered to be a particular region of clouds surrounding the central engine where the clouds are dusty and optically thick. In this framework, the magnetic field plays an important role in the creation, morphology and evolution of the torus. If the dust grains within the clouds are assumed to be aligned by paramagnetic alignment, then the ratio of the intrinsic polarisation and visual extinction, P(%)/Av, is a function of the magnetic field strength. To estimate the visual extinction through the torus and constrain the polarisation mechanisms in the nucleus of AGN, we developed a polarisation model to fit both the total and polarised flux in a 1.2" (~263pc) aperture of the type 2 AGN, IC5063. The polarisation model is consistent with the nuclear polarisation observed at K being produced by dichroic absorption from aligned dust grains with a visual extinction through the torus of 48$\pm$2 mag. We estimated the intrinsic polarisation arising from dichroic absorption to be P$_{K}^{dic}$=12.5$\pm$2.7%. We consider the physical conditions and environment of the gas and dust for the torus of IC5063. Then, through paramagnetic alignment, we estimate a magnetic field strength in the range of 12-128mG in the NIR emitting regions of the torus of IC5063. Alternatively, we estimate the magnetic field strength in the plane of the sky using the Chandrasekhar-Fermi method. The minimum magnetic field strength in the plane of the sky is estimated to be 13 and 41 mG depending of the conditions within the torus of IC5063. These techniques afford the chance to make a survey of AGN, to investigate the effects of magnetic field strength on the torus, accretion, and interaction to the host galaxy.