Near-infrared Polarization Research Articles

Near-Infrared Polarization Images of the Orion Nebula

Wide-field (~8' x 8') and deep near-infrared (JHKs bands) polarization images of the Orion nebulae (IRNe) around young stellar objects (YSOs), both massive and low-mass. We found the IRNe around both IRc2 and BN to be very extensive, suggesting that there might be two extended (>0.7 pc) bipolar/monopolar IRNe in these sources. We discovered at least 13 smaller-scale (~0.01-0.1 pc) IRNe around less-massive YSOs including the famous source theta^2 Ori C. We also suggest the presence of many unresolved (<690 AU) systems around low-mass YSOs and young brown dwarfs showing possible intrinsic polarizations. Wide-field infrared polarimetry is thus demonstrated to be a powerful technique in revealing IRNe and hence potential disk/outflow systems among high-mass to substellar YSOs.

First Two‐Micron Imaging Polarimetry of β Pictoris

High-resolution K-band imaging polarimetry of the β Pic dust disk has been conducted with adaptive optics and a coronagraph using the Subaru 8.2 m telescope. Polarization of ~10% is detected out to r ~ 120 AU with a centrosymmetric vector pattern around the central star, confirming that the disk is seen as an infrared reflection nebula. We have modeled our near-infrared and previous optical polarization results in terms of dust scattering in the disk and have found that both the degrees of polarization and the radial intensity profiles are well reproduced. We argue that the observed characteristics of the disk dust are consistent with the presence of ice-filled fluffy aggregates consisting of submicron grains in the β Pic system. There is a gap around 100 AU in both the intensity and polarization profiles, which suggests a paucity of planetesimals in this region. The radial intensity profile also shows ripple-like structures, which are indicative of the presence of multiple planetesimal belts, as in the case of the M-type Vega-like star AU Mic.

Determination of orientational states in impact-polystyrene specimens by near-infrared polarization spectroscopy

To measure the orientational state of opaque high-impact polystyrene (HIPS) samples, the dichroic ratios of different absorption bands have been determined in the near-infrared (NIR) transmission spectra measured with polarized radiation. For injection molded plates, dichroic ratios close to one were observed, indicating very low orientation effects in these specimens. However, a larger anisotropy was detected in the thermoformed cups and additionally different processing conditions could be discriminated by the dichroic effects in the NIR polarization spectra. Thus, NIR transmission spectroscopy with polarized radiation proved to be a convenient and rapid tool to determine orientation phenomena in HIPS samples and may also be implemented as a light-fiber-coupled on-line process control technique. POLYM. ENG. SCI. 46:381–383, 2006. © 2006 Society of Plastics Engineers

Near-infrared polarization study of L1641S

Near-infrared polarization study of L1641S

Near-infrared polarization study of L1641S

H-band polarimetric images and Ks-band images of star formation region L1641S are presented. Two reflection nebulae, Re50N and Re50, are in the north and south of the region, respectively. The polarization maps of two nebulae exhibit high degrees of polarization and centrosymmetric patterns, indicating the single scattering and small dust grains in the nebulae. There are two infrared sources, IRS1 and IRS2 in the nebula Re50N. IRS1 is the illuminating source of the nebulae and the driving source of CO outflow; IRS2 is suggested to provide considerable light at optical wavelengths. The high polarization in Re50N can be interpreted as surface scattering from the outflow at an inclination of 30 degrees. Based on the polarization arc structure, we further identified the bipolar structure of the nebula Re50N. The FU Orionis phenomenon in L1641S is discussed at the end of this paper.

High-Resolution Near-Infrared Imaging and Polarimetry of Four Proto-Planetary Nebulae

High-resolution near-infrared Hubble Space Telescope (HST) NICMOS (F160W, F222M) images and polarization (2 ?m) observations were made of four bipolar proto?planetary nebulae (PPNs): IRAS 17150-3224, 17441-2411, 17245-3951, and 16594-4656. The first three of these are viewed nearly edge-on, and for the first time the central stars in them are seen. Color maps reveal a reddened torus between the bipolr lobes in the edge-on cases, with bluer lobes. The polarization values are high, with maximum values ranging from 40% to 80%. The polarization patterns are basically centrosymmetric, with some deviations in the low-polarization equatorial regions. For IRAS 17150-3224, circumstellar arcs are seen at 1.6 ?m, along with a newly discovered loop in the equatorial region. Bright caps are seen at the end of the lobes, indicating that they are not open-ended. A distinct point-symmetric pattern is seen in the strengths of the polarization vectors, especially in IRAS 17150-3224. HST NICMOS observations provide a valuable complement to the WFPC2 visible images in deriving the basic structure of bipolar PPNs.

Simultaneous Optical and Near‐Infrared Spectropolarimetry of Type 2 Seyfert Galaxies

We present optical and near-infrared spectropolarimetry of the nuclei of four type 2 Seyfert galaxies, Mrk 463E, Mrk 1210, NGC 1068, and NGC 4388. The data were obtained simultaneously, covering the wavelength range of 0.46-2.5 μm. We model the polarizations from two dust-scattering components: (1) scattering in dusty regions in ionization cones and (2) scattering in a torus surrounding a type 1 nucleus. The polarizations from electron scattering in the cones and dichroic absorption by aligned dust grains in the torus are also compared with the observations. We confirmed that a combination of electron and dust scattering in the ionization cones is the preferred mechanism for the optical continuum polarization. For the near-infrared, dichroic absorption by aligned grains can explain the continuum polarization of Mrk 463E and Mrk 1210 as well as NGC 1068. Visual optical depths of the order of 10-20 are estimated for dichroic absorption in these nuclei. Dust scattering in the torus, whose grain size distribution is assumed to be the same as in the Galactic diffuse interstellar medium, cannot reproduce the observed spectral slope of the near-infrared polarization and total nuclear flux simultaneously. However, this might only indicate that the grain size distribution in the torus of active galactic nuclei (AGNs) is different, and dust scattering with moderate optical depth and dominated by large grains might provide a reasonable explanation for the near-infrared radiation from AGNs.

Spectral polarization imaging of human rectum-membrane-prostate tissues

Human rectum-membrane-prostate tissue samples were studied using a near-infrared spectral polarization imaging technique to detect small objects and structural changes inside prostate tissues through the rectum. Four modeling samples were made with a small piece of absorber or prostate tissue dyed with a contrast agent (indocyanine green) embedded inside a large piece of prostate tissue in rectum-membrane-prostate structures. The depth of the foreign objects underneath the surface of the rectum-membrane-prostate structures was varied from a millimeter to a centimeter to obtain the critical imaging distance. Different spectral polarization imaging methods with and without contrast agents were performed and compared. The results show that small objects hidden inside the host prostate tissues in the rectum-membrane-prostate structures at depths of 2.5, 4.0, and 7.5 mm can be imaged and identified using the scattering light imaging, tissue emission wing imaging, and contrast agent fluorescence imaging methods, respectively. Our results indicate the potential of imaging and detecting structural changes and cancers inside prostate tissue though rectum-membrane-prostate tissues using this noninvasive spectral polarization imaging technique.

High-resolution imaging of ultracompact HII regions

We present the rst near-infrared images of the two massive southern star-forming regions G11.11- 0.40 and G341.21-0.21, obtained with adaptive optics at sub-arcsecond resolution. Together with conventional narrow-band near-infrared images and polarization maps, mid-infrared data, millimetre and radio data, we were able to determine the morphological structure and to constrain the stellar content of the regions. In both cases the molecular cloud cores have masses of about 500 M and contain clusters of OB stars. This supports the view that massive stars do not form in isolation. In the case of G11.11-0.40 we could identify the central O star responsible for the ionization of the ultracompact Hii region. Our results for G341.21-0.21 indicate that this source is a precursor of an ultracompact Hii region.

Pre-Main Sequence Binaries with Aligned Disks?

We present the results of a study performed with the goal to investigate whether low-mass pre-main sequence binary stars are formed by multiple fragmentation or via stellar capture. If binaries form preferentially by fragmentation, we expect their disks to be co-planar. On the other hand, the capture scenario will lead to a random distribution of disk orientations. We performed near-infrared polarization measurements of 49 young visual binary stars in the K band with SOFI at the NTT. The near-infrared excess radiation of the targets mostly point to the presence of disks. For a major fraction of the sample, evidence for disks is also obvious from other features (outflows, jets, Herbig-Haro objects). We derived the disk orientation from the orientation of the polarization vector of both components of each binary. This statistical study allows to test which hypothesis (co-planarity, random orientation) is consistent with the observed distribution of polarimetric position angles. We find evidence that the disks are preferentially aligned.

A near-infrared polarized bipolar cone in the Circinus galaxy

We present near-infrared broad-band polarization images of the nuclear regions of the Circinus galaxy in the J, H and K bands. For the first time the south-eastern reflection cone is detected in polarized light, which is obscured at optical wavelengths behind the galactic disk. This biconical structure is clearly observed in J and H band polarized flux whilst in the K band a more compact structure is detected. Total flux J-K and H-K colour maps reveal a complex colour gradient toward the south-east direction (where the Circinus galactic disk is nearer to us). We find enhanced extinction in an arc shaped structure, at about 200pc from the nucleus, probably part of the star-formation ring. We model the polarized flux images with the scattering and torus model of Young etal, with the same basic input parameters as used by Alexander etal in the spectropolarimetry modelling of Circinus. The best fit to the polarized flux is achieved with a torus radius of ~16pc, and a visual extinction Av, through the torus, to the near-infrared emission regions of >66 mags.

Near‐Infrared Spectropolarimetry of Three Prototype Low‐Mass Young Stellar Objects in the Taurus Dark Cloud

We present near-infrared spectropolarimetric data between 0.9 and 4.2 μm for three prototypes of low-mass young stellar objects (YSOs), L1551 IRS 5, HL Tau, and T Tau in the Taurus dark cloud. These sources are in different classes in the standard spectral classification scheme of low-mass YSOs by Lada. The polarization curves of the observed sources show distinct differences. The class I protostar L1551 IRS 5 shows a flat polarization curve with high polarization through the observed wavelengths. It also shows a polarization excess at the 3.1 μm ice band absorption feature. The flat-spectrum HL Tau, which is thought to be in a transient phase from class I to class II, shows a steep decrease of polarization with increasing wavelengths from 1.0 to 2.5 μm, while it shows a flat polarization curve with high polarization in optical wavelengths and a slowly decreasing slope with small polarization in 3-4 μm. The class II source T Tau displays small polarization no more than 2% through the observed wavelengths; the polarization in the shorter wavelengths from optical to 1.3 μm decreases with increasing wavelengths. T Tau also shows an increasing polarization curve in the longer wavelengths over 1.6 μm, which is most likely to come from the infrared companion T Tau S (Kobayashi et al.). The prominent differences of the observed near-infrared polarization curves can be clearly understood in terms of the standard spectral classification scheme of low-mass YSOs. Thus near-infrared spectropolarimetry could serve as a potentially powerful diagnostic of circumstellar material, complementary to the standard spectral classification.

Near-infrared imaging polarimetry of NGC 1068

We present near-infrared polarization images of the nuclear region of NGC 1068. For the first time, extended reflection nebulosity from the south-western cone, which is obscured at optical wavelengths, is detected. Polarized flux images show the region of enhanced scattering, or polarized knot, ∼ 4.5 arcsec north-east of the nucleus. Our photometry of the nucleus shows an increase in luminosity compared with earlier observations, which is consistent with the brightening recently reported by Glass. We have successfully adapted the nuclear aperture model of Young et al. to fit the polarized flux images. We find that the basic geometrical parameters of inclination (43°), position angle (PA, 34°) and opening half-angle (40°) of the scattering cones are entirely consistent with our earlier model, with the north-eastern cone having the same PA as the large-scale radio structure. However, an inner scattering cone of inclination 34°, PA 10° and opening half-angle of 15° is required to fit the observed polarized flux distribution to the north-east of the nucleus. This inner cone has the same PA as that of the small-scale (subarcsec) radio jet between sources S and C, implying that source S is the radio source closest to the central engine. Such a cone to the south-west of the nucleus is presumably obscured by the torus.

Polarization models of bipolar reflection nebulae -- I

We have developed a model for optically thin reflection nebulae surrounding young stellar objects. We present the results of a parameter-space study in which we have elucidated several diagnostic characteristics which we can apply to the interpretation of polarization measurements in the outer regions of optically thin bipolar reflection nebulae. The possibility of scattering from randomly oriented, small ellipsoidal particles is also discussed. In this paper the model has been applied specifically to R Monocerotis (R Mon), for which optical and near-infrared polarization maps exist. The modelling suggests that scattering occurs at the cavity walls and at an inner optical jet. Some reasonable constraints have been placed upon the nature of the scattering particles based upon the appearance of polarization maps of R Mon at optical and infrared wavelengths.

The internight variability of the optical to near-infrared flux density and polarization of the blazars 0215 + 015 and 0851 + 202 during outbursts

The internight variability of the optical to near-infrared flux density and polarization of the blazars 0215 + 015 and 0851 + 202 during outbursts

The Distribution of Warm Dust in the Star-forming Region Cepheus A: Infrared Constraints

In order to determine the distribution of dust in the cloud associated with the star-forming region Cepheus A, we have obtained new, high angular resolution far-infrared (FIR) maps (at 50 and 100 μm) of this extended infrared source and polarimetric images (1.65 and 2.2 μm) of the reflection nebulosity, IRS 6, associated with this young stellar object. From our FIR maps we calculate the dust temperature and optical depth at 100 μm. Cepheus A has moderate optical depths (τ<SUB>100</SUB> μm ≤ 0.6), and its dust temperature ranges from 30 to 55 K. The two-dimensional map of the 100 microns optical depth indicates that there is a region of lower dust column density near the peak of the FIR emission. A radiative transfer code was used to model the available photometry and the FIR data of Cepheus A. A spherical dust cloud with a central young star was assumed, and the input parameters in this model were varied in order to reproduce the spectral energy distribution and the high angular resolution profiles at FIR wavelengths. The model that gives the best fit to the observations requires a dust cloud of the following characteristics: R<SUB>outer</SUB> = 0.5 pc, R<SUB>inner</SUB> = 0.07 pc, τ<SUB>100</SUB> = 0.15, α = 1.5, where R<SUB>outer</SUB>, R<SUB>inner</SUB>, τ<SUB>100</SUB> and α are the outer radius, inner radius, optical depth at 100 μm, and the exponent of the power law in the emitting-dust density gradient: n<SUB>d</SUB>(r) = n<SUB>0</SUB>(r/r<SUB>0</SUB>)<SUP>-α</SUP>. The inner radius used in this model (R<SUB>inner</SUB> = 0.07 pc) is similar in size to the "cavity" derived from the two-dimensional map of the dust optical depth at 100 μm. For small distances (r &lt; 0.15 pc) from the infrared peak, a second density gradient is derived from the distribution of the near-infrared (NIR) polarization. In this inner region of the dust cloud the NIR polarization distribution indicates that the density of the scattering dust should remain constant or increase slightly with distance. Our results are consistent with current star formation theories: a young stellar object surrounded by an infalling envelope with a characteristic density distribution of: n<SUB>d</SUB>(r) ∝r<SUP>-1.5</SUP>, a circumstellar disk, and a cavity (R<SUB>inner</SUB> ∼ 0.07 pc) in which n<SUB>d</SUB> is constant, created by the dispersal of the initial dust cloud by a strong stellar wind.

Near-infrared polarization in the bipolar outflow OH 0739-14

We present linear polarization observations of the bipolar outlfow source OH 0739-14 from 1.2 to 3.6 micrometers. The high levels of polarization (approximatly 47% in the bipolar lobes) and the angles of the vectors in the outflow lobes imply that the 1.2-3.6 micrometer polarization is due to single scattering by dust grains of light from the central source or from its immediate vicinity. Our polarization measurements, combined with phase-lag measurements of variability in the nebula by Kastner et al. (1992), tightly constrain the inclination angle i between the bipolar axis and the plane of the sky to be 35 deg less than or = i less than or = 37 deg. We observe the percentage polarization of the bipolar lobes to be constant with wavelength from 1.2 to 3.6 micrometers, which rules out any significant contribution by unpolarized emission, such as tiny grain emission, to the 3.6 micrometer emission. We propose to explain the K-L' color of the nebula as due to illumination by both the central star and by thermal emission from dust in a surrounding circumstellar shell with a dust temperature of 600-1000 K. Using this model, we find a relatively high minimum scattering optical depth at 3.75 micrometers of tau omega greater than 0.1. This is difficult to reconcile with Rayleigh scattering, which would then imply optically thick scattering at wavelengths of 1.2 and 1.65 micrometers, in constrast to the observations. We also find that the albedo of the grains at 3.75 micrometers and probably at 2.2 micrometers is higher than predicted for normal interstellar grains.

Broken symmetry: The structure of the dust envelope of IRC +10216

view Abstract Citations (56) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Broken Symmetry: The Structure of the Dust Envelope of IRC +10216 Kastner, Joel H. ; Weintraub, David A. Abstract We present polarimetric, coronagraphic near-infrared images of the reflection nebula surrounding the carbon star IRC +10216. These images demonstrate convincingly that the dust envelope is not spherically symmetric. In unocculted images at J (1.25 micrometers) and in occulted images at H (1.65 micrometers) and K (2.2 micrometers), the nebula appears elongated, with major axis lying at position angle approximately 20 deg. The position angle of elongation is the same as that previously determined from near-infrared speckle interferometry for the inner approximately 1 sec of the envelope. The elliptical symmetry of the J polarimetric map offers additional evidence of the axial symmetry of the envelope and indicates that the equatorial plane of IRC +10216 lies perpendicular to the major axis of the nebula. The polarization map also indicates that the source of illumination -- presumably the stellar photosphere or hot dust located very near the photosphere -- is directly detected at wavelengths as short as approximately 1 micrometers. We find that the density distribution of grains in the polar regions is roughly n varies as r-2 and estimate that the scattering dust mass within 12 sec in radius of the central star is approximately 5 x 10-6 solar masses. These results support a model in which the envelope of IRC +10216 is weakly bipolar and is viewed at an intermediate inclination angle such that we have a direct line of sight to the central star. The axisymmetric near-infrared intensity and polarization morphologies are best understood in terms of enhanced mass loss in the equatorial plane. An examination of previous near-infrared and millimeter-wave mapping observations supports this hypothesis. These observations make clear that axisymmetric structure can be well established before an intermediate-mass star leaves the asymptotic giant branch. It is possible that the dust envelope of IRC +10216 presents an early manifestation of the more profound bipolar structure that characterizes highly evolved preplanetary nebulae. Publication: The Astrophysical Journal Pub Date: October 1994 DOI: 10.1086/174774 Bibcode: 1994ApJ...434..719K Keywords: Broken Symmetry; Carbon Stars; Cosmic Dust; Density Distribution; Infrared Astronomy; Optical Polarization; Reflection Nebulae; Stellar Envelopes; Astronomical Interferometry; Astronomical Polarimetry; Coronagraphs; Infrared Imagery; Stellar Evolution; Astronomy; ISM: DUST; EXTINCTION; ISM: STRUCTURE; POLARIZATION; ISM: REFLECTION NEBULAE; STARS: CARBON; STARS: INDIVIDUAL ALPHANUMERIC: IRC; 10216 full text sources ADS | data products SIMBAD (6)

A study of the Chamaeleon I dark cloud and T-association – VI. Interstellar polarization, grain alignment and magnetic field

We present new measurements of optical and near-infrared linear polarization towards 39 field stars reddened by dust in the Chamaeleon I dark cloud. New and previously published data are combined in a detailed investigation of the wavelength dependence of interstellar polarization in the cloud. The observations are well represented by the Serkowski formula, with values of the wavelength of maximum polarization (lambda(max)) in the range 0.47-0.75 mum. The highest values of lambda(max) are found in lines of sight that intercept the dense central region of the cloud. The ratio of total to selective extinction (R(V) = A(V)/E(B-V)) is only weakly correlated with lambda(max), suggesting a degree of independence among the populations of grains responsible for optical extinction and polarization. We show that the ratio of polarization to reddening is unusually high in Cha I, with p(max)/A(V) congruent-to 4.5 per cent mag-1 in some lines of sight, indicating a remarkable degree of alignment efficiency in comparison to other dark clouds. The mean direction of the magnetic field in the plane of the sky is perpendicular to the long axis of the cloud and parallel to the external magnetic field in the Galactic neighbourhood of Chamaeleon, suggesting that the cloud formed by uniform collapse along field lines. Our observations provide important constraints on theoretical models for both grain alignment and the relation between magnetic field, cloud collapse and star formation.

The massive molecular outflow from CRL 2136 IRS 1

view Abstract Citations (32) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Massive Molecular Outflow from CRL 2136 IRS 1 Kastner, Joel H. ; Weintraub, David A. ; Snell, Ronald L. ; Sandell, G. ; Aspin, C. ; Hughes, D. H. ; Baas, F. Abstract Maps of rotational CO emission toward the star-formation region CRL 2136 reveal an arcminute-scale bipolar outflow that appears to be driven by the massive young stellar objects IRS 1. The projected outflow axis is roughly perpendicular to the disk plane previously inferred from near-infrared images and polarization maps. High-velocity wings are present in both (12)CO and (13)CO spectra, suggesting the (12)CO optical depths in the outflowing gas are large; we estimate the high-velocity gas contains approximately 50 solar mass, making this molecular outflow one of the more massive known. We find that the region within approximately 1 min of CRL 2136 constitutes a significant concentration of the molecular mass in the ambient cloud. Submillimeter photometry and mapping shows that CRL 2136 is a strong, extended source of continuum emission. The emission likely arises with grains heated to 40-60 K by IRS 1. Comparison of the estimated thermal dust mass (approximately 1 solar mass within approximately 8 sec of IRS 1), the mass in high-velocity gas, and the scattering dust mass we derived previously suggests that the gas-to-dust mass ratio in the outflow is between approximately 10 and approximately 100, where the value depends on what proportion of the submillimeter emission originates with dust in the ambient cloud and/or circumstellar disk. The apparent extreme youth of IRS 1 compared with the dynamical age of the outflow, and the tremendous mass of swept-up molecular material, suggests the outflow began early in the formation of the young stellar object and implies the outflow cannot be radiatively driven. We present evidence that infall toward IRS 1 is ongoing; transfer of angular momentum from this infalling material may drive the outflow. Publication: The Astrophysical Journal Pub Date: April 1994 DOI: 10.1086/174015 Bibcode: 1994ApJ...425..695K Keywords: Interstellar Matter; Mass Distribution; Molecular Clouds; Radio Astronomy; Star Formation; Angular Momentum; Carbon Isotopes; Kinematics; Momentum Transfer; Near Infrared Radiation; Polarization (Waves); Radio Observation; Submillimeter Waves; Astrophysics; ISM: DUST; EXTINCTION; ISM: INDIVIDUAL ALPHANUMERIC: CRL 2136; ISM: JETS AND OUTFLOWS; ISM: MOLECULES; STARS: FORMATION full text sources ADS | data products SIMBAD (8)