Wavelength Dependence Of Interstellar Polarization Research Articles

The wavelength dependence of interstellar polarization in the Local Hot Bubble

The properties of dust in the interstellar medium (ISM) nearest the Sun are poorly understood because the low column densities of dust toward nearby stars induce little photometric reddening, rendering the grains largely undetectable. Stellar polarimetry offers one pathway to deducing the properties of this diffuse material. Here we present multi-wavelength aperture polarimetry measurements of seven bright stars chosen to probe interstellar polarization near the edge of the Local Hot Bubble (LHB) - an amorphous region of relatively low density interstellar gas and dust extending ~70-150 pc from the Sun. The measurements were taken using the HIgh Precision Polarimetric Instrument (HIPPI) on the 3.9-m Anglo-Australian Telescope. HIPPI is an aperture stellar polarimeter with a demonstrated sensitivity of 4.3 parts-per-million (ppm). Of the stars observed two are polarized to a much greater degree than the others; they have a wavelength of maximum polarization ($\lambda_{max}$) of ~550 $\pm$ 20 nm - similar to that of stars beyond the LHB - and we conclude that they are in the wall of the LHB. The remaining five stars have polarizations of ~70 to 160 ppm, of these four have a much bluer $\lambda_{max}$, ~350 $\pm$ 50 nm. Bluer values of $\lambda_{max}$ may indicate grains shocked during the evolution of the Loop I Superbubble. The remaining star, HD 4150 is not well fit by a Serkowski curve, and may be intrinsically polarized.

THE EFFICIENCY AND WAVELENGTH DEPENDENCE OF NEAR-INFRARED INTERSTELLAR POLARIZATION TOWARD THE GALACTIC CENTER

Near-infrared polarimetric imaging observations toward the Galactic center have been carried out to examine the efficiency and wavelength dependence of interstellar polarization. A total area of about 5.7 deg$^2$ is covered in the $J$, $H$, and $K_S$ bands. We examined the polarization efficiency, defined as the ratio of degree of polarization to color excess. The interstellar medium between the Galactic center and us shows the polarization efficiency lower than that in the Galactic disk by a factor of three. Moreover we investigated the spatial variation of the polarization efficiency by comparing it with those of color excess, degree of polarization, and position angle. The spatial variations of color excess and degree of polarization depend on the Galactic latitude, while the polarization efficiency varies independently of the Galactic structure. Position angles are nearly parallel to the Galactic plane, indicating the longitudinal magnetic field configuration between the Galactic center and us. The polarization efficiency anticorrelates with dispersions of position angles. The low polarization efficiency and its spatial variation can be explained by the differences of the magnetic field directions along the line-of-sight. From the lower polarization efficiency, we suggest a higher strength of a random component relative to a uniform component of the magnetic field between the Galactic center and us. We also derived the ratios of degree of polarization $p_H/p_J$ = 0.581 $\pm$ 0.004 and $p_{K_S}/p_H$ = 0.620 $\pm$ 0.002. The power law indices of the wavelength dependence of polarization are $\beta_{JH}$ = 2.08 $\pm$ 0.02 and $\beta_{HK_S}$ = 1.76 $\pm$ 0.01. Therefore the wavelength dependence of interstellar polarization exhibits flattening toward longer wavelengths in the range of 1.25$-$2.14 $\micron$. The flattening would be caused by aligned large-size dust grains.

Interstellar Polarization in M31

The wavelength dependence of interstellar polarization due to dust in M31 has been observed along four sight lines. Only one sight line had been measured previously. The globular clusters, S78, S150, S233, and Baade 327 were used as point sources to probe the interstellar dust in M31. The Serkowski law produces good fits for all the sight lines, although the relationship between K and λmax may be different from that found in the Galaxy. The results of this study imply that the slope K/λmax may be significantly larger in M31. The Serkowski curves are significantly narrower than those of the same λmax in the Galaxy and may require extreme modifications to the size distributions of silicate particles. The fits for the four sight lines reveal values of λmax ranging from 4800 to 5500 A. These are consistent with average values of λmax measured in the Galaxy and the Magellanic Clouds. The range measured for M31 corresponds to RV values of 2.7–3.1. The range in RV seen in the Galaxy is 2.5–5.5 implying, for this small sample, that the average size of interstellar grains in M31 is typically smaller than that seen for Galactic grains if the nature of the grains is the same. Also, the polarization efficiency for these sight lines is large, although some bias is expected since sight lines known to have significant interstellar polarization were selected for the sample.

Optical polarimetry, high–resolution spectroscopy and IR analysis of the Chamaeleon I dark cloud

We present optical polarimetry and high res- olution spectroscopy of a sample of stars toward the Chamaeleon I dark cloud. We use our polarimetry which includes 33 stars to study the wavelength dependence of the degree and position angle of polarization. From ts to the normalized wavelength dependence of interstellar polarization, we derive estimates of Max ranging from 4500 A to 6700 A, and PMax ranging from 3 to 8%. The values ofMax were found to be well correlated with the IRAS 100 m intensity, whilePMax was found to increase with EB V. High resolution spectra of the Ca II, CH, and CH + lines were obtained for 10 stars, which show two compo- nents of Ca II in absorption at 3.0 <v LSR < 5k m s 1 , andvLSR= 3.0 km s 1 and a single strong molecular CH absorption component at 3.0 <v LSR < 5.0 km s 1 . From our data we found, by interpretation of the vari- ous correlations between the polarimetry, photometry and IRAS fluxes, the following: the probable presence of shocked molecular gas; a warm molecular CH component; small dust grains at the edges of the cloud, and larger grains in the central parts, which are causing the polarization. Our results provide a consistent picture of the gas and dust content in the Cha I region, where larger grains, re- sponsible of the starlight polarization, exist in the center of the cloud, surrounded by envelopes of warmer molecular and atomic material.

Astro-2 Observations of Interstellar Dust and Gas in the Large Magellanic Cloud

view Abstract Citations (36) References (55) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Astro-2 Observations of Interstellar Dust and Gas in the Large Magellanic Cloud Clayton, Geoffrey C. ; Green, J. ; Wolff, Michael J. ; Zellner, Nicolle E. B. ; Code, A. D. ; Davidsen, Arthur F. ; WUPPE Science Team ; HUT Science Team Abstract This paper presents the first UV (1400-3200 A) polarimetry and far-UV (950-1200 A) spectrophotometry ever obtained for reddened stars in the Large Magellanic Cloud (LMC). We derive the UV wavelength dependence of interstellar polarization down to 1400 A and that of extinction down to near the Lyman limit. We also measure column densities of H_2_ along these lines of sight in the LMC. We have obtained these data with the Hopkins Ultraviolet Telescope (HUT) and the Wisconsin Ultraviolet Photo- Polarimeter Experiment (WUPPE) using the Astro-2 Observatory, which flew on the Space Shuttle in 1995 March. The UV interstellar polarization in the LMC shows a wavelength dependence similar to that seen in the Galaxy. The magnitude of the polarization in the UV lies on or above an extrapolation of the Serkowski curve. This is consistent with the wavelength dependence seen for low λ_max_ sight lines in the Galaxy. The far-UV extinction in the LMC continues to rise to 10.5 micron^-1^, which confirms that large numbers of small grains are present. The measured column densities of H_2_ with respect to H I are low compared to the Galaxy and track the previously measured lower dust abundance. The H_2_ abundance may be regulated by the amount of dust present. These new data will allow a comparison of how interstellar dust properties vary in different galactic environments. Publication: The Astrophysical Journal Pub Date: March 1996 DOI: 10.1086/176971 Bibcode: 1996ApJ...460..313C Keywords: ISM: DUST; EXTINCTION; GALAXIES: ISM; ISM: ABUNDANCES; GALAXIES: MAGELLANIC CLOUDS; POLARIZATION; ULTRAVIOLET: GALAXIES full text sources ADS | data products SIMBAD (11) MAST (3) NED (1) Related Materials (1) Erratum: 1997ApJ...485..920C

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.

Ultraviolet interstellar linear polarization. I - Applicability of current dust grain models

view Abstract Citations (61) References (65) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet Interstellar Linear Polarization. I. Applicability of Current Dust Grain Models Wolff, Michael J. ; Clayton, Geoffrey C. ; Meade, Marilyn R. Abstract UV spectropolarimetric observations yielding data on the wavelength-dependence of interstellar polarization along eight lines of sight facilitate the evaluation of dust grain models previously used to fit the extinction and polarization in the visible and IR. These models pertain to bare silicate/graphite grains, silicate cores with organic refractory mantles, silicate cores with amorphous carbon mantles, and composite grains. The eight lines-of-sight show three different interstellar polarization dependences. Publication: The Astrophysical Journal Pub Date: February 1993 DOI: 10.1086/172243 Bibcode: 1993ApJ...403..722W Keywords: Astronomical Models; Astronomical Polarimetry; Cosmic Dust; Linear Polarization; Ultraviolet Astronomy; Carbon; Interstellar Extinction; Interstellar Matter; Silicates; Astrophysics; ISM: DUST; EXTINCTION; POLARIZATION; ULTRAVIOLET: INTERSTELLAR full text sources ADS | data products SIMBAD (8) MAST (2) Related Materials (4) Part 2: 1995ApJ...445..947C Part 3: 1997ApJ...478..395W Part 4: 1997AJ....114.1132C Part 5: 1999ApJ...510..905M

The first spectropolarimetric study of the wavelength dependence of interstellar polarization in the ultraviolet

The first UV spectropolarimetry along six lines of sight with significant interstellar polarization is reported. The observations were obtained with the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE) during the Astro-1 mission. HD 37903, HD 62542 and HD 99264 show a wavelength dependence which follows the Serkowski relation extrapolated into the UV. HD 25443 and Alpha Cam have UV polarization well in excess of the Serkowski extrapolation. HD 197770 clearly shows a polarization bump which closely matches the 2175 A extinction feature. This bump polarization can be fitted by small aligned graphite disks. The differences along various lines of sight might be the result of differences in the environments which affect the size and alignment of the grains.

The wavelength dependence of interstellar polarization in the Large Magellanic Cloud

view Abstract Citations (32) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The wavelength dependence of interstellar polarization in the LMC. Clayton, G. C. ; Martin, P. G. ; Thompson, I. Abstract The wavelength dependence of interstellar polarization in the Large Magellanic Cloud has been studied. It was found that the data were fitted well by the empirical Serkowski relation used for Galactic stars. The range in λmax, the wavelength of maximum polarization, is also like that found in the Galaxy. The grains in both galaxies have similar optical polarization properties. Publication: The Astrophysical Journal Pub Date: February 1983 DOI: 10.1086/160663 Bibcode: 1983ApJ...265..194C Keywords: Interstellar Extinction; Magellanic Clouds; Milky Way Galaxy; Optical Polarization; Polarized Light; Stellar Spectrophotometry; Infrared Radiation; Interstellar Matter; Stellar Spectra; Wavelengths; Astrophysics full text sources ADS | data products SIMBAD (25) NED (1)

The wavelength dependence of interstellar polarization in M31

view Abstract Citations (17) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The wavelength dependence of interstellar polarization in M31. Martin, P. G. ; Shawl, S. J. Abstract The wavelength dependence of interstellar polarization has been measured at one position in M31. The low value of the wavelength of maximum polarization (0.43 + or - 0.06 micron) suggests a small particle size and is consistent with the low value of the ratio of total to selective extinction (2.5 + or - 0.14) found in previous photometric determinations. Baade 327 was found to have a high polarization, 6.3%, and hence has an unexpectedly high alignment efficiency (5%/mag) for such a highly reddened cluster. Publication: The Astrophysical Journal Pub Date: July 1979 DOI: 10.1086/183004 Bibcode: 1979ApJ...231L..57M Keywords: Andromeda Galaxy; Globular Clusters; Interstellar Extinction; Interstellar Matter; Polarization (Waves); Astronomical Photometry; Wavelengths; Astrophysics; Andromeda Nebula:Interstellar Matter; Andromeda Nebula:Polarization full text sources ADS | data products NED (3)

Wavelength dependence of interstellar polarization and ratio of total to selective extinction

view Abstract Citations (1017) References (54) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Wavelength dependence of interstellar polarization and ratio of total to selective extinction. Serkowski, K. ; Mathewson, D. S. ; Ford, V. L. Abstract A multichannel polarimeter-photometer which uses dichroic filters to separate the (UBVR) spectral regions is described. The instrument was used with a 24-inch rotatable tube telescope for polarimetric observation of nearby stars. Polarization data for 364 nearby stars are tabulated, together with the wavelength dependence of linear and interstellar polarization. Publication: The Astrophysical Journal Pub Date: February 1975 DOI: 10.1086/153410 Bibcode: 1975ApJ...196..261S Keywords: Astronomical Catalogs; Interstellar Extinction; Polarization Characteristics; Stellar Spectra; Astronomical Photometry; Interstellar Matter; Polarimetry; Star Clusters; Stellar Spectrophotometry; Tables (Data); Ubv Spectra; Wavelengths; Astrophysics full text sources ADS | data products SIMBAD (330)

Interstellar Polarization

A review of observational data on interstellar polarization is given. The degree of fluctuation in the direction of the galactic magnetic field is discussed. An empirical formula is given which fits all the observations of the wavelength dependence of interstellar polarization when they are normalized with the wavelength λmax of maximum polarization. Well-defined regions on the sky with values of λmax deviating from an average are found. Values of λmax are correlated with the ratio of total to selective interstellar extinction. A unified wavelength dependence of interstellar extinction is obtained by normalizing the observations with the wavelength λmax of maximum interstellar polarization.

Polarization within the Interstellar 4430 Å Absorption Band

IT was reported by Nandy and Seddon1 recently that the wavelength dependence of interstellar polarization for the star HD 198478 shows a conspicuous band-like feature in a wavelength region coincident with the 4430 A interstellar absorption band. The increase in polarization near the band centre above that of the neighbouring continuum could be in the range 50–100% within the accuracy of the existing data. No satisfactory theoretical interpretation of this phenomenon has yet been given. It seems likely that the new data may hold a clue which could help in the understanding of the nature of diffuse interstellar bands.

Polarization-wavelength Profile of the Interstellar 4430 Å Absorption Band

KNOWLEDGE of the scattering and polarizing properties of interstellar grains has now reached the stage where very specific models are being proposed for the composition and size distribution of these grains. It is evident that high resolution studies of the wavelength dependence of interstellar extinction and polarization will provide important tests of the proposed grain models. Although much work has been done on detailed studies of interstellar extinction, the detailed wavelength dependence of interstellar polarization at a higher resolution needs more study. Another related problem concerns the possibility that the diffuse interstellar bands, the most intense of which occurs at 4430 A, may be polarized differently from the neighbouring continuum: the amount and nature of this difference, if any, may give a clue to their origin. Spectrophotometry of these bands is always difficult because of the width and shallowness of the features, and polarization studies are correspondingly more difficult. By the use of a Wollaston prism at the Cassegrain focus of the 36-inch telescope of the Royal Observatory, Edinburgh, we have been able to derive a polarization profile across the 4430 band. This report describes the method and presents the preliminary results.

Regional Variations in the Wavelength Dependence of Interstellar Polarization

view Abstract Citations (17) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Regional Variations in the Wavelength Dependence of Interstellar Polarization Serkowski, K. ; Robertson, John W. Abstract Polarirnetric observations were made in the UB V spectral regions for 38 southern stars with large interstellar polarization. The distribution on the sky of all stars with known ratio pV/pB of the amount of polarization in the yellow spectral region to that in the blue is discussed; for the stars more distant than 500 Pc the correlation between the values of pv/pB vanishes for stars separated by an angular distance of about 12°. The stars for which this ratio is smaller than the median value 1 035 occur in several groups, the most prominent of them around the galactic longitudes 1" = 900 and 270° and around the Double Cluster in Perseus. The largest values of pv/pB occur along the Milky Way at 1" = 2900_3450 and in the relatively nearby associations in Ophiuchus-lJpper Scorpius and in Orion. Stars nearer than 500 pc seem to have values of pV/pB higher than those of more distant stars. The wavelength of maximum interstellar polarization is related to the curvature of the extinction curve between 5500 and 9000 A but does not seem to be directly related to the ratio R of total to selective extinction Publication: The Astrophysical Journal Pub Date: November 1969 DOI: 10.1086/150208 Bibcode: 1969ApJ...158..441S full text sources ADS | data products SIMBAD (53)

Interstellar Polarization by Graphite–Silicate Grain Mixtures

The observed wavelength dependence of interstellar polarization may be understood on the basis of graphite–silicate grain mixtures.

Wavelength Dependence of Interstellar Polarization by Graphite Grains

THE interstellar extinction curve recently extended into the far ultra-violet1,2 has revealed a structure which cannot be fitted by ice grains of the type proposed by van de Hulst3. The theoretical extinction curve predicted for graphite grains has, however, been shown to fit the observations much better4,5, indicating that graphite rather than ice may be the major contributor to interstellar extinction.

A Search for the Regional Variations in the Wavelength Dependence of Interstellar Polarization

The Polarization of 19 Bright, Highly Polarized Stars was measured from March until July 1965, with a differential polarimeter installed at the Cassegrain focus of the 90-cm telescope of the Toruń Observatory in Poland. The stellar light was split by the calcite Wollaston prism into two beams falling upon the cathodes of the photomultipliers. The observations were made at eight position angles of the polarimeter differing by 45°, alternately with and without the quartz depolarizer. The yellow 2-mm Schott GG 14 and the blue Schott BG 12 (l-mm) + GG 13 (2-mm) filters were used. No optical elements except the depolarizer were placed between the Wollaston prism and the telescope mirrors.Usually only the Stokes parameters having the larger absolute values were accurately measured. The resulting polarization ratios pv/pB of the Stokes parameters expressed in magnitudes, measured with yellow and blue filters, are given in the ninth column of table I.