Wavelength Dependence Of Polarization Research Articles

Wavelength Dependence of Polarization by Small Graphite Flakes

Wavelength dependence of polarization by small graphite flakes with anisotropic dielectric constant

Wavelength dependence of polarization. VI. Molecular scattering at the skin of interstellar particles

view Abstract Citations (2) References (2) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Wavelength dependence of polarization. VI. Molecular scattering at the skin of interstellar particles Gehrels, T. Abstract The pronounced shape (called "characteristic curve") of the wavelength dependence of interstellar polarization is qualitatively explained with molecular scattering at the surface of interstellar particles. Publication: The Astronomical Journal Pub Date: February 1966 DOI: 10.1086/109856 Bibcode: 1966AJ.....71...62G full text sources ADS | Related Materials (44) Part 1: 1960AJ.....65..466G Part 2: 1960PGLO...40..467G Part 3: 1960AJ.....65..470G Part 4: 1960PGLO...41..470G Part 5: 1964AJ.....69..826G Part 6: 1964PGLO...62..826G Part 7: 1965AJ.....70..447G Part 8: 1965AJ.....70..403C Part 9: 1965AJ.....70..579G Part 11: 1966AJ.....71..111G Part 12: 1966AJ.....71..355C Part 13: 1967AJ.....72..631G Part 14: 1967AJ.....72..887C Part 15: 1968AJ.....73...20C Part 16: 1968AJ.....73..677K Part 17: 1969AJ.....74...85S Part 18: 1969AJ.....74..190G Part 19: 1969AJ.....74..433C Part 20: 1969AJ.....74..446C Part 21: 1969AJ.....74..528C Part 22: 1969AJ.....74.1179C Part 23: 1969AJ.....74.1066P Part 24: 1970AJ.....75...54C Part 25: 1970AJ.....75..182Z Part 26: 1971AJ.....76..645Z Part 27: 1971AJ.....76..651Z Part 28: 1971AJ.....76..576K Part 29: 1974AJ.....79..565C Part 30: 1974AJ.....79..581C Part 31: 1974AJ.....79..590G Part 32: 1975AJ.....80..595S Part 33: 1975AJ.....80..602S Part 34: 1975AJ.....80..702C Part 35: 1976AJ.....81..641K Part 36: 1977AJ.....82..908C Part 37: 1979AJ.....84..356C Part 38: 1979AJ.....84..671G Part 39: 1979AJ.....84.1244S Part 40: 1979AJ.....84..683L Part 41: 1979AJ.....84.1200C Part 42: 1979AJ.....84.1419D Part 43: 1979AJ.....84.1802S Part 44: 1980AJ.....85..564S Part 45: 1980AJ.....85..751S

Dispersion of Interstellar Polarization

The Wavelength Dependence of Polarization as observed in 32 stars, for which the Henry Draper numbers are given, is shown in figure 1. Details of some of these observations are presented in reference 1.The equipment is now being used with the new 154-cm Catalina reflector of the Lunar and Planetary Laboratory at the University of Arizona. The instrumental polarizations are nearly zero. The data processing and observing techniques have been further improved; the precision is mainly determined by statistics such that the internal probable error in the percentage polarization is ±0.03 percent (±0.0006 magnitude) for a half-hour observation per filter on objects brighter than about 7 magnitudes. The wavelength λ ranges from 0.33 to 0.95 μ covered by seven filters of bandwidth of about 0.05 μ. The wavelength range is being extended to 1.2, 1.6, and 2.2 μ and, with high-altitude ballooning, to 0.28 and 0.22 μ.

The Color Dependence of Interstellar Polarization

Measurements of the Interstellar Polarization of Starlight at different wavelengths have been reported by several observers in references 1 to 8. With a few exceptions the wavelength range of the measurements is still relatively small, and up to now only a few dozens of stars have been measured with high precision. There is still a remarkable discrepancy between the results of different observers, as can be seen in figure 1. The scattering of the individual values is significantly larger than the probable error given by the respective authors. One of the most serious error sources seems to be the instrumental polarization which itself is highly color dependent. (See ref. 9.)Nevertheless, even if a much greater individual error is assumed, a remarkable conclusion can be drawn: the wavelength dependence of polarization is not the same for all stars.

Dispersion of Polarization in Reflection Nebulae

A Few Observations Were Made in NGC 7023 with filters at 0.36, 0.56, and 0.74 μ The wavelength dependence of polarization fitted with a straight line shows an appreciable rise with longer wavelengths. (See refs. 1 and 2.) The observations at the three filters were compared with Mie calculations obtained from Dr. B. M. Herman and General S. R. Browning of the University of Arizona for various refractive indices and particle sizes. Only single particle sizes have been considered, and therefore the results are preliminary. The present work represents a first reconnaissance to learn the techniques and some of the geometrical conditions.A firm conclusion, however, is reached in ruling out purely graphitic and purely metallic interstellar grains. The reasoning is as follows: The polarizations in various reflection nebulae (observed by Elvius and Hall) are “positive” and strong, and the color dependence is strong, with a fairly steep rise toward longer wavelengths; this behavior occurs for scattering angles from 20° to 70°. Such behavior is found in the Mie calculations at 2<a/λ ≅ 1.5. (See ref. 3.)

POLARIZATION AND COLOR MEASURES OF NGC 2261

In a previous paper1 the writer presented polarization observations of Hubble's Variable Nebula, NGC 2261, with an effective wavelength of about 4800 Â. The present paper is a study of the wavelength dependence of this polarization. These results and other results included here indicate that the light of NGC 2261 is due to a reflection process2 rather than to synchrotron emission as more recently suggested.3 Measures of the sky background and of several regions in the object were obtained with a photoelectric polarimeter incorporating a Glan-Foucault analyzer and mounted on the 69-inch Perkins reflector of the Ohio Wesleyan and Ohio State Universities at the Lowell Observatory. The Schott filters UG1, BG 12, and OG 5 were used. Wratten filter 2B was used with BG 12 to remove energy of wavelengths less than 4000 Â. The resulting effective wavelengths were close to 3640 Â, 4390 Â, and 5850 Â with half-intensity widths for each filter of 300 Â, 300 Â, and 250 Â, respectively. The strong Hs emission at A 4861 reported for R Monocerotis,4 the exciting star, was not transmitted by the filters used. Weak emission at Hy A. 4340, and for [O n] A 3727, was transmitted by the filters. The observations of November and December 1964 of NGC 2261 were kindly obtained, at my request, by A. Elvius and J. S. Hall in the course of their extensive program to determine the wavelength dependence of polarization for galactic and extragalactic objects. The observations of January 1965 were obtained by the writer with the same equipment. All reductions were made by the writer. The data in Table I show the wavelength dependence of polarization along a north-south line through R Monocerotis. The zero point of the position angles of January 9, 1965, was set from observations of polarization standard No. 16.5

The Wavelength Dependence of Polarization

Preliminary results are described of a program of polarimetry and photometry. Astronomical telescopes and a differential polarimeter are used with calibration by a Lyot depolarizer. The wide-band filters have effective wavelengths between 3250 Å and 9900 Å. The problems of instrumental polarization and depolarization are discussed; most of the instrumental effects can be avoided by proper aluminization of the telescope mirrors. The multiple molecular scattering of the sunlit sky and of the poles of Jupiter is closely represented by the Rayleigh-Chandrasekhar theory; the optical depth at the Jovian poles is 0.4–0.8. The same particle sizes that explain the interstellar reddening, 0.05–0.3 μ, are found from the interstellar polarization. Strong polarization-wavelength dependence is found for Venus and for lunar regions, but the detailed explanations require extension of the wavelength range. The range of wavelengths will be extended by using high-altitude balloons and spacecraft.