scholarly journals Dispersion of Interstellar Polarization

1965 ◽  
Vol 7 ◽  
pp. 57-64
Author(s):  
Thomas Gehrels
Keyword(s):  
Data Processing ◽  
High Altitude ◽  
Wavelength Range ◽  
Wavelength Dependence ◽  
Probable Error ◽  
Percentage Polarization ◽  
University Of Arizona ◽  
The University ◽  
Observing Techniques

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.

scholarly journals A Spectropolarimetric Atlas of 61 Bright Northern Be Stars

2000 ◽  
Vol 175 ◽  
pp. 48-50 ◽  
Author(s):  
Karen S. Bjorkman ◽  
Marilyn R. Meade ◽  
Brian L. Babler
Keyword(s):  
Wavelength Range ◽  
Spectral Resolution ◽  
Wavelength Dependence ◽  
Be Stars ◽  
University Of Wisconsin ◽  
Time Period ◽  
Ccd Detector ◽  
Ccd Observations ◽  
Full Analysis ◽  
The University

AbstractWe are developing an atlas of spectropolarimetric observations of 61 bright northern Be stars obtained from 1989-94 using the halfwave polarimeter (HPOL) at the 0.9m telescope of the University of Wisconsin Pine Bluff Observatory (PBO). The data cover the wavelength range from about 3400-7600Å, with a spectral resolution of about 25Å. This atlas will contain all data (297 observations total) obtained as part of a survey program with HPOL during the time when the detector in use was a dual Reticon array; the survey observations with HPOL continue, using a new CCD detector which extends the spectral coverage out to 1.05μm and improves the spectral resolution to about 12Å. The CCD observations will be presented later in a second volume of the atlas.Only a brief summary of the findings of the survey from the first 5 years of the project is presented here. A full analysis of the data will be included in a paper to be published elsewhere. The general wavelength dependence of polarization for classical Be stars can be considered on the basis of these observations, and results on polarimetric variability are available. In particular, we find that 56% (20 of 36) of the Be stars observed 3 or more times from 1989-94 show significantly variable polarization at the level of 0.1% changes (inclusion of preliminary results from the continuing CCD survey indicates that the percentage is even higher). The timescales for these changes range from as short as night-to-night to as long as several months. Several of the stars showed evidence for polarimetric “outbursts” during the time period covered by the observations.

scholarly journals Infrared Observations of the Planetary Nebula NGC 7027

1968 ◽  
Vol 34 ◽  
pp. 76-76
Author(s):  
F.C. Gillett ◽  
F.J. Low ◽  
W.A. Stein
Keyword(s):  
Wavelength Range ◽  
Planetary Nebula ◽  
Sensitive Element ◽  
Infrared Observations ◽  
Stellar Radiation ◽  
University Of Arizona ◽  
Ngc 7027 ◽  
Infrared Spectrometer ◽  
The University

An infrared spectrometer has been constructed with a resolution of Δλ/λ≈0·02 for observations in the wavelength range from 2·8 to 15 µ using a gallium-doped germanium bolometer (Low, 1961) as the radiation-sensitive element. Observations of the planetary nebula NGC 7027 were made with this instrument in May and June 1967 at the Catalina Observing Station of the University of Arizona. It was discovered that there was a measurable continuum flux from this object in the wavelength range from 7·5–14 µ that compared in value with the strength of stellar radiation from α Lyr (A0) at about λ = 9 µ. These observations are described in detail elsewhere (Gillett et al., 1967).

scholarly journals The Color Dependence of Interstellar Polarization

1965 ◽  
Vol 7 ◽  
pp. 45-50
Author(s):  
Alfred Behr
Keyword(s):  
High Precision ◽  
Wavelength Range ◽  
Wavelength Dependence ◽  
Probable Error ◽  
Individual Values ◽  
Error Sources ◽  
Instrumental Polarization ◽  
The Individual

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.

scholarly journals Dispersion of Polarization in Reflection Nebulae

1965 ◽  
Vol 7 ◽  
pp. 105-109
Author(s):  
Thomas Gehrels
Keyword(s):  
Single Particle ◽  
Wavelength Dependence ◽  
Refractive Indices ◽  
Particle Sizes ◽  
Firm Conclusion ◽  
Straight Line ◽  
University Of Arizona ◽  
The University ◽  
Reflection Nebulae ◽  
Made In

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.)

RADIOCARBON IN MEXICO: FROM PROPORTIONAL COUNTERS TO AMS

Radiocarbon ◽  
2021 ◽  
pp. 1-7
Author(s):  
Corina Solís ◽  
Efraín Chávez ◽  
Arcadio Huerta ◽  
María Esther Ortiz ◽  
Alberto Alcántara ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Sample Preparation ◽  
High Voltage ◽  
Accelerator Mass Spectrometry ◽  
Science And Technology ◽  
National Council ◽  
University Of Arizona ◽  
Technological Developments ◽  
High Voltage Engineering ◽  
The University

ABSTRACT Augusto Moreno is credited with establishing the first radiocarbon (14C) laboratory in Mexico in the 1950s, however, 14C measurement with the accelerator mass spectrometry (AMS) technique was not achieved in our country until 2003. Douglas Donahue from the University of Arizona, a pioneer in using AMS for 14C dating, participated in that experiment; then, the idea of establishing a 14C AMS laboratory evolved into a feasible project. This was finally reached in 2013, thanks to the technological developments in AMS and sample preparation with automated equipment, and the backing and support of the National Autonomous University of Mexico and the National Council for Science and Technology. The Mexican AMS Laboratory, LEMA, with a compact 1 MV system from High Voltage Engineering Europa, and its sample preparation laboratories with IonPlus automated graphitization equipment, is now a reality.

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