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The Structure of the Galactic Magnetic Field toward the High-Latitude Clouds
We present the results of an optical polarization survey toward thegalactic anticenter, in the area 5h >= alpha >= 2h and 6 deg <=delta <= 12 deg. This region is characterized by the presence of astream of high-velocity H I as well as high galactic latitude molecularclouds. We used our polarization data together with 100 mu m IRAS mapsof the region to study the relation between the dust distribution andthe geometry of the magnetic field. We find that there is a correlationbetween the percent polarization and the 100 mu m flux such that P(%)<= (0.16 +/- 0.05)F100. When the IRAS flux is converted into H Icolumn densities this becomes P(%) <= (0.13 +/- 0.03)N20 - 0.22,which is consistent with previous interstellar medium studies on therelation between reddening and polarization. This correlation indicatesthat our survey is as deep as IRAS and that the magnetic field geometrydoes not change strongly with the optical depth in the lines of sightthat we have studied. The implied lower limit to the distance of oursurvey is 500--700 pc at galactic latitudes b = -20 deg and 100 pc at b= -50 deg. Our main finding is that the magnetic field is perpendicularto the H I high-velocity stream as well as the molecular cloud MBM 16 inthe high-latitude region. The field is also perpendicular to thevelocity gradient in the stream. Closer to the plane, the magnetic fieldis parallel to the dust filaments that extend like a plume toward thehalo. Our observations indicate that the galactic magnetic field towardthe high-latitude clouds is toroidal. We propose a model in which fluxtubes that rise out of the galactic plane become force-free andpredominantly toroidal at high latitudes. The high-latitude clouds maybe gas streams that are falling back toward the galactic plane withinsuch buoyant braided ropes of magnetic flux.
| The Henry Draper Extension Charts: A catalogue of accurate positions, proper motions, magnitudes and spectral types of 86933 stars
The Henry Draper Extension Charts (HDEC), published in the form offinding charts, provide spectral classification for some 87000 starsmostly between 10th and 11th magnitude. This data, being highlyvaluable, as yet was practically unusable for modern computer-basedastronomy. An earlier pilot project (Roeser et al. 1991) demonstrated apossibility to convert this into a star catalogue, using measurements ofcartesian coordinates of stars on the charts and positions of theAstrographic Catalogue (AC) for subsequent identification. We presenthere a final HDEC catalogue comprising accurate positions, propermotions, magnitudes and spectral classes for 86933 stars of the HenryDraper Extension Charts.
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Группы:
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Наблюдательные данные и астрометрия
| Созвездие: | Орион |
| Прямое восхождение: | 04h48m53.56s |
| Склонение: | +10°23'05.0" |
| Видимая звёздная величина: | 9.839 |
| Собственное движение RA: | -2.5 |
| Собственное движение Dec: | -1 |
| B-T magnitude: | 10.287 |
| V-T magnitude: | 9.876 |
Каталоги и обозначения:
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