Interstellar Reddening at High Galactic Latitudes

1973 ◽  
Vol 52 ◽  
pp. 263-267
Author(s):  
A. G. Davis Philip
Keyword(s):  
Main Sequence ◽  
Galactic Plane ◽  
Galactic Latitude ◽  
Early Type ◽  
High Galactic Latitude ◽  
Early Type Stars

Measures in the Strömgren four-color and Hβ systems provide an accurate way to determine color excesses of early-type stars. Fourteen areas at high galactic latitude have now been searched for faint A stars which are then measured photoelectrically to obtain the color excesses. Non-main sequence A stars, which are easily detected by means of the four-color photometry, are not included in the analysis. Within 40° of each pole, the reddening is essentially zero, Eb–y = 0.00 north of the galactic plane and Eb–y = 0.01 south of the plane.

scholarly journals CP Stars at High Galactic Latitude: Photometry Near the Galactic Poles ,

1993 ◽  
Vol 138 ◽  
pp. 592-602
Author(s):  
H. Schneider
Keyword(s):  
Galactic Latitude ◽  
Early Type ◽  
High Galactic Latitude ◽  
Mean Frequency ◽  
Photometric Observations ◽  
Early Type Stars

AbstractThe results of photometric observations of early type stars in regions around the Galactic poles are presented. The aim of these investigations was to search for CP2 and CP1 and to establish new and more precise frequencies for such objects including fainter stars.A mean frequency of 24.7% was found for the CP1 stars, 23.7% for the hot CP2, and 11.7% for the cooler ones, but with large differences between the two regions investigated.Furthermore, a substantial number of stars (20) were found to be good candidates for λ Boo stars.

scholarly journals Infrared observations of high galactic latitude early-type stars

1991 ◽  
Vol 249 (2) ◽  
pp. 336-338 ◽  
Author(s):  
A. Fitzsimmons ◽  
F. P. Keenan ◽  
E. S. Conlon ◽  
P. L. Dufton ◽  
P. M. Williams
Keyword(s):  
Galactic Latitude ◽  
Early Type ◽  
High Galactic Latitude ◽  
Infrared Observations ◽  
Early Type Stars

scholarly journals The Connection with B[e] stars

2000 ◽  
Vol 175 ◽  
pp. 26-36 ◽  
Author(s):  
Franz-Josef Zickgraf
Keyword(s):  
Common Property ◽  
Main Sequence ◽  
Emission Lines ◽  
Circumstellar Dust ◽  
Evolutionary Status ◽  
Be Stars ◽  
Early Type ◽  
Circumstellar Envelopes ◽  
Early Type Stars ◽  
Uniform Group

AbstractThe characteristics of the various types of B[e] stars are discussed and compared with those of classical Be stars. Both groups of stars are characterized by the presence of emission lines in their spectra, in particular of hydrogen. However, there are also significant differences between these classes. Classical Be stars lack hot circumstellar dust and strong forbidden low-excitation emission lines, which are typical characteristics produced by B[e]-type stars. While classical Be stars are a rather uniform group of early-type stars, B[e]-type stars form a quite heterogeneous group, very often of poorly known evolutionary status, comprising such diverse types of objects as near main-sequence objects, evolved lowmass proto-planetray nebulae and massive evolved hot supergiants. Even pre-main sequence Herbig Ae/Be stars sometimes find their way into the group of B[e] stars. However, despite these dissimilarities classical Be stars and B[e]-type stars, share a common property, namely the nonsphericity of their circumstellar envelopes.

scholarly journals A Comparison of Luminosity Calibrations for MK Classifications of OB Stars

1979 ◽  
Vol 47 ◽  
pp. 81-86
Author(s):  
Janet Rountree Lesh
Keyword(s):  
Main Sequence ◽  
Early Type ◽  
Class V ◽  
Ob Stars ◽  
Early Type Stars

It has been apparent for some time that there is a need for a single luminosity calibration to be used with modern MK types for early-type stars, at least from 0 through middle B. The widely used calibration of Blaauw (1963) has to be replaced because the refinement of the MK system - as reflected in the large collections of spectral types by Lesh (1968), Hiltner, Garrison, and Schild (1969) and Walborn (1971) - has led to a lower mean luminosity for most main sequence subgroups of early-type stars, as the higher luminosity stars tend to move out of class V. Thus the calibrations of Lesh (1968) and Walborn (1972, 1973) are systematically fainter than Blaauw’s

scholarly journals Correlation of Infrared Emission with H I and CO Gas in the High Latitude Cloud Area L1642

1990 ◽  
Vol 139 ◽  
pp. 216-217
Author(s):  
T. Liljeström ◽  
R. Laureijs
Keyword(s):  
Galactic Plane ◽  
Molecular Data ◽  
Infrared Emission ◽  
Galactic Latitude ◽  
Optical Extinction ◽  
Suitable Candidate ◽  
High Galactic Latitude ◽  
Dust Clouds ◽  
Background Gas ◽  
Co Gas

The high-galactic-latitude cloud L1642 (l = 210.8°, b = −36.7°) is a suitable candidate to relate IR measurements with atomic and molecular data because it has a reasonable size with respect to the rather poor (IRAS) IR resolution, a moderate optical extinction and an isolated location in the direction towards the galactic anticenter. The exceptionally high galactic latitude of −36.7° implies that L1642 is some 60 pc below the galactic plane (if r ≈ 100 pc is adopted for its distance). L1642 is thus sufficiently far off the galactic plane to minimize the confusion by background gas and dust clouds.

scholarly journals 2.3 GHz Radio Emission From Sco OB2

1980 ◽  
Vol 85 ◽  
pp. 105-106
Author(s):  
E.E. Baart ◽  
G. de Jager ◽  
P. I. Mountfort
Keyword(s):  
Star Formation ◽  
Radio Emission ◽  
Galactic Plane ◽  
Galactic Latitude ◽  
Dark Cloud ◽  
High Galactic Latitude ◽  
Lyman Continuum

The Sco OB2 Association is convenient for investigation as it has a high galactic latitude and is therefore remote from the confusion of the galactic plane. Its distance is accurately known and this permits fairly precise estimates to be made of the Lyman continuum photon fluxes responsible for the radio emission. It includes the ρ Ophiuci dark cloud where star formation is occurring.

scholarly journals Reddening Distances for Planetary Nebulae from Broad Band BVIc CCD Imaging

1993 ◽  
Vol 155 ◽  
pp. 180-180
Author(s):  
D.L. Pollacco ◽  
G. Ramsay
Keyword(s):  
Main Sequence ◽  
Galactic Plane ◽  
Spectral Response ◽  
Broad Band ◽  
Ccd Imaging ◽  
Accuracy Comparison ◽  
Lower Accuracy ◽  
Ubv Photometry ◽  
Early Type Stars ◽  
Type Classification

If the zero age main sequence is expressed in the (V–I) versus (B–V)–(V–I) plane the reddening lines are found to lie at a great enough angle to allow reasonably accurate spectral type classification for stars later than ∼ F5. Earlier spectral types can also be identified but with lower accuracy. Comparison with the Q method of UBV photometry and with spectra of some of the program stars shows that the BVIc technique produces reliable results. As late–type stars constitute the most numerous spectral types and are plentiful in all galactic plane directions BVIc reddening distances can be derived close to the desired direction (although to smaller distances than techniques that utilize early type stars). The applicability of the technique is further enhanced by the use of CCDs which generally have a spectral response well suited for BVIc imaging observations. Using the new technique the distance to the PN NGC2440 was found to be (3100 ± 320)pc.

scholarly journals Photospheric and “Chromospheric” CIV Lines in B-Main-Sequence Stars

1986 ◽  
Vol 116 ◽  
pp. 113-116
Author(s):  
Fiorella Castelli ◽  
Carlo Morossi ◽  
Roberto Stalio
Keyword(s):  
High Temperature ◽  
Stellar Wind ◽  
High Velocity ◽  
Main Sequence ◽  
Stellar Atmosphere ◽  
Uv Spectra ◽  
Spectral Lines ◽  
Early Type ◽  
Main Sequence Stars ◽  
Early Type Stars

The presence in the far-UV spectra of early-type stars of spectral lines of superionized atoms is argument of controversial debate among astronomers. Presently there is agreement on the non-radiative origin of these ions but not on the proposed mechanisms for their production nor on the proposed locations in the stellar atmosphere where they are abundant. Cassinelli et al. (1978) suggest that the Auger mechanism is operative in a cool wind blowing above a narrow corona to produce these ions; Lucy and White (1980) introduce radiative instabilities growing into hot blobs distributed across the stellar wind; Doazan and Thomas (1982) make these ions to be formed in both pre- and post-coronal, high temperature regions at low and high velocity respectively.

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