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A search for very young Planetary Nebulae
Despite numerous efforts, the transition from Asymptotic Giant Branch(AGB) stars to Planetary Nebulae (PN) is a poorly understood phase ofstellar evolution. We have therefore carried out interferometric (VLA)radio observations of a sample of hot post-AGB stars, selected on thebasis of their optical and infrared properties. Ten sources out of the16 observed were detected. This indicates that most of our targets aresurrounded by a nebula where the ionization has already started. Thisdefinitively determines the evolutionary status of the selected sourcesand provides us with a unique sample of very young Planetary Nebulae(yPNe). A comparison with another sample of yPNe confirms our workinghypothesis that our targets are indeed very young, probably just in thetransition toward PN. Finding transition objects is extremely importantas they can provide unique clues for a better understanding of thisimportant phase of stellar evolution.
| BVR Photometry of Northern Hemisphere Luminous Stars. III. LS and HD Stars
CCD-based BVR photometry of 48 previously unobserved stars drawn fromvolumes V and VI of the Luminous Stars in the Northern Milky Way,Luminous Stars in the Southern Milky Way, and HD catalogs is reported.
| UBV beta Database for Case-Hamburg Northern and Southern Luminous Stars
A database of photoelectric UBV beta photometry for stars listed in theCase-Hamburg northern and southern Milky Way luminous stars surveys hasbeen compiled from the original research literature. Consisting of over16,000 observations of some 7300 stars from over 500 sources, thisdatabase constitutes the most complete compilation of such photometryavailable for intrinsically luminous stars around the Galactic plane.Over 5000 stars listed in the Case-Hamburg surveys still lackfundamental photometric data.
| Photometric study of faint early-type stars in the southern Milky Way
UBV photoelectric observations are presented for 101 faint early-type(mainly OB) stars in four regions of the southern Milky Way: two inVela, one in Centaurus, and one in Circinus; H-beta data are also givenfor the brightest stars. Objective-prism plates showing the H-alpharegion of the spectrum are used, together with published results fromother authors, to recognize Be stars in the sample. A new young opencluster related to the H II region RCW 38 in Vela is found at 1.7 kpcfrom the sun, and the existence of at least a spur in the local armtowards galactic longitude of about 270 deg is favored; whether such afeature extends beyond that distance cannot be decided from the data.Most of the stars studied in the Centaurus region seem to belong to theCentaurus OB 1 association, at 2.4 kpc from the sun, and lie in theSagittarius-Carina arm. It is not clear if the stars observed in theCircinus region are physically related to each other, but theirdistances to the sun also place most of them in the Sagittarius-Carinaarm.
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