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Ýlgili Makaleler
A Survey of Ca II H and K Chromospheric Emission in Southern Solar-Type Stars
More than 800 southern stars within 50 pc have been observed forchromospheric emission in the cores of the Ca II H and K lines. Most ofthe sample targets were chosen to be G dwarfs on the basis of colors andspectral types. The bimodal distribution in stellar activity first notedin a sample of northern stars by Vaughan and Preston in 1980 isconfirmed, and the percentage of active stars, about 30%, is remarkablyconsistent between the northern and southern surveys. This is especiallycompelling given that we have used an entirely different instrumentalsetup and stellar sample than used in the previous study. Comparisons tothe Sun, a relatively inactive star, show that most nearby solar-typestars have a similar activity level, and presumably a similar age. Weidentify two additional subsamples of stars -- a very active group, anda very inactive group. The very active group may be made up of youngstars near the Sun, accounting for only a few percent of the sample, andappears to be less than ~0.1 Gyr old. Included in this high-activitytail of the distribution, however, is a subset of very close binaries ofthe RS CVn or W UMa types. The remaining members of this population maybe undetected close binaries or very young single stars. The veryinactive group of stars, contributting ~5%--10% to the total sample, maybe those caught in a Maunder Minimum type phase. If the observations ofthe survey stars are considered to be a sequence of snapshots of the Sunduring its life, we might expect that the Sun will spend about 10% ofthe remainder of its main sequence life in a Maunder Minimum phase.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| Ultraviolet observations of planetary nebulae - NGC 6572, NGC 5315 and BD + 30 deg 3639
IUE observations of the planetary nebulae NGC 6572, NGC 5315, and BD+30deg 3639 are presented, and physical parameters and ionic abundances forthe three objects are obtained. The chemical composition for NGC 6572 islog C = -3.60, log N = -3.67, log O = -3.27, and log Ne = -3.8. For theother two objects, the stellar WR contribution to the UV is verysignificant; short and long wavelength spectra are shown for bothobjects with characteristic WR features, and separate WR spectra arepresented for comparison. For these nebulae, the carbon abundance onlywas obtained. For NGC 5315, log C = -3.01 and for BD+30 deg 3639, log Cwas greater than -3.27.
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| Takýmyýldýz: | Yay |
| Sað Açýklýk: | 18h07m21.28s |
| Yükselim: | -36°52'24.9" |
| Görünürdeki Parlaklýk: | 8.288 |
| Uzaklýk: | 98.717 parsek |
| özdevim Sað Açýklýk: | -4.9 |
| özdevim Yükselim: | -83.4 |
| B-T magnitude: | 8.933 |
| V-T magnitude: | 8.342 |
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