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The O-Na and Mg-Al anticorrelations in turn-off and early subgiants in globular clusters
High dispersion spectra (R>~ 40 000) for a quite large number ofstars at the main sequence turn-off and at the base of the giant branchin NGC 6397 and NGC 6752 were obtained with the UVES on Kueyen (VLTUT2). The [Fe/H] values we found are -2.03+/- 0.02+/- 0.04\ and -1.42+/-0.02+/- 0.04\ for NGC 6397 and NGC 6752 respectively, where the firsterror bars refer to internal and the second ones to systematic errors(within the abundance scale defined by our analysis of 25 subdwarfs withgood Hipparcos parallaxes). In both clusters the [Fe/H]'s obtained forTO-stars agree perfectly (within a few percent) with that obtained forstars at the base of the RGB. The [O/Fe]=0.21+/- 0.05 value we obtainfor NGC 6397 is quite low, but it agrees with previous results obtainedfor giants in this cluster. Moreover, the star-to-star scatter in both Oand Fe is very small, indicating that this small mass cluster ischemically very homogenous. On the other hand, our results show clearlyand for the first time that the O-Na anticorrelation (up to now seenonly for stars on the red giant branches of globular clusters) ispresent among unevolved stars in the globular cluster NGC 6752, a moremassive cluster than NGC 6397. A similar anticorrelation is present alsofor Mg and Al, and C and N. It is very difficult to explain the observedNa-O, and Mg-Al anticorrelation in NGC 6752 stars by a deep mixingscenario; we think it requires some non internal mechanism. Based ondata collected at the European Southern Observatory, Chile.
| Visual multiples. VII - MK classifications
Classifications are given for 865 components of visual multiples; theyshow no systematic differences from the MK system, and the random errorsare one subclass in type and two-thirds of a luminosity class. It isfound that at least 1% of the F-type IV and V stars are weak-lined, 32%of the A4-F1 IV and V stars are Am, and 5% of the A0-A3 IV and V starsare early-type Am. Attention is called to the large fraction (55%) ofthe A3-A9 III-V stars that are of luminosity classes III or IV, unlikethe percentage (16%) at neighboring types.
| Variations in Light of the Spectrum Variables 73 Draconis and IOTA Cassiopeiae.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1953ApJ...117...21P&db_key=AST
| Photographic magnitudes of stars brighter than 7m.75 between +75° and +80° declination (Errata: 11 270)
Not Available
| Yerkes actinometry. Zone +73deg to +90deg.
Not Available
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Osservazione e dati astrometrici
| Costellazione: | Cefeo |
| Ascensione retta: | 21h12m03.89s |
| Declinazione: | +76°18'36.6" |
| Magnitudine apparente: | 7.1 |
| Distanza: | 164.474 parsec |
| Moto proprio RA: | 11 |
| Moto proprio Dec: | 7.7 |
| B-T magnitude: | 6.969 |
| V-T magnitude: | 7.09 |
Cataloghi e designazioni:
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