273 research outputs found
THE HOT END OF EVOLUTIONARY HORIZONTAL BRANCHES
No full textIn this paper we investigate the hot end of the horizontal branch (HE), presenting evolutionary constraints concerning the C-M diagram location and the gravity of hot HE stars. According to the adopted evolutionary scenario, we predict an upper limit for HE temperatures of about log T-e = 4.45, remarkably cooler than previous estimates. We find that such a theoretical prescription appears in good agreement with available observational data concerning both stellar temperatures and gravities. Finally, the problem of gaps in the HE distribution is discussed, suggesting that, at least in the case of the cluster NGC 6752, evolutionary gaps, a bimodal distribution of CNO, and stellar rotation should all play a negligible role
ADVANCED EVOLUTIONARY PHASES OF LOW-MASS STARS - THE ROLE OF THE ORIGINAL HELIUM
No full textWe present evolutionary He burning models which cover both the HE and AGE evolutionary phases, as computed for the metallicities Z = 10(-4), 10(-3) and for two assumptions on the value of the original He content Y = 0.20, 0.27. We found that both the difference in luminosity between the AGE and the HE, and the number ratio of AGE to HE stars appear quite unaffected by the amount of original He, allowing a relevant test for the efficiency of internal mixing during the central He burning phase. Data concerning HE evolution have been connected with the evolutionary times of the corresponding RGB stars to recalibrate the parameter R as a function of Y for the two investigated metallicities. Comparisons with previous calibrations disclose variations which are not negligible, and which should be taken into account when R is used to derive constraints on the amount of cosmological helium. The critical role of the HE luminosity on the evaluation of R is briefly discussed
Mass segregation of different populations inside the cluster NGC 6101
No full textWe have used ESO telescopes at La Silla and the Hubble Space Telescope (HST) in order to obtain accurate B, V, I CCD photometry for the stars located within 200" (similar or equal to2 half-mass radii, r(h) = 1.71') from the center of the cluster NGC 6101. Color-Magnitude Diagrams (CMDs) extending from the red-giant tip to about 5 magnitudes below the main-sequence turnoff MSTO (V = 20.05 +/- 0.05) have been constructed. The following results have been obtained from the analysis of the CMDs: a) The overall morphology of the main branches confirms previous results from the literature, in particular the existence of a sizeable population of 73 "blue stragglers" (BSS), which had been already partly detected (27). They are considerably more concentrated than either the subgiant branch (SGB) or the main sequence (MS) stars, and have the same spatial distribution as the horizontal branch (HB) stars (84% probability from K-S test). An hypothesis on the possible BSS progeny is also presented. b) The HB is narrow and the bulk of stars is blue, as expected for a typical metal-poor globular cluster. c) The derived magnitudes for the HB and the MSTO, V-ZAHB = 16.59 +/- 0.10, V-TO = 20.05 +/- 0.05, coupled with the values E(B - V) = 0.1, [Fe/H] = -1.80, Y = 0.23 yield a distance modulus (m - M)(v) = 16.23 and an age similar to other "old" metal-poor globular clusters. In particular, from the comparison with theoretical isochrones, we derive for this cluster an age of 13 Gyrs. d) By using the large statistical sample of Red Giant Branch (RGB) stars, we detected with high accuracy the position of the bump in the RGB luminosity function. This observational feature has been compared with theoretical prescriptions, yielding a good agreement within the current theoretical and observational uncertainties
Chemical profiling of the fruits of Styrax officinalis L. from Monti Lucretili (Latium region, Central Italy). Chemotaxonomy and nutraceutical potential
No full textIn this work, the first phytochemical analysis ever performed on the fruits of Styrax officinalis L. (Styracaceae) collected from a population vegetating in the Mounts Lucretili National Park (Italy) was reported. Fifteen compounds were identified: tri-α-linolenoyl-sn-glycerol (1), 1,2-di-α-linolenoyl-3-linoleoyl-sn-glycerol (2), 1-α-linolenoyl-2-palmitoyl-sn-glycerol (3), 1,2-di-α-linolenoyl-sn-glycerol (4), egonol (5), emethylegonol (6), homoegonol (7), 1,5-anhydro-D-mannitol (8), glucose (9), sucrose (10), 6'-O-benzoyl-sucrose (11), raffinose (12), lactic acid (13), succinic acid (14) and glutamic acid (15). These compounds belong to seven different classes of natural metabolites and most of them have chemotaxonomic relevance. Moreover, S. officinalis might be an useful source of enantiopure 1,5-anhydro-D-mannitol which has several medicinal potentialities and is a versatile building block in organic synthesis, in particular for what concern the “Green” approaches, of valuable and potentially biologically active molecules. The presence of compounds (1-15) provides also a phytochemical rationale for the ancient ethnopharmacological uses of the species and affords evidences on its nutraceutical potentialities even for their consumption as
food in human nutrition as it actually happens for animals
S-process nucleosynthesis in massive stars and the weak component. I - Evolution and neutron captures in a 25 solar mass star
No full textEvolutionary calculations of a typical massive star are run in order to
analyze the n-capture process occurring during the hydrostatic core
He-burning phase, studying the effects of variations in the C-12(alpha,
gamma)O-16 and Ne-22(alpha, n)Mg-25 rates within their present
uncertainties and in other nuclear inputs. The nucleosynthetic mechanism
is characterized by a low mean neutron density, which never exceeds 10
to the 6th n/cu cm. A good production of the s-isotopes in the atomic
mass range 70-90 is found, the actual neutron exposure depending on some
critical parameters. Important contributions are also found for several
light n-rich species and for the heavy rare isotopes Gd-152 and Ta-180.
How s-processing in a typical massive star compares with predictions by
classical analysis is addressed
First phytochemical analysis of the fruits of an Italian endemic species with ethno-pharmacological and nutraceutical properties: Styrax officinalis L.
No full text
White Dwarfs in omega Centauri: Preliminary Evidence
No full textWe present accurate and deep multiband B,R,Hα data for the globular cluster ω Cen collected with the Advanced Camera for Surveys on HST. The photometric catalogue includes more than one million stars. By adopting severe selection criteria we identified more than 600 bona fide White Dwarfs (WDs). Empirical evidence suggests that a small sample of WDs are Hα-bright. The comparison between WD isochrones and observations shows a reasonable agreement at fainter magnitudes and a mismatch at the brighter ones
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