2,088 research outputs found
Effective temperatures of red giants in the APOKASC catalogue and the mixing length calibration in stellar models
Red giants in the updated APOGEE-Kepler catalogue, with estimates of mass,
chemical composition, surface gravity and effective temperature, have recently
challenged stellar models computed under the standard assumption of solar
calibrated mixing length. In this work, we critically reanalyse this sample of
red giants, adopting our own stellar model calculations. Contrary to previous
results, we find that the disagreement between the effective temperature scale
of red giants and models with solar calibrated mixing length disappears when
considering our models and the APOGEE-Kepler stars with scaled solar metal
distribution. However, a discrepancy shows up when alpha-enhanced stars are
included in the sample. We have found that assuming mass, chemical composition
and effective temperature scale of the APOGEE-Kepler catalogue, stellar models
generally underpredict the change of temperature of red giants caused by
alpha-element enhancements at fixed [Fe/H]. A second important conclusion is
that the choice of the outer boundary conditions employed in model calculations
is critical. Effective temperature differences (metallicity dependent) between
models with solar calibrated mixing length and observations appear for some
choices of the boundary conditions, but this is not a general resultComment: 8 pages, 10 figures, Astronomy & Astrophysics, in pres
double muscled and conventional cattle have the same net energy requirements if these are related to mature and current body protein mass and to gain composition
The hypothesis tested in this paper is that double-muscled (DBM) and conventional cattle, considerably differing in body composition, have similar NE requirements when: a) NE(m) is scaled as a function of current (P(i)) and adult (P(m)) protein mass; and b) ME for gain (ME(g)) is estimated from protein (Pr) and lipid (Lr) retention and their partial ME use efficiencies, the k(p) and k(l) values, respectively. First, 2 databases were examined: 1 was developed combining well known literature information from comparative slaughter trials conducted on British beef steers; the other was based on a trial conducted using extremely lean DBM Piemontese bulls. From the first database, NE(m) was calculated to be 1.625 Ă— P(i) Ă· P(m) Ă— P(m)(0.73) (MJ/kg(0.73)). From the second database, the daily ME(g) was determined as 22.8 MJ Ă— Pr Ă· k(p) + 38.74 MJ Ă— Lr Ă· k(l), assuming (from prior reports) that k(p) = 0.20 and k(l) = 0.75. Thereafter, ME(m) was defined as ME intake minus ME(g), and, hence, NE(m) was predicted as 1.625 Ă— P(i) Ă· P(m) Ă— P(m)(0.73) (where 1.625 was the value obtained from the first dataset). The resulting k(m) (NE(m)/ME(m)) averaged 0.67. This k(m) value did not differ from that (0.65; P = 0.12) predicted by Garrett's equation, which uses dietary ME content as the only predictive variable. Second, the procedure was tested for the ability to detect effects on k(m) caused by increasing BW and dietary factors not estimable from the dietary ME content only. Data were gathered from a trial involving 48 DBM Piemontese bulls divided into 4 groups fed 1 of 4 diets differing in CP content (145 or 108 g/kg DM), with or without addition of 80 g/d of rumen-protected CLA (rpCLA). Bulls were examined at 3 consecutive periods of growth, corresponding to 365, 512 and 631 kg of average BW. All energy balance items were influenced by increasing BW, except k(m) (P = 0.61), in agreement with the expectation that NE(m) requirement depends on the degree of maturity (P(i)/P(m)) and the P(m)(0.73) of an animal, whereas k(m) reflects characteristics of the feed provided. The k(m) value was also influenced by the CP Ă— rpCLA interaction (P = 0.013). We conclude that DBM and British beef steers have similar NE requirements when these are scaled as a function of P(i) and P(m), and gain composition, considering Pr, k(p), Lr and k(l). The proposed procedure will be useful to predict the energy requirements and feed use in cattle of different types that vary in BW, provided that body and gain compositions are known or accurately predicted
Chemical abundance anticorrelations in globular cluster stars: The effect on cluster integrated spectra
It is widely accepted that individual Galactic globular clusters harbor two
coeval generations of stars, the first one born with the `standard'
-enhanced metal mixture observed in field Halo objects, the second one
characterized by an anticorrelated CN-ONa abundance pattern overimposed on the
first generation, -enhanced metal mixture. We have investigated with
appropriate stellar population synthesis models how this second generation of
stars affects the integrated spectrum of a typical metal rich Galactic globular
cluster, like 47\,Tuc, focusing our analysis on the widely used Lick-type
indices. We find that the only indices appreciably affected by the abundance
anticorrelations are Ca4227, G4300, , and NaD. The
age-sensitive Balmer line, Fe line and the [MgFe] indices widely used to
determine age, Fe and total metallicity of extragalactic systems are largely
insensitive to the second generation population. Enhanced He in second
generation stars affects also the Balmer line indices of the integrated
spectra, through the change of the turn off temperature and -- in the
assumption that the mass loss history of both stellar generations is the same
-- the horizontal branch morphology of the underlying isochrones.Comment: Accepted for publication in Ap
Burro di malga: una specialitĂ di oggi con profonde radici nel passato
Una nicchia nella nicchia dove l'elevata qualità è intrinsecamente legata alla tradizione e alla ricchezza in biodiversità microbica che porta a uno sviluppo aromatico molto interessant
A Library of Integrated Spectra of Galactic Globular Clusters
We present a new library of integrated spectra of 40 Galactic globular
clusters, obtained with the Blanco 4-m telescope and the R-C spectrograph at
the Cerro Tololo Interamerican Observatory. The spectra cover the range ~ 3350
-- 6430 A with ~ 3.1 A (FWHM) resolution. The spectroscopic observations and
data reduction were designed to integrate the full projected area within the
cluster core radii in order to properly sample the light from stars in all
relevant evolutionary stages. The S/N values of the flux-calibrated spectra
range from 50 to 240/A at 4000 A and from 125 to 500/A at 5000 A. The selected
targets span a wide range of cluster parameters, including metallicity,
horizontal-branch morphology, Galactic coordinates, Galactocentric distance,
and concentration. The total sample is thus fairly representative of the entire
Galactic globular cluster population and should be valuable for comparison with
similar integrated spectra of unresolved stellar populations in remote systems.
For most of the library clusters, our spectra can be coupled with deep
color-magnitude diagrams and reliable metal abundances from the literature to
enable the calibration of stellar population synthesis models. In this paper we
present a detailed account of the observations and data reduction. The spectral
library is publicly available in electronic format from the National Optical
Astronomical Observatory website.Comment: 39 Pages, including 2 tables and 15 Figures. To appear in the
Astrophysical Journal, Supplement Serie
A Substantial Population of Low Mass Stars in Luminous Elliptical Galaxies
The stellar initial mass function (IMF) describes the mass distribution of
stars at the time of their formation and is of fundamental importance for many
areas of astrophysics. The IMF is reasonably well constrained in the disk of
the Milky Way but we have very little direct information on the form of the IMF
in other galaxies and at earlier cosmic epochs. Here we investigate the stellar
mass function in elliptical galaxies by measuring the strength of the Na I
doublet and the Wing-Ford molecular FeH band in their spectra. These lines are
strong in stars with masses <0.3 Msun and weak or absent in all other types of
stars. We unambiguously detect both signatures, consistent with previous
studies that were based on data of lower signal-to-noise ratio. The direct
detection of the light of low mass stars implies that they are very abundant in
elliptical galaxies, making up >80% of the total number of stars and
contributing >60% of the total stellar mass. We infer that the IMF in massive
star-forming galaxies in the early Universe produced many more low mass stars
than the IMF in the Milky Way disk, and was probably slightly steeper than the
Salpeter form in the mass range 0.1 - 1 Msun.Comment: To appear in Natur
Effects of water extracts from chicory and BHT on the in vitro rumen degradation of feeds.
Effects of Butyl-Hydroxyl-Toluene (BHT) and of Red Chicory Extract (RCE) on kinetics of gas production (GP) and rumen degradability values (OMd, NDFd and in vitro true OM degradability - IVTOMD) of two feeds (meadow hay and corn meal) were evaluated using an in vitro automatic batch system. For each feed 2 increasing dosages (0.15 and 1.5 mg/g of feed) of BHT and RCE and a Control (C) were tested in 4 replications and 2 incubations. First incubation lasted 72h, the 2nd one was stopped at the times on which half of GP was produced (t½), which were 9 and 16 h for corn and hay, respectively. From the supernatants of the 2nd incubation, VFA, NH3, N content of the residual NDF were analysed and the microbial N balance was computed. The 2 feeds significantly affected rumen fermentation parameters; BHT significantly increased asymptotic GP, t½ and IVTOMD (P<0.01), decreased the proportion of butyrate (P<0.01) but did not affect microbial N balance; RCE did not influence any of the parameters measured with respect to C, except for a significant increase of the estimated N available for microbes at the higher dosage
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