2,469 research outputs found
Clump stars in the Solar Neighbourhood
Hipparcos data has allowed the identification of a large number of clump
stars in the Solar Neighbourhood. We discuss our present knowledge about their
distributions of masses, ages, colours, magnitudes, and metallicities. We point
out that the age distribution of clump stars is ``biased'' towards
intermediate-ages. Therefore, the metallicity information they contain is
different from that provided by the local G dwarfs. Since accurate abundance
determinations are about to become available, these may provide useful
constraints to chemical evolution models of the local disc.Comment: 6 pages, proc. of the Sept. 20-24, 1999 Vulcano Workshop "The
chemical evolution of the Milky Way: stars vs. clusters", eds. F. Matteucci,
F. Giovanell
Probing populations of red giants in the galactic disk with CoRoT
The detection with CoRoT of solar-like oscillations in nearly 800 red giants
in the first 150-days long observational run paves the way for detailed studies
of populations of galactic-disk red giants. We investigate which information on
the observed population can be recovered by the distribution of the observed
seismic constraints: the frequency of maximum oscillation power (nu_max) and
the large frequency separation (Deltanu). We propose to use the observed
distribution of nu_max and of Deltanu as a tool for investigating the
properties of galactic red-giant stars through comparison with simulated
distributions based on synthetic stellar populations. We can clearly identify
the bulk of the red giants observed by CoRoT as red-clump stars, i.e.
post-flash core-He-burning stars. The distribution of nu_max and of Deltanu
gives us access to the distribution of the stellar radius and mass, and thus
represent a most promising probe of the age and star formation rate of the
disk, and of the mass-loss rate during the red-giant branch.
CoRoT observations are supplying seismic constraints for the most populated
class of He-burning stars in the galactic disk. This opens a new access gate to
probing the properties of red-giant stars that, coupled with classical
observations, promises to extend our knowledge of these advanced phases of
stellar evolution and to add relevant constraints to models of composite
stellar populations in the Galaxy.Comment: 4 pages, 6 figures, accepted in A&A Letter
Lie Superalgebras and the Multiplet Structure of the Genetic Code II: Branching Schemes
Continuing our attempt to explain the degeneracy of the genetic code using
basic classical Lie superalgebras, we present the branching schemes for the
typical codon representations (typical 64-dimensional irreducible
representations) of basic classical Lie superalgebras and find three schemes
that do reproduce the degeneracies of the standard code, based on the
orthosymplectic algebra osp(5|2) and differing only in details of the symmetry
breaking pattern during the last step.Comment: 34 pages, 9 tables, LaTe
The Asymptotic Giant Branch and the Tip of the Red Giant Branch as Probes of Star Formation History: The Nearby Dwarf Irregular Galaxy KKH 98
We investigate the utility of the asymptotic giant branch (AGB) and the red
giant branch (RGB) as probes of the star formation history (SFH) of the nearby
(D=2.5 Mpc) dwarf irregular galaxy, KKH 98. Near-infrared (IR) Keck Laser Guide
Star Adaptive Optics (AO) images resolve 592 IR bright stars reaching over 1
magnitude below the Tip of the Red Giant Branch. Significantly deeper optical
(F475W and F814W) Hubble Space Telescope images of the same field contain over
2500 stars, reaching to the Red Clump and the Main Sequence turn-off for 0.5
Gyr old populations. Compared to the optical color magnitude diagram (CMD), the
near-IR CMD shows significantly tighter AGB sequences, providing a good probe
of the intermediate age (0.5 - 5 Gyr) populations. We match observed CMDs with
stellar evolution models to recover the SFH of KKH 98. On average, the galaxy
has experienced relatively constant low-level star formation (5 x 10^-4 Mo
yr^-1) for much of cosmic time. Except for the youngest main sequence
populations (age < 0.1 Gyr), which are typically fainter than the AO data flux
limit, the SFH estimated from the the 592 IR bright stars is a reasonable match
to that derived from the much larger optical data set. Differences between the
optical and IR derived SFHs for 0.1 - 1 Gyr populations suggest that current
stellar evolution models may be over-producing the AGB by as much as a factor
of three in this galaxy. At the depth of the AO data, the IR luminous stars are
not crowded. Therefore these techniques can potentially be used to determine
the stellar populations of galaxies at significantly further distances.Comment: 15 pages, 14 figs, accepted for publication in Ap
Basic physical parameters of a selected sample of evolved stars
We present the detailed spectroscopic analysis of 72 evolved stars, including
the [Fe/H] determination for the whole sample. These metallicities, together
with the Teff values and the absolute V magnitude derived from Hipparcos
parallaxes, are used to estimate basic stellar parameters (ages, masses, radii,
(B-V)o and log g using theoretical isochrones and a Bayesian estimation method.
The (B-V)o values so estimated turn out to be in excellent agreement with the
observed (B-V), confirming the reliability of the (Teff,(B-V)o) relation used
in the isochrones. The estimated diameters have been compared with limb
darkening-corrected ones measured with independent methods, finding an
agreement better than 0.3 mas within the 1-10 mas interval. We derive the
age-metallicity relation for the solar neighborhood; for the first time such a
relation has been derived from observations of field giants rather than from
open clusters and field dwarfs and subdwarfs. The age-metallicity relation is
characterized by close-to-solar metallicities for stars younger than ~4 Gyr,
and by a large [Fe/H] spread with a trend towards lower metallicities for
higher ages. We find that the [Fe/H] dispersion of young stars (less than 1
Gyr) is comparable to the observational errors, indicating that stars in the
solar neighbourhood are formed from interstellar matter of quite homogeneous
chemical composition. The three giants of our sample which have been proposed
to host planets are not metal rich, what is at odds with those for main
sequence stars. However, two of these stars have masses much larger than a
solar mass so we may be sampling a different stellar population from most
radial velocity searches for extrasolar planets. We also confirm that the
radial velocity variability tends to increase along the RGB.Comment: 17 pgs, 19 fig
Photometric Analysis of the Optical Counterpart of the Black Hole HMXB M33 X-7
Aims: Study the high-mass X-ray binary X-7 in M33 using broad-band optical
data.
Methods: We used recently published CFHT r' and i' data for variable stars in
M33 to extract the light curve of the optical counterpart of X-7. We combined
these data with DIRECT B and V measurements in order to search for an
independent optical modulation with the X-ray periodicity. The periodic
modulation is modelled with the ellipsoidal effect. We used UBVRr'i' magnitudes
of the system to constrain the temperature and radius of the optical component.
Results: The optical data revealed a periodicity of 3.4530 +- 0.0014 days,
which is consistent with the known X-ray period. Double modulation, which we
attributed to ellipsoidal modulation, is clearly seen in four different optical
bands. The absolute magnitude in six optical bands is most consistent with a
stellar counterpart with 33000 < T_{eff} < 47000 K and 15 < R < 20 R_{\sun}. We
modelled the optical periodic modulation and derived the masses of the two
components as a function of the orbital inclination and the radius of the
stellar component. The resulting mass range for the compact object is 1.3 < M <
23 M_{\sun}.
Conclusions: The system is probably a black hole HMXB, similar to Cyg X-1,
LMC X-1 and LMC X-3.Comment: Accepted for publication in A&
Herbaceous Vegetation Dynamic after Cut and Burn Shrub Plants in Southern Brazil
A savanna area at Serra do Sudeste in southern Brazil, was studied during four years to evaluate the influence of cutting and burning shrub plants on dynamic of herbaceous vegetation. The cover of each species in 44 permanent quadrats (0,25 m2) and in each area (cut and burned) was evaluated. The results suggested that grasses and legumes were favored by cutting shrub plants. Burning favored forbs in the first years after disturbance and retarded the development of native forage species desirable for grazing
Correlation Function of Galaxy Groups
We use the Updated Zwicky Catalog of galaxies (Falco et al. 1999) to generate
a catalog of groups, by means of a friend-of-friend algorithm. The correlation
length of the total sample is well fitted with a power law with parameters and for values of . Three subsamples defined by
the range of group virial masses were used to have their clustering
properties examined throughout the autocorrelation function. We find an
increase of the amplitude of the correlation function according to the group
masses which extends the results of the relation for galaxy systems
at small . For completeness we have also analyzed a sample of groups
obtained from the Southern Sky Redshift Survey (da Costa et al.1998) in the
range of virial masses to compare the results with those obtained from
GUZC.Comment: 9 figures, accepted for publication in Ap
Early clinical predictors and correlates of long-term morbidity in bipolar disorder
OBJECTIVES:
Identifying factors predictive of long-term morbidity should improve clinical planning limiting disability and mortality associated with bipolar disorder (BD).
METHODS:
We analyzed factors associated with total, depressive and mania-related long-term morbidity and their ratio D/M, as %-time ill between a first-lifetime major affective episode and last follow-up of 207 BD subjects. Bivariate comparisons were followed by multivariable linear regression modeling.
RESULTS:
Total % of months ill during follow-up was greater in 96 BD-II (40.2%) than 111 BD-I subjects (28.4%; P=0.001). Time in depression averaged 26.1% in BD-II and 14.3% in BD-I, whereas mania-related morbidity was similar in both, averaging 13.9%. Their ratio D/M was 3.7-fold greater in BD-II than BD-I (5.74 vs. 1.96; P<0.0001). Predictive factors independently associated with total %-time ill were: [a] BD-II diagnosis, [b] longer prodrome from antecedents to first affective episode, and [c] any psychiatric comorbidity. Associated with %-time depressed were: [a] BD-II diagnosis, [b] any antecedent psychiatric syndrome, [c] psychiatric comorbidity, and [d] agitated/psychotic depressive first affective episode. Associated with %-time in mania-like illness were: [a] fewer years ill and [b] (hypo)manic first affective episode. The long-term D/M morbidity ratio was associated with: [a] anxious temperament, [b] depressive first episode, and [c] BD-II diagnosis.
CONCLUSIONS:
Long-term depressive greatly exceeded mania-like morbidity in BD patients. BD-II subjects spent 42% more time ill overall, with a 3.7-times greater D/M morbidity ratio, than BD-I. More time depressed was predicted by agitated/psychotic initial depressive episodes, psychiatric comorbidity, and BD-II diagnosis. Longer prodrome and any antecedent psychiatric syndrome were respectively associated with total and depressive morbidity
Limpeza de campo na Serra do Sudeste, RS: efeito do corte e queima de plantas lenhosas, visando aumentar as áreas de pastoreio.
Sistema da produção da região; O problema e a pesquisa realizada; Resultados; Conclusões.bitstream/item/110551/1/LIMPEZA-DE-CAMPO-NA-SERRA.pd
- …