94 research outputs found
Sur veleno delle tenie
De las investigaciones hechas por uno de nosotros sobre algunas ténias del hombre, y aquellas más recientes de Mingazzini sobre algunos helmintos intestinales, resulta la confirmación experimental de la antigua opinión que la acción nociva producida por las ténias es debida á una sustancia tóxica elaborada por ellas, de preferencia á la irritación mecánica y á las alteraciones anatómicas provocadas por estos parásitos sobre la mucosa intestinal del huésped. Partiendo de ahÃ, nosotros hemos creido interesante repetir estas experiencias con algunas modificaciones y con el control de las lesiones histológicas.Traducción del artÃculo "Sul veleno delle tenie" del Giornale della Reale Societá ed Accademia Veterinaria Italiana, 1901, num 30. por el Prof. Mathis.Facultad de Ciencias Agrarias y Forestale
New Photometric Calibration of the Wide Field Camera 3 Detectors
We present a new photometric calibration of the WFC3-UVIS and WFC3-IR
detectors based on observations collected from 2009 to 2020 for four white
dwarfs, namely GRW+70~5824, GD~153, GD~71, G191B2B, and a G-type star, P330E.
These calibrations include recent updates to the Hubble Space Telescope primary
standard white dwarf models and a new reference flux for Vega. Time-dependent
inverse sensitivities for the two WFC3-UVIS chips, UVIS1 and UVIS2, were
calculated for all 42 full-frame filters, after accounting for temporal changes
in the observed count rates with respect to a reference epoch in 2009. We also
derived new encircled energy values for a few filters and improved sensitivity
ratios for the two WFC3-UVIS chips by correcting for sensitivity changes with
time. Updated inverse sensitivity values for the 20 WFC3-UVIS quad filters and
for the 15 WF3-IR filters were derived by using the new models for the primary
standards and the new Vega reference flux and, in the case of the IR detector,
new flat fields. However, these values do not account for any sensitivity
changes with time. The new calibration provides a photometric internal
precision better than 0.5% for the wide-, medium-, and narrow-band WFC3-UVIS
filters, 5% for the quad filters, and 1% for the WFC3-IR filters. As of October
15, 2020, an updated set of photometric keywords are populated in the WFC3
image headers.Comment: 38 pages, 23 figures, accepted for publication on the Astronomical
Journa
An abundance study of red-giant-branch stars in the Hercules dwarf spheroidal galaxy
Using high-resolution spectroscopy, we provide a determination of [Fe/H] and
[Ca/H] for confirmed red-giant branch member stars of the Hercules dwarf
spheroidal galaxy. Based on this we explore the ages of the prevailing stellar
populations in Hercules, and the enrichment history from supernovae.
Additionally, we provide a new simple metallicity calibration for Stromgren
photometry for metal-poor, red giant branch stars. We find that the red-giant
branch stars of the Hercules dSph galaxy are more metal-poor than estimated in
our previous study that was based on photometry alone. Additionally, we find an
abundance trend such that [Ca/Fe] is higher for more metal-poor stars, and
lower for more metal-rich stars, with a spread of about 0.8 dex. The [Ca/Fe]
trend suggests an early rapid chemical enrichment through supernovae of type
II, followed by a phase of slow star formation dominated by enrichment through
supernovae of type Ia. A comparison with isochrones indicates that the red
giants in Hercules are older than 10 Gyr.Comment: 12 pages, 11 figures. Accepted for publication in A&
MAD@VLT: Deep into the Madding Crowd of Omega Centauri
We present deep and accurate Near-Infrared (NIR) photometry of the Galactic
Globular Cluster (GC) Omega Cen. Data were collected using the Multi-Conjugate
Adaptive Optics Demonstrator (MAD) on VLT (ESO). The unprecedented quality of
the images provided the opportunity to perform accurate photometry in the
central crowded regions. Preliminary results indicate that the spread in age
among the different stellar populations in Omega Cen is limited.Comment: 6 pages, 3 figures, to appear in the Springer Astrophysics and Space
Science Proceedings, "Science with the VLT in the ELT era", ed. A. Moorwoo
The Masses of Population II White Dwarfs
Globular star clusters are among the first stellar populations to have formed
in the Milky Way, and thus only a small sliver of their initial spectrum of
stellar types are still burning hydrogen on the main-sequence today. Almost all
of the stars born with more mass than 0.8 M_sun have evolved to form the white
dwarf cooling sequence of these systems, and the distribution and properties of
these remnants uniquely holds clues related to the nature of the now evolved
progenitor stars. With ultra-deep HST imaging observations, rich white dwarf
populations of four nearby Milky Way globular clusters have recently been
uncovered, and are found to extend an impressive 5 - 8 magnitudes in the
faint-blue region of the H-R diagram. In this paper, we characterize the
properties of these population II remnants by presenting the first direct mass
measurements of individual white dwarfs near the tip of the cooling sequence in
the nearest of the Milky Way globulars, M4. Based on Gemini/GMOS and Keck/LRIS
multiobject spectroscopic observations, our results indicate that 0.8 M_sun
population II main-sequence stars evolving today form 0.53 +/- 0.01 M_sun white
dwarfs. We discuss the implications of this result as it relates to our
understanding of stellar structure and evolution of population II stars and for
the age of the Galactic halo, as measured with white dwarf cooling theory.Comment: Accepted for Publication in Astrophys. J. on Aug. 05th, 2009. 19
pages including 9 figures and 2 tables (journal format
White Dwarfs in Omega Centauri: Preliminary Evidence
We present accurate and deep multiband B,R,Halpha data for the globular
cluster Omega 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 Halpha-bright. The
comparison between WD isochrones and observations shows a reasonable agreement
at fainter magnitudes and a mismatch at the brighter ones
Star Counts in the Globular Cluster Omega Centauri. I. Bright Stellar Components
We present an extensive photometry on HB, RGB, and MSTO stars in Omega Cen.
The central regions of the cluster were covered with a mosaic of F435W, F625W,
and F658N-band data collected with ACS/HST. The outer reaches were covered with
a large set of U,B,V,I-band data collected with the [email protected] ESO/MPI telescope.
The final catalogue includes ~1.7 million stars. We identified ~3,200 likely HB
stars and ~12,500 stars brighter than the subgiant branch and fainter than the
RGB bumps. The HB morphology changes with the radial distance. The relative
number of extreme HB stars decreases from ~30% to ~21% when moving from the
center toward the outer regions of the cluster, while the fraction of less hot
HB stars increases from ~62% to ~72%. We performed a detailed comparison
between observed ratios of different stellar tracers and predictions based on
canonical evolutionary models with a primordial helium (Y=0.23) content and
metal abundances (Z=0.0002,0.001) that bracket the observed spread in
metallicity of Omega Cen stars. We found that the empirical star counts of HB
stars are on average larger (30%-40%) than predicted. Moreover, the rate of HB
stars is 43% larger than the MSTO rate. The discrepancy between the rate of HB
compared with the rate of RG and MSTO stars supports the evidence that we are
facing a true excess of HB stars. The same comparison was performed by assuming
a mix of stellar populations made with 70% of canonical stars and 30% of
He-enhanced stars. The discrepancy between theory and observations decreases by
a factor of two when compared with rates predicted by canonical He content
models, but still 15%-25% (Y=0.42) and 15%-20% (Y=0.33) higher than observed.
Furthermore, the ratio between HB and MSTO star counts are ~24% (Y=0.42) and
30% (Y=0.33) larger than predicted lifetime ratios.Comment: 54 pages, 17 figures,to be published in ApJ, see link at
http://stellari.wiki.zoho.co
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