2,707 research outputs found
MUSE observations of M87: radial gradients for the stellar initial-mass function and the abundance of Sodium
Based on MUSE integral-field data we present evidence for a radial variation
at the low-mass end of the stellar initial-mass function (IMF) in the central
regions of the giant early-type galaxy NGC4486 (M87). We used state-of-the-art
stellar population models and the observed strength of various IMF-sensitive
absorption-line features to solve for the best low-mass tapered "bimodal" form
of the IMF, while accounting also for radial variations in stellar metallicity,
the overall -elements abundance, and the abundance of individual
elements such as Ti, O, Na and Ca. Our analysis reveals a strong IMF gradient
in M87, corresponding to an exceeding fraction of low-mass stars compared to
the case of the Milky Way toward the center of M87 that drops to nearly
Milky-way levels by 0.4 . This IMF gradient is found to correlate well
with both the radial profile for stellar metallicity and for -elements
abundance but not with stellar velocity dispersion. Such IMF variations
correspond to over a factor two increase in stellar mass-to-light M/L ratio
compared to the case of a Milky-way like IMF, consistent with other
investigations into IMF gradients in early-type galaxies, including recent
dynamical constraints on M/L radial variations in M87 by Oldham & Auger. In
addition to constraining the IMF in M87 we also looked into the abundance of
Sodium, which turned up to be super-Solar over the entire radial range of our
MUSE observations and to exhibit a considerable negative gradient. These
findings suggest an additional role of metallicity in boosting the Na-yields in
the central, metal-rich regions of M87 during its early and brief
star-formation history. Our work adds the case of M87 to the few objects that
as of today have radial constraints on their IMF or [Na/Fe] abundance, while
also illustrating the accuracy that MUSE could bring to this kind of
investigations.Comment: 17 pages, 13 figures, re-submitted for publication on MNRAS following
the referee's comment
Non-thermal radiation from a pulsar wind interacting with an inhomogeneous stellar wind
Binaries hosting a massive star and a non-accreting pulsar are powerful
non-thermal emitters due to the interaction of the pulsar and the stellar wind.
The winds of massive stars are thought to be inhomogeneous, which could have an
impact on the non-thermal emission. We study numerically the impact of the
presence of inhomogeneities or clumps in the stellar wind on the high-energy
non-thermal radiation of high-mass binaries hosting a non-accreting pulsar. We
compute the trajectories and physical properties of the streamlines in the
shocked pulsar wind without clumps, with a small clump, and with a large one.
This information is used to compute the synchrotron and inverse Compton
emission from the non-thermal populations, accounting also for the effect of
gamma-ray absorption through pair creation. A specific study is done for PSR
B1259-63/LS2883. When stellar wind clumps perturb the two-wind interaction
region, the associated non-thermal radiation in the X-ray band,of synchrotron
origin, and in the GeV-TeV band, of inverse Compton origin, is affected by
several effects: (i) strong changes in the the plasma velocity direction that
result in Doppler boosting factor variations, (ii) strengthening of the
magnetic field that mainly enhances the synchrotron radiation, (iii)
strengthening of the pulsar wind kinetic energy dissipation at the shock,
potentially available for particle acceleration, and (iv) changes in the rate
of adiabatic losses that affect the lower energy part of the non-thermal
particle population. The radiation above 100 GeV detected, presumably, during
the post-periastron crossing of the Be star disc in PSR B1259-63/LS2883, can be
roughly reproduced assuming that the crossing of the disc is modeled as the
encounter with a large inhomogeneity.Comment: 13 pages, 12 figures, submitted to A&
III Seminari Lligams: Paisatges i fortificacions
Ponència/Visita 1: El poblat ibèric d'Ullastret. Una fortalesa de l'antiguitat.
Conferència 2: La fortificació moderna, tot un "paisatge" estratègic.
Visita guiada 3: El castell de Bellaguarda
INTEGRAL and XMM-Newton observations towards the unidentified MeV source GRO J1411-64
The COMPTEL unidentified source GRO J1411-64 was observed by INTEGRAL, and
its central part, also by XMM-Newton. The data analysis shows no hint for new
detections at hard X-rays. The upper limits in flux herein presented constrain
the energy spectrum of whatever was producing GRO J1411-64, imposing, in the
framework of earlier COMPTEL observations, the existence of a peak in power
output located somewhere between 300-700 keV for the so-called low state. The
Circinus Galaxy is the only source detected within the 4 location error
of GRO J1411-64, but can be safely excluded as the possible counterpart: the
extrapolation of the energy spectrum is well below the one for GRO J1411-64 at
MeV energies. 22 significant sources (likelihood ) were extracted and
analyzed from XMM-Newton data. Only one of these sources, XMMU
J141255.6-635932, is spectrally compatible with GRO J1411-64 although the fact
the soft X-ray observations do not cover the full extent of the COMPTEL source
position uncertainty make an association hard to quantify and thus risky. The
unique peak of the power output at high energies (hard X-rays and gamma-rays)
resembles that found in the SED seen in blazars or microquasars. However, an
analysis using a microquasar model consisting on a magnetized conical jet
filled with relativistic electrons which radiate through synchrotron and
inverse Compton scattering with star, disk, corona and synchrotron photons
shows that it is hard to comply with all observational constrains. This and the
non-detection at hard X-rays introduce an a-posteriori question mark upon the
physical reality of this source, which is discussed in some detail
Potential effects of oilseed rape expressing oryzacystatin-1 (OC-1) and of purified insecticidal proteins on larvae of the solitary bee Osmia bicornis
Despite their importance as pollinators in crops and wild plants, solitary bees have not previously been included in non-target testing of insect-resistant transgenic crop plants. Larvae of many solitary bees feed almost exclusively on pollen and thus could be highly exposed to transgene products expressed in the pollen. The potential effects of pollen from oilseed rape expressing the cysteine protease inhibitor oryzacystatin-1 (OC-1) were investigated on larvae of the solitary bee Osmia bicornis (= O. rufa). Furthermore, recombinant OC-1 (rOC-1), the Bt toxin Cry1Ab and the snowdrop lectin Galanthus nivalis agglutinin (GNA) were evaluated for effects on the life history parameters of this important pollinator. Pollen provisions from transgenic OC-1 oilseed rape did not affect overall development. Similarly, high doses of rOC-1 and Cry1Ab as well as a low dose of GNA failed to cause any significant effects. However, a high dose of GNA (0.1%) in the larval diet resulted in significantly increased development time and reduced efficiency in conversion of pollen food into larval body weight. Our results suggest that OC-1 and Cry1Ab expressing transgenic crops would pose a negligible risk for O. bicornis larvae, whereas GNA expressing plants could cause detrimental effects, but only if bees were exposed to high levels of the protein. The described bioassay with bee brood is not only suitable for early tier non-target tests of transgenic plants, but also has broader applicability to other crop protection products
How does noise affect our health? Analysing a project-based activity in statistics at secondary level
Teaching statistics through projects brings to life in the classroom aspects of working with data that are not usually part of traditional paper-and-pencil activities. There exists a generalized agreement about the positive effects of this kind of teaching proposals and number of international and local initiatives to foster them at secondary and tertiary level. Despite all this, their sustainability as normalized classroom activities is very fragile, given in particular the extra amount of work required to teachers willing to implement them. Research in didactics can help better understand the conditions that enable the introduction and management of statistics projects in the classroom, as well as the – sometimes invisible – constraints that hinder their development. We illustrate it with a case study based on the implementation of a statistics project in a classroom of Grade 9 students, using recent developments of the anthropological theory of the didactic.Founded by project RTI2018-101153-B-C21, Programa Estatal de I+D+i orientado a los Retos de la
Sociedad (MCIU/AEI/FEDER, UE).Peer ReviewedObjectius de Desenvolupament Sostenible::4 - Educació de QualitatPostprint (published version
A practical approach to statistics through SRP
The paper explains the design and the first part of the implementation of a project within the subject of Statistics with first year students in a Bachelor’s degree in ICT Systems Engineering in Manresa School of Engineering, part of the Universitat Politècnica de Catalunya. We use the methodology of study and research paths within the Anthropological Theory of the Didactic and under the paradigm of “Questioning the world”.
The project topic is the “water”. The experience is linked to a broader UPC-driven project, called AquaeSTEAM, based on questions to spark new ideas and science and technology solutions to solve water-related problems. After narrowing down the issue to concrete problematic questions, the students analyse data published in IDESCAT, the Statistical Institute of Catalonia, related to water consumption, both domestic and industrial, factors related to climate change, such as temperature and pluviometry, among others, and will also carry out a survey to link all these studies with the water footprint. The implementation sheds light on the conditions needed to integrate project-based proposals in the traditional organisation of the subject. It also provides information about the changes that may take place to facilitate the integration, in both the subject’s content and instructional structure (lectures and tutorials). The conditions required are then compared with other experiences of study and research paths in engineering education carried out these past years in the Anthropological Theory of the Didactic.Peer ReviewedPostprint (published version
BDM Dark Matter: CDM with a core profile and a free streaming scale
We present a new dark matter model BDM which is an hybrid between hot dark
matter HDM and cold dark matter CDM, in which the BDM particles behave as HDM
above the energy scale E_c and as CDM below this scale. Evolution of structure
formation is similar to that of CDM model but BDM predicts a nonvanishing free
streaming l_fs scale and a inner galaxy core radius r_core, both quantities
determined in terms of a single parameter E_c, which corresponds to the phase
transition energy scale of the subjacent elementary particle model. For
energies above E_c or for a scale factor a smaller then a_c, with a<a_c<a_{eq},
the particles are massless and rho redshifts as radiation. However, once the
energy becomes E\leq E_c or a>a_c then the BDM particles acquire a large mass
through a non perturbative mechanism, as baryons do, and rho redshifts as
matter with the particles having a vanishing velocity. Typical energies are
E_c=O(10-100) eV giving a l_fs \propto E_c^{-4/3}\lesssim Mpc and m_fs\propto
E_c^{-4}\lesssim 10^9 M\odot. A l_fs\neq 0, r_core\neq 0 help to resolve some
of the shortcomings of CDM such as overabundance substructure in CDM halos and
numerical fit to rotation curves in dwarf spheroidal and LSB galaxies. Finally,
our BDM model and the phase transition scale E_c can be derived from particle
physics.Comment: 7 pages, 8 figure
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