3,534 research outputs found
A state-of-the-art analysis of the dwarf irregular galaxy NGC 6822
We present a detailed photometric study of the dwarf irregular galaxy NGC
6822 aimed at investigating the properties of its stellar populations and, in
particular, the presence of stellar radial gradients. Our goal is to analyse
the stellar populations in six fields, which cover the whole bar of this dwarf
galaxy. We derived the quantitative star formation history (SFH) of the six
fields using the IAC method, involving IAC-pop/MinnIAC codes. The solutions we
derived show an enhanced star formation rate (SFR) in Fields 1 and 3 during the
past 500 Myr. The SFRs of the other fields are almost extinguished at very
recent epochs and. We study the radial gradients of the SFR and consider the
total mass converted into stars in two time intervals (between 0 and 0.5 Gyr
ago and between 0.5 and 13.5 Gyr ago). We find that the scale lengths of the
young and intermediate-to-old populations are perfectly compatible, with the
exception of the young populations in Fields 1 and 3. The recent SF in these
two fields is greater than in the other ones. This might be an indication that
in these two fields we are sampling incipient spiral arms. Further evidence and
new observations are required to prove this hypothesis. In addition, we derived
the age-metallicity relations. As expected, the metallicity increases with time
for all of the fields. We do not observe any radial gradient in the
metallicity.Comment: 9 pages, 11 figures, Accepted to A&
Spatially resolved LMC star formation history: I. Outside in evolution of the outer LMC disk
We study the evolution of three fields in the outer LMC disk Rgc=3.5-6.2 Kpc.
Their star formation history indicates a stellar populations gradient such that
younger stellar populations are more centrally concentrated. We identify two
main star forming epochs, separated by a period of lower activity between ~7
and ~4 Gyr ago. Their relative importance varies from a similar amount of stars
formed in the two epochs in the innermost field, to only 40% of the stars
formed in the more recent epoch in the outermost field. The young star forming
epoch continues to the present time in the innermost field, but lasted only
till ~0.8 and 1.3 Gyr ago at Rgc=5.5 degrees and 7.1 degrees, respectively.
This gradient is correlated with the measured HI column density and implies an
outside-in quenching of the star formation, possibly related to a variation of
the size of the HI disk. This could either result from gas depletion due to
star formation or ram-pressure stripping, or from to the compression of the gas
disk as ram-pressure from the Milky Way halo acted on the LMC interstellar
medium. The latter two situations may have occurred when the LMC first
approached the Milky Way.Comment: 15 pages, 13 figures, 4 tables. MNRAS, in pres
TASTE. III. A homogeneous study of transit time variations in WASP-3b
The TASTE project is searching for low-mass planets with the Transit Timing
Variation (TTV) technique, by gathering high-precision, short-cadence light
curves for a selected sample of transiting exoplanets. It has been claimed that
the "hot Jupiter" WASP-3b could be perturbed by a second planet. Presenting
eleven new light curves (secured at the IAC80 and UDEM telescopes) and
re-analyzing thirty-eight archival light curves in a homogeneous way, we show
that new data do not confirm the previously claimed TTV signal. However, we
bring evidence that measurements are not consistent with a constant orbital
period, though no significant periodicity can be detected. Additional dynamical
modeling and follow-up observations are planned to constrain the properties of
the perturber or to put upper limits to it. We provide a refined ephemeris for
WASP-3b and improved orbital/physical parameters. A contact eclipsing binary,
serendipitously discovered among field stars, is reported here for the first
time.Comment: 10 pages, 6 figures, 4 tables; accepted for publication in A&
The Star Formation History in a SMC field: IAC-star/IAC-pop at work
We present a progress report of a project to study the quantitative star
formation history (SFH) in different parts of the Small Magellanic Cloud (SMC).
We use the information in [(B-R), R] color-magnitude diagrams (CMDs), which
reach down to the oldest main-sequence turnoffs and allow us to retrieve the
SFH in detail. We show the first results of the SFH in a SMC field located in
the Southern direction (at 1 kpc from the SMC center). This field is
particularly interesting because in spite of being located in a place in which
the HI column density is very low, it still presents a recent enhancement of
star formation.Comment: Poster presented at: Stellar Populations as Building Blocks of
Galaxies, Proceedings IAU Symposium No. 241, 200
Multiple stellar populations in Magellanic Cloud clusters. III. The first evidence of an extended main sequence turn-off in a young cluster: NGC1856
Recent studies have shown that the extended main-sequence turn off (eMSTO) is
a common feature of intermediate-age star clusters in the Magellanic Clouds
(MCs). The most simple explanation is that these stellar systems harbor
multiple generations of stars with an age difference of a few hundred Myrs.
However, while an eMSTO has been detected in a large number of clusters with
ages between ~1-2 Gyrs, several studies of young clusters in both MCs and in
nearby galaxies do not find any evidence for a prolonged star-formation
history, i.e. for multiple stellar generations. These results have suggested
alternative interpretation of the eMSTOs observed in intermediate-age star
clusters. The eMSTO could be due to stellar rotation mimicking an age spread or
to interacting binaries. In these scenarios, intermediate-age MC clusters would
be simple stellar populations, in close analogy with younger clusters.
Here we provide the first evidence for an eMSTO in a young stellar cluster.
We exploit multi-band Hubble Space Telescope photometry to study the ~300-Myr
old star cluster NGC1856 in the Large Magellanic Cloud and detected a broadened
MSTO that is consistent with a prolonged star-formation which had a duration of
about 150 Myrs. Below the turn-off, the MS of NGC1856 is split into a red and
blue component, hosting 33+/-5% and 67+/-5% of the total number of MS stars,
respectively. We discuss these findings in the context of
multiple-stellar-generation, stellar-rotation, and interacting-binary
hypotheses.Comment: 14 pages, 10 figures, accepted for publication in MNRA
Linear elastic mechanical system interacting with coupled thermo-electro-magnetic fields
[EN] A fully-coupled thermodynamic-based transient finite element formulation is proposed in this article for electric, magnetic, thermal and mechanic fields interactions limited to the linear case. The governing equations are obtained from conservation principles for both electric and magnetic flux, momentum and energy. A full-interaction among different fields is defined through Helmholtz free-energy potential, which provides that the constitutive equations for corresponding dual variables can be derived consistently. Although the behavior of the material is linear, the coupled interactions with the other fields are not considered limited to the linear case. The implementation is carried out in a research version of the research computer code FEAP by using 8-node isoparametric 3D solid elements. A range of numerical examples are run with the proposed element, from the relatively simple cases of piezoelectric, piezomagnetic, thermoelastic to more complicated combined coupled cases such as piezo-pyro-electric, or piezo-electro-magnetic. In this paper, some of those interactions are illustrated and discussed for a simple geometry.This work was supported jointly by Hauts-de-France Region (CR Picardie) (120-2015-RDISTRUCT-000010 and RDISTRUCT-000010) and EU funding (FEDER) for Chaire-de-Mecanique (120-2015-RDISTRUCTF-000010 and RDISTRUCTI-000004). Also, by the grant Ministerio de Educacion, Cultura y Deporte PRX16/00501. This support is gratefully acknowledged.Moreno-Navarro, P.; Ibrahimbegovich, A.; Pérez-Aparicio, JL. (2018). Linear elastic mechanical system interacting with coupled thermo-electro-magnetic fields. Coupled Systems Mechanics, an international journal (Online). 7(1):5-25. https://doi.org/10.12989/csm.2018.7.1.005S5257
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