7,795 research outputs found
Representative galaxy age-metallicity relationships
The ongoing surveys of galaxies and those for the next generation of
telescopes will demand the execution of high-CPU consuming machine codes for
recovering detailed star formation histories (SFHs) and hence age-metallicity
relationships (AMRs). We present here an expeditive method which provides
quick-look AMRs on the basis of representative ages and metallicities obtained
from colour-magnitude diagram (CMD) analyses. We have tested its perfomance by
generating synthetic CMDs for a wide variety of galaxy SFHs. The representative
AMRs turn out to be reliable down to a magnitude limit with a photometric
completeness factor higher than 85 per cent, and trace the chemical
evolution history for any stellar population (represented by a mean age and an
intrinsic age spread) with a total mass within ~ 40 per cent of the more
massive stellar population in the galaxy.Comment: 12 pages, 11 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
The age-metallicity relationship in the Fornax spheroidal dwarf galaxy
We produce a comprehensive field star age-metallicity relationship (AMR) from
the earliest epoch until ~ 1 Gyr ago for three fields in the Fornax dSph galaxy
by using VI photometric data obtained with FORS1 at the VLT. We find that the
innermost one does not contains dominant very old stars (age > 12 Gyr), whereas
the relatively outer field does not account for representative star field
populations younger than ~ 3 Gyr. When focusing on the most prominent stellar
populations, we find that the derived AMRs are engraved by the evidence of a
outside-in star formation process. The studied fields show bimodal metallicity
distributions peaked at [Fe/H] = (-0.95 +- 0.15) dex and (-1.15 or -1.25 +-
0.05) dex, respectively, but only during the first half of the entire galaxy
lifetime. Furthermore, the more metal-rich population appears to be more
numerous in the outer fields, while in the innermost Fornax field the
contribution of both metallicity populations seems to be similar. We also find
that the metallicity spread ~ 6 Gyr ago is remarkable large, while the
intrinsic metallicity dispersion at ~ 1-2 Gyr results smaller than that for the
relatively older generations of stars. We interpret these outcomes as a result
of a possible merger of two galaxies that would have triggered a star formation
bursting process that peaked between ~ 6 and 9 Gyr ago, depending on the
position of the field in the galaxy.Comment: 7 pages, 5 figures, MNRAS, in pres
Rational points in the moduli space of genus two
We build a database of genus 2 curves defined over which contains
all curves with minimal absolute height , all curves with moduli
height , and all curves with extra automorphisms in
standard form defined over with height .
For each isomorphism class in the database, an equation over its minimal field
of definition is provided, the automorphism group of the curve, Clebsch and
Igusa invariants. The distribution of rational points in the moduli space
for which the field of moduli is a field of definition is
discussed and some open problems are presented
Dual Mode Control of an Inverted Pendulum: Design, Analysis and Experimental Evaluation
We present an inverted pendulum design using readily available V-slot rail components and
3D printing to construct custom parts. To enable the examination of different pendulum
characteristics, we constructed three pendulum poles of different lengths. We implemented
a brake mechanism to modify sliding friction resistance and built a paddle that can be
attached to the ends of the pendulum poles. A testing rig was also developed to consistently
apply disturbances by tapping the pendulum pole, characterizing balancing performance.
We perform a comprehensive analysis of the behavior and control of the pendulum. This
begins by considering its dynamics, including the nonlinear differential equation that
describes the system, its linearization, and its representation in the s-domain. The primary
focus of this work is the development of two distinct control modes for the pendulum: a
velocity control mode, designed to balance the pendulum while the cart is in motion, and a
position control mode, aimed at maintaining the pendulum cart at a specific location. For
this, we derived two different state space models: one for implementing the velocity control
mode and another for the position control mode. In the position control mode, integral action
applied to the cart position ensures that the inverted pendulum remains balanced and
maintains its desired position on the rail. For both models, linear observer-based state
feedback controllers were implemented. The control laws are designed as linear quadratic
regulators (LQR), and the systems are simulated in MATLAB. To actuate the physical
pendulum system, a stepper motor was used, and its controller was assembled in a DIN rail
panel to simplify the integration of all necessary components. We examined how the
optimized performance, achieved with the medium-length pendulum pole, translates to poles
of other lengths. Our findings reveal distinct behavioral differences between the control
modes
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
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