998 research outputs found
Stellar population analysis of two ellipticals
The spatial distributions of the mean luminosity-weighted stellar age,
metallicity, and alpha/Fe ratio along both photometric axes of two nearby
elliptical galaxies have been obtained using Lick index measurements on long
slit spectra in order to reconstruct the star formation history in their
kinematically distinct subsystems. Lick indexes were compared with those of
single-aged stellar population (SSP) models. A population synthesis method was
also applied in order to help disentangling the age-metallicity degeneracy. The
stars characteristics are associated with their kinematics: they are older and
alpha-enhanced in the not rotating bulge of NGC 1052 and counter rotating core
of NGC 7796, while they show a strong spread of alpha/Fe and age along the
rotating disk of NGC 1052 and an outwards radial decreasing of them outside the
core of NGC 7796.Comment: 2 pages, to appear in the Proceedings of IAU Symposium 241 "Stellar
populations as building blocks of galaxies", A. Vazdekis & R. Peletier, ed
Latent-heat and non-linear vortex liquid at the vicinity of the first-order phase transition in layered high-Tc superconductors
In this work we revisit the vortex matter phase diagram in layered
superconductors solving still open questions by means of AC and DC local
magnetic measurements in the paradigmatic BiSrCaCuO
compound. We show that measuring with AC magnetic techniques is mandatory in
order to probe the bulk response of vortex matter, particularly at
high-temperatures where surface barriers for vortex entrance dominate. From the
-evolution of the enthalpy and latent-heat at the transition we
find that, contrary to previous reports, the nature of the dominant interlayer
coupling is electromagnetic in the whole temperature range. By studying the
dynamic properties of the phase located at , we reveal
the spanning in a considerable fraction of the phase diagram of a non-linear
vortex phase suggesting bulk pinning might play a role even in the liquid
vortex phase.Comment: arXiv admin note: substantial text overlap with arXiv:1212.456
Polycyclic Aromatic Hydrocarbon in the Central Region of the Seyfert 2 Galaxy NGC1808
We present mid infrared (MIR) spectra of the Seyfert 2 (Sy 2) galaxy NGC
1808, obtained with the Gemini's Thermal-Region Camera Spectrograph (T-ReCS) at
a spatial resolution of 26 pc. The high spatial resolution allowed us to detect
bright polycyclic aromatic hydrocarbons (PAHs) emissions at 8.6micron and
11.3micron in the galaxy centre (26 pc) up to a radius of 70 pc from the
nucleus. The spectra also present [Ne ii]12.8micron ionic lines, and H2
S(2)12.27micron molecular gas line. We found that the PAHs profiles are similar
to Peeters's A class, with the line peak shifted towards the blue. The
differences in the PAH line profiles also suggests that the molecules in the
region located 26 pc NE of the nucleus are more in the neutral than in the
ionised state, while at 26 pc SW of the nucleus, the molecules are mainly in
ionised state. After removal of the underlying galaxy contribution, the nuclear
spectrum can be represented by a Nenkova's clumpy torus model, indicating that
the nucleus of NGC 1808 hosts a dusty toroidal structure with an angular cloud
distribution of sigma = 70degree, observer's view angle i = 90degree, and an
outer radius of R0 = 0.55 pc. The derived column density along the line of
sight is NH = 1.5 x 10^24 cm-2, which is sufficient to block the hard radiation
from the active nucleus, and would explain the presence of PAH molecules near
to the NGC 1808's active nucleus.Comment: Accepted by MNRAS 2012 December
High resolution imaging of the early-type galaxy NGC 1380: an insight into the nature of extended extragalactic star clusters
NGC 1380 is a lenticular galaxy located near the centre of the Fornax Cluster
northeast of NGC 1399. The globular cluster system of this galaxy was
previously studied only from the ground. Recent studies of similar early-type
galaxies, specially lenticular ones, reveal the existence of star clusters that
apparently break up the traditional open/globular cluster dichotomy. With
higher quality photometry from HST/WFPC2 we study the star clusters in NGC
1380, measuring their magnitudes, colours, sizes and projected distances from
the centre of the galaxy. We used deep archival HST/WFPC2 in the B and V bands.
We built colour magnitude diagrams from which we selected a sample of cluster
candidates. We also analysed their colour distribution and measured their
sizes. Based on their location in the luminosity-size diagram we estimated
probabilities of them being typical globular clusters as those found in the
Galaxy. A total of about 570 cluster candidates were found down to V=26.5. We
measured sizes for approximately 200 of them. The observed colour distribution
has three apparent peaks. Likewise for the size distribution. We identified the
smaller population as being mainly typical globular clusters, while the more
extended objects have small probabilities of being such objects. Different
correlations between absolute magnitudes, sizes, colours and location were
inferred for these cluster sub-populations. Most extended clusters (Reff > 4
pc) share similar properties to the diffuse star clusters reported to inhabit
luminous early-type galaxies in the Virgo galaxy cluster such as being of low
surface brightness and fainter than MV ~ -8. We also report on a small group of
(Reff ~ 10 pc), -8< MV < -6, red clusters located near the centre of NGC 1380,
which may be interpreted as faint fuzzies.Comment: accepted for publication in A&
Anisotropic response of the moving vortex lattice in superconducting MoGe amorphous films
We have performed magnetic susceptibility measurements in MoGe
amorphous thin films biased with an electrical current using anisotropic coils.
We tested the symmetry of the vortex response changing the relative orientation
between the bias current and the susceptibility coils. We found a region in the
DC current - temperature phase diagram where the dynamical vortex structures
behave anisotropically. In this region the shielding capability of the
superconducting currents measured by the susceptibility coils is less effective
along the direction of vortex motion compared to the transverse direction. This
anisotropic response is found in the same region where the peak effect in the
critical current is developed. On rising temperature the isotropic behavior is
recovered.Comment: 10 pages, 4 figure
Measurement of mesoscopic High- superconductors using Si mechanical micro-oscillators
In a superconducting mesoscopic sample, with dimensions comparable to the
London penetration depth, some properties are qualitatively different to those
found in the bulk material. These properties include magnetization, vortex
dynamics and ordering of the vortex lattice. In order to detect the small
signals produced by this kind of samples, new instruments designed for the
microscale are needed. In this work we use micromechanical oscillators to study
the magnetic properties of a BiSrCaCuO disk with a
diameter of 13.5 microns and a thickness of 2.5 microns. The discussion of our
results is based on the existence and contribution of inter and intra layer
currents.Comment: 4 pages, 6 figure
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