11,010 research outputs found
Variable stars in Terzan 5: additional evidence of multi-age and multi-iron stellar populations
Terzan 5 is a complex stellar system in the Galactic bulge, harboring stellar
populations with very different iron content ({\Delta}[Fe/H] ~1 dex) and with
ages differing by several Gyrs. Here we present an investigation of its
variable stars. We report on the discovery and characterization of three RR
Lyrae stars. For these newly discovered RR Lyrae and for six Miras of known
periods we provide radial velocity and chemical abundances from spectra
acquired with X-SHOOTER at the VLT. We find that the three RR Lyrae and the
three short period Miras (P<300 d) have radial velocity consistent with being
Terzan 5 members. They have sub-solar iron abundances and enhanced
[{\alpha}/Fe], well matching the age and abundance patterns of the 12 Gyr
metal-poor stellar populations of Terzan 5. Only one, out of the three long
period (P>300 d) Miras analyzed in this study, has a radial velocity consistent
with being Terzan 5 member. Its super-solar iron abundance and solar-scaled
[{\alpha}/Fe] nicely match the chemical properties of the metal rich stellar
population of Terzan 5 and its derived mass nicely agrees with being several
Gyrs younger than the short period Miras. This young variable is an additional
proof of the surprising young sub-population discovered in Terzan 5.Comment: 20 pages, 4 figures, in press on the Ap
Isospectrality of conventional and new extended potentials, second-order supersymmetry and role of PT symmetry
We develop a systematic approach to construct novel completely solvable
rational potentials. Second-order supersymmetric quantum mechanics dictates the
latter to be isospectral to some well-studied quantum systems.
symmetry may facilitate reconciling our approach to the requirement that the
rationally-extended potentials be singularity free. Some examples are shown.Comment: 13 pages, no figure, some additions to introduction and conclusion, 4
more references; to be published in Special issue of Pramana - J. Phy
Performance of a cryogenic system prototype for the XENON1T Detector
We have developed an efficient cryogenic system with heat exchange and
associated gas purification system, as a prototype for the XENON1T experiment.
The XENON1T detector will use about 3 ton of liquid xenon (LXe) at a
temperature of 175K as target and detection medium for a dark matter search. In
this paper we report results on the cryogenic system performance focusing on
the dynamics of the gas circulation-purification through a heated getter, at
flow rates above 50 Standard Liter per Minute (SLPM). A maximum flow of 114
SLPM has been achieved, and using two heat exchangers in parallel, a heat
exchange efficiency better than 96% has been measured
Casimir-like tunneling-induced electronic forces
We study the quantum forces that act between two nearby conductors due to
electronic tunneling. We derive an expression for these forces by calculating
the flux of momentum arising from the overlap of evanescent electronic fields.
Our result is written in terms of the electronic reflection amplitudes of the
conductors and it has the same structure as Lifshitz's formula for the
electromagnetically mediated Casimir forces. We evaluate the tunneling force
between two semiinfinite conductors and between two thin films separated by an
insulating gap. We discuss some applications of our results.Comment: 8 pages, 3 figs, submitted to Proc. of QFEXT'05, to be published in
J. Phys.
Theoretical current-voltage characteristics of ferroelectric tunnel junctions
We present the concept of ferroelectric tunnel junctions (FTJs). These
junctions consist of two metal electrodes separated by a nanometer-thick
ferroelectric barrier. The current-voltage characteristics of FTJs are analyzed
under the assumption that the direct electron tunneling represents the dominant
conduction mechanism. First, the influence of converse piezoelectric effect
inherent in ferroelectric materials on the tunnel current is described. The
calculations show that the lattice strains of piezoelectric origin modify the
current-voltage relationship owing to strain-induced changes of the barrier
thickness, electron effective mass, and position of the conduction-band edge.
Remarkably, the conductance minimum becomes shifted from zero voltage due to
the piezoelectric effect, and a strain-related resistive switching takes place
after the polarization reversal in a ferroelectric barrier. Second, we analyze
the influence of the internal electric field arising due to imperfect screening
of polarization charges by electrons in metal electrodes. It is shown that, for
asymmetric FTJs, this depolarizing-field effect also leads to a considerable
change of the barrier resistance after the polarization reversal. However, the
symmetry of the resulting current-voltage loop is different from that
characteristic of the strain-related resistive switching. The crossover from
one to another type of the hysteretic curve, which accompanies the increase of
FTJ asymmetry, is described taking into account both the strain and
depolarizing-field effects. It is noted that asymmetric FTJs with dissimilar
top and bottom electrodes are preferable for the non-volatile memory
applications because of a larger resistance on/off ratio.Comment: 14 pages, 8 figure
Chemical and Photometric Evolution of Extended Ultraviolet Disks: Optical Spectroscopy of M83 (NGC5236) and NGC4625
We present the results from the analysis of optical spectra of 31
Halpha-selected regions in the extended UV (XUV) disks of M83 (NGC5236) and
NGC4625 recently discovered by GALEX. The spectra were obtained using IMACS at
Las Campanas Observatory 6.5m Magellan I telescope and COSMIC at the Palomar
200-inch telescope, respectively for M83 and NGC4625. The line ratios measured
indicate nebular oxygen abundances (derived from the R23 parameter) of the
order of Zsun/5-Zsun/10. For most emission-line regions analyzed the line
fluxes and ratios measured are best reproduced by models of photoionization by
single stars with masses in the range 20-40 Msun and oxygen abundances
comparable to those derived from the R23 parameter. We find indications for a
relatively high N/O abundance ratio in the XUV disk of M83. Although the
metallicities derived imply that these are not the first stars formed in the
XUV disks, such a level of enrichment could be reached in young spiral disks
only 1 Gyr after these first stars would have formed. The amount of gas in the
XUV disks allow maintaining the current level of star formation for at least a
few Gyr.Comment: 52 pages, 8 tables, 7 figures, accepted for publication in Ap
The Earliest Near-infrared Time-series Spectroscopy of a Type Ia Supernova
We present ten medium-resolution, high signal-to-noise ratio near-infrared
(NIR) spectra of SN 2011fe from SpeX on the NASA Infrared Telescope Facility
(IRTF) and Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North, obtained
as part of the Carnegie Supernova Project. This data set constitutes the
earliest time-series NIR spectroscopy of a Type Ia supernova (SN Ia), with the
first spectrum obtained at 2.58 days past the explosion and covering -14.6 to
+17.3 days relative to B-band maximum. C I {\lambda}1.0693 {\mu}m is detected
in SN 2011fe with increasing strength up to maximum light. The delay in the
onset of the NIR C I line demonstrates its potential to be an effective tracer
of unprocessed material. For the first time in a SN Ia, the early rapid decline
of the Mg II {\lambda}1.0927 {\mu}m velocity was observed, and the subsequent
velocity is remarkably constant. The Mg II velocity during this constant phase
locates the inner edge of carbon burning and probes the conditions under which
the transition from deflagration to detonation occurs. We show that the Mg II
velocity does not correlate with the optical light-curve decline rate
{\Delta}m15. The prominent break at ~1.5 {\mu}m is the main source of concern
for NIR k-correction calculations. We demonstrate here that the feature has a
uniform time evolution among SNe Ia, with the flux ratio across the break
strongly correlated with {\Delta}m15. The predictability of the strength and
the onset of this feature suggests that the associated k-correction
uncertainties can be minimized with improved spectral templates.Comment: 14 pages, 13 figures, accepted for publication in Ap
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