2,658 research outputs found
Optical Spectroscopy of X-Mega targets in the Carina Nebula - VI. FO 15: a new O-Type double-lined eclipsing binary
We report the discovery of a new O-type double-lined spectroscopic binary
with a short orbital period of 1.4 days. We find the primary component of this
binary, FO 15, to have an approximate spectral type O5.5Vz, i.e. a
Zero-Age-Main-Sequence star. The secondary appears to be of spectral type
O9.5V. We have performed a numerical model fit to the public ASAS photometry,
which shows that FO 15 is also an eclipsing binary. We find an orbital
inclination of ~ 80 deg. From a simultaneous light-curve and radial velocity
solution we find the masses and radii of the two components to be 30 +/- 1 and
16 +/- 1 solar masses and 7.5 +/- 0.5 and 5.3 +/- 0.5 solar radii. These radii,
and hence also the luminosities, are smaller than those of normal O-type stars,
but similar to recently born ZAMS O-type stars. The absolute magnitudes derived
from our analysis locate FO 15 at the same distance as Eta Carinae. From
Chandra and XMM X-ray images we also find that there are two close X-ray
sources, one coincident with FO 15 and another one without optical counterpart.
This latter seems to be a highly variable source, presumably due to a
pre-main-sequence stellar neighbour of FO 15.Comment: 11 pages, 9 figures, 3 tables. Accepted for publication in MNRAS.
Higher resolution version available at
http://lilen.fcaglp.unlp.edu.ar/papers2006.htm
Time Dependent Current Oscillations Through a Quantum Dot
Time dependent phenomena associated to charge transport along a quantum dot
in the charge quantization regime is studied. Superimposed to the Coulomb
blockade behaviour the current has novel non-linear properties. Together with
static multistabilities in the negative resistance region of the I-V
characteristic curve, strong correlations at the dot give rise to
self-sustained current and charge oscillations. Their properties depend upon
the parameters of the quantum dot and the external applied voltages.Comment: 4 pages, 3 figures; to appear in PR
Molecular Gas, Dust and Star Formation in Galaxies: II. Dust properties and scalings in \sim\ 1600 nearby galaxies
We aim to characterize the relationship between dust properties. We also aim
to provide equations to estimate accurate dust properties from limited
observational datasets.
We assemble a sample of 1,630 nearby (z<0.1) galaxies-over a large range of
Mstar, SFR - with multi-wavelength observations available from wise, iras,
planck and/or SCUBA. The characterization of dust emission comes from SED
fitting using Draine & Li dust models, which we parametrize using two
components (warm and cold ). The subsample of these galaxies with global
measurements of CO and/or HI are used to explore the molecular and/or atomic
gas content of the galaxies.
The total Lir, Mdust and dust temperature of the cold component (Tc) form a
plane that we refer to as the dust plane. A galaxy's sSFR drives its position
on the dust plane: starburst galaxies show higher Lir, Mdust and Tc compared to
Main Sequence and passive galaxies. Starburst galaxies also show higher
specific Mdust (Mdust/Mstar) and specific Mgas (Mgas/Mstar). The Mdust is more
closely correlated with the total Mgas (atomic plus molecular) than with the
individual components. Our multi wavelength data allows us to define several
equations to estimate Lir, Mdust and Tc from one or two monochromatic
luminosities in the infrared and/or sub-millimeter.
We estimate the dust mass and infrared luminosity from a single monochromatic
luminosity within the R-J tail of the dust emission, with errors of 0.12 and
0.20dex, respectively. These errors are reduced to 0.05 and 0.10 dex,
respectively, if the Tc is used. The Mdust is correlated with the total Mism
(Mism \propto Mdust^0.7). For galaxies with Mstar 8.5<log(Mstar/Msun) < 11.9,
the conversion factor \alpha_850mum shows a large scatter (rms=0.29dex). The SF
mode of a galaxy shows a correlation with both the Mgass and Mdust: high
Mdust/Mstar galaxies are gas-rich and show the highest SFRs.Comment: 24 pages, 28 figures, 6 tables, Accepted for publication in A&
Correlation Effects in Side-Coupled Quantum Dots
Using Wilson's numerical renormalization group (NRG) technique we compute
zero-bias conductance and various correlation functions of a double quantum dot
(DQD) system. We present different regimes within a phase diagram of the DQD
system. By introducing a negative Hubbard U on one of the quantum dots, we
simulate the effect of electron-phonon coupling and explore the properties of
the coexisting spin and charge Kondo state. In a triple quantum dot (TQD)
system a multi-stage Kondo effect appears where localized moments on quantum
dots are screened successively at exponentially distinct Kondo temperatures.Comment: 13 pages, 10 figure
Decisional and Behavioral Procrastination: How They Relate to Self-Discrepancies
A self-discrepancy is a gap between the perceived real self and other standards like the ideal self. One hundred and eighty-one college students completed a self-report measure of self-discrepancies and decisional and behavioral procrastination. Regression analysis showed that overall dysfunctional procrastination (the composite measure of both kinds of procrastination) significantly varied as a function of self-discrepancies. The amount of variance explained was small. Those scoring high in self-discrepancies were more likely to be dysfunctional procrastinators than those scoring low. The discrepancy between the actual-self and the ought-to self was the strongest predictor of dysfunctional procrastination. When decisional and behavioral procrastination were analyzed separately, only decisional procrastination significantly varied as a function of self-discrepancies
Dynamic instabilities in resonant tunneling induced by a magnetic field
We show that the addition of a magnetic field parallel to the current induces
self sustained intrinsic current oscillations in an asymmetric double barrier
structure. The oscillations are attributed to the nonlinear dynamic coupling of
the current to the charge trapped in the well, and the effect of the external
field over the local density of states across the system. Our results show that
the system bifurcates as the field is increased, and may transit to chaos at
large enough fields.Comment: 4 pages, 3 figures, accepted in Phys. Rev. Letter
GS305+04-26:Revisiting the ISM around the CenOB1 stellar association
Massive stars deeply modify their surrounding ISM via their high throughput
of ionizing photons and their strong stellar winds. In this way they may create
large expanding structures of neutral gas. We study a new large HI shell,
labelled GS305+04-26, and its relationship with the OB association CenOB1. To
carry out this study we have used a multi-wavelenght approach. We analyze
neutral hydrogen (HI) line data retrieved from the Leiden-Argentina-Bonn (LAB)
survey, new spectroscopic optical observations obtained at CASLEO, and make use
of proper motion databases available via Internet. The analysis of the HI data
reveals a large expanding structure GS305+04-26 centered at
(l,b)=(305^{\degr}, +4^{\degr}) in the velocity range from -33 to -17 km/s.
Based on its central velocity, -26 km/s, and using standard galactic rotation
models, a distance of 2.5(+-)0.9 kpc is inferred. This structure, elliptical in
shape, has major and minor axis of 440 and 270 pc, respectively. Its expansion
velocity, total gaseous mass, and kinetic energy are ~8 km/s, (2.4(+-)0.5)x10^5
Mo, and (1.6(+-)0.4)x10^{50} erg, respectively. Several stars of the
OB-association CenOB1 are seen projected onto, and within, the boundaries of
GS305+04-26. Based on an analysis of proper motions, new members of CenOB1 are
identified. The mechanical energy injected by these stars could have been the
origin of this HI structure.Comment: 14 pages, 6 figures, A&A (in press
VALES: IV. Exploring the transition of star formation efficiencies between normal and starburst galaxies using APEX/SEPIA Band-5 and ALMA at low redshift
In this work we present new APEX/SEPIA Band-5 observations targeting the CO
() emission line of 24 Herschel-detected galaxies at .
Combining this sample {with} our recent new Valpara\'iso ALMA Line Emission
Survey (VALES), we investigate the star formation efficiencies (SFEs =
SFR/) of galaxies at low redshift. We find the SFE of our sample
bridges the gap between normal star-forming galaxies and Ultra-Luminous
Infrared Galaxies (ULIRGs), which are thought to be triggered by different star
formation modes. Considering the as the SFR and the
ratio, our data show a continuous and smooth increment as a function of
infrared luminosity (or star formation rate) with a scatter about 0.5 dex,
instead of a steep jump with a bimodal behaviour. This result is due to the use
of a sample with a much larger range of sSFR/sSFR using LIRGs, with
luminosities covering the range between normal and ULIRGs. We conclude that the
main parameters controlling the scatter of the SFE in star-forming galaxies are
the systematic uncertainty of the conversion factor, the gas
fraction and physical size.Comment: 9pages, 7 figures, 1 table, accepted for publication in MNRA
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