893 research outputs found
GIARPS High-resolution Observations of T Tauri stars (GHOsT). I. Jet line emission
The mechanism for jet formation in the disks of T Tauri stars is poorly
understood. Observational benchmarks to launching models can be provided by
tracing the physical properties of the kinematic components of the wind and jet
in the inner 100 au of the disk surface. In the framework of the GHOsT (GIARPS
High-resolution Observations of T Tauri stars) project, we aim to perform a
multi-line analysis of the velocity components of the gas in the jet
acceleration zone. We analyzed the GIARPS-TNG spectra of six objects in the
Taurus-Auriga complex (RY Tau, DG Tau, DL Tau, HN Tau, DO Tau, RW Aur A).
Thanks to the combined high-spectral resolution (R=50000-115000) and wide
spectral coverage (~400-2400 nm) we observed several O, S+, N, N+, and Fe+
forbidden lines spanning a large range of excitation and ionization conditions.
In four objects (DG Tau, HN Tau, DO Tau, RW Aur A), temperature (T_e), electron
and total density (n_e, n_H), and fractional ionization (x_e) were derived as a
function of velocity through an excitation and ionization model. The abundance
of gaseous iron, X(Fe), a probe of the dust content in the jet, was derived in
selected velocity channels. The physical parameters vary smoothly with
velocity, suggesting a common origin for the different kinematic components. In
DG Tau and HN Tau, T_e, x_e, and X(Fe) increase with velocity (roughly from
6000 K, 0.05, 10% X(Fe)_sun to 15000 K, 0.6, 90% X(Fe)_sun). This trend is in
agreement with disk-wind models in which the jet is launched from regions of
the disk at different radii. In DO Tau and RW Aur A, we infer x_e < 0.1, n_H
~10^6-7 cm^-3, and X(Fe) <~ X(Fe)_sun at all velocities. These findings are
tentatively explained by the formation of these jets from dense regions inside
the inner, gaseous disk, or as a consequence of their high degree of
collimation.Comment: Accepted by A&
GIARPS High-resolution Observations of T Tauri stars (GHOsT). II. Connecting atomic and molecular winds in protoplanetary disks
In the framework of the GIARPS High-resolution Observations of T Tauri stars
(GHOsT) project, we aim to characterize the atomic and molecular winds in a
sample of classical T Tauri stars (CTTs) of the Taurus-Auriga region. We
analyzed the flux calibrated [OI] 630 nm and 2.12 lines
in a sample of 36 CTTs observed at the Telescopio Nazionale Galileo with the
HARPS and GIANO spectrographs. We decomposed the line profiles into different
kinematic Gaussian components and focused on the most frequently detected
component, the narrow low-velocity (v )
component (NLVC). We found that the line is detected in 17 sources
( detection rate), and [OI] is detected in all sources but one. The
NLV components of the and [OI] emission are kinematically linked,
with a strong correlation between the peak velocities and the full widths at
half maximum of the two lines. Assuming Keplerian broadening, we found that the
[OI] NVLC originates from a disk region between 0.05 and 20 au and that of in a region from 2 and 20 au. We did not find any clear correlation
between v of the and [OI] NVLC and the outer disk inclination.
This result is in line with previous studies. Our results suggest that
molecular and neutral atomic emission in disk winds originate from regions that
might overlap, and that the survival of molecular winds in disks strongly
depends on the gas exposure to the radiation from the central star. Our results
demonstrate the potential of wide-band high-resolution spectroscopy in linking
tracers of different manifestations of the same phenomenon.Comment: 22 pages, 10 figures, 6 tables, accepted for publication in A&
Light Quark Masses in Multi-Quark Interactions
We suggest and discuss in detail a multi-quark three flavor Lagrangian of the
Nambu -- Jona-Lasinio type, which includes a set of effective interactions
proportional to the current quark masses. It is shown that within the dynamical
chiral symmetry breaking regime, the masses of the pseudo Goldstone bosons and
their chiral partners, members of the low lying scalar nonet, are in perfect
agreement with current phenomenological expectations. The role of the new
interactions is analyzed.Comment: 8 pages, published versio
The Gaia -ESO Survey : Empirical determination of the precision of stellar radial velocities and projected rotation velocities
Context. The Gaia-ESO Survey (GES) is a large public spectroscopic survey at the European Southern Observatory Very Large Telescope. Aims. A key aim is to provide precise radial velocities (RVs) and projected equatorial velocities (v sin i) for representative samples of Galactic stars, which will complement information obtained by the Gaia astrometry satellite. Methods. We present an analysis to empirically quantify the size and distribution of uncertainties in RV and v sin i using spectra from repeated exposures of the same stars. Results. We show that the uncertainties vary as simple scaling functions of signal-to-noise ratio (S/N) and v sin i, that the uncertainties become larger with increasing photospheric temperature, but that the dependence on stellar gravity, metallicity and age is weak. The underlying uncertainty distributions have extended tails that are better represented by Student's t-distributions than by normal distributions. Conclusions. Parametrised results are provided, which enable estimates of the RV precision for almost all GES measurements, and estimates of the v sin i precision for stars in young clusters, as a function of S/N, v sin i and stellar temperature. The precision of individual high S/N GES RV measurements is 0.22-0.26 kms-1, dependent on instrumental configuration.Peer reviewedFinal Accepted Versio
The Infrared Behaviour of the Pure Yang-Mills Green Functions
We review the infrared properties of the pure Yang-Mills correlators and
discuss recent results concerning the two classes of low-momentum solutions for
them reported in literature; i.e. decoupling and scaling solutions. We will
mainly focuss on the Landau gauge and pay special attention to the results
inferred from the analysis of the Dyson-Schwinger equations of the theory and
from "{\it quenched}" lattice QCD. The results obtained from properly
interplaying both approaches are strongly emphasized.Comment: Final version to be published in FBS (54 pgs., 11 figs., 4 tabs
The Gaia-ESO Survey : The analysis of high-resolution UVES spectra of FGK-type stars
Date of Acceptance: 01/09/2014Context. The ongoing Gaia-ESO Public Spectroscopic Survey is using FLAMES at the VLT to obtain high-quality medium-resolution Giraffe spectra for about 105 stars and high-resolution UVES spectra for about 5000 stars. With UVES, the Survey has already observed 1447 FGK-type stars. Aims. These UVES spectra are analyzed in parallel by several state-of-the-art methodologies. Our aim is to present how these analyses were implemented, to discuss their results, and to describe how a final recommended parameter scale is defined. We also discuss the precision (method-to-method dispersion) and accuracy (biases with respect to the reference values) of the final parameters. These results are part of the Gaia-ESO second internal release and will be part of its first public release of advanced data products. Methods. The final parameter scale is tied to the scale defined by the Gaia benchmark stars, a set of stars with fundamental atmospheric parameters. In addition, a set of open and globular clusters is used to evaluate the physical soundness of the results. Each of the implemented methodologies is judged against the benchmark stars to define weights in three different regions of the parameter space. The final recommended results are the weighted medians of those from the individual methods. Results. The recommended results successfully reproduce the atmospheric parameters of the benchmark stars and the expected Teff-log g relation of the calibrating clusters. Atmospheric parameters and abundances have been determined for 1301 FGK-type stars observed with UVES. The median of the method-to-method dispersion of the atmospheric parameters is 55 K for Teff, 0.13 dex for log g and 0.07 dex for [Fe/H]. Systematic biases are estimated to be between 50-100 K for Teff, 0.10-0.25 dex for log g and 0.05-0.10 dex for [Fe/H]. Abundances for 24 elements were derived: C, N, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ba, Nd, and Eu. The typical method-to-method dispersion of the abundances varies between 0.10 and 0.20 dex. Conclusions. The Gaia-ESO sample of high-resolution spectra of FGK-type stars will be among the largest of its kind analyzed in a homogeneous way. The extensive list of elemental abundances derived in these stars will enable significant advances in the areas of stellar evolution and Milky Way formation and evolution.Peer reviewe
The WEBT Campaign on the Blazar 3C279 in 2006
The quasar 3C279 was the target of an extensive multiwavelength monitoring
campaign from January through April 2006, including an optical-IR-radio
monitoring campaign by the Whole Earth Blazar Telescope (WEBT) collaboration.
In this paper we focus on the results of the WEBT campaign. The source
exhibited substantial variability of optical flux and spectral shape, with a
characteristic time scale of a few days. The variability patterns throughout
the optical BVRI bands were very closely correlated with each other. In
intriguing contrast to other (in particular, BL Lac type) blazars, we find a
lag of shorter- behind longer-wavelength variability throughout the RVB ranges,
with a time delay increasing with increasing frequency. Spectral hardening
during flares appears delayed with respect to a rising optical flux. This, in
combination with the very steep IR-optical continuum spectral index of ~ 1.5 -
2.0, may indicate a highly oblique magnetic field configuration near the base
of the jet. An alternative explanation through a slow (time scale of several
days) acceleration mechanism would require an unusually low magnetic field of <
0.2 G, about an order of magnitude lower than inferred from previous analyses
of simultaneous SEDs of 3C279 and other FSRQs with similar properties.Comment: Accepted for publication in Ap
Multifrequency monitoring of the blazar 0716+714 during the GASP-WEBT-AGILE campaign of 2007
Since the CGRO operation in 1991-2000, one of the primary unresolved
questions about the blazar gamma-ray emission has been its possible correlation
with the low-energy (in particular optical) emission. To help answer this
problem, the Whole Earth Blazar Telescope (WEBT) consortium has organized the
GLAST-AGILE Support Program (GASP) to provide the optical-to-radio monitoring
data to be compared with the gamma-ray detections by the AGILE and GLAST
satellites. This new WEBT project started in early September 2007, just before
a strong gamma-ray detection of 0716+714 by AGILE. We present the GASP-WEBT
optical and radio light curves of this blazar obtained in July-November 2007,
about various AGILE pointings at the source. We construct NIR-to-UV spectral
energy distributions (SEDs), by assembling GASP-WEBT data together with UV data
from the Swift ToO observations of late October. We observe a contemporaneous
optical-radio outburst, which is a rare and interesting phenomenon in blazars.
The shape of the SEDs during the outburst appears peculiarly wavy because of an
optical excess and a UV drop-and-rise. The optical light curve is well sampled
during the AGILE pointings, showing prominent and sharp flares. A future
cross-correlation analysis of the optical and AGILE data will shed light on the
expected relationship between these flares and the gamma-ray events.Comment: 5 pages, 5 figures, to be published in A&A (Letters); revised to
match the final version (changes in Fig. 5 and related text
The unprecedented optical outburst of the quasar 3C 454.3. The WEBT campaign of 2004-2005
The radio quasar 3C 454.3 underwent an exceptional optical outburst lasting
more than 1 year and culminating in spring 2005. The maximum brightness
detected was R = 12.0, which represents the most luminous quasar state thus far
observed (M_B ~ -31.4). In order to follow the emission behaviour of the source
in detail, a large multiwavelength campaign was organized by the Whole Earth
Blazar Telescope (WEBT). Continuous optical, near-IR and radio monitoring was
performed in several bands. ToO pointings by the Chandra and INTEGRAL
satellites provided additional information at high energies in May 2005. The
historical radio and optical light curves show different behaviours. Until
about 2001.0 only moderate variability was present in the optical regime, while
prominent and long-lasting radio outbursts were visible at the various radio
frequencies, with higher-frequency variations preceding the lower-frequency
ones. After that date, the optical activity increased and the radio flux is
less variable. This suggests that the optical and radio emissions come from two
separate and misaligned jet regions, with the inner optical one acquiring a
smaller viewing angle during the 2004-2005 outburst. Moreover, the colour-index
behaviour (generally redder-when-brighter) during the outburst suggests the
presence of a luminous accretion disc. A huge mm outburst followed the optical
one, peaking in June-July 2005. The high-frequency (37-43 GHz) radio flux
started to increase in early 2005 and reached a maximum at the end of our
observing period (end of September 2005). VLBA observations at 43 GHz during
the summer confirm theComment: 7 pages, 4 figures, to be published in A&
Holographic rho mesons in an external magnetic field
We study the rho meson in a uniform magnetic field eB using a holographic
QCD-model, more specifically a D4/D8/Dbar8 brane setup in the confinement phase
at zero temperature with two quenched flavours. The parameters of the model are
fixed by matching to corresponding dual field theory parameters at zero
magnetic field. We show that the up- and down-flavour branes respond
differently to the presence of the magnetic field in the dual QCD-like theory,
as expected because of the different electromagnetic charge carried by up- and
down-quark. We discuss how to recover the Landau levels, indicating an
instability of the QCD vacuum at eB = m_rho^2 towards a phase where charged rho
mesons are condensed, as predicted by Chernodub using effective QCD-models. We
improve on these existing effective QCD-model analyses by also taking into
account the chiral magnetic catalysis effect, which tells us that the
constituent quark masses rise with eB. This turns out to increase the value of
the critical magnetic field for the onset of rho meson condensation to eB = 1.1
m_rho^2 = 0.67 GeV^2. We briefly discuss the influence of pions, which turn out
to be irrelevant for the condensation in the approximation made.Comment: 26 pages, 10 .pdf figures, v2: version accepted for publication in
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