5,735 research outputs found
On the age of the magnetically active WW Psa and TX Psa members of the beta Pictoris association
There are a variety of different techniques available to estimate the ages of
pre-main-sequence stars. Components of physical pairs, thanks to their strict
coevality and the mass difference, such as the binary system analysed in this
paper, are best suited to test the effectiveness of these different techniques.
We consider the system WW Psa + TX Psa whose membership of the 25-Myr beta
Pictoris association has been well established by earlier works. We investigate
which age dating technique provides the best agreement between the age of the
system and that of the association. We have photometrically monitored WW Psa
and TX Psa and measured their rotation periods as P = 2.37d and P = 1.086d,
respectively. We have retrieved from the literature their Li equivalent widths
and measured their effective temperatures and luminosities. We investigate
whether the ages of these stars derived using three independent techniques are
consistent with the age of the beta Pictoris association. We find that the
rotation periods and the Li contents of both stars are consistent with the
distribution of other bona fide members of the cluster. On the contrary, the
isochronal fitting provides similar ages for both stars, but a factor of about
four younger than the quoted age of the association, or about 30% younger when
the effects of magnetic fields are included. We explore the origin of the
discrepant age inferred from isochronal fitting, including the possibilities
that either the two components may be unresolved binaries or that the basic
stellar parameters of both components are altered by enhanced magnetic
activity. The latter is found to be the more reasonable cause, suggesting that
age estimates based on the Li content is more reliable than isochronal fitting
for pre-main-sequence stars with pronounced magnetic activity.Comment: Accepted by Astronomy and Astrophysics on December 13, 2016. 13 pages
and 11 figure
A METHODOLOGICALAPPROACH TO COMPARE PROSAND CONS OF DELOCALIZING VILLAGES: SOCIO-ECONOMICAND TECHNICAL ISSUES
New transit observations for HAT-P-30 b, HAT-P-37 b, TrES-5 b, WASP-28 b, WASP-36 b, and WASP-39 b
We present new transit light curves for planets in six extrasolar planetary
systems. They were acquired with 0.4-2.2 m telescopes located in west Asia,
Europe, and South America. When combined with literature data, they allowed us
to redetermine system parameters in a homogeneous way. Our results for
individual systems are in agreement with values reported in previous studies.
We refined transit ephemerides and reduced uncertainties of orbital periods by
a factor between 2 and 7. No sign of any variations in transit times was
detected for the planets studied.Comment: Submitted to Acta Astronomic
Multiwavelength campaign on Mrk 509. V. Chandra-LETGS observation of the ionized absorber
We present here the results of a 180 ks Chandra-LETGS observation as part of
a large multi-wavelength campaign on Mrk 509. We study the warm absorber in Mrk
509 and use the data from a simultaneous HST-COS observation in order to assess
whether the gas responsible for the UV and X-ray absorption are the same. We
analyzed the LETGS X-ray spectrum of Mrk 509 using the SPEX fitting package. We
detect several absorption features originating in the ionized absorber of the
source, along with resolved emission lines and radiative recombination
continua. The absorption features belong to ions with, at least, three distinct
ionization degrees. The lowest ionized component is slightly redshifted (v =
+73 km/s) and is not in pressure equilibrium with the others, and therefore it
is not likely part of the outflow, possibly belonging to the interstellar
medium of the host galaxy. The other components are outflowing at velocities of
-196 and -455 km/s, respectively. The source was observed simultaneously with
HST-COS, finding 13 UV kinematic components. At least three of them can be
kinematically associated with the observed X-ray components. Based on the
HST-COS results and a previous FUSE observation, we find evidence that the UV
absorbing gas might be co-located with the X-ray absorbing gas and belong to
the same structure.Comment: 12 pages, 7 figures, 9 tables. Accepted for publication in Astronomy
& Astrophysic
Multiwavelength campaign on Mrk 509. VI. HST/COS observations of the far-ultraviolet spectrum
We present medium resolution (R~20,000) HST/COS ultraviolet spectra covering
1155-1760 A of the Seyfert 1 Mrk 509 obtained simultaneously with a
Chandra/LETGS spectrum as part of a multiwavelength campaign in 2009 that
included observations with XMM-Newton, SWIFT, and Integral. Our high S/N
spectrum detects additional complexity in the absorption troughs from a variety
of sources in Mrk 509, including the outflow from the active nucleus, the ISM
and halo of the host galaxy, and infalling clouds or stripped gas from a merger
that are illuminated by the AGN. Variability between the STIS and COS
observation of the -400 km/s component allows us to set an upper limit on its
distance of < 250 pc. Similarly, variability of a component at +150 km/s
between two prior FUSE observations limits its distance to < 1.5 kpc. The UV
absorption only partially covers the emission from the AGN nucleus. Covering
fractions are lower than those previously seen with STIS, and are comparable to
those seen with FUSE. Given the larger apertures of COS and FUSE compared to
STIS, we favor scattered light from an extended region near the AGN as the
explanation for the partial covering. As observed in prior X-ray and UV
spectra, the UV absorption has velocities comparable to the X-ray absorption,
but the bulk of the ultraviolet absorption is in a lower ionization state with
lower total column density than the gas responsible for the X-ray absorption.
We conclude that the outflow from the active nucleus is a multiphase wind.Comment: 21 pages, 9 figures. Accepted for publication in Astronomy &
Astrophysics, 26 May 201
Multiwavelength campaign on Mrk 509. I. Variability and spectral energy distribution
(Abridged) Active galactic nuclei show a wealth of interesting physical
processes, some of which are poorly understood. We want to address a number of
open questions, including the location and physics of the outflow from AGN, the
nature of the continuum emission, the geometry and physical state of the X-ray
broad emission line region, the Fe-K line complex, the metal abundances of the
nucleus and finally the interstellar medium of our own Galaxy. We study one of
the best targets for these aims, the Seyfert 1 galaxy Mrk 509 with a
multiwavelength campaign using five satellites (XMM-Newton, INTEGRAL, Chandra,
HST and Swift) and two ground-based facilities (WHT and PAIRITEL). Our
observations cover more than five decades in frequency, from 2 um to 200 keV.
The combination of high-resolution spectroscopy and time variability allows us
to disentangle and study the different components. Our campaign covers 100 days
from September to December 2009, and is centred on a simultaneous set of deep
XMM-Newton and INTEGRAL observations with regular time intervals, spanning
seven weeks. We obtain a continuous light curve in the X-ray and UV band,
showing a strong, up to 60% flux increase in the soft X-ray band during the
three weeks in the middle of our deepest monitoring campaign, and which is
correlated with an enhancement of the UV flux. This allows us to study the time
evolution of the continuum and the outflow. By stacking the observations, we
have also obtained one of the best X-ray and UV spectra of a Seyfert galaxy
ever obtained. In this paper we also study the effects of the spectral energy
distribution (SED) that we obtained on the photo-ionisation equilibrium. Thanks
to our broad-band coverage, uncertainties on the SED do not strongly affect the
determination of this equilibrium.Comment: 10 pages, 5 figures, 2 tables. Accepted for publication in Astronomy
& Astrophysic
Testing Comptonizing coronae on a long BeppoSAX observation of the Seyfert 1 galaxy NGC 5548
We test accurate models of Comptonization spectra over the high quality data
of the BeppoSAX long look at NGC 5548, allowing for different geometries of the
scattering region, different temperatures of the input soft photon field and
different viewing angles. We find that the BeppoSAX data are well represented
by a plane parallel or hemispherical corona viewed at an inclination angle of
30. For both geometries the best fit temperature of the soft photons
is close to 15 eV. The corresponding best fit values of the hot
plasma temperature and optical depth are 250--260 keV and
0.16--0.37 for the slab and hemisphere respectively. These values
are substantially different from those derived fitting the data with a
power-law + cut off approximation to the Comptonization component (kT_{\rm
e}\lta 60 keV, 2.4). This is due to the fact that accurate
Comptonization spectra in anisotropic geometries show "intrinsic" curvature
which reduces the necessity of a high energy cut-off. The Comptonization
parameter derived for the slab model {is} larger than predicted for a two phase
plane parallel corona in energy balance, suggesting that a more
``photon-starved'' geometry is necessary. The spectral softening detected
during a flare which occurred in the central part of the observation
corresponds to a decrease of the Comptonization parameter, probably associated
with an increase of the soft photon luminosity, the {hard} photon luminosity
remaining constant.Comment: 36 pages, 9 figures, accepted by Ap
A 1 m Gas Time Projection Chamber with Optical Readout for Directional Dark Matter Searches: the CYGNO Experiment
The aim of the CYGNO project is the construction and operation of a 1~m
gas TPC for directional dark matter searches and coherent neutrino scattering
measurements, as a prototype toward the 100-1000~m (0.15-1.5 tons) CYGNUS
network of underground experiments. In such a TPC, electrons produced by
dark-matter- or neutrino-induced nuclear recoils will drift toward and will be
multiplied by a three-layer GEM structure, and the light produced in the
avalanche processes will be readout by a sCMOS camera, providing a 2D image of
the event with a resolution of a few hundred micrometers. Photomultipliers will
also provide a simultaneous fast readout of the time profile of the light
production, giving information about the third coordinate and hence allowing a
3D reconstruction of the event, from which the direction of the nuclear recoil
and consequently the direction of the incoming particle can be inferred. Such a
detailed reconstruction of the event topology will also allow a pure and
efficient signal to background discrimination. These two features are the key
to reach and overcome the solar neutrino background that will ultimately limit
non-directional dark matter searches.Comment: 5 page, 7 figures, contribution to the Conference Records of 2018
IEEE NSS/MI
The beta Pictoris association: Catalog of photometric rotational periods of low-mass members and candidate members
We intended to compile the most complete catalog of bona fide members and
candidate members of the beta Pictoris association, and to measure their
rotation periods and basic properties from our own observations, public
archives, and exploring the literature. We carried out a multi-observatories
campaign to get our own photometric time series and collected all archived
public photometric data time series for the stars in our catalog. Each time
series was analyzed with the Lomb-Scargle and CLEAN periodograms to search for
the stellar rotation periods. We complemented the measured rotational
properties with detailed information on multiplicity, membership, and projected
rotational velocity available in the literature and discussed star by star. We
measured the rotation periods of 112 out of 117 among bona fide members and
candidate members of the beta Pictoris association and, whenever possible, we
also measured the luminosity, radius, and inclination of the stellar rotation
axis. This represents to date the largest catalog of rotation periods of any
young loose stellar association. We provided an extensive catalog of rotation
periods together with other relevant basic properties useful to explore a
number of open issues, such as the causes of spread of rotation periods among
coeval stars, evolution of angular momentum, and lithium-rotation connection.Comment: Forthcoming article, Received: 20 June 2016 / Accepted: 09 September
2016; 40 pages, 2 figures. The online figures A1-A73 are available at CD
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