10,411 research outputs found
Detection of magnetic field in the B2 star Oph A with ESO FORS2
Circumstantial evidence suggests that magnetism and enhanced X-ray emission
are likely correlated in early B-type stars: similar fractions of them (
10 %) are strong and hard X-ray sources and possess strong magnetic fields. It
is also known that some B-type stars have spots on their surface. Yet up to now
no X-ray activity associated with spots on early-type stars was detected. In
this Letter we report the detection of a magnetic field on the B2V star
Oph A. Previously, we assessed that the X-ray activity of this star is
associated with a surface spot, herewith we establish its magnetic origin. We
analyzed FORS2 ESO VLT spectra of Oph A taken at two epochs and detected
a longitudinal component of the magnetic field of order of G in one
of the datasets. The detection of the magnetic field only at one epoch can be
explained by stellar rotation which is also invoked to explain observed
periodic X-ray activity. From archival HARPS ESO VLT high resolution spectra we
derived the fundamental stellar parameters of Oph A and further
constrained its age. We conclude that Oph A provides strong evidence for
the presence of active X-ray emitting regions on young magnetized early type
stars.Comment: 4 pages, 1 figure, 2 tables, accepted as a "Letter to the Editor" to
Astronomy & Astrophysic
Is there a tensionless Kardar-Parisi-Zhang universality class above one dimension? An Ising model approach
The Kardar-Parisi-Zhang (KPZ) equation is a paradigm of generic scale
invariance, for which it represents a conspicuous universality class. Recently,
the tensionless case of this equation has been shown to provide a different
universality class by itself. This class describes the -- intrinsically
anomalous -- scaling of one-dimensional (1D) fronts for several physical
systems that feature ballistic dynamics. In this work, we show that the
evolution of certain 1D fronts defined for a 2D Ising system also belongs to
the tensionless KPZ universality class. Nevertheless, the Ising fronts exhibit
multiscaling, at variance with the continuous equation. The discrete nature of
these fronts provides an alternative approach to assess the dynamics for the 2D
front case (for a 3D Ising system), since the direct integration of the
tensionless KPZ equation blows up in this case. In spite of the agreement
between the 1D scaling of the Ising fronts and the tensionless KPZ equation,
the fluctuation statistics in 1D and the full behavior in 2D are strongly
conditioned by boundary effects.Comment: 9 pages, 9 figure
The 2011 October Draconids Outburst. II. Meteoroid Chemical Abundances from Fireball Spectroscopy
On October 8, 2011 the Earth crossed dust trails ejected from comet
21P/Giacobini-Zinner in the late 19th and early 20th Century. This gave rise to
an outburst in the activity of the October Draconid meteor shower, and an
international team was organized to analyze this event. The SPanish Meteor
Network (SPMN) joined this initiative and recorded the October Draconids by
means of low light level CCD cameras. In addition, spectroscopic observations
were carried out. Tens of multi-station meteor trails were recorded, including
an extraordinarily bright October Draconid fireball (absolute mag. -10.5) that
was simultaneously imaged from three SPMN meteor ob-serving stations located in
Andalusia. Its spectrum was obtained, showing a clear evolution in the relative
intensity of emission lines as the fireball penetrated deeper into the
atmosphere. Here we focus on the analysis of this remarkable spectrum, but also
discuss the atmospheric trajectory, atmospheric penetration, and orbital data
computed for this bolide which was probably released during
21P/Giacobini-Zinner return to perihelion in 1907. The spectrum is discussed
together with the tensile strength for the October Draconid meteoroids. The
chemical profile evolution of the main rocky elements for this extremely bright
bolide is compared with the elemental abundances obtained for 5 October
Draconid fireballs also recorded during our spectroscopic campaign but observed
only at a single station. Significant chemical heterogeneity between the small
meteoroids is found as we should expect for cometary aggregates being formed by
diverse dust components.Comment: Manuscript in press in Monthly Notices of the Royal Astronomical
Society. Accepted for publication in MNRAS on April 28th, 2013 Manuscript
Pages: 28 Tables: 5 Figures: 12. Manuscript associated: "The 2011 October
Draconids outburst. I. Orbital elements, meteoroid fluxes and
21P/Giacobini-Zinner delivered mass to Earth" by Trigo-Rodriguez et al. is
also in press in the same journa
Warps and correlations with intrinsic parameters of galaxies in the visible and radio
From a comparison of the different parameters of warped galaxies in the
radio, and especially in the visible, we find that: a) No large galaxy (large
mass or radius) has been found to have high amplitude in the warp, and there is
no correlation of size/mass with the degree of asymmetry of the warp. b) The
disc density and the ratio of dark to luminous mass show an opposing trend:
smaller values give more asymmetric warps in the inner radii (optical warps)
but show no correlation with the amplitude of the warp; however, in the
external radii neither is there any correlation with the asymmetry. c) A third
anticorrelation arises from a comparison of the amplitude and degree of
asymmetry in the warped galaxies. Hence, it seems that very massive dark matter
haloes have nothing to do with the formation of warps but only with the degree
of symmetry in the inner radii, and are unrelated to the warp shape for the
outermost radii. Denser discs show up the same dependence.Comment: 13 pages, 2 figures, accepted to be published in A&
Intracluster stars in the Virgo cluster core
We have investigated the properties of the diffuse light in the Virgo cluster
core region, based on the detection of intracluster planetary nebulae (PNe) in
four fields. We eliminate the bias from misclassified faint continuum objects,
using improved Monte Carlo simulations, and the contaminations by high redshift
Ly galaxies, using the Ly luminosity function in blank fields.
Recent spectroscopic observations confirm that our photometric PN samples are
well-understood. We find that the diffuse stellar population in the Virgo core
region is inhomogeneous on scales of 30'-90': there exist significant
field-to-field variations in the number density of PNe and the inferred amount
of intracluster light, with some empty fields, some fields dominated by
extended Virgo galaxy halos, and some fields dominated by the true intracluster
component. There is no clear trend with distance from M87. The mean surface
luminosity density, its rms variation, and the mean surface brightness of
diffuse light in our 4 fields are L
arcmin, L arcmin, and
mag arcsec respectively. Our results indicate that
the Virgo cluster is a dynamically young environment, and that the intracluster
component is associated at least partially with local physical processes like
galaxy interactions or harassment. We also argue, based on kinematic evidence,
that the so-called 'over-luminous' PNe in the halo of M84 are dynamically
associated with this galaxy, and must thus be brighter than and part of a
different stellar population from the normal PN population in elliptical
galaxies.Comment: 31 pages, 6 figure. In press on the Astronomical Journa
Black Hole Scattering from Monodromy
We study scattering coefficients in black hole spacetimes using analytic
properties of complexified wave equations. For a concrete example, we analyze
the singularities of the Teukolsky equation and relate the corresponding
monodromies to scattering data. These techniques, valid in full generality,
provide insights into complex-analytic properties of greybody factors and
quasinormal modes. This leads to new perturbative and numerical methods which
are in good agreement with previous results.Comment: 28 pages + appendices, 2 figures. For Mathematica calculation of
Stokes multipliers, download "StokesNotebook" from
https://sites.google.com/site/justblackholes/techy-zon
Fossil Groups Origins III. Characterization of the sample and observational properties of fossil systems
(Abridged) Fossil systems are group- or cluster-sized objects whose
luminosity is dominated by a very massive central galaxy. In the current cold
dark matter scenario, these objects formed hierarchically at an early epoch of
the Universe and then slowly evolved until present day. That is the reason why
they are called {\it fossils}. We started an extensive observational program to
characterize a sample of 34 fossil group candidates spanning a broad range of
physical properties. Deep band images were taken for each candidate and
optical spectroscopic observations were obtained for 1200 galaxies. This
new dataset was completed with SDSS DR7 archival data to obtain robust cluster
membership and global properties of each fossil group candidate. For each
system, we recomputed the magnitude gaps between the two brightest galaxies
() and the first and fourth ranked galaxies ()
within 0.5 . We consider fossil systems those with mag or mag within the errors. We find
that 15 candidates turned out to be fossil systems. Their observational
properties agree with those of non-fossil systems. Both follow the same
correlations, but fossils are always extreme cases. In particular, they host
the brightest central galaxies and the fraction of total galaxy light enclosed
in the central galaxy is larger in fossil than in non-fossil systems. Finally,
we confirm the existence of genuine fossil clusters. Combining our results with
others in the literature, we favor the merging scenario in which fossil systems
formed due to mergers of galaxies. The large magnitude gap is a
consequence of the extreme merger ratio within fossil systems and therefore it
is an evolutionary effect. Moreover, we suggest that at least one candidate in
our sample could represent a transitional fossil stage.Comment: 14 pages, 11 figures, accepted for publication in A&
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