arXiv subjects

J. Salas

Publications and source records attributed to J. Salas.

14 recordsLinked to original sources

arXiv2019

MONOS: Multiplicity Of Northern O-type Spectroscopic systems. I. Project description and spectral classifications and visual multiplicity of previously known objects

[ABRIDGED] AIMS. MONOS is collecting information and studying O-type spectroscopic binaries with delta > -20 deg. In this 1st paper we describe the sample and provide spectral classifications and additional information for objects with previous SB or EB orbits. In the future we will test the validity of previous solutions and calculate new SB orbits. METHODS.The spectra in this paper have 2 sources: GOSSS, which is obtaining blue-violet R~2500 spectroscopy of thousands of massive stars, and LiLiMaRlin, a library of libraries of high-resolution spectroscopy of massive stars obtained from 4 different surveys and additional data from our own observing programs and public archives. We also use lucky images from AstraLux. RESULTS. We present homogeneous spectral classifications for 92 O-type spectroscopic multiple systems and 10 optical companions. We discuss the visual multiplicity of each system with the support of AstraLux images and additional sources. For 11 O-type objects and for 6 B-type objects we present their first GOSSS spectral classifications. For 2 known EBs we detect SB2/SB1 lines for the first time, to which we add a third system already reported by us recently. For 2 previous SB1 systems we detect their SB2 nature for the first time and give their first separate spectral classifications, something we also do for a 3rd object just recently identified as a SB2. We also detect 9 new astrometric companions and provide updated information on several others. For sigma Ori AaAbB we provide spectral classifications for the 3 components with a single observation for the first time thanks to a lucky spectroscopy observation obtained close to the Aa,Ab periastron and for theta^1 Ori CaCb we add it to the class of Galactic Of?p stars, raising the number of its members to 6. Our sample of O-type spectroscopic binaries contains more triple/higher-order systems than double systems.

astro-ph.SR↗

arXiv2014

A photometric variability study of massive stars in Cygnus OB2

We have conducted a 1.5 year-long variability study of the stars in the Cygnus OB2 association, the region in the northern hemisphere with the highest density of optically visible massive stars. The survey was conducted using four pointings in the Johnson $R$ and $I$ bands with a 35 cm Meade LX200-ACF telescope equipped with a 3.2 Mpixel SBIG ST10-XME CCD camera and includes 300+ epochs in each filter. A total of 1425 objects were observed with limiting magnitudes of 15 in $R$ and 14 in $I$. The photometry was calibrated using reference stars with existing $UBVJHK$ photometry. Bright stars have precisions better than 0.01 magnitudes, allowing us to detect 52 confirmed and 19 candidate variables, many of them massive stars without previous detections as variables. Variables are classified as eclipsing, pulsating, irregular/long period, and Be. We derive the phased light curves for the eclipsing binaries, with periods ranging from 1.3 to 8.5 days.

astro-ph.SR↗

arXiv2012

Families of small regular graphs of girth 7

The first known families of cages arised from the incidence graphs of generalized polygons of order $q$, $q$ a prime power. In particular, $(q+1,6)$--cages have been obtained from the projective planes of order $q$. Morever, infinite families of small regular graphs of girth 5 have been constructed performing algebraic operations on $\mathbb{F}_q$. In this paper, we introduce some combinatorial operations to construct new infinite families of small regular graphs of girth 7 from the $(q+1,8)$--cages arising from the generalized quadrangles of order $q$, $q$ a prime power.

math.CO↗

arXiv2002

Exact Finite-Size-Scaling Corrections to the Critical Two-Dimensional Ising Model on a Torus. II. Triangular and hexagonal lattices

We compute the finite-size corrections to the free energy, internal energy and specific heat of the critical two-dimensional spin-1/2 Ising model on a triangular and hexagonal lattices wrapped on a torus. We find the general form of the finite-size corrections to these quantities, as well as explicit formulas for the first coefficients of each expansion. We analyze the implications of these findings on the renormalization-group description of the model.

cond-mat.stat-mech↗

arXiv2001

Exact Finite-Size-Scaling Corrections to the Critical Two-Dimensional Ising Model on a Torus

We analyze the finite-size corrections to the energy and specific heat of the critical two-dimensional spin-1/2 Ising model on a torus. We extend the analysis of Ferdinand and Fisher to compute the correction of order L^{-3} to the energy and the corrections of order L^{-2} and L^{-3} to the specific heat. We also obtain general results on the form of the finite-size corrections to these quantities: only integer powers of L^{-1} occur, unmodified by logarithms (except of course for the leading $\log L$ term in the specific heat); and the energy expansion contains only odd powers of L^{-1}. In the specific-heat expansion any power of L^{-1} can appear, but the coefficients of the odd powers are proportional to the corresponding coefficients of the energy expansion.

cond-mat.stat-mech↗

arXiv2000

Dynamic critical behavior of cluster algorithms for 2D Ashkin-Teller and Potts models

We study the dynamic critical behavior of two algorithms: the Swendsen-Wang algorithm for the two-dimensional Potts model with q=2,3,4 and a Swendsen-Wang-type algorithm for the two-dimensional symmetric Ashkin-Teller model on the self-dual curve. We find that the Li--Sokal bound on the autocorrelation time τ_{{\rm int},{\cal E}} \geq const \times C_H is almost, but not quite sharp. The ratio τ_{{\rm int},{\cal E}}/C_H appears to tend to infinity either as a logarithm or as a small power (0.05 \ltapprox p \ltapprox 0.12). We also show that the exponential autocorrelation time τ_{{\rm exp},{\cal E}} is proportional to the integrated autocorrelation time τ_{{\rm int},{\cal E}}.

cond-mat.stat-mech↗

arXiv1998

The 3-State Potts Antiferromagnet on the Hexagonal Lattice

We study the 3-state hexagonal-lattice Potts antiferromagnet by a Monte Carlo simulation using the Wang-Swendsen-Kotecky cluster algorithm. We study the staggered susceptibility and the correlation length, and we confirm that this model is disordered at all temperatures T>=0. We also measure the ground-state entropy density.

cond-mat.stat-mech↗

arXiv1998

The 3-State Square-Lattice Potts Antiferromagnet at Zero Temperature

We study the 3-state square-lattice Potts antiferromagnet at zero temperature by a Monte Carlo simulation using the Wang-Swendsen-Kotecký cluster algorithm, on lattices up to $1024 \times 1024$. We confirm the critical exponents predicted by Burton and Henley based on the height representation of this model.

cond-mat.stat-mech↗

arXiv1995

Dynamic Critical Behavior of a Swendsen-Wang-Type Algorithm for the Ashkin-Teller Model

We study the dynamic critical behavior of a Swendsen-Wang-type algorithm for the Ashkin--Teller model. We find that the Li--Sokal bound on the autocorrelation time ($τ_{{\rm int},{\cal E}} \ge {\rm const} \times C_H$) holds along the self-dual curve of the symmetric Ashkin--Teller model, and is almost but not quite sharp. The ratio $τ_{{\rm int},{\cal E}} / C_H$ appears to tend to infinity either as a logarithm or as a small power ($0.05 \leq p \leq 0.12$). In an appendix we discuss the problem of extracting estimates of the exponential autocorrelation time.

hep-lat↗

arXiv1995

Low--Temperature Series for Renormalized Operators: the Ferromagnetic Square--Lattice Ising Model.

A method for computing low--temperature series for renormalized operators in the two--dimensional Ising model is proposed. These series are applied to the study of the properties of the truncated renormalized Hamiltonians when we start at very low temperature and zero field. The truncated Hamiltonians for majority rule, Kadanoff transformation and decimation for $2 \times 2$ blocks depend on the how we approach the first--order phase--transition line. These Renormalization Group transformations are multi--valued and discontinuous at this first--order transition line when restricted to some finite--dimensional interaction space.

hep-lat↗

arXiv1994

Tricritical Behavior of Two-Dimensional Scalar Field Theories

We compute by Monte Carlo numerical simulations the critical exponents of two-dimensional scalar field theories at the $λϕ^6$ tricritical point. The results are in agreement with the Zamolodchikov conjecture based on conformal invariance.

hep-lat↗

arXiv1993

"The Ising model on spherical lattices: dimer versus Monte Carlo approach"

We study, using dimer and Monte Carlo approaches, the critical properties and finite size effects of the Ising model on honeycomb lattices folded on the tetrahedron. We show that the main critical exponents are not affected by the presence of conical singularities. The finite size scaling of the position of the maxima of the specific heat does not match, however, with the scaling of the correlation length, and the thermodynamic limit is attained faster on the spherical surface than in corresponding lattices on the torus.

hep-lat↗

arXiv1993

Finite Size Analysis of the One-dimensional $q = \infty$ Clock Model

We analyze the finite size scaling of the $q$-state clock model in the $q \rightarrow \infty$ limit. The behaviors of the specific heat, Binder-Landau and U4 cumulants agree with the Borgs-Kotecký ansätz for first order phase transitions. However, we find that the leading correction to the position of the extremal points of these quantities is not universal. On the other hand, the finite size corrections to the mass gap behave like for second order phase transitions. In particular, the curves corresponding to different size approximations do not cross in the vicinity of the transition points. The feature is associated to the existence of a divergent correlation length and holds for a wider class of models.

hep-lat↗

arXiv1993

Exact renormalization-group analysis of first order phase transitions in clock models

We analyze the exact behavior of the renormalization group flow in one-dimensional clock-models which undergo first order phase transitions by the presence of complex interactions. The flow, defined by decimation, is shown to be single-valued and continuous throughout its domain of definition, which contains the transition points. This fact is in disagreement with a recently proposed scenario for first order phase transitions claiming the existence of discontinuities of the renormalization group. The results are in partial agreement with the standard scenario. However in the vicinity of some fixed points of the critical surface the renormalized measure does not correspond to a renormalized Hamiltonian for some choices of renormalization blocks. These pathologies although similar to Griffiths-Pearce pathologies have a different physical origin: the complex character of the interactions. We elucidate the dynamical reason for such a pathological behavior: entire regions of coupling constants blow up under the renormalization group transformation. The flows provide non-perturbative patterns for the renormalization group behavior of electric conductivities in the quantum Hall effect.

hep-lat↗