5,892 research outputs found
The mass of Albireo Aa and the nature of Albireo AB: New aspects from Gaia DR2
Aims: We aim to clarify the nature of Albireo AB and specifically to decipher
whether it is an optical or physical pair. We also try to determine the mass of
Albireo Aa. Methods: We scrutinize and compare the available absolute
astrometric data (from Hipparcos and Gaia DR2) of Albireo A and B, and we
investigate the relative orbit of the pair Albireo Aa,Ac using orbit solutions
based on ground-based interferometric measurements. Results: The mass of
Albireo Aa (K3 II) is surprisingly small; only an upper limit of about 0.7
solar masses could be derived. The systemic proper motion of Aa,Ac differs from
that of component B by about 10 mas/year with an uncertainty of less than 2
mas/year. Albireo AB is therefore most probably an optical double. Conclusions:
Specific astrometric and spectroscopic follow-up observations clarifying the
surprising mass estimate for Albireo Aa are recommended.Comment: 4 pages, 3 figures, accepted by Astron. Astrophy
Axigluon Phenomenology using ATLAS dijet data
In recent years, there has been a renewed interest on axigluons as part of a
possible extension of strong interactions at high energies. In this work, we
use recent ATLAS measurements of the dijet spectrum in order to set limits on
the axigluon mass and coupling to quarks. We pay special attention to the
methodology used to extract the resonant contribution from theoretical
simulations. Finally, we present some predictions for the next LHC run at
TeV
Isospin violation in the vector form factors of the nucleon
A quantitative understanding of isospin violation is an increasingly
important ingredient for the extraction of the nucleon's strange vector form
factors from experimental data. We calculate the isospin violating electric and
magnetic form factors in chiral perturbation theory to leading and
next-to-leading order respectively, and we extract the low-energy constants
from resonance saturation. Uncertainties are dominated largely by limitations
in the current knowledge of some vector meson couplings. The resulting bounds
on isospin violation are sufficiently precise to be of value to on-going
experimental studies of the strange form factors.Comment: 13 pages, 8 figures, uses RevTe
Thermophysical properties of warm dense hydrogen
We study the thermophysical properties of warm dense hydrogen using quantum
molecular dynamics simulations. New results are presented for the pair
distribution functions, the equation of state, the Hugoniot curve, and the
reflectivity. We compare with available experimental data and predictions of
the chemical picture. Especially, we discuss the nonmetal-to-metal transition
which occurs at about 40 GPa in the dense fluid
Parasites Recovered From Overwintering Mimosa Webworm, \u3ci\u3eHomadaula Anisocentra\u3c/i\u3e (Lepidoptera: Plutellidae)
The mimosa webworm, Homadaula anisocentra, overwinters in the pupal stage. Two parasites, Parania geniculata and Elasmus albizziae, are associated with overwintering pupae or the immediate prepupal larvae. Combined parasitism during the winters of 1981-82,1982-83, and 1983-84 was 2.1,3.9, and 2.9%, respectively
The Star Cluster Population of M51: II. Age distribution and relations among the derived parameters
We use archival Hubble Space Telescope observations of broad-band images from the ultraviolet (F255W-filter) through the near infrared (NICMOS F160W-filter) to study the star cluster population of the interacting spiral galaxy M 51. We obtain age, mass, extinction, and effective radius estimates for 1152 star clusters in a region of ~7.3 × 8.1 kpc centered on the nucleus and extending into the outer spiral arms. In this paper we present the data set and exploit it to determine the age distribution and relationships among the fundamental parameters (i.e. age, mass, effective radius). We show the critical dependence of the age distribution on the sample selection, and confirm that using a constant mass cut-off, above which the sample is complete for the entire age range of interest, is essential. In particular, in this sample we are complete only for masses above 5× 104~M? for the last 1 Gyr. Using this dataset we find: i) that the cluster formation rate seems to have had a large increase ~50-70 Myr ago, which is coincident with the suggested second passage of its companion, NGC 5195; ii) a large number of extremely young (<10 Myr) star clusters, which we interpret as a population of unbound clusters of which a large majority will disrupt within the next ~10 Myr; and iii) that the distribution of cluster sizes can be well approximated by a power-law with exponent, -? = -2.2 ± 0.2, which is very similar to that of Galactic globular clusters, indicating that cluster disruption is largely independent of cluster radius. In addition, we have used this dataset to search for correlations among the derived parameters. In particular, we do not find any strong trends between the age and mass, mass and effective radius, nor between the galactocentric distance and effective radius. There is, however, a strong correlation between the age of a cluster and its extinction, with younger clusters being more heavily reddened than older clusters
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