Visual orbit for the low-mass binary Gliese 22 AC from speckle interferometry

Based on 14 data points obtained with near-infrared speckle interferometry and covering an almost entire revolution, we present a first visual orbit for the low-mass binary system Gliese 22 AC. The quality of the orbit is largely improved with respect to previous astrometric solutions. The dynamical system mass is 0.592 +- 0.065 solar masses, where the largest part of the error is due to the Hipparcos parallax. A comparison of this dynamical mass with mass-luminosity relations on the lower main sequence and theoretical evolutionary models for low-mass objects shows that both probably underestimate the masses of M dwarfs. A mass estimate for the companion Gliese 22 C indicates that this object is a very low-mass star with a mass close to the hydrogen burning mass limit.Comment: Accepted by Astronomy and Astrophysics, 6 pages, 2 figure

Effect of RecA inactivation and detoxification systems on the evolution of ciprofloxacin resistance in Escherichia coli

Background Suppression of SOS response and overproduction of reactive oxygen species (ROS) through detoxification system suppression enhance the activity of fluoroquinolones. Objectives To evaluate the role of both systems in the evolution of resistance to ciprofloxacin in an isogenic model of Escherichia coli. Methods Single-gene deletion mutants of E. coli BW25113 (wild-type) (ΔrecA, ΔkatG, ΔkatE, ΔsodA, ΔsodB), double-gene (ΔrecA-ΔkatG, ΔrecA-ΔkatE, ΔrecA-ΔsodA, ΔrecA-ΔsodB, ΔkatG-ΔkatE, ΔsodB-ΔsodA) and triple-gene (ΔrecA-ΔkatG-ΔkatE) mutants were included. The response to sudden high ciprofloxacin pressure was evaluated by mutant prevention concentration (MPC). The gradual antimicrobial pressure response was evaluated through experimental evolution and antibiotic resistance assays. Results For E. coli BW25113 strain, ΔkatE, ΔsodB and ΔsodB/ΔsodA mutants, MPC values were 0.25 mg/L. The ΔkatG, ΔsodA, ΔkatG/katE and ΔrecA mutants showed 2-fold reductions (0.125 mg/L). The ΔkatG/ΔrecA, ΔkatE/ΔrecA, ΔsodA/ΔrecA, ΔsodB/ΔrecA and ΔkatG/ΔkatE/ΔrecA strains showed 4–8-fold reductions (0.03–0.06 mg/L) relative to the wild-type. Gradual antimicrobial pressure increased growth capacity for ΔsodA and ΔsodB and ΔsodB/ΔsodA mutants (no growth in 4 mg/L) compared with the wild-type (no growth in the range of 0.5–2 mg/L). Accordingly, increased growth was observed with the mutants ΔrecA/ΔkatG (no growth in 2 mg/L), ΔrecA/ΔkatE (no growth in 2 mg/L), ΔrecA/ΔsodA (no growth in 0.06 mg/L), ΔrecA/ΔsodB (no growth in 0.25 mg/L) and ΔrecA/ΔkatG/ΔkatE (no growth in 0.5 mg/L) compared with ΔrecA (no growth in the range of 0.002–0.015 mg/L). Conclusions After RecA inactivation, gradual exposure to ciprofloxacin reduces the evolution of resistance. After suppression of RecA and detoxification systems, sudden high exposure to ciprofloxacin reduces the evolution of resistance in E. coli.Plan Nacional de I+D+i 2013-2016 and the Instituto de Salud Carlos III (projects and PI17/01501 and PI20-00239)Subdirección General de Redes y Centros de Investigación Cooperativa, Ministerio de Economía, Industria y Competitividad, Spanish Network for Research in Infectious Diseases (REIPI; RD16/0016/0001 and REIPI RD16/ 0016/0009

Orbit Determination of Close Binary Systems using Lucky Imaging

We present relative positions of visual binaries observed during 2009 with the FastCam "lucky-imaging" camera at the 1.5-m Carlos Sanchez Telescope (TCS) at the Observatorio del Teide. We obtained 424 CCD observations (averaged in 198 mean relative positions) of 157 binaries with angular separations in the range 0.14-15.40", with a median separation of 0.51". For a given system, each CCD image represents the sum of the best 10-25% images from 1000-5000 short-exposure frames. Derived internal errors were 7 mas in r and 1.2^{\circ} (9 mas) in q. When comparing to systems with very well-known orbits, we find that the rms deviation in r residuals is 23 mas, while the rms deviation in q residuals is 0.73 deg/r. We confirmed 18 Hipparcos binaries and we report new companions to BVD 36 A and J 621 B. For binaries with preliminary orbital parameters, the relative radial velocity was estimated as well. We also present four new revised orbits computed for LDS 873, BU 627 A-BC, BU 628 and HO 197 AB. This work is the first results on visual binaries using the FastCam lucky-imaging camera.Comment: 23 pages, 10 figures, 14 tables, accepted August 18th, 2011, to be published in MNRA

Tracing the young massive high-eccentricity binary system Theta 1 Orionis C through periastron passage

The nearby high-mass star binary system Theta 1 Orionis C is the brightest and most massive of the Trapezium OB stars at the core of the Orion Nebula Cluster, and it represents a perfect laboratory to determine the fundamental parameters of young hot stars and to constrain the distance of the Orion Trapezium Cluster. Between January 2007 and March 2008, we observed T1OriC with VLTI/AMBER near-infrared (H- and K-band) long-baseline interferometry, as well as with bispectrum speckle interferometry with the ESO 3.6m and the BTA 6m telescopes (B'- and V'-band). Combining AMBER data taken with three different 3-telescope array configurations, we reconstructed the first VLTI/AMBER closure-phase aperture synthesis image, showing the T1OriC system with a resolution of approx. 2 mas. To extract the astrometric data from our spectrally dispersed AMBER data, we employed a new algorithm, which fits the wavelength-differential visibility and closure phase modulations along the H- and K-band and is insensitive to calibration errors induced, for instance, by changing atmospheric conditions. Our new astrometric measurements show that the companion has nearly completed one orbital revolution since its discovery in 1997. The derived orbital elements imply a short-period (P=11.3 yrs) and high-eccentricity orbit (e=0.6) with periastron passage around 2002.6. The new orbit is consistent with recently published radial velocity measurements, from which we can also derive the first direct constraints on the mass ratio of the binary components. We employ various methods to derive the system mass (M_system=44+/-7 M_sun) and the dynamical distance (d=410+/-20 pc), which is in remarkably good agreement with recently published trigonometric parallax measurements obtained with radio interferometry.Comment: 15 pages, 15 figures, accepted by A&

The impact of neos and their fragments recorded from the ground : ongoing research lines of the spanish fireball network

A continuous monitoring of the night sky all over Spain will be completed in 2009. This involves the recording over a very large surface area of 500,000 km2, but new CCD and video cameras operated by the Spanish Meteor and Fireball Network (SPMN) allows this target to be achieved. Through the use of these new techniques the SPMN can obtain new information regarding the dynamical processes that deliver meteorites to the Earth. It transpires that the main asteroid belt is not the only source of these fireballs, Near Earth Objects (NEOs) and Jupiter Family Comets (JFCs) may also play a role. To obtain more information in this regard, new efforts are needed to compare the orbits of large meteoroids reaching the Earth with those of the members of NEO and JFC populations. By numerically integrating their orbits back in time it may be possible to identify meteoroids delivered by other mechanisms like such as catastrophic disruptions or collisions

The Villalbeto de la Peña meteorite fall: I. Fireball energy, meteorite recovery, strewn field, and petrography

An impressive daylight fireball was observed from Spain, Portugal, and the south of France at 16h46m45s UTC on January 4, 2004. The meteoroid penetrated into the atmosphere, generating shock waves that reached the ground and produced audible booms. The associated airwave was recorded at a seismic station located 90 km north of the fireball trajectory in Spain, and at an infrasound station in France located 750 km north-east of the fireball. The absolute magnitude of the bolide has been determined to be -18 ± 1 from a casual video record. The energy released in the atmosphere determined from photometric, seismic, and infrasound data was about 0.02 kilotons (kt). A massive fragmentation occurred at a height of 28 ± 0.2 km, resulting in a meteorite strewn field of 20 ± 6 km. The first meteorite specimen was found on January 11, 2004, near the village of Villalbeto de la Pena, in northern Palencia (Spain). To date, about 4.6 kg of meteorite mass have been recovered during several recovery campaigns. The meteorite is a moderately shocked (S4) L6 ordinary chondrite with a cosmic-ray-exposure age of 48 ± 5 Ma. Radioisotope analysis shows that the original body had a mass of 760 ± 150 kg, which is in agreement with the estimated mass obtained from photometric and seismic measurements

Spectroscopic and Mechanistic Studies of Heterodimetallic Forms of Metallo-β-lactamase NDM-1

In an effort to characterize the roles of each metal ion in metallo-β-lactamase NDM-1, heterodimetallic analogues (CoCo-, ZnCo-, and CoCd-) of the enzyme were generated and characterized. UV–vis, 1H NMR, EPR, and EXAFS spectroscopies were used to confirm the fidelity of the metal substitutions, including the presence of a homogeneous, heterodimetallic cluster, with a single-atom bridge. This marks the first preparation of a metallo-β-lactamase selectively substituted with a paramagnetic metal ion, Co(II), either in the Zn1 (CoCd-NDM-1) or in the Zn2 site (ZnCo-NDM-1), as well as both (CoCo-NDM-1). We then used these metal-substituted forms of the enzyme to probe the reaction mechanism, using steady-state and stopped-flow kinetics, stopped-flow fluorescence, and rapid-freeze-quench EPR. Both metal sites show significant effects on the kinetic constants, and both paramagnetic variants (CoCd- and ZnCo-NDM-1) showed significant structural changes on reaction with substrate. These changes are discussed in terms of a minimal kinetic mechanism that incorporates all of the data