14 research outputs found
Towards a consistent model of the hot quadruple system HD 93206 = QZ Carin\ae: II. N-body model
HD 93206 is early-type massive stellar system, composed of components
resolved by direct imaging (Ab, Ad, B, C, D) as well as a compact sub-system
(Aa1, Aa2, Ac1, Ac2). Its geometry was already determined on the basis of
extensive photometric, spectroscopic and interferometric observations. However,
the fundamental absolute parameters are still not known precisely enough. We
use an advanced N-body model to account for all mutual gravitational
perturbations among the four close components, and all observational data
types, including: astrometry, radial velocities, eclipse timing variations,
squared visibilities, closure phases, triple products, normalized spectra, and
spectral-energy distribution (SED). The respective model has 38 free
parameters, namely three sets of orbital elements, component masses, and their
basic radiative properties (, , ). We revised the
fundamental parameters of QZ Car as follows. For a model with the nominal
extinction coefficient , the best-fit masses are
, , , , with uncertainties of the order of , and the
system distance . In an alternative model, where
we increased the weights of RV and TTV observations and relaxed the SED
constraints, because extinction can be anomalous with , the
distance is smaller, . This would correspond to
that of Collinder 228 cluster. Independently, this is confirmed by dereddening
of the SED, which is only then consistent with the early-type classification
(O9.7Ib for Aa1, O8III for Ac1). Future modelling should also account for an
accretion disk around Ac2 component.Comment: A&A, submitte
Labeled EF-Tus for rapid kinetic studies of pretranslocation complex formation
The universally conserved translation elongation factor EF-Tu delivers aminoacyl(aa)-tRNA in the form of an aa-tRNA·EF-Tu·GTP ternary complex (TC) to the ribosome where it binds to the cognate mRNA codon within the ribosomal A-site, leading to formation of a pretranslocation (PRE) complex. Here we describe preparation of QSY9 and Cy5 derivatives of the variant E348C-EF-Tu that are functional in translation elongation. Together with fluorophore derivatives of aa-tRNA and of ribosomal protein L11, located within the GTPase associated center (GAC), these labeled EF-Tus allow development of two new FRET assays that permit the dynamics of distance changes between EF-Tu and both L11 (Tu-L11 assay) and aa-tRNA (Tu-tRNA assay) to be determined during the decoding process. We use these assays to examine: (i) the relative rates of EF-Tu movement away from the GAC and from aa-tRNA during decoding, (ii) the effects of the misreading-inducing antibiotics streptomycin and paromomycin on tRNA selection at the A-site, and (iii) how strengthening the binding of aa-tRNA to EF-Tu affects the rate of EF-Tu movement away from L11 on the ribosome. These FRET assays have the potential to be adapted for high throughput screening of ribosomal antibiotics
Towards a consistent model of the hot quadruple system HD 93206 = QZ Carinae - I. Observations and their initial analyses
The hot nine-component system HD 93206, which contains a gravitationally
bounded eclipsing Ac1+Ac2 binary (~d) and a spectroscopic Aa1+Aa2
(~d) binary can provide~important insights into the origin and
evolution of massive stars. Using archival and new spectra, and a~rich
collection of ground-based and space photometric observations, we carried out a
detailed study of this object. We provide a much improved description of both
short orbits and a good estimate of the mutual period of both binaries of about
14500~d (i.e. 40 years). For the first time, we detected weak lines of the
fainter component of the 6.0~d eclipsing binary in the optical region of the
spectrum, measured their radial velocities, and derived a mass ratio of , which is the opposite of what was estimated from the
International Ultraviolet explorer (IUE) spectra. We confirm that the eclipsing
subsystem Ac is semi-detached and is therefore in a phase of large-scale mass
transfer between its components. The Roche-lobe filling and spectroscopically
brighter component Ac1 is the less massive of the two and is eclipsed in the
secondary minimum. We show that the bulk of the \ha emission, so far believed
to be associated with the eclipsing system, moves with the primary O9.7I
component Aa1 of the 20.73~d spectroscopic binary. However, the weak emission
in the higher Balmer lines seems to be associated with the accretion disc
around component Ac2. We demonstrate that accurate masses and other basic
physical properties including the distance of this unique system can be
obtained but require a more sophisticated modelling. A~first step in this
direction is presented in the accompanying Paper~II (Bro\v{z} et al.).Comment: 20 pages, 12 Figure