576 research outputs found
Substructure in the Andromeda Galaxy Globular Cluster System
In the most prominent current scenario of galaxy formation, galaxies form
hierarchically through the merger of smaller systems. Such mergers could leave
behind dynamical signatures which may linger long after the event. In
particular, the globular cluster system (GCS) of a merging satellite galaxy may
remain as a distinct sub-population within the GCS of a massive galaxy. Using
the latest available globular cluster velocities and metallicities, we present
the results of a search for grouping in the GCS of our nearest large spiral
galaxy neighbor, M31. A modified friends-of-friends algorithm is used to
identify a number of possible merger remnants in projected position, radial
velocity and [Fe/H] parameter space. Numerical simulations are used to check
that such merger remnants are indeed plausible over the timescales of interest.
The identification of stellar streams associated with these groups is required
in order to confirm that they represent merger remnants.Comment: 19 pages, 3 figures, accepted for publication in the Ap
Systematic detection of magnetic fields in massive, late-type supergiants
We report the systematic detection of magnetic fields in massive (M > 5
M) late-type supergiants, using spectropolarimetric observations
obtained with ESPaDOnS at the Canada-France-Hawaii Telescope. Our observations
reveal detectable Stokes V Zeeman signatures in Least-Squares Deconvolved mean
line profiles in one-third of the observed sample of more than 30 stars. The
signatures are sometimes complex, revealing multiple reversals across the line.
The corresponding longitudinal magnetic field is seldom detected, although our
longitudinal field error bars are typically 0.3 G (). These
characteristics suggest topologically complex magnetic fields, presumably
generated by dynamo action. The Stokes V signatures of some targets show clear
time variability, indicating either rotational modulation or intrinsic
evolution of the magnetic field. We also observe a weak correlation between the
unsigned longitudinal magnetic field and the CaII K core emission equivalent
width of the active G2Iab supergiant ~Dra and the G8Ib supergiant
~Gem.Comment: 8 pages, 1 table, 6 figures, accepted for publication in MNRA
Integrated Colours of Milky Way Globular Clusters and Horizontal Branch Morphology
Broadband colours are often used as metallicity proxies in the study of
extragalactic globular clusters. A common concern is the effect of variations
in horizontal branch (HB) morphology--the second-parameter effect--on such
colours. We have used UBVI, Washington, and DDO photometry for a compilation of
over 80 Milky Way globular clusters to address this question. Our method is to
fit linear relations between colour and [Fe/H], and study the correlations
between the residuals about these fits and two quantitative measures of HB
morphology. While there is a significant HB effect seen in U-B, for the
commonly used colours B-V, V-I, and C-T_1, the deviations from the baseline
colour-[Fe/H] relations are less strongly related to HB morphology. There may
be weak signatures in B-V and C-T_1, but these are at the limit of
observational uncertainties. The results may favour the use of B-I in studies
of extragalactic globular clusters, especially when its high [Fe/H]-sensitivity
is considered.Comment: 19 pages, including 26 figures. AN in press. Figure 9 stubbornly
resists attempts to correct i
Disabled people, medical inadmissibility, and the differential politics of immigration
This paper is concerned with the impact of medical inadmissibility provisions in Canada’s immigration law on applicants with disabilities. The paper draws on key informant interviews, policy analysis, and Ministry of Immigration data on medical inadmissibility findings. We follow the lead of recent mobilities scholarship to examine how the immigration system is enacted, reproduced, and contested over time. From this perspective, we see that recent court challenges to the statutory provisions have created additional procedural space for applicants to contest findings of inadmissibility. However, the legitimacy of excessive demand as a basis for exclusion remains firmly in place, while recent immigration policy changes signal an intensification of measures to limit the social reproductive costs of immigration
Gemini/GMOS Imaging of Globular Cluster Systems in Five Early-type Galaxies
This paper presents deep high quality photometry of globular cluster (GC)
systems belonging to five early-type galaxies covering a range of mass and
environment. Photometric data were obtained with the Gemini North and Gemini
South telescopes in the filter passbands g', r', and i'. The combination of
these filters with good seeing conditions allows an excellent separation
between GC candidates and unresolved field objects. Bimodal GC colour
distributions are found in all five galaxies. Most of the GC systems appear
bimodal even in the (g' -r') vs (r' -i') plane. A population of
resolved/marginally resolved GC and Ultra Compact Dwarf candidates was found in
all the galaxies. A search for the so-called "blue tilt" in the
colour-magnitude diagrams reveals that NGC 4649 clearly shows that phenomenon
although no conclusive evidence was found for the other galaxies in the sample.
This "blue tilt" translates into a mass-metallicity relation given by Z \propto
M^0.28\pm0.03 . This dependence was found using a new empirical (g' -i') vs
[Z/H] relation which relies on an homogeneous sample of GC colours and
metallicities. This paper also explores the radial trends in both colour and
surface density for the blue (metal-poor) and red (metal-rich) GC
subpopulations. As usual, the red GCs show a steeper radial distribution than
the blue ones. Evidence of galactocentric colour gradients is found in some of
the GC systems, being more significant for the two S0 galaxies in the sample.
Red GC subpopulations show similar colours and gradients to the galaxy halo
stars in their inner region. A GC mean colour-galaxy luminosity relation,
consistent with [Z/H] \propto L_B ^0.26\pm0.08, is present for the red GCs. An
estimate of the total GC populations and specific frequency SN values is
presented for NGC 3115, NGC 3379, NGC 3923 and NGC 4649.Comment: 23 pages, 13 figures and 9 tables. Tables A1 and A2 will be published
in full online only. Accepted for publication in MNRA
Bicistronic DNA display for in vitro selection of Fab fragments
In vitro display methods are superior tools for obtaining monoclonal antibodies. Although totally in vitro display methods, such as ribosome display and mRNA display, have the advantages of larger library sizes and quicker selection procedures compared with phage display, their applications have been limited to single-chain Fvs due to the requirement for linking of the mRNA and the nascent protein on the ribosome. Here we describe a different type of totally in vitro method, DNA display, that is applicable to heterodimeric Fab fragments: in vitro compartmentalization in water-in-oil emulsions allows the linking of an oligomeric protein and its encoding DNA with multiple ORFs. Since previously used emulsions impaired the synthesis of functional Fab fragments, we modified conditions for preparing emulsions, and identified conditions under which it was possible to enrich Fab fragments 106-fold per three rounds of affinity selection. Furthermore, we confirmed that genes encoding stable Fab fragments could be selected from a Fab fragment library with a randomized hydrophobic core in the constant region by applying heat treatment as a selection pressure. Since this method has all advantages of both phage display and totally in vitro display, it represents a new option for many applications using display methods
Defining the structural requirements for ribose 5-phosphate-binding and intersubunit cross-talk of the malarial pyridoxal 5-phosphate synthase
Most organisms synthesise the B(6) vitamer pyridoxal 5-phosphate (PLP) via the glutamine amidotransferase PLP synthase, a large enzyme complex of 12 Pdx1 synthase subunits with up to 12 Pdx2 glutaminase subunits attached. Deletion analysis revealed that the C-terminus has four distinct functionalities: assembly of the Pdx1 monomers, binding of the pentose substrate (ribose 5-phosphate), formation of the reaction intermediate I(320), and finally PLP synthesis. Deletions of distinct C-terminal regions distinguish between these individual functions. PLP formation is the only function that is conferred to the enzyme by the C-terminus acting in trans, explaining the cooperative nature of the complex
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