New HST WFC3/UVIS observations augment the stellar-population complexity of omega Centauri

We used archival multi-band Hubble Space Telescope observations obtained with the Wide-Field Camera 3 in the UV-optical channel to present new important observational findings on the color-magnitude diagram (CMD) of the Galactic globular cluster omega Centauri. The ultraviolet WFC3 data have been coupled with available WFC/ACS optical-band data. The new CMDs, obtained from the combination of colors coming from eight different bands, disclose an even more complex stellar population than previously identified. This paper discusses the detailed morphology of the CMDs.Comment: 17 pages, 14 figures (11 in low res), 3 tables. Accepted for publication in AJ on June 19, 201

The connection between missing AGB stars and extended horizontal branches

Recent surveys confirm early results about a deficiency or even absence of CN-strong stars on the asymptotic giant branch (AGB) of globular clusters (GCs), although with quite large cluster-to-cluster variations. In general, this is at odds with the distribution of CN band strengths among first ascent red giant branch (RGB) stars. Norris et al. proposed that the lack of CN-strong stars in some clusters is a consequence of a smaller mass of these stars that cannot evolve through the full AGB phase. In this short paper we found that the relative frequency of AGB stars can change by a factor of two between different clusters. We also find a very good correlation between the minimum mass of stars along the horizontal branch (Gratton et al. 2010) and the relative frequency of AGB stars, with a further dependence on metallicity. We conclude that indeed the stars with the smallest mass on the HB cannot evolve through the full AGB phase, being AGB-manque'. These stars likely had large He and N content, and large O-depletion. We then argue that there should not be AGB stars with extreme O depletion, and few of them with a moderate one.Comment: 5 Pages, 2 figures, A&A Accepte

The Acidic Probe LysoSensor™ is not Useful for Acrosome Evaluation of Cryopreserved Ram Spermatozoa

P. 363-367To try new acrosomal probes for assessing ram spermatozoa, we compared the LysoSensor™ probe, which labels acidic organelles, with the frequently used peanut agglutinin acrosomal probe (PNA‐PE; phycoerythrin as fluorescent moiety). The previous microscopic observations showed a lack of relationship of LysoSensor™ with acrosomal status. Semen was obtained from five rams and frozen in four pools. Each pool was analysed carrying out a triple staining propidium ioide/PNA‐PE/LysoSensor™ Green DND‐189 to test acrosome labelling, and a double staining SYBR‐14/PI, to assess sperm viability. Stained samples were analysed by flow cytometry. All measurements were replicated. Data were processed using agreement and repeatability tests. LysoSensor™ labelling did not agree with PNA (mean of differences: 30.8%; coefficient of agreement: 22.6%), confirming microscopic observations. Nevertheless, when LysoSensor™ was compared with SYBR‐14/PI, the agreement was high (mean of differences: −0.05%; coefficient of agreement: 5.07%). Repeatability of both methods was high and similar. LysoSensor™ did not seem to specifically stain the acrosome, but it may accumulate in the cytoplasm and label viable spermatozoa. Therefore, LysoSensor™ might not be used as an acrosomal probe in ram spermatozoa, but it could be used in other kind of studies, taking advantage of its pH sensitivity.S

NGC 2419: a large and extreme second generation in a currently undisturbed cluster

We analyse complementary HST and SUBARU data for the globular cluster NGC 2419. We make a detailed analysis of the horizontal branch (HB), that appears composed by two main groups of stars: the luminous blue HB stars ---that extend by evolution into the RR Lyrae and red HB region--- and a fainter, extremely blue population. We examine the possible models for this latter group and conclude that a plausible explanation is that they correspond to a significant (~30 %) extreme second generation with a strong helium enhancement (Y~0.4). We also show that the color dispersion of the red giant branch is consistent with this hypothesis, while the main sequence data are compatible with it, although the large observational error blurs the possible underlying splitting. While it is common to find an even larger (50 -- 80) percentage of second generation in a globular cluster, the presence of a substantial and extreme fraction of these stars in NGC 2419 might be surprising, as the cluster is at present well inside the radius beyond which the galactic tidal field would be dominant. If a similar situation had been present in the first stages of the cluster life, the cluster would have retained its initial mass, and the percentage of second generation stars should have been quite small (up to ~10 %). Such a large fraction of extreme second generation stars implies that the system must have been initially much more massive and in different dynamical conditions than today. We discuss this issue in the light of existing models of the formation of multiple populations in globular clusters.Comment: 14 pages, 14 figures (5 in low resolution format), 3 tables, accepted for publication in MNRA

Symmetry implies independence

Given a quantum system consisting of many parts, we show that symmetry of the system's state, i.e., invariance under swappings of the subsystems, implies that almost all of its parts are virtually identical and independent of each other. This result generalises de Finetti's classical representation theorem for infinitely exchangeable sequences of random variables as well as its quantum-mechanical analogue. It has applications in various areas of physics as well as information theory and cryptography. For example, in experimental physics, one typically collects data by running a certain experiment many times, assuming that the individual runs are mutually independent. Our result can be used to justify this assumption.Comment: LaTeX, contains 4 figure

Action research and democracy

This contribution explores the relationship between research and learning democracy. Action research is seen as being compatible with the orientation of educational and social work research towards social justice and democracy. Nevertheless, the history of action research is characterized by a tension between democracy and social engineering. In the social-engineering approach, action research is conceptualized as a process of innovation aimed at a specific Bildungsideal. In a democratic approach action research is seen as research based on cooperation between research and practice. However, the notion of democratic action research as opposed to social engineering action research needs to be theorized. So called democratic action research involving the implementation by the researcher of democracy as a model and as a preset goal, reduces cooperation and participation into instruments to reach this goal, and becomes a type of social engineering in itself. We argue that the relationship between action research and democracy is in the acknowledgment of the political dimension of participation: ‘a democratic relationship in which both sides exercise power and shared control over decision-making as well as interpretation’. This implies an open research design and methodology able to understand democracy as a learning process and an ongoing experiment

Hydrogen-like nitrogen radio line from hot interstellar and warm-hot intergalactic gas

Hyperfine structure lines of highly-charged ions may open a new window in observations of hot rarefied astrophysical plasmas. In this paper we discuss spectral lines of isotopes and ions abundant at temperatures 10^5-10^7 K, characteristic for warm-hot intergalactic medium, hot interstellar medium, starburst galaxies, their superwinds and young supernova remnants. Observations of these lines will allow to study bulk and turbulent motions of the observed target and will broaden the information about the gas ionization state, chemical and isotopic composition. The most prospective is the line of the major nitrogen isotope having wavelength 5.65 mm (Sunyaev and Churazov 1084). Wavelength of this line is well-suited for observation of objects at z=0.15-0.6 when it is redshifted to 6.5-9 mm spectral band widely-used in ground-based radio observations, and, for example, for z>=1.3, when the line can be observed in 1.3 cm band and at lower frequencies. Modern and future radio telescopes and interferometers are able to observe the absorption by 14-N VII in the warm-hot intergalactic medium at redshifts above z=0.15 in spectra of brightest mm-band sources. Sub-millimeter emission lines of several most abundant isotopes having hyperfine splitting might also be detected in spectra of young supernova remnants.Comment: 12 pages, 5 figures, accepted by Astronomy Letters; v3: details added; error fixe

HST Observations of New Horizontal Branch Structures in the Globular Cluster omega Centauri

The globular cluster omega Centauri contains the largest known population of very hot horizontal branch (HB) stars. We have used the Hubble Space Telescope to obtain a far-UV/optical color-magnitude diagram of three fields in omega Cen. We find that over 30% of the HB objects are ``extreme'' HB or hot post-HB stars. The hot HB stars are not concentrated toward the cluster center, which argues against a dynamical origin for them. A wide gap in the color distribution of the hot HB stars appears to correspond to gaps found earlier in several other clusters. This suggests a common mechanism, probably related to giant branch mass loss. The diagram contains a significant population of hot sub-HB stars, which we interpret as the ``blue-hook'' objects predicted by D'Cruz et al. (1996a). These are produced by late He-flashes in stars which have undergone unusually large giant branch mass loss. omega Cen has a well-known spread of metal abundance, and our observations are consistent with a giant branch mass loss efficiency which increases with metallicity.Comment: Submitted to ApJ, 12 pages, including 3 figures, also available at http://www.physics.usyd.edu.au/~noella/research.htm

Formation of Multiple Populations in Globular Clusters: Another Possible Scenario

While chemical composition spreads are now believed to be a universal characteristic of globular clusters (GCs), not all of them present multiple populations in their color-magnitude diagrams (CMDs). Here we present a new scenario for the formation of GCs, in an attempt to qualitatively explain this otherwise intriguing observational framework. Our scenario divides GCs into three groups, depending on the initial mass (M_I) of the progenitor structure (PS), as follows. i) Massive PSs can retain the gas ejected by massive stars, including the ejecta of core-collapse SNe. ii) Intermediate-mass PSs can retain at least a fraction of the fast winds of massive stars, but none of the core-collapse SNe ejecta. iii) Low-mass PSs can only retain the slow winds of intermediate-mass stars. Members of the first group would include omega Centauri (NGC 5139), M54 (NGC 6715), M22 (NGC 6656), and Terzan 5, whereas NGC 2808 (and possibly NGC 2419) would be members of the second group. The remaining GCs which only present a spread in light elements, such as O and Na, would be members of the third group. According to our scenario, the different components in omega Cen should not display a sizeable spread in age. We argue that this is consistent with the available observations. We give other simple arguments in favor of our scenario, which can be described in terms of two main analytical relations: i) Between the actual observed ratio between first and second generation stars (R_SG^FG) and the fraction of first generation stars that have been lost by the GC (S_L); and ii) Between S_L and M_I. We also suggest a series of future improvements and empirical tests that may help decide whether the proposed scenario properly describes the chemical evolution of GCs.Comment: Accepted for publication in Astronomy and Astrophysic

A Qualitative Study Exploring How the Aims, Language and Actions of Yoga for Pregnancy Teachers May Impact Upon Women's Self-efficacy for Labour and Birth

As women's anxiety and the rate of medical intervention in labour and birth continue to increase, it is important to identify how antenatal education can increase women's confidence and their ability to manage the intense sensations of labour. To report a grounded theory study of how the aims, language and actions of yoga for pregnancy teachers may impact upon women's self-efficacy for labour and birth. Yoga for pregnancy classes in three locations were filmed. Semi-structured interviews were undertaken with the teachers to explore what they were trying to achieve in their classes, and how. Interviews and classes were transcribed and analysed using grounded theory. There was considerable consistency in the teachers’ aims, the language they used in classes and in their thinking about class structure. Four main themes emerged: creating a sisterhood, modelling labour, building confidence and enhancing learning. Teachers see yoga for pregnancy as a multi-faceted, non-prescriptive intervention that enhances women's physical, emotional and social readiness for labour and birth, and supports women to make their own decisions across the transition to parenthood. Women's self-efficacy for labour is complex and multi-factorial. This study offers insights into the factors which may be involved in increasing it. These include not only traditional elements of yoga such as postures, breathing and meditation, but also the creation of safe, women-only groups where anxieties, experiences and stories can be shared, and pain-coping techniques for labour learned and practised