Embryonic and post-embryonic utilization and subcellular localization of the nuclear receptor SpSHR2 in the sea urchin

SpSHR2 (Strongylocentrotus purpuratus steroid hormone receptor 2) is a nuclear receptor, encoded by a maternal RNA in the sea urchin embryo. These maternal SpSHR2 transcripts, which are present in all cells, persist until the blastula stage and then are rapidly turned over. A small fraction of the embryonic SpSHR2 protein is maternal, but the majority of this nuclear receptor in the embryo is the product of new synthesis, presumably from the maternal RNA after fertilization. In agreement with the mRNA distribution, the SpSHR2 protein is also detected in all embryonic cells. Contrary to the RNA though, the SpSHR2 protein persists throughout embryonic development to the pluteus stage, long after the mRNA is depleted. Following fertilization and as soon as the 2-cell stage, the cytoplasmic SpSHR2 protein enters rapidly into the embryonic nuclei where it appears in the form of speckles. During subsequent stages (from fourth cleavage onward), SpSHR2 resides in speckled form in both the nucleus and the cytoplasm of the embryonic cells. The cytoplasmic localization of SpSHR2 differs between polarized and non-polarized cells, maintaining an apical position in the ectoderm and endoderm versus a uniform distribution in mesenchyme cells. Following the end of embryonic development (pluteus stage), the SpSHR2 protein is depleted from all tissues. During the ensuing four weeks of larval development, the SpSHR2 is not detected in either the larval or the rudiment cells which will give rise to the adult. Just prior to metamorphosis, at about 35 days post-fertilization, the protein is detected again but in contrast to the uniform distribution in the early embryo, the larval SpSHR2 is specifically expressed in cells of the mouth epithelium and the epaulettes. In adult ovaries and testes, SpSHR2 is specifically detected in the myoepithelial cells surrounding the ovarioles and the testicular acini. Nuclear SpSHR2 in blastula extracts binds to the C1R hormone response element in the upstream promoter region of the CyIIIb actin gene indicating that the latter may be a target of this nuclear receptor in the sea urchin embryo

A detailed study of the enigmatic cluster M82F

We present a detailed study of the stellar cluster M82F, using multi-band high resolution HST imaging and deep ground based optical slit and integral field spectroscopy. Using the imaging we create colour maps of the cluster and surrounding region in order to search for substructure. We find a large amount of substructure, which we interpret as the result of differential extinction across the projected face of the cluster. With this interpretation, we are able to construct a spatially resolved extinction map across the cluster which is used to derive the intrinsic flux distribution. Fitting cluster profiles (King and EFF) to the intrinsic images we find that the cluster is 15-30% larger than previous estimates, and that no strong evidence of mass segregation in this cluster exists. Using the optical spectra, we find that the age of M82F is 60-80 Myr and from its velocity conclude that the cluster is not physically associated with a large HII region that it is projected upon, both in agreement with previous studies. The reconstructed integral field maps show that that majority of the line emission comes from a nearby HII region. The spatial dependence of the line widths (implying the presence of multiple components)measured corresponds to the extinction map derived from photometry, indicating that the gas/dust clouds responsible for the extinction are also partially ionised. Even with the wealth of observations presented here, we do not find a conclusive solution to the problem of the high light-to-mass ratio previously found for this cluster and its possible top-heavy stellar IMF.Comment: 12 pages, 7 figures, accepted MNRA

Constraining star cluster disruption mechanisms

Star clusters are found in all sorts of environments and their formation and evolution is inextricably linked to the star formation process. Their eventual destruction can result from a number of factors at different times, but the process can be investigated as a whole through the study of the cluster age distribution. Observations of populous cluster samples reveal a distribution following a power law of index approximately -1. In this work we use M33 as a test case to examine the age distribution of an archetypal cluster population and show that it is in fact the evolving shape of the mass detection limit that defines this trend. That is to say, any magnitude-limited sample will appear to follow a dN/dt=1/t, while cutting the sample according to mass gives rise to a composite structure, perhaps implying a dependence of the cluster disruption process on mass. In the context of this framework, we examine different models of cluster disruption from both theoretical and observational standpoints.Comment: To appear in the proceedings of IAU Symposium 266: "Star Clusters: Basic Galactic Building Blocks Throughout Time And Space", eds. R. de Grijs and J. Lepin

A spectroscopic census of the M82 stellar cluster population

We present a spectroscopic study of the stellar cluster population of M82, the archetype starburst galaxy, based primarily on new Gemini-North multi-object spectroscopy of 49 star clusters. These observations constitute the largest to date spectroscopic dataset of extragalactic young clusters, giving virtually continuous coverage across the galaxy; we use these data to deduce information about the clusters as well as the M82 post-starburst disk and nuclear starburst environments. Spectroscopic age-dating places clusters in the nucleus and disk between (7, 15) and (30, 270) Myr, with distribution peaks at ~10 and ~140 Myr respectively. We find cluster radial velocities in the range (-160, 220) km/s (wrt the galaxy centre) and line of sight Na I D interstellar absorption line velocities in (-75, 200) km/s, in many cases entirely decoupled from the clusters. As the disk cluster radial velocities lie on the flat part of the galaxy rotation curve, we conclude that they comprise a regularly orbiting system. Our observations suggest that the largest part of the population was created as a result of the close encounter with M81 ~220 Myr ago. Clusters in the nucleus are found in solid body rotation on the bar. The possible detection of WR features in their spectra indicates that cluster formation continues in the central starburst zone. We also report the potential discovery of two old populous clusters in the halo of M82, aged >8 Gyr. Using these measurements and simple dynamical considerations, we derive a toy model for the invisible physical structure of the galaxy, and confirm the existence of two dominant spiral arms.Comment: Accepted for publication in the Astrophysical Journa

Design of a UDE Frequency Selective Filter to Reject Periodical Disturbances

In this paper a new filter design for the Uncertainty and Disturbance Estimator (UDE) is proposed to reject periodical disturbances when a limited bandwidth is required for the control output. The motivation comes from several applications where the system actuator may introduce a bandwidth limitation, as a result of internal delays, or when the actuator itself is a limited bandwidth closed-loop system. When the traditional UDE approach is applied in these systems, the stability requirements impose a limitation over the effective bandwidth of the UDE filter and therefore disturbances cannot be fully rejected by the filter. In the case where the expected disturbance is periodical with a known fundamental frequency, the proposed UDE filter is designed as a chain of filters to match selected bands of the expected disturbance spectrum and fully reject them while maintaining the desired stability margins. A design example of a power inverter application is investigated and extensive simulation results are provided to verify the proposed UDE filter design

The Snapshot Hubble U-Band Cluster Survey (SHUCS) II. Star Cluster Population of NGC 2997

We study the star cluster population of NGC 2997, a giant spiral galaxy located at 9.5 Mpc and targeted by the Snapshot Hubble U-band Cluster Survey (SHUCS). Combining our U-band imaging from SHUCS with archival BVI imaging from HST, we select a high confidence sample of clusters in the circumnuclear ring and disk through a combination of automatic detection procedures and visual inspection. The cluster luminosity functions in all four filters can be approximated by power-laws with indices of $-1.7$ to $-2.3$. Some deviations from pure power-law shape are observed, hinting at the presence of a high-mass truncation in the cluster mass function. However, upon inspection of the cluster mass function, we find it is consistent with a pure power-law of index $-2.2\pm0.2$ despite a slight bend at $\sim$$2.5\times10^{4}$ M$_{\odot}$. No statistically significant truncation is observed. From the cluster age distributions, we find a low rate of disruption ($\zeta\sim-0.1$) in both the disk and circumnuclear ring. Finally, we estimate the cluster formation efficiency ($\Gamma$) over the last 100 Myr in each region, finding $7\pm2$% for the disk, $12\pm4$% for the circumnuclear ring, and $10\pm3$% for the entire UBVI footprint. This study highlights the need for wide-field UBVI coverage of galaxies to study cluster populations in detail, though a small sample of clusters can provide significant insight into the characteristics of the population.Comment: 31 pages, 9 figures, accepted to the A