The Near-IR-Optical-UV Emission of BL Lacertae Objects

Near--infrared, optical and ultraviolet quasi--simultaneous observations of 11 BL Lacertae objects are reported. For all but one source the dereddened spectral flux distribution in the $8\cdot10^{13}-2\cdot10^{15}$ Hz frequency range can be described by a single power law f$_\nu \propto \nu^{-\alpha}$ with average spectral index $$ = 0.88 $\pm$ 0.42 (standard deviation) plus, where relevant, the contribution of the host galaxy. In most cases the non simultaneous soft X--ray fluxes obtained by the {\it Einstein Observatory} lie on or below the extrapolation of the power law. The results are compared with the average spectral properties of other samples of BL Lacs studied separately in the IR--optical and in the UV bands. The implications for existing models of the objects are shortly discussed.Comment: 23 pages, latex file, 2 figures available as postscript files appended at the end of the latex text file, Ref. S.I.S.S.A. 31/94/

Reclassification of the nearest quasar pair candidate: SDSS J15244+3032 - RXS J15244+3032

We present optical spectroscopy of the nearest quasar pair listed in the 13th edition of the Veron-Cetty & Veron catalogue, i.e. the two quasars SDSS J15244+3032 and RXS J15244+3032 (redshift z~0.27, angular separation ~7 arcsec, and line-of-sight velocity difference ~1900 km/s). This system would be an optimal candidate to investigate the mutual interaction of the host galaxies with ground based optical imaging and spectroscopy. However, new optical data demonstrate that RXS J15244+3032 is indeed a star of spectral type G. This paper includes data gathered with the Asiago 1.82m telescope (Cima Ekar Observatory, Asiago, Italy).Comment: 5 pages, 2 figures, 1 table. Accepted for publication in APS

HST Observations of the Optical Jets of PKS 0521-365, 3C371, and PKS 2201+044

HST observations have led to the discovery of the optical counterpart of the radio jet of PKS 2201+044, and to a detailed analysis of the optical jets of PKS 0521-365 and 3C371. At HST spatial resolution these jets are well resolved, displaying knotty morphologies. When compared with radio maps of appropriate resolution, a clear one-to-one correspondence between optical and radio structures is found, showing that all detected optical structures are indeed related to the radio synchrotron emission. Photometry of the brightest knots shows that the radio-to-optical spectral index and the derived intensity of the equipartition magnetic field are approximately constant along the jet. Thus, present observations suggest that the electron energy distribution does not change significantly all along the jet.Comment: Accepted for publications on the Astrphysical Journal. Contains 14 pages and 5 figure

Evidence for anisotropic motion of the clouds in broad-line regions of BL Lacertae objects

The masses of central massive black holes in BL Lac objects are estimated from their host galaxy absolute magnitude at R-band by using the empirical relation between absolute magnitude of host galaxy and black hole mass. Only a small fraction of BL Lac objects exhibit weak broad-line emission, and we derive the sizes of the broad-line regions (BLRs) in these BL Lac objects from the widths of their broad emission lines on the assumption of the clouds being virilized in BLRs. It is found that the sizes of the BLRs in these sources are usually 2-3 orders of magnitude larger than that expected by the empirical correlation between BLR size and optical luminosity defined by a sample of Seyfert galaxies and quasars. We discuss a variety of possibilities and suggest it may probably be attributed to anisotropic motion of the BLR clouds in these BL Lac objects. If the BLR geometry of these sources is disk-like, the viewing angles between the axis and the line of sight are in the range of 2-12 degrees, which is consistent with the unification schemes.Comment: 5 pages, accepted for publication in Ap

Spatial and temporal variability of disease refuges in an estuary: Implications for the development of resistance

Although the concept of genetic refuge has long been employed in ecological and paleoecological context, it has only rarely been used to identify regions where organisms are protected from diseases that affect the rest of a population. The refuges harbor individuals that have not been exposed to selective mortality and remain susceptible to the disease. They represent a reservoir of susceptibility alleles that can mix with those from resistant survivors of disease and can retard the development of resistance in the population as a whole. Two water-borne protistan parasites affect oysters along the east coast of the United States: Haplosporidium nelsoni (MSX disease) and Perkinsus marinus (dermo disease). Both are sensitive to low salinity and their prevalence is reduced in the upper reaches of estuaries. We investigated the temporal and spatial structure and extent of putative refuges from these diseases in the upper Delaware Bay, USA and their potential to affect the development of resistance in the oyster population. Our results showed that refuges occurred as a continuum of zones, regions where a pathogen (1) was not present; (2) was present, but did not cause observable infections; and (3) caused infection, but neither disease nor mortality. The zones were transient, driven only partly by short-term climatic conditions, and differed according to parasite: H. nelsoni was often not present in the refuges, as inferred by the absence of polymerase chain reaction (PCR) – positive signals on the gills, and when it was present, it did not always cause lethal, or even histologically detectable, infections. In contrast, P. marinus was present in all upper estuary areas sampled, where it caused detectable, although not necessarily lethal-level, infections. Thus, a significant fraction of the oyster population is protected from selective mortality in these refuges even when the parasites are present. An incursion of H. nelsoni into the upper Bay in the 1980s left most of the surviving population highly resistant to MSX disease, although populations in the upper-most reaches are still susceptible. The lack of selection pressure in the refuges likely helps to retard the development of resistance to dermo disease, and theoretically could cause resistance to MSX disease to regress although there is no evidence to date that this has occurred

Suppression of epithelial folding at actomyosin-enriched compartment boundaries downstream of Wingless signalling

Epithelial folding shapes embryos and tissues during development. Here, we investigate the coupling between epithelial folding and actomyosin-enriched compartmental boundaries. The mechanistic relationship between the two is unclear, because actomyosin-enriched boundaries are not necessarily associated with folds. Also, some cases of epithelial folding occur independently of actomyosin contractility. We investigated the shallow folds called parasegment grooves that form at boundaries between anterior and posterior compartments in the early Drosophila embryo. We demonstrate that formation of these folds requires the presence of an actomyosin enrichment along the boundary cell-cell contacts. These enrichments, which require Wingless signalling, increase interfacial tension not only at the level of the adherens junctions but also along the lateral surfaces. We find that epithelial folding is normally under inhibitory control because different genetic manipulations, including depletion of the Myosin II phosphatase Flapwing, increase the depth of folds at boundaries. Fold depth correlates with the levels of Bazooka (Baz), the Par-3 homologue, along the boundary cell-cell contacts. Moreover, Wingless and Hedgehog signalling have opposite effects on fold depth at the boundary that correlate with changes in Baz planar polarity.This work was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) [BB/J010278/1] and the Wellcome Trust [099234/Z/12/Z to B.S.; 099130/Z/12/Z to CAIC]. J.M.U. was supported by a Postdoctoral Fellowship [I-D+i 2008-2011] from Ministerio de Educación, Cultura y Deporte (Spanish Ministry of Education), E.S. by a University of Cambridge Herchel Smith Postdoctoral Fellowship and L.M. by an Engineering and Physical Sciences Research Council (EPSRC) Research Software Engineer Fellowship. Deposited in PMC for immediate release