The 21-cm line emission from a 7x6deg^2^ region east of and adjoining the Small Magellanic Cloud (SMC) has been observed with the Australia Telescope Compact Array and the Parkes telescopes. This region represents the westernmost part of the Magellanic Bridge, a gas-rich tail extending ~14{deg} to the Large Magellanic Cloud. A rich and complex neutral hydrogen (HI) structure containing shells, bubbles and filaments is revealed. On the larger scale, the HI of the Bridge is organized into two velocity components. This bimodality, which appears to originate in the SMC, converges to a single velocity component within the observed region. A census of shell-like structures suggests a shell population with characteristics similar to that of the SMC.
Stellar variability in the near-infrared (NIR) remains largely unexplored. The exploitation of public science archives with data-mining methods offers a perspective for a time-domain exploration of the NIR sky. We perform a comprehensive search for stellar variability using the optical-NIR multiband photometric data in the public Calibration Database of the WFCAM Science Archive (WSA), with the aim of contributing to the general census of variable stars and of extending the current scarce inventory of accurate NIR light curves for a number of variable star classes.
The ionizing continuum from active galactic nuclei is fundamental for interpreting their broad emission lines and understanding their impact on the surrounding gas. Furthermore, it provides hints on how matter accretes on to supermassive black holes. Using Hubble Space Telescope's Wide Field Camera 3, we have constructed the first stacked ultraviolet (rest-frame wavelengths 600-2500{AA}) spectrum of 53 luminous quasars at z=~2.4, with a state-of-the-art correction for the intervening Lyman forest and Lyman continuum absorption. The continuum slope (f_{nu}_{prop.to}{nu}^{alpha}{nu}^) of the full sample shows a break at ~912{AA} with spectral index {alpha}_{nu}_=-0.61+/-0.01 at {lambda}>912{AA} and a softening at shorter wavelengths ({alpha}_{nu}_=-1.70+/-0.61 at {lambda}<=912{AA}). Our analysis proves that a proper intergalactic medium absorption correction is required to establish the intrinsic continuum emission of quasars. We interpret our average ultraviolet spectrum in the context of photoionization, accretion disc models, and quasar contribution to the ultraviolet background. We find that observed broad line ratios are consistent with those predicted assuming an ionizing slope of {alpha}_ion_=-2.0, similar to the observed ionizing spectrum in the same wavelength range. The continuum break and softening are consistent with accretion disc plus X-ray corona models when black hole spin is taken into account. Our spectral energy distribution yields a 30 per cent increase to previous estimates of the specific quasar emissivity, such that quasars may contribute significantly to the total specific Lyman limit emissivity estimated from the Ly{alpha} forest at z<3.2.
We present the results of an optical multi-band survey for low-mass pre-main sequence (PMS) stars and young brown dwarfs (BDs) in the Chamaeleon II (Cha II) dark cloud. This survey constitutes the complementary optical data to the c2d Spitzer Legacy survey in Cha II.
We have carried out Wide Field Planetary Camera 2 (WFPC2) F160BW, F555W, and F656N imaging of four young populous clusters: NGC 330, in the Small Magellanic Cloud, and NGC 1818, 2004, and 2100, in the Large Magellanic Cloud. We report photometric results for these four clusters, including identification using photometric colors of the cluster Be star population. We present theoretical WFPC2 and broadband colors and bolometric corrections for LMC and SMC metallicities. The use of the far-UV F160BW filter enables accurate determination of the effective temperatures for stars in the vicinity of the main-sequence turnoff and on the unevolved main sequence.
We present deep VI photometry of stars in the globular cluster M5 (NGC 5904) based on images taken with the Hubble Space Telescope. The resulting color-magnitude diagram reaches below V~7mag, revealing the upper 2-3mag of the white dwarf cooling sequence and main-sequence stars 8mag and more below the turnoff.
The Wisconsin H-Alpha Mapper has been designed to produce a survey of H-Alpha emission from the interstellar medium (ISM) over the entire northern sky. The instrument combines a 0.6 meter telescope and a dual-etalon 15cm Fabry-Perot spectrometer. In the primary spectral mode, an exposure captures a 200km/s spectral region with 8-12km/s velocity resolution from a one-degree beam on the sky. With a large-aperture design and modern CCD technology, WHAM can detect Galactic emission as faint as 0.05 Rayleighs in a 30 second exposure. For gas at 10000K, this observed intensity corresponds to an emission measure of about 0.1cm^-6^pc, more than 10 million times fainter than the Orion Nebula.
In a framework where galaxies form hierarchically, extended stellar haloes are predicted to be an ubiquitous feature around Milky Way-like galaxies and to consist mainly of the shredded stellar component of smaller galactic systems. The type of accreted stellar systems are expected to vary according to the specific accretion and merging history of a given galaxy, and so is the fraction of stars formed in-situ versus accreted. Analysis of the chemical properties of Milky Way halo stars out to large Galactocentric radii can provide important insights into the properties of the environment in which the stars that contributed to the build-up of different regions of the Milky Way stellar halo formed. In this work we focus on the outer regions of the Milky Way stellar halo, by determining chemical abundances of halo stars with large present-day Galactocentric distances, >15 kpc. The data-set we acquired consists of high resolution HET/HRS, Magellan/MIKE and VLT/UVES spectra for 28 red giant branch stars covering a wide metallicity range, -3.1<[Fe/H]<-0.6. We show that the ratio of alpha-elements over Fe as a function of [Fe/H] for our sample of outer halo stars is not dissimilar from the pattern shown by MW halo stars from solar neighborhood samples. On the other hand, significant differences appear at [Fe/H]>-1.5 when considering chemical abundance ratios such as [Ba/Fe], [Na/Fe], [Ni/Fe], [Eu/Fe], [Ba/Y]. Qualitatively, this type of chemical abundance trends are observed in massive dwarf galaxies, such as Sagittarius and the Large Magellanic Cloud. This appears to suggest a larger contribution in the outer halo of stars formed in an environment with high initial star formation rate and already polluted by asymptotic giant branch stars with respect to inner halo samples.
