Dust in the Ionized Medium of the Galaxy: GHRS Measurements of Al III and S III

We present interstellar absorption line measurements of the ions S III and Al III towards six stars using archival Goddard High Resolution Spectrograph data. The ions Al III and S III trace heavily depleted and non-depleted elements, respectively, in ionized gas. We use the photoionization code CLOUDY to derive the ionization correction relating N(Al III)/N(S III) to the gas-phase abundance [Al/S]_i in the ionized gas. For spectral types considered here, the corrections are small and independent of the assumed ionization parameter. Using the results of these photoionization models, we find [Al/S]_i = -1.0 in the ionized gas towards three disk stars. These values of [Al/S]_i (=[Al/H]_i) imply that Al-bearing grains are present in the ionized nebulae around these stars. If the WIM of the Galaxy is photoionized by OB stars, our data for two halo stars imply [Al/S]_i = -0.4 to -0.5 in the WIM and thus the presence of dust grains containing Al in this important phase of the ISM. While photoionization appears to be the most likely origin of the ionization for Al III and S III, we cannot rule out confusion from the presence of hot, collisionally ionized gas along two sightlines. We find that [Al/S]_i in the ionized gas along the six sightlines is anti-correlated with the electron density and average sightline neutral density. The degree of grain destruction in the ionized medium of the Galaxy is not much higher than in the warm neutral medium. The existence of grains in the ionized regions studied here has important implications for the thermal balance of these regions. (Abstract Abridged)Comment: 30 pages including 8 embedded tables and 8 embedded figures. Accepted for publication in the Astrophysical Journa

Distances to Galactic high-velocity clouds. I. Cohen Stream, complex GCP, cloud g1

The high- and intermediate-velocity interstellar clouds (HVCs/IVCs) are tracers of energetic processes in and around the Milky Way. Clouds with near-solar metallicity about one kpc above the disk trace the circulation of material between disk and halo (the Galactic Fountain). The Magellanic Stream consists of gas tidally extracted from the SMC, tracing the dark matter potential of the Milky Way. Several other HVCs have low-metallicity and appear to trace the continuing accretion of infalling intergalactic gas. These assertions are supported by the metallicities (0.1 to 1 solar) measured for about ten clouds in the past decade. Direct measurements of distances to HVCs have remained elusive, however. In this paper we present four new distance brackets, using VLT observations of interstellar \CaII H and K absorption toward distant Galactic halo stars. We derive distance brackets of 5.0 to 11.7 kpc for the Cohen Stream (likely to be an infalling low-metallicity cloud), 9.8 to 15.1 kpc for complex GCP (also known as the Smith Cloud or HVC40-15+100 and with still unknown origin), 1.0 to 2.7 kpc for an IVC that appears associated with the return flow of the Fountain in the Perseus Arm, and 1.8 to 3.8 kpc for cloud g1, which appears to be in the outflow phase of the Fountain. Our measurements further demonstrate that the Milky Way is accreting substantial amounts of gaseous material, which influences the Galaxy's current and future dynamical and chemical evolution.Comment: Accepted by Ap

Interstellar and Circumstellar Optical & Ultraviolet Lines Towards SN1998S

We have observed SN1998S which exploded in NGC3877, with the UES at the WHT and with the E230M echelle of STIS aboard HST. Both data sets were obtained at two seperate epochs. From our own Galaxy we detect interstellar absorption lines of CaII, FeII, MgI, and probably MnII from the edge of the HVC Complex M. We derive gas-phase abundances which are very similar to warm disk clouds in the local ISM, which we believe argues against the HVC material having an extragalactic origin. At the velocity of NGC3877 we detect interstellar MgI, MgII, MnII, CaII, & NaI. Surprisingly, one component is seen to increase by a factor of ~1 dex in N(NaI) and N(MgI) between the two epochs over which the data were taken. Unusually, our data also show narrow Balmer, HeI, and metastable FeII P-Cygni profiles, with a narrow absorption component superimposed on the bottom of the profile's absorption trough. Both the broad and narrow components of the optical lines are seen to increase substantially in strength between the two epochs. Most of the low-ionization absorption can be understood in terms of gas co-rotating with the disk of NGC 3877, providing the SN is at the back of an HI disk with a similar thickness to that of our own Galaxy. However, the variable absorption components, and the classic P-Cygni emission profiles, most likely arise in slow-moving circumstellar outflows originating from the red supergiant progenitor of SN1998S. [Abridged.]Comment: Accepted by ApJ, 26 pages including 9 figure

Highly-Ionized High-Velocity Gas in the Vicinity of the Galaxy

We report the results of an extensive FUSE study of high velocity OVI absorption along 102 complete sight lines through the Galactic halo. The high velocity OVI traces a variety of phenomena, including tidal interactions with the Magellanic Clouds, accretion of gas, outflow from the Galactic disk, warm/hot gas interactions in a highly extended Galactic corona, and intergalactic gas in the Local Group. We identify 85 high velocity OVI features at velocities of -500 < v(LSR) < +500 km/s along 59 of the 102 sight lines. Approximately 60% of the sky (and perhaps as much as 85%) is covered by high velocity H+ associated with the high velocity OVI. Some of the OVI is associated with known high velocity HI structures (e.g., the Magellanic Stream, Complexes A and C), while some OVI features have no counterpart in HI 21cm emission. The smaller dispersion in the OVI velocities in the GSR and LGSR reference frames compared to the LSR is necessary (but not conclusive) evidence that some of the clouds are extragalactic. Most of the OVI cannot be produced by photoionization, even if the gas is irradiated by extragalactic background radiation. Collisions in hot gas are the primary OVI ionization mechanism. We favor production of some of the OVI at the boundaries between warm clouds and a highly extended [R > 70 kpc], hot [T > 10^6 K], low-density [n < 10^-4 cm^-3] Galactic corona or Local Group medium. A hot Galactic corona or Local Group medium and the prevalence of high velocity OVI are consistent with predictions of galaxy formation scenarios. Distinguishing between the various phenomena producing high velocity OVI will require continuing studies of the distances, kinematics, elemental abundances, and physical states of the different types of high velocity OVI features found in this study. (abbreviated)Comment: 78 pages of text/tables + 31 figures, AASTeX preprint format. All figures are in PNG format due to astro-ph space restrictions. Bound copies of manuscript and two accompanying articles are available upon request. Submitted to ApJ

Distribution and Kinematics of O VI in the Galactic Halo

FUSE spectra of 100 extragalactic objects are analyzed to obtain measures of O VI absorption along paths through the Milky Way thick disk/halo. Strong O VI absorption over the approximate velocity range from -100 to 100 km/s reveals a widespread but highly irregular distribution of thick disk O VI, implying the existence of substantial amounts of hot gas with T ~ 3x10^5 K in the Milky Way halo. Large irregularities in the distribution of the absorbing gas are found to be similar over angular scales extending from less than one to 180 degrees, indicating a considerable amount of small and large scale structure in the gas. The overall distribution of Galactic O VI is not well described by a symmetrical plane-parallel layer of patchy O VI absorption. The simplest departure from such a model that provides a reasonable fit to the observations is a plane-parallel patchy absorbing layer with a scale height of 2.3 kpc, and a 0.25 dex excess of O VI in the northern Galactic polar region. The O VI absorption has a Doppler parameter b = 30 to 99 km/s, with an average value of 60 km/s . Thermal broadening alone cannot explain the large observed profile widths. The average O VI absorption velocities toward high latitude objects range from -46 to 82 km/s, with a sample average of 0 km/s and a standard deviation of 21 km/s. O VI associated with the thick disk moves both toward and away from the plane with roughly equal frequency. A combination of models involving the radiative cooling of hot fountain gas, the cooling of supernova bubbles in the halo, and the turbulent mixing of warm and hot halo gases is required to explain the presence of O VI and other highly ionized atoms found in the halo. (abbreviated)Comment: 70 pages, single-spaced, PDF format. Bound copies of this manuscript and two accompanying articles are available upon request. Submitted to ApJ

The 0.5MJ transiting exoplanet WASP-13b

We report the discovery of WASP-13b, a low-mass M_{\rm p} = 0.46 ^_~M_J transiting exoplanet with an orbital period of 4.35298 $\pm$ 0.00004 days. The transit has a depth of 9 mmag, and although our follow-up photometry does not allow us to constrain the impact parameter well (0 < b < 0.46), with radius in the range $R_{\rm p}$ ~ 1.06-1.21 RJ the location of WASP-13b in the mass-radius plane is nevertheless consistent with H/He-dominated, irradiated, low core mass and core-free theoretical models. The G1V host star is similar to the Sun in mass (M__ ~M_{\odot}) and metallicity ([M/H] = 0.0$\pm$0.2), but is possibly older ( 8.5^_{\rm -4.9} Gyr)

An Accurate Distance to High-Velocity Cloud Complex C

We report an accurate distance of d = 10+/-2.5kpc to the high-velocity cloud Complex C. Using high signal-to-noise Keck/HIRES spectra of two horizontal-branch stars, we have detected CaII K absorption lines from the cloud. Significant non-detections toward a further 3 stars yield robust lower distance limits. The resulting HI mass of Complex C is 4.9^{+2.8}_{-2.2} x 10^6 Msun; a total mass of 8.2^{+4.6}_{-2.6} x 10^6 Msun is implied, after corrections for helium and ionization. At 10kpc, Complex C has physical dimensions 3x15 kpc, and if it is as thick as it is wide, then the average density is log ~ -2.5. We estimate the contribution of Complex C to the mass influx may be as high as ~0.14 Msun/yr.Comment: Resubmitted to ApJ. 8 figure

New periodic variable stars coincident with ROSAT sources discovered using SuperWASP

We present optical lightcurves of 428 periodic variable stars coincident with ROSAT X-ray sources, detected using the first run of the SuperWASP photometric survey. Only 68 of these were previously recognised as periodic variables. A further 30 of these objects are previously known pre-main sequence stars, for which we detect a modulation period for the first time. Amongst the newly identified periodic variables, many appear to be close eclipsing binaries, their X-ray emission is presumably the result of RS CVn type behaviour. Others are probably BY Dra stars, pre-main sequence stars and other rapid rotators displaying enhanced coronal activity. A number of previously catalogued pulsating variables (RR Lyr stars and Cepheids) coincident with X-ray sources are also seen, but we show hat these are likely to be misclassifications. We identify four objects which are probable low mass eclipsing binary stars, based on their very red colour and light curve morphology

A FUSE Survey of Molecular Hydrogen in Intermediate-Velocity Clouds in the Milky Way Halo

Far Ultraviolet Spectroscopic Explorer (FUSE) data is used to investigate the molecular hydrogen (H_2) content of intermediate-velocity clouds (IVCs) in the lower halo of the Milky Way. We analyze interstellar absorption towards 56 (mostly extragalactic) background sources to study H_2 absorption in the Lyman- and Werner bands in 61 IVC components at H I column densities >10^19 cm^-2. For data with good S/N (~9 per resolution element and higher), H_2 in IVC gas is convincingly detected in 14 cases at column densities varying between ~10^14 and ~10^17 cm^-2. We find an additional 17 possible H_2 detections in IVCs in FUSE spectra with lower S/N. The molecular hydrogen fractions, f, vary between 10^-6 and 10^-3, implying a dense, mostly neutral gas phase that is probably related to the Cold Neutral Medium (CNM) in these clouds. If the H_2 stays in formation-dissociation equlibrium, the CNM in these clouds can be characterized by compact (D~0.1 pc) filaments with volume densities on the order of n_H~30 cm^-3. The relatively high detection rate of H_2 in IVC gas implies that the CNM in these clouds is ubiquitous. More dense regions with much higher molecular fractions may exist, but it would be difficult to detect them in absorption because of their small size.Comment: 36 pages, 11 figures; accepted for publication in Ap

Intellectual disability, sensation and thinking through affect

The WASP consortium is conducting an ultra-wide field survey of stars between 8–15 mag from both hemispheres. Our primary science goal is to detect extra-solar ‘hot-Jupiter’-type planets that eclipse (or transit) bright host stars and for which further detailed investigation will be possible. We summarize the design of the SuperWASP instruments and describe the first results from our northern station SW-N, sited in La Palma, Canary Islands. Our second station, which began operations this year, is located at the South African Astronomical Observatory. Between April and September, 2004, SW-N continuously observed ~6.7 million stars. The consortium's custom-written, fully automated data reduction pipeline has been used to process these data, and the information is now stored in the project archive, held by the Leicester database and archive service (LEDAS). We have applied a sophisticated, automated algorithm to identify the low-amplitude (~0.01 mag), brief (~few hours) signatures of transiting exoplanets. In addition, we have assessed each candidate in the light of all available catalogue information in order to reject data artefacts and astrophysical false positive detections. The highest priority candidates are currently being subjected to further observations in order to select the true planets. Once the exoplanets are confirmed, a host of exciting opportunities are open to us. In this paper, we describe two techniques that exploit the transits in order to detect other objects within the same system. The first involves determining precise epochs for a sequence of transit events in order to detect the small timing variations caused by the gravitational pull of other planets in the same system. The second method employs ultra-high precision photometry of the transits to detect the deviations caused by the presence of exoplanetary moons. Both of these techniques are capable of detecting objects the size of terrestrial planets