Search

This paper presents a component-level comparison of the polarized v = 1 J = 1-0, v = 2 J = 1-0 and v = 1 J = 2-1 SiO maser emission towards the supergiant star VY CMa at milliarcsecond-scale, as observed using the Very Long Baseline Array at λ = 7 and 3 mm. An earlier paper considered overall maser morphology and constraints on SiO maser excitation and pumping derived from these data. The goal of the current paper is to use the measured polarization properties of individual co-spatial components detected across multiple transitions to provide constraints on several competing theories for the transport of polarized maser emission. This approach minimizes the significant effects of spatial blending. We present several diagnostic tests designed to distinguish key features of competing theoretical models for maser polarization. The number of coincident features is limited by sensitivity however, particularly in the v = 1 J = 2-1 transition at 86 GHz, and deeper observations are needed. Preliminary conclusions based on the current data provide some support for: (i) spin-independent solutions for linear polarization; (ii) the influence of geometry on the distribution of fractional linear polarization with intensity; and, (iii) π/2 rotations in linear polarization position angle arising from transitions across the Van Vleck angle (sin 2θ = 2/3) between the maser line of sight and magnetic field. There is weaker evidence for several enumerated non-Zeeman explanations for circular polarization. The expected 2:1 ratio in circular polarization between J = 1-0 and J = 2-1 predicted by standard Zeeman theory cannot unfortunately be tested conclusively due to insufficient coincident components. [ABSTRACT FROM AUTHOR]

Our closest neighbours, the Local Group dwarf spheroidal (dSph) galaxies, are extremely quiescent and dim objects, where thermal and non-thermal diffuse emissions lack, so far, of detection. In order to possibly study the dSph interstellar medium, deep observations are required. They could reveal non-thermal emissions associated with the very low level of star formation, or to particle dark matter annihilating or decaying in the dSph halo. In this work, we employ radio observations of six dSphs, conducted with the Australia Telescope Compact Array in the frequency band 1.1-3.1 GHz, to test the presence of a diffuse component over typical scales of few arcmin and at an rms sensitivity below 0.05 mJy beam-1.We observed the dSph fields with both a compact array and long baselines. Short spacings led to a synthesized beam of about 1 arcmin and were used for the extended emission search. The high-resolution data mapped background sources, which in turn were subtracted in the short-baseline maps, to reduce their confusion limit. We found no significant detection of a diffuse radio continuum component. After a detailed discussion on the modelling of the cosmic ray (CR) electron distribution and on the dSph magnetic properties, we present bounds on several physical quantities related to the dSphs, such that the total radio flux, the angular shape of the radio emissivity, the equipartition magnetic field, and the injection and equilibrium distributions of CR electrons. Finally, we discuss the connection to far-infrared and X-ray observations. [ABSTRACT FROM AUTHOR]

Dwarf spheroidal (dSph) galaxies are key objects in near-field cosmology, especially in connection to the study of galaxy formation and evolution at small scales. In addition, dSphs are optimal targets to investigate the nature of dark matter. However, while we begin to have deep optical photometric observations of the stellar population in these objects, little is known so far about their diffuse emission at any observing frequency, and hence on thermal and non-thermal plasma possibly residing within dSphs. In this paper, we present deep radio observations of six local dSphs performed with the Australia Telescope Compact Array (ATCA) at 16 cm wavelength. We mosaicked a region of radius of about 1 deg around three 'classical' dSphs, Carina, Fornax, and Sculptor, and of about half of degree around three 'ultrafaint' dSphs, BootesII, Segue2, and Hercules. The rms noise level is below 0.05 mJy for all the maps. The restoring beams full width at half-maximum ranged from 4.2 arcsec × 2.5 arcsec to 30.0 arcsec × 2.1 arcsec in the most elongated case. A catalogue including the 1392 sources detected in the six dSph fields is reported. The main properties of the background sources are discussed, with positions and fluxes of brightest objects compared with the FIRST, NVSS, and SUMSS observations of the same fields. The observed population of radio emitters in these fields is dominated by synchrotron sources. We compute the associated source number counts at 2 GHz down to fluxes of 0.25 mJy, which prove to be in agreement with AGN count models. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the physical state of H i absorbing gas at low redshift ( z = 0.25) using a subset of cosmological, hydrodynamic simulations from the OverWhelmingly Large Simulations project, focusing in particular on broad ( [ABSTRACT FROM AUTHOR]

We investigate the kinematic properties of gas and galaxies in the Local Group (LG) using high-resolution simulations performed by the hestia (High-resolution Environmental Simulations of The Immediate Area) collaboration. Our simulations include the correct cosmography surrounding LG-like regions consisting of two main spiral galaxies of ∼1012 M⊙, their satellites and minor isolated galaxies, all sharing the same large-scale motion within a volume of a few Mpc. We characterize the gas and galaxy kinematics within the simulated LGs, from the perspective of the Sun, to compare with observed trends from recent HST /COS absorption-line observations and LG galaxy data. To analyse the velocity pattern of LG gas and galaxies seen in the observational data, we build sky maps from the local standard of rest, and the Galactic and LG barycentre frames. Our findings show that the establishment of a radial velocity dipole at low/high latitudes, near the preferred barycentre direction, is a natural outcome of simulation kinematics for material outside the Milky Way virial radius after removing Galaxy rotation when the two main LG galaxies are approaching. Our results favour a scenario where gas and galaxies stream towards the LG barycentre producing a velocity dipole resembling observations. While our study shows in a qualitative way the global matter kinematics in the LG as part of its ongoing assembly, quantitative estimates of gas-flow rates and physical conditions of the LG gas have to await a more detailed modelling of the ionization conditions, which will be presented in a follow-up paper. [ABSTRACT FROM AUTHOR]

ABSTRACT We investigate the origin and physical properties of O vi absorbers at low redshift ( z= 0.25) using a subset of cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations (OWLS) project. Intervening O vi absorbers are believed to trace shock-heated gas in the warm-hot intergalactic medium (WHIM) and may thus play a key role in the search for the missing baryons in the present-day Universe. When compared to observations, the predicted distributions of the different O vi line parameters (column density , Doppler parameter , rest equivalent width Wr) from our simulations exhibit a lack of strong O vi absorbers, a discrepancy that has also been found by Oppenheimer & Davé. This suggests that physical processes on subgrid scales (e.g. turbulence) may strongly influence the observed properties of O vi systems. We find that the intervening O vi absorption arises mainly in highly metal enriched ( 10−1≪ Z/Z⊙≲ 1) gas at typical overdensities of 1 ≪ρ/〈ρ〉≲ 102. One-third of the O vi absorbers in our simulation are found to trace gas at temperatures T < 105 K, while the rest arises in gas at higher temperatures, most of them around T= 105.3 ± 0.5 K. These temperatures are much higher than inferred by Oppenheimer & Davé, probably because that work did not take the suppression of metal-line cooling by the photoionizing background radiation into account. While the O vi resides in a similar region of ( ρ, T)-space as much of the shock-heated baryonic matter, the vast majority of this gas has a lower metal content and does not give rise to detectable O vi absorption. As a consequence of the patchy metal distribution, O vi absorbers in our simulations trace only a very small fraction of the cosmic baryons ( <2 per cent) and the cosmic metals. Instead, these systems presumably trace previously shock-heated, metal-rich material from galactic winds that is now mixing with the ambient gas and cooling. The common approach of comparing O vi and H i column densities to estimate the physical conditions in intervening absorbers from QSO observations may be misleading, as most of the H i (and most of the gas mass) is not physically connected with the high-metallicity patches that give rise to the O vi absorption. [ABSTRACT FROM AUTHOR]

The pervasive presence of warm gas in galaxy haloes suggests that the circumgalactic medium (CGM) is multiphase in its ionization structure and complex in its kinematics. Some recent state-of-the-art cosmological galaxy simulations predict an azimuthal dependence of CGM metallicities. We investigate the presence of such a trend by analysing the distribution of gas properties in the CGM around 47 z < 0.7 galaxies from the Multiphase Galaxy Halos Survey determined using a cloud-by-cloud, multiphase, ionization modelling approach. We identify three distinct populations of absorbers: cool clouds (T ∼ 104.1 K) in photoionization equilibrium, warm–hot collisionally ionized clouds (T ∼ 104.5–105 K) affected by time-dependent photoionization, and hotter clouds (T ∼ 105.4–106 K) with broad O  vi and Ly α absorption consistent with collisional ionization. We find that fragmentation can play a role in the origin of cool clouds, that warm–hot clouds are out of equilibrium due to rapid cooling, and that hotter clouds are representative of virialized halo gas in all but the lowest mass galaxies. The metallicities of clouds do not depend on the azimuthal angle or other galaxy properties for any of these populations. At face value, this disagrees with the simplistic model of the CGM with bipolar outflows and cold-mode planar accretion. However, the number of clouds per sightline is significantly larger close to the minor and major axes. This implies that the processes of outflows and accretion are contributing to these CGM cloud populations, and our sightlines are probing gas of mixed origins at all azimuthal angles in these low-redshift galaxies. [ABSTRACT FROM AUTHOR]

Isotopic ratios in water vapour carry important information about the water reservoir on Mars. Localized variations in these ratios can inform us about the water cycle and surface–atmosphere exchanges. On the other hand, the global isotopic composition of the atmosphere carries the imprints of the long-term fractionation, providing crucial information about the early water reservoir and its evolution throughout history. Here, we report the analysis of measurements of the D/H and 18O/16O isotopic ratios in water vapour in different seasons (L S = 15○, 127○, 272○, and 305○) made with the Echelon-Cross-Echelle Spectrograph (EXES) aboard the Stratospheric Observatory for Infrared Astronomy (SOFIA). These measurements, free of telluric absorption, provide a unique tool for constraining the global isotopic composition of Martian water vapour. We find the maximum planetary D/H ratio in our observations during the northern summer (D/H = 5.2 ± 0.2 with respect to the Vienna Standard Mean Ocean Water, VSMOW) and to exhibit relatively small variations throughout the year (D/H = 5.0 ± 0.2 and 4.3 ± 0.4 VSMOW during the northern winter and spring, respectively), which are to first order consistent though noticeably larger than the expectations from condensation-induced fractionation. Our measurements reveal the annually averaged isotopic composition of water vapour to be consistent with D/H = 5.0 ± 0.2 and 18O/16O = 1.09 ± 0.08 VSMOW. In addition, based on a comparison between the SOFIA/EXES measurements and the predictions from a Global Climate Model, we estimate the D/H in the northern polar ice cap to be |$\sim\!{5}~{{\ \rm per\ cent}}$| larger than that in the atmospheric reservoir (D/Hice = 5.3 ± 0.3 VSMOW). [ABSTRACT FROM AUTHOR]

Recent observations have revealed remarkable insights into the gas reservoir in the circumgalactic medium (CGM) of galaxy haloes. In this paper, we characterize the gas in the vicinity of Milky Way and Andromeda analogues in the hestia (High resolution Environmental Simulations of The Immediate Area) suite of constrained Local Group (LG) simulations. The hestia suite comprise of a set of three high-resolution arepo -based simulations of the LG, run using the Auriga galaxy formation model. For this paper, we focus only on the z = 0 simulation data sets and generate mock skymaps along with a power spectrum analysis to show that the distributions of ions tracing low-temperature gas (H  i and Si  iii) are more clumpy in comparison to warmer gas tracers (O  vi , O  vii , and O  viii). We compare to the spectroscopic CGM observations of M31 and low-redshift galaxies. hestia underproduces the column densities of the M31 observations, but the simulations are consistent with the observations of low-redshift galaxies. A possible explanation for these findings is that the spectroscopic observations of M31 are contaminated by gas residing in the CGM of the Milky Way. [ABSTRACT FROM AUTHOR]

Stellar intensity interferometers correlate photons within their coherence time and could overcome the baseline limitations of existing amplitude interferometers. Intensity interferometers do not rely on phase coherence of the optical elements and thus function without high-grade optics and light combining delay lines. However, the coherence time of starlight observed with realistic optical filter bandwidths (⁠|$\gt {0.1}\, {\rm nm}$|⁠) is usually much smaller than the time resolution of the detection system (⁠|$\gt {10}\, {\rm ps}$|⁠), resulting in a greatly reduced correlation signal. Reaching high signal-to-noise ratio in a reasonably short measurement time can be achieved in different ways: either by increasing the time resolution, which increases the correlation signal height, or by increasing the photon rate, which decreases statistical uncertainties of the measurement. We present laboratory measurements employing both approaches and directly compare them in terms of signal-to-noise ratio. A high-time-resolution interferometry setup designed for small-to-intermediate-sized optical telescopes and thus lower photon rates (diameters |$\lt \,$| some metres) is compared to a setup capable of measuring high photon rates, which is planned to be installed at Cherenkov telescopes with dish diameters of |$\gt {10}\, {\rm m}$|⁠. We use a xenon lamp as a common light source simulating starlight. Both setups measure the expected correlation signal and work at the expected shot-noise limit of statistical uncertainties for measurement times between 10 min and 23 h. We discuss the quantitative differences in the measurement results and give an overview of suitable operation regimes for each of the interferometer concepts. [ABSTRACT FROM AUTHOR]

Spectroscopic observations play essential roles in astrophysics. They are crucial for determining physical parameters in our Universe, providing information about the chemistry of various astronomical environments. The proper execution of the spectroscopic analysis requires accounting for all the physical effects that are compatible to the signal-to-noise ratio. We find in this paper the influence on spectroscopy from the atomic/ground state alignment owing to anisotropic radiation and modulated by interstellar magnetic field, has significant impact on the study of interstellar gas. In different observational scenarios, we comprehensively demonstrate how atomic alignment influences the spectral analysis and provide the expressions for correcting the effect. The variations are even more pronounced for multiplets and line ratios. We show the variation of the deduced physical parameters caused by the atomic alignment effect, including alpha-to-iron ratio ([X/Fe]) and ionization fraction. Synthetic observations are performed to illustrate the visibility of such effect with current facilities. A study of Photodissociation regions in ρ Ophiuchi cloud is presented to demonstrate how to account for atomic alignment in practice. Our work has shown that due to its potential impact, atomic alignment has to be included in an accurate spectroscopic analysis of the interstellar gas with current observational capability. [ABSTRACT FROM AUTHOR]

We present high spectral resolution mid-IR observations of SiS towards the C-rich AGB star IRC + 10216 carried out with the Texas Echelon-cross-Echelle Spectrograph mounted on the NASA Infrared Telescope Facility. We have identified 204 ro-vibrational lines of 28Si32S, 26 of 29Si32S, 20 of 28Si34S, and 15 of 30Si32S in the frequency range 720-790 cm-1. These lines belong to bands v = 1-0, 2-1, 3-2, 4-3, and 5-4, and involve rotational levels with Jlow ≲ 90. About 30 per cent of these lines are unblended or weakly blended and can be partially or entirely fitted with a code developed to model the mid-IR emission of a spherically symmetric circumstellar envelope composed of expanding gas and dust. The observed lines trace the envelope at distances to the star ≲35R* (≃0.7 arcsec). The fits are compatible with an expansion velocity of 1 + 2.5(r/R* - 1) km s-1 between 1 and 5R*, 11 kms -1 between 5 and 20R*, and 14.5 km s -1 outwards. The derived abundance profile of 28Si32S with respect to H2 is 4.9 x 10-6 between the stellar photosphere and 5R*, decreasing linearly down to 1.6 x 10-6 at 20R* and to 1.3 x 10-6 at 50R*. 28Si32S seems to be rotationally under local thermodynamic equilibrium (LTE) in the region of the envelope probed with our observations and vibrationally out of LTE in most of it. There is a red-shifted emission excess in the 28Si32 S lines of band v = 1-0 that cannot be found in the lines of bands v = 2-1,3-2,4-3, and 5-4. This excess could be explained by an enhancement of the vibrational temperature around 20R* behind the star. The derived isotopic ratios 28Si/29Si, and 32S/34S are 17 and 14, compatible with previous estimates. [ABSTRACT FROM AUTHOR]

We present high-resolution mid-infrared spectra of M dwarfs. The mid-infrared region of the spectra of cool low-mass stars contains pure rotational water vapour transitions that may provide us with a new methodology in the determination of the effective temperatures for low-mass stars. We identify and assign water transitions in these spectra and determine how sensitive each pure rotational water transition is to small (25 K) changes in effective temperature. We find that, of the 36 confirmed and assigned pure rotational water transitions, at least 10 should be sensitive enough to be used as temperature indicators. [ABSTRACT FROM AUTHOR]

The environment of high-redshift galaxies is characterized by both wind-driven outflowing gas and gravitationally infalling streams. To investigate such galaxy–IGM interplay we have generated synthetic optical absorption line spectra piercing the volume surrounding a starbursting analogue of a Lyman-break galaxy selected in a z≈ 3 output from a smoothed particle hydrodynamics simulation, including a detailed treatment of mechanical feedback from winds. Distributions for several observable species (H i, C iii, C iv, Si ii, Si iii, Si iv, O vi, O vii and O viii) have been derived by post-processing the simulation outputs. The hot-wind material is characterized by the presence of high-ionization species such as O vi, O vii and O viii (the latter two observable only in X-ray bands); the colder infalling streams can be instead identified by the combined presence of Si ii, Si iii and C iii optical absorption together with O vi that surrounds the cooler gas clumps. However, both line profile and pixel optical depth analysis of the synthetic spectra show that the intergalactic filament in which the wind-blowing galaxy is embedded produces absorption signatures that closely mimic those of the wind environment. We conclude that it may be difficult to clearly identify wind-blowing galaxies and their complex gaseous environment at high redshift in optical QSO absorption-line spectra based solely on the observed ion-absorption patterns. [ABSTRACT FROM AUTHOR]

We present a new method aimed at improving the efficiency of component by component ionization modelling of intervening quasar absorption-line systems. We carry out cloud-by-cloud, multiphase modelling making use of cloudy and Bayesian methods to extract physical properties from an ensemble of absorption profiles. Here, as a demonstration of method, we focus on four weak, low-ionization absorbers at low redshift, because they are multiphase but relatively simple to constrain. We place errors on the inferred metallicities and ionization parameters for individual clouds, and show that the values differ from component to component across the absorption profile. Our method requires user input on the number of phases and relies on an optimized transition for each phase, one observed with high resolution and signal-to-noise ratio. The measured Doppler parameter of the optimized transition provides a constraint on the Doppler parameter of H  i , thus providing leverage in metallicity measurements even when hydrogen lines are saturated. We present several tests of our methodology, demonstrating that we can recover the input parameters from simulated profiles. We also consider how our model results are affected by which radiative transitions are covered by observations (for example, how many H  i transitions) and by uncertainties in the b parameters of optimized transitions. We discuss the successes and limitations of the method, and consider its potential for large statistical studies. This improved methodology will help to establish direct connections between the diverse properties derived from characterizing the absorbers and the multiple physical processes at play in the circumgalactic medium. [ABSTRACT FROM AUTHOR]

Average flow patterns of ions around comet 67P detected by the RPC-ICA instrument onboard Rosetta are presented both as a time series and as a spatial distribution of the average flow in the plane perpendicular to the comet – Sun direction (Y–Z plane in the coordinate systems used). Cometary ions in the energy range up to 60 eV flow radially away from the nucleus in the Y–Z plane, irrespective of the direction of the magnetic field, throughout the mission. These ions may however be strongly affected by the spacecraft potential, the uncertainty due to this is briefly discussed. Inside the solar wind ion cavity and in the periods just before and after, the cometary pick up ions moving antisunward are deflected against the inferred solar wind electric field direction. This is opposite to what is observed for lower levels of mass-loading. These pick up ions are behaving in a similar way to the solar wind ions and are deflected due to mass-loading. A spatial asymmetry can be seen in the observations of deflected pick up ions, with motion against the electric field primarily within a radius of 200 km of the nucleus and also in the negative electric field hemisphere. Cometary ions observed by RPC-ICA typically move in the antisunward direction throughout the mission. These are average patterns, full-resolution data show very much variability. [ABSTRACT FROM AUTHOR]

We present an analysis of the evolution of circumstellar dust and molecules in the environment of the very late thermal pulse object V4334 Sgr (Sakurai's object) over an ∼20-yr period, drawing on ground-, airborne-, and space-based infrared photometry and spectroscopy. The dust emission, which started in 1997, resembles a blackbody that cooled from ∼1200 K in 1998 August to ∼180 K in 2016 July. The dust mass, assuming amorphous carbon, was ∼5 × 10−10 M⊙ in 1998 August, and we estimate that the total dust mass was ∼2 × 10−5 M⊙ by ∼2016. The appearance of a near-infrared excess in 2008 suggests that a new episode of (or renewed) mass-loss began then. We infer lower limits on the bolometric luminosity of the embedded star from that of the dust shell, which rose to ∼16 000 L⊙ before declining to ∼3000 L⊙. There is evidence for weak 6–7  μ m absorption, which we attribute to hydrogenated amorphous carbon formed in material ejected by Sakurai's object during a mass ejection phase that preceded the 1997 event. We detect small hydrocarbon and other molecules in the spectra, and trace the column densities in hydrogen cyanide (HCN) and acetylene (C2H2). We use the former to determine the 12C/13C ratio to be 6.4 ± 0.7, 14 times smaller than the Solar system value. [ABSTRACT FROM AUTHOR]

We have combined spectroscopic and photometric data from the Sloan Digital Sky Survey with 1.4 GHz radio observations, conducted as part of the Stripe 82 1–2 GHz Snapshot Survey using the Karl G. Jansky Very Large Array, which covers ∼100 sq deg, to a flux limit of 88  $$\mu$$ Jy rms. Cross-matching the $$11\, 768$$ radio source components with optical data via visual inspection results in a final sample of 4794 cross-matched objects, of which 1996 have spectroscopic redshifts and 2798 objects have photometric redshifts. Three previously undiscovered giant radio galaxies were found during the cross-matching process, which would have been missed using automated techniques. For the objects with spectroscopy, we separate radio-loud active galactic nuclei (AGN) and star-forming galaxies (SFGs) using three diagnostics and then further divide our radio-loud AGN into the high and low excitation radio galaxy (HERG and LERG) populations. A control-matched sample of HERGs and LERGs, matched on stellar mass, redshift, and radio luminosity, reveals that the host galaxies of LERGs are redder and more concentrated than HERGs. By combining with near-infrared data, we demonstrate that LERGs also follow a tight K − $$z$$ relationship. These results imply the LERG populations are hosted by population of massive, passively evolving early-type galaxies. We go on to show that HERGs, LERGs, quasars, and SFGs in our sample all reside in different regions of a Wide-field Infrared Survey Explorer colour–colour diagram. This cross-matched sample bridges the gap between previous 'wide but shallow' and 'deep but narrow' samples and will be useful for a number of future investigations. [ABSTRACT FROM AUTHOR]

We present a sample of 34 weak metal line absorbers at z < 0.3 selected by the simultaneous >3σ detections of the Si IIλ1260 and CIIλ1334 absorption lines, with Wr (Si II) < 0.2 Å and Wr(C II) < 0.3 Å, in archival HST/COS spectra. Our sample increases the number of known low-z 'weak absorbers' by a factor of >5. The column densities of HI and low-ionization metal lines obtained from Voigt profile fitting are used to build simple photoionization models. The inferred densities and line-of-sight thicknesses of the absorbers are in the ranges of -3.3 < log nH/cm-3 < -2.4 and -1 pc--50 kpc (median ≈500 pc), respectively. Most importantly, 85 per cent (50 per cent) of these absorbers show a metallicity of [Si/H] > -1.0(0.0). The fraction of systems showing near-/supersolar metallicity in our sample is significantly higher than in the HI-selected sample of Wotta et al., and the galaxy-selected sample of Prochaska et al., of absorbers probing the circum-galactic medium at similar redshift. A search for galaxies has revealed a significant galaxy-overdensity around these weak absorbers compared to random positions with a median impact parameter of 166 kpc from the nearest galaxy. Moreover, we find the presence of multiple galaxies in ≈80 per cent of the cases, suggesting group environments. The observed dN/dz of 0.8 ± 0.2 indicates that such metalenriched, compact, dense structures are ubiquitous in the haloes of low-z group galaxies. We suggest that these are transient structures that are related to galactic outflows and/or stripping of metal-rich gas from galaxies. [ABSTRACT FROM AUTHOR]

The Rosetta orbiter witnessed several hundred diamagnetic cavity crossings (unmagnetized regions) around comet 67P/Churyumov-Gerasimenko during its two year survey of the comet. The characteristics of the plasma environment inside these diamagnetic regions are studied using in situ measurements by the Rosetta Plasma Consortium instruments. Although the unmagnetized plasma density has been observed to exhibit little dynamics compared to the very dynamical magnetized cometary plasma, we detected several localized dynamic plasma structures inside those diamagnetic regions. These plasma structures are not related to the direct ionization of local cometary neutrals. The structures are found to be steepened, asymmetric plasma enhancements with typical rising-to-descending slope ratio of ~2.8 (±1.9), skewness ~0.43 (±0.36), mean duration of ~2.7 (±0.9) min and relative density variation ΔN/N of ~0.5 (±0.2), observed close to the electron exobase. Similar steepened plasma density enhancements were detected at the magnetized boundaries of the diamagnetic cavity as well as outside the diamagnetic region. The plausible scalelength and propagation direction of the structures are estimated from simple plasma dynamics considerations. It is suggested that they are large-scale unmagnetized plasma enhancements, transmitted from the very dynamical outer magnetized region to the inner magnetic field-free cavity region. [ABSTRACT FROM AUTHOR]

The Rosetta orbiter witnessed several hundred diamagnetic cavity crossings (unmagnetized regions) around comet 67P/Churyumov-Gerasimenko during its two year survey of the comet. The characteristics of the plasma environment inside these diamagnetic regions are studied using in situ measurements by the Rosetta Plasma Consortium instruments. Although the unmagnetized plasma density has been observed to exhibit little dynamics compared to the very dynamical magnetized cometary plasma, we detected several localized dynamic plasma structures inside those diamagnetic regions. These plasma structures are not related to the direct ionization of local cometary neutrals. The structures are found to be steepened, asymmetric plasma enhancements with typical rising-to-descending slope ratio of∼2.8 (±1.9), skewness ∼0.43 (±0.36), mean duration of∼2.7 (±0.9) min and relative density variation ▵ N/N of∼0.5 (±0.2), observed close to the electron exobase. Similar steepened plasma density enhancements were detected at the magnetized boundaries of the diamagnetic cavity as well as outside the diamagnetic region. The plausible scalelength and propagation direction of the structures are estimated from simple plasma dynamics considerations. It is suggested that they are large-scale unmagnetized plasma enhancements, transmitted from the very dynamical outer magnetized region to the inner magnetic field-free cavity region. [ABSTRACT FROM AUTHOR]

As part of our ongoing effort to investigate transit timing variations (TTVs) of known exoplanets, we monitored transits of the four exoplanets HAT-P-18b, HAT-P-19b, HAT-P-27b/WASP- 40b and WASP-21b. All of them are suspected to show TTVs due to the known properties of their host systems based on the respective discovery papers. During the past three years 46 transit observations were carried out, mostly using telescopes of the Young Exoplanet Transit Initiative. The analyses are used to refine the systems? orbital parameters. In all cases we found no hints for significant TTVs, or changes in the system parameters inclination, fractional stellar radius and planet-to-star radius ratio. However, comparing our results with those available in the literature shows that we can confirm the already published values. [ABSTRACT FROM AUTHOR]

We study the gas distribution in the Milky Way and Andromeda using a constrained cosmological simulation of the Local Group (LG) within the context of the CLUES (Constrained Local UniversE Simulations) project. We analyse the properties of gas in the simulated galaxies at z = 0 for three different phases: ‘cold’, ‘hot’ and H i, and compare our results with observations. The amount of material in the hot halo (Mhot ≈ 4–5 × 1010 M⊙), and the cold (Mcold(r ≲ 10 kpc) ≈ 108 M⊙) and H i ($M_{\rm H\,{\small i}}(r\lesssim 50\,{\rm kpc})\approx 3{-}4\times 10^8\, {M_{\odot}}$) components displays reasonable agreement with observations. We also compute the accretion/ejection rates together with the H i (radial and all-sky) covering fractions. The integrated H i accretion rate within r = 50 kpc gives ∼0.2–0.3 M⊙ yr−1, i.e. close to that obtained from high-velocity clouds in the Milky Way. We find that the global accretion rate is dominated by hot material, although ionized gas with T ≲ 105 K can contribute significantly too. The net accretion rates of all material at the virial radii are 6–8 M⊙ yr−1. At z = 0, we find a significant gas excess between the two galaxies, as compared to any other direction, resulting from the overlap of their gaseous haloes. In our simulation, the gas excess first occurs at z ∼ 1, as a result of the kinematical evolution of the LG. [ABSTRACT FROM AUTHOR]

To interpret H[sub 2] quasar absorption-line observations in damped Lyα clouds (DLAs), we model the H[sub 2] spatial distribution within a DLA. Based on numerical simulations of disc structures with parameters similar to those derived for such absorbers, we calculate the H[sub 2] distribution as a function of ultraviolet background (UVB) intensity and dust-to-gas ratio. For typical values of these two quantities we find that the area in which the H[sub 2] fraction exceeds 10[sup -6] (typical observational detection limit) only covers ...10 per cent of the disc surface, i.e. H[sub 2] has a very inhomogeneous, clumpy distribution even at these low abundance levels. This explains the relative paucity of H[sub 2] detections in DLAs. We also show the dependence of the covering fraction of H[sub 2] on dust-to-gas ratio and UVB intensity, and we comment on the physics governing the H[sub 2] chemical network at high redshift. [ABSTRACT FROM AUTHOR]