Search

Close double degenerate binaries are one of the favoured progenitor channels for type Ia supernovae, but it is unclear how many suitable systems there are in the Galaxy. We report results of a large radial velocity survey for double degenerate (DD) binaries using the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY – SPY). Exposures taken at different epochs are checked for radial velocity shifts indicating close binary systems. We observed 689 targets classified as DA white dwarfs (displaying hydrogen-rich atmospheres), of which 46 were found to possess a cool companion. We measured radial velocities (RV) of the remaining 643 DA white dwarfs. We managed to secure observations at two or more epochs for 625 targets, supplemented by eleven objects meeting our selection criteria from literature. The data reduction and analysis methods applied to the survey data are described in detail. The sample contains 39 double degenerate binaries, only four of which were previously known. Twenty are double-lined systems, in which features from both components are visible, the other 19 are single-lined binaries. We provide absolute RVs transformed to the heliocentric system suitable for kinematic studies. Our sample is large enough to sub-divide by mass: 16 out of 44 low mass targets (≤0.45 M⊙) are detected as DDs, while just 23 of the remaining 567 targets with multiple spectra and mass > 0.45 M⊙are double. The detected fraction amongst the low mass objects (36.4 ± 7.3%) is significantly higher than for the higher-mass, carbon-oxygen core dominated part of the sample (3.9 ± 0.8%), but it is much lower than expected from the detection efficiency for companion masses of 0.05 M⊙or higher and a 100% binary fraction. This suggests either companion stars of with a mass below 0.05 M⊙or some of the low mass white dwarfs are single.

Absorption-line systems detected in high resolution quasar spectra can be used to compare the value of dimensionless fundamental constants such as the fine-structure constant, α, and the proton-to-electron mass ratio, μ = mp/me, as measured in remote regions of the Universe to their value today on Earth. In recent years, some evidence has emerged of small temporal and also spatial variations in α on cosmological scales which may reach a fractional level of ≈ 10 ppm (parts per million). We are conducting a Large Programme of observations with the Very Large Telescope's Ultraviolet and Visual Echelle Spectrograph (UVES), and are obtaining high-resolution (R ≈ 60000) and high signal-to-noise ratio (S/N ≈ 100) spectra calibrated specifically to study the variations of the fundamental constants. We here provide a general overview of the Large Programme and report on the first results for these two constants, discussed in detail in Molaro et al. (2013) and Rahmani et al. (2013). A stringent bound for Δα /α is obtained for the absorber at zabs = 1.6919 towards HE 2217-2818. The absorption profile is complex with several very narrow features, and is modeled with 32 velocity components. The relative variation in α in this system is +1.3 ± 2.4stat ± 1.0sys ppm if Al II λ 1670 A and three FeII transitions are used, and +1.1 ± 2.6stat ppm in a slightly different analysis with only FeII transitions used. This is one of the tightest bounds on α -variation from an individual absorber and reveals no evidence for variation in α at the 3-ppm precision level (1σ confidence). The expectation at this sky position of the recently-reported dipolar variation of α is (3.2–5.4) ± 1.7 ppm depending on dipole model used and this constraint of Δα /α at face value is not supporting this expectation but not inconsistent with it at the 3σ level. For the proton-to-electron mass ratio the analysis of the H2 absorption lines of the zabs ≈ 2.4018 damped Lyα system towards HE 0027–1836 provides Δμ /μ = (–7.6 ± 8.1stat ± 6.3sys) ppm which is also consistent with a null variation. The cross-correlation analysis between individual exposures taken over three years and comparison with almost simultaneous asteroid observations revealed the presence of a possible wavelength dependent velocity drift as well as of inter-order distortions which probably dominate the systematic error and are a significant obstacle to achieve more accurate measurements. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

(Abridged) Aims. We derive the physical properties of a filament discovered in the dark cometary-shaped cloud L1251. Methods. Mapping observations in the NH3(1,1) and (2,2) inversion lines, encompassing 300 positions toward L1251, were performed with the Effelsberg 100-m telescope at a spatial resolution of 40 arcsec and a spectral resolution of 0.045 km/s. Results. The filament L1251A consists of three condensations (alpha, beta, and gamma) of elongated morphology, which are combined in a long and narrow structure covering a 38 arcmin by 3 arcmin angular range. The opposite chirality (dextral and sinistral) of the alpha+beta and gamma condensations indicates magnetic field helicities of two types, negative and positive, which were most probably caused by dynamo mechanisms. We estimated the magnetic Reynolds number Rm > 600 and the Rossby number R < 1, which means that dynamo action is important., 21 pages, 10 figures, 1 table. Accepted for publication in A&A

So far the only seemingly significant indication of a cosmological variation exists for the proton-to-electron mass ratio as stated by Reinhold et al. (2006). The measured indication of variation is based on the combined analysis of H2 absorption systems in the spectra of Q0405-443 and Q0347-383 at z=2.595 and z=3.025, respectively. The high resolution data of the latter is reanalyzed in this work to examine the influence of different fitting procedures and further potential nonconformities. This analysis cannot reproduce the significance achieved by the previous detection., 10 pages, 8 figures, as to appear in EPJ special - ACFC 2007 conference proceedings

The Single Ion Differential alpha Measurement (SIDAM) method for measuring fine stucture variations (daa)and its figures of merit are illustrated together with the results produced by means of FeII absorption lines of QSO intervening systems. The method provides daa ~= -0.12(+/- 1.79) ppm (parts-per-million) at zabs = 1.15 towards HE 0515--4414 and daa = 5.66(+/-2.67) ppm at zabs= 1.84 towards Q 1101--264, which are so far the most accurate measurements for single systems. SIDAM analysis for 3 systems from the Chand et al. (2004) sample provides inconsistent results which we interpret as due to calibration errors of the Chand et al. data at the level of about 10 ppm. In one system evidence for photo-ionization Doppler shift between MgII and FeII lines is found. This evidence has important bearings on the Many Multiplet method where the signal for daa variability is carried mainly by systems involving MgII absorbers. Some correlations are also found in the Murphy et al. sample which suggest larger errors than previously reported. Thus, we consider unlikely that both the Chand et al. and Murphy et al. datasets could provide an estimate of daa with an accuracy at the level of 1 ppm. A new spectrograph like the ESPRESSO project will be crucial to make progress in the astronomical determination of daa., Talk given at ACFC 2007 "Atomic Clocks and Fundamental Constants" conference, Bad Honnef, June 2007, Savely Karshenboim and Ekkehard Peik editors

The Antares nebula is a peculiar emission nebula seen in numerous Fe II lines and in radio free-free emission, probably associated with the H II region caused by alpha Sco B in the wind of alpha Sco A. High-resolution spectra with spatial resolution were used to study the emission line spectrum, the physical nature of the nebula and to determine the mass-loss rate of the M supergiant alpha Sco A.

Aims. We reconstruct the spectral shape of the quasar ionizing radiation in the extreme-UV range (1 Ryd ≤ E 4R yd which is attributed to the He ii Lyman continuum opacity (τ He II c ∼ 1). A most likely source of this opacity is a quasar accretion disk wind. The corresponding column density of H i in the wind is estimated as a few times 10 16 cm −2 . This amount of neutral hydrogen should cause a weak continuum depression at λ 4 Ryd with the depth of this break depending on the angle with the rotational axis of the accretion disk (the larger the angle the deeper the break). The QSO spectra with a discontinuity at 4 Ryd can influence the rate of He ii reionization in the intergalactic medium and partly explain the inhomogeneous (patchy) ionization structure of the intergalactic He ii observed at z ∼ 3.

We present the quantitative methods used for selecting candidate metal-poor stars in the Hamburg/ESO objective-prism survey (HES). The selection is based on the strength of the Ca II K line, B-V colors (both measured directly from the digital HES spectra), as well as J-K colors from the 2 Micron All Sky Survey. The KP index for Ca II K can be measured from the HES spectra with an accuracy of 1.0 Angstrom, and a calibration of the HES B-V colors, using CCD photometry, yields a 1-sigma uncertainty of 0.07 mag for stars in the color range 0.3 < B-V < 1.4. These accuracies make it possible to reliably reject stars with [Fe/H] > -2.0 without sacrificing completeness at the lowest metallicities. A test of the selection using 1121 stars of the HK survey of Beers, Preston, and Shectman present on HES plates suggests that the completeness at [Fe/H] < -3.5 is close to 100% and that, at the same time, the contamination of the candidate sample with false positives is low: 50% of all stars with [Fe/H] > -2.5 and 97% of all stars with [Fe/H] > -2.0 are rejected. The selection was applied to 379 HES fields, covering a nominal area of 8853 square degrees of the southern high Galactic latitude sky. The candidate sample consists of 20,271 stars in the magnitude range 10 < B < 18. A comparison of the magnitude distribution with that of the HK survey shows that the magnitude limit of the HES sample is about 2 mag fainter. Taking the overlap of the sky areas covered by both surveys into account, it follows that the survey volume for metal-poor stars has been increased by the HES by about a factor of 10 with respect to the HK survey. We have already identified several very rare objects with the HES, including, e.g., the three most heavy-element deficient stars currently known., 11 pages, 10 figures, accepted for publication in A&A

Aims. To obtain limits on the variation of the fine-structure constant alpha and the electron-to-proton mass ratio mu over different cosmological epochs. Methods. A new approach based on the comparison of redshifts of far infrared (FIR) fine-structure lines and low-lying rotational transitions in CO is proposed which is in principle more sensitive by a factor of 10 compared to QSO metal absorption lines. Results. Estimations of the quotient F = alpha^2/mu obtained for two distant quasars J1148+5251 (z = 6.42) and BR1202-0725 (z = 4.69) provide Delta F/F = (0.1+/-1.0)10^{-4} and (1.4+/-1.5)10^{-4}, respectively. The obtained limits are consistent with no variation of physical constants at the level of 0.01% over a period of 13 Gyr. Conclusions. Upcoming observations of quasars and distant galaxies in FIR fine-structure lines of different species and in CO low rotational lines at the SOFIA, HSO, and ALMA are expected to improve the current limit by, at least, an order of magnitude., 5 pages, to appear in A&A main journal

Context. Extended atmospheres of late-type supergiants are of special interest with regard to the mass-loss process, the circumstellar physico-chemistry, and the evolution of stars. Aims. The circumstellar envelope of α Sco A (M1.5 Iab) has been subject of intensive studies. Nevertheless the mechanism that is responsible for the mass outflow is still poorly understood. High-resolution spectroscopy is required to re-investigate the wind properties of the supergiant. Methods. We present HST/GHRS observation of α Sco B (B2.5 V) showing numerous absorption lines that arises from matter being ejected by the supergiant primary. Multiple absorption features indicates that the wind material is not smoothly distributed but rather concentrated in discrete condensations. The column density and velocity structure of the absorption components is estimated using a nonlinear least-squares fit procedure. Results. We have identified four distinct absorption systems with rest frame velocities of –0.5, –8.4, –14.4, and –19.9 km s −1 .A n additional component is seen in Al iii at 7.8 km s −1 probably constraining the position of the hot companion. With a spherical outflow geometry we would obtain a time average mass-loss rate due to episodic events up to u

Context. We present a detailed spectroscopic analysis of the stars with helium-dominated spectra in the ESO Supernova la Progenitor Survey (SPY). Aims. Atmospheric parameters, masses, and abundances of trace hydrogen are determined and discussed in the context of spectral evolution of white dwarfs. Methods. The spectra are compared with theoretical model atmospheres using a Χ 2 fitting technique, leading to determinations of effective temperature, surface gravity, and hydrogen abundance. Results. Our final sample contains 71 objects, of which 6 are new detections and 14 are reclassified from DB to DBA because of the presence of H lines. One is a cool DO with weak He II lines, 2 are composite DB+dM. 55% of the DB sample show hydrogen and are thus DBA, a significantly higher fraction than found before. Conclusions. The large incidence of DBA, and the derived total hydrogen masses are compatible with the scenario that DBs "reappear" around 30000 K from the DB gap by mixing and diluting a thin hydrogen layer of the order of 10 -15 M ⊙ . This hydrogen mass is then during the evolution continuously increased by interstellar accretion. There are indications that the accretion rate increases smoothly with age or decreasing temperature, a trend which continuous even below the current low temperature limit (Dufour 2006). A remaining mystery is the low accretion rate of H compared to that of Ca observed in the DBZA, but a stellar wind extending down to the lowest temperatures with decreasing strength might be part of the solution.

We present an analysis of the Lyman alpha forests of five quasar spectra in the near UV. Properties of the intergalactic medium (IGM) at an intermediate redshift interval (0.9 < z < 1.9) are studied. The amount of baryons in the diffuse photoionised IGM and the warm-hot intergalactic medium (WHIM) are traced to get constraints on the redshift evolution of the different phases of the intergalactic gas. The baryon density of the diffuse IGM is determined with photoionisation calculations under the assumption of local hydrostatic equilibrium. We assume that the gas is ionised by a metagalactic background radiation with a Haardt & Madau (2001) spectrum. The WHIM is traced with broad Lyman alpha (BLA) absorption. The properties of a number of BLA detections are studied. Under the assumption of collisional ionisation equilibrium a lower limit to the baryon density could be estimated. It is found that the diffuse photoionised IGM contains at least 25% of the total baryonic matter at redshifts 1 < z < 2. For the WHIM a lower limit of 2.4% could be determined. Furthermore the data indicates that the intergalactic gas is in a state of evolution at z=1.5. We confirm that a considerable part of the WHIM is created between z=1 and z=2., 6 pages, 1 figure, accepted for publication in A&A

Recent analyses of the intergalactic UV background by means of the HeII Lyman alpha forest assume that HeII and HI absorption features have the same line widths. We omit this assumption to investigate possible effects of thermal line broadening on the inferred HeII/HI ratio eta and to explore the potential of intergalactic HeII observations to constrain the thermal state of the IGM. Deriving a simple relation between the column density and the temperature of an absorber we develop a procedure to fit the parameters of a power law temperature-density relation and eta simultaneously. In an alternative approach the temperature of an absorber, eta, and the redshift scale of eta variations are estimated simultaneously. Tests with artificial data show that well-constrained results can be obtained only if the signal-to-noise ratio in the HeII forest is S/N > 20. Thus, it is impossible to give an estimate of the temperature-density relation with the HeII data available at present (S/N ~5). However, we find that only 45% of the lines in our sample favor turbulent line widths. Furthermore, the inferred eta values are on average about 0.05 dex larger if a thermal component is taken into account, and their distribution is 46% narrower in comparison to a purely turbulent fit. Therefore, variations of eta on a 10% level may be related to the presence of thermal line broadening. The apparent correlation between the strength of the HI absorption and the eta value, which has been found in former studies, essentially disappears if thermal broadening is taken into account. In the redshift range 2.58 < z < 2.74 towards the quasars HE2347-4342 and HS1700+6416 we obtain eta ~ 100. (abridged), accepted for publication by A&A, 11 pages, 13 figures

We present a reanalysis of the HeII Lyman alpha absorption towards the quasars HS1700+6416 and HE2347-4342 using new high S/N, optical observations. An alternative analysis method is applied, which fits the high quality, optical HI data directly to the HeII spectrum. The results are compared to those inferred from standard line profile analyses. This new method enables us to derive redshift scales characterizing the fluctuations of the column density ratio eta. We find eta changing smoothly with redshift on typical scales of Delta z ~ 0.01-0.03 corresponding to 8-24 h^-1 Mpc comoving. The real length scales of variations of the column density ratio might be even larger, since part of the fluctuations may be caused by noise in the HeII data and by effects due to the applied method. However, eta variations on small scales of a few Mpc with an amplitude of about +/- 1.5 dex cannot be ruled out completely. The data shows an apparent correlation between low eta regions and the presence of metal line absorbers, which corresponds to the more general correlation of low eta and strong HI absorption. Thermal line broadening is suggested as a probable explanation for this apparent correlation, since both fit methods would severely underestimate eta for absorbers with log N(HI) > 13 if the line width was dominated by thermal broadening. Indeed, lines located close to the cut-off of the b(N) distribution yield lower column density ratios compared to the whole sample, in particular if high density absorbers are considered. We argue that the apparent correlation of eta with the strength of the HI absorption is caused by insufficient consideration of thermal broadened lines by the standard analysis. As unbiased value of the column density ratio, we find eta ~80 in agreement with previous estimates., 15 pages, 11 figures, recommended for publication in A&A

We investigate the evolution and the statistical properties of the Lya absorbers of the intergalactic medium (IGM) in the largely unexplored redshift range z=0.5-1.9. We use high-resolution (R > 30,000) UV (STIS) and optical (VLT/UVES and Keck/HIRES) spectra of nine bright quasars with z_em 0. The stronger absorbers thin out faster (gamma=1.50+-0.45). The break in their evolution predicted for z=1.5-1.7 cannot be seen down to z=0.7. On the other hand, a comparison with values from the literature for the local number density gives a hint that this break occurs at lower redshift. 2. The distribution of the column densities of the absorbers is complete down to N_HI=10^12.90 cm^-2. It can be approximated by a single power law with the exponent beta=1.60+-0.03 over almost three orders of magnitude. beta is redshift independent. 3. The Lya lines with lower column densities as well as the higher column density lines show marginal clustering with a 2 sigma significance over short distances (Delta v < 200 km/s and Delta v < 100 km/s, respectively). We do not see any difference in the clustering with either column density or redshift.

We identify an important set of key areas where an advanced observational Ultraviolet capability would have major impact on studies of cosmology and Galaxy formation in the young Universe. Most of these are associated with the Universe at z < 3–4. We address the issues associated with Dark matter evidence in the local Universe and the impact of the Warm-Hot Intergalactic Medium WHIM on the local Baryon count. The motivations to make ultraviolet (UV) studies of supernovae (SNe) are reviewed and discussed in the light of the results obtained so far by means of IUE and HST observations. It appears that UV studies of SNe can, and do lead to fundamental results not only for our understanding of the SN phenomenon, such as the kinematics and the metallicity of the ejecta, but also for exciting new findings in Cosmology, such as the tantalizing evidence for “dark energy” that seems to pervade the Universe and to dominate its energetics. The need for additional and more detailed UV observations is also considered and discussed.

International audience; Progress of modern astrophysics requires the access to the electromagnetic spectrum in the broadest energy range. The Ultraviolet is a fundamental energy domain since it is one of the most powerful tool to study plasmas at temperatures in the 3,000 300,000 K range as well as electronic transitions of the most abundant molecules in the Universe. Moreover, the UV radiation field is a powerful astrochemical and photoionizing agent. The objective of this review is to describe the crucial issues that require access to the UV range. A summary has been added to the end with a more classic view of UV needs by astronomical object type; this approach is followed at length in the rest of the contributions of this issue.

We present a detailed analysis of a very high resolution (R\approx 112,000) spectrum of the quasar HE 0515-4414 obtained using the High Accuracy Radial velocity Planet Searcher (HARPS) mounted on the ESO 3.6 m telescope at the La Silla observatory. The HARPS spectrum, of very high wavelength calibration accuracy (better than 1 m\AA), is used to search for possible systematic inaccuracies in the wavelength calibration of the UV Echelle Spectrograph (UVES) mounted on the ESO Very Large Telescope (VLT). We have carried out cross-correlation analysis between the Th-Ar lamp spectra obtained with HARPS and UVES. The shift between the two spectra has a dispersion around zero of \sigma\simeq 1 m\AA. This is well within the wavelength calibration accuracy of UVES (i.e \sigma\simeq 4 m\AA). We show that the uncertainties in the wavelength calibration induce an error of about, \Delta\alpha/\alpha\le 10^{-6}, in the determination of the variation of the fine-structure constant. Thus, the results of non-evolving \Delta\alpha/\alpha reported in the literature based on UVES/VLT data should not be heavily influenced by problems related to wavelength calibration uncertainties. Our higher resolution spectrum of the z_{abs}=1.1508 damped Lyman-\alpha system toward HE 0515-4414 reveals more components compared to the UVES spectrum. Using the Voigt profile decomposition that simultaneously fits the high resolution HARPS data and the higher signal-to-noise ratio UVES data, we obtain, \Delta\alpha/\alpha=(0.05\pm0.24)x10^{-5} at z_{abs}=1.1508. This result is consistent with the earlier measurement for this system using the UVES spectrum alone., Comment: 14 pages, 13 figures, Accepted in A&A

We report the discovery of a 16th magnitude star, HE0437-5439, with a heliocentric radial velocity of +723+-3km/s. A quantitative spectral analysis of high-resolution optical spectra obtained with the VLT and the UVES spectrograph shows that HE0437-5439 is a main sequence B-type star with Teff=20350K, log g=3.77, solar within a factor of a few helium abundance and metal content, rotating at v sin i=54km/s. Using appropriate evolutionary tracks we derive a mass of 8 Msun and a corresponding distance of 61 kpc. Its galactic rest frame velocity is at least 563km/s, almost twice the local Galactic escape velocity, indicating that the star is unbound to the Galaxy. Numerical kinematical experiments are carried out to constrain its place of birth. It has been suggested that such hyper-velocity stars can be formed by the tidal disruption of a binary through interaction with the super-massive black hole at the Galactic center (GC). HE0437-5439 needs about 100Myrs to travel from the GC to its presentposition, much longer than its main sequence lifetime of 25Myrs. This can only be reconciled if HE0437-5439 is a blue straggler star. In this case, the predicted proper motion is so small that it can only be measured by future space missions. Since the star is much closer to the Large Magellanic Cloud (LMC, 18kpc) than to the GC, it can reach its position from the center of the LMC. The proper motion predicted in this case is about 2mas/y (relative to the LMC), large enough to be measurable with conventional techniques from the ground. The LMC origin could also be tested by a high-precision abundance analysis., Comment: 13 pages, 4 figures. Astrophysical Journal Letters, accepted

We present the results of analysis of ``snapshot'' spectra of 253 metal-poor halo stars -3.8 < [Fe/H] < -1.5 obtained in the HERES survey. The spectra are analysed using an automated line profile analysis method based on the Spectroscopy Made Easy codes of Valenti & Piskunov. Elemental abundances of moderate precision have been obtained for 22 elements, C, Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Sr, Y, Zr, Ba, La, Ce, Nd, Sm, and Eu, where detectable. Among the sample of 253 stars, we find 8 r-II stars and 35 r-I stars. We also find three stars with strong enhancements of Eu which are s-process rich. A significant number of new very metal-poor stars are confirmed: 49 stars with [Fe/H] < -3 and 181 stars with -3 < [Fe/H] < -2. We find one star with [Fe/H] < -3.5. We find the scatter in the abundance ratios of Mg, Ca, Sc, Ti, Cr, Fe, Co, and Ni, with respect to Fe and Mg, to be similar to the estimated relative errors and thus the cosmic scatter to be small, perhaps even non-existent. The elements C, Sr, Y, Ba and Eu, and perhaps Zr, show scatter at [Fe/H] < -2.5 significantly larger than can be explained from the errors in the analysis, implying scatter which is cosmic in origin. Significant scatter is observed in abundance ratios between light and heavy neutron-capture elements at low metallicity and low levels of r-process enrichment. (*** abridged ***), Accepted for A&A; 31 pages, 2 electronic tables presently available at http://www.astro.uu.se/~barklem/papers/heres_tables.tar.gz ; Minor corrections added

We search for faint Ca II lines in the spectra of about 800 apparently single white dwarfs observed at high resolution for the SPY (ESO Supernova Progenitor Survey) survey. Photospheric Ca is detected in 24 DAZ; in 25 mostly hot objects the observed lines must be interstellar. We also rediscover 9 strong H and K lines in helium-dominated atmospheres and discover for the first time faint lines in 8 DB. Most of these also show faint hydrogen lines and are thus classified DBAZ. The distribution of metal abundances is discussed and compared with the predictions of the accretion/diffusion scenario. We argue that the observations are easier to understand in a scenario of continuous ongoing accretion with rates varying with the conditions of the ambient medium, rather than with the strongly idealized "two phase accretion/diffusion scenario" of Dupuis et al. (1992, 1993a,b).

We describe the decomposition of QSO absorption line ensembles applying an evolutionary forward modelling technique. The modelling is optimized using an evolution strategy (ES) based on a novel concept of completely derandomized self-adaption. The algorithm is described in detail. Its global optimization performance in decomposing a series of simulated test spectra is compared to that of classical deterministic algorithms. Our comparison demonstrates that the ES is a highly competitive algorithm capable to calculate the optimal decomposition without requiring any particular initialization., 9 pages, 5 figures, accepted for publication in Astron. Astrophys., corrected figure misplacements, full resolution manuscript can be obtained at http://www.hs.uni-hamburg.de/EN/Ins/Per/Quast/

We present the analysis of a high-resolution, high-quality sample of optical spectra for 76 subdwarf B (sdB) stars from the ESO Supernova Ia Progenitor Survey (SPY). Effective temperature, surface gravity, and photospheric helium abundance are determined simultaneously by fitting the profiles of hydrogen and helium lines using synthetic spectra calculated from LTE and NLTE model atmospheres. We perform a detailed comparison of our measurements with theoretical calculations, both for single star evolution and for binary population synthesis models of close binary evolution. The luminosity evolution given by the standard EHB evolutionary tracks from Dorman et al. (1993) shows an overall agreement in shape with our observations, although a constant offset in luminosity exists. The various simulation sets for binary formation channels of sdB stars calculated by Han et al. (2003) are compared individually to our data for testing our current understanding of sdB formation processes and the physical effects involved. The best-matching sets manage to reproduce the observed sdB distribution in the temperature-gravity-plane well. However, they do not match the observed cumulative luminosity function, indicating that theoretical improvement is necessary. We also investigate composite-spectrum objects showing clear signatures of a cool companion with optical and infrared photometry. These stars have cool main sequence companions of spectral types F to K. Typical helium abundances of composite and non-composite sdB stars do not differ., Comment: 21 pages, 18 figures, accepted for publication in Astronomy and Astrophysics; replaced version with minor changes from language editing

We present an analysis of the complex associated system of the high-redshift QSO HE2347-4342. Absorption features of HI, CIII, CIV, NV, and OVI with up to 16 components occur in the optical spectral range located up to 1500 km/s redwards from the emission line. Apparently, CIV and NV show the line locking effect. A quantivative analysis of the line distribution comparing simulated spectra with randomly distributed doublets reveals, however, no statistical evidence for its physical reality. Using photoionization calculations to emulate the observed ion column densities we constrain the quasar's spectral energy distribution. Absorbers in the velocity range of 200 - 600 km/s can be modelled successfully with a spectral index of alpha ~ -3 at energies higher than 3 - 4 Ryd, which is an energy distribution similar to the QSO continuum suggested by Mathews & Ferland (1987). The analysis of a group of high velocity absorbers (v > 1300 km/s) leads to a harder energy distribution. The large amount of helium (log N(HeII) > 16.3) associated with these absorbers implies that they are responsible for the observed absence of the proximity effect (Reimers et al. 1997). Clouds located more distant from the quasar may be shielded from the high energy part of the quasar continuum due to optically thick absorption shortward of 228 Angstrom by the high velocity absorbers. A group of absorbers with 900 < v < 1200 km/s, in particular a cloud at 1033 km/s, which has the most reliable column density measurements, can be modelled neither with photoionzation nor under the assumption of collisionally ionized gas., 11 pages, 8 figures, accepted by A&A

We provide an in-depth analysis of the He II and H I absorption in the intergalactic medium (IGM) at redshifts z = 2.3-2.9 toward HE 2347-4342, using spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Ultraviolet-Visual Echelle Spectrograph (UVES) on the VLT telescope. Following up on our earlier study (Kriss et al. 2001, Science, 293, 1112), we focus here on two major topics: (1) small-scale variability (Delta z = 10^-3) in the ratio eta = N(He II)/N(H I); and (2) an observed correlation of high-eta absorbers (soft radiation fields) with voids in the (H I) Ly-alpha distribution. These effects may reflect fluctuations in the ionizing sources on scales of 1 Mpc, together with radiative transfer through a filamentary IGM whose opacity variations control the penetration of 1-5 ryd radiation over 30-40 Mpc distances. Owing to photon statistics and backgrounds, we can measure optical depths over the ranges 0.1 < tau(HeII) < 2.3 and 0.02 < tau(HI) < 3.9, and reliably determine values of eta = 4 tau(HeII)/tau(HI) over the range 0.1 to 460. Values of eta = 20-200 are consistent with models of photoionization by quasars with observed spectral indices alpha_s = 0-3. Values of eta > 200 may require additional contributions from starburst galaxies, heavily filtered quasar radiation, or density variations. Regions with eta < 30 may indicate the presence of local hard sources. We find that eta is higher in "void" regions, where H I is weak or undetected and 80% of the path length has eta > 100. These voids may be ionized by soft sources (dwarf starbursts) or by QSO radiation softened by escape from the AGN cores or transfer through the "cosmic web". The apparent differences in ionizing spectra may help to explain the 1.45 Gyr lag between the reionization epochs, z(HI) = 6.2 +/-0.2 and z(HeII) = 2.8 +/-0.2., 27 pages, 7 figures, to appear in ApJ

We present the results of a radial velocity (RV) survey of 46 subdwarf B (sdB) and 23 helium-rich subdwarf O (He-sdO) stars. We detected 18 (39%) new sdB binary systems, but only one (4%) He-sdO binary. Orbital parameters of nine sdB and sdO binaries, derived from follow-up spectroscopy, are presented. Our results are compared with evolutionary scenarios and previous observational investigations., Comment: To appear in "Extreme Horizontal Branch Stars and Related Objects", Astrophysics and Space Science, Kluver Academic Publishers, edited by P.F.L. Maxted

We report on the analysis of high-resolution optical spectra for 77 subdwarf B (sdB) stars from the ESO Supernova Ia Progenitor Survey. Effective temperature, surface gravity, and photospheric helium abundance are determined simultaneously by spectral line profile fitting of hydrogen and helium lines, and are found to be in agreement with previous studies of sdB stars. 24 objects show spectral signs of a cool companion, being either companion absorption lines or a flux contribution at Halpha. Five stars with relatively high luminosity show peculiar Halpha profiles, possibly indicating stellar winds. Our results are compared to recent theoretical simulations by Han et al. (2003) for the distribution in effective temperature and surface gravity, and are found to agree very well with these calculations. Finally we present a binary system consisting of two helium-rich hot subdwarfs., Comment: 8 pages, 6 figures. To appear in "Extreme Horizontal Branch Stars and Related Objects", Astrophysics and Space Science, Kluwer Academic Publishers, edited by P. F. L. Maxted

A new molecular hydrogen cloud is found in the sub-damped Ly-alpha absorber [log N(HI)=19.88+/-0.05] at the redshift z=1.15 toward the bright quasar HE0515-4414 (zem = 1.71). More than 30 absorption features in the Lyman band system of H2 are identified in the UV spectrum of this quasar obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope. The H2-bearing cloud shows a total H2 column density N(H2)=(8.7^{+8.7}_-{4.0}) 10^16 cm^-2, and a fractional molecular abundance f(H2)=(2.3^{+2.3}_{-1.1}) 10^-3 derived from the H2 lines arising from the J=0-5 rotational levels of the ground electronic vibrational state. The estimated rate of photodissociation at the cloud edge I_0, 10 pages, 7 figures, accepted for publication in A&A

In the course of our search for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY) we discovered HE2209-1444 to be a double-lined system consisting of two DA white dwarfs. From the analysis of the radial velocity curve we determined the period of the system to be P = 6h 38m 47s. The semi-amplitudes for both individual components are 109 km/s each. A model atmosphere analysis enabled us to derive individual temperatures for both components (8490 K and 7140 K, resp.) and masses of 0.58 Msol for each component. The total mass of the system is 1.15 +/- 0.07 Msol. The system will loose angular momentum due to gravitational wave radiation and therefore will merge within 5 Gyrs -- less than a Hubble time. HE2209-1444 is the second massive, short period double degenerate detected by SPY. Its total mass is about 20 % below the Chandrasekhar mass limit and therefore it does not qualify as a potentional SN Ia progenitor. However, together with our previous detections it supports the view that Chandrasekhar mass systems do exist.

We present the Hamburg/RASS Catalogue (HRC) of optical identifications of X-ray sources at high-galactic latitude. The HRC includes all X-ray sources from the ROSAT Bright Source Catalogue (RASS-BSC) with galactic latitude |b| >= 30 degr and declination delta >= 0 degr. In this part of the sky covering ~10 000 deg^2 the RASS-BSC contains 5341 X-ray sources. For the optical identification we used blue Schmidt prism and direct plates taken for the northern hemisphere Hamburg Quasar Survey (HQS) which are now available in digitized form. The limiting magnitudes are 18.5 and 20, respectively. For 82% of the selected RASS-BSC an identification could be given. For the rest either no counterpart was visible in the error circle or a plausible identification was not possible. With ~42% AGN represent the largest group of X-ray emitters, \~31% have a stellar counterpart, whereas galaxies and cluster of galaxies comprise only ~4% and ~5%, respectively. In ~3% of the RASS-BSC sources no object was visible on our blue direct plates within 40 arcsec around the X-ray source position. The catalogue is used as a source for the selection of (nearly) complete samples of the various classes of X-ray emitters., 20 pages, 23 figures, accepted for publication in Astronomy & Astrophysics

Spectroscopy with HST/STIS Echelle and VLT/UVES of the bright QSO HE 0515-4414 (z_em =1.73, B = 15.0) offers for the first time the opportunity to study the Lyman alpha forest in the redshift range 0.9 < z < 1.7 at a resolution ~ 10 km/s. The number density evolution of the Lyman alpha lines is well described by the power law approach dn/dz = (dn/dz)_0 (1+z)^gamma. We derive gamma = 2.23 +/- 1.21 for the strong lines (13.64 < log N_HI < 16.00), in agreement with the Lyman alpha forest evolution for z > 1.7. The expected slow-down in their evolution does not appear earlier than z ~ 1. For the weak lines (13.10 < log N_HI < 14.00) we find that the HE 0515-4414 data for z > 1 follow the trend with gamma = 1.40 known from z > 1.7 observations, i.e. we confirm the difference in evolution between weak and strong lines. We use the two-point velocity correlation function (TPCF) to search for clustering of the Lyman alpha lines, yet we detect no excess in the TPCF on scales up to 10,000 km/s., Comment: Accepted for publication in A&A Letters. 5 pages, 6 figures

In the course of our search for double degenerate (DD) binaries as potential progenitors of type Ia supernovae with the UVES spectrograph at the ESO VLT (ESO SN Ia Progenitor surveY - SPY) we discovered that the white dwarf HE 1414-0848 is a double-lined DA+DA binary with an orbital period of P = 12h 25m 39s. Semi-amplitudes of 128km/s and 100km/s are derived for the individual components. The amplitude ratio and the measured difference in gravitational redshift is used to estimate the masses of the individual components: 0.55Msol and 0.71Msol. Hence the total mass of the HE 1414-0848 system is 1.26Msol, only 10% below the Chandrasekhar limit. The results of a model atmosphere analysis are consistent with our mass estimated from the orbit. Temperatures of the individual components are also determined. Possible scenarios for the formation of this system are discussed. The system will merge due to loss of angular momentum via gravitational wave radiation after two Hubble times. HE 1414-0848 does not qualify as a SN Ia progenitor, but it is the most massive close DD known today., 7 pages, 7 figures, A&A, accepted

We have obtained a high resolution, high S=N UVES spectrum of the bright QSO HE 2243 6031 to analyze the damped Ly system (DLA) observed at z =2 :33. We measure column densities for H i ,N i ,A lii, Si ii ,P ii ,S ii ,A ri ,C rii ,F eii ,N iii ,Z nii ,C ii O i ,a nd Aliii and put upper limits on the abundances of Mn ii, S iii ,F eiii ,P iii ,a nd Nii. The metallicity of this system is 1=12 solar at a neutral hydrogen column density of logN(H i )=2 0:7. From the observed ratios (Zn/Cr) = 0:01 0:05 and (S/Si) = 0:06 0:03 we conclude that dust is very likely absent from the ISM of this protogalaxy. We observe an enhancement of the /Fe-peak ratios of +0:2 dex for various elements, a marked odd-even eect in Mn, and a strong underabundance of N relative to Si and S, (N/Si,S) = 1a t (Si/H) = 0:86. All of these ratios support an environment that is in an early evolutionary stage, where the onset of star formation has begun only shortly before the DLA was observed. We also perform a cloud-by-cloud analysis { without precedent at high redshift { and nd a tight correlation of all low-ionization species with respect to Fe ii extending over 2.5 orders of magnitude in N(Fe ii). We interpret this trend as being due to homogeneous physical conditions (very mild ionization eects, common dust-destruction histories, same chemical composition) and propose that this line-of-sight encounters absorbing clouds that share a common environment. In addition, photoionization models show that these single clouds are shielded from the external ionizing radiation, so the fraction of ionized gas is small and, except for argon, does not influence the measured metal abundances. The observed Al iii/low-ion ratios suggest the mildly ionized gas occurs in shells surrounding neutral cores of Al ii.

Over the past decade, our team has pursued a quest to search for the optically brightest quasars in the entire extragalactic sky, by means of automated quasar selection using digitised objective prism spectra. We give a brief overview over the observational database and selection strategies and present some of the major survey highlights

The baryon density of the universe Ω B is well measured indirectly from Big-Bang nucleo-synthesis, in particular by recent measurements of the D/H ratio in high-redshift QSO absorption systems. In addition, very recent measurements of the second maximum of the power-spectrum of the CMB fine scale anisotropy allow to constrain Ω B at z ≈ 1000. Both results agree and yield Ω B = 0.02h −2. Direct measurements of the diffuse baryonic component (intergalactic gas) at redshifts z = 3 and 1.5 and in the local universe are reviewed and shown to be much more difficult. Available observations are consistent with the hypothesis that at z = 3 and possibly still at z = 1.5 nearly all baryons are located in the highly ionized Lα forest component, while at later epochs the contribution of a low-density, shock-heated component (105–107 K), the so called warm-hot intergalactic medium (WHIM), occupies with decreasing redshift an increasing fraction of all baryons. Methods to detect this component and the difficulty to make quantitative estimates are described. In the local universe 1/3 of all baryons may be hidden in the WHIM. Yet at z = 1.5, this component contains at least a factor of 5 less material.

(Abridged) Aims. We intend to derive statistical properties of stochastic gas motion inside the dense low mass star forming molecular cores traced by NH3(1,1) and (2,2) emission lines. Methods. We use the spatial two-point autocorrelation (ACF) and structure functions calculated from maps of the radial velocity fields. Results. We find oscillating ACFs which eventually decay to zero with increasing lags on scales of 0.04, 11 pages, 16 figures, 3 tables, to be published in Astronomy and Astrophysics

STIS Echelle observations at a resolution of 10 km/s and UVES/VLT spectroscopy at a resolution of 7 km/s of the luminous QSO HE 0515-4414 (z_em = 1.73, B = 15.0) reveal four intervening O VI absorption systems in the redshift range 1.2 < z_abs < 1.7 (1.38503, 1.41601, 1.60175, 1.67359). In addition two associated systems at z = 1.69707 and z = 1.73585 are present. For the first time high resolution observations allow to measure radial velocities of H I, C IV and O VI simultaneously in several absorption systems (1.385, 1.674, 1.697) with the result that significant velocity differences (up to 18 km/s) are observed between H I and O VI, while smaller differences (up to 5 km/s) are seen between C IV and O VI. We tentatively conclude that H I, O VI, and C IV are not formed in the same volumes and that therefore implications on ionization mechanisms are not possible from observed column density ratios O VI/H I or O VI/C IV. The number density of O VI absorbers with W_rest > 25 mA is dN/dz < 10, roughly a factor of 5 less than what has been found by Tripp at al. (2000) at low redshift. An estimate of the cosmological mass-density of the O VI-phase yields Omega_b(O VI) = 0.0003 h^{-1}_{75} for [O/H] = -1 and an assumed ionization fraction O VI/O = 0.2. This corresponds to an increase by roughly a factor of 15 between z = 1.5 (this work) and the value found by Tripp et al. (2000) at z = 0.21, if the same oxygen abundance [O/H] = -1 is assumed. Agreement with the simulations by Dave et al. (2001) can be obtained, if the oxygen abundance increases by a factor of 3 over the same redshift interval., Comment: 8 pages, 1 figure, accepted for publication in A&A

HR 2554 is an eclipsing binary system that contains a G6 II primary star and an A dwarf secondary. We have obtained ultraviolet spectra during two eclipses of HR 2554 in 1994 March–April and 1995 May using the HST Goddard High Resolution Spectrograph (GHRS) to study the atmospheric structure of the primary and to better establish the properties of the binary system. We have determined accurate orbital elements for both components, using new and existing optical spectra for the primary and the GHRS spectra for the secondary, in conjunction with eclipse photometry presented in 1992 by Schroder & Hunsch. The derived orbital period is 195.258 ± 0.003 days, the derived radii are 31.3 ± 0.9 R⊙ and 1.9 ± 0.1 R⊙, and the derived masses are 3.14 ± 0.17 M⊙ and 1.98 ± 0.11 M⊙, respectively. The resulting positions of HR 2554 in the Hertzsprung-Russell (H-R) diagram are somewhat inconsistent with the independent evolution of the component stars; in particular, the G star primary is both overluminous and too blue for its mass. The difficulties might be overcome if the metallicity of the system were unusually low ([Fe/H] ~ -1), but this possibility appears to be ruled out by the [Fe/H] = -0.04 determination of Eggen. We suspect HR 2554 has undergone a more complicated evolutionary history involving mass transfer than has been considered previously.

Using new HST/FOS, NTT/EMMI, and Keck/HIRES spectra of the gravitationally-lensed double QSO HE 1104-1805 AB (z=2.31, \theta=3.2), and assuming UV photoionization by a metagalactic radiation field, we derive physical conditions (ionization levels, metal abundances and cloud sizes along the lines of sight) in five CIV+MgII absorption systems clustered around z=1.66 along the two lines of sight. Three of these systems are associated with a damped Ly-alpha (DLA) system with logN(HI)=20.85, which is observed in A. The other two systems are associated with a Lyman-limit system with logN(HI)=17.57 (B). The CIV and MgII line profiles in A resemble those in the B spectra, and span \Delta v=360 km/s. Assuming that the relative metal abundances in these absorption systems are the same as observed in the DLA system, we find that the observed N(CIV)/N(MgII) ratios imply ionization parameters of log\Gamma=-2.95 to -2.35. Consequently, these clouds should be small (0.5-1.6 kpc with a hydrogen density n_H= 100 kpc) highly ionized low-density clouds (n_H\sim e-4 cm-3), in which OVI, but only weak CIV absorption occurs. In this state, log\Gamma>=-1.2 reproduces the observed ratio of N(OVI)/N(NV)>60. These results are discussed in view of the disk/halo and hierarchical structure formation models., Comment: LaTeX, 49 pages including 10 figures, minor changes introduced. Now in press at ApJ (1999 March 10 issue)

We present a further list of 274 bright QSOs, 106 (195) of which have (17.5), selected semiautomatically from objective prism plates taken with the Calar Alto 80 cm Schmidt telescope. All QSOs have been confirmed by follow-up spectroscopy and we display their flux-calibrated spectra. We also discuss the completeness of our search technique and demonstrate that for and we have been able to recover roughly 85% of known QSOs; 10% were lost due to overlaps while 5% were lost during the selection process. In particular the bright QSOs (17 with ) are potential targets for follow-up spectroscopy both at high-resolution from the ground and in the ultraviolet from space.

The Hamburg Quasar Survey is a wide-angle objective prism survey for finding bright QSOs in the northern extragalactic sky ($|b| > 20^{\circ}$; $\delta > 0^{\circ}$). The taking of the prism plates for 567 fields covering this area was completed in 1997. Including direct plates for fields with $\delta > 20^{\circ}$ the plate archive contains now 1871 plates. In this paper we present a first list of 121 quasars, which were verified by slit spectroscopy in the years 1986-1991, while experiments to develop efficient selection techniques were made. The sample contains objects with brightnesses $15\leq B \leq 19.5$ and redshifts $z\leq 2.8$ collected over various parts of the sky, for which objective prism plates were available at that time.

We present the Hamburg/RASS Catalogue of optical identications (HRC). The catalogue contains op- tical information about objects inside the error circles of ROSAT All-Sky Survey (RASS) sources. The information was gathered from objective prism and direct plates taken by the Hamburg Quasar Survey (HQS). The plates enable an eective selection of several X-ray emitting classes of objects, as there are galaxies, AGN, QSOs, galaxy clusters and several types of galactic stars, in particular M dwarfs, hot white dwarfs and cataclysmic variables. In the cur- rent state (November 1996) the HRC contains information about 3847 X-ray positions and covers about 8480 deg 2 of the high galactic latitude (jbj > 20) northern sky. For 81:2% of the X-ray sources a plausible optical counter- part is given. The counterparts of the remaining sources are probably faint ( B> 18:5) AGN and galaxy clusters. The HRC is available electronically together with nding charts taken from the digitized direct HQS plates.

HE0512–3329 is a gravitationally-lensed double QSO with damped Ly $\alpha$ systems observed at $z=0.931$ in front of both QSO images (DLA A and B). We have obtained spatially resolved HST STIS and optical VLT UVES spectra of both QSOs in order to study differences in the metal abundances across the lines of sight. We detect substantial differences, of roughly 0.5 dex, in both [Mn/H] and [Fe/H], on a transverse scale of 5 $h^{-1}$ kpc. Differential dust depletion appears as the most plausible explanation.

We present an accurate analysis of the H2 absorption lines from the zabs ~ 2.4018 damped Ly{\alpha} system towards HE 0027-1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Southern Observatory Large Programme "The UVES large programme for testing fundamental physics" to constrain the variation of proton-to-electron mass ratio, {\mu} = mp/me. We perform cross-correlation analysis between 19 individual exposures taken over three years and the combined spectrum to check the wavelength calibration stability. We notice the presence of a possible wavelength dependent velocity drift especially in the data taken in 2012. We use available asteroids spectra taken with UVES close to our observations to confirm and quantify this effect. We consider single and two component Voigt profiles to model the observed H2 absorption profiles. We use both linear regression analysis and Voigt profile fitting where {\Delta}{\mu}/{\mu} is explicitly considered as an additional fitting parameter. The two component model is marginally favored by the statistical indicators and we get {\Delta}{\mu}/{\mu} = (-2.5 +/- 8.1(stat) +/- 6.2(sys)) ppm. When we apply the correction to the wavelength dependent velocity drift we find {\Delta}{\mu}/{\mu} = (-7.6 +/- 8.1(stat) +/- 6.3(sys)) ppm. It will be important to check the extent to which the velocity drift we notice in this study is present in UVES data used for previous {\Delta}{\mu}/{\mu} measurements., Comment: Accepted for publication in MNRAS

Absorption line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, {\alpha}, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations of {\alpha} on cosmological scales which may reach a fractional level of ~ 10 ppm (parts per million). To test these claims we are conducting a Large Program with the VLT UVES . We are obtaining high-resolution (R ~ 60000 and high signal-to-noise ratio (S/N ~ 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this Program, that of HE 2217-2818. We apply the Many Multiplet method to measure {\alpha} in 5 absorption systems towards this quasar: zabs = 0.7866, 0.9424, 1.5558, 1.6279 and 1.6919. The most precise result is obtained for the absorber at zabs = 1.6919 where 3 Fe II transitions and Al II {\lambda}1670 have high S/N and provide a wide range of sensitivities to {\alpha}. The absorption profile is complex, with several very narrow features, and requires 32 velocity components to be fitted to the data. Our final result for the relative variation in {\alpha} in this system is Delta{\alpha}/{\alpha} = +1.3 +/- 2.4stat +/- 1.0sys ppm. This is one of the tightest current bounds on {\alpha} variation from an individual absorber. The absorbers towards quasar HE 2217-2818 reveal no evidence for variation in {\alpha} at the 3 ppm precision level (1{\sigma} confidence). If the recently reported 10 ppm dipolar variation of {\alpha} across the sky were correct, the expectation at this sky position is (3.2-5.4) +/-1.7 ppm depending on dipole model used . Our constraint of Delta{\alpha}/{\alpha}=+1.3+/-2.4stat +/-1.0sys ppm is not inconsistent with this expectation., Comment: 17 pages, 8 figures, accepted Astronomy Astrophysics 2013

(Abridged) Aims. To probe the spectral energy distribution (SED) of the ionizing background radiation at z ~ 2 and to specify the sources contributing to the intergalactic radiation field. Methods. The spectrum of a bright quasar HS1103+6416 (zem = 2.19) contains five successive metal-line absorption systems at zabs = 1.1923, 1.7193, 1.8873, 1.8916, and 1.9410. The systems are optically thin and reveal multiple lines of different metal ions with the ionization potentials lying in the extreme ultraviolet (EUV) range (1 Ryd to 0.2 keV). For each system, the EUV SED of the underlying ionization field is reconstructed by means of a special technique developed for solving the inverse problem in spectroscopy. For the zabs = 1.8916 system, the analysis also involves the HeI resonance lines of the Lyman series and the HeI 504 A continuum, which are seen for the first time in any cosmic object except the Sun. Results. From one system to another, the SED of the ionizing continuum changes significantly, indicating that the intergalactic ionization field at z ~ 2 fluctuates at the scale of at least Delta_z ~ 0.004. This is consistent with Delta_z ~ 0.01 estimated from HeII and HI Lyman-alpha forest measurements between the redshifts 2 and 3., 29 pages, 18 figures, 3 tables, accepted for publication in A\&A

(Abridged) Aims. In the present part of our survey we search for ammonia emitters in the Aquila rift complex which trace the densest regions of molecular clouds. Methods. From a CO survey carried out with the Delingha 14-m telescope we selected ~150 targets for observations in other molecular lines. Here we describe the mapping observations in the NH3(1,1) and (2,2) inversion lines of the first 49 sources performed with the Effelsberg 100-m telescope. Results. The NH3(1,1) and (2,2) emission lines are detected in 12 and 7 sources, respectively. Among the newly discovered NH3 sources, our sample includes the following well-known clouds: the starless core L694-2, the Serpens cloud Cluster B, the Serpens dark cloud L572, the filamentary dark cloud L673, the isolated protostellar source B335, and the complex star-forming region Serpens South. Angular sizes between 40" and 80" (~0.04-0.08 pc) are observed for compact starless cores but as large as 9' (~0.5 pc) for filamentary dark clouds. The measured kinetic temperatures of the clouds lie between 9K and 18K. From NH3 excitation temperatures of 3-8K we determine H2 densities with typical values of ~(0.4-4) 10^4 cm^-3. The masses of the mapped cores range between ~0.05 and ~0.5M_solar. The relative ammonia abundance, X= [NH3]/[H2], varies from 10^-7 to 5 10^-7 with the mean = (2.7+/-0.6) 10^-7 (estimated from spatially resolved cores assuming the filling factor eta = 1). In two clouds, we observe kinematically split NH3 profiles separated by ~1 km/s. The splitting is most likely due to bipolar molecular outflows for one of which we determine an acceleration of, Comment: 28 pages, 22 figures, 6 tables, accepted for publication in A&A

The methanol molecule CH3OH has a complex microwave spectrum with a large number of very strong lines. This spectrum includes purely rotational transitions as well as transitions with contributions of the internal degree of freedom associated with the hindered rotation of the OH group. The latter takes place due to the tunneling of hydrogen through the potential barriers between three equivalent potential minima. Such transitions are highly sensitive to changes in the electron-to-proton mass ratio, mu = m_e/m_p, and have different responses to mu-variations. The highest sensitivity is found for the mixed rotation-tunneling transitions at low frequencies. Observing methanol lines provides more stringent limits on the hypothetical variation of mu than ammonia observation with the same velocity resolution. We show that the best quality radio astronomical data on methanol maser lines constrain the variability of mu in the Milky Way at the level of |Delta mu/mu| < 28x10^{-9} (1sigma) which is in line with the previously obtained ammonia result, |Delta mu/mu| < 29x10^{-9} (1��). This estimate can be further improved if the rest frequencies of the CH3OH microwave lines will be measured more accurately., 7 pages, 1 table, 1 figure. Accepted for publication in ApJ

We describe a new method to search for metal-poor candidates from the Hamburg/ESO objective-prism survey (HES) based on identifying stars with apparently strong CH G-band strengths for their colors. The hypothesis we exploit is that large over-abundances of carbon are common among metal-poor stars. The selection was made by considering two line indices in the 4300A region, applied directly to the low-resolution prism spectra. This work also extends a previously published method by adding bright sources to the sample. The spectra of these stars suffer from saturation effects, compromising the index calculations and leading to an undersampling of the brighter candidates. Visual inspection and classification of the spectra from the HES plates yielded a list of 5,288 new metal-poor candidates, which are presently being used as targets for medium-resolution spectroscopic follow-up. Estimates of the stellar atmospheric parameters, as well as carbon abundances, are now available for 117 of the first candidates, based on follow-up medium-resolution spectra obtained with the SOAR 4.1m and Gemini 8m telescopes. We demonstrate that our new method improves the metal-poor star fractions found by our pilot study by up to a factor of three in the same magnitude range, as compared with our pilot study based on only one CH G-band index. Our selection scheme obtained roughly a 40% success rate for identification of stars with [Fe/H] < -1.0; the primary contaminant is late-type stars with near solar abundances and, often, emission line cores that filled in the CaII K line on the prism spectrum. Because the selection is based on carbon, we greatly increase the numbers of known CEMP stars from the HES with intermediate metallicities -2.0 < [Fe/H] < -1.0, which previous survey efforts undersampled. There are eight newly discovered stars with [Fe/H] < -3.0 in our sample, including two with [Fe/H] < -3.5., 18 pages, 13 figures; accepted for publication in AJ

(Abridged) In our previous work we found a statistically significant offset Delta V = 27 m/s between the radial velocities of the HC3N(2-1) and NH3(1,1) transitions observed in molecular cores from the Milky Way. This may indicate that the electron-to-proton mass ratio, mu = m_e/m_p, increases by 3x10^{-8} when measured under interstellar conditions with matter densities of more than 10 orders of magnitude lower as compared with laboratory (terrestrial) environments. We now map four molecular cores L1498, L1512, L1517, and L1400K selected from our previous sample in order to estimate systematic effects in Delta V due to possible velocity gradients. We find that in two cores L1498 and L1512 the NH3(1,1) and HC3N(2-1) transitions closely trace the same material and show an offset of Delta V = 26.9 +/- 1.2_stat +/- 3.0_sys m/s throughout the entire clouds. The measured velocity offset, being expressed in terms of Delta mu = (mu_obs - mu_lab)/mu_lab, gives Delta mu = (26 +/- 1_stat +/- 3_sys)x10^{-9}., 14 pages, 5 figures, 6 tables. Accepted for publication in Astronomy and Astrophysics