Astrophysics

A principal challenge currently facing biologists is how to connect the complete DNA sequence of an organism to its development and behaviour. Large-scale targeted-deletions have been successful in defining gene functions in the single-celled yeast Saccharomyces cerevisiae, but comparable analyses have yet to be performed in an animal. Here we describe the use of RNA interference to inhibit the function of ,86% of the 19,427 predicted genes of C. elegans. We identified mutant phenotypes for 1,722 genes, about two-thirds of which were not previously associated with a phenotype. We find that genes of similar functions are clustered in distinct, multi-megabase regions of individual chromosomes; genes in these regions tend to share transcriptional profiles. Our resulting data set and reusable RNAi library of 16,757 bacterial clones will facilitate systematic analyses of the connections among gene sequence, chromosomal location and gene function in C. elegans. The ability to inactivate a target gene transiently by RNAi 1 has greatly accelerated the analysis of loss-of-function phenotypes in C. elegans and other organisms. Although several large-scale RNAibased screens have been used to study gene function in C. elegans 2-4 , in total only about a third of the predicted genes have been analysed so far. Genome-wide RNAi analyses would not only provide a key resource for studying gene function in C. elegans but should also address important issues in functional genomics, such as the global organization of gene functions in a metazoan genome. In addition, because more than half of the genes in C. elegans have a human homologue, this kind of functional analysis in the worm should provide insights into human gene function.

So far the masses of about 50 active galactic nuclei have been measured through the reverberation mapping technique (RM). Most measurements have been performed for objects of moderate luminosity and redshift, based on Hβ, which is also used to calibrate the scaling relation which allows single-epoch (SE) mass determination based on AGN luminosity and the width of different emission lines. The SE mass obtained from CIV(1549 Å) line shows a large spread around mean values, due to complex structure and gas dynamics of the relevant emission region. Direct RM measures of CIV exist for only 6 AGNs of low luminosity and redshift, and only one luminous quasar ). We have collected since 2003 photometric and spectroscopic observations of PG1247+267, the most luminous quasar ever analyzed for RM. We provide light curves for the continuum and for CIV(1549 Å) and CIII](1909 Å), and measures of the reverberation time lags based on the SPEAR method . The sizes of the line emission regions are in a ratio R CIII] /R CIV ∼ 2, similar to the case of Seyfert galaxies, indicating for the first time a similar ionization stratification in a luminous quasar and low luminosity nuclei. Due to relatively small broad line region size and relatively narrow line widths, we estimate a small mass and an anomalously high Eddington ratio. We discuss the possibility that either the shape of the emission region or an amplification of the luminosity caused by gravitational lensing may be in part responsible of the result.

Context. Active galaxies are characterized by variability at every wavelength, with timescales from hours to years depending on the observing window. Optical variability has proven to be an effective way of detecting AGNs in imaging surveys, lasting from weeks to years. Aims. In the present work we test the use of optical variability as a tool to identify active galactic nuclei in the VST multiepoch survey of the COSMOS field, originally tailored to detect supernova events. Methods. We make use of the multiwavelength data provided by other COSMOS surveys to discuss the reliability of the method and the nature of our AGN candidates. Results. The selection on the basis of optical variability returns a sample of 83 AGN candidates; based on a number of diagnostics, we conclude that 67 of them are confirmed AGNs (81% purity), 12 are classified as supernovae, while the nature of the remaining 4 is unknown. For the subsample of AGNs with some spectroscopic classification, we find that Type 1 are prevalent (89%) compared to Type 2 AGNs (11%). Overall, our approach is able to retrieve on average 15% of all AGNs in the field identified by means of spectroscopic or X-ray classification, with a strong dependence on the source apparent magnitude (completeness ranging from 26% to 5%). In particular, the completeness for Type 1 AGNs is 25%, while it drops to 6% for Type 2 AGNs. The rest of the X-ray selected AGN population presents on average a larger rms variability than the bulk of non-variable sources, indicating that variability detection for at least some of these objects is prevented only by the photometric accuracy of the data. The low completeness is in part due to the short observing span: we show that increasing the temporal baseline results in larger samples as expected for sources with a red-noise power spectrum. Our results allow us to assess the usefulness of this AGN selection technique in view of future wide-field surveys.

Preliminary results of a study of automatically detected variable objects are presented. The sample is divided into stellar and diffuse objects and the corresponding integrated counts as a function of magnitude are evaluated and compared with results in the literature.

We have isolated a sample of 14 candidate variable objects with extended image structure to B J = 22.5 in 0.284 deg 2 of Selected Area 57. The majority of candidates are blue (U -B < 0) and relatively compact. At fainter magnitudes, there is a steep rise in the number of variable objects. These objects are also compact and blue, and some of them are likely to be truly stellar. Twelve of the B J ≤ 22.5 candidates have been observed spectroscopically over limited ranges of wavelength and a variety of resulting signal-to-noise. Three of the four brightest have broad emission lines characteristic of Seyfert 1 galaxies. The fourth has a highly variable spectrum consistent with Seyfert-like activity. A fifth candidate has emission line ratios nominally consistent with a Seyfert 2 galaxy. In most cases where we have not been able to confirm a Seyfert spectroscopic type, the spectra are of insufficient quality or coverage to rule out such a classification. Based on spectroscopic and photometric redshift information, the majority of candidates have luminosities less than 10% of

We performed a new analysis of B and R light curves of a sample of PG quasars. We confirm the variability-redshift correlation and its explanation in terms of spectral variability, coupled with the increase of rest-frame observing frequency for quasars at high redshift. The analysis of the instantaneous spectral slope for the whole quasar samples indicates both an inter-QSO and intra-QSO variability-luminosity correlation. Numerical simulations show that the latter correlation cannot be entirely due to the addition of the host galaxy emission to a nuclear spectrum of variable luminosity but constant shape, implying a spectral variability of the nuclear component. Changes of accretion rate are also insufficient to explain the amount of spectral variation, while hot spots possibly caused by local disk instabilities can explain the observations.

The variability of the continuum spectral energy distribution has been analyzed for a complete magnitude-limited sample of quasars in Selected Area 57, observed at two epochs in the photographic U, F, and N bands with the Mayall 4 m telescope at Kitt Peak National Observatory. Changes da of B J , the spectral slope a appear correlated with brightness variations indicating an average hardening d log f l , of the spectrum in the bright phases. This conÐrms that the correlation of variability with redshift, found in a single observing band, is due to intrinsic spectral changes. The average observed relation daÈd log f l is consistent with the spectral change due to temperature variation of a blackbody of about 2.5 ] 104 K.

Context. Variability is a property shared by virtually all active galactic nuclei (AGNs), and was adopted as a criterion for their selection using data from multi epoch surveys. Low Luminosity AGNs (LLAGNs) are contaminated by the light of their host galaxies, and cannot therefore be detected by the usual colour techniques. For this reason, their evolution in cosmic time is poorly known. Consistency with the evolution derived from X-ray detected samples has not been clearly established so far, also because the low luminosity population consists of a mixture of different object types. LLAGNs can be detected by the nuclear optical variability of extended objects. Aims. Several variability surveys have been, or are being, conducted for the detection of supernovae (SNe). We propose to re-analyse these SNe data using a variability criterion optimised for AGN detection, to select a new AGN sample and study its properties. Methods. We analysed images acquired with the wide field imager at the 2.2 m ESO/MPI telescope, in the framework of the STRESS supernova survey. We selected the AXAF field centred on the Chandra Deep Field South where, besides the deep X-ray survey, various optical data exist, originating in the EIS and COMBO-17 photometric surveys and the spectroscopic database of GOODS. Results. We obtained a catalogue of 132 variable AGN candidates. Several of the candidates are X-ray sources. We compare our results with an HST variability study of X-ray and IR detected AGNs, finding consistent results. The relatively high fraction of confirmed AGNs in our sample (60%) allowed us to extract a list of reliable AGN candidates for spectroscopic follow-up observations.

Context. Supermassive black holes with masses of 10 5 -10 9 M are believed to inhabit most, if not all, nuclear regions of galaxies, and both observational evidence and theoretical models suggest a scenario where galaxy and black hole evolution are tightly related. Luminous AGNs are usually selected by their non-stellar colours or their X-ray emission. Colour selection cannot be used to select low-luminosity AGNs, since their emission is dominated by the host galaxy. Objects with low X-ray to optical ratio escape even the deepest X-ray surveys performed so far. In a previous study we presented a sample of candidates selected through optical variability in the Chandra Deep Field South, where repeated optical observations were performed in the framework of the STRESS supernova survey. Aims. The analysis is devoted to breaking down the sample in AGNs, starburst galaxies, and low-ionisation narrow-emission line objects, to providing new information about the possible dependence of the emission mechanisms on nuclear luminosity and blackhole mass, and eventually studying the evolution in cosmic time of the different populations. Methods. We obtained new optical spectroscopy for a sample of variability selected candidates with the ESO NTT telescope. We analysed the new spectra, together with those existing in the literature and studied the distribution of the objects in U -B and B -V colours, optical and X-ray luminosity, and variability amplitude. Results. A large fraction (17/27) of the observed candidates are broad-line luminous AGNs, confirming the efficiency of variability in detecting quasars. We detect: i) extended objects which would have escaped the colour selection and ii) objects of very low X-ray to optical ratio, in a few cases without any X-ray detection at all. Several objects resulted to be narrow-emission line galaxies where variability indicates nuclear activity, while no emission lines were detected in others. Some of these galaxies have variability and X-ray to optical ratio close to active galactic nuclei, while others have much lower variability and X-ray to optical ratio. This result can be explained by the dilution of the nuclear light due to the host galaxy. Conclusions. Our results demonstrate the effectiveness of supernova search programmes to detect large samples of low-luminosity AGNs. A sizable fraction of the AGN in our variability sample had escaped X-ray detection (5/47) and/or colour selection (9/48). Spectroscopic follow-up to fainter flux limits is strongly encouraged.

Aims. The aim of the present paper is to identify and study the properties and galactic content of groups and clusters in the GOODS-South field up to z ∼ 2.5, and to analyse the physical properties of galaxies as a continuous function of environmental density up to high redshift. Methods. We used the deep (z 850 ∼ 26), multi-wavelength GOODS-MUSIC catalogue, which has a 15% of spectroscopic redshifts and accurate photometric redshifts for the remaining fraction. On these data, we applied a (2+1)D algorithm, previously developed by our group, that provides an adaptive estimate of the 3D density field. We supported our analysis with simulations to evaluate the purity and the completeness of the cluster catalogue produced by our algorithm. Results. We find several high-density peaks embedded in larger structures in the redshift range 0.4-2.5. From the analysis of their physical properties (mass profile, M 200 , σ v , L X , U -B vs. B diagram), we find that most of them are groups of galaxies, while two are poor clusters with masses a few times 10 14 M . For these two clusters we find from the Chandra 2Ms data an X-ray emission significantly lower than expected from their optical properties, suggesting that the two clusters are either not virialised or are gas poor. We find that the slope of the colour magnitude relation, for these groups and clusters, is constant at least up to z ∼ 1. We also analyse the dependence on environment of galaxy colours, luminosities, stellar masses, ages, and star formations. We find that galaxies in high-density regions are, on average, more luminous and massive than field galaxies up to z ∼ 2. The fraction of red galaxies increases with luminosity and with density up to z ∼ 1.2. At higher z this dependence on density disappears. The variation of galaxy properties as a function of redshift and density suggests that a significant change occurs at z ∼ 1.5-2.

Context. It has been shown that the luminosity of active galactic nuclei and the size of their broad line region obey a simple relation of the type R BLR = aL γ , from faint Seyfert nuclei to bright quasars, allowing single-epoch determination of the central black hole mass M BH = bL γ ∆ 2 H β from their luminosity L and width of H β emission line. Adopting this mass determination for cosmological studies requires the extrapolation to high redshift and luminosity of a relation whose calibration relies so far on reverberation mapping measurements performed for L < ∼ 10 46 erg s -1 and redshift z < ∼ 0.4. Aims. We initiated a campaign for the spectrophotometric monitoring of a few luminous, intermediate redshift quasars whose apparent magnitude, V < 15.7, allows observations with a 1.8 m telescope, aimed at proving that emission lines vary and respond to continuum variations even for luminosities > ∼ 10 47 erg s -1 , and determining eventually their M BH from reverberation mapping. Methods. We have repeatedly performed simultaneous spectrophotometric observations of quasars and reference stars to determine relative variability of continuum and emission lines. We describe the observations and methods of analysis. Results. For the quasars PG 1634+706 and PG 1247+268 we obtain light-curves respectively for CIII](λλ1909 Å), MgII(λλ2798 Å) and for CIV(λλ1549 Å), CIII](λλ1909 Å) emission lines with the relevant continua. During 3.2 years of observation, in the former case no continuum variability was detected and the evidence for line variability is marginal, while in the latter case both continuum and line variability are detected with high significance and the line variations appear correlated with continuum variations. Conclusions. The detection of the emission line variability in a quasar with L ∼ 10 47 erg s -1 encourages the continuation of the monitoring campaign which should provide a black hole mass estimate in another 5-6 years, constraining the mass-luminosity relation in a poorly explored range of luminosity.

Context. The X-ray variability of the active galactic nuclei (AGN) has been most often investigated with studies of individual, nearby sources, and only a few ensemble analyses have been applied to large samples in wide ranges of luminosity and redshift. Aims. We aim to determine the ensemble variability properties of two serendipitously selected AGN samples extracted from the catalogues of XMM-Newton and Swift, with redshift between ∼0.2 and ∼4.5, and X-ray luminosities, in the 0.5-4.5 keV band, between ∼10 43 erg/s and ∼10 46 erg/s. Methods. We used the structure function (SF), which operates in the time domain, and allows for an ensemble analysis even when only a few observations are available for individual sources and the power spectral density (PSD) cannot be derived. The SF is also more appropriate than fractional variability and excess variance, because these parameters are biased by the duration of the monitoring time interval in the rest-frame, and therefore by cosmological time dilation. Results. We find statistically consistent results for the two samples, with the SF described by a power law of the time lag, approximately as SF ∝ τ 0.1 . We do not find evidence of the break in the SF, at variance with the case of lower luminosity AGNs. We confirm a strong anti-correlation of the variability with X-ray luminosity, accompanied by a change of the slope of the SF. We find evidence in support of a weak, intrinsic, average increase of X-ray variability with redshift. Conclusions. The change of amplitude and slope of the SF with X-ray luminosity provides new constraints on both single oscillator models and multiple subunit models of variability.

Context. The study of high-redshift bright quasars is crucial to gather information about the history of galaxy assembly and evolution. Variability analyses can provide useful data on the physics of quasar processes and their relation with the host galaxy. Aims. In this study, we aim to measure the black hole mass of the bright lensed BAL QSO APM 08279+5255 at z = 3.911 through reverberation mapping, and to update and extend the monitoring of its C IV absorption line variability. Methods. We perform the first reverberation mapping of the Si IV and C IV emission lines for a high-luminosity quasar at high redshift with the use of 138 R-band photometric data and 30 spectra available over 16 years of observations. We also cross-correlate the C IV absorption equivalent width variations with the continuum light curve to estimate the recombination time lags of the various absorbers and infer the physical conditions of the ionised gas. Results. We find a reverberation-mapping time lag of ∼900 rest-frame days for both Si IV and C IV emission lines. This is consistent with an extension of the BLR size-to-luminosity relation for active galactic nuclei up to a luminosity of ∼10 48 erg s -1 , and implies a black hole mass of 10 10 M . Additionally, we measure a recombination time lag of ∼160 days in the rest frame for the C IV narrow absorption system, which implies an electron density of the absorbing gas of ∼2.5 × 10 4 cm -3 . Conclusions. The measured black hole mass of APM 08279+5255 indicates that the quasar resides in an under-massive host-galaxy bulge with M bulge ∼ 7.5M BH , and that the lens magnification is lower than ∼8. Finally, the inferred electron density of the narrow-line absorber implies a distance of the order of 10 kpc of the absorbing gas from the quasar, placing it within the host galaxy.

Aims. We investigate the properties of cluster ClG 0332-2747 at z = 0.734 in the GOODS-South field, which was undetected in the Chandra 2Ms observations. We explore possible scenarios to explain the discrepancy between its low X-ray emission and that expected from the M -L X relation. Methods. We use the large public spectroscopic database available in the GOODS-South field to estimate the dynamical mass and the virialization status of ClG 0332-2747. Cluster members selected from their photometric redshift are used with spectroscopic ones to analyse the galaxy population of the cluster. In the newly released Chandra 4Ms observations we detect a faint extended X-ray emission associated to the cluster. Finally, we compare the optical and X-ray properties of ClG 0332-2747 with the predictions of a well-tested semianalytic model. Results. We estimate the velocity dispersion and the virial mass considering all 44 spectroscopic members, or 20 red-sequence members only. We obtain σ v = 634 ± 105 km s -1 , M 200 = 3.07 +1.57 -1.16 × 10 14 M in the former case, and slightly lower values in the latter case. The cluster appears to have reached the virial equilibrium: it shows a perfectly Gaussian velocity distribution and no evidence for substructures. ClG 0332-2747 contains a high fraction of bright red galaxies and is dominated by a very massive (1.1 × 10 12 M ) old brightest cluster galaxy (BCG), suggesting that it formed at an early epoch. We detect a faint extended X-ray source centred on the BCG, with a total X-ray luminosity of L X ∼ 2 × 10 42 erg s -1 (0.1-2.4 keV). This L X is lower by a factor of ∼10-20 than expected according to the M -L X relation. We provide a possible explanation of this discrepancy in assigning it to the effects of AGN feedback on the ICM: the semianalytic model reproduces the M -L X relation measured from "X-ray bright" clusters, and it predicts a high scatter at low masses owing to heating and expulsion of the cluster gas. Interestingly, the model clusters with an evolved galaxy population like ClG 0332-2747 present the largest scatter in X-ray luminosity. However, the low X-ray emission of ClG 0332-2747 is just marginally compatible with predictions, which indicates that additional feedback effects should be included in the model. Conclusions. We propose a scenario where "X-ray underluminous" clusters are explained by the strong feedback effect on the ICM in highly evolved clusters. Our hypothesis can be tested by the combined analysis of the galaxy population and of the X-ray emission in large cluster samples.

Aims. We study galaxy clustering and explore the dependence of galaxy properties on the the environment up to a redshift z ∼ 1, on the basis of a deep multi-band survey in the Chandra Deep Field South. Methods. We have developed a new method which combines galaxy angular positions and photometric redshifts to estimate the local galaxy number-density. This allows both the detection of overdensities in the galaxy distribution and the study of the properties of the galaxy population as a function of the environmental density. Results. We detect two moderate overdensities at z ∼ 0.7 and z ∼ 1 previously identified spectroscopically. We find that the fraction of red galaxies within each structure increases with volume density, extending to z ∼ 1 previous results. We measure "red sequence" slopes consistent with the values found in X-ray selected clusters, supporting the notion that the mass-metallicity relation hold constant up to z ∼ 1. Conclusions. Our method based on photometric redshifts allows to extend structure detection and density estimates up to the limits of photometric surveys, i.e. considerably deeper than spectroscopic surveys. Since X-ray cluster detection at high redshift is presently limited to massive relaxed structures, galaxy volume density based on photometric redshift appears as a valuable tool in the study of galaxy evolution.

We present results on a search of heavily obscured active galaxies z > 1.7 using the rest-frame 9-20 keV excess for X-ray sources detected in the deep XMM-CDFS survey. Out of 176 sources selected with the conservative detection criteria (>8σ) in the first source catalogue of Ranalli et al. (in prep.), 46 objects lie in the redshift range of interest with the median redshift z 2.5. Their typical rest-frame 10-20 keV luminosity is 10 44 erg s -1 , as observed. Among optically faint objects that lack spectroscopic redshift, four were found to be strongly absorbed X-ray sources, and the enhanced Fe K emission or absorption features in their X-ray spectra were used to obtain X-ray spectroscopic redshifts. Using the X-ray colour-colour diagram based on the rest-frame 3-5 keV, 5-9 keV, and 9-20 keV bands, seven objects were selected for their 9-20 keV excess and were found to be strongly absorbed X-ray sources with column density of N H ≥ 0.6 × 10 24 cm -2 , including two possible Compton thick sources. While they are emitting at quasar luminosity, ∼3/4 of the sample objects are found to be absorbed by N H > 10 22 cm -2 . A comparison with local AGN at the matched luminosity suggests an increasing trend of the absorbed source fraction for high-luminosity AGN towards high redshifts.

The Selected Area 57 is one of the best studied fields of the sky at all wavelengths and AGN samples have been selected with different techniques, including optical variability. We present preliminary analysis of a mediumdeep XMM-Newton observation of the field, yielding 140 X-ray sources, 90 of which are identified in the optical band.

Low Luminosity Active Galactic Nuclei (LLAGNs) are contaminated by the light of their host galaxies, thus they cannot be detected by the usual colour techniques. For this reason their evolution in cosmic time is poorly known. Variability is a property shared by virtually all active galactic nuclei, and it was adopted as a criterion to select them using multi epoch surveys. Here we report on two variability surveys in different sky areas, the Selected Area 57 and the Chandra Deep Field South.

Variability is a main property of active galactic nuclei (AGN) and it was adopted as a selection criterion using multi epoch surveys conducted for the detection of supernovae (SNe). We have used two SN datasets. First we selected the AXAF field of the STRESS project, centered in the Chandra Deep Field South where, besides the deep X-ray surveys also various optical catalogs exist. Our method yielded 132 variable AGN candidates. We then extended our method including the dataset of the ESSENCE project that has been active for 6 years, producing high quality light curves in the R and I bands. We obtained a sample of ∼4800 variable sources, down to R=22, in the whole 12 deg 2 ESSENCE field. Among them, a subsample of ∼500 high priority AGN candidates was created using as secondary criterion the shape of the structure function. In a pilot spectroscopic run we have confirmed the AGN nature for nearly all of our candidates.

Optical spectral variability of quasars and BL Lac Objects is compared by means of the spectral variability parameter β (Trevese & Vagnetti 2002). Both kinds of objects change their spectral slopes α, becoming bluer when brighter, but BL Lac Objects have smaller β values and are clearly separated from quasars in the αβ plane. Models accounting for the origin of the variability are discussed for both classes of objects.

A new analysis of the variability of the spectral slope of PG QSOs has been performed, on the basis of recent literature data in the B and R photometric bands. Preliminary results confirm our previous findings concerning the increase of variability with the rest-frame observing frequency. We also find a correlation of the spectral slope with luminosity, consistent with temperature changes of an emitting black body.

Context. Variability, both in X-ray and optical/UV, affects the well-known anti-correlation between the α ox spectral index and the UV luminosity of active galactic nuclei, contributing part of the dispersion around the average correlation (intra-source dispersion) in addition to the differences among the time-average α ox values from source to source (inter-source dispersion). Aims. We aim to evaluate the intrinsic α ox variations in individual objects and their effect on the dispersion of the α ox -L UV anticorrelation. Methods. We used simultaneous UV/X-ray data from Swift observations of a low-redshift sample to derive the epoch-dependent α ox (t) indices. We corrected for the host galaxy contribution by a spectral fit of the optical/UV data. We computed ensemble structure functions to analyse the variability of multi-epoch data. Results. We find a strong intrinsic α ox variability, which significantly contributes (∼40% of the total variance) to the dispersion of the α ox -L UV anti-correlation (intra-source dispersion). The strong X-ray variability and weaker UV variability of this sample are comparable to other samples of low-z active galactic nuclei, and are neither caused by the high fraction of strongly variable narrow line Seyfert 1 galaxies, nor by dilution of the optical variability by the host galaxies. Dilution instead affects the slope of the anticorrelation, which steepens, once corrected, and becomes similar to higher luminosity sources. The structure function of α ox increases with the time lag up to about one month. This indicates the important contribution of the intermediate-to-long timescale variations, which are possibly generated in the outer parts of the accretion disk.

Measurements of the W ± → ± ν and Z → + -production cross sections (where ± = e ± , µ ± ) in proton-proton collisions at √ s = 13 TeV are presented using data recorded by the ATLAS experiment at the Large Hadron Collider, corresponding to a total integrated luminosity of 81 pb -1 . The total inclusive W ± -boson production cross sections times the singlelepton-flavour branching ratios are σ tot W + = 11.83 ± 0.02 (stat) ± 0.32 (sys) ± 0.25 (lumi) nb and σ tot W -= 8.79 ± 0.02 (stat) ± 0.24 (sys) ± 0.18 (lumi) nb for W + and W -, respectively. The total inclusive Z-boson production cross section times leptonic branching ratio, within the invariant mass window 66 < m < 116 GeV, is σ tot Z = 1.981 ± 0.007 (stat) ± 0.038 (sys) ± 0.042 (lumi) nb. The W + , W -, and Z-boson production cross sections and cross-section ratios within a fiducial region defined by the detector acceptance are also measured. The crosssection ratios benefit from significant cancellation of experimental uncertainties, resulting in σ fid W + /σ fid W -= 1.295±0.003 (stat)±0.010 (sys) and σ fid W ± /σ fid Z = 10.31±0.04 (stat)±0.20 (sys). Theoretical predictions, based on calculations accurate to next-to-next-to-leading order for quantum chromodynamics and to next-to-leading order for electroweak processes and which employ different parton distribution function sets, are compared to these measurements.

In May 2002, the BL Lacertae object (BL Lac), 1ES1959+650, was detected in the Very High Energy (VHE) regime by the VERITAS collaboration using the Whipple γ-ray observatory. During the following two months, the VERITAS collaboration observed episodes of flaring; at times, the nightly average VHE signal was three times as bright as the Crab Nebula, the standard candle in VHE astronomy. 1ES1959+650 was also monitored in the optical and X-ray bands. The X-ray light curve showed periodic behavior and correlation with the VHE and the optical bands.

We are conducting a long-term deep spectral survey to investigate the distribution of Ap and Am stars in selected fields of the Milky Way and in open star clusters of different ages. The spectral survey is based on objective prism spectra obtained with an eight degree prism attached to the 70/98 cm meniscus telescope (f/3, 135 Å mm−1at Hδ) at the Abastumani Observatory. Kodak IIIa-J emulsions hypersensitized by baking in nitrogen gas are used in combination with a 500 Å FWHM filter centered on Hδ. A limiting magnitude ofmB= 14 was reached in an exposure time of 120 m. Study of the objective prism plates is still in a very early stage. Observations of the central part of the same field taken with a CCD resulted in a limiting magnitudemB= 16. On the basis of spectral material obtained, a wide range of spectra may be classified in the MK system.

We present the results of optical photometry of BL Lacertae carried out using ST-6 CCD camera attached to the Newtonian focus of the 70 cm meniscus telescope of Abastumani Observatory. On the basis of observations conducted since August 1997 during more than 550 nights about 17000 frames were collected. They have been reduced using Daophot II.It has been shown that optical variability of BL Lacertae is very complex. The maximum variation was observed at long-term scale and is equal to equals to 3.0 mag (rms=0.03) in B band, while the variation in V and R bands are within 2.71 mag (0.02) and 2.53 mag (0.01), respectively. This means that variations are larger at shorter wavelength or the object become bluer in the active phase. It were also demonstrated that BL Lacertae shows intra-day variability within 0.30 mag (0.02), while intra-hour variability within 0.10 mag (0.01) magnitudes.

We give a brief summary of the ongoing Abastumani Active Galactic Nuclei Monitoring Program started in the May 1997. More than 110000 frames are obtained during more than 1300 nights of observations for about 50 target objects, among them gamma-ray, X-ray and optical blazars. All observations were done in the BVRI bands using ST-6 CCD based photometer attached to the Newtonian focus of 70-cm meniscus telescope.

A low dispersion spectral survey (1250 ~/mm near HT) made with the 70-cm meniscus telescope in the region 90 ~ ~ ~ ~ 115 ~ , --'5~ ~ b ~ +5 ~ has led to the discovery of 267 carbon stars, 146 of which have been found for the first time. The distribution of the carbon stars in the investigated region with respect to latitude and longitude is uniform, and they have a Poisson surface distribution. The "nearest-neighbor" method shows that there is no excess of pairs of carbon stars or possible members of star clusters above their mathematical expectation.

We present intensive optical, infrared, and radio monitoring observations of the BL Lac object OJ 287, taken between the years 1993-1998. Two large optical outbursts were detected at the predicted times in November 1994 and December 1995. The detection of these outbursts supports the binary black hole model for OJ 287. Optical and radio polarisation observations show large variability in the degree of polarisation and position angle, very similar to those observed during the 1983/84 outburst in OJ 287. The polarisation position angles show very similar behaviour during these observations, indicating that, at least, the magnetic field orientations in radio and optical bands are related in OJ 287. Optical and infrared light curves show continuous variability in time scales ranging from tens of minutes to years. In the radio bands we have observed some of the lowest ever measured flux levels. During the first optical outburst in November 1994 the observed radio flux was very low, but during the second optical outburst radio bands also showed high flux levels. This is a puzzling observation, which can hopefully be used for discriminating between different outburst models. On top of the large outbursts OJ 287 has displayed flaring activity in time scales from days to weeks and shorter time scale flickering.

We present UBVRI light curves of BL Lacertae from May 2000 to January 2001, obtained by 24 telescopes in 11 countries. More than 15 000 observations were performed in that period, which was the extension of the Whole Earth Blazar Telescope (WEBT) campaign originally planned for July-August 2000. The exceptional sampling reached allows one to follow the flux behaviour in fine detail. Two different phases can be distinguished in the light curves: a first, relatively low-brightness phase is followed by an outburst phase, after a more than 1 mag brightening in a few weeks. Both the time duration (about 100 d) and the variation amplitude (roughly 0.9 mag) are similar in the two phases. Rapid flux oscillations are present all the time, involving variations up to a few tenths of mag on hour time scales, and witnessing an intense intraday activity of this source. In particular, a half-mag brightness decrease in about 7 h was detected on August 8-9, 2000, immediately followed by a ∼0.4 mag brightening in 1.7 h. Colour indexes have been derived by coupling the highest precision B and R data taken by the same instrument within 20 min and after subtracting the host galaxy contribution from the fluxes. The 620 indexes obtained show that the optical spectrum is weakly sensitive to the long-term trend, while it strictly follows the short-term flux behaviour, becoming bluer when the brightness increases. Thus, spectral changes are not related to the host galaxy contribution, but they are an intrinsic feature of fast flares. We suggest that the achromatic mechanism causing the long-term flux base-level modulation can be envisaged in a variation of the relativistic Doppler beaming factor, and that this variation is likely due to a change of the viewing angle. Discrete correlation function (DCF) analysis reveals the existence of a characteristic time scale of variability of ∼7 h in the light curve of the core WEBT campaign, while no measurable time delay between variations in the B and R bands is found.

The spectra of active galactic nuclei usually exhibit wings in some emission lines, such as [O iii]λλ5007, 4959, with these wings generally being blueshifted and related to strong winds and outflows. The aim of this work was to analyse the [O iii] emission lines in broad-line Seyfert 1 (BLS1) galaxies in order to detect the presence of wings, and to study the [O iii] line properties and their possible connection with the central engine. In addition, we attempted to compare the black hole mass distribution in both BLS1 galaxies with symmetric and blue-asymmetric [O iii] profiles. For this purpose, we carried out a spectroscopic study of a sample of 45 nearby southern BLS1 galaxies from the Six Degree Field Galaxy survey. The [O iii] emission lines were well-fitted using a single Gaussian function in 23 galaxies, while 22 objects presented a wing component and required a double-Gaussian decomposition. By computing the radial velocity difference between the wing and core centroids (i.e...

We present the light curves of chromospherically active binary systems, RT And and ER Vul, obtained during 1995-1998 in BV/UBVR filters at the Ankara University Observatory and the T ÜB İTAK National Observatory. In addition, the spot distributions for these systems are investigated by using the Wilson-Devinney program. Outside of the eclipses, the light curve variations are attributed to large cool spots located on one of components of the systems. While three spots were located on the primary component in the case of RT And, the location of three spots were considered on the secondary star in the case of ER Vul. From the spot motions in longitudes between 1995 and 1998, it was inferred that the migration period of the distortion wave has at value of 6.6 years for RT And.

High-resolution spectroscopic observations of the eclipsing RS CVn-type active close binaries SV Camelopardalis and XY Ursae Majoris reveal excess emission components in the Hα and Hβ lines. We have used the spectral subtraction technique to separate the excess emission from the photospheric background and find that in both stars the excess emission is associated with the secondary, cooler component. Analysis of the EWHα/EW Hβ ratio indicates that in both cases the emission is probably associated with surface plage regions or prominences viewed against the stellar disks. We find no evidence of excess absorption features associated with extended prominence-like material in these systems.

The study of stellar populations has gained importance in the last years thanks to the availability of high quality spectra of a considerable number of galaxies (for example the Sloan Digital Sky Survey-SDSS). Extracting the greater amount of information from ...

We present orbital parameters for six double-lined spectroscopic binaries (ι Pegasi, ω Draconis, 12 Boötis, V1143 Cygni, β Aurigae, and Mizar A) and two double-lined triple star systems (κ Pegasi and η Virginis). The orbital fits are based upon high-precision radial velocity observations made with a dispersed Fourier Transform Spectrograph, or dFTS, a new instrument which combines interferometric and dispersive elements. For some of the double-lined binaries with known inclination angles, the quality of our RV data permits us to determine the masses M 1 and M 2 of the stellar components with relative errors as small as 0.2%.

DISTANCIA MEDIA AL SOL (millones de km) DIAMETRO ECUATORIAL (kilómetros) DENSIDAD (gramos por centímetro cúbico) DURACION DEL DIA (respecto al terrestre) DURACION DEL AÑO (respecto al terrestre) NUMERO DE LUNAS CONOCIDAS COMPOSICION ATMOSFERICA

This theory challenges the mainstream view that Venus is the hottest planet. It proposes that Mercury, due to its proximity to the Sun and unfiltered solar radiation, is the most heated planetary body during its daytime, making it the true hottest planet under specific thermodynamic conditions.

We find the spectrum P (ω)dω of the gravitational wave background produced in the early universe in string theory. We work in the framework of the recently discussed String Driven Cosmology, whose scale factors are computed with the low-energy effective string equations as well as selfconsistent solutions of General Relativity with a gas of strings as source. The scale factor evolution is described by an early string driven inflationary stage with an instantaneous transition to a radiation dominated stage and successive matter dominated stage. This is a string cosmology expanding evolution always running on positive proper cosmic time. The spectrum of the generated gravitons is computed in the framework of Quantum Field Theory and in the appropiated effective String Cosmology context. We study and show explicitly the effect of the dilaton field, characteristic to this kind of cosmologies. We compute the spectrum for the same evolution description with three differents approachs. Some features of gravitational wave spectra, as peaks and asymptotic behaviours, are found direct consequences of the dilaton involved in the string low energy effective action and not only of the scale factor evolution. We make use of a careful treatment of the scale factor evolution and involved transitions. This allows us to compute a full prediction on the power spectrum of gravitational waves without any free-parameters. A comparative analysis of different treatments, solutions and compatibility with observational bounds or detection perspectives is made.

We compare the maximal abundance of massive systems predicted in different dynamical dark energy (DDE) models at high redshifts z ≈ 4 -7 with the measured abundance of the most massive galaxies observed to be already in place at such redshifts. The aim is to derive constraints for the evolution of the dark energy equation of state parameter w which are complementary to existing probes. We adopt the standard parametrization for the DDE evolution in terms of the local value w 0 and of the look-back time derivative w a of the equation of state. We derive constraints on combinations of (w 0 , w a ) in the different DDE models by using three different, independent probes: (i) the observed stellar mass function of massive objects at z ≥ 6 derived from the CANDELS survey; (ii) the estimated volume density of massive halos derived from the observation of massive, star-forming galaxies detected in the submillimeter range at z ≈ 4; (iii) The rareness of he most massive system (estimated gas mass exceeding 3 • 10 11 M ) observed to be in place at z ≈ 7, a far-infrared-luminous object recently detected in the South Pole Telescope (SPT) survey. Finally, we show that the combination of our results from the three above probes excludes a sizable fraction of the DDE parameter space w a -3/4 -(w 0 + 3/2) presently allowed (or even favored) by existing probes.

We show that the recently measured UV luminosity functions of ultra-faint lensed galaxies at z ≈ 6 in the Hubble Frontier Fields provide an unprecedented probe for the mass m X of the Warm Dark Matter candidates independent of baryonic physics. Comparing the measured abundance of the faintest galaxies with the maximum number density of dark matter halos in WDM cosmologies sets a robust limit m X ≥ 2.9 keV for the mass of thermal relic WDM particles at a 1-σ confidence level, m X ≥ 2.4 keV at 2-σ, and m X ≥ 2.1 keV at 3-σ. These constitute the tightest constraints on WDM particle mass derived to date from galaxy abundance independently of the baryonic physics involved in galaxy formation. We discuss the impact of our results on the production mechanism of sterile neutrinos. In particular, if sterile neutrinos are responsible for the 3.5 keV line reported in observations of X-ray clusters, our results firmly rule out the Dodelson-Widrow production mechanism, and yield m sterile 6.1 keV for sterile neutrinos produced via the Shi-Fuller mechanism.

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