AimsMost models identify the X-ray bright North Polar Spur (NPS) with a hot interstellar (IS) bubble in the Sco-Cen star-forming region at ≃130 pc. An opposite view considers the NPS as a distant structure associated with Galactic nuclear outflows. Constraints on the NPS distance can be obtained by comparing the foreground IS gas column inferred from X-ray absorption to the distribution of gas and dust along the line of sight. Absorbing columns towards shadowing molecular clouds simultaneously constrain the CO-H2 conversion factor.MethodsWe derived the columns of X-ray absorbing matter N Habs from spectral fitting of dedicated XMM-Newton observations towards the NPS southern terminus (l II ≃ 29°, b II ≃ +5 to +11°). The distribution of the IS matter was obtained from absorption lines in stellar spectra, 3D dust maps and emission data, including high spatial resolution CO measurements recorded for this purpose.ResultsN Habs varies from ≃ 4.3 to ≃ 1.3 × 1021 cm-2 along the 19 fields. Relationships between X-ray brightness, absorbing column and hardness ratio demonstrate a brightness decrease with latitude governed by increasing absorption. The comparison with absorption data, local and large-scale dust maps rules out a NPS near side closer than 300 pc. The correlation between N Habs and the reddening increases with the sightline length from 300 pc to 4 kpc and is the tightest with Planck τ 353GHz -based reddening, suggesting a much larger distance. N(H)/E(B-V) τ ≃ 4.1 × 1021 cm-2 mag-1, close to Fermi-Planck determinations. N Habs absolute values are compatible with HI-CO clouds at -5 ≤ V LSR ≤ +25 to +45 km s-1 and a NPS potentially far beyond the Local Arm. A shadow cast by a b=+9° molecular cloud constrains X CO in that direction to ≤ 1.0 × 1020 cm-2 K-1 km-1 s. The average X CO over the fields is ≤ 0.75 × 1020 cm-2 K-1 km-1 s.
ContextIn July 2015, the high-mass X-ray binary V0332+53 underwent a giant outburst, a decade after the previous one. V0332+53 hosts a strongly magnetized neutron star. During the 2004-2005 outburst, an anti-correlation between the centroid energy of its fundamental cyclotron resonance scattering features (CRSFs) and the X-ray luminosity was observed.AimsThe long (≈ 100 d) and bright (L x ≈ 1038 erg s-1) 2015 outburst offered the opportunity to study during another outburst the unique properties of the fundamental CRSF and its dependence on the X-ray luminosity.MethodsThe source was observed by the INTEGRAL satellite for ~ 330 ks. We exploit the spectral resolution at high energies of the SPectrometer on INTEGRAL (SPI) and the Joint European X-ray Monitors to characterize its spectral properties, focusing in particular on the CRSF-luminosity dependence. We complement the data of the 2015 outburst with those collected by SPI in 2004-2005 and left unpublished so far.ResultsWe find a highly significant anti-correlation of the centroid energy of the fundamental CRSF and the 3 -100 keV luminosity of E 1 ∝ -0.095(8)L 37 keV. This trend is observed for both outbursts. We confirm the correlation between the width of the fundamental CRSF and the X-ray luminosity previously found in the JEM-X and IBIS dataset of the 2004-2005 outburst. By exploiting the RXTE/ASM and Swift/BAT monitoring data we also report on the detection of a ~ 34 d modulation superimposed on the mean profiles and roughly consistent with the orbital period of the pulsar. We discuss possible interpretations of such variability.
Context:Jets are dynamic, impulsive, well-collimated plasma events that develop at many different scales and in different layers of the solar atmosphere.Aims:Jets are believed to be induced by magnetic reconnection, a process central to many astrophysical phenomena. Within the solar atmosphere, jet-like events develop in many different environments, e.g., in the vicinity of active regions as well as in coronal holes, and at various scales, from small photospheric spicules to large coronal jets. In all these events, signatures of helical structure and/or twisting/rotating motions are regularly observed. The present study aims to establish that a single model can generally reproduce the observed properties of these jet-like events.Methods:In this study, using our state-of-the-art numerical solver ARMS, we present a parametric study of a numerical tridimensional magnetohydrodynamic (MHD) model of solar jet-like events. Within the MHD paradigm, we study the impact of varying the atmospheric plasma β on the generation and properties of solar-like jets.Results:The parametric study validates our model of jets for plasma β ranging from 10-3 to 1, typical of the different layers and magnetic environments of the solar atmosphere. Our model of jets can robustly explain the generation of helical solar jet-like events at various β ≤ 1. This study introduces the new original result that the plasma β modifies the morphology of the helical jet, explaining the different observed shapes of jets at different scales and in different layers of the solar atmosphere.Conclusions:Our results allow us to understand the energisation, triggering, and driving processes of jet-like events. Our model allows us to make predictions of the impulsiveness and energetics of jets as determined by the surrounding environment, as well as the morphological properties of the resulting jets.
We present near-infrared H-band (1.65 micron) surface photometry of 558 galaxies in the Coma Supercluster and in the Virgo cluster. This data set, obtained with the Arcetri NICMOS3 camera ARNICA mounted on the Gornergrat Infrared Telescope, is aimed at complementing, with observations of mostly early-type objects, our NIR survey of spiral galaxies in these regions, presented in previous papers of this series. Magnitudes at the optical radius, total magnitudes, isophotal radii and light concentration indices are derived. We confirm the existence of a positive correlation between the near-infrared concentration index and the galaxy H-band luminosity. (Tables 1 and 2 are only available in electronic form upon request to gavazzi@uni.mi.astro.it)
Adaptive Optics (AO) has been developed to compensate the wavefront deformation due to the atmospheric turbulence. The wavefront correction, however, is often only partial and a residual blur is present in a long exposure image. It is therefore important to deconvolve the image to do accurate photometry or to detect faint structures. For this, the point spread function (PSF) has to be known. The PSF is highly variable in time and difficult to calibrate. We developed an algorithm which reconstructs the PSF of the ADONIS AO system from the wavefront sensor measurements. We present the results obtained for different observing conditions and discuss the limits of the method. We prove the existence of a local non-stationary turbulence from analyzing the spatial and temporal behaviour of the turbulent phase. We found difficult to achieve photometric precision higher than 5 to 10% on secondary components of multiple systems with flux ratio larger than 4.
We have used the 20 m Onsala and 15 m SEST telescopes to observe the CO J = 1 --> 0 (simultaneously with CO J = 2 --> 1 at SEST) and HCN J = 1 --> 0 (simultaneously with CS J = 3 --> 2 at SEST) transitions in 20 Seylert galaxies. The sample consists of the 18 galaxies detected in CO J = 1 --> 0 by Heckman et al. (1989) plus 2 which were riot detected in their survey. We have successfully detected all of the galaxies in the CO transition and 13 in HCN of which NGCs 1667, 2273, 5033, 5135, 6814 and Mrk 273 are new detections. For the galaxies in which the beam-width exceeds approximate to 10 kpc we find that LHCN/LCO approximate to 1/6, i.e. a global ratio similar to that of ultraluminous infrared galaxies and over 10 times the ratio for normal spiral galaxies. This implies that LFIR/LCO (L-FIR similar to 10(11) L-. Seyferts) approximate to 10 LFIR/LCO (normal spirals) and we believe that the far infrared fluxes in our sample arise from star-burst activity, although we cannot rule out the possibility of a contribution from active galactic nuclei.
The point spread function (PSF) of an adaptive optics system evolves in the Field Of View (FOV). This variation strongly limits the conventional deconvolution methods for the processing of wide FOV images. A theoretical expression of this PSF variation is derived. This expression is both validated on simulations and experimental data. It is then applied to the a posteriori processing of stellar fields. Using the available prior information about the object (point-like sources), this technique allows the restoration of the star parameters (positions and intensities) with a precision much better than the conventional methods, in a FOV much larger than the isoplanatic field.
We present here the very first spectropolarimetric results obtained with the multiline spectroscopy mode (MTR) of THEMIS. The principal problems found during the data analysis are exposed. A first characterisation of the quality of this observing mode is given.
Two time-dependent sets of two-dimensional hydrodynamic models of solar granulation have been analyzed to obtain dependence of simulated thermal convection on the horizontal size of the convection cells. The two sets of models treat thermal convection either as fully non-stationary, multiscale convection (granular convection is a surface phenomenon) or as quasi-steady-state convection cells (they treat granular convection as a collection of deep-formed cells). The following results were obtained:1) quasi-steady convection cells can be divided into 3 groups according to their properties and evolution, namely small-scale (up to L similar to 900 km)? intermediate-scale (1000 - 1500 km) and large-scale (larger 1500 km) convection cells. For the first group thermal damping due to radiative exchange of energy, mostly ill the horizontal direction, is very important. Large-scale cells build up a pressure excess, which can lead to their total fragmentation. Similar precesses also acts on the fully non-stationary convection.2) The largest horizontal size of convection cells for which steady-state solutions can be obtained is about 1500 km. This corresponds to granules, i.e. the bright parts of the convection cells, with a diameter of about 1000 km.3) In addition to the zone of high convective instability associated with the partial ionization of hydrogen, we identify another layer harboring important dynamic processes in steady-state models. Just below the hydrogen-ionization layer pressure fluctuations and the acoustic flux are reduced. Steady-state models with reflecting lateral boundaries even exhibit an inversion of pressure fluctuations there.4) From observational point of view the surface convection differs from steady-state deep treatment of thermal convection in the dependence of vertical granular velocities on their sizes for small-scale inhomogeneous. However, they cannot be distinguished by the dependence of temperature or emergent intensity of brightness structures.5) Both kinds of models demonstrate the inversion of density in subphotospheric layers. It is more pronounced in small-scale cells and inside hot upflows.6) The brightness of simulated granules linearly increases with their size for small granules and is approximately constant or even decreases slightly for larger granules. For intergranular lanes the simulations predict a decrease of their brightness with increasing size. It falls very rapidly for narrow lanes and remains unchanged for broader lanes.7) A quantitative comparison of the brightness properties of simulated granulation with real observations shows that the strong size-dependence of the properties of the smallest simulated granules is not accessible to current observations due to their limited spatial resolution. The observed size dependences result rather from spatial smoothing and the granule-finding algorithm. We do not exclude, however, an influence of the limitations of the 2-D treatment of thermal convection on the present results.
We report. on a homogeneous dynamical analysis of a sample of 21 round (17 E0/E1, 4 E2) elliptical galaxies. We present new kinematic data for eight of these galaxies and new photometry for one object. The remaining kinematic and photometric data and the required distance information are taken from the literature. The analysis uses non-parametric spherical models and takes into account line profile information as well as velocity dispersions. We present model fits to the kinematic data and the derived radial profiles of orbital anisotropy and B-band mass-to-light ratio, including confidence intervals. The circular velocity curves resulting from our model fits are all consistent with being flat outside R approximate to 0.3 R-e. Generally, the M/L ratio profiles show an outward increase, although models based on luminous matter are ruled out at 95% confidence only for three galaxies (NGC 2434, NGC 7507, NGC 7626). For NGC 1399, NGC 4472, NGC 4486, and NGC 4636, where X-ray observations are available, the mass profiles of the best fit models match the ones derived from the X-ray analysis. The best models for most galaxies are isotropic to slightly radially anisotropic, with typical beta less than or similar to 0.3, in a few cases beta less than or similar to 0.5 at R-e/2. We discuss the generally small effects of flattening along the line-of-sight (the expected < c/a > = 0.79 for this sample of luminous ellipticals) and of small embedded disks. Our results suggest that elliptical galaxies have surprisingly uniform dynamical properties.
Stromgren and H beta photometry of O and B type stars, generally brighter than 9.5 mag is reported for the field. of the Carina Spiral Feature. The observations are based on the PPM catalogue identifications and are designed to improve the completeness of the existing uvby beta data for the bright early-type stars in the field. We present new uvby photometry for 283 stars and H beta photometry for 225 of them. These observations are part of all ongoing effort to study the structure of selected star-forming regions in the Milky Way by means of uvby beta photometry. A comparison of the new data to other uvby beta data sets for this field is presented.
The Asiago Database on Photometric Systems (ADPS) is a compilation of basic information and refer- ence data on 167 optical, ultraviolet and infrared photo- metric systems. Thirty-four additional systems are briefly described. In compiling this census we have relied on pub- lished information only. In Paper II the photometric sys- tems will be inter-compared, calibrated and parameterised by means of synthetic photometry using uniform criteria and the same set of input spectra and extinction laws.
Optical positions of 2978 objects listed in the Second Byurakan Survey (SBS) were obtained using the Digitized Sky Survey (DSS), and are given with an rms uncertainty arcsec in each coordinate.
Spectral types are determined from low resolution optical spectra of 40 IRAS sources with far-infrared colours similar to planetary nebulae. The presence of circumstellar dust, high galactic latitude, and early supergiant or giant spectral type, sometimes with emission in the Balmer lines, indicate that some of these stars are low mass stars in the post-AGB stage of evolution.
We describe the construction of a catalogue of galaxies in the optical eld of the Hubble Deep Field South. The HDF-S observations produced WFPC2 images inU; B; V ,a ndI, the version 1 data have been made pub- lic on 23 November 1999. The eective eld of view is 4.38 arcmin 2 ,a nd the 5 limiting magnitudes (in a FWHM aperture) are 28.87, 29.71, 30.19, 29.58 in the U; B; V and I bands, respectively. We created a catalogue for each pass-band (I814,V606,B450,U300), using simulations to ac- count for incompleteness and spurious sources contamina- tion. Along with photometry in all bands, we determined on the I814-selected catalogue (I814 < 26) structural pa- rameters, such as a metric apparent size, derived from the petrosian radius, an asymmetry index, light concen- tration indexes and the mean surface brightness within the petrosian radius.
This paper presents flux-calibrated integrated spectra in the range 3600 9000 A for 7 concentrated, relatively populous Galactic open clusters. We perform si- multaneous estimates of age and foreground interstellar reddening by comparing the continuum distribution and line strengths of the cluster spectra with those of tem- plate cluster spectra with known parameters. For ve clus- ters these two parameters have been determined for the rst time (Ruprecht 144, BH 132, Pismis 21, Lyng a 11 and BH 217), while the results here derived for the remain- ing two clusters (Hogg 15 and Melotte 105) show very good agreement with previous studies based mainly on colour-magnitude diagrams. We also provide metallicity estimates for six clusters from the equivalent widths of CaII triplet and TiO features. The present cluster sample improves the age resolution around solar metal content in the cluster spectral library for population synthesis. We compare the properties of the present sample with those of clusters in similar directions. Hogg 15 and Pismis 21 are among the most reddened clusters in sectors centered at l = 270 and l =0 , respectively. Besides, the present results would favour an important dissolution rate of star clusters in these zones.
We analyse three clusters of galaxies, Abell 901 (z=0.17), Abell 1437 (z=0.13) and Abell 3570 (z=0.037). They have low to intermediate X-ray fluxes and an irregular morphology in the ROSAT All-Sky Survey (RASS). These clusters are chosen to test the abilities and limitations of the RASS in terms of cluster fluxes and cluster morphologies. Therefore some “worst” cases are used here. X-ray observations with the ROSAT/HRI and optical spectroscopic observations are carried out. The ROSAT/HRI observations, which have a much better spatial resolution than the RASS, reveal in two of the three cases a significantly different morphology than seen in the RASS. The reasons are point sources which could not be resolved in the RASS and were therefore confused with the cluster emission. For A3570 we could confirm the relaxed state of the cluster by the optical determination of a small velocity dispersion. In the cluster with the lowest flux (Abell 901) the countrate measurement is strongly affected by point sources, in the two other cases the countrate measurements of the RASS are reliable, i.e. they are reproduced by the ROSAT/HRI measurement. We conclude that for clusters with a flux of a few times 10^-12 erg/cm^2/s or smaller, which show at the same time a non-relaxed morphology, the flux measurement of the RASS can be seriously affected by fore- or background sources. We point out that an all-sky survey of a second ABRIXAS mission would provide a much clearer source distinction for low-flux clusters and thus a much improved countrate determination.
We have conducted a search for "dust chimneys" in a sample of 10 highly-inclined spiral galaxies (i = 86 - 90 degrees) which we had previously observed in the H alpha emission line (Rand 1996). We have procured B-band CCD images for the purpose and employed unsharp-masking techniques to accentuate the structure of the dust lane. A scattering+absorption radiation transfer model enabled us to separate 5 galaxies from the sample which are sufficiently inclined (i > 87 degrees) for us to reliably identify and quantify dust clouds residing at over 2 scale-heights above the disk. Three of these galaxies possess numerous curvi-linear chimney structures stretching up to 2 kpc from the midplane and the fraction of total galactic dust contained in such structures is of order 1%. Optical extinction offers a lower limit to the amount of dust contained in the extraplanar layer but, by examining the transparent submm thermal emission from NGC 891, we fix an upper limit of 5%. Our results are consistent with a similar recent study by Howk & Savage (1999) which indicates that about half of quiescent spiral disks possess detectable dust chimneys.We have compared our optical images with the corresponding H alpha emission-line radiation. We do not find a detailed spatial correspondance between dust chimneys and either sites of recent star-formation or the extraplanar diffuse ionized gas. This is somewhat surprising given that FIR-bright galaxies, such as M 82, are known to entrain dust at the working surface of the starburst-driven outflow (traced in H alpha). It is possible a global correlation exists, with disks experiencing overall higher rates of star-formation also possessing the greatest number of chimneys. This may indicate a timescale difference between the two phenomena with the H alpha phase lasting similar to 10(6) yr but chimneys requiring similar to 10(7) yr to form.Additionally, we have investigated the edge-on disk NGC 55 which, being ten times closer than galaxies in our main sample, allows us to examine in greater spatial detail the relationship between chimneys and recent star-formation. Our discussion touches upon high latitude dust and supershells observed in the Milky Way. We rule out quiescent disks as prolific sources of intergalactic grains and metals but note that the rate at which dust is expelled from the main dust layer is comparable to the rate at which it is produced by disk stars (suggesting that it may be an important regulatory process).
A complete exploitation of the imaging properties of the Large Binocular Telescope (LBT) will require a generalization of the restoration methods which apply to the case of a single image. Several different observations must be combined to obtain a high-resolution representation of a given target. The purpose of this paper is to extend to this problem some of the most used restoration methods, including linear methods such as Tikhonov regularization as well as iterative regularization methods providing positive solution. The proposed methods are implemented and tested on simulated LBT images' of diffuse and point-like objects. The results are discussed both from the point of view of the accuracy and from that of the computational efficiency, because LBT images may contain, in principle, up to 10(8) pixels.
During the second flight of the ORFEUS-SPAS mission in November/December 1996, the Echelle spec- trometer was used extensively by the Principal and Guest Investigator teams as one of the two focal plane in- struments of the ORFEUS telescope. The spectrum of HD 93521 was obtained during this mission with a total integration time of 1740 s. This spectrum shows numer- ous sharp interstellar absorption lines. We identied 198 lines of molecular hydrogen including at least 7 lines with a high velocity component. Also most of the 67 identi- ed interstellar metal lines are visible with a high velocity component. We present plots of the complete ORFEUS II Echelle spectrum together with tables of all identied interstel- lar absorption lines including all 14 detectable H I lines. In addition several identied stellar lines, partially with narrow absorption components, and stellar wind lines are given in a separate table.
