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The infrared void in the Lupus dark clouds revisited: a polarimetric approach
The results of B-band CCD imaging linear polarimetry obtained for starsfrom the Hipparcos catalogue are used to re-examine the distribution ofthe local interstellar medium towards the IRAS 100-μm emission voidin the Lupus dark clouds. The analysis of the obtainedparallax-polarization diagram assigns to the dark cloud Lupus1 adistance between 130 and 150pc and assures the existence of a low columndensity region coincident with the observed infrared void. Moreover,there are clear indications of the existence of absorbing material atdistances closer than 60-100pc, which may be associated with theinterface boundary between the Local Bubble and its neighbourhood LoopIsuperbubble.
| Evidence for Spectropolarimetric Diversity in Type Ia Supernovae
We present single-epoch, postmaximum spectropolarimetry of four Type Iasupernovae (SNe Ia) that span a range of spectral and photometricproperties: SN 2002bf and SN 2004dt exhibit unusually high-velocity (HV)absorption lines. SN 1997dt is probably somewhat subluminous, and SN2003du is slightly overluminous. We detect polarization modulationsacross strong lines in all four objects, demonstrating that all areintrinsically polarized. However, the nature and degree of thepolarization varies considerably. Including all SNe Ia studied thus far,the following order emerges in terms of increasing strength ofline-polarization features: ordinary/overluminous
| The buried Balmer-edge signatures from quasars
In our previous paper, we reported the detection of a Balmer edgeabsorption feature in the polarized flux of one quasar (Ton202). We havenow found similar Balmer edge features in the polarized flux of fourmore quasars (4C09.72, 3C95, B21208+32, 3C323.1), and possibly a fewmore, out of 14 newly observed with the Very Large Telescope and theKeck Telescope. In addition, we also re-observed Ton202, but we did notdetect such a dramatic feature, apparently due to polarizationvariability (the two observations are 1 yr apart). The polarizationmeasurements of some quasars are affected by an interstellarpolarization in our Galaxy, but the measurements have been corrected forthis effect reasonably well.As the broad emission lines are essentially unpolarized and thepolarization is confined only to the continuum in the five quasarsincluding Ton202 in both epochs, the polarized flux is considered tooriginate interior to the broad emission-line region. The Balmer edgefeature seen in the polarized flux is most simply interpreted as anintrinsic spectral feature of the quasar ultraviolet/optical continuum,or the `Big Blue Bump' emission. In this case, the edge feature seen inabsorption indeed indicates the thermal and optically thick nature ofthe continuum emitted. However, we also discuss other possibleinterpretations.
| ARIES imaging polarimeter.
An Imaging Polarimeter has been fabricated for use with liquid- N2cooled CCD camera and is designed to suit 104-cm Sampurnanand telescopewith an f/13 focus at Aryabhatta Research Institute of ObservationalSciences (ARIES), Naini Tal. The instrument measures the linearpolarisation in broad B, V and R band and has a field of view ~ 20' x20'. We are presenting here some observations regarding the polarisationof some polarised as well as unpolarised stars with a view to show theperformance of our polarimeter.
| VLT spectropolarimetry of two powerful radio galaxies at z ~ 1.4: ultraviolet continuum, emission-line properties and the nature of high-redshift dust
Deep spectropolarimetric observations, obtained with the Very LargeTelescope, are presented for two powerful radio galaxies, 0850-206 (z =1.3373) and 1303+091 (z = 1.4093). These observations cover therest-frame wavelength range ~1450-3750 Å. New radio observationsand continuum images of the same sources are also presented. Thesegalaxies are the first two observed from a complete sample of nine radiosources with redshifts in the range 1.3 <= z <= 1.5 (selected fromthe equatorial sample of powerful radio sources of Best, Röttgering& Lehnert), as part of a project aimed to investigate themulticomponent nature of the ultraviolet (UV) continuum in radiogalaxies and, in particular, any variations of the continuum propertieswith the radio source age.The larger radio source of the two, 0850-206, presents a high continuumfractional polarization, averaging 17 per cent across the observedwavelength range and reaching 24 per cent at rest-frame wavelengths of<~2000 Å. The smaller radio source, 1303+091, shows a lowercontinuum polarization, averaging 8 per cent and rising to 11 per centfor rest-frame wavelengths >~3000 Å. For both galaxies, theposition angle of the electric vector is generally constant withwavelength and within ~15° of perpendicular to the radio axis. Boththeir total flux spectra and polarized flux spectra reveal the2200-Ådust feature, and comparison with dust scattering modelssuggests that the composition of the dust in these galaxies is similarto that of Galactic dust. In 0850-206, scattered quasar radiationdominates the UV continuum emission, with the nebular continuumaccounting for no more than ~22 per cent and no requirement for anyadditional emission component such as emission from young stars. Incontrast, in 1303+091, unpolarized radiation could be a majorconstituent of the UV continuum emission, with starlight accounting forup to ~50 per cent and the nebular continuum accounting for ~11 percent.The emission-line properties of the galaxies are also studied from theirtotal intensity spectra. Comparison of the measured emission-line ratioswith both shock- and photoionization models shows that the nuclear andextended gas in these galaxies is mainly photoionized by the centralactive nucleus.
| Spectropolarimetry of the borderline Seyfert 1 galaxy ESO 323-G077
We report the detection of high linear polarization in the brightSeyfert 1 galaxy ESO 323-G077. Based on opticalspectropolarimetry with FORS1 at the VLT we find a continuumpolarization which ranges from 2.2% at 8300 Å to 7.5% at 3600Å. Similar amounts of linear polarization are found for the broademission lines, while the narrow lines are not polarized. The positionangle of the polarization (theta =84o) is independent of thewavelength and found to be perpendicular to the orientation of theextended [O III] emission cone of this galaxy. Within the standard modelof Seyfert nuclei the observations can be well understood assuming thatthis AGN is observed at an inclination angle where the nucleus ispartially obscured and seen mainly indirectly in the light scattered bydust clouds within or above the torus and the illuminated inner edge ofthe dust torus itself. Hence we conclude that ESO 323-G077 is aborderline Seyfert 1 galaxy which can provide important information onthe geometric properties of active nuclei.Based on observations obtained at the ESO VLT UT1 (Antu) at CerroParanal, Chile (ESO program 66.B-0063).
| High resolution K_S polarization mapping of OH 231.8+4.2 (OH 0739-14) with SOFI} polarimetry of OH 231.8+4.2
The bipolar reflection nebula OH 231.8+4.2 (OH 0739-14) centred on theMira variable star QX Pup has been mapped at KS in linearpolarization using the ESO SOFI near-infrared multi-mode instrument. Thelarge scale linear polarization features agree with previous studies,validating the polarimetric mode of the instrument. However the highspatial resolution of the polarization map reveals considerablestructure, some of which finds correspondence in the surface brightnessimages. The core is crossed by low polarization filaments; the northernlobe reveals an axial finger and a rim of very high linear polarization(upto 80%) whilst the southern lobe shows less polarization contrast.There is a trend in polarization perpendicular to the bipolar axis inboth lobes. The individual linear polarization features most probablyarise from localised dust structures with distinct orientations leadingto differing polarization through single scattering. A single scatteringgeometric model, consisting of two lobes of ellipsoidal section and acentral dense disk, is considered which can explain the general featuresof the intensity and polarization images.
| The Structure of the Galactic Magnetic Field toward the High-Latitude Clouds
We present the results of an optical polarization survey toward thegalactic anticenter, in the area 5h >= alpha >= 2h and 6 deg <=delta <= 12 deg. This region is characterized by the presence of astream of high-velocity H I as well as high galactic latitude molecularclouds. We used our polarization data together with 100 mu m IRAS mapsof the region to study the relation between the dust distribution andthe geometry of the magnetic field. We find that there is a correlationbetween the percent polarization and the 100 mu m flux such that P(%)<= (0.16 +/- 0.05)F100. When the IRAS flux is converted into H Icolumn densities this becomes P(%) <= (0.13 +/- 0.03)N20 - 0.22,which is consistent with previous interstellar medium studies on therelation between reddening and polarization. This correlation indicatesthat our survey is as deep as IRAS and that the magnetic field geometrydoes not change strongly with the optical depth in the lines of sightthat we have studied. The implied lower limit to the distance of oursurvey is 500--700 pc at galactic latitudes b = -20 deg and 100 pc at b= -50 deg. Our main finding is that the magnetic field is perpendicularto the H I high-velocity stream as well as the molecular cloud MBM 16 inthe high-latitude region. The field is also perpendicular to thevelocity gradient in the stream. Closer to the plane, the magnetic fieldis parallel to the dust filaments that extend like a plume toward thehalo. Our observations indicate that the galactic magnetic field towardthe high-latitude clouds is toroidal. We propose a model in which fluxtubes that rise out of the galactic plane become force-free andpredominantly toroidal at high latitudes. The high-latitude clouds maybe gas streams that are falling back toward the galactic plane withinsuch buoyant braided ropes of magnetic flux.
| A catalog of far-ultraviolet point sources detected with the fast FAUST Telescope on ATLAS-1
We list the photometric measurements of point sources made by the FarUltraviolet Space Telescope (FAUST) when it flew on the ATLAS-1 spaceshuttle mission. The list contains 4698 Galactic and extragalacticobjects detected in 22 wide-field images of the sky. At the locationssurveyed, this catalog reaches a limiting magnitude approximately afactor of 10 fainter than the previous UV all-sky survey, TDl. Thecatalog limit is approximately 1 x 10-14 ergs A sq cm/s,although it is not complete to this level. We list for each object theposition, FUV flux, the error in flux, and where possible anidentification from catalogs of nearby stars and galaxies. Thesecatalogs include the Michigan HD (MHD) and HD, SAO, the HIPPARCOS InputCatalog, the Position and Proper Motion Catalog, the TD1 Catalog, theMcCook and Sion Catalog of white dwarfs, and the RC3 Catalog ofGalaxies. We identify 2239 FAUST sources with objects in the stellarcatalogs and 172 with galaxies in the RC3 catalog. We estimate thenumber of sources with incorrect identifications to be less than 2%.
| An atlas of Hubble Space Telescope photometric, spectrophotometric, and polarimetric calibration objects
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990AJ.....99.1243T&db_key=AST
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Osservazione e dati astrometrici
| Costellazione: | Cratere |
| Ascensione retta: | 10h56m44.26s |
| Declinazione: | -20°39'52.6" |
| Magnitudine apparente: | 9.293 |
| Moto proprio RA: | -12.2 |
| Moto proprio Dec: | 6.4 |
| B-T magnitude: | 9.516 |
| V-T magnitude: | 9.312 |
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