References of "Cabanac, R"
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See detailEarly-type stars observed in the ESO UVES Paranal Observatory Project - IV. Studies of CN, CH+ and CH in the interstellar medium
Smoker, J.; Ledoux, C.; Jehin, Emmanuel ULg et al

in Monthly Notices of the Royal Astronomical Society (2013)

High spectral resolution (˜80 000) and signal-to-noise observations from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project (UVES-POP) are used to study the interstellar molecular ... [more ▼]

High spectral resolution (˜80 000) and signal-to-noise observations from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project (UVES-POP) are used to study the interstellar molecular lines CN (3874 Å), CH[SUP]+[/SUP] (3957, 4232 Å) and CH (3886, 4300 Å) towards 74 O- and B-type stellar sightlines. Additionally, archive data are presented for 140 ELODIE early-type stellar sightlines at R = 42 000, plus 25 FEROS at R = 48 000 and 3 UVES at R > 50 000, mainly in the CH[SUP]+[/SUP] (4232 Å) and CH (3886, 4300 Å) transitions. Detection rates are ˜45 per cent for CN and ˜67 per cent for the other lines in the POP sample, and ˜10-15 per cent for CH[SUP]+[/SUP] and CH lines in the additional sample. CH and CH[SUP]+[/SUP] are well correlated between log[N(CH) cm[SUP]-2[/SUP]]˜12-14, implying that these clouds are CH[SUP]+[/SUP]-like CH and not CN-like CH. CH is also very well correlated with Na I D in the range log[N(Na I cm[SUP]-2[/SUP]]) ˜12.2-14.2. A few sightlines show tentative velocity shifts of ˜2 km s[SUP]-1[/SUP] between CH and CH[SUP]+[/SUP], which appear to be caused by differences in component strength in blends, and hence do not provide firm evidence for shocks. Finally, we describe a search for [SUP]13[/SUP]CH[SUP]+[/SUP] in a sightline towards HD 76341. No [SUP]13[/SUP]CH[SUP]+[/SUP] is detected, placing a limit on the [SUP]13[/SUP]CH[SUP]+[/SUP] to [SUP]12[/SUP]CH[SUP]+[/SUP] ratio of ˜0.01. If a formal fit is attempted, the equivalent width ratio in the two isotopes is a factor ˜90 but with large errors. [less ▲]

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See detailLarge-Scale Alignments of Quasar Polarization Vectors: Evidence at Cosmological Scales for Very Light Pseudoscalar Particles Mixing with Photons ?
Hutsemekers, Damien ULg; Payez, Alexandre ULg; Cabanac, R et al

in Bastien, Pierre (Ed.) Astronomical Polarimetry 2008: Science from Small to Large Telescopes. ASPC 449 (2011, November 01)

Based on a sample of 355 quasars with significant optical polarization, we found that quasar polarization vectors are not randomly oriented over the sky as naturally expected. The probability that the ... [more ▼]

Based on a sample of 355 quasars with significant optical polarization, we found that quasar polarization vectors are not randomly oriented over the sky as naturally expected. The probability that the observed distribution of polarization angles is due to chance is lower than 0.1%. The polarization vectors of the light from quasars are aligned although the sources span huge regions of the sky (˜ 1 Gpc). Groups of quasars located along similar lines of sight but at different redshifts (typically z ≍ 0.5 and z ≍ 1.5) are characterized by different preferred directions of polarization. These characteristics make the observed alignment effect difficult to explain in terms of a local contamination by interstellar polarization in our Galaxy. Interpreted in terms of a cosmological-size effect, we show that the dichroism and birefringence predicted by a mixing between photons and very light pseudoscalar particles within a magnetic field can qualitatively reproduce the observations. We find that circular polarization measurements could help constrain this mechanism. [less ▲]

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See detailEarly-type stars observed in the ESO UVES Paranal Observatory Project - III. Sub-parsec and au-scale structure in the interstellar medium
Smoker, J. V.; Bagnulo, S.; Cabanac, R. et al

in Monthly Notices of the Royal Astronomical Society (2011), 414

UVES interstellar observations from the Paranal Observatory Project are presented for early-type stars located in the line of sight to the nearby open clusters IC 2391 (Omni Vel) and NGC 6475 (M7), with ... [more ▼]

UVES interstellar observations from the Paranal Observatory Project are presented for early-type stars located in the line of sight to the nearby open clusters IC 2391 (Omni Vel) and NGC 6475 (M7), with spectroscopic resolution R˜ 80 000 and signal-to-noise ratios in the Ti II (3383 Å), Ca II K, CH[SUP]+[/SUP] (4232 Å), Na I D and K I (7698 Å) lines of several hundred. The sightlines are a mixture of cluster and non-cluster objects. A total of 22 early-type stars (A and B type) are present in our sample towards IC 2391, with 21 towards NGC 6475/M7, and enable us to probe for differences in column density on scales from ˜0.07 to 7.3 and ˜0.05 to 4.9 pc in the respective clusters. Additionally, towards Praesepe the Na I D interstellar variation only is probed towards 13 sightlines and transverse scales of ˜0.16-10.7 pc at R= 70 000. Towards IC 2391 variations are found in Ti II, Ca II K and Na I D column density in different sightlines of up to 0.7, 1.0 and 1.8 dex (excluding one star), respectively. This kind of variability correlates well with the Hipparcos parallax of the objects, and probes structure within the Local Bubble. For cluster-only objects the variations are 0.3, 0.3 and 0.5 dex, respectively. For the field of view towards NGC 6475 the corresponding maximum variations are somewhat smaller, being 0.5, 0.3, 0.8 and 1.0 dex for Ti II, Ca II K, Na I and K I, respectively, for all objects and 0.4, 0.2, 0.6 and 0.7 dex for the cluster-only objects. These are uncorrelated with parallax, and again demonstrate that Ca II K tends to be more smoothly distributed than Na I D. A few likely cluster sightlines show evidence for CH[SUP]+[/SUP] and variations in this molecular species of a factor of 10 in equivalent width over sub-pc scales. Towards Praesepe variation in interstellar Na I D is small, being a maximum of only ˜0.4 dex (including measurement errors), but with fewer sightlines studied. Overall, the scatter in the data is similar for the singly ionized species Ti II and Ca II, lending more support to the hypothesis that these two species sample similar parts of the interstellar medium (ISM). This also appears to be the case for the neutral species Na I D and K I in the one cluster studied. Finally, multiple-epoch observations from a variety of archive sources are used to search for astronomical unit (au) scale structure in the ISM towards 46 sightlines. There are tentative indications of structure on scales of tens to thousands of au for three sightlines. Future observations will confirm the veracity or otherwise of the time-variable components and others presented. Based on observations taken at UT2, Kueyen, Cerro Paranal, Chile, ESO DDT programme 265.D-5655(A), UVES Paranal Observatory Project and using FEROS on the ESO 2.2-m telescope, La Silla, Chile, programme ID 078.C-0493(A), the Observatoire de Haute Provence, France, the Pic du Midi telescope, France and the AAO archive. [less ▲]

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See detailOptical circular polarization in quasars
Hutsemekers, Damien ULg; Borguet, Benoît ULg; Sluse, D. et al

in Astronomy and Astrophysics (2010), 520(Letters), 71-5

We present new optical circular polarization measurements with typical uncertainties <0.1% for a sample of 21 quasars. All but two objects have null circular polarization. We use this result to constrain ... [more ▼]

We present new optical circular polarization measurements with typical uncertainties <0.1% for a sample of 21 quasars. All but two objects have null circular polarization. We use this result to constrain the polarization due to photon-pseudoscalar mixing along the line of sight. We detect significant (> 3σ) circular polarization in two blazars with high linear polarization and discuss the implications of this result for quasar physics. In particular, the recorded polarization degrees may be indicative of magnetic fields as strong as 1 kG or a significant contribution of inverse Compton scattering to the optical continuum. Based on observations made with ESO Telescopes at the La Silla Observatory (Chile). ESO program ID: 79.A-0625(B).Appendices are only available in electronic form at <A href="http://www.aanda.org">http://www.aanda.org</A> [less ▲]

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See detailExploring the magnetic topologies of cool stars
Morin, J.; Donati, J *-F; Petit, P. et al

in IAU Symposium Proceedings (2010, September 01)

Magnetic fields of cool stars can be directly investigated through the study of the Zeeman effect on photospheric spectral lines using several approaches. With spectroscopic measurement in unpolarised ... [more ▼]

Magnetic fields of cool stars can be directly investigated through the study of the Zeeman effect on photospheric spectral lines using several approaches. With spectroscopic measurement in unpolarised light, the total magnetic flux averaged over the stellar disc can be derived but very little information on the field geometry is available. Spectropolarimetry provides a complementary information on the large-scale component of the magnetic topology. With Zeeman-Doppler Imaging (ZDI), this information can be retrieved to produce a map of the vector magnetic field at the surface of the star, and in particular to assess the relative importance of the poloidal and toroidal components as well as the degree of axisymmetry of the field distribution. The development of high-performance spectropolarimeters associated with multi-lines techniques and ZDI allows us to explore magnetic topologies throughout the Hertzsprung-Russel diagram, on stars spanning a wide range of mass, age and rotation period. These observations bring novel constraints on magnetic field generation by dynamo effect in cool stars. In particular, the study of solar twins brings new insight on the impact of rotation on the solar dynamo, whereas the detection of strong and stable dipolar magnetic fields on fully convective stars questions the precise role of the tachocline in this process. [less ▲]

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See detailSmall Scale Structure in the ISM towards IC 2391 and NGC 6475
Smoker, J. V.; Hunter, I.; Keenan, F. P. et al

in Haverkorn, M.; Goss, M. (Eds.) SINS - Small Ionized and Neutral Structures in the Diffuse Interstellar Medium (2007, July 01)

We describe UVES spectroscopic observations towards early-type stars located in the nearby open clusters IC 2391 (D=175 pc) and NGC 6475/M 7 (D=301 pc), with resolution ˜80,000 and S/N ratio per pixel of ... [more ▼]

We describe UVES spectroscopic observations towards early-type stars located in the nearby open clusters IC 2391 (D=175 pc) and NGC 6475/M 7 (D=301 pc), with resolution ˜80,000 and S/N ratio per pixel of ˜140 to ˜360. The aim is to investigate the small-scale structure variations within parts of the local ISM and determine how they are dependent on element and ionisation stage observed, thus providing information on cloud parameters such as structure and sizes. The data used are taken from on-line versions of the Paranal Observatory Project (POP: http://www.eso.org/uvespop). A total of 25 early-type stars (A and B-type) are present in our sample towards IC 2391 with 23 towards NGC 6475/M 7, and enable us to probe differences in column densities on scales from ˜0.07--7.3-pc and ˜0.05---4.9-pc (in the respective clusters) for the optical transitions detected (Ti II (3383Å), Ca II (3933Å), Na I (5889, 5895Å) and K I (7698Å)). Towards NGC 6475 the Ca II column density is found to be constant to ˜0.15 dex over scales of ˜0.4--4-pc. A much greater scatter in the measurements for Na I D is observed with differences of up to ˜0.45 dex in sightlines separated by ˜4 pc. In the future work we will perform the same analysis for Ti II and K I towards both clusters. [less ▲]

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See detailAbundance analysis of 5 early-type stars in the young open cluster IC 2391
Stütz, Ch; Bagnulo, S.; Jehin, Emmanuel ULg et al

in Astronomy and Astrophysics (2006), 451

Aims.It is unclear whether chemically peculiar stars of the upper main sequence represent a class completely distinct from normal A-type stars, or whether there exists a continuous transition from the ... [more ▼]

Aims.It is unclear whether chemically peculiar stars of the upper main sequence represent a class completely distinct from normal A-type stars, or whether there exists a continuous transition from the normal to the most peculiar late F- to early B-type stars. A systematic abundance analysis of open cluster early-type stars would help to relate the observed differences of the chemical abundances of the photospheres to other stellar characteristics, without being concerned by possible different original chemical composition. Furthermore, if a continuous transition region from the very peculiar to the so called normal A-F stars exists, it should be possible to detect objects with mild peculiarities.<BR /> Methods: .As a first step of a larger project, an abundance analysis of 5 F-A type stars in the young cluster IC 2391 was performed using high resolution spectra obtained with the UVES instrument of the ESO VLT.<BR /> Results: .Our targets seem to follow a general abundance pattern: close to solar abundance of the light elements and iron peak elements, heavy elements are slightly overabundant with respect to the sun, similar to what was found in previous studies of normal field A-type stars of the galactic plane. We detected a weakly chemically peculiar star, HD 74044. Its element pattern contains characteristics of CP1 as well as CP2 stars, enhanced abundances of iron peak elements and also higher abundances of Sc, Y, Ba and Ce. We did not detect a magnetic field in this star (detection limit was 2 kG). We also studied the star SHJM 2, proposed as a pre-main sequence object in previous works. Using spectroscopy we found a high surface gravity, which suggests that the star is very close to the ZAMS.<BR /> [less ▲]

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See detailEarly-type stars observed in the ESO UVES Paranal Observatory Project - I. Interstellar NaI UV, TiII and CaII K observations*
Hunter, I.; Smoker, J. V.; Keenan, F. P. et al

in Monthly Notices of the Royal Astronomical Society (2006), 367

We present an analysis of interstellar NaI (λ[SUB]air[/SUB]= 3302.37 and 3302.98 Å), TiII(λ[SUB]air[/SUB]= 3383.76 Å) and CaII K (λ[SUB]air[/SUB]= 3933.66 Å) absorption features for 74 sightlines towards ... [more ▼]

We present an analysis of interstellar NaI (λ[SUB]air[/SUB]= 3302.37 and 3302.98 Å), TiII(λ[SUB]air[/SUB]= 3383.76 Å) and CaII K (λ[SUB]air[/SUB]= 3933.66 Å) absorption features for 74 sightlines towards O- and B-type stars in the Galactic disc. The data were obtained from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project, at a spectral resolution of 3.75 km s[SUP]-1[/SUP] and with mean signal-to-noise ratios per pixel of 260, 300 and 430 for the NaI, TiII and CaII observations, respectively. Interstellar features were detected in all but one of the TiII sightlines and all of the CaII sightlines. The dependence of the column density of these three species with distance, height relative to the Galactic plane, HI column density, reddening and depletion relative to the solar abundance has been investigated. We also examine the accuracy of using the NaI column density as an indicator of that for HI. In general, we find similar strong correlations for both Ti and Ca, and weaker correlations for Na. Our results confirm the general belief that Ti and Ca occur in the same regions of the interstellar medium (ISM) and also that the TiII/CaII ratio is constant over all parameters. We hence conclude that the absorption properties of Ti and Ca are essentially constant under the general ISM conditions of the Galactic disc. [less ▲]

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See detailPolarimetric Standard Stars Observed with FORS1 at ESO-VLT
Mason, E.; Bagnulo, S.; Szeifert, T. et al

in ASP Conference Series (2005, December 01), 343

A Paranal Observatory project aims to analyze all the polarimetric standard stars in use at FORS1 to both check they have a constant polarization signal and measure the instrumental polarization ... [more ▼]

A Paranal Observatory project aims to analyze all the polarimetric standard stars in use at FORS1 to both check they have a constant polarization signal and measure the instrumental polarization. Preliminary results for 3 standards in the FORS1 calibration plans are presented. [less ▲]

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See detailDeep Impact: Observations from a Worldwide Earth-Based Campaign
Meech, K. J.; Ageorges, N.; A'Hearn, M. F. et al

in Science (2005), 310

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign ... [more ▼]

On 4 July 2005, many observatories around the world and in space observed the collision of Deep Impact with comet 9P/Tempel 1 or its aftermath. This was an unprecedented coordinated observational campaign. These data show that (i) there was new material after impact that was compositionally different from that seen before impact; (ii) the ratio of dust mass to gas mass in the ejecta was much larger than before impact; (iii) the new activity did not last more than a few days, and by 9 July the comet's behavior was indistinguishable from its pre-impact behavior; and (iv) there were interesting transient phenomena that may be correlated with cratering physics. [less ▲]

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See detailMapping extreme-scale alignments of quasar polarization vectors
Hutsemekers, Damien ULg; Cabanac, R.; Lamy, H. et al

in Astronomy and Astrophysics (2005), 441

Based on a new sample of 355 quasars with significant optical polarization and using complementary statistical methods, we confirm that quasar polarization vectors are not randomly oriented over the sky ... [more ▼]

Based on a new sample of 355 quasars with significant optical polarization and using complementary statistical methods, we confirm that quasar polarization vectors are not randomly oriented over the sky with a probability often in excess of 99.9%. The polarization vectors appear coherently oriented or aligned over huge ( 1 Gpc) regions of the sky located at both low (z Ë 0.5) and high (z Ë 1.5) redshifts and characterized by different preferred directions of the quasar polarization. In fact, there seems to exist a regular alternance along the line of sight of regions of randomly and aligned polarization vectors with a typical comoving length scale of 1.5 Gpc. Furthermore, the mean polarization angle bartheta appears to rotate with redshift at the rate of 30° per Gpc. The symmetry of the the bartheta -z relation is mirror-like, the mean polarization angle rotating clockwise with increasing redshift in North Galactic hemisphere and counter-clockwise in the South Galactic one. These characteristics make the alignment effect difficult to explain in terms of local mechanisms, namely a contamination by interstellar polarization in our Galaxy. While interpretations like a global rotation of the Universe can potentially explain the effect, the properties we observe qualitatively correspond to the dichroism and birefringence predicted by photon-pseudoscalar oscillation within a magnetic field. Interestingly, the alignment effect seems to be prominent along an axis not far from preferred directions tentatively identified in the Cosmic Microwave Background maps. Although many questions and more particularly the interpretation of the effect remain open, alignments of quasar polarization vectors appear as a promising new way to probe the Universe and its dark components at extremely large scales. [less ▲]

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See detailAlignments of quasar polarization vectors (Hutsemekers+, 2005)
Hutsemekers, Damien ULg; Cabanac, R.; Lamy, H. et al

Textual, factual or bibliographical database (2005)

The table contains linear polarization measurements for 355 QSOs. (3 data files).

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See detailNew optical polarization measurements of quasi-stellar objects. The data
Sluse, D.; Hutsemekers, Damien ULg; Lamy, H. et al

in Astronomy and Astrophysics (2005), 433

New linear polarization measurements (mainly in the V band) are presented for 203 quasi-stellar objects (QSOs). The sample is made up of 94 QSOs located in the North Galactic Pole (NGP) region and of 109 ... [more ▼]

New linear polarization measurements (mainly in the V band) are presented for 203 quasi-stellar objects (QSOs). The sample is made up of 94 QSOs located in the North Galactic Pole (NGP) region and of 109 QSOs in the South Galactic Pole (SGP) region. First time measurements have been obtained for 184 QSOs. Among them, 109 known radio-emitters, 42 known Broad Absorption Line (BAL) QSOs, and 1 gravitationally lensed quasi-stellar object. We found high polarization levels (p > 3%) for 12 QSOs, including the BAL QSO <ASTROBJ>SDSS J1409+0048</ASTROBJ>. For 10 objects, measurements obtained at different epochs do exist. Two of them show evidence for variability: the highly polarized BL Lac candidate <ASTROBJ>PKS 1216-010</ASTROBJ> and the radio source <ASTROBJ>PKS 1222+037</ASTROBJ>. Based on observations collected at the European Southern Observatory (ESO, La Silla and Paranal). Table 4 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/433/757 [less ▲]

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See detailThe UVES Paranal Observatory Project: a public library of high resolution stellar spectra
Jehin, Emmanuel ULg; Bagnulo, S.; Melo, C. et al

in Hill, V. (Ed.) From Lithium to Uranium: Elemental Tracers of Early Cosmic Evolution (2005)

The UVES Paranal Observatory Project (POP), is an ESO public database of about 400 stars whose high quality spectra were obtained with UVES, the high resolution spectrometer of the VLT. All stars were ... [more ▼]

The UVES Paranal Observatory Project (POP), is an ESO public database of about 400 stars whose high quality spectra were obtained with UVES, the high resolution spectrometer of the VLT. All stars were observed with two instrument modes, in order to cover almost completely the optical region (300-1000 nm). The resolving power is about 80000, and for most of the spectra, the typical S/N ratio is 300-500 in the V band. Program stars fall into two groups, stars belonging to open clusters IC2391 and NGC6475, and bright field stars. For field stars, the only selection criterion applied was to cover the largest possible variety of spectral types in the HR diagram, including peculiar objects, e.g., Ap and Bp stars, Wolf-Rayet stars, Be stars, carbon stars and metal poor stars. The spectra have been reduced, coadded and merged and various products can be downloaded from a public area. For each star the final spectrum may be displayed through a dedicated user-friendly Spectral Preview Interface. The database is accessible at http://www.eso.org/uvespop [less ▲]

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See detailOptical polarization of 203 QSOs (Sluse+, 2005)
Sluse, D.; Hutsemekers, Damien ULg; Lamy, H. et al

Textual, factual or bibliographical database (2004)

This Table contains linear polarization measurements (mainly in the V band) of 203 QSOs. First time measurements have been obtained for 184 objects. Among them 109 known radio emitters, 42 BAL and 1 ... [more ▼]

This Table contains linear polarization measurements (mainly in the V band) of 203 QSOs. First time measurements have been obtained for 184 objects. Among them 109 known radio emitters, 42 BAL and 1 gravitationally lensed QSO. (1 data file). [less ▲]

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See detailThe UVES Paranal Observatory Project: A Library of High- Resolution Spectra of Stars across the Hertzsprung-Russell Diagram
Bagnulo, S.; Jehin, Emmanuel ULg; Ledoux, C. et al

in The Messenger (2003), 114

We present the UVES Paranal Observatory Project, consisting of acquisition, reduction, and public release of high-resolution, large wavelength coverage, and high signal-to-noise ratio stellar spectra ... [more ▼]

We present the UVES Paranal Observatory Project, consisting of acquisition, reduction, and public release of high-resolution, large wavelength coverage, and high signal-to-noise ratio stellar spectra obtained with the UVES instrument of the ESO Very Large Telescope. Data for about 400 stars across the Hertzsprung-Russell diagram have been taken and reduced by members of the Paranal Science Operations Team and made publicly available through a WEB interface at www.eso.org/uvespop. [less ▲]

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