References of "Hutsemekers, Damien"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailThe Herschel view of the nebula around the luminous blue variable star AG Carinae
Vamvatira-Nakou, Chloi ULg; Hutsemekers, Damien ULg; Royer, P. et al

in Astronomy and Astrophysics (in press)

Far-infrared Herschel PACS imaging and spectroscopic observations of the nebula around the luminous blue variable (LBV) star AG Car have been obtained along with optical imaging in the Halpha+[NII] filter ... [more ▼]

Far-infrared Herschel PACS imaging and spectroscopic observations of the nebula around the luminous blue variable (LBV) star AG Car have been obtained along with optical imaging in the Halpha+[NII] filter. In the infrared light, the nebula appears as a clumpy ring shell that extends up to 1.2 pc with an inner radius of 0.4 pc. It coincides with the Halpha nebula, but extends further out. Dust modeling of the nebula was performed and indicates the presence of large grains. The dust mass is estimated to be ~ 0.2 Msun. The infrared spectrum of the nebula consists of forbidden emission lines over a dust continuum. Apart from ionized gas, these lines also indicate the existence of neutral gas in a photodissociation region that surrounds the ionized region. The abundance ratios point towards enrichment by processed material. The total mass of the nebula ejected from the central star amounts to ~ 15 Msun, assuming a dust-to-gas ratio typical of LBVs. The abundances and the mass-loss rate were used to constrain the evolutionary path of the central star and the epoch at which the nebula was ejected, with the help of available evolutionary models. This suggests an ejection during a cool LBV phase for a star of ~ 55 Msun with little rotation. [less ▲]

Detailed reference viewed: 19 (9 ULg)
Full Text
See detailLarge-scale polarization alignments of quasars in the JVAS/CLASS 8.4-GHz surveys
Pelgrims, Vincent ULg; Hutsemekers, Damien ULg

Poster (2015, May)

We analyse the large sample of polarization measurements of the flat-spectrum radio sources of the JVAS/CLASS 8.4-GHz surveys compiled by Jackson et al. (2007). We tested the uniformity of the ... [more ▼]

We analyse the large sample of polarization measurements of the flat-spectrum radio sources of the JVAS/CLASS 8.4-GHz surveys compiled by Jackson et al. (2007). We tested the uniformity of the polarization position angles for a wide range of angular (2D) and comoving (3D) separations and studied the several subsamples, dividing the main sample of 4155 sources regarding their object type (QSO, galaxies, radio sources,...). We found regions of the sky of about 20 degree radius in which quasars (only) have correlated polarization position angles. Those regions coincide with the regions of alignment at optical wavelength pinpointed in 1998 by Hutsemékers. [less ▲]

Detailed reference viewed: 15 (0 ULg)
Full Text
See detailAlignments of quasar axes with large-scale structures
Hutsemekers, Damien ULg; Braibant, Lorraine ULg; Pelgrims, Vincent ULg et al

Poster (2015, March)

Based on measurements of optical linear polarization of quasars belonging to large groups at redshift z ~ 1.3, we found that quasar spin axes are likely parallel to their host large-scale structures ... [more ▼]

Based on measurements of optical linear polarization of quasars belonging to large groups at redshift z ~ 1.3, we found that quasar spin axes are likely parallel to their host large-scale structures (Hutsemékers et al. 2014). These observations can constrain models of the coevolution of AGN, galaxies and large-scale structures. [less ▲]

Detailed reference viewed: 19 (4 ULg)
Full Text
Peer Reviewed
See detailTRAPPIST monitoring of comet C/2012 F6 (Lemmon)
Opitom, Cyrielle ULg; Jehin, Emmanuel ULg; Manfroid, Jean ULg et al

in Astronomy and Astrophysics (2015), 574

We report the results of the long-term narrowband photometry and imaging monitoring of comet C/2012 F6 (Lemmon) with the robotic TRAPPIST telescope (La Silla Observatory). Observations covered 52 nights ... [more ▼]

We report the results of the long-term narrowband photometry and imaging monitoring of comet C/2012 F6 (Lemmon) with the robotic TRAPPIST telescope (La Silla Observatory). Observations covered 52 nights pre- and post-perihelion between December 11, 2012, and June 11, 2013 (perihelion: 24 March, 2013). We followed the evolution of the OH, NH, CN, C[SUB]3[/SUB], and C[SUB]2[/SUB] production rates computed with the Haser model as well as the evolution of the A(θ)fρ parameter as a proxy for the dust production. All five gas species display similar slopes for the heliocentric dependence. An asymmetry about perihelion is observed, the rate of brightening being steeper than the rate of fading. The chemical composition of the comet's coma changes slightly along the orbit: the relative abundance of C[SUB]2[/SUB] to CN increases with the heliocentric distance (r) below -1.4 au and decreases with r beyond 1.4 au while the C[SUB]3[/SUB]-to-CN ratio is constant during our observations. The behavior of the dust is different from that of the gas, the slope of the heliocentric dependence becoming steeper in early February, correlated to a change in the visual lightcurve slope. However, the dust color does not vary during the observations. The application of several enhancement techniques on the images revealed structures in the CN, C[SUB]3[/SUB], and C[SUB]2[/SUB] images. These features imply the existence of one or several active zone(s) on the comet nucleus. The shape of the structures is similar in these three filters and changes from a roughly hourglass shape in December and January to a corkscrew shape in February and March. The structures in the continuum filters (sampling the dust) are not correlated to those observed for the gas. During several full nights in February, we observed changes in the CN and C[SUB]2[/SUB] structures that repeated periodically because of the nucleus rotation, our derived rotational period being of 9.52 ± 0.05 h. Full Tables 2, 4, 6 are only available at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A> (ftp://130.79.128.5) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A38">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/574/A38</A> [less ▲]

Detailed reference viewed: 14 (2 ULg)
Full Text
Peer Reviewed
See detailForbidden oxygen lines at various nucleocentric distances in comets
Decock, Alice ULg; Jehin, Emmanuel ULg; Rousselot, P. et al

in Astronomy and Astrophysics (2015), 573

Aims: We study the formation of the [OI] lines - that is, 5577.339 Å (the green line), 6300.304 Å and 6363.776 Å (the two red lines) - in the coma of comets and determine the parent species of the oxygen ... [more ▼]

Aims: We study the formation of the [OI] lines - that is, 5577.339 Å (the green line), 6300.304 Å and 6363.776 Å (the two red lines) - in the coma of comets and determine the parent species of the oxygen atoms using the ratio of the green-to-red-doublet emission intensity, I[SUB]5577[/SUB]/(I[SUB]6300[/SUB] + I[SUB]6364[/SUB]), (hereafter the G/R ratio) and the line velocity widths. <BR /> Methods: We acquired high-resolution spectroscopic observations at the ESO Very Large Telescope of comets C/2002 T7 (LINEAR), 73P-C/Schwassmann-Wachmann 3, 8P/Tuttle, and 103P/Hartley 2 when they were close to Earth (<0.6 au). Using the observed spectra, which have a high spatial resolution (<60 km/pixel), we determined the intensities and widths of the three [OI] lines. We spatially extracted the spectra to achieve the best possible resolution of about 1-2'', that is, nucleocentric projected distances of 100 to 400 km depending on the geocentric distance of the comet. We decontaminated the [OI] green line from C[SUB]2[/SUB] lines blends that we identified. <BR /> Results: The observed G/R ratio in all four comets varies as a function of nucleocentric projected distance (between ~0.25 to ~0.05 within 1000 km). This is mainly due to the collisional quenching of O([SUP]1[/SUP]S) and O([SUP]1[/SUP]D) by water molecules in the inner coma. The observed green emission line width is about 2.5 km s[SUP]-1[/SUP] and decreases as the distance from the nucleus increases, which can be explained by the varying contribution of CO[SUB]2[/SUB] to the O([SUP]1[/SUP]S) production in the innermost coma. The photodissociation of CO[SUB]2[/SUB] molecules seem to produce O([SUP]1[/SUP]S) closer to the nucleus, while the water molecule forms all the O([SUP]1[/SUP]S) and O([SUP]1[/SUP]D) atoms beyond 10[SUP]3[/SUP] km. Thus we conclude that the main parent species producing O([SUP]1[/SUP]S) and O([SUP]1[/SUP]D) in the inner coma is not always the same. The observations have been interpreted in the framework of the previously described coupled-chemistry-emission model, and the upper limits of the relative abundances of CO[SUB]2[/SUB] were derived from the observed G/R ratios. Measuring the [OI] lines might provide a new way to determine the CO[SUB]2[/SUB] relative abundance in comets. Based on observations made with ESO Telescope at the La Silla Paranal Observatory under programs ID 073.C-0525, 277.C-5016, 080.C-0615 and 086.C-0958.Tables 3 and 4 are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201424403/olm">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 11 (0 ULg)
Full Text
Peer Reviewed
See detailMonte Carlo Simulation of Metastable Oxygen Photochemistry in Cometary Atmospheres
Bisikalo, D. V.; Shematovich, V. I.; Gérard, Jean-Claude ULg et al

in The Astrophysical Journal (2015), 798

Cometary atmospheres are produced by the outgassing of material, mainly H[SUB]2[/SUB]O, CO, and CO[SUB]2[/SUB] from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical ... [more ▼]

Cometary atmospheres are produced by the outgassing of material, mainly H[SUB]2[/SUB]O, CO, and CO[SUB]2[/SUB] from the nucleus of the comet under the energy input from the Sun. Subsequent photochemical processes lead to the production of other species generally absent from the nucleus, such as OH. Although all comets are different, they all have a highly rarefied atmosphere, which is an ideal environment for nonthermal photochemical processes to take place and influence the detailed state of the atmosphere. We develop a Monte Carlo model of the coma photochemistry. We compute the energy distribution functions (EDF) of the metastable O([SUP]1[/SUP]D) and O([SUP]1[/SUP]S) species and obtain the red (630 nm) and green (557.7 nm) spectral line shapes of the full coma, consistent with the computed EDFs and the expansion velocity. We show that both species have a severely non-Maxwellian EDF, that results in broad spectral lines and the suprathermal broadening dominates due to the expansion motion. We apply our model to the atmosphere of comet C/1996 B2 (Hyakutake) and 103P/Hartley 2. The computed width of the green line, expressed in terms of speed, is lower than that of the red line. This result is comparable to previous theoretical analyses, but in disagreement with observations. We explain that the spectral line shape does not only depend on the exothermicity of the photochemical production mechanisms, but also on thermalization, due to elastic collisions, reducing the width of the emission line coming from the O([SUP]1[/SUP]D) level, which has a longer lifetime. [less ▲]

Detailed reference viewed: 16 (3 ULg)
Full Text
Peer Reviewed
See detailAlignment of quasar polarizations with large-scale structures
Hutsemekers, Damien ULg; Braibant, Lorraine ULg; Pelgrims, Vincent ULg et al

in Astronomy and Astrophysics (2014), 572

We have measured the optical linear polarization of quasars belonging to Gpc scale quasar groups at redshift z ~ 1.3. Out of 93 quasars observed, 19 are significantly polarized. We found that quasar ... [more ▼]

We have measured the optical linear polarization of quasars belonging to Gpc scale quasar groups at redshift z ~ 1.3. Out of 93 quasars observed, 19 are significantly polarized. We found that quasar polarization vectors are either parallel or perpendicular to the directions of the large-scale structures to which they belong. Statistical tests indicate that the probability that this effect can be attributed to randomly oriented polarization vectors is on the order of 1%. We also found that quasars with polarization perpendicular to the host structure preferentially have large emission line widths while objects with polarization parallel to the host structure preferentially have small emission line widths. Considering that quasar polarization is usually either parallel or perpendicular to the accretion disk axis depending on the inclination with respect to the line of sight, and that broader emission lines originate from quasars seen at higher inclinations, we conclude that quasar spin axes are likely parallel to their host large-scale structures. Based on observations made with ESO Telescopes at the La Silla Paranal Observatory under program ID 092.A-0221.Table 1 is available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201424631/olm">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 56 (18 ULg)
Full Text
See detailThe TRAPPIST comet survey in 2014
Jehin, Emmanuel ULg; Opitom, Cyrielle ULg; Manfroid, Jean ULg et al

in Bulletin of the American Astronomical Society (2014, November 01), 46

TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) is a 60-cm robotic telescope that has been installed in June 2010 at the ESO La Silla Observatory [1]. Operated from Liège (Belgium) it is ... [more ▼]

TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) is a 60-cm robotic telescope that has been installed in June 2010 at the ESO La Silla Observatory [1]. Operated from Liège (Belgium) it is devoted to the detection and characterisation of exoplanets and to the study of comets and other small bodies in the Solar System. A set of narrowband cometary filters designed by the NASA for the Hale-Bopp Observing Campaign [2] is permanently mounted on the telescope along with classic Johnson-Cousins filters. We describe here the hardware and the goals of the project. For relatively bright comets (V < 12) we measure several times a week the gaseous production rates (using a Haser model) and the spatial distribution of several species among which OH, NH, CN, C2 and C3 as well as ions like CO+. The dust production rates (Afrho) and color of the dust aredetermined through four dust continuum bands from the UV to the red (UC, BC, GC, RC filters). We will present the dust and gas production rates of the brightest comets observed in 2014: C/2012 K1 (PANSTARRS), C/2014 E2 (Jacques), C/2013 A1 (Siding Springs) and C/2013 V5 (Oukaimeden). Each of these comets have been observed at least once a week for several weeks to several months. Light curves with respect to the heliocentric distance will be presented and discussed. [1] Jehin et al., The Messenger, 145, 2-6, 2011.[2] Farnham et al., Icarus, 147, 180-204, 2000. [less ▲]

Detailed reference viewed: 30 (1 ULg)
Full Text
See detailTRAPPIST monitoring of comet C/2013 A1 (Siding Spring)
Opitom, Cyrielle ULg; Jehin, Emmanuel ULg; Manfroid, Jean ULg et al

in Bulletin of the American Astronomical Society (2014, November 01), 46

C/2013 A1 (Siding Spring) is a long period comet discovered by Robert H McNaught at Siding Spring Observatory in Australia on January 3, 2013 at 7.2 au from the Sun. This comet will make a close encounter ... [more ▼]

C/2013 A1 (Siding Spring) is a long period comet discovered by Robert H McNaught at Siding Spring Observatory in Australia on January 3, 2013 at 7.2 au from the Sun. This comet will make a close encounter with Mars on October 19, 2014. At this occasion the comet will be extensively observed both from Earth and from several orbiters around Mars.On September 20, 2013 when the comet was around 5 au from the Sun, we started a monitoring with the TRAPPIST robotic telescope installed at La Silla observatory [1]. A set of narrowband cometary filters designed by the NASA for the Hale-Bopp Observing Campaign [2] is permanently mounted on the telescope along with classic Johnson-Cousins B, V, Rc, and Ic filters.We observed the comet continuously at least once a week from September 20, 2013 to April 6, 2014 with broad band filters. We then recovered the comet on May 20. At this time we could detect the gas and started the observations with narrow band filters until early November, covering the close approach to Mars and the perihelion passage.We present here our first results about comet Siding Springs. From the images in the broad band filters and in the dust continuum filters we derived A(θ)fρ values [3] and studied the evolution of the comet activity with the heliocentric distance from September 20, 2013 to early November 2014. We could also detect gas since May 20, 2014. We thus derived gas production rates using a Haser model [4]. We present the evolution of gas production rates and gas production rates ratios with the heliocentric distance.Finally, we discuss the dust and gas coma morphology. [less ▲]

Detailed reference viewed: 29 (3 ULg)
Full Text
See detailDistant activity of comet C/2006 W3 (Christensen) as observed with Herschel
de Val-Borro, M.; Bockelée-Morvan, D.; Jehin, Emmanuel ULg et al

in Muinonen, Karri (Ed.) Asteroids, Comets, Meteors - Book of Abstracts (2014, July 01)

We aimed to measure the H_2O and dust production rates in C/2006 W3 (Christensen) with the Herschel Space Observatory at a heliocentric distance of ˜ 5 au and compare these data with previous post ... [more ▼]

We aimed to measure the H_2O and dust production rates in C/2006 W3 (Christensen) with the Herschel Space Observatory at a heliocentric distance of ˜ 5 au and compare these data with previous post-perihelion Herschel and ground-based observations at ˜ 3.3 au from the Sun (Bockelée-Morvan et al. 2010b). We have searched for emission in the H_2O and NH_3 ground-state rotational transitions at 557 GHz and 572 GHz, simultaneously, toward comet C/2006 W3 (Christensen) with the Heterodyne Instrument for the Far Infrared (HIFI) onboard Herschel on UT 1.5 September 2010. Photometric observations of the dust coma in the 70 μ m to 160 μ m channels were acquired with the Photodetector Array Camera and Spectrometer (PACS) instrument on UT 26.5 August 2010. A tentative 4-σ H_2O line emission feature was found in the spectra obtained with the HIFI wide-band and high-resolution spectrometers, from which we derive a water production rate of 2.0(5)×10^{27} molec. s^{-1}. A 3-σ upper limit for the ammonia production rate of < 1.5×10^{27} molec. s^{-1} is obtained taking into account the contribution from all hyperfine components (Biver et al. 2012). The dust thermal emission was detected in the 70-μ m to 160-μ m filters, with a more extended emission in the blue channel. We fit the radial dependence of the surface brightness with radially symmetric profiles for the blue and red bands. The dust production rates, obtained for a dust size distribution index that explains the fluxes at the photocenters of the PACS images, lie in the range 70-110 kg s^{-1}. Scaling the CO production rate measured post-perihelion at 3.20-3.32 au, these values correspond to a dust-to-gas production rate ratio in the range 0.3-0.4. The blueshift of the water line detected by HIFI suggests preferential emission from the subsolar point. However, it is also possible that water sublimation occurs in small ice-bearing grains that are emitted from an active region on the nucleus surface at a speed of ˜ 0.2 km s^{-1}. The dust production rates derived in August 2010 are roughly one order of magnitude lower than in September 2009, suggesting that the dust-to-gas production rate ratio remained approximately constant during the period when the activity became increasingly dominated by CO outgassing. These data will complement available Herschel observations of the distant activity of other comets such as 29P/Schwassmann-Wachmann 1 (Bockelée-Morvan et al. 2010a) and main-belt comets 176P/LINEAR and P/2012 T1 (PANSTARRS) (de Val-Borro et al. 2012, O'Rourke et al. 2013). [less ▲]

Detailed reference viewed: 3 (0 ULg)
Full Text
See detailThe activity cycle of 67P/Churyumov-Gerasimenko
Snodgrass, C.; Barrera, L.; Boehnhardt, H. et al

in Muinonen, Karri (Ed.) Asteroids, Comets, Meteors - Book of Abstracts (2014, July 01)

We present ground-based observations of comet 67P/Churyumov-Gerasimenko, target of the Rosetta mission, and an assessment on its activity levels. Based on imaging in the R-band, we measure the brightness ... [more ▼]

We present ground-based observations of comet 67P/Churyumov-Gerasimenko, target of the Rosetta mission, and an assessment on its activity levels. Based on imaging in the R-band, we measure the brightness of the coma within various apertures and use this to assess the amount of dust in the coma. We find that the comet begins to show detectable activity at a pre-perihelion distance from the Sun of 4.3 au, and then shows a smooth increase in production to a peak around one month after perihelion passage. The behaviour of the comet is consistent from one orbit to another, based on archival images taken over three apparitions, and we therefore use the heliocentric lightcurve to make predictions for the 2014/5 period while Rosetta is operating at the comet. We find that the Afρ parameter, measured within an aperture of radius 10,000 km at the comet, is proportional to r^{-3.2}, pre-perihelion [1]. We also attempt to make predictions on the gas production rate by fitting a model to the observed brightness values. This is done by assuming various parameters about the nucleus and dust, many of which are reasonably well constrained for 67P, and solving an energy balance equation that gives the sublimation rate of various ices as a function of solar illumination [2]. The model then links the gas production rate to the total amount of dust in the coma, and its brightness. We find that only a small fraction of the surface area (1.4 %) needs to be active for water sublimation, with an extra peak (up to 4 %) for a month either side of perihelion, while an even smaller area is producing CO_2 (0.04-0.09 %) [1]. The predictions can now be tested against new observations, and we will present the latest results from our 2014 monitoring of 67P. We are performing regular R-band imaging on the comet using the VLT, and early indications in March 2014 indicate that the comet does appear to have returned to activity as expected. By the time of the ACM meeting we will have around 4 months of imaging to make a clear assessment of the trend between 4.4 and 3.8 au, which will allow a comparison with our model and therefore predictions to be made of how well 67P appears to be following its previous activity pattern. By July, we will also have obtained the first of a series of VLT/FORS visible wavelength spectra, to make a direct search for gas emission lines. These will represent some of the most distant spectroscopic observations of a Jupiter family comet coma. Preliminary results will be shown from these spectra, which will also constrain the expected evolution of activity as Rosetta approaches the comet. [less ▲]

Detailed reference viewed: 6 (0 ULg)
Full Text
See detailHigh-resolution spectra of comet C/2013 R1 (Lovejoy)
Rousselot, P.; Decock, A.; Jehin, Emmanuel ULg et al

in Muinonen, Karri (Ed.) Asteroids, Comets, Meteors - Book of Abstracts (2014, July 01)

Comet C/2013 R1 (Lovejoy) is a long-period comet discovered on 7 September 2013 by Terry Lovejoy with a 0.2-m telescope (Guido et al., 2013), it passed its perihelion (0.81 au) on 22 December 2013. It was ... [more ▼]

Comet C/2013 R1 (Lovejoy) is a long-period comet discovered on 7 September 2013 by Terry Lovejoy with a 0.2-m telescope (Guido et al., 2013), it passed its perihelion (0.81 au) on 22 December 2013. It was a bright comet visible to the naked eye. We obtained high-resolution spectra of this comet immediately after its perihelion passage during 4 nights in the period 23-26 December 2013. These spectra have been obtained with the 3.5-m Telescopio Nazionale Galileo (TNG) and the High Accuracy Radial velocity Planet Searcher in North hemisphere (HARPS-N) echelle spectrograph. HARPS-N is an echelle spectrograph covering the spectral range from 383 to 693 nm, with a spectral resolution of R=115000 (Cosentino et al., 2012). It is designed to measure stellar radial velocities in view of detecting extrasolar planets. Our observations are the first successful cometary observations performed with this instrument. They demonstrate that this spectrograph can also be efficient for getting cometary spectra, even if the sensitivity of this instrument is low in the blue part of its spectral coverage. We will present the results of our data analysis for these spectra. This analysis is focused on isotopic ratios, mainly ^{12}C/^{13}C with C_2 emission lines (with the method described in Rousselot et al. 2012) and ^{14}N/^{15}N with ^{14}NH_2 and ^{15}NH_2 emission lines (with the line wavelengths given in Rousselot et al. 2014), atomic oxygen emission lines at 557.7, 630.0 and 636.4 nm (intensity ratios and widths, see Decock et al. 2013) and relative production rates of the detected species. [less ▲]

Detailed reference viewed: 5 (0 ULg)
Full Text
See detailTRAPPIST monitoring of comets C/2012 S1 (ISON) and C/2013 R1 (Lovejoy)
Opitom, Cyrielle ULg; Jehin, Emmanuel ULg; Manfroid, Jean ULg et al

in Muinonen, Karri (Ed.) Asteroids, Comets, Meteors - Book of Abstracts (2014, July 01)

We present the results of a dense photometric monitoring of comets C/2012 S1 (Ison) and C/2013 R1 (Lovejoy) using narrow-band cometary filters and the 60-cm TRAPPIST robotic telescope [1]. We were able to ... [more ▼]

We present the results of a dense photometric monitoring of comets C/2012 S1 (Ison) and C/2013 R1 (Lovejoy) using narrow-band cometary filters and the 60-cm TRAPPIST robotic telescope [1]. We were able to isolate the emission of the OH, NH, CN, C_2, and C_3 radicals for both comets as well as the dust continuum in four bands. By applying a Haser model [2] and fitting the observed profiles, we derive gas production rates. From the continuum bands, we computed the dust Afρ parameters [3]. We were able to follow the evolution of the gas and dust activity of these comets for weeks, looking for changes with the heliocentric distance, study the coma morphology, and analyze their composition and dust coma properties. Comet C/2012 S1 (ISON) was observed about three times a week from October 12 (r=1.43 au) to November 23, 2013. It was then at a heliocentric distance of 0.33 au, only five days before perihelion, when it disintegrated. This dense monitoring allowed us to detect fast changes of the cometary activity. We observed a slowly rising activity in October and early November, and two major outbursts around November 13 and November 19 [4], the gas and dust production rates being multiplied by at least a factor of five during each outburst and then slowly decreasing in the following days. These outbursts were correlated with changes in gas-production-rate ratios. The coma morphology study revealed strong jets in both gas and dust filters. Since the comet was very active in November, we were even able to detect OH jets in our images. Comet C/2013 R1 (Lovejoy) was observed before perihelion from September 9 (r=1.94 au) to November 16 (r=1.12 au), 2013 when the comet was too far North. We recovered the comet post-perihelion on February 13 (r=1.24 au), 2014 and planned to observe it until May (r=2.5 au) with narrow-band filters. We compare the evolution of gas and dust activity as well as the evolution of gas production rates ratios on both sides of perihelion. The morphological study of both gas and dust coma we already performed on pre-perihelion images revealed structures in gas and dust filters. We compare the gas and dust features in all filters and study their evolution. [less ▲]

Detailed reference viewed: 6 (0 ULg)
Full Text
See detailThe TRAPPIST comet survey
Jehin, Emmanuel ULg; Opitom, Cyrielle ULg; Manfroid, Jean ULg et al

in Muinonen, Karri (Ed.) Asteroids, Comets, Meteors - Book of Abstracts (2014, July 01)

TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) is a 60-cm robotic telescope that has been installed in June 2010 at the ESO La Silla Observatory [1]. Operated from Liège (Belgium) it is ... [more ▼]

TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) is a 60-cm robotic telescope that has been installed in June 2010 at the ESO La Silla Observatory [1]. Operated from Liège (Belgium) it is devoted to the detection and characterisation of exoplanets and to the study of comets and other small bodies in the Solar System. We describe here the hardware and the goals of the project and give an overview of the comet production rates monitoring after three years of operations. The telescope and observatory --- TRAPPIST's optical tube unit is a Ritchey-Chretien 0.6 meter telescope with a focal length of 4.8 meter. It is associated with a German equatorial mount that is, thanks to its direct drive system, extremely fast (up to 50 deg/s), accurate (tracking accuracy without autoguider better than 2'' in 10 min), and free of periodic error. The instrument is a Peltier cooled commercial camera equipped with a Fairchild 3041 back-illuminated 2k×2k chip. The pixel scale is 0.64''/pixel. Three read-out modes are available, the shortest read-out time being 2s. The total field of view of the camera is 22'×22'. It is associated to a custom-made dual filter wheel. One of the filter wheel contains broad band filters (Johnson B, V, R, Cousins Ic, Sloan z, and a special I+z filter), while the other contains the narrow-band NASA HB cometary filters (OH, NH, CN, CO+, C3, and C2 gaseous species; UC, BC, GC and RC solar continuum windows and a NaI D filter) [2]. The telescope is protected by a 5 meter diameter dome that was totally refurbished and automatized. The observatory is fully robotic and equipped with a weather station, an UPS and webcams. The la Silla site is excellent with more than 300 clear nights per year and the telescope has proven to be very reliable with a small amount of technical downtime. Comet monitoring --- For relatively bright comets (V < 12) we measure several times a week the gaseous production rates (using a Haser model) and the spatial distribution of several species among which OH, NH, CN, C2 and C3 as well as ions like CO+. The dust production rates (Afrho) and color of the dust are determined through four dust continuum bands (UC, BC, GC, RC). Such regular measurements are rare because of the lack of observing time on larger telescopes. Yet they are very valuable as they show how the gas production rate of each species evolves with respect to the distance to the Sun. Those observations allow to determine the composition of the comets and the chemical class to which they belong (rich or poor in carbon for instance [3]), possibly revealing the origin of those classes but also if there are some changes of the abundance ratios along the orbit (evolutionary effects). Indeed with half a dozen of comets observed each year --- and as long as possible along their orbit --- this program will provide a good statistical sample after a few years. We will present the results of this monitoring after three years of operations. Thanks to the way the telescope is operated, follow-up of split comets and of special outburst events is possible right after an alert is given and can bring important information on the nature of comets. In addition to providing the productions rates of the different species through a proper photometric calibration, image analysis can reveal coma features (jets, fans, tails), that can lead to the detection of active regions and measure the rotation period of the nucleus. The monitoring is also useful to assess the gas and dust activity of a given comet in order to prepare more detailed observations with larger telescopes. Such data can be obtained at any time under request. Finally a dozen of faint comets (V < 20) are monitored once a week through B, V, Rc, Ic filters and magnitudes and positions are sent to the MPC. [less ▲]

Detailed reference viewed: 5 (0 ULg)
Full Text
See detailWater, hydrogen cyanide, and dust production from the distant comet 29P/Scwassmann-Wachmann 1
Bockelee-Morvan, D.; Biver, N.; Opitom, Cyrielle ULg et al

in Muinonen, Karri (Ed.) Asteroids, Comets, Meteors - Book of Abstracts (2014, July 01)

Comet 29P/Schwassmann-Wachmann is a periodic comet, also classified as a Centaur, orbiting on a nearly circular orbit at 6 au from the Sun. It is well known for its permanent activity driven by CO ... [more ▼]

Comet 29P/Schwassmann-Wachmann is a periodic comet, also classified as a Centaur, orbiting on a nearly circular orbit at 6 au from the Sun. It is well known for its permanent activity driven by CO outgassing, and its episodic outbursts. Comet 29P was observed in 2010--2011 with the Herschel space observatory. Observations of water and ammonia were performed with the Heterodyne Instrument for the Far-Infrared (HIFI). One set of measurements was obtained two days after a major outburst (16 Apr. 2010). Images of the dust coma at 70 and 160 μ m were obtained using the Photodetector Array Camera and Spectrometer (PACS). To support these observations, observations of CO and HCN were undertaken at the 30-m telescope of the Institut de radioastronomie millimétrique (IRAM). We present an overview of this set of observations. H_2O and CO are detected. We also obtain the first detection of HCN in this distant comet. Relative abundances are similar to those measured in the coma of comet C/1995 O1 (Hale-Bopp) when at r_h = 6 au from the Sun, but strongly differ from coma compositions at r_h = 1 au. The line profiles show evidence that both H_2O, HCN are released from long-lived icy grains. Detailed modeling of water production from icy-grain suggests continuous release of icy grains from the nucleus. The thermal emission from the nucleus is detected in the PACS 70 μ m images. The thermal emission from dust grains is analyzed with a thermal model of dust emission, which takes into account the dust size distribution. Both the size index and the dust production rate are measured. [less ▲]

Detailed reference viewed: 4 (0 ULg)
Full Text
Peer Reviewed
See detailMicrolensing of the broad-line region in the quadruply imaged quasar HE0435-1223
Braibant, Lorraine ULg; Hutsemekers, Damien ULg; Sluse, Dominique ULg et al

in Astronomy and Astrophysics (2014), 565

Using infrared spectra of the z = 1.693 quadruply lensed quasar HE0435-1223 acquired in 2009 with the spectrograph SINFONI at the ESO Very Large Telescope, we have detected a clear microlensing effect in ... [more ▼]

Using infrared spectra of the z = 1.693 quadruply lensed quasar HE0435-1223 acquired in 2009 with the spectrograph SINFONI at the ESO Very Large Telescope, we have detected a clear microlensing effect in images A and D. While microlensing affects the blue and red wings of the Hα line profile in image D very differently, it de-magnifies the line core in image A. The combination of these different effects sets constraints on the line-emitting region; these constraints suggest that a rotating ring is at the origin of the Hα line. Visible spectra obtained in 2004 and 2012 indicate that the MgII line profile is microlensed in the same way as the Hα line. Our results therefore favour flattened geometries for the low-ionization line-emitting region, for example, a Keplerian disk. Biconical models cannot be ruled out but require more fine-tuning. Flux ratios between the different images are also derived and confirm flux anomalies with respect to estimates from lens models with smooth mass distributions. Based on observations made with the ESO-VLT, Paranal, Chile; Proposal 084.B-0013 (PI: Rix).Tables 2, 3 and Appendix A are available in electronic form at <A href="http://www.aanda.org/10.1051/0004-6361/201423633/olm">http://www.aanda.org</A> [less ▲]

Detailed reference viewed: 27 (14 ULg)
Full Text
See detailMeasurements of the 14N/15N isotopic ratio in comets's ammonia
Rousselot, P.; Pirali, O.; Jehin, Emmanuel ULg et al

Conference (2014, May)

La détermination des rapports isotopiques de l'azote dans les différents objets du système solaire est importante pour une bonne compréhension de leur origine. Les mesures du rapport 14N/15N faites jusqu ... [more ▼]

La détermination des rapports isotopiques de l'azote dans les différents objets du système solaire est importante pour une bonne compréhension de leur origine. Les mesures du rapport 14N/15N faites jusqu'à présent ont montré une grande dispersion des valeurs (de 50 à 441), tous les objets du système solaire excepté Jupiter apparaissant enrichis en 15N comparés à la nébuleuse protosolaire. Différentes explications ont été proposées pour expliquer les valeurs observées, qui sont complexes à interpréter car dues non seulement au réservoir d'origine de l'azote d'où provient l'objet étudié mais également à des mécanismes de fractionnement isotopique. Le cas des comètes, dans ce contexte, est intéressant, car leur composition est supposée relativement proche de celle de la nébuleuse protosolaire et la seule valeur disponible jusqu'à l'année dernière, avait été calculée à partir de la molécule HCN et du radical CN (issu du HCN). Ce rapport était d'environ 150, bien en dessous de la valeur mesurée dans l'atmosphère terrestre (272). Les comètes contiennent beaucoup d'azote sous forme de NH3, photodissocié en NH2 dont les raies sont nombreuses dans le spectre visible. Il était donc possible de mesurer le rapport 14N/15N dans l'ammoniac pour vérifier l'influence possible de phénomènes de fractionnement isotopique entre le HCN et le NH3, ceci à condition de connaître avec précision les longueurs d'onde des raies de 15NH2. Pour déterminer ces longueurs d'onde, nous avons mesuré le spectre d'émission de la transition Ã2A1~X2B1 de 14NH2 et 15NH2 dans la gamme spectrale 5700 Å – 6000 Å sur la ligne AILES du synchrotron SOLEIL, avec un spectromètre par transformée de Fourier. L'analyse de ces spectres a permis, au final, la détection du 15NH2 dans les spectres cométaires et la première détermination du rapport 14N/15N dans l'ammoniac des comètes. [less ▲]

Detailed reference viewed: 6 (1 ULg)
Full Text
Peer Reviewed
See detailThe XMM-Newton view of the yellow hypergiant IRC+10420 and its surroundings
De Becker, Michaël ULg; Hutsemekers, Damien ULg; Gosset, Eric ULg

in New Astronomy (2014), 29

Among evolved massive stars likely in transition to the Wolf-Rayet phase, IRC +10420 is probably one of the most enigmatic. It belongs to the category of yellow hypergiants and it is characterized by ... [more ▼]

Among evolved massive stars likely in transition to the Wolf-Rayet phase, IRC +10420 is probably one of the most enigmatic. It belongs to the category of yellow hypergiants and it is characterized by quite high mass loss episodes. Even though IRC+10420 benefited of many observations in several wavelength domains, it has never been a target for an X-ray observatory. We report here on the very first dedicated observation of IRC+10420 in X-rays, using the XMM-Newton satellite. Even though the target is not detected, we derive X-ray flux upper limits of the order of 1–3 ×10−14 erg cm−2 s−1 (between 0.3 and 10.0 keV), and we discuss the case of IRC+10420 in the framework of emission models likely to be adequate for such an object. Using the Optical/UV Monitor on board XMM-Newton, we present the very first upper limits of the flux density of IRC +10420 in the UV domain (between 1800 and 2250 Å and between 2050 and 2450 Å). Finally, we also report on the detection in this field of 10 X-ray and 7 UV point sources, and we briefly discuss their properties and potential counterparts at longer wavelengths. [less ▲]

Detailed reference viewed: 44 (11 ULg)
Full Text
See detailTRAPPIST monitoring of comet C/2012 F6 (Lemmon)
Opitom, Cyrielle ULg; Jehin, Emmanuel ULg; Manfroid, Jean ULg et al

Poster (2014, April)

C/2012 F6 (Lemmon) is a long period comet discovered by the Mount Lemmon Survey on 2012 March 23 at 5 AU from the sun. C/2012 F6 (Lemmon) reached perihelion on March 23, 2013 at 0.73 AU from the sun. In ... [more ▼]

C/2012 F6 (Lemmon) is a long period comet discovered by the Mount Lemmon Survey on 2012 March 23 at 5 AU from the sun. C/2012 F6 (Lemmon) reached perihelion on March 23, 2013 at 0.73 AU from the sun. In December 2012 the comet was unexpectedly bright, allowing us to make an extensive monitoring during several months with both broadband and narrowband filters to follow the evolution of the comet chemical composition. The monitoring was made with TRAPPIST robotic telescope installed at La Silla observatory [1]. TRAPPIST is a 60-cm telescope dedicated to the study of exoplanets and small bodies in the solar system. The telescope is equipped with a 2Kx2K FLI Proline CCD camera very sensitive in the blue and the red. A set of narrowband cometary filters designed by the NASA for the Hale-Bopp Observing Campaign [2] is permanently mounted on the telescope along with classic Johnson-Cousins B, V, Rc, and Ic filters. We observed the comet from December 11, 2012 to March 4, 2013 (pre-perihelion) and from April 29, 2013 to June 11, 2013 (post-perihelion). At least 2 or 3 observing runs per week were programmed during this period. We collected 1358 images on 52 nights. In January and February the comet visibility allowed us to make several long runs and to detect the comet rotational variability. From the comet images in narrowband filters we studied the gaseous coma chemical composition and activity by deriving OH, NH, CN, C2 and C3 production rates using a classical Haser model [3]. The production and properties of the dust component were studied through the observation of C/2012 F6 (Lemmon) with narrowband continuum filters at 344.2 nm (UC), 444.9 nm (BC), 525.7 nm (GC) and 713.0 nm (RC). We used A(θ)fρ [4] parameter as a proxy for the dust production. [less ▲]

Detailed reference viewed: 19 (1 ULg)