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 Publications of Damien Hutsemekers     Results 1-20 of 315. 1 2 3 4 5 6 7 8 9 10   Photometry and high-resolution spectroscopy of comet 21P/Giacobini-Zinner during its 2018 apparitionMoulane, Y.; Jehin, Emmanuel ; Rousselot, P. et alE-print/Working paper (2020)We report on photometry and high resolution spectroscopy of the chemically peculiar Jupiter-family Comet (hereafter JFC) 21P/Giacobini- Zinner. Comet 21P is a well known member of the carbon-chain ... [more ▼]We report on photometry and high resolution spectroscopy of the chemically peculiar Jupiter-family Comet (hereafter JFC) 21P/Giacobini- Zinner. Comet 21P is a well known member of the carbon-chain depleted family but displays also a depletion of amines. We monitored continuously the comet over more than seven months with the two TRAPPIST telescopes (TN and TS), covering a large heliocentric distance range from 1.60 au inbound to 2.10 au outbound with a perihelion at 1.01 au on September 10, 2018. We computed and followed the evolution of the dust (represented by Af$\rho$) and gas production rates of the daughter species OH, NH, CN, C$_3$, and C$_2$ and their relative abundances to OH and to CN over the comet orbit. We compared them to those measured in the previous apparitions. The activity of the comet and its water production rate reached a maximum of (3.72$\pm$0.07)$\times$10$^{28}$ molec/s on August 17, 2018 (r$_h$=1.07 au), 24 days before perihelion. The peak value of A(0)f$\rho$ was reached on the same date (1646$\pm$13) cm in the red filter. The abundance ratios of the various species are remarkably constant over a large range of heliocentric distances, before and after perihelion, showing a high level of homogeneity of the ices in the surface of the nucleus. The behaviour and level of the activity of the comet is also remarkably similar over the last five orbits. About the coma dust colour, 21P shows reflectively gradients similar to JFCs. We obtained a high resolution spectrum of 21P with UVES at ESO VLT one week after perihelion. Using the CN B-X (0,0) violet band, we measured $^{12}$C/$^{13}$C and $^{14}$N/$^{15}$N isotopic ratios of 100$\pm$10 and 145$\pm$10, respectively, both in very good agreement with what is usually found in comets. [less ▲]Detailed reference viewed: 22 (1 ULiège) Tracking the state transitions in changing-look active galactic nuclei through their polarized-light echoesMarin, Frédéric; Hutsemekers, Damien in Astronomy and Astrophysics (2020), 636Context. Variations in the mass accretion rate appear to be responsible for the rapid transitions in spectral type that are observed in increasingly more active galactic nuclei (AGNs). These objects are ... [more ▼]Context. Variations in the mass accretion rate appear to be responsible for the rapid transitions in spectral type that are observed in increasingly more active galactic nuclei (AGNs). These objects are now labeled "changing-look" AGNs and are key objects for understanding the physics of accretion onto supermassive black holes.
Aims: We aim to complement the analysis and interpretation of changing-look AGNs by modeling the polarization variations that can be observed, in particular, polarized-light echoes.
Methods: We built a complex and representative model of an AGN and its host galaxy and ran radiative transfer simulations to obtain realistic time-dependent polarization signatures of changing-look objects. Based on actual data, we allowed the system to become several times fainter or brighter within a few years, assuming a rapid change in accretion rate.
Results: We obtain time-dependent polarization signatures of distant high-luminosity (quasars) and nearby low-luminosity (Seyferts) changing-look AGNs for a representative set of inclinations. We predict the evolution of the continuum polarization for future polarimetric campaigns with the goal to better understand the physics at work in these objects. We also investigate highly inclined AGNs that experience strong accretion rate variations without appearing to change state. We apply our modeling to Mrk 1018, the best-documented case of a changing-look AGN, and predict a variation in its polarization after the recent dimming of its continuum.
Conclusions: We demonstrate that polarization monitoring campaigns that cover the transitions that are observed in changing-look AGNs might bring crucial information on the geometry and composition of all the reprocessing regions within the nucleus. In particular, specific features in the time variation of the polarization position angle can provide a new and efficient method for determining AGN inclinations. [less ▲]Detailed reference viewed: 21 (3 ULiège) Forbidden atomic carbon, nitrogen, and oxygen emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)Raghuram, S.; Hutsemekers, Damien ; Opitom, C. et alin Astronomy and Astrophysics (2020), 635Context. The N[SUB]2[/SUB] and CO-rich and water-depleted comet C/2016 R2 (Pan-STARRS) - hereafter "C/2016 R2" - is a unique comet for detailed spectroscopic analysis.
Aims: We aim to explore the ... [more ▼]Context. The N[SUB]2[/SUB] and CO-rich and water-depleted comet C/2016 R2 (Pan-STARRS) - hereafter "C/2016 R2" - is a unique comet for detailed spectroscopic analysis.
Aims: We aim to explore the associated photochemistry of parent species, which produces different metastable states and forbidden emissions, in this cometary coma of peculiar composition.
Methods: We reanalyzed the high-resolution spectra of comet C/2016 R2 obtained in February 2018 using the UVES spectrograph of the European Southern Observatory Very Large Telescope. Various forbidden atomic emission lines of [CI], [NI], and [OI] were observed in the optical spectrum of this comet when it was at 2.8 au from the Sun. The observed forbidden emission intensity ratios are studied in the framework of a couple-chemistry emission model.
Results: The model calculations show that CO[SUB]2[/SUB] is the major source of both atomic oxygen green and red doublet emissions in the coma of C/2016 R2 (while for most comets it is generally H[SUB]2[/SUB]O), whereas, CO and N[SUB]2[/SUB] govern the atomic carbon and nitrogen emissions, respectively. Our modeled oxygen green-to-red-doublet and carbon-to- nitrogen emission ratios are higher by a factor of three than what is found from observations. These discrepancies could be due to uncertainties associated with photon cross sections or unknown production and/or loss sources. Our modeled oxygen green-to-red-doublet emission ratio is close to what is seen in observations when we consider an O[SUB]2[/SUB] abundance with a production rate of 30% relative to the CO production rate. We constrained the mean photodissociation yield of CO, producing C([SUP]1[/SUP]S) at about 1%, a quantity which has not been measured in the laboratory. The collisional quenching is not a significant loss process for N([SUP]2[/SUP]D) though its radiative lifetime is significant (~10 h). Hence, the observed [NI] doublet- emission ratio ([NI] 5198/5200) of 1.22, which is smaller than the terrestrial measurement by a factor 1.4, is mainly due to the characteristic radiative decay of N([SUP]2[/SUP]D). [less ▲]Detailed reference viewed: 20 (1 ULiège) Spatially separated continuum sources revealed by microlensing in the gravitationally lensed broad absorption line quasar SDSS J081830.46+060138.0⋆Hutsemekers, Damien ; Sluse, Dominique ; Kumar, P.in Astronomy and Astrophysics (2020), 633Gravitational microlensing is a powerful tool for probing the inner structure of distant quasars. In this context, we have obtained spectropolarimetric observations of the two images of the broad ... [more ▼]Gravitational microlensing is a powerful tool for probing the inner structure of distant quasars. In this context, we have obtained spectropolarimetric observations of the two images of the broad absorption line (BAL) quasar SDSS J081830.46+060138.0 (J0818+0601) at redshift z ≃ 2.35. We first show that J0818+0601 is actually gravitationally lensed, and not a binary quasar. A strong absorption system detected at z = 1.0065 ± 0.0002 is possibly due to the lensing galaxy. Microlensing is observed in one image and it magnifies the emission lines, the continuum, and the BALs differently. By disentangling the part of the spectrum that is microlensed from the part that is not microlensed, we unveil two sources of continuum that must be spatially separated: a compact one, which is microlensed, and an extended one, which is not microlensed and contributes to two thirds of the total continuum emission. J0818+0601 is the second BAL quasar in which an extended source of rest-frame ultraviolet continuum is found. We also find that the images are differently polarized, suggesting that the two continua might be differently polarized. Our analysis provides constraints on the BAL flow. In particular, we find that the outflow is seen with a nonzero onset velocity, and stratified according to ionization.

The reduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz- bin/cat/J/A+A/633/A101

Based on observations made with ESO Very Large Telescope at the Paranal Observatory under program ID 100.B-0590. [less ▲]Detailed reference viewed: 32 (3 ULiège) Changing-look Seyfert galaxies with optical linear polarization measurementsMarin, F.; Hutsemekers, Damien ; Agis-Gonzalez, Beatriz in SF2A-2019: Proceedings of the Annual meeting of the French Society of Astronomy and Astrophysics (2019, December 01)In this lecture note, we make the case for new (spectro)polarimetric measurements of changing-look'' AGNs (CLAGNs), a subclass of the AGN family tree that shows long-term (months to years) large flux ... [more ▼]In this lecture note, we make the case for new (spectro)polarimetric measurements of changing-look'' AGNs (CLAGNs), a subclass of the AGN family tree that shows long-term (months to years) large flux variability associated with the appearance or disappearance of optical broad emission lines. We discuss how polarization measurements could help to distinguish which of the several scenarios proposed to explain such variations is/are the most likely. We collected all the past polarization measurements of nearby, Seyfert-like CLAGNs and take stock that almost all polarimetric information we have on those fascinating objects dates from the 80's and 90's. We thus explain how polarization could help us understanding the physical processes happening in the first parsecs of CLAGNs and why new polarization monitoring campaigns are strongly needed. [less ▲]Detailed reference viewed: 20 (3 ULiège) VizieR Online Data Catalog: SDSS J081830.46+060138.0 spectropolarimetry (Hutsemekers+, 2020)Hutsemekers, Damien ; Sluse, Dominique ; Kumar, P.Textual, factual or bibliographical database (2019)This Table contains the spectropolarimetric data obtained for images A and B of the gravitationally lensed quasar SDSS J081830.46+060138 on December 24 and 25, 2017, with FORS2 at the ESO VLT.

(1 ... [more ▼]This Table contains the spectropolarimetric data obtained for images A and B of the gravitationally lensed quasar SDSS J081830.46+060138 on December 24 and 25, 2017, with FORS2 at the ESO VLT.

(1 data file). [less ▲]Detailed reference viewed: 22 (2 ULiège) Comet 66P/du Toit: not a near-Earth main belt cometYang, Bin; Jehin, Emmanuel ; Pozuelos, Francisco J. et alin Astronomy and Astrophysics (2019), 631Context. Main belt comets (MBCs) are a peculiar class of volatile- containing objects with comet-like morphology and asteroid-like orbits. However, MBCs are challenging targets to study remotely due to ... [more ▼]Context. Main belt comets (MBCs) are a peculiar class of volatile- containing objects with comet-like morphology and asteroid-like orbits. However, MBCs are challenging targets to study remotely due to their small sizes and the relatively large distance they are from the Sun and the Earth. Recently, a number of weakly active short-period comets have been identified that might originate in the asteroid main belt. Among all of the known candidates, comet 66P/du Toit has been suggested to have one of the highest probabilities of coming from the main belt.
Aims: The main goal of this study is to investigate the physical properties of 66P via spectroscopic and imaging observations to constrain its formation conditions. In particular, the isotopic abundance ratio and the ortho-to-para ratio (OPR) of gaseous species can be derived via high-resolution spectroscopy, which is sensitive to the formation temperature of the nucleus.
Methods: We obtained medium and high-resolution spectra of 66P from 300-2500 nm with the X-shooter and the UVES instruments at the Very Large Telescope in July 2018. We also obtained a series of narrow-band images of 66P to monitor the gas and dust activity between May and July 2018 with TRAPPIST-South. In addition, we applied a dust model to characterize the dust coma of 66P and performed dynamical simulations to study the orbital evolution of 66P.
Results: We derive the OPR of ammonia (NH[SUB]3[/SUB]) in 66P to be 1.08 ± 0.06, which corresponds to a nuclear spin temperature of 34 K. We compute the production rates of OH, NH, CN, C[SUB]3[/SUB], and C[SUB]2[/SUB] radicals and measure the dust proxy, Afρ. The dust analysis reveals that the coma can be best-fit with an anisotropic model and the peak dust production rate is about 55 kg s[SUP]-1[/SUP] at the perihelion distance of 1.29 au. Dynamical simulations show that 66P is moderately asteroidal with the capture time, t[SUB]cap[/SUB] 10[SUP]4[/SUP] yr.
Conclusions: Our observations demonstrate that the measured physical properties of 66P are consistent with typical short-period comets and differ significantly from other MBCs. Therefore, 66P is unlikely to have a main belt origin. [less ▲]Detailed reference viewed: 19 (2 ULiège) Constraining the geometry and kinematics of the quasar broad emission line region using gravitational microlensing. II. Comparing models with observations in the lensed quasar HE0435-1223Hutsemekers, Damien ; Braibant, L.; Sluse, Dominique et alin Astronomy and Astrophysics (2019), 629The quadruply lensed quasar HE0435-1223 shows a clear microlensing effect that affects differently the blue and red wings of the Hα line profile in its image D. To interpret these observations, and ... [more ▼]The quadruply lensed quasar HE0435-1223 shows a clear microlensing effect that affects differently the blue and red wings of the Hα line profile in its image D. To interpret these observations, and constrain the broad emission line region (BLR) properties, the effect of gravitational microlensing on quasar broad emission line profiles and their underlying continuum has been simulated considering representative BLR models and microlensing magnification maps. The amplification and distortion of the Hα line profile, characterized by a set of four indices, can be reproduced by the simulations. Although the constraints on the BLR models set by the observed single-epoch microlensing signal are not very robust, we found that flattened geometries (Keplerian disk and equatorial wind) can more easily reproduce the observed line profile deformations than a biconical polar wind. With an additional independent constraint on the size of the continuum source, the Keplerian disk model of the Hα BLR is slightly favored. [less ▲]Detailed reference viewed: 22 (1 ULiège) VLT multi-instrument observations of comet 46P/WirtanenOpitom, Cyrielle; Hutsemekers, Damien ; Manfroid, Jean et alConference (2019, September 01)We present observations of the Jupiter family comet 46P/Wirtanen performed at the ESO/VLT in December 2018 with three different instruments: the high-resolution spectrographs UVES and ESPRESSO, and the ... [more ▼]We present observations of the Jupiter family comet 46P/Wirtanen performed at the ESO/VLT in December 2018 with three different instruments: the high-resolution spectrographs UVES and ESPRESSO, and the MUSE integral field spectrograph. Combining those observations, we investigate the coma composition and main activity drivers of 46P, as well as species parentage and jets in its coma. [less ▲]Detailed reference viewed: 24 (2 ULiège) Modeling of the CO+ emission spectrum in comet C/2016 R2 (PanSTARRS)Rousselot, Philippe; Jehin, Emmanuel ; Curti, Mathieu et alConference (2019, September 01)The long period comet C/2016 R2 (PanSTARRS), discovered on 2016 September 7 by the PansSTARRS telescope, presented an unusual composition. Most of the emission lines due to radicals usually abundant in ... [more ▼]The long period comet C/2016 R2 (PanSTARRS), discovered on 2016 September 7 by the PansSTARRS telescope, presented an unusual composition. Most of the emission lines due to radicals usually abundant in comets (such as C2, CN, C3 ) appeared to be faint while unexpected strong emission lines due to N2+ and CO+ ions were clearly apparent in the spectra obtained in the optical range (some fainter CO2+ emission lines were also present). It is the first comet with such bright N2+ emission lines but also the brightness and abundance of CO+ lines allow to study this ion in great details. We obtained in February 2018 high resolution spectra with the ESO 8-m Very Large Telescope and the UVES spectrograph, that allowed us to obtain a CO+ spectrum with an unprecedented signal-to-noise ratio. We also developed a fluorescence model for CO+ to model these spectra. We will present these observations, their modeling and a first estimate of the 12C/13C isotopic ratio for CO+ ions in comet C/2016 R2. It is the first measurement of such a ratio with ground-based telescopes, the only related measurement published so far being done in situ in the coma of comet 67P/Churyumov-Gerasimenko by the ROSINA instrument on-board the Rosetta spacecraft for CO and CO2 molecules. [less ▲]Detailed reference viewed: 39 (3 ULiège) The unique spectrum of comet C/2016 R2 (PanSTARRS)Jehin, Emmanuel ; Opitom, Cyrielle; Hutsemekers, Damien et alConference (2019, September 01)We present optical observations of the long period comet C/2016 R2 (PanSTARRS) performed with the high resolution UVES spectrograph at the ESO VLT (Paranal), complemented by low resolution spectra at INT ... [more ▼]We present optical observations of the long period comet C/2016 R2 (PanSTARRS) performed with the high resolution UVES spectrograph at the ESO VLT (Paranal), complemented by low resolution spectra at INT (La Palma) and narrow-band imaging obtained with the TRAPPIST telescopes. We show that this comet has a unique chemical composition, with strong N2+ and CO+ emission lines in the optical, several well detected CO2+ bands while the usual radicals CN, C3, C2, are very faint. OH, OH+ and H2O+ as well as NH and NH2, are not detected, suggesting that C/2016 R2 is a comet rich in N2 and CO ices but poor in water and ammonia. We will present new results obtained from these observations and discuss the origin of this type of comets. [less ▲]Detailed reference viewed: 35 (3 ULiège) Search for water outgassing of (1) Ceres near perihelionRousselot, P.; Opitom, C.; Jehin, Emmanuel et alin Astronomy and Astrophysics (2019), 628Context. (1) Ceres is the largest body in the main asteroid belt and one of the most intriguing objects in the solar system, in part because of the discovery of water outgassing by the Herschel Space ... [more ▼]Context. (1) Ceres is the largest body in the main asteroid belt and one of the most intriguing objects in the solar system, in part because of the discovery of water outgassing by the Herschel Space Observatory (HSO) and its still-debated origin. Ceres was the target of NASA's Dawn spacecraft for 3.5 yr, which achieved a detailed characterization of the dwarf planet. The possible influence of the local flux of solar energetic particles (SEP) on the production of a Cerean exosphere and water vapor has been suggested, in addition to the sublimation of water ice that depends on the temperature, meaning the heliocentric distance.
Aims: We used the opportunity of both the perihelion passage of (1) Ceres in April 2018, and the presence of Dawn in its vicinity (for measuring the SEP flux in real time) to check the influence of heliocentric distance and SEP flux on water outgassing.
Methods: We searched for OH emission lines near the limb of Ceres in the near-UV with the UVES spectrograph mounted on the 8-m ESO Very Large Telescope. Two spectra were recorded when Ceres was close to its perihelion, in February 2018, and with Dawn spacecraft orbiting Ceres. It was possible to simultaneously measure energetic particles around Ceres at the time of our observations.
Results: Our observations did not permit detection of OH emission lines to a very high sensitivity level. This level is estimated to correspond to a global water production rate of Q[SUB]H[SUB]2[/SUB]O[/SUB] ∽ 2 × 10[SUP]26[/SUP] molecules s[SUP]-1[/SUP], similar to the water production rate derived from HSO observations. The solar energetic particles flux measured around Ceres was negligible at the time of these observations.
Conclusions: Our observations support the idea that heliocentric distance (i.e., the sublimation of water ice) does not play a major role in the water emission from Ceres. This production rate could be either related to SEP events or to other mechanisms, possibly of endogenic origin. Based on observations collected at the European Southern Observatory under ESO program 2100.C-5038(A). [less ▲]Detailed reference viewed: 45 (4 ULiège) Polarization of changing-look quasarsHutsemekers, Damien ; Agis-Gonzalez, Beatriz ; Marin, F. et alin Astronomy and Astrophysics (2019), 625If the disappearance of the broad emission lines observed in changing- look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization ... [more ▼]If the disappearance of the broad emission lines observed in changing- look quasars originates from the obscuration of the quasar core by dusty clouds moving in the torus, high linear optical polarization would be expected in those objects. We then measured the rest-frame UV-blue linear polarization of a sample of 13 changing-look quasars, 7 of them being in a type 1.9-2 state. For all quasars but one the polarization degree is lower than 1%. This suggests that the disappearance of the broad emission lines cannot be attributed to dust obscuration, and supports the scenario in which changes of look are caused by a change in the rate of accretion onto the supermassive black hole. Such low polarization degrees also indicate that these quasars are seen under inclinations close to the system axis. One type 1.9-2 quasar in our sample shows a high polarization degree of 6.8%. While this polarization could be ascribed to obscuration by a moving dusty cloud, we argue that this is unlikely given the very long time needed for a cloud from the torus to eclipse the broad emission line region of that object. We propose that the high polarization is due to the echo of a past bright phase seen in polar-scattered light. This interpretation raises the possibility that broad emission lines observed in the polarized light of some type 2 active galactic nuclei can be echoes of past type 1 phases and not evidence of hidden broad emission line regions. Based on observations made with the William Herschel telescope operated on the island of La Palma by the Isaac Newton Group of Telescopes in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias and observations made with ESO Very Large Telescope at the Paranal Observatory under program ID 101.B-0209. [less ▲]Detailed reference viewed: 32 (3 ULiège) High resolution optical spectroscopy of the N2-rich comet C/2016 R2 (PanSTARRS)Opitom, C.; Hutsemekers, Damien ; Jehin, Emmanuel et alin Astronomy and Astrophysics (2019), 624Context. Early observations of comet C/2016 R2 (PanSTARRS) have shown that the composition of this comet is very peculiar. Radio observations have revealed a CO-rich and HCN-poor comet and an optical coma ... [more ▼]Context. Early observations of comet C/2016 R2 (PanSTARRS) have shown that the composition of this comet is very peculiar. Radio observations have revealed a CO-rich and HCN-poor comet and an optical coma dominated by strong emission bands of CO[SUP]+[/SUP] and, more surprisingly, N[SUB]2[/SUB][SUP]+[/SUP].
Aims: The strong detection of N[SUB]2[/SUB][SUP]+[/SUP] in the coma of C/2016 R2 provided an ideal opportunity to measure the [SUP]14[/SUP]N/[SUP]15[/SUP]N isotopic ratio directly from N[SUB]2[/SUB][SUP]+[/SUP] for the first time, and to estimate the N[SUB]2[/SUB]/CO ratio, which is an important diagnostic to constrain formation models of planetesimals, in addition to the more general study of coma composition.
Methods: We obtained high resolution spectra of the comet in February 2018 when it was at 2.8 au from the Sun. We used the UVES spectrograph of the European Southern Observatory Very Large Telescope, complemented with narrowband images obtained with the TRAPPIST telescopes.