http://hdl.handle.net/2268/155 Chercher dans ce canal chercher http://orbi.ulg.ac.be/simple-search http://hdl.handle.net/2268/149098 Titre: Venus nitric oxide nightglow mapping from SPICAV nadir observations. <br/> <br/>Auteur, co-auteur: Stiepen, Arnaud; Gérard, Jean-Claude; Dumont, Maïté; Cox, Cédric; Bertaux, Jean-Loup <br/> <br/>Résumé: Nitric oxide δ (190-240 nm) and γ (255-270 nm) emissions on the Venus nightside have been observed with Venus Express SPICAV instrument operated in the nadir mode. These ultraviolet emissions arise from the desexcitation of excited NO molecules created by radiative recombination of O(3P) and N(4S) atoms. These atoms are produced on the dayside of the planet through photodissociation of CO2 and N2 molecules and are transported to the nightside by the global subsolar to antisolar circulation. We analyze a wide dataset of nadir observations obtained since 2006 to determine the statistical distribution of the NO nightglow and its variability. Individual observations show a great deal of variability and may exhibit multiple maxima along latitudinal cuts. We compare this global map with the results obtained during the Pioneer-Venus mission and with the recent O2(a1Δg) nightglow map. The NO airglow distribution shows a statistical bright region extending from 01:00 and 03:30 local time and 25°N to 10°S, very similar to the Pioneer result obtained 35 years earlier during maximum solar activity conditions. The shift from the antisolar point and the difference with the O2 airglow indicate that superrotating zonal winds are statistically weak near 97 km, but play an important role in the lower thermosphere. We compare these results with other evidence for superrotation in the thermosphere and point out possible sources of momentum transfer. http://hdl.handle.net/2268/149095 Titre: Cartographie du nightglow de Vénus <br/> <br/>Auteur, co-auteur: Stiepen, Arnaud http://hdl.handle.net/2268/149093 Titre: Etude des émission UV de Mars et Vénus <br/> <br/>Auteur, co-auteur: Stiepen, Arnaud http://hdl.handle.net/2268/149065 Titre: Study of a solar concentrator for space based on a diffractive/refractive optical combination <br/> <br/>Auteur, co-auteur: Michel, Céline; Loicq, Jerôme; Mazzoli, Alexandra; Languy, Fabian; Habraken, Serge <br/> <br/>Résumé: This paper presents a new design of a planar solar concentrator for space applications focusing on two spatially separated PV cells, allowing independent control of output power of each cell. It has the advantages of both spectral splitting and solar concentration by the combination of a blaze transmission diffraction grating and a flat cylindrical Fresnel lens. An optical optimization has been realized and two variations of configuration have been developed to improve tracking tolerance: first, a design completed by secondary reflective concentrators and second, a symmetrical configuration composed of two lenses. First numerical results are presented, highlighting the possibility to design a concentrator at about 10×, with an electrical output power about 290W/m² lens and less than 10% losses for tracking errors lower than ±0.9°. http://hdl.handle.net/2268/148972 Titre: Spectral modelling of massive binary systems <br/> <br/>Auteur, co-auteur: Palate, Matthieu; Rauw, Grégor; Koenigsberger, Gloria; Moreno, Edmundo <br/> <br/>Résumé: Context. The spectra of massive binaries may be affected by interactions between the stars in the system. These are believed to produce observational phenomena such as the Struve-Sahade effect. Aims: We simulate the spectra of massive binaries at different phases of the orbital cycle, accounting for the gravitational influence of the companion star on the shape and physical properties of the stellar surface. Methods: We used the Roche potential modified to account for radiation pressure to compute the stellar surface of close circular systems. We furthermore used the tidal interactions with dissipation of energy through shear code for surface computations of eccentric systems. In both cases, we accounted for gravity darkening and mutual heating generated by irradiation to compute the surface temperature. We then interpolated non-local thermodynamic equilibrium (NLTE) plane-parallel atmosphere model spectra in a grid to obtain the local spectrum at each surface point. We finally summed all contributions, accounting for the Doppler shift, limb-darkening, and visibility to obtain the total synthetic spectrum. We computed different orbital phases and different sets of physical and orbital parameters. Results: Our models predict line strength variations through the orbital cycle, but fail to completely reproduce the Struve-Sahade effect. Including radiation pressure allows us to reproduce a surface temperature distribution that is consistent with observations of semi-detached binary systems. Conclusions: Radiation pressure effects on the stellar surface are weak in (over)contact binaries and well-detached systems but can become very significant in semi-detached systems. The classical von Zeipel theorem is sufficient for the spectral computation. Broad-band light curves derived from the spectral computation are different from those computed with a model in which the stellar surfaces are equipotentials of the Roche potential scaled by the instantaneous orbital separation. In many cases, the fit of two Gaussian/Lorentzian profiles fails to properly measure the equivalent width of the lines and leads to apparent variations that could explain some of the effects reported in the literature. http://hdl.handle.net/2268/148930 Titre: What asteroseismology can teach us about stellar evolution: the case of subdwarf B stars <br/> <br/>Auteur, co-auteur: Van Grootel, Valérie; Fontaine, Gilles; Charpinet, Stephane; Brassard, Pierre; Green, Elizabeth M.; Randall, Suzanna K. <br/> <br/>Résumé: Subdwarfs B (sdB) stars are hot (Teff=20,000-40,000 K) and compact (log g= 5.0-6.2) evolved objects that form the very hot end of the horizontal branch, the so-called Extreme Horizontal Branch (EHB). Understanding the formation of sdB stars is one of the remaining challenges of stellar evolution theory. Competing scenarios have been proposed to account for the existence of such evolved objects, and give quite different mass distributions for resulting sdB stars. Detailed asteroseismic analyses, including mass estimates, of 15 pulsating hot B subdwarfs have been published since a decade. The masses have also been reliably determined by light curve modeling and spectroscopy for 7 sdB components of eclipsing or reflection binaries. I will present in the talk the empirical mass distributions of sdB stars on the basis of these samples. I will discuss how these empirical mass distributions, although still based on small-number statistics, compare with the expectations of stellar evolution theory. In particular, the two He-white dwarfs merger scenario does not seem to be the dominant channel to form isolated sdB stars, while the post-red giant branch scenario is reinforced. This opens new questions on the extreme mass loss of red giants to form extreme horizontal branch stars, possibly in connection with the recently discovered close planets orbiting sdB stars. http://hdl.handle.net/2268/147737 Titre: DUst Around NEarby Stars. The survey observational results <br/> <br/>Auteur, co-auteur: Eiroa, C; Marshall, J; Mora, A; Montesinos, B; Absil, Olivier; Augereau, J-C; Bayo, A; Bryden, G; Danchi, W; del Burgo, C; Ertel, S; Fridlund, M; Heras, A; Krivov, A; Launhardt, R; Liseau, R; Löhne, T; Maldonado, J; Pilbratt, G; Roberge, A; Rodmann, J; Sanz-Forcada, J; Solano, E; Stapelfeldt, K; Thébault, P; Wolf, S <br/> <br/>Résumé: Context. Debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. Their solar system's counterparts are the asteroid and Edgeworth-Kuiper belts. Aims. The DUNES survey aims at detecting extra-solar analogues to the Edgeworth-Kuiper belt around solar-type stars, putting in this way the solar system into context. The survey allows us to address some questions related to the prevalence and properties of planetesimal systems. Methods. We used Herschel/PACS to observe a sample of nearby FGK stars. Data at 100 and 160 μm were obtained, complemented in some cases with observations at 70 μm, and at 250, 350 and 500 μm using SPIRE. The observing strategy was to integrate as deep as possible at 100 μm to detect the stellar photosphere. Results. Debris discs have been detected at a fractional luminosity level down to several times that of the Edgeworth-Kuiper belt. The incidence rate of discs around the DUNES stars is increased from a rate of ∼ 12.1% ± 5% before Herschel to ∼ 20.2% ± 2%. A significant fraction (∼ 52%) of the discs are resolved, which represents an enormous step ahead from the previously known resolved discs. Some stars are associated with faint far-IR excesses attributed to a new class of cold discs. Although it cannot be excluded that these excesses are produced by coincidental alignment of background galaxies, statistical arguments suggest that at least some of them are true debris discs. Some discs display peculiar SEDs with spectral indexes in the 70–160 μm range steeper than the Rayleigh-Jeans one. An analysis of the debris disc parameters suggests that a decrease might exist of the mean black body radius from the F-type to the K-type stars. In addition, a weak trend is suggested for a correlation of disc sizes and an anticorrelation of disc temperatures with the stellar age. http://hdl.handle.net/2268/147414 Titre: Hot stars in the whole CoRoT mission <br/> <br/>Auteur, co-auteur: Briquet, Maryline http://hdl.handle.net/2268/147412 Titre: Two new SB2 binaries with main sequence B-type pulsators in the Kepler field <br/> <br/>Auteur, co-auteur: Pápics, P. I.; Tkachenko, A.; Aerts, C.; Briquet, Maryline; Marcos-Arenal, P.; Beck, P. G.; Uytterhoeven, K.; Triviño Hage, A.; Southworth, J.; Clubb, K. I.; Bloemen, S.; Degroote, P.; Jackiewicz, J.; McKeever, J.; Van Winckel, H.; Niemczura, E.; Gameiro, J. F.; Debosscher, J. <br/> <br/>Résumé: Context: OB stars are important in the chemistry and evolution of the Universe, but the sample of targets well understood from an asteroseismological point of view is still too limited to provide feedback on the current evolutionary models. Our study extends this sample with two spectroscopic binary systems. AIMS. Our goal is to provide orbital solutions, fundamental parameters and abundances from disentangled high-resolution high signal-to-noise spectra, as well as to analyse and interpret the variations in the Kepler light curve of these carefully selected targets. This way we continue our efforts to map the instability strips of beta Cep and SPB stars using the combination of high-resolution ground-based spectroscopy and uninterrupted space-based photometry. Methods: We fit Keplerian orbits to radial velocities measured from selected absorption lines of high-resolution spectroscopy using synthetic composite spectra to obtain orbital solutions. We use revised masks to obtain optimal light curves from the original pixel-data from the Kepler satellite, which provided better long term stability compared to the pipeline processed light curves. We use various time-series analysis tools to explore and describe the nature of variations present in the light curve. Results: We find two eccentric double-lined spectroscopic binary systems containing a total of three main sequence B-type stars (and one F-type component) of which at least one in each system exhibits light variations. The light curve analysis (combined with spectroscopy) of the system of two B stars points towards the presence of tidally excited g modes in the primary component. We interpret the variations seen in the second system as classical g mode pulsations driven by the kappa mechanism in the B type primary, and explain the unexpected power in the p mode region as a result of nonlinear resonant mode excitation. <br/> <br/>Commentaires: Accepted for publication in Astronomy and Astrophysics on 04/04/2013, 21 pages, 25 figures, 7 tables http://hdl.handle.net/2268/147405 Titre: Evolution of the Io footprint brightness I: Far-UV observations <br/> <br/>Auteur, co-auteur: Bonfond, Bertrand; Hess, Sébastien; Gérard, Jean-Claude; Grodent, Denis; Radioti, Aikaterini; Chantry, Virginie; Saur, Joachim; Jacobsen, Sven; Clarke, John <br/> <br/>Résumé: The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the brightness and precipitated power for each individual spot, using the image database gathered from 1997 to 2009 with the Hubble Space Telescope in the Far-UV domain. We show that the relative brightness of the spots varies with the System III longitude, which is a further indication that they originate from different processes. Moreover, our novel measurement method based on 3D simulations of the auroral features allows to derive the precipitated energy fluxes from images on which the emission region is observed at a slant angle. Peak values as high as 2000 mW/m2 are observed for the main spot, probably triggering a localized and sudden heating of the atmosphere. Additionally, strong brightness differences are observed from one hemisphere to another. This result indicates that the location of Io in the plasma torus is not the only parameter to control the brightness, but that the magnetic field asymmetries also play a key role. Finally, we present new data confirming that significant variations of the spots’ brightness on timescales of 2-4 minutes are ubiquitous, which suggests a relationship with intermittent double layers close to Jovian surface. <br/> <br/>Commentaires: Submitted to PSS on Nov. 28th 2012. Not reviewed yet. http://hdl.handle.net/2268/147198 Titre: GAIA and the spectroscopic binaries: what to expect in terms of orbit determination? <br/> <br/>Auteur, co-auteur: Pourbaix, D.; Jancart, Sylvie <br/> <br/>Résumé: Not Available <br/> <br/>Commentaires: ISBN: 298 http://hdl.handle.net/2268/147178 Titre: Warm Spitzer Occultation Photometry of WASP-26b at 3.6{\mu}m and 4.5{\mu}m <br/> <br/>Auteur, co-auteur: Mahtani, D. P.; Maxted, P. F. L.; Anderson, D. R.; Smith, A. M. S.; Smalley, B.; Tregloan-Reed, J.; Southworth, J.; Madhusudhan, N.; Collier Cameron, A.; Gillon, Michaël; Harrington, J.; Hellier, C.; Pollacco, D.; Queloz, D.; Triaud, A. H. M. J.; West, R. G. <br/> <br/>Résumé: We present new warm Spitzer occultation photometry of WASP-26 at 3.6{\mu}m and 4.5{\mu}m along with new transit photometry taken in the g,r and i bands. We report the first detection of the occultation of WASP-26b, with occultation depths at 3.6{\mu}m and 4.5{\mu}m of 0.00126 +/- 0.00013 and 0.00149 +/- 0.00016 corresponding to brightness temperatures of 1825+/-80K and 1725+/-89K, respectively. We find that the eccentricity of the orbit is consistent with a circular orbit at the 1{\sigma} level with a 3{\sigma} upper limit of e < 0.04. According to the activity-inversion relation of Knutson et al. (2010), WASP-26b is predicted to host a thermal inversion. The brightness temperatures deduced from the eclipse depths are consistent with an isothermal atmosphere, although it is within the uncertainties that the planet may host a weak thermal inversion. The data are equally well fit by atmospheric models with or without a thermal inversion. We find that variation in activity of solar-like stars does not change enough over the time-scales of months or years to change the interpretation of the Knutson et al. (2010) activity-inversion relation, provided that the measured activity level is averaged over several nights. Further data are required to fully constrain the thermal structure of the atmosphere because the planet lies very close to the boundary between atmospheres with and without a thermal inversion. <br/> <br/>Commentaires: 11 Pages,8 Figures,5 Tables, Accepted for Publication in MNRAS http://hdl.handle.net/2268/147125 Titre: WASP-80b: a gas giant transiting a cool dwarf <br/> <br/>Auteur, co-auteur: Triaud, A. H. M. J.; Anderson, D. R.; Collier Cameron, A.; Doyle, A. P.; Fumel, Aurélie; Gillon, Michaël; Hellier, C.; Jehin, Emmanuel; Lendl, M.; Lovis, C.; Maxted, P. F. L.; Pepe, F.; Pollacco, D.; Queloz, D.; Ségransan, D.; Smalley, B.; Smith, A. M. S.; Udry, S.; West, R. G.; Wheatley, P. J. <br/> <br/>Résumé: We report the discovery of a planet transiting the star <ASTROBJ>WASP-80</ASTROBJ> (<ASTROBJ>1SWASP J201240.26-020838.2</ASTROBJ>; <ASTROBJ>2MASS J20124017-0208391</ASTROBJ>; <ASTROBJ>TYC 5165-481-1</ASTROBJ>; <ASTROBJ>BPM 80815</ASTROBJ>; V = 11.9, K = 8.4). Our analysis shows this is a 0.55 ± 0.04 M[SUB]jup[/SUB], 0.95 ± 0.03 R[SUB]jup[/SUB] gas giant on a circular 3.07 day orbit around a star with a spectral type between K7V and M0V. This system produces one of the largest transit depths so far reported, making it a worthwhile target for transmission spectroscopy. We find a large discrepancy between the vsini[SUB]⋆[/SUB] inferred from stellar line broadening and the observed amplitude of the Rossiter-McLaughlin effect. This can be understood either by an orbital plane nearly perpendicular to the stellar spin or by an additional, unaccounted for source of broadening. Using WASP-South photometric observations, from Sutherland (South Africa), confirmed with the 60 cm TRAPPIST robotic telescope, EulerCam, and the CORALIE spectrograph on the Swiss 1.2 m Euler Telescope, and HARPS on the ESO 3.6 m (Prog ID 089.C-0151), all three located at La Silla Observatory, Chile.Radial velocity and photometric data are available in electronic form at the CDS via anonymous ftp to <A href="http://cdsarc.u-strasbg.fr">cdsarc.u-strasbg.fr</A>(<A href="http://130.79.128.5">130.79.128.5</A>) or via <A href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/551/A80">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/551/A80</A> http://hdl.handle.net/2268/147116 Titre: Particle-accelerating colliding-wind binaries: from the study of a few objects to a science case study <br/> <br/>Auteur, co-auteur: De Becker, Michaël <br/> <br/>Résumé: The study of massive stars, and in particular of colliding-wind binaries, revealed the capability of some of them to accelerate particles up to relativistic energies. Since the 1980's, what appeared at first sight to be an anomaly in their observational properties turns out to be the signature of important physical processes at work in a large number of objects. In this contribution, I summarize the current census of information relevant to the catalogue of Particle-Accelerating Colliding-Wind Binaries (PACWBs) that constitute a particular class of objects likely to contribute to the production of low energy Galactic cosmic-rays. On the basis of this census of information, some prospects for future observational strategies are discussed. http://hdl.handle.net/2268/147076 Titre: Fast-evolving weather for the coolest of our two new substellar neighbours <br/> <br/>Auteur, co-auteur: Gillon, Michaël; Triaud, A. H. M. J.; Jehin, Emmanuel; Delrez, Laetitia; Opitom, Cyrielle; Magain, Pierre; Lendl, M.; Queloz, D. <br/> <br/>Résumé: We present the results of an intense photometric monitoring in the near-infrared (~0.9 microns) with the TRAPPIST robotic telescope of the newly discovered binary brown dwarf WISE J104915.57-531906.1, the third closest system to the Sun at a distance of only 2 pc. Our twelve nights of photometric time-series reveal a quasi-periodic (P = 4.87+-0.01 h) variability with a maximal peak-peak amplitude of ~11% and strong night-to-night evolution. We attribute this variability to the rotational modulation of fast-evolving weather patterns in the atmosphere of the coolest component (~T1-type) of the binary. No periodic signal is detected for the hottest component (~L8-type). For both brown dwarfs, our data allow us to firmly discard any unique transit during our observations for planets >= 2 Rearth. For orbital periods smaller than ~9.5 h, transiting planets are excluded down to an Earth-size. <br/> <br/>Commentaires: 4 pages, 4 figures. Submitted as Letter to A&A. Second version shortened to match the format of A&A Letters, with a few minor modifications http://hdl.handle.net/2268/147036 Titre: The X-ray under-luminosity of the O-type supergiants HD16691 and HD14947 revealed by XMM-Newton <br/> <br/>Auteur, co-auteur: De Becker, Michaël <br/> <br/>Résumé: The members of the scarce category of Of^+ supergiants present properties that are intermediate between regular O-stars and Wolf-Rayet (WR) stars. Significant similarities between these transitional stars and WN-type objects are now clearly established, at least in the visible and near-infrared domains, pointing to common stellar wind properties. In this study, we report on the first dedicated X-ray observations of HD16691 (O4If^+) and HD14947 (O5f^+), revealing a soft thermal spectrum in agreement with the expected X-ray emission from a single O-type star. However, the X-ray luminosity of our targets is slightly lower than expected for single O-type stars, suggesting that the particular properties of their stellar wind has also a significant impact on the X-ray emission of these objects on the way to the WN category. We argue that the X-ray under-luminosity of HD16691 and HD14947 may be interpreted as the signature in X-rays of the intermediate stage between O and WR stars, as a consequence of enhanced wind density. http://hdl.handle.net/2268/147009 Titre: The soundtrack of RR Lyrae in Omega Cen at high-frequency <br/> <br/>Auteur, co-auteur: Calamida, A.S.; Randall, S.K.; Monelli, M.; Bono, G.; Buonanno, R.; Strampelli, G.; Catelan, M.; Van Grootel, Valérie; Alonso, M.L.; Stetson, P.B.; Stellingwerf, R.F. <br/> <br/>Commentaires: We present preliminary Sloan u',g'-band light curves for a sample of known RR Lyrae variables in the Galactic globular cluster Omega Cen. Results are based on the partial reduction of multi-band time series photometric data collected during six consecutive nights with the visitor instrument ULTRACAM mounted on the New Technology Telescope (La Silla, ESO). This facility allowed us to simultaneously observe in three different bands (Sloan u',g',r') a field of view of about 6x6 arcminutes. The telescope and the good seeing conditions allowed us to sample the light curves every 15 seconds. We ended up with a data set of about 6,000 images per night per filter, for a total of more than 200,000 images of the selected field. This data set allowed us to detect different kind of variables, such as RR-Lyraes, SX Phoenicis, eclipsing binaries, semi-regulars. More importantly, we were able for the first time to sample at high-frequency cluster RR Lyraes in the u',g'-band and to show in detail the pulsation phases across the dip located along the rising branch of RR-Lyraes. http://hdl.handle.net/2268/146941 Titre: Chemical surface inhomogeneities in late B-type stars with Hg and Mn peculiarity: I. Spot evolution in HD 11753 on short and long time scales <br/> <br/>Auteur, co-auteur: Korhonen, Heidi; Gonzalez, J.F.; Briquet, Maryline; Flores Soriano, M.; Hubrig, S.; Savanov, I.; Hackman, T.; Ilyin, I.V.; Eulaers, Eva; Pessemier, Wim http://hdl.handle.net/2268/146938 Titre: COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses: XII. Time delays of the doubly lensed quasars SDSS~J1206+4332 and HS~2209+1914 <br/> <br/>Auteur, co-auteur: Eulaers, Eva; Tewes, Malte; Magain, Pierre; Courbin, Frédéric; Asfandiyarov, Ildar; Ehgamberdiev, Shurat; Rathna Kumar, S.; Stalin, C.S.; Prabhu, T.P.; Meylan, George; Van Winckel, Hans <br/> <br/>Résumé: Aims. Within the framework of the COSMOGRAIL collaboration we present 7- and 8.5-year-long light curves and time-delay esti- mates for two gravitationally lensed quasars: SDSS J1206+4332 and HS 2209+1914. Methods. We monitored these doubly lensed quasars in the R-band using four telescopes: the Mercator, Maidanak, Himalayan Chandra, and Euler Telescopes, together spanning a period of 7 to 8.5 observing seasons from mid-2004 to mid-2011. The pho- tometry of the quasar images was obtained through simultaneous deconvolution of these data. The time delays were determined from these resulting light curves using four very different techniques: a dispersion method, a spline fit, a regression difference technique, and a numerical model fit. This minimizes the bias that might be introduced by the use of a single method. Results. The time delay for SDSS J1206+4332 is ∆tAB = 111.3 ± 3 days with A leading B, confirming a previously published result within the error bars. For HS 2209+1914 we present a new time delay of ∆tBA = 20.0 ± 5 days with B leading A. Conclusions. The combination of data from up to four telescopes have led to well-sampled and nearly 9-season-long light curves, which were necessary to obtain these results, especially for the compact doubly lensed quasar HS 2209+1914. http://hdl.handle.net/2268/146873 Titre: Parasitic interference in nulling interferometry <br/> <br/>Auteur, co-auteur: Matter, A.; Defrère, D.; Danchi, W. C.; Lopez, B.; Absil, Olivier <br/> <br/>Résumé: Nulling interferometry aims to detect faint objects close to bright stars. Its principle is to produce a destructive interference along the line of sight so that the stellar flux is rejected, while the flux of the off-axis source can be transmitted. In practice, various instrumental perturbations can degrade the nulling performance. Any imperfection in phase, amplitude or polarization produces a spurious flux that leaks to the interferometer output and corrupts the transmitted off-axis flux. One of these instrumental perturbations is the crosstalk phenomenon, which occurs because of multiple parasitic reflections inside transmitting optics, and/or diffraction effects related to beam propagation along finite size optics. It can include a crosstalk of a beam with itself, and a mutual crosstalk between different beams. This can create a parasitic interference pattern, which degrades the intrinsic transmission map - or intensity response - of the interferometer. In this context, we describe how this instrumental effect impairs the performance of a Bracewell interferometer. A simple formalism is developed to derive the corresponding modified intensity response of the interferometer, as a function of the two parameters of interest: the crosstalk level (or contamination rate) and the phase shift between the primary and secondary - parasitic - beams. We then apply our mathematical approach to a few scientific cases, both analytically and using the GENIESIM simulation software, adapted to handle coherent crosstalk. Our results show that a coherent crosstalk level of about 1 per cent implies a 20 per cent drop of the signal-to-noise ratio at most. Careful attention should thus be paid to reduce the crosstalk level inside an interferometric instrument and ensure an instrumental stability that provides the necessary sensitivity through calibration procedures.