A dedicated photometric system for the detection of Wolf-Rayet stars

We present here tests of a five-filter photometric system aimed at WR classification. In addition to the well-known easy separation between the WN and WC spectral types, these tests indicate interesting potentialities in the discrimination of subgroups among the WN and the WC which look well related to the classical subtypes. The proposed combinations of filters (or derived ones) bear enough discriminating power to satisfy some evolutionary studies in crowded fields where spectroscopic follow-up is not possible.Comment: 10 pages, 7 figures, uses l-aa.sty and psfig for figure inclusion. Also available at http://vela.astro.ulg.ac.be/preprint/P10 Accepted for publication in Astronomy & Astrophysics Supp

VLT observations of the highly ionized nebula around Brey2

We present the first high resolution HeII 4686 images of the high excitation nebula around the WR star Brey 2 in the LMC. This nebula presents a striking morphology: a small arc-like feature some 3.6pc in radius is particularly prominent in the HeII 4686 line. We further discover a previously unknown faint HeII emission that extends over an area of 22*17 pc^2. An even fainter HeII emission is apparently associated with the interstellar bubble blown by the progenitor of Brey2. The total HeII flux corresponds to an ionizing flux of 4*10^{47} photons/s. Halpha, [OIII], and HeI 5876 images and long-slit spectra are also examined in this letter, enabling us to investigate the detailed physical properties at various locations of the nebula.Comment: 4 pages, 3 figures (2 in jpg), accepted by A&A Letters, also available from http://vela.astro.ulg.ac.be/Preprints/P80/index.htm

Photonic Passbands and Zeropoints for the Stromgren uvby system

Photonic passbands have been derived for the uvby standard system by convolving the original filter passbands of Str\"omgren and Perry with atmospheric extinction and the QE of a cooled 1P21 photomultiplier tube. Using these new passbands, synthetic photometry was calculated for all the stars in the extensive NGSL and MILES spectrophotometric libraries and compared with the homogenised b-y, m1 and c1 indices in the Hauck-Mermilliod 1998 catalog and the derived u - v and v - b colors. Excellent agreement between observed and synthetic photometry was achieved with regression slopes near unity. Slightly better fits were obtained by considering stars with b-y 0.5, separately. It is recommended that these new passbands be used together with the provided transformation equations to generate synthetic photometry from model atmosphere fluxes and observed spectrophotometry. Synthetic photometry was also carried out using the natural system of the 4-channel spectrograph-photometers and those of Cousins and Eggen in order to explore the systematic dfferences that could be expected between their instrumental systems and the standard system.Comment: 15 pages, including 10 figure

TRAPPIST photometry and imaging monitoring of comet C/2013 R1(Lovejoy): Implications for the origin of daughter species

We report the results of the narrow band photometry and imaging monitoring of comet C/2013 R1 (Lovejoy) with the robotic telescope TRAPPIST (La Silla observatory). We gathered around 400 images over 8 months pre- and post-perihelion between September 12, 2013 and July 6, 2014. We followed the evolution of the OH, NH, CN, C3 , and C2 production rates computed with the Haser model as well as the evolution of the dust production. All five gas species display an asymmetry about perihelion, the rate of brightening being steeper than the rate of fading. The study of the coma morphology reveals gas and dust jets which indicate one or several active zone(s) on the nucleus. The dust, C2 , and C3 morphologies present some similarities while the CN morphology is different. OH and NH are enhanced in the tail direction. The study of the evolution of the comet activity shows that the OH, NH, and C2 production rates evolution with the heliocentric distance is correlated to the dust evolution. The CN and, to a lesser extent, the C3 do not display such a correlation with the dust. These evidences and the comparison with parent species production rates indicate that C2 and C3 on one side and OH and NH on the other side could be -at least partially- released from organic-rich grains and icy grains. On the contrary, all evidences point to HCN being the main parent of CN in this comet.Comment: Accepted for publication in Astronomy & Astrophysics, 10 page

The atypical emission-line star Hen3-209

We analyse observations, spanning 15 years, dedicated to the extreme emission-line object Hen3-209. Our photometric data indicate that the luminosity of the star undergoes marked variations with a peak-to-peak amplitude of 0.65mag. These variations are recurrent, with a period of 16.093+-0.005d. The spectrum of Hen3-209 is peculiar with many different lines (HI, HeI, FeII,...) showing P Cygni profiles. The line profiles are apparently changing in harmony with the photometry. The spectrum also contains [OIII] lines that display a saddle profile topped by three peaks, with a maximum separation of about 600km/s. Hen3-209 is most likely an evolved luminous object suffering from mass ejection events and maybe belonging to a binary system.Comment: 6p, 5 fig, accepted for publication in MNRAS (www.blackwell-synergy.com

Phase resolved X-ray spectroscopy of HDE228766: Probing the wind of an extreme Of+/WNLha star

HDE228766 is a very massive binary system hosting a secondary component, which is probably in an intermediate evolutionary stage between an Of supergiant and an WN star. The wind of this star collides with the wind of its O8 II companion, leading to relatively strong X-ray emission. Measuring the orbital variations of the line-of-sight absorption toward the X-ray emission from the wind-wind interaction zone yields information on the wind densities of both stars. X-ray spectra have been collected at three key orbital phases to probe the winds of both stars. Optical photometry has been gathered to set constraints on the orbital inclination of the system. The X-ray spectra reveal prominent variations of the intervening column density toward the X-ray emission zone, which are in line with the expectations for a wind-wind collision. We use a toy model to set constraints on the stellar wind parameters by attempting to reproduce the observed variations of the relative fluxes and wind optical depths at 1 keV. The lack of strong optical eclipses sets an upper limit of about 68 degrees on the orbital inclination. The analysis of the variations of the X-ray spectra suggests an inclination in the range 54 - 61 degrees and indicates that the secondary wind momentum ratio exceeds that of the primary by at least a factor 5. Our models further suggest that the bulk of the X-ray emission arises from the innermost region of the wind interaction zone, which is from a region whose outer radius, as measured from the secondary star, lies between 0.5 and 1.5 times the orbital separation

Observational signatures of past mass-exchange episodes in massive binaries: The case of LSS 3074

The role of mass and momentum exchanges in close massive binaries is very important in the subsequent evolution of the components. Such exchanges produce several observational signatures such as asynchronous rotation and altered chemical compositions, that remain after the stars detach again. We investigated these effects for the close O-star binary LSS 3074 (O4 f + O6-7 :(f):), which is a good candidate for a past Roche lobe overflow (RLOF) episode because of its very short orbital period, P = 2.185 days, and the luminosity classes of both components. We determined a new orbital solution for the system. We studied the photometric light curves to determine the inclination of the orbit and Roche lobe filling factors of both stars. Using phase-resolved spectroscopy, we performed the disentangling of the optical spectra of the two stars. We then analysed the reconstructed primary and secondary spectra with the CMFGEN model atmosphere code to determine stellar parameters, such as the effective temperatures and surface gravities, and to constrain the chemical composition of the components. We confirm the apparent low stellar masses and radii reported in previous studies. We also find a strong overabundance in nitrogen and a strong carbon and oxygen depletion in both primary and secondary atmospheres, together with a strong enrichment in helium of the primary star. We propose several possible evolutionary pathways through a RLOF process to explain the current parameters of the system. We confirm that the system is apparently in overcontact configuration and has lost a significant portion of its mass to its surroundings. We suggest that some of the discrepancies between the spectroscopic and photometric properties of LSS 3074 could stem from the impact of a strong radiation pressure of the primary

A Spectroscopic study of the non-thermal radio emitter Cyg OB2 #8A: Discovery of a new binary system

We present the results of a spectroscopic campaign revealing that the non-thermal radio emitter Cyg OB2 #8A is an O6 + O5.5 binary system. We propose the very first orbital solution indicating a period of about 21.9 days. The system appears to be eccentric (0.24 +/- 0.04) and is likely seen under a rather low inclination angle. The mass ratio of the components is close to unity. The impact of the binarity of this star in the framework of our understanding of non-thermal radio emission from early-type stars is briefly discussed.Comment: 4 pages, 3 postscript figures, accepted by A&A as a lette

TRAPPIST: a robotic telescope dedicated to the study of planetary systems

We present here a new robotic telescope called TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope). Equipped with a high-quality CCD camera mounted on a 0.6 meter light weight optical tube, TRAPPIST has been installed in April 2010 at the ESO La Silla Observatory (Chile), and is now beginning its scientific program. The science goal of TRAPPIST is the study of planetary systems through two approaches: the detection and study of exoplanets, and the study of comets. We describe here the objectives of the project, the hardware, and we present some of the first results obtained during the commissioning phase.Comment: To appear in Detection and Dynamics of Transiting Exoplanets, Proceedings of Haute Provence Observatory Colloquium (23-27 August 2010), eds. F. Bouchy, R.F. Diaz & C.Moutou, Platypus press 201

The CN Isotopic Ratios In Comets

Our aim is to determine the isotopic ratios (12)C/(13)C and (14)N/(15)N in a variety of comets and link these measurements to the formation and evolution of the solar system. The (12)C/(13)C and (14)N/(15)N isotopic ratios are measured for the CN radical by means of high-resolution optical spectra of the R branch of the B-X (0, 0) violet band. 23 comets from different dynamical classes have been observed, sometimes at various heliocentric and nucleocentric distances, in order to estimate possible variations of the isotopic ratios in parent molecules. The (12)C/(13)C and (14)N/(15)N isotopic ratios in CN are remarkably constant (average values of, respectively, 91.0 +/- 3.6 and 147.8 +/- 5.7) within our measurement errors, for all comets whatever their origin or heliocentric distance. While the carbon isotopic ratio does agree with the terrestrial value (89), the nitrogen ratio is a factor of two lower than the terrestrial value (272), indicating a fractionation in the early solar system, or in the protosolar nebula, common to all the comets of our sample. This points towards a common origin of the comets independently of their birthplaces, and a relationship between HCN and CN.NSFAstronom