arXiv subjects

Henri M. J. Boffin

Publications and source records attributed to Henri M. J. Boffin.

At least 91 records · Page 5Linked to original sources

arXiv2012

A carbon dwarf wearing a Necklace: first proof of accretion in a post-common-envelope binary central star of a planetary nebula with jets

The formation of collimated outflows or jets in planetary nebulae (PNe) is not well understood. There is no evidence for active accretion disks in PNe making it difficult to decide which of several proposed jet formation scenarios may be correct. A handful of wide binary central stars of PNe are known to have accreted carbon and slow neutron capture (s-process) enhanced material, the immediate progenitors of barium stars, however no close binary analogues are known to have passed through a common-envelope (CE) phase. Here we present spectroscopy of The Necklace taken near lightcurve minimum that for the first time reveals a carbon-rich (C/O > 1) companion, a carbon dwarf, in a post-CE central star. As unevolved stars do not produce carbon, the chemical enhancement of the secondary can only be explained by accretion from the primary. Accretion most likely happened prior to the CE phase via wind accretion as not enough material can be accreted during the short CE phase. The pair of jets in The Necklace, which are observed to be older than the PN, are therefore likely to have been launched from an accretion disk around the companion during this early accretion phase. This discovery adds significant weight to the emerging scenario that jets in post-CE PNe are primarily launched by an accretion disk around a main-sequence companion before the CE phase.

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arXiv2012

Discovery of Two Very Wide Binaries with Ultracool Companions and a New Brown Dwarf at the L/T Transition

We present the discovery and spectroscopic follow-up of a nearby late-type L dwarf (2M0614+3950), and two extremely wide very-low-mass binary systems (2M0525-7425AB and 2M1348-1344AB), resulting from our search for common proper motion pairs containing ultracool components in the Two Micron All Sky Survey (2MASS) and the Wide-field Infrared Survey Explorer (WISE) catalogs. The near-infrared spectrum of 2M0614+3950 indicates a spectral type L$9 \pm 1$ object residing at a distance of $26.0 \pm 1.8$ pc. The optical spectrum of 2M0525-7425A reveals an M$3.0 \pm 0.5$ dwarf primary, accompanied by a secondary previously classified as L2. The system has an angular separation of $\sim 44"$, equivalent to $\sim 2000 $AU at distance of $46.0 \pm 3.0$ pc. Using optical and infrared spectra, respectively, we classify the components of 2M1348-1344AB as M$4.5 \pm 0.5$ and T$5.5 \pm 1$. The angular separation of $\sim 68"$ is equivalent to $\sim 1400 $AU at a distance of $20.7 \pm 1.4$ pc. 2M1348-1344AB is one of only six very wide (separation $>$ 1000 AU) systems containing late T dwarfs known to date.

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arXiv2012

The enigmatic central star of the planetary nebula PRTM 1

The central star of the planetary nebula PRTM 1 (PN G243.8-37.1) was previously found to be variable by M. Pena and colleagues. As part of a larger programme aimed towards finding post common-envelope binary central stars we have monitored the central star of PRTM 1 spectroscopically and photometrically for signs of variability. Over a period of ~3 months we find minimal radial velocity (<10 km/s) and photometric (< 0.2 mag) variability. The data suggest a close binary nucleus can be ruled out at all but the lowest orbital inclinations, especially considering the spherical morphology of the nebula which we reveal for the first time. Although the current data strongly support the single star hypothesis, the true nature of the central star of PRTM 1 remains enigmatic and will require further radial velocity monitoring at higher resolution to rule out a close binary. If in the odd case that it is a close binary, it would be the first such case in a spherical planetary nebula, in contradiction to current thinking.

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arXiv2012

Discovery of New Faint Northern Galactic Planetary Nebulae

We present the discovery of 6 nebular objects made by amateur astronomers. Four of these discoveries are clearly planetary nebulae (PNe), one is a possible PN, and another is a likely H II region. The bipolar nebula Ou4 presents the largest angular extent ever found : over one degree on the sky! We consider various scenarios that could explain such a nebula. Ou4 could be one of the nearest PNe known, though its possible PN nature will need confirmation.

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arXiv2012

The central Blue Straggler population in four outer-halo globular clusters

Using HST/WFPC2 data, we have performed a comparative study of the Blue Straggler Star (BSS) populations in the central regions of the globular clusters AM 1, Eridanus, Palomar 3, and Palomar 4. Located at distances RGC > 50 kpc from the Galactic Centre, these are (together with Palomar 14 and NGC 2419) the most distant clusters in the Halo. We determine their colour-magnitude diagrams and centres of gravity. The four clusters turn out to have similar ages (10.5-11 Gyr), significantly smaller than those of the inner-Halo globulars, and similar metallicities. By exploiting wide field ground based data, we build the most extended radial density profiles from resolved star counts ever published for these systems. These are well reproduced by isotropic King models of relatively low concentration. BSSs appear to be significantly more centrally segregated than red giants in all globular clusters, in agreement with the estimated core and half-mass relaxation times which are smaller than the cluster ages. Assuming that this is a signature of mass segregation, we conclude that AM 1 and Eridanus are slightly dynamically more evolved than Pal 3 and Pal 4.

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arXiv2011

A barium-rich binary central star in Abell 70

We have found the central star of Abell 70 (PN G038.1-25.4, hereafter A 70) to be a binary consisting of a G8 IV-V secondary and a hot white dwarf. The secondary shows enhanced Ba II and Sr II features, firmly classifying it as a barium star. The nebula is found to have Type-I chemical abundances with helium and nitrogen enrichment, which combined with future abundance studies of the central star, will establish A 70 as a unique laboratory for studying s-process AGB nucleosynthesis.

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arXiv2010

A Renaissance study of Am stars. I. The mass ratio distribution

Triggered by the study of Carquillat & Prieur (2007, MNRAS, 380, 1064) of Am binaries, I reanalyse their sample of 60 orbits to derive the mass ratio distribution (MRD), assuming as they did a priori functional forms, i.e. a power law or a Gaussian. The sample is then extended using orbits published by several groups and a full analysis of the MRD is made, without any assumption on the functional form. I derive the MRD using a Richardson-Lucy inversion method, assuming a fixed mass of the Am primary and randomly distributed orbital inclinations. Using the large sub-sample of double-lined spectroscopic binaries, I show that this methodology is indeed perfectly adequate. Using the inversion method, applied to my extended sample of 162 systems, I find that the final MRD can be approximated by a uniform distribution.

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arXiv2009

Astronomy and the Media: a love story?

With the availability of nice images and amazing, dramatic stories, the fundamental questions it addresses, and the attraction is exerces on many, it is often assumed that astronomy is an obvious topic for the media. Looking more carefully, however, one realises that the truth is perhaps not as glamorous as one would hope, and that, although well present in the media, astronomy's coverage is rather tiny, and often, limited to the specialised pages or magazines.

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arXiv2008

V2051 Oph after superoutburst: out-of-plane material and the superhump light source

We performed a detailed spectroscopic analysis of the dwarf nova V2051 Oph at the end of its 1999 superoutburst. We studied and interpreted the simultaneous behaviour of various emission lines. We obtained high-resolution echelle spectroscopic data at ESO's NTT with EMMI, covering the spectral range of 4000--7500 Angstrom. The analysis was performed using standard IRAF tools. The indirect imaging technique of Doppler tomography was applied, in order to map the accretion disc and distinguish between the different emission sources. The spectra are characterised by strong Balmer emission, together with lines of HeI and the iron triplet FeII 42. All lines are double-peaked, but the blue-to-red peak strength and central absorption depth vary. The primary's velocity was found to be 84.9 km/sec. The spectrograms of the emission lines reveal the prograde rotation of a disc-like emitting region and, for the Balmer and HeI lines, an enhancement of the red-wing during eclipse indicates a bright spot origin. The modulation of the double-peak separation shows a highly asymmetric disc with non-uniform emissivity. This is confirmed by the Doppler maps, which apart from the disc and bright spot emission also indicate an additional region of enhanced emission in the 4th quadrant (+Vx, -Vy), which we associate with the superhump light source. Given the behaviour of the iron triplet and its distinct differences from the rest of the lines, we attribute its existence to an extended gas region above the disc. Its origin can be explained through the fluorescence mechanism.

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arXiv2004

Numerical Simulation of the Surface Flow on the Companion Star in a Close Binary System II. Construction of Doppler maps and application to Galactic supersoft X-ray sources

We perform three-dimensional numerical simulations of surface flows on the companion star in a semi-detached binary system and construct the corresponding Doppler maps. The mass ratio of the binary system, $q=M_2/M_1$, considered here is $q=0.05, 0.33, 0.5, 1, 2$, and 3. For all cases, we obtain the H-, L1-, and L2-eddies, as found in our previous work, and confirm that the flow pattern does not heavily depend on the mass ratio. We propose that this kind of problem be dubbed ``{\it stellar meteorology}.'' The Doppler maps at the position of the companion show a structure tilted towards clockwise direction and presenting deviations from the critical Roche surface due to the L1-eddy and the L2-eddy on the companion star. We apply our results to the Galactic supersoft X-ray source RX J0019.8+2156 and try to attribute the low radial velocity component of the emission lines of He II $λ4686$ observed recently to the irradiated spot on the surface of the companion rather than that of the white dwarf or the accretion disc. Based on the comparison between the observations and our constructed Doppler map, we estimate the mass of the companion star in RX J0019.8+2156 to be $\sim 2 M_{\odot}$ assuming the mass of the white dwarf star to be around $0.6 M_{\odot}$.

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arXiv2003

Observational properties of visual binaries as modelled using a synthetic catalogue, I: For visual apparent magnitudes $m_v < 15$

A simulated binary star catalogue is created that represents the full sky distribution of stars, excluding those with galactic latitude $|b|<10\degr$, down to $m_v < 15$. The catalogue is compatible with observed magnitude and number distributions of the HST Guide Star Catalog. The simulated catalogue is analyzed for observational properties of visual binary stars, both in a general context without taking any observational constraints into account, and using different observability criteria that model the observational capability of the astrometric DIVA satellite. It is shown that several observational bias effects should be taken into account when final output catalogues are analyzed. The results indicate that $Δm_v$ distribution peaks at $Δm_v \approx 7$ and to maximize the number of binary detections with large mass ratios, the magnitude threshold should be set as high as possible. This is especially important if low mass $M<0.2 M_{\sun}$ secondaries are studied. The predicted number of optical pairs is calculated and for large magnitude differences close to the galactic plane and toward the galactic center it may be difficult to discriminate between a red companion and a low-mass foreground/background star for distant double stars for which no parallax measurements are available. Using optimal detection procedures for optical double stars it is estimated that, depending on the assumed double star distributions, 60%-70% of all the visual binary stars in the catalogue with separations $0.0625\arcsec<θ<3.5\arcsec$, $m_{v}(\mathrm{secondary})<22$, and $Δm<10$ could be observed during the DIVA or similar missions.

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arXiv2003

HD 112914 : A nearby one solar mass binary system

In paper 167 of his serie published in The Observatory, Griffin presented the spectroscopic orbit of HD 112914, a late main sequence star. He also noticed that this star, also known as HIP 63406, was one of the few for which the DMSA/O Annex of the Hipparcos Catalogue derived an orbit prior to any spectroscopic one. Albeit in agreement with each others, the astrometric orbit was however determined with rather large uncertainties. Here, we have reanalysed the Hipparcos Intermediate Astrometric Data (IAD) using Griffin'spectroscopic orbit to obtain a much more precise astrometric orbit. Several parameters of the HD 112914 system are now well constrained.

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arXiv2002

Numerical simulation of the surface flow of a companion star in a close binary system

We simulate numerically the surface flow of a gas-supplying companion star in a semi-detached binary system. Calculations are carried out for a region including only the mass-losing star, thus not the mass accreting star. The equation of state is that of an ideal gas characterized by a specific heat ratio gamma, and the case with gamma=5/3 is mainly studied. A system of eddies appears on the surface of the companion star: an eddy in the low pressure region near the L1 point, one around the high pressure at the north pole, and one or two eddies around the low pressure at the opposite side of the L1 point. Gas elements starting near the pole region rotate clockwise around the north pole (here the binary system rotates counter-clockwise as seen from the north pole). Because of viscosity, the gas drifts to the equatorial region, switches to the counter-clockwise eddy near the L1 point and flows through the L1 point to finally form the L1 stream. The flow field in the L1 region and the structure of the L1 stream are also considered.

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arXiv2001

High resolution simulations of star formation

In order to study the capabilities of SPH in self-gravitating hydrodynamical problems, we have performed a series of three-dimensional numerical simulations of the collapse of a rotating homogeneous cloud, varying the number of particles and the artificial viscosity prescription.

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arXiv2001

Direct Monte Carlo simulations of accretion discs

We apply the Direct Simulation Monte Carlo (DSMC) method, developed originally to calculate rarefied gas dynamical problems, to study the gas flow in an accretion disc in a close binary system. The method involves viscosity and thermal conduction automatically, and can thus simulate turbulent viscosity (alpha viscosity).

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arXiv2001

Spiral waves in accretion discs - theory

Spirals shocks have been widely studied in the context of galactic dynamics and protostellar discs. They may however also play an important role in some classes of close binary stars, and more particularly in cataclysmic variables. In this paper, we review the physics of spirals waves in accretion discs, present the results of numerical simulations and consider whether theory can be reconcilied with observations.

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arXiv1998

Three-dimensional SPH simulations of accretion discs

We discuss some 3D numerical simulations of accretion discs using the SPH method and a polytropic equation of state. We show that discs exist even for as large value of the polytropic index as 1.2, and that these discs are always in hydrostatic balance. We also show that even without any inflow, spiral shocks appear in the discs.

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arXiv1998

Spiral Structure in IP Peg: Confronting Theory and Observations

The first convincing piece of evidence of spiral structure in the accretion disc in IP Pegasi was found by Steeghs et al. (1997). We performed two kinds of 2D hydrodynamic simulations, a SFS finite volume scheme and a SPH scheme, with a mass ratio of 0.5. Both results agreed well with each other. We constructed Doppler maps and line flux-binary phase relations based on density distributions, the results agreeing well with those obtained by observation.

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