arXiv subjects

Henri M. J. Boffin

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

At least 37 records · Page 2Linked to original sources

arXiv2022

A tale of caution: the tails of NGC 752 are much longer than claimed

Understanding the exact extent and content of tidal tails of open clusters provide useful clues on how field stars populate the Milky Way. We reanalyse, using Gaia EDR3 data, the tails around the open cluster NGC 752. Compared to previous analyses, we look at a much wider region around the cluster and use first the convergent point method, coupled with a clustering analysis using DBSCAN. We find that the cluster, located 433 pc away and well described by a Plummer profile, has very long and asymmetric tails, extending more than 260 pc on the sky (from tip to tip) - four times larger than previously thought - and contains twice as many stars. Numerical models computed with PETAR serve as guide and confirm our analysis. The tails follows the predictions from models, but the trailing tail appears slightly distorted, possibly indicating that the cluster had a complicated history of galactic encounters. Applying an alternative method to the newly developed compact convergent method, we potentially trace the cluster's tidal tails to their full extent, covering several thousands of parsecs and more than 1,000 stars. Our analysis therefore opens a new window on the study of open clusters, whose potential will be fully unleashed with future Gaia data releases.

astro-ph.GA↗

arXiv2022

TOI-2046b, TOI-1181b and TOI-1516b, three new hot Jupiters from \textit{TESS}: planets orbiting a young star, a subgiant and a normal star

We present the confirmation and characterization of three hot Jupiters, TOI-1181b, TOI-1516b, and TOI-2046b, discovered by the TESS space mission. The reported hot Jupiters have orbital periods between 1.4 and 2.05 days. The masses of the three planets are $1.18\pm0.14$ M$_{\mathrm{J}}$, $3.16\pm0.12$\, M$_{\mathrm{J}}$, and 2.30 $\pm 0.28$ M$_{\mathrm{J}}$, for TOI-1181b, TOI-1516b, and TOI-2046b, respectively. The stellar host of TOI-1181b is a F9IV star, whereas TOI-1516b and TOI-2046b orbit F main sequence host stars. The ages of the first two systems are in the range of 2-5 Gyrs. However, TOI-2046 is among the few youngest known planetary systems hosting a hot Jupiter, with an age estimate of 100-400 Myrs. The main instruments used for the radial velocity follow-up of these three planets are located at Ondřejov, Tautenburg and McDonald Observatory, and all three are mounted on 2-3 meter aperture telescopes, demonstrating that mid-aperture telescope networks can play a substantial role in the follow-up of gas giants discovered by \textit{TESS} and in the future by \textit{PLATO}.

astro-ph.EP↗

arXiv2022

Constraints on TESS albedos for five hot Jupiters

Photometric observations of occultations of transiting exoplanets can place important constraints on the thermal emission and albedos of their atmospheres. We analyse photometric measurements and derive geometric albedo ($A_\mathrm{g}$) constraints for five hot Jupiters observed with TESS in the optical: WASP-18 b, WASP-36 b, WASP-43 b, WASP-50 b and WASP-51 b. For WASP-43 b, our results are complemented by a VLT/HAWK-I observation in the near-infrared at $2.09~μ$m. We derive the first geometric albedo constraints for WASP-50 b and WASP-51 b: $A_\mathrm{g}<0.445$ and $A_\mathrm{g}<0.368$, respectively. We find that WASP-43 b and WASP-18 b are both consistent with low geometric albedos ($A_\mathrm{g}<0.16$) even though they lie at opposite ends of the hot Jupiter temperature range with equilibrium temperatures of $\sim1400$ K and $\sim2500$ K, respectively. We report self-consistent atmospheric models which explain broadband observations for both planets from TESS, \HST, \Spitzer and VLT/HAWK-I. We find that the data of both hot Jupiters can be explained by thermal emission alone and inefficient day-night energy redistribution. The data do not require optical scattering from clouds/hazes, consistent with the low geometric albedos observed.

astro-ph.EP↗

arXiv2022

Follow the Index: A new proposal

Despite all its well-known flaws and calls for its dismissal, the notorious $h$-index is still used in many instances when awarding grants, or promoting and hiring scientists. To address this, I set out to devise a better index, with the twofold aim of taking into account the authors' respective contributions and considerably reducing the pollution of the scientific literature. Finally, I present a strategy that is guaranteed to be best for all researchers.

astro-ph.IM↗

arXiv2021

MUSE spectroscopy of planetary nebulae with high abundance discrepancies

We present MUSE deep integral-field unit spectroscopy of three planetary nebulae(PNe) with high abundance discrepancy factors (ADF > 20): NGC 6778, M 1-42 and Hf 2-2. We have constructed flux maps for more than 40 emission lines, and use them to build extinction, electron temperature (T$_e$), electron density (n$_e$), and ionic abundances maps of a number of ionic species. The effects of the contribution of recombination to the auroral [N II] and [O II] lines on T$_e$ and the abundance maps of low-ionization species are evaluated using recombination diagnostics. As a result, low T$_e$ values and a downward gradient of T$_e$ are found toward the inner zones of each PN. Spatially, this nearly coincides with the increase of abundances of heavy elements measured using recombination lines in the inner regions of PNe, and strongly supports the presence of two distinct gas phases: a cold and metal-rich and a warm one with "normal" metal content. We have simultaneously constructed, for the first time, the ADF maps of O$^+$ and O$^{2+}$ and found that they centrally peak for all three PNe under study. We show that the main issue when trying to compute realistic abundances from either ORLs or CELs is to estimate the relative contribution of each gas component to the H I emission, and we present a method to evaluate it. It is also found that, for the studied high-ADF PNe, the amount of oxygen in the cold and warm regions is of the same order.

astro-ph.SR↗

arXiv2021

A Spectral Survey of WASP-19b with ESPRESSO

High resolution precision spectroscopy provides a multitude of robust techniques for probing exoplanetary atmospheres. We present multiple VLT/ESPRESSO transit observations of the hot-Jupiter exoplanet WASP-19b with previously published but disputed atmospheric features from low resolution studies. Through spectral synthesis and modeling of the Rossiter-McLaughlin (RM) effect we calculate stellar, orbital and physical parameters for the system. From narrow-band spectroscopy we do not detect any of H\,I, Fe\,I, Mg\,I, Ca\,I, Na\,I and K\,I neutral species, placing upper limits on their line contrasts. Through cross correlation analyses with atmospheric models, we do not detect Fe\,I and place a 3$σ$ upper limit of $\log\,(X_{\textrm{Fe}}/X_\odot) \approx -1.83\,\pm\,0.11$ on its mass fraction, from injection and retrieval. We show the inability to detect the presence of H$_2$O for known abundances, owing to lack of strong absorption bands, as well as relatively low S/N ratio. We detect a barely significant peak (3.02\,$\pm$\,0.15\,$σ$) in the cross correlation map for TiO, consistent with the sub-solar abundance previously reported. This is merely a hint for the presence of TiO and does \textit{not} constitute a confirmation. However, we do confirm the presence of previously observed enhanced scattering towards blue wavelengths, through chromatic RM measurements, pointing to a hazy atmosphere. We finally present a reanalysis of low resolution transmission spectra of this exoplanet, concluding that unocculted starspots alone cannot explain previously detected features. Our reanalysis of the FORS2 spectra of WASP-19b finds a $\sim$\,100$\times$ sub-solar TiO abundance, precisely constrained to $\log\,X_{\textrm{TiO}} \approx -7.52 \pm 0.38$, consistent with the TiO hint from ESPRESSO. We present plausible paths to reconciliation with other seemingly contradicting results.

astro-ph.EP↗

arXiv2021

The secret of the elixir of youth of blue straggler stars

Using Gaia EDR3, we study the most spectacular and photogenic cluster of Ptolemy. After deriving its membership, we identify in its colour-magnitude diagram a star that definitively decided to straggle and dress in blue. Further analysis with the FARCE telescope allows us to discover in its light curve the secret of its rejuvenation, which we gladly share in this paper. This research is an important contribution to attain the ultimate goal of astronomy as professed by DJ Format.

astro-ph.SR↗

arXiv2021

The 800pc long tidal tails of the Hyades star cluster: Possible discovery of candidate epicyclic overdensities from an open star cluster

The tidal tails of stellar clusters provide an important tool for studying the birth conditions of the clusters and their evolution, coupling, and interaction with the Galactic potential. We present the N-body evolution of a Hyades-like stellar cluster with backward-integrated initial conditions on a realistic 3D orbit in the Milky Way computed within the AMUSE framework. For the first time, we explore the effect of the initial cluster rotation and the presence of lumps in the Galactic potential on the formation and evolution of tidal tails. We show that the tidal tails are not naturally clustered in any coordinate system. Models with initial rotation result in significant differences in the cluster mass loss and follow different angular momentum time evolution. The orientation of the tidal tails relative to the motion vector of the cluster and the current cluster angular momentum constrain the initial rotation of the cluster. We highlight the use of the convergent point (CP) method in searches for co-moving groups and introduce a new compact CP (CCP) method that accounts for internal kinematics based on an assumed model. Using the CCP method, we are able to recover candidate members of the Hyades tidal tails in the Gaia DR2 and eDR3 reaching a total extent of almost 1kpc. We confirm the previously noted asymmetry in the detected tidal tails. In the eDR3 data we recovered spatial overdensities in the leading and trailing tails that are kinematically consistent with being epicyclic overdensities and thus present candidates for the first such detection in an open star cluster. We show that the epicyclic overdensities are able to provide constraints not only on the cluster properties, but also on the Galactic potential. Finally, based on N-body simulations, a close encounter with a massive Galactic lump can explain the observed asymmetry in the tidal tails of the Hyades.(abriged)

astro-ph.GA↗

arXiv2020

ESO's Exposure Time Calculator 2.0

Users of the La Silla Paranal Observatory have to rely on the ESO Exposure Time Calculator (ETC) to prepare their observations. A project has been started at ESO to modernise the ETC, based on a python backend and an angular-based front-end. The ETC 2.0 will have a programmatic interface to enable the results to be included in an automated quality control loop and to communicate with the Phase 1 proposal preparation and the Phase 2 observation preparation tools, the ESO science archive, as well as with scripts runs by external users or instruments. The first version of an ETC 2.0 has been released for the 4MOST instrument and further versions will be released over the next years for all new La Silla, VLT and ELT instruments. The ETC of the current La Silla and VLT instruments will also be migrated progressively, with improved instrument description.

astro-ph.IM↗

arXiv2020

The post-common-envelope binary central star of the planetary nebula ETHOS 1

We present a detailed study of the binary central star of the planetary nebula ETHOS 1 (PN G068.1+11.0). Simultaneous modelling of light and radial velocity curves reveals the binary to comprise a hot and massive pre-white-dwarf with an M-type main-sequence companion. A good fit to the observations was found with a companion that follows expected mass-temperature-radius relationships for low-mass stars, indicating that despite being highly irradiated it is consistent with not being significantly hotter or larger than a typical star of the same mass. Previous modelling indicated that ETHOS 1 may comprise the first case where the orbital plane of the central binary does not lie perpendicular to the nebular symmetry axis, at odds with the expectation that the common envelope is ejected in the orbital plane. We find no evidence for such a discrepancy, deriving a binary inclination in agreement with that of the nebula as determined by spatio-kinematic modelling. This makes ETHOS 1 the ninth post-common-envelope planetary nebula in which the binary orbital and nebular symmetry axes have been shown to be aligned, with as yet no known counter-examples. The probability of finding such a correlation by chance is now less than 0.00002%.

astro-ph.SR↗

arXiv2020

The post-common-envelope binary central star of the planetary nebula PN G283.7-05.1: A possible post-red-giant-branch planetary nebula central star

We present the discovery and characterisation of the post-common-envelope central star system in the planetary nebula PN G283.7$-$05.1. Deep images taken as part of the POPIPlaN survey indicate that the nebula may possess a bipolar morphology similar to other post-common-envelope planetary nebulae. Simultaneous light and radial velocity curve modelling reveals the newly discovered binary system to comprise a highly-irradiated, M-type main-sequence star in a 5.9 hour orbit with a hot pre-white-dwarf. The nebular progenitor is found to have a particularly low mass of around 0.4 M$_\odot$, making PN G283.7$-$05.1 one of only a handful of candidate planetary nebulae to be the product of a common-envelope event while still on the red giant branch. Beyond its low mass, the model temperature, surface gravity and luminosity are all found to be consistent with the observed stellar and nebular spectra through comparison with model atmospheres and photoionisation modelling. However, the high temperature (T$_\mathrm{eff}\sim$95kK) and high luminosity of the central star of the nebula are not consistent with post-RGB evolutionary tracks.

astro-ph.SR↗

arXiv2020

White Paper on MAAT@GTC

MAAT is proposed as a visitor mirror-slicer optical system that will allow the OSIRIS spectrograph on the 10.4-m Gran telescopio CANARIAS (GTC) the capability to perform Integral Field Spectroscopy (IFS) over a seeing-limited FoV 14.20''x10'' with a slice width of 0.303''. MAAT@GTC will enhance the resolution power of OSIRIS by 1.6 times as compared to its 0.6'' wide long-slit. All the eleven OSIRIS grisms and volume-phase holographic gratings will be available to provide broad spectral coverage with moderate resolution (R=600 up to 4100) in the 3600 - 10000 Å wavelength range. MAAT unique observing capabilities will broaden its use to the needs of the GTC community to unveil the nature of most striking phenomena in the universe well beyond time-domain astronomy. The GTC equipped with OSIRIS+MAAT will also play a fundamental role in synergy with other facilities, some of them operating on the northern ORM at La Palma. This White Paper presents the different aspects of MAAT@GTC - including scientific and technical specifications, outstanding science cases, and an outline of the instrument concept.

astro-ph.IM↗

arXiv2020

A Plague of Magnetic Spots Among the Hot Stars of Globular Clusters

Six decades and counting, the formation of hot ~20,000-30,000 K Extreme Horizontal Branch (EHB) stars in Galactic Globular Clusters remains one of the most elusive quests in stellar evolutionary theory. Here we report on two discoveries shattering their currently alleged stable luminosity. The first EHB variability is periodic and cannot be ascribed to binary evolution nor pulsation. Instead, we here attribute it to the presence of magnetic spots: superficial chemical inhomogeneities whose projected rotation induces the variability. The second EHB variability is aperiodic and manifests itself on time-scales of years. In two cases, the six-year light curves display superflare events a mammoth several million times more energetic than solar analogs. We advocate a scenario where the two spectacular EHB variability phenomena are different manifestations of diffuse, dynamo-generated, weak magnetic fields. Ubiquitous magnetic fields, therefore, force an admittance into the intricate matrix governing the formation of all EHBs, and traverse to their Galactic field counterparts. The bigger picture is one where our conclusions bridge similar variability/magnetism phenomena in all radiative-enveloped stars: young main-sequence stars, old EHBs and defunct white dwarfs.

astro-ph.SR↗

arXiv2020

Masses of the components of SB2 binaries observed with Gaia. V. Accurate SB2 orbits for 10 binaries and masses of the components of 5 binaries

Double-lined spectroscopic binaries (SB2s) are one of the main sources of stellar masses, as additional observations are only needed to give the inclinations of the orbital planes in order to obtain the individual masses of the components. For this reason, we are observing a selection of SB2s using the SOPHIE spectrograph at the Haute-Provence observatory in order to precisely determine their orbital elements. Our objective is to finally obtain masses with an accuracy of the order of one percent by combining our radial velocity (RV) measurements and the astrometric measurements that will come from the Gaia satellite. We present here the RVs and the re-determined orbits of 10 SB2s. In order to verify the masses we will derive from Gaia, we obtained interferometric measurements of the ESO VLTI for one of these SB2s. Adding the interferometric or speckle measurements already published by us or by others for 4 other stars, we finally obtain the masses of the components of 5 binary stars, with masses ranging from 0.51 to 2.2 solar masses, including main-sequence dwarfs and some more evolved stars whose location in the HR diagram has been estimated.

astro-ph.SR↗

arXiv2020

TOI-503: The first known brown dwarf-Am star binary from the TESS mission

We report the discovery of an intermediate-mass transiting brown dwarf, TOI-503b, from the TESS mission. TOI-503b is the first brown dwarf discovered by TESS and orbits a metallic-line A-type star with a period of $P=3.6772 \pm 0.0001$ days. The light curve from TESS indicates that TOI-503b transits its host star in a grazing manner, which limits the precision with which we measure the brown dwarf's radius ($R_b = 1.34^{+0.26}_{-0.15} R_J$). We obtained high-resolution spectroscopic observations with the FIES, Ondřejov, PARAS, Tautenburg, and TRES spectrographs and measured the mass of TOI-503b to be $M_b = 53.7 \pm 1.2 M_J$. The host star has a mass of $M_\star = 1.80 \pm 0.06 M_\odot$, a radius of $R_\star = 1.70 \pm 0.05 R_\odot$, an effective temperature of $T_{\rm eff} = 7650 \pm 160$K, and a relatively high metallicity of $0.61\pm 0.07$ dex. We used stellar isochrones to derive the age of the system to be $\sim$180 Myr, which places its age between that of RIK 72b (a $\sim$10 Myr old brown dwarf in the Upper Scorpius stellar association) and AD 3116b (a $\sim$600 Myr old brown dwarf in the Praesepe cluster). We argue that this brown dwarf formed in-situ, based on the young age of the system and the long circularization timescale for this brown dwarf around its host star. TOI-503b joins a growing number of known short-period, intermediate-mass brown dwarfs orbiting main sequence stars, and is the second such brown dwarf known to transit an A star, after HATS-70b. With the growth in the population in this regime, the driest region in the brown dwarf desert ($35-55 M_J \sin{i}$) is reforesting and its mass range shrinking.

astro-ph.SR↗

arXiv2019

Uncovering a 260 pc wide, 35 Myr old filamentary relic of star formation

Several recent studies have shown that the Vela OB2 region hosts a complex constellation of sub-populations with ages in the range 10 to 50 Myr. Such populations might represent the best example of the outcome of clustered star formation in Giant Molecular clouds (GMC). We use Gaia DR2 data over an area of 40 deg radius around the open cluster Collinder 135 to extend the study of the stellar populations of the Vela OB2 region over an area of several hundreds of parsecs on sky. Detailed clustering algorithms combined with the exquisite astrometric quality of the GAIA catalogue allow us to detect a new cluster named BBJ 1 that shows the same age as NGC 2547 (30 to 35 Myr), but located at a distance of 260 pc from it. Deeper investigation of the region via clustering in 5D parameter space and in the colour-magnitude diagram allows us to detect a filamentary structure of stars that bridges the two clusters. Given the extent in space of such structure (260 pc) and the young age (~35 Myr), we exclude that such population originates by the same mechanism responsible to create tidal streams around older clusters. Even if we miss a complete picture of the 3D motion of the studied stellar structure because of the lack of accurate radial velocity measurements, we propose that such structure represent the detection of a 35 Myr old outcome of a mechanism of filamentary star formation in a GMC.

astro-ph.SR↗

arXiv2019

My companion is bigger than your companion!

We provide an analysis of the mass ratio distribution as gathered from almost all of the 559 orbital solutions derived by Professor Roger Griffin in his long series in the Observatory Magazine about "Spectroscopic Binary Orbits from Photoelectric Radial Velocities". The total distribution we determine is close to a uniform one, with a dearth of the smallest companions and an excess of almost twins. When splitting our sample between main-sequence and red giant primaries, however, we discover a different picture: the excess of twins is limited to the main-sequence stars, for which it appears even more pronounced. The mass-ratio distributions of red giants is characterised by a decline of systems with mass ratio above 0.6 and an excess of systems with a mass ratio around 0.25, which we attribute to post-mass transfer systems. The difference between the two mass-ratio distributions is likely due to the different primary masses they sample.

astro-ph.SR↗

arXiv2019

A stellar relic filament in the Orion star forming region

We report the discovery of the oldest stellar substructure in the Orion star forming region (OSFR), the Orion relic filament. The relic filament is physically associated with the OSFR as demonstrated by Gaia DR2 photometry and astrometry, as well as targeted radial velocity follow-up observations of a bright sub-sample of proper-motion selected candidate members. Gaia DR2 parallaxes place the Orion relic filament in the more distant part of the OSFR, approx. 430pc from the Sun. Given its age, velocity dispersion, spatial extent, and shape, it is not possible for the Orion relic filament to have formed as a single stellar cluster, even taking into account residual gas expulsion. The relic filament is also too young to be a tidal stream, since Galactic tides act on much longer time scales of order 100 Myr. It therefore appears likely that the structure formed from a molecular cloud filament similar to Orion A in the OSFR and retained its morphology despite decoupling from its natal gas. Hence, the Orion relic filament bears witness to the short-lived evolutionary phase between gas removal and dispersion due to shears and tides, and provides crucial new insights into how stars are formed in molecular clouds.

astro-ph.SR↗