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Protostellar multiplicity is common at all stages and mass ranges. However, the factors that determine the multiplicity of protostellar systems have not been systematically characterized through their molecular gas. Nobeyama 45m Radio Observatory OTF maps of HCN, HNC, HCO$^+$, and N$_2$H$^+$ (J = 1--0) toward five subregions in Perseus, complemented with single pointing APEX observations of HNC (J = 4--3) are used to derive physical parameters of the dense gas. Both observations have angular resolutions of $\sim$18", equivalent to $\sim$5000 AU scales at the distance of Perseus. Kinetic gas temperature is derived from the $I$(HCN)/$I$(HNC) J = 1--0 ratio, and H$_2$ density is obtained from the HNC J=4--3/J=1--0 ratio. These parameters are used to obtain the N$_2$H$^+$ and HCO$^+$ gas masses. The inferred and derived parameters are compared to source parameters. Inferred mean kinetic gas temperature ($I$(HCN)/$I$(HNC) J=1--0 ratio; ranging between 15 and 26 K), and H$_2$ volumetric density (HNC J=4--3/J=1--0; 10$^5$ -- 10$^6$ cm$^{-3}$) do not show correlations with multiplicity in Perseus. The derived gas and dust masses, 1.3 to 16 $\times~10^{-9}$ M$_{\odot}$ for the N$_2$H$^+$ gas mass, 0.1 to 25 M$_{\odot}$ for envelope dust masses (850 $\mu$m), and 0.8 to 10 $\times~10^{-10}$ M$_{\odot}$ for the HCO$^+$ gas mass, are correlated to multiplicity and number of protostellar components. The warm gas masses are a factor of 16 lower than the cold gas masses. This work shows that gas and dust mass is correlated to multiplicity at $\sim$5000 AU scales in Perseus. Higher order multiples tend to have higher gas and dust masses in general, while close binaries (separations $\leq$7") and single protostars have similar gas and dust mass distributions. On the other hand, H$_2$ density and kinetic gas temperature do not show any correlation with multiplicity., Comment: 25 pages, 12 figures, 3 appendices. Accepted for publication in A&A. The abstract has been modified to comply with arXiv's character limit

The Near-InfraRed Planet Searcher or NIRPS is a precision radial velocity spectrograph developed through collaborative efforts among laboratories in Switzerland, Canada, Brazil, France, Portugal and Spain. NIRPS extends to the 0.98-1.8 $\mu$m domain of the pioneering HARPS instrument at the La Silla 3.6-m telescope in Chile and it has achieved unparalleled precision, measuring stellar radial velocities in the infrared with accuracy better than 1 m/s. NIRPS can be used either stand-alone or simultaneously with HARPS. Commissioned in late 2022 and early 2023, NIRPS embarked on a 5-year Guaranteed Time Observation (GTO) program in April 2023, spanning 720 observing nights. This program focuses on planetary systems around M dwarfs, encompassing both the immediate solar vicinity and transit follow-ups, alongside transit and emission spectroscopy observations. We highlight NIRPS's current performances and the insights gained during its deployment at the telescope. The lessons learned and successes achieved contribute to the ongoing advancement of precision radial velocity measurements and high spectral fidelity, further solidifying NIRPS' role in the forefront of the field of exoplanets., Comment: Proceeding at the SPIE Astronomical Telescopes + Instrumentation conference [Yokohama,Japan; June 2024]

The chromospheric emission estimated in the core of different lines, such as Ca II H & K, Na D1 and D2, and Halpha, is not always correlated between lines, as the Ca II H & K and Halpha emission time series are anti-correlated for a few percent of the stars, contrary to what is observed on the Sun. This puzzling result has been observed for both solar-type and M stars. Our objective is to characterise these relationships in more detail using complementary criteria, based on a set of spectra obtained with HARPS for a large sample of M dwarfs, to evaluate whether or not additional processes are required to explain the observations. We analysed the time average and variability of the Ca, Na, and Halpha emissions for 177 M0-M8 stars. We computed synthetic Halpha time series based on different assumptions of plage properties. The statistical properties of our sample, in terms of correlations and slopes between indices at different timescales, differ from what we previously obtained for FGK stars, with fewer stars with a null correlation, and a weaker dependence of the correlations on timescale. However, there can be a large dispersion from one season to another for stars. We find a clear indication of a change in the slope sign from the relation between averaged Ca (or Na) and Halpha for the most massive M dwarfs, as well as a change in slope in the Na-Ca relation. At this stage, we are not able to find simple plage properties that, alone, are sufficient to reproduce the observations. Simulations shows that it is not straightforward to compare the temporal variability correlation and the integrated indices and demonstrate the need for complex activity patterns to explain some of the observations. We conclude that the relation between these indices exhibits a large diversity in behaviour. More detailed simulations with complex activity patterns are necessary to understand these observations., Comment: Paper accepted in Astronomy and Astrophysics 15 January 2024

Transiting planets with orbital periods longer than 40 d are extremely rare among the 5000+ planets discovered so far. The lack of discoveries of this population poses a challenge to research into planetary demographics, formation, and evolution. Here, we present the detection and characterization of HD88986b, a potentially transiting sub-Neptune, possessing the longest orbital period among known transiting small planets (< 4 R$_{\oplus}$) with a precise mass measurement ($\sigma_M/M$ > 25%). Additionally, we identified the presence of a massive companion in a wider orbit around HD88986. Our analysis reveals that HD88986b, based on two potential single transits on sector 21 and sector 48 which are both consistent with the predicted transit time from the RV model, is potentially transiting. The joint analysis of RV and photometric data show that HD88986b has a radius of 2.49$\pm$0.18 R$_{\oplus}$, a mass of 17.2$^{+4.0}_{-3.8}$ M$_{\oplus}$, and it orbits every 146.05$^{+0.43}_{-0.40}$ d around a subgiant HD88986 which is one of the closest and brightest exoplanet host stars (G2V type, R=1.543 $\pm$0.065 R$_{\odot}$, V=$6.47\pm 0.01$ mag, distance=33.37$\pm$0.04 pc). The nature of the outer, massive companion is still to be confirmed; a joint analysis of RVs, Hipparcos, and Gaia astrometric data shows that with a 3$\sigma$ confidence interval, its semi-major axis is between 16.7 and 38.8 au and its mass is between 68 and 284 M$_{Jup}$. HD88986b's wide orbit suggests the planet did not undergo significant mass loss due to extreme-ultraviolet radiation from its host star. Therefore, it probably maintained its primordial composition, allowing us to probe its formation scenario. Furthermore, the cold nature of HD88986b (460$\pm$8 K), thanks to its long orbital period, will open up exciting opportunities for future studies of cold atmosphere composition characterization., Comment: 37 pages, accepted to be published in A&A

The two-planet transiting system LHS 1140 has been extensively observed since its discovery in 2017, notably with $Spitzer$, HST, TESS, and ESPRESSO, placing strong constraints on the parameters of the M4.5 host star and its small temperate exoplanets, LHS 1140 b and c. Here, we reanalyse the ESPRESSO observations of LHS 1140 with the novel line-by-line framework designed to fully exploit the radial velocity content of a stellar spectrum while being resilient to outlier measurements. The improved radial velocities, combined with updated stellar parameters, consolidate our knowledge on the mass of LHS 1140 b (5.60$\pm$0.19 M$_{\oplus}$) and LHS 1140 c (1.91$\pm$0.06 M$_{\oplus}$) with unprecedented precision of 3%. Transits from $Spitzer$, HST, and TESS are jointly analysed for the first time, allowing us to refine the planetary radii of b (1.730$\pm$0.025 R$_{\oplus}$) and c (1.272$\pm$0.026 R$_{\oplus}$). Stellar abundance measurements of refractory elements (Fe, Mg and Si) obtained with NIRPS are used to constrain the internal structure of LHS 1140 b. This planet is unlikely to be a rocky super-Earth as previously reported, but rather a mini-Neptune with a $\sim$0.1% H/He envelope by mass or a water world with a water-mass fraction between 9 and 19% depending on the atmospheric composition and relative abundance of Fe and Mg. While the mini-Neptune case would not be habitable, a water-abundant LHS 1140 b potentially has habitable surface conditions according to 3D global climate models, suggesting liquid water at the substellar point for atmospheres with relatively low CO$_2$ concentration, from Earth-like to a few bars., Comment: 31 pages, 18 figures, accepted for publication in ApJL

We develop a high-dimensional neural network potential (NNP) to describe the structural and energetic properties of borophene deposited on silver. This NNP has the accuracy of DFT calculations while achieving computational speedups of several orders of magnitude, allowing the study of extensive structures that may reveal intriguing moir\'e patterns or surface corrugations. We describe an efficient approach to constructing the training data set using an iterative technique known as the "adaptive learning approach". The developed NNP potential is able to produce, with an excellent agreement, the structure, energy and forces of DFT. Finally, the calculated stability of various borophene polymorphs, including those not initially included in the training dataset, shows better stabilization for $\nu\sim0.1$ hole density, and in particular for the allotrope $\alpha$ ($\nu=\frac{1}{9}$). The stability of borophene on the metal surface is shown to depend on its orientation, implying structural corrugation patterns that can only be observed from long time simulations on extended systems. The NNP also demonstrates its ability to simulate vibrational densities of states and produce realistic structures, with simulated STM images closely matching the experimental ones.

Context: The search for extrasolar planets around the nearest M dwarfs is a crucial step towards identifying the nearest Earth-like planets. One of the main challenges in this search is that M dwarfs can be magnetically active and stellar activity can produce radial velocity (RV) signals that could mimic those of a planet. Aims: We aim to investigate whether the 2.2 day period observed in optical RVs of the nearby active M dwarf star Gl 388 (AD Leo) is due to stellar activity or to a planet that corotates with the star as suggested in the past. Methods: We obtained quasi-simultaneous optical RVs of Gl 388 from 2019 to 2021 with SOPHIE (R~75k) at the OHP in France, and near-IR RV and Stokes V measurements with SPIRou at the CFHT (R~70k). Results: The SOPHIE RV time series displays a periodic signal with a 2.23+-0.01 day period and 23.6+-0.5 m/s amplitude, which is consistent with previous HARPS observations obtained in 2005-2006. The SPIRou RV time series is flat at 5 m/s rms and displays no periodic signals. RV signals of amplitude higher than 5.3 m/s at a period of 2.23 days can be excluded with a confidence level higher than 99%. Using the modulation of the longitudinal magnetic field (Bl) measured with SPIRou, we derive a stellar rotation period of 2.2305+-0.0016 days. Conclusions: SPIRou RV measurements provide solid evidence that the periodic variability of the optical RVs of Gl 388 is due to stellar activity rather than to a corotating planet. The magnetic activity nature of the optical RV signal is further confirmed by the modulation of Bl with the same period. The SPIRou campaign on Gl 388 demonstrates the power of near-IR RV to confirm or infirm planet candidates discovered in the optical around active stars. SPIRou observations reiterate how effective spectropolarimetry is at determining the stellar rotation period., Comment: 25 pages, 23 figures, Accepted by Astronomy and Astrophysics; [v2] version implementing A&A language editor suggestions; [v3] improved ascii characters for ADS metadata visualization; [v4] minor corrections added in proof

(Abridged) Context. Most massive stars are located in multiple stellar systems. Magnetic fields are believed to be essential in the accretion and ejection processes around single massive protostars. Aims. Our aim is to unveil the influence of magnetic fields in the formation of multiple massive stars, in particular on the fragmentation modes and properties of the multiple protostellar system. Methods. Using RAMSES, we follow the collapse of a massive pre-stellar core with (non-ideal) radiation-(magneto-)hydrodynamics. We choose a setup which promotes multiple stellar system formation. Results. In the purely hydrodynamical models, we always obtain (at least) binary systems. When more than two stars are present, their gravitational interaction triggers mergers until there are two stars left. The following gas accretion increases their orbital separation and hierarchical fragmentation occurs so that both stars host a comparable disk and stellar system which then form similar disks as well. We identify several modes of fragmentation: Toomre-unstable disk fragmentation, arm-arm collision and arm-filament collision. Disks grow in size until they fragment and become truncated as the newly-formed companion gains mass. When including magnetic fields, the picture evolves: the primary disk produces less fragments, arm-filament collision is absent. Magnetic fields reduce the initial orbital separation but do not affect its further evolution, which is mainly driven by gas accretion. With magnetic fields, the growth of individual disks is regulated even in the absence of fragmentation or truncation. Conclusions. Hierarchical fragmentation is seen in unmagnetized and magnetized models. Magnetic fields, including non-ideal effects, are important because they remove certain fragmentation modes and limit the growth of disks, which is otherwise only limited through fragmentation., Comment: 16 pages, 11 figures. Accepted for publication in Astronomy & Astrophysics

M dwarfs are active stars that exhibit variability in chromospheric emission and photometry at short and long timescales, including long cycles that are related to dynamo processes. This activity also impacts the search for exoplanets because it affects the radial velocities. We analysed a large sample of 177 M dwarfs observed with HARPS (2003-2020) in order to characterise the long-term variability of these stars. We compared the variability obtained in three chromospheric activity indices (Ca II H & K, the Na D doublet, and Halpha) and with ASAS photometry. We focused on the detailed analysis of the chromospheric emission based on linear, quadratic, and sinusoidal models. We used various tools to estimate the significance of the variability and to quantify the improvement brought by the models. In addition, we analysed complementary photometric time series for the most variable stars to be able to provide a broader view of the long-term variability in M dwarfs. We find that most stars are significantly variable, even the quietest stars. Most stars in our sample (75%) exhibit a long-term variability, which manifests itself mostly through linear or quadratic variability, although the true behaviour may be more complex. We found significant variability with estimated timescales for 24 stars, and estimated the lower limit for a possible cycle period for an additional 9 stars that were not previously published. We found evidence of complex variability because more than one long-term timescale may be present for at least 12 stars, together with significant differences between the behaviour of the three activity indices. This complexity may also be the source of the discrepancies observed between previous publications. We conclude that long-term variability is present for all spectral types and activity level in M dwarfs, without a significant trend with spectral type or mean activity level., Comment: article accepted in Astronomy and Astrophysics, February 2023, 31 pages

(Abridged) Most massive stars are located in multiple systems. The modeling of disk fragmentation, a possible mechanism leading to stellar multiplicity, relies on parallel 3D simulation codes whose agreement remains to be evaluated. Using the Cartesian AMR code RAMSES, we compare disk fragmentation in a centrally-condensed protostellar system to the study of Oliva & Kuiper (2020) performed on a grid in spherical coordinates using PLUTO. Two RAMSES runs are considered and give qualitatively distinct pictures. When allowing for unlimited sink particle creation, gas fragmentation leads to a multiple stellar system whose multiplicity is affected by the grid when triggering fragmentation and by numerically-assisted mergers. On the other hand, using a unique, central, fixed sink particle, a centrally-condensed system forms, similar to that reported in PLUTO. The RAMSES-PLUTO comparison is performed with the latter: agreement between the two codes is found regarding the first rotationally-supported disk formation, the presence of an accretion shock onto it, the first fragmentation phase. Gaseous fragments form and their properties are in agreement between the two codes. As a minor difference, fragments dynamics causes the disk structure to be sub-Keplerian in RAMSES whereas it is found to be Keplerian and reaches quiescence in PLUTO. We attribute this discrepancy to the central star being twice less massive in RAMSES because of the different stellar accretion subgrid models. In a centrally-condensed system, the agreement between RAMSES and PLUTO regarding many of the collapse properties and fragmentation process is good. Fragmentation occurring in the innermost region and numerical choices (use of sink particles, grid) have a crucial impact when similar but smooth initial conditions are employed - more crucial than the code's choice - on the system's outcome, multiple or centrally-condensed., Comment: 17 pages, 16 figures; accepted for publication in A&A

Binary black holes emit gravitational waves as they inspiral towards coalescence. Searches for electromagnetic counterparts to these gravitational waves rely on looking for common sources producing both signals. In this paper, we take a different approach: we investigate the impact of radiation zone effects, including retardation effects and gravitational wave propagation onto the circumbinary disk around stellar-mass, spinning black holes, using general relativistic hydrodynamical simulations. Then we used a general relativistic ray-tracing code to extract its X-ray spectrum and lightcurve. This allowed us to show that radiation zone effects leave an imprint onto the disk, leading to quasi-periodic patterns in the X-ray lightcurve. The amplitude of the modulation is weak (<1%) but increases with time and is strongly dependent on the inclination angle., Comment: 6 pages, 5 figures. Accepted for publication in AN

Accreting binary black holes (BBHs) are multi-messenger sources, emitting copious electromagnetic (EM) and gravitational waves. One of their most promising EM signatures is the lightcurve modulation caused by a strong, unique and extended azimuthal overdensity structure orbiting at the inner edge of the circumbinary disc (CBD), dubbed "lump". In this paper, we investigate the origin of this structure using 2D general-relativistic (GR) hydrodynamical simulations of a CBD in an approximate BBH spacetime. First, we use the symmetric mass-ratio case to study the transition from the natural m = 2 mode to m = 1. The asymmetry with respect to m = 2 grows exponentially, pointing to an instability origin. We indeed find that the CBD edge is prone to a (magneto-)hydrodynamical instability owing to the disc edge density sharpness: the Rossby Wave Instability (RWI). The RWI criterion is naturally fullfilled at the CBD edge and we report the presence of vortices, which are typical structures of the RWI. The RWI is also at work in the asymmetric mass-ratio cases (from 0.1 to 0.5). However, the CBD edge sharpness decreases with a decreasing mass ratio, and so the lump. By proposing a scenario for this lump formation, our work further supports its existence in astrophysical CBDs and potential source for an EM signature of BBHs. Finally, because the RWI is not caused by GR effects, it is also a robust candidate for the lump origin in CBDs around non-compact objects, e.g. binary protostars., Comment: 11 pages, 11 figures. Accepted for publication in MNRAS

Accreting supermassive binary black holes (SMBBHs) are potential targets for multi-messenger astronomy as they emit gravitational waves (GW) while their environment emits electromagnetic (EM) waves. In order to get the most out of a joint GW-EM detection we first need to obtain theoretically-predicted EM signals unambiguously linked to BBHs. In that respect, this is the first of a series of papers dedicated to accreting pre-merger BBHs and their associated EM observables. Here, we extend our Numerical Observatory of Violent Accreting systems, e-NOVAs, to any spacetime. Unlike previous studies, almost exclusively focused on the inner regions, we investigated the impact of the BBH on its outer circumbinary disc, located in the radiation (or wave) zone, after implementing an approximate analytical spacetime of spinning, inspiralling BBHs in e-NOVAs. We follow the formation of a weak spiral structure in disc density arising from the retardation effects in the radiation zone metric. Simulation data are then post-processed with a general-relativistic ray-tracing code incorporating the same BBH spacetime, assuming SMBBH sources. The density spiral creates a small (<1%) but unambiguous modulation of the lightcurve at the semi-orbital period. This signal, although weak, is fundamentally different from that of an axisymmetric disc around a single BH providing a lower limit on the impact of a BBH on its outer disc. This potential difference being found, we study how binary parameters impact this modulation in order to find the optimal case which is a high source inclination of any binary mass ratio (from 0.1 to 1)., Comment: 14 pages, 11 figures. Accepted for publication in MNRAS

We present an alternative to conventional Electron Paramagnetic Resonance (EPR) spectroscopy equipment. Avoiding the use of bulky magnets and magnetron equipment, we use the photoluminescence of an ensemble of Nitrogen-Vacancy centers at the surface of a diamond. Monitoring their relaxation time (or T1), we detected their cross-relaxation with a compound of interest. In addition, the EPR spectra are encoded through a localized magnetic field gradient. While recording previous data took 12 minutes per data point with individual NV centers, we were able to reconstruct a full spectrum at once in $3\; \textrm{seconds}$, over a range from $3$ to $11\; \textrm{Gauss}$. In terms of sensitivity, only $0.5\; {\mu}\textrm{L}$ of a $1\; {\mu}\textrm{M}$ hexaaquacopper (II) ion solution was necessary., Comment: Main text (16 pages, 6 Figures) + Supplementary (6 Pages, 7 Figures)

We present a new algorithm for precision radial velocity (pRV) measurements, a line-by-line (LBL) approach designed to handle outlying spectral information in a simple but efficient manner. The effectiveness of the LBL method is demonstrated on two datasets, one obtained with SPIRou on Barnard's star, and the other with HARPS on Proxima Centauri. In the near-infrared, the LBL provides a framework for m/s-level accuracy in pRV measurements despite the challenges associated with telluric absorption and sky emission lines. We confirm with SPIRou measurements spanning 2.7 years that the candidate super-Earth on a 233-day orbit around Barnard's star is an artifact due to a combination of time-sampling and activity. The LBL analysis of the Proxima Centauri HARPS post-upgrade data alone easily recovers the Proxima b signal and also provides a 2-sigma detection of the recently confirmed 5-day Proxima d planet, but argues against the presence of the candidate Proxima c with a period of 1900 days. We provide evidence that the Proxima c signal is associated with small, unaccounted systematic effects affecting the HARPS-TERRA template matching RV extraction method for long-period signals. Finally, the LBL framework provides a very effective activity indicator, akin to the full width at half maximum derived from the cross-correlation function, from which we infer a rotation period of $92.1^{+4.2}_{-3.5}$ days for Proxima., Comment: Accepted for publication in AJ