arXiv subjects

Rosine Lallement

Publications and source records attributed to Rosine Lallement.

At least 19 recordsLinked to original sources

arXiv2026

Abundances of CNO in candidate young metal-poor stars

In this contribution we investigate the CNO abundances in five apparently young evolved stars, with the aim of discriminating between truly young stars and stars that were rejuvenated by accreting mass from another star. Stars that have accreted mass are expected to show low C and O and a very low [C/O] ratio, as displayed by some stars in the Globular Cluster 47 Tuc, that are believed to have undergone mass-transfer. In our sample the low [C/O] ratios observed appear to be compatible with their evolutionary status. There is thus no indication for these stars having accreted mass.__

astro-ph.GA↗

arXiv2025

The Gaia RVS Benchmark Stars. III . Confirmed and New High Radial Velocity Stars From Gaia DR3

High-velocity stars are interesting targets to unveil the formation of the Milky Way. In fact they can be recently accreted from an infalling dwarf galaxies or they can be the result of a turbulent merging of galaxies. Gaia is providing the community a way to select stars for their kinematics and the radial velocity, one of the speed components, is derived from the Gaia RVS spectrum. High absolute radial velocity values are sensitive to be false positive. They are rare and as such they are more easily impacted than lower velocity stars, by contamination by very low SNR spurious measures. We here investigate a sample of 26 stars with Gaia absolute radial velocity in excess of 500___km/s with spectroscopic follow-up observations with UVES. For all but one star the extreme radial velocity is confirmed and these stars are all metal-poor and, as expected, enhanced in the elements. The complete chemical inventory confirm the large star-to-star scatter for the heavy elements and their on average larger ratio over iron with respect to the Sun, in agreement with the literature.

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arXiv2024

Ultraviolet extinction correlation with 3D dust maps using white dwarfs

Accurate astrometric and photometric measurements from Gaia have led to the construction of 3D dust extinction maps which can now be used for estimating the integrated extinctions of Galactic sources located within 5 kpc. These maps based on optical observations may not be reliable for use in the ultraviolet (UV) which is more sensitive to reddening. Past studies have focused on studying UV extinction using main-sequence stars but lack comparison with 3D dust maps. White dwarfs with well-modeled hydrogen-dominated (DA) atmospheres provide an advantage over main-sequence stars affected by magnetic activity. In this work, we study the variation of UV extinction with 3D dust maps utilising HST and GALEX observations of DA white dwarfs located within 300 pc. We used HST COS spectroscopic data of 76 sight lines to calculate the optical extinction from Si II column densities and validate our results with the kinematic model predictions of the local interstellar medium. Also, we combined GALEX and Gaia photometric observations of 1158 DA white dwarfs to study UV reddening by comparing observed and modeled colour-colour relations. We calculated GALEX non-linearity corrections and derived reddening coefficients (R(NUV-G) = 6.52 +/- 1.53 and R(FUV-G) = 6.04 +/- 2.41) considering their variations with optical extinction (Av < 0.1 mag), and found them to be in good agreement with known extinction laws. HST analysis suggests a positive bias of 0.01-0.02 mag in the optical extinction from 3D maps depending on the Galactic latitude. These results independently confirm the validity of 3D dust maps to deredden the optical and UV observations of white dwarfs.

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arXiv2024

Radial velocities: direct application of Pierre Connes' shift finding algorithm to Cross-Correlation Functions

Pipelines of state-of-the-art spectrographs dedicated to planet detection provide, for each exposure, series of Cross-Correlation Functions (CCFs) built with a Binary Mask (BM), and the absolute radial velocity (RV) derived from Gaussian fit of a weighted average CCF$_{tot}$ of the CCFs. Here we tested the benefits of the application of the shift finding algorithm developed by Pierre Connes directly to the total CCF$_{tot}$, comparing the resulting RV shifts (DRVs) with the results of the Gaussian fits. In a second step, we investigated how the individual DRV profiles along the velocity grid can be used as an easy tool for detection of stellar line shape variations. We tested this new algorithm on 1151 archived spectra of the K2.5 V star HD 40307 obtained with ESO/ESPRESSO during a one-week campaign in 2018. Tests were performed based on the comparison of DRVs with RVs from Gaussian fits. DRV profiles along the velocity grid (DRV(i)) were scrutinized and compared with direct CCF$_{tot}$ ratios. The dispersion of residuals from a linear fit to RVs from 406 spectra recorded within one night, was found to be $σ$=1.03 and 0.83 ms$^{-1}$ for the Gaussian fit and the new algorithm respectively, a significant 20\% improvement in accuracy. The two full one-week series obtained during the campaign were also fitted with a 3-planet system Keplerian model. The residual divergence between data and best-fit model is significantly smaller for the new algorithm than for the Gaussian fit. This new algorithm is an easy tool allowing to obtain additional diagnostics on the RV measurements in series of exposures. It increases the accuracy of velocity variation determinations. Also, departures from constancy of the DRVi profiles, as well as varying differences between RVs from this new method and RVs from a Gaussian fit provide diagnostics of line shape variations due to stellar activity.

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arXiv2023

The EDIBLES Survey. VII. A survey of C2 and C3 in interstellar clouds

We carried out a sensitive survey of C$_2$ and C$_3$ using the EDIBLES data set. We also expanded our searches to C$_4$, C$_5$, and $^{13}$C$^{12}$C isotopologue in the most molecule-rich sightlines. We fit synthetic spectra generated following a physical excitation model to the C$_2$ (2-0) Phillips band to obtain the C$_2$ column density ($N$) as well as the kinetic temperature ($T_\textrm{kin}$) and number density ($n$) of the host cloud. The C$_3$ molecule was measured through its $\tilde{A} - \tilde{X}$ (000-000) electronic origin band system. We simulated the excitation of this band with a double-temperature Boltzmann distribution. We present the largest combined survey of C$_2$ and C$_3$ to date in which the individual transitions can be resolved. In total we detected C$_2$ in 51 velocity components along 40 sightlines, and C$_3$ in 31 velocity components along 27 sightlines. The two molecules are detected in the same velocity components. We find a very good correlation between $N$(C$_2$) and $N$(C$_3$) with Pearson $r = 0.93$ and an average $N$(C$_2$)/$N$(C$_3$) ratio of 15.5$\pm$1.4. A comparison with the behaviour of the C$_2$ DIBs shows that there are no clear differences among sightlines with and without detection of C$_2$ and C$_3$. This is in direct contrast to the better-studied non-C$_2$ DIBs who have reduced strengths in molecule-rich environments. We also identify for the first time the $Q$(2), $Q$(3), and $Q$(4) transitions of the $^{13}$C$^{12}$C (2-0) Phillips band in a stacked average spectrum, and estimate the isotopic ratio of carbon $^{12}$C/$^{13}$C as 79$\pm$8. Our search for the C$_4$ and C$_5$ optical bands was unsuccessful.

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arXiv2023

Deep learning denoising by dimension reduction: Application to the ORION-B line cubes

Context. The availability of large bandwidth receivers for millimeter radio telescopes allows the acquisition of position-position-frequency data cubes over a wide field of view and a broad frequency coverage. These cubes contain much information on the physical, chemical, and kinematical properties of the emitting gas. However, their large size coupled with inhomogenous signal-to-noise ratio (SNR) are major challenges for consistent analysis and interpretation.Aims. We search for a denoising method of the low SNR regions of the studied data cubes that would allow to recover the low SNR emission without distorting the signals with high SNR.Methods. We perform an in-depth data analysis of the 13 CO and C 17 O (1 -- 0) data cubes obtained as part of the ORION-B large program performed at the IRAM 30m telescope. We analyse the statistical properties of the noise and the evolution of the correlation of the signal in a given frequency channel with that of the adjacent channels. This allows us to propose significant improvements of typical autoassociative neural networks, often used to denoise hyperspectral Earth remote sensing data. Applying this method to the 13 CO (1 -- 0) cube, we compare the denoised data with those derived with the multiple Gaussian fitting algorithm ROHSA, considered as the state of the art procedure for data line cubes.Results. The nature of astronomical spectral data cubes is distinct from that of the hyperspectral data usually studied in the Earth remote sensing literature because the observed intensities become statistically independent beyond a short channel separation. This lack of redundancy in data has led us to adapt the method, notably by taking into account the sparsity of the signal along the spectral axis. The application of the proposed algorithm leads to an increase of the SNR in voxels with weak signal, while preserving the spectral shape of the data in high SNR voxels.Conclusions. The proposed algorithm that combines a detailed analysis of the noise statistics with an innovative autoencoder architecture is a promising path to denoise radio-astronomy line data cubes. In the future, exploring whether a better use of the spatial correlations of the noise may further improve the denoising performances seems a promising avenue. In addition,

astro-ph.IM↗

arXiv2022

The EDIBLES survey V: Line profile variations in the $λλ$5797, 6379, and 6614 diffuse interstellar bands as a tool to constrain carrier sizes

Several diffuse interstellar bands (DIBs) have profiles with resolved sub-peaks that resemble rotational bands of large molecules. Analysis of these profiles can constrain the sizes and geometries of the DIB carriers, especially if the profiles exhibit clear variations along lines of sight probing different physical conditions. Using the extensive data set from the EDIBLES survey we searched for systematic variations in the peak-to-peak separation of these sub-peaks for the $λλ$5797, 6379, and 6614 DIBs in lines of sight with a single dominant interstellar cloud. We used the spectra of twelve single-cloud sight lines to measure the peak-to-peak separation in the band profile substructures for these DIBs. We adopted the rotational contour formalism to infer the rotational constant for each DIB carrier and the rotational excitation temperature in the sight lines. We compared these to rotational constants for linear and spherical molecules to estimate the DIB carrier sizes. All three DIBs have peak separations that vary systematically between lines of sight, indicating correlated changes in the rotational excitation temperatures. We derived $B_{6614}$=$(22.2\pm8.9)\times 10^{-3}$ cm$^{-1}$, consistent with previous estimates. Assuming a similar rotational temperature for the $λ$6614 DIB carrier and assuming a linear carrier, we found B$_{5797}^{\rm linear}=(5.1\pm2.0)\times10^{-3}~{\rm cm}^{-1}$ and B$_{6379}^{\rm linear} =(2.3\pm0.9)\times10^{-3}~{\rm cm}^{-1}$. If the carriers of those DIBs however are spherical species, their rotational constants are half that value, $B_{5797}^{\rm spherical} = (2.6\pm1.0)\times10^{-3}~{\rm cm}^{-1}$ and $B_{6379}^{\rm spherical} = (1.1\pm0.4)\times10^{-3}~{\rm cm}^{-1}$. We estimate molecule sizes that range from 7--9 carbon atoms ($λ$6614 carrier, linear) to 77--114 carbon atoms ($λ$6379, spherical).

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arXiv2022

North Polar Spur/Loop I: gigantic outskirt of the Northern Fermi bubble or nearby hot gas cavity blown by supernovae?

Radio continuum, microwave and gamma-ray images of the Milky Way reveal a conspicuous, loop-like structure that fills almost half of the northern Galactic hemisphere, called Loop I. The interior of Loop I is shining in soft X-rays, and its eastern base is a bright, elongated structure dubbed the North Polar Spur (NPS). After 40 years of debates, two contradictory views of Loop I/NPS are still defended: on the one hand, the NPS is a volume of expanding hot gas that envelops and extends the northern Fermi Bubble (FB) known to be blown by the Galactic center, and Loop I marks the shock front; on the other hand, the NPS is a nearby cavity of hot gas blown by supernovae, Loop I is its shock front and they are coincidentally located in the direction of the FB. To an observer at the Sun, both structures can produce the same perspective view, although the former has a size comparable to the Milky Way itself, and the latter a diameter of a few hundreds parsecs. The energy involved varies by 3-4~orders of magnitude, and the solution has various important consequences. I discuss recent results which have a connection with Loop I/NPS, overlooked or used as arguments in the two opposite ways. They involve very different spacecraft, from a 12 Kg Cubesat (HaloSat) to major space-borne observatories (HST, Gaia, and Spektr-RG). I make use of 3D~maps of dust and a massive star catalog. Considering all constraints, it is clear that there is no entirely local or entirely distant scenario that is free from contradictions with some of the data analyses or from improbable coincidences. I discuss a speculative scenario, partially inspired by recent BF and Milky Way gas models, combining near and far aspects and seeming to be able to meet the various constraints. However, new data and models are needed to bring the controversy to a close and we can still expect new episodes of this long story.

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arXiv2019

Updated extraction of the APOGEE 1.5273 μm diffuse interstellar band: a Planck view on the carrier depletion in dense cores

The latest SDSS/APOGEE data release DR14 has provided an increased number of stellar spectra in the H band and associated stellar models using an innovative algorithm known as The Cannon. We took advantage of these novelties to extract the 15 273 Å near-infrared DIB and to study its link with dust extinction and emission. We modified our automated fitting methods dedicated to hot stars and used in earlier studies with some adaptations motivated by the change from early- or intermediate-type stars to red giants. A new method has also been developed to quantify the upper limits on DIB strengths. We compared our DIB measurements with the stellar extinctions Av from the Starhorse database. We then compared the resulting DIB-extinction ratio with the dust optical depth derived from Planck data, globally and also separately for nearby off-Plane cloud complexes. Our analysis has led to the production of a catalog containing 124 064 new measurements of the 15 273 Å DIB, allowing us to revisit the correlation between DIB strength and dust reddening. The new data reveal clearly that the sky-averaged 15 273 Å DIB strength is linearly correlated with Av over two orders as reported by earlier studies but leveling-off with respect to extinction for highly reddened lines-of-sight behind dense clouds. The comparison with Planck individual optical depths reveals in a conspicuous way this DIB depletion in the dense cores and shows it applies to all off-Plane dense clouds. APOGEE measurements confirm the ubiquity of the 15 273 Å DIB carrier decrease with respect to dust grains in dense cloud cores, in a manner that can be empirically related to the dust optical depth reached in the cloud.

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arXiv2017

The ESO Diffuse Interstellar Bands Large Exploration Survey: EDIBLES I. Project description, survey sample and quality assessment

The carriers of the diffuse interstellar bands (DIBs) are largely unidentified molecules ubiquitously present in the interstellar medium (ISM). After decades of study, two strong and possibly three weak near-infrared DIBs have recently been attributed to the C60+ fullerene based on observational and laboratory measurements. There is great promise for the identification of the over 400 other known DIBs, as this result could provide chemical hints towards other possible carriers. In an effort to systematically study the properties of the DIB carriers, we have initiated a new large-scale observational survey: the ESO Diffuse Interstellar Bands Large Exploration Survey (EDIBLES). The main objective is to build on and extend existing DIB surveys to make a major step forward in characterising the physical and chemical conditions for a statistically significant sample of interstellar lines-of-sight, with the goal to reverse-engineer key molecular properties of the DIB carriers. EDIBLES is a filler Large Programme using the Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope at Paranal, Chile. It is designed to provide an observationally unbiased view of the presence and behaviour of the DIBs towards early-spectral-type stars whose lines-of-sight probe the diffuse-to-translucent ISM. Such a complete dataset will provide a deep census of the atomic and molecular content, physical conditions, chemical abundances and elemental depletion levels for each sightline. Achieving these goals requires a homogeneous set of high-quality data in terms of resolution (R ~ 70000 -- 100000), sensitivity (S/N up to 1000 per resolution element), and spectral coverage (305--1042 nm), as well as a large sample size (100+ sightlines). In this first paper the goals, objectives and methodology of the EDIBLES programme are described and an initial assessment of the data is provided.

astro-ph.GA↗

arXiv2017

Three-dimensional mapping of the local interstellar medium with composite data

Three-dimensional maps of the Galactic interstellar medium are general astrophysical tools. Reddening maps may be based on the inversion of color excess measurements for individual target stars or on statistical methods using stellar surveys. Three-dimensional maps based on diffuse interstellar bands (DIBs) have also been produced. All methods benefit from the advent of massive surveys and from Gaia data. We first updated our previous local dust maps based on a regularized Bayesian inversion of individual color excess data by replacing Hipparcos or photometric distances with Gaia Data Release 1 values when available. Secondly, we complemented this database with a series of ~5,000 color excess values estimated from the strength of the lambda 15273 DIB toward stars from SDSS/APOGEE, possessing a Gaia parallax. Third, we computed a low-resolution map based on a grid of Pan-STARRS reddening measurements by means of a new hierarchical technique and used this map as the prior distribution during the inversion of the two other datasets. Here we present a first attempt to combine different datasets and methods to improve the local maps. The use of Gaia parallaxes introduces significant changes in some areas and globally increases the compactness of the structures. Additional DIB-based data make it possible to assign distances to clouds located behind closer opaque structures and do not introduce contradictory information for the close structures. A more realistic prior distribution instead of a plane-parallel homogeneous distribution helps better define the structures. We validated the results through comparisons with other maps and with soft X-ray data. Our study demonstrates that the combination of various tracers is a potential tool for more accurate maps. An online tool makes it possible to retrieve maps and reddening estimations (http://stilism.obspm.fr).

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arXiv2016

Stability of the interstellar hydrogen inflow longitude from 20 years of SOHO/SWAN observations

Aims. A recent debate on the decade-long stability of the interstellar He flow vector, and in particular the flow longitude, has prompted us to check for any variability in the interstellar H flow vector as observed by the SWAN instrument on board SOHO. Methods. We used a simple model-independent method to determine the interstellar H flow longitude, based on the parallax effects induced on the Lyman-α intensity measured by SWAN following the satellite motion around the Sun. Results. Our results show that the interstellar H flow vector longitude does not vary significantly from an average value of 252.9$^{\circ}$ $\pm$ 1.4$^{\circ}$ throughout the 20-year span of the SWAN dataset, further strengthening the arguments for the stability of the interstellar gas flow.

astro-ph.SR↗

arXiv2016

A catalog of 1.5273 micron diffuse interstellar bands based on APOGEE hot telluric calibrators

High resolution stellar spectroscopic surveys provide massive amounts of diffuse interstellar bands (DIBs) measurements. Data can be used to study the distribution of the DIB carriers and those environmental conditions that favor their formation. In parallel, recent studies have also proved that DIBs extracted from stellar spectra constitute new tools for building the 3D structure of the Galactic Interstellar Medium (ISM). The amount of details on the structure depends directly on the quantity of available lines of sight (LOS). Therefore there is a need to construct databases of high-quality DIB measurements as large as possible. We aim at providing the community with a catalog of high-quality measurements of the 1.5273 micron DIB towards a large fraction of the Apache Point Observatory Galactic Evolution Experiment (APOGEE) hot stars observed to correct for the telluric absorption and not used for ISM studies so far. This catalog would complement the extensive database recently extracted from the APOGEE observations and used for 3D ISM mapping. We devised a method to fit the stellar continuum of the hot calibration stars and extracted the DIB from the normalized spectrum. Severe selection criteria based on the absorption characteristics are applied to the results. In particular limiting constraints on the DIB widths and Doppler shifts are deduced from the HI 21 cm measurements, following a new technique of decomposition of the emission spectra. From ~16 000 available hot telluric spectra we have extracted ~ 6700 DIB measurements and their associated uncertainties. The statistical properties of the extracted absorptions are examined and our selection criteria are shown to provide a robust dataset. The resulting catalog contains the DIB total equivalent widths, central wavelengths and widths. We briefly illustrate its potential use for the stellar and interstellar communities.

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arXiv2016

The Detailed Science Case for the Maunakea Spectroscopic Explorer: the Composition and Dynamics of the Faint Universe

MSE is an 11.25m aperture observatory with a 1.5 square degree field of view that will be fully dedicated to multi-object spectroscopy. More than 3200 fibres will feed spectrographs operating at low (R ~ 2000 - 3500) and moderate (R ~ 6000) spectral resolution, and approximately 1000 fibers will feed spectrographs operating at high (R ~ 40000) resolution. MSE is designed to enable transformational science in areas as diverse as tomographic mapping of the interstellar and intergalactic media; the in-situ chemical tagging of thick disk and halo stars; connecting galaxies to their large scale structure; measuring the mass functions of cold dark matter sub-halos in galaxy and cluster-scale hosts; reverberation mapping of supermassive black holes in quasars; next generation cosmological surveys using redshift space distortions and peculiar velocities. MSE is an essential follow-up facility to current and next generations of multi-wavelength imaging surveys, including LSST, Gaia, Euclid, WFIRST, PLATO, and the SKA, and is designed to complement and go beyond the science goals of other planned and current spectroscopic capabilities like VISTA/4MOST, WHT/WEAVE, AAT/HERMES and Subaru/PFS. It is an ideal feeder facility for E-ELT, TMT and GMT, and provides the missing link between wide field imaging and small field precision astronomy. MSE is optimized for high throughput, high signal-to-noise observations of the faintest sources in the Universe with high quality calibration and stability being ensured through the dedicated operational mode of the observatory. (abridged)

astro-ph.IM↗

arXiv2015

Towards DIB mapping in galaxies beyond 100 Mpc. A radial profile of the $λ$5780.5 diffuse interstellar band in AM 1353-272 B

Diffuse Interstellar Bands (DIBs) are non-stellar weak absorption features of unknown origin found in the spectra of stars viewed through one or several clouds of Interstellar Medium (ISM). Research of DIBs outside the Milky Way is currently very limited. Specifically spatially resolved investigations of DIBs outside of the Local Group is, to our knowledge, inexistent. Here, we explore the capability of the high sensitivity Integral Field Spectrograph, MUSE, as a tool to map diffuse interstellar bands at distances larger than 100 Mpc. We use MUSE commissioning data for AM 1353-272 B, the member with highest extinction of the "The Dentist's Chair", an interacting system of two spiral galaxies. High signal-to-noise spectra were created by co-adding the signal of many spatial elements distributed in a geometry of concentric elliptical half-rings. We derived decreasing radial profiles for the equivalent width of the $λ$5780.5 DIB both in the receding and approaching side of the companion galaxy up to distances of $\sim$4.6 kpc from the center of the galaxy. Likewise, interstellar extinction, as derived from the Halpha/Hbeta line ratio displays a similar trend, with decreasing values towards the external parts. This translates into an intrinsic correlation between the strength of the DIB and the extinction within AM 1353-272 B consistent with the current existing global trend between these quantities when using measurements for both Galactic and extragalactic sight lines. Mapping of DIB strength in the Local Universe as up to now only done for the Milky Way seems feasible. This offers a new approach to study the relationship between DIBs and other characteristics and species of the ISM in different conditions as those found in our Galaxy to the use of galaxies in the Local Group and/or single sightlines towards supernovae, quasars and galaxies outside the Local Group.

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arXiv2014

3D maps of the local interstellar medium: searching for the imprints of past events

Inversion of interstellar gas or dust columns measured along the path to stars distributed in distance and direction allows reconstructing the distribution of interstellar matter (ISM) in 3D. A low resolution IS dust map based on the reddening of 23,000 stars illustrates the potential of future maps. It reveals the location of the main IS clouds within $\sim$1kpc and, owing to biases towards weakly reddened targets, regions devoid of IS matter. It traces the Local Bubble and neighboring cavities, including a giant, $\geq$1000 pc long cavity located beyond the so-called $β$CMa tunnel, bordered by the main constituents of the Gould belt (GB), the rotating and expanding ring of clouds and young stars, inclined by $\sim$ 20$^{\circ}$ to the galactic plane. From comparison with diffuse X-ray background and absorption data it appears that the giant cavity is filled with warm, ionized and dust-poor gas in addition to million K gas. This set of structures must reflect the main events that occurred in the past. It has been suggested that the Cretaceus-Tertiary mass extinction may be due to a gamma-ray burst (GRB) in the massive globular cluster (GC) 47 Tuc during its close encounter with the Sun $\sim$70 Myrs ago. Given the mass, speed and size of 47 Tuc, wherever it crossed the Galactic plane it must have produced at the crossing site significant dynamical effects on the disk stars and IS clouds, and triggered star formation. Interestingly, first-order estimates suggest that the GB dynamics and age could match the consequences of the cluster crossing. Additionally, the giant ionized, dust-free cavity could be related to an intense flux of hard radiation, and dust-gas decoupling after the burst could explain the high variability and pattern of the D/H ratio in the nearby gaseous ISM. Future Gaia data should confirm or dismiss this hypothesis.

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arXiv2014

Dust properties inside molecular clouds from coreshine modeling and observations

Context. Using observations to deduce dust properties, grain size distribution, and physical conditions in molecular clouds is a highly degenerate problem. Aims. The coreshine phenomenon, a scattering process at 3.6 and 4.5 $μ$m that dominates absorption, has revealed its ability to explore the densest parts of clouds. We want to use this effect to constrain the dust parameters. The goal is to investigate to what extent grain growth (at constant dust mass) inside molecular clouds is able to explain the coreshine observations. We aim to find dust models that can explain a sample of Spitzer coreshine data. We also look at the consistency with near-infrared data we obtained for a few clouds. Methods. We selected four regions with a very high occurrence of coreshine cases: Taurus-Perseus, Cepheus, Chameleon and L183/L134. We built a grid of dust models and investigated the key parameters to reproduce the general trend of surface bright- nesses and intensity ratios of both coreshine and near-infrared observations with the help of a 3D Monte-Carlo radiative transfer code. The grid parameters allow to investigate the effect of coagulation upon spherical grains up to 5 $μ$m in size derived from the DustEm diffuse interstellar medium grains. Fluffiness (porosity or fractal degree), ices, and a handful of classical grain size distributions were also tested. We used the near- and mostly mid-infrared intensity ratios as strong discriminants between dust models. Results. The determination of the background field intensity at each wavelength is a key issue. In particular, an especially strong background field explains why we do not see coreshine in the Galactic plane at 3.6 and 4.5 $μ$m. For starless cores, where detected, the observed 4.5 $μ$m / 3.6 $μ$m coreshine intensity ratio is always lower than $\sim$0.5 which is also what we find in the models for the Taurus-Perseus and L183 directions. Embedded sources can lead to higher fluxes (up to four times greater than the strongest starless core fluxes) and higher coreshine ratios (from 0.5 to 1.1 in our selected sample). Normal interstellar radiation field conditions are sufficient to find suitable grain models at all wavelengths for starless cores. The standard interstellar grains are not able to reproduce observations and, due to the multi-wavelength approach, only a few grain types meet the criteria set by the data. Porosity does not affect the flux ratios while the fractal dimension helps to explain coreshine ratios but does not seem able to reproduce near-infrared observations without a mix of other grain types. Conclusions. Combined near- and mid-infrared wavelengths confirm the potential to reveal the nature and size distribution of dust grains. Careful assessment of the environmental parameters (interstellar and background fields, embedded or nearby reddened sources) is required to validate this new diagnostic.

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arXiv2014

The Interstellar H Flow: Updated Analysis of SOHO/SWAN Data

We update two kinds of results obtained with the SWAN instrument on board SOHO. First, we use H cell data recorded in 2001 and derive the H flow direction in the same way we performed the study at solar minimum. We compare with the Helium flow and doing so we correct for the coordinate system change between the Ulysses and SOHO mission. The deflection plane we obtain is compatible with the previous result within error bars, confirming the predominant role of the interstellar magnetic field. Secondly, we extend the derivation of solar wind ionization temporal evolution as a function of heliolatitude. The pattern for the present solar minimum is strikingly different from the previous minimum, with a much wider slow solar wind equatorial belt which persists until at least 2008. Comparing with synoptic LASCO/C2 electron densities we infer from a preliminary study that the acceleration of the high speed solar wind occurs at a higher altitude during this minimum, a change expansion models should be able to explain.

astro-ph.SR↗