arXiv subjects

Jean-Marie Malherbe

Publications and source records attributed to Jean-Marie Malherbe.

At least 19 recordsLinked to original sources

arXiv2026

Some polarized lines of the second solar spectrum (SrI, CaI, BaII, C2, MgH, NdII) observed at the Meudon Solar Tower spectropolarimeter

The second solar spectrum is the spectrum of the Stokes parameter Q (linear polarization) close to the solar limb. It is made of a few polarized lines with Q/I of about 1% (such as CaI, SrI, or BaII), but most lines exhibit weaker polarization. This paper presents processing of unpublished observations made in 2008 with the Meudon solar tower spectropolarimeter, which are of interest for weak and turbulent unresolved magnetic field measurements in the quiet Sun, through the Hanle effect.

astro-ph.IM↗

arXiv2026

Polarized lines of the second solar spectrum (SrI, SrII, CaI, BaII) observed at the Pic du Midi Turret Dome spectropolarimeter with the slit orthogonal to the limb

The second solar spectrum is the spectrum of the Stokes parameter Q (linear polarization) close to the solar limb. It differs significantly of the usual intensity spectrum (Stokes parameter I). The second solar spectrum contains in the blue just a few polarized lines with Q/I of about 1% (such as CaI, SrI, SrII, BaII, most lines exhibit much weaker polarization. This paper presents new processing of observations made in 2004-2006 with the Pic du Midi Turret Dome spectropolarimeter, which are of strong interest for weak and turbulent unresolved magnetic field measurements in the quiet Sun, through the interpretation of the Hanle effect. As the slit was orthogonal to the limb, the polarization rate Q/I is determined precisely and continuously up to 80'' distance of the limb.

astro-ph.IM↗

arXiv2026

Datacubes of H$α$, CaII K, CaII H and H$ε$ line profiles of the full solar disk recorded daily at Meudon observatory since 2017 and some typical profiles of solar features

Systematic observations of the Sun are performed at Meudon observatory since 1908 under the form of monochromatic images. However, a major technical improvement occurred in 2017; since this date, spectroscopic datacubes are obtained daily with the spectroheliograph and a fast CCD camera. Line profiles of H$α$ (6562.8 A), CaII K (3933.7 A), CaII H (3968.5 A) and H$ε$ (3970.1 A in the wing of CaII H) are recorded over the full solar disk under the form of 3D FITS files (x, y, $λ$). The optical spectral resolution is 0.15 A for Calcium and H$ε$ (0.093 A/pixel), and 0.25 A for H$α$ (0.155 A/pixel); the spatial sampling is about 1 arc sec (the usual seeing is 2 arcsec). Datacubes are freely available since July 2017 in raw TIF (level 0) or processed FITS (level 1) format. Access to observations and typical line profiles associated to solar features are presented.

astro-ph.IM↗

arXiv2026

Weak polarized lines of the second solar spectrum (Na, Al, H, He, Ti, Li, Sc, C2 and MgH) observed at the Pic du Midi turret dome

The second solar spectrum is the solar spectrum of Stokes parameter Q observed in linear polarization close to the solar limb. It differs significantly of the usual intensity spectrum (Stokes parameter I). The second solar spectrum contains in the visible range a few polarized lines with Q/I > 1% (such as CaI, SrI, SrII, BaII), but most lines exhibit weak or very faint polarization rates (Q/I < 0.3%). This paper presents unpublished observations made in 2004-2006 of weak polarized lines performed with the Pic du Midi Turret Dome spectropolarimeter, such as atomic lines of Na, Al, H, He, Ti, Li, Sc as well as C2 and MgH molecules.

astro-ph.IM↗

arXiv2026

70 years of spectroscopy of the photosphere and the solar chromosphere at the Pic du Midi Observatory (1956-2026)

Observations of the solar corona at the Pic du Midi began with Bernard Lyot and his spectro coronagraph installed on the multi-purpose equatorial mount of the Baillaud cupola. It was not until 1956 that domes and instruments specifically dedicated to observations of the photosphere and the solar chromosphere appeared. On the occasion of the International Geophysical Year, a solar spectroscopy laboratory was created to the west of the Pic du Midi, based on two spectrographs of 4 m and 9 m focal length. In 1961 the turret dome appeared to the east of the Pic, later equipped with an 8 m spectrograph. Around 1965, the Baillaud dome finally specialized in the corona with a new table and new spectrographs. At the same time, a revolution in infrastructure took place at the Pic in a few years, which we present as well as the solar spectrographs and their goal.

astro-ph.IM↗

arXiv2026

150 years of ground-based solar instrumentation at Meudon observatory (1876-2026)

The Sun has been observed through a telescope for four centuries. However, its study made a prodigious leap at the end of the nineteenth century with the appearance of photography and spectroscopy, then at the beginning of the following century with the invention of the coronagraph and monochromatic filters, and finally in the second half of the twentieth century with the advent of large ground-based telescopes and space exploration. This article retraces the main stages of solar instrumental developments in Meudon, from its foundation by Jules Janssen in 1876 to the present day, limited to ground-based or balloon instrumentation, designed in Meudon and installed there or in other places (Nan{\c c}ay, Pic du Midi, Canary Islands). The Meudon astronomers played a pioneering role in the history of solar physics through the experimentation of innovative techniques. After the golden age of inventions, came the time of large instruments, studied in Meudon but often installed in more favourable sites, and that of space, in a framework of international collaboration, but this is not discussed here.

astro-ph.IM↗

arXiv2025

The Paris Meudon ground based support to the NASA Solar Maximum Mission in the eighties

The Solar Maximum Mission of NASA was one of the first satellites with on board digitization of observations. It was launched for the solar maximum of cycle 21 (1980) in order to study the solar activity. It carried many instruments, such as coronagraphs, X and $γ$ ray detectors, an Ultra Violet spectrometer and a radiometer. Ground based support was offered by many institutes, such as Paris Meudon observatory under the form of systematic observations or coordinated campaigns with specific instruments. We present here the Meudon Solar Tower (MST) and magnetograph which offered in the eighties a major contribution with observations of velocity and magnetic fields of the photosphere and chromosphere, while SMM was observing the transition region and corona above.

astro-ph.IM↗

arXiv2025

Hidden magnetic fields of the quiet Sun derived from Hanle depolarization of lines of the "second solar spectrum" at the limb from Pic du Midi observations

This paper is based on a dataset of many strongly polarized solar lines belonging to the ''second solar spectrum'', i.e. the spectrum near the limb in linear scattering polarization. The observations were done at the Pic du Midi Turret Dome in 2006. The solar spectra were recorded at high spectral resolution (R = 400000) with the spectrograph slit orthogonal to the solar limb, so that $μ$ = cos$θ$ continuously varied from 0 .0 to 0.45. The crystal liquid polarimeter delivered the linear polarization rate (Q/I). Strong lines such as CaII 3934 Å, CaI 4227 Å, SrI 4607 Å, SrII 4078 Å, BaII 4554 Å were studied. We measured the Hanle depolarization with the help of models predicting the polarization envelope with no magnetic field and we got values in the range 13-25 Gauss for the unresolved turbulent magnetic field, and we found that it often decreases towards the limb, revealing an altitude gradient. This present analysis was not yet published and spectra shown here become freely available to the research community.

astro-ph.IM↗

arXiv2025

High polarization lines of the second solar spectrum of the Solar limb

We present a dataset of high resolution spectra of the Sun of many strongly polarized lines belonging to the second solar spectrum, i.e. the spectrum near the limb in linear polarization (scattering polarization). These solar spectra were obtained in full Stokes polarimetry (I, Q/I, U/I, V/I) in the quiet Sun at various distances from the limb, and at disk centre for comparison, with the ground based CNRS THEMIS telescope. Polarization rates Q/I up to 7% are obtained in CaI 4227 Å line at $μ$ = cos$θ$ = 0, while 2% is reached in SrI 4607 Å line and 1.4% in BaII 4554 Å. The spectra shown here are freely available in FITS format to the research community.

astro-ph.IM↗

arXiv2025

The golden age of solar magnetography at Paris-Meudon observatory in the second half of the twentieth century

This paper describes advances in solar magnetography and developments in instrumental techniques of polarimetry and spectroscopy made at Paris-Meudon observatory in the second half of the twentieth century. The adventure started from Lyot expertise and extended progressively to the measurement of vector magnetic fields using various and improving polarimetric techniques (such as beam exchange or grid) or new spectroscopic methods (such as the MSDP imaging slicer), at Meudon and Pic du Midi, ending by the achievement of the state-of-the-art optimized and polarization free telescope THEMIS in 1999.

astro-ph.IM↗

arXiv2025

The role of Trees of Fragmenting Granules (TFG) in the formation of the solar supergranular pattern from Hinode observations

We present in this paper an exceptional scientific dataset allowing to investigate the structure and evolution of the interior of solar supergranulation cells. Trees of Fragmenting Granules (TFG) and associated flows were evidenced using Local Correlation Tracking techniques (LCT) from a 24 H duration sequence of Hinode (JAXA/NASA) observations. The treatment of the dataset exhibits the evolution of the TFG and shows that their mutual interactions are able to build horizontal flows with longer lifetime than granules (1 to 2 hours) over a scale of 10 arcsec (the mesogranulation). These flows act on the diffusion of the intranetwork magnetic elements and also on the location and shape of the network. Hence, the TFG appear as one of the major elements involved in supergranular formation and evolution.

astro-ph.SR↗

arXiv2025

High resolution spectra of the [6297-6303] and [6361-6367] Angstr{ö}m domains (including forbidden OI lines) of the Sun and brightest stars

We present a dataset of high resolution spectra of the Sun and ten bright stars of the domains [6297-6303] and [6361-6367] Angtr{ö}m. Solar spectra were obtained in the quiet Sun at various distances from disk centre with the ground based Meudon Solar Tower and Themis telescope (12 mÅ resolution) and with the Solar Optical Telescope (SOT) onboard the Hinode satellite (21 mÅ resolution). Spectra of 10 bright stars (magnitude \< 2) were also got with Themis at 12 mÅ resolution. These spectral domains contain the faint and forbidden OI lines (6300.31 Å and 6363.79 Å) that are useful for the research of Oxygen abundance. The spectra shown here are freely available in FITS format to the research community.

astro-ph.IM↗

arXiv2024

The foundation of "Saint V{é}ran-Paul Felenbok" astronomical observatory

This paper is dedicated to the memory of Paul Felenbok (1936-2020) who was astronomer at Paris-Meudon observatory, and founded in 1974, fifty years ago, a high altitude station (2930 m), above Saint V{é}ran village in the southern Alps (Queyras). It was initially devoted to the study of the solar corona. Following solar eclipses (1970, 1973) observed with the Lallemand electronic camera, the main goal was to detect with this sensitive detector the structures of the far and hot corona in forbidden lines, using either narrow bandpass filters or spectroscopy. But everything had to be done prior to observations: a track, a house for astronomers, a dome and a complex instrument. We summarize here this fantastic adventure, which was partly successful in terms of scientific results and had to stop in 1982; however, the activity of the station resumed after 1989 under the auspices of the ``AstroQueyras'' association, which replaced the coronagraph by a 62 cm night telescope from Haute Provence observatory; the station extended later with two 50 cm telescopes, was rebuilt in 2015 and received the visit of thousands of amateurs.

astro-ph.IM↗

arXiv2024

A compilation of solar atlases (from Delbouille, Kurucz, Gandorfer, Stenflo) at disk centre and at limb from $λ$ 3000 Å to $λ$ 8800 Å

We present in this paper a compilation of solar atlases from $λ$ 3000 Å to $λ$ 8800 Å with spectral lines identified by the Moore table and with the corresponding equivalent Lande factors g*. We used two spectra at disk centre ($μ$ = 1.0), from Delbouille and Kurucz, and two spectra at the limb from Stenflo and Gandorfer, respectively at $μ$ = 0.145 and $μ$ = 0.10.

astro-ph.IM↗

arXiv2024

Transport of the magnetic flux away from a decaying sunspot via convective motions

Aims. The aim of this paper is to consider relationship between the decay of sunspots and convection via the motion of the family of granules and how the diffusion mechanism of magnetic field operates in a decaying sunspot. Methods. We report the decay of a sunspot observed by the 1.6m Goode Solar Telescope (GST) with the TiO Broadband Filter Imager (BFI) and the Near-InfraRed Imaging Spectropolarimeter (NIRIS). The analysis was aided by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamic Observatory (SDO). In the first step, we followed the decay of the sunspot with HMI data over three days by constructing its evolving area and total magnetic flux. In the second step, the high spatial and temporal resolution of the GST instruments allowed us to analyze the causes of the decay of the sunspot. Afterward, we followed the emergence of granules in the moat region around the sunspot over six hours. The evolution of the trees of fragmenting granules (TFGs) was derived based on their relationship with the horizontal surface flows. Results. We find that the area and total magnetic flux display an exponential decrease over the course of the sunspot decay. We identified 22 moving magnetic features (MMFs) in the moats of pores, which is a signature of sunspot decay through diffusion. We note that the MMFs were constrained to follow the borders of TFGs during their journey away from the sunspot. Conclusions. The TFGs and their development contribute to the diffusion of the magnetic field outside the sunspot. The conclusion of our analysis shows the important role of the TFGs in sunspot decay. Finally, the the family of granules evacuates the magnetic field.

astro-ph.SR↗

arXiv2024

The quadruple spectroheliograph of Meudon observatory (1909-1959)

The spectroheliograph was invented independently by Henri Deslandres (France) and George Hale (USA) in 1892, following the spectroscopic method suggested by Jules Janssen in 1869. This instrument is dedicated to the production of monochromatic images of the Sun in order to reveal the structures of the photosphere and the chromosphere at various altitudes. Sporadic observations started in Paris, but Deslandres moved soon to Meudon and designed, with Lucien d'Azambuja, an universal and powerful instrument, the quadruple spectroheliograph. It was devoted to systematic observations of the Sun (the long-term activity survey since 1908) and scientific research in solar physics. This paper describes the instrument and presents some original observations made with the high dispersion 7-metre spectrograph. It was dismantled in the sixties, but the solar patrol continued with the 3-metre chambers with H$α$ and CaII K lines, and is still working today with the numerical version of the spectroheliograph.

astro-ph.IM↗

arXiv2024

The Haute Provence monochromatic heliograph (1958-1994)

Bernard Lyot invented the monochromatic birefringent filter in 1933 in order to investigate the coronal emissions of solar structures above the limb with the coronagraph installed at the Pic du Midi observatory. The filter was improved later and he made the first observations of the chromosphere above the solar disk in 1948, at Meudon. After his death, Grenat and Laborde continued the development in the frame of the coming International Geophysical Year (IGY 1957-1958). A modern H$α$ heliograph was completed soon and the flare patrol started in 1956. This instrument was reproduced by two companies (SECASI and OPL) and disseminated around the world in order to contribute to the IGY common effort dedicated to the solar activity survey. We describe in this short paper the capabilities of one of these copies operating at Haute Provence station from 1958 to 1994.

astro-ph.IM↗

arXiv2024

In pursuit of the Sun, from Jules Janssen to the present day

The Sun has been observed through a telescope for four centuries. However, its study made a prodigious leap at the end of the nineteenth century with the appearance of photography and spectroscopy, then at the beginning of the following century with the invention of the coronagraph and monochromatic filters, and finally in the second half of the twentieth century with the advent of space exploration (satellites, probes). This makes it possible to observe the radiations hidden by the Earth's atmosphere (Ultra Violet, X-rays, $γ$) and to carry out ''in situ'' measurements in the solar environment. This article retraces the major stages of this fantastic epic in which renowned scientists such as Janssen, Deslandres, d'Azambuja, Lyot and Dollfus entered the scene, giving the Paris-Meudon Observatory a pioneering role in the history of solar physics until 1960. After this golden age, space exploration required large resources shared between nations, which could no longer be implemented within teams or even individual institutes. The development of numerical simulation, a new research tool, also required the pooling of supercomputers.

astro-ph.IM↗