63 research outputs found
La lettre du 4 septembre 1917 relative au classement des vestiges de guerre dans la Somme
Entre juin et novembre 1916, la bataille de la Somme laisse dans les zones française et britannique un paysage dévasté par des bombardements et des combats violents et meurtriers. Des villages entiers ont disparu, les sols sont retournés et truffés d’obus et d’amas de pierres. Les Allemands n’ont reculé que de quelques kilomètres. À partir de mars 1917, le front se déplace, après que les Allemands ont abandonné le saillant Arras-Noyon-Roye et se sont repliés sur la ligne Hindenburg. Dès le mo..
Le fonds « Moscou » au département de l’armée de Terre
Commencées en 2003, les opérations de classement du deuxième lot d’archives rapatriées de Moscou ont connu une accélération en 2006, avec l’affectation d’une véritable équipe d’archivistes. Depuis près de trois ans, plusieurs étapes essentielles ont été franchies. En vertu du principe de respect des fonds, un premier lotissement a été opéré par producteur, c’est-à-dire par institution, puis un lotissement plus fin par bureau et par section. Le plan de classement des archives rapatriées de Mos..
La lettre du 4 septembre 1917 relative au classement des vestiges de guerre dans la Somme
Entre juin et novembre 1916, la bataille de la Somme laisse dans les zones française et britannique un paysage dévasté par des bombardements et des combats violents et meurtriers. Des villages entiers ont disparu, les sols sont retournés et truffés d’obus et d’amas de pierres. Les Allemands n’ont reculé que de quelques kilomètres. À partir de mars 1917, le front se déplace, après que les Allemands ont abandonné le saillant Arras-Noyon-Roye et se sont repliés sur la ligne Hindenburg. Dès le mo..
The Pristine Dwarf-Galaxy survey -- V. The edges of the dwarf galaxy Hercules
We present a new spectroscopic study of the dwarf galaxy Hercules (d ~ 132
kpc) with data from the Anglo-Australian Telescope and its AAOmega spectrograph
together with the Two Degree Field multi-object system to solve the conundrum
that whether Hercules is tidally disrupting. We combine broadband photometry,
proper motions from Gaia, and our Pristine narrow-band and
metallicity-sensitive photometry to efficiently weed out the Milky Way
contamination. Such cleaning is particularly critical in this kinematic regime,
as both the transverse and heliocentric velocities of Milky Way populations
overlap with Hercules. Thanks to this method, three new member stars are
identified, including one at almost 10rh of the satellite. All three have
velocities and metallicities consistent with that of the main body. Combining
this new dataset with the entire literature cleaned out from contamination
shows that Hercules does not exhibit a velocity gradient (d/dX =
0.1+0.4/-0.2 km s-1 arcmin-1) and, as such, does not show evidence to undergo
tidal disruption
The Pristine Dwarf-Galaxy survey - II. In-depth observational study of the faint Milky Way satellite Sagittarius II
We present an extensive study of the Sagittarius II (Sgr II) stellar system using MegaCam g and
i photometry, narrow-band, metallicity-sensitive calcium H&K doublet photometry and Keck
II/DEIMOS multiobject spectroscopy. We derive and refine the Sgr II structural and stellar
properties inferred at the time of its discovery. The colour–magnitude diagram implies Sgr II
is old (12.0 ± 0.5 Gyr) and metal poor. The CaHK photometry confirms the metal-poor nature
of the satellite ([Fe/H] CaHK = −2.32 ± 0.04 dex) and suggests that Sgr II hosts more than one
single stellar population (σ CaHK
[FeH] = 0.11+0.05 −0.03 dex). Using the Ca infrared triplet measured from
our highest signal-to-noise spectra, we confirm the metallicity and dispersion inferred from
the Pristine photometric metallicities ([Fe/H]spectro = −2.23 ± 0.05 dex, σspectro
[Fe/H] = 0.10+0.06 −0.04
dex). The velocity dispersion of the system is found to be σv = 2.7+1.3 −1.0 km s−1 after excluding
two potential binary stars. Sgr II’s metallicity and absolute magnitude (MV = −5.7 ± 0.1
mag) place the system on the luminosity–metallicity relation of the Milky Way dwarf galaxies
despite its small size. The low but resolved metallicity and velocity dispersions paint the picture
of a slightly dark-matter-dominated satellite (M/L = 23.0+32.8 −23.0 M L−1
). Furthermore, using
the Gaia Data Release 2, we constrain the orbit of the satellite and find an apocentre of
118.4+28.4 −23.7 kpc and a pericentre of 54.8+3.3 −6.1 kpc. The orbit of Sgr II is consistent with the
trailing arm of the Sgr stream and indicates that it is possibly a satellite of the Sgr dSph that
was tidally stripped from the dwarf’s influence.ES, KY, and AA gratefully acknowledge funding by the Emmy
Noether programme from the Deutsche Forschungsgemeinschaft
(DFG). This work has been published under the framework of the
IdEx Unistra and benefits from a funding from the state managed
by theFrench National Research Agency as part of the investments
for the future program. NFM, RI, and NL gratefully acknowledge
support from the French National Research Agency (ANR) funded
project ‘Pristine’ (ANR-18-CE31-0017) along with funding from
CNRS/INSU through the Programme National Galaxies et Cosmologie and through the CNRS grant PICS07708. The authors
thank the International Space Science Institute (ISSI), Berne,
Switzerland for providing financial support and meeting facilities
to the international team ‘Pristine’. JIGH acknowledges financial
support from the Spanish Ministry project MINECO AYA2017-
86389-P, and from the Spanish MINECO under the 2013 Ramon y ´
Cajal program MINECO RYC-2013-14875.
BPML gratefully acknowledges support from FONDECYT postdoctoral fellowship No. 316051
The First Post-Kepler Brightness Dips of KIC 8462852
We present a photometric detection of the first brightness dips of the unique variable star KIC 8462852 since the end of the Kepler space mission in 2013 May. Our regular photometric surveillance started in October 2015, and a sequence of dipping began in 2017 May continuing on through the end of 2017, when the star was no longer visible from Earth. We distinguish four main 1-2.5% dips, named "Elsie," "Celeste," "Skara Brae," and "Angkor", which persist on timescales from several days to weeks. Our main results so far are: (i) there are no apparent changes of the stellar spectrum or polarization during the dips; (ii) the multiband photometry of the dips shows differential reddening favoring non-grey extinction. Therefore, our data are inconsistent with dip models that invoke optically thick material, but rather they are in-line with predictions for an occulter consisting primarily of ordinary dust, where much of the material must be optically thin with a size scale <<1um, and may also be consistent with models invoking variations intrinsic to the stellar photosphere. Notably, our data do not place constraints on the color of the longer-term "secular" dimming, which may be caused by independent processes, or probe different regimes of a single process
The Pristine Survey – VI. The first three years of medium-resolution follow-up spectroscopy of Pristine EMP star candidates★
We present the results of a 3-year long, medium-resolution spectroscopic campaign aimed at identifying very metal-poor stars from candidates selected with the CaHK, metallicity-sensitive Pristine survey. The catalogue consists of a total of 1007 stars, and includes 146 rediscoveries of metal-poor stars already presented in previous surveys, 707 new very metal-poor stars with [Fe/H]<−2.0, and 95 new extremely metal-poor stars with [Fe/H]<−3.0. We provide a spectroscopic [Fe/H] for every star in the catalogue, and [C/Fe] measurements for a subset of the stars (10% with [Fe/H]<−3 and 24% with −3<[Fe/H]<−2) for which a carbon determination is possible, contingent mainly on the carbon abundance, effective temperature and S/N of the stellar spectra. We find an average carbon enhancement fraction ([C/Fe] ≥ +0.7) of 41 ± 4% for stars with −3<[Fe/H]<−2 and 58 ± 14% for stars with [Fe/H]<−3, and report updated success rates for the Pristine survey of 56 % and 23 % to recover stars with [Fe/H]<−2.5 and [Fe/H]<−3, respectively. Finally, we discuss the current status of the survey and its preparation for providing targets to upcoming multi-object spectroscopic surveys such as WEAVE
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