We present a dynamical measurement of the tangential motion of the Andromeda system, the ensemble consisting of the Andromeda galaxy (M31) and its satellites. The system is modelled as a structure ...with cosmologically motivated velocity dispersion and density profiles, and we show that our method works well when tested using the most massive substructures in high-resolution ... cold dark matter (...CDM) simulations. Applied to the sample of 40 currently known galaxies of this system, we find a value for the velocity along the East and North directions of v sub( East) = -111.5 plus or minus 70.2 km s super( -1) and v sub( North) = 99.4 plus or minus 60.0 km s super( -1), implying a transverse velocity significantly higher than previous estimates of the proper motion of M31 itself. This result has significant implications on estimates of the mass of the Local Group, as well as on its past and future history. (ProQuest: ... denotes formulae/symbols omitted.)
Context.
Thanks to ongoing efforts to compute accurate stellar ages, we are able to characterise stars in different regions of the Milky Way. The
Gaia
and
Kepler
space-missions, along with ...ground-based spectroscopic surveys such as APOGEE, provide a unique way to study the chemo-kinematics relations as a function of age through the Galactic stellar populations and provide new constraints to Galactic evolution models.
Aims.
We investigate the properties of the double sequences of the Milky Way discs visible in the
α
/Fe versus Fe/H diagram, which are usually associated to the chemical thin and thick discs at the solar circle. In the framework of Galactic formation and evolution, we discuss the complex relationships between age, metallicity,
α
/Fe, and the radial, azimuthal, and vertical components of the space velocities.
Methods.
We study stars with measured chemical and seismic properties from the APOGEE spectroscopic survey and the
Kepler
satellite, respectively. In addition, astrometry from the
Gaia
satellite is available for the majority of the sample. We separate the
α
/Fe−Fe/H diagram into three stellar populations: the thin disc, the high-
α
metal-poor thick disc, and the high-
α
metal-rich thick disc and characterise each of these in the age-chemo-kinematics parameter space. Because of the model-dependent nature of the ages inferred from asteroseismology, and because they depend on the quality of the input spectroscopic information, we compare results obtained from different APOGEE data releases (DR14 and DR16). We also use age determinations from two recent works in the literature. In addition, we use the Besançon stellar populations synthesis model to highlight selection biases and mechanisms (such as mergers and secular evolution) not included in the model.
Results.
The thin disc exhibits a flat age–metallicity relation while
α
/Fe increases with stellar age. We confirm no correlation between radial and vertical velocities with Fe/H,
α
/Fe, and age for each stellar population. Considering both samples,
V
φ
decreases with age for the thin disc, while
V
φ
increases with age for the high-
α
metal-poor thick disc. We show that this difference is not due to sample selection. Although the age distribution of the high-
α
metal-rich thick disc is very close to that of the high-
α
metal-poor thick disc between 7 and 14 Gyr, its kinematics seems to follow that of the thin disc. This feature, not predicted by the hypotheses included in the Besançon Galaxy Model, suggests a different origin and history for this population. Finally, we show that there is a maximum dispersion of the vertical velocity,
σ
Z
, with age for the high-
α
metal-poor thick disc around 8 Gyr. The comparisons with the Besançon Galaxy Model simulations suggest a more complex chemo-dynamical scheme to explain this feature, most likely including mergers and radial migration effects.
ABSTRACT
We present an analysis of the proper motion of the Andromeda galaxy (M31), based on the Early Third Data Release of the Gaia mission. We use the Gaia photometry to select young blue ...main-sequence stars and apply several quality cuts to obtain clean samples of these tracers. After correcting the proper motion measurements for the internal rotation of the M31 disc motion, we derive an apparent motion of $52.5 \pm 5.8{\rm \, \mu as\,yr^{-1}}$ with respect to the Gaia reference frame, or $61.9 \pm 9.7{\rm \, \mu as\,yr^{-1}}$ after applying a zero-point correction determined from quasars within 20° from M31 and a correction from systemic biases. Accounting for the Solar reflex motion, we deduce a relative velocity between Andromeda and the Milky way (in a non-rotating frame at the current location of the Sun) of $42.2 \pm 39.3 {\rm \, km\, s^{-1}}$ along right ascension ($40.0 \pm 39.3 {\rm \, km\, s^{-1}}$ along galactic longitude) and $-59.4 \pm 30.3 {\rm \, km\, s^{-1}}$ along declination ($-60.9 \pm 30.3 {\rm \, km\, s^{-1}}$ along galactic latitude), with a total transverse velocity of $V_{\rm trans} = 82.4 \pm 31.2 {\rm \, km\, s^{-1}}$. These values are consistent with (but more accurate than) earlier Hubble Space Telescope measurements that predict a future merger between the two galaxies. We also note a surprisingly large difference in the derived proper motion between the blue stars in M31 and samples of red stars that appear to lie in that galaxy. We propose several hypotheses to explain the discrepancy but found no clear evidence with the current data to privilege any one of them.
We present a study of the intrinsic deprojected ellipticity distribution of the satellite dwarf galaxies of the Andromeda galaxy, assuming that their visible components have a prolate shape, which is ...a natural outcome of simulations. Different possibilities for the orientation of the major axis of the prolate dwarf galaxies are tested, pointing either as close as possible to the radial direction towards the centre of Andromeda, or tangential to the radial direction, or with a random angle in the plane that contains the major axis and the observer. We find that the mean intrinsic axis ratio is ∼1/2, with small differences depending on the assumed orientation of the population. Our deprojections also suggest that a significant fraction of the satellites, ∼10 per cent, are tidally disrupted remnants. We find that there is no evidence of any obvious difference in the morphology and major axis orientation between satellites that belong to the vast thin plane of corotating galaxies around Andromeda and those that do not belong to this structure.
In anticipation of the Gaia astrometric mission, a large sample of spectroscopic binaries has been observed since 2010 with the Sophie spectrograph at the Haute–Provence Observatory. Our aim is to ...derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient finally to obtain the masses of the components with relative errors as small as 1 per cent when the astrometric measurements of Gaia are taken into account. Simultaneously, the luminosities of the components in the Gaia photometric band G will also be obtained. Our observation program started with 200 SBs, including 152 systems that were only known as single-lined. Thanks to the high efficiency of the Sophie spectrograph, an additional component was found for 25 SBs. After rejection of five multiple systems, 20 new SB2s were retained, including eight binaries with an evolved primary, and their mass ratios were derived. Our final sample contains 68 SB2s, including two late-type giants and 10 other evolved stars.
The process of crop domestication began 10,000 years ago in the transition of early humans from hunter/gatherers to pastoralists/farmers. Recent research has revealed the identity of some of the main ...genes responsible for domestication. Two of the major domestication events in barley were (i) the failure of the spike to disarticulate and (ii) the six-rowed spike. The former mutation increased grain yield by preventing grain loss after maturity, while the latter resulted in an up to 3-fold increase in yield potential. Here we provide an overview of the disarticulation systems and inflorescence characteristics, along with the genes underlying these traits, occurring in the Triticeae tribe.
In anticipation of the Gaia astrometric mission, a large sample of spectroscopic binaries has been observed since 2010 with the Spectrographe pour l'Observation des PHénomènes des Intérieurs ...Stellaires et des Exoplanètes spectrograph at the Haute–Provence Observatory. Our aim is to derive the orbital elements of double-lined spectroscopic binaries (SB2s) with an accuracy sufficient to finally obtain the masses of the components with relative errors as small as 1 per cent when the astrometric measurements of Gaia are taken into account. In this paper, we present the results from five years of observations of 10 SB2 systems with periods ranging from 37 to 881 d. Using the todmor algorithm, we computed radial velocities from the spectra, and then derived the orbital elements of these binary systems. The minimum masses of the components are then obtained with an accuracy better than 1.2 per cent for the 10 binaries. Combining the radial velocities with existing interferometric measurements, we derived the masses of the primary and secondary components of HIP 87895 with an accuracy of 0.98 and 1.2 per cent, respectively.
ABSTRACT
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 per cent 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 four other stars, we finally obtain the masses of the components of five 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.
Recent advances in the understanding of T cell activation have led to new
therapeutic approaches in the treatment of immunological disorders. One
attractive target of intervention has been the ...blockade of T cell costimulatory
pathways, which result in more selective effects on only those T cells that
have encountered specific antigen. In fact, in some instances, costimulatory
pathway antagonists can induce antigen-specific tolerance that prevents the
progression of autoimmune diseases and organ graft rejection. In this review,
we summarize the current understanding of these complex costimulatory pathways
including the individual roles of the CD28, CTLA-4, B7-1 (CD80), and B7-2
(CD86) molecules. We present evidence that suggests that multiple mechanisms
contribute to CD28/B7-mediated T cell costimulation in disease settings that
include expansion of activated pathogenic T cells, differentiation of Th1/Th2
cells, and the migration of T cells into target tissues. Additionally, the
negative regulatory role of CTLA-4 in autoimmune diseases and graft rejection
supports a dynamic but complex process of immune regulation that is prominent
in the control of self-reactivity. This is most apparent in regulation of the
CD4
+
CD25
+
CTLA-4
+
immunoregulatory T cells that control multiple autoimmune diseases. The
implications of these complexities and the potential for use of these therapies
in clinical immune intervention are discussed.
This work presents the upscaling of the tunnel IBC technology on large area, Czochralski (Cz) n-type wafers. At the junction level, a self-aligned PECVD masking technology has been developed for the ...deposition of hydrogenated nano-crystalline silicon (nc-Si:H) layers on industrial 6-inch pseudo-square wafers. This damage free patterning technology allows state-of-the-art passivation with a minority carrier lifetime of 9 ms at an injection level of 1015 cm-3, thus enabling extremely long diffusion lengths up to several millimetres. The use of indium-free, cost effective aluminium-doped zinc oxide strongly reduces the materials bill of the tunnel-IBC technology while maintaining very low contact resistance for both the electron and the hole contacts. Remarkably, these tunnel-IBC devices demonstrated a conversion efficiency of 25% on large area (90.25 cm2) industrial wafer with a thickness of 155 μm. Series resistance analysis points out probable losses from the hole contact and the base. The limitation of the Transfer Length Method is discussed when used to extract the hole contact resistance.
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