350 research outputs found
The Gaia-ESO Survey: membership and initial mass function of the. Velorum cluster
Context. Understanding the properties of young open clusters, such as the Initial Mass Function (IMF), star formation history and dynamic evolution, is crucial to obtain reliable theoretical predictions of the mechanisms involved in the star formation process.
Aims. We want to obtain a list, as complete as possible, of confirmed members of the young open cluster Îł Velorum, with the aim of deriving general cluster properties such as the IMF.
Methods. We used all available spectroscopic membership indicators within the Gaia-ESO public archive together with literature photometry and X-ray data and, for each method, we derived the most complete list of candidate cluster members. Then, we considered photometry, gravity and radial velocities as necessary conditions to select a subsample of candidates whose membership was confirmed by using the lithium and Hα lines and X-rays as youth indicators.
Results.We found 242 confirmed and 4 possible cluster members for which we derived masses using very recent stellar evolutionary models. The cluster IMF in the mass range investigated in this study shows a slope of α = 2.6 ± 0.5 for 0.5 < M/Mâ < 1.3 and α = 1.1 ± 0.4 for 0.16 < M/Mâ < 0.5 and is consistent with a standard IMF.
Conclusions. The similarity of the IMF of the young population around Îł2Vel to that in other star forming regions and the field suggests it may have formed through very similar processes
Gaia-ESO Survey: Gas dynamics in the Carina nebula through optical emission lines
Aims. We present observations from the Gaia-ESO Survey in the lines of Hα, [N II], [S II] and He I of nebular emission in the central part of the Carina Nebula.
Methods. We investigate the properties of the two already known kinematic components (approaching and receding, respectively), which account for the bulk of emission. Moreover, we investigate the features of the much less known low-intensity high-velocity (absolute RV >50 km/s) gas emission.
Results. We show that gas giving rise to Hα and He I emission is dynamically well correlated, but not identical, to gas seen through forbidden-line emission. Gas temperatures are derived from line-width ratios, and densities from [S II] doublet ratios. The spatial variation of N ionization is also studied, and found to differ between the approaching and receding components. The main result is that the bulk of the emission lines in the central part of Carina arises from several distinct shell-like expanding regions, the most evident found around η Car, the Trumpler 14 core, and the starWR25. Such âshells" are non-spherical, and show distortions probably caused by collisions with other shells or colder, higher-density gas. Part of them is also obscured by foreground dust lanes, while only very little dust is found in their interior. Preferential directions, parallel to the dark dust lanes, are found in the shell geometries and physical properties, probably related to strong density gradients in the studied region. We also find evidence that the ionizing flux emerging from η Car and the surrounding Homunculus nebula varies with polar angle. The high-velocity components in the wings of Hα are found to arise from expanding dust reflecting the η Car spectrum
The Gaia-ESO Survey: a kinematical and dynamical study of four young open clusters
Context.
The origin and dynamical evolution of star clusters is an important topic in stellar astrophysics. Several models have been
proposed to understand the formation of bound and unbound clusters and their evolution, and these can be tested by examining the
kinematical and dynamical properties of clusters over a wide range of ages and masses.
Aims.
We use the
Gaia
-ESO Survey products to study four open clusters (IC 2602, IC 2391, IC 4665, and NGC 2547) that lie in the
age range between 20 and 50 Myr.
Methods.
We employ the gravity index
Îł
and the equivalent width of the lithium line at 6708 Ă
, together with e
ff
ective temperature
T
e
ff
, and the metallicity of the stars in order to discard observed contaminant stars. Then, we derive the cluster radial velocity disper-
sions
Ï
c
, the total cluster mass M
tot
, and the half mass radius
r
hm
. Using the
Gaia
-DR1 TGAS catalogue, we independently derive the
intrinsic velocity dispersion of the clusters from the astrometric parameters of cluster members.
Results.
The intrinsic radial velocity dispersions derived by the spectroscopic data are larger than those derived from the TGAS data,
possibly due to the di
ff
erent masses of the considered stars. Using M
tot
and
r
hm
we derive the virial velocity dispersion
Ï
v
ir
and we
find that three out of four clusters are supervirial. This result is in agreement with the hypothesis that these clusters are dispersing, as
predicted by the "residual gas expulsion" scenario. However, recent simulations show that the virial ratio of young star clusters may
be overestimated if it is determined using the global velocity dispersion, since the clusters are not fully relaxed
Phosphorylation of Rab-coupling protein by LMTK3 controls Rab14-dependent EphA2 trafficking to promote cell:cell repulsion
The Rab GTPase effector, Rab-coupling protein (RCP) is known to promote invasive behaviour in vitro by controlling integrin and receptor tyrosine kinase (RTK) trafficking, but how RCP influences metastasis in vivo is unclear. Here we identify an RTK of the Eph family, EphA2, to be a cargo of an RCP-regulated endocytic pathway which controls cell:cell repulsion and metastasis in vivo. Phosphorylation of RCP at Ser435 by Lemur tyrosine kinase-3 (LMTK3) and of EphA2 at Ser897 by Akt are both necessary to promote Rab14-dependent (and Rab11-independent) trafficking of EphA2 which generates cell:cell repulsion events that drive tumour cells apart. Genetic disruption of RCP or EphA2 opposes cell:cell repulsion and metastasis in an autochthonous mouse model of pancreatic adenocarcinomaâwhereas conditional knockout of another RCP cargo, α5 integrin, does not suppress pancreatic cancer metastasisâindicating a role for RCP-dependent trafficking of an Eph receptor to drive tumour dissemination in vivo
The Gaia-ESO Survey: evidence of atomic diffusion in M67?
Investigating the chemical homogeneity of stars born from the same molecular cloud at virtually the same time is very important for our understanding of the chemical enrichment of the interstellar medium and with it the chemical evolution of the Galaxy. One major cause of inhomogeneities in the abundances of open clusters is stellar evolution of the cluster members. In this work, we investigate variations in the surface chemical composition of member stars of the old open cluster M67 as a possible consequence of atomic diffusion effects taking place during the main-sequence phase. The abundances used are obtained from high-resolution UVES/FLAMES spectra within the framework of the Gaia-ESO Survey. We find that the surface abundances of stars on the main sequence decrease with increasing mass reaching a minimum at the turn-off. After deepening of the convective envelope in subgiant branch stars, the initial surface abundances are restored. We found the measured abundances to be consistent with the predictions of stellar evolutionary models for a cluster with the age and metallicity of M67. Our findings indicate that atomic diffusion poses a non-negligible constraint on the achievable precision of chemical tagging methods
The Gaia-ESO Survey: The inner disk, intermediate-age open cluster Trumpler 23
Milky Way open clusters are very diverse in terms of age, chemical
composition, and kinematic properties. Intermediate-age and old open clusters
are less common, and it is even harder to find them inside the solar
Galactocentric radius, due to the high mortality rate and strong extinction
inside this region. NGC 6802 is one of the inner disk open clusters (IOCs)
observed by the -ESO survey (GES). This cluster is an important target
for calibrating the abundances derived in the survey due to the kinematic and
chemical homogeneity of the members in open clusters. Using the measurements
from -ESO internal data release 4 (iDR4), we identify 95 main-sequence
dwarfs as cluster members from the GIRAFFE target list, and eight giants as
cluster members from the UVES target list. The dwarf cluster members have a
median radial velocity of km s, while the giant cluster
members have a median radial velocity of km s and a median
[Fe/H] of dex. The color-magnitude diagram of these cluster
members suggests an age of Gyr, with and
. We perform the first detailed chemical abundance analysis of NGC
6802, including 27 elemental species. To gain a more general picture about
IOCs, the measurements of NGC 6802 are compared with those of other IOCs
previously studied by GES, that is, NGC 4815, Trumpler 20, NGC 6705, and
Berkeley 81. NGC 6802 shows similar C, N, Na, and Al abundances as other IOCs.
These elements are compared with nucleosynthetic models as a function of
cluster turn-off mass. The , iron-peak, and neutron-capture elements
are also explored in a self-consistent way
The Gaia-ESO Survey: A lithium-rotation connection at 5 Myr?
Context. The evolution of lithium abundance in cool dwarfs provides a unique probe of non-standard processes in stellar evolution.
Aims. We investigate here the lithium content of young low-mass stars in the 5 Myr-old star forming region NGC 2264 and its relationship with rotation.
Methods. We combine lithium equivalent width measurements (EW(Li)) from the Gaia-ESO Survey with the determination of rotational periods from the CSI 2264 survey.We consider only bona fide non accreting cluster members in order to minimize uncertainties on EW(Li).
Results. We report the existence of a relationship between lithium content and rotation in NGC 2264 at an age of 5 Myr. The Lirotation connection is seen over a restricted temperature range (Te_=3800â4400 K) where fast rotators are Li-rich compared to slow ones. This correlation is similar to, albeit of lower amplitude than, the Li-rotation connection previously reported for K dwarfs in the 125 Myr-old Pleiades cluster. We investigate whether the non-standard pre-main sequence models developed so far to explain the
Pleiades results, which are based on episodic accretion, pre-main sequence core-envelope decoupling, and/or radius inflation due to enhanced magnetic activity, can account for an early development of the Li-rotation connection. While radius inflation appears to be the most promising possibility, each of these models has issues. We therefore also discuss external causes that might operate during the first few Myr of pre-main sequence evolution, such as planet engulfment and/or steady disk accretion, as possible candidates for the common origin for Li-excess and fast rotation in young low-mass pre-main sequence stars.
Conclusions. The emergence of a connection between lithium content and rotation rate at such an early age as 5 Myr suggests a complex link between accretion processes, early angular momentum evolution, and possibly planet formation, which likely impactsearly stellar evolution and still is to be fully deciphered
Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector
The inclusive and dijet production cross-sections have been measured for jets
containing b-hadrons (b-jets) in proton-proton collisions at a centre-of-mass
energy of sqrt(s) = 7 TeV, using the ATLAS detector at the LHC. The
measurements use data corresponding to an integrated luminosity of 34 pb^-1.
The b-jets are identified using either a lifetime-based method, where secondary
decay vertices of b-hadrons in jets are reconstructed using information from
the tracking detectors, or a muon-based method where the presence of a muon is
used to identify semileptonic decays of b-hadrons inside jets. The inclusive
b-jet cross-section is measured as a function of transverse momentum in the
range 20 < pT < 400 GeV and rapidity in the range |y| < 2.1. The bbbar-dijet
cross-section is measured as a function of the dijet invariant mass in the
range 110 < m_jj < 760 GeV, the azimuthal angle difference between the two jets
and the angular variable chi in two dijet mass regions. The results are
compared with next-to-leading-order QCD predictions. Good agreement is observed
between the measured cross-sections and the predictions obtained using POWHEG +
Pythia. MC@NLO + Herwig shows good agreement with the measured bbbar-dijet
cross-section. However, it does not reproduce the measured inclusive
cross-section well, particularly for central b-jets with large transverse
momenta.Comment: 10 pages plus author list (21 pages total), 8 figures, 1 table, final
version published in European Physical Journal
The Gaia -ESO Survey: The origin and evolution of s -process elements
Several works have found an increase of the abundances of the s-process
neutron-capture elements in the youngest Galactic stellar populations, giving
important constraints to stellar and Galactic evolution. We aim to trace the
abundance patterns and the time-evolution of five s-process elements in the
first peak, Y and Zr, and in the second peak, Ba, La and Ce using the Gaia-ESO
idr5 results. From the UVES spectra of cluster member stars, we determined the
average composition of clusters with ages >0.1 Gyr. We derived statistical ages
and distances of field stars, and we separated them in thin and thick disc
populations. We studied the time evolution and dependence on metallicity of
abundance ratios using open clusters and field stars. Using our large and
homogeneous sample of open clusters, thin and thick disc stars, spanning an age
range larger than 10 Gyr, we confirm an increase towards young ages of
s-process abundances in the Solar neighbourhood. These trends are well defined
for open clusters and stars located nearby the solar position and they may be
explained by a late enrichment due to significant contribution to the
production of these elements from long-living low-mass stars. At the same time,
we found a strong dependence of the s-process abundance ratios with the
Galactocentric distance and with the metallicity of the clusters and field
stars. Our results, derived from the largest and homogeneous sample of
s-process abundances in the literature, confirm the growth with decreasing
stellar ages of the s-process abundances in both field and open cluster stars.
At the same time, taking advantage of the abundances of open clusters located
in a wide Galactocentric range, they open a new view on the dependence of the
s-process evolution on the metallicity and star formation history, pointing to
different behaviours at various Galactocentric distances
Observation of associated near-side and away-side long-range correlations in âsNN=5.02ââTeV proton-lead collisions with the ATLAS detector
Two-particle correlations in relative azimuthal angle (ÎÏ) and pseudorapidity (Îη) are measured in âsNN=5.02ââTeV p+Pb collisions using the ATLAS detector at the LHC. The measurements are performed using approximately 1ââÎŒb-1 of data as a function of transverse momentum (pT) and the transverse energy (ÎŁETPb) summed over 3.1<η<4.9 in the direction of the Pb beam. The correlation function, constructed from charged particles, exhibits a long-range (2<|Îη|<5) ânear-sideâ (ÎÏâŒ0) correlation that grows rapidly with increasing ÎŁETPb. A long-range âaway-sideâ (ÎÏâŒÏ) correlation, obtained by subtracting the expected contributions from recoiling dijets and other sources estimated using events with small ÎŁETPb, is found to match the near-side correlation in magnitude, shape (in Îη and ÎÏ) and ÎŁETPb dependence. The resultant ÎÏ correlation is approximately symmetric about Ï/2, and is consistent with a dominant cosâĄ2ÎÏ modulation for all ÎŁETPb ranges and particle pT
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