210 research outputs found
Na-O anticorrelation and HB. IX. Kinematics of the program clusters. A link between systemic rotation and HB morphology?
We use accurate radial velocities for 1981 member stars in 20 Galactic
globular clusters, collected within our large survey aimed at the analysis of
the Na-O anti-correlation, to study the internal kinematics of the clusters. We
performed the first systematic exploration of the possible connections between
cluster kinematics and the multiple populations phenomenon in GCs. We did not
find any significant correlation between Na abundance and either velocity
dispersion or systemic rotation. We searched for systemic rotation in the eight
clusters of our sample that lack such analysis from previous works in the
literature (NGC2808, NGC5904, NGC6171, NGC6254, NGC6397, NGC6388, NGC6441, and
NGC6838). These clusters are found to span a large range of rotational
amplitudes, from ~0.0 km/s (NGC6397) to ~13.0 km/s (NGC6441). We found a
significant correlation between the ratio of rotational velocity to central
velocity dispersion (V_{rot}/sigma_0) and the Horizontal Branch Morphology
parameter (B-R)/(B+R+V). V_{rot}/sigma_0 is found to correlate also with
metallicity, possibly hinting to a significant role of dissipation in the
process of formation of globular clusters. V_{rot} is found to correlate well
with (B-R)/(B+R+V), M_V, sigma_0 and [Fe/H]. All these correlations strongly
suggest that systemic rotation may be intimately linked with the processes that
led to the formation of globular clusters and the stellar populations they
host.Comment: Accepted for publication on Astronomy & Astrophysics. Pdflatex, 16
pages, 16 pdf figures. The position angles of the rotation axes have been
corrected, since the values reported in the previous version were erroneous.
The results of the analysis are unchanged. The manuscript has also been
processed by a language edito
The normal chemistry of multiple stellar populations in the dense globular cluster NGC 6093 (M 80)
We present the abundance analysis of 82 red giant branch stars in the dense,
metal-poor globular cluster NGC 6093 (M 80), the largest sample of stars
analyzed in this way for this cluster. From high resolution UVES spectra of 14
stars and intermediate resolution GIRAFFE spectra for the other stars we
derived abundances of O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,
Zn, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu. On our UVES metallicity scale the mean
metal abundance of M 80 is [Fe/H]=-1.791+/-0.006+/-0.076 (+/-statistical
+/-systematic error) with rms=0.023 (14 stars). M 80 shows star to star
variations in proton-capture elements, and the extension of the Na-O
anticorrelation perfectly fit the relations with (i) total cluster mass, (ii)
horizontal branch morphology, and (iii) cluster concentration previously found
by our group. The chemistry of multiple stellar populations in M 80 does not
look extreme. The cluster is also a typical representative of halo globular
clusters for what concerns the pattern of alpha-capture and Fe-group elements.
However we found that a significant contribution from the s-process is required
to account for the distribution of neutron-capture elements. A minority of
stars in M 80 seem to exhibit slightly enhanced abundances of s-process
species, compatible with those observed in M 22 and NGC 1851, although further
confirmation from larger samples is required.Comment: 18 pages, 21 figures, 10 tables; accepted for publication on
Astronomy and Astrophysic
The extreme chemistry of multiple stellar populations in the metal-poor globular cluster NGC 4833
Our FLAMES survey of Na-O anticorrelation in globular clusters (GCs) is
extended to NGC 4833, a metal-poor GC with a long blue tail on the horizontal
branch (HB). We present the abundance analysis for a large sample of 78 red
giants based on UVES and GIRAFFE spectra acquired at the ESO-VLT. We derived
abundances of Na, O, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y,
Ba, La, Nd. This is the first extensive study of this cluster from high
resolution spectroscopy. On the scale of our survey, the metallicity of NGC
4833 is [Fe/H]=-2.015+/-0.004+/-0.084 dex (rms=0.014 dex) from 12 stars
observed with UVES, where the first error is from statistics and the second one
refers to the systematic effects. The iron abundance in NGC 4833 is homogeneous
at better than 6%. On the other hand, the light elements involved in
proton-capture reactions at high temperature show the large star-to-star
variations observed in almost all GCs studied so far. The Na-O anticorrelation
in NGC 4833 is quite extended, as expected from the high temperatures reached
by stars on the HB, and NGC 4833 contains a conspicuous fraction of stars with
extreme [O/Na] ratios. More striking is the finding that large star-to-star
variations are seen also for Mg, which spans a range of more than 0.5 dex in
this GC. Depletions in Mg are correlated to the abundances of O and
anti-correlated with Na, Al, and Si abundances. This pattern suggests the
action of nuclear processing at unusually high temperatures, producing the
extreme chemistry observed in the stellar generations of NGC 4833. This extreme
changes are also seen in giants of the much more massive GCs M 54 and omega
Cen, and our conclusion is that NGC 4833 has probably lost a conpicuous
fraction of its original mass due to bulge shocking, as also indicated by its
orbit.Comment: 18 pages, 16 figures, 11 tables; accepted for publication on
Astronomy and Astrophysic
NGC 362: another globular cluster with a split red giant branch
We obtained FLAMES GIRAFFE+UVES spectra for both first and second-generation
red giant branch (RGB) stars in the globular cluster (GC) NGC 362 and used them
to derive abundances of 21 atomic species for a sample of 92 stars. The
surveyed elements include proton-capture (O, Na, Mg, Al, Si), alpha-capture
(Ca, Ti), Fe-peak (Sc, V, Mn, Co, Ni, Cu), and neutron-capture elements (Y, Zr,
Ba, La, Ce, Nd, Eu, Dy). The analysis is fully consistent with that presented
for twenty GCs in previous papers of this series. Stars in NGC 362 seem to be
clustered into two discrete groups along the Na-O anti-correlation, with a gap
at [O/Na] 0 dex. Na-rich, second generation stars show a trend to be more
centrally concentrated, although the level of confidence is not very high. When
compared to the classical second-parameter twin NGC 288, with similar
metallicity, but different horizontal branch type and much lower total mass,
the proton-capture processing in stars of NGC 362 seems to be more extreme,
confirming previous analysis. We discovered the presence of a secondary RGB
sequence, redder than the bulk of the RGB: a preliminary estimate shows that
this sequence comprises about 6% of RGB stars. Our spectroscopic data and
literature photometry indicate that this sequence is populated almost
exclusively by giants rich in Ba, and probably rich in all s-process elements,
as found in other clusters. In this regards, NGC 362 joins previously studied
GCs like NGC 1851, NGC 6656 (M 22), and NGC 7089 (M 2).Comment: 16 pages, 23 figures, 11 tables, accepted for publication on
Astronomy and Astrophysic
Discovery of Carbon/Oxygen depleted Blue Straggler Stars in 47 Tucanae: the chemical signature of a mass-transfer formation process
We use high-resolution spectra obtained with the ESO Very Large Telescope to
measure surface abundance patterns of 43 Blue Stragglers stars (BSS) in 47 Tuc.
We discovered that a sub-population of BSS shows a significant depletion of
Carbon and Oxygen with respect to the dominant population. This evidence would
suggest the presence of CNO burning products on the BSS surface coming from a
deeply peeled parent star, as expected in the case of mass-transfer process.
This is the first detection of a chemical signature clearly pointing to a
specific BSS formation process in a globular cluster.Comment: Published on 2006, August 10, in ApJ 647, L5
Improved Line Data for the Swan System 12C13C Isotopologue
We present new, accurate predictions for rotational line positions, excitation energies, and transition probabilities of the 12C 13C isotopologue Swan d3Π-a3Πsystem 0-0, 0-1, 0-2, 1-0, 1-1, 1-2, 2-0, 2-1, and 2-2 vibrational bands. The line positions and energy levels were predicted through new analyses of published laboratory data for the 12C13C lines. Transition probabilities were derived from recent computations of transition dipole moments and related quantities. The 12C13C line data were combined with similar data for 12C2, reported in a companion paper, and applied to produce synthetic spectra of carbon-rich metal-poor stars that have strong C2 Swan bands. The matches between synthesized and observed spectra were used to estimate band head positions for a few of the 12C13C vibrational bands and to verify that the new computed line data match observed spectra. The much weaker C2 lines of the bright red giant Arcturus were also synthesized in the band head regions. © 2014. The American Astronomical Society
The Magnesium Isotopologues of MgH in the A2Î -X 2ÎŁ+ System
Using laboratory hollow cathode spectra we have identified lines of the less common magnesium isotopologues of MgH, 25MgH and 26MgH, in the A2Π-X2Σ+ system. Based on the previous analysis of 24MgH, molecular lines have been measured and molecular constants derived for 25MgH and 26MgH. Term values and linelists, in both wavenumber and wavelength units, are presented. The A2Π-X2Σ+ system of MgH is important for measuring the magnesium isotope ratios in stars. Examples of analysis using the new linelists to derive the Mg isotope ratio in a metal poor dwarf and giant are shown. © 2013. The American Astronomical Society
Precise reddening and metallicity of NGC6752 from FLAMES spectra
(abridged) Accurate reddenings for Globular Clusters could be obtained by
comparing the colour-temperature obtained using temperatures from
reddening-free indicator (Halpha), with that given by standard
colour-temperature calibrations. From a single 1300 seconds exposure with
FLAMES at VLT2 we obtained spectra centred on Halpha (R=6000, 5<S/N<50) for 120
stars near the turn-off of NGC6752. This set of spectra was used to derive
effective temperatures from fittings of Halpha profiles with typical errors of
about +/- 200 K and reddening estimates with individual errors of 0.05 mag.
Averaging all individual reddenings, a high precision reddening estimate has
been obtained for the cluster: E(B-V)=0.046 +/- 0.005. The same exposure
provided UVES spectra of seven stars near the red giant branch bump (R=40000,
20<S/N<40) that provided Fe abundances with internal errors of 0.026 dex, and
with average metallicity [Fe/H]= -1.48 +/- 0.01 +/- 0.06 dex (random +
systematic). Abundances were obtained for several other elements, allowing e.g.
an accurate estimate of the ratio between the alpha-elements and Fe
([alpha/Fe]=+0.27 +/- 0.01). The O-Na anticorrelation is evident from our UVES
data, in agreement with past results. This analysis shows the power of FLAMES
for analysis of globular clusters: the accurate reddenings and metal abundances
obtained by a procedure like that described here, combined with distance
determinations from cluster dynamics or main sequence fitting, and high quality
colour-magnitude diagrams, could allow derivation of ages with errors below 1
Gyr for individual globular clusters.Comment: accepted for publication on A&
Boo-1137 - An Extremely Metal-Poor Star in the Ultra-Faint Dwarf Spheroidal Galaxy Bo\"{o}tes I
We present high-resolution, high-S/N spectra of an extremely metal- poor
giant star Boo-1137 in the "ultra-faint" dwarf spheroidal galaxy (dSph) Bootes
I (absolute magnitude Mv ~ -6.3). With [Fe/H] = -3.7, this the most metal-poor
star yet identified in an ultra-faint dSph.
Comparison of relative abundances, [X/Fe], for some 15 elements with those of
the extremely metal-poor giants of the Galactic halo shows Boo-1137 is "normal"
with respect to C and N, the odd-Z elements Na and Al, the Fe-peak elements,
and the n-capture elements Sr and Ba, in comparison with the bulk of the halo
with [Fe/H] < -3.0. The alpha- elements Mg, Si, Ca, and Ti are all higher by
Delta[X/Fe] ~ 0.2 than average halo values. Monte-Carlo analysis indicates
Delta[alpha/Fe] values this large are expected with probability ~ 0.02. The
abundance pattern in Boo-1137 suggests inhomogeneous chemical evolution,
consistent with the wide internal spread in Fe abundances we reported earlier.
The similarity of most of the Boo-1137 relative abundances with respect to halo
values, and the fact that the alpha-elements are all offset by a similar small
amount from the halo averages, points to the same underlying galaxy-scale
stellar initial mass function, but that Boo-1137 likely originated in a
star-forming region where the abundances reflect either poor mixing of
supernova (SN) ejecta, or poor sampling of the SN progenitor mass range, or
both.Comment: 33 pages, 6 figures, submitted to Astrophysical Journa
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