4 research outputs found
Fluorine Abundances in the Globular Cluster M 4
We present chemical abundances for the elements carbon, sodium, and fluorine
in 15 red giants of the globular cluster M 4, as well as six red giants of the
globular cluster Centauri. The chemical abundances were calculated in
LTE via spectral synthesis. The spectra analyzed are high-resolution spectra
obtained in the near-infrared region around 2.3m with the Phoenix
spectrograph on the 8.1m Gemini South Telescope, the IGRINS spectrograph on the
McDonald Observatory 2.7m Telescope, and the CRIRES spectrograph on the ESO
8.2m Very Large Telescope. The results indicate a significant reduction in the
fluorine abundances when compared to previous values from the literature for M
4 and Centauri, due to a downward revision in the excitation
potentials of the HF(1-0) R9 line used in the analysis. The fluorine abundances
obtained for the M 4 red giants are found to be anti-correlated with those of
Na, following the typical pattern of abundance variations seen in globular
clusters between distinct stellar populations. In M 4, as the Na abundance
increases by +0.4 dex, the F abundance decreases by -0.2 dex. A
comparison with abundance predictions from two sets of stellar evolution models
finds that the models predict somewhat less F depletion (-0.1 dex) for
the same increase of +0.4 dex in Na
Ages and metallicities of stellar clusters using S-PLUS narrow-band integrated photometry: the Small Magellanic Cloud
The Magellanic Clouds are the most massive and closest satellite galaxies of
the Milky Way, with stars covering ages from a few Myr up to 13 Gyr. This makes
them important for validating integrated light methods to study stellar
populations and star-formation processes, which can be applied to more distant
galaxies. We characterized a set of stellar clusters in the Small Magellanic
Cloud (SMC), using the .
This is the first age (metallicity) determination for 11 (65) clusters of this
sample. Through its 7 narrow bands, centered on important spectral features,
and 5 broad bands, we can retrieve detailed information about stellar
populations. We obtained ages and metallicities for all stellar clusters using
the Bayesian spectral energy distribution fitting code .
With a sample of clusters in the color range , for which
our determined parameters are most reliable, we modeled the age-metallicity
relation of SMC. At any given age, the metallicities of SMC clusters are lower
than those of both the Gaia Sausage-Enceladus disrupted dwarf galaxy and the
Milky Way. In comparison with literature values, differences are
log(age) and [Fe/H], which is
comparable to low-resolution spectroscopy of individual stars. Finally, we
confirm a previously known gradient, with younger clusters in the center and
older ones preferentially located in the outermost regions. On the other hand,
we found no evidence of a significant metallicity gradient.Comment: 12 pages, 11 figure
Fluorine Abundances in the Galactic Nuclear Star Cluster
International audienceAbundances of fluorine (19F), as well as isotopic ratios of 16O/17O, are derived in a sample of luminous young (~107-108 yr) red giants in the Galactic center (with galactocentric distances ranging from 0.6-30 pc), using high-resolution infrared spectra and vibration-rotation lines of H19F near λ2.3 Όm. Five of the six red giants are members of the Nuclear star cluster that orbits the central supermassive black hole. Previous investigations of the chemical evolution of 19F in Galactic thin and thick-disk stars have revealed that the nucleosynthetic origins of 19F may be rather complex, resulting from two, or more, astrophysical sites; fluorine abundances behave as a primary element with respect to Fe abundances for thick-disk stars and as a secondary element in thin-disk stars. The Galactic center red giants analyzed fall within the thin-disk relation of F with Fe, having near-solar, to slightly larger, abundances of Fe ( = +0.08 ± 0.04), with a slight enhancement of the F/Fe abundance ratio ( = +0.28 ± 0.17). In terms of their F and Fe abundances, the Galactic center stars follow the thin-disk population, which requires an efficient source of 19F that could be the winds from core-He burning Wolf-Rayet stars, or thermally pulsing AGB stars, or a combination of both. The observed increase of [F/Fe] with increasing [Fe/H] found in thin-disk and Galactic center stars is not predicted by any published chemical evolution models that are discussed, thus a quantitative understanding of yields from the various possible sources of 19F remains unknown
Evidence of deep mixing in IRS 7, a cool massive supergiant member of the Galactic nuclear star cluster
International audienceThe centre of the Milky Way contains stellar populations spanning a range in age and metallicity, with a recent star formation burst producing young and massive stars. Chemical abundances in the most luminous stellar member of the nuclear star cluster (NSC), IRS 7, are presented for 19F, 12C, 13C, 14N, 16O, 17O, and Fe from a local thermodynamic equilibrium analysis based on spherical modelling and radiative transfer with a 25-Mâ model atmosphere, whose chemistry was tailored to the derived photospheric abundances. We find IRS 7 to be depleted heavily in both 12C (~-0.8 dex) and 16O (~-0.4 dex), while exhibiting an extremely enhanced 14N abundance (~+1.1 dex), which are isotopic signatures of the deep mixing of CNO-cycled material to the stellar surface. The 19F abundance is also heavily depleted by ~1 dex relative to the baseline fluorine of the NSC, providing evidence that fluorine along with carbon constrain the nature of the deep mixing in this very luminous supergiant. The abundances of the minor isotopes 13C and 17O are also derived, with ratios of 12C/13C ~ 5.3 and 16O/17O ~ 525. The derived abundances for IRS 7, in conjunction with previous abundance results for massive stars in the NSC, are compared with rotating and non-rotating models of massive stars and it is found that the IRS 7 abundances overall follow the behaviour predicted by stellar models. The depleted fluorine abundance in IRS 7 illustrates, for the first time, the potential of using the 19F abundance as a mixing probe in luminous red giants