Negueruela, I.; Simón-Díaz, S.; Lorenzo, J.; Castro, N.; Herrero, A.
Bibliographical reference
Astronomy and Astrophysics, Volume 584, id.A77, 15 pp.
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12
2015
Journal
Citations
11
Refereed citations
9
Description
Context. The young open cluster Dolidze 25, in the direction of the
Galactic anticentre, has been attributed a very low metallicity, with
typical abundances between -0.5 and -0.7 dex below solar. Aims:
We intend to derive accurate cluster parameters and accurate stellar
abundances for some of its members. Methods: We have obtained a
large sample of intermediate- and high-resolution spectra for stars in
and around Dolidze 25. We used the fastwind code to generate stellar
atmosphere models to fit the observed spectra. We derive stellar
parameters for a large number of OB stars in the area, and abundances of
oxygen and silicon for a number of stars with spectral types around B0.
Results: We measure low abundances in stars of Dolidze 25. For
the three stars with spectral types around B0, we find 0.3 dex (Si) and
0.5 dex (O) below the values typical in the solar neighbourhood. These
values, even though not as low as those given previously, confirm
Dolidze 25 and the surrounding H ii region Sh2-284 as the most
metal-poor star-forming environment known in the Milky Way. We derive a
distance 4.5 ± 0.3 kpc to the cluster (rG ≈ 12.3
kpc). The cluster cannot be older than ~3 Myr, and likely is not much
younger. One star in its immediate vicinity, sharing the same distance,
has Si and O abundances at most 0.15 dex below solar.
Conclusions: The low abundances measured in Dolidze 25 are compatible
with currently accepted values for the slope of the Galactic metallicity
gradient, if we take into account that variations of at least
±0.15 dex are observed at a given radius. The area traditionally
identified as Dolidze 25 is only a small part of a much larger
star-forming region that comprises the whole dust shell associated with
Sh2-284 and very likely several other smaller H ii regions in its
vicinity.
Based on observations made with the Nordic Optical Telescope, the
Mercator Telescope, and the telescopes of the Isaac Newton Group.
Related projects
The IACOB project: A new Era in the Study of Galactic OB Stars
IACOB is an ambitious long-term project whose main scientific goal is to provide an unprecedented empirical overview of the main physical properties of Galactic massive O- and B-type stars which can be used as definitive anchor point for our theories of stellar atmospheres, winds, interiors and evolution of massive stars
Sergio
Simón Díaz