69 research outputs found
Discovery of a binary-origin classical Cepheid in a binary system with a 59-day orbital period
We report the discovery of a surprising binary configuration of the
double-mode Cepheid OGLE-LMC-CEP-1347 pulsating in the first (P_1=0.690d) and
second overtone (P_2=0.556d) modes. The orbital period (P_orb=59d) of the
system is five times shorter than the shortest known to date (310d) for a
binary Cepheid. The Cepheid itself is also the shortest-period one ever found
in a binary system and the first double-mode Cepheid in a spectroscopically
double-lined binary. OGLE-LMC-CEP-1347 is most probably on its first crossing
through the instability strip, as inferred from both its short period and fast
period increase, consistent with evolutionary models, and from the short
orbital period (not expected for binary Cepheids whose components have passed
through the red giant phase). Our evolutionary analysis yielded a
first-crossing Cepheid with a mass in a range of 2.9-3.4 Msun (lower than any
measured Cepheid mass), consistent with observations. The companion is a stable
star, at least two times fainter and less massive than the Cepheid (preliminary
mass ratio q=0.55), while also redder and thus at the subgiant or more advanced
evolutionary stage. To match these characteristics, the Cepheid has to be a
product of binary interaction, most likely a merger of two less massive stars,
which makes it the second known classical Cepheid of binary origin. Moreover,
further evolution of the components may lead to another binary interaction.Comment: 6 pages, 4 figures, 1 table, published in The Astrophysical Journal
Letter
Metallicities and ages for 35 star clusters and their surrounding fields in the Small Magellanic Cloud
In this work we study 35 stellar clusters in the Small Magellanic Cloud (SMC)
in order to provide their mean metallicities and ages. We also provide mean
metallicities of the fields surrounding the clusters. We used Str\"omgren
photometry obtained with the 4.1 m SOAR telescope and take advantage of and colors for which there is a metallicity calibration presented in
the literature. The spatial metallicity and age distributions of clusters
across the SMC are investigated using the results obtained by Str\"omgren
photometry. We confirm earlier observations that younger, more metal-rich star
clusters are concentrated in the central regions of the galaxy, while older,
more metal-poor clusters are located farther from the SMC center. We construct
the age-metallicity relation for the studied clusters and find good agreement
with theoretical models of chemical enrichment, and with other literature age
and metallicity values for those clusters. We also provide the mean
metallicities for old and young populations of the field stars surrounding the
clusters, and find the latter to be in good agreement with recent studies of
the SMC Cepheid population. Finally, the Str\"omgren photometry obtained for
this study is made publicly available.Comment: 22 pages, 12 figures, 6 tables, Accepted for publication in A&
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