Journal Article

Uniform detection of the pre-main-sequence population in the five embedded clusters related to the H <span class="smallCaps">ii</span> region NGC 2174 (Sh2-252)

C. Bonatto and E. Bica

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 414, issue 4, pages 3769-3776
Published in print July 2011 | ISSN: 0035-8711
Published online July 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.18693.x
Uniform detection of the pre-main-sequence population in the five embedded clusters related to the H ii region NGC 2174 (Sh2-252)

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We investigate five embedded clusters (ECs) and the extended stellar group itself of the prominent H ii region NGC 2174 (Sh2-252), which presents scarce and heterogeneous information coming from the optical and infrared. Considering the discrepant values of distance and age, the clusters and the H ii region appear to be physically unrelated. The analysis is based on field-star-decontaminated 2MASS photometry, which allows sampling of the pre-main sequence (PMS). We find that Sh2-252A, C, E, NGC 2175s and Teu 136 are small ECs (radius within 1.0–2.3 pc) characterized by a similar age (∼5 Myr), reddening (AV∼ 1), distance from the Sun (d∼ 1.4 kpc) and low mass (60–200 M). This age is consistent with the H ii region, the presence of O and B stars still in the main sequence (MS) and the dominance (≳95 per cent by number) of PMS stars in the colour–magnitude diagrams (CMDs). NGC 2175 is not a star cluster, but an extended stellar group that encompasses the ECs Sh2-252 A and C. It contains ∼36 per cent of the member stars (essentially PMS) in the area, with the remaining belonging to the two ECs. CMDs of the overall star-forming region and the ECs provide d= 1.4 ± 0.4 kpc for the NGC 2174 complex, consistent with the value estimated for the physically related association Gem OB1. Our uniform approach shows that NGC 2174 and its related ECs (except, perhaps, for Teu 136) are part of a single star-forming complex. CMD similarities among the ECs and with the overall region suggest a coeval (to within ±5 Myr) star-forming event extending for several Myr. At least four ECs originated in the event, together with the off-cluster star formation that probably gave rise to the scattered stars of NGC 2175.

Keywords: open clusters and associations: general; open clusters and associations: individual: NGC 2174 (Sh2-252)

Journal Article.  4946 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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