Red supergiants around the obscured open cluster Stephenson 2
Contribuinte(s) |
Universidad de Alicante. Departamento de Física, Ingeniería de Sistemas y Teoría de la Señal Astrofísica Estelar (AE) |
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Data(s) |
13/11/2013
13/11/2013
19/10/2012
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Resumo |
Context. Several clusters of red supergiants have been discovered in a small region of the Milky Way close to the base of the Scutum-Crux Arm and the tip of the Long Bar. Population synthesis models indicate that they must be very massive to harbour so many supergiants. Amongst these clusters, Stephenson 2, with a core grouping of 26 red supergiants, is a strong candidate to be the most massive young cluster in the Galaxy. Aims. Stephenson 2 is located close to a region where a strong over-density of red supergiants had been found. We explore the actual cluster size and its possible connection to this over-density. Methods. Taking advantage of Virtual Observatory tools, we have performed a cross-match between the DENIS, USNO-B1 and 2MASS catalogues to identify candidate obscured luminous red stars around Stephenson 2, and in a control nearby region. More than 600 infrared bright stars fulfill our colour criteria, with the vast majority having a counterpart in the I band and >400 being sufficiently bright in I to allow observation with a 4-m class telescope. We observed a subsample of ~250 stars, using the multi-object, wide-field, fibre spectrograph AF2 on the WHT telescope in La Palma, obtaining intermediate-resolution spectroscopy in the 7500–9000 Å range. We derived spectral types and luminosity classes for all these objects and measured their radial velocities. Results. Our targets turned out to be G and K supergiants, late (≥ M4) M giants, and M-type bright giants (luminosity class II) and supergiants. We found ~35 red supergiants with radial velocities similar to Stephenson 2 members, spread over the two areas surveyed. In addition, we found ~40 red supergiants with radial velocities incompatible in principle with a physical association. Conclusions. Our results show that Stephenson 2 is not an isolated cluster, but part of a huge structure likely containing hundreds of red supergiants, with radial velocities compatible with the terminal velocity at this Galactic longitude (and a distance ~6 kpc). In addition, we found evidence of several populations of massive stars at different distances along this line of sight. This research is partially supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) under grants AYA2010-21697-C05-05, AYA2011-24052 and CSD2006-70, and by the Generalitat Valenciana (ACOMP/2012/134). |
Identificador |
Astronomy & Astrophysics. 2012, 547: A15. doi:10.1051/0004-6361/201219540 0004-6361 (Print) 1432-0746 (Online) http://hdl.handle.net/10045/33808 10.1051/0004-6361/201219540 |
Idioma(s) |
eng |
Publicador |
EDP Sciences |
Relação |
http://dx.doi.org/10.1051/0004-6361/201219540 |
Direitos |
© ESO, 2012 info:eu-repo/semantics/openAccess |
Palavras-Chave | #Stars: evolution #Supergiants #Open clusters and associations: individual: Stephenson 2 #Galaxy: structure #Virtual observatory tools #Astronomía y Astrofísica |
Tipo |
info:eu-repo/semantics/article |