Detalles de publicación
PP 018019
Identifying two groups of massive stars aligned in the l ∼ 38◦ Galactic direction
(1) Unidad de Astronomıa, Universidad de Antofagasta, Antofagasta, Chile.
(2) Instituto de Astrofısica de Canarias, c/Vıa Lactea s/n, 38205 La Laguna, Tenerife, Spain.
(3) Departamento de Astrofısica, Universidad de La Laguna, E-38205 La Laguna, Tenerife, Spain.
(4) Centro de Estudios de F ısica del Cosmos de Aragon (CEFCA), E-44001, Teruel, Spain.
(5) Departamento de Astrofısica, Universidad Complutense de Madrid, E-38040, Madrid, Spain.
(6) Centro de Astrobiologıa, CSIC-INTA. Ctra. Torrejon a Ajalvir km.4, E-28850 Torrejon de Ardoz, Madrid, Spain.
(7) Instituto de Fısica y Astronomıa, Facultad de Ciencias, Universidad de Valparaıso, Valparaıso, Chile.
(8) Millennium Institute of Astrophysics, MAS.
Context. Recent near-infrared data have contributed to unveil massive and obscured stellar populations in both new and previously known clusters in our Galaxy. These discoveries lead us to view the Milky Way as an active star-forming machine.
Aims. We look for young massive cluster candidates as over-densities of OB-type stars. The first search, focused on the Galactic direction l = 38◦ , resulted in the detection of two objects with a remarkable population of OB-type star candidates.
Methods. With a modified version of the friends-of-friends algorithm AUTOPOP and using 2MASS and UKIDSS-GPS near-infrared (J, H, and K) photometry for one of our cluster candidates (named Masgomas-6) we selected 30 stars for multi-object and long-slit H- and K-spectroscopy. With the spectral classification and the near-infrared photometric data, we derive individual distance, extinction and radial velocity.
Results. Of the 30 spectroscopically observed stars, 20 are classified as massive stars, including OB-types (dwarfs, giants and super-
giants), two red supergiants, two Wolf-Rayet (WR122-11 and the new WR122-16), and one transitional object (the LBV candidate
IRAS 18576+0341). The individual distances and radial velocities do not agree with a single cluster, indicating that we are observing
two populations of massive stars in the same line-of-sight: Masgomas-6a and Masgomas-6b. The first group of massive stars, located
at 3.9+0.4 kpc, contains both Wolf-Rayets and most of the OB-dwarfs, and Masgomas-6b, at 9.6 ± 0.4 kpc, hosts the LBV candidate −0.3
and an evolved population of supergiants. We are able to identify massive stars at two Galactic arms, but we can not clearly identify whether these massive stars form clusters or associations.
Key words. Infrared: stars - Galaxy: open clusters and associations - Stars: early-types, supergiants, massive, Wolf-Rayet.
Aims. We look for young massive cluster candidates as over-densities of OB-type stars. The first search, focused on the Galactic direction l = 38◦ , resulted in the detection of two objects with a remarkable population of OB-type star candidates.
Methods. With a modified version of the friends-of-friends algorithm AUTOPOP and using 2MASS and UKIDSS-GPS near-infrared (J, H, and K) photometry for one of our cluster candidates (named Masgomas-6) we selected 30 stars for multi-object and long-slit H- and K-spectroscopy. With the spectral classification and the near-infrared photometric data, we derive individual distance, extinction and radial velocity.
Results. Of the 30 spectroscopically observed stars, 20 are classified as massive stars, including OB-types (dwarfs, giants and super-
giants), two red supergiants, two Wolf-Rayet (WR122-11 and the new WR122-16), and one transitional object (the LBV candidate
IRAS 18576+0341). The individual distances and radial velocities do not agree with a single cluster, indicating that we are observing
two populations of massive stars in the same line-of-sight: Masgomas-6a and Masgomas-6b. The first group of massive stars, located
at 3.9+0.4 kpc, contains both Wolf-Rayets and most of the OB-dwarfs, and Masgomas-6b, at 9.6 ± 0.4 kpc, hosts the LBV candidate −0.3
and an evolved population of supergiants. We are able to identify massive stars at two Galactic arms, but we can not clearly identify whether these massive stars form clusters or associations.
Key words. Infrared: stars - Galaxy: open clusters and associations - Stars: early-types, supergiants, massive, Wolf-Rayet.