An analysis of the Milky Way

We perform a study of the spatial and kinematical distribution of young open clusters in the solar neighbourhood, discerning between bound clusters and transient stellar condensations within our sample. Then, we discriminate between Gould Belt (GB) and local Galactic disc (LGD) members, using our previous estimate of the structural parameters of both systems obtained from a sample of O-B6 Hipparcos stars. Single membership probabilities of the clusters are also calculated in the separation process. Using this classified sample, we analyse the spatial structure and the kinematic behaviour of the cluster system in the GB. The two star formation regions that dominate and give the GB its characteristic-inclined shape show a striking difference in their content of star clusters: while Ori OB1 is richly populated by open clusters, not a single one can be found within the boundaries of Sco OB2. This is mirrored in the velocity space, translating again into an abundance of clusters in the region of the kinematic space populated by the members of Ori OB1, and a marginal number of them associated with Sco OB2. We interpret all these differences by characterizing the Orion region as a cluster complex typically surrounded by a stellar halo, and the Sco-Cen region as an OB association in the outskirts of the complex. In the light of these results, we study the nature of the GB with respect to the optical segment of the Orion Arm, and we propose that the different content of star clusters, the different heights over the Galactic plane and the different residual velocities of Ori OB1 and Sco OB2 can be explained in terms of their relative position to the density maximum of the Local Arm in the solar neighbourhood. Although morphologically intriguing, the GB appears to be the result of our local and biased view of a larger star cluster complex in the Local Arm, that could be explained by the internal dynamics of the Galactic disc.

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Section: Analysis and Discussionmentioning

confidence: 99%

Hierarchical star formation: stars and stellar clusters in the Gould Belt

Elías¹,

Alfaro²,

Cabrera-Caño³

2009

Monthly Notices of the Royal Astronomical Society

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“…Since the pioneering work of Becker (1956), who traced the local spiral structure from the young star clusters distribution within a radius of 2 kpc, each time that a new catalog of star clusters has been tailored, the corresponding map of this local spiral structure has been drawn again (e.g., Janes & Adler 1982). The results of doing this show a series of cluster groupings with typical sizes the order of 1 kpc (Efremov & Sitnik 1988;Alfaro et al 1991Alfaro et al , 1992) that seem to follow three segments of spiral arms which have received the names of Carina-Sagittarius Arm, Perseus Arm and Orion Arm (also known as Local Arm).…”

Section: The Orion Armmentioning

confidence: 99%

Hierarchical Star Formation: Stars and Stellar Clusters in the Gould Belt

Elias,

Alfaro,

Cabrera-Cano

2009

Preprint

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We perform a study of the spatial and kinematical distribution of young open clusters in the solar neighborhood, discerning between bound clusters and transient stellar condensations within our sample. Then, we discriminate between Gould Belt (GB) and local Galactic disk (LGD) members, using a previous estimate (Elias et al. 2006a) of the structural parameters of both systems obtained from a sample of O-B6 Hipparcos stars. Single membership probabilities of the clusters are also calculated in the separation process. Using this classified sample we analyze the spatial structure and the kinematic behavior of the cluster system in the GB. The two star formation regions that dominate and give the GB its characteristic inclined shape show a striking difference in their content of star clusters: while Ori OB1 is richly populated by open clusters, not a single one can be found within the boundaries of Sco OB2. This is mirrored in the velocity space, translating again into an abundance of clusters in the region of the kinematic space populated by the members of Ori OB1, and a marginal number of them associated to Sco OB2. We interpret all these differences by characterizing the Orion region as a cluster complex typically surrounded by a stellar halo, and the Sco-Cen region as an OB association in the outskirts of the complex. In the light of these results we study the nature of the GB with respect to the optical segment of the Orion Arm, and we propose that the different content of star clusters, the different heights over the Galactic plane and the different residual velocities of Ori OB1 and Sco OB2 can be explained in terms of their relative position to the density maximum of the Local Arm in the solar neighborhood. Although morphologically intriguing, the Gould Belt appears to be the result of our local and biased view of a larger star cluster complex in the Local Arm, that could be explained by the internal dynamics of the Galactic disk.

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“…At one point Carina was even considered to be the center of our stellar system (Charlier 1916;Trumpler 1930). Becker (1956) and Bok (1956) originally suggested that this impressive apparent concentration of young stars is a tangentially observed segment of a spiral arm. Graham & Lynga's (1965) objective prism survey revealed that there are faint OB-stars as distant as 8-10 kpc.…”

Section: Introductionmentioning

confidence: 99%

The Carina spiral feature: Strömgren-β photometry approach

Kaltcheva¹,

Scorcio²

2010

A&A

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Aims. In recent years a significant development has become evident in the study of the stellar structure of the Galactic disk. This is especially true for the 3rd Galactic quadrant, where the stellar population was extensively investigated beyond 10 kpc, revealing details about the warped geometry of the thin and thick disks and outer arm. The 4th Galactic quadrant offers even better opportunity to follow the distribution of the young stellar populace to a large distance, since the line of sight is parallel to the largest single segment of a spiral arm seen from our position in the Galaxy: the Carina spiral feature. This paper further contributes to the study of the structure of the Galactic disk in the direction of Carina field utilizing homogeneous photometric distances of a sample of about 600 bright early-type stars seen in this direction up to 6 kpc. Methods. The derived stellar distances are based on uvbyβ photometry. All O and B type stars with uvbyβ data presently available are included in the study. Results. The photometry-derived parameters allow us to study the structure and characteristics of this segment of the Carina arm. We find that the stellar distribution is consistent with a location of the apparent edge of the arm at l = 287 • . Toward the edge of the arm the warp of the Galactic plane can be traced up to 6 kpc where it reaches negative 200 pc. The field toward the edge seems to be much more complex than harboring just one OB association, and it is likely that some of the apparent concentrations in this field represent parts of long segments of the edge. In the 284 • -289 • longitude range an interarm space about 1 kpc wide is found beyond 850 pc from the Sun. The giant molecular clouds and open clusters do not follow the edge of the arm as defined by the OB stars and indicate a possible presence of an age gradient in a direction perpendicular to the formal Galactic plane.

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An analysis of the Milky Way

Cited by 7 publications

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Hierarchical star formation: stars and stellar clusters in the Gould Belt

Hierarchical star formation: stars and stellar clusters in the Gould Belt

Hierarchical Star Formation: Stars and Stellar Clusters in the Gould Belt

The Carina spiral feature: Strömgren-β photometry approach

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