The Carina spiral feature: Strömgren-β photometry approach^*

II. Distances and space distribution of the O and B stars

Department of Physics & Astronomy, University of Wisconsin Oshkosh, 800 Algoma Blvd., Oshkosh, WI 54901-8644, USA e-mail: kaltchev@uwosh.edu

Received: 2 October 2009
Accepted: 29 January 2010

Abstract

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 = .  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 – 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.