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Astron. Astrophys. 332, 71-76 (1998)

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1. Introduction

Because of its proximity, considerable attention has been paid to the spiral feature known as the Local Arm. Optical and 21 cm observations have long been available. Buss et al. (1994) in the ultraviolet, Fatoohi et al. (1996) in gamma-rays, Oliver et al. (1996) in CO, have, more recently, among others, reported observations at other wavelengths. Dynamic properties have been analyzed by Palous (1987), Comeron & Torra (1991) and others.

In the near infrared, recent surveys (e.g. Odenwald & Schwartz 1993; Freudenreich et al. 1994; Garzón et al. 1993) have provided significant information, but the application of these to the study of the Local Arm has been insufficient. Ortiz & Lepine (1993) themselves found their description of the Local Arm to be unsatisfactory. More infrared observations are necessary and the main purpose of this work is to compensate for this shortcoming.

We report our own observations with the 1.5 "Carlos Sánchez" telescope in Tenerife, used to search the infrared morphology of the closest spiral feature; this was undertaken bearing in mind the following goals:

1.- To observe the first quadrant region of the arm, which in practice limits attention to the longitude range [FORMULA]. Observations extend to slightly higher longitudes, but here interpretation becomes difficult because the arm is too close.

2.- To use high spatial resolution techniques in order to observe individual stars. We determine stellar counts instead of total fluxes. We can in this way perform detailed analysis at various magnitude ranges. The immediate advantage is that this procedure constitutes a natural filter: very bright magnitude stars must, necessarily, be nearby. The importance of the contribution of other components is thus minimized. This probably compensates for the considerable observation time, which in practice means a reduced number of scans. COBE data, for instance, are poorer resolution flux data, and are therefore less suitable to study a close feature like the Local Arm, as they are contaminated by the contribution of larger scale features behind it.

3.- To discriminate between the different contributions to the star counts from other galactic components, mainly the exponential component of the disc. It is to be emphasized that the northern warp of our galaxy is just behind the Local Arm in its first quadrant portion.

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© European Southern Observatory (ESO) 1998

Online publication: March 10, 1998