# A distant OB association around RAFGL 5475

## TL;DR

This study identifies a new OB association near RAFGL 5475 through near-infrared imaging, revealing early-type stars and suggesting a previously unknown massive star formation region at 4 kpc in the Scutum-Centaurus arm.

## Contribution

It reports the discovery of a new OB association around RAFGL 5475 based on near-infrared observations, expanding knowledge of stellar populations in that galactic region.

## Key findings

- Presence of a population of early-type stars near RAFGL 5475
- Likely association of these stars with the interstellar medium structures
- Location of the new OB association at 4 kpc in the Scutum-Centaurus arm

## Abstract

Observations of the galactic disk at mid-infrared and longer wavelengths reveal a wealth of structures indicating the existence of complexes of recent massive star formation. However, little or nothing is known about the stellar component of those complexes. We have carried out observations aiming at the identification of early-type stars in the direction of the bright infrared source RAFGL~5475, around which several interstellar medium structures usually associated with the presence of massive stars have been identified. Our observations have the potential of revealing the suspected but thus far unknown stellar component of the region around RAFGL~5475. We have carried out near-infrared imaging observations ($JHK_S$ bands) designed to reveal the presence of early-type stars based on their positions in color-color and color-magnitude diagrams centered on the location of RAFGL~5475. We took into account the possibility that candidates found might belong to a foreground population physically related either to M16 or M17, two giant HII regions lying midway between the Sun and RAFGL~5475. The near-infrared color-color diagram shows clear evidence for the presence of a moderately obscured population of early-type stars in the region imaged. By studying the distribution of extinction in their direction and basic characteristics of the interstellar medium we show that these new early-type stars are most likely associated with RAFGL~5475. By investigating the possible existence of massive early-type stars in the direction of RAFGL~5475 we have discovered the existence of a new OB association. A very preliminary assessment of its contents suggests the presence of several O-type stars, some of them likely to be associated with structures in the interstellar medium. The new association is located at 4 kpc from the Sun in the Scutum-Centaurus arm.