Image #: SCI2011_0006
Title: Comparison of images of the W40 star-forming region made at wavelengths ranging from visible light to far infrared
Caption: The name W40 designates this object’s number in a catalog of HII regions, clouds of ionized hydrogen often associated with star formation and massive stars. W40 is in the constellation Aquila the Eagle, visible in the Northern hemisphere’s autumn sky. W40 itself is a difficult target for optical astronomers because it lies less than 3 degrees from the central plane of the Milky Way, at a distance of about 1600 light years behind obscuring clouds of interstellar dust and gas.
(Left column) This visible-light image is from the Digitized Sky Survey, a compendium of astronomical data archived at the Space Telescope Science Institute. The W40 region is not especially prominent at visual wavelengths due to intervening interstellar dust. Traces of both bright nebulae and dense, opaque dark clouds can be seen in this view. The light sources in this image are stars, starlight reflected from nebular material, and the glow of nebular gas ionized by ultraviolet radiation from the stars. The blue box shows the field of view covered by the near-infrared images in the middle column. (NASA / ESA / NSF / AURA / STScI / DSS).
(Middle Column) This near-infrared image is a composite produced by SOFIA Basic Science Principal Investigators Shuping and Vacca using archived Spitzer infrared space telescope data. The interstellar dust in the foreground and within the W40 region is mostly transparent at these wavelengths, so W40 stands out prominently and one can view into the interior of the nebula to see embedded protostars. Some of these objects were labeled with IRS (“InfraRed Source”) numbers by earlier investigators. The bright sources in this image are stars, protostars, nebular gas, and hot dust surrounding the embedded stars. The blue box shows the field of view covered by the mid-infrared images in the right column. (The component Spitzer images were taken by the IRAC camera at wavelengths of 3.6, 4.5, and 8.0 microns.) (NASA / Spitzer / Caltech-JPL / IRAC team)
(Right Column) This mid-infrared image is a composite of 5.4 micron (blue), 24.2 micron (green) and 34.8 micron (red) images taken with SOFIA’s FORCAST camera in May 2011 by Shuping and Vacca. The field of view is approximate 3 arcminutes on a side. The bright sources in this image are protostars and thermal emission from dust and gas that are construction material for new stars and planets. Emission at 24 and 35 microns is primarily from warm dust, both in the background nebula and in the circumstellar environments of the stellar sources. Some of the protostars seen in the Spitzer near-infrared image are seen here, but the SOFIA data allow easier determination of their dust temperatures. The hottest object, appearing blue and located at lower left, has very little dust surrounding it and is likely nearest to completing its evolution into a fully-fledged star. The other protostars represented by white in this color balance are cooler and thus have a large amount of circumstellar dust, some of it probably in a disk surrounding the central star. Hence these stars are still in the process of forming out of their natal gas and dust. At the upper right is the source IRS 3A which appears as a single star at shorter wavelengths (e.g. in the optical and Sptizer images), but becomes a large, roughly circular patch of emission in our FORCAST images. This is still somewhat of a mystery, but it is possible that IRS 3A is a protostar embedded in a small “cocoon” of gas and dust left over from its initial formation.
Credit: NASA / DLR / USRA / DSI / Shuping & Vacca / FORCAST team