26Al Radioactivity in the Galaxy26Al Map and spectrum

(Version in deutscher Sprache hier)
Nucleosynthesis in cosmic sources can be observed through a variety of, mostly indirect, measurements; examples are stellar photospheric absorption lines, or mass spectrometry of meteoritic inclusions. Gamma-rays from radioactive by-products of nucleosynthesis ejecta provide a rather direct measurement, in comparison, as their decay gamma-ray measurements with satellite-borne telescopes provide direct isotopic constraints to the physics of nuclear burning regions inside these sources. Yet, the technique of gamma-ray telescopes is complex, and less precise than the alternatives for cosmic abundance measurements, mainly from two reasons: Spatial resolutions of ~degrees and signal-to-background ratios of ~% restrict contributions from gamma-ray astronomy to nearby sources in the Galaxy. There are, however, advantages to gamma-ray astronomical data: They provide isotopic information, are unaffected by physical conditions in/around the source such as temperature or density, and gamma-rays are nearly un-attenuated along the line-of-sight due to their penetrating nature (attenuation length ~few g/cm2). Longer-lived isotopes such as 26Al (t~1.04 Myrs) will reflect the kinematic properties in an interstellar medium around massive star sources, which is otherwise hard to study due to its hot and diluted nature. The MPE high-energy astrophysics group studies the gamma-ray sky in 26Al emission since the developement of the Compton telescope technique in the 1970ies. First results from the MPE balloone-borne instrument (1982) were followed by the all-sky studies with the COMPTEL telescope aboard the NASA space observatory 'Compton' (1991-2000), spectrosopic studies followed with the SPI spectrometer aboard ESA's INTEGRAL space mission (2002-current).

26Al Science Results: Imaging from COMPTEL aboard the Compton Gamma-Ray Observatory and Spectroscopy from SPI aboard the INTEGRAL Observatory

assembled by Roland Diehl 
26Al Map and spectrum
This Figure shows the COMPTEL Map of the 26Al Sky, plus the INTEGRAL/SPI Spectrum of the 26Al Line from the Inner Galaxy. (click for larger version in jpg or pdf)
If you use & show figures from here, please give credits as advised
(specific references given with the respective figure) or to MPE Garching/Roland Diehl .
Thank you.

Update May 2009: 26Al along Galactic Star Formation Regions
imageSpectral and Intensity Variations along the Plane of the Galaxy

Using the imaging spectrometer on ESA’s Gamma-Ray Observatory INTEGRAL, measurements of the gamma-ray line from radioactive decay of  26Al (T1/2~720000 years) can now be distinguished from different regions which host young stars in the Galaxy.

This spatially-resolved spectroscopy shows that the line centroid indeed traces the bulk motion imposed by large-scale rotation within the Galaxy, and that the line in general is narrow. A suggested broadening in the Aquila region hints at recent young-star activity, possibly embedded within interstellar clouds and hence unnoticed in other tracers.
imaging spectroscopy 26Al

Update January 2006: 26Al and the Galactic Supernova and Star Formation Rates
imageDetermining the Galactic Supernova Rate through Radioactivity

Using the spectrometer on ESA’s Gamma-Ray Observatory INTEGRAL, a precision measurement of the gamma-ray line from radioactive decay of  26Al (T1/2~720000 years) demonstrates that this radioactivity reflects the entire population of massive, young stars in the Galaxy.

Radioactive 26Al is ejected into interstellar space together with other new elements, when massive stars reach the terminal phases of their evolution and finally explode as supernovae. Using the gamma-ray spectrometer SPI on INTEGRAL, an international team of researchers led by MPE scientists obtained a unpredecented precision measurement of the 26Al decay gamma-ray line . From the otherwise heavily occulted inner region of the Galaxy, they recognized the signatur of galactic rotation intheir data. This led the team to conclude that observed 26Al gamma-rays represent the massive star population over the full extent of the Galaxy. From the total amount of observed 26Al, this corresponds to a rate of supernovae from massive stars (i.e. "Types Ib/c and II") of two per century.
26Al gamma-rays
(illustration of 26Al astronomy and Galaxy science: radioactive decay of the 26Al isotope produces the excited 26Mg nucleus, which emits a gamma-ray photon of specific energy upon its transition into its stable ground state. The INTEGRAL satellite measures those gamma-rays since its launch in October 2002. Precision spectroscopy revealed the signature of the Galaxy's differential rotation, which shifts the line centroids from regions of the inner Galalx through the Doppler effect in acharacteristic way. The background image shows the Milky way, as it would appear at visible wavelengths, if projected into a Galactic coordinate system where the plane of the Galaxy is a horizontal straight line; superimposed is the 26Al sky image from COMPTEL, which shows bright emission from regions with massive young stars. pdf pdf2, and jpg versions.)

Below, you find more graphs and images...
the Galactic 26Al emission regions (... for education/overview; by Roland Diehl; credits: MPE 2001)


Spectroscopy Results

SPI and 26Al: schematic
A scheme of the science goals: Radioactive decay as measured by INTEGRAL from 26Al decay, and the signature of Galactic rotation. The background image of the milky way is overlaid with the COMPTEL map of 26Al emission. Reference: MPE, Oct 2005

The signature of galactic rotation, as discovered with SPI. Reference: Diehl et al., Nature, 2006

inner-Galaxy spectrum
26Al line shape as measured from the inner Galaxy with INTEGRAL. Reference: Diehl et al., A&A, 2006

Results on Specific Sources/Regions:
Vela Region:


COMPTEL Limits on 1.809 MeV Gamma-Rays from GammaVelorum, 9 Years of Data (ref.: Diehl et al.,  unpublished)


COMPTEL Limits on 26Al 1.809 MeV Line Emission from Gamma2 Velorum, 5 Years of Data
(ref.: Oberlack et al., , A&A 353, 715-721 (2000))
vela SNR

Orion Region:
orion map

COMPTEL Map of Orion Region (ref. Diehl et al., IAU212, 706 (2002))

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copyright Roland Diehl, MPE Garching