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Investigating Supernova Remnant HB9 and Nearby H II Region G159.2+3.3
Recent observations conducted by Chinese astronomers have focused on the supernova remnant (SNR) designated as HB9, illuminating its characteristics and exploring its potential link to an adjacent area of ionized atomic hydrogen known as the H II region G159.2+3.3. The findings from this observational initiative have been detailed in a study released on August 9 through the preprint server arXiv.
Supernova remnants are the expansive and often diffuse remnants of supernova explosions. They consist of matter expelled during the blast and interstellar material that has been collected by the shockwave generated by the detonation of the star. The study of SNRs is crucial for understanding galactic evolution, as they disseminate heavy elements produced in the explosion and contribute to the heating of the interstellar medium. Furthermore, they are considered significant in the acceleration of cosmic rays within galaxies.
New stars emerge within giant molecular clouds, which subsequently ionize the surrounding gases and give rise to H II regions. When these stars end their life cycles in explosions, they leave behind SNRs, yet the specific physical interactions between SNRs and the enclosed H II regions have not been extensively explored until now.
HB9, estimated to be around 6,600 years old and located approximately 2,000 light-years from Earth, is viewed as a relatively young SNR. It displays a shell-type morphology in radio emissions and spans roughly 2 degrees in angular size. In close proximity lies G159.2+3.3, which appears denser and brighter than HB9, located about 2 degrees north from the southern edge of HB9’s shell.
A team of researchers, spearheaded by Jiang-Tao Li from the Purple Mountain Observatory in Nanjing, utilized the McGraw-Hill 1.3m telescope at the Michigan-Dartmouth-MIT (MDM) observatory to delve into the relationship between HB9 and G159.2+3.3.
The observations revealed that HB9 is notably bright in gamma-ray emissions, although its structure does not seem to correlate strongly with the existing molecular clouds in the vicinity. A faint association, however, was detected linking this remnant to the infrared-bright shell surrounding G159.2+3.3.
The data collected indicate that the morphology of G159.2+3.3 aligns with typical characteristics of galactic H II regions. This suggests that the emissions observed in the Balmer line and radio frequencies within the region are likely thermal in nature, while the infrared-emitting shell is composed of dust heated by ultraviolet radiation from young stellar objects.
The study assessed the radial velocity of the southeastern shell of HB9, registering between -30 and +50 km/s, which the researchers interpret as indicative of shock heating caused by the supernova event. Additionally, they computed a median electron density for this section of HB9, found to be around 100 cm-3. Interestingly, G159.2+3.3 exhibited a lower median density of approximately 50 cm-3, hinting that it may be situated at a greater distance than HB9, suggesting a lack of physical connection between the two entities.
“The density estimation implies that G159.2+3.3, despite its apparent brightness and compactness, is likely positioned significantly farther away from HB9, indicating no physical linkage. This remains true unless the compressed gas within HB9 possesses a considerably reduced filling factor,” the authors of the study concluded.
More information: Jiang-Tao Li et al., Optical observations of the Galactic SNR HB9 and H II region G159.2+3.3, arXiv (2024). DOI: 10.48550/arxiv.2408.05016
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phys.org