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Antares and Rho Oph regions
Antares and Rho Oph regions
Credit: Giuseppe Donatiello
The Ophiuchus Molecular Cloud Complex is a nearby region of low-mass star formation in the Gould Belt. In reality this is a generic name to indicate a certain number of substructures located at different distances and not necessarily connected.
The complex includes two dense clouds, LDN1688 and 1689, located at the ends of large-scale filaments extending in a northeasterly direction (Loren et al. 1990).
More strictly, the dense dark cloud LDN1688, 134 pcs away, is called the Ophiuchus Molecular Cloud. LDN1689 is instead found at 144 pc based on Gaia DR2 measurements (Ortiz-Leon et al. 2018).
The stellar content of the Ophiuchus star-forming complex has long been studied, revealing a rich environment of young stellar objects (YSOs), protostellar sources and prestellar cores at various evolutionary stages. While LDN1688 hosts dense star formation activity, L1689 is more quiescent (Nutter et al. 2006). Despite its significant mass, L1689 does not exhibit the same star formation activity as other regions of the Gould Belt, such as M16.
The entire Ophiuchus complex is under the strong influence and feedback of the Sco OB2 association.
Antares (α Scorpii) is a red supergiant about 170 pc (550 light years) away, therefore it is placed prospectively behind the molecular complex. Nonetheless, it is shrouded in a large reflection nebula that diffuses its light. The yellower color of this nebula is not a calibration error but an effect due to scattering which tends to shift the peak of light to shorter wavelengths. The star is a double view. Antares B is a sequence and mag 5.5 star of spectral type B2.5V (Evans 1966).
Antares is a red supergiant M1.5 Iab variable star and the brightest star in Scorpius (mag +1.07). It is one of the largest known, with a radius approximately 680 times that of the Sun. Being in an advanced stage of evolution, with a current mass 15 times that of the Sun, it is destined to explode as a supernova within 100,000 years [The Perkins Catalog of Revised MK Types for the Cooler Stars].
It forms a binary system with a smaller, hotter companion, Antares B [A&A, 700, A36 (2025)] [MNRAS, Volume 529, Issue 4, April 2024, Pages 3630–3650].
Like all red supergiants, it is losing mass at a rapid rate and is producing a cloud of dust. This material is particularly evident in the mid-infrared, but the star's light is sufficient to produce scattering on neutral dust clouds. Scattering causes the "reflected" light to shift slightly to shorter wavelengths, which is why the cloud surrounding the star appears distinctly orange/yellow instead of red.
Galactic Environment
Antares is part of the Scorpius-Centaurus stellar association, one of the closest OB associations to Earth. This association is divided into three subgroups, and Antares belongs to the Superior Scorpius subgroup [John M. Carpenter et al 2025 ApJ 978 117].
NGC 6144 is a small globular cluster at 8.1 kpc (about 32,000 light-years) [The Astronomical Journal, Volume 119, Issue 4, pp. 1793-1802].
The two globular clusters are much more distant. M4 is about 2.2 kpc (7500 light years) away while NGC 6144 is even 8.1 kpc 8 (about 32,000 light years).
flussistellari.wordpress.com/2023/06/22/un-lavoro-in-cors...
Antares and Rho Oph regions
Antares and Rho Oph regions
Credit: Giuseppe Donatiello
The Ophiuchus Molecular Cloud Complex is a nearby region of low-mass star formation in the Gould Belt. In reality this is a generic name to indicate a certain number of substructures located at different distances and not necessarily connected.
The complex includes two dense clouds, LDN1688 and 1689, located at the ends of large-scale filaments extending in a northeasterly direction (Loren et al. 1990).
More strictly, the dense dark cloud LDN1688, 134 pcs away, is called the Ophiuchus Molecular Cloud. LDN1689 is instead found at 144 pc based on Gaia DR2 measurements (Ortiz-Leon et al. 2018).
The stellar content of the Ophiuchus star-forming complex has long been studied, revealing a rich environment of young stellar objects (YSOs), protostellar sources and prestellar cores at various evolutionary stages. While LDN1688 hosts dense star formation activity, L1689 is more quiescent (Nutter et al. 2006). Despite its significant mass, L1689 does not exhibit the same star formation activity as other regions of the Gould Belt, such as M16.
The entire Ophiuchus complex is under the strong influence and feedback of the Sco OB2 association.
Antares (α Scorpii) is a red supergiant about 170 pc (550 light years) away, therefore it is placed prospectively behind the molecular complex. Nonetheless, it is shrouded in a large reflection nebula that diffuses its light. The yellower color of this nebula is not a calibration error but an effect due to scattering which tends to shift the peak of light to shorter wavelengths. The star is a double view. Antares B is a sequence and mag 5.5 star of spectral type B2.5V (Evans 1966).
Antares is a red supergiant M1.5 Iab variable star and the brightest star in Scorpius (mag +1.07). It is one of the largest known, with a radius approximately 680 times that of the Sun. Being in an advanced stage of evolution, with a current mass 15 times that of the Sun, it is destined to explode as a supernova within 100,000 years [The Perkins Catalog of Revised MK Types for the Cooler Stars].
It forms a binary system with a smaller, hotter companion, Antares B [A&A, 700, A36 (2025)] [MNRAS, Volume 529, Issue 4, April 2024, Pages 3630–3650].
Like all red supergiants, it is losing mass at a rapid rate and is producing a cloud of dust. This material is particularly evident in the mid-infrared, but the star's light is sufficient to produce scattering on neutral dust clouds. Scattering causes the "reflected" light to shift slightly to shorter wavelengths, which is why the cloud surrounding the star appears distinctly orange/yellow instead of red.
Galactic Environment
Antares is part of the Scorpius-Centaurus stellar association, one of the closest OB associations to Earth. This association is divided into three subgroups, and Antares belongs to the Superior Scorpius subgroup [John M. Carpenter et al 2025 ApJ 978 117].
NGC 6144 is a small globular cluster at 8.1 kpc (about 32,000 light-years) [The Astronomical Journal, Volume 119, Issue 4, pp. 1793-1802].
The two globular clusters are much more distant. M4 is about 2.2 kpc (7500 light years) away while NGC 6144 is even 8.1 kpc 8 (about 32,000 light years).
flussistellari.wordpress.com/2023/06/22/un-lavoro-in-cors...