Thursday, March 18, 2021

Carina OB1

Carina OB1 is a giant OB association, located at a distance of around 7,500 light years in the constellation of Carina.

The 70 light years across region lies within an emission nebula, and it is the most massive stellar association in our Galaxy. It contains some of the most massive and luminous stars in the Milky Way.

The association includes the clusters Collinder 228, IC 2581, NGC 3293, NGC 3324, Trumpler 14, Trumpler 15, and Trumpler 16. 

Carina OB1 contains numerous very massive young stars which are distributed over the open clusters mentioned above. The mean age of the stellar population at each cluster is comparable, thus it is believed that all stars were formed roughly during the same period. 

Collinder 228 is located in the southern region of the Carina Nebula. It is a loose open star cluster. QZ Carinae is its most massive member. This is a multiple star that consists of two binaries. QZ Carinae A1 is an O9.7I-type with a mass around 40 M☉(solar masses) and a temperature of around 32,000 K (Kelvin). QZ Carinae A2 is a B2V-type with a mass around 10 M☉ and a temperature around 22,000 K. QZ Carinae B1 is an O8III-type star with a mass of 14 M☉ and a temperature around 32,500 K, while its companion is an O9V-type with a mass of 28 M☉ and a temperature of 32,500 K.

The open cluster NGC 3293 is located in the southern Carina Nebula. It consists of more than 100 bright stars and its most notable member is red pulsating giant V361 Carinae, a M1.5Iab-Ib type star.

The open cluster known as NGC 3324 is located northwest of the Carina Nebula. It is associated with the emission nebula IC 2599. The two form what is known as the Gabriela Mistral Nebula.

The two open star clusters Trumpler 14 and 16 are located in the inner region of the Carina Nebula. They are the main clusters of the Carina OB1. Around 2,000 stars have been identified in Trumpler 14, which has a total mass of around 4,300 M☉. The most notable member of Trumpler 14 is HD 93129, a triple star system. It consists of the binary HD 93129 A and HD 93129B. The binary system consists of an O2If-type star with a mass of 70 M☉ and temperature of 42,500 Kelvin and an O3.5V with a mass of 110 M☉ and temperature of 52, 000 Kelvin. HD 93129 B is an O3.5 V-type star with a mass of 44 M☉ and a temperature of 44,000 K. The most notable members of Trumpler 16 are Eta Carinae and WR 25. The luminous blue variable Eta Carinae (η Car) is a binary system consisting of a primary component with a mass of 100 M☉ and a temperature in the range of 9,400 – 35,200 K, while its component has a mass in the range of 30-80 M☉ and a temperature around 37,200 K. WR 25 is a binary system with a Wolf-Rayet and hot luminous companion. The primary is a O2.5If*-type star with a mass around 75 M☉, while its companion whose type is not known accurately, has a mass of around 25M☉. The average temperature of the system is around 50,000 K.

The open cluster Trumpler 15 is on the outskirts of the Carina Nebula and observations suggest that it is slightly older than Trumpler 14 and 16.

Finally, in the open cluster of IC 2581 the most interesting source is V399, a Cepheid variable star, with a periodicity of 47.25 days and a temperature around 8,000 K.

Image: Composite infrared image of the Carina OB1 association, taken with ESO’s VLT. The image was created using broadband filters. The filters are centred at 1.25 μm (J-band, blue channel), 1.65 μm, (H-band, green), and at 2.2 μm (Ks-band, red).

Image Credit: ESO/T. Preibisch

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