Orion OB1 (Ori OB1) is a contingent group of several dozen hot giant stars of
spectral types O and B in
Orion. Associated are thousands of lower-mass stars, and a (smaller but significant) number of
protostars. It is part of the larger
Orion molecular cloud complex. Owing to its relative closeness and complexity it is the most closely studied OB association.[1]
The Orion OB1 consists of the following subgroups:[1][3]
Orion OB1a - the group of stars northwest of the Orion Belt stars with an average age of about 12 million years. Within this grouping is another subgroup known as the 25 Orionis group.[4][5] They are located near the star of
Bellatrix.
Orion OB1b - the three bright stars
ζ Ori (Alnitak),
ε Ori (Alnilam), and
δ Ori (Mintaka) which make up the
asterism known as "Orion's Belt", and minor stars. This group has an average age of approximately 8 million years and is further subdivided into three subgroups.[6][7]
^Warren, W. H. Jr.; Hesser, J. E. (June 1977). "A photometric study of the Orion OB 1 association. I - Observational data". Astrophysical Journal Supplement Series. 34: 115–206.
Bibcode:
1977ApJS...34..115W.
doi:
10.1086/190446.
^Warren, W. H. Jr.; Hesser, J. E. (April 1978). "A photometric study of the Orion OB 1 association. III - Subgroup analyses". Astrophysical Journal Supplement Series. 36: 497–572.
Bibcode:
1978ApJS...36..497W.
doi:
10.1086/190510.
^N. Calvet et al., The Astronomical Journal 129:935–946 (2005)
^J. Hernandez et al., Astrophys. J. 652:472-481 (2006)
Orion OB1 (Ori OB1) is a contingent group of several dozen hot giant stars of
spectral types O and B in
Orion. Associated are thousands of lower-mass stars, and a (smaller but significant) number of
protostars. It is part of the larger
Orion molecular cloud complex. Owing to its relative closeness and complexity it is the most closely studied OB association.[1]
The Orion OB1 consists of the following subgroups:[1][3]
Orion OB1a - the group of stars northwest of the Orion Belt stars with an average age of about 12 million years. Within this grouping is another subgroup known as the 25 Orionis group.[4][5] They are located near the star of
Bellatrix.
Orion OB1b - the three bright stars
ζ Ori (Alnitak),
ε Ori (Alnilam), and
δ Ori (Mintaka) which make up the
asterism known as "Orion's Belt", and minor stars. This group has an average age of approximately 8 million years and is further subdivided into three subgroups.[6][7]
^Warren, W. H. Jr.; Hesser, J. E. (June 1977). "A photometric study of the Orion OB 1 association. I - Observational data". Astrophysical Journal Supplement Series. 34: 115–206.
Bibcode:
1977ApJS...34..115W.
doi:
10.1086/190446.
^Warren, W. H. Jr.; Hesser, J. E. (April 1978). "A photometric study of the Orion OB 1 association. III - Subgroup analyses". Astrophysical Journal Supplement Series. 36: 497–572.
Bibcode:
1978ApJS...36..497W.
doi:
10.1086/190510.
^N. Calvet et al., The Astronomical Journal 129:935–946 (2005)
^J. Hernandez et al., Astrophys. J. 652:472-481 (2006)