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Draft:Cepheus OB2 Region

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Cepheus OB2 region
Nebula
Observation data: J2000.0 epoch
Right ascension21h 51m
s[1]
Declination+60° 00′ :″[1]
Distance2930[2] ly   (900[2] pc)
Apparent dimensions (V)6°
ConstellationCepheus
Notable featuresOB association connected to nebulosity
DesignationsI Cep
See also: Lists of nebulae

The Cepheus OB2 region is a system of molecular clouds and H II regions associated with a bright OB association, known as Cepheus OB2; the system is visible in the northern constellation of Cepheus.

The association is located in the Orion Arm at a distance of approximately 900 parsecs (2930 light-years) from the Solar System and appears to be associated with the nebulae IC 1396 and Sh2-134; several infrared sources and molecular jets have been observed in the clouds of this region, indicating that star formation phenomena are still active in the region.[3]

Observation

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Map of the Cepheus OB2 region.

The region of the sky where the Cepheus OB2 association is located occupies the southern portion of the constellation Cepheus, along the northern Milky Way; its stellar components are easily confused with the rich background star fields visible in this direction. Among the brightest stars belonging to this group is Lambda Cephei, which with its magnitude of 5.05 is visible even to the naked eye, provided the sky is clear and dark. Among the nebular regions linked to this association, IC 1396 undoubtedly stands out, a vast system of ionized gas famous for hosting the cloud vdB 142, well known by the nickname Elephant's Trunk.[3]

The declination of the association is strongly northern, favouring its observation from the Northern Hemisphere, where it appears circumpolar down to low latitudes; from the Southern Hemisphere, the observation period is therefore very limited and the areas where it is visible are restricted to the tropical belt. The months suitable for its observation in the evening sky are between July and December.[a][3]

Characteristics and structure

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The Elephant's Trunk (vdB 142), located within the IC 1396 system.

Cepheus OB2 is the easternmost and southernmost of the numerous OB associations of Cepheus; it was discovered in 1968 and is located at a short distance, both in terms of perspective and actual distance, from the large dark nebula complex that forms the Cygnus Rift and is almost in contact with the Cygnus OB7 association. Its distance from us is estimated at about 800[4] or 900 parsecs,[2] comparable to the clouds of the Rift, with which it also shares the same radial velocity.[4] This association contains 75 very bright stars, among which is the blue giant runaway star Lambda Cephei.

It is thought that Cepheus OB2 is divided into two subgroups of different ages: the younger one, catalogued as Cepheus OB2b, coincides with the open cluster Tr 37, one of the youngest known clusters, with an estimated age of about 3.7 million years;[5] in the 1970s, it was suggested that the bright star Mu Cephei (the Garnet Star) was a member of Tr 37, while the main responsible for exciting the large nebula associated with the cluster, IC 1396, belongs to this association.[6] The second subgroup, Cepheus OB2a, contains a large number of massive evolved stars that are scattered over a wide area between galactic latitudes 100°–106° and longitudes +2°–+8°; its age is estimated at about 8 million years and it contains the cluster NGC 7160.[7]

Cepheus OB2a is surrounded by a ring-shaped nebular structure, known as the Cepheus Bubble; the mass of the molecular gas of this bubble is at least 100,000 M⊙, while the mass of the atomic gas would be up to four times greater.[3] It is believed that this structure is what remains of the explosion of an ancient supernova, which occurred about 2–3 million years ago; this event may have been the cause of the initiation of the star formation processes that led to the birth of the association, as seems to be testified by the presence of some H II regions and infrared radiation sources that appear to contain young stars in formation.[8] The star that exploded as a supernova was part of a previous generation of massive stars, whose surviving companions can be sought among the members of the open cluster NGC 7160.[3]

Studies on the metallicity of the association's stars indicate that they are metal-poor.[9] The low- and intermediate-mass stars belong to different stellar populations and were born at different times and in various subgroups during the evolution of the association; the groups of coeval low-mass stars are found in both sub-associations of Cepheus OB2. Other studies have focused on the populations of T Tauri stars linked to the association; using data obtained from the Spitzer Space Telescope in the infrared wavelengths, it was possible to detect the existence of several protoplanetary disks rich in amorphous silica and simple silicates (such as olivine) around these stars.[10]

Among the runaway stars that originally belonged to the Cepheus OB2 association, in addition to the aforementioned Lambda Cephei, is the blue star HD 197911, responsible, along with two other stars, for the ionization of the gases of the nebula Sh2-130.[11]

Star formation phenomena

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The Cepheus OB2 region is located in a section of the Orion Arm very rich in neutral molecular clouds and ionized gas. Studies of infrared emissions located in the clouds associated with Cepheus OB2 indicate that star formation phenomena are still active within them, mainly concerning the formation of low- and intermediate-mass stars.[3]

The large nebular system of IC 1396, extending for about 1°, appears to be one of the most active in the region. Inside it, several dozen dense globules have been identified, among which is the famous structure known as the Elephant's Trunk (vdB 142).[12][13] Infrared searches have instead been conducted for the location of young stellar objects associated with the globules; it was thus discovered that only six sources associated with globules possess a structure and luminosity such as to be caused by external heating, while most of them would not be linked to star formation phenomena.[13] It is believed that in globules with the smallest mass, star formation is often influenced by the radiation pressure of a bright star located nearby; in a study conducted on one of these, illuminated by the bright blue giant HD 206267, it was suggested that the star operates in a dual manner on the mass distribution of the globule: through evaporation caused by photoionization and through gas compression produced by radiation pressure.[14]

Some sources of infrared radiation[15] and a maser with water H2O emissions[16] have also been identified in the nearby nebula Sh2-134; linked to this cloud are also some molecular clouds visible at the wavelength of CO, among which [DBY94] 153 and [DBY94] 156 stand out, respectively with a mass equal to 510 and 450 M⊙.[17] Other processes may also be active in the nebula Sh2-137.[18]

Notes

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  1. ^ A declination of 60°N equates to an angular distance from the north celestial pole of 30°; this means that north of 30°N the object appears circumpolar, while south of 30°S the object never rises.

See also

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References

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  1. ^ a b "Simbad Query Result". Retrieved 24 March 2013.
  2. ^ a b c Contreras, Maria E.; Sicilia-Aguilar, Aurora; Muzerolle, James; Calvet, Nuria; Berlind, Perry; Hartmann, Lee (2002). "A Study of Intermediate-Mass Stars in Trumpler 37". The Astronomical Journal. 124 (3): 1585–1592. doi:10.1086/341825. Retrieved 24 March 2013. {{cite journal}}: Unknown parameter |month= ignored (help)
  3. ^ a b c d e f Patel, Nimesh A.; Goldsmith, Paul F.; Heyer, Mark H.; Snell, Ronald L.; Pratap, Preethi (1998). "Origin and Evolution of the Cepheus Bubble". The Astrophysical Journal. 507 (1): 241–253. doi:10.1086/306305. Retrieved 24 March 2013.
  4. ^ a b Dame, T. M.; Thaddeus, P. (1985). "A wide-latitude CO survey of molecular clouds in the northern Milky Way". Astrophysical Journal. 297: 751–765. doi:10.1086/163573. Retrieved 24 March 2013.
  5. ^ Marschall, Laurence A.; Karshner, Gary B.; Comins, Neil F. (1990). "Photometry of the young open cluster Trumpler 37". Astronomical Journal. 99: 1536–1547. doi:10.1086/115437. Retrieved 24 March 2013.
  6. ^ Harvin, James A. (2004). "Doppler Tomography of the Massive Compact Binary Stars in the Multiple Star Systems δ Orionis and HD 206267". The Publications of the Astronomical Society of the Pacific. 116 (816): 186. doi:10.1086/381874. Retrieved 24 March 2013.
  7. ^ Kun, M.; Kiss, Z. T.; Balog, Z. (2008). Star Forming Regions in Cepheus (pdf). Handbook of Star Forming Regions, Volume I: The Northern Sky ASP Monograph Publications, Bo Reipurth. p. 1. ISBN 978-1-58381-670-7.
  8. ^ Balazs, L. G.; Kun, M. (1989). "Star-forming processes in Cepheus OB2". Astronomische Nachrichten. 310 (5): 385–388. Retrieved 24 March 2013.
  9. ^ Daflon, Simone; Cunha, Katia; Becker, Sylvia R. (1999). "Chemical Abundances of OB Stars in the Cepheus OB2 Association". The Astrophysical Journal. 522 (2): 950–959. doi:10.1086/307683. Retrieved 24 March 2013.
  10. ^ Sicilia-Aguilar, Aurora; Henning, Thomas; Dullemond, Cornelis P.; Patel, Nimesh; Juhász, Attila; Bouwman, Jeroen; Sturm, Bernhard (2011). "Dust Properties and Disk Structure of Evolved Protoplanetary Disks in Cep OB2: Grain Growth, Settling, Gas and Dust Mass, and Inside-out Evolution". The Astrophysical Journal. 742 (1): 35. doi:10.1088/0004-637X/742/1/39. Retrieved 24 March 2013.
  11. ^ Hoogerwerf, R.; de Bruijne, J. H. J.; de Zeeuw, P. T. (2001). "On the origin of the O and B-type stars with high velocities. II. Runaway stars and pulsars ejected from the nearby young stellar groups". Astronomy and Astrophysics. 365: 49–77. doi:10.1051/0004-6361:20000014. Retrieved 24 March 2013.
  12. ^ Gyul'Budagyan, A. L. (1985). "Radial systems of dark globules". Astrophysics. 23 (2): 538–544. doi:10.1007/BF01007381. Retrieved 24 March 2013.
  13. ^ a b Schwartz, Richard D.; Wilking, Bruce A.; Giulbudagian, Armen L. (1991). "A search for embedded young stellar objects in and near the IC 1396 complex". Astrophysical Journal. 370: 263–271. doi:10.1086/169812. Retrieved 24 March 2013.
  14. ^ Froebrich, D.; Scholz, A.; Eislöffel, J.; Murphy, G. C. (2005). "Star formation in globules in IC 1396". Astronomy and Astrophysics. 432 (2): 575–584. doi:10.1051/0004-6361:20041791. Retrieved 24 March 2013.
  15. ^ Helou, George; Walker, D. W. (1988). "Infrared astronomical satellite (IRAS) catalogs and atlases. Volume 7: The small scale structure catalog". Infrared astronomical satellite (IRAS) catalogs and atlases. 7: 1–265. Retrieved 24 March 2013.
  16. ^ Wouterloot, J. G. A.; Brand, J.; Fiegle, K. (1993). "IRAS sources beyond the solar circle. III - Observations of H2O, OH, CH3OH and CO". Astronomy and Astrophysics Supplement Series. 98 (3): 589–636. Retrieved 24 March 2013.
  17. ^ Dobashi, Kazuhito; Bernard, Jean-Phillipe; Yonekura, Yoshinori; Fukui, Yasuo (1994). "Molecular clouds in Cygnus. 1: A large-scale (13)CO survey". Astrophysical Journal Supplement Series. 95 (2): 419–456. doi:10.1086/192106. Retrieved 24 March 2013.
  18. ^ Avedisova, V. S. (2002). "A Catalog of Star-Forming Regions in the Galaxy". Astronomy Reports. 46 (3): 193–205. doi:10.1134/1.1463097. Retrieved 26 March 2013.

Bibliography

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General texts

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Specific texts

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On stellar evolution

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  • Lada, C. J.; Kylafits, N. D. (1999). The Origin of Stars and Planetary Systems. Kluwer Academic Publishers. ISBN 0-7923-5909-7.
  • De Blasi, A. (2002). Le stelle: nascita, evoluzione e morte (in Italian). Bologna: CLUEB. ISBN 88-491-1832-5.
  • Abbondi, C. (2007). Universo in evoluzione dalla nascita alla morte delle stelle (in Italian). Sandit. ISBN 88-89150-32-7.

On the Cepheus OB2 association

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Star charts

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  • Taki, Toshimi (2005). "Taki's 8.5 Magnitude Star Atlas". Archived from the original on 5 November 2018. Retrieved 24 March 2013.
  • Tirion; Rappaport; Lovi (1987). Uranometria 2000.0 - Volume I - The Northern Hemisphere to -6°. Richmond, Virginia, USA: Willmann-Bell, inc. ISBN 0-943396-14-X.
  • Tirion; Sinnott (1998). Sky Atlas 2000.0 (2 ed.). Cambridge, USA: Cambridge University Press. ISBN 0-933346-90-5.
  • Tirion (2001). The Cambridge Star Atlas 2000.0 (3 ed.). Cambridge, USA: Cambridge University Press. ISBN 0-521-80084-6.
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