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Monoceros Arc (220° - 210°)

Submitted by Kevin Jardine on 19 August, 2008 - 22:37

Sh 2-284 is a group of several HII regions ionised by members of the star cluster Dolidze 25 in the Milky Way's Monoceros arc.

Source: Dean Salman -

This sector provides a window into the Milky Way's Outer Arm region as well as containing an unusual large and cold molecular cloud complex with little visible star formation.

Sh 2-282

The HII region Sh 2-282 (LBN 978) is likely ionised by the O9.5 III pulsating variable giant HD 47432 at a distance of 1500 ± 300 parsecs according to Avedisova. [1] A more recent study finds at least 8 cometary globules in the nebula and gives a distance estimate of 1250 pc. [2]. Either estimate suggests that this star is part of the Mon OB2 association which is discussed in more detail in the commentary on the Fox Fur and Rosette (210° - 200°) sector to the west. Russeil concludes that Sh 2-282 and BFS54 are part of the same star formation region at a distance of 1170 +/ 290 pc. BFS54 is ionised by the B3 star HD 289120 [3] and is also known as the reflection nebula NGC 2282 or VDB 85.

Monoceros Arc

Russeil concludes that Sh 2-283, Sh 2-284, Sh 2-285 and Sh 2-286 are all part of the same star formation region at a distance of 7890 ± 290 pc. [3] These HII regions thus appear to form a significant arc in the Milky Way's Outer Arm region. There seems to be no name for this arc in the scientific literature. I suggest "the Monoceros arc" as all of these nebulae are located in the constellation Monoceros.

The brightest of these nebulae at radio, hydrogen-alpha and infrared frequencies is Sh 2-284 (LBN 983), which is ionised by the star cluster Dolidze 25. Avedisova gives a lower distance estimate of 5200 ± 800 pc for Sh 2-284. [1] Detailed images of this large object show that it also contains a number of smaller HII regions.

Dolidze 25 is surprisingly understudied for an important Outer arm ionising cluster. It does not appear in Kharchenko's cluster catalog. [4] Moffat, Fitzgerald and Jackson list 5 ionising stars:


This hydrogen-alpha image shows the major nebulae in this sector.

Source: Galactic Plane Explorer hydrogen-alpha image

Crampton lists 3 ionising stars that may be associated with Sh 2-284: HD 48691 (B0.5 IV), BD +00 1576 (O9 III) and LS VI +00 19 (OB). [6] SIMBAD identifies this last star with Cl* Dolidze 25 MV 1. Reynolds also lists BD +00 1576 as an ionising star for Sh 2-284. [7] Turbide and Moffat add [TM93] SH 2-284 45 (B1:V:) and [TM93] SH 2-284 30 (B1:) [8] (although these may not really be new stars as they have the same spectral types as Cl* Dolidze 25 MV 15 and Cl* Dolidze 25 MV 17).

The only paper focusing exclusively on Dolidze 25 examines the spectra of the stars Cl* Dolidze 25 MV 15, Cl* Dolidze 25 MV 17 and Cl* Dolidze 25 MV 22 and concludes that the cluster is unusually metal-deficient.

The Avedisova star formation region catalog lists 33 components for Sh 2-284, including 3 water masers. [Avedisova 1939]

Sh 2-283, to the southwest of Sh 2-284, contains the infrared star group [BDS2003] 84. [9] Turbide and Moffat identify a B0:V: class ionising star, [TM93] SH 2-283 22. [8]

The large filamentary nebula to the northeast of Sh 2-284, visible in hydrogen-alpha, resembles a supernova remnant and indeed is identified as SNR G213.0-00.6 in a 2003 paper based on radio emission by Reich, Zang and Fuerst. [10] These authors use a very low (2400 pc) distance estimate for Sh 2-284 and argue that SNR G213.0-00.6 may be interacting with Sh 2-284. As most authorities give a distance estimate for Sh 2-284 that is two or three times larger, it seems more likely that SNR G213.0-00.6 is a foreground object. SNR G213.0-00.6 is missing from the Green supernova remnant catalog. [11]

Sh 2-285 is ionised by two B0 V stars [12] and contains the infrared star group [BDS2003] 85. [9] Avedisova identifies one of these B0 V stars as LS VI -00 9. [1]

Sh 2-286 is located well to the east of the other objects in the Monoceros arc just south of a large prominent nebulosity visible in hydrogen-alpha. Although Russeil places Sh 2-286 in the Monoceros arc, she also states "no distance is available" for this nebula. [3] BFS and Avedisova also give no distance estimates. [13], [1] However, the Avedisova catalog lists the molecular cloud [MAB97] 217.38-1.38 as one of 8 components of the star formation region including Sh 2-286 [Avedisova 1974] and this molecular cloud is believed to lie at a distance of 6200 parsecs. [14] Russeil herself gives a similar distance estimate of 6600 pc for Sh 2-286 in a 2003 paper. [15] Fich and Blitz give a very uncertain range of 8770 ± 2910 pc. [16] Sh 2-286 contains the infrared star group [BDS2003] 88. [9]

Other Outer Arm Objects

BFS58 is located at a very uncertain distance of 8760 ± 2860 pc [16] and appears behind the Sh 2-287 molecular cloud complex described below. It may be associated with the iron-rich Iron-clad nebula, IRAS 06562-0337, which contains a young B0-B2 class stellar object still emerging within a dense molecular cloud. This nebula is believed to lie at a very uncertain distance of 7000 ± 3000 pc. [17]

Sh 2-289 lies at the huge distance of 10100 pc according to Lahulla. [18] Avedisova gives a lower estimate of 5600 ± 1600 pc and lists two B-class ionising stars. [1] Turbide and Moffatt add an additional O9.5V class ionising star, [TM93] SH 2-289 19, and give an age of 6 million years. [8] Fich and Blitz give an intermediate distance of 7900 ± 800 pc. [16] Sh 2-289 is located well below the galactic plane, and this may in part be related to an outer galaxy warp in the third quadrant which bends the galactic disk downwards. [19]

This spectacular Hubble space telescope image shows light from the mysterious V838 Mon nova illuminating dust clouds surrounding the star system.

Source: NASA's Hubble Space Telescope

The Nova V838 Mon

In January 2002, one component of the previously unknown binary star V838 Mon (217.7975°, +1.0522°) suddenly expanded rapidly into an enormous cool supergiant, increasing its luminosity 10 thousand times and temporarily becoming the brightest star in the Milky Way. Light from the star illuminated dust clouds previously released from the system, creating a spectacular and rapidly changing light echo observed by the Hubble space telescope. The star system, which also includes a B3 V class companion and is surrounded by a sparse star cluster, is believed to lie at a distance of 6100 ± 600 pc, placing it in the Milky Way's Outer Arm region. [20], [21]

BFS 53

The small faint nebula BFS 53 is located in a similar direction to the Monoceros arc but is a foreground object at a distance of 4010 ± 730 pc according to Russeil. [3] The Avedisova catalog associates BFS 53 with the carbon star IRAS 06420+0108. [Avedisova 1934]

Sh 2-287 and the Maddalena cloud

This sector contains GAL 216-02.5, an unusual large cold molecular cloud with no visible star formation. Often called the Maddalena cloud, this object was first described by Maddalena and Thaddeus in a 1985 paper and is prominent at microwave frequencies. The original paper estimated a distance of 3000 pc, implying a size of 250 x 100 pc, and containing from 700 thousand to 1.1 million solar masses of gas. [22] A follow-up paper in 1996 suggests that this cloud may be part of a larger molecular complex including Sh 2-287 and reduces the parameters to a distance of 2300 pc containing about 340 thousand solar masses of molecular gas. Even this lower estimate makes it one of the most massive molecular cloud complexes in the solar neighbourhood. [23]

Sh 2-287 (LBN 1012) is part of a molecular cloud complex to the north of the Maddalena cloud. This complex is described in a 2005 paper by M.E. van den Ancker:

It consists of two main components of similar sizes and CO column densities, which are connected by a tenuous bridge. The northern component harbours its densest core, associated with the bipolar nebula NS14. The faint HII region S287 is associated with the other component.


This microwave image shows the major molecular clouds in this sector, dominated by the massive cool Maddalena cloud and the Sh 2-287 molecular complex to its north. This image also shows the ionising stars, clusters and associations in this sector.

Source: Galactic Plane Explorer microwave image

According to Avedisova, Sh 2-287 is ionised by the O9.5 V star LS VI -04 19 at a distance of 3300 ± 800 pc, a bit further than the Williams and Maddalena estimate. Neckel and Staude give a closer 2100 pc estimate. [25] Lada and Lada list two small embedded star clusters in Sh 2-287, based on results published in 1994 by Hodapp [26], which they call S287 N and S287 C. They give distances of 1400 pc for both clusters - considerably closer than the usual distance estimates for Sh 2-287. [27]

The bipolar nebula [NS84] 14 (BFS57), located across a narrow bridge of molecular gas from Sh 2-287, is illuminated (and ionised) by a trapezium system of four stars with spectral types B0.5, B1, B9 and A5 at a distance of 2300 pc. [28], [29]

A group of small nebulae lie in a similar direction to [NS84] 14: BFS55 - BFS59. BFS56 contains the infrared star cluster [IBP2002] CC03. [30] Fich and Blitz find that all of these nebulae with the exception of BFS58 have distances of about 2000 pc, placing them in a similar location to [NS84] 14.

Avedisova gives a distance estimate of 1300 ± 500 pc for BFS55 and says that it is ionised by the B0.5 IV class multiple subgiant HD 51756. [1]

The Avedisova catalog combines [NS84] 14 (BFS57) and BFS56 together into one star formation region. [Avedisova 1975]

BFS59 appears to contain the infrared star grouping [BDS2003] 89 which lies at a distance of about 1400 pc. [9]

Sh 2-288 (IC 466), located to the north of the Sh 2-287 molecular cloud, seems to be at a similar distance or just slightly further away, with BFS giving an estimate of 3000 pc. [13] It contains the infrared cluster [DB2001] Cl 35 [31] and is ionised by an O9V class star. [32] Avedisova gives a very uncertain distance estimate of 4100 ± 2000 pc and lists two uncatalogued B1 V and B1 III ionising stars. [1]

NGC 2311 and Mon OB3

Kharchenko identifies an ionising cluster, NGC 2311, that seems to be part of the larger Sh 2-287 molecular complex. She gives one ionising star, TYC 4809-819-2 (B2/3 II), a distance of 2000 parsecs and an age of 398.1 million years. [4] J.A. Graham suggested in 1971 that there are two groups of OB stars in this direction, one at 2400 pc and another possibly at 3800 pc. [33] Subsequent authors (eg. [34], [35]) list a new OB association, Mon OB3, in this direction which is not included in Ruprecht's official IAU list of OB associations.

Humphreys lists 3 ionising members of Mon OB3: HD 51452 (B0 III:NN), LS VI -04 19 (O9.5 V) and Sh 2-287 5 (O9.5 V), as well as the B9 IB supergiant HD 51509. [34]

BFS 60

The tiny nearby nebula BFS 60 has a distance of 780 ± 510 pc according to Fich and Blitz. [16]

Nebulae in this sector


 1. ^ Avedisova, V. S. & Kondratenko, G. I. 1984, Nauchnye Informatsii, Exciting stars and the distances of the diffuse nebulae

 2. ^ Carrasco-González, C., López, R., Gyulbudaghian, A., Anglada, G., & Lee, C. W. 2006, Astronomy and Astrophysics, A new radial system of dark globules in Monoceros

 3. ^ Russeil, D., Adami, C., & Georgelin, Y. M. 2007, Astronomy and Astrophysics, Revised distances of Northern HII regions

 4. ^ Kharchenko, N. V., Piskunov, A. E., Röser, S., Schilbach, E., & Scholz, R.-D. 2005, Astronomy and Astrophysics, Astrophysical parameters of Galactic open clusters

 5. ^ Moffat, A. F. J., Jackson, P. D., & Fitzgerald, M. P. 1979, Astronomy and Astrophysics Supplement Series, The rotation and structure of the galaxy beyond the solar circle. I - Photometry and spectroscopy of 276 stars in 45 H II regions and other young stellar groups toward the galactic anticentre

 6. ^ Crampton, D. 1971, Astronomical Journal, Observations of stars in H II regions: Spectral classification and UBV photometry.

 7. ^ Reynolds, R. J. 1987, Astrophysical Journal, A view of the galactic H-alpha background - L = 208-218 deg, B = -2 to +8 deg

 8. ^ Turbide, Luc & Moffat, Anthony F. J. 1993, Astronomical Journal, Precision photometry of young stellar groups towards the outer Galactic disk and the Galactic rotation curve

 9. ^ Bica, E., Dutra, C. M., Soares, J., & Barbuy, B. 2003, Astronomy and Astrophysics, New infrared star clusters in the Northern and Equatorial Milky Way with 2MASS

10. ^ Reich, W., Zhang, X., & Fürst, E. 2003, Astronomy and Astrophysics, 35 cm observations of a sample of large supernova remnants

11. ^ Green, D. A. 2004, Bulletin of the Astronomical Society of India, Galactic supernova remnants: an updated catalogue and some statistics. and here for the most current version of this supernova remnant catalog.

12. ^ Kilian-Montenbruck, J., Gehren, T., & Nissen, P. E. 1994, Astronomy and Astrophysics, The galactic distribution of chemical elements as derived from B-stars in open clusters. 2: NGC 6611, S 285, and S 289

13. ^ Blitz, L., Fich, M., & Stark, A. A. 1982, Astrophysical Journal Supplement Series, Catalog of CO radial velocities toward galactic H II regions

14. ^ May, J., Alvarez, H., & Bronfman, L. 1997, Astronomy and Astrophysics, Physical properties of molecular clouds in the southern outer Galaxy.

15. ^ Russeil, D. 2003, Astronomy and Astrophysics, Star-forming complexes and the spiral structure of our Galaxy

16. ^ Fich, M. & Blitz, L. 1984, Astrophysical Journal, Optical H II regions in the outer galaxy

17. ^ Bachiller, R., Perez Gutierrez, M., & Garcia-Lario, P. 1998, Astronomy and Astrophysics, IRAS06562-0337, the Iron-clad Nebula: a young star embedded in a molecular cloud

18. ^ Lahulla, J. F. 1989, Astronomical Journal, Multicolor UBVRI observations of S289, S300, and S309

19. ^ Vázquez, Ruben A., May, Jorge, Carraro, Giovanni, Bronfman, Leonardo, Moitinho, André, & Baume, Gustavo 2008, Astrophysical Journal, Spiral Structure in the Outer Galactic Disk. I. The Third Galactic Quadrant

20. ^ Bond, Howard E., Henden, Arne, Levay, Zoltan G., Panagia, Nino, Sparks, William B., Starrfield, Sumner, Wagner, R. Mark, Corradi, R. L. M., & Munari, U. 2003, Nature, An energetic stellar outburst accompanied by circumstellar light echoes

21. ^ Sparks, William B., Bond, Howard E., Cracraft, Misty, Levay, Zolt, Crause, Lisa A., Dopita, Michael A., Henden, Arne A., Munari, Ulisse, Panagia, Nino, Starrfield, Sumner G., Sugerman, Ben E., Wagner, R. Mark, & White, Richard L. 2008, Astronomical Journal, V838 Monocerotis: a Geometric Distance from Hubble Space Telescope Polarimetric Imaging of its Light Echo

22. ^ Maddalena, R. J. & Thaddeus, P. 1985, Astrophysical Journal, A large, cold, and unusual molecular cloud in Monoceros

23. ^ Williams, Jonathan P. & Maddalena, Ronald J. 1996, Astrophysical Journal, A Large Photodissociation Region around the Cold, Unusual Cloud G216-2.5

24. ^ van den Ancker, M. E. 2005, Astronomy and Astrophysics, Mid-infrared imaging of a young bipolar nebula in the S287 molecular cloud

25. ^ Neckel, T. & Staude, H. J. 1992, Astronomy and Astrophysics, Optical Traces of Two IRAS Sources Driving Bipolar Outflows in the S:287 Molecular Cloud

26. ^ Hodapp, Klaus-Werner 1994, Astrophysical Journal Supplement Series, A K' imaging survey of molecular outflow sources

27. ^ Lada, Charles J. & Lada, Elizabeth A. 2003, Annual Review of Astronomy and Astrophysics, Embedded Clusters in Molecular Clouds

28. ^ Neckel, Th., Staude, H. J., & Meisenheimer, K. 1987, Mitteilungen der Astronomischen Gesellschaft Hamburg, New Observations of the Bipolar Nebula NS 14

29. ^ Howard, Eric M., Pipher, Judith L., & Forrest, William J. 1998, Astrophysical Journal, A Near-Infrared Study of the NS 14 Bipolar Nebula

30. ^ Ivanov, V. D., Borissova, J., Pessev, P., Ivanov, G. R., & Kurtev, R. 2002, Astronomy and Astrophysics, Discovery of new Milky Way star clusters candidates in the 2MASS point source catalog

31. ^ Dutra, C. M. & Bica, E. 2001, Astronomy and Astrophysics, New infrared star clusters and candidates in the Galaxy detected with 2MASS

32. ^ Hunter, Deidre A. & Massey, Philip 1990, Astronomical Journal, Small Galactic H II regions. I - Spectral classifications of massive stars

33. ^ Graham, J. A. 1971, Astronomical Journal, The distances of two faint OB star groups in Monoceros

34. ^ Humphreys, R. M. 1978, Astrophysical Journal Supplement Series, Studies of luminous stars in nearby galaxies. I. Supergiants and O stars in the Milky Way. and the unpublished catalogs available here.

35. ^ Turner, David G., Pedreros, Mario H., & Walker, Alistair R. 1998, Astronomical Journal, Galactic Clusters with Associated Cepheid Variables. VI. Anonymous van den Bergh (C0634+031) and CV Monocerotis