Lower's nebula (Sh 2-261) is located near the edge of the constellation Orion the Hunter.
Source: Davide De Martin - http://www.skyfactory.org
The Ori OB1 association and its surrounding molecular clouds are located far below the galactic plane and will be discussed in a future commentary on our local system of stars, the Gould Belt. The constellation Orion the Hunter does extend into the galactic plane in this sector, however. The Gem OB1 molecular clouds are partly in Orion, as are Lower's nebula (Sh 2-261) and numerous other interesting objects between 200° and 190°.
Gem OB1
The Gem OB1 molecular clouds described in the commentary on the Jellyfish (190°-180°) sector extend into this sector. Just east of the Monkey Head nebula (Sh 2-252) is a complex of 5 HII regions including Sh 2-254 to Sh 2-258, as well as BFS 52 and Sh 2-259.
The Sh 2-254 to Sh 2-258 complex is embedded in a 27 thousand solar mass molecular cloud, with much of the mass concentrated in a central core located between the two bright nebulae Sh 2-255 (IC 2162) and Sh 2-257. [1] The best available overview of this complex is given by Chavarria and colleagues in a preprint based on Spitzer observations. [2] Russeil gives the distance to the complex as 2460 ± 160 parsecs [3], which is compatible with the Avedisova estimate of 2500 ± 400 parsecs. [4] Moffat, Fitzgerald and Jackson give as ionising stars:
- Sh 2-254: BD +18 1123 (O9.5V)
- Sh 2-255: SLS 19 (B0 III neb)
- Sh 2-257: BD +18 1124 (B0V) plus 3 other stars with no measured spectral types
They also list the magnitudes of suspected ionising stars for the smaller nebulae Sh 2-256 and Sh 2-258 but give no catalog identifications or spectral types for them. [5] SIMBAD gives the spectral type for BD +18 1123 = HD 253247 as B1V and for BD +18 1124 = HD 253327 as B0.5V. SLS 19 is listed in SIMBAD as ALS 19 = MFJ SH 2-254 3 with an unclear but B-class spectrum. The SIMBAD designation for ALS 19 appears to be a mistake as the Moffat, Fitzgerald and Jackson paper associates this star with Sh 2-255, not the larger more diffuse Sh 2-254.
Sh 2-254, Sh 2-256 and Sh 2-258 contain the infrared clusters respectively [DB 2001] 30, [DB 2001] 31 and [DB 2001] 32. [6] The luminous far-infrared source Sh 2-255N is located near Sh 2-255 and contains a massive proto-cluster. [7] Several other papers have been published describing intense infrared sources near or embedded in Sh 2-255. [8], [9]
The Avedisova catalog lists 80 components in the star formation region associated with the Sh 2-254 to Sh 2-258 complex, including 11 masers. [Avedisova 1858]
BFS 52 is associated with the infrared source IRAS 06117+1901 that contains the cluster [DB 2001] 30. [6] Russeil gives a distance estimate of 2200 parsecs for BFS 52, placing it at about the same distance, or perhaps slightly closer than, the Sh 2-254 to Sh 2-258 complex. [10].
Sh 2-259, on the other hand, appears to be located much further away with distance estimates of 8300 [11] or 8000 ± 1400 parsecs [4]. It is ionised by a B1V class star. [12]
This hydrogen-alpha image shows the most prominent HII regions and supernova remnants in this sector, including Lower's nebula (Sh 2-261) and the Sh 2-254 to Sh 2-258 complex.
Source: Galactic Plane Explorer hydrogen-alpha image
The supernova remnant SNR G192.8-1.1 = SNR G193.3-01.5 is visible at radio frequencies in the sky between the Sh 2-254 to Sh 2-258 complex and Sh 2-261 and may lie at a distance of 4000 pc according to Caswell [13] (supported by a more recent 3900 pc estimate from Case and Bhattacharya [14]) or 2600 pc according to Huang and Thaddeus [15]. Huang and Thaddeus conclude that SNR G192.8-1.1 is part of the Gem OB1 molecular clouds. At one point it was speculated that SNR G192.8-1.1 was part of a much larger supernova remnant called the Origem Loop, but this larger remnant probably does not exist. [13]
Gem OB1 subregions 4 and 6
The region of the galactic plane below the Sh 2-254 to Sh 2-258 complex (from about -1° to -5° latitude) is visually obscured and no optically visible nebulae or ionising stars are cataloged there. Carpenter, Snell and Schloerb divide the molecular clouds in this direction into two complexes: Gem OB1 subregion 6 in the east and Gem OB1 subregion 4 in the west. They estimate that these subregions each contain 21 thousand solar masses of gas and dust. [16] Gem OB1 subregion 6 includes the Herbig B7e Orion variable star HD 250550, which forms part of the star formation region [Avedisova 1859]. The HII region WFS 6 = RAFGL 5173 is part of an Avedisova star formation region with 50 components in this same subregion, including a massive Herbig-Haro outflow from a young star [17], a water maser and an infrared cluster. [Avedisova 1854] The Avedisova catalog lists several other star formation regions in this direction containing young stars and Bok globules. [18] Gem OB1 subregion 4 contains the star formation region [Avedisova 1845], which includes the infrared source IRAS 05561+1804.
Lower's nebula
The HII region Sh 2-261 is often called Lower's nebula because it appears on a photographic plate taken by the father-and-son team of Harold and Charles Lower in 1939. The Lowers were amateur astronomers, accomplished telescope makers and pioneering astrophotographers from San Diego, California. Harold Lower published a pamphlet in 1939 describing an 8 inch Schmidt camera that he and his son had constructed several years previously. He notes that the camera has been especially useful in photographing what are now called HII regions:
Another field which we have found interesting is searching for diffuse galactic nebulae which photograph strongly by red light. By the use of red-sensitive film and a deep red filter we have been able to photograph a number of nebulae which are exceedingly faint on blue-sensitive negatives. [19]
Lower's nebula appears to be located well in front of the Gem OB1 molecular clouds at a distance of about 1000 parsecs. [20] Sharpless suggests that the nebula is ionised by the O7.5V class runaway star HD 41997. [21], [22]
Sh 2-253 and W15
Sh 2-253 is well above the Gem OB1 molecular clouds. It is most visible in hydrogen-alpha (although a faint "rim" is also visible at radio frequencies [23]). Several papers have concluded that it is ionised by stars found in the cluster Bochum 1. [4], [5] The cluster Alessi 58 = DSH J0625.7+1954 is also located nearby. [24] Neither Bochum 1 nor Alessi 58 occurs in the Kharchenko catalog of confirmed bright star clusters, however. [25]
According to Avedisova, Sh 2-253 is located at a distance of 4100 ± 400 parsecs and is ionised by the B1.5V class LS V +20 40. She associates this nebula and the star cluster Bochum 1. [4] This is compatible with the BFS distance estimate of 4400 parsecs. [11] On the other hand, Yadav and Sagar derive a distance of 2800 +/ 400 parsecs and an age of 10±5 million years for Bochum 1 using cluster photometry. [26] Reed gives a spectral type for LS 47 = LS V +19 5 in this direction as O8III, contradicting the B0 class given by SIMBAD. Moffat, Fitzgerald and Jackson list 3 O-class stars in this direction: LS 44 = HD 44811, LS 46 and LS 47. They note that only the B1.5V class LS V +20 40 appears within the nebula. [5] SIMBAD gives an O7.5V class for the double star HD 44811 but cites B classes for the others.
The radio source W15 that appears northeast of Sh-253 probably does not exist. Westerhout noted "probably 0-line error" in his catalog. [27]
The Gem OB1 molecular clouds dominate the western half of this microwave image, which also shows the major ionising stars, clusters and associations in this direction. Visible are the Gem OB1 association in the west, the Mon OB1 association in the east, and the ionising clusters NGC 2169 and Bochum 1.
Source: Galactic Plane Explorer microwave image
Sh 2-266 to Sh 2-272
Sh 2-266 is located well above Sh 2-268 and may be a ring nebula surrounding the Be class Orion-type variable supergiant MWC 137, at a distance of 6000 pc. [28] The Avedisova catalog lists 20 components, including two water masers and an infrared cluster (IRAS 06145+1455). [Avedisova 1874]
Sh 2-267 is sometimes misidentified as a planetary nebula. In fact, it is an HII region containing the infrared cluster [BDS 2003] 81 at a distance of 3500 parsecs. [29] Lahulla gives a slightly larger distance estimate of 4500 pc and says that the nebula is ionised by an O9V star. [30]
Sh 2-268 and Sh 2-270 are prominent in hydrogen-alpha to the southeast of Lower's nebula. SIMBAD identifies Sh 2-268 with the two Lynds nebulae LBN 874 (196.11°, -2.50°) and LBN 873 (195.63°, -2.51°) and this identification is taken directly from the Lynds catalog itself. [31] Sh 2-268 is, indeed a large nebula. The Sharpless catalog gives the position of Sh 2-268 as (196.4° -2.8°) and its diameter as 1 degree. [21] However, a look at this region in hydrogen-alpha suggests that LBN 873 is a separate nebula that lies mostly or entirely outside the boundary of Sh 2-268.
Russeil gives a distance estimate of 1300 pc for Sh 2-268, similar to Lower's nebula [10] Avedisova gives a similar distance estimate of 1140 ± 250 pc for Sh 2-268 and suggests that it is ionised by the B1 III giant HD 42352 = LS VI +13 5. [4]
There are two O9V stars visible within the hydrogen-alpha nebulosity in the general direction of Sh 2-268. These are LS VI +13 4 = HD 252682 and LS VI +13 6 = HD 252845. There is strangely little in the scientific literature about either star.
The ionising cluster NGC 2169 appears in the centre of the hydrogen-alpha emission associated with LBN 873. Kharchenko gives a distance of 1032 pc and an age of 7.7 million years. She lists 5 ionising stars. These are HD 252214 (B2.5V), HD 252248 (B2V), HD 41943 (B1V), HIP 29126 (B1), and DM +13 1124 (B1V).
Russeil gives a distance of 6800 pc for Sh 2-270, placing it in the Outer arm. [10] Carpenter, Snell, and Schloerb give a somewhat lower distance estimate for Sh 2-270 of 4800 parsecs [32] In a second paper, Carpenter and his colleagues find that Sh 2-270 contains an infrared star cluster (IRAS 06073+1249) embedded in a 1000 solar mass molecular cloud. [33] Neckel and Staude state that Sh 2-270 is a bipolar nebula [NS84] 8 and that the best explanation for the radio, visual and infrared emission from this direction would be for a nebula located at a distance of 2100 pc and ionised by a B0.5V class star. [34] The Avedisova catalog lists 14 components in the direction of Sh 2-270, including a water maser and the infrared source IRAS 06080+1233. [Avedisova 1879]
Sh 2-269 lies in front of a 8700 solar mass giant molecular cloud at a distance of about 3800 pc. It is bisected by a dust lane and is ionised by two stars in the western side of the nebula. One is a B0.5 V star, the other is visible only in the infrared and appears to be either O8 or O9.5. [35] The western side of the nebula contains an infrared cluster with at least 79 stars. [36] The Avedisova catalog [Avedisova 1878] lists 15 components for this nebula, including 3 masers, the infrared source IRAS 06117+1350 and the Herbig-Haro object HH 191.
The HII region Sh 2-271 is embedded in a 9800 solar mass molecular cloud at a distance of 4800 pc. [37] It contains the infrared cluster [BDS 2003] 82 [29]. Avedisova concludes that Sh 2-271 and Sh 2-272 are part of the same star forming complex at a distance of 4600 ± 1200 pc. She suggests that it is ionised by two stars with classes O9V and B1V. [4] BFS also comment that Sh 2-271 and Sh 272 are "related" and give a distance estimate of 4800 ± 500 pc for both nebulae. [11]
There are several mysterious radio sources visible in this direction, including Kes 1 and 4C 14.18. Not much appears in the scientific literature about either source.
Mon OB1
The large Mon OB1 association starts to appear in the eastern part of this sector and includes a few B-class stars as well as the star formation region [Avedisova 1880], which includes the young stellar object IRAS 06210+1432 = [KW97] 28-49. Mon OB1 is discussed in detail in the commentary on the Rosette (210° - 200°) sector to the east.
Nebulae in this sector
Notes
1. ^ Heyer, Mark H., Snell, Ronald L., Morgan, James, & Schloerb, F. Peter 1989, Astrophysical Journal, A CO and far-infrared study of the S254-S258 region
2. ^ Chavarria, L., Allen, L., Hora, J. L., Brunt, C., & Fazio, G. G. 2008, ArXiv e-prints, Spitzer observations of the Massive star forming complex S254-S258: structure and evolution
3. ^ Russeil, D., Adami, C., & Georgelin, Y. M. 2007, Astronomy and Astrophysics, Revised distances of Northern HII regions
4. ^ Avedisova, V. S. & Kondratenko, G. I. 1984, Nauchnye Informatsii, Exciting stars and the distances of the diffuse nebulae
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. ^ Dutra, C. M. & Bica, E. 2001, Astronomy and Astrophysics, New infrared star clusters and candidates in the Galaxy detected with 2MASS
7. ^ Cyganowski, C. J., Brogan, C. L., & Hunter, T. R. 2007, Astronomical Journal, Evidence for a Massive Protocluster in S255N
8. ^ Itoh, Yoichi, Tamura, Motohide, Suto, Hiroshi, Hayashi, Saeko S., Murakawa, Koji, Oasa, Yumiko, Nakajima, Yasushi, Kaifu, Norio, Kosugi, George, Usuda, Tomonori, & Doi, Yoshiyuk 2001, Publications of the Astronomical Society of Japan, Near-Infrared Observations of S 255-2 : The Heart of a Massive YSO Cluster
9. ^ Ojha, Devendra, Tamura, Motohide, & Sirius Team 2006, Bulletin of the Astronomical Society of India, Luminosity functions of YSO clusters in Sh-2 255, W3 main and NGC 7538 star forming regions
10. ^ Russeil, D. 2003, Astronomy and Astrophysics, Star-forming complexes and the spiral structure of our Galaxy
11. ^ Blitz, L., Fich, M., & Stark, A. A. 1982, Astrophysical Journal Supplement Series, Catalog of CO radial velocities toward galactic H II regions
12. ^ Deharveng, L., Zavagno, A., & Caplan, J. 2005, Astronomy and Astrophysics, Triggered massive-star formation on the borders of Galactic H II regions. I. A search for ``collect and collapse'' candidates
13. ^ Caswell, J. L. 1985, Astronomical Journal, Is G192.8-1.1 a discrete supernova remnant, or part of the Origem loop?
14. ^ Case, Gary L. & Bhattacharya, Dipen 1998, Astrophysical Journal, A New Sigma -D Relation and Its Application to the Galactic Supernova Remnant Distribution
15. ^ Huang, Y.-L. & Thaddeus, P. 1986, Astrophysical Journal, Molecular clouds and supernova remnants in the outer galaxy
16. ^ Carpenter, John M., Snell, Ronald L., & Schloerb, F. Peter 1995, Astrophysical Journal, Anatomy of the Gemini OB1 molecular cloud complex
17. ^ Devine, David, Bally, John, Reipurth, Bo, Shepherd, Debra, & Watson, Alan 1999, Astronomical Journal, A Giant Herbig-Haro Flow from a Massive Young Star in G192.16-3.82
18. ^ Avedisova, V. S. 2002, Astronomy Reports, A Catalog of Star-Forming Regions in the Galaxy
19. ^ Lower, H. A. 1939, Leaflet of the Astronomical Society of the Pacific, The Schmidt Camera
20. ^ Chavarria-K., C., de Lara, E., & Hasse, Ilse 1987, Astronomy and Astrophysics, Eight-colour photometry of stars associated with selected Sharpless H II regions at L exp II of about 190 deg - S 252, S 254, S 255, S 257, and S 261
21. ^ Sharpless, Stewart 1959, Astrophysical Journal Supplement Series, A Catalogue of H II Regions.
22. ^ Moffat, A. F. J., Marchenko, S. V., Seggewiss, W., van der Hucht, K. A., Schrijver, H., Stenholm, B., Lundstrom, I., Setia Gunawan, D. Y. A., Sutantyo, W., van den Heuvel, E. P. J., de Cuyper, J.-P., & Gomez, A. E. 1998, Astronomy and Astrophysics, Wolf-Rayet stars and O-star runaways with HIPPARCOS. I. Kinematics
23. ^ Fich, Michel 1993, Astrophysical Journal Supplement Series, A VLA survey of optically visible galactic H II regions
24. ^ Kronberger, M., Teutsch, P., Alessi, B., Steine, M., Ferrero, L., Graczewski, K., Juchert, M., Patchick, D., Riddle, D., Saloranta, J., Schoenball, M., & Watson, C. 2006, Astronomy and Astrophysics, New galactic open cluster candidates from DSS and 2MASS imagery
25. ^ Kharchenko, N. V., Piskunov, A. E., Röser, S., Schilbach, E., & Scholz, R.-D. 2005, Astronomy and Astrophysics, Astrophysical parameters of Galactic open clusters
26. ^ Yadav, R. K. S. & Sagar, R. 2003, Bulletin of the Astronomical Society of India, UBVRI CCD photometry of the OB associations Bochum 1 and Bochum 6.
27. ^ Westerhout, G. 1958, Bulletin of the Astronomical Institutes of the Netherlands, A survey of the continuous radiation from the Galactic System at a frequency of 1390 Mc/s
28. ^ Esteban, Cesar & Fernandez, Matilde 1998, Monthly Notices of the Royal Astronomical Society, S266: a ring nebula around a Galactic B[e] supergiant?
29. ^ 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
30. ^ Lahulla, J. F. 1987, Astronomical Journal, Observations of stars in H II regions - UBVRI photometry
31. ^ Lynds, Beverly T. 1965, Astrophysical Journal Supplement Series, Catalogue of Bright Nebulae.
32. ^ Carpenter, John M., Snell, Ronald L., & Schloerb, F. Peter 1990, Astrophysical Journal, Molecular clouds associated with luminous far-infrared sources in the outer Galaxy
33. ^ Carpenter, John M., Snell, Ronald L., Schloerb, F. P., & Skrutskie, M. F. 1993, Astrophysical Journal, Embedded star clusters associated with luminous IRAS point sources
34. ^ Neckel, T. & Staude, H. J. 1984, Astronomy and Astrophysics, A survey of bipolar and cometary nebulae - Photographic and photometric observations
35. ^ Godbout, Steve, Joncas, Gilles, Durand, Daniel, & Arsenault, Robin 1997, Astrophysical Journal, The H II Region Sharpless 269. I. Morphological Study of the Radial Velocity, Velocity Dispersion, and Density Fields
36. ^ Eiroa, C. & Casali, M. M. 1995, Astronomy and Astrophysics, The S 269 stellar cluster.
37. ^ Hunter, Deidre A., Thronson, Harley A., Jr., & Wilton, Charles 1990, Astronomical Journal, Small Galactic H II regions. II - The molecular clouds and star formation