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Jellyfish (190° - 180°)

Submitted by Kevin Jardine on 10 July, 2008 - 09:56

The Jellyfish supernova remnant is about 12,700 years old and is part of the Gem OB1 association, which is located about 1500 to 2000 parsecs away in the outer galaxy.

Source: Dean Salman -

The Jellyfish supernova remnant (SNR 189.1+03.0, Sh 2-248, IC 443) which appears within the molecular clouds surrounding the Gem OB1 association, is one of the most prominent objects in this direction, which is usually considered to be relatively empty. Nevertheless, there are many interesting objects in this sector, including the star cluster Messier 35, a flaring neutron star, and what may be the closest O-star to our solar system. Messier 1 (SNR 184.6-5.8, Sh 2-244), the famous Crab nebula supernova remnant, is also located well below the galactic plane in this direction.

A flaring neutron star

Flavia's star, the double star system HD 245770 (LS V +26 5), which is believed to lie at a distance of about 2000 parsecs, and is visible in the direction of the eastern edge of the Simeis 147 (Sh 2-240) supernova remnant, has been intensely studied by astronomers. The brightest visual component is an O9.5IIIe giant, but what has attracted most of the attention is its companion, which appears to be a neutron star with an orbital period of 110 days. Bright X-ray bursts are occasionally observed from the neutron star, and these may be caused by material falling inwards from an accretion disk of gas and dust surrounding the star. [1]

The mystery of Sh 2-241

The nebulae Sh 2-241 and Sh 2-242 appear in the sky near the supernova remnant Sh 2-240 (SNR 180.0-01.7,Simeis 147). Sh 2-241 is a blister on the side of a molecular cloud at a distance of 5300 ± 1100 parsecs, and appears to be ionized by the O9V star LS V +30 31. [2] Avedisova adds a second unnamed B0.5V ionising star and gives a closer (but overlapping) distance estimate of 4500 ± 1200 parsecs. [3] Deharveng and colleagues give a similar estimate of 4700 parsecs. [4] Sh 2-241 is likely a massive star formation region. [5] Images of the nebula in hydrogen-alpha show that it is composed of a bright knot at the tip of a cone of more diffuse nebula. The Sharpless designation applies to the entire nebulosity, not just the bright knot.

The O9V class star LS V +30 31 at (180.9343° +04.0421°) is located at a distance of only 130 parsecs, according to observations made by the Hipparcos astrometry satellite [6], which makes it possibly the closest known O-star to our solar system. This contradicts the large 4500-5300 parsec distance estimates for Sh 2-241, suggesting that either LS V +30 31 is not the ionising star for Sh 2-241 or that this nebula is far closer than the available distance estimates suggest. LS V +30 31 and HIP 28711 are listed separately in SIMBAD but the Hipparcos paper identifies them. [6] The parallax of HIP 28711 is 7.59 mas (with an error of 2.75 mas), which is 132 parsecs, and the Hipparcos catalog does indeed give the spectral type as O9V.

The recently re-reduced Hipparcos catalog simply deepens the mystery as the new parallax for HIP 28711 is given as 9.19 mas (with an error of 2.85 mas). This makes the star even closer (109 parsecs). [7] (data accessed through Astrogrid).

The reflection nebula vdB 65 = DG 86 [8] is near in the sky to Sh 2-241, but vdB 65 is apparently a much closer object at a distance of 1100 parsecs associated with LDN 1557 and is part of a complex of molecular clouds and dark nebulae that also includes LDN 1550, 1555, and 1560. [9]

Sh 2-242, Sh 2-243 and W11

Avedisova concludes that the HII region Sh 2-242 is excited by two unnamed B0V and B0IV-V stars and appears to lie at a distance of 2200 ± 220 parsecs. [3] This is compatible with the BFS estimate of 2100 parsecs. [10] A 1990 paper gives an estimate of 2700 parsecs. [11] Lada and Lada find that Sh 2-242 contains an 81 solar mass star cluster visible in infrared [12] and the Avedisova catalog associates Sh 2-242 with the infrared cluster [DB2001] Cl 25. [Avedisova 1798] Stark and Brand find that the nebula is associated with a giant molecular cloud. [13]

There is little or nothing visible at the location of Sh 2-243 (LBN 830) at visible frequencies on the DSS2 or IPHAS plates, or at infrared or radio frequencies either. BFS do not give a distance estimate for Sh 2-243 because they detect two quite different velocities in the carbon monoxide gas in this direction. [10] Russeil gives an estimate for the distance to Sh 2-243 as 2000 parsecs [14], which seems compatible with the prominent molecular cloud mapped in this direction and displayed in Figures 1 and 2 of a Japanese study of this region. [9] There is little in the scientific literature beyond these references, so all that can be concluded is that it is unclear what Sharpless originally detected but there is definitely a significant molecular cloud in this direction visible in microwaves. Having said that, the Avedisova catalog does associate Sh 2-243 with a star formation region that also includes the reflection nebula DG 68 = [SS62] 45, a hydroxyl maser, the infrared source IRAS 05363+2317 and several radio sources. [Avedisova 1809]

Westerhout detected a radio source (W11) just south of Sh 2-243, but his notes say "probably 0-line error" [15], and there is no obvious object in this direction.

This radio image shows the most prominent HII regions and supernova remnants in this sector. The Jellyfish supernova remnant and the adjacent HII region Sh 2-249 dominate this sector at radio frequencies.

Source: Galactic Plane Explorer radio image

An outer void

The galactic plane between these nebulae and the Gemini molecular clouds seems empty, with only the tiny nebulae BFS48, BFS49 and BFS50 lighting the void. Not much is seen in this region of the galactic plane at infrared, radio or microwave frequencies. There is an intriguing hint of a large circular nebula in WHAM hydrogen-alpha, visible in the Galactic Plane Explorer around (184.3°, 0.75°) with the brightest spot near the infrared source IRAS 05553+2642 [Avedisova 1803], but this does not show up in the more detailed IPHAS hydrogen-alpha images, so this clearly needs more investigation.

Stark and Brand find that BFS48 is associated with a giant molecular cloud. [13] BFS 49 and BFS 50 both contain infrared star clusters, designated [BDS2003] 76 and [BDS2003] 77 respectively. [16]

One much more famous object lurks well below the galactic plane at (184.60°, -5.80°) - the Crab nebula (SNR 184.6-05.8, M1, W9, Sh 2-244). This supernova remnant is one of the most studied objects listed in the SIMBAD astronomical database with 3346 scientific papers referring to it. It is the remains of a supernova observed in 1054 [17] and is believed to lie at a distance of about 1930 parsecs. [18]

Commenting on the emptiness in this sector, S.W. McCuskey wrote

No evidence exists among the OB stars for a spiral arm beyond the local concentration in which the sun is embedded. [19]

Radio observations well above and below the galactic plane, however, have found hydrogen gas moving at high velocity in this sector, and some researchers such as Heiles have interpreted this as an expanding shell in this sector centred around the galactic plane. [20]

A detailed study of this high velocity gas comes to quite a different conclusion - that this gas is from high velocity clouds, perhaps originating from the Milky Way's halo, which are crashing through the galactic disk because of gravitational attraction. [21] It seems that the emptiness of the outer galaxy gives us a clear view of a vast cosmic meteor shower.

Approaching Gem OB1

Brighter stars start to appear again in the eastern part of the sector, which is dominated by a complex of molecular clouds surrounding the Gem OB1 association.

The star cluster Messier 35 (NGC 2168) lies well in front of Gem OB1 at a distance of 830 parsecs and is 151 million years old, according to Kharchenko, who lists 4 ionising stars, all B-class. [22] A 2003 study using the 3.6 meter Canada-France-Hawaii Telescope noted that NGC 2168 contains more than 1000 stars in total and gives slightly larger estimates of 912 (+70 or -65) parsecs and 180 million years. [23]

The star cluster NGC 2129 is found at about the same distance as Gem OB1 with a distance of 1515 parsecs and an age of 12 million years according to Kharchenko [22], or a distance of 2200 +/ 200 parsecs and an age of 10 million years according to a 2006 study. [24] Kharchenko lists one ionising star, the B2III:e giant HD 250289. The 2006 study identifies 37 probable members.

Humphreys concludes that NGC 2129 is part of a small OB association, which she also calls NGC 2129, and lists three ionising members: the two B2I supergiants HD 40003 and HD 250290 and the B3III giant HD 250241 at an average distance of about 1810 parsecs. [25] Reed also lists the O8Ia supergiant LS V +23 8 in this direction. [Reed] SIMBAD says that LS V +23 8 is a B-class star, but a 2003 study supports the O8Ia class and gives a distance modulus of 12.5 (about 3200 parsecs) [26], suggesting a location in the Perseus arm.

Collinder 89 lies at a distance of 800 parsecs and is 31.6 million years old according to Kharchenko. She lists 7 ionising stars, including the O9Vp class HD 255055. [22] Negueruela, Steele, and Bernabeu describe HD 255055 as a "likely member of Gem OB1" and note that it is "immersed in diffuse nebulosity". [27] A 1986 study lists a distance of 2480 parsecs for HD 255055. [20] Humphreys lists HD 255055 as one of the ionising stars for the Gem OB1 association, with a distance modulus of 11.97, which works out to be the same estimate as in the 1986 study, 2480 parsecs. [25] Sharpless lists HD 255055 as one of the ionising stars of Sh 2-249 [Sh], which is usually listed as part of Gem OB1. [28]

Gem OB1

The most detailed study of the Gem OB1 region appears in two papers published in 1995 by Carpenter, Snell and Schloerb. [29], [30] This OB association appears at a distance of about 1500 to 2000 parsecs and is embedded in a large complex of molecular clouds containing about 320 thousand solar masses of gas and dust. It includes the HII regions Sh 2-247, Sh 2-252, Sh 2-254 to Sh 2-258, and BFS 52 as well as the Jellyfish supernova remnant (SNR 189.1+03.0, Sh 2-248, IC 443). [29] Other studies add Sh 2-249 to this list [28].

The Gem OB1 molecular clouds are the moist prominent objects in this microwave image, which also shows the major ionising stars, clusters and associations in this direction.

Source: Galactic Plane Explorer microwave image

Humphreys lists 17 OB stars in Gem OB1, including 4 O-class stars, as well as 3 M-class supergiants. [25] The hottest of these stars is HD 42088 (O6.5 V).

Avedisova lists HD 42088 as one of the ionising stars of Sh 2-252 [3], which is commonly called the Monkey Head nebula. Sh 2-252 appears to surround the star cluster NGC 2175.[31] However, Kharchenko lists no star cluster in this direction [22] and a 2005 paper separates the stars in this direction into 10 distinct groups with distances ranging from 410 to 8100 parsecs. [32] So NGC 2175 may not be a real star cluster. Fountain, Gary and O'Dell argue that HD 42088 alone can explain almost all the ionisation seen in the nebula. They explain the dynamics of the region as a double blister created by molecular gas ionised by HD 42088 and suspended between two or possibly three larger clouds of neutral atomic hydrogen. [33] Felli and colleagues seem to disagree, however, stating that HD 42088 can only explain about half the ionisation observed in the region near the radio source Sh 2-252 B, for example, and that less visible embedded stars must be responsible for the rest. [34] A later study concludes that the main ionising star for Sh 2-252 B is the B1V class LSV +20 16. [35]

Sh 2-252 lies at a distance of 2200 ± 300 parsecs [31], 2000 parsecs [29] or 2180 ± 550 parsecs [3] which seems to associate this nebula with the Gem OB1 molecular clouds in the same direction. The Avedisova catalog lists 53 components for the star formation region associated with Sh 2-252, including the cometary nebula [NS84] 7 (IRAS 06055+2039, RAFGL 5179). [Avedisova 1842] IRAS 06055+2039 contains a 2-3 million year old star cluster embedded in a 7 to 9 thousand solar mass molecular cloud. It is associated with Sh 2-252 A, which is one of 6 radio sources that have been detected in the direction of the nebula. Of these, 4 are compact radio sources (Sh 2-252 A, B, C and E), one more diffuse (Sh 2-252 F) and one apparently extragalactic (Sh 2-252 D). Sh 2-252 F is ionised by HD 42088. The compact sources likely all have their own embedded ionisation sources in addition to HD 42088. [36], [34] Sh 2-252 E is associated with a cluster of 21 stars embedded in the brightest knot of nebulosity in Sh 2-252. This cluster does not seem to have a formal catalog name but is sometimes referred to as the "Christbaumhäufchen" (Christmas tree cluster) and includes two prominent B1V and A0 class stars. Sh 2-252 C may be ionised by the B-class star LS V +20 17. [35], [37]

The Sh 2-247 HII region is associated with a 37 thousand solar mass molecular cloud. The nebula lies at a distance of 2200 pc and appears to be physically connected through CO filaments with Sh 2-252. The exciting star is the B0 III giant LS V 21 27. [38] According to the Avedisova catalog, the star formation region associated with Sh 2-247 contains 51 components, including 9 masers, the infrared cluster IRAS 06061+2151 = WB89 755, and the young stellar object IRAS 06058+2138 = WB89 752. [Avedisova 1830]

Sharpless lists 6 possible ionising stars for the HII region Sh 2-249. [Sh] The hottest of these is the the O9Vp class HD 255055, which Kharchenko says is a member of the star cluster Collinder 89 at a distance of only 800 parsecs. [22] Avedisova lists three B-class ionising stars for Sh 2-249 (but not HD 255055) and gives a distance estimate of 1250 ± 200 parsecs. [3] BFS give a distance estimate of 1600 parsecs. [10] The O9V star HD 256035, one of the four O-stars Humphreys associates with Gem OB1, ionises the southern portion of Sh 2-249, Sh 2-249S. [39]

Sh 2-249 is also associated with the HII region BFS51, the reflection nebula vdB 75, the dark clouds LDN 1564 and LDN 1567, and the molecular cloud [KOY98] 102. [9] The Avedisova catalog mentions two reflection nebula: LBN 845 and IC 444. [Avedisova 1834] Sh 2-249 and the nearby Jellyfish supernova remnant Sh 2-248 do not seem to be physically associated but may have developed within the same molecular cloud. [40]

The Jellyfish supernova remnant appears to be about 12,700 years old [41]. It is located at a distance of about 1500 parsecs [42] and has a complex 3-shell structure [39]. Parts of this structure are bright in X-rays and one of the shells may be associated with a second, much older supernova remnant. [43]

Nebulae in this sector


 1. ^ Giovannelli, F., Bernabei, S., Rossi, C., & Sabau-Graziati, L. 2007, Astronomy and Astrophysics, HeI doubled emission lines from A0535+26 ≡ HDE 245770. A possible interpretation

 2. ^ Vallee, J. P. 1987, Astrophysics and Space Science, Physical parameters of the diffuse molecular cloud envelope at G180.9 + 4.1, next to S241

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

 4. ^ 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

 5. ^ Wu, Yue-Fang, Yang, Chuan-Yi, & Li, Yue-Xing 1999, Chinese Astronomy and Astrophysics, High velocity gas in S241 and IRAS 19529+2704

 6. ^ Patriarchi, P., Morbidelli, L., & Perinotto, M. 2003, Astronomy and Astrophysics, A study of R<SUB>V</SUB> in Galactic O stars from the 2MASS catalogue

 7. ^ van Leeuwen, F. 2007, Astronomy and Astrophysics, Validation of the new Hipparcos reduction

 8. ^ Lee, Y., Jung, J. H., Chung, H. S., Kim, H.-G., Park, Y.-S., Kim, H. R., Kim, B.-G., Kim, J., & Han, S.-T. 1999, Astronomy and Astrophysics Supplement Series, Galactic anticenter CO survey. I. Area l=178(deg) to 186(deg) , b=3fdg 5 to 6(deg)

 9. ^ Kawamura, Akiko, Onishi, Toshikazu, Yonekura, Yoshinori, Dobashi, Kazuhito, Mizuno, Akira, Ogawa, Hideo, & Fukui, Yasuo 1998, Astrophysical Journal Supplement Series, A 13CO Survey of Molecular Clouds in Gemini and Auriga

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

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

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

13. ^ Stark, Antony A. & Brand, Jan 1989, Astrophysical Journal, Kinematics of molecular clouds. II - New data on nearby giant molecular clouds

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

15. ^ 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

16. ^ 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

17. ^ Peterson, L. E. 1998, Revista Mexicana de Astronomia y Astrofisica Conference Series, The Crab Nebula at High Energies - a Historical Perspective

18. ^ Trimble, Virginia 1973, Publications of the Astronomical Society of the Pacific, The Distance to the Crab Nebula and NP 0532

19. ^ McCuskey, S. W. 1967, Astronomical Journal, The stellar distribution in the galactic anticenter.

20. ^ Kulkarni, S. R. & Mathieu, R. 1986, Astrophysics and Space Science, Distance to the anti-center shell

21. ^ Tamanaha, Christopher M. 1997, Astrophysical Journal Supplement Series, The Anticenter Shell and the Anticenter Chain

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

23. ^ Kalirai, Jasonjot Singh, Fahlman, Gregory G., Richer, Harvey B., & Ventura, Paolo 2003, Astronomical Journal, The CFHT Open Star Cluster Survey. IV. Two Rich, Young Open Star Clusters: NGC 2168 (M35) and NGC 2323 (M50)

24. ^ Carraro, Giovanni, Chaboyer, Brian, & Perencevich, James 2006, Monthly Notices of the Royal Astronomical Society, The young open cluster NGC 2129

25. ^ 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.

26. ^ Negueruela, I. & Marco, A. 2003, Astronomy and Astrophysics, Stellar tracers of the Cygnus Arm. I. Spectroscopic study of bright photometric candidates

27. ^ Negueruela, I., Steele, I. A., & Bernabeu, G. 2004, Astronomische Nachrichten, On the class of Oe stars\fnmsep

28. ^ Fesen, R. A. 1984, Astrophysical Journal, The nature of the filaments northeast of the supernova remnant IC 443

29. ^ Carpenter, John M., Snell, Ronald L., & Schloerb, F. Peter 1995, Astrophysical Journal, Anatomy of the Gemini OB1 molecular cloud complex

30. ^ Carpenter, John M., Snell, Ronald L., & Schloerb, F. Peter 1995, Astrophysical Journal, Star Formation in the Gemini OB1 Molecular Cloud Complex

31. ^ Haikala, L. K. 1995, Astronomy and Astrophysics, UBVRI photometry and polarimetry of the stars in S252 (NGC 2175). II. Interpretation.

32. ^ Khachikian, E. Ye., Hovhanessian, R. Kh., & Epremian, R. A. 2005, Astrophysics, Distribution of early type stars and dusty matter in the direction of the star cluster NGC 2175

33. ^ Fountain, W. F., Gary, G. A., & Odell, C. R. 1983, Astrophysical Journal, An H-alpha velocity study of S252

34. ^ Felli, M., Habing, H. J., & Israel, F. P. 1977, Astronomy and Astrophysics, Aperture synthesis observations of galactic H II regions. V - The galactic nebula S 252 /NGC 2175/

35. ^ 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

36. ^ Tej, A., Ojha, D. K., Ghosh, S. K., Kulkarni, V. K., Verma, R. P., Vig, S., & Prabhu, T. P. 2006, Astronomy and Astrophysics, A multiwavelength study of the massive star-forming region IRAS 06055+2039 (RAFGL 5179)

37. ^ Chavarria-K., C., Leitherer, C., de Lara, E., Sanchez, O., & Zickgraf, F.-J. 1989, Astronomy and Astrophysics, Further observations of stars associated with the Sharpless H II region SH 2-252, and of the Herbig A0e star SH 2-252b

38. ^ Koempe, C., Baudry, A., Joncas, G., & Wouterloot, J. G. A. 1989, Astronomy and Astrophysics, Multi-line observations and analysis of the Sharpless 247/252 gas complex

39. ^ Braun, R. & Strom, R. G. 1986, Astronomy and Astrophysics, The structure and dynamics of evolved supernova remnants - The IC 443 complex

40. ^ Donati-Falchi, A. & Tofani, G. 1984, Astronomy and Astrophysics, Hydrogen recombination lines towards the SNR IC 443 and the H II region S 249

41. ^ Parkes, G. E., Charles, P. A., Culhane, J. L., & Ives, J. C. 1977, Monthly Notices of the Royal Astronomical Society, The X-ray spectrum and structure of the supernova remnant IC 443

42. ^ Bykov, A. M., Bocchino, F., & Pavlov, G. G. 2005, Astrophysical Journal, A Hard Extended X-Ray Source in the IC 443 Supernova Remnant Resolved by Chandra: A Fast Ejecta Fragment or a New Pulsar Wind Nebula?

43. ^ Asaoka, I. & Aschenbach, B. 1994, Astronomy and Astrophysics, An X-ray study of IC443 and the discovery of a new supernova remnant by ROSAT