Triggered massive-star formation on the borders of Galactic H II regions. III. Star formation at the

Context. Massive-star formation triggered by the expansion of HII regions. Aims. To understand if sequential star formation is taking place at the periphery of the HII region Sh2-219. Methods. We present 12CO(2-1) line observations of this region, obtained at the IRAM 30-m telescope (Pico Veleta, Spain). Results. In the optical, Sh2-219 is spherically symmetric around its exciting star; furthermore it is surrounded along three quarters of its periphery by a ring of atomic hydrogen. This spherical symmetry breaks down at infrared and millimetre wavelengths. A molecular cloud of about 2000\msol lies at the southwestern border of Sh2-219, in the HI gap. Two molecular condensations, elongated along the ionization front, probably result from the interaction between the expanding HII region and the molecular cloud. In this region of interaction there lies a cluster containing many highly reddened stars, as well as a massive star exciting an ultracompact HII region. More surprisingly, the brightest parts of the molecular cloud form a `chimney', perpendicular to the ionization front. This chimney is closed at its south-west extremity by H-alpha walls, thus forming a cavity. The whole structure is 7.5 pc long. A luminous H-alpha emission-line star, lying at one end of the chimney near the ionization front, may be responsible for this structure. Confrontation of the observations with models of HII region evolution shows that Sh2-219 is probably 10^5 yr old. The age and origin of the near-IR cluster observed on the border of Sh2-219 remain unknown.

[1]  R. Indebetouw,et al.  Interpreting Spectral Energy Distributions from Young Stellar Objects. II. Fitting Observed SEDs Using a Large Grid of Precomputed Models , 2006, astro-ph/0612690.

[2]  F. Martins,et al.  UBVJHK synthetic photometry of Galactic O stars , 2006, astro-ph/0606587.

[3]  M. Skrutskie,et al.  The Two Micron All Sky Survey (2MASS) , 2006 .

[4]  S. Inutsuka,et al.  Dynamical Expansion of Ionization and Dissociation Front around a Massive Star. II. On the Generality of Triggered Star Formation , 2005, astro-ph/0511165.

[5]  S. Ellingsen.  Methanol Masers: Reliable Tracers of the Early Stages of High-Mass Star Formation , 2005, astro-ph/0510218.

[6]  A. Zavagno,et al.  Triggered massive-star formation on the borders of Galactic HII regions , 2005, Proceedings of the International Astronomical Union.

[7]  D. Schaerer,et al.  A new calibration of stellar parameters of Galactic O stars , 2005, astro-ph/0503346.

[8]  C. Clarke,et al.  Photoionizing feedback in star cluster formation , 2005, astro-ph/0501160.

[9]  A. Zavagno,et al.  Triggered massive-star formation on the borders of Galactic H II regions I. A search for "collect and collapse" candidates , 2004, astro-ph/0412602.

[10]  S. Inutsuka,et al.  Dynamical Expansion of Ionization and Dissociation Fronts around a Massive Star. I. A Mode of Triggered Star Formation , 2004, astro-ph/0411080.

[11]  A. Greve,et al.  A 230 GHz heterodyne receiver array for the IRAM 30 m telescope , 2004 .

[12]  R. Indebetouw,et al.  The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 μm Using GLIMPSE Data , 2004, astro-ph/0406403.

[13]  Astronomy,et al.  Triggered massive-star formation at the border of the HII region Sh 104 , 2003, astro-ph/0309018.

[14]  I. Cruz-Gonzalez,et al.  Sequential star formation at the periphery of the HII regions Sh 217 and Sh 219 , 2002, astro-ph/0212383.

[15]  Linda J. Smith,et al.  Realistic ionizing fluxes for young stellar populations from 0.05 to 2 Z , 2002, astro-ph/0207554.

[16]  E. Oliva,et al.  Astronomy Astrophysics manuscript no. , 2001 .

[17]  Elizabeth A. Lada,et al.  Disk Frequencies and Lifetimes in Young Clusters , 2001, astro-ph/0104347.

[18]  P. Kroupa.  Binary Stars in Young Clusters - a Theoretical Perspective , 2000, astro-ph/0010347.

[19]  A. Cox,et al.  Allen's astrophysical quantities , 2000 .

[20]  L. Deharveng,et al.  Oxygen and helium abundances in Galactic H ii regions — I. Observations , 2000 .

[21]  L. Deharveng,et al.  Oxygen and helium abundances in Galactic H ii regions — II. Abundance gradients , 2000 .

[22]  Francesco Palla,et al.  Star Formation in the Orion Nebula Cluster , 1999 .

[23]  Wolfgang Wild,et al.  The beam pattern of the IRAM 30-m telescope (a reflector with several surface error distributions) , 1998 .

[24]  J. Scalo.  The IMF Revisited: A Case for Variations , 1997, astro-ph/9712317.

[25]  D. Leahy.  Radio and Optical Observations of the H ii Region Sharpless 219 , 1997 .

[26]  J. Franco,et al.  Photoionized and Photodissociated Regions around Main-Sequence Stars , 1996 .

[27]  M. Beech,et al.  Formation and evolution of massive stars , 1994 .

[28]  A. Whitworth,et al.  The Preferential Formation of High-Mass Stars in Shocked Interstellar Gas Layers , 1994 .

[29]  B. Reipurth,et al.  HH 80-81: A Highly collimated Herbig-Haro complex powered by a massive young star , 1993 .

[30]  M. Fich.  A VLA Survey of Optically Visible Galactic H II Regions , 1993 .

[31]  R. G. Wsdmsley,et al.  Effects Of Temperature And Humidity On Thin Film Disk Lubricant Mobility , 1993 .

[32]  D. Leahy,et al.  H I photodissociation zones around two H II regions in Auriga, Sh 217 and Sh 219 , 1992 .

[33]  C. Lada,et al.  Interpreting Infrared Color-Color Diagrams: Circumstellar Disks around Low- and Intermediate-Mass Young Stellar Objects , 1992 .

[34]  P. Dewdney,et al.  The development of H I dissociation zones around new H II regions , 1992 .

[35]  P. Pişmiş,et al.  A COMPARATIVE STUDY OF MORPHOLOGY AND VELOCITY FIELD OF THE EMISSION NEBULAE S153, S207, S211, AND A71 , 1991 .

[36]  D. Leahy,et al.  Radio emission from the supernova remnant G160. 9 + 2. 6 (HB9) , 1991 .

[37]  R. Treffers,et al.  Fabry-Perot H-alpha Observations of Galactic H II Regions , 1990 .

[38]  F. Lockman,et al.  A Survey of Radio H II Regions in the Northern Sky (Lockman+ 1989) , 1989 .

[39]  R. Levreault.  Molecular Outflows and Mass Loss in Pre Main-Sequence Stars , 1988 .

[40]  P. Stetson.  DAOPHOT: A COMPUTER PROGRAM FOR CROWDED-FIELD STELLAR PHOTOMETRY , 1987 .

[41]  R. Wilson,et al.  The relationship between carbon monoxide abundance and visual extinction in interstellar clouds. , 1982 .

[42]  A. Stark,et al.  Catalog of CO radial velocities toward galactic H II regions , 1982 .

[43]  C. Lada,et al.  Sequential formation of subgroups in OB associations , 1977 .

[44]  N. Panagia,et al.  Some physical parameters of early-type stars , 1973 .

[45]  S. Bergh,et al.  An Optical Atlas of Galactic Supernova Remnants , 1973 .

[46]  S. V. Pikel'ner.  PHYSICS OF THE INTERSTELLAR MEDIUM , 1960 .

[47]  S. Sharpless.  A Catalogue of H II Regions. , 1959 .

[48]  John Scott Drilling,et al.  in Allen''''s Astrophysical Quantities , 2000 .

[49]  E. Churchwell,et al.  High-Velocity Molecular Gas from High-Mass Star Formation Regions , 1996 .

[50]  Alan P. Boss,et al.  Formation of Binary Stars , 1993 .

[51]  G. Rieke,et al.  The interstellar extinction law from 1 to 13 microns. , 1985 .

[52]  L. Lucy.  The Formation of Binary Stars , 1981 .