Evolution of X-ray emission from young massive star clusters

The evolution of X-ray emission from young massive star clusters is modelled, taking into account the emission from the stars as well as from the cluster wind. It is shown that the level and character of the soft (0.2‐10 keV) X-ray emission change drastically with cluster age and are tightly linked with stellar evolution. Using the modern X-ray observations of massive stars, we show that the correlation between bolometric and X-ray luminosity known for single O stars also holds for O + O and (Wolf‐Rayet) WR + O binaries. The diffuse emission originates from the cluster wind heated by the kinetic energy of stellar winds and supernova explosions. To model the evolution of the cluster wind, the mass and energy yields from a population synthesis are used as input to a hydrodynamic model. It is shown that in a very young cluster the emission from the cluster wind is low. When the cluster evolves, WR stars are formed. Their strong stellar winds power an increasing X-ray emission of the cluster wind. Subsequent supernova explosions pump the level of diffuse emission even higher. Clusters at this evolutionary stage may have no X-ray-bright stellar point sources, but a relatively high level of diffuse emission. A supernova remnant may become a dominant X-ray source, but only for a short time interval of a few thousand years. We retrieve and analyse Chandra and XMM‐Newton observations of six massive star clusters located in the Large Magellanic Cloud (LMC). Our model reproduces the observed diffuse and point-source emission from these LMC clusters, as well as from the Galactic clusters Arches, Quintuplet and NGC 3603. Ke yw ords: stars: winds, outflows ‐ stars: Wolf‐Rayet ‐ open clusters and associations: general ‐ Magellanic Clouds ‐ X-rays: stars.

[1]  A. J. Drake,et al.  Variability-selected Quasars in MACHO Project Magellanic Cloud Fields , 2002, astro-ph/0209513.

[2]  A. Moffat,et al.  The Wolf-Rayet Binary V444 Cygni Under the Spectroscopic Microscope. II. Physical Parameters of the Wolf-Rayet Wind and the Zone of Wind Collision , 1997 .

[3]  An XMM-Newton observation of the massive binary HD 159176 , 2004, astro-ph/0402663.

[4]  X-ray evidence for wind-wind collision in the Wolf-Rayet binary V444 Cygni , 1999 .

[5]  R. Kudritzki,et al.  WINDS FROM HOT STARS , 2000 .

[6]  I. Howarth,et al.  A spectropolarimetric survey of northern hemisphere Wolf–Rayet stars , 1998 .

[7]  C. Law,et al.  X-Ray Observations of Stellar Clusters Near the Galactic Center , 2004 .

[8]  A. M. Genderen.  S Doradus variables in the Galaxy and the Magellanic Clouds , 2001 .

[9]  S. P. Reynolds,et al.  Supernova Remnants in the Sedov Expansion Phase: Thermal X-Ray Emission , 2000 .

[10]  N. Schulz,et al.  Chandra Observations of Variable Embedded X-Ray Sources in Orion. I. Resolving the Orion Trapezium , 2000, astro-ph/0011366.

[11]  H. Sana,et al.  Phase-resolved X-ray and optical spectroscopy of the massive binary HD 93403 ? , 2002 .

[12]  R. Ignace,et al.  XMM-Newton observations of the nitrogen-rich Wolf-Rayet star WR 1. , 2003 .

[13]  M. Cervino,et al.  Evolutionary synthesis models of starbursts IV. Soft X-ray emission , 2002, astro-ph/0206331.

[14]  R. Ignace,et al.  The Conspicuous Absence of X-ray Emission from Carbon-Enriched Wolf-Rayet Stars. , 2003, astro-ph/0303025.

[15]  Y. Nazé,et al.  An X-Ray Investigation of the NGC 346 Field in the Small Magellanic Cloud I. The Luminous Blue Variable HD 5980 and the NGC 346 Cluster , 2002 .

[16]  J. Mermilliod,et al.  High-mass binaries in the very young open cluster NGC 6231. Implication for cluster and star formation , 2001 .

[17]  S. Sciortino,et al.  Chandra X-Ray Observation of the Orion Nebula Cluster. II. Relationship between X-Ray Activity Indicators and Stellar Parameters , 2002, astro-ph/0208475.

[18]  S. Penner.  Physics of shock waves and high-temperature hydrodynamic phenomena - Ya.B. Zeldovich and Yu.P. Raizer (translated from the Russian and then edited by Wallace D. Hayes and Ronald F. Probstein); Dover Publications, New York, 2002, 944 pp., $34. , 2003 .

[19]  W. Schmutz,et al.  XMM-Newton high-resolution X-ray spectroscopy of the Wolf-Rayet object WR 25 in the Carina OB1 association , 2003 .

[20]  Jorge Cantó,et al.  The Hot, Diffuse Gas in a Dense Cluster of Massive Stars , 2000 .

[21]  J. Hughes,et al.  ASCA X-Ray Spectroscopy of Large Magellanic Cloud Supernova Remnants and the Metal Abundances of the Large Magellanic Cloud , 1998 .

[22]  W. Hamann,et al.  Hydrodynamic model atmospheres for WR stars - Self-consistent modeling of a WC star wind , 2004, astro-ph/0410697.

[23]  Morton S. Roberts,et al.  X-Ray Emission from a Sample of Young Supernovae , 2003 .

[24]  Denis Foo Kune,et al.  Starburst99: Synthesis Models for Galaxies with Active Star Formation , 1999, astro-ph/9902334.

[25]  A. Pollock,et al.  The ROSAT PSPC survey of the Wolf-Rayet stars , 1995 .

[26]  R. Chevalier,et al.  Wind from a starburst galaxy nucleus , 1985, Nature.

[27]  J. Cassinelli,et al.  New Challenges for Wind Shock Models: The Chandra Spectrum of the Hot Star δ Orionis , 2002 .

[28]  J. Puls,et al.  Stellar and wind parameters of Galactic O-stars - The influence of line-blocking/blanketing , 2004 .

[29]  S. Kahn,et al.  X-Ray Spectroscopy of η Carinae with XMM-Newton , 2002, astro-ph/0209087.

[30]  G. Rauw,et al.  The Interacting Early-Type Binary BD +40°4220 (V729 Cyg): Modeling the Colliding Winds Region , 1999 .

[31]  S. Skinner,et al.  X-Ray Emission from Colliding Wind Shocks in the Wolf-Rayet Binary WR 140 , 2000 .

[33]  W. Schmutz,et al.  XMM-Newton and Very Large Array Observations of the Variable Wolf-Rayet Star EZ Canis Majoris: Evidence for a Close Companion? , 2002, astro-ph/0207171.

[34]  On the origin of brown dwarfs and free-floating planetary-mass objects , 2003, astro-ph/0309645.

[35]  W. Schmutz,et al.  XMM-Newton Detection of Hard X-Ray Emission in the Nitrogen-Type Wolf-Rayet Star WR 110 , 2002, astro-ph/0203270.

[36]  Eugene Serabyn,et al.  Massive Stars in the Arches Cluster , 2002, astro-ph/0208145.

[37]  M. Audard,et al.  Wind clumping and the wind-wind collision zone in the Wolf-Rayet binary gamma ² Velorum observations at high and low state. XMM-Newton observations at high and low state , 2004 .

[38]  D. Vanbeveren,et al.  The effects of binaries on the evolution of Wolf-Rayet type spectral features in starbursts , 2003 .

[39]  S. P. Portegies Zwart,et al.  A Dozen Colliding-Wind X-Ray Binaries in the Star Cluster R136 in the 30 Doradus Region , 2001, astro-ph/0106109.

[40]  K. Gayley,et al.  Line-driven Instability Growth Rates in Wolf-Rayet Winds , 1995 .

[41]  I. Stevens,et al.  The cluster wind from local massive star clusters , 2003, astro-ph/0301038.

[42]  K. A. Hucht,et al.  Wolf-Rayet Stars: Binaries, Colliding Winds, Evolution , 1995 .

[43]  Ian S. McLean,et al.  Massive Stars in the Quintuplet Cluster , 1999 .

[44]  Stellar evolution with rotation XII. Pre-supernova models , 2004, astro-ph/0406552.

[45]  B. Mason,et al.  ICCD Speckle Observations of Binary Stars. XIX. An Astrometric/Spectroscopic Survey of O Stars , 1998 .

[46]  S. Woosley,et al.  EVOLUTION AND EXPLOSION OF MASSIVE STARS * , 1978, Reviews of Modern Physics.

[47]  P. Crowther,et al.  The enigmatic WR46: A binary or a pulsator in disguise. II. The spectroscopy , 2002 .

[48]  A. D. Mackey,et al.  Surface brightness profiles and structural parameters for 53 rich stellar clusters in the Large Magellanic Cloud , 2002, astro-ph/0209031.

[49]  Karel A. van der Hucht,et al.  The VIIth catalogue of galactic Wolf–Rayet stars , 2001 .

[50]  M. Bessell,et al.  The Initial Mass Function and Stellar Content of NGC 3603 , 2004 .

[51]  H. Sana,et al.  A phase-resolved XMM–Newton campaign on the colliding-wind binary HD 152248 , 2004, astro-ph/0402412.

[52]  UK,et al.  In hot pursuit of the hidden companion of η Carinae: an X-ray determination of the wind parameters , 2002, astro-ph/0201105.

[53]  H. Sana,et al.  WR 20a: a massive cornerstone binary system comprising two extreme early-type stars ⋆ , 2004, astro-ph/0404551.

[54]  F. Seward,et al.  X-ray emission from the Carina Nebula and the associated early stars , 1982 .

[55]  T. Morel,et al.  Hydrogen in the atmosphere of the evolved WN3 Wolf–Rayet star WR 3: defying an evolutionary paradigm? , 2004 .