Science.gov

Sample records for hot massive stars

  1. Hot Massive Stars: The Impact of HST

    NASA Astrophysics Data System (ADS)

    Crowther, Paul A.

    We review the contribution of Hubble Space Telescope to the study of hot, luminous stars. Optical and IR imaging have permitted spatially resolved observations of young, massive clusters within Local Group galaxies, such as R136, NGC 3603 and Arches, revealing unprecedented concentrations of very massive O stars. UV spectroscopy of field OB stars in the Magellanic Clouds have provided suitable templates for interpretation of metal-poor star-forming galaxies at high-redshift. Spectacular imaging provides the detailed structure of ejecta nebulae from individual stars, including the Homunculus associated with η Carinae and M1-67, associated with a Wolf-Rayet star. HST has permitted individual massive stars to be spatially resolved in giant HII regions located beyond the Local Group, such as NGC 604, plus individual clusters, dominated by the light of massive stars within starburst galaxies at larger distances, such as NGC 3125. UV spectroscopy of young, massive clusters in the extremely metal-poor HII galaxy I Zw 18 include signatures of large numbers of Wolf-Rayet stars.

  2. Hot, Massive Stars in I Zw 18

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Lindler, D.; Malumuth, E.

    2011-01-01

    I Zw 18 is one of the most primitive blue, compact dwarf galaxies. The ionized gas in I Zw 18 has a low oxygen abundance (O approx.1/30 Osun) and nitrogen abundance (N-1/100 Nsun) (Pequignot 2008). We have obtained a far-UV spectrum of the northwest massive star cluster of I Zw 18 using Hubble's Cosmic Origins Spectrograph (COS). The spectrum is compatible with continuous star-formation over the past approx.10 Myr, and a very low metallicity, log Z/Zsun 1.7, although the stellar surface may be enhanced in carbon. Stellar wind lines are very weak, and the edge velocity of wind lines is very low (approx.250 km/s).

  3. Massive Stars

    NASA Astrophysics Data System (ADS)

    Livio, Mario; Villaver, Eva

    2009-11-01

    Participants; Preface Mario Livio and Eva Villaver; 1. High-mass star formation by gravitational collapse of massive cores M. R. Krumholz; 2. Observations of massive star formation N. A. Patel; 3. Massive star formation in the Galactic center D. F. Figer; 4. An X-ray tour of massive star-forming regions with Chandra L. K. Townsley; 5. Massive stars: feedback effects in the local universe M. S. Oey and C. J. Clarke; 6. The initial mass function in clusters B. G. Elmegreen; 7. Massive stars and star clusters in the Antennae galaxies B. C. Whitmore; 8. On the binarity of Eta Carinae T. R. Gull; 9. Parameters and winds of hot massive stars R. P. Kudritzki and M. A. Urbaneja; 10. Unraveling the Galaxy to find the first stars J. Tumlinson; 11. Optically observable zero-age main-sequence O stars N. R. Walborn; 12. Metallicity-dependent Wolf-Raynet winds P. A. Crowther; 13. Eruptive mass loss in very massive stars and Population III stars N. Smith; 14. From progenitor to afterlife R. A. Chevalier; 15. Pair-production supernovae: theory and observation E. Scannapieco; 16. Cosmic infrared background and Population III: an overview A. Kashlinsky.

  4. Hot, Massive Stars in the Extremely Metal-Poor Galaxy, I Zw 18

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Malumuth, Eliot M.

    2010-01-01

    The extremely metal-poor galaxy I Zw 18, is the Rosetta Stone for understanding z=7-8 galaxies now being discovered by Hubb|e's Wide Field Camera 3 (HST/WFC3). Using HST/STIS images and recently obtained HST/COS ultraviolet spectra, we derive information about the hot, massive stars in this galaxy including stellar abundances, constraints on the stellar IMF and mass distribution of young clusters containing hot, massive stars.

  5. General X-ray properties of hot, massive stars

    NASA Astrophysics Data System (ADS)

    Nazé, Yaël

    2011-01-01

    The recent X-ray observatories have not yet provided a large survey comparable (in sky coverage) to that based upon the ROSAT All-Sky Survey (RASS). However, two limited surveys exist : the 2XMM catalog for XMM-Newton (294 OB stars detected) and the Carina large-scale survey from Chandra (129 OB stars detected). Medium-resolution (CCD) spectra were analyzed and led to new results on the relationship between the X-ray luminosity and the bolometric luminosity, as well as on the typical properties (plasma temperature, variability) of these objects. This contribution thus presents the results of the first high-sensitivity investigation of the overall high-energy properties of a sizeable sample of hot stars.

  6. Some Thoughts on the Disk Formation Mechanisms of Hot Massive Stars

    NASA Astrophysics Data System (ADS)

    Li, Qingkang; Cassinelli, Joe

    2015-08-01

    Although there is a lot of research on the disks of hot massive stars, both theoretically and observationally, the disk formation mechanisms still remain puzzle and have been in debate in decades. There are two main models with regarding to the mechanisms. One of them is the wind colliding models in combination with stellar rotation, magnetic fields, or/and pulsation. The other types are decretion models. Due to there is lots of discussion on the later models, we would like to take the former types into account again and show some premature results in the poster.

  7. A LIBRARY OF THEORETICAL ULTRAVIOLET SPECTRA OF MASSIVE, HOT STARS FOR EVOLUTIONARY SYNTHESIS

    SciTech Connect

    Leitherer, Claus; Ortiz Otalvaro, Paula A.; Bresolin, Fabio; Kudritzki, Rolf-Peter; Lo Faro, Barbara; Pauldrach, Adalbert W. A.; Pettini, Max; Rix, Samantha A. E-mail: pauortizo@gmail.co E-mail: kud@ifa.hawaii.ed E-mail: uh10107@usm.uni-muenchen.d E-mail: srix@ing.iac.e

    2010-08-15

    We computed a comprehensive set of theoretical ultraviolet spectra of hot, massive stars with the radiation-hydrodynamics code WM-Basic. This model atmosphere and spectral synthesis code is optimized for computing the strong P Cygni type lines originating in the winds of hot stars, which are the strongest features in the ultraviolet spectral region. The computed set is suitable as a spectral library for inclusion in evolutionary synthesis models of star clusters and star-forming galaxies. The chosen stellar parameters cover the upper left Hertzsprung-Russell diagram at L {approx}> 10{sup 2.75} L {sub sun} and T {sub eff} {approx}> 20,000 K. The adopted elemental abundances are 0.05 Z {sub sun}, 0.2 Z {sub sun}, 0.4 Z {sub sun}, Z {sub sun}, and 2 Z {sub sun}. The spectra cover the wavelength range from 900 to 3000 A and have a resolution of 0.4 A. We compared the theoretical spectra to data of individual hot stars in the Galaxy and the Magellanic Clouds obtained with the International Ultraviolet Explorer and Far Ultraviolet Spectroscopic Explorer satellites and found very good agreement. We built a library with the set of spectra and implemented it into the evolutionary synthesis code Starburst99 where it complements and extends the existing empirical library toward lower chemical abundances. Comparison of population synthesis models at solar and near-solar composition demonstrates consistency between synthetic spectra generated with either library. We discuss the potential of the new library for the interpretation of the rest-frame ultraviolet spectra of star-forming galaxies. Properties that can be addressed with the models include ages, initial mass function, and heavy-element abundance. The library can be obtained both individually or as part of the Starburst99 package.

  8. Evolutionary helium and CNO anomalies in the atmospheres and winds of massive hot stars

    NASA Technical Reports Server (NTRS)

    Walborn, Nolan R.

    1987-01-01

    The ubiquitous evidence for processed materials in the atmospheres, winds, and circumstellar ejecta of massive stars is reviewed. A broad array of normal and peculiar evolutionary stages is considered, up to and including Type II supernova progenitors. The quantitative analysis of these spectra is difficult, and until recently for the most part only qualitative or approximate results have been available. However, several important current programs promise reliable abundance calculations. A significant emerging result is that the morphologically normal majority of both hot and cold supergiants may already display an admixture of CNO-cycle products in their atmospheres. It may become possible in this way to identify blue supergiants returning from the red supergiant region, as appears to have been the case for the SN 1987A progenitor.

  9. Radiative Transfer Modeling of the Winds and Circumstellar Environments of Hot and Cool Massive Stars

    NASA Astrophysics Data System (ADS)

    Lobel, A.

    2010-06-01

    We present modeling research work of the winds and circumstellar environments of a variety of prototypical hot and cool massive stars using advanced radiative-transfer calculations. This research aims at unraveling the detailed physics of various mass-loss mechanisms of luminous stars in the upper portion of the H-R diagram. Very recent 3D radiative-transfer calculations, combined with hydrodynamic simulations, show that radiatively-driven winds of OB supergiants are structured due to large-scale density and velocity fields caused by rotating bright spots at the stellar equator. The mass-loss rates computed from matching Discrete Absorption Components (DACs) in IUE observations of HD 64760 (B Ib) do not reveal appreciable changes from the rates of unstructured (smooth) wind models. Intermediate yellow supergiants (such as the yellow hypergiant ρ Cas, F-G Ia0), on the other hand, show prominent spectroscopic signatures of strongly increased mass-loss rates during episodic outbursts that cause dramatic changes of the stellar photospheric conditions. Long-term high-resolution spectroscopic monitoring of cool hypergiants near the Yellow Evolutionary Void reveals that their mass-loss rates and wind-structure are dominated by photospheric eruptions and large-amplitude pulsations that impart mechanical momentum to the circumstellar environment by propagating acoustic (shock) waves. In massive red supergiants, however, clear evidence for mechanical wave propagation from the sub-photospheric convection zones is lacking, despite their frequently observed spectroscopic and photometric variability. Recent spatially resolved HST-STIS observations inside Betelgeuse's (M Iab) very extended chromosphere and dust envelope show evidence of warm chromospheric gas far beyond the dust-condensation radius of radiative-transfer models. Models for these long-term spectroscopic observations demonstrate that the chromospheric pulsations are not spherically symmetric. The STIS observations

  10. Hot, Massive Stars in the Extremely Metal-Poor Galaxy, I Zw 18

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Malumuth, Eliot M.

    2010-01-01

    The carbon-enhanced metal-poor galaxy, I Zw 18, is the Rosetta Stone for understanding galaxies in the early universe by providing constraints on the IMF of massive stars, the role of galaxies in reionization of the universe, mixing of newly synthesized material in the ISM, and gamma-ray bursts at low metallicity, and on the earliest generations of stars producing the observed abundance pattern. We describe these constraints as derived from analyses of HST/COS spectra of I Zw 18 including stellar atmosphere analysis and photo-ionization modeling of both the emission and absorption spectra of the nebular material and interstellar medium.

  11. On the Weak-Wind Problem in Massive Stars: X-Ray Spectra Reveal a Massive Hot Wind in mu Columbae

    NASA Technical Reports Server (NTRS)

    Huenemoerder, David P.; Oskinova, Lidia M.; Ignace, Richard; Waldron, Wayne L.; Todt, Helge; Hamaguchi, Kenji; Kitamoto, Shunji

    2012-01-01

    Mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"--identified from cool wind UV/optical spectra--is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma-the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays.

  12. CHEMICAL SEGREGATION TOWARD MASSIVE HOT CORES: THE AFGL2591 STAR-FORMING REGION

    SciTech Connect

    Jimenez-Serra, I.; Zhang, Q.; Viti, S.; Martin-Pintado, J.; De Wit, W.-J. E-mail: qzhang@cfa.harvard.edu E-mail: jmartin@cab.inta-csic.es

    2012-07-01

    We present high angular resolution observations (0.''5 Multiplication-Sign 0.''3) carried out with the Submillimeter Array (SMA) toward the AFGL2591 high-mass star-forming region. Our SMA images reveal a clear chemical segregation within the AFGL2591 VLA 3 hot core, where different molecular species (Types I, II, and III) appear distributed in three concentric shells. This is the first time that such a chemical segregation is ever reported at linear scales {<=}3000 AU within a hot core. While Type I species (H{sub 2}S and {sup 13}CS) peak at the AFGL2591 VLA 3 protostar, Type II molecules (HC{sub 3}N, OCS, SO, and SO{sub 2}) show a double-peaked structure circumventing the continuum peak. Type III species, represented by CH{sub 3}OH, form a ring-like structure surrounding the continuum emission. The excitation temperatures of SO{sub 2}, HC{sub 3}N, and CH{sub 3}OH (185 {+-} 11 K, 150 {+-} 20 K, and 124 {+-} 12 K, respectively) show a temperature gradient within the AFGL2591 VLA 3 envelope, consistent with previous observations and modeling of the source. By combining the H{sub 2}S, SO{sub 2}, and CH{sub 3}OH images, representative of the three concentric shells, we find that the global kinematics of the molecular gas follow Keplerian-like rotation around a 40 M{sub Sun} star. The chemical segregation observed toward AFGL2591 VLA 3 is explained by the combination of molecular UV photodissociation and a high-temperature ({approx}1000 K) gas-phase chemistry within the low extinction innermost region in the AFGL2591 VLA 3 hot core.

  13. Theoretical Modelling of Hot Stars

    NASA Astrophysics Data System (ADS)

    Najarro, F.; Hillier, D. J.; Figer, D. F.; Geballe, T. R.

    1999-06-01

    Recent progress towards model atmospheres for hot stars is discussed. A new generation of NLTE wind blanketed models, together with high S/N spectra of the hot star population in the central parsec, which are currently being obtained, will allow metal abundance determinations (Fe, Si, Mg, Na, etc). Metallicity studies of hot stars in the IR will provide major constraints not only on the theory of evolution of massive stars but also on our efforts to solve the puzzle of the central parsecs of the Galaxy. Preliminary results suggest that the metallicity of the Pistol Star is 3 times solar, thus indicating strong chemical enrichment of the gas in the Galactic Center.

  14. KEPLER-14b: A MASSIVE HOT JUPITER TRANSITING AN F STAR IN A CLOSE VISUAL BINARY

    SciTech Connect

    Buchhave, Lars A.; Latham, David W.; Carter, Joshua A.; Desert, Jean-Michel; Torres, Guillermo; Adams, Elisabeth R.; Charbonneau, David B.; Dupree, Andrea K.; Fressin, Francois; Bryson, Stephen T.; Howell, Steve B.; Ciardi, David R.; Fischer, Debra A.; Gautier, Thomas N.; Isaacson, Howard; Marcy, Geoffrey W.; Jenkins, Jon M.

    2011-11-01

    We present the discovery of a hot Jupiter transiting an F star in a close visual (0.''3 sky projected angular separation) binary system. The dilution of the host star's light by the nearly equal magnitude stellar companion ({approx}0.5 mag fainter) significantly affects the derived planetary parameters, and if left uncorrected, leads to an underestimate of the radius and mass of the planet by 10% and 60%, respectively. Other published exoplanets, which have not been observed with high-resolution imaging, could similarly have unresolved stellar companions and thus have incorrectly derived planetary parameters. Kepler-14b (KOI-98) has a period of P = 6.790 days and, correcting for the dilution, has a mass of M{sub p} = 8.40{sup +0.35}{sub -0.34} M{sub J} and a radius of R{sub p} = 1.136{sup +0.073}{sub -0.054} R{sub J}, yielding a mean density of {rho}{sub p} = 7.1 {+-} 1.1 g cm{sup -3}.

  15. Massive star archeology in globular clusters

    NASA Astrophysics Data System (ADS)

    Chantereau, W.; Charbonnel, C.; Meynet, G.

    2015-01-01

    Globular clusters are among the oldest structures in the Universe and they host today low-mass stars and no gas. However, there has been a time when they formed as gaseous objects hosting a large number of short-lived, massive stars. Many details on this early epoch have been depicted recently through unprecedented dissection of low-mass globular cluster stars via spectroscopy and photometry. In particular, multiple populations have been identified, which bear the nucleosynthetic fingerprints of the massive hot stars disappeared a long time ago. Here we discuss how massive star archeology can be done through the lense of these multiple populations.

  16. Massive Stars: Stellar Populations

    NASA Astrophysics Data System (ADS)

    Bianchi, Luciana

    2007-07-01

    Massive stars dominate the chemical and dynamical evolution of the ISM, and ultimately of their parent galaxy and the universe, because of their fast evolution and intense supersonic winds. Four decades ago, the first rocket UV spectra of massive stars revealed the importance of mass loss and began to change our understanding of their evolution. Recently, advances in stellar modeling, and the observation of crucial ions in the far-UV spectral range, led to the resolution of long-standing issues in our understanding of massive star atmospheres. A revised (downwards) calibration of Teff for early spectral types is emerging as a result. Meanwhile, HST imaging, and large ground-based telescopes with multislit spectroscopic capabilities, had opened the possibility of resolved studies of stellar populations in Local Group galaxies, which sample a variety of metallicity and environment conditions. More recently, GALEX is providing a global, deep view of the young stellar populations for hundreds of nearby galaxies, revealing their recent star-formation history and modalities. The wide-field coverage and sensitivity of the GALEX UV imaging, easily detecting extremely low levels of star formation, is again changing some of our views on massive star formation in galaxies.

  17. Young Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Portegies Zwart, Simon F.; McMillan, Stephen L. W.; Gieles, Mark

    2010-09-01

    Young massive clusters (YMCs) are dense aggregates of young stars that form the fundamental building blocks of galaxies. Several examples exist in the Milky Way Galaxy and the Local Group, but they are particularly abundant in starburst and interacting galaxies. The few YMCs that are close enough to resolve are of prime interest for studying the stellar mass function and the ecological interplay between stellar evolution and stellar dynamics. The distant unresolved clusters may be effectively used to study the star-cluster mass function, and they provide excellent constraints on the formation mechanisms of young cluster populations. YMCs are expected to be the nurseries for many unusual objects, including a wide range of exotic stars and binaries. So far only a few such objects have been found in YMCs, although their older cousins, the globular clusters, are unusually rich in stellar exotica. In this review, we focus on star clusters younger than ˜100 Myr, more than a few current crossing times old, and more massive than ˜104M⊙; the size of the cluster and its environment are considered less relevant as distinguishing parameters. We describe the global properties of the currently known young massive star clusters in the Local Group and beyond, and discuss the state of the art in observations and dynamical modeling of these systems. In order to make this review readable by observers, theorists, and computational astrophysicists, we also review the cross-disciplinary terminology.

  18. Hot Subluminous Stars

    NASA Astrophysics Data System (ADS)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung–Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  19. Massive soliton stars

    NASA Technical Reports Server (NTRS)

    Chiu, Hong-Yee

    1990-01-01

    The structure of nontopological solutions of Einstein field equations as proposed by Friedberg, Lee, and Pang (1987) is examined. This analysis incorporates finite temperature effects and pair creation. Quarks are assumed to be the only species that exist in interior of soliton stars. The possibility of primordial creation of soliton stars in the incomplete decay of the degenerate vacuum in early universe is explored. Because of dominance of pair creation inside soliton stars, the luminosity of soliton stars is not determined by its radiative transfer characteristics, and the surface temperature of soliton stars can be the same as its interior temperature. It is possible that soliton stars are intense X-ray radiators at large distances. Soliton stars are nearly 100 percent efficient energy converters, converting the rest energy of baryons entering the interior into radiation. It is possible that a sizable number of baryons may also be trapped inside soliton stars during early epochs of the universe. In addition, if soliton stars exist they could assume the role played by massive black holes in galactic centers.

  20. Hot Subluminous Stars

    NASA Astrophysics Data System (ADS)

    Heber, U.

    2016-08-01

    Hot subluminous stars of spectral type B and O are core helium-burning stars at the blue end of the horizontal branch or have evolved even beyond that stage. Most hot subdwarf stars are chemically highly peculiar and provide a laboratory to study diffusion processes that cause these anomalies. The most obvious anomaly lies with helium, which may be a trace element in the atmosphere of some stars (sdB, sdO) while it may be the dominant species in others (He-sdB, He-sdO). Strikingly, the distribution in the Hertzsprung–Russell diagram of He-rich versus He-poor hot subdwarf stars of the globular clusters ω Cen and NGC 2808 differ from that of their field counterparts. The metal-abundance patterns of hot subdwarfs are typically characterized by strong deficiencies of some lighter elements as well as large enrichments of heavy elements. A large fraction of sdB stars are found in close binaries with white dwarf or very low-mass main sequence companions, which must have gone through a common-envelope (CE) phase of evolution. Because the binaries are detached they provide a clean-cut laboratory to study this important but yet poorly understood phase of stellar evolution. Hot subdwarf binaries with sufficiently massive white dwarf companions are viable candidate progenitors of type Ia supernovae both in the double degenerate as well as in the single degenerate scenario as helium donors for double detonation supernovae. The hyper-velocity He-sdO star US 708 may be the surviving donor of such a double detonation supernova. Substellar companions to sdB stars have also been found. For HW Vir systems the companion mass distribution extends from the stellar into the brown dwarf regime. A giant planet to the acoustic-mode pulsator V391 Peg was the first discovery of a planet that survived the red giant evolution of its host star. Evidence for Earth-size planets to two pulsating sdB stars have been reported and circumbinary giant planets or brown dwarfs have been found around HW

  1. Spectropolarimetry of hot, luminous stars

    NASA Technical Reports Server (NTRS)

    Schulte-Ladbeck, Regina E.

    1994-01-01

    I review polarimetric observations of presumably single, hot luminous stars. The stellar types discussed are OB stars. B(e) supergiants, Luminous Blue Variables (LBV), Wolf-Rayet (W-R) stars, and type II supernovae (SN). It is shown that variable, intrinsic polarization is a common phenomenon in that part of the Hertzsprung-Russell (HR) diagram which these stars occupy. However, much observational work remains to be done before we can answer the most basic, statistical questions about the polarimetric properties of different groups of hot, luminous stars. Insight into the diagnostic power of polarization observations has been gained, but cannot be exploited without detailed models. Thus, while polarimetric observations do tell us that the mass-loss processes of all types of massive stars are time-dependent and anisotropic, the significance that this might have for the accuracy of their stellar parameters and evolutionary paths remains elusive.

  2. Really Hot Stars

    NASA Astrophysics Data System (ADS)

    2003-04-01

    Spectacular VLT Photos Unveil Mysterious Nebulae Summary Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation". This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile). In a dedicated search for the origin of their individual characteristics, a team of astronomers - mostly from the Institute of Astrophysics & Geophysics in Liège (Belgium) [1] - have secured the first detailed, highly revealing images of four highly ionized nebulae in the Magellanic Clouds, two small satellite galaxies of our home galaxy, the Milky Way, only a few hundred thousand light-years away. In three nebulae, they succeeded in identifying the sources of energetic radiation and to eludicate their exceptional properties: some of the hottest, most massive stars ever seen, some of which are double. With masses of more than 20 times that of the Sun and surface temperatures above 90 000 degrees, these stars are truly extreme. PR Photo 09a/03: Nebula around the hot star AB7 in the SMC. PR Photo 09b/03: Nebula near the hot Wolf-Rayet star BAT99

  3. The evolution of massive stars

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The hypotheses underlying theoretical studies of the evolution of massive model stars with and without mass loss are summarized. The evolutionary tracks followed by the models across theoretical Hertzsprung-Russell (HR) diagrams are compared with the observed distribution of B stars in an HR diagram. The pulsational properties of models of massive star are also described.

  4. Massive Stars in Interactive Binaries

    NASA Astrophysics Data System (ADS)

    St.-Louis, Nicole; Moffat, Anthony F. J.

    Massive stars start their lives above a mass of ~8 time solar, finally exploding after a few million years as core-collapse or pair-production supernovae. Above ~15 solar masses, they also spend most of their lives driving especially strong, hot winds due to their extreme luminosities. All of these aspects dominate the ecology of the Universe, from element enrichment to stirring up and ionizing the interstellar medium. But when they occur in close pairs or groups separated by less than a parsec, the interaction of massive stars can lead to various exotic phenomena which would not be seen if there were no binaries. These depend on the actual separation, and going from wie to close including colliding winds (with non-thermal radio emission and Wolf-Rayet dust spirals), cluster dynamics, X-ray binaries, Roche-lobe overflow (with inverse mass-ratios and rapid spin up), collisions, merging, rejuventation and massive blue stragglers, black-hole formation, runaways and gamma-ray bursts. Also, one wonders whether the fact that a massive star is in a binary affects its parameters compared to its isolated equivalent. These proceedings deal with all of these phenomena, plus binary statistics and determination of general physical properties of massive stars, that would not be possible with their single cousins. The 77 articles published in these proceedings, all based on oral talks, vary from broad revies to the lates developments in the field. About a third of the time was spent in open discussion of all participants, both for ~5 minutes after each talk and 8 half-hour long general dialogues, all audio-recorded, transcribed and only moderately edited to yield a real flavour of the meeting. The candid information in these discussions is sometimes more revealing than the article(s) that preceded them and also provide entertaining reading. The book is suitable for researchers and graduate students interested in stellar astrophysics and in various physical processes involved when

  5. Massive stars: Starbursts

    NASA Astrophysics Data System (ADS)

    González Delgado, Rosa María

    2007-07-01

    Starbursts are the preferred place where massive stars form; the main source of thermal and mechanical heating in the interstellar medium, and the factory where the heavy elements form. Thus, starbursts play an important role in the origin and evolution of galaxies. Starbursts are bright at ultraviolet (UV) wavelengths, and after the pioneering IUE program, high spatial and spectral resolution UV observations of local starburst galaxies, mainly taken with HST and FUSE, have made relevant contributions to the following issues: a) The determination of the initial mass function (IMF) in violent star forming systems in low and high metallicity environments, and in dense (e.g. in stellar clusters) and diffuse environments: A Salpeter IMF with high-mass stars constrains well the UV properties. b) Stellar clusters are an important mode of star formation in starbursts. c) The role of starbursts in AGN: Nuclear starbursts can dominate the UV light in Seyfert 2 galaxies, having bolometric luminosities similar to the estimated bolometric luminosities of the obscured AGN. d) The interaction between massive stars and the interstellar medium: Outflows in cold, warm and coronal phases leave their imprints on the UV interstellar lines. Outflows of a few hundred km s%u22121 are ubiquitous phenomena in starbursts. Despite the very significant progress obtained over the past two decades of UV observations of starbursts, there are important problems that still need to be solved. High-spatial resolution UV observations of nearby starbursts are crucial to further progress in understanding the violent star formation processes in galaxies, the interaction between the stellar clusters and the interstellar medium, and the variation of the IMF. High-spatial resolution spectra are also needed to isolate the light from the center to the disk in UV luminous galaxies found by GALEX. Thus, a new UV mission furnished with an intermediate spectral resolution spectrograph with high spatial

  6. Mass loss of massive stars

    NASA Astrophysics Data System (ADS)

    Martins, F.

    2015-12-01

    In this contribution we review the properties of the winds of massive stars. We focus on OB stars, red supergiants, Luminous Blue Variables (LBVs) and Wolf-Rayet stars. For each type of star, we summarize the main wind properties and we give a brief description of the physical mechanism(s) responsible for mass loss.

  7. Massive Star Burps, Then Explodes

    NASA Astrophysics Data System (ADS)

    2007-04-01

    event was a complete surprise," added Alex Filippenko, leader of the UC Berkeley/Keck supernova group and a member of NASA'S Swift team. "It opens up a fascinating new window on how some kinds of stars die." All the observations suggest that the supernova's blast wave took only a few weeks to reach the shell of material ejected two years earlier, which did not have time to drift very far from the star. As the wave smashed into the ejecta, it heated the gas to millions of degrees, hot enough to emit copious X-rays. The Swift satellite saw the supernova continue to brighten in X-rays for 100 days, something that has never been seen before in a supernova. All supernovae previously observed in X-rays have started off bright and then quickly faded to invisibility. "You don't need a lot of mass in the ejecta to produce a lot of X-rays," notes Immler. Swift's ability to monitor the supernova's X-ray rise and decline over six months was crucial to his team's mass determination. But he adds that Chandra's sharp resolution enabled his group to resolve the supernova from a bright X-ray source that appears in the field of view of Swift's X-ray Telescope. "We could not have made this measurement without Chandra," says Immler, who will submit his team's paper next week to the Astrophysical Journal. "The synergy between Swift's fast response and its ability to observe a supernova every day for a long period, and Chandra's high spatial resolution, is leading to a lot of interesting results." Foley and his colleagues, whose paper appears in the March 10 Astrophysical Journal Letters, propose that the star recently transitioned from a Luminous Blue Variable (LBV) star to a Wolf-Rayet star. An LBV is a massive star in a brief but unstable phase of stellar evolution. Similar to the 2004 eruption, LBVs are prone to blow off large amounts of mass in outbursts so extreme that they are frequently mistaken for supernovae, events dubbed "supernova impostors." Wolf-Rayet stars are hot, highly

  8. Population synthesis of massive stars

    NASA Astrophysics Data System (ADS)

    Vanbeveren, Dany

    2014-09-01

    This review deals with massive star population synthesis with a realistic population of binaries. We focus on the comparison between observed star numbers (as a function of metallicity) and theoretically predicted numbers of stellar populations in regions of continuous star formation and in starburst regions. Special attention is given to the O-type/WR/red supergiant stellar population, the population of blue supergiants, the pulsar and binary pulsar population, and the supernova rates. Finally, we consider massive double compact star mergers and the link with gravitational wave sources (the advanced LIGO II) and r-process element production sites.

  9. Really Hot Stars

    NASA Astrophysics Data System (ADS)

    2003-04-01

    Spectacular VLT Photos Unveil Mysterious Nebulae Summary Quite a few of the most beautiful objects in the Universe are still shrouded in mystery. Even though most of the nebulae of gas and dust in our vicinity are now rather well understood, there are some which continue to puzzle astronomers. This is the case of a small number of unusual nebulae that appear to be the subject of strong heating - in astronomical terminology, they present an amazingly "high degree of excitation". This is because they contain significant amounts of ions, i.e., atoms that have lost one or more of their electrons. Depending on the atoms involved and the number of electrons lost, this process bears witness to the strength of the radiation or to the impact of energetic particles. But what are the sources of that excitation? Could it be energetic stars or perhaps some kind of exotic objects inside these nebulae? How do these peculiar objects fit into the current picture of universal evolution? New observations of a number of such unusual nebulae have recently been obtained with the Very Large Telescope (VLT) at the ESO Paranal Observatory (Chile). In a dedicated search for the origin of their individual characteristics, a team of astronomers - mostly from the Institute of Astrophysics & Geophysics in Liège (Belgium) [1] - have secured the first detailed, highly revealing images of four highly ionized nebulae in the Magellanic Clouds, two small satellite galaxies of our home galaxy, the Milky Way, only a few hundred thousand light-years away. In three nebulae, they succeeded in identifying the sources of energetic radiation and to eludicate their exceptional properties: some of the hottest, most massive stars ever seen, some of which are double. With masses of more than 20 times that of the Sun and surface temperatures above 90 000 degrees, these stars are truly extreme. PR Photo 09a/03: Nebula around the hot star AB7 in the SMC. PR Photo 09b/03: Nebula near the hot Wolf-Rayet star BAT99

  10. Nearby regions of massive star formation

    NASA Astrophysics Data System (ADS)

    Bally, John; Cunningham, Nathaniel; Moeckel, Nickolas; Smith, Nathan

    Observations of the nearest regions of massive star formation such as Orion are reviewed. Early-type stars in the local OB associations, as well as their superbubbles and supershells provide a fossil record of massive star birth in the Solar vicinity over about the last 40 Myr. This record shows that most massive stars are born from dense, high-pressure, hot cores which spawn transient clusters that dissipate into the field soon after formation. A large fraction (15 to 30%) of massive stars are high-velocity runaways moving at more than 20 km s^{-1}. High-mass stars have a larger companion fraction than their lower-mass siblings. The Orion star forming complex contains the nearest site of on-going massive star formation. Studies of the Orion Nebula and the dense molecular cloud core located immediately behind the HII region provide our sharpest view of massive star birth. This region has formed a hierarchy of clusters within clusters. The Trapezium, OMC-1S, and OMC-1 regions represent three closely spaced sub-clusters within the more extended Orion Nebula Cluster. The oldest of these sub-clusters, which consists of the Trapezium stars, has completely emerged from its natal core. The OMC-1S and OMC-1 regions, are still highly embedded and forming clusters of additional moderate and high mass stars. Over a dozen YSOs embedded in OMC-1S are driving jets and outflows, many of which are injecting energy and momentum into the Orion Nebula. Recent proper motion measurements indicate that the Becklin-Neugebauer object is a high-velocity star moving away from the OMC1 core with a velocity of 30 km s^{-1}, making it the youngest high-velocity star known. Source I may be moving in the opposite direction with a velocity of about 12 km s^{-1}. The projected separation between source I and BN was less than few hundred AU about 500 years ago. The spectacular bipolar molecular outflow and system of shock-excited H_2 fingers emerging from OMC-1 has a dynamical age of about 1100

  11. Feedback During Massive Star Formation

    NASA Astrophysics Data System (ADS)

    Tanaka, Kei; Tan, Jonathan C.; Zhang, Yichen

    2016-01-01

    We present models of photoionization of massive protostellar cores, and show the impact of this ionization feedback on the efficiency of star formation and its observational features. Based on the Core Accretion scenario, we construct the collapse model of rotating massive-protostellar cloud cores together with a protostellar evolutional calculation, including feedback effects from a MHD disk wind, photoionization and radiation pressure. First, the MHD wind creates a bipolar outflow whose opening angle increases over the timescale of mass accretion. The ionizing luminosity dramatically increases after the protostar reaches ~ 5 Msun due to Kelvin-Helmholz contraction, and the MHD wind is photoionized when the protostellar mass reaches ~ 10 - 20 Msun. As the ionizing and bolometric luminosities increase, the outflow opening angle becomes wider due to radiation pressure feedback. By this combination of feedback processes, the envelope is eroded and the mass infall rate is significantly reduced to that arriving only from the disk-shielded equatorial region. At a protostellar mass of ~ 50 - 100 Msun, depending on the initial core properties, the mass accretion is halted by disk photoevaporation. In this way, feedback significantly reduces the star formation efficiency when forming massive stars from massive cloud cores, which could produce a cutoff at the high-mass end of the initial mass function. Along this evolutionary calculation, we also compute the detailed structure of the photoionized regions using a ray-tracing radiative transfer code and evaluate their emission signatures. Their free-free continuum and recombination line emissions are consistent with the variety of observed radio sources associated with massive protostars, i.e., jets and ultra/hyper-compact HII regions. The comparison between our models and such observations enables us to better define the evolutionary sequence of massive star formation.

  12. Spectra of hot stars

    NASA Astrophysics Data System (ADS)

    Hillier, D. John

    2015-08-01

    Non-LTE modeling is essential for interpreting the spectra of O stars and their decendents, and much progress has been made. The major uncertainty associated with analyzing photospheric spectra of O stars arises from issues related to microturbulence and macroturbulence. Many supergiants, for example, have microturbulent velocities that approach the sound speed, while macroturbulent velocities are often several times the sound speed. The cause of this turbulence is unknown, but may be related to pulsation, an underlying convection zone associated with the Fe opacity bump, or feedback from the stellar wind. Determining accurate abundances in O stars is hampered by the lack of lines belonging to low-z elements. Many species only have a few observable lines, and some of these are subject to complex non-LTE effects. A characteristic of massive stars is the existence of a stellar wind which is driven by radiation pressure. Radiation driving is inherently unstable, and this leads to winds with an inhomogeneous structure. Major issues that are still unresolved include: How are winds driven through the sonic point? What is the nature of the inhomogeneities, and how do the properties of these inhomogeneities change with density and velocity? How important is spatial porosity, and porosity in velocity space? What is the structure of the shocks, and in what stars do the shocks fail to cool? With Wolf-Rayet (W-R) stars the major uncertainty arises because the classic spectroscopic radius (i.e., the location where τ = 2/3) often refers to a location in the wind — not necessarily the stellar radius associated with stellar evolution models. Derived radii are typically several times those predicted by stellar evolution calculations, although for strong-lined W-R stars it is possible to construct models that are consistent with evolution calculations. The driving of the winds in these stars is strongly coupled to the closeness of the stars to the Eddington limit and to their

  13. Massive Compact Stars as Quark Stars

    NASA Astrophysics Data System (ADS)

    Rodrigues, Hilário; Barbosa Duarte, Sérgio; de Oliveira, José Carlos T.

    2011-03-01

    High-mass compact stars have been reported recently in the literature, providing strong constraints on the properties of the ultra dense matter beyond the saturation nuclear density. In view of these results, the calculations of quark star or hybrid star equilibrium structure must be compatible with the provided observational data. But since the equations of state used in describing quark matter are in general too soft in comparison with the equation of states used to describe the hadronic or nuclear matter, the calculated quark star models presented in the literature are in general not suitable to explain the stability of highly-compact massive objects. In this work, we present the calculations of a spherically symmetric quark star structure by using an equation of state that takes into account the superconducting color-flavor locked phase of the strange quark matter. In addition, some fundamental aspects of QCD (asymptotic freedom and confinement) are considered by means of a phenomenological description of the deconfined quark phase, the density-dependent quark mass model. The quark matter behavior introduced by this model stiffens the corresponding equation of state. We thus investigate the influence of this model on the mass-radius diagram of quark stars. We obtain massive quark stars due to the stiffness of the equation of state, when a reasonable parameterization of the color superconducting gap is used. Models of quark stars enveloped by a nucleonic crust composed of a nuclear lattice embedded in an electron gas, with nuclei close to neutron drip line, are also discussed.

  14. The Massive Star Population in M101

    NASA Astrophysics Data System (ADS)

    Grammer, Skyler H.

    five annuli, examine the effects that a metallicity gradient and variable SFH have on the predicted ratios, and compare to the observed values. We find that the radial behavior of our modeled blue to red supergiant ratios is highly sensitive to both spatial variations in the SFH and metallicity. Incorporating the derived SFH into the modeled ratios, we are able to reproduce the observed values at large radii (low metallicity), but at small radii (high metallicity) the modeled and observed ratios are discrepant. Though photometry has proven to be a powerful tool to identify candidate evolved massive stars and their effects on their host galaxy, spectroscopy is necessary to study the physical properties of individual stars. We observed moderate-resolution optical spectra for 56 of the brightest stars in the direction to M101 using the Multiple Mirror Telescope. We also created light curves for each target using multi-epoch U BV R images from the Large Binocular Telescope. We separate the spectroscopially confirmed members of M101 into four groups: hot supergiants, intermediate supergiants, emission-line stars, and LBVs. Several stars in each group are discussed in detail. Of the spectroscopically confirmed members, we find that eight meet our criterion for variability. We present light curves for the known LBV candidates, V2, V4, and V9, and introduce a new candidate: 9492 &barbelow;14 &barbelow;11998. Additionally, we identify 20 new variables in M101. Lacking spectra, we separated the variables, by their photometric properties, into three groups: hot, intermediate, and cool. We find two hot stars with V-band variability of +/-1 magnitude; we flag these stars as LBV candidates. Of the intermediate and cool variables, we identify several stars with low- to moderate-amplitude variability (0.1--0.5 magnitudes).

  15. PRISM Polarimetry of Massive Stars

    NASA Astrophysics Data System (ADS)

    Kerkstra, Brennan; Lomax, Jamie R.; Bjorkman, Karen S.; Bjorkman, Jon Eric; Skiff, Brian; Covey, Kevin R.; Wisniewski, John P.

    2016-01-01

    We present the early results from our long-term, multi-epoch filter polarization survey of massive stars in and around young Galactic clusters. These BVRI polarization data were obtained using the PRISM instrument mounted on the 1.8m Perkins Telescope at Lowell Observatory. We first detail the creation of our new semi-automated polarization data reduction pipeline that we developed to process these data. Next, we present our analysis of the instrumental polarization properties of the PRISM instrument, via observations of polarized and unpolarized standard stars. Finally, we present early results on the total and intrinsic polarization behavior of several isolated, previously suggested classical Be stars, and discuss these results in the context of the larger project.BK acknowledges support from a NSF/REU at the University of Oklahoma. This program was also supported by NSF-AST 11411563, 1412110, and 1412135.

  16. MASSIVE INFANT STARS ROCK THEIR CRADLE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    that are responsible for lighting up this cloud of gas. The apparently innocuous-looking star at the very center of the nebula, just below the brightest region, is actually about 30 times more massive and almost 200,000 times brighter than our Sun. The intense light and powerful stellar 'winds' from this ultra-bright star have cleared away the surrounding gas to form a large cavity. The bubble is approximately 25 light-years in diameter - about the same size as the famous star-forming Orion Nebula. The Orion Nebula is sculpted by intense radiation from newly born stars in the same way as N83B. Astronomers estimate that the spherical void in N83B must have been carved out of the nebula very recently - in astronomical terms - maybe as little as 30,000 years ago. The hottest star in N83B is 45 times more massive than the Sun and is embedded in the brightest region in the nebula. This bright region, situated just above the center, is only about 2 light-years across. The region's small size and its intense glow are telltale signs of a very young, massive star. This star is the youngest newcomer to this part of the Large Magellanic Cloud. The Hubble image shows a bright arc structure just below the luminous star. This impressive ridge may have been created in the glowing gas by the hot star's powerful wind. Measurements of the age of this star and neighboring stars in the nebula show that they are younger than the nebula's central star. Their formation may have been 'triggered' by the violent wind from the central star. This 'chain-reaction' of stellar births seems to be common in the Universe. About 20 young and luminous stars have been identified in the region, but it may well be that many more massive stars remain undetected in other areas of the Large Magellanic Cloud, hidden by dust in small clusters like N83B. To the right of the glowing N83B is a much larger diffuse nebula, known as DEM22d, which is partly obscured by an extended lane of dust and gas. This image is

  17. INTERNAL GRAVITY WAVES IN MASSIVE STARS: ANGULAR MOMENTUM TRANSPORT

    SciTech Connect

    Rogers, T. M.; Lin, D. N. C.; McElwaine, J. N.; Lau, H. H. B. E-mail: lin@ucolick.org E-mail: hblau@astro.uni-bonn.de

    2013-07-20

    We present numerical simulations of internal gravity waves (IGW) in a star with a convective core and extended radiative envelope. We report on amplitudes, spectra, dissipation, and consequent angular momentum transport by such waves. We find that these waves are generated efficiently and transport angular momentum on short timescales over large distances. We show that, as in Earth's atmosphere, IGW drive equatorial flows which change magnitude and direction on short timescales. These results have profound consequences for the observational inferences of massive stars, as well as their long term angular momentum evolution. We suggest IGW angular momentum transport may explain many observational mysteries, such as: the misalignment of hot Jupiters around hot stars, the Be class of stars, Ni enrichment anomalies in massive stars, and the non-synchronous orbits of interacting binaries.

  18. Recovery From Giant Eruptions in Massive Stars

    NASA Astrophysics Data System (ADS)

    Kashi, A.; Davidson, K.; Humphreys, R. M.

    2015-12-01

    We perform radiation hydrodynamic simulations to study how very massive stars recover from giant eruptions. The post eruption star experience strong mass loss due to strong winds, driven by radial pulsations in the star*s interior, that operate by the κ-mechanism. The mass loss history obtained in our simulations resembles η Car*s history.

  19. Perspectives for hot stars in the next decade

    NASA Astrophysics Data System (ADS)

    Rauw, G.

    2016-06-01

    XMM-Newton has deeply changed our picture of X-ray emission of hot, massive stars. High-resolution X-ray spectroscopy as well as monitoring of these objects revealed a number of previously unexpected features that challenge our understanding of the dynamics of the stellar winds of massive stars. In this contribution, I will briefly summarize the results obtained over the past 15 years and highlight the perspectives for the next decade. It is anticipated that coordinated (X-ray and optical or UV) monitoring and time-critical observations of either single or binary massive stars will become the most important topics in this field over the coming years. Synergies with existing or forthcoming X-ray observatories (NuStar, Astro-H, eROSITA) will also play a major role and will further enhance the importance of XMM-Newton in our quest for understanding the physics of hot, massive stars.

  20. Radiative ablation of disks around massive stars

    NASA Astrophysics Data System (ADS)

    Kee, Nathaniel Dylan

    Hot, massive stars (spectral types O and B) have extreme luminosities (10. 4 -10. 6 L?) that drive strong stellar winds through UV line-scattering.Some massive stars also have disks, formed by either decretion from the star (as in the rapidly rotating "Classical Be stars"), or accretion during the star's formation. This dissertation examines the role of stellar radiation in driving (ablating) material away from these circumstellar disks. A key result is that the observed month to year decay of Classical Be disks can be explained by line-driven ablation without, as previously done, appealing to anomalously strong viscous diffusion. Moreover, the higher luminosity of O stars leads to ablation of optically thin disks on dynamical timescales of order a day, providing a natural explanation for the lack of observed Oe stars. In addition to the destruction of Be disks, this dissertation also introduces a model for their formation by coupling observationally inferred non-radial pulsation modes and rapid stellar rotation to launch material into orbiting Keplerian disks of Be-like densities. In contrast to such Be decretion disks, star-forming accretion disks are much denser and so are generally optically thick to continuum processes. To circumvent the computational challenges associated with radiation hydrodynamics through optically thick media, we develop an approximate method for treating continuum absorption in the limit of geometrically thin disks. The comparison of ablation with and without continuum absorption shows that accounting for disk optical thickness leads to less than a 50% reduction in ablation rate, implying that ablation rate depends mainly on stellar properties like luminosity. Finally, we discuss the role of "thin-shell mixing" in reducing X-rays from colliding wind binaries. Laminar, adiabatic shocks produce well understood X-ray emission, but the emission from radiatively cooled shocks is more complex due to thin-shell instabilities. The parameter

  1. Molecular Outflows in Massive Star Forming Regions

    NASA Astrophysics Data System (ADS)

    Cunningham, Nichol

    2015-11-01

    This thesis presents millimetre continuum and molecular line observations exploring the properties of molecular outflows towards massive star forming regions. Massive stars produce some of the most energetic phenomena in the Galaxy, yet we still do not have a comprehensive understanding of how they actually form. Outflows are known to play a key role in this formation process and their properties, particularly how they change depending on the mass, luminosity and evolution of the driving source can shed light on how massive stars actually form. This thesis presents observations at both high (SMA 3 arcsecond) and low (JCMT 15 arcsecond) spatial resolution of the known jet/outflow tracers, SiO and 12CO, towards a sample massive star forming region drawn from the RMS survey. Furthermore, the presence of infall signatures is explored through observations of HCO+ and H13CO+, and the hot core nature of the regions is probed using tracers such as CH3CN, HC3N and CH3OH. SiO is detected towards approximately 50% of the massive young stellar objects and HII regions in the JCMT sample. The detection of SiO appears to be linked to the age of the RMS source, with the likely younger sources showing a stronger dependence with SiO. The presence of SiO also appears to be linked to the CO velocity, with SiO more efficiently tracing sources with higher velocity dispersions. In the MOPRA observations towards a sample of 33 RMS sources, CH3CN is detected towards 66% of the sources, with the redder likely younger sources having the largest rotational temperatures. This thesis presents the first interferometric SiO (5-4) and 12CO (2-1) observations, taken with the SMA, towards the massive star forming region G203.3166/NGC 2264-C. In this intermediate/massive star forming cluster, SiO is again tracing the youngest sources. Both the SiO and 12CO emission trace two bipolar, high velocity outflows towards the mm brightest, IR-dark, likely youngest sources in this reg! ion. In contrast the IR

  2. The Embedded Phase of Massive Star Formation

    NASA Astrophysics Data System (ADS)

    van der Tak, Floris

    2000-11-01

    This thesis studies the physical and chemical structure of a set of massive young stars which are surrounded by a thick envelope of dust and gas, the earliest known phase of massive star formation. The primary scientific questions addressed are: (i) What is the evolutionary order of the phenomena associated with massive star formation? (ii) What is the physical and chemical structure of the envelopes of massive young stars? How do they compare to those of low-mass stars? Do specific molecules trace different stages? (iii) What are the masses of any circumstellar disks, and on what time scales are they dispersed? To answer these questions, a sample of infrared and submillimeter sources has been selected on high luminosity, close distance, isolated location and high mid-infrared flux. We present observations of these sources with single-dish submillimeter antennas, millimeter interferometers and near-infrared spectroscopy, and also discuss ISO spectra. For the interpretation, we have developed models with a detailed physical structure, combined with chemical differentiation, which is strongly coupled to the temperature. Some of the conclusions are: The envelopes of massive young stars are well described by centrally heated spherical models, with masses of ~ 100-1000 Modot within radii of ~0.1 pc. For a power-law density structure n(r) = n0 (r / r0)-α, we find α = 1.0-1.5 for the younger sources, significantly lower than α ≅ 2 found for the envelopes of low-mass stars at a comparable stage of evolution. This difference may indicate that the support against gravitational collapse in high-mass cores is by nonthermal (e.g., turbulent) pressure, and in low-mass cores by thermal pressure. For the more evolved sources, α = 1.5-2.0 fits the data best. Unlike in low-mass star formation, the near-infrared emission decreases as the envelope warms up, indicates that the hot dust close to the star is destroyed and/or pushed out by stellar radiation or mass loss. The

  3. Massive OB stars at varying Z

    NASA Astrophysics Data System (ADS)

    Herrero, A.; Garcia, M.; Simón-Díaz, S.; Camacho, I.; Sabín-Sanjulián, C.; Castro, N.

    2015-01-01

    Massive stars play a key role in environments with very different metallicities. To interpret the role of massive stars in these systems we have to know their properties at different metallicities. The Local Group offers an excellent laboratory to this aim.

  4. Isolated Hot Stars in Galactic Center Vicinity

    NASA Technical Reports Server (NTRS)

    Cotera, Angela S.; Simpson, Janet P.; Erickson, Edwin F.; Colgan, Sean W. J.; Burton, Michael G.; Allen, David A.

    1999-01-01

    Using near-infrared imaging and spectroscopy, we discuss the discovery of six emission-line sources within approx. 20 pc of Sgr A West but outside of the central parsec. The objects are coincident with stars seen in. the J, H, and K' images; all have Br(gamma) (2.166 microns) in emission, several also have He I (2.058 and 2.112/3 micrometers), and some have He II (2.189 micrometers) emission lines. Comparison of the H- and K-band spectra of the newly discovered stars with recently published infrared spectral atlases of optically classified stars suggests that most of these stars are similar to massive stars in transition (e.g., Ofpe/WN9, B[e], and LBV), although one is definitely a WN6 star. Two of the potential stars are associated with the radio emission regions A-D near Sgr A East, three are near or within the radio emission regions Hl-H8, the last is near GO.10+0.02 and is likely to be associated with the GO.12+0.02 (Arches) cluster of stars, discussed in a previous paper. The stars are shown to be significant sources of ionization for their associated radio emission regions, with several capable of completely ionizing the regions. These results provide additional support for the idea that these thermal radio regions, and similar such regions in the Galactic center, are indeed photoionized by hot young stars.

  5. Evolved Massive Stars in the Local Group

    NASA Astrophysics Data System (ADS)

    Drout, M. R.; Massey, P.

    2015-05-01

    In this manuscript we describe a number of recent advances in the study of evolved massive stars in the Local Group, with an emphasis on how representative populations of these stars can be used to test models of massive star evolution. In honor of the 50th anniversary of the Cerro Tololo Inter-American Observatory (CTIO) we attempt to put these finding in some historical context by discussing how our understanding of the various stages in the lives of massive stars has evolved since Cerro Tololo was first selected as the site for the observatory which would become CTIO.

  6. First Circumstellar Disk around a Massive Star

    NASA Astrophysics Data System (ADS)

    1998-06-01

    Observations with an infrared-sensitive instrument at the ESO 3.6-m telescope at La Silla have for the first time shown the presence of a disk around a hot and massive star, known as G339.88-1.26 . Until now, disks have only been found around less massive stars. Planets are formed in such disks. The new discovery may thus have important implications for our understanding of the formation of planetary systems around stars. TIMMI observations Observations at mid-infrared wavelengths were carried out in July 1997 by Bringfried Stecklum (Landessternwarte Thüringen, Tautenburg, Germany) and Hans-Ulrich Käufl (ESO), using the TIMMI instrument at the ESO 3.6-m telescope. Additional measurements were carried out in March 1998. TIMMI ( T hermal I nfrared M ulti M ode I nstrument) is a general-purpose camera spectrometer operating at a wavelength of 10 µm. To reach sufficient sensitivity, the camera must be cooled to approx. -260 o C, i.e. a few degrees above the absolute minimum, by use of liquid Helium. Astronomical objects whose temperatures are between -120 o C and 300 o C radiate most of their energy at this wavelength. In addition, dust and haze that are absolutely impenetrable for light visible to the human eye, are often found to be nearly transparent at this wavelength. This is why fire-fighters now use similar equipment to look through smoke. G339.88-1.26: A very special object ESO PR Photo 22a/98 ESO PR Photo 22a/98 [JPEG, 800k] This image is a true-color composite of near-infrared observations of the sky region around the radio source G339.88-1.26 with the ESO/MPI 2.2-m telescope at La Silla. In this image, the visible colors red, green and blue have been used to represent the infrared filters J, H and K (at 1.25, 1.63 and 2.2 µm wavelength, respectively). No object is visible at the position of the radio source, even at these near-infrared wavelengths. A dark band of absorbing dust is clearly visible, exactly at the position of the object (indicated by an

  7. Massive star birth: A crossroads of Astrophysics

    NASA Astrophysics Data System (ADS)

    Cesaroni, R.; Felli, M.; Churchwell, E.; Walmsley, M.

    Massive stars, those with between 10 and 100 times the mass of the Sun, are among the rarest stars of all. They live fast and die young, but during their short lives produce the most dramatic effects on the surrounding interstellar medium in terms of dynamics, ionization, and chemical enrichment. Until a few decades ago massive star birth was literally shrouded in mystery, since these stars are born deep inside dense clouds of swirling dust and gas that obscures our view. At IAU S227, more than 200 of the world's leading astronomers presented a cornucopia of new results concerning the birth and infancy of massive stars. These proceedings show the achievements reached in this field, due to observations in the radio at mm and sub-mm wavelengths and in the infrared, and to theoretical models that simulate what happens in the cradle of a massive star.

  8. Massive Wolf-Rayet stars on the verge to explode

    NASA Astrophysics Data System (ADS)

    Tramper, F.; Straal, S. M.; Sanyal, D.; Sana, H.; de Koter, A.; Gräfener, G.; Langer, N.; Vink, J. S.; de Mink, S. E.; Kaper, L.

    The enigmatic oxygen-sequence Wolf-Rayet stars represent a rare stage in the evolution of massive stars. Their properties can provide unique constraints on the pre-supernova evolution of massive stars. This work presents the results of a quantitative spectroscopic analysis of the known single WO stars, with the aim to obtain the key stellar parameters and deduce their evolutionary state.X-Shooter spectra of the WO stars are modeled using the line-blanketed non-local thermal equilibrium atmosphere code cmfgen. The obtained stellar parameters show that the WO stars are very hot, with temperatures ranging from 150 kK to 210 kK. Their chemical composition is dominated by carbon (>50%), while the helium mass fraction is very low (down to 14%). Oxygen mass fractions reach as high as 25%. These properties can be reproduced with dedicated evolutionary models for helium stars, which show that the stars are post core-helium burning and very close to their eventual supernova explosion. The helium-star masses indicate initial masses or approximately 40 - 60M⊙.Thus, WO stars represent the final evolutionary stage of stars with estimated initial masses of 40 - 60M⊙. They are post core-helium burning and may explode as type Ic supernovae within a few thousand years.

  9. Evolution of Massive Stars at Low Metallicity

    NASA Astrophysics Data System (ADS)

    Meynet, Georges; Walborn, Nolan R.; Hunter, Ian; Martayan, Christophe; van Marle, Allard Jan; Marchenko, Sergey; Vink, Jorick S.; Limongi, Marco; Levesque, Emily M.; Modjaz, Maryam

    2008-06-01

    This paper reports the contributions made on the occasion of the Special Session entitled “Evolution of Massive Stars at Low Metallicity” which was held on Sunday, December 9, 2007 in Kauai (USA).

  10. Massive Stars: Input Physics and Stellar Models

    NASA Astrophysics Data System (ADS)

    El Eid, M. F.; The, L.-S.; Meyer, B. S.

    2009-10-01

    We present a general overview of the structure and evolution of massive stars of masses ≥12 M ⊙ during their pre-supernova stages. We think it is worth reviewing this topic owing to the crucial role of massive stars in astrophysics, especially in the evolution of galaxies and the universe. We have performed several test computations with the aim to analyze and discuss many physical uncertainties still encountered in massive-star evolution. In particular, we explore the effects of mass loss, convection, rotation, 12C( α, γ)16O reaction and initial metallicity. We also compare and analyze the similarities and differences among various works and ours. Finally, we present useful comments on the nucleosynthesis from massive stars concerning the s-process and the yields for 26Al and 60Fe.

  11. Identifying new massive stars in Carina

    NASA Astrophysics Data System (ADS)

    Alexander, Michael J.; McSwain, M. Virginia; Povich, Matthew S.; Hanes, Richard J.

    2015-01-01

    We have conducted an optical and infrared spectroscopic survey of 94 candidate OB stars in the Great Carina Nebula. Candidates were selected on the basis of their infrared spectral energy distributions, which was used to estimate bolometric luminosity and effective temperature. Additionally, the presence of X-ray emission -- a sign of young, dynamic atmospheres -- was used to increase the likelihood of selecting newly formed massive stars associated with the Carina star formation region. Here, we present the preliminary results of this study including spectral types and the OB star confirmation rate. We also discuss the spatial distribution of the new OB stars with respect to the various clusters and sub-clusters and speculate on the implications of additional massive stars on the global mass function of the Carina star forming complex.

  12. Magnetism in massive early-type stars

    NASA Astrophysics Data System (ADS)

    Grunhut, J. H.; Wade, G. A.

    2013-02-01

    In the last five years our knowledge of magnetism in early-type stars has significantly improved because of the new gen- eration of high-resolution spectropolarimeters (ESPaDOnS@CFHT, Narval@TBL, HARPSpol@ESO). The success of the Magnetism in Massive Stars (MiMeS) Project, for example, has greatly improved our understanding of the magnetic properties of massive early-type stars; however, it was mainly focused on single stars. Summarized here is our general understanding of stellar magnetism in early-type stars and the recent findings from the MiMeS project. As recent results suggest a significant fraction of early-type stars are in binaries, this implies that the interplay between magnetic fields and binarity has yet to be investigated in any significant detail. To this end, the current analysis of the recently discovered magnetic field in the rapidly-rotating secondary star of the close, massive binary system known as Plaskett's star - a unique system that is testing our current theories of binarity and magnetism in early-type stars, and a target for investigation in the recently accepted Binarity and Magnetic Interactions in various classes of Stars (BinaMIcS) Large Programs at CFHT and TBL - is discussed.

  13. How Massive Single Stars End Their Life

    NASA Technical Reports Server (NTRS)

    Heger, A.; Fryer, C. L.; Woosley, S. E.; Langer, N.; Hartmann, D. H.

    2003-01-01

    How massive stars die-what sort of explosion and remnant each produces-depends chiefly on the masses of their helium cores and hydrogen envelopes at death. For single stars, stellar winds are the only means of mass loss, and these are a function of the metallicity of the star. We discuss how metallicity, and a simplified prescription for its effect on mass loss, affects the evolution and final fate of massive stars. We map, as a function of mass and metallicity, where black holes and neutron stars are likely to form and where different types of supernovae are produced. Integrating over an initial mass function, we derive the relative populations as a function of metallicity. Provided that single stars rotate rapidly enough at death, we speculate on stellar populations that might produce gamma-ray bursts and jet-driven supernovae.

  14. Olivier Chesneau's Work on Massive Stars

    NASA Astrophysics Data System (ADS)

    Millour, F.

    2015-12-01

    Olivier Chesneau challenged several fields of observational stellar astrophysics with bright ideas and an impressive amount of work to make them real in the span of his career, from his first paper on P Cygni in 2000, up to his last one on V838 Mon in 2014. He was using all the so-called high-angular resolution techniques since it helped his science to be made, namely study in details the inner structure of the environments around stars, be it small mass (AGBs), more massive (supergiant stars), or explosives (Novae). I will focus here on his work on massive stars.

  15. Placing Observational Constraints on Massive Star Models

    NASA Astrophysics Data System (ADS)

    Rosenfield, Philip

    2011-10-01

    The lives and deaths of massive stars are intricately linked to the evolution of galaxies. Yet, despite their integral importance to understanding galaxy evolution, models of massive stars are inconsistent with observations. These uncertainties can be traced to limited observational constraints available for improving massive star models. A sensitive test of the underlying physics of massive stars, e.g., convection, rotation, and mass loss is to measure the ratio of blue core helium burning stars {BHeB} to red core helium burning stars {RHeB}, 5-20Msun stars in the stage evolution immediately following the main sequence. Even the most sophisticated models cannot accurately predict the observed ratio over a range of metallicities, suggesting an insufficient understanding of the underlying physics. However, observational measurements of this ratio over a wide range of environments would provide substantial constraints on the physical parameters governing the evolution of all stars >5 Msun.We propose to place stringent observational constraints on the physics of massive star evolution by uniformly measuring the B/R HeB ratio in a wide range of galaxies. The HST archive contains high quality optical imaging of resolved stellar populations of dozens of nearby galaxies. From the ANGST program, we identified 38 galaxies, spanning 2 dex in metallicity that have significant BHeB and RHeB populations. Using this sample, we will empirically characterize the colors of the BHeB and RHeB sequences as a function of luminosity and metallicity, measure the B/R ratio, and constrain the lifetimes of the BHeB and RHeBs in the Padova stellar evolution models and the Cambridge STARS code.

  16. Near-Infrared Mass Loss Diagnostics for Massive Stars

    NASA Technical Reports Server (NTRS)

    Sonneborn, George; Bouret, J. C.

    2010-01-01

    Stellar wind mass loss is a key process which modifies surface abundances, luminosities, and other physical properties of hot, massive stars. Furthermore, mass loss has to be understood quantitatively in order to accurately describe and predict massive star evolution. Two urgent problems have been identified that challenge our understanding of line-driven winds, the so-called weak-wind problem and wind clumping. In both cases, mass-loss rates are drastically lower than theoretically expected (up to a factor 1001). Here we study how the expected spectroscopic capabilities of the James Webb Space Telescope (JWST), especially NIRSpec, could be used to significantly improve constraints on wind density structures (clumps) and deep-seated phenomena in stellar winds of massive stars, including OB, Wolf-Rayet and LBV stars. Since the IR continuum of objects with strong winds is formed in the wind, IR lines may sample different depths inside the wind than UV-optical lines and provide new information about the shape of the velocity field and clumping properties. One of the most important applications of IR line diagnostics will be the measurement of mass-loss rates in massive stars with very weak winds by means of the H I Bracket alpha line, which has been identified as one of the most promising diagnostics for this problem.

  17. Triggered star formation in the environment of young massive stars

    NASA Astrophysics Data System (ADS)

    Gritschneder, Matthias; Naab, T.; Heitsch, F.; Burkert, A.

    Recent observations with the Spitzer Space Telescope show clear evidence that star formation takes place in the surrounding of young massive O-type stars, which are shaping their environment due to their powerful radiation and stellar winds. In this work we investigate the effect of ionising radiation of massive stars on the ambient interstellar medium (ISM): In particular we want to examine whether the UV-radiation of O-type stars can lead to the observed pillar-like structures and can trigger star formation. We developed a new implementation, based on a parallel Smooth Particle Hydrodynamics code (VINE), that allows an efficient treatment of the effect of ionising radiation from massive stars on their turbulent gaseous environment. Here we present first results at very high resolution. We show that ionising radiation can trigger the collapse of an otherwise stable molecular cloud. The arising structures resemble observed structures (e.g. the pillars of creation in the Eagle Nebula (M16) or the Horsehead Nebula B33). Including the effect of gravitation we find small regions that can be identified as formation places of individual stars. We conclude that ionising radiation from massive stars alone can trigger substantial star formation in molecular clouds.

  18. RCW 108: Massive Young Stars Trigger Stellar Birth

    NASA Technical Reports Server (NTRS)

    2008-01-01

    RCW 108 is a region where stars are actively forming within the Milky Way galaxy about 4,000 light years from Earth. This is a complicated region that contains young star clusters, including one that is deeply embedded in a cloud of molecular hydrogen. By using data from different telescopes, astronomers determined that star birth in this region is being triggered by the effect of nearby, massive young stars.

    This image is a composite of X-ray data from NASA's Chandra X-ray Observatory (blue) and infrared emission detected by NASA's Spitzer Space Telescope (red and orange). More than 400 X-ray sources were identified in Chandra's observations of RCW 108. About 90 percent of these X-ray sources are thought to be part of the cluster and not stars that lie in the field-of-view either behind or in front of it. Many of the stars in RCW 108 are experiencing the violent flaring seen in other young star-forming regions such as the Orion nebula. Gas and dust blocks much of the X-rays from the juvenile stars located in the center of the image, explaining the relative dearth of Chandra sources in this part of the image.

    The Spitzer data show the location of the embedded star cluster, which appears as the bright knot of red and orange just to the left of the center of the image. Some stars from a larger cluster, known as NGC 6193, are also visible on the left side of the image. Astronomers think that the dense clouds within RCW 108 are in the process of being destroyed by intense radiation emanating from hot and massive stars in NGC 6193.

    Taken together, the Chandra and Spitzer data indicate that there are more massive star candidates than expected in several areas of this image. This suggests that pockets within RCW 108 underwent localized episodes of star formation. Scientists predict that this type of star formation is triggered by the effects of radiation from bright, massive stars such as those in NGC 6193. This radiation may cause the interior of gas

  19. Modeling populations of rotationally mixed massive stars

    NASA Astrophysics Data System (ADS)

    Brott, I.

    2011-02-01

    Massive stars can be considered as cosmic engines. With their high luminosities, strong stellar winds and violent deaths they drive the evolution of galaxies through-out the history of the universe. Despite the importance of massive stars, their evolution is still poorly understood. Two major issues have plagued evolutionary models of massive stars until today: mixing and mass loss On the main sequence, the effects of mass loss remain limited in the considered mass and metallicity range, this thesis concentrates on the role of mixing in massive stars. This thesis approaches this problem just on the cross road between observations and simulations. The main question: Do evolutionary models of single stars, accounting for the effects of rotation, reproduce the observed properties of real stars. In particular we are interested if the evolutionary models can reproduce the surface abundance changes during the main-sequence phase. To constrain our models we build a population synthesis model for the sample of the VLT-FLAMES Survey of Massive stars, for which star-formation history and rotational velocity distribution are well constrained. We consider the four main regions of the Hunter diagram. Nitrogen un-enriched slow rotators and nitrogen enriched fast rotators that are predicted by theory. Nitrogen enriched slow rotators and nitrogen unenriched fast rotators that are not predicted by our model. We conclude that currently these comparisons are not sufficient to verify the theory of rotational mixing. Physical processes in addition to rotational mixing appear necessary to explain the stars in the later two regions. The chapters of this Thesis have been published in the following Journals: Ch. 2: ``Rotating Massive Main-Sequence Stars I: Grids of Evolutionary Models and Isochrones'', I. Brott, S. E. de Mink, M. Cantiello, N. Langer, A. de Koter, C. J. Evans, I. Hunter, C. Trundle, J.S. Vink submitted to Astronomy & Astrop hysics Ch. 3: ``The VLT-FLAMES Survey of Massive

  20. Four open questions in massive star evolution

    NASA Astrophysics Data System (ADS)

    Meynet, G.; Eggenberger, P.; Ekström, S.; Georgy, C.; Groh, J.; Maeder, A.; Saio, H.; Moriya, T.

    2013-12-01

    We discuss four questions dealing with massive star evolution. The first one is about the origin of slowly rotating, non-evolved, nitrogen rich stars. We propose that these stars may originate from initially fast rotating stars whose surface has been braked down. The second question is about the evolutionary status of α-Cygni variables. According to their pulsation properties, these stars should be post red supergiant stars. However, some stars at least present surface abundances indicating that they should be pre red supergiant stars. How to reconcile these two contradictory requirements? The third one concerns the various supernova types which are the end point of the evolution of stars with initial masses between 18 and 30M⊙, i.e. the most massive stars which go through a red supergiant phase during their lifetime. Do they produce types IIP, IIL, IIn, IIb or Ib supernovae or do they end without producing any SN event? Finally, we shall discuss reasons why so few progenitors of type Ibc supernovae have yet been detected?

  1. New evolutionary tracks of massive stars with PARSEC

    NASA Astrophysics Data System (ADS)

    Chen, Yang; Bressan, Alessandro; Girardi, Leo; Marigo, Paola

    2015-08-01

    We present new evolutionary tracks of massive stars that complement the already published PARSEC database and supersede the old Padova evolutionary tracks of massive stars, which are more than 20 years old. We consider a broad range of metallicities, from Z=0.0001 to Z=0.04, and initial masses up to M=350 M⊙. The evolution is computed from the pre-main sequence phase up to the central carbon ignition. We supplement the new tracks with new tables of theoretical bolometric corrections in several photometric systems, obtained by homogenizing stellar atmosphere models of hot and cool stars, PoWR, WM-basic, ATLAS9 and Phoenix.The mass, age and metallicity grids are fully adequate to perform detailed investigations of the properties of very young stellar systems, in local and distant galaxies.

  2. Wind channeling, magnetospheres, and spindown of magnetic massive stars

    NASA Astrophysics Data System (ADS)

    Owocki, S. P.; ud-Doula, A.; Townsend, R. H. D.; Petit, V.; Sundqvist, J. O.; Cohen, D. H.

    2014-08-01

    A subpopulation (~10%) of hot, luminous, massive stars have been revealed through spectropolarimetry to harbor strong (hundreds to tens of thousand Gauss), steady, large-scale (often significantly dipolar) magnetic fields. This review focuses on the role of such fields in channeling and trapping the radiatively driven wind of massive stars, including both in the strongly perturbed outflow from open field regions, and the wind-fed ``magnetospheres'' that develop from closed magnetic loops. For B-type stars with weak winds and moderately fast rotation, one finds ``centrifugal magnetospheres'', in which rotational support allows magnetically trapped wind to accumulate to a large density, with quite distinctive observational signatures, e.g. in Balmer line emission. In contrast, more luminous O-type stars have generally been spun down by magnetic braking from angular momentum loss in their much stronger winds. The lack of centrifugal support means their closed loops form a ``dynamical magnetosphere'', with trapped material falling back to the star on a dynamical timescale; nonetheless, the much stronger wind feeding leads to a circumstellar density that is still high enough to give substantial Balmer emission. Overall, this review describes MHD simulations and semi-analytic dynamical methods for modeling the magnetospheres, the magnetically channeled wind outflows, and the associated spin-down of these magnetic massive stars.

  3. HAT-P-56b: An Inflated Massive Hot Jupiter Transiting a Bright F Star Followed Up with K2 Campaign 0 Observations

    NASA Astrophysics Data System (ADS)

    Huang, C. X.; Hartman, J. D.; Bakos, G. Á.; Penev, K.; Bhatti, W.; Bieryla, A.; de Val-Borro, M.; Latham, D. W.; Buchhave, L. A.; Csubry, Z.; Kovács, G.; Béky, B.; Falco, E.; Berlind, P.; Calkins, M. L.; Esquerdo, G. A.; Lázár, J.; Papp, I.; Sári, P.

    2015-09-01

    We report the discovery of HAT-P-56b by the HATNet survey, an inflated hot Jupiter transiting a bright F-type star in Field 0 of NASA's K2 mission. We combine ground-based discovery and follow-up light curves with high precision photometry from K2, as well as ground-based radial velocities from the Tillinghast Reflector Echelle Spectrograph on the Fred Lawrence Whipple Observatory 1.5 m telescope to determine the physical properties of this system. HAT-P-56b has a mass of 2.18 {M}{{J}}, radius of 1.47 {R}{{J}}, and transits its host star on a near-grazing orbit with a period of 2.7908 day. The radius of HAT-P-56b is among the largest known for a planet with {M}p\\gt 2 {M}{{J}}. The host star has a V-band magnitude of 10.9, mass of 1.30 {M}⊙ , and radius of 1.43 {R}⊙ . The periodogram of the K2 light curve suggests that the star is a γ Dor variable. HAT-P-56b is an example of a ground-based discovery of a transiting planet, where space-based observations greatly improve the confidence in the confirmation of its planetary nature, and also improve the accuracy of the planetary parameters. Based on observations obtained with the Hungarian-made Automated Telescope Network. Based in part on observations obtained with the Tillinghast Reflector 1.5 m telescope and the 1.2 m telescope, both operated by the Smithsonian Astrophysical Observatory at the Fred Lawrence Whipple Observatory in Arizona. Based in part on observations obtained with the Apache Point Observatory 3.5 m telescope, which is owned and operated by the Astrophysical Research Consortium. Based in part on observations obtained with the Kepler Space Craft in the K2 Campaign 0 Mission.

  4. Massive Stars in the Quintuplet Cluster

    NASA Astrophysics Data System (ADS)

    Figer, Donald F.; McLean, Ian S.; Morris, Mark

    1999-03-01

    We present near-infrared photometry and K-band spectra of newly identified massive stars in the Quintuplet cluster, one of the three massive clusters projected within 50 pc of the Galactic center. We find that the cluster contains a variety of massive stars, including more unambiguously identified Wolf-Rayet stars than any cluster in the Galaxy, and over a dozen stars in earlier stages of evolution, i.e., luminous blue variables (LBVs), Ofpe/WN9, and OB supergiants. One newly identified star is the second luminous blue variable in the cluster, after the ``Pistol star.'' Although we are unable to provide certain spectral classifications for the five enigmatic Quintuplet-proper members, we tentatively propose that they are extremely dusty versions of the WC stars found elsewhere in the cluster and similar to the dozen or so known examples in the Galaxy. Although the cluster parameters are uncertain because of photometric errors and uncertainties in stellar models, i.e., extrapolating initial masses and estimating ionizing fluxes, we have the following conclusions. Given the evolutionary stages of the identified stars, the cluster appears to be about 4+/-1 Myr old, assuming coeval formation. The total mass in observed stars is ~103 Msolar, and the implied mass is ~104 Msolar, assuming a lower mass cutoff of 1 Msolar and a Salpeter initial mass function. The implied mass density in stars is greater than or similar to a few thousand Msolar pc-3. The newly identified stars increase the estimated ionizing flux from this cluster by about an order of magnitude with respect to earlier estimates, to 1050.9 photons s-1, or roughly what is required to ionize the nearby ``Sickle'' H II region (G0.18-0.04). The total luminosity from the massive cluster stars is ~107.5 Lsolar, enough to account for the heating of the nearby molecular cloud, M0.20-0.033. We propose a picture that integrates most of the major features in this part of the sky, excepting the nonthermal filaments. We

  5. The initial conditions of massive star evolution

    NASA Astrophysics Data System (ADS)

    Sana, Hugues

    2016-07-01

    Massive stars are some of the most energetic building blocks of galaxies. They are the progenitors of supernovae and of neutrons stars and black holes, the coallescence of which is one of the most likely detectable sources of gravitational waves. Yet their formation remains poorly understood. As a consequence, the mechanisms that set initial parameters such as rotation rates, multiplicity and orbital distributions are also ill constrained. These quantities are however critical as they affect the internal mixing, the rate and nature of the interactions, the stars final fates and their end-of-life products. In this presentation, I will review existing and new observations that allow us to better constraints these parameters, hence the initial conditions for massive star evolution.

  6. Comments on the Evolution of Massive Stars

    NASA Astrophysics Data System (ADS)

    El Eid, M. F.; The, L.-S.; Meyer, B. S.

    We describe in a brief form present results we have obtained from a careful and up to date study of the evolution of massive stars including their advanced evolutionary phases beyond the oxygen burning phase. We describe the effects of mass loss, treatment of convection in inhomogeneous stellar layers and the rate of the 12C(α,γ)16O reaction on the properties of stellar models in the interesting case of a 25 M⊙ star of solar-like initial metallicity.

  7. The Pistol Star and Unstable Massive Stars at the Galactic Center

    NASA Astrophysics Data System (ADS)

    Najarro, F.

    2005-09-01

    We present recent results on quantitative spectroscopic studies of the Pistol Star and other massive stars in the Quintuplet and Arches clusters. Thanks to the impressive evolution of IR detectors and the new generation of line blanketed models for the extended atmospheres of hot stars we are able to accurately derive the physical properties of the massive stars in these clusters. Our analysis of the LBVs in the Quintuplet cluster provides, for the first time, a direct estimate of α-elements and Fe chemical abundances in these objects. Preliminary results point to a slightly enhanced enrichment of α-elements compared to Fe and suggest an initial mass function dominated by massive stars, as found for the Arches cluster. On the other hand, from our analysis of the Arches cluster, we introduce a new method to estimate metallicity in very young clusters based on the N abundance of WNL stars and the theory of evolution of massive stars. Results indicating solar metallicity are presented.

  8. Probing massive stars around gamma-ray burst progenitors

    NASA Astrophysics Data System (ADS)

    Lu, Wenbin; Kumar, Pawan; Smoot, George F.

    2015-10-01

    Long gamma-ray bursts (GRBs) are produced by ultra-relativistic jets launched from core collapse of massive stars. Most massive stars form in binaries and/or in star clusters, which means that there may be a significant external photon field (EPF) around the GRB progenitor. We calculate the inverse-Compton scattering of EPF by the hot electrons in the GRB jet. Three possible cases of EPF are considered: the progenitor is (I) in a massive binary system, (II) surrounded by a Wolf-Rayet-star wind and (III) in a dense star cluster. Typical luminosities of 1046-1050 erg s-1 in the 1-100 GeV band are expected, depending on the stellar luminosity, binary separation (I), wind mass-loss rate (II), stellar number density (III), etc. We calculate the light curve and spectrum in each case, taking fully into account the equal-arrival time surfaces and possible pair-production absorption with the prompt γ-rays. Observations can put constraints on the existence of such EPFs (and hence on the nature of GRB progenitors) and on the radius where the jet internal dissipation process accelerates electrons.

  9. Hot subdwarf stars and their connection to thermonuclear supernovae

    NASA Astrophysics Data System (ADS)

    Geier, S.; Kupfer, T.; Ziegerer, E.; Heber, U.; Németh, P.; Irrgang, A.; pre=", team

    2016-07-01

    Hot subdwarf stars (sdO/Bs) are evolved core helium-burning stars with very thin hydrogen envelopes, which can be formed by common envelope ejection. Close sdB binaries with massive white dwarf (WD) companions are potential progenitors of thermonuclear supernovae type Ia (SN Ia). We discovered such a progenitor candidate as well as a candidate for a surviving companion star, which escapes from the Galaxy. More candidates for both types of objects have been found by crossmatching known sdB stars with proper motion and light curve catalogues. The Gaia mission will provide accurate astrometry and light curves of all the stars in our hot subdwarf sample and will allow us to compile a much larger all-sky catalogue of those stars. In this way we expect to find hundreds of progenitor binaries and ejected companions.

  10. Massive stars. A chemical signature of first-generation very massive stars.

    PubMed

    Aoki, W; Tominaga, N; Beers, T C; Honda, S; Lee, Y S

    2014-08-22

    Numerical simulations of structure formation in the early universe predict the formation of some fraction of stars with several hundred solar masses. No clear evidence of supernovae from such very massive stars has, however, yet been found in the chemical compositions of Milky Way stars. We report on an analysis of a very metal-poor star SDSS J001820.5-093939.2, which possesses elemental-abundance ratios that differ significantly from any previously known star. This star exhibits low [α-element Fe] ratios and large contrasts between the abundances of odd and even element pairs, such as scandium/titanium and cobalt/nickel. Such features have been predicted by nucleosynthesis models for supernovae of stars more than 140 times as massive as the Sun, suggesting that the mass distribution of first-generation stars might extend to 100 solar masses or larger. PMID:25146286

  11. Towards Realistic Modeling of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Gnedin, O.; Li, H.

    2016-06-01

    Cosmological simulations of galaxy formation are rapidly advancing towards smaller scales. Current models can now resolve giant molecular clouds in galaxies and predict basic properties of star clusters forming within them. I will describe new theoretical simulations of the formation of the Milky Way throughout cosmic time, with the adaptive mesh refinement code ART. However, many challenges - physical and numerical - still remain. I will discuss how observations of massive star clusters and star forming regions can help us overcome some of them. Video of the talk is available at https://goo.gl/ZoZOfX

  12. Probing Massive Star Cluster Formation with ALMA

    NASA Astrophysics Data System (ADS)

    Johnson, Kelsey

    2015-08-01

    Observationally constraining the physical conditions that give rise to massive star clusters has been a long-standing challenge. Now with the ALMA Observatory coming on-line, we can finally begin to probe the birth environments of massive clusters in a variety of galaxies with sufficient angular resolution. In this talk I will give an overview of ALMA observations of galaxies in which candidate proto-super star cluster molecular clouds have been identified. These new data probe the physical conditions that give rise to super star clusters, providing information on their densities, pressures, and temperatures. In particular, the observations indicate that these clouds may be subject to external pressures of P/k > 108 K cm-3, which is consistent with the prevalence of optically observed adolescent super star clusters in interacting galaxy systems and other high pressure environments. ALMA observations also enable an assessement of the molecular cloud chemical abundances in the regions surrounding super star clusters. Molecular clouds associated with existing super star clusters are strongly correlated with HCO+ emission, but appear to have relatively low ratio of CO/HCO+ emission compared to other clouds, indicating that the super star clusters are impacting the molecular abundances in their vicinity.

  13. QUARK MATTER IN MASSIVE COMPACT STARS

    SciTech Connect

    Weissenborn, Simon; Pagliara, Giuseppe; Schaffner-Bielich, Juergen; Sagert, Irina; Hempel, Matthias

    2011-10-10

    The recent observation of the pulsar PSR J1614-2230 with a mass of 1.97 {+-} 0.04 M{sub sun} gives a strong constraint on the quark and nuclear matter equations of state (EoS). We explore the parameter ranges for a parameterized EoS for quark stars. We find that strange stars, made of absolutely stable strange quark matter, comply with the new constraint only if effects from the strong coupling constant and color-superconductivity are taken into account. Hybrid stars, compact stars with a quark matter core and a hadronic outer layer, can be as massive as 2 M{sub sun}, but only for a significantly limited range of parameters. We demonstrate that the appearance of quark matter in massive stars crucially depends on the stiffness of the nuclear matter EoS. We show that the masses of hybrid stars stay below the ones of hadronic and pure quark stars, due to the softening of the EoS at the quark-hadron phase transition.

  14. Super-Massive Stars: Dense Star-Gas Systems

    NASA Astrophysics Data System (ADS)

    Amaro-Seoane, Pau; Spurzem, Rainer; Just, Andreas

    We use a gaseous model and a semi-analytical approach to study the evolution of a super-massive central gaseous object (a super-massive star, {SMS} from now on) in an AGN and its evolution by interactions with the surrounding stellar system. Our future work in this field is outlined, which aims at a more detailed study of energy flows in the interstellar medium, stellar evolution and the relation between QSOs and galaxy formation.

  15. Formation and Assembly of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    McMillan, Stephen

    The formation of stars and star clusters is a major unresolved problem in astrophysics. It is central to modeling stellar populations and understanding galaxy luminosity distributions in cosmological models. Young massive clusters are major components of starburst galaxies, while globular clusters are cornerstones of the cosmic distance scale and represent vital laboratories for studies of stellar dynamics and stellar evolution. Yet how these clusters form and how rapidly and efficiently they expel their natal gas remain unclear, as do the consequences of this gas expulsion for cluster structure and survival. Also unclear is how the properties of low-mass clusters, which form from small-scale instabilities in galactic disks and inform much of our understanding of cluster formation and star-formation efficiency, differ from those of more massive clusters, which probably formed in starburst events driven by fast accretion at high redshift, or colliding gas flows in merging galaxies. Modeling cluster formation requires simulating many simultaneous physical processes, placing stringent demands on both software and hardware. Simulations of galaxies evolving in cosmological contexts usually lack the numerical resolution to simulate star formation in detail. They do not include detailed treatments of important physical effects such as magnetic fields, radiation pressure, ionization, and supernova feedback. Simulations of smaller clusters include these effects, but fall far short of the mass of even single young globular clusters. With major advances in computing power and software, we can now directly address this problem. We propose to model the formation of massive star clusters by integrating the FLASH adaptive mesh refinement magnetohydrodynamics (MHD) code into the Astrophysical Multi-purpose Software Environment (AMUSE) framework, to work with existing stellar-dynamical and stellar evolution modules in AMUSE. All software will be freely distributed on-line, allowing

  16. HOT STARS WITH HOT JUPITERS HAVE HIGH OBLIQUITIES

    SciTech Connect

    Winn, Joshua N.; Albrecht, Simon; Fabrycky, Daniel; Johnson, John Asher

    2010-08-01

    We show that stars with transiting planets for which the stellar obliquity is large are preferentially hot (T{sub eff} > 6250 K). This could explain why small obliquities were observed in the earliest measurements, which focused on relatively cool stars drawn from Doppler surveys, as opposed to hotter stars that emerged more recently from transit surveys. The observed trend could be due to differences in planet formation and migration around stars of varying mass. Alternatively, we speculate that hot-Jupiter systems begin with a wide range of obliquities, but the photospheres of cool stars realign with the orbits due to tidal dissipation in their convective zones, while hot stars cannot realign because of their thinner convective zones. This in turn would suggest that hot Jupiters originate from few-body gravitational dynamics and that disk migration plays at most a supporting role.

  17. MASSIVE STAR FORMATION IN NGC 2074

    SciTech Connect

    Fleener, Christine E.; Chu, Y.-H.; Gruendl, Robert A.; Payne, James T.; Chen, C.-H. Rosie

    2010-01-15

    Spitzer observations of the Large Magellanic Cloud (LMC) have revealed a large population of young stellar objects (YSOs), but complementary high-resolution images in the optical or near-IR wavelengths are still needed to resolve the multiplicity and immediate environments of the YSOs. The Hubble Space Telescope imaged the star-forming region NGC 2074 in the LMC during its 100,000th orbit, providing an opportunity to more closely examine the YSOs and their environments in this region. We have studied the 10 YSO candidates identified from Spitzer observations, confirming their nature and determining their physical parameters by modeling their spectral energy distributions. The majority of the YSOs and central stars of ultracompact H II regions in NGC 2074 have masses consistent with spectral types of early B to late O. The co-existence of massive early-type O stars and the less massive YSOs indicates that their formation may have started at a similar time, a few 10{sup 5} yr ago. NGC 2074 provides an opportunity to study the evolution of massive stars at their infancy.

  18. The Evolution and Stability of Massive Stars

    NASA Astrophysics Data System (ADS)

    Shiode, Joshua Hajime

    Massive stars are the ultimate source for nearly all the elements necessary for life. The first stars forge these elements from the sparse set of ingredients supplied by the Big Bang, and distribute enriched ashes throughout their galactic homes via their winds and explosive deaths. Subsequent generations follow suit, assembling from the enriched ashes of their predecessors. Over the last several decades, the astrophysics community has developed a sophisticated theoretical picture of the evolution of these stars, but it remains an incomplete accounting of the rich set of observations. Using state of the art models of massive stars, I have investigated the internal processes taking place throughout the life-cycles of stars spanning those from the first generation ("Population III") to the present-day ("Population I"). I will argue that early-generation stars were not highly unstable to perturbations, contrary to a host of past investigations, if a correct accounting is made for the viscous effect of convection. For later generations, those with near solar metallicity, I find that this very same convection may excite gravity-mode oscillations that produce observable brightness variations at the stellar surface when the stars are near the main sequence. If confirmed with modern high-precision monitoring experiments, like Kepler and CoRoT, the properties of observed gravity modes in massive stars could provide a direct probe of the poorly constrained physics of gravity mode excitation by convection. Finally, jumping forward in stellar evolutionary time, I propose and explore an entirely new mechanism to explain the giant eruptions observed and inferred to occur during the final phases of massive stellar evolution. This mechanism taps into the vast nuclear fusion luminosity, and accompanying convective luminosity, in the stellar core to excite waves capable of carrying a super-Eddington luminosity out to the stellar envelope. This energy transfer from the core to the

  19. Theoretical Developments in Understanding Massive Star Formation

    NASA Astrophysics Data System (ADS)

    Yorke, H. W.; Bodenheimer, P.

    2008-05-01

    Except under special circumstances massive stars in galactic disks will form through accretion. The gravitational collapse of a molecular cloud core will initially produce one or more low-mass quasi-hydrostatic objects of a few Jupiter masses. Through subsequent accretion the masses of these cores grow as they simultaneously evolve toward hydrogen-burning central densities and temperatures. We review the evolution of accreting (proto-)stars, including new results calculated with a publicly available stellar evolution code written by the authors. The evolution of accreting stars depends strongly on the accretion history. We find that for the high accretion rates considered, ˜10^{-3} M_⊙yr^{-1}, stars of ˜5-10 M_⊙ tend to bloat up to radii which may exceed 100 R_⊙. Because of the high rate of binarity among massive stars, we expect that these large radii during short phases of evolution will result in mass transfer, common envelope evolution, and a higher number of tight binaries with periods of a few days.

  20. Instability considerations for massive star eruptions

    SciTech Connect

    Guzik, J. A.

    2004-01-01

    We propose a mechanism to explain the observed properties of the giant eruptions of 'supernova imposters' such as {eta} Car and P Cyg. This mechanism must be episodic, generate a large amount of energy, and be very deep-seated, in order to lift about 10 solar masses out of the deep gravitational potential well of these massive evolved stars. We suggest that nonradial gravity mode oscillations capable of existing in the core grow slowly to sufficient amplitude to cause an episode of mixing. This mixing generates a burst of nuclear energy deep in the star that is responsible for the observed large mass ejection and bolometric magnitude increase.

  1. Hot Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Adelman, Saul J.; Upgren, Arthur R.; Adelman, Carol J.

    2011-03-01

    Participants; Preface; Foreword; Acknowledgements; Part I. Introductory Papers: 1. What is the galaxy's halo population?; 2. Theoretical properties of horizontal-branch stars; 3. A review of A-type horizontal-branch stars; Part II. Surveys: 4. A progress report on the Edinburgh-Cape object survey; 5. A 300 square degree survey of young stars at high galactic latitudes; 6. The isolation of a new sample of B stars in the halo; 7. A northern catalog of FHB/A stars; 8. Recent progress on a continuing survey of galactic globular clusters for blue stragglers; 9. UV observations with FAUST and the galactic model; 10. Hot stars at the South Galactic Pole; Part III. Clusters: 11. Population II horizontal branches: a photometric study of globular clusters; 12. The period-shift effect in Oosterhoff type II globular clusters; 13. UV photometry of hot stars in omega centauri; 14. Spectroscopic and UBV observations of blue stars at the NGP; 15. Population I horizontal branches: probing the halo-to-disk transition; Part IV. Stars: 16. Very hot subdwarf O stars; 17. Quantitative spectroscopy of the very hot subluminous O-stars: K646, PG1159-035, and KPD0005+5106; 18. Analyzing the helium-rich hot sdO stars in the Palomar Green Survey; 19. Late type companions of hot sd O stars; 20. Hot stars in globular clusters; 21. Faint blue stars from the Hamburg Schmidt Survey; 22. Stellar winds and the evolution of sdB's to sdO's; 23. Halo stars in the Vilnius photometric system; 24. Horizontal branch stars in the geneva photometric system; 25. Zeeman observations of FHB stars and hot subdwarf stars; 26. What does a FHB star's spectrum look like?; 27. A technique for distinguishing FHB stars from A-type stars; 28. eEemental abundances of halo A and interloper stars; 29. The mass of blue horizontal branch stars in the globular cluster NGC6397; 30. IUE observations of blue HB stars in the globular clusters M3 and NGC6752; 31. Metallicities and kinematics of the local RR lyraes: lukewarm stars

  2. Hot Stars in the Galactic Halo

    NASA Astrophysics Data System (ADS)

    Adelman, Saul J.; Upgren, Arthur R.; Adelman, Carol J.

    1994-08-01

    Participants; Preface; Foreword; Acknowledgements; Part I. Introductory Papers: 1. What is the galaxy's halo population?; 2. Theoretical properties of horizontal-branch stars; 3. A review of A-type horizontal-branch stars; Part II. Surveys: 4. A progress report on the Edinburgh-Cape object survey; 5. A 300 square degree survey of young stars at high galactic latitudes; 6. The isolation of a new sample of B stars in the halo; 7. A northern catalog of FHB/A stars; 8. Recent progress on a continuing survey of galactic globular clusters for blue stragglers; 9. UV observations with FAUST and the galactic model; 10. Hot stars at the South Galactic Pole; Part III. Clusters: 11. Population II horizontal branches: a photometric study of globular clusters; 12. The period-shift effect in Oosterhoff type II globular clusters; 13. UV photometry of hot stars in omega centauri; 14. Spectroscopic and UBV observations of blue stars at the NGP; 15. Population I horizontal branches: probing the halo-to-disk transition; Part IV. Stars: 16. Very hot subdwarf O stars; 17. Quantitative spectroscopy of the very hot subluminous O-stars: K646, PG1159-035, and KPD0005+5106; 18. Analyzing the helium-rich hot sdO stars in the Palomar Green Survey; 19. Late type companions of hot sd O stars; 20. Hot stars in globular clusters; 21. Faint blue stars from the Hamburg Schmidt Survey; 22. Stellar winds and the evolution of sdB's to sdO's; 23. Halo stars in the Vilnius photometric system; 24. Horizontal branch stars in the geneva photometric system; 25. Zeeman observations of FHB stars and hot subdwarf stars; 26. What does a FHB star's spectrum look like?; 27. A technique for distinguishing FHB stars from A-type stars; 28. eEemental abundances of halo A and interloper stars; 29. The mass of blue horizontal branch stars in the globular cluster NGC6397; 30. IUE observations of blue HB stars in the globular clusters M3 and NGC6752; 31. Metallicities and kinematics of the local RR lyraes: lukewarm stars

  3. Very Massive Stars in the local Universe

    NASA Astrophysics Data System (ADS)

    Vink, Jorick S.; Heger, Alexander; Krumholz, Mark R.; Puls, Joachim; Banerjee, S.; Castro, N.; Chen, K.-J.; Chenè, A.-N.; Crowther, P. A.; Daminelli, A.; Gräfener, G.; Groh, J. H.; Hamann, W.-R.; Heap, S.; Herrero, A.; Kaper, L.; Najarro, F.; Oskinova, L. M.; Roman-Lopes, A.; Rosen, A.; Sander, A.; Shirazi, M.; Sugawara, Y.; Tramper, F.; Vanbeveren, D.; Voss, R.; Wofford, A.; Zhang, Y.

    2015-03-01

    Recent studies have claimed the existence of very massive stars (VMS) up to 300 M ⊙ in the local Universe. As this finding may represent a paradigm shift for the canonical stellar upper-mass limit of 150 M ⊙, it is timely to discuss the status of the data, as well as the far-reaching implications of such objects. We held a Joint Discussion at the General Assembly in Beijing to discuss (i) the determination of the current masses of the most massive stars, (ii) the formation of VMS, (iii) their mass loss, and (iv) their evolution and final fate. The prime aim was to reach broad consensus between observers and theorists on how to identify and quantify the dominant physical processes.

  4. Dust in regions of massive star formation

    NASA Technical Reports Server (NTRS)

    Wolfire, Mark G.; Cassinelli, J. P.

    1989-01-01

    It is suggested that protostars increase mass by accreting the surrounding gas and dust. Grains are destroyed as they near the central protostar creating a dust shell or cocoon. Radiation pressure acting on the grains can halt the inflow of material thereby limiting the amount of mass accumulated by the protostar. General constraints were considered on the initial dust-to-gas ratio and mass accretion rates that permit inflow. These results were constrained further by constructing a numerical model, including radiative deceleration on grains and grain destruction processes. Also the constraints on dust properties were investigated which allow the formation of massive stars. The obtained results seem to suggest that massive star formation requires rather extreme preconditioning of the grain and gas environment.

  5. Transiting exoplanets from the CoRoT space mission. XIV. CoRoT-11b: a transiting massive ``hot-Jupiter'' in a prograde orbit around a rapidly rotating F-type star

    NASA Astrophysics Data System (ADS)

    Gandolfi, D.; Hébrard, G.; Alonso, R.; Deleuil, M.; Guenther, E. W.; Fridlund, M.; Endl, M.; Eigmüller, P.; Csizmadia, Sz.; Havel, M.; Aigrain, S.; Auvergne, M.; Baglin, A.; Barge, P.; Bonomo, A. S.; Bordé, P.; Bouchy, F.; Bruntt, H.; Cabrera, J.; Carpano, S.; Carone, L.; Cochran, W. D.; Deeg, H. J.; Dvorak, R.; Eislöffel, J.; Erikson, A.; Ferraz-Mello, S.; Gazzano, J.-C.; Gibson, N. B.; Gillon, M.; Gondoin, P.; Guillot, T.; Hartmann, M.; Hatzes, A.; Jorda, L.; Kabath, P.; Léger, A.; Llebaria, A.; Lammer, H.; MacQueen, P. J.; Mayor, M.; Mazeh, T.; Moutou, C.; Ollivier, M.; Pätzold, M.; Pepe, F.; Queloz, D.; Rauer, H.; Rouan, D.; Samuel, B.; Schneider, J.; Stecklum, B.; Tingley, B.; Udry, S.; Wuchterl, G.

    2010-12-01

    The CoRoT exoplanet science team announces the discovery of CoRoT-11b, a fairly massive hot-Jupiter transiting a V = 12.9 mag F6 dwarf star (M_* = 1.27±0.05 M⊙, R_* = 1.37±0.03 R⊙, Teff = 6440±120 K), with an orbital period of P = 2.994329±0.000011 days and semi-major axis a = 0.0436±0.005 AU. The detection of part of the radial velocity anomaly caused by the Rossiter-McLaughlin effect shows that the transit-like events detected by CoRoT are caused by a planet-sized transiting object in a prograde orbit. The relatively high projected rotational velocity of the star (v sin i = 40±5 km s-1) places CoRoT-11 among the most rapidly rotating planet host stars discovered so far. With a planetary mass of Mp = 2.33±0.34 MJup and radius Rp =1.43±0.03 RJup, the resulting mean density of CoRoT-11b (ρp = 0.99±0.15 g/cm3) can be explained with a model for an inflated hydrogen-planet with a solar composition and a high level of energy dissipation in its interior. The CoRoT space mission, launched on 2006 December 27, has been developed and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA (RSSD and Science Programme), Germany and Spain.

  6. The hot γ Doradus and Maia stars

    NASA Astrophysics Data System (ADS)

    Balona, L. A.; Engelbrecht, C. A.; Joshi, Y. C.; Joshi, S.; Sharma, K.; Semenko, E.; Pandey, G.; Chakradhari, N. K.; Mkrtichian, David; Hema, B. P.; Nemec, J. M.

    2016-08-01

    The hot γ Doradus stars have multiple low frequencies characteristic of γ Dor or SPB variables, but are located between the red edge of the SPB and the blue edge of the γ Dor instability strips where all low-frequency modes are stable in current models of these stars. Though δ Sct stars also have low frequencies, there is no sign of high frequencies in hot γ Dor stars. We obtained spectra to refine the locations of some of these stars in the H-R diagram and conclude that these are, indeed, anomalous pulsating stars. The Maia variables have multiple high frequencies characteristic of β Cep and δ Sct stars, but lie between the red edge of the β Cep and the blue edge of the δ Sct instability strips. We compile a list of all Maia candidates and obtain spectra of two of these stars. Again, it seems likely that these are anomalous pulsating stars which are currently not understood.

  7. The hot γ Doradus and Maia stars

    NASA Astrophysics Data System (ADS)

    Balona, L. A.; Engelbrecht, C. A.; Joshi, Y. C.; Joshi, S.; Sharma, K.; Semenko, E.; Pandey, G.; Chakradhari, N. K.; Mkrtichian, David; Hema, B. P.; Nemec, J. M.

    2016-05-01

    The hot γ Doradus stars have multiple low frequencies characteristic of γ Dor or SPB variables, but are located between the red edge of the SPB and the blue edge of the γ Dor instability strips where all low-frequency modes are stable in current models of these stars. Though δ Sct stars also have low frequencies, there is no sign of high frequencies in hot γ Dor stars. We obtained spectra to refine the locations of some of these stars in the H-R diagram and conclude that these are, indeed, anomalous pulsating stars. The Maia variables have multiple high frequencies characteristic of β Cep and δ Sct stars, but lie between the red edge of the β Cep and the blue edge of the δ Sct instability strips. We compile a list of all Maia candidates and obtain spectra of two of these stars. Again, it seems likely that these are anomalous pulsating stars which are currently not understood.

  8. Proper Motions of Massive Stars in 30 Doradus

    NASA Astrophysics Data System (ADS)

    Lennon, Daniel

    2013-10-01

    We propose an ambitious proper motion survey of massive stars in the 30 Doradus region of the Large Magellanic Cloud using the unique capabilities of HST. We will derive the directions of motion of massive runaway stars, searching in particular for massive stars which have been ejected from the central very massive cluster R136. These data will be combined with radial velocities from the VLT-FLAMES Survey of the Tarantula Nebula and with atmospheric analyses and stellar evolution models to constrain their origins. We will also search for very young isolated massive stars to test models of single-star formation. This work is highly relevant to star formation, cluster dynamics, the origin of field WR stars and GRBs, the creation of very massive stars by runaway mergers, and the possible formation of intermediate-mass black holes.

  9. On the Formation of Massive Stars

    NASA Astrophysics Data System (ADS)

    Yorke, Harold W.; Sonnhalter, Cordula

    2002-04-01

    We calculate numerically the collapse of slowly rotating, nonmagnetic, massive molecular clumps of masses 30, 60, and 120 Msolar, which conceivably could lead to the formation of massive stars. Because radiative acceleration on dust grains plays a critical role in the clump's dynamical evolution, we have improved the module for continuum radiation transfer in an existing two-dimensional (axial symmetry assumed) radiation hydrodynamic code. In particular, rather than using ``gray'' dust opacities and ``gray'' radiation transfer, we calculate the dust's wavelength-dependent absorption and emission simultaneously with the radiation density at each wavelength and the equilibrium temperatures of three grain components: amorphous carbon particles, silicates, and ``dirty ice''-coated silicates. Because our simulations cannot spatially resolve the innermost regions of the molecular clump, however, we cannot distinguish between the formation of a dense central cluster or a single massive object. Furthermore, we cannot exclude significant mass loss from the central object(s) that may interact with the inflow into the central grid cell. Thus, with our basic assumption that all material in the innermost grid cell accretes onto a single object, we are able to provide only an upper limit to the mass of stars that could possibly be formed. We introduce a semianalytical scheme for augmenting existing evolutionary tracks of pre-main-sequence protostars by including the effects of accretion. By considering an open outermost boundary, an arbitrary amount of material could, in principal, be accreted onto this central star. However, for the three cases considered (30, 60, and 120 Msolar originally within the computation grid), radiation acceleration limited the final masses to 31.6, 33.6, and 42.9 Msolar, respectively, for wavelength-dependent radiation transfer and to 19.1, 20.1, and 22.9 Msolar for the corresponding simulations with gray radiation transfer. Our calculations

  10. Magnetic fields and massive star formation

    SciTech Connect

    Zhang, Qizhou; Keto, Eric; Ho, Paul T. P.; Ching, Tao-Chung; Chen, How-Huan; Qiu, Keping; Girart, Josep M.; Juárez, Carmen; Liu, Hauyu; Tang, Ya-Wen; Koch, Patrick M.; Rao, Ramprasad; Lai, Shih-Ping; Li, Zhi-Yun; Frau, Pau; Li, Hua-Bai; Padovani, Marco; Bontemps, Sylvain

    2014-09-10

    Massive stars (M > 8 M {sub ☉}) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 μm obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of ≲0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within 40° of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks (≲ 10{sup 3} AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample of massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scales of 0.01-0.1 pc in the context of massive star and cluster star formation.

  11. The simultaneous formation of massive stars and stellar clusters

    NASA Astrophysics Data System (ADS)

    Smith, Rowan J.; Longmore, Steven; Bonnell, Ian

    2009-12-01

    We show that massive stars and stellar clusters are formed simultaneously, the global evolution of the forming cluster is what allows the central stars to become massive. We predict that massive star-forming clumps, such as those observed in Motte et al., contract and grow in mass leading to the formation of massive stars. This occurs as mass is continually channelled from large radii on to the central protostars, which can become massive through accretion. Using smoothed particle hydrodynamic simulations of massive star-forming clumps in a giant molecular cloud, we show that clumps are initially diffuse and filamentary, and become more concentrated as they collapse. Simulated interferometry observations of our data provide an explanation as to why young massive star-forming regions show more substructure than older ones. The most massive stars in our model are found within the most bound cluster. Most of the mass accreted by the massive stars was originally distributed throughout the clump at low densities and was later funnelled to the star due to global infall. Even with radiative feedback no massive pre-stellar cores are formed. The original cores are of intermediate mass and gain their additional mass in the protostellar stage. We also find that cores which form low-mass stars exist within the volume from which the high-mass stars accrete, but are largely unaffected by this process.

  12. Massive Infrared-Quiet Dense Cores: Unveiling the Initial Conditions of High-Mass Star Formation

    NASA Astrophysics Data System (ADS)

    Motte, F.; Bontemps, S.; Schneider, N.; Schilke, P.; Menten, K. M.

    2008-05-01

    As Th. Henning said at the conference, cold precursors of high-mass stars are now ``hot topics''. We here propose some observational criteria to identify massive infrared-quiet dense cores which can host the high-mass analogs of Class~0 protostars and pre-stellar condensations. We also show how far-infrared to millimeter imaging surveys of entire complexes forming OB stars are starting to unveil the initial conditions of high-mass star formation.

  13. NEARBY MASSIVE STAR CLUSTER YIELDS INSIGHTS INTO EARLY UNIVERSE

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A NASA Hubble Space Telescope 'family portrait' of young, ultra-bright stars nested in their embryonic cloud of glowing gases. The celestial maternity ward, called N81, is located 200,000 light-years away in the Small Magellanic Cloud (SMC), a small irregular satellite galaxy of our Milky Way. Hubble's exquisite resolution allows astronomers to pinpoint 50 separate stars tightly packed in the nebula's core within a 10 light-year diameter - slightly more than twice the distance between earth and the nearest star to our sun. The closest pair of stars is only 1/3 of a light-year apart (0.3 arcseconds in the sky). This furious rate of mass loss from these super-hot stars is evident in the Hubble picture that reveals dramatic shapes sculpted in the nebula's wall of glowing gases by violent stellar winds and shock waves. A pair of bright stars in the center of the nebula is pouring out most of the ultraviolet radiation to make the nebula glow. Just above them, a small dark knot is all that's left of the cold cloud of molecular hydrogen and dust the stars were born from. Dark absorption lanes of residual dust trisect the nebula. The nebula offers a unique opportunity for a close-up glimpse at the 'firestorm' accompanying the birth of extremely massive stars, each blazing with the brilliance of 300,000 of our suns. Such galactic fireworks were much more common billions of years ago in the early universe, when most star formation took place. The 'natural-color' view was assembled from separate images taken with the Wide Field and Planetary Camera 2, in ultraviolet light and two narrow emission lines of ionized Hydrogen (H-alpha, H-beta). The picture was taken on September 4, 1997. Credit: Mohammad Heydari-Malayeri (Paris Observatory, France), NASA/ESA

  14. The massive star content of blue irregular galaxies

    NASA Technical Reports Server (NTRS)

    Lamb, S. A.; Hunter, D. A.; Gallagher, J. S., III

    1986-01-01

    Three regions of recent star formation in blue irregular galaxies were observed with the IUE in the short wavelength, low dispersion mode. The spectra indicate that the massive star content is similar in 2 of the 3 regions and is best fit by a synthesized spectrum of a burst of massive stars 2.5 to 3.0 million yr old.

  15. H II REGIONS: WITNESSES TO MASSIVE STAR FORMATION

    SciTech Connect

    Peters, Thomas; Banerjee, Robi; Klessen, Ralf S.; Low, Mordecai-Mark Mac; Galvan-Madrid, Roberto; Keto, Eric R.

    2010-03-10

    We describe the first three-dimensional simulation of the gravitational collapse of a massive, rotating molecular cloud that includes heating by both non-ionizing and ionizing radiation. These models were performed with the FLASH code, incorporating a hybrid, long characteristic, ray-tracing technique. We find that as the first protostars gain sufficient mass to ionize the accretion flow, their H II regions are initially gravitationally trapped, but soon begin to rapidly fluctuate between trapped and extended states, in agreement with observations. Over time, the same ultracompact H II region can expand anisotropically, contract again, and take on any of the observed morphological classes. In their extended phases, expanding H II regions drive bipolar neutral outflows characteristic of high-mass star formation. The total lifetime of H II regions is given by the global accretion timescale, rather than their short internal sound-crossing time. This explains the observed number statistics. The pressure of the hot, ionized gas does not terminate accretion. Instead, the final stellar mass is set by fragmentation-induced starvation. Local gravitational instabilities in the accretion flow lead to the build-up of a small cluster of stars, all with relatively high masses due to heating from accretion radiation. These companions subsequently compete with the initial high-mass star for the same common gas reservoir and limit its mass growth. This is in contrast to the classical competitive accretion model, where the massive stars are never hindered in growth by the low-mass stars in the cluster. Our findings show that the most significant differences between the formation of low-mass and high-mass stars are all explained as the result of rapid accretion within a dense, gravitationally unstable, ionized flow.

  16. FRAGMENTATION AT THE EARLIEST PHASE OF MASSIVE STAR FORMATION

    SciTech Connect

    Zhang Qizhou; Wang Yang; Pillai, Thushara; Rathborne, Jill

    2009-05-01

    We present 1.3 mm continuum and spectral line images of two massive molecular clumps P1 and P2 in the G28.34+0.06 region with the Submillimeter Array (SMA). While the two clumps contain masses of 1000 and 880 M {sub sun}, respectively, P1 has a luminosity OF <10{sup 2} L {sub sun}, and a lower gas temperature and smaller line width than P2. Thus, P1 appears to be at a much earlier stage of massive star formation than P2. The high-resolution SMA observations reveal two distinctive cores in P2 with masses of 97 and 49 M {sub sun}, respectively. The 4 GHz spectral bandpass captures line emission from CO isotopologues, SO, CH{sub 3}OH, and CH{sub 3}CN, similar to hot molecular cores harboring massive young stars. The P1 clump, on the other hand, is resolved into five cores along the filament with masses from 22 to 64 M {sub sun} and an average projected separation of 0.19 pc. Except {sup 12}CO, no molecular line emission is detected toward the P1 cores at a 1{sigma} rms of 0.1 K. Since strong {sup 12}CO and C{sup 18}O emissions are seen with the single-dish telescope at a resolution of 11'', the nondetection of these lines with the SMA indicates a depletion factor up to 10{sup 3}. While the spatial resolution of the SMA is better than the expected Jeans length, the masses in P1 cores are much larger than the thermal Jeans mass, indicating the importance of turbulence and/or magnetic fields in cloud fragmentation. The hierarchical structures in the P1 region provide a glimpse of the initial phase of massive star and cluster formation.

  17. Energetic Supernovae of Very Massive Primordial Stars

    NASA Astrophysics Data System (ADS)

    Chen, Ke-Jung; Woosley, Stan

    2015-08-01

    Current models of the formation of the first stars in the universe suggest that these stars were very massive, having a typical mass scale of hundreds of solar masses. Some of them would die as pair instability supernovae (PSNe) which might be the biggest explosions of the universe. We present the results from multidimensional numerical studies of PSNe with a new radiation-hydrodynamics code, CASTRO and with realistic nuclear reaction networks. We simulate the fluid instabilities that occur in multiple spatial dimensions and discuss how the resulting mixing affects the explosion, mixing, and nucleosynthesis of these supernovae. Our simulations provide useful predictions for the observational signatures of PSNe, which might soon be examined by the James Webb Space Telescope.

  18. Binary interaction dominates the evolution of massive stars.

    PubMed

    Sana, H; de Mink, S E; de Koter, A; Langer, N; Evans, C J; Gieles, M; Gosset, E; Izzard, R G; Le Bouquin, J-B; Schneider, F R N

    2012-07-27

    The presence of a nearby companion alters the evolution of massive stars in binary systems, leading to phenomena such as stellar mergers, x-ray binaries, and gamma-ray bursts. Unambiguous constraints on the fraction of massive stars affected by binary interaction were lacking. We simultaneously measured all relevant binary characteristics in a sample of Galactic massive O stars and quantified the frequency and nature of binary interactions. More than 70% of all massive stars will exchange mass with a companion, leading to a binary merger in one-third of the cases. These numbers greatly exceed previous estimates and imply that binary interaction dominates the evolution of massive stars, with implications for populations of massive stars and their supernovae. PMID:22837522

  19. Limiting Accretion onto Massive Stars by Fragmentation-Induced Starvation

    SciTech Connect

    Peters, Thomas; Klessen, Ralf S.; Mac Low, Mordecai-Mark; Banerjee, Robi; /ZAH, Heidelberg

    2010-08-25

    Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems that themselves belong to large clusters containing stars of all masses. The radiative heating does not prevent fragmentation, but does lead to a higher Jeans mass, resulting in fewer and more massive stars than would form without the heating. This mechanism reproduces the observed relation between the total stellar mass in the cluster and the mass of the largest star. It predicts strong clumping and filamentary structure in the center of collapsing cores, as has recently been observed. We speculate that a similar mechanism will act during primordial star formation.

  20. LIMITING ACCRETION ONTO MASSIVE STARS BY FRAGMENTATION-INDUCED STARVATION

    SciTech Connect

    Peters, Thomas; Klessen, Ralf S.; Banerjee, Robi; Low, Mordecai-Mark Mac

    2010-12-10

    Massive stars influence their surroundings through radiation, winds, and supernova explosions far out of proportion to their small numbers. However, the physical processes that initiate and govern the birth of massive stars remain poorly understood. Two widely discussed models are monolithic collapse of molecular cloud cores and competitive accretion. To learn more about massive star formation, we perform and analyze simulations of the collapse of rotating, massive, cloud cores including radiative heating by both non-ionizing and ionizing radiation using the FLASH adaptive-mesh refinement code. These simulations show fragmentation from gravitational instability in the enormously dense accretion flows required to build up massive stars. Secondary stars form rapidly in these flows and accrete mass that would have otherwise been consumed by the massive star in the center, in a process that we term fragmentation-induced starvation. This explains why massive stars are usually found as members of high-order stellar systems that themselves belong to large clusters containing stars of all masses. The radiative heating does not prevent fragmentation, but does lead to a higher Jeans mass, resulting in fewer and more massive stars than would form without the heating. This mechanism reproduces the observed relation between the total stellar mass in the cluster and the mass of the largest star. It predicts strong clumping and filamentary structure in the center of collapsing cores, as has recently been observed. We speculate that a similar mechanism will act during primordial star formation.

  1. Sudden Radiative Braking in Colliding Hot-Star Winds

    NASA Astrophysics Data System (ADS)

    Gayley, K. G.; Owocki, S. P.; Cranmer, S. R.

    1997-02-01

    Hot, massive stars have strong stellar winds, and in hot-star binaries these winds can undergo violent collision. Because such winds are thought to be radiatively driven, radiative forces may also play an important role in moderating the wind collision. However, previous studies have been limited to considering how such forces may inhibit the initial acceleration of the companion stellar wind. In this paper we analyze the role of an even stronger radiative braking effect, whereby the primary wind is rather suddenly decelerated by the radiative momentum flux it encounters as it approaches a bright companion. We further show that the braking location and velocity law along the line of centers between the stars can be approximated analytically using a simple one-dimensional analysis. The results of this analysis agree well with a detailed two-dimensional hydrodynamical simulation of the wind collision in the WR + O binary V444 Cygni and demonstrate that radiative braking can significantly alter the bow-shock geometry and reduce the strength of the wind collision. We then apply the derived analytic theory to a set of 14 hot-star binary systems, and conclude that radiative braking is likely to be of widespread importance for wind-wind collisions in WR + O binaries with close to medium separation, D <~ 100 R⊙. It may also be important in other types of hot-star binaries that exhibit a large imbalance between the component wind strengths.

  2. Sudden Radiative Braking in Colliding Hot-Star Winds

    NASA Astrophysics Data System (ADS)

    Gayley, K.; Owocki, S.; Cranmer, S.

    1996-05-01

    Hot, massive stars have strong stellar winds, and in hot-star binaries these winds can undergo violent collision. Because such winds are thought to be radiatively driven, radiative forces may also play an important role in moderating the wind collision. However, previous studies have been limited to considering how such forces may inhibit the initial acceleration of the companion stellar wind. In this poster we describe the role of an even stronger radiative braking effect, whereby the primary wind is rather suddenly decelerated by the radiative momentum flux it encounters as it approaches a bright companion. We show that the braking location and velocity law along the line of centers between the stars can be approximated analytically using a simple one-dimensional analysis. The results of this analysis agree well with a detailed two-dimensional hydrodynamical simulation of the wind collision in the WR+O binary V444 Cygni, and demonstrate that radiative braking can significantly alter the bow-shock geometry and reduce the strength of the wind collision. We also apply the derived analytic theory to a set of 14 hot-star binary systems, and conclude that radiative braking is likely to be of widespread importance for wind-wind collisions in WR+O binaries with close to medium separation, D <= 100 Rsun. It may also be important in other types of hot-star binaries that exhibit a large imbalance between the component wind strengths.

  3. A MASSIVE RUNAWAY STAR FROM 30 DORADUS

    SciTech Connect

    Evans, C. J.; Walborn, N. R.; Massa, D.; Lennon, D. J.; Crowther, P. A.; Henault-Brunet, V.; Taylor, W. D.; Howarth, I. D.; Sana, H.; Van Loon, J. Th.

    2010-06-01

    We present the first ultraviolet (UV) and multi-epoch optical spectroscopy of 30 Dor 016, a massive O2-type star on the periphery of 30 Doradus in the Large Magellanic Cloud. The UV data were obtained with the Cosmic Origins Spectrograph on the Hubble Space Telescope as part of the Servicing Mission Observatory Verification program after Servicing Mission 4, and reveal no. 016 to have one of the fastest stellar winds known. From analysis of the C IV {lambda}{lambda}1548-51 doublet we find a terminal velocity, v {sub {infinity}} = 3450 {+-} 50 km s{sup -1}. Optical spectroscopy is from the VLT-FLAMES Tarantula Survey, from which we rule out a massive companion (with 2 days < P < 1 yr) to a confidence of 98%. The radial velocity of no. 016 is offset from the systemic value by -85 km s{sup -1}, suggesting that the star has traveled the 120 pc from the core of 30 Doradus as a runaway, ejected via dynamical interactions.

  4. The MiMeS Survey of Magnetism in Massive Stars

    NASA Astrophysics Data System (ADS)

    Wade, G. A.; Grunhut, J. H.; MiMeS Collaboration

    2012-12-01

    The Magnetism in Massive Stars (MiMeS) survey represents a high-precision systematic search for magnetic fields in hot, massive OB stars. To date, MiMeS Large Programs (ESPaDOnS@CFHT, Narval@TBL, HARPSpol@ESO3.6 m) and associated PI programs (FORS@VLT) have yielded nearly 1200 circular spectropolarimetric observations of over 350 OB stars. Within this sample, 20 stars are detected as magnetic. Follow-up observations of new detections reveals (i) a large diversity of magnetic properties, (ii) ubiquitous evidence for magnetic wind confinement in optical spectra of all magnetic O stars, and (iii) the presence of strong, organized magnetic fields in all known Galactic Of?p stars, and iv) a complete absence of magnetic fields in classical Be stars.

  5. Evolutionary Connections Between RSGs and Other Massive Stars

    NASA Astrophysics Data System (ADS)

    Smith, Nathan

    2015-08-01

    Red supergiants are an important mass-loss phase near the end of a massive star's life, but there are many other evolved mass-losing stars that populate the HR Diagram, and not all massive stars will pass through a red supergiant phase. This talk will provide an overview of other types of massive stars and how they relate to red supergiants. Mass loss by red supergiant winds will be weighed against the mass loss of other massive stars in terms of their contribution to pre-supernova evolution, focussing on trends with initial mass and metallicity. Moreover, some other evolved massive stars have already been RSG or will be in the future, and circumstellar material is an important clue in this regard. Last, the diversity of different supernova explosions, their circumstellar material, and statistics of SN types provide important constraints on the role of RSGs in the latest phases of evolution and mass loss.

  6. Pair instability supernovae of very massive population III stars

    SciTech Connect

    Chen, Ke-Jung; Woosley, Stan; Heger, Alexander; Almgren, Ann; Whalen, Daniel J.

    2014-09-01

    Numerical studies of primordial star formation suggest that the first stars in the universe may have been very massive. Stellar models indicate that non-rotating Population III stars with initial masses of 140-260 M {sub ☉} die as highly energetic pair-instability supernovae. We present new two-dimensional simulations of primordial pair-instability supernovae done with the CASTRO code. Our simulations begin at earlier times than previous multidimensional models, at the onset of core contraction, to capture any dynamical instabilities that may be seeded by core contraction and explosive burning. Such instabilities could enhance explosive yields by mixing hot ash with fuel, thereby accelerating nuclear burning, and affect the spectra of the supernova by dredging up heavy elements from greater depths in the star at early times. Our grid of models includes both blue supergiants and red supergiants over the range in progenitor mass expected for these events. We find that fluid instabilities driven by oxygen and helium burning arise at the upper and lower boundaries of the oxygen shell ∼20-100 s after core bounce. Instabilities driven by burning freeze out after the SN shock exits the helium core. As the shock later propagates through the hydrogen envelope, a strong reverse shock forms that drives the growth of Rayleigh-Taylor instabilities. In red supergiant progenitors, the amplitudes of these instabilities are sufficient to mix the supernova ejecta.

  7. A hot compact dust disk around a massive young stellar object.

    PubMed

    Kraus, Stefan; Hofmann, Karl-Heinz; Menten, Karl M; Schertl, Dieter; Weigelt, Gerd; Wyrowski, Friedrich; Meilland, Anthony; Perraut, Karine; Petrov, Romain; Robbe-Dubois, Sylvie; Schilke, Peter; Testi, Leonardo

    2010-07-15

    Circumstellar disks are an essential ingredient of the formation of low-mass stars. It is unclear, however, whether the accretion-disk paradigm can also account for the formation of stars more massive than about 10 solar masses, in which strong radiation pressure might halt mass infall. Massive stars may form by stellar merging, although more recent theoretical investigations suggest that the radiative-pressure limit may be overcome by considering more complex, non-spherical infall geometries. Clear observational evidence, such as the detection of compact dusty disks around massive young stellar objects, is needed to identify unambiguously the formation mode of the most massive stars. Here we report near-infrared interferometric observations that spatially resolve the astronomical-unit-scale distribution of hot material around a high-mass ( approximately 20 solar masses) young stellar object. The image shows an elongated structure with a size of approximately 13 x 19 astronomical units, consistent with a disk seen at an inclination angle of approximately 45 degrees . Using geometric and detailed physical models, we found a radial temperature gradient in the disk, with a dust-free region less than 9.5 astronomical units from the star, qualitatively and quantitatively similar to the disks observed in low-mass star formation. Perpendicular to the disk plane we observed a molecular outflow and two bow shocks, indicating that a bipolar outflow emanates from the inner regions of the system. PMID:20631793

  8. Discovering Massive Runaway Stars with Infrared Bowshock Nebulae: Identifying Twelve New Early-Type Stars using SMOG

    NASA Astrophysics Data System (ADS)

    Chick, William T.; Andrews, Julian E.; Kobulnicky, Henry A.; Povich, Matthew S.; Dale, Daniel A.; Munari, Stephan; Olivier, Grace M.; Schurhammer, Danielle; Sorber, Rebecca L.; Wernke, Heather N.

    2016-01-01

    Massive O and B type stars are crucial to the evolution of the interstellar medium, dominating the production of ionizing radiation, mechanical energy, and heavy elements. However, due to their short lives and relative scarcity, these stars are some of the least well understood and are difficult to locate outside of large star forming regions. A small but significant fraction of these massive stars have been observed to be high-velocity runaway stars moving rapidly away from their origin. When these stars encounter nebular gas they create characteristic arc-shaped bowshocks of heated compressed dust and gas. Using the distinct infrared emission morphology of the hot dust, these bowshock nebulae are predicted to give the location of the massive early type stars.Visual inspection of 24-micron band images from the Spitzer Mapping of the Outer Galaxy (SMOG) revealed 12 new bowshock nebula candidates. Follow up optical spectroscopy from the Wyoming Infrared Observatory confirmed that all 12 of the associated stellar sources are early-type stars. Combined with related results from visual searches for bowshock nebulae using WISE and Spitzer surveys in the inner Galaxy, we have identified over 85 new early type bowshock supporting stellar sources, a 95% success rate. We conclude that morphological selection of arc-shared infrared nebulae with a symmetrically placed star is an efficient way to discover early type stars.This work is supported by the National Science Foundation under grants AST-1063146 (REU), AST-1411851 (RUI), and AST-1412845.

  9. The Hot Horizontal-Branch Stars in omega Centauri

    NASA Technical Reports Server (NTRS)

    Moehler, S.; Dreizler, S.; Lanz, T.; Bono, G.; Sweigart, A. V.; Calamida, A.; Nonino, M.

    2010-01-01

    Context. UV observations of some massive globular clusters have revealed a significant population of stars hotter and fainter than the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario where stars experience the helium flash while on the white dwarf cooling curve or by the progeny of the helium-enriched sub-population recently postulated to exist in some clusters. Previous spectroscopic analyses of blue hook stars in co Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C, N enrichment could not be verified. Aims. We compare observed effective temperatures, surface gravities, helium abundances, and carbon line strengths (where detectable) of our targets stars to the predictions of the two scenarios. Methods. Moderately high resolution spectra of hot HB stars in the globular cluster omega-Cen were analysed for radial velocity variations, atmospheric parameters and abundances using LTE and non-LTE model atmospheres. Results. We find no evidence for close binaries among our target stars. All stars below 30 000 K are helium-poor and very similar to HB stars observed in that temperature range in other globular clusters. In the temperature range 30000 K to 50000 K we find that 28% of our stars are helium-poor (log ((sup n)He/(sup n )H)< - 1.6), while 72% have roughly solar or super-solar helium abundance (log ((sup n)He/(sup n )H) >/= -1.5). We also find carbon enrichment strongly correlated with helium enrichment, with a maximum carbon enrichment of 3% by mass. Conclusions. The strong carbon enrichment in tandem with helium enrichment is predicted by the late hot flasher scenario, but not by the helium-enrichment scenario. We conclude that the helium-rich HB stars in omega-Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence.

  10. The properties of low-metallicity massive stars

    NASA Astrophysics Data System (ADS)

    Tramper, F.

    2014-11-01

    My thesis has two main topics: the study of low-metallicity massive stars, and the study of the suspected final stage of massive stars from a certain initial mass range, the WO stars. All the data that has been used in this thesis has been obtained with the X-Shooter spectrograph on ESO's Very Large Telescope. As the formation of massive stars was favored in the metal-free early universe, the properties and evolution of low-metallicity massive stars gives insight in the influence of these stars in the young universe. I have quantitatively analyzed six O-type stars in the low-metallicity dwarf galaxies IC1613, WLM and NGC3109. These stars appear to have surprisingly strong winds, and do not agree with theoretical predictions. The analysis of four more O stars confirms this finding. The low-metallicity temperature scale, recent star formation history of the galaxies and the evolutionary state of the O stars are also discussed. The enigmatic WO stars are very rare (only 9 are known), and are thought to represent the final stage of some of the most massive stars. The spectra of most of these stars have never been modeled in detailed using expanding atmosphere codes. I have modeled the spectrum of the low-metallicity WO star DR1 and find abundances comparable to carbon Wolf-Rayet stars, but a much higher stellar temperature. The study of the other known single WO stars (5 in total) shows that most of them show very high carbon and oxygen abundances, and have less then 40% of helium left (by mass). The found stellar abundances will be used to constrain the initial masses of the stars and their evolutionary path. They are also used to constrain the illusive carbon to oxygen thermonuclear reaction rate.

  11. STAR: Characterizing hot quark matter

    NASA Astrophysics Data System (ADS)

    Van Buren, G.; STAR Collaboration

    2013-04-01

    With discovery of Quark Gluon Plasma well-established at RHIC, the STAR Experiment continues to work toward a more complete understanding of properties of the produced matter, and the conditions necessary for the phase change. We will present recent progress on characterizing quark matter at high temperature through a wide variety of measurement techniques in STAR's repertoire: from observing species suppression and correlations, to determining statistical moments and prospecting for symmetry-breaking. RHIC has further embarked on a program to study this matter through a range of conditions achieved by varying the collision energies, which are hoped to span and locate the QCD critical point. We will show how STAR's toolkit is already providing intriguing results from the the first phase of this program and discuss possible future directions for the program.

  12. Hot-Jupiter Breakfasts Realign Stars

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-08-01

    Two researchers at the University of Chicago have recently developed a new theory to explain an apparent dichotomy in the orbits of planets around cool vs. hot stars. Their model proposes that the spins of cool stars are affected when they ingest hot Jupiters (HJs) early in their stellar lifetimes. A Puzzling Dichotomy: In exoplanet studies, there is a puzzling difference observed between planet orbits around cool and hot (those with Teff ≥ 6250 K) stars: the orbital planes of planets around cool stars are primarily aligned with the host star's spin, whereas the orbital planes of planets around hot stars seem to be randomly distributed. Previous attempts to explain this dichotomy have focused on tidal interactions between the host star and the planets observed in the system. Now Titos Matsakos and Arieh Königl have taken these models a step further — by including in their calculations not only the effects of observed planets, but also those of HJs that may have been swallowed by the star long before we observed the systems. Modeling Meals: Plots of the distribution of the obliquity λ for hot Jupiters around cool hosts (upper plot) and hot hosts (lower plot). The dashed line shows the initial distribution, the bins show the model prediction for the final distribution after the systems evolve, and the black dots show the current observational data. [Matsakos & Königl, 2015]" class="size-thumbnail wp-image-223" height="386" src="http://aasnova.org/wp-content/uploads/2015/08/fig22-260x386.png" width="260" /> Plots of the distribution of the obliquity λ for hot Jupiters around cool hosts (upper plot) and hot hosts (lower plot). The dashed line shows the initial distribution, the bins show the model prediction for the final distribution after the systems evolve, and the black dots show the current observational data. [Matsakos & Königl, 2015] The authors' model assumes that as HJs are formed and migrate inward through the protoplanetary disk, they stall out near

  13. Hot Jupiters and cool stars

    SciTech Connect

    Villaver, Eva; Mustill, Alexander J.; Livio, Mario; Siess, Lionel

    2014-10-10

    Close-in planets are in jeopardy, as their host stars evolve off the main sequence (MS) to the subgiant and red giant phases. In this paper, we explore the influences of the stellar mass (in the range 1.5-2 M {sub ☉}), mass-loss prescription, planet mass (from Neptune up to 10 Jupiter masses), and eccentricity on the orbital evolution of planets as their parent stars evolve to become subgiants and red giants. We find that planet engulfment along the red giant branch is not very sensitive to the stellar mass or mass-loss rates adopted in the calculations, but quite sensitive to the planetary mass. The range of initial separations for planet engulfment increases with decreasing mass-loss rates or stellar masses and increasing planetary masses. Regarding the planet's orbital eccentricity, we find that as the star evolves into the red giant phase, stellar tides start to dominate over planetary tides. As a consequence, a transient population of moderately eccentric close-in Jovian planets is created that otherwise would have been expected to be absent from MS stars. We find that very eccentric and distant planets do not experience much eccentricity decay, and that planet engulfment is primarily determined by the pericenter distance and the maximum stellar radius.

  14. UBV photometry of hot white dwarf stars

    NASA Astrophysics Data System (ADS)

    Cheselka, Mathew; Holberg, J. B.; Watkins, Ron; Collins, James; Tweedy, R. W.

    1993-12-01

    Johnson UBV photometry has been obtained for a set of hot degenerate stars, primarily DA and DO white dwarfs from among those detected in the Palomar-Green survey of UV excess objects. Most of our program stars have estimated effective temperatures (Teff) in the range 22,000 to 80,000 K and have no previous photometry. Some objects selected are also x-ray and extreme ultraviolet sources from the ROSAT all sky survey. The importance of precise photometric measurements in the analysis of x-ray data is discussed. A discrepancy between the observed colors and predicted colors is noted, and possibly accounted for by difficulties in defining the atmospheric cutoff of the U band and a general lack of hot stars used to define the photometric transformation between theoretical and observed colors.

  15. Probing Isolated Massive Star Formation in the LMC

    NASA Astrophysics Data System (ADS)

    Stephens, Ian

    2012-10-01

    Whether massive stars can form in isolation is one of the most debated questions in star formation. Observations of main sequence O-stars indicate that 5-10% of them form in isolation, but models of massive star formation suggest that massive stars should form in cluster environments. Isolated massive young stellar objects {YSOs} are better suited to address whether or not massive stars truly form in isolation since YSOs have had less time to disrupt their natal environment or move away from their stellar siblings. We have developed a unique sample of 7 candidates for isolated massive YSOs in the LMC. Within 80 pc, these objects are not associated with 1} other massive and intermediate-mass YSOs, 2} OB associations, and 3} giant molecular clouds {GMCs}. In all cases ground-based H-alpha observations show that they are affiliated with non-elongated, small HII regions and therefore are unlikely to be part of a runaway population. We request WFC3/UVIS and IR observations in the F656N, F555W, F814W, F110W, and F160W bands to examine the interstellar environment and determine the main sequence and pre-main sequence {PMS} populations down to 0.7 solar masses. In addition, coordinated parallel ACS/WFC F555W, F814W, and F658N observations will be used to assess the nearby control-field populations. From these observations we can search for lower-mass PMS stars, infer the local star formation history, and determine whether evidence exists for remnants of a disrupted GMC. With this statistically significant sample, we will have the ability to assess the possibility of massive stars forming in isolation.

  16. KELT-9b: A Case Study in Dynamical Planet Ingestion by a Hot Host Star

    NASA Astrophysics Data System (ADS)

    Collins, Karen A.; Stassun, Keivan; Gaudi, B. Scott; Beatty, Thomas G.; Zhou, George; Latham, David W.; Bieryla, Allyson; Eastman, Jason D.; Siverd, Robert; Crepp, Justin R.; Pepper, Joshua

    2016-05-01

    Nearly all of the known transiting extra-solar planets orbit stars with masses similar to, or less massive than, the Sun. Such stars typically do not evolve substantially over their hydrogen-fusion lifetime of roughly 10 billion years or more. In contrast, stars much more massive than the Sun evolve on much shorter timescales, and thus the planets they host represent important test cases for how such systems evolve as their parent stars expand -- perhaps engulfing their planets. Most planetary systems orbiting such massive stars have been found around stars that have already exhausted their core hydrogen, cooled, swelled, and likely erased the knowledge of their progenitor close-in planetary systems. In contrast, KELT-9b is a "hot Jupiter" orbiting a star with a mass of 2.2 Msun. The star is still unevolved and therefore still very hot (surface temperature ~ 10,000 K) and therefore the planet is extremely hot. The planet is on a near-polar orbit, likely resulting in orbital precession that will be detectable within a few years. Given the extreme planet temperature, large planet-to-star radius ratio, large planetary atmospheric scale height, and short orbital period, this system is an exceptionally good target for follow-up studies of the planet's atmosphere, which may exhibit unusual photochemistry due to the extreme amounts of high-energy radiation it receives.

  17. Mid-Infrared Interferometry of Dust around Massive Evolved Stars

    NASA Astrophysics Data System (ADS)

    Rajagopal, Jayadev; Menut, Jean-Luc; Wallace, D.; Danchi, W. C.; Chesneau, O.; Lopez, B.; Monnier, J. D.; Ireland, M.; Tuthill, P. G.

    2007-12-01

    We report long-baseline interferometric measurements of circumstellar dust around massive evolved stars with the MIDI instrument on the Very Large Telescope Interferometer and provide spectrally dispersed visibilities in the 8-13 μm wavelength band. We also present diffraction-limited observations at 10.7 μm on the Keck Telescope with baselines up to 8.7 m, which explore larger scale structure. We have resolved the dust shells around the late-type WC stars WR 106 and WR 95 and the enigmatic NaSt 1 (formerly WR 122), suspected to have recently evolved from a luminous blue variable (LBV) stage. For AG Car, the prototypical LBV in our sample, we marginally resolve structure close to the star, distinct from the well-studied detached nebula. The dust shells around the two WC stars show fairly constant size in the 8-13 μm MIDI band, with Gaussian half-widths of ~25 to 40 mas, and the Keck observations reveal an additional extended structure around WR 106. The visibility profiles for NaSt 1 obtained from two MIDI baselines indicate a compact source embedded in an extended structure. The compact dust we detect around NaSt 1 and AG Car favors recent or ongoing dust formation. Using the measured visibilities, we build spherically symmetric radiative transfer models of the WC dust shells, which enable detailed comparison with existing SED-based models. Our results indicate that the inner radii of the shells are within a few tens of AU from the stars. In addition, our models favor grain size distributions with large (~1 μm) dust grains. This proximity of the inner dust to the hot central star emphasizes the difficulty faced by current theories in forming dust in the hostile environment around WR stars. Although we detect no direct evidence for binarity for these objects, dust production in a colliding-wind interface in a binary system is a feasible mechanism in WR systems under these conditions.

  18. Proper Motions of Isolated Massive Stars Near the Galactic Center

    NASA Astrophysics Data System (ADS)

    Lennon, Daniel

    2014-10-01

    The Galactic Center is one of the most perplexing and unusual regions of the Galaxy. Not only is it home to the central massive black hole but it contains three very massive young star clusters within the central 30 pc; the Arches, Quintuplet and Central clusters. Furthermore, emission-line surveys have revealed the presence of what appears to be a diaspora of ~40 very massive isolated Wolf-Rayet-like stars scattered throughout the region, outside of these massive clusters. Their origin is currently unkown but the suspected causes include such diverse and exotic mechanisms as ejection by dynamical interaction within the massive clusters, ejection by supernovae events within those clusters old enough to have SN, ejection by interaction with the central black hole, stellar mergers in the field, and in situ star formation of isolated massive stars. These processes however should all leave clear and distinct dynamical signatures on their products.We propose using WFC3/IR to conduct a survey of ~150 square arcminutes the Galactic Center region to measure relative proper motions to an accuracy of 10 km/s for stars with masses as low as a few solar masses (late B-type). Our objectives include determining which of the known isolated massive stars are runaways, estimating their probable places of origin, discovering less luminous runaways that are invisible to emission line surveys, characterizing the dynamical properties of runaway stars in all luminosty ranges, and searching for signs of tidally disrupted massive clusters. The survey will have lasting legacy value to those trying to unravel the physics of galactic centers and the environments around massive black holes.

  19. Proper Motions of Isolated Massive Stars Near the Galactic Center

    NASA Astrophysics Data System (ADS)

    Lennon, Daniel

    2012-10-01

    The Galactic Center is one of the most perplexing and unusual regions of the Galaxy. Not only is it home to the central massive black hole but it contains three very massive young star clusters within the central 30 pc; the Arches, Quintuplet and Central clusters. Furthermore, emission-line surveys have revealed the presence of what appears to be a diaspora of 40 very massive isolated Wolf-Rayet-like stars scattered throughout the region, outside of these massive clusters. Their origin is currently unkown but the suspected causes include such diverse and exotic mechanisms as ejection by dynamical interaction within the massive clusters, ejection by supernovae events within those clusters old enough to have SN, ejection by interaction with the central black hole, stellar mergers in the field, and in situ star formation of isolated massive stars. These processes however should all leave clear and distinct dynamical signatures on their products.We propose using WFC3/IR to conduct a survey of 150 square arcminutes the Galactic Center region to measure relative proper motions to an accuracy of 10 km/s for stars with masses as low as a few solar masses {late B-type}. Our objectives include determining which of the known isolated massive stars are runaways, estimating their probable places of origin, discovering less luminous runaways that are invisible to emission line surveys, characterizing the dynamical properties of runaway stars in all luminosty ranges, and searching for signs of tidally disrupted massive clusters. The survey will have lasting legacy value to those trying to unravel the physics of galactic centers and the environments around massive black holes.

  20. ATLASGAL - towards a complete sample of massive star forming clumps

    NASA Astrophysics Data System (ADS)

    Urquhart, J. S.; Moore, T. J. T.; Csengeri, T.; Wyrowski, F.; Schuller, F.; Hoare, M. G.; Lumsden, S. L.; Mottram, J. C.; Thompson, M. A.; Menten, K. M.; Walmsley, C. M.; Bronfman, L.; Pfalzner, S.; König, C.; Wienen, M.

    2014-09-01

    By matching infrared-selected, massive young stellar objects (MYSOs) and compact H II regions in the Red MSX Source survey to massive clumps found in the submillimetre ATLASGAL (APEX Telescope Large Area Survey of the Galaxy) survey, we have identified ˜1000 embedded young massive stars between 280° < ℓ < 350° and 10° < ℓ < 60° with | b | < 1.5°. Combined with an existing sample of radio-selected methanol masers and compact H II regions, the result is a catalogue of ˜1700 massive stars embedded within ˜1300 clumps located across the inner Galaxy, containing three observationally distinct subsamples, methanol-maser, MYSO and H II-region associations, covering the most important tracers of massive star formation, thought to represent key stages of evolution. We find that massive star formation is strongly correlated with the regions of highest column density in spherical, centrally condensed clumps. We find no significant differences between the three samples in clump structure or the relative location of the embedded stars, which suggests that the structure of a clump is set before the onset of star formation, and changes little as the embedded object evolves towards the main sequence. There is a strong linear correlation between clump mass and bolometric luminosity, with the most massive stars forming in the most massive clumps. We find that the MYSO and H II-region subsamples are likely to cover a similar range of evolutionary stages and that the majority are near the end of their main accretion phase. We find few infrared-bright MYSOs associated with the most massive clumps, probably due to very short pre-main-sequence lifetimes in the most luminous sources.

  1. "Wonderful" Star Reveals its Hot Nature

    NASA Astrophysics Data System (ADS)

    2005-04-01

    For the first time an X-ray image of a pair of interacting stars has been made by NASA's Chandra X-ray Observatory. The ability to distinguish between the interacting stars - one a highly evolved giant star and the other likely a white dwarf - allowed a team of scientists to observe an X-ray outburst from the giant star and find evidence that a bridge of hot matter is streaming between the two stars. "Before this observation it was assumed that all the X-rays came from a hot disk surrounding a white dwarf, so the detection of an X-ray outburst from the giant star came as a surprise," said Margarita Karovska of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and lead author article in the latest Astrophysical Journal Letters describing this work. An ultraviolet image made by the Hubble Space Telescope was a key to identifying the location of the X-ray outburst with the giant star. X-ray studies of this system, called Mira AB, may also provide better understanding of interactions between other binary systems consisting of a "normal" star and a collapsed star such as a white dwarf, black hole or a neutron star, where the stellar objects and gas flow cannot be distinguished in an image. HST Ultraviolet Image of Mira HST Ultraviolet Image of Mira The separation of the X-rays from the giant star and the white dwarf was made possible by the superb angular resolution of Chandra, and the relative proximity of the star system at about 420 light years from Earth. The stars in Mira AB are about 6.5 billion miles apart, or almost twice the distance of Pluto from the Sun. Mira A (Mira) was named "The Wonderful" star in the 17th century because its brightness was observed to wax and wane over a period of about 330 days. Because it is in the advanced, red giant phase of a star's life, it has swollen to about 600 times that of the Sun and it is pulsating. Mira A is now approaching the stage where its nuclear fuel supply will be exhausted, and it will collapse

  2. The Prevalence and Impact of Wolf–Rayet Stars in Emerging Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Sokal, Kimberly R.; Johnson, Kelsey E.; Indebetouw, Rémy; Massey, Philip

    2016-08-01

    We investigate Wolf–Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point in the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4 m Mayall Telescope at Kitt Peak National Observatory and the 6.5 m MMT.4 We identify 21 sources with significantly detected WR signatures, which we term “emerging WR clusters.” WR features are detected in ˜50% of the radio-selected sample, and thus we find that WR stars are commonly present in currently emerging massive star clusters. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process.

  3. The Prevalence and Impact of Wolf–Rayet Stars in Emerging Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Sokal, Kimberly R.; Johnson, Kelsey E.; Indebetouw, Rémy; Massey, Philip

    2016-08-01

    We investigate Wolf–Rayet (WR) stars as a source of feedback contributing to the removal of natal material in the early evolution of massive star clusters. Despite previous work suggesting that massive star clusters clear out their natal material before the massive stars evolve into the WR phase, WR stars have been detected in several emerging massive star clusters. These detections suggest that the timescale for clusters to emerge can be at least as long as the time required to produce WR stars (a few million years), and could also indicate that WR stars may be providing the tipping point in the combined feedback processes that drive a massive star cluster to emerge. We explore the potential overlap between the emerging phase and the WR phase with an observational survey to search for WR stars in emerging massive star clusters hosting WR stars. We select candidate emerging massive star clusters from known radio continuum sources with thermal emission and obtain optical spectra with the 4 m Mayall Telescope at Kitt Peak National Observatory and the 6.5 m MMT.4 We identify 21 sources with significantly detected WR signatures, which we term “emerging WR clusters.” WR features are detected in ∼50% of the radio-selected sample, and thus we find that WR stars are commonly present in currently emerging massive star clusters. The observed extinctions and ages suggest that clusters without WR detections remain embedded for longer periods of time, and may indicate that WR stars can aid, and therefore accelerate, the emergence process.

  4. Effects of stellar evolution and ionizing radiation on the environments of massive stars

    NASA Astrophysics Data System (ADS)

    Mackey, J.; Langer, N.; Mohamed, S.; Gvaramadze, V. V.; Neilson, H. R.; Meyer, D. M.-A.

    2014-09-01

    We discuss two important effects for the astrospheres of runaway stars: the propagation of ionizing photons far beyond the astropause, and the rapid evolution of massive stars (and their winds) near the end of their lives. Hot stars emit ionizing photons with associated photoheating that has a significant dynamical effect on their surroundings. 3-D simulations show that H ii regions around runaway O stars drive expanding conical shells and leave underdense wakes in the medium they pass through. For late O stars this feedback to the interstellar medium is more important than that from stellar winds. Late in life, O stars evolve to cool red supergiants more rapidly than their environment can react, producing transient circumstellar structures such as double bow shocks. This provides an explanation for the bow shock and linear bar-shaped structure observed around Betelgeuse.

  5. X-ray diagnostics of massive star winds

    NASA Astrophysics Data System (ADS)

    Oskinova, Lidia M.

    2016-09-01

    Nearly all types of massive stars with radiatively driven stellar winds are X-ray sources that can be observed by the presently operating powerful X-ray telescopes. In this review I briefly address recent advances in our understanding of stellar winds obtained from X-ray observations. X-rays may strongly influence the dynamics of weak winds of main sequence B-type stars. X-ray pulsations were detected in a β Cep type variable giving evidence of tight photosphere-wind connections. The winds of OB dwarfs with subtypes later than O9V may be predominantly in a hot phase, and X-ray observations offer the best window for their studies. The X-ray properties of OB supergiants are largely determined by the effects of radiative transfer in their clumped stellar winds. The recently suggested method to directly measure mass-loss rates of O stars by fitting the shapes of X-ray emission lines is considered but its validity cannot be confirmed. To obtain robust quantitative information on stellar wind parameters from X-ray spectroscopy, a multiwavelength analysis by means of stellar atmosphere models is required. Independent groups are now performing such analyses with encouraging results. Joint analyses of optical, UV, and X-ray spectra of OB supergiants yield consistent mass-loss rates. Depending on the adopted clumping parameters, the empirically derived mass-loss rates are a factor of a few smaller or comparable to those predicted by standard recipes (Vink et al., 2001). All sufficiently studied O stars display variable X-ray emission that might be related to corotating interaction regions in their winds. In the latest stages of stellar evolution, single red supergiants (RSG) and luminous blue variable (LBV) stars do not emit observable amounts of X-rays. On the other hand, nearly all types of Wolf-Rayet (WR) stars are X-ray sources. X-ray spectroscopy allows a sensitive probe of WR wind abundances and opacities.

  6. The massive star population of Cygnus OB2

    NASA Astrophysics Data System (ADS)

    Wright, Nicholas J.; Drew, Janet E.; Mohr-Smith, Michael

    2015-05-01

    We have compiled a significantly updated and comprehensive census of massive stars in the nearby Cygnus OB2 association by gathering and homogenizing data from across the literature. The census contains 169 primary OB stars, including 52 O-type stars and 3 Wolf-Rayet stars. Spectral types and photometry are used to place the stars in a Hertzsprung-Russell diagram, which is compared to both non-rotating and rotating stellar evolution models, from which stellar masses and ages are calculated. The star formation history and mass function of the association are assessed, and both are found to be heavily influenced by the evolution of the most massive stars to their end states. We find that the mass function of the most massive stars is consistent with a `universal' power-law slope of Γ = 1.3. The age distribution inferred from stellar evolutionary models with rotation and the mass function suggest the majority of star formation occurred more or less continuously between 1 and 7 Myr ago, in agreement with studies of low- and intermediate-mass stars in the association. We identify a nearby young pulsar and runaway O-type star that may have originated in Cyg OB2 and suggest that the association has already seen its first supernova. Finally we use the census and mass function to calculate the total mass of the association of 16 500^{+3800}_{-2800} M⊙, at the low end, but consistent with, previous estimates of the total mass of Cyg OB2. Despite this Cyg OB2 is still one of the most massive groups of young stars known in our Galaxy making it a prime target for studies of star formation on the largest scales.

  7. Unravelling the Mystery of Massive Star Birth - All Stars are Born the Same Way

    NASA Astrophysics Data System (ADS)

    2010-07-01

    of a screw on the International Space Station, or more than ten times the resolution possible with current visible-light telescopes in space. With this unique capability, complemented by observations done with another of ESO's telescopes, the 3.58-metre New Technology Telescope at La Silla, Kraus and colleagues were able to detect a disc around IRAS 13481-6124. "This is the first time we could image the inner regions of the disc around a massive young star", says Kraus. "Our observations show that formation works the same for all stars, regardless of mass." The astronomers conclude that the system is about 60 000 years old, and that the star has reached its final mass. Because of the intense light of the star - 30 000 times more luminous than our Sun - the disc will soon start to evaporate. The flared disc extends to about 130 times the Earth-Sun distance - or 130 astronomical units (AU) - and has a mass similar to that of the star, roughly twenty times the Sun. In addition, the inner parts of the disc are shown to be devoid of dust. "Further observations with the Atacama Large Millimeter/submillimeter Array (ALMA), currently being constructed in Chile, could provide much information on these inner parts, and allow us to better understand how baby massive stars became heavy," concludes Kraus. More information This research was presented in a paper to appear in this week issue of Nature ("A hot compact dust disk around a massive young stellar object", by S. Kraus et al.). The team is composed of Stefan Kraus (University of Michigan, USA), Karl-Heinz Hofmann, Karl M. Menten, Dieter Schertl, Gerd Weigelt, Friedrich Wyrowski, and Anthony Meilland (Max-Planck-Institut für Radioastronomie, Bonn, Germany),Karine Perraut (Laboratoire d'Astrophysique de Grenoble, France), Romain Petrov and Sylvie Robbe-Dubois (Université de Nice Sophia-Antipolis/CNRS/Observatoire de la Côte d'Azur, France), Peter Schilke (Universität zu Köln, Germany), and Leonardo Testi (ESO).

  8. 25 GHz methanol masers in regions of massive star formation

    NASA Astrophysics Data System (ADS)

    Britton, Tui R.; Voronkov, Maxim A.

    2012-07-01

    The bright 25 GHz series of methanol masers is formed in highly energetic regions of massive star formation and provides a natural signpost of shocked gas surrounding newly forming stars. A systematic survey for the 25 GHz masers has only recently been carried out. We present the preliminary results from the interferometric follow up of 51 masers at 25 GHz in the southern sky.

  9. Why UV Observatories are crucial to understand massive stars ?

    NASA Astrophysics Data System (ADS)

    Garcia Garcia, Miriam

    2012-07-01

    Each Ultraviolet (UV) mission has brought a breakthrough to our knowledge of massive stars. The first rocket UV spectra of O-type stars showed powerful P-Cygni profiles, which revealed that O stars have an expanding atmosphere or stellar wind. After IUE, FUSE and HST-STIS we now know that these winds are not static nor homogeneous, with shocks and mechanisms for extra ionization in the outflow. Radiation driven winds are actually one of the main pillars of the current paradigm of massive stars, as through mass-removal they dictate the sequence of evolutionary stages, duration, ionizing power and yields to the ISM, and the fate of the star as supernova. But many questions remain open: the weak-wind problem, the driving mechanism of very metal-poor massive stars (our connection to the first stars), and a proper characterization of wind inhomogeneities and shocks, to name a few. HST-COS and the up-coming WSO spectrographs will play a crucial role in solving these issues --crucial to calculate massive star feedback to the Universe-- thanks to the wealth of UV metallic transitions that offer many diagnostics to these physical phenomena.

  10. Dynamical ejections of massive stars from young star clusters under diverse initial conditions

    NASA Astrophysics Data System (ADS)

    Oh, Seungkyung; Kroupa, Pavel

    2016-05-01

    We study the effects that initial conditions of star clusters and their massive star population have on dynamical ejections of massive stars from star clusters up to an age of 3 Myr. We use a large set of direct N-body calculations for moderately massive star clusters (Mecl ≈ 103.5 M⊙). We vary the initial conditions of the calculations, such as the initial half-mass radius of the clusters, initial binary populations for massive stars and initial mass segregation. We find that the initial density is the most influential parameter for the ejection fraction of the massive systems. The clusters with an initial half-mass radius rh(0) of 0.1 (0.3) pc can eject up to 50% (30)% of their O-star systems on average, while initially larger (rh(0) = 0.8 pc) clusters, that is, lower density clusters, eject hardly any OB stars (at most ≈ 4.5%). When the binaries are composed of two stars of similar mass, the ejections are most effective. Most of the models show that the average ejection fraction decreases with decreasing stellar mass. For clusters that are efficient at ejecting O stars, the mass function of the ejected stars is top-heavy compared to the given initial mass function (IMF), while the mass function of stars that remain in the cluster becomes slightly steeper (top-light) than the IMF. The top-light mass functions of stars in 3 Myr old clusters in our N-body models agree well with the mean mass function of young intermediate-mass clusters in M 31, as reported previously. This implies that the IMF of the observed young clusters is the canonical IMF. We show that the multiplicity fraction of the ejected massive stars can be as high as ≈ 60%, that massive high-order multiple systems can be dynamically ejected, and that high-order multiples become common especially in the cluster. We also discuss binary populations of the ejected massive systems. Clusters that are initially not mass-segregated begin ejecting massive stars after a time delay that is caused by mass

  11. GRBs as Probes of Massive Stars Near and Far

    NASA Astrophysics Data System (ADS)

    Fynbo, Johan P. U.; Malesani, Daniele

    2008-06-01

    Long-duration gamma-ray bursts are the manifestations of massive stellar death. Due to the immense energy release they are detectable from most of the observable universe. In this way they allow us to study the deaths of single (or binary) massive stars possibly throughout the full timespan massive stars have existed in the Universe. GRBs provide a means to infer information about the environments and typical galaxies in which massive stars are formed. Two main obstacles remain to be crossed before the full potential of GRBs as probes of massive stars can be harvested: i) we need to build more complete and well understood samples in order not to be fooled by biases, and ii) we need to understand to which extent GRBs may be intrinsically biased in the sense that they are only formed by a limited subset of massive stars defined by most likely a restricted metallicity interval. I describe the status of an ongoing effort to build a more complete sample of long-duration GRBs with measured redshifts. Already now we can conclude that the environments of GRB progenitors are very diverse with metallicities ranging from solar to a hundredth solar and extinction ranging from none to AV > 5 mag. We have also identified a sightline with significant escape of Lyman continuum photons and another with a clear 2175 Å extinction bump.

  12. VLT-Flames Tarantula Survey and Multiplicity of Massive Stars

    NASA Astrophysics Data System (ADS)

    Sana, H.

    2013-06-01

    The VLT-Flames Tarantula Survey (VFTS) has obtained optical spectroscopy of over 800 OB and Wolf-Rayet stars in the 30 Doradus region with the aim to investigate a number of questions regarding the formation, evolution and final fate of the most massive stars and the dynamics of the region. In this presentation, I will review some of the most important results obtained by the VFTS so far. The multi-epoch strategy was designed to identify spectroscopic binaries, and I will describe the binary properties in the 30 Dor region in the broader context of our knowledge of the multiplicity of massive stars.

  13. Eccentricity boost of stars around shrinking massive black hole binaries

    NASA Astrophysics Data System (ADS)

    Iwasa, Mao; Seto, Naoki

    2016-06-01

    Based on a simple geometrical approach, we analyze the evolution of the Kozai-Lidov mechanism for stars around shrinking massive black hole binaries on circular orbits. We find that, due to a peculiar bifurcation pattern induced by the Newtonian potential of stellar clusters, the orbit of stars could become highly eccentric. This transition occurs abruptly for stars with small initial eccentricities. The approach presented in this paper may be useful for studying the Kozai-Lidov mechanism in various astrophysical contexts.

  14. The evolutionary tracks of young massive star clusters

    SciTech Connect

    Pfalzner, S.; Steinhausen, M.; Vincke, K.; Menten, K.; Parmentier, G.

    2014-10-20

    Stars mostly form in groups consisting of a few dozen to several ten thousand members. For 30 years, theoretical models have provided a basic concept of how such star clusters form and develop: they originate from the gas and dust of collapsing molecular clouds. The conversion from gas to stars being incomplete, the leftover gas is expelled, leading to cluster expansion and stars becoming unbound. Observationally, a direct confirmation of this process has proved elusive, which is attributed to the diversity of the properties of forming clusters. Here we take into account that the true cluster masses and sizes are masked, initially by the surface density of the background and later by the still present unbound stars. Based on the recent observational finding that in a given star-forming region the star formation efficiency depends on the local density of the gas, we use an analytical approach combined with N-body simulations to reveal evolutionary tracks for young massive clusters covering the first 10 Myr. Just like the Hertzsprung-Russell diagram is a measure for the evolution of stars, these tracks provide equivalent information for clusters. Like stars, massive clusters form and develop faster than their lower-mass counterparts, explaining why so few massive cluster progenitors are found.

  15. Discovery of X-ray pulsations from a massive star.

    PubMed

    Oskinova, Lidia M; Nazé, Yael; Todt, Helge; Huenemoerder, David P; Ignace, Richard; Hubrig, Swetlana; Hamann, Wolf-Rainer

    2014-01-01

    X-ray emission from stars much more massive than the Sun was discovered only 35 years ago. Such stars drive fast stellar winds where shocks can develop, and it is commonly assumed that the X-rays emerge from the shock-heated plasma. Many massive stars additionally pulsate. However, hitherto it was neither theoretically predicted nor observed that these pulsations would affect their X-ray emission. All X-ray pulsars known so far are associated with degenerate objects, either neutron stars or white dwarfs. Here we report the discovery of pulsating X-rays from a non-degenerate object, the massive B-type star ξ(1) CMa. This star is a variable of β Cep-type and has a strong magnetic field. Our observations with the X-ray Multi-Mirror (XMM-Newton) telescope reveal X-ray pulsations with the same period as the fundamental stellar oscillations. This discovery challenges our understanding of stellar winds from massive stars, their X-ray emission and their magnetism. PMID:24892504

  16. Searching for Massive Star Clusters around Luminous Blue Variables

    NASA Astrophysics Data System (ADS)

    Stensland, Jared; Edwards, M. L.; Mikles, V. J.

    2011-01-01

    We present a method to search for the massive birth clusters of Luminous Blue Variables (LBVs). Using theoretical absolute magnitudes of early-type stars, we calculated expected color and magnitude limits for candidate massive stars at the distance and reddening of the Pistol Star and FMM 362 in the Quintuplet. We then applied these cuts to stars found in the 2MASS catalog surrounding the LBVs. By using a well-characterized cluster, we were able to confirm the method's effectiveness and determine the color and magnitude criteria that eliminated the highest number of false candidates while recovering the largest number of known massive cluster members. We then calculated and applied similar cuts to stars within a 1pc radius of WRA 751 to confirm its cluster, Teutsch 143a, discovered by Pasquali et al (2006) and later investigated by Froebrich et al (2008). We used our method to select 22 strong candidate massive cluster stars, 18 medium confidence candidates and 39 weak candidates, categorized based on their colors and magnitudes. These stars are prime candidates for follow-up spectroscopy to determine their spectral types and confirm cluster membership. We plan to apply a similar method to other LBVs without known birth clusters.

  17. Tidal evolution of stars hosting massive planets

    NASA Astrophysics Data System (ADS)

    Ferraz-Mello, Sylvio; Pereira, Elielson S.; Moda, Lucas F. R.

    2015-08-01

    The tidal interaction between one close-in companion (exoplanet or brown-dwarf) and its host star transfers angular momentum from the orbit of the companion to the rotation of the star. In this communication, we present one model for the exchange of angular momentum between the orbit of the companion and the rotation of the star, due to the tidal interaction, and discuss the limits in which the transfer is significant. If the star is active, its rotation period is initially increasing due to the star's wind braking, but at some point the braking is overcome by the tidal transfer of angular momentum from the planet orbit and the rotation period starts decreasing, up to an inward spiraling of the planet orbit and its eventual fall in the star, when a rapid decrease in the star rotation period is seen. In non-active stars, the rotation period is driven towards the neighborhood of the orbital period. For a complete study of several cases see Ferraz-Mello et al. astro-ph/1503.04369. One consequence of these results is that the presence of a significant tidal torque does not allow us to use the gyrochronology rules to estimate the age of a star hosting a large close-in companion. Simulations using hypothetical values show that a companion with mass over 1 Jupiter mass in an orbit within 0.04 AU from a solar-type star (i.e. with period less than 3 days) produces in the rotation of the star an evolution different from that predicted for single stars.

  18. Models of the circumstellar medium of evolving, massive runaway stars moving through the Galactic plane

    NASA Astrophysics Data System (ADS)

    Meyer, D. M.-A.; Mackey, J.; Langer, N.; Gvaramadze, V. V.; Mignone, A.; Izzard, R. G.; Kaper, L.

    2014-11-01

    At least 5 per cent of the massive stars are moving supersonically through the interstellar medium (ISM) and are expected to produce a stellar wind bow shock. We explore how the mass-loss and space velocity of massive runaway stars affect the morphology of their bow shocks. We run two-dimensional axisymmetric hydrodynamical simulations following the evolution of the circumstellar medium of these stars in the Galactic plane from the main sequence to the red supergiant phase. We find that thermal conduction is an important process governing the shape, size and structure of the bow shocks around hot stars, and that they have an optical luminosity mainly produced by forbidden lines, e.g. [O III]. The Hα emission of the bow shocks around hot stars originates from near their contact discontinuity. The Hα emission of bow shocks around cool stars originates from their forward shock, and is too faint to be observed for the bow shocks that we simulate. The emission of optically thin radiation mainly comes from the shocked ISM material. All bow shock models are brighter in the infrared, i.e. the infrared is the most appropriate waveband to search for bow shocks. Our study suggests that the infrared emission comes from near the contact discontinuity for bow shocks of hot stars and from the inner region of shocked wind for bow shocks around cool stars. We predict that, in the Galactic plane, the brightest, i.e. the most easily detectable bow shocks are produced by high-mass stars moving with small space velocities.

  19. The massive binary companion star to the progenitor of supernova 1993J.

    PubMed

    Maund, Justyn R; Smartt, Stephen J; Kudritzki, Rolf P; Podsiadlowski, Philipp; Gilmore, Gerard F

    2004-01-01

    The massive star that underwent a collapse of its core to produce supernova (SN)1993J was subsequently identified as a non-variable red supergiant star in images of the galaxy M81 taken before explosion. It showed an excess in ultraviolet and B-band colours, suggesting either the presence of a hot, massive companion star or that it was embedded in an unresolved young stellar association. The spectra of SN1993J underwent a remarkable transformation from the signature of a hydrogen-rich type II supernova to one of a helium-rich (hydrogen-deficient) type Ib. The spectral and photometric peculiarities were best explained by models in which the 13-20 solar mass supergiant had lost almost its entire hydrogen envelope to a close binary companion, producing a 'type IIb' supernova, but the hypothetical massive companion stars for this class of supernovae have so far eluded discovery. Here we report photometric and spectroscopic observations of SN1993J ten years after the explosion. At the position of the fading supernova we detect the unambiguous signature of a massive star: the binary companion to the progenitor. PMID:14712269

  20. The Formation of Massive Stars and Star Clusters in the Milky Way

    NASA Astrophysics Data System (ADS)

    Battersby, C. D.

    2013-10-01

    The life cycle of stars and gas in the Milky Way illuminates and shapes our view of the universe. This cycle is driven largely by massive stars through their immense ionizing radiation, powerful winds and outflows, and explosive supernovae, yet the processes leading to their formation remain elusive. I review the status of our understanding of massive star and cluster formation, beginning with a theoretical framework outlining the varying modes proposed for the accumulation of material onto forming stars: core accretion and competitive accretion. The observable consequences of each theory and their current statuses are discussed. I then delve into the growing body of observations toward massive star and cluster forming regions, focusing on recent observations of the structure and evolution of cluster- forming regions at early stages. I conclude with an outlook for the next stages in the field of massive star formation.

  1. On the onset of secondary stellar generations in giant star-forming regions and massive star clusters

    SciTech Connect

    Palouš, J.; Wünsch, R.; Tenorio-Tagle, G.

    2014-09-10

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star-forming regions driven by a constant star formation rate and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons, and the integrated mechanical luminosity of the star-forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T ∼ 10{sup 4} K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in size. Here we evaluate the possible self-shielding of thermally unstable clumps against the UV radiation field. Self-shielding allows for a further compression of the reinserted matter, which rapidly develops a high-density neutral core able to absorb in its outer skin the incoming UV radiation. Under such conditions the cold (T ∼ 10 K) neutral cores soon surpass the Jeans limit and become gravitationally unstable, creating a new stellar generation with the matter reinserted by former massive stars. We present the results of several calculations of this positive star formation feedback scenario promoted by strong radiative cooling and mass loading.

  2. On the Onset of Secondary Stellar Generations in Giant Star-forming Regions and Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Palouš, J.; Wünsch, R.; Tenorio-Tagle, G.

    2014-09-01

    Here we consider the strong evolution experienced by the matter reinserted by massive stars, both in giant star-forming regions driven by a constant star formation rate and in massive and coeval superstar clusters. In both cases we take into consideration the changes induced by stellar evolution on the number of massive stars, the number of ionizing photons, and the integrated mechanical luminosity of the star-forming regions. The latter is at all times compared with the critical luminosity that defines, for a given size, the lower mechanical luminosity limit above which the matter reinserted via strong winds and supernova explosions suffers frequent and recurrent thermal instabilities that reduce its temperature and pressure and inhibit its exit as part of a global wind. Instead, the unstable reinserted matter is compressed by the pervasive hot gas, and photoionization maintains its temperature at T ~ 104 K. As the evolution proceeds, more unstable matter accumulates and the unstable clumps grow in size. Here we evaluate the possible self-shielding of thermally unstable clumps against the UV radiation field. Self-shielding allows for a further compression of the reinserted matter, which rapidly develops a high-density neutral core able to absorb in its outer skin the incoming UV radiation. Under such conditions the cold (T ~ 10 K) neutral cores soon surpass the Jeans limit and become gravitationally unstable, creating a new stellar generation with the matter reinserted by former massive stars. We present the results of several calculations of this positive star formation feedback scenario promoted by strong radiative cooling and mass loading.

  3. New Frontiers in Stellar Astrophysics: Massive Stars as Cosmological Tools

    NASA Astrophysics Data System (ADS)

    Levesque, Emily M.

    2015-01-01

    Massive stars are crucial building blocks in the study of star-forming galaxies, stellar evolution, and transient events, and their applications as fundamental astrophysical tools span a broad range of subfields. Unfortunately, many key traits of massive stars - from their physical properties and ionizing radiation to their evolution and core-collapse deaths - remain poorly understood. I will discuss several current research programs focused on developing a comprehensive picture of massive stars across the cosmos. These include observational surveys and population synthesis models of star-forming galaxies; progenitor and host environment studies of transient phenomena such as supernovae and gamma-ray bursts; and the remarkable reach of extragalactic stellar observations, which recently led to the discovery of the first Thorne-Zytkow object candidate. With cutting-edge theoretical models and the capabilities of current ground-based and orbital observatories, we are ideally poised to make substantial progress in our understanding of massive stars over the coming decade. This in turn will equip us with the tools we need to take full advantage of the frontiers opened up by new observational facilities such as JWST, the ELTs, and LSST, allowing us to immediately begin probing the new corners of the universe that they reveal.

  4. The formation of massive star systems by accretion.

    PubMed

    Krumholz, Mark R; Klein, Richard I; McKee, Christopher F; Offner, Stella S R; Cunningham, Andrew J

    2009-02-01

    Massive stars produce so much light that the radiation pressure they exert on the gas and dust around them is stronger than their gravitational attraction, a condition that has long been expected to prevent them from growing by accretion. We present three-dimensional radiation-hydrodynamic simulations of the collapse of a massive prestellar core and find that radiation pressure does not halt accretion. Instead, gravitational and Rayleigh-Taylor instabilities channel gas onto the star system through nonaxisymmetric disks and filaments that self-shield against radiation while allowing radiation to escape through optically thin bubbles. Gravitational instabilities cause the disk to fragment and form a massive companion to the primary star. Radiation pressure does not limit stellar masses, but the instabilities that allow accretion to continue lead to small multiple systems. PMID:19150809

  5. Light element production by low energy nuclei from massive stars

    NASA Technical Reports Server (NTRS)

    Vangioni-Flam, E.; Casse, M.; Ramaty, R.

    1997-01-01

    The Orion complex is a source of gamma rays attributed to the de-excitation of fast carbon and oxygen nuclei excited through interactions with ambient hydrogen and helium. This has consequences for the production and evolution of light isotopes in the Galaxy, as massive stars appear as prolific sources of C-O rich low energy nuclei. The different stages of massive star evolution are considered in relation to the acceleration of nuclei to moderate energies. It is concluded that the low energy nuclear component originating from massive stars plays a larger role than the usual Galactic cosmic rays in shaping the evolution of Li-6, Be-9, B-10 and B-11, especially in the early Galactic evolution. The enhancement of the B-11/B-10 ratio observed in meteorites and in the interstellar medium is attributed to the interaction of low energy carbon nuclei with ambient H and to a lesser degree, to neutrino spallation.

  6. Advanced Spectral Library II: Hot Stars

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas

    2013-10-01

    Stars are the bright matter of the Universe. Without them, it would be a dull and dreary place indeed: no light, no heavy elements, no planets, no life. It also is safe to say that stellar spectroscopy is a cornerstone of astrophysics, providing much of what we know concerning temperatures and masses of stars, their compositions, planets, and the dynamics and evolution of the galaxies they inhabit. This is especially true for the satellite ultraviolet, owing to the rich collection of atomic and ionic transitions found there. Unfortunately, the archive of Space Telescope Imaging Spectrograph rarely achieves the high S/N of the best ground-based spectra, and relatively few objects have the full wavelength coverage for which the powerful, highly multiplexed, second generation Hubble instrument was designed. Our aim is to collect STIS UV echelle spectra - comparable in S/N and resolution to the best ground-based material - for a diverse sample of representative stars, to build an Advanced Spectral Library; a foundation for astrophysical exploration: stellar, interstellar, and beyond. Our first effort, in Cycle 18, involved cool stars. Now we turn attention to the hot side of the H-R diagram.Our Treasury program will provide detailed stellar "atlases," based on advanced processing of the STIS echellegrams. Members of our broad collaboration will analyze these data for specific purposes, such as dynamics of O-star mass-loss; detection of rare species in sharp-lined B stars; and properties and kinematics of local interstellar clouds; but public release {based on the "ASTRAL-I" model} will enable many other investigations by a much wider community, for decades to come.

  7. Hot Gas Flows in T Tauri Stars

    NASA Astrophysics Data System (ADS)

    Ardila, David R.; Herczeg, G.; Gregory, S. G.; Ingleby, L.; France, K.; Brown, A.; Edwards, S.; Linsky, J.; Yang, H.; Valenti, J. A.; Johns-Krull, C. M.; Alexander, R.; Bergin, E. A.; Bethell, T.; Brown, J.; Calvet, N.; Espaillat, C.; Hervé, A.; Hillenbrand, L.; Hussain, G.; Roueff, E.; Schindhelm, E.; Walter, F. M.

    2013-01-01

    We describe observations of the hot gas 1e5 K) ultraviolet lines C IV and He II, in Classical and Weak T Tauri Stars (CTTSs, WTTSs). Our goal is to provide observational constraints for realistic models. Most of the data for this work comes from the Hubble proposal “The Disks, Accretion, and Outflows (DAO) of T Tau stars” (PI Herczeg). The DAO program is the largest and most sensitive high resolution spectroscopic survey of young stars in the UV ever undertaken and it provides a rich source of information for these objects. The sample of high resolution COS and STIS spectra presented here comprises 35 stars: one Herbig Ae star, 28 CTTSs, and 6 WTTSs. For CTTSs, the lines consist of two kinematic components. The relative strengths of the narrow and broad components (NC, BC) are similar in C IV but in He II the NC is stronger than the BC, and dominates the line profile. We do not find correlations between disk inclination and the velocity centroid, width, or shape of the CIV line profile. The NC of the C IV line in CTTSs increases in strength with accretion rate, and its contribution to the line increases from ˜20% to ˜80%, for the accretion rates considered here (1e-10 to 1e-7 Msun/yr). The CTTSs C IV lines are redshifted by ˜20 km/s while the CTTSs He II are redshifted by ˜10 km/s. Because the He II line and the C IV NC have the same width in CTTSs and in WTTSs, but are correlated with accretion, we suggest that they are produced in the stellar transition region. The accretion shock model predicts that the velocity of the post-shock emission should be 4x smaller than the velocity of the pre-shock emission. Identifying the post-shock emission with the NC and the pre-shock with the BC, we find that this is approximately the case in 11 out of 23 objects. The model cannot explain 11 systems in which the velocity of the NC is smaller than the velocity of the BC, or systems in which one of the velocities is negative (five CTTSs). The hot gas lines in some systems

  8. Grain processes in massive star formation

    NASA Technical Reports Server (NTRS)

    Wolfire, M. G.; Cassinelli, J. P.

    1986-01-01

    Observational evidence suggests that stars greater than 100 M(solar) exist in the Galaxy and Large Magellanic Cloud (LMC), however classical star formation theory predicts stellar mass limits of only approx. 60 M(solar). A protostellar accretion flow consists of inflowing gas and dust. Grains are destroyed as they are near the central protostar creating a dust shell or cocoon. Radiation pressure acting on the grain can halt the inflow of material thereby limiting the amount of mass accumulated by the protostar. We first consider rather general constraints on the initial grain to gas ratio and mass accretion rates that permit inflow. We further constrain these results by constructing a numerical model. Radiative deceleration of grains and grain destruction processes are explicitly accounted for in an iterative solution of the radiation-hydrodynamic equations. Findings seem to suggest that star formation by spherical accretion requires rather extreme preconditioning of the grain and gas environment.

  9. On the massive star-forming capacity of molecular clouds

    NASA Technical Reports Server (NTRS)

    Franco, Jose; Shore, Steven N.; Tenorio-Tagle, Guillermo

    1994-01-01

    Assuming that photoionization is the self-limiting process for continued star formation, we estimate the maximum number of massive (OB) stars that can form within a molecular cloud. The most efficient cloud destruction mechanism in the early stages of H II region evolution is the evaporation of the cloud by stars located near the cloud boundary. The maximum number of OB stars is of order 1 per 10(exp 4) solar mass of average molecular gas, or 10 per 10(exp 4) solar mass of dense molecular gas. The resulting star-forming efficiencies within cloud complexes range from 2% to 16% depending on both the location of the stars in the cloud and the details of the initial mass function, with an overall value of about 5% for average molecular gas.

  10. Massive Star Formation: Characterising Infall and Outflow in dense cores.

    NASA Astrophysics Data System (ADS)

    Akhter, Shaila; Cunningham, Maria; Harvey-Smith, Lisa; Jones, Paul Andrew; Purcell, Cormac; Walsh, Andrew John

    2015-08-01

    Massive stars are some of the most important objects in the Universe, shaping the evolution of galaxies, creating chemical elements, and hence shaping the evolution of the Universe. However, the processes by which they form, and how they shape their environment during their birth processes, are not well understood. We are using NH3 data from the "The H2O Southern Galactic Plane Survey" (HOPS) to define the positions of dense cores/clumps of gas in the southern Galactic plane that are likely to form stars. Due to its effective critical density, NH3 can detect massive star forming regions effectively compared to other tracers. We did a comparative study with different methods for finding clumps and found Fellwalker as the best. We found ~ 10% of the star forming clumps with multiple components and ~ 90% clumps with single component along the line of sight. Then, using data from the "The Millimetre Astronomy Legacy Team 90 GHz" (MALT90) survey, we search for the presence of infall and outflow associated with these cores. We will subsequently use the "3D Molecular Line Radiative Transfer Code" (MOLLIE) to constrain properties of the infall and outflow, such as velocity and mass flow. The aim of the project is to determine how common infall and outflow are in star forming cores, hence providing valuable constraints on the timescales and physical process involved in massive star formation.

  11. Astronomers Discover Rotating Disk Around Young, Massive Star

    NASA Astrophysics Data System (ADS)

    1999-01-01

    Astronomers using radio telescopes in New Mexico and California have discovered a giant, rotating disk of material around a young, massive star, indicating that very massive stars as well as those closer to the size of the Sun may be circled by disks from which planets are thought to form. This is the most massive young star for which such a disk has yet been found. Debra Shepherd of the California Institute of Technology (Caltech) and Stan Kurtz of the National Autonomous University of Mexico, used the National Science Foundation's Very Large Array (VLA) radio telescope and telescopes of Caltech's Owens Valley Radio Observatory (OVRO) to make a detailed study of an object called G192.16-3.82, in the constellation Orion. They announced their findings at the American Astronomical Society's meeting in Austin, TX, today. What astronomers call Young Stellar Objects (YSOs) -- stars still in the process of formation -- are enigmatic objects, both drawing in material from their surroundings and expelling material outward at the same time. "The details of the interaction between these two processes are poorly understood," Shepherd said. "In addition, most theories are based on observing low-mass stars, and we don't know if things work the same way with higher-mass stars." "We now have the first unambiguous evidence for a rotating disk around a high-mass star that also is powering an outflow," Shepherd said. "We need to make more observations to confirm the finding, but this information will help test theories of how such young stellar objects operate." It has been difficult to study massive star formation, because massive stars are rarer than smaller ones, they tend to form in clusters, making observations more difficult, and there are few of them forming relatively nearby. The object that Shepherd and Kurtz chose is reasonably isolated. "We think it provides us with a good laboratory for studying the process," Kurtz said. The young star at the core of G192.16-3.82 is

  12. Dynamical Models of Winds from Rotating Hot Stars

    NASA Astrophysics Data System (ADS)

    Cranmer, Steven R.

    1996-08-01

    The hottest and most massive stars (spectral types O, B, Wolf-Rayet) have strong stellar winds that are believed to be driven by line scattering of the star's continuum radiation field. The atmospheres and winds of many hot stars exhibit the effects of rapid rotation, pulsation, and possibly surface magnetic fields, inferred from observations of ultraviolet spectral lines and polarization. The complex time variability in these observations is not yet well understood. The purpose of this dissertation is to model the dynamics of winds around rotating hot stars and synthesize theoretical observational diagnostics to compare with actual data. Before dealing with rotation, however, we derive the theory of radiative driving of stellar winds, and uncover several new useful aspects of the theory for spherical, nonrotating stars. The presence of limb darkening of the stellar radiation is found to be able to increase the mass flux by 10-15% over standard models assuming a uniformly-bright star, and the wind's asymptotic terminal velocity should decrease by the same amount. We also introduce a new approximation method for estimating the terminal velocity, which is both conceptually simpler and more physically transparent than existing approximation algorithms. Finally, from theoretical line profile modeling we find that observational determinations of the terminal speed may be underestimated by several hundred km/s if unsaturated P Cygni lines are used. Rotation affects a star by introducing centrifugal and Coriolis forces, decreasing the effective gravity and making the star oblate. This in turn redistributes the emerging radiative flux to preferentially heat the stellar poles, an effect known as gravity darkening. Although previous models have computed the increase in equatorial mass flux due to the lower effective gravity there, none have incorporated gravity darkening. We find that the brighter (darker) flux from the poles (equator) has a much stronger impact on the mass

  13. Dynamical Models for High-Energy Emission from Massive Stars

    NASA Astrophysics Data System (ADS)

    Owocki, Stanley %FAA(University of Delaware)

    Massive stars are prominent sources of X-rays and gamma-rays detected by both targeted and survey observations from orbiting telescopes like Chandra, XMM/Newton, RXTE, and Fermi. Such high-energy emissions represent key probes of the dynamics of massive-star mass loss, and their penetration through many magnitudes of visible interstellar extinction makes them effective beacons of massive stars in distant reaches of the Galaxy, and in young, active star-forming regions. The project proposed here will develop a comprehensive theoretical framework for interpreting both surveys and targeted observations of high-energy emission from massive stars. It will build on our team's extensive experience in both theoretical models and observational analyses for three key types of emission mechanisms in the stellar wind outflows of these stars, namely: 1) Embedded Wind Shocks (EWS) arising from internal instabilities in the wind driving; 2) shocks in Colliding Wind Binary (CWB) systems; and 3) High-Mass X-ray Binaries (HMXB) systems with interaction between massive-star wind with a compact companion (neutron star or black hole). Taking advantage of commonalities in the treatment of radiative driving, hydrodynamics, shock heating and cooling, and radiation transport, we will develop radiation hydrodynamical models for the key observational signatures like energy distribution, emission line spectrum, and variability, with an emphasis on how these can be used in affiliated analyses of both surveys like the recent Chandra mapping of the Carina association, and targeted observations of galactic X-ray and gamma-ray sources associated with each of the above specific model types. The promises of new clumping-insensitive diagnostics of mass loss rates, and the connection to mass transfer and binarity, all have broad relevance for understanding the origin, evolution, and fate of massive stars, in concert with elements of NASA's Strategic Subgoal 3D. Building on our team's expertise, the

  14. Sulfur-bearing Molecules in Massive Star-forming Regions: Observations of OCS, CS, H2S, and SO

    NASA Astrophysics Data System (ADS)

    Li, Juan; Wang, Junzhi; Zhu, Qingfeng; Zhang, Jiangshui; Li, Di

    2015-03-01

    We studied the sulfur chemistry of massive star-forming regions through single-dish submillimeter spectroscopy. OCS, O13CS, 13CS, H2S, and SO transitions were observed toward a sample of massive star-forming regions with embedded UCH ii or CH ii regions. These sources could be divided into H ii-hot core and H ii-only sources based on their CH3CN emission. Our results show that the OCS line of thirteen sources is optically thick, with optical depth ranging from 5 to 16. Column densities of these molecules were computed under LTE conditions. CS column densities were also derived using its optically thin isotopologue 13CS. H2S is likely to be the most abundant gas-phase sulfuretted molecule in hot massive cores. Both the column density and abundance of sulfur-bearing molecules decrease significantly from H ii-hot core to H ii-only sources. Ages derived from hot core models appear to be consistent with star formation theories, suggesting that abundance ratios of [CS]/[SO], [SO]/[OCS], and [OCS]/[CS] could be used as chemical clocks in massive star-forming regions.

  15. Chandra Observatory Uncovers Hot Stars In The Making

    NASA Astrophysics Data System (ADS)

    2000-11-01

    Cambridge, Mass.--In resolving the hot core of one of the Earth's closest and most massive star-forming regions, the Chandra X-ray Observatory showed that almost all the young stars' temperatures are more extreme than expected. Orion Trapezium JPEG, TIFF, PS The Orion Trapezium as observed on October 31st UT 05:47:21 1999. The colors represent energy, where blue and white indicate very high energies and therefore exterme temperatures. The size of the X-ray source in the image also reflects its brightness, i.e. more bright sources appear larger in size. The is an artifact caused by the limiting blur of the telescope optics. The projected diameter of the field of view is about 80 light days. Credit: NASA/MIT Orion Trapezium JPEG, TIFF, PS The Orion Trapezium as observed on November 24th UT 05:37:54 1999. The colors represent energy, where blue and white indicate very high energies and therefore exterme temperatures. The size of the X-ray source in the image also reflects its brightness, i.e. more bright sources appear larger in size. The is an artifact caused by the limiting blur of the telescope optics. The projected diameter of the field of view is about 80 light days. Credit: NASA/MIT The Orion Trapezium Cluster, only a few hundred thousand years old, offers a prime view into a stellar nursery. Its X-ray sources detected by Chandra include several externally illuminated protoplanetary disks ("proplyds") and several very massive stars, which burn so fast that they will die before the low mass stars even fully mature. One of the major highlights of the Chandra observations are identification of proplyds as X-ray point source in the near vicinity of the most massive star in the Trapezium. Previous observations did not have the ability to separate the contributions of the different objects. "We've seen high temperatures in stars before, but what clearly surprised us was that nearly all the stars we see appear at rather extreme temperatures in X-rays, independent of

  16. Hot subdwarf stars in the Galactic halo Tracers of prominent events in late stellar evolution

    NASA Astrophysics Data System (ADS)

    Geier, Stephan; Kupfer, Thomas; Schaffenroth, Veronika; Heber, Ulrich

    2016-08-01

    Hot subdwarf stars (sdO/Bs) are the stripped cores of red giants located at the bluest extension of the horizontal branch. They constitute the dominant population of UV-bright stars in old stellar environments and are most likely formed by binary interactions. We perform the first systematic, spectroscopic analysis of a sample of those stars in the Galactic halo based on data from SDSS. In the course of this project we discovered 177 close binary candidates. A significant fraction of the sdB binaries turned out to have close substellar companions, which shows that brown dwarfs and planets can significantly influence late stellar evolution. Close hot subdwarf binaries with massive white dwarf companions on the other hand are good candidates for the progenitors of type Ia supernovae. We discovered a hypervelocity star, which not only turned out to be the fastest unbound star known in our Galaxy, but also the surviving companion of such a supernova explosion.

  17. INTERNAL GRAVITY WAVES MODULATE THE APPARENT MISALIGNMENT OF EXOPLANETS AROUND HOT STARS

    SciTech Connect

    Rogers, T. M.; Lin, D. N. C.; Lau, H. H. B. E-mail: lin@ucolick.org

    2012-10-10

    We propose that the observed misalignment between extrasolar planets and their hot host stars can be explained by angular momentum transport within the host star. Observations have shown that this misalignment is preferentially around hot stars, which have convective cores and extended radiative envelopes. This situation is amenable to substantial angular momentum transport by internal gravity waves (IGW) generated at the convective-radiative interface. Here, we present numerical simulations of this process and show that IGW can modulate the surface rotation of the star. With these two-dimensional simulations, we show that IGW could explain the retrograde orbits observed in systems such as HAT-P-6 and HAT-P-7. However, extension to high-obliquity objects will await future three-dimensional simulations. We note that these results also imply that individual massive stars should show temporal variations in their v sin i measurements.

  18. An Unstable Truth: How Massive Stars get their Mass

    NASA Astrophysics Data System (ADS)

    Rosen, Anna L.; Krumholz, Mark R.; McKee, Christopher F.; Klein, Richard I.

    2016-08-01

    The pressure exerted by massive stars' radiation fields is an important mechanism regulating their formation. Detailed simulation of massive star formation therefore requires an accurate treatment of radiation. However, all published simulations have either used a diffusion approximation of limited validity; have only been able to simulate a single star fixed in space, thereby suppressing potentially-important instabilities; or did not provide adequate resolution at locations where instabilities may develop. To remedy this we have developed a new, highly accurate radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform three-dimensional radiation-hydrodynamic simulations of the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channeled to the stellar system via gravitational and Rayleigh-Taylor (RT) instabilities, in agreement with previous results using stars capable of moving, but in disagreement with methods where the star is held fixed or with simulations that do not adequately resolve the development of RT instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of instability, but does not suppress it entirely provided the edges of radiation-dominated bubbles are adequately resolved. Instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. Our results suggest that RT features should be present around accreting massive stars throughout their formation.

  19. Solar-like oscillations in a massive star.

    PubMed

    Belkacem, Kévin; Samadi, Réza; Goupil, Marie-Jo; Lefèvre, Laure; Baudin, Fréderic; Deheuvels, Sébastien; Dupret, Marc-Antoine; Appourchaux, Thierry; Scuflaire, Richard; Auvergne, Michel; Catala, Claude; Michel, Eric; Miglio, Andrea; Montalban, Josefina; Thoul, Anne; Talon, Suzanne; Baglin, Annie; Noels, Arlette

    2009-06-19

    Seismology of stars provides insight into the physical mechanisms taking place in their interior, with modes of oscillation probing different layers. Low-amplitude acoustic oscillations excited by turbulent convection were detected four decades ago in the Sun and more recently in low-mass main-sequence stars. Using data gathered by the Convection Rotation and Planetary Transits mission, we report here on the detection of solar-like oscillations in a massive star, V1449 Aql, which is a known large-amplitude (beta Cephei) pulsator. PMID:19541991

  20. The 3D Death of a Massive Star

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2015-07-01

    What happens at the very end of a massive star's life, just before its core's collapse? A group led by Sean Couch (California Institute of Technology and Michigan State University) claim to have carried out the first three-dimensional simulations of these final few minutes — revealing new clues about the factors that can lead a massive star to explode in a catastrophic supernova at the end of its life. A Giant Collapses In dying massive stars, in-falling matter bounces off the of collapsed core, creating a shock wave. If the shock wave loses too much energy as it expands into the star, it can stall out — but further energy input can revive it and result in a successful explosion of the star as a core-collapse supernova. In simulations of this process, however, theorists have trouble getting the stars to consistently explode: the shocks often stall out and fail to revive. Couch and his group suggest that one reason might be that these simulations usually start at core collapse assuming spherical symmetry of the progenitor star. Adding Turbulence Couch and his collaborators suspect that the key is in the final minutes just before the star collapses. Models that assume a spherically-symmetric star can't include the effects of convection as the final shell of silicon is burned around the core — and those effects might have a significant impact! To test this hypothesis, the group ran fully 3D simulations of the final three minutes of the life of a 15 solar-mass star, ending with core collapse, bounce, and shock-revival. The outcome was striking: the 3D modeling introduced powerful turbulent convection (with speeds of several hundred km/s!) in the last few minutes of silicon-shell burning. As a result, the initial structure and motions in the star just before core collapse were very different from those in core-collapse simulations that use spherically-symmetric initial conditions. The turbulence was then further amplified during collapse and formation of the shock

  1. On the evolution and explosion of massive stars

    SciTech Connect

    Limongi, Marco; Chieffi, Alessandro

    2008-05-21

    We review our recent progresses on the presupernova evolution of massive stars in the range 11-120 M{sub {center_dot}} of solar metallicity. Special attention will be devoted to the effect of the mass loss rate during the Wolf-Rayet stages in determining the structure and the physical properties of the star prior the supernova explosion. We also discuss the explosive yields and the initial mass-remnant mass relation in the framework of the kinetic bomb induced explosion and hence the contribution of these stars to the global chemical enrichment of the interstellar medium.

  2. Massive Star Clusters in Dwarf Galaxies

    NASA Astrophysics Data System (ADS)

    Larsen, Soeren

    2015-08-01

    Dwarf galaxies are often characterized by very high globular cluster specific frequencies, in some cases exceeding that of the Milky Way by a factor of 100 or more. Moreover, the GCs are typically much more metal-poor than the bulk of the field stars, so that a substantial fraction (up to 20-25% or more) of all metal-poor stars in some dwarf galaxies are associated with GCs. The metal-poor components of these galaxies thus represent an extreme case of the "specific frequency problem". In this talk I will review the current status of our understanding of GC systems in dwarf galaxies. Particular emphasis will be placed on the implications of the high GC specific frequencies for the amount of mass loss the clusters could have experienced and the constraints this provides on theories for the origin of multiple populations in globular clusters.

  3. The close-binary content of massive star clusters

    NASA Astrophysics Data System (ADS)

    van den Berg, Maureen C.

    2015-08-01

    The fates of star clusters and the binaries in them are closely intertwined. Close binaries support a cluster against core collapse, while stellar encounters in the dense cores of massive star clusters shape the properties and numbers of the binaries. Observations of massive globular clusters with the Chandra X-ray Observatory have revealed hundreds of close binaries. I will present new results from deep HST observations of massive star clusters including 47Tuc, M28, and M4, that are aimed at classifying the X-ray source populations. Besides exotic systems such as low-mass X-ray binaries and millisecond pulsars, more mundane systems such as magnetically active binaries and accreting white dwarfs have been found. I will discuss how a breakdown of sources by class has revealed how the various binary populations bear the imprints of stellar encounters: some are dominated by dynamical creation, others by dynamical destruction. I will also discuss the effects on the integrated X-ray emissivity of massive star clusters, which is suppressed compared to lower-density environments.

  4. Pre-Supernova Mass Loss Predictions for Massive Stars

    NASA Astrophysics Data System (ADS)

    Vink, J. S.; de Koter, A.; Kotak, R.

    2008-06-01

    Massive stars and supernovae (SNe) have a huge impact on their environment. Despite their importance, a comprehensive knowledge of which massive stars produce which SNe is hitherto lacking. We use a Monte Carlo method to predict the mass-loss rates of massive stars in the Hertzsprung-Russell Diagram (HRD) covering all phases from the OB main sequence, the unstable Luminous Blue Variable (LBV) stage, to the final Wolf-Rayet (WR) phase. Although WR produce their own metals, a strong dependence of the mass-loss rate on the initial iron abundance is found at sub-solar metallicities (1/10 -- 1/100 solar). This may present a viable mechanism to prevent the loss of angular momentum by stellar winds, which could inhibit GRBs occurring at solar metallicities -- providing a significant boost to the collapsar model. Furthermore, we discuss recently reported quasi-sinusoidal modulations in the radio lightcurves of SN 2001ig and SNe 2003bg. We show that both the sinusoidal behaviour and the recurrence timescale of these modulations are consistent with the predicted mass-loss behaviour of LBVs. We discuss potential ramifications for the ``Conti'' scenario for massive star evolution.

  5. Massive Stars in Colliding Wind Systems: the GLAST Perspective

    SciTech Connect

    Reimer, Anita; Reimer, Olaf; /Stanford U., HEPL /KIPAC, Menlo Park

    2011-11-29

    Colliding winds of massive stars in binary systems are considered as candidate sites of high-energy non-thermal photon emission. They are already among the suggested counterparts for a few individual unidentified EGRET sources, but may constitute a detectable source population for the GLAST observatory. The present work investigates such population study of massive colliding wind systems at high-energy gamma-rays. Based on the recent detailed model (Reimer et al. 2006) for non-thermal photon production in prime candidate systems, we unveil the expected characteristics of this source class in the observables accessible at LAT energies. Combining the broadband emission model with the presently cataloged distribution of such systems and their individual parameters allows us to conclude on the expected maximum number of LAT-detections among massive stars in colliding wind binary systems.

  6. Eta Carinae in the Context of the Most Massive Stars

    NASA Technical Reports Server (NTRS)

    Gull, Theodore R.; Damineli, Augusto

    2009-01-01

    Eta Car, with its historical outbursts, visible ejecta and massive, variable winds, continues to challenge both observers and modelers. In just the past five years over 100 papers have been published on this fascinating object. We now know it to be a massive binary system with a 5.54-year period. In January 2009, Car underwent one of its periodic low-states, associated with periastron passage of the two massive stars. This event was monitored by an intensive multi-wavelength campaign ranging from -rays to radio. A large amount of data was collected to test a number of evolving models including 3-D models of the massive interacting winds. August 2009 was an excellent time for observers and theorists to come together and review the accumulated studies, as have occurred in four meetings since 1998 devoted to Eta Car. Indeed, Car behaved both predictably and unpredictably during this most recent periastron, spurring timely discussions. Coincidently, WR140 also passed through periastron in early 2009. It, too, is a intensively studied massive interacting binary. Comparison of its properties, as well as the properties of other massive stars, with those of Eta Car is very instructive. These well-known examples of evolved massive binary systems provide many clues as to the fate of the most massive stars. What are the effects of the interacting winds, of individual stellar rotation, and of the circumstellar material on what we see as hypernovae/supernovae? We hope to learn. Topics discussed in this 1.5 day Joint Discussion were: Car: the 2009.0 event: Monitoring campaigns in X-rays, optical, radio, interferometry WR140 and HD5980: similarities and differences to Car LBVs and Eta Carinae: What is the relationship? Massive binary systems, wind interactions and 3-D modeling Shapes of the Homunculus & Little Homunculus: what do we learn about mass ejection? Massive stars: the connection to supernovae, hypernovae and gamma ray bursters Where do we go from here? (future

  7. The Role of Rotation in the Evolution of Massive Stars

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Lanz, Thierry M.

    2002-01-01

    Recent evolutionary models of massive stars predict important effects of rotation including: increasing the rate of mass-loss; lowering the effective gravity; altering the evolutionary track on the HRD; extending the main-sequence phase (both on the HR diagram and in time); and mixing of CNO-processed elements up to the stellar surface. Observations suggest that rotation is a more important factor at lower metallicities because of higher initial rotational velocities and weaker winds. This makes the SMC, a low-metallicity galaxy (Z= 0.2 solar Z), an excellent environment for discerning the role of rotation in massive stars. We report on a FUSE + STIS + optical spectral analysis of 17 O-type stars in the SMC, where we found an enormous range in N abundances. Three stars in the sample have the same (low) CN abundances as the nebular material out of which they formed, namely C = 0.085 solar C and N = 0.034 solar N. However, more than half show N approx. solar N, an enrichment factor of 30X! Such unexpectedly high levels of N have ramifications for the evolution of massive stars including precursors to supernovae. They also raise questions about the sources of nitrogen in the early universe.

  8. The Role of Rotation in the Evolution of Massive Stars

    NASA Technical Reports Server (NTRS)

    Heap, Sara R.; Lanz, Thierry M.

    2003-01-01

    Recent evolutionary models of massive stars predict important effects of rotation including: increasing the rate of mass loss; lowering the effective gravity; altering the evolutionary track on the Hertzsprung-Russel Diagram (HRD); extending the main-sequence phase (both on the HR diagram and in time); and mixing of CNO-processed elements up to the stellar surface. Observations suggest that rotation is a more important factor at lower metallicities because of higher initial rotational velocities and weaker winds. This makes the Small Magellanic Cloud (SMC), a low-metallicity galaxy (Z=0.2 solar Z), an excellent environment for discerning the role of rotation in massive stars. We report on a FUSE+STIS+optical spectral analysis of 17 O-type stars in the SMC, where we found an enormous range in N abundances. Three stars in the sample have the same (low) CN abundances as the nebular material out of which they formed, namely C=0.085 solar C and N=0.034 solar N. However, more than half show N approx. solar N, an enrichment factor of 30X! Such unexpectedly high levels of N have ramifications for the evolution of massive stars including precursors to supernovae. They also raise questions about the sources of nitrogen in the early universe. This study was supported in part by grants from NASA's ADP, HST GO-7437, and FUSE B134.

  9. Presupernova evolution and explosion of massive stars with mass loss

    NASA Astrophysics Data System (ADS)

    Limongi, M.; Chieffi, A.

    2007-08-01

    We review the main properties of solar metallicity massive stars in the range 11-120 Msolar. The influence of the mass loss on the hydrostatic burning stages as well as the final explosion is discussed in some detail. We find that the minimum masses that enter the WNL, WNE and WC stages are 30 Msolar, 35 Msolar and 40 Msolar respectively; the limiting mass between stars exploding as SNII and SNIb/c is between 30 and 35 Msolar the limiting mass between stars forming neutron stars and black holes after the explosion is between 25-30 Msolar. We also discuss the properties of the chemical yields integrated over a Salpeter IMF and we find that stars with M >= 35 Msolar contribute for ~ 60% to the production of C, N and for ~ 40% to the production Sc and s-process elements up to Zr, while they do not produce any intermediate mass element because of the large remnant masses.

  10. Late stages of massive star evolution and nucleosynthesis

    SciTech Connect

    Nomoto, Ken'ichi; Hashimoto, Masa-aki

    1986-01-01

    The evolution of massive stars in the mass range of 8 to 25 M solar mass is reviewed. The effect of electron degeneracy on the gravothermal nature of stars is discussed. Depending on the stellar mass, the stars form three types of cores, namely, non-degenerate, semi-degenerate, and strongly degenerate cores. The evolution for these cases is quite distinct from each other and leads to the three different types of final fate. It is suggested that our helium star model, which is equivalent to a 25 M solar mass star, will form a relatively small mass iron core despite the faster /sup 12/C(..cap alpha..,..gamma..)/sup 16/O reaction. 50 refs., 21 figs.

  11. Curtain-Lifting Winds Allow Rare Glimpse into Massive Star Factory

    NASA Astrophysics Data System (ADS)

    2003-06-01

    Formation of Exceedingly Luminous and Hot Stars in Young Stellar Cluster Observed Directly Summary Based on a vast observational effort with different telescopes and instruments, ESO-astronomer Dieter Nürnberger has obtained a first glimpse of the very first stages in the formation of heavy stars. These critical phases of stellar evolution are normally hidden from the view, because massive protostars are deeply embedded in their native clouds of dust and gas, impenetrable barriers to observations at all but the longest wavelengths. In particular, no visual or infrared observations have yet "caught" nascent heavy stars in the act and little is therefore known so far about the related processes. Profiting from the cloud-ripping effect of strong stellar winds from adjacent, hot stars in a young stellar cluster at the center of the NGC 3603 complex, several objects located near a giant molecular cloud were found to be bona-fide massive protostars, only about 100,000 years old and still growing. Three of these objects, designated IRS 9A-C, could be studied in more detail. They are very luminous (IRS 9A is about 100,000 times intrinsically brighter than the Sun), massive (more than 10 times the mass of the Sun) and hot (about 20,000 degrees). They are surrounded by relative cold dust (about 0°C), probably partly arranged in disks around these very young objects. Two possible scenarios for the formation of massive stars are currently proposed, by accretion of large amounts of circumstellar material or by collision (coalescence) of protostars of intermediate masses. The new observations favour accretion, i.e. the same process that is active during the formation of stars of smaller masses. PR Photo 16a/03: Stellar cluster and star-forming region NGC 3603. PR Photo 16b/03: Region near very young, massive stars IRS 9A-C in NGC 3603 (8 bands from J to Q). How do massive stars form? This question is easy to pose, but so far very difficult to answer. In fact, the processes

  12. Rb and Zr abundances in massive Galactic AGB stars revisited

    NASA Astrophysics Data System (ADS)

    Pérez-Mesa, V.; Zamora, O.; García-Hernández, D. A.; Plez, B.; Manchado, A.; Karakas, A. I.; Lugaro, M.

    2016-07-01

    We report new abundances of Rb and Zr in a sample of massive Galactic asymptotic giant branch (AGB) stars that were previously studied with hydrostatic models by using more realistic dynamical model atmospheres. We use a modified version of the spectral synthesis code Turbospectrum, and consider the presence of a circumstellar envelope and a radial wind in the modelling of these Galactic AGB stars. The Rb and Zr are determined from the 7800 Å Rb I resonant line and the 6474 Å ZrO bandhead, respectively, and they are compared with the AGB nucleosynthesis theoretical predictions. The derived Rb abundances are much lower (∼⃒1-2 dex) with the new dynamical models, while the Zr abundances, however, are closer to the hydrostatic values. The new model atmospheres can help to resolve the problem of the mismatch between the observations and the nucleosynthesis theoretical predictions of massive AGB stars.

  13. UH cosmic rays: Possible origin in massive stars

    NASA Technical Reports Server (NTRS)

    Wefel, J. P.; Schramm, D. N.; Blake, J. B.

    1977-01-01

    The origin of the Z greater than 28, ultraheavy, cosmic rays in supernova explosions of massive stars is considered. For Z greater than 70, the UH data is dominated by an r-process source distribution, but for the elements just beyond iron, 29 or = Z less than 36, the data cannot be explained by any single process of nucleosynthesis. This problem is solved naturally in a massive star model by secondary neutron capture reactions occuring during core helium burning and during explosive carbon burning. Interstellar propagation calculations were performed with these episodes of synthesis as source distributions, and the results offer an explanation for the current UH cosmic-ray data. The heavy element synthesis during explosive carbon burning is reexamined using more realistic initial conditions given by the post-helium-burning configuration of the star. Effects of preferential acceleration are considered, and experimental tests are discussed.

  14. GRAVITATIONAL SLINGSHOT OF YOUNG MASSIVE STARS IN ORION

    SciTech Connect

    Chatterjee, Sourav; Tan, Jonathan C. E-mail: jt@astro.ufl.edu

    2012-08-01

    The Orion Nebula Cluster (ONC) is the nearest region of massive star formation and thus a crucial testing ground for theoretical models. Of particular interest among the ONC's {approx}1000 members are: {theta}{sup 1} Ori C, the most massive binary in the cluster with stars of masses 38 and 9 M{sub Sun }; the Becklin-Neugebauer (BN) object, a 30 km s{sup -1} runaway star of {approx}8 M{sub Sun }; and the Kleinmann-Low (KL) nebula protostar, a highly obscured, {approx}15 M{sub Sun} object still accreting gas while also driving a powerful, apparently 'explosive' outflow. The unusual behavior of BN and KL is much debated: How did BN acquire its high velocity? How is this related to massive star formation in the KL nebula? Here, we report the results of a systematic survey using {approx}10{sup 7} numerical experiments of gravitational interactions of the {theta}{sup 1}C and BN stars. We show that dynamical ejection of BN from this triple system at its observed velocity leaves behind a binary with total energy and eccentricity matching those observed for {theta}{sup 1}C. Five other observed properties of {theta}{sup 1}C are also consistent with it having ejected BN and altogether we estimate that there is only a {approx}< 10{sup -5} probability that {theta}{sup 1}C has these properties by chance. We conclude that BN was dynamically ejected from the {theta}{sup 1}C system about 4500 years ago. BN then plowed through the KL massive star-forming core within the last 1000 years causing its recently enhanced accretion and outflow activity.

  15. New very massive stars in Cygnus OB2

    NASA Astrophysics Data System (ADS)

    Negueruela, I.; Marco, A.; Herrero, A.; Clark, J. S.

    2008-08-01

    Context: The compact association Cygnus OB2 is known to contain a large population of massive stars, but its total mass is currently a matter of debate. While recent surveys have uncovered large numbers of OB stars in the area around Cyg OB2, detailed study of the optically brightest among them suggests that most are not part of the association. Aims: We observed an additional sample of optically faint OB star candidates, with the aim of checking if more obscured candidates are correspondingly more likely to be members of Cyg OB2. Methods: Low resolution spectra of 9 objects allow the rejection of one foreground star and the selection of four O-type stars, which were later observed at higher resolution. In a subsequent run, we observed three more stars in the classification region and three other stars in the far red. Results: We identify five (perhaps six) new evolved very massive stars and three main sequence O-type stars, all of which are likely to be members of Cyg OB2. The new findings allow a much better definition of the upper HR diagram, suggesting an age ~2.5 Myr for the association and hinting that the O3-5 supergiants in the association are blue stragglers, either younger or following a different evolutionary path from other cluster members. Though the bulk of the early stars seems to belong to an (approximately) single-age population, there is ample evidence for the presence of somewhat older stars at the same distance. Conclusions: Our results suggest that, even though Cyg OB2 is unlikely to contain as many as 100 O-type stars, it is indeed substantially more massive than was thought prior to recent infrared surveys. Figure [see full textsee full textsee full textsee full textsee full textsee full textsee full text] and Table [see full textsee full textsee full textsee full textsee full textsee full textsee full text] are only available in electronic form at http://www.aanda.org

  16. Mid-Infrared Spectroscopy of the Most Massive Stars

    NASA Astrophysics Data System (ADS)

    Figer, Donald; Najarro, Paco; Stolovy, Susan

    2004-09-01

    The most massive star that can form is presently defined by observations of a class of very rare stars having inferred initial masses of ~200 solar masses. There are only a few such stars in the Galaxy, including the Pistol Star, FMM362, and LBV 1806-20, the first two being located near the Galactic center, and third located in the disk near W31. Each has only recently been identified as so massive within the past 10 years through the analysis of infrared observations, but they are otherwise too faint, due to extinction, to observe at shorter wavelengths. These stars appear to be very luminous (L>10^6.3 solar luminosities), "blue" (T>10000 K), and variable (delta K~1 mag.), and the Pistol Star has ejected 10 solar masses of material in the past 10000 years. In addition, these stars have near-infrared spectra similar to those of prototypical Luminous Blue Variables, i.e. Eta Car and AG Car. Given their apparent violation of the Humphries-Davidson limit, they are presumably in a short-lived phase of stellar evolution that is often associated with rapid mass-loss through episodic eruptions of their outer atmospheres. We propose to determine the physical properties of these stars and the velocity and ionization structure in their winds by using spectra obtained with the high resolution modes of the Infrared Spectrograph (IRS) on the Spitzer Space Telescope. The 10 to 40 micron wavelength region is ideally suited for accessing a variety of lines from transitions of hydrogen, helium, iron, silicon, sulfur, among others; indeed, through our models, we predict that sufficiently sensitive spectra will yield over 300 spectral lines. In addition, we predict that the mid-infrared continuum will be dominated by free-free emission generated in the thick winds associated with these stars, an effect that should be clearly detectable in the spectra.

  17. The formation of massive stars: A 30 MO case study

    NASA Astrophysics Data System (ADS)

    Beech, Martin

    1993-07-01

    Pre-main sequence evolutionary tracks have been calculated for a series of massive star models under Hayashi's canonical theory and Stahler's mass accretion paradigm. Canonical pre-main sequence tracks for 15-60 solar mass (SM) stars were calculated with both Cox-Stewart (CS) and Rogers-Iglesias (RI) opacities. The differences between the two sequences were systematically explored. The final pre-main sequence phase of the canonical evolution and the onset of central hydrogen burning is discussed. Arrival of a massive star on the zero age main sequence (ZAMS) is defined and the characteristics of the upper ZAMS models are determined. A systematic investigation of pre-main sequence tracks revealed a boundary in the central density versus central temperature plane, beyond which the models always had a central convective core. In a study of a sequence of accretion models, beyond about 17 SM their characteristics became increasingly more luminous and cooler compared to the same-mass canonical ZAMS models. In the main sequence phase, the accretion build model evolved at essentially the same effective temperature as the canonical model but at a lower luminosity. An upper stellar birthline is proposed, defining a boundary in the Hertzsprung Russell diagram beyond which massive stars first become optically visible.

  18. Tidal capture of stars by a massive black hole

    NASA Technical Reports Server (NTRS)

    Novikov, I. D.; Pethick, C. J.; Polnarev, A. G.

    1992-01-01

    The processes leading to tidal capture of stars by a massive black hole and the consequences of these processes in a dense stellar cluster are discussed in detail. When the amplitude of a tide and the subsequent oscillations are sufficiently large, the energy deposited in a star after periastron passage and formation of a bound orbit cannot be estimated directly using the linear theory of oscillations of a spherical star, but rather numerical estimates must be used. The evolution of a star after tidal capture is discussed. The maximum ratio R of the cross-section for tidal capture to that for tidal disruption is about 3 for real systems. For the case of a stellar system with an empty capture loss cone, even in the case when the impact parameter for tidal capture only slightly exceeds the impact parameter for direct tidal disruption, tidal capture would be much more important than tidal disruption.

  19. The Origin of Nonradiative Heating/momentum in Hot Stars

    NASA Technical Reports Server (NTRS)

    Underhill, A. B. (Editor); Michalitsianos, A. G. (Editor)

    1985-01-01

    The origin of nonradiative heating and momentum in the atmospheres of stars is studied. The similarities and differences between what occurs in the hot stars and what occurs in cool stars are emphasized. Key points in the theory are reviewed. Areas requiring new study are indicated.

  20. Simulating the Birth of Massive Star Clusters: Is Destruction Inevitable?

    NASA Astrophysics Data System (ADS)

    Rosen, Anna

    2013-10-01

    Very early in its operation, the Hubble Space Telescope {HST} opened an entirely new frontier: study of the demographics and properties of star clusters far beyond the Milky Way. However, interpretation of HST's observations has proven difficult, and has led to the development of two conflicting models. One view is that most massive star clusters are disrupted during their infancy by feedback from newly formed stars {i.e., "infant mortality"}, independent of cluster mass or environment. The other model is that most star clusters survive their infancy and are disrupted later by mass-dependent dynamical processes. Since observations at present have failed to discriminate between these views, we propose a theoretical investigation to provide new insight. We will perform radiation-hydrodynamic simulations of the formation of massive star clusters, including for the first time a realistic treatment of the most important stellar feedback processes. These simulations will elucidate the physics of stellar feedback, and allow us to determine whether cluster disruption is mass-dependent or -independent. We will also use our simulations to search for observational diagnostics that can distinguish bound from unbound clusters, and to predict how cluster disruption affects the cluster luminosity function in a variety of galactic environments.

  1. Interaction of massive stars with the interstellar medium

    NASA Astrophysics Data System (ADS)

    de Geus, E. J.

    This paper reviews observations and theory regarding the interaction between massive stars in open clusters and OB associations and the interstellar medium. The results of a systematic study of the gas and dust surrounding a large sample of open clusters are described. Different models for the bubbles blown by stellar winds of O-type stars are discussed, and the effects of subsequent supernova are investigated. The effects of correlated supernovae on the morphology of the interstellar gas and on the communication of the disk with the halo of a galaxy are presented.

  2. HOT GAS LINES IN T TAURI STARS

    SciTech Connect

    Ardila, David R.; Herczeg, Gregory J.; Gregory, Scott G.; Hillenbrand, Lynne A.; Ingleby, Laura; Bergin, Edwin; Bethell, Thomas; Calvet, Nuria; France, Kevin; Brown, Alexander; Edwards, Suzan; Johns-Krull, Christopher; Linsky, Jeffrey L.; Yang, Hao; Valenti, Jeff A.; Abgrall, Herve; Alexander, Richard D.; Brown, Joanna M.; Espaillat, Catherine; Hussain, Gaitee; and others

    2013-07-01

    For Classical T Tauri Stars (CTTSs), the resonance doublets of N V, Si IV, and C IV, as well as the He II 1640 A line, trace hot gas flows and act as diagnostics of the accretion process. In this paper we assemble a large high-resolution, high-sensitivity data set of these lines in CTTSs and Weak T Tauri Stars (WTTSs). The sample comprises 35 stars: 1 Herbig Ae star, 28 CTTSs, and 6 WTTSs. We find that the C IV, Si IV, and N V lines in CTTSs all have similar shapes. We decompose the C IV and He II lines into broad and narrow Gaussian components (BC and NC). The most common (50%) C IV line morphology in CTTSs is that of a low-velocity NC together with a redshifted BC. For CTTSs, a strong BC is the result of the accretion process. The contribution fraction of the NC to the C IV line flux in CTTSs increases with accretion rate, from {approx}20% to up to {approx}80%. The velocity centroids of the BCs and NCs are such that V{sub BC} {approx}> 4 V{sub NC}, consistent with the predictions of the accretion shock model, in at most 12 out of 22 CTTSs. We do not find evidence of the post-shock becoming buried in the stellar photosphere due to the pressure of the accretion flow. The He II CTTSs lines are generally symmetric and narrow, with FWHM and redshifts comparable to those of WTTSs. They are less redshifted than the CTTSs C IV lines, by {approx}10 km s{sup -1}. The amount of flux in the BC of the He II line is small compared to that of the C IV line, and we show that this is consistent with models of the pre-shock column emission. Overall, the observations are consistent with the presence of multiple accretion columns with different densities or with accretion models that predict a slow-moving, low-density region in the periphery of the accretion column. For HN Tau A and RW Aur A, most of the C IV line is blueshifted suggesting that the C IV emission is produced by shocks within outflow jets. In our sample, the Herbig Ae star DX Cha is the only object for which we find a

  3. Hyperspectral Imagers for the Study of Massive Star Nebulae

    NASA Astrophysics Data System (ADS)

    Drissen, L.; Alarie, A.; Martin, T.; Spiomm/Sitelle Team

    2012-12-01

    We present two wide-field imaging Fourier transform spectrometers built by our team to study the interstellar medium around massive stars in the Milky Way and nearby galaxies. SpIOMM, attached to the Mont Mégantic 1.6-m telescope, is capable of obtaining the visible spectrum of every source of light in a 12 arcminute field of view, with a spectral resolution ranging from R = 1 (wide-band image) to R = 25 000, resulting in about a million spectra with a spatial resolution of one arcsecond. SITELLE will be a similar instrument attached to the Canada-France-Hawaii telescope, and will be in operation in early 2013. We illustrate SpIOMM's capabilities to study the interactions between massive stars and their environment.

  4. Relativistic stars in de Rham-Gabadadze-Tolley massive gravity

    NASA Astrophysics Data System (ADS)

    Katsuragawa, Taishi; Nojiri, Shin'ichi; Odintsov, Sergei D.; Yamazaki, Masashi

    2016-06-01

    We study relativistic stars in the simplest model of the de Rham-Gabadadze-Tolley massive gravity which describes the massive graviton without a ghost propagating mode. We consider the hydrostatic equilibrium and obtain the modified Tolman-Oppenheimer-Volkoff equation and the constraint equation coming from the potential terms in the gravitational action. We give analytical and numerical results for quark and neutron stars and discuss the deviations compared with general relativity and F (R ) gravity. It is shown that the theory under investigation leads to a small deviation from general relativity in terms of density profiles and mass-radius relation. Nevertheless, such a deviation may be observable in future astrophysical probes.

  5. THE ROLE OF THE MAGNETOROTATIONAL INSTABILITY IN MASSIVE STARS

    SciTech Connect

    Wheeler, J. Craig; Kagan, Daniel; Chatzopoulos, Emmanouil

    2015-01-20

    The magnetorotational instability (MRI) is key to physics in accretion disks and is widely considered to play some role in massive star core collapse. Models of rotating massive stars naturally develop very strong shear at composition boundaries, a necessary condition for MRI instability, and the MRI is subject to triply diffusive destabilizing effects in radiative regions. We have used the MESA stellar evolution code to compute magnetic effects due to the Spruit-Tayler (ST) mechanism and the MRI, separately and together, in a sample of massive star models. We find that the MRI can be active in the later stages of massive star evolution, leading to mixing effects that are not captured in models that neglect the MRI. The MRI and related magnetorotational effects can move models of given zero-age main sequence mass across ''boundaries'' from degenerate CO cores to degenerate O/Ne/Mg cores and from degenerate O/Ne/Mg cores to iron cores, thus affecting the final evolution and the physics of core collapse. The MRI acting alone can slow the rotation of the inner core in general agreement with the observed ''initial'' rotation rates of pulsars. The MRI analysis suggests that localized fields ∼10{sup 12} G may exist at the boundary of the iron core. With both the ST and MRI mechanisms active in the 20 M {sub ☉} model, we find that the helium shell mixes entirely out into the envelope. Enhanced mixing could yield a population of yellow or even blue supergiant supernova progenitors that would not be standard SN IIP.

  6. The Role of the Magnetorotational Instability in Massive Stars

    NASA Astrophysics Data System (ADS)

    Wheeler, J. Craig; Kagan, Daniel; Chatzopoulos, Emmanouil

    2015-01-01

    The magnetorotational instability (MRI) is key to physics in accretion disks and is widely considered to play some role in massive star core collapse. Models of rotating massive stars naturally develop very strong shear at composition boundaries, a necessary condition for MRI instability, and the MRI is subject to triply diffusive destabilizing effects in radiative regions. We have used the MESA stellar evolution code to compute magnetic effects due to the Spruit-Tayler (ST) mechanism and the MRI, separately and together, in a sample of massive star models. We find that the MRI can be active in the later stages of massive star evolution, leading to mixing effects that are not captured in models that neglect the MRI. The MRI and related magnetorotational effects can move models of given zero-age main sequence mass across "boundaries" from degenerate CO cores to degenerate O/Ne/Mg cores and from degenerate O/Ne/Mg cores to iron cores, thus affecting the final evolution and the physics of core collapse. The MRI acting alone can slow the rotation of the inner core in general agreement with the observed "initial" rotation rates of pulsars. The MRI analysis suggests that localized fields ~1012 G may exist at the boundary of the iron core. With both the ST and MRI mechanisms active in the 20 M ⊙ model, we find that the helium shell mixes entirely out into the envelope. Enhanced mixing could yield a population of yellow or even blue supergiant supernova progenitors that would not be standard SN IIP.

  7. A BUTTERFLY-SHAPED 'PAPILLON' NEBULA YIELDS SECRETS OF MASSIVE STAR BIRTH

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A NASA Hubble Space Telescope view of a turbulent cauldron of starbirth, called N159, taking place 170,000 light-years away in our satellite galaxy, the Large Magellanic Cloud (LMC). Torrential stellar winds from hot newborn massive stars within the nebula sculpt ridges, arcs, and filaments in the vast cloud, which is over 150 light-years across. A rare type of compact ionized 'blob' is resolved for the first time to be a butterfly-shaped or 'Papillon' (French for 'butterfly') nebula, buried in the center of the maelstrom of glowing gases and dark dust. The unprecedented details of the structure of the Papillon, itself less than 2 light-years in size (about 2 arcseconds in the sky), are seen in the inset. A possible explanation of this bipolar shape is the outflow of gas from massive stars (over 10 times the mass of our sun) hidden in the central absorption zone. Such stars are so hot that their radiation pressure halts the infall of gas and directs it away from the stars in two opposite directions. Presumably, a dense equatorial disk formed by matter still trying to fall in onto the stars focuses the outstreaming matter into the bipolar directions. This observation is part of a search for young massive stars in the LMC. Rare are the cases where we can see massive stars so early after their birth. The red in this true-color image is from the emission of hydrogen and the yellow from high excitation ionized oxygen. The picture was taken on September 5, 1998 with the Wide Field Planetary Camera 2. The Hubble observations of the Papillon nebula were conducted by the European astronomers Mohammad Heydari-Malayeri (Paris Observatory, France) and co-investigators Michael Rosa (Space Telescope-European Coordinating Facility, European Southern Observatory, Germany), Vassilis Charmandaris (Paris Observatory), Lise Deharveng (Marseille Observatory, France), and Hans Zinnecker (Astrophysical Institute, Potsdam, Germany). Their work is submitted for publication in the European

  8. Stochastic excitation of gravity waves in rapidly rotating massive stars

    NASA Astrophysics Data System (ADS)

    Mathis, S.; Neiner, C.

    2015-01-01

    Stochastic gravity waves have been recently detected and characterised in stars thanks to space asteroseismology and they may play an important role in the evolution of stellar angular momentum. In this context, the observational study of the CoRoT hot Be star HD 51452 suggests a potentially strong impact of rotation on stochastic excitation of gravito-inertial waves in rapidly rotating stars. In this work, we present our results on the action of the Coriolis acceleration on stochastic wave excitation by turbulent convection. We study the change of efficiency of this mechanism as a function of the waves' Rossby number and we demonstrate that the excitation presents two different regimes for super-inertial and sub-inertial frequencies. Consequences for rapidly rotating early-type stars and the transport of angular momentum in their interiors are discussed.

  9. Preface: X-ray emission from hot stars and their winds

    NASA Astrophysics Data System (ADS)

    Oskinova, Lidia

    2016-09-01

    With the advent of highly sensitive X-ray observatories, X-ray astrophysics has become a versatile tool to study highly energetic processes in a wide variety of astrophysical contexts. Hot stars are no exception to this rule. Indeed, X-rays provide an important observational window for studies of such stars. Observations obtained with modern X-ray telescopes over the last decade and a half have revolutionized our understanding of hot stars and their winds. X-ray spectroscopy, time monitoring, and imaging allow us to probe stellar atmospheres, magnetospheres, stellar winds and give us new insight into their impact on the interstellar medium and the galactic ecology. While some questions about X-ray emission from massive stars have been answered, many unexpected findings point out that our picture of stellar winds is not yet complete. The new theories and models of X-ray emission from hot stars were developed in parallel or, sometimes, ahead of the arrival of the new data. This special issue is aimed at summarizing our current knowledge of X-ray emission from hot stars as well as at opening new avenues for investigation in anticipation of the next generation of X-ray telescopes.

  10. X-RAY EMISSION FROM MAGNETIC MASSIVE STARS

    SciTech Connect

    Nazé, Yaël; Petit, Véronique; Rinbrand, Melanie; Owocki, Stan; Cohen, David; Ud-Doula, Asif; Wade, Gregg A.

    2014-11-01

    Magnetically confined winds of early-type stars are expected to be sources of bright and hard X-rays. To clarify the systematics of the observed X-ray properties, we have analyzed a large series of Chandra and XMM-Newton observations, corresponding to all available exposures of known massive magnetic stars (over 100 exposures covering ∼60% of stars compiled in the catalog of Petit et al.). We show that the X-ray luminosity is strongly correlated with the stellar wind mass-loss rate, with a power-law form that is slightly steeper than linear for the majority of the less luminous, lower- M-dot B stars and flattens for the more luminous, higher- M-dot O stars. As the winds are radiatively driven, these scalings can be equivalently written as relations with the bolometric luminosity. The observed X-ray luminosities, and their trend with mass-loss rates, are well reproduced by new MHD models, although a few overluminous stars (mostly rapidly rotating objects) exist. No relation is found between other X-ray properties (plasma temperature, absorption) and stellar or magnetic parameters, contrary to expectations (e.g., higher temperature for stronger mass-loss rate). This suggests that the main driver for the plasma properties is different from the main determinant of the X-ray luminosity. Finally, variations of the X-ray hardnesses and luminosities, in phase with the stellar rotation period, are detected for some objects and they suggest that some temperature stratification exists in massive stars' magnetospheres.

  11. Massive Stars and the Ionization of the Diffuse Medium

    NASA Astrophysics Data System (ADS)

    Kahre, Lauren E.; Walterbos, Rene A. M.

    2015-08-01

    Diffuse ionized Gas (DIG, sometimes called the warm ionized medium or WIM) has been recognized as a major component of the interstellar medium (ISM) in disk galaxies. A general understanding of the characteristics of the DIG is emerging, but several questions remain unanswered. One of these is the ionization mechanism for this gas, believed to be connected to OB stars and HII regions. Using 5-band (NUV (2750 A), U, V, B, and I) photometric imaging data from the Hubble Space Telescope (HST) Legacy Extragalactic Ultraviolet Survey (LEGUS) and ground-based Halpha data from the Local Volume Legacy (LVL) survey and HST Halpha data from LEGUS, we will investigate the photoionization of HII regions and DIG in nearly 50 galaxies. The 5-band photometry will enable us to determine properties of the most massive stars and reddening corrections for specific regions within a galaxy. Luminosities and ages for groups and clusters will be obtained from SED-fitting of photometric data. For individual stars ages will be determined from isochrone-fitting using reddening-corrected color-magnitude diagrams. We can then obtain estimates of the ionizing luminosities by matching these photometric properties for massive stars and clusters to various stellar atmosphere models. We will compare these predictions to the inferred Lyman continuum production rates from reddening-corrected ground- and HST-based Halpha data for HII regions and DIG. This particular presentation will demonstrate the above process for a set of selected regions in galaxies within the LEGUS sample. It will subsequently be expanded to cover the full LEGUS sample, with the overall goals of obtaining a better understanding of the radiative energy feedback from massive stars on the ISM, particularly their ability to ionize the surrounding ISM over a wide range of spatial scales and SFR surface densities, and to connect the ionization of the ISM to HII region morphologies.

  12. THE MASSIVE STAR-FORMING REGIONS OMNIBUS X-RAY CATALOG

    SciTech Connect

    Townsley, Leisa K.; Broos, Patrick S.; Feigelson, Eric D.; Getman, Konstantin V.; Kuhn, Michael A.; Garmire, Gordon P.; Bouwman, Jeroen; Povich, Matthew S.

    2014-07-01

    We present the Massive Star-forming Regions (MSFRs) Omnibus X-ray Catalog (MOXC), a compendium of X-ray point sources from Chandra/ACIS observations of a selection of MSFRs across the Galaxy, plus 30 Doradus in the Large Magellanic Cloud. MOXC consists of 20,623 X-ray point sources from 12 MSFRs with distances ranging from 1.7 kpc to 50 kpc. Additionally, we show the morphology of the unresolved X-ray emission that remains after the cataloged X-ray point sources are excised from the ACIS data, in the context of Spitzer and WISE observations that trace the bubbles, ionization fronts, and photon-dominated regions that characterize MSFRs. In previous work, we have found that this unresolved X-ray emission is dominated by hot plasma from massive star wind shocks. This diffuse X-ray emission is found in every MOXC MSFR, clearly demonstrating that massive star feedback (and the several-million-degree plasmas that it generates) is an integral component of MSFR physics.

  13. The Massive Star-Forming Regions Omnibus X-Ray Catalog

    NASA Astrophysics Data System (ADS)

    Townsley, Leisa K.; Broos, Patrick S.; Garmire, Gordon P.; Bouwman, Jeroen; Povich, Matthew S.; Feigelson, Eric D.; Getman, Konstantin V.; Kuhn, Michael A.

    2014-07-01

    We present the Massive Star-forming Regions (MSFRs) Omnibus X-ray Catalog (MOXC), a compendium of X-ray point sources from Chandra/ACIS observations of a selection of MSFRs across the Galaxy, plus 30 Doradus in the Large Magellanic Cloud. MOXC consists of 20,623 X-ray point sources from 12 MSFRs with distances ranging from 1.7 kpc to 50 kpc. Additionally, we show the morphology of the unresolved X-ray emission that remains after the cataloged X-ray point sources are excised from the ACIS data, in the context of Spitzer and WISE observations that trace the bubbles, ionization fronts, and photon-dominated regions that characterize MSFRs. In previous work, we have found that this unresolved X-ray emission is dominated by hot plasma from massive star wind shocks. This diffuse X-ray emission is found in every MOXC MSFR, clearly demonstrating that massive star feedback (and the several-million-degree plasmas that it generates) is an integral component of MSFR physics.

  14. The Massive Star Forming Region Cygnus OB2

    NASA Astrophysics Data System (ADS)

    Wright, Nicholas James; Drake, J. J.; Drew, J. E.

    2009-12-01

    We present a multi-wavelength study of the massive star forming Cygnus OB2. Cygnus OB2 is the northern hemisphere's most massive star forming region and hosts a tremendously rich and diverse stellar population, with thousands of OB stars. The strong and highly variable extinction in the direction of the association have hindered previous studies of the region, but recent deep photometric surveys in the optical and near-infrared are opening the region up for study. The appreciation of the pivotal status of Cyg OB2 has led to a number of recent ambitious surveys of the cluster and its setting within the Cygnus-X region at X-ray, infrared and radio wavelengths. Chandra X-ray observations of two fields in the center of the association reveal 1720 X-ray sources, which we have combined with optical and near-IR photometry from the IPHAS and UKIDSS surveys. Near-IR photometry reveals a stellar population with a spread of ages greater than previously thought, overturning the picture of coeval star formation in the region. The distribution of young sources in the region shows evidence for clustering and significant mass segregation, which we judge to be primordial given the cluster's age.

  15. Evidence for a bifurcation in massive star evolution

    NASA Astrophysics Data System (ADS)

    Maeder, Andre

    1986-07-01

    The effects of rotationally induced mixing on the evolution of massive stars is examined. Models show that, due to the high radiative viscosity, the diffusion coefficient is sufficiently large to mix most massive stars during their MS lifetime. However, below a critical rotation velocity, diffusive mixing is efficiently prevented by the mu-gradient. A wide bifurcation appears in the evolutionary tracks. Below critical rotation, the evolution is essentially classical with unmodified redwards tracks in the HR diagram. Above critical rotation, the evolutionary tracks go upwards and bluewards, very close to those of fully homogeneous evolution. In this case the model composition is rapidly characterized by He and N enrichments, C and O depletions. The homogeneous models lead to the formation of WR stars before the end of the H-burning phase, which increases the WR lifetime; there is probably no WNE stage in this homogeneous evolutionary scheme. For the classically evolving stars, diffusion may increase the size of the convective core as overshooting does; diffusion may also produce moderate changes of the surface C/N and O/N ratios.

  16. Nucleosynthesis of Short-lived Radioactivities in Massive Stars

    NASA Technical Reports Server (NTRS)

    Meyer, B. S.

    2004-01-01

    A leading model for the source of many of the short-lived radioactivities in the early solar nebula is direct incorporation from a massive star [1]. A recent and promising incarnation of this model includes an injection mass cut, which is a boundary between the stellar ejecta that become incorporated into the solar cloud and those ejecta that do not [2-4]. This model also includes a delay time between ejection from the star and incorporation into early solar system solid bodies. While largely successful, this model requires further validation and comparison against data. Such evaluation becomes easier if we have a better sense of the nature of the synthesis of the various radioactivities in the star. That is the goal of this brief abstract.

  17. Evolution of massive stars in very young clusters and associations

    NASA Technical Reports Server (NTRS)

    Stothers, R. B.

    1985-01-01

    Statistics concerning the stellar content of young galactic clusters and associations which show well defined main sequence turnups have been analyzed in order to derive information about stellar evolution in high-mass galaxies. The analytical approach is semiempirical and uses natural spectroscopic groups of stars on the H-R diagram together with the stars' apparent magnitudes. The new approach does not depend on absolute luminosities and requires only the most basic elements of stellar evolution theory. The following conclusions are offered on the basis of the statistical analysis: (1) O-tupe main-sequence stars evolve to a spectral type of B1 during core hydrogen burning; (2) most O-type blue stragglers are newly formed massive stars burning core hydrogen; (3) supergiants lying redward of the main-sequence turnup are burning core helium; and most Wolf-Rayet stars are burning core helium and originally had masses greater than 30-40 solar mass. The statistics of the natural spectroscopic stars in young galactic clusters and associations are given in a table.

  18. Can very compact and very massive neutron stars both exist?

    NASA Astrophysics Data System (ADS)

    Drago, Alessandro; Lavagno, Andrea; Pagliara, Giuseppe

    2014-02-01

    The existence of neutron stars with masses of ˜2M⊙ requires a stiff equation of state at high densities. On the other hand, the necessary appearance also at high densities of new degrees of freedom, such as hyperons and Δ resonances, can lead to a strong softening of the equation of state with resulting maximum masses of ˜1.5M⊙ and radii smaller than ˜10 km. Hints for the existence of compact stellar objects with very small radii have been found in recent statistical analyses of quiescent low-mass X-ray binaries in globular clusters. We propose an interpretation of these two apparently contradicting measurements, large masses and small radii, in terms of two separate families of compact stars: hadronic stars, whose equation of state is soft, can be very compact, while quark stars, whose equation of state is stiff, can be very massive. In this respect an early appearance of Δ resonances is crucial to guarantee the stability of the branch of hadronic stars. Our proposal could be tested by measurements of radii with an error of ˜1 km, which is within reach of the planned Large Observatory for X-ray Timing satellite, and it would be further strengthened by the discovery of compact stars heavier than ˜2M⊙.

  19. Massive stars and expanding shells within the violent interstellar medium

    NASA Astrophysics Data System (ADS)

    Thilker, David Allan

    Massive stars have a tremendous impact on their surroundings, largely due to a prodigious production rate of Lyman continuum photons and their inevitable termination in a supernova explosion. A single OB star may ionize a sufficiently luminous HII region to remain detectable out to distances of many Mpc. By concentrating the mechanical power of many high mass stars in a limited volume over a short time period, OB associations are known to produce large expanding bubbles in the interstellar medium (ISM). Aperture synthesis observations of HI in nearby galaxies clearly reveal the bubbly character of the diffuse ISM and highlight the connection with massive stars. In this dissertation I close the loop between theory and observations regarding massive stars, their incipient HII regions, and related expanding shells, all in the hope of learning more about the diffuse ISM. The research described herein has three main components: (1)object recognition in the context of HI datacubes and hydrodynamic shell models, (2)automated photometry of HII regions in crowded narrowband images, and (3)population synthesis modeling of stellar clusters and expanding shells in disk galaxies. I have created efficient procedures for conducting a census of HI superbubbles and young massive star clusters in nearby galaxies, plus a modeling framework allowing one to check these databases for relative agreement. My population synthesis algorithm predicts ensemble characteristics: of a disk-galaxy shell population, given details of the stellar cluster formation process and global properties of the galaxy in question. My automated HI object recognition method has made possible the Las Cruces/Dwingeloo Supershell Survey (LCDSS) of 21 nearby disk galaxies. In this dissertation I present early LCDSS results for NGC 300, NGC 2403, M81, and M101. Furthermore, I demonstrate the technique for photometry of HII regions by analyzing a small sample of 11 prominent spirals. The photometric measurements are

  20. Stellar Feedback in Massive Star-Forming Regions

    NASA Astrophysics Data System (ADS)

    Baldwin, Jack; Pellegrini, Eric; Ferland, Gary; Murray, Norm; Hanson, Margaret

    2008-02-01

    Star formation rates and chemical evolution are controlled in part by the interaction of stellar radiation and winds with the remnant molecular gas from which the stars have formed. We are carrying out a detailed, panchromatic study in the two nearest giant star-forming regions to nail down the physics that produces the 10-20 parsec bubbles seen to surround young massive clusters in the Milky Way. This will determine if and how the clusters disrupt their natal giant molecular clouds (GMCs). Here we request 4 nights on the Blanco telescope to obtain dense grids of optical long-slit spectra criss-crossing each nebula. These will cover the [S II] doublet (to measure N_e) and also [O III], H(beta), [O I], H(alpha) and [N II] to measure the ionization mechanism and ionization parameter, at ~3000 different spots in each nebula. From this we can determine a number of dynamically important quantities, such as the gas density and temperature, hence pressure in and around these bubbles. These quantities can be compared to the dynamical (gravitationally induced) pressure, and the radiation pressure. All can be employed in dynamical models for the evolution of a GMC under the influence of an embedded massive star cluster. This research will elucidate the detailed workings of the star-forming regions which dominate the star formation rate in the Milky Way, and also will steadily improve our calibration and understanding of more distant, less well-resolved objects such as ULIRGS, Lyman break, and submillimeter galaxies.

  1. Massive star formation by accretion. I. Disc accretion

    NASA Astrophysics Data System (ADS)

    Haemmerlé, L.; Eggenberger, P.; Meynet, G.; Maeder, A.; Charbonnel, C.

    2016-01-01

    Context. Massive stars likely form by accretion and the evolutionary track of an accreting forming star corresponds to what is called the birthline in the Hertzsprung-Russell (HR) diagram. The shape of this birthline is quite sensitive to the evolution of the entropy in the accreting star. Aims: We first study the reasons why some birthlines published in past years present different behaviours for a given accretion rate. We then revisit the question of the accretion rate, which allows us to understand the distribution of the observed pre-main-sequence (pre-MS) stars in the HR diagram. Finally, we identify the conditions needed to obtain a large inflation of the star along its pre-MS evolution that may push the birthline towards the Hayashi line in the upper part of the HR diagram. Methods: We present new pre-MS models including accretion at various rates and for different initial structures of the accreting core. We compare them with previously published equivalent models. From the observed upper envelope of pre-MS stars in the HR diagram, we deduce the accretion law that best matches the accretion history of most of the intermediate-mass stars. Results: In the numerical computation of the time derivative of the entropy, some treatment leads to an artificial loss of entropy and thus reduces the inflation that the accreting star undergoes along the birthline. In the case of cold disc accretion, the existence of a significant swelling during the accretion phase, which leads to radii ≳ 100 R⊙ and brings the star back to the red part of the HR diagram, depends sensitively on the initial conditions. For an accretion rate of 10-3M⊙ yr-1, only models starting from a core with a significant radiative region evolve back to the red part of the HR diagram. We also obtain that, in order to reproduce the observed upper envelope of pre-MS stars in the HR diagram with an accretion law deduced from the observed mass outflows in ultra-compact HII regions, the fraction of the

  2. Mass loss from evolved massive stars: self-consistent modeling of the wind and photosphere

    NASA Astrophysics Data System (ADS)

    Groh, J. H.

    2007-03-01

    This work analyzes the mass loss phenomenon in evolved massive stars through self-consistent modeling of the wind and photosphere of such stars, using the radiative transfer code CMFGEN. In the first part, fundamental physical parameters of Wolf-Rayet stars of spectral types WN3-w (WR 46 e WR 152) and WN6-s (WR 136) were obtained. The results clearly indicate that hydrogen is present on the surface of those stars in a considerable fraction, defying current evolutionary models. For both WN subtypes, significant difference between the physical parameters obtained here and in previous works were noticed. The 20-year evolution of the luminous blue variable (LBV) AG Carinae was analyzed in detail in the second part of this work. The results indicate unexpected changes in the current paradigm of massive star evolution during the S Dor cycle. In this work, the high rotational velocity obtained during the hot phases, and the transition between the bistability regimes of line-driven winds were detected for the first time in LBVs. Those results need to be considered in future analysis of such massive stars. This Thesis also presents a pioneering study about the impact of the time variability effects on the analysis of the winds of LBVs. The results achieved here are valid for the whole LBV class, and show that the mass-loss rates derived from Hα and radio free-free emission are affected by time-dependent effects. The mass-loss rate evolution during the S Dor cycle, derived using time-dependent models, implies that LBV eruptions begin well before the maximum in the visual lightcurve during this phase. The analysis of the full S Dor cycle of AG Car rule out that the S Dor variability is caused exclusively by an expanding pseudo-photosphere. The AG Car hydrostatic radius was found to vary by a factor of six between cool and hot phases, while the bolometric luminosity is 50% higher during the hot phase. Both results provide observational contraints for the physical mechanism

  3. Non-LTE model atmospheres for hot evolved stars.

    NASA Astrophysics Data System (ADS)

    Werner, K.; Dreizler, S.; Heber, U.; Hunger, K.; Rauch, T.

    During the last years the authors have developed a computer code to construct non-LTE model atmospheres for hot stars including line blanketing effects. The particular methods gave way to the computation of non-LTE model atmospheres which account for many more opacity sources than could be treated within the classical complete linearisation approach by Auer and Mihalas. With this code it became possible for the first time to calculate grids of realistic non-LTE line blanketed model atmospheres for subdwarf O-stars in a critical temperature range as well as for the extremely hot (100,000K to 150,000K) so-called PG1159 stars. Both groups of stars consist of objects being in advanced evolutionary stages representing immediate White Dwarf progenitors. The atmospheres of these stars are enriched or even dominated by nuclear processed material, namely either by helium (sdO stars) or also by carbon and oxygen (PG1159 stars).

  4. Massive stars: Their lives in the interstellar medium; Proceedings of the Symposium, ASP Annual Meeting, 104th, Univ. of Wisconsin, Madison, June 23-25, 1992

    NASA Astrophysics Data System (ADS)

    Cassinelli, Joseph P.; Churchwell, Edward B.

    1993-01-01

    Various papers on massive stars and their relationship to the interstellar medium are presented. Individual topics addressed include: observations of newly formed massive stars, star formation with nonthermal motions, embedded stellar clusters in H II regions, a Milky Way concordance, NH3 and H2O masers, PIGs in the Trapezium, star formation in photoevaporating molecular clouds, massive star evolution, mass loss from cool supergiant stars, massive runaway stars, CNO abundances in three A-supergiants, mass loss from late-type supergiants, OBN stars and blue supergiant supernovae, the most evolved W-R stars, X-ray variability in V444 Cygni, highly polarized stars in Cassiopeia, H I bubbles around O stars, interstellar H I LY-alpha absorption, shocked ionized gas in 30 Doradus, wind mass and energy deposition. Also discussed are: stellar wind bow shocks, O stars giant bubbles in M33, Eridanus soft X-ray enhancement, wind-blown bubbles in ejecta medium, nebulae around W-R stars, highly ionized gas in the LMC, cold ionized gas around hot H II regions, initial mass function in the outer Galaxy, late stages in SNR evolution, possible LBV in NGC 1313, old SN-pulsar association, cold bright matter near SN1987A, starbursts in the nearby universe, giant H II regions, powering the superwind in NGC 253, obscuration effects in starburst Galactic nuclei, starburst propagation in dwarf galaxies, 30 Doradus, W-R content of NGC 595 and NGC 604, Cubic Cosmic X-ray Background Experiment.

  5. Star Formation in Massive Clusters via Bondi Accretion

    NASA Astrophysics Data System (ADS)

    Murray, Norman; Chang, Philip

    2012-02-01

    Essentially all stars form in giant molecular clouds (GMCs). However, inside GMCs, most of the gas does not participate in star formation; rather, denser gas accumulates in clumps in the GMC, with the bulk of the stars in a given GMC forming in a few of the most massive clumps. In the Milky Way, these clumps have masses M cl <~ 5 × 10-2 of the GMC, radii r cl ~ 1 pc, and free-fall times τcl ~ 2 × 105 yr. We show that clumps inside GMCs should accrete at a modified Bondi accretion rate, which depends on clump mass as \\dot{M}_{cl}\\sim M_{cl}^{5/4}. This rate is initially rather slow, usually slower than the initial star formation rate inside the clump (we adopt the common assumption that inside the clump, \\dot{M}_*=\\epsilon _ffM_{cl}/\\tau _{cl}, with epsilonff ≈ 0.017). However, after ~2 GMC free-fall times τGMC, the clump accretion rate accelerates rapidly; formally, the clump can accrete the entire GMC in ~3τGMC. At the same time, the star formation rate accelerates, tracking the Bondi accretion rate. If the GMC is disrupted by feedback from the largest clump, half the stars in that clump form in the final τGMC before the GMC is disrupted. The theory predicts that the distribution of effective star formation rates, measured per GMC free-fall time, is broad, ranging from ~0.001 up to 0.1 or larger and that the mass spectrum of star clusters is flatter than that of clumps, consistent with observations.

  6. Influence of X-ray radiation on the hot star wind ionization state and on the radiative force

    NASA Astrophysics Data System (ADS)

    Krtička, Jiří; Kubát, Jiří

    2016-09-01

    Hot stars emit large amounts of X-rays, which are assumed to originate in the supersonic stellar wind. Part of the emitted X-rays is subsequently absorbed in the wind and influences its ionization state. Because hot star winds are driven radiatively, the modified ionization equilibrium affects the radiative force. We review the recent progress in modeling the influence of X-rays on the radiative equilibrium and on the radiative force. We focus particularly on single stars with X-rays produced in wind shocks and on binaries with massive components, which belong to the most luminous objects in X-rays.

  7. Rayleigh scattering in the atmospheres of hot stars

    NASA Astrophysics Data System (ADS)

    Fišák, J.; Krtička, J.; Munzar, D.; Kubát, J.

    2016-05-01

    Context. Rayleigh scattering is a result of an interaction of photons with bound electrons. Rayleigh scattering is mostly neglected in calculations of hot star model atmospheres because most of the hydrogen atoms are ionized and the heavier elements have a lower abundance than hydrogen. In atmospheres of some chemically peculiar stars, helium overabundant regions containing singly ionized helium are present and Rayleigh scattering can be a significant opacity source. Aims: We evaluate the contribution of Rayleigh scattering by neutral hydrogen and singly ionized helium in the atmospheres of hot stars with solar composition and in the atmospheres of helium overabundant stars. Methods: We computed several series of model atmospheres using the TLUSTY code and emergent fluxes using the SYNSPEC code. These models describe atmospheres of main sequence B-type stars with different helium abundance. We used an existing grid of models for atmospheres with solar chemical composition and we calculated an additional grid for helium-rich stars with N(He)/N(H) = 10. Results: Rayleigh scattering by neutral hydrogen can be neglected in atmospheres of hot stars, while Rayleigh scattering by singly ionized helium can be a non-negligible opacity source in some hot stars, especially in helium-rich stars.

  8. Star formation in massive Milky Way molecular clouds: Building a bridge to distant galaxies

    NASA Astrophysics Data System (ADS)

    Willis, Sarah Elizabeth

    The Kennicutt-Schmidt relation is an empirical power-law linking the surface density of the star formation rate (SigmaSFR) to the surface density of gas (Sigmagas ) averaged over the observed face of a starforming galaxy Kennicutt (1998). The original presentation used observations of CO to measure gas density and H alpha emission to measure the population of hot, massive young stars (and infer the star formation rate). Observations of Sigma SFR from a census of young stellar objects in nearby molecular clouds in our Galaxy are up to 17 times higher than the extragalactic relation would predict given their Sigmagas. These clouds primarily form low-mass stars that are essentially invisible to star formation rate tracers. A sample of six giant molecular cloud (GMC) complexes with signposts of massive star formation was identified in our galaxy. The regions selected have a range of total luminosity and morphology. Deep ground-based observations in the near-infrared with NEWFIRM and IRAC observations with the Spitzer Space Telescope were used to conduct a census of the young stellar content associated with each of these clouds. The star formation rates from the stellar census in each of these regions was compared with the star formation rates measured by extragalactic star formation rate tracers based on monochromatic mid-infrared luminosities. Far-infrared Herschel observations from 160 through 500 mum were used to determine the column density and temperature in each region. The region NGC 6334 served as a test case to compare the Herschel column density measurements with the measurements for near-infrared extinction. The combination of the column density maps and the stellar census lets us examine SigmaSFR vs. Sigma gas for the massive GMCs. These regions are consistent with the results for the low-mass molecular clouds, indicating Sigma SFR levels that are higher than predicted based on Sigma gas. The overall Sigmagas levels are higher for the massive star forming

  9. Astronomers Discover Most Massive Neutron Star Yet Known

    NASA Astrophysics Data System (ADS)

    2010-10-01

    Astronomers using the National Science Foundation's Green Bank Telescope (GBT) have discovered the most massive neutron star yet found, a discovery with strong and wide-ranging impacts across several fields of physics and astrophysics. "This neutron star is twice as massive as our Sun. This is surprising, and that much mass means that several theoretical models for the internal composition of neutron stars now are ruled out," said Paul Demorest, of the National Radio Astronomy Observatory (NRAO). "This mass measurement also has implications for our understanding of all matter at extremely high densities and many details of nuclear physics," he added. Neutron stars are the superdense "corpses" of massive stars that have exploded as supernovae. With all their mass packed into a sphere the size of a small city, their protons and electrons are crushed together into neutrons. A neutron star can be several times more dense than an atomic nucleus, and a thimbleful of neutron-star material would weigh more than 500 million tons. This tremendous density makes neutron stars an ideal natural "laboratory" for studying the most dense and exotic states of matter known to physics. The scientists used an effect of Albert Einstein's theory of General Relativity to measure the mass of the neutron star and its orbiting companion, a white dwarf star. The neutron star is a pulsar, emitting lighthouse-like beams of radio waves that sweep through space as it rotates. This pulsar, called PSR J1614-2230, spins 317 times per second, and the companion completes an orbit in just under nine days. The pair, some 3,000 light-years distant, are in an orbit seen almost exactly edge-on from Earth. That orientation was the key to making the mass measurement. As the orbit carries the white dwarf directly in front of the pulsar, the radio waves from the pulsar that reach Earth must travel very close to the white dwarf. This close passage causes them to be delayed in their arrival by the distortion of

  10. The Energetic Impact of Massive Stars on the ISM

    NASA Astrophysics Data System (ADS)

    Freyer, Tim; Hensler, Gerhard

    We present results of numerical simulations carried out with a 2D radiation hydrodynamics code in order to study the impact of massive stars on their surrounding interstellar medium. The interaction of the photoionized H II region with the stellar wind bubble can form a variety of interesting structures like shells, clouds, fingers, and spokes. These results shed light on the open question whether the complex structures that can be found in H II regions are relics from the time before the gas became ionized, or rather formed by dynamical processes in the course of the H II region evolution. We have also analysed the transfer and deposit of the stellar wind and radiation energy into the circumstellar medium until the star explodes as a supernova. Though the total mechanical wind energy supplied by a 60 Msolar star is negligible compared to the accumulated energy of the Lyman continuum photons, at the end of the star's lifetime the kinetic energy of bulk motion in the circumstellar gas is 4 times higher than in the same model without wind while the thermal energy of warm, photoionized gas is lower by some 45 %. Our results document the necessity to consider both, the ionizing radiation and the stellar wind of the star for an appropriate description of the circumstellar medium.

  11. Nucleosynthesis above the iron group in massive stars

    SciTech Connect

    Hoffman, R D; Woosley, S E; Weaver, T A

    2000-10-11

    The production of nuclei up to and including the light s-process component at A {approx} 60-90 is calculated for all stages of stable and explosive nuclear burning in stars of 15 and 25 M{sub {circle_dot}}. An extended nuclear reaction network of 480 isotopes is employed along with approximately two dozen recent revisions to key nuclear reaction rates. As noted previously, the new rates suggest a greatly diminished production of {sup 17}O and {sup 18}O in massive stars. {sup 22}Ne is also moderately enhanced. We find that a combination of pre-explosive s-process, {gamma}-process, and (mild) r-processes in massive stars give a consistently solar production of almost all isotopes from mass 64 through 90. However, even after the late stages of evolution are complete and the explosion is over, this same group of elements is overproduced compared to what is needed for the sun, especially in the 25 M{sub {circle_dot}} model.

  12. Hot stars observed by XMM-Newton. I. The catalog and the properties of OB stars

    NASA Astrophysics Data System (ADS)

    Nazé, Y.

    2009-11-01

    Aims: Following the advent of increasingly sensitive X-ray observatories, deep observations of early-type stars became possible. However, the results for only a few objects or clusters have until now been reported and there has been no large survey comparable to that based upon the ROSAT All-Sky Survey (RASS). Methods: A limited survey of X-ray sources, consisting of all public XMM-Newton observations (2XMMi) and slew survey data (XMMSL1), is now available. The X-ray counterparts to hot, massive stars have been searched for in these catalogs. Results: About 300 OB stars were detected with XMM-Newton. Half of them were bright enough for a spectral analysis to be possible, and we make available the detailed spectral properties that were derived. The X-ray spectra of O stars are represented well by low (<1 keV) temperature components and seem to indicate that an absorption column is present in addition to the interstellar contribution. The X-ray fluxes are well correlated with the bolometric fluxes, with a scatter comparable to that of the RASS studies and thus larger than found previously with XMM-Newton for some individual clusters. These results contrast with those of B stars that exhibit a large scatter in the LX - LBOL relation, no additional absorption being found, and the fits indicate a plasma at higher temperatures. Variability (either within one exposure or between multiple exposures) was also investigated whenever possible: short-term variations are far more rare than long-term ones (the former affects a few percent of the sample, while the latter concerns between one third and two thirds of the sources). Conclusions: This paper presents the results of the first high-sensitivity investigation of the overall high-energy properties of a sizable sample of hot stars. Based on observations collected with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA), and accessed via the 2XMMi and

  13. Formation, Evolution, and Survival of Massive Star Clusters

    NASA Astrophysics Data System (ADS)

    Fall, Michael

    2015-08-01

    This talk presents a synoptic theory for the formation, evolution, and survival of massive star clusters. These objects are important in the ecology of galaxies, as the sites of star formation and stellar feedback, as the building blocks of stellar populations. The talk is organized around the mass function of star clusters (i.e., the spectrum of cluster masses) and how it evolves with time (age). Observations show some remarkable similarities in the mass functions of clusters in different galaxies, analogous to the similarities in stellar initial mass functions (IMFs). Explaining the similarity of the mass functions of star clusters is one of the goals and successes of the theory presented here. A byproduct of this theory is a unified concept of star clusters of all types: associations, open clusters, populous clusters, globular clusters, etc. The physical processes that affect the mass functions of star clusters include the following: star formation and stellar feedback in the gas-dominated protoclusters, and the subsequent gravitational effects in the gas-free clusters, primarily stellar mass loss, tidal interactions with passing molecular clouds, and internal two-body relaxation. These processes all reduce the masses of clusters, thus lowering the amplitude of their mass function, but in such a way that the shape of the mass function is nearly preserved. The talk presents a quantitative, albeit approximate, analysis of all these effects. As a result of recent developments, there is now a growing connection between theory and observation in this field. The work presented here points to some future observations that would strengthen this connection.

  14. Dynamical Interactions Make Hot Jupiters in Open Star Clusters

    NASA Astrophysics Data System (ADS)

    Shara, Michael M.; Hurley, Jarrod R.; Mardling, Rosemary A.

    2016-01-01

    Explaining the origin and evolution of exoplanetary hot Jupiters remains a significant challenge. One possible mechanism for the production of hot Jupiters is planet-planet interactions, which produce them from planets born far from their host stars but near their dynamical stability limits. In the much more likely case of planets born far from their dynamical stability limits, can hot Jupiters be formed in star clusters? Our N-body simulations answer this question in the affirmative, and show that hot Jupiter formation is not a rare event, occurring in ˜1% of star cluster planetary systems. We detail three case studies of the dynamics-induced births of hot Jupiters on highly eccentric orbits that can only occur inside star clusters. The hot Jupiters’ orbits bear remarkable similarities to those of some of the most extreme exoplanets known: HAT-P-32b, HAT-P-2b, HD 80606b, and GJ 876d. If stellar perturbations formed these hot Jupiters, then our simulations predict that these very hot inner planets are often accompanied by much more distant gas giants in highly eccentric orbits.

  15. Effects of Ionization Feedback in Massive Star Formation

    NASA Astrophysics Data System (ADS)

    Peters, Thomas; Banerjee, R.; Klessen, R. S.; Mac Low, M.

    2009-01-01

    We present 3D high-resolution radiation-hydrodynamical simulations of massive star formation. We model the collapse of a massive molecular cloud core forming a high-mass star in its center. We use a version of the FLASH code that has been extended by including sink particles which are a source of both ionizing and non-ionizing radiation. The sink particles evolve according to a prestellar model which determines the stellar and accretion luminosities. Radiation transfer is done using the hybrid characteristics raytracing approach on the adaptive mesh developed by Rijkhorst et al. (2006). The radiative transfer module has been augmented to allow simulations with arbitrarily high resolution. Our highest resolution models resolve the disk scale height by at least 16 zones. Opacities for non-ionizing radiation have been added to account for the accretion heating, which is expected to be strong at the initial stage of star formation and believed to prevent fragmentation. Studies of collapsing massive cores show the formation of a gravitationally highly unstable disk. The accretion heating is not strong enough to suppress this instability. The ionizing radiation builds up an H II region around the protostar, which destroys the accretion disk close to it. We describe preliminary results, with a focus on how long the H II region remains confined by the accretion flow, and whether it can ever cut off accretion entirely. Thomas Peters acknowledges support from a Kade Fellowship for his visit to the American Museum of Natural History. He is a fellow of the International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg and the Heidelberg Graduate School of Fundamental Physics. We also thank the DFG for support via the Emmy Noether Grant BA 3607/1 and the individual grant KL1358/5.

  16. Lithium and zirconium abundances in massive Galactic O-rich AGB stars

    NASA Astrophysics Data System (ADS)

    García-Hernández, D. A.; García-Lario, P.; Plez, B.; Manchado, A.; D'Antona, F.; Lub, J.; Habing, H.

    2007-02-01

    Lithium and zirconium abundances (the latter taken as representative of s-process enrichment) are determined for a large sample of massive Galactic O-rich AGB stars, for which high-resolution optical spectroscopy has been obtained (R˜ 40 000{-}50 000). This was done by computing synthetic spectra based on classical hydrostatic model atmospheres for cool stars and using extensive line lists. The results are discussed in the framework of "hot bottom burning" (HBB) and nucleosynthesis models. The complete sample is studied for various observational properties such as the position of the stars in the IRAS two-colour diagram ([ 12] - [25] vs. [ 25] - [60] ), Galactic distribution, expansion velocity (derived from the OH maser emission), and period of variability (when available). We conclude that a considerable fraction of these sources are actually massive AGB stars (M>3{-}4 M⊙) experiencing HBB, as deduced from the strong Li overabundances we found. A comparison of our results with similar studies carried out in the past for the Magellanic Clouds (MCs) reveals that, in contrast to MC AGB stars, our Galactic sample does not show any indication of s-process element enrichment. The differences observed are explained as a consequence of metallicity effects. Finally, we discuss the results obtained in the framework of stellar evolution by comparing our results with the data available in the literature for Galactic post-AGB stars and PNe. Based on observations at the 4.2 m William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofisica de Canarias. Also based on observations with the ESO 3.6 m telescope at La Silla Observatory (Chile). Tables [see full text]-[see full text] are only available in electronic form at http://www.aanda.org

  17. LIMB-DARKENED RADIATION-DRIVEN WINDS FROM MASSIVE STARS

    SciTech Connect

    Cure, M.; Cidale, L.

    2012-10-01

    We calculated the influence of the limb-darkened finite-disk correction factor in the theory of radiation-driven winds from massive stars. We solved the one-dimensional m-CAK hydrodynamical equation of rotating radiation-driven winds for all three known solutions, i.e., fast, {Omega}-slow, and {delta}-slow. We found that for the fast solution, the mass-loss rate is increased by a factor of {approx}10%, while the terminal velocity is reduced about 10%, when compared with the solution using a finite-disk correction factor from a uniformly bright star. For the other two slow solutions, the changes are almost negligible. Although we found that the limb darkening has no effects on the wind-momentum-luminosity relationship, it would affect the calculation of synthetic line profiles and the derivation of accurate wind parameters.

  18. How Very Massive Metal Free Stars Start Cosmological Reionization

    SciTech Connect

    Wise, John H.; Abel, Tom

    2007-11-07

    The initial conditions and relevant physics for the formation of the earliest galaxies are well specified in the concordance cosmology. Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include non-equilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the Case B approximation using adaptively ray traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of {approx}10{sup 6}. These first sources of reionization are highly intermittent and anisotropic and first photoionize the small scales voids surrounding the halos they form in, rather than the dense filaments they are! embedded in. As the merging objects form larger, dwarf sized galaxies, the escape fraction of UV radiation decreases and the H II regions only break out on some sides of the galaxies making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately 5 ionizing photons are needed per sustained ionization when star formation in 10{sup 6} M{sub {circle_dot}} halos are dominant in the calculation. As the halos become larger than {approx}10{sup 7} M{sub {circle_dot}}, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15--50, in calculations with stellar feedback only. Supernova feedback in these more massive halos creates a more diffuse medium, allowing the stellar radiation to escape more easily and maintaining the ratio of 5 ionizing

  19. Massive Emission-Line Stars in Nearby Galaxies

    NASA Astrophysics Data System (ADS)

    Lim, P. L.; Holtzman, J. A.; Walterbos, R. A. M.

    2003-12-01

    The evolution of massive stars is still poorly understood because of critical effects of mass loss during the post-main sequence phase. Of particular relevance is the Luminous Blue Variable phase, during which high mass loss may occur over a brief period. It would be useful to know the mass range of stars that enter this phase, and the life time of the phase. For that, better estimates of the numbers of LBVs in different environments is crucial. In a study of M31, we detected candidate LBVs as luminous stars with strong Hα emission-lines and no nebular [SII] emission. (King, N.L., Walterbos, R.A.M., & Braun, R., 1998, ApJ, 507:210-220). HST's sensitivity offers the capability to identify these candidate LBVs in galaxies beyond the Local Group. We identify massive Hα emmision-line stars in nearby spiral galaxies within 10 Mpc, using data from the HST WFPC2 archive. We obtained stellar photometry in Hα (F656N) and various broadband filters, with methods developed for the HST Local Group Stellar Photometry archive (Holtzman, J., Afonso, C., & Dolphin, A., 2003, ApJS, submitted). We identify candidates based on the amount of Hα excess in two-color plots. We also require an absolute magnitude MV ≤ -5, and photometry fit parameters consistent with point source characteristics. Candidates are inspected visually on the images for verification purpose. We find promising candidates in several nearby galaxies. We will present a catalog of the objects, and discuss their properties and the environments in which they are found. Support for this work was provided by NASA through grant numbers AR-08372.01-97A and HST-AR-08749.01-A from the Space Telescope Science Institute, which is operated by AURA, Inc. under NASA contract NAS5-26555.

  20. Massive star-forming regions across the galaxy

    NASA Astrophysics Data System (ADS)

    Rygl, Kazi Lucie Jessica

    2010-04-01

    Star-forming regions trace the spiral structure of the Galaxy. They are regions of increased column density and therefore traced well by the extinction in the mid-infrared based on the Spitzer/GLIMPSE 3.6-4.5 micron color excess maps. A sample of 25 high extinction clouds (HECs) was studied in the 1.2 mm dust continuum emission, and followed up by observations of ammonia plus several other molecules using the Effelsberg 100m, IRAM 30m and APEX telescopes. With these data we want to investigate the most early stages of massive star formation, which are currently still largely unknown. Three cloud classes were defined from their morphology in the 1.2 mm continuum maps: the early diffuse HECs, with a low contrast between the clump and cloud emission; the peaked HECs, with an increased contrast; the late multiply peaked HECs, with more than one clump and a high contrast between the clump and the cloud emission. The clouds are cold (T 16 K) and massive (M 800 M_sun) and contain dense clumps (n 10^5 cm^{-3}) of 0.3 pc in size. These clumps were investigated for evidence of gravitational collapse or expansion, for high velocity outflows, and for the presence of young stellar objects. Based on these results we interpret the three cloud classes as an evolutionary sequence of star-forming clouds. Accurate distances are a crucial parameter for establishing the mass, size, and luminosity of an object. Also, for understanding the spiral structure of the Galaxy trustworthy distances are necessary. The most accurate method to measure these is the trigonometric parallax. Using the European Very Large Baseline Interferometry Network of radio antennas we measured, for the first time, parallaxes of 6.7 GHz methanol masers. This transition belongs to the strongest maser species in the Galaxy, it is stable and observed toward numerous massive star-forming regions. We measured distances and proper motions toward L 1287, L 1206, NGC 281-W, ON 1 and S 255, and obtained their 3-dimensional

  1. PROTOSTELLAR OUTFLOWS AND RADIATIVE FEEDBACK FROM MASSIVE STARS

    SciTech Connect

    Kuiper, Rolf; Yorke, Harold W.; Turner, Neal J. E-mail: Harold.W.Yorke@jpl.nasa.gov

    2015-02-20

    We carry out radiation hydrodynamical simulations of the formation of massive stars in the super-Eddington regime including both their radiative feedback and protostellar outflows. The calculations start from a prestellar core of dusty gas and continue until the star stops growing. The accretion ends when the remnants of the core are ejected, mostly by the force of the direct stellar radiation in the polar direction and elsewhere by the reradiated thermal infrared radiation. How long the accretion persists depends on whether the protostellar outflows are present. We set the mass outflow rate to 1% of the stellar sink particle's accretion rate. The outflows open a bipolar cavity extending to the core's outer edge, through which the thermal radiation readily escapes. The radiative flux is funneled into the polar directions while the core's collapse proceeds near the equator. The outflow thus extends the ''flashlight effect'', or anisotropic radiation field, found in previous studies from the few hundred AU scale of the circumstellar disk up to the 0.1 parsec scale of the core. The core's flashlight effect allows core gas to accrete on the disk for longer, in the same way that the disk's flashlight effect allows disk gas to accrete on the star for longer. Thus although the protostellar outflows remove material near the core's poles, causing slower stellar growth over the first few free-fall times, they also enable accretion to go on longer in our calculations. The outflows ultimately lead to stars of somewhat higher mass.

  2. Massive stars on the verge of exploding: the properties of oxygen sequence Wolf-Rayet stars

    NASA Astrophysics Data System (ADS)

    Tramper, F.; Straal, S. M.; Sanyal, D.; Sana, H.; de Koter, A.; Gräfener, G.; Langer, N.; Vink, J. S.; de Mink, S. E.; Kaper, L.

    2015-09-01

    Context. Oxygen sequence Wolf-Rayet (WO) stars are a very rare stage in the evolution of massive stars. Their spectra show strong emission lines of helium-burning products, in particular highly ionized carbon and oxygen. The properties of WO stars can be used to provide unique constraints on the (post-)helium burning evolution of massive stars, and their remaining lifetimes and the expected properties of their supernovae. Aims: We aim to homogeneously analyze the currently known presumed-single WO stars to obtain the key stellar and outflow properties and to constrain their evolutionary state. Methods: We use the line-blanketed non-local thermal equilibrium atmosphere code cmfgen to model the X-Shooter spectra of the WO stars and to deduce the atmospheric parameters. We calculate dedicated evolutionary models to determine the evolutionary state of the stars. Results: The WO stars have extremely high temperatures that range from 150 kK to 210 kK, and very low surface helium mass fractions that range from 44% down to 14%. Their properties can be reproduced by evolutionary models with helium zero-age main sequence masses of MHe,ini = 15-25 M⊙ that exhibit a fairly strong (a few times 10-5M⊙ yr-1), homogeneous (fc> 0.3) stellar wind. Conclusions: WO stars represent the final evolutionary stage of stars with estimated initial masses of Mini = 40-60 M⊙. They are post core-helium burning and predicted to explode as type Ic supernovae within a few thousand years. Based on observations obtained at the European Southern Observatory under program IDs 091.C-0934 and 093.D-0591.Appendices are available in electronic form at http://www.aanda.org

  3. Properties of massive stars in four clusters of the VVV survey

    NASA Astrophysics Data System (ADS)

    Hervé, A.; Martins, F.; Chené, A.-N.; Bouret, J.-C.; Borissova, J.

    2016-05-01

    The evolution of massive stars is only partly understood. Observational constraints can be obtained from the study of massive stars located in young massive clusters. The ESO Public Survey "VISTA Variables in the Vía Lácteá (VVV)" discovered several new clusters hosting massive stars. We present an analysis of massive stars in four of these new clusters. Our aim is to provide constraints on stellar evolution and to better understand the relation between different types of massive stars. We use the radiative transfer code CMFGEN to analyse K-band spectra of twelve stars with spectral types ranging from O and B to WN and WC. We derive the stellar parameters of all targets as well as surface abundances for a subset of them. In the Hertzsprung-Russell diagram, the Wolf-Rayet stars are more luminous or hotter than the O stars. From the log(C/N)-log(C/He) diagram, we show quantitatively that WN stars are more chemically evolved than O stars, WC stars being more evolved than WN stars. Mass loss rates among Wolf-Rayet stars are a factor of 10 larger than for O stars, in agreement with previous findings.

  4. The Hottest Horizontal-Branch Stars in Omega Centauri: Late Hot Flasher vs. Helium Enrichment

    NASA Technical Reports Server (NTRS)

    Moehler, S.; Dreizler, S.; Lanz, T.; Bono, G.; Sweigart, A V.; Calamida, A.; Monelli, M.; Nonino, M.

    2007-01-01

    UV observations of some massive globular clusters uncovered a significant population of very hot stars below the hot end of the horizontal branch (HB), the so-called blue hook stars. This feature might be explained either by the late hot flasher scenario here stars experience the helium flash while on the white dwarf cooling curve or by the helium-rich sub-population recently postulated to exist in some clusters. Spectroscopic analyses of blue hook stars in omega Cen and NGC 2808 support the late hot flasher scenario, but the stars contain much less helium than expected and the predicted C, N enrichment could not be verified from existing data. We want to determine effective temperatures, surface gravities and abundances of He, C, N in blue hook and canonical extreme horizontal branch (EHB) star candidates. Moderately high resolution spectra of stars at the hot end of the blue horizontal branch in the globular cluster omega Cen were analysed for atmospheric parameters (T(sub eff), log g) and abundances using LTE and Non-LTE model atmospheres. In the temperature range 30,000 K to 50,000 K we find that 37% of our stars are helium-poor (log nHe/nH less than -2), 49% have solar helium abundance within a factor of 3 (-1.5 less than or equal to log nHe/nH less than or equal to -0.5) and 14% are helium rich (log nHe/nH greater than -0.4). We also find carbon enrichment in step with helium enrichment, with a maximum carbon enrichment of 3% by mass. At least 30% of the hottest HB stars in omega Centauri show helium abundances well above the predictions from the helium enrichment scenario (Y = 0.42 corresponding to log nHe/nH approximately equal to -0.74). In addition the most helium-rich stars show strong carbon enrichment as predicted by the late hot flasher scenario. We conclude that the helium-rich HB stars in omega Cen cannot be explained solely by the helium-enrichment scenario invoked to explain the blue main sequence.

  5. Hadron-quark crossover and hot neutron stars at birth

    NASA Astrophysics Data System (ADS)

    Masuda, Kota; Hatsuda, Tetsuo; Takatsuka, Tatsuyuki

    2016-02-01

    We construct a new isentropic equation of state (EOS) at finite temperature, "Rover," on the basis of the hadron-quark crossover at high density. By using the new EOS, we study the structure of hot neutron stars at birth with typical lepton fraction (Y_l=0.3-0.4) and typical entropy per baryon (hat {S}=1{-}2). Due to the gradual appearance of quark degrees of freedom at high density, the temperature T and the baryon density ρ at the center of hot neutron stars with hadron-quark crossover are found to be smaller than those without the crossover by a factor of two or more. Typical energy release due to the contraction of a hot neutron star to a cold neutron star with mass M=1.4 M_{⊙} is shown to be about 0.04 M_{⊙}, with a spin-up rate of about 14%.

  6. Observations of hot stars and eclipsing binaries with FRESIP

    NASA Technical Reports Server (NTRS)

    Gies, Douglas R.

    1994-01-01

    The FRESIP project offers an unprecedented opportunity to study pulsations in hot stars (which vary on time scales of a day) over a several year period. The photometric data will determine what frequencies are present, how or if the amplitudes change with time, and whether there is a connection between pulsation and mass loss episodes. It would initiate a new field of asteroseismology studies of hot star interiors. A search should be made for selected hot stars for inclusion in the list of project targets. Many of the primary solar mass targets will be eclipsing binaries, and I present estimates of their frequency and typical light curves. The photometric data combined with follow up spectroscopy and interferometric observations will provide fundamental data on these stars. The data will provide definitive information on the mass ratio distribution of solar-mass binaries (including the incidence of brown dwarf companions) and on the incidence of planets in binary systems.

  7. Intermediate Luminosity Transients: their connection to Massive Stars, Episodic Mass Loss, and Supernovae

    NASA Astrophysics Data System (ADS)

    Prieto, Jose

    2013-06-01

    I will discuss a growing class of optical transients with typical peak luminosities between novae and supernovae. I will present their observational properties and their links to evolved massive stars, including the full range from massive AGB stars (8-10 Mo) to the most massive stars (> 100 Mo) like Eta Carinae. I will put their observational properties in the context of propsed physical mechanisms, including episodic mass-loss events, stellar mergers, and supernovae.

  8. Hot Subdwarf Stars and the ZAHeMS

    NASA Astrophysics Data System (ADS)

    Brown, D.

    2014-04-01

    The precise evolutionary mechanism for the production of hot subdwarf stars remains unsolved, though there are many plausible explanations. One general group of hypotheses proposes that sdB/EHB stars are the result of various processes typical of their single-star progeny, quite possibly very much affected by chemical environment and stellar wind mass loss. An alternative set of hypothesis proposes that such hot subdwarf/EHB objects are the result of binary interactions. Following the methodology of Han et al. (2002, 2003) in their binary population synthesis study of the evolutionary channels of sdB stars in the Galactic field for Z=0.02, this study has conducted a binary population synthesis investigation at various metallicities in order to examine the production of hot subwarf stars in different environments. Although it is found that metallicity is not a major factor in the production of such helium burning stars, there are a number of second-order effects. Results yield some hot subdwarf stars placed in areas below the ZAHeMS (in the log10g,log10 Teff diagram) which could give some information on the production of low-mass sdBs.

  9. Massive Star Formation in a Gravitationally-Lensed H II Galaxy at z = 3.357

    SciTech Connect

    Villar-Martin, M; Stern, D; Hook, R N; Rosati, P; Lombardi, M; Humphrey, A; Fosbury, R; Stanford, S A; Holden, B P

    2004-03-02

    The Lynx arc, with a redshift of 3.357, was discovered during spectroscopic follow-up of the z = 0.570 cluster RX J0848+4456 from the ROSAT Deep Cluster Survey. The arc is characterized by a very red R - K color and strong, narrow emission lines. Analysis of HST WFPC 2 imaging and Keck optical and infrared spectroscopy shows that the arc is an H II galaxy magnified by a factor of {approx} 10 by a complex cluster environment. The high intrinsic luminosity, the emission line spectrum, the absorption components seen in Ly{alpha} and C IV, and the restframe ultraviolet continuum are all consistent with a simple H II region model containing {approx} 10{sup 6} hot O stars. The best fit parameters for this model imply a very hot ionizing continuum (T{sub BB} {approx} 80, 000 K), high ionization parameter (log U {approx} -1), and low nebular metallicity (Z/Z{sub {circle_dot}} {approx} 0.05). The narrowness of the emission lines requires a low mass-to-light ratio for the ionizing stars, suggestive of an extremely low metallicity stellar cluster. The apparent overabundance of silicon in the nebula could indicate enrichment by past pair instability supernovae, requiring stars more massive than {approx}140M{sub {circle_dot}}.

  10. Dynamic Star Formation in the Massive DR21 Filament

    SciTech Connect

    Schneider, N.; Csengeri, T.; Bontemps, S.; Motte, F.; Simon, R.; Hennebelle, P.; Federrath, C.; Klessen, R.; /ZAH, Heidelberg /KIPAC, Menlo Park

    2010-08-25

    The formation of massive stars is a highly complex process in which it is unclear whether the star-forming gas is in global gravitational collapse or an equilibrium state supported by turbulence and/or magnetic fields. By studying one of the most massive and dense star-forming regions in the Galaxy at a distance of less than 3 kpc, i.e. the filament containing the well-known sources DR21 and DR21(OH), we attempt to obtain observational evidence to help us to discriminate between these two views. We use molecular line data from our {sup 13}CO 1 {yields} 0, CS 2 {yields} 1, and N{sub 2}H{sup +} 1 {yields} 0 survey of the Cygnus X region obtained with the FCRAO and CO, CS, HCO{sup +}, N{sub 2}H{sup +}, and H{sub 2}CO data obtained with the IRAM 30m telescope. We observe a complex velocity field and velocity dispersion in the DR21 filament in which regions of the highest column-density, i.e., dense cores, have a lower velocity dispersion than the surrounding gas and velocity gradients that are not (only) due to rotation. Infall signatures in optically thick line profiles of HCO{sup +} and {sup 12}CO are observed along and across the whole DR21 filament. By modelling the observed spectra, we obtain a typical infall speed of {approx}0.6 km s{sup -1} and mass accretion rates of the order of a few 10{sup -3} M{sub {circle_dot}} yr{sup -1} for the two main clumps constituting the filament. These massive clumps (4900 and 3300 M{sub {circle_dot}} at densities of around 10{sup 5} cm{sup -3} within 1 pc diameter) are both gravitationally contracting. The more massive of the clumps, DR21(OH), is connected to a sub-filament, apparently 'falling' onto the clump. This filament runs parallel to the magnetic field. Conclusions. All observed kinematic features in the DR21 filament (velocity field, velocity dispersion, and infall), its filamentary morphology, and the existence of (a) sub-filament(s) can be explained if the DR21 filament was formed by the convergence of flows on large

  11. The evolution of galaxy star formation activity in massive haloes

    NASA Astrophysics Data System (ADS)

    Popesso, P.; Biviano, A.; Finoguenov, A.; Wilman, D.; Salvato, M.; Magnelli, B.; Gruppioni, C.; Pozzi, F.; Rodighiero, G.; Ziparo, F.; Berta, S.; Elbaz, D.; Dickinson, M.; Lutz, D.; Altieri, B.; Aussel, H.; Cimatti, A.; Fadda, D.; Ilbert, O.; Le Floch, E.; Nordon, R.; Poglitsch, A.; Xu, C. K.

    2015-02-01

    Context. There is now a large consensus that the current epoch of the cosmic star formation history (CSFH) is dominated by low mass galaxies while the most active phase, between redshifts 1 and 2, is dominated by more massive galaxies, which evolve more quickly. Aims: Massive galaxies tend to inhabit very massive haloes, such as galaxy groups and clusters. We aim to understand whether the observed "galaxy downsizing" could be interpreted as a "halo downsizing", whereas the most massive haloes, and their galaxy populations, evolve more rapidly than the haloes with lower mass. Methods: We studied the contribution to the CSFH of galaxies inhabiting group-sized haloes. This is done through the study of the evolution of the infra-red (IR) luminosity function of group galaxies from redshift 0 to redshift ~1.6. We used a sample of 39 X-ray-selected groups in the Extended Chandra Deep Field South (ECDFS), the Chandra Deep Field North (CDFN), and the COSMOS field, where the deepest available mid- and far-IR surveys have been conducted with Spitzer MIPS and with the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel satellite. Results: Groups at low redshift lack the brightest, rarest, and most star forming IR-emitting galaxies observed in the field. Their IR-emitting galaxies contribute ≤10% of the comoving volume density of the whole IR galaxy population in the local Universe. At redshift ≳1, the most IR-luminous galaxies (LIRGs and ULIRGs) are mainly located in groups, and this is consistent with a reversal of the star formation rate (SFR) vs. density anti-correlation observed in the nearby Universe. At these redshifts, group galaxies contribute 60-80% of the CSFH, i.e. much more than at lower redshifts. Below z ~ 1, the comoving number and SFR densities of IR-emitting galaxies in groups decline significantly faster than those of all IR-emitting galaxies. Conclusions: Our results are consistent with a "halo downsizing" scenario and highlight the

  12. Combining magnetic and seismic studies to constrain processes in massive stars

    NASA Astrophysics Data System (ADS)

    Neiner, Coralie; Degroote, Pieter; Coste, Blanche; Briquet, Maryline; Mathis, Stéphane

    2014-08-01

    The presence of pulsations influences the local parameters at the surface of massive stars and thus it modifies the Zeeman magnetic signatures. Therefore it makes the characterisation of a magnetic field in pulsating stars more difficult and the characterisation of pulsations is thus required for the study of magnetic massive stars. Conversely, the presence of a magnetic field can inhibit differential rotation and mixing in massive stars and thus provides important constraints for seismic modelling based on pulsation studies. As a consequence, it is necessary to combine spectropolarimetric and seismic studies for all massive classical pulsators. Below we show examples of such combined studies and the interplay between physical processes.

  13. The role of low-mass star clusters in forming the massive stars in DR 21

    NASA Astrophysics Data System (ADS)

    Rivilla, V. M.; Jiménez-Serra, I.; Martín-Pintado, J.; Sanz-Forcada, J.

    2014-01-01

    We have studied the young low-mass pre-main sequence (PMS) stellar population associated with the massive star-forming region DR 21 by using archival X-ray Chandra observations and by complementing them with existing optical and infrared (IR) surveys. The Chandra observations have revealed for the first time a new highly extincted population of PMS low-mass stars previously missed in observations at other wavelengths. The X-ray population exhibits three main stellar density peaks, coincident with the massive star-forming regions, being the DR 21 core the main peak. The cross-correlated X-ray/IR sample exhibits a radial `Spokes-like' stellar filamentary structure that extends from the DR 21 core towards the northeast. The near-IR data reveal a centrally peaked structure for the extinction, which exhibits its maximum in the DR 21 core and gradually decreases with the distance to the N-S cloud axis and to the cluster centre. We find evidence of a global mass segregation in the full low-mass stellar cluster, and of a stellar age segregation, with the youngest stars still embedded in the N-S cloud, and more evolved stars more spatially distributed. The results are consistent with the scenario where an elongated overall potential well created by the full low-mass stellar cluster funnels gas through filaments feeding stellar formation. Besides the full gravitational well, smaller scale local potential wells created by dense stellar sub-clusters of low-mass stars are privileged in the competition for the gas of the common reservoir, allowing the formation of massive stars. We also discuss the possibility that a stellar collision in the very dense stellar cluster revealed by Chandra in the DR 21 core is the origin of the large-scale and highly energetic outflow arising from this region.

  14. Massive Star Formation at Millimeter and Submillimeter Wavelengths

    NASA Astrophysics Data System (ADS)

    Su, Yu-Nung

    2004-06-01

    This dissertation investigates massive star formation in the Milky Way via millimeter and submillimeter observations of luminous young stellar objects. First, I describe a snapshot continuum and multi-molecular-line survey with the BIMA array aimed at characterizing very young high-mass stars. The target sample consists of eleven luminous IRAS sources associated with very young ultracompact (UC) HII regions, which have weak cm-wave flux densities and very compact angular sizes despite their small (kinematic) distances. In this way, I hope to preferentially select and study extremely young high-mass stars. Most of the 3 millimeter continuum emission shows multiple components, which is consistent with the picture of a clustered formation mode of massive stars. I identify five 3 mm dust sources as good candidates for high-mass protostars because they are coincident in position with their luminous IRAS counterparts and dense molecular gas as traced by H13CO+ emission, yet not detected at 3.6 cm. The typical dust and gas mass of the 3 mm components is a few tens M_sun, while the 3 mm components with centimeter counterparts are ~5 times less massive than those not associated with centimeter continuum, suggesting that some 3 mm sources with centimeter counterparts may relate to very young intermediate-mass stars. On the other hand, due to the relatively weak centimeter luminosity of a few mJy kpc^2, some target centimeter continuum sources could correspond to stellar winds/jets rather than real HII . Furthermore, I present near-IR photometry of the target compact centimeter sources obtained from the new released Two Micron All Sky Survey archival data. Second, I present millimeter observations with the BIMA array of the bipolar molecular outflows associated with the luminous far-IR sources IRAS 21519+5613 and IRAS 22506+5944. Although outflows have been identified as a common occurrence in the formation of both high-and low-mass stars, only about ten molecular outflows

  15. JET FORMATION FROM MASSIVE YOUNG STARS: MAGNETOHYDRODYNAMICS VERSUS RADIATION PRESSURE

    SciTech Connect

    Vaidya, Bhargav; Porth, Oliver; Fendt, Christian; Beuther, Henrik E-mail: fendt@mpia.de

    2011-11-20

    Observations indicate that outflows from massive young stars are more collimated during their early evolution compared to later stages. Our paper investigates various physical processes that impact the outflow dynamics, i.e., its acceleration and collimation. We perform axisymmetric magnetohydrodynamic (MHD) simulations particularly considering the radiation pressure exerted by the star and the disk. We have modified the PLUTO code to include radiative forces in the line-driving approximation. We launch the outflow from the innermost disk region (r < 50 AU) by magnetocentrifugal acceleration. In order to disentangle MHD effects from radiative forces, we start the simulation in pure MHD and later switch on the radiation force. We perform a parameter study considering different stellar masses (thus luminosity), magnetic flux, and line-force strength. For our reference simulation-assuming a 30 M{sub Sun} star-we find substantial de-collimation of 35% due to radiation forces. The opening angle increases from 20 Degree-Sign to 32 Degree-Sign for stellar masses from 20 M{sub Sun} to 60 M{sub Sun }. A small change in the line-force parameter {alpha} from 0.60 to 0.55 changes the opening angle by {approx}8 Degree-Sign . We find that it is mainly the stellar radiation that affects the jet dynamics. Unless the disk extends very close to the star, its force is too small to have much impact. Essentially, our parameter runs with different stellar masses can be understood as a proxy for the time evolution of the star-outflow system. Thus, we have shown that when the stellar mass (thus luminosity) increases with age, the outflows become less collimated.

  16. The chemical composition of Galactic ring nebulae around massive stars

    NASA Astrophysics Data System (ADS)

    Esteban, C.; Mesa-Delgado, A.; Morisset, C.; García-Rojas, J.

    2016-08-01

    We present deep spectra of ring nebulae associated with Wolf-Rayet (WR) and O-type stars: NGC 6888, G2.4+1.4, RCW 58, S 308, NGC 7635 and RCW 52. The data have been taken with the 10m Gran Telescopio Canarias and the 6.5m Clay Telescope. We extract spectra of several apertures in some of the objects. We derive C$^{++}$ and O$^{++}$ abundances from faint recombination lines in NGC 6888 and NGC 7635, permitting to derive their C/H and C/O ratios and estimate the abundance discrepancy factor (ADF) of O$^{++}$. The ADFs are larger than the typical ones of normal HII regions but similar to those found in the ionised gas of star-forming dwarf galaxies. We find that chemical abundances are rather homogeneous in the nebulae where we have spectra of several apertures: NGC 6888, NGC 7635 and G2.4+1.4. We obtain very high values of electron temperature in a peripheral zone of NGC 6888, finding that shock excitation can reproduce its spectral properties. We find that all the objects associated with WR stars show N enrichment. Some of them also show He enrichment and O deficiency as well as a lower Ne/O than expected, this may indicate the strong action of the ON and NeNa cycles. We have compared the chemical composition of NGC 6888, G2.4+1.4, RCW 58 and S 308 with the nucleosynthesis predicted by stellar evolution models of massive stars. We find that non-rotational models of stars of initial masses between 25 and 40 solar masses seem to reproduce the observed abundance ratios of most of the nebulae.

  17. The chemical composition of Galactic ring nebulae around massive stars

    NASA Astrophysics Data System (ADS)

    Esteban, C.; Mesa-Delgado, A.; Morisset, C.; García-Rojas, J.

    2016-08-01

    We present deep spectra of ring nebulae associated with Wolf-Rayet (WR) and O-type stars: NGC 6888, G2.4+1.4, RCW 58, S 308, NGC 7635 and RCW 52. The data have been taken with the 10m Gran Telescopio Canarias and the 6.5m Clay Telescope. We extract spectra of several apertures in some of the objects. We derive C2+ and O2+ abundances from faint recombination lines in NGC 6888 and NGC 7635, permitting to derive their C/H and C/O ratios and estimate the abundance discrepancy factor (ADF) of O2+. The ADFs are larger than the typical ones of normal H II regions but similar to those found in the ionized gas of star-forming dwarf galaxies. We find that chemical abundances are rather homogeneous in the nebulae where we have spectra of several apertures: NGC 6888, NGC 7635 and G2.4+1.4. We obtain very high values of electron temperature in a peripheral zone of NGC 6888, finding that shock excitation can reproduce its spectral properties. We find that all the objects associated with WR stars show N enrichment. Some of them also show He enrichment and O deficiency as well as a lower Ne/O than expected, this may indicate the strong action of the ON and NeNa cycles. We have compared the chemical composition of NGC 6888, G2.4+1.4, RCW 58 and S 308 with the nucleosynthesis predicted by stellar evolution models of massive stars. We find that non-rotational models of stars of initial masses between 25 and 40 M⊙ seem to reproduce the observed abundance ratios of most of the nebulae.

  18. How Very Massive Metal-Free Stars Start Cosmological Reionization

    NASA Technical Reports Server (NTRS)

    Wise, John H.; Abel, Tom

    2008-01-01

    The initial conditions and relevant physics for the formation of the earliest galaxies are well specified in the concordance cosmology. Using ab initio cosmological Eulerian adaptive mesh refinement radiation hydrodynamical calculations, we discuss how very massive stars start the process of cosmological reionization. The models include nonequilibrium primordial gas chemistry and cooling processes and accurate radiation transport in the case B approximation using adaptively ray-traced photon packages, retaining the time derivative in the transport equation. Supernova feedback is modeled by thermal explosions triggered at parsec scales. All calculations resolve the local Jeans length by at least 16 grid cells at all times and as such cover a spatial dynamic range of approx.10(exp 6). These first sources of reionization are highly intermittent and anisotropic and first photoionize the small-scale voids surrounding the halos they form in, rather than the dense filaments they are embedded in. As the merging objects form larger, dwarf-sized galaxies, the escape fraction of UV radiation decreases and the H II regions only break out on some sides of the galaxies, making them even more anisotropic. In three cases, SN blast waves induce star formation in overdense regions that were formed earlier from ionization front instabilities. These stars form tens of parsecs away from the center of their parent DM halo. Approximately five ionizing photons are needed per sustained ionization when star formation in 10(exp 6) stellar Mass halos is dominant in the calculation. As the halos become larger than approx.10(exp 7) Stellar Mass, the ionizing photon escape fraction decreases, which in turn increases the number of photons per ionization to 15-50, in calculations with stellar feedback only. Radiative feedback decreases clumping factors by 25% when compared to simulations without star formation and increases the average temperature of ionized gas to values between 3000 and 10,000 K.

  19. Imprints of recoiling massive black holes on the hot gas of early-type galaxies

    NASA Astrophysics Data System (ADS)

    Devecchi, B.; Rasia, E.; Dotti, M.; Volonteri, M.; Colpi, M.

    2009-04-01

    Anisotropic gravitational radiation from a coalescing black hole (BH) binary is known to impart recoil velocities of up to ~1000kms-1 to the remnant BH. In this context, we study the motion of a recoiling BH inside a galaxy modelled as a Hernquist sphere, and the signature that the hole imprints on the hot gas, using N-body/smoothed particle hydrodynamics simulations. Ejection of the BH results in a sudden expansion of the gas ending with the formation of a gaseous core, similarly to what is seen for the stars. A cometary tail of particles bound to the BH is initially released along its trail. As the BH moves on a return orbit, a nearly spherical swarm of hot gaseous particles forms at every apocentre: this feature can live up to ~108 years. If the recoil velocity exceeds the sound speed initially, the BH shocks the gas in the form of a Mach cone in density near each supersonic pericentric passage. We find that the X-ray fingerprint of a recoiling BH can be detected in Chandra X-ray maps out to a distance of Virgo. For exceptionally massive BHs, the Mach cone and the wakes can be observed out to a few hundred of milliparsec. The detection of the Mach cone is of twofold importance as it can be a probe of high-velocity recoils, and an assessment of the scatter of the MBH - Mbulge relation at large BH masses.

  20. Massive star formation within the Leo 'primordial' ring.

    PubMed

    Thilker, David A; Donovan, Jennifer; Schiminovich, David; Bianchi, Luciana; Boissier, Samuel; de Paz, Armando Gil; Madore, Barry F; Martin, D Christopher; Seibert, Mark

    2009-02-19

    Few intergalactic, plausibly primordial clouds of neutral atomic hydrogen (H(i)) have been found in the local Universe, suggesting that such structures have either dispersed, become ionized or produced a stellar population on gigayear timescales. The Leo ring, a massive (M(H(i)) approximately 1.8 x 10(9)M[symbol: see text], M[symbol: see text] denoting the solar mass), 200-kpc-wide structure orbiting the galaxies M105 and NGC 3384 with a 4-Gyr period, is a candidate primordial cloud. Despite repeated atttempts, it has previously been seen only from H i emission, suggesting the absence of a stellar population. Here we report the detection of ultraviolet light from gaseous substructures of the Leo ring, which we attribute to recent massive star formation. The ultraviolet colour of the detected complexes is blue, implying the onset of a burst of star formation or continuous star formation of moderate (approximately 10(8)-yr) duration. Measured ultraviolet-visible photometry favours models with low metallicity (Z approximately Z[symbol: see text]/50-Z[symbol: see text]/5, Z[symbol: see text] denoting the solar metallicity), that is, a low proportion of elements heavier than helium, although spectroscopic confirmation is needed. We speculate that the complexes are dwarf galaxies observed during their formation, but distinguished by their lack of a dark matter component. In this regard, they resemble tidal dwarf galaxies, although without the enrichment preceding tidal stripping. If structures like the Leo ring were common in the early Universe, they may have produced a large, yet undetected, population of faint, metal-poor, halo-lacking dwarf galaxies. PMID:19225520

  1. Massive Young Star Clusters in M33: Stochastic Star Formation Ruled Out

    NASA Astrophysics Data System (ADS)

    González-Lópezlira, R. A.; Pflamm-Altenburg, J.; Kroupa, P.

    2014-09-01

    It is widely accepted that the distribution function of the masses of young star clusters is universal and can be purely interpreted as a probability density distribution function with a constant upper mass limit. As a result of this picture, the masses of the most massive objects would be exclusively determined by the size of the sample. Conversely we show, with very high confidence, that the masses of the most massive young (< 10 Myr) star clusters in the flocculent galaxy M33 decrease with increasing galactocentric radius, in contradiction with a constant shape and upper mass limit of the cluster mass function. Moreover, by comparing the radial distributions of gas surface densities and highest cluster masses, we find that M_{max} ∝ Σ_{gas, total}^{3.8 ± 0.3}, M_{max} ∝ Σ_{H_2}^{1.2± 0.1} and M_{max} ∝ Σ_{SFR}^{0.9 ± 0.1}. Hence, in M33 we can rule out stochastic star formation. The change of the maximum cluster mass there must be due to physical causes, i.e., very massive star clusters may require special physical conditions, like high gas surface densities, in order to form.

  2. The Very Massive Star Content of the Nuclear Star Clusters in NGC 5253

    NASA Astrophysics Data System (ADS)

    Smith, L. J.; Crowther, P. A.; Calzetti, D.; Sidoli, F.

    2016-05-01

    The blue compact dwarf galaxy NGC 5253 hosts a very young starburst containing twin nuclear star clusters, separated by a projected distance of 5 pc. One cluster (#5) coincides with the peak of the Hα emission and the other (#11) with a massive ultracompact H ii region. A recent analysis of these clusters shows that they have a photometric age of 1 ± 1 Myr, in apparent contradiction with the age of 3–5 Myr inferred from the presence of Wolf-Rayet features in the cluster #5 spectrum. We examine Hubble Space Telescope ultraviolet and Very Large Telescope optical spectroscopy of #5 and show that the stellar features arise from very massive stars (VMSs), with masses greater than 100 M ⊙, at an age of 1–2 Myr. We further show that the very high ionizing flux from the nuclear clusters can only be explained if VMSs are present. We investigate the origin of the observed nitrogen enrichment in the circumcluster ionized gas and find that the excess N can be produced by massive rotating stars within the first 1 Myr. We find similarities between the NGC 5253 cluster spectrum and those of metal-poor, high-redshift galaxies. We discuss the presence of VMSs in young, star-forming galaxies at high redshift; these should be detected in rest-frame UV spectra to be obtained with the James Webb Space Telescope. We emphasize that population synthesis models with upper mass cutoffs greater than 100 M ⊙ are crucial for future studies of young massive star clusters at all redshifts.

  3. A Hot and Massive Accretion Disk around the High-mass Protostar IRAS 20126+4104

    NASA Astrophysics Data System (ADS)

    Chen, Huei-Ru Vivien; Keto, Eric; Zhang, Qizhou; Sridharan, T. K.; Liu, Sheng-Yuan; Su, Yu-Nung

    2016-06-01

    We present new spectral line observations of the CH3CN molecule in the accretion disk around the massive protostar IRAS 20126+4104 with the Submillimeter Array, which, for the first time, measure the disk density, temperature, and rotational velocity with sufficient resolution (0.″37, equivalent to ∼600 au) to assess the gravitational stability of the disk through the Toomre-Q parameter. Our observations resolve the central 2000 au region that shows steeper velocity gradients with increasing upper state energy, indicating an increase in the rotational velocity of the hotter gas nearer the star. Such spin-up motions are characteristics of an accretion flow in a rotationally supported disk. We compare the observed data with synthetic image cubes produced by three-dimensional radiative transfer models describing a thin flared disk in Keplerian motion enveloped within the centrifugal radius of an angular-momentum-conserving accretion flow. Given a luminosity of 1.3 × 104 L ⊙, the optimized model gives a disk mass of 1.5 M ⊙ and a radius of 858 au rotating about a 12.0 M ⊙ protostar with a disk mass accretion rate of 3.9 × 10‑5 M ⊙ yr‑1. Our study finds that, in contrast to some theoretical expectations, the disk is hot and stable to fragmentation with Q > 2.8 at all radii which permits a smooth accretion flow. These results put forward the first constraints on gravitational instabilities in massive protostellar disks, which are closely connected to the formation of companion stars and planetary systems by fragmentation.

  4. Gravity as main driver of non-thermal motions in massive star forming regions

    NASA Astrophysics Data System (ADS)

    Traficante, A.; Fuller, G. A.; Smith, R.; Billot, N.; Duarte-Cabral, A.; Peretto, N.; Molinari, S.; Pineda, J. E.

    2016-05-01

    The origin of the observed non-thermal motions in massive star forming regions is still unclear. These motions can originate from local turbulence or from self-gravity and the two scenarios lead to two different star formation mechanisms. The recent findings of Heyer et al. ([5]) have supported self-gravity as main driver of the non-thermal motions, although without a clear interpretation of the results. In this contribution we introduce a new formalism to describe the relation between gravity and kinetic motion in massive star formation. We show that the Heyer findings are a particular result of this description and have a direct physical interpretation. We applied this formalism to different surveys of massive star forming regions covering all spatial scales from giant molecular clouds down to massive cores, including new data from massive candidate starless clumps. The results presented in this contribution strongly support a chaotic, gravitationally driven global collapse scenario as massive star formation mechanism.

  5. Resolved photometry of extragalactic young massive star clusters

    NASA Astrophysics Data System (ADS)

    Larsen, S. S.; de Mink, S. E.; Eldridge, J. J.; Langer, N.; Bastian, N.; Seth, A.; Smith, L. J.; Brodie, J.; Efremov, Yu. N.

    2011-08-01

    Aims: We present colour-magnitude diagrams (CMDs) of young massive star clusters in several galaxies located well beyond the Local Group. The richness of these clusters allows us to obtain large samples of post-main sequence stars and test how well the observed CMDs are reproduced by canonical stellar isochrones. Methods: We use imaging of seven clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC 7793 obtained with the Advanced Camera for Surveys on board the Hubble Space Telescope and carry out PSF-fitting photometry of individual stars in the clusters. The clusters have ages in the range ~(5-50) × 106 years and masses of ~105 M⊙-106 M⊙. Although crowding prevents us from obtaining photometry in the inner regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. Results: In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergiants from the main sequence complicates this comparison. In several cases we observe a large spread (1-2 mag) in the luminosities of the supergiant stars that cannot be accounted for by observational errors. We find that this spread can be reproduced by including an age spread of ~(10-30) × 106 years in the models. However, age spreads cannot fully account for the observed morphology of the CMDs and other processes, such as the evolution of interacting binary stars, may also play a role. Conclusions: Colour-magnitude diagrams can be successfully obtained for massive star

  6. Quasi-stars: accreting black holes inside massive envelopes

    NASA Astrophysics Data System (ADS)

    Begelman, Mitchell C.; Rossi, Elena M.; Armitage, Philip J.

    2008-07-01

    We study the structure and evolution of `quasi-stars', accreting black holes embedded within massive hydrostatic gaseous envelopes. These configurations may model the early growth of supermassive black hole seeds. The accretion rate on to the black hole adjusts so that the luminosity carried by the convective envelope equals the Eddington limit for the total mass, M* + MBH ~ M*. This greatly exceeds the Eddington limit for the black hole mass alone, leading to rapid growth of the black hole. We use analytic models and numerical stellar structure calculations to study the structure and evolution of quasi-stars. We show that the photospheric temperature of the envelope scales as Tph ~ M-2/5BHM7/20*, and decreases with time while the black hole mass increases. Once Tph < 104 K, the photospheric opacity drops precipitously and Tph hits a limiting value, analogous to the Hayashi track for red giants and protostars, below which no hydrostatic solution for the convective envelope exists. For metal-free (Population III) opacities, this limiting temperature is approximately 4000 K. After a quasi-star reaches this limiting temperature, it is rapidly dispersed by radiation pressure. We find that black hole seeds with masses between 103 and 104Msolar could form via this mechanism in less than a few Myr.

  7. Evolution and Nucleosynthesis in Massive Stars of Zero Metallicity

    NASA Astrophysics Data System (ADS)

    Heger, Alexander; Woosley, Stan E.; Waters, Richard

    We follow the evolution of rotating, zero metallicity stars in the mass range 15-250 M_⊙ from the zero-age main sequence to core collapse. Detailed nucleosynthesis is computed using a 199 isotope network complete up to germanium. In addition to the expected overabundance of alpha-isotopes in the final yields (compared to similar mass stars of solar metallicity), we find evidence for the production of primary 14 N. Stars more massive than ≳ 100 M_⊙ on the main sequence will encounter the electron-positron pair instability following helium burning. For currently favored values of nuclear cross sections and convection algorithm, we determine critical helium core masses for pulsational pair instability, prompt Explosion, or prompt block hole formation of 45, 65, and 140 M_⊙ respectively. Towards the upper end of the mass range that explodes, very large quantities of 56 Ni are produced and the explosion should be extremely bright. The high mass models that wake black holes might be potential progenitors of gamma-ray bursts (GRB) of enormous energy.

  8. OT1_tgull_3: The Homunculus: Clues to Massive Ejection from the Most Massive Stars

    NASA Astrophysics Data System (ADS)

    Gull, T.

    2010-07-01

    Eta Carinae is a lynchpin between mass ejection by highly evolved massive stars and the enriched ISM. The Homunculus, a very dusty, neutral bipolar shell ejected in the 1840s, is known to contain at least 12 solar masses, based upon gas/dust=100. But this ejecta is very N-rich with C and O being 0.02 that of solar abundance. What dust formed and how much total mass was ejected? Our ultimate goal is to obtain the total ejected mass. We propose to obtain full spectral scans of the Homunculus with PACS and SPIRES and selected scans with HIFI. We will use these spectra to identify molecules and atomic species associated with this C- and O-depleted gas. While most of this depletion is due to CNO processing and conduction in stars > 60 solar masses, additional depletion is likely due to the first molecules and dust formed at high temperatures during the 1840s eruption. In line of sight we see overabundances of metals not ordinarily seen in the ISM: Sr, Sc, V. These metals have been trapped in atomic state due to limited O and C being available to form molecules. Yet dust has still formed. But what kind of dust? Through existing HST/STIS and VLT/UVES spectra combined with the proposed Herschel spectra and detailed modeling, we will gain much better insight on how molecules and dust can formed in depleted C,O conditions, and in turn provide an improved estimate of the total mass loss. Implications from this study apply to the first massive stars and the earliest dust in the Universe.

  9. The Blob, the Very Rare Massive Star and the Two Populations

    NASA Astrophysics Data System (ADS)

    2005-04-01

    The nebula N214 [1] is a large region of gas and dust located in a remote part of our neighbouring galaxy, the Large Magellanic Cloud. N214 is a quite remarkable site where massive stars are forming. In particular, its main component, N214C (also named NGC 2103 or DEM 293), is of special interest since it hosts a very rare massive star, known as Sk-71 51 [2] and belonging to a peculiar class with only a dozen known members in the whole sky. N214C thus provides an excellent opportunity for studying the formation site of such stars. Using ESO's 3.5-m New Technology telescope (NTT) located at La Silla (Chile) and the SuSI2 and EMMI instruments, astronomers from France and the USA [3] studied in great depth this unusual region by taking the highest resolution images so far as well as a series of spectra of the most prominent objects present. N214C is a complex of ionised hot gas, a so-called H II region [4], spreading over 170 by 125 light-years (see ESO PR Photo 12b/05). At the centre of the nebula lies Sk-71 51, the region's brightest and hottest star. At a distance of ~12 light-years north of Sk-71 51 runs a long arc of highly compressed gas created by the strong stellar wind of the star. There are a dozen less bright stars scattered across the nebula and mainly around Sk-71 51. Moreover, several fine, filamentary structures and fine pillars are visible. The green colour in the composite image, which covers the bulk of the N214C region, comes from doubly ionised oxygen atoms [5] and indicates that the nebula must be extremely hot over a very large extent. The Star Sk-71 51 decomposed ESO PR Photo 12c/05 ESO PR Photo 12c/05 The Cluster Around Sk-71 51 [Preview - JPEG: 400 x 620 pix - 189k] [Normal - JPEG: 800 x 1239 pix - 528k] Caption: ESO PR Photo 12c/05 shows a small field around the hot star Sk-71 51 as seen through the V filter. The left image shows a single frame after subtraction of the nebular background. The image quality - or seeing - is roughly 8.5 pixels

  10. COLLAPSE OF MOLECULAR CLOUD CORES WITH RADIATION TRANSFER: FORMATION OF MASSIVE STARS BY ACCRETION

    SciTech Connect

    Sigalotti, Leonardo Di G.; Daza-Montero, Judith; De Felice, Fernando

    2009-12-20

    Most early radiative transfer calculations of protostellar collapse have suggested an upper limit of approx40 M{sub sun} for the final stellar mass before radiation pressure can exceed the star's gravitational pull and halt the accretion. Here we perform further collapse calculations, using frequency-dependent radiation transfer coupled to a frequency-dependent dust model that includes amorphous carbon particles, silicates, and ice-coated silicates. The models start from pressure-bounded, logatropic spheres of mass between 5 M{sub sun} and 150 M{sub sun} with an initial nonsingular density profile. We find that in a logatrope the infall is never reversed by the radiative forces on the dust and that stars with masses approx>100 M{sub sun} may form by continued accretion. Compared to previous models that start the collapse with a rho propor to r{sup -2} density configuration, our calculations result in higher accretion times and lower average accretion rates with peak values of approx5.8 x 10{sup -5} M{sub sun} yr{sup -1}. The radii and bolometric luminosities of the produced massive stars (approx>90 M{sub sun}) are in good agreement with the figures reported for detected stars with initial masses in excess of 100 M{sub sun}. The spectral energy distribution from the stellar photosphere reproduces the observed fluxes for hot molecular cores with peaks of emission from mid- to near-infrared.