bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiperiodicity in semiregular variables
Authors: Kiss L.L. , Szatmáry K.
Published: July 2016

We present a detailed period analysis for 98 red semiregular variables by means of Fourier and wavelet analysis of long-term visual observations carried out by amateur astronomers. The overwhelming majority of the studied stars show multiperiodic behaviour. We found two significant periods in 62 variables, while there are definite signs of three periods in 13 stars. 20 stars turned out to be monoperiodic with small instabilities in the period. Since this study deals with the general trends, we want to find only the most dominant periods.

The distribution of periods and period ratios is examined in the (log P1, log P0/P1) plots. Three significant and two less obvious sequences are present which can be explained as the straight consequence of different pulsational modes. This hypothesis is supported by the multiperiodic variables with three periods. A clear distinction between C-rich and O-rich stars has been found in these diagrams suggesting a connection between the chemistry and pulsational characteristics.
Fifteen Years of High Angular Resolution Studies of Mira's Atmosphere
Authors: Karovska Margarita
Published: July 2016

I describe here results from high-angular resolution imaging studies of o Ceti (Mira). In 1983, we discovered that the atmosphere of the prototype of Mira-type variables is not symmetric. Since then, a number of multiwavelength high-angular resolution observations have confirmed the presence of asymmetries in Mira's atmosphere, and detected asymmetries in the atmospheres of other Mira-type variables. The high-angular resolution images of Mira obtained over the past fifteen years, including recent HST observations, show that the strength and shape of the asymmetries change as a function of wavelength and time. Plausible mechanisms for these asymmetries include hot spots, nonspherical pulsations, interaction with the companion and bipolar outflow. The presence of asymmetries in Miras could have serious impact on evolutionary models, and on the development of model atmospheres.
Multiwavelength Studies of Mira Ceti-type Variable Stars
Authors: Esipov V.F. , Pashchenko M.I. , Rudnitskij G.M. , Kozin M.V. , Lekht E.E. , Nadjip A.E. , Fomin S.V.
Published: July 2016

Since 1994, observations of a sample of about 20 Mira Ceti-type and semiregular variables have been carried out in three spectral ranges: radio (H2O maser line λ = 1.35 cm), optical (spectroscopy and UBV photometry) and infrared (JHKLM photometry). Time series of the Hα emission intensity and H2O line flux, covering several periods of the stars, have been obtained. Correlation of the intensity variations of the H2O maser with optical variability in the maser stars RR Aql, U Ori, VX Sgr and others was confirmed. One of the most interesting results is the flare of the H2O maser emission in R Leo, which happened in autumn 1997, 14 months after a flare of the Hα emission.
The 14 μm Band of Carbon Stars
Authors: Yamamura I. , de Jong T. , Waters L.B.F.M. , Cami J. , Justtanont K.
Published: July 2016

We have studied the absorption bands around 14 μm in the spectra of 11 carbon stars with mass-loss rates ranging from 10−8 to 10−4 M⊙ yr−1, based on data obtained with the Short Wavelength Spectrometer (SWS) on board the Infrared Space Observatory (ISO). All stars clearly show a C2H2 absorption band peaking at 13.7 μm, while the contribution from HCN molecules is small in this wavelength region. A simple plane-parallel LTE model with two layers at different temperatures is used to derive the C2H2 abundances in the outer photosphere and in the circumstellar envelope. We find that (1) the column density of the hot-layer, placed at about 3R* with a temperature of 1400 K is roughly the same for all stars regardless of the mass-loss rate, and (2) the contribution of cool molecules in the circumstellar envelope increases with the dust mass-loss rate, (3) the abundance of C2H2 in the two layers is about the same, i.e. no obvious depletion of C2H2 molecules seems to occur in the circumstellar envelope.
OH 231.8+4.2: its energetic bipolar outflow and rich chemistry
Authors: Sánchez Contreras C. , Bujarrabal V. , Alcolea J. , Miranda Luis F. , Zweigle J.
Published: July 2016

We report results from observations taken at different wavelengths (optical, radio and NIR) of the bipolar Protoplanetary Nebula OH 231.8+4.2. Radio interferometry with high spatial resolution has been particularly revealing. We study the complex structure and dynamics of this object as well as its rich chemistry.
AGB and post-AGB stars at high angular resolution
Authors: Lopez Bruno
Published: July 2016

High angular resolution observations have provided some valuable information on the circumstellar environment of AGB and post-AGB stars.

We review the recent results obtained in this field and focus on observations showing evidence of non-sphericity at different spatial scales (envelope, jets, binarity, maser clumps, stellar “photosphere”, hot spots, etc.). Such studies provide many informations/constraints not yet fully understood and seldom included in models.

Although the available observations are very nice and interesting, they sometimes show limited performances with regards to what is needed to analyse the onset of the winds. We try to show, here, what must be gained to improve our present knowledge.
Post-AGB Evolution
Authors: Van Winckel Hans
Published: July 2016

This review focuses on the evolution of single and binary optically bright post-AGB stars and the relation between the photospheric chemical abundances and the circumstellar material.

Surface abundance determinations of optically bright post-AGB stars offer a powerful tool, not only to clarify the evolutionary nature of the objects themselves, but also to constrain theoretical calculations for chemical evolution. However, a survey of recent results shows that the chemical patterns observed are very diverse and that several different classes can be distinguished. The most striking result is that only a minor fraction, namely the 21 μm objects, are conform to standard post third dredge-up theory.

In recent years it became clear that binarity can influence the late evolutionary stages considerably. A second part therefore discusses the varied and fundamental impact of the presence of a companion on the evolution of post-AGB systems.
Are there carbon stars in the Bulge?
Authors: Ng Yuen Keong
Published: July 2016

The Bulge carbon stars have been a mystery since their discovery by Azzopardi et al. (1991), because they are about too faint to be regarded as genuine AGB stars, if located inside the metal-rich Bulge . Part of the mystery can be solved if these carbon stars are related to the Sagittarius dwarf galaxy . They are in that case not old and metal-rich, but young, ∼0.1 Gyr, with SMC-like metallicity (Ng 1998).

The σRV = 113 ± 14 km s−1 (Tyson & Rich 1991) radial velocity dispersion of the stars appears to be consistent with Bulge membership. On the other hand, a similar velocity dispersion could be the result from an induced star formation event when the SDG crosses the galactic midplane. It is suggested that the carbon stars are tracers of such an event and that they therefore are located at distances related to the SDG. However, the majority of the carbon stars are not member of the SDG, nor are they similar to the C-stars which are member of the SDG.

The radial velocities can be used to determine a possible membership to the SDG. However, they do not give information about the distance of the stars. In particular, if the stars are located at a distance comparable to the SDG. This implies that only the period-luminosity relation (Groenewegen & Whitelock 1996) can be used to distinguish unambiguously if the carbon stars are located at Bulge-like or SDG-like distances. Thus far only carbon stars with reliable periods have been identified at a SDG related distance (Ng & Schultheis 1997; Whitelock 1998).
A critical look at the role of AGB stars in stellar population synthesis
Authors: Lançon A.
Published: July 2016

Asymptotic giant branch stars are essential contributors to the near and mid-IR emission of intermediate age (108-109 yr old) stellar populations. Detecting this light will set constraints on the star formation history in galaxies and, conversely, the search for AGB signatures in well studied populations will help us reduce some of the still large uncertainties in AGB models. This paper reviews how AGB stars are currently included in population synthesis models and which spectral features can be used to identify their emission in galaxy light; targets for observational tests are suggested, and some observational and theoretical difficulties are discussed.
Stellar Content of Local Group Galaxies - An Introduction
Authors: van den Bergh Sidney
Published: July 2016

In The Realm of the Nebulae, Hubble (1936) first drew attention to the fact that the Milky Way system and the Andromeda galaxy belong to a small cluster that also contains M32, M33, the Magellanic Clouds, NGC 205, NGC 6822 and IC 1613. Hubble also listed IC 10 as a possible member of what he referred to as “the Local Group”. Inspection of the prints of the Palomar Sky Survey shows (van den Bergh 1962) that a large fraction of all field galaxies are located in such small groups or clusters. Our Milky Way system therefore appears to be situated in a rather typical region of space. All of the well-established Local Group members that are listed above are at distances D ≤ 1.0 Mpc. A conservative limit D < 1.5 Mpc may therefore be used to search for new Local Group members. An additional criterion for physical membership in the Local Group is that a candidate member with solar apex distance θ and radial velocity Vr should lie close to the Vr versus cos θ relation for well-established Local Group members (Courteau & van den Bergh 1999). Finally candidates may be disqualified from membership if they appear projected on nearby groups of galaxies that are centered at distances greater than 1.5 Mpc. In particular the Local Group candidates NGC 1560, NGC 1569, UGC-A86 and Cassiopeia 1 were excluded because they appear projected on (or near) the IC 342/Maffei group. Furthermore NGC 55 and UKS 2323-326 were excluded because they appear projected on (or near) the Sculptor (= South Polar) group. Observational data on 35 probable Local Group members are given in Table 1.
Interesting Variables near the Quintuplet Cluster
Authors: Glass I. S. , Matsumoto S. , Carter B. S. , Sekiguchi K.
Published: July 2016

Two of the five cocoon stars in the “Quintuplet” cluster of young, luminous objects, located about 30 pc in projection from the Galactic Centre, are variables. The nearby “Pistol Star”, also called the “Serendipitous Star”, and a similar object, both suspected on spectroscopic grounds of being Luminous Blue Variables, have indeed been found to vary, confirming their tentative classification. A further variable apparent member of the cluster is probably a Mira in the same line of sight.
ISO Observations of AGB Stars in the Small Magellanic Cloud
Authors: Blommaert J.A.D.L. , Groenewegen M.A.T. , Cioni M. R. , Habing H. J. , van Loon J.Th. , Trams N. R.
Published: July 2016

We used ISOCAM and ISOPHOT to observe the spectral energy distribution between 3.6 and 60 μm of AGB stars in the Small Magellanic Cloud detected by IRAS. CAM-CVF spectra are made which enable us to establish the carbon- or oxygen-rich nature of the stars.

We are in the process of analysing this data using a radiative transfer model. This will provide us with accurate determinations of luminosity and mass loss rate. Combining the results on the SMC, LMC and Galaxy we hope to address the open question of the metallicity dependencies of the mass loss rate. This in turn is important in the ejection of matter by AGB stars into the interstellar medium.
Spectroscopy of Red Giants of the Sagittarius Dwarf Galaxy
Authors: Marconi G. , Bonifacio P. , Pasquini L. , Molaro P.
Published: July 2016

The photometric study of the Sagittarius dwarf galaxy by Marconi et al. (1998) has suggested the presence of a spread in metallicity (-0.7 ≤ [Fe/H] ≤ −1.6), which may result from different bursts of star formation. We present the results from a Multi Object Slit spectroscopy program carried out at the NTT with the aim to determine spectroscopic abundances of Sagittarius giants selected from the CCD photometry. From our intermediate resolution (R~1500) spectra, radial velocities are determined to confirm the membership and metallicities are derived by using spectral synthesis codes for stars down to V ~ 18, i.e. below the RGB clump. Out of 57 observed stars, 23 have a radial velocity consistent with Sagittarius membership; here we present results for 8 of these. No star with [Fe/H]< −1.0 is found, three stars are found to be metal-rich.
Deep Stellar Photometry of IC 10
Authors: Tikhonov N. A.
Published: July 2016

Results of VRI photometry are presented, based on 1-m, 6-m and HST telescope frames taken in different parts of IC 10. From comparison of the location in CM diagrams of branches of blue supergiants it was found that E(B - V) = 0.98. The distance modulus estimation from TRGB is (m - M)I = 23.8 ± 0.1. The ages of brightest stars of the east star complex are derived from comparison with theoretical isochrones. It is possible that IC 10 is a galaxy with an extended red giant disk.
Stellar Populations and Local Group Membership of the Dwarf Galaxy DDO 210
Authors: Lee Myung Gyoon
Published: July 2016

Deep BVI CCD photometry of dwarf galaxy DD0 210 obtained in this study shows that the resolved stellar population in this galaxy consists of a dominant old red giant population and some young stars. We have estimated the distance to this galaxy using the I-band magnitude of the tip of the red giant branch, obtaining a value of 1030±50 kpc. This result combined with the velocity of DDO 210 shows that DDO 210 is a member of the Local Group.
Metallicity-dependent Spectral Evolution
Authors: Traat Peeter
Published: July 2016

The initial chemical composition of stars is, besides the mass, another key factor in stellar evolution. Through stellar lifetimes and impact on radiation output and nucleosynthesis of stars it is controlling both the pace of evolution of galactic matter/light and changes in their integrated observables and spectra.
Two Species of Local Group Dwarf Spheroidals
Authors: Takeuchi Tsutomu T. , Hirashita Hiroyuki
Published: July 2016

We analyzed 10 dwarf spheroidal galaxies (dSphs) in the Local Group, and found two distinct sequences on the Mvir/L - Mvir plane: Mvir/L ∝ Mvir1.6 for Mvir < 108M⊙ whereas Mvir/L ≃ const. for Mvir > 108M⊙ (Mvir and L are the virial mass and the total luminosity of a dSph, respectively). We interpret the discontinuity as the threshold for the gas in dSphs to be blown away by successive supernovae. We succeeded in giving a quantitative explanation of the discontinuity mass of 108M⊙ as the blow-away condition. We further derived the above relation for the low-mass dSphs, assuming that the initial star formation rate of the dSphs is proportional to the inverse of the cooling time. The relation of high-mass dSphs is also explained along with the same consideration, with the condition that the gas cannot be blown away.
On the spatial distribution of the galactic Wolf-Rayet stars
Authors: Alfaro Emilio J. , Cerviño Miguel , Rubiño J.A. , Cabrera-Caño Jesus , Vílchez José M.
Published: July 2016

From a new compilation of spectral types and photometry (version April '98 on the Web) performed by van der Hucht for the Galactic WR stars, we have estimated the distance using two different luminosity-spectral type calibrations. Both determinations lead to similar results. On the basis of newly determined distances we have performed a quantitative analysis of the spatial density distribution for the WN and WC spectral types as well as for the whole WR sample and compared them to the one depicted by the large star-forming regions delineated by the population of young open clusters (YOCs). WR stars show a clumpy distribution similar to the one shown by the YOCs and the WN and WC spectral classes present different galactic distributions as well. Otherwise, variations of the WC/WN quotient do not show a clear correlation with the galactic metallicity gradient, on the contrary this ratio seems to be constant on regions of about 1 kpc in size and shows significant variations (even by a factor of 8) between the closest star-forming complexes.
The identification of the star SPH 2 as a new WN4 star with strong C IV
Authors: Bastos Pereira Claudio , Machado Maria Auxiliadora Delgado
Published: July 2016

We report on the spectroscopic observation of a new Wolf-Rayet star not already identified. This star is located in our Galaxy, in the Canis Majoris region and was found during a southern spectroscopic survey of stars previously identified as Hα emission objects. The star, SPH 2, after Schwartz, Persson & Hamann (1990), shows the main characteristics of a WN star and a strong C IV 5808 Å emission line typical of a WC star.
Wolf-Rayet star spectra from 1150 Å to 1200 Å
Authors: Nichols Joy S. , Linsky Jeffrey L.
Published: July 2016

The NEWSIPS-reprocessing of IUE data permits the extraction of spectra to wavelengths as short as 1150 Å. We present representative well-exposed IUE spectra of Wolf-Rayet stars covering the 1150–1220 Å region with a resolution of 0.1 Å. The C III 1175 Å line in WC and some WN stars typically shows a P-Cygni profile, with dacs apparent in time series spectra. Superimposed on the stellar spectra are many strong interstellar absorption lines of N I, Si II and other species. These spectra are a guide to a portion of the wavelength region to be covered by FUSE, and an indication of the new information that will be available in the far-UV range with FUSE.
Long-term spectroscopy of Wolf-Rayet binaries
Authors: Schweickhardt Jörg , Schmutz Werner , Kaufer Andreas , Stahl Otto , Wolf Bernhard
Published: July 2016

We are investigating two long-period WR+O binaries, γ2 Velorum (WC8+O7.5, P = 78.5d) and WR 22 (WN7+abs+O, P = 80.3 d). We derive new orbital elements for both binaries and we give preliminary results of our analysis of the expansion velocity and ionization structure of γ2 Vel.
The stellar parameters of the SMC WR binary HD 5980
Authors: Schweickhardt Jörg , Schmutz Werner
Published: July 2016

We present the temporal variation of the stellar parameters of the erupting star in HD 5980. We derive the effective temperature and radius from the observed changes of the visual magnitude. Our analysis is based on the assumption that the luminosity of the erupting star remained constant and that the brightness of the second star did not vary.
A deep survey for Galactic Wolf-Rayet stars. II. Implications for galactic structure and massive star formation
Authors: Shara Michael M. , Potter Michael , Moffat Anthony F.J. , Lamontagne Robert , Smith Lindsey F. , Niemela Virpi S.
Published: July 2016

We have completed a direct narrow-band/broad-band Schmidt-plate survey of large areas of the southern Milky Way for new Wolf-Rayet stars as faint as 19th b magnitude. The 31 newly detected stars in the completed survey are amongst the reddest and/or most distant known in the Galaxy. We have obtained spectra of all candidate WR stars in the 22 fields stretching from l = 282° to l = 341° in longitude, and Δb = 3.5° in latitude, covering about 180 square degrees. We also observed two isolated Milky Way fields centered at l = 0° and l = 8°. Eighteen new WR stars are reported here for the first time. Combined with the 13 new WR stars we have already reported in Carina, our list of 31 new Galactic WR stars reaches 3–4 magnitudes fainter than previous surveys. Thirteen of the 18 new WR stars reported here are of subtype WN, while five are of subtype WC. Our new WR stars clearly demonstrate an increasing WN/WC number ratio with increasing Galactocentric distance.
HST-FOS spatially resolved spectral classification of compact WR/Of+OB groups in the LMC
Authors: Walborn Nolan R. , Drissen Laurent , Parker Joel Wm. , Saha Abhijit
Published: July 2016

Spectroscopy of the individual stellar components in four compact OB multiple systems of the LMC, previously imaged with the HST-WFPCS, has been performed with the HST-FOS. In every case, the uncontaminated spectra of the WR and/or Of-type components have been observed for the first time. The spectra of the normal OB companions provide information about the initial masses and ages of the peculiar objects. Several additional evolved and peculiar objects within these systems have also been discovered.
Modelling and quantitative analyses of Wolf-Rayet spectra: recent progress and results
Authors: Hamann Wolf-Rainer , Koesterke Lars , Gräfener Götz
Published: July 2016

The quantitative analysis of Wolf-Rayet type spectra requires non-LTE models for expanding atmospheres which have been developed in the last decade. Idealizing assumptions of the so-called standard model are spherical symmetry, homogeneity and stationarity. While the first generations of models were restricted to simple atoms (helium, hydrogen), we now apply more advanced calculations which account for complex model atoms (nitrogen, carbon, oxygen). The re-analysis of the Galactic WN sample from the nitrogen lines led to a substantial revision of the stellar parameters, as far as the WNE-w subclass is concerned. Wind inhomogeneity ('clumping') has been accounted for in a first-order approximation. The degree of clumping is derived from the electron-scattering wings of strong lines. With clumped models, considerably lower mass-loss rates (by a factor two or more) are obtained, while other empirical parameters are not affected significantly. An overview is given about the fundamental parameters of Wolf-Rayet stars as obtained from spectral analyses, including new results on WN stars in the LMC.
The extreme P-Cygni star HDE 316285
Authors: Hillier D. John , Crowther Paul A. , de la Parra Francisco Najarro , Fullerton Alexander W.
Published: July 2016

New line-blanketed models for the P-Cygni star HDE 316285 have been calculated. Representative model atoms for H, He I, He II, Ca I, Ca II, Mg I, Mg II, Al II, Al III, Fe II, and Fe III are included in the calculations. We confirm the basic parameters derived by Hillier et al. (1998) in an earlier unblanketed study, and also confirm that many of the optical metal lines are produced by continuum fluorescence. The charge exchange reaction Fe2+ + H ⇌ Fe+ + H + modifies the Fe ionization structure and significantly enhances the strength of the optical Fe II emission lines.
Modelling of line-profile variability in WC stars
Authors: Oskinova Lydia M. , Kholtygin Alexander F. , Kostenko F.V.
Published: July 2016

Suppose that the atmosphere of a WC star is formed by clumps embedded in the homogeneous spherically symmetric stellar wind. A single clump may be modeled as a part of the spherical layer restricted with a surface of a cone. Present the gas density in the cone as a sum of gas density in homogeneous atmosphere and gas density in a clump:
Here nk(r) is the gas density in the homogeneous atmosphere, Dcl is the ratio of gas densities at a point r = rcl, and δ is the size of the clumps in units rcl.
Time-resolved optical-UV spectroscopy of colliding wind effects
Authors: Moffat Anthony F.J.
Published: July 2016

It is in the ultraviolet-optical domain where the strongest known emission lines arise in hot star winds. In the case of hot-star binaries, culminating in the relatively common, strong-wind WR+O systems, similar line-emission is seen in the cooling flows downstream from the highly compressed, X-ray emitting heads of the bow shock regions produced when the two winds collide. Time-resolved UV-optical spectroscopy of these flows around a complete orbit can provide important constraints not only on the colliding wind process itself, but also on the winds and the orbit. Spectroscopic wind-wind collision effects have now been seen in every relatively close WR+O system (P ≲ 100 d) that has been adequately observed so far.
3D non-LTE radiative transfer: a new code and its application to γ2 Velorum
Authors: Folini Doris , Walder Rolf
Published: July 2016

A new approach to 3D optically thick non-LTE radiative transfer for moving media is presented. As a first application, we look at the ionization state of the colliding winds interaction zone between two stars.
A Fabry-Perot study of Wolf-Rayet ring nebulae in M 33
Authors: Marston Anthony P. , Drissen Laurent , Godbout Steve
Published: July 2016

We present a kinematical study of ring nebulae surrounding Wolf-Rayet stars in the Local Group galaxy M 33, based on Fabry-Perot data obtained at the CFHT. Most of these rings show evidence for multiple phases of mass ejection from the central star. Variations are noted in the [OIII]/Hα emission-line ratios across several ring nebulae generally associated a variation in kinematics. Significant [O III] emission appears to arise from the collision between the fast WR wind and surrounding ejecta from a prior phase, such as a RSG or LBV.
High-resolution spectroscopic study of the planetary nebula Abell 78
Authors: Medina Selene , Peña Miriam
Published: July 2016

High resolution optical spectra of the planetary nebula Abell 78 were gathered, covering the wavelength ranges 3500–6600 Å and 3358–7361 Å, with a spectral resolution of ∼0.1 Å. Two different regions of Abell 78 are analyzed: the strongest knot near the central star which is thought to be a mass-loaded wind from the central star, and the outer, hydrogen-rich envelope. Physical parameters and chemical composition of both regions are estimated. The inner knot appears to be cooler and denser than the hydrogen-rich envelope. The chemical composition of the inner knot shows that there is almost no hydrogen near the central star and the emission is dominated by helium and processed material which has been dredged-up from the inner layers of the star. The outer, hydrogen-rich envelope appears to be deficient in heavy elements, mainly in oxygen, compared to the average abundances that are found among galactic planetary nebulae.
2MASS observations of Wolf-Rayet stars and galaxies
Authors: Van Dyk Schuyler D. , Jarrett Thomas H. , Cutri Roc M. , Skrutskie Michael F.
Published: July 2016

The Two Micron All Sky Survey (2MASS) has observed a number of Wolf-Rayet stars and galaxies at J (1.25 μm), H (1.65 μm), and Ks (2.17 μm), as part of its systematic coverage of the entire sky with automated 1.3-m telescopes at Mt. Hopkins, AZ, and CTIO, Chile. The cameras observe the sky in the three channels simultaneously, using 256 x 256 HgCdTe-detector arrays. The survey samples the sky in 6° x 8.'3 tiles. The 2MASS Production Processing System transforms the raw binary survey data to final atlas images and source extractions with precise photometric calibration and astrometric positions. The survey's 10σ sensitivity is 15.8 mag at J, 15.1 at H, and 14.3 at Ks. In this poster we will present results from our analysis of several objects. We have observed WR stars both with and without associated ring nebulae. 2MASS imaging of the WR galaxies is far less affected by extinction, which can obscure much of the star formation activity. We will place these starburst dwarf galaxies in context with other galaxies, based on their near-IR colors and properties.
Radiative colliding winds models: the stagnation point singularity
Authors: Zhekov Svetozar A. , Myasnikov A. V. , Belov N. A.
Published: July 2016

The singularity at the stagnation point in steady-state colliding winds has a big influence on the structure of the radiative interaction region. None of the existing numerical models treats properly this mathematical problem. As a result, all the available models cannot be used for deriving the stellar winds parameters by making a comparison with the observed X-ray properties.
R 136a and its implications for understanding Wolf-Rayet stars and Wolf-Rayet galaxies
Authors: Heap Sara R.
Published: July 2016

We argue that the WR phenomenon is simply a consequence of very high mass-loss rates (i.e., it is independent of initial mass, composition, or evolutionary status) and that it occurs in very massive main-sequence stars. We explore this argument using new HST observations of R 136a, the compact cluster containing three high-mass WR stars on the main sequence. We suggest that the underlying cause of the WR phenomemon in these stars is mass-loss enhanced by rapid rotation. Finally, we explore the implications of luminous, main-sequence WR stars for interpreting unresolved WR star clusters and galaxies.
What the galaxies of the Local Group tell us about massive star evolution
Authors: Massey Philip
Published: July 2016

We consider what we've learned about massive star evolution from observations of the resolved stellar content of Local Group galaxies. Studies of mixed-age (galaxy-wide) and coeval (single associations) populations reveal much about massive star evolution, and how it is controlled by metallicity, demonstrating the ‘Conti scenario’ in action! The number of WC stars to WN stars increases with increasing metallicity, as expected: in regions of higher metallicity stars of somewhat lower luminosity can evolve all the way to the WC stage. The exception is the starburst galaxy IC 10, for which I speculate that the IMF may be weighted towards high mass stars. The highest luminosity red supergiants are lacking in galaxies of higher metallicity, suggesting that the stars that would have become these RSGs are spending more of their time as WRs. The presence of luminous RSGs is highly correlated with the presence of WC and WN stars in OB associations, suggesting that many massive stars evolve through both a RSG and WR stage. The relative number of RSGs and WRs does decrease strongly with increasing metallicity, again consistent with higher metallicity systems leading to increased time in the WR phase. The various WC subclasses appear to be the result of the influence of metallicity on stellar wind structure in these stars, and are not due to to differences in mass or luminosity. Data on the field population in the Magellanic Clouds suggest that stars more massive than 30 become WRs in the LMC, while the limit may be more like 50 in the SMC, again as expected. Studies of the turn-off masses in clusters and associations in the MCs and Milky Way are nearing completion, while investigations in the more distant galaxies of the Local Group are just getting underway. For the LMC we find the following: WNE stars come from a large mass range of progenitor (30–100 ), and have very large (negative) bolometric corrections (−6 to −8 mag). The Ofpe/WN9 stars seem to come from lower mass progenitor (20–30 ), and have more modest BCs (−1 to −3 mag). WC stars come from stars with masses > 60–70 , and have BCs of −3 to −4 mag. Both ‘B2I+WN3’ systems and LBV stars like S Doradus are found only in clusters containing very high turn off masses (>70–90 ).
Infrared modeling of the starburst clone NGC 3603
Authors: Devost Daniel , Leitherer Claus
Published: July 2016

We present results of an HST archive study of the star cluster NGC 3603. The color-magnitude diagram (CMD) and the radial profiles have been derived using HST-nicmos F110W and F171M images. As expected, the CMD shows that the cluster is very young (< 3 Myr) and that a significant portion of the stellar population (M < 4M⊙) is on the pre-main sequence phase. From the radial profiles, we derive a similar half-light radius for both wavebands of 0.17 pc.
Star formation in NGC 3603
Authors: Tapia Mauricio , Pérez Brenda
Published: July 2016

NGC 3603 is the most massive optically visible H II region in our Galaxy and is considered to be the Galactic analogue to 30 Doradus and, thus, a prototype of the starburst phenomenon. Its core, known as WR 43 (HD 97950), contains several dozens of O-B0 stars within 35″. These have been studied with very high resolution in the optical and near-IR. Melnick, Tapia & Terlevich (1989) concluded that the starburst cluster has an age spread of 1 to 2 Myr and that its boundaries extend to ∼60″, while Eisenhauer et al. (1998) determined that the lower mass stars in the core are younger than 1 Myr.
Hard X-ray-to-radio energy distributions in starburst galaxies
Authors: Cerviño Miguel , Mas-Hesse J. Miguel
Published: July 2016

We present in this contribution the predictions on the multiwavelength spectral energy distribution of our evolutionary population synthesis models including single and binary stellar systems. The high energy computations include the emission associated to X-ray binaries and supernovae remnants, as well as the mechanical energy released into the interstellar medium, which can be partially reprocessed into thermal X-rays. With these components we compute the spectral energy distribution of starburst galaxies from X-ray to radio ranges, and analyze finally the effects of the high energy emission on the H and He ionizing continuum.
Wolf-Rayet stars in extragalactic star-forming regions
Authors: Pindao Maximilien
Published: July 2016

We performed a search of Wolf-Rayet stars features in optical spectra of two large samples of H II regions and H II galaxies. The main results are a list of galaxies/regions containing WR stars (of which seven are new WR galaxies) and a second list of possible WR galaxies/regions with WR stars.
The dwarf Wolf-Rayet galaxy II Zw 33
Authors: Walter Fabian , Brinks Elias
Published: July 2016

II Zw 33 is a gas-rich Wolf-Rayet galaxy with a low surface-brightness companion galaxy. Neither II Zw 33 nor its companion need any dark matter in order to explain the observed rotation curves. The available observations support a scenario in which the companion has triggered the current burst of star formation in II Zw 33.
Wolf-Rayet stars as tracing the AGN-starburst connection
Authors: Kunth Daniel , Contini Thierry
Published: July 2016

We stress the importance of Wolf-Rayet stars for the understanding of the AGN phenomenon in galaxies. WR stars provide an unique opportunity to explore from the ground whether non-thermal nuclear activity and circumnuclear starbursts are connected. We review the known reported WR signatures observed so far in AGNs and point out some intrincacies related to the analysis of the spectra, linked to reddening correction, the origin of the Hβ line, etc. Finally, we advocate that integral field spectroscopy is a very promising tool to study this problem and present preliminary results of a long-term project that have been obtained at the CFHT in 1998.
Gas and hidden star formation in NGC 5253
Authors: Turner Jean L. , Beck Sara C. , Ho Paul T.P.
Published: July 2016

We confirm the presence of compact H II regions in the center of the starburst in NGC 5253 through the detection of optically thick free-free emission. The number of O-type stars implied by the excitation of these nebulae is nearly two orders of magnitude larger than what is indicated by the radio continuum fluxes. The compact H II regions are located 70 pc to the north of the location of the Wolf-Rayet feature. Implied extinctions are extremely high. Not all WR galaxies can be identified as such due to extinction.
Wolf-Rayet stars in Active Galactic Nuclei
Authors: Williams Robin J.R. , Dyson John E. , Perry Judith J.
Published: July 2016

Starbursts, black holes and AGN have strong observational links, as discussed elsewhere in these proceedings. Perry & Dyson (1985 (PD), see also Perry 1994) studied the role of shocks around supernovae and stellar wind bubbles in the nuclei of active galaxies. Both the ejecta and the ambient ISM are initially shocked to high temperatures. PD found that while the shocked gas is maintained at high pressure by ram pressure, it cools rapidly, to then produce the observed optical and UV emission lines. The mass supply rate from the nuclear starburst, inferred from the strength of the emission lines, tallies well with that required by an accreting black hole to generate the observed luminosity. A symbiosis between a starburst stellar cluster and an accreting black hole naturally generates the observational features associated with QSOs.
Summary talk
Authors: Dyson John E.
Published: July 2016

A personal perspective of the meeting is given.
Star Formation from Turbulent Fragmentation
Authors: Klessen Ralf S.
Published: July 2016

Star formation is intimately linked to the dynamical evolution of molecular clouds. Turbulent fragmentation determines where and when protostellar cores form, and how they contract and grow in mass via accretion from the surrounding cloud material. Using numerical models of self-gravitating supersonic turbulence, efficiency, spatial distribution and timescale of star formation in turbulent interstellar clouds are estimated. Turbulence that is not continuously replenished or that is driven on large scales leads to a rapid formation of stars in a clustered mode, whereas interstellar turbulence that carries most energy on small scales results in isolated star formation with low efficiency. The clump mass spectrum for models of pure hydrodynamic turbulence is steeper than the observed one, but gets close to it when gravity is included. The mass spectrum of dense cores is log-normal for decaying and large-wavelength turbulence, similar to the IMF, but is too flat in the case of small-scale turbulence. The three-dimensional models of molecular cloud fragmentation can be combined with dynamical pre-main sequence stellar evolution calculations to obtain a consistent description of all phases of the star formation process. First results are reported for a one solar mass protostar.
Impulsively triggered star formation
Authors: Whitworth Anthony
Published: July 2016

I contend that impulsively triggered star formation is at least as important as spontaneous quasistatic star formation regulated by ambipolar diffusion, and probably more so. To support this contention, I describe and discuss SPH simulations of (i) star formation triggered by colliding clouds and expanding nebulae (HII regions, stellar-wind bubbles, and supernova remnants); (ii) violent interactions between protostellar discs and the resulting genesis of binary systems and low-mass companions; and (iii) protostellar collapse induced by a sudden increase in external pressure.
Two collaborative experiments in star cluster evolution
Authors: Heggie Douglas C.
Published: July 2016

We summarise the specification and some previously unpublished results of the collaborative experiment (“Kyoto I”) that was carried out at the time of the Kyoto General Assembly of the IAU. As the subject has advanced considerably since then, and codes have become more elaborate, we describe an agreed proposal for a new experiment ("Kyoto II").
Isolated and Interacting Galaxies: Simulations with GRAPE
Authors: Athanassoula E.
Published: July 2016

I present N-body simulations of isolated and interacting galaxies, made on GRAPE machines. In particular I discuss the formation and evolution of N-body bars and compare their properties to those of bars in early-type and late-type galactic discs. I argue that the halo can help the bar grow, contrary to previous beliefs, by taking positive angular momentum from it via its resonant stars. I then focus on the interaction and subsequent merging of a barred disc galaxy with a spheroidal satellite. The evolution depends strongly on the mass (density) of the satellite and may lead to its destruction or to the destruction of the bar.
Constraining the Distribution of Dark Matter Lumps Around the Milky Way Using Tidal Debris
Authors: Johnston Kathryn V. , Spergel David N. , Haydn Christian
Published: July 2016

Dwarf galaxies that fall into the Milky Way's potential are tidally disrupted. Their tidal tails are one of the most powerful probes of the mass distribution in the Galaxy. If the distribution of dark matter in the Galaxy is lumpy, then these lumps will scatter stars in the stream and alter its shape. We describe our approach to using the tidal debris to constrain substructure in the Galaxy halo.
A multi-phase model for simulations of galaxy formation
Authors: Springel Volker , Hernquist Lars
Published: July 2016

We discuss SPH simulations of galaxy formation which use a hybrid method to describe a two-phase structure of the star forming ISM on unresolved scales. Our modeling includes radiative cooling, heating due to a UV background, growth of cold clouds embedded in an ambient hot gas, star formation out of cloud material, feedback due to supernovae in the form of thermal heating and cloud evaporation, starbursts that can lead to galactic outflows, and metal enrichment. Our particular model for the treatment of the two-phase structure is based on a modified and extended version of the grid-based approach of Yepes et al. (1997). We discuss the properties of the feedback model and show how it stabilizes star forming disk galaxies and reduces the cosmic star formation rate to a level consistent with current observational constraints.
Numerical studies of galaxy formation using special purpose hardware
Authors: Steinmetz Matthias
Published: July 2016

I review recent progress in numerically simulating the formation and evolution of galaxies in hierarchically clustering universes. Special emphasis is given to results based on high-resolution gas dynamical simulations using the N-body hardware integrator GRAPE. Applications address the origin of the spin of disk galaxies, the structure and kinematics of damped Ly-α systems, and the origin of galaxy morphology and of galaxy scaling laws.
The Starlab Environment for Dense Stellar Systems
Authors: Hut Piet
Published: July 2016

Traditionally, a simulation of a dense stellar system required choosing an initial model, running an integrator, and analyzing the output. Almost all of the effort went into writing a clever integrator that could handle binaries, triples and encounters between various multiple systems efficiently. Recently, the scope and complexity of these simulations has increased dramatically, for three reasons: 1) the sheer size of the data sets, measured in Terabytes, make traditional ‘awking and grepping’ of a single output file impractical; 2) the addition of stellar evolution data brings qualitatively new challenges to the data reduction; 3) increased realism of the simulations invites realistic forms of ‘SOS’: Simulations of Observations of Simulations, to be compared directly with observations. We are now witnessing a shift toward the construction of archives as well as tailored forms of visualization including the use of virtual reality simulators and planetarium domes, and a coupling of both with budding efforts in constructing virtual observatories. This review describes these new trends, presenting Starlab as the first example of a full software environment for realistic large-scale simulations of dense stellar systems.
Panel Discussion
Authors: Sugimoto Daiichiro , Athanassoula Evangelia , Heggie Douglas C.
Published: July 2016

Four panelists gave their reports. Three of them are complied here. Additional comments are included in the report by the moderator Sugimoto.
High resolution simulations of star formation
Authors: Boffin Henri M. J. , Francis Neil , Whitworth Anthony P.
Published: July 2016

In order to study the capabilities of SPH in self-gravitating hydrodynamical problems, we have performed a series of three-dimensional numerical simulations of the collapse of a rotating homogeneous cloud, varying the number of particles and the artificial viscosity prescription.
Coupling Chemical Evolution with SPH
Authors: Carraro Giovanni , Portinari Laura , Lia Cesario
Published: July 2016

We present a new statistical algorithm of Chemical Evolution implemented into the Tree-SPH code developed by Lia & Carraro (2000).
The differential energy distribution of the universal density profile of dark halo
Authors: Habe Asao , Hanyu Chiaki
Published: July 2016

We study the differential energy distribution of dark matter halos, carrying out cosmological N-body simulation. From our simulation, we give an analytical formula of the differential energy distribution of dark matter in the halos. Density distribution from the analytical formula is consistent with the Navarro, Frenk, and White (NFW) profile. We find that a parameter in our analytical formula of differential energy distribution is related with the slope of inner cusp of dark halo. We discuss physical reason of form of the analytical formula.
A regularized N-body algorithm for gravitational collapse clustering
Authors: Hidaka Jun
Published: July 2016

In N-body problem, it is necessary to regularize forces between close encountering particles to conserve their total energy. Without regularization, these particles has rapid change of their energy. We can, therefore, select close encountering particles looking at their energy and apply regularization to them. We discuss application of this scheme to spherically collapsing case.
The Local Mass Conservation in SPH
Authors: Imaeda Yusuke , Inutsuka Shu-ichiro
Published: July 2016

Smoothed particle hydrodynamics (SPH) is one of the widely used methods to calculate the various astrophysical fluid dynamics. However, standard SPH cannot accurately describe the long-term evolution of shear flows: The large density error emerges within a dynamical timescale, and the amplitude of the error becomes larger than the value of density itself (Δρ ≳ ρ), when we take the mean separation of the particles as the smoothing length. The origin of error is due to the inaccurate description of the continuity equation in the standard SPH formalism. To ensure the local mass conservation property, we have reformulated SPH, in which we distinguish the particle velocity and the fluid velocity for the updation of the particle positions. We find that the present modification provides an accurate description of the density evolution in SPH.
Evolution of Planetesimals in Planetary Debris Disks
Authors: Kenyon Scott J. , Bromley Benjamin C.
Published: July 2016

Dusty planetary disks can form quickly around young stars and linger, despite the depletion of dust through mechanisms such as Poynting-Robertson drag. Planetesimals in the disk can replenish the dust with an efficiency that depends on their mass and velocity distributions. Here, we describe a numerical program to track the evolution of planetesimals through merging, fragmentation and drag. Our current effort is focused on coupling a Fokker-Planck solver with N-body calculations to follow the detailed behavior of larger planetesimals. Our results demonstrate the importance of gravitational stirring in dust production. Furthermore, stirring by planets larger than Pluto can generate the large scale heights seen in several dusty disks.
Simulations of disks in binary systems using parallelized SPH to reach extreme spatial resolution
Authors: Molteni D. , Fauci F. , Gerardi G. , Valenza M. A.
Published: July 2016

Results of 3D numerical simulations of the gas transfer in close binary systems show that it is possible the production of accretion streams having low specific angular momentum in a region close to the accreting star. These streams are mainly placed above the orbital disc. The eventual formation of such bulges and shock heated flows is interesting in the context of advection dominated solutions and for the explanation of spectral properties of the Black Hole candidates in binary systems. We set up a parallelized version of 3D S.P.H. code, using domain decomposion. with increasing spatial resolution around the compact star.
Cloud mass function in a gas rich dwarf galaxy
Authors: Saitou Takayuki , Habe Asao , Okamoto Takashi
Published: July 2016

We study cloud mass function (here after CMF) obtained in a Grape-SPH simulation of model galaxy. The CMF can be fitted by a simple power law, and its power law index is ∼ −2.0, which closes to the observational results.