bluuebunny/crossref_metadata_2025 huggingface dataset:
Long Baseline Interferometric Observations of Circumstellar Dust Shells at 11 Microns
Authors: Danchi W.C. , Greenhill L. , Bester M. , Degiacomi C.G. , Townes C.H. , Wolfire M.G.
Published: July 2016

The spatial distribution of dust around a sample of well-known late-type stars has been studied with the Infrared Spatial Interferometer (ISI) located at Mt. Wilson. Currently operating with a single baseline as a heterodyne interferometer at 11.15 μm, the ISI has obtained visibility curves of these stars. Radiative transfer modeling of the visibility curves has yielded estimates of the inner radii of the dust shells, the optical depth at 11 μm, and the temperature of the dust at the inner radii. For stars in which the dust is resolved, estimates of the stellar diameter and temperature can also be made. Broadly speaking two classes of stars have been found. One class has inner radii of their dust shells very close to the photospheres of the stars themselves (3–5 stellar radii) and at a higher temperature (~ 1200 K) than previously measured. This class includes VY CMa, NML Tau, IRC +10216, and o Ceti. For the latter two the visibility curves change with the luminosity phase of the star and new dust appears to form at still smaller radii during minimum luminosity. The second class of stars has dust shells with substantially larger inner radii and very little dust close to the stars, and includes α Ori, α Sco, α Her, R Leo, and χ Cyg. This indicates sporadic production of dust and no dust formation within the last several decades.
Pupil Plane Interferometry: Some Conclusions from SCASIS
Authors: de Vos C.M. , Bregman J. D. , Schwarz U. J.
Published: July 2016

In this contribution we summarize some conclusions from the SCASIS project. The project, which concerns a multiple shearing pupil plane interferometer, was started in 1986 and was concluded in 1992 with the PhD thesis of de Vos.
Overview: Low-zObservations:Of Interacting and Merging Galaxies
Authors: Schweizer Francois
Published: July 2016

Gravitational interactions and mergers affect the morphologies and dynamics of galaxies from our Local Group to the limits of the observable universe. Observations of interacting galaxies at low redshifts (z≲ 0.2) yield detailed information about many of the processes at work. I briefly review these processes and the growing evidence that mergers play a major role in the delayed formation of elliptical and early-type disk galaxies both in the field and in clusters. Low-zobservations clearly contradict the notion of a single epoch of E formation atz≳ 2; instead, E and S0 galaxies continue forming to the present. The different rates of E and S0 formation inferred from observations of distant and nearby clusters may partially reflect the dependence of dynamical friction on mass: Major, E-forming mergers may tend to occur earlier than minor, S0-forming mergers because the dynamical friction is strongest for equal-mass galaxies.
What Can We Learn from the Local Group About the Role of Interactions in Galaxy Formation
Authors: Freeman K.C.
Published: July 2016

This talk is mainly about the halos and bulges of Local Group galaxies, in particular those of the Milky Way and M31, and what they can tell us about the role of interactions in galaxy formation. Bulges are potentially of particular interest for galaxy formation because they are widely suspected to be the seeds for galaxy formation. Sites of active star formation at high redshift are often regarded as spheroids in the process of formation. In this talk, I will say little about disks because their formation is conceptually understood, although many details remain uncertain. To form such flat systems, a fairly undisturbed dissipative process is needed. This process occurred fairly early: the disks appear to be in place by a redshift z = 1 (Ellis 1997), with a distribution of scalelengths that is similar to the distribution at z = 0.
The Magellanic Stream and the Magellanic Cloud System
Authors: Fujimoto M. , Sawa T. , Kumai Y.
Published: July 2016

A tidal model has been introduced to the triple system of the Galaxy, Large and Small Magellanic Clouds (the LMC and SMC hereafter) and successfully reproduced the Magellanic Stream (Murai and Fujimoto 1980; Lin and Lynden-Bell 1982; Gardiner et al. 1994; Gardiner and Noguchi 1995; Lin et al. 1995), a narrow band of diffuse atomic hydrogen gas emerging from the SMC region, passing by the South Galactic Pole along an overhead great circle spanning over 100° (Wannier and Wrixon 1972; Mathewson et al. 1974). The LMC and SMC have a hydrogen bridge and common envelope (Hindman 1964; McGee and Milton 1966) and, therefore, we can consider that they have been in a binary state for the Hubble time, revolving together around the Galaxy with a halo whose mass is larger than 1012M⊙ if the flat rotation curve extends up to more than 100 kpc. The strong gravitational force due to this heavy halo attracts the Magellanic Stream and produces the high negative radial velocities (Murai and Fujimoto 1980).
The High-Velocity Clouds: Galactic or Intergalactic?
Authors: Van Woerden Hugo , Schwarz Ulrich J. , Peletier Reynier F. , Wakker Bart P. , Kalberla Peter M. W.
Published: July 2016

Nature and origin of the high-velocity clouds (HVCs) remain enigmatic after thirty years (Wakker & van Woerden 1997,ARA&A,35, 217), owing to lack of distance information. Hypotheses range from supernova shells at 100 pc to intergalactic clouds at 1 Mpc. On statistical grounds, Blitz et al. (1996,BAAS,28, 1349) claim that the HVCs are “remnants of Local Group formation, best explained as members of the Local Group of galaxies”. Reliable distances must come from the presence or absence of absorption at the HVC's velocity in spectra of stars at different distances. For Complex A, MgII absorption is seen inHSTspectra of the Seyfert galaxy Mrk 106, but not in the star PG0859+593 at 4 kpc (Wakker et al. 1996,ApJ,473, 834). La Palma spectra of the RR Lyr star AD UMa at 11 kpc distance show CaII absorption by Complex A at both K and H, which is lacking at 4 kpc. These absorptions are not confused with stellar metal lines. Our distance bracket 4 <d< 11 kpc places Complex A in the Galactic Halo, at 2.5 <z< 7.5 kpc above the plane; a distance similar to Local Group galaxies is excluded. The HI mass implied lies between 0.15 and 1.2 times 106M⊙. Our result precludes local origins for this HVC. It allows an origin in a Galactic Fountain, or in interaction of infalling intergalactic material (from the Magellanic System or the Local Group) with the Galactic Halo.
Towards an Interaction Model of M81, M82 and NGC 3077
Authors: Thomson R.C. , Laine S. , Turnbull A.
Published: July 2016

Thomson (1992) suggested that the Cen A group of galaxies may be the result of one interaction. Here we report full N-body simulations made to study this proposal in the M81-M82-NGC 3077 group.
An HI Line Survey of Polar Ring Galaxies
Authors: Van Driel W. , Arnaboldi M. , Combes F. , Sparke L.S.
Published: July 2016

We have observed a total of 74 polar ring galaxies (PRGs), PRG candidates and related objects at 3 radio observatories: Green Bank (Richter et al. 1994, AJ, 107, 1), Effelsberg (Huchtmeier 1997, A&A, 319, 401) and Nançay (van Driel et al. 1997, A&AS, in press; van Driel et al. 1998, A&A, in prep.). Our main aim is to identify systems suitable for HI synthesis mapping, crucial for an understanding of their dynamical state. Most objects were selected using one or more of the following 3 (<8000 km/s), or blue magnitude brighter than 15.5 mag, or kinematically confirmed PRG or good PRG candidate. A total of 62 objects were detected, 39 of which with more than one telescope.
Making Spirals with Counter-Rotating Disks: The Case of NGC 4550
Authors: Pfenniger D.
Published: July 2016

A single merger scenario for making galaxies such as NGC 4550 possessing equal coplanar counter-rotating stellar disks is investigated by collisionless N-body technique. The scenario is successful in producing an axisymmetric disk made of two almost equal counter-rotating populations. The final disk shows a clear bimodal line profile in the outer part, which demonstrates that disk-disk mergers do not always produce ellipticals.
Fundamental Plane and Merger Scenario
Authors: Bekki K.
Published: July 2016

The Fundamental Plane (FP) is one of the most important universal relations in early type galaxies because it contains valuable information about the formative and evolutionary process of galaxies (Djorgovski & Davis 1987, Dressler et al. 1987). The commonly used form of the scaling relation in the FP is described as Re = σAIB, where Re, σ, and I are effective radius, central velocity dispersion, and mean surface brightness of elliptical galaxies, respectively. The exponents A, B are considered to be 1.56 ± 0.07 and −0.94 ± 0.09 in the FP derived by K band photometry, respectively, and these values deviate significantly from the values A = 2.0 and B = −1.0 expected from virial theorem (Pahre et al. 1995; Djorgovski, Pahre, & de Carvalho 1996). This apparent deviation requires that the ratio of dynamical mass (M) to luminosity of elliptical galaxies (L) depends on M as M/L ∝ Mα (α = 0.12 ± 0.03 for K band). Possible interpretations for the required dependence of M/L on M are generally considered to be divided into the following two. One is that the required dependence of M/L on M results from the fact that the mean stellar age and metalicity of elliptical galaxies depend systematically on M. The other is that the required dependence reflects the M dependence of structural and kinematical properties of elliptical galaxies (“nonhomology”). Although we should not neglect the importance of stellar populations in generating the M dependence of the M/L (Renzini & Ciotti 1993), we here consider that the origin of the required M dependence of M/L is closely associated with the structural and kinematical properties dependent on M or L in elliptical galaxies.
Formation of Boxy/Peanut-Shaped Bulges in Spiral Galaxies: Accretion or Bar Instability?
Authors: Bureau M. , Freeman K.C.
Published: July 2016

Boxy/peanut-shaped bulge galaxies constitute at least 20-30% of all spirals. Distribution functions and numerical simulations studies have shown that the slow decay of the orbit of a companion into a larger spiral can lead to the formation of a boxy/peanut bulge. However, the bar-buckling instability now appears a more likely process. Thin bars either do not form or, as shown by N-body simulations, buckle and settle with an increased thickness, appearing boxy or peanut-shaped when seen edge-on. This project aims to determine the dynamical state of a sample of 30 edge-on spirals, 3/4 of which have boxy/peanut-shaped bulges, half having close-by companions.
Bright Star Clusters in the Antennae Analyzed with Evolutionary Synthesis
Authors: Fritze Uta , Alvensleben V. , Kurth Oliver
Published: July 2016

The Antennae galaxies (NGC 4038/39) are a pair of relatively nearby (D ~ 19 Mpc for H0 = 75) gas-rich spirals of comparable mass in the process of merging with extensive dynamical and evolutionary synthesis modeling available. With HST WFPC1 Whitmore & Schweizer (1995) (WS95) detected 738 bright Young Star Clusters (YSCs) around the Antennae. YSCs have been detected in many interacting and starbursting galaxies, but the YSC system in the Antennae is the most populous one, well defining an exponential Luminosity Function (LF) over more than 5 mag above the completeness limit. Problems arising from crowding of the YSCs on a bright and variable galaxy background and from the PSF of WFPC1 may cause blending of YSCs and an overestimation of their effective radii.
Gas and Dust in Ultraluminous Galactic Nuclei
Authors: Scoville N.Z. , Yun M.S.
Published: July 2016

Millimeter-wave interferometry has clearly shown the existence of enormous masses (109 – 1010M⊙) of molecular gas concentrated in the nuclear regions (R < 500 pc) of many luminous and ultraluminous infrared galaxies. In these systems, molecular gas is an obvious source of fuel for nuclear starbursts and active galactic nuclei (AGN). In several ultraluminous systems (e.g., Arp 220 and Mrk 231), there now exists CO (2-1) interferometry at ≤ 1″ resolution which reveals for the first time extremely dense, gaseous accretion disks on the scale 50-300 pc. Based on the low velocity dispersion of the molecular gas in the nuclear disks, we believe them to be extremely thin (10-50 pc). In addition, high brightness temperatures in the CO lines (10-20 K) imply that these disks are nearly uniformly filled with a continuous gas distribution, rather than being relatively isolated, self-gravitating GMCs. Although the gas is ‘uniformly’ distributed, the gas densities must be high, > 104 cm−3. When viewed near the plane of the disk, the central AGNs, if they exist, will be totally obscured at optical and near infrared wavelengths. In Mrk 231, our line of sight is probably within 60° of the disk axis, but in Arp 220 the disk is closer to edge-on. In fact, recent near infrared imaging of Arp 220 with the NICMOS camera on the HST reveals totally opaque dust disks embedded within the central star clusters of both nuclei.
Proto–Globular Cluster Candidates in NGC 1275
Authors: Brodie Jean P.
Published: July 2016

The discovery, with HST imaging, of proto–globular cluster candidates in NGC 1275 (Holtzman et al. 1992) was regarded by many as a major success of the merger model for globular cluster formation (e.g. Ashman & Zepf 1992) and has been cited in support of the idea that elliptical galaxies form from the merger of two or more spiral galaxies. A prediction of the Ashman & Zepf model was that newly-formed clusters should be observable in currently or recently merging systems. The NGC 1275 clusters constitute an important test of globular cluster formation models. NGC 1275 is the peculiar cD galaxy at the center of the Perseus cluster. It shows evidence for a merger history and may indeed be undergoing a merger at present. It also has one of the largest known cooling flows.
CO Observations of Luminous IR Galaxy Mergers
Authors: Gao Y. , Solomon P.M.
Published: July 2016

Luminous starbursts are observed to occur mostly as a result of a collision/merger in gas-rich galaxies, and most luminous infrared galaxies (LIGs) are indeed gas-rich mergers. In order to determine the relationship between the IR and molecular gas properties and the galaxy-galaxy interactions, we study LIG mergers in the intermediate merging process. We have observed nearly 20 LIG mergers and together with the CO data in the literature, we have found a correlation between the CO luminosity, LCO, and the projected separation of merger nuclei, RSep, in > 50 LIG mergers. The correlation suggests the molecular content is decreasing as merging advances and is better established with ~ 40 LIG mergers excluding ultraluminous ones, which resembles more a volume-limited, statistically complete sample of LIG mergers. In addition, an anti-correlation between LIR/LCO (the measure of star formation efficiency, SFE) and RSep is evident. One interpretation is that the molecular gas content of LIG mergers is being rapidly depleted due to the merger-induced starbursts and the increase of SFE as merging progresses.
Formation of Plumes in the Head-On Collisions of Galaxies
Authors: Korchagin Vladimir , Tsuchiya Toshio , Wada Keiichi
Published: July 2016

We have studied the collisional interaction of disk galaxies using SPH and N-body numerical simulations. We follow the dynamics of a two-component star-gas disk centrifugally balanced by the gravity of a rigid halo. A companion galaxy is modeled self-consistently, and its two-component disk is balanced by the potential of the stellar halo. This model allows us to follow the dynamics of the gas component in the colliding galaxies simultaneously with the dynamics of the collisionless halo of the companion.
Single Stellar Populations: Colors and Indices
Authors: Kurth O.M. , Fritze U. , Alvensleben V. , Fricke K.J.
Published: July 2016

To determine metallicity and age distributions of globular clusters (GCs) in distant galaxies–now accessible, e.g. to Keck spectroscopy–it is important to have reliable calibrations of the color-metallicity, color-age, and index-metallicity relations.
New Models for Massive Star Populations in Young Starbursts: Summary of the Models and Applications
Authors: Schaerer Daniel , Vacca William D.
Published: July 2016

Using the latest stellar evolution models, theoretical stellar spectra, and a compilation of observed emission line strengths from Wolf-Rayet (WR) stars, we have constructed evolutionary synthesis models for young starbursts (Schaerer & Vacca 1997; see also Schaerer 1996). We provide detailed predictions of UV and optical emission line strengths for both the WR stellar lines and the major nebular hydrogen and helium emission lines, as a function of several input parameters related to the starburst episode.
The Nuclear Interstellar Medium of Ultraluminous Infrared Galaxies
Authors: Van Der Werf P.P.
Published: July 2016

Ultraluminous infrared galaxies (ULIRGs) form the dominant component of the local galaxy population at the highest luminosities (e.g., Sanders & Mirabel 1996 and references therein). They are major mergers of gas-rich galaxies and are characterized by a molecular interstellar medium (ISM) that is concentrated in the central kpc, where it forms a dynamically significant, or perhaps dominant, component (Scoville et al., 1991). Sanders et al. (1988) proposed that ULIRGs might harbor, or evolve into, dust-enshrouded quasars, formed in their obscured centers.
Evolution of Very Luminous Infrared Galaxies
Authors: Wu H. , Zou Z.L. , Xia X.Y. , Deng Z. G.
Published: July 2016

We have completed spectroscopic observations (Wu et al. 1997a) of a sample of 73 very luminous infrared galaxies (log(LIR/L⊙) ≥ 11.5;H0 = 50 km s−1 Mpc−1) from the 2-Jy catalogue (Strauss et al. 1992) using the 2.16m telescope at the Beijing Astronomical Observatory. Spectral and interacting classifications are performed for the sample (Wu et al. 1997b). These statistical results provide strong evidence for the idea that interactions trigger nuclear activity and enhance the infrared luminosity. With the decrease of nuclear separation, relative velocity and specific angular momentum decrease rapidly, while on the contrary, both infrared luminosity and Hα equivalent width increase. Dynamical friction plays an important role even when two galaxies have large separation. This provides a favorable condition for strong star formation. We construct a simple merger sequence, from interaction class 1 to 4, to class 5 and 6 and then to the class 0 regarded as being in the stage of advanced merger. Along this sequence, spectral types change from HII-like to AGN-like. Considering the strong correlation of very luminous infrared galaxies in spectral classification schemes, it is reliable that infrared luminous galaxies evolve from HII-like galaxies to AGN-like galaxies. The different properties of infrared luminous Seyfert 1s and optically selected Seyfert 1s suggest that infrared luminous galaxies could evolve into optical Seyfert 1s in the last stage.
VLA Observations of Neutral Hydrogen in Compact Groups
Authors: Williams B.A. , Van Gorkom J.H. , Yun Min , Verdes-Montenegro Lourdes
Published: July 2016

VLA images of the neutral hydrogen (HI) in the direction of HCG 2, 16, 33, 88, and 92 (Stephan's Quintet) are examined. In HCG 2 and 16, the HI gas is bound to the individual galaxies but shows definite signs of tidal interaction; while in HCG 92, the more compact configuration, the HI gas is contained within a few prominent cloud features well displaced from the optical positions of any of the spiral members. In every case, the motions of the gas are consistent with the motions of the galaxies within the Hickson groups. A range of kinematical properties is observed for the HI gas, from well-ordered rotation, to small-scale systematic gradients within the cloud features.
The X-Ray Properties of Nearby Abell Clusters from the ROSAT All-Sky-Survey
Authors: Ledlow Michael J. , Voges Wolfgang , Owen Frazer N. , Burns Jack O.
Published: July 2016

Using the ROSAT All-Sky-Survey (RASS), we examine the X-ray properties of a statistically complete sample of 294 nearby (z < 0.09) Abell clusters from our VLA 20cm survey (Ledlow & Owen 1995) and 49 Poor Groups (z < 0.03) (Burns et al. 1996). Our analysis includes a catalog of all significant (> 3σ) X-ray peaks, an analysis of the X-ray extents, identification of ICM emission, comparison to optical cluster properties, and a cross-correlation with our radio galaxy catalogue. We will make optical/X-ray overlays of the cluster fields available over the WWW in the near future (see http://astro.nmsu.edu/~mledlow for updates).
Evolution of Dwarf Galaxies in High Pressure Environments
Authors: Murakami I. , Babul A.
Published: July 2016

We use 2D hydrodynamical calculations to examine the effect of the external medium on evolution of supernova-driven outflows from dwarf galaxies. Babul & Rees (1992) have suggested a high external pressure may be able to prevent the outflows from escaping beyond the galaxy and that this material, as it cools and falls back into the galaxy, would serve as fuel for a second epoch of star formation. When thermal pressure is dominant, such evolution of the outflows is seen in our simulations and the gas falls back into the galaxy. Babul & Rees, however, did not take into account the possibility that in high pressure environments such as clusters, galaxies are moving and therefore, subject to ram pressure. In our simulations, we find that ram pressure causes the mass shell associated with the outflow to fragment into clumps. These clumps remain in the vicinity of the galaxy for a few tens of million years before being swept away. The distribution of the clouds gives the galaxy in our simulations a characteristic “head-tail” appearance. If the clouds experience star formation during this epoch, we would expect that the light distribution would also show this “head-tail” feature. The tail-like structure is a transient feature that will eventually disappear. We speculate that galaxies observed by Dickinson (1996) in the z = 1.15 cluster around 3C324 are such galaxies.
The First Stars
Authors: Arnett David
Published: July 2016

The possible nature of the first generation of stars is considered, using a star of 25M⊙as an example. General nucleosynthesis and the production of CNO catalysts is examined in detail. The increase in neutron excess and its significance for yields from explosive burning is discussed. An estimate of the ratio of ionizing photons to heavy elements produced is derived, for use in early universe simulations.
Abundances fromz=0 toz=5
Authors: G. York Donald
Published: July 2016

Interstellar abundances are compared for the Milky Way disk, the Milky Way halo, the Large and Small Magellanic Clouds and the damped Lyman alpha systems among the QSO absorption line systems. While a new set of observational aspects of element formation in the Universe is emerging, including a dearth of formation activity fromz=5 toz=3, the predicted signal of [Si/Fe] decreasing from highzto lowz, as Type I supernovae start contributing to Fe production, has not yet been seen.
The Formation of First Generation Stars and Globular Clusters in Protogalactic Clouds
Authors: Lin D.N.C. , Murray S.D.
Published: July 2016

Within collapsing protogalaxies, thermal instability leads to the formation of a population of cool fragments which are confined by the pressure of a residual hot background medium. The critical mass required for the cold clouds to become gravitationally unstable and to form stars is determined by both their internal temperature and external pressure. Massive first generation stars form in primordial clouds with sufficient column density to shield themselves from external UV photons emitted by nearby massive stars or AGNs. Less massive photoionized clouds gain mass as they undergo cohesive collisions with each other, and lose mass due to ram pressure stripping by the residual halo gas. Collisions may also trigger thermal instability and fragmentation into cloudlets. While most cloudlets have substellar masses, the largest become self-gravitating and collapse to form protostellar cores without further fragmentation. The initial stellar mass function is established as these cores capture additional residual cloudlets. Energy dissipation from the mergers ensures that the cluster remains bound in the limit of low star formation efficiency. Dissipation also promotes the formation and retention of the most massive stars in the cluster center. On the scale of the protogalactic clouds, the formation of massive stars generates intense UV radiation which photoionizes gas and quenches star formation in nearby regions. As gas density accumulates in the center of the the galactic potential, the self regulated star formation rate increases. At the location where most of the residual gas can be converted into stars on its internal dynamical timescale, a galaxy attains its asymptotic kinematic structure such as exponential profiles, Tully-Fisher, and Faber-Jackson laws.
X-Ray Coronae from Stars
Authors: Pallavicini R.
Published: July 2016

A number of major advances in stellar coronal physics have occurred since 1990 mainly as a consequence of imaging observations by ROSAT and spectroscopic observations by ASCA. These can be summarised as follows:

1.

an all-sky survey has been performed by ROSAT at a sensitivity of ~ 2 × 10−13 erg cm−2 s−1, complemented by pointed observations an order of magnitude deeper;

2.

complete mapping and deeper pointings have been obtained for virtually all open clusters closer than ~ 500 pc, and covering the age range from ~ 30 Myr to ~ 700 Myr;

3.

complete mapping and deeper paintings have been obtained for several Star Forming Regions (SFRs) covering the age range ~ 1 to ~ 10 Myr;

4.

spectroscopic observations of bright coronal sources have been obtained with EUVE and ASCA allowing the derivation of the temperature structure and elemental abundances.
The Astro-E Mission
Authors: Ogawara Y.
Published: July 2016

The past three decades have seen an explosion in high-energy astrophysics. We have found X-ray astronomy to be an indispensable tool in understanding our Universe. The discipline has become mature, and future X-ray observatories must be more highly specialized. High-resolution spectroscopic imaging in the band above 2 keV, systematically exploited by ASCA, has led to much new astrophysical knowledge. ASCA has also been playing a particularly important role in studying sources hidden behind dense material. Astro-E, the successor of ASCA, is scheduled for launch in the year 2000 by the Institute of Space and Astronautical Science (ISAS) with its newly developed M-V rocket (Ogawara & Inoue 1997). Our new Astro-E observatory features high energy resolution and high sensitivity over the broad energy range 0.5 keV to 600 keV. The general emphasis of the observatory is to provide large collecting areas at higher energies, with angular resolution good enough to avoid the confusion limit. This paper provides a brief description of the performance of the Astro-E instruments.
GRO J1744-28 and the Rapid Burster; Bizarre Objects!
Authors: Lewin Walter H.G.
Published: July 2016

The bursts from GRO J1744-28 are due to accretion instabilities as is the case for type II bursts in the Rapid Burster. Both sources are transient Low-Mass X-ray Binaries, and they both exhibit unusual quasi-periodic-oscillations in their persistent X-ray flux following several (not all) of the type II bursts. There are important differences too. GRO J1744-28 is an X-ray pulsar; the Rapid Burster is not. In addition, the pattern of bursts and the burst peak luminosities are very different for the two sources. Time intervals between the rapidly repetitive bursts in the Rapid Burster can be as short as 10 sec, in 1744-28 they are as short as 200 sec. The peak luminosities of the bursts from GRO J1744-28 can exceed the Eddington luminosity (for assumed isotropic emission) by one to two orders of magnitude. The QPO centroid frequencies (see above) differ by an order of magnitude (~0.04 Hz for the Rapid Burster, and 0.3 Hz for GRO J1744-28). The difference in behavior p obably lies in the difference in the magnetic dipole field strength of the accreting neutron stars (for GRO J1744-28 it is almost certainly much higher than for the Rapid Burster). It remains puzzling, why GRO J1744-28 and the Rapid Burster are the only known sources which exhibit rapidly repetitive type II bursts.
Gamma-Ray Burst Observations with BATSE
Authors: Fishman Gerald J.
Published: July 2016

Gamma-ray bursts (GRBs) will be recorded as one of the outstanding new phenomena discovered in astronomy this century. About once per day, a burst of gamma rays appears from a random direction on the sky. Often, the burst outshines all other sources of gamma-rays in the sky, combined. This paper reviews some of the key observed phenomenon of bursts in the hard x-ray/gamma-ray region, as observed with the BATSE experiment on the Compton Gamma Ray Observatory. The observed time profiles, spectral properties and durations of gamma-ray bursts cover a wide range. Recent breakthroughs in the observation of gamma-ray burst counterparts and afterglows in other wavelength regions have marked the beginning of a new era in gamma-ray burst research. Those observations are described in following papers in these proceedings.
Diffuse EUV Emission from Clusters of Galaxies
Authors: Bowyer S. , Lieu R. , Mittaz J. P.
Published: July 2016

Diffuse EUV emission has been detected in five clusters of galaxies: Virgo(Lieu et al., 1996a), Coma (Lieu et al., 1996b), Abell 1795, Abell 2199, and Abell 4038. These results were 'obtained with the Deep Survey Telescope of the Extreme Ultraviolet Explorer (Bowyer and Malina, 1991) using a Lex/B filter which covers the 60 to 170 A band. The extent of this diffuse emission from these clusters r_anges from 20' to 40' in diameter. The statistical significance of these results varies from 8 to 50 standard deviations. Some EUV emission would be expected fromthe low-energy tail of the wellstudied X-ray cluster emission, However, the EUV emission detected is far greater than the expected emission from the X-ray-emitting gas. Marginal sigatures of this “soft excess” are often present in the lowest energy resolution band of the ROSAT PSPC where it is typically less than a 20% effect. In the case of Abell 2199, no low energy excess is present in the ROSAT data. In the data taken with EUVE, however, the excesses range from 70% to 600%.
Chemical Abundances of Early Type Stars
Authors: Tanaka S. , Kitamoto S. , Suzuki T. , Torii K. , Corcoran M.F. , Waldron W.
Published: July 2016

X-rays from early-type stars are emitted by the corona or the stellar wind. The materials in the surface layer of early-type stars are not contaminated by nuclear reactions in the stellar inside. Therefore, abundance study of the early-type stars provides us an information of the abundances of the original gas. However, the X-ray observations indicate low-metallicity, which is about 0.3 times of cosmic abundances. This fact raises the problem on the cosmic abundances.
X-Ray Observations of Orion OBib Association
Authors: Nakano M.
Published: July 2016

The signs of the active star formation in the Orion region are mainly found in the direction of the two giant molecular clouds - Ori A and Ori B -. Recent objective prism survey in the Orion region shows large number of Hα emission-line stars distributed outside of the giant molecular clouds (Nakano et al., 1995). Many weak-lined T Tauri star candidates are also discovered by the discrimination analysis of the X-ray sources found in the ROSAT all sky survey (RASS) (Sterzik et al., 1995). Although such huge number of pre-main sequence stars outside of the molecular cloud was not expected, their nature is still in controversial (Neuhäuser, 1997). To know the X-ray properties of these sources in the Orion region, we have carried out the ASCA observations.
ASCA Observations of Class I Protostars in the Rho Oph Dark Cloud
Authors: Tsuboi Y. , Koyama K. , Kamata Y. , Yamauchi S.
Published: July 2016

On 1993 August 20, we observed the Rho-Oph dark cloud and detected hard X-rays from Class I sources (Koyama et al.(1994), Kamata et al.(1997)). One of the sources (EL29) showed a flare-like variability, while another (WL6) exhibited sinusoidal variation with no large spectral change. The later would be due to a spin of the protostar. The sinusoidal period of about 1 day is shorter than spin periods of TTSs of ~3-7 day.
Multifrequency Spectral Studies of SNRs
Authors: Zhang X.Z. , Wu X.J. , Higgs L.A. , Landecker T.L. , Green D.A. , Leahy D.A.
Published: July 2016

Radio supernova remnants(SNRs) of large angular diameter are obvious objects for multifrequency spectral studies from long wavelengths to short wavelengths, as resolutions at low frequency are usually about several arcminutes. An international cooperation consists of MRAO, BAO, DRAO, MPI, and astronomers from Beijing University, Beijing Normal University, China and Calgary University, Canada. This international collaboration is also a part of the Panorramic Spectral Imaging of the Milky Way (PI R. Taylor). Some results on HB21, G78.2+2.1, and HB9 are presented in this paper.
Pulsar Nebulae
Authors: Shibata Shinpei , Kawai Nobuyuki , Tamura Keisuke
Published: July 2016

Recent observation with ASCA reveals that radio pulsars own X-ray diffuse nebulae around them. 11 such nebulae have been reported (Harrus, Hughes & Helfand 1996, Shibata et al. 1997, Kawai, Tamura & Shibata 1997). It is most likely that these nebulae are synchrotron nebuale powered by the pulsar wind, the outflow of relativistic particles. Kawai, Tamura and Shibata (1997) reduced an empirical law for the nebula luminosity Lx as a function of the rotation power Ėrot of the central pulsar: Lx/Ėrot = −12.3 + 0.27 log Ėrot.
Magnetic Reconnection as the Origin of Galactic Ridge X-Ray Emission
Authors: Tanuma S. , Yokoyama T. , Kudoh T. , Shibata K. , Matsumoto R. , Makishima K.
Published: July 2016

We present a scenario for the origin of the hot plasma in our Galaxy, as a model of a strong X-ray emission (LX(2 – 10keV) ~ 1038 erg s−1), called Galactic Ridge X-ray Emission (GRXE), which has been observed near the Galactic plane. GRXE is thermal emission from hot component (~ 7 keV) and cool component (~ 0.8 keV). Observations suggest that the hot component is diffuse, and is not escaping away freely. Both what heats the hot component and what confines it in the Galactic ridge are still remained puzzling, while the cool component is believed to be made by supernovae. We propose a new scenario: the hot component of GRXE plasma is heated by magnetic reconnection, and confined in the helical magnetic field produced by magnetic reconnection or in the current sheet and magnetic field. We solved also the 2-dimensional magnetohydrodynamic (MHD) equations numerically to study how the magnetic reconnection creates hot plasmas and magnetic islands (helical tubes), and how the magnetic islands confine the hot plasmas in Galaxy. We conclude that the magnetic reconnection is able to heat up the cool component to hot component of GRXE plasma if the magnetic field is localized into intense flux tube with Blocal ~ 30 μG (the volume filling factor of f ~ 0.1).
X-Ray Obervation of the Normal Spiral Galaxies NGC2903 and NGC628 with ASCA
Authors: Mizuno T. , Ohbayashi H. , Iyomoto N. , Makishima K.
Published: July 2016

X-ray emission from spiral galaxies without activity is thought to consist of low-mass X-ray binaries (LMXBs), and the Einstein observations established the relation between X-ray (0.2-4 keV) and optical luminosities as log(LX/LB) ~ −4 (Fabbiano, 1992). This relation has been used when discussing the activity other than LMXBs (Iyomoto, 1996). However, spectral information of Einstein Observatory was rather poor above 3 keV, where LMXBs would emit significant energy flux. Therefore we performed ASCA observations of two normal spirals, NGC2903 and NGC628, in order to better calibrate the LX - LB relation.
Clusters of Galaxies in a Flat CHDM Universe
Authors: Habe A. , Hanyu C. , Yachi S.
Published: July 2016

Cold and hot dark matter (CHDM) model is one of viable models which can reproduce the large scale structure of the universe. HDM may affect structure of clusters of galaxies in CHDM universe. Bryan et al. (1994) gave numerical results of CHDM model that explain some statistical features of X-ray clusters of galaxies, e.g. X-ray luminosiry-temperature realtion, L ∝~ T3.5, without considering radiative processes. However their numerical resolution is insufficient to resolve the cores of X-ray clusters. So, we simulate the formation of clusters in CHDM universe more carefully.
Two-Dimensional Accretion Disk Models of a Neutron Star
Authors: Fujita M. , Okuda T.
Published: July 2016

We investigate the accretion disks around compact objects with high mass accretion rates near the Eddington's critical value ME, where radiation pressure and electron scattering are dominant. This raises next problems: (a) whether stable disks could exist in relation to the theory of thermal instabilities of the disk and (b) what characteristic features the disks have if the stable disks exist. A non-rotating neutron star with the mass M = 1.4M⊙, radius R* = 107cm and the accretion rate Mac = 2.0 and 0.5Mac (models 1 and 2) is considered as the compact object. We assume the α-model for the viscosity and solve the set of two-dimensional time-dependent hydrodynamic equations coupled with radiation transport. The numerical method used is basically the same as one described by Kley and Hensler (1987) and Kley (1989) but we include some improvements in solving the difference equations (Okuda et al. 1997). The initial configuration consists of a cold, dense, and optically thick disk which is given by the standard α-model (Shakura and Sunyaev 1973) and a rarefied optically thin atmosphere around the disk.
X-Ray Fluctuations from the Advection-Dominated Accretion Disk with a Critical Behavior
Authors: Takeuchi M.
Published: July 2016

The new model for X-ray fluctuations of Cyg X-1, which is based on the fluid dynamics, is presented. The model is the optically thin and advection-dominated accretion disk model, which has a critical behavior.
Testing the Central Engines in AGNs
Authors: Yamazaki N. , Taniguchi Y. , Kaburaki O.
Published: July 2016

It is very important to estimate the relationship between the central blackhole mass MBH and bolometric luminosity Lbol of AGNs, because such a relation may be useful to judge the validity of various models for AGNs (Koratkar & Gaskell 1991, hereafter KG91). The predictions of various models are summerized in Table 1, where B is the magnetic field around the central object.
Importance of the High Energy Channel for the Gamma-Ray Burst Data
Authors: Mészáros A. , Bagoly Z. , Balázs L. G. , Horváth I. , Mészáros P.
Published: July 2016

Extensive data bases on Gamma-Ray Burst (GRB) properties such as the BATSE 3B catalog (Meegan et al. 1996) contain a wealth of statistical information. The nine entries of the 3B database for each GRB consist of two durations, T50, T90, which contain 50% and 90% of the burst energy, respectively; four fluences (time-integrated energy fluxes) F1, F2, F3, F4, defined over different energy channels; and three measures of the peak flux (each summed over the four energy channels), measured over three different resolution timescales (64 ms, 256 ms and 1024 ms). Thus the initial number of variables is n = 9. There is, of course, some incompleteness in the catalog. There are 625 GRBs having all 9 non-zero quantities, and only they are considered here.
Optical Follow-Up Observations of ASCA Lynx Deep Survey
Authors: Ohta K. , Akiyama M. , Nakanishi K. , Yamada T. , Hayashida K. , Kii T. , Ogasaka Y.
Published: July 2016

Since the bulk of the energy density of the Cosmic X-ray Background (CXB) resides in the harder energy band than that of the ROSAT band (0.5-2 keV) and since the X-ray sources identified in the ROSAT band have X-ray spectra softer than that of the CXB, investigation of nature of the X-ray sources at the harder energy band is indispensable to solve the origin of the CXB. However, only 2-3% of the CXB in the hard band (2-10 keV) had been resolved into discrete sources (Piccinotti et al. 1982, ApJ 253, 485). We present our preliminary results of optical follow-up observations of the ASCA Lynx deep survey.
UV energy distributions of active cool stars
Authors: Morossi C. , Franchini M. , Malagnini M.L.
Published: July 2016

We present semi-empirical models based on the “minimum-temperature-concept” in order to provide a description of the UV spectra of solar type stars consistent with the observational data.
Determining the masses of white dwarfs in magnetic cataclysmic variables from x-ray observations
Authors: Wu Kinwah , Cropper Mark , Ramsay Gavin
Published: July 2016

A method to determine the masses of white dwarfs in magnetic cataclysmic variables from X-ray observations is presented. The method is appropriate for both eclipsing and non-eclipsing systems, for it is insensitive to the orbital inclination of the systems.
Empirical surface gravities
Authors: Maxted P. F. L.
Published: July 2016

The surface gravity of a star (log g) is a fundamental parameter in models of stellar atmospheres. Given suitable spectra, log g can be determined from such models with an accuracy of 0.1dex, at best. Detached eclipsing binary stars can provide values of log g an order of magnitude more accurate than this, though for a more limited range of stars. Naturally, less accurate surface gravities can be obtained for a wider range of eclipsing binary stars.

These facts are well known, so in this short review I will outline the types of stars to which the two methods have be usefully applied and might be applied in the near future. This naturally leads to the question of where the two ranges overlap and the comparison of results from the two methods. Techniques for allowing this comparison to made directly will be described. Surface gravities derived from winds in hot stars and (indirectly) from gravitational redshifts in white dwarf stars will also be covered briefly.
The effective temperatures of hot stars
Authors: Crowther P.A.
Published: July 2016

We review the effective temperature scale of hot (≤ 10 kK) stars, including results from direct, continuum and ionization equilibrium techniques. We discuss the impact of recent developments in theoretical model atmospheres for OB subdwarfs, dwarfs and supergiants, white dwarfs and Wolf Rayet stars and present a revised Teff scale for OB stars. Direct techniques coupled with Kurucz model atmospheres allow Strömgren photometry to be used as a sensitive Teff indicator for normal stars with Teff ≥ 25 kK. Reliable Teff determinations for hotter, low surface gravity and H-deficient stars require sophisticated ionization equilibrium techniques, generally considering non-LTE and line-blanketing effects.
The broadening of metallic lines in cool stars
Authors: Anstee S. D. , O'Mara B. J. , Ross J. E.
Published: July 2016

A theory for the broadening of spectral lines by collisions with atomic hydrogen developed by Anstee and O'Mara [1] is described and when applied to strong lines of elements in the sun leads to abundances which are independent of non-thermal motions in the photosphere and in excellent agreement with meteoritic values. In the case of the solar abundance of iron the results lead to a resolution of recent conflict concerning possible differences between the abundance of iron in the sun and meteorites. Excellent results obtained with the Mg b-lines permit these lines to be used in abundance determinations in other stars and also makes them particularly useful in determining the temperature structure in cool stars.
Theory of low mass stars, brown dwarfs and extra-solar giant planets
Authors: Chabrier Gilles , Baraffe Isabelle
Published: July 2016

Accurate modeling of the mechanical and thermal properties of very-lowmass stars (VLMS), Brown Dwarfs (BD) and Extra-solar Giant Planets (EGP) is of prior importance for a wide range of physical and astrophysical problems, from the fundamental physics point of view to the astrophysical and cosmological implications. They provide natural laboratories to test the different theories, equations of state, nuclear reaction rates, model atmospheres aimed at describing the physics of dense and cool objects. They represent the largest stellar population in the Galaxy, and thus provide a substantial contribution to the Galactic (disk) mass budget. Finally they represent one of the most intriguing questions in our understanding of the formation of star-like objects: are planet and star formation processes really different? Is there, and if so what is, a minimum mass for the formation of star-like objects? This field has blossomed recently with the discovery of several brown dwarfs (Nakajima et al, 1995; Rebolo et al., 1995) and numerous exoplanets since 51 Pegasi (Mayor and Queloz 1995; Mayor, this conference), which provide important information to challenge the theory.
The Asymptotic Giant Branch
Authors: Lattanzio J. C. , Frost C. A.
Published: July 2016

For stars with masses between about 1 and 8 M⊙ the ascent of the Asymptotic Giant Branch (AGB) is the last nuclear powered evolutionary stage. Following this the stars eject a planetary nebula and fade as white dwarfs. Although only short in duration, the AGB is very important due to the nucleosynthesis which occurs. Here we briefly review the species produced and the mechanism for their production. We then discuss the current uncertainties in quantitative predictions of this nucleosynthesis, which centre on our determination of convective boundaries.
Theory, observation and experiment: stellar hydrodynamics
Authors: Arnett David
Published: July 2016

Computer technology now allows two dimensional (2D) simulations, with complex microphysics, of stellar hydrodynamics and evolutionary sequences, and holds the promise for 3D. Careful validation of astrophysical methods, by laboratory experiment, by critical comparison of numerical and analytical methods, and by observation are necessary for the development of simulation methods with reliable predictive capability. Recent and surprising results from isotopic patterns in pre-solar grains, 2D hydrodynamic simulations of stellar evolution, and laser tests and computer simulations of Richtmeyer-Meshkov and Rayleigh-Taylor instabilities will be discussed, and related to stellar evolution and supernovae.
Chemical evolution of galaxies — challenges for stellar astronomy
Authors: Sadler Elaine M.
Published: July 2016

I discuss several current problems in understanding the chemical evolution of galaxies which have particular relevance for fundamental stellar astronomy.
Globular cluster ages: are they converging?
Authors: VandenBerg Don A.
Published: July 2016

Since the early 1970's, the consensus “best estimate” of the age of the Galactic globular cluster (GC) system has been 15–16 ±3 Gyr. However, a number of recent studies, which are briefly reviewed herein, have suggested that this estimate is too high by ≳ 15%. Based on a consideration of new stellar models and the latest developments concerning the cluster distance scale, the present paper lends support to the notion that the first globulars began to form in the Galaxy 13–14 Gyr ago. In addition, our analysis of absolute GC ages adds to the mounting evidence that the dispersion in age among clusters having similar metallicities is probably quite small. As a consequence, age can hardly be the primary factor causing the wide diversity in their horizontal-branch morphologies.