bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new compact groups sample in the southern sky
Authors: Iovino A. 
Published: July 2016

AbstractCompact groups of galaxies are an extreme class of object, ideal for the study of galaxy interactions and their effects. In this paper we present a new algorithm, devised to select compact groups from digitized catalogues of galaxies and especially suited to reach fainter magnitudes. We present also the results obtained from the redshift survey of the bright subsample of such groups.
Properties of Dust in Giant Elliptical Galaxies: The rôle of the Environment
Authors: Goudfrooij Paul 
Published: July 2016

AbstractThe properties of dust in giant elliptical galaxies are reviewed, with particular emphasis on the influence of the environment.After normalizing by the optical luminosities, a strong anticorrelation between the masses of dust and hot gas in X-ray bright ellipticals is found. Furthermore, large-scale, regularly-shaped dust lanes (which are symmetric with respect to the galaxy nucleus) are only found to be present in ellipticals with the lowest ratios of the mass of hot gas to the blue luminosity (Mhot/LB ≲ 0.04 in solar units). This can be explained by the short time scale for the destruction of dust grains within the hot, X-ray- emitting gas compared to the formation timescale of such dust lanes in early-type galaxies.Dust within ellipticals in “loose” environments (i.e. in the field or in loose groups) is typically characterized by small values of RV ≡ AV/EB−V (i-e. small characteristic grain sizes), and distributed in dust lanes with a smooth, relaxed morphology. On the other hand, dust in ellipticals that are in or near the center of dense groups or clusters is typically much more irregularly distributed, and characterized by RV values that are close to the Galactic one.I predict that ellipticals containing “relaxed” dust lanes with typical dust masses of 106 − 107M⊙ do not contain hot, X-ray-emitting gas.
Observational properties of galaxies in small systems
Authors: Jõeveer M. 
Published: July 2016

AbstractThe mean absolute luminosities and diameters of galaxies in double and triple configurations are compared with the same characteristics for single galaxies. Members of optical pairs and triplets are used as the sample of single galaxies. The mean luminosities of galaxies in physical pairs and triplets are found to be the same as for single galaxies. At the same absolute luminosity, single galaxies have larger diameters compared to galaxies in pairs and triplets.
Deep Optical Imaging of the Compact Group “Seyfert’s Sextet”
Authors: Nishiura S. 
Published: July 2016

AbstractThe compact group of galaxies “Seyfert’s Sextet” shows irregularly shaped soft X-ray morphology. In order to understand its origin, we have obtained a deep optical (VR + I) image of the group. Our image shows that a faint envelope surrounds the member galaxies. We find that optical and soft X-ray images are significantly similar in morphology. This similarity provides direct morphological evidence that the dark matter in Seyfert’s Sextet was originally associated with the individual galaxies and is now spreading out around the group.
On the Verge of Coalescence: a Dusty Group of Galaxies
Authors: Temporin S. , Weinberger R. , Kerber F. 
Published: July 2016

AbstractWe have found a new, very compact group of galaxies characterized by a median projected separation between galaxies of 5.2/h kpc and a very low velocity dispersion. All the observed member galaxies show emission line spectra and a disturbed morphology. From these properties it emerges that this compact group is in an extremely advanced stage of evolution.
Inventory of Galaxy Properties in Small Scale Structures
Authors: Tanvuia L. , Kelm B. , Focardi P. , Rampazzo R. , Zeilinger W. W. 
Published: July 2016

AbstractWe report on a broad-band R surface photometric and low resolution spectroscopic study of a set of galaxies located in small groups and pairs of galaxies considered to be in low density environment. Groups span a wide range in density and show different morphological mix. We are analyzing systemic velocities, photometric parameters and spectral properties of the dominant galaxies in the groups. Our aim is to investigate the connection between interaction and induced galaxy activity, from star formation to AGN activity.
Detection of hot plasma around M96 in the Leo-I group
Authors: Pedersen K. 
Published: July 2016

AbstractThe nearby (D = 11 Mpc) sparse group of galaxies, Leo-I, is in many respects unique. It is the nearest group containing both bright spirals (M96 and M95) and a bright elliptical (M105). A giant (diameter ca. 200 kpc) intergalactic Hɪ ring orbits the central M105/NGC3384 galaxy pair and appears to interact with M96. If M96 is really in the group core, the Leo-I group provides an unusually “clean” route to determining the Hubble constant. In our 22 ksec ASCA SIS exposure of M96 we have detected diffuse X-ray emission extending more than 10 arcminutes North of M96, in the direction of the Hɪ ring. The morphology and spectral characteristics of the diffuse emission shows that M96 has recently interacted with the Hɪ ring, indicating that M96, the Hɪ ring and the central galaxy M105 are at the same distance within a few percent.
Understanding low and high velocity dispersion compact groups
Authors: Mamon G. A. 
Published: July 2016

AbstractA galaxy system must have a minimum velocity dispersion for its mass to be greater than the sum of the masses of its galaxies. Nearly half of the nearby Hickson compact groups (HCGs) have too low a velocity dispersion in comparison with the rotational velocities of their spiral galaxies and internal velocity dispersions of their early types.A detailed study of the low velocity dispersion group, HCG 16 – the only known group of late-type galaxies with diffuse intergalactic X-ray emitting hot gas – reveals that half of the diffuse X rays are associated with foreground/background sources and the remaining gas is clumpy and mostly associated with the bright galaxies of the group. The large-scale environment of the group suggests that HCG 16 lies where a cosmological filament falls perpendicularly onto a large-scale sheet.The observed frequency of compact groups is lower than predicted from the extended Press-Schechter formalism, which also predicts that most 1013 M⊙ objects in the Universe must be fairly old and hence have already coalesced into single objects, reminiscent of elliptical galaxies over-luminous in X-rays that are now being discovered.Thus, the low survival time of dense groups against the merging instability is no longer a worry for compact groups, as they form in large enough numbers. I show why other arguments against the reality of HCGs no longer hold, partly because of the biases of Hickson’s sample.
Stephan’s Quintet: Implications for Compact Groups
Authors: Sulentic Jack W. 
Published: July 2016

AbstractWe review old and new observational data for Stephan’s Quintet (SQ), the most famous compact galaxy group. Recently obtained multi-wavelength data has helped to clarify the past and present evolutionary history of this group. If SQ is typical of the compact group phenomenon, then: 1) the groups evolve slowly, resisting merging, due to the injection of energy from high velocity intruders and 2) show low levels of enhanced star formation because individual component ISM’s are quickly stripped via intruder collisions with resultant gas either too hot or cold/diffuse to form many stars. Infall of residual near nuclear gas may also stimulate the development of AGN.
Minor Mergers and the Formation of Shell Galaxies
Authors: Charmandaris V. , Combes F. 
Published: July 2016

AbstractWe present a new mechanism which can explain the observed radial displacement between the stellar and gaseous shells observed around early type galaxies. Our model is based on the well-known phasewrapping process taking into account that a fraction of the interstellar medium is clumpy and consequently it experiences a low dynamical friction during a merging event. Moreover, our recent detection of cold molecular gas associated with the outer shells of Centaurus A is in agreement with the proposed model. This suggests that a considerable fraction of molecular gas in minor mergers may be distributed away from the nuclear regions and remain undetected.
Masaai warrior shield: The life time of a three body system
Authors: Lehto Harry J. , Heinämäki Pekka , Chernin Arthur D. , Valtonen Mauri J. 
Published: July 2016

AbstractWe have investigated the behavior of a general Newtonian three body system using the simplest initial conditions. We calculated the evolution of about a million bound three body systems. Within our resolution these cover all the possible initial states. All these systems eventually decay with one body being ejected from the residual binary system. The overall pattern representing the decay time scales projected on a homology map is dominated by resonances. In general appearance it reminds us of a traditional Masaai warrior shield.
Star Formation and Environment in Compact Groups of Galaxies
Authors: Iglesiás-Paramo J. , Vílchez J. M. 
Published: July 2016

AbstractHα luminosities are presented in order to study the Star Formation Rates (SFRs) of a sample of galaxies in compact groups from Hickson's (1982) catalogue. Although the comparison of the SFRs of the disk galaxies in our sample with those of a sample of field galaxies yielded no difference between the average SFRs for disk galaxies in compact groups and in the field, environmental effects seem to influence the Hα luminosities of late and early-type galaxies in compact groups. No relationship was found between the total normalized Hα luminosities of the groups and some dynamical parameters, indicating that the dynamical state of the group does not influence the SFR of the group. The lack of dominant interaction induced starbursts in our sample is compatible with a scenario for compact groups of galaxies in which the dark matter of the group is arranged in a common halo, thereby preventing a fast collapse of the galaxies.
On the Initial Mass Function of Be Stars and the Missing Be Stars of Late Spectral Types
Authors: Zorec J. 
Published: July 2016

AbstractThis is an attempt at determining the IMF (Initial Mass Function) of Be stars relative to that of B stars in the vicinity of the Sun. We have represented the IMF as a power function of the stellar mass Mβ, so that the relative IMF is then proportional to Mβ(Be)–β(B). Allowing for systematic differences in the counting of Be stars due to their apparent overluminosity, a difference β(Be) – β(B) ~ 0 is found, which may indicate that there are no huge intrinsic differences between the two types of objects. In these calculations changes of spectral types due to high rotation were not taken into account. This effect may still strongly affect the results obtained. By extrapolating the MβBe) – β(B) curve to spectral types later than B7, we reckon that in a volume limited to the apparent magnitude V = 7 there may be about 150 still undetected Be stars of late spectral types.
Spectroscopic Investigations of the Main-Sequence B Stars in the Association Cas OB2 and the Open Cluster Platais 1 (C2128+488)
Authors: Usenko I.A. , Kovtjukh V.V. , Andrievsky S.M. , Klochkova V.G. , Panchuk V.E. , Ermakov S.V. 
Published: July 2016

AbstractA spectroscopic investigation of four main-sequence stars in the association Cas OB2 (HD 17327A and B, HD 16893, HD 17443) and of two stars in the open cluster Platais 1 (No. 1 (1921) and No. 111 (1600)) was carried out using high-resolution CCD spectra, obtained with echelle-spectrometer ”LYNX” (6-m telescope, Special Astrophysical Observatory, Russian Academy of Sciences). We have determined the atmospheric parameters for the program stars, their projected rotational velocities and elemental abundances in their atmospheres. Two new HgMn stars - HD 17327A and Platais No. 1 - were detected. HD 17443 is not a Be star.
Long-Term Variability in the Winds of λ Eridani and 66 Ophiuchi
Authors: Peters Geraldine J. 
Published: July 2016

AbstractVariations in the winds of the Be stars λ Eri and 66 Oph during the lifetime of the IUE spacecraft and the response of the Hα-emitting disk to these changes are briefly discussed. Common behavior is identified and evidence for cyclical variability on a time scale of ∼1 yr is presented.
Multiperiodic Variability and Outbursts of 28 Cygni
Authors: Tubbesing S. , Rivinius Th. , Wolf B. , Kaufer A. 
Published: July 2016

Abstract28 Cygni was observed during two seasons spectroscopically. The radial velocities of more than 15 spectral lines were measured and searched for periodic variability. Two closely spaced periods were found. A two-dimensional analysis of the line profile variability yielded the same periods and provided the power and phase distribution across the line profiles. An outburst covered by our data coincides with the time of constructive interference of both periods. 28 Cyg is the second case for which outbursts seem to be triggered by multi-mode beating.
On the Excitation Mechanism for the Nonradial Pulsations in ϵ Persei
Authors: Kambe Eiji , Saio Hideyuki , Lee Umin 
Published: July 2016

AbstractWe have examined whether the kappa-mechanism at the ”Z” opacity bump can excite overstable nonradial pulsation (NRP) modes such as those responsible for the line-profile variations (lpv) observed for ϵ Persei (Gies et al. 1999).From the lpv modeling with realistic stellar parameters and the state-of-the-art codes, we confirmed that the observed lpv can generally be explained by the modes with l values suggested by Gies et al. (1999). We have also found that some tesseral modes, which have smaller m than those of sectoral modes, can reproduce the observed lpv well for the periods of 3.51hr/3.84 hr and 4.06hr/4.54 hr. Our linear non-adiabatic nonradial pulsation analysis applied to massive (13M⊙––14M⊙) stars shows that the periods of higher |m| values in the co-rotating frame are too long to be excited by the Z-bump kappa-mechanism while the smaller |m| values give marginal consistency.
Recent Spectroscopic Evidence for Aperiodic Activity in Classical Be Stars
Authors: Smith Myron A. 
Published: July 2016

AbstractThis review focuses on aperiodic line profile activity in several Be stars, ignoring attributes of pulsations probably occurring in any of the stars studied. Herein, I discuss spectroscopic evidence of heating (and cooling) of regions of Be star atmospheres, of line profile transients called dimples and high velocity absorptions. These features will be interpreted in terms of mass ejections (not necessarily permanent). Some of these events are violent and spasmodic, some are ordered and quasisteady, and some are associated with downflows. I close with new evidence for time-varying, corotating clouds suspended over a few Be stars.
Can Magnetic Fields Be Detected in Be Stars?
Authors: Mathys Gautier , Smith Myron A. 
Published: July 2016

AbstractThe results of observations aimed at detecting magnetic fields in the Be star λ Eri are reported. The observational data are analyzed both through application of an approximate analytical method and through computation of a number of simple numerical models in view of deriving constraints on the magnetic fields. General conclusions are drawn about future prospects for magnetic field detections in Be stars.
Surface Magnetic Fields in Early-Type Stars
Authors: Airapetian V. S. 
Published: July 2016

AbstractRecent observations imply magnetic activity in atmospheres of early-type stars. We explore the possibility that stressed surface magnetic fields can be driven by inertial oscillations, such as r-modes which are vorticity waves. We show that vorticIAL MOTIOns are able to supply helicity to drive magnetic activity in stellar atmospheres.
Chinese and Japanese Participation in B/Be Star Campaigns
Authors: Hao J. 
Published: July 2016

AbstractIn the early 1980’s, astronomers at the Beijing Astronomical Observatory (BAO) entered a collaboration in a long term photometric observing project on Be stars which included about 30 stars. For example, in 1983 the group at BAO organized a multi-site campaign to measure the short term variability of EW Lac, KX And, KY And, o And, and LQ And. In 1989, 48 Per was selected to be one of the targets of MuSiCoS campaign in which many stellar astronomers at the BAO participated. In 1991, the Be group at the BAO joined a campaign on the prototypical nonradially pulsating B star, 53 Per. In 1992, French & Chinese astronomers proposed a joint campaign on o And and EW Lac. Astronomers in Japan are also active in Be star campaigns and in 1993-5 they organized several campaigns on few well known Be stars (ζ Oph, EW Lac, ϒ Cas, λ Eri and 28 Cyg).
Results from MuSiCoS Campaigns on Be stars
Authors: Henrichs H.F. , Neiner C. , Hubert A.M. , Floquet M. , Team MuSiCoS ,   and MuSiCoS Team
Published: July 2016

AbstractThe contribution of the MuSiCoS project (a multisite network of 2m class telescopes) to Be-star research is summarized. Some preliminary results of the 1998 campaign on ω Ori are shown.
Polarization from Be Disks with 1-Armed Density Waves
Authors: Ignace R. 
Published: July 2016

AbstractThe polarization of Be disks that are not axisymmetric is discussed, with results given for one-armed density waves or global disk oscillations (GDO). Polarimetric diagnostics of electron scattering Be disks are presented, including the expected behavior at (a) optical wavelengths where the star is the dominant source of luminosity and (b) infrared wavelengths where the disk is more luminous than the star. Results for detached disks are given. A qualitative discussion of polarization at Hα is also presented.
Reflections on Scattered Light: Monte Carlo Simulations of the Flux and Polarization Curves of β Lyrae
Authors: Hoffman Jennifer L. , Whitney Barbara A. , Nordsieck Kenneth H. 
Published: July 2016

AbstractPolarimetry has proven to be a useful observational tool in the study of Be stars. In recent years, Monte Carlo radiative transfer methods have often been used in modeling polarimetric measurements, since they allow accurate predictions of flux and polarization via numerical simulation of the interaction of light with matter, even in systems with complex configurations. We have extended these two complementary techniques to the investigation of binary Be stars by developing a Monte Carlo code that models the flux and polarization phase curves of a binary-disk system. We here present the latest results matching geometrical model configurations with our own spectropolarimetric observations of the Algol binary β Lyrae.
On the Characteristics of Circumstellar Envelopes in Be Stars near the Central Object
Authors: Moujtahid A. , Zorec J. , Hubert A.M. 
Published: July 2016

AbstractObserved visible energy distributions of Be stars were studied with analytic flux distributions produced by flattened circumstellar envelopes. The theoretical representation of emitted fluxes also allows for density distribution effects in the region where the visible continuum emission/absorption is raised. Two main conclusions were reached: (a) regions responsible for spectrophotometric ”shell” phases have, on average, steeper density distributions than those producing the spectrophotometric ”Be” phases; (b) the mean temperatures of the studied circumstellar envelope regions shows a linear relation with their mean ”inverse” extent R*/R.
Correlated Spectroscopic and Spectrophotometric Behaviours of Be Stars
Authors: Moujtahid A. , Hubert A.M. , Zorec J. , Ballereau D. , Chauville J. , Floquet M. , Mon M. 
Published: July 2016

AbstractCorrelations between long-term spectrophotometric and optical spectroscopic variations are investigated in some Be stars. Using spectrophotometric variations as a function of time and a compilation of spectroscopic measurements, we investigated temporal variations of emission and shell line parameters. In some cases time lags between spectroscopic and spectrophotmetric variations could be estimated. We could not find precise relations between the spectroscopic and spectrophotometric behaviours, but a number of tendencies could be derived which give information on physical parameters of circumstellar envelopes in Be stars.
The Emitting Envelope of Pleione between 1987 and 1998
Authors: Ballereau D. , Chauville J. , Zorec J. , Morrell N. 
Published: July 2016

AbstractWe analyze a series of spectroscopic observations of the Hβ and Fe II λ4924Å lines of the Be-shell star Pleione (HD23862), which entered a new Be phase since 1988. Their evolution show that the Hβ-emitting envelope expands regularly from 1987 to 1996 (r/r*=8.6 to 25.0), then diminishes slightly in 1997-98 (r/r*=20.0). The Fe II-emitting envelope expands regularly between 1987 and 1998 (r/r*=6.7 to 13.4), but remains always inside the Hβ-one. The evolution of the emitting envelope of Pleione is similar to the one observed between 1954 and 1972, and this one should decrease regularly in the next years, if the former scenario is repeated.
IUE Spectra of Be Star CX Dra: Evidence for Winds
Authors: Škoda Petr , Koubský Pavel 
Published: July 2016

AbstractThe Be binary star CX Dra has been observed with the IUE satellite over a period of 14 years. More than 60 SWP high resolution spectra were obtained. After processing the quotient flux spectra of the Al III and Si IV lines show very complicated behaviour. The most important features are the violet shifted components in these lines which show very negative velocities (up to −800 km/s) in a particular phase interval.
X Per in 1996 - 1999: the Variability of Hydrogen and Helium lines
Authors: Kolka I. , Eenmäe T. , Puss A. , Leedjärv L. 
Published: July 2016

AbstractWe present the results of high-resolution (0.24Å/pix) monitoring of the variability of Hα and He I 6678 lines in the spectrum of X Per in 1996-99 at Tartu Observatory. The main characteristics of the line variability distinguishable in our data are:1) the intensity of emission peaks in both lines varies with a cycle-length ≈450 days, and displays a phase-lag between curves of two lines considered,2) in a cycle, both violet or red emission peaks emerge at high Doppler velocities but attain their maxima and disappear gradually at much lower velocities,3) despite of the considerable variability of equivalent width (EW) of both lines, the “relative emission measure” (EW(Hα)/EW(HeI)) behaves more constantly.
Energy Balance in Circumstellar Envelopes
Authors: Millar C. E. , Marlborough J. M. , Sigut T. A. A. 
Published: July 2016

AbstractWe have successfully determined the kinetic temperature of the electron gas as a function of position in the circumstellar envelopes of Be stars. Our method yields a self-consistent solution of the equation for energy conservation, thus eliminating the necessity to assume arbitrarily a temperature for the gas. Our technique has been applied to Be stars of differing spectral classes, and we have also used several models for the distribution of the circumstellar material. The observed shape and relative line strength of the Hα line for several Be stars were matched successfully with these models. Recently we have begun to investigate the role of the diffuse radiation field in the Lyman continuum using the on-the-spot approximation. As a preliminary step to including metallic line cooling by the circumstellar gas, we have determined iron ionization fractions throughout the disks of both an early-type and a late-type Be star.