bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Fornax Spectroscopic Survey — Low Surface Brightness Galaxies in Fornax
Authors: Drinkwater M.J. , Phillipps S. , Jones J.B. 
Published: July 2016

AbstractThe Fornax Spectroscopic Survey is a large optical spectroscopic survey of all 14 000 objects with 16.5 < BJ < 19.7 in a 12 deg2 area of sky centered on the Fornax Cluster. We are using the 400-fibre Two Degree Field spectrograph on the Anglo-Australian Telescope: the multiplex advantage of this system allows us to observe objects conventionally classified as “stars” as well as “galaxies”. This is the only way to minimise selection effects caused by image classification or assessing cluster membership.In this paper we present the first measurements of low surface brightness (LSB) galaxies we have detected both in the Fornax Cluster and among the background field galaxies. The new cluster members include some very low luminosity (MB ≈ −11.5 mag) dwarf ellipticals, whereas the background LSB galaxies are luminous (−19.6 < MB < −17.0 mag) disk-like galaxies.
Galaxy Pairs and Triplets at Medium Redshifts from the Sloan Digital Sky Survey (SDSS)
Authors: Infante L. , Strauss M. A. , Bahcall N. , Knapp G. R. ,   For the SDSS Collaboration
Published: July 2016

AbstractWe have identified close pairs and triplets of galaxies in SDSS commissioning imaging data. The data set is from one of the SDSS equatorial scans covering an area close to 100 square degrees. We have estimated the angular correlation function of these galaxy systems and show that they appear to be appreciably more strongly clustered than are single galaxies.
Kinematics of early-type galaxies in compact groups: HCG 67, HCG 74 and HCG 79
Authors: Bonfanti P. , Simien F. , Rampazzo R. , Prugniel Ph. 
Published: July 2016

AbstractWe present measurements of stellar kinematics for seven early-type galaxies in HCG 67, HCG 74 and HCG 79. These data are aimed at studying the relation between the environment and the dynamics, structure and stellar content of early-type galaxies. In the present three groups, the kinematic features we observed cannot be associated unambiguously to physical interactions. Visible morphological peculiarities do not appear correlated with kinematical perturbations.
NGC 4622 versus NGC 3081 Disks: Encounter versus Intrinsic Rings
Authors: Freeman Tarsh , Byrd Gene , Ousley Derrick 
Published: July 2016

AbstractStar formation processes in galaxies are far from being understood. Resonance rings of star formation are a common phenomenon of early-type barred spiral galaxies. Most rings are regions of enhanced star formation via gas cloud collisions near resonances, under the action of a gravitational bar perturbation. A small number of rings may form in response to a mild tidal interaction with a nearby companion. In either case, resonance rings are natural dynamical experiments in star formation stellar association time evolution. We study star formation in two galaxies where resonance rings probably have these two different modes of origin. NGC 3081 has four bi-symmetric star-forming rings that are probably connected to bar-driven gas dynamics, while NGC 4622 is a non-barred spiral where a strong one-sided ring may be connected to a past tidal interaction. We model the young clusters in the rings as two-fold and one-fold periodic orbits, respectively. We show that age indicators, Hα emission and the color index B – I, vary with position angle around the rings in a two-fold and one-fold sense as predicted by our models. The success of these models shows that future high resolution observations can be used to separate the individual associations from the underlying disk light so as to study their evolution and luminosity function.
Interpretation of Rotation Curves of Giant Galaxies in the Local Group with the Truncated Disk Model: the Milky Way
Authors: Nikiforov I. I. , Petrovskaya I. V. , Ninković S. 
Published: July 2016

In some external edge-on spiral galaxies, such as NGC 891, 4244, 4565 and 5907, the observed light distribution exhibits a sharp truncation in the outer parts (e.g., Casertano 1983, hereafter C83). As a rule, such galaxies are known to be warped in their gas disk, the deformation starting at about their optical cut-off radius. These facts suggest a truncation in the disk density distribution. Moreover, the rotation velocity of these galaxies starts decreasing at about the same radius, which can also be considered as the "signature" of truncation (see C83).Both giant spiral galaxies in the Local Group, the Milky Way and M31, have a dip in the average rotation velocity which can be produced by a truncation of the galactic disk. Ninković & Petrovskaya (1992) constructed from Haud’s (1981) rotation curve for M31 a model including, like C83’s for NGC 5907, a truncated exponential disk and a halo. The truncation distance was found to be close to the radius beyond which warping of the hydrogen layer of M31 begins.
The Be Phenomenon
Authors: Balona L.A. 
Published: July 2016

AbstractAn overview of the Be phenomenon is given with particular emphasis on the problem of the mass loss mechanism. We assume that the principal mechanism of mass loss in these stars is magneto-centrifugal acceleration (MCA). Within this framework, we discuss how particular features of Be stars which distinguish them from normal B stars can be understood. The frequency distribution of Be stars relative to normal B stars in the Galaxy and Magellanic Clouds is discussed. The distribution of equatorial velocities, activity in the visual and X-ray regions and photospheric activity all point towards a magnetic model and seem to be qualitatively consistent with the MCA hypothesis. Periodic variations in light and line profiles offer particularly important clues. In this respect, the recent discovery of co-rotating photospheric clouds in several Be stars strongly suggests gas trapped in closed field lines. We investigate the dynamics of an outburst and suggest that the localized nature of these events imply magnetic flaring and acceleration of mass due to connection and disconnection of field lines. Finally, suggestions for further progress are presented.
Physical Properties and Evolutionary Stage of Be Stars
Authors: Harmanec P. 
Published: July 2016

AbstractThe determination of accurate and reliable basic physical properties of Be stars is a very complicated task which, among other things, requires a good knowledge of the variability pattern of each particular object. Possible confusion between a rotationally distorted photosphere and a pseudophotosphere – an inner optically thick part of a gradually formed envelope which temporarily mimics a photosphere – is discussed in some detail in relation to the stellar effective temperature, brightness and rate of rotation. It is shown that the currently available data allow us to set relatively stringent limits on possible radii of at least some brighter Be stars, but very few direct determinations of mass have been made. The only exceptions are the Be stars in eclipsing binaries. The trouble is, however, that all of them are interacting binaries for which reliable orbital solutions are seriously hampered by the presence of gas streams and by strong interactions between the binary components. Moreover, their masses need not be representative for the whole population of Be stars.An answer to the question about the evolutionary stage of Be stars is even more uncertain since it is closely related to the principal, as yet unanswered question about the origin of the Be phenomenon itself.
A Spectroscopic Study of Be stars in the SMC Cluster NGC 330
Authors: Hummel W. , Gässler W. , Muschielok B. , Szeifert T. , Seifert W. , Appenzeller I. , Rupprecht G. 
Published: July 2016

AbstractWe present low resolution spectroscopy of about 20 Be stars in the SMC cluster NGC 330 to confirm the high contents of Be stars in this cluster.
The ST3 Mission, and its Capabilities for Be Star Observations
Authors: Linfield R. P. 
Published: July 2016

AbstractThe ST3 mission will launch a space optical interferometer into heliocentric orbit, for observation of 50–100 sources on baselines of 40–200 m, during a time span of 3–4.5 months. The angular resolution in the 450–900 nm passband will be ≈ 500 microarcseconds. For Be stars, a velocity resolution of 50–100 km/s can be achieved by operating the interferometer in a Fourier Transform Spectrometer mode. This should allow spectrally resolved measurements of the brightness distribution in circumstellar disks, but will be limited to stars brighter than a visual magnitude of ≈ 5.
ISO Observations of Be Stars
Authors: Waters L.B.F.M. , Trams N.R. , Hony S. , de Koter A. , Morris P.W. , Zaal P.A. , Marlborough J.M. , Millar C.E. , Vandenbussche B. 
Published: July 2016

AbstractWe discuss the infrared spectral energy distribution of Be stars, focusing on new results obtained with the Infrared Space Observatory. The 60-160 μm flux of some Be stars is higher than expected, which may be due to cold dust or an outer disk component with enhanced densities. The infrared spectrum of Be stars is dominated by numerous HI recombination lines, whose line strengths show a complex behaviour. The electron temperature in the disk of ϒ Cas was found to be about 9500 K, and evidence for an elevated temperature near the upper part of the disk is presented. Be stars may be recognized from their infrared spectrum on the basis of HI line flux ratios.
Observed Periodic Phenomena
Authors: Baade D. 
Published: July 2016

AbstractThe wide range of periodic and cyclic variabilities commonly observed in Be stars and their circumstellar disks is reviewed. Many of them are related to the basic nonradial pulsation, the effects of which may range from the photosphere to the disk. Through pulsation-triggered outbursts, some stars may owe their Be characteristics largely to their intrinsic variability. However, because late-type Be stars do not normally show detectable short-periodic variability, this is probably not true of all Be stars. Comparisons are made with other variable early-type stars.
Short-period Variations of 28 CMa during 1998/9
Authors: Balona L.A. , James D. 
Published: July 2016

AbstractThe Be star 28 CMa was one of the first periodic Be stars to be discovered and shows very large line profile variations with a period of 1.37 d. Recently, it has been shown that the line profile and light variations can be modeled by a patch of gas suspended above the photosphere. We present echelle observations of the Hβ and Hϒ line and several helium and metal absorption lines. We show that the radial velocity variations of these lines are unchanged since they were first observed two decades ago. We also examined several emission lines of Fe II and show that they do not partake of the periodic variation. We attribute the periodic variations of the lines formed close to the photosphere to a co-rotating cloud, whereas the Fe II emission lines are formed in the circumstellar disk outside the co-rotating radius.
Doppler Imaging of Non-radially Pulsating Stars
Authors: Jankov S. , Janot-Pacheco E. , Leister N.V. 
Published: July 2016

AbstractIn addition to the common applications (temperature, magnetic field, abundance distributions) the Doppler Imaging technique can also be applied to non-radial stellar pulsations (NRP). Due to their rapid rotation, the Be stars are ideal candidates for Doppler Imaging. However, for the stars for which the periodic temporal line profile variability is produced by multiple mode NRP, the classical Doppler image in not an appropriate representation. When the corotating frequencies of existing pulsation modes are non-zero, the reference frame in which the resulting NRP is quasi-stationary cannot be defined. The technique can be applied “mode-by-mode”, which is illustrated in time-wavelength and Fourier frequency domain, using the time-resolved sequence of high resolution, high signal-to-noise ratio spectra of the Be star ζ Oph.
Multi-frequency Variations in the Be star ζ Ophiuchi
Authors: de Souza A.D. , Janot-Pacheco E. , Leister N.V. , Jankov S. , Hubert A.M. , Floquet M. 
Published: July 2016

AbstractIn this work we have adopted the non radial pulsation (NRP) model in order to explain the rapid spectroscopic time variations observed in the Be star ζ Ophiuchi. Time series analysis were performed with CLEAN and Sequential CLEANEST techniques. We have also applied a different version of the Local CLEANEST that is optimized for multiperiodic signals observed in monosite campaigns. The frequencies of 7.19 and 11.89 cycles/day have been identified. These frequencies were found in previous papers about the star.
The magnetic field of β Cep and the Be phenomenon
Authors: Henrichs H.F. , de Jong J.A. , Donati J.-F. , Catala C. , Wade G.A. , Shorlin S.L.S. , Veen P.M. , Nichols J.S. , Kaper L. 
Published: July 2016

AbstractNew circular spectropolarimetric observations of the B1 IIIe star β Cep (υsini = 25 km s−1) show a sinusoidally varying weak longitudinal magnetic field (~ 200 G peak-to-peak). The period corresponds to the 12 day period in the stellar wind variations observed in ultraviolet spectral lines. Maximum field occurs at maximum emission in the UV wind lines. This gives compelling evidence for a magnetic-rotator model for this star, with an unambiguous rotation period of 12 days.The similarity between the Hα emission phases in β Cep and in Be stars suggests that the origin of the Be phenomenon does not have to be rapid rotation: we propose that in β Cep the velocity to bring material in (Keplerian) orbit is provided by the high corotation velocity at the Alfvén radius (~10 R*), whereas in Be stars this is done by the rapid rotation of the surface. In both cases the cause of the emission phases has still to be found. Weak temporary magnetic fields remain the strongest candidate.A full paper, with results including additional measurements in June and July 1999, will appear in A & A.
HEROS Be Star Campaigns
Authors: Štefl S. , Rivinius T. 
Published: July 2016

AbstractSystematic Be star observations with the HEROS spectrograph have been carried out in several long observing runs and seasons, mainly at the ESO La Silla Observatory. The HEROS data represents one of the most extended spectroscopic data sets for the Be star research. More complete and efficient diagnostics and a higher frequency resolution in analyses of periodic spectral variations were achieved, thanks to a combination of relatively high spectral resolution, a large sample of monitored spectral lines of different formation properties, long observing runs, and a relatively high frequency of observations of main targets.Important results concerning different parts of the extended atmospheres of Be stars and having strong impact on our understanding of these objects have been achieved.
Long-term Variability in Be-Star disks
Authors: Telting J.H. 
Published: July 2016

AbstractBe stars can switch between non-disk, gradual disk growth, disk-loss events, and shell-line phases. Many aspects of this Be phenomenon are still not understood. In this paper I review recent work on variability in Be-star disks, divided in four different topics: disk growth (Section 1), long-term V/R variations and global disk oscillations (Section 2), spectacular variations (Section 3), and, concisely, the disk variability in Be/X-ray binaries (Section 4).
A Connection Between V/R and Polarization in Be Stars
Authors: McDavid David , Bjorkman K.S. , Bjorkman J.E. , Okazaki A.T. 
Published: July 2016

AbstractOkazaki (1991) and Papaloizou, Savonije, & Henrichs (1992) suggested that the quasi-cyclic V/R variability observed in the emission line profiles of many Be stars is caused by a precessing one-armed density wave in the circumstellar disk. It seems likely that the changing aspect of such a non-axisymmetric density pattern might also lead to a related variation of the continuum polarization. We have searched for such an effect in two well-studied Be shell stars, ζ Tau and 48 Lib, based on data compiled from several groups of observers from 1984 to 1998. Using the Monte Carlo radiation transfer code of Wood, Bjorkman, Whitney, & Code (1996), we have calculated the polarization due to electron scattering in Be disks in the presence of one-armed density perturbations. Although the notorious long and short term deviations from strict periodicity present in Be stars make it difficult to rigorously demonstrate the connection between the V/R variability and the polarization variations, we have been able to find specific modes that are consistent with the observed V/R line profile variations together with the suspected polarization cycles.
Near Infrared Spectroscopic Observations of Early-type Be Stars
Authors: Ashok N. M. , Banerjee D. P. K. 
Published: July 2016

AbstractThe medium resolution (R=1000) near infrared spectra of 30 early type Be stars obtained during the period October 1998-April 1999 are presented. The Paschen β and Brackett γ lines are seen in emission in majority of these stars. The higher order Brackett series lines from m=10 to 19 are detected in emission with significant strength compared to the Brackett γ emission line flux indicating the effect of optical depth. The Fe II line at 1.6873μm is detected in a small number of stars indicating existence of higher density and lower temperature emission zone.
Mid-Infrared Spectra of Be Stars
Authors: Rinehart S.A. , Houck J.R. 
Published: July 2016

AbstractWe present medium-resolution (R ~ 600) mid-infrared (8-13.3μm) spectra of γ Cas and a coadded spectrum of nine Be stars. A large number of lines have been observed and identified in these spectra, including 39 hydrogen recombination lines in the spectrum of γ Cas. In the majority of our spectra, all of the observed lines are attributable to hydrogen recombination. Two additional sources, β Lyr and MWC 349, show [Ne II] emission and β Lyr also displays [He I] emission. We tabulate the effective line strength and line widths for the observed lines, and briefly discuss the physical implications of the observed line series. We also use a simple model of free-free emission to characterize the disks around these sources.
A Spectroscopic and Photometric Study of the Shell Star EW Lac
Authors: Cao Huilai , Li Zhongwei , Huang Lin , Guo Yulian 
Published: July 2016

AbstractWe report on combined spectroscopic and photometric observations of EW Lac during its outburst of 1983. At this time the star’s Hα and Hβ lines showed strong doubled-peaked emission profiles which were variable with time. UBV photometry exhibited a long-term and frequent erratic short-term variations. The amplitude of U, B and V variations reached about 0.3 magnitude on October 15, 1983. Both Hβ emission and the structure of the shell absorption lines of the star also displayed anomalous behavior in 1983. It is evident that this star was in a strong active phase at that time.
The Be Phenomenon in Pleione
Authors: Hirata Ryuko , Shimada Michihiro R. , Masuda Seiji , Katahira Jun-ichi 
Published: July 2016

AbstractThe spectral change of Pleione in the present Be phase (1988-1999) is briefly described. The Hα emission reached its maximum in 1995-1999. The V/R values of Hγ and metallic lines changed from V/R < 1 in 1995 to V/R > 1 in 1998-1999. The broad component of Mg II λ4481 line further weakened in Be phase.The long-term variation in 1968-1999 is shown for several observational quantities. These quantities which reflect various levels from the photosphere up to the outer envelope did not change in a parallel way. The basic unsolved problems are pointed out.
Spectral and Photometric Evolution of V725 Tau (1996-1999): Towards a Shell Phase?
Authors: Piccioni A. , Bartolini C. , Bernabei S. , Galleti S. , Giovannelli F. , Guarnieri A. , Sabau-Graziati L. , Valentini G. , Villada M. 
Published: July 2016

AbstractHDE 245770 = V725 Tau, the optical counterpart of A0535+26, presented in the last three years a period of uncommon optical faintness and of exceptionally low spectral activity. Photometric data obtained in 1997 and 1998 show a fading in all color, followed in 1999 by a nearly constant phase in which the star attained the lowest level of the last 23 years. In 1998 the emission lines became much fainter than in 1997, changing slowly from emission to absorption. In November 1998 only Hα was still showing a weak emission with an absorption core; this behaviour suggests the occurrence of a shell phase.
Search for Evidence of Radiative Equilibrium Departures in Extended Atmospheres
Authors: Venero Roberto , Cidale Lydia , Ringuelet Adela 
Published: July 2016

AbstractThrough the analysis of line profiles of atoms in different ionization stages, we study the source function behavior of those elements that allow us to outline temperature structures in moving extended atmospheres. The radiative transfer equation is solved in the comoving frame and NLTE for multilevel atoms.
Pulsar Searches at Effelsberg — Past, Present & Future
Authors: Lorimer D.R. , Kramer M. 
Published: July 2016

AbstractIt is fair to say that pulsar searches with the 100-m Effelsberg telescope have had something of a checkered history — after all, for many years, this was the largest radio telescope in the world never to have found a pulsar! This situation has, happily, changed. In this review we summarize recent discoveries of weak pulsars along the Galactic plane, give a progress report on a survey for highly dispersed pulsars in the Galactic centre and, in the spirit of this meeting, speculate on what should be a bright future for pulsar searches with this instrument.
Slow pulsars from the STScI/NAIC drift scan search
Authors: Xilouris K. M. , Fruchter A. , Lorimer D.R. , Eder J. , Vazquez A. 
Published: July 2016

AbstractThe unique sensitivity of the Arecibo telescope at 430 MHz motivated a drift scan search of the visible sky divided up into eight declination strips. Based on an analysis of the data collected in the region assigned to us, eight new long-period pulsars have so far been discovered.
A Fast Search Technique for Binary Pulsars
Authors: Ransom Scott M. 
Published: July 2016

AbstractI describe a computationally simple, efficient, and sensitive method to search long observations for pulsars in binary systems. The technique looks for orbitally induced sidebands in the power spectrum around a nominal spin frequency, enabling it to detect pulsars in high- or low-mass binaries with short orbital periods (Porb≲ 5 h).
Pulsar timing at Kalyazin (Russia)
Authors: Doroshenko O.V. , Ilyasov Yu.P. , Oreshko V.V. 
Published: July 2016

AbstractRegular timing observations of millisecond and binary pulsars are made with the 64-m radio telescope at Kalyazin (Russia). Filterbank 160-channel receiver is used for observations at 0.6 GHz in two circular orthogonal polarization. Precise local time service (based upon a rubidium standards and hydrogen maser) is used for measurements of Times-of-Arrival (TOA) from radio pulsars. A local time scale is compared by GPS and TV-systems with the basic AT-scales (UTC(USNO) and UTC(SU)) within an accuracy about 50nsper day. Recently the second 1.4 GHz receiver (250 kHz × 64 channels) was constructed and installed at Kalyazin radio telescope. There is a possibility to combine a part of the 1.4 GHz back-end with the 2.2 GHz front-end to produce timing observations at three frequencies simultaneously. We present a results of precise timing observations conducted by the Kalyazin pulsar system. Most of data were obtained at 0.6 GHz in 1997–1999. The data will be used for valuable applications in fundamental metrology, interstellar medium, general relativity and pulsar physics itself.