bluuebunny/crossref_metadata_2025 huggingface dataset:
What Causes the HI Holes in Gas-Rich LSB Dwarfs?
Authors: Rhode Katherine L. , Salzer John J. , Westpfahl David J.
Published: July 2016

We have carried out a deep, multi-color imaging study of Holmberg II (Ho II) and several other nearby LSB dwarf galaxies for which detailed HI maps exist. The formation of the HI holes in these galaxies has been attributed to multiple supernovae (SNe) occurring within windblown shells around young, massive star clusters. To search for evidence of the clusters, we have compared optical images with the HI maps and measured magnitudes and colors of objects in and around the HI holes.

Although the SN scenario requires that detectable star clusters should often be present in the centers of the HI holes, our observations have in most cases failed to reveal these clusters at the expected magnitudes. In fact, many of the HI holes are located in regions of very low optical surface brightness, which show no evidence of recent star formation.
The Structure of the Multi-Phase ISM in Low Surface Brightness Galaxies
Authors: Spaans M.
Published: July 2016

The multi-phase structure of the interstellar medium in low surface brightness galaxies is investigated and compared to observations. It is found that the ambient pressure and metallicity very strongly influence the abundances of molecular hydrogen and carbon monoxide. The emissivity of the latter is computed and found to agree naturally with the upper limits measured for low surface brightness galaxies. The implications for star formation efficiency and galaxy evolution are discussed.
The HST/LCO Measurement of the Optical Extragalactic Background Light
Authors: Bernstein R.A.
Published: July 2016

We present the first detection of the mean flux of the optical extragalactic background light (EBL) at 3000, 5500, and 8000Å, derived from coordinated data sets from HST and Las Campanas Observatory. To isolate the extragalactic component, we have measured and subtracted the flux from foreground sources explicitly. In addition to detections in all three bands, we identify the minimum surface brightness contributed by resolved galaxies (23 < V < 28 AB mag) using a non-standard method of aperture photometry to which these data are uniquely suited. Individually resolved galaxies account for ~ 30% of the mean EBL coming from galaxies fainter than V = 23 AB mag. Taking into account the effective surface brightness detection limits of the deepest galaxy counts, and the results of LSB surveys at low redshift, the EBL we detect can be explained by galaxy populations already cataloged.
Detecting the Low Surface Brightness Universe: the Extragalactic Background Light and LSB Galaxies
Authors: Väisänen P. , Tollestrup E.V.
Published: July 2016

Individual sources are detected ideally to a confusion limit at a given wavelength, but there is still much information beyond that. Absolute background brightness measurements provide a crucial constraint to models describing the undetected population of sources in the distant – and/or low surface brightness – universe. We calculate how much low surface brightness galaxies (LSB) would contribute to the the overall extragalactic background light (EBL) and review the status of EBL measurements in the optical and infrared wavelengths. To be able to push deeper the detection limits on very faint sources a fluctuation analysis method is introduced. The use of these different approaches together is essential when studying the very faint and low surface brightness universe.
The Complex Kinematics of Galaxies in Hickson 67
Authors: Bettoni D. , Buson L. M.
Published: July 2016

The kinematics of galaxies belonging to the Hickson compact group HCG67 are investigated. The latter consists of four galaxies, three of which (a, c, d) are embedded in a common envelope. The fourth galaxy (b) is a spiral that is detected both in radio and in IR wave-bands. Our observations show that the three galaxies in apparent interaction are probably caught during an ongoing merger process.
HI Image Synthesis of Southern Compact Groups
Authors: Babic B. , Price R. M. , Jones K.
Published: July 2016

Four southern compact groups, the Hickson Compact Groups HCG 22 and HCG 26 (Hickson 1982), and the groups AM 1238–396 and ESO 410-G(024—026) have been imaged in HI, along with 12cm continuum using the Australia Telescope Compact Array (ATCA). The initial findings for the latter two groups are presented here. While ESO 410-G is not in fact a physical group, due to the discordant redshifts amongst the members, it is however presented here.

Overall for all the groups we find no other sources of HI in the field that might indicate that these are part of a larger loose group structure. This is not always the case, as with HCG 23 (Williams 1995) and HCG 95 (Hutchmeier 1999), both of whom find additional Hɪ sources within the primary beam accordant with the compact group’s velocity.

The HI is also clearly associated with each of the individual member galaxies in all cases, except for HCG 26, which envelopes the whole group as was also shown by Williams and van Gorkom (Williams 1995).
Small Group Dynamics and Extended Gas
Authors: Combes F.
Published: July 2016

Interactions between galaxies have spectacular effects on gas dynamics, and small galaxy groups are a privileged place to investigate them. In particular, they could test the existence of cold H2 gas as dark matter in the outer parts of galaxies. HI observations have revealed that galaxies in small groups are deficient in atomic gas, like in richer galaxy clusters such as Virgo, although in a lesser extent. Galaxy interactions could be the cause of this deficiency, stripping the gas out of galaxies and enriching the inter-cluster medium (ICM) in hot gas, which in turn strips gas through ram pressure. Alternatively, the gas present at the formation of the group could have been heated to its virial temperature, and be observed now as X-rays. The dynamical processes related to this extended gas in small galaxy groups are reviewed.
New Dwarf Galaxies in the IC342/Maffei Group
Authors: Huchtmeier W. K. , Karachentsev I. D. , Karachentseva V. E.
Published: July 2016

This is a report on the detection of HI emission from three ‘new’ dwarf galaxies Perseus A, Perseus B, and Camelopardalis D in the IC342/Maffei group of galaxies and of Draco A. The actual number of (probable) member galaxies of this group increases to 19 galaxies. Its velocity dispersion is 86 kms−1. With a distance of 2.2±0.5 Mpc this group is the nearest to the Local Group and might have considerable dynamical influence on the Local Group.
Compact Galaxy Groups in the South
Authors: Price R. M. , Babic B. , Jones K.
Published: July 2016

Compact groups are intermediate between single and binary galaxy systems, and clusters of galaxies. Because of their small numbers of members, and the small separations between the members of each group, they are good candidates for the study of galaxy interactions and mergers. In particular, high resolution imaging of these systems in neutral hydrogen can yield important data on interactions between galaxies.

The radio telescopes of the Australian National Telescope Facility (ATNF) are especially well suited to the study of neutral hydrogen gas in these systems. The Parkes 64-m telescope has a 15 arcminute FWHM beam at 21 centimeters wavelength which is sufficient to include the sky area of a typical compact group. Parkes was used for detection of HI in nine southern groups and for determination of their approximate velocities, if not previously known. Follow-up observations with the ATNF Compact Array synthesis telescope provided high resolution (20 arcsecond) images with appropriate frequency resolution to determine velocity fields for the gas distribution.
Small Galaxy Groups in the Universe
Authors: Cavaliere A.
Published: July 2016

I discuss the steering role played by small groups of galaxies concerning sources and structures on widely different scales: the very compact quasars, and the extended atmospheres of hot intracluster gas. The evolution of such sources out to substantial z is ruled by astrophysical processes taking place in early small groups.
On the Nature of Compact Groups of Galaxies
Authors: de Carvalho Reinaldo R.
Published: July 2016

Based on the spectroscopic survey of de Carvalho et al. (1997), we analyse the structural and dynamical properties of 17 Hickson Compact Groups (HCG). This analysis probes a region of 0.5° × 0.5° around each group and shows that most are part of larger structures. Our results also suggest that the Hickson sample is composed of different dynamical stages of the group’s evolution. Specifically, we identify three possible evolutionary phases among groups in the sample: loose groups, [core+halo] systems and compact groups, each one presenting a distinct surface density profile. This sequence is consistent with the replenishment scenario for the formation and evolution of compact groups within larger and less dense systems.
N-body simulations of interactions and mergings in small galaxy groups
Authors: Athanassoula E.
Published: July 2016

In this paper I focus on three topics related to the dynamical evolution of small galaxy groups, for which the input of N-body simulations has been decisive. These are the merging rates in compact groups, the properties of remnants of multiple mergers, and the evolution of disc galaxies surrounded by one or more satellites. The short dynamical times of compact groups make it difficult to understand why such groups are observed at all. N-body simulations have pointed out two possible classes of solutions to this problem. The first one proposes that there is ongoing formation of compact groups, or that the longevity of the group is due to secondary infall. For the second class of solutions the longevity of compact groups is due either to their specific initial conditions, or to a massive common halo, encompassing the whole group. I discuss here these alternatives, together with their respective advantages and disadvantages. I then turn to the structure of remnants of multiple mergers and compare the results of N-body simulations with the properties of observed elliptical galaxies. Finally I discuss the dynamical evolution of a disc galaxy surrounded by one or more spherical satellites.
A Numerical Experiment of a Triple Merger of Spirals
Authors: Aceves Héctor
Published: July 2016

Several studies have addressed the topic of spiral interactions in pairs or in small groups (Barnes 1998). However there is no specific study, to our knowledge, of interacting triplets of spirals. Here we present a preliminary report of ongoing research on the dynamics of triplets that includes galaxies of different morphology. In particular we follow a triplet of equal-mass spirals until a merger remnant that resembles an elliptical-like galaxy has been formed.

It is known that the HI component of spirals is a good tracer of interactions. Indeed, several triplets (e.g. in M81 group) that do not appear to be perturbed in optical images do so in H I maps. Although a self-consistent treatment of gas requires the inclusion of e.g. pressure forces, we use here a test-particle approach to study it during a triple interaction of spirals; this can yield information about the large-scale kinematical features of gaseous tails.
Binary Galaxy Spin Correlations in Small Galaxy Groups
Authors: Wirén S. , Valtonen M. J. , Liu B.
Published: July 2016

Statistics of spin orientations in binary galaxies may be used as a tool to study the formation process of galaxies. Helou (1984) found that the spins of spiral galaxies in binary systems are anticorrelated, and he suggested that it may have to do with the inclination dependence of the galaxy merger process. We study this dependence in small groups of galaxies. An N-body code is developed which uses an inclination dependent dynamical friction law to affect mergers of galaxies. It is found that some correlation results in this way in groups, which have initially random spin orientations.
Dynamics and Merging in Compact Galaxy Groups
Authors: Zheng J.-Q. , Valtonen M. J. , Chernin A. D. , Wiren S.
Published: July 2016

By using a few body code with a frictional force we study the dynamics of small galaxy groups. The results have been compared with observational data on triples and binaries by Karachentsev et al. We start with four to five galaxy groups initially and take samples of the groups when the membership has dropped to two or three. It is possible to find merger evolution models which agree with observations. One interesting factor is the mass-to-light ratio of the observed systems: we find the best fit with the models when the mass-to-light ratio is about 50 in solar units.
Black hole ejections in mergers of small groups of galaxies
Authors: Heinämäki Pekka , Valtonen Mauri
Published: July 2016

The formation of a multiple black hole system via merging processes of galaxies is simulated. Starting from the hierarchical halo merger model by Lacey and Cole (1993) and the general assumption that supermassive black holes (> 106M⊙) are common in the nuclei of galaxies we followed the formation of a four black hole system. Ultimately, instability of the four body system led to 835 symmetric two-sided slingshot ejections out of 10,000 simulations. This result was applied to the most straightforward application of the slingshot process, namely to the origin of extended radio sources.
Tidal Perturbation and Active Galaxy Nuclei
Authors: Byrd Gene , Valtonen Mauri
Published: July 2016

Theories of nuclear activity mechanisms in disk galaxies (such as Seyfert galaxies) range from intrinsic (e.g. bars) to external (tidal perturbation by passing companions). The Byrd et al. (1986, 1987) simulation survey determined the tidal perturbation necessary to induce nuclear activity. Observational surveys have raised doubt as to the tidal explanation of Seyfert-type activity in galaxies with some suggesting a weak or nonexistent correlation between tidal perturbation and Seyfert activity compared to a normal sample. The simulations show a several hundred million year delay in the appearance of activity after perturbation and a similar duration which can explain these null results. For double galaxies, we derive from the tidal hypothesis that: (1) There should be an excess of pairs where both are active over pairs with one active. (2) Nuclear activity will be preferentially excluded from pairs which are unequal and favorably distributed to pairs where the members are equal. (3) The size of pair members to create activity can be smaller if the pair members are equal in size than if they are unequal. (4) Pairs where one or both members are active should have a smaller velocity difference times separation than if both are normal. All the predictions are seen in observations of activity in Karachentsev’s (1983) list of double galaxies. Optimally, statistical studies of nuclear activity and companions should include their sizes, separations, and radial velocities relative to the primary. The study by Dultzin-Hacyan et al. (1999) which finds an excess of large companions around Seyfert 2 galaxies is a step in the right direction.
Wide triplets of galaxies
Authors: Chernin A. D. , Dolgachev V. P. , Domozhilova L. M.
Published: July 2016

Triple systems of galaxies with the typical mass ∼ 10h13M⊙ and crossing time about the Hubble time provide evidence for ongoing collapse on the space scale ∼ 1 Mpc. This is confirmed by a set of computer simulations with the use of free-fall models.
The connection between dark matter, internal motions and configurational properties of triple galaxies
Authors: Kiseleva L.
Published: July 2016

Numerical simulations of the dynamics of triplets of galaxies show that virial estimations of the individual masses of triplets are unreliable because of strong nonsteadiness of these groups and projection effects. However, the mass of a typical small galaxy group can be estimated statistically, from data on a whole homogeneous ensemble of groups such as, for example, Karachentsev’s Catalogue of compact galaxy triplets. The characteristic total mass of a triplet from this catalogue is 4 - 7 times greater than the visible mass when the standard mass-to-light ratio is assumed. This suggests the presence of some considerable amount of dark matter even in these compact triplets. In wide triplets of galaxies the amount of dark matter may be significantly larger. The presence of distributed dark matter makes motions of galaxies in triplets more stochastic. In this case the existence of long-lived hierarchical configurations (temporary binaries) in triple systems becomes much less probable than without dark matter. The analysis of internal motions of galaxies in triplets and their configurations may be interpreted as additional non-dynamical evidence of the presence of dark matter in galaxy triplets.
Deducing the orbit of the radio galaxy 3C 129
Authors: Nilsson K. , Valtonen M. , Zheng J.-Q. , Byrd G. , Korhonen H. , Andersen M. I.
Published: July 2016

We have obtained new optical spectra of the radio galaxy 3C 129 and the giant galaxy close to it. From these spectra we deduce a relative radial velocity of 710 km s−1 between the two galaxies. Using the orbit calculations of Byrd & Valtonen (1978) and the new observations we obtain a new value, 3.3 × 1014M⊙, for the mass of the system.
On the Formation of Small Groups of Galaxies at High Redshifts
Authors: Saslaw William C.
Published: July 2016

Cosmological many-body clustering agrees with the spatial and velocity distribution functions of galaxies at low redshifts, and it can be extended to high redshifts z ≈ 3 or more. The high redshift distribution functions are predicted to have a particular form. In the simplest case, there are no free parameters in this prediction, but the degree of clustering depends sensitively on Ω0. Current observations of small groups at high redshifts suggest that Ω0 = 0.3 ± 0.2 for Einstein-Friedmann cosmologies.
Merging galaxies in compact groups: analytical theory
Authors: Kontorovich Victor M.
Published: July 2016

The predominance of minor mergers, i.e. the non-locality of mergings, results in a mass function slope (“Shechter” index) intermediate between a power-law index of a spectrum with constant mass flux and that of constant flux of the number of massive galaxies. The index proves to be close to that of the faint end of the galaxy luminosity function.
Be Star Surveys in Open Clusters with Balmer-line Photometry
Authors: Capilla Gemma , Fabregat Juan , Baines Deborah
Published: July 2016

We present CCD Hα and Hβ photometry of young open clusters. We show that the comparison of the α and β photometric indices provides an efficient tool for identifying emission line stars. We report on the discovery of several new Be stars.

The preliminary results of our survey are the following: i. the younger clusters (age < 10 Myr) are almost lacking of Be stars, ii. clusters in the age interval 10–30 Myr are rich in Be stars. Almost all of them are of spectral types earlier than B5, while late-type Be stars are scarce. These results point towards an evolutionary interpretation of the Be phenomenon, in the sense that Be stars are close to the end of their main sequence lifetime.
Discovery of New Be Stars in the Galactic Open Cluster NGC7128
Authors: Balog Z. , Vinkó J. , Fűrész G. , Alfaro E. J. , Delgado A. J. , Moitinho A.
Published: July 2016

We present medium resolution spectroscopy (λ/Δλ ≈ 7,000) covering 6500-6750 Å of three emission stars in the highly reddened young open cluster NGC7128. Two of them were previously unknown. The known Be star (V1814 Cyg) is an irregular variable; one of the newly discovered stars is an eclipsing binary (V1481 Cyg) (Jerzykiewicz et al., 1996.). Physical parameters of the cluster have been determined from new UBV and uvbyHβ photometric measurements.
Be Stars in the Magellanic Clouds
Authors: Keller Stefan C. , Bessell M.S. , DaCosta G.S.
Published: July 2016

We present the results of our studies of Be stars within the Magellanic Clouds. We have studied the Be population within four young populous clusters, NGC 330 in the SMC, NGC 1818, 2004 and 2100 in the LMC as well as the field population around NGC 2004. The Be fraction within each cluster is seen to peak towards the luminosity of the main sequence turnoff. The field, which exhibits a large spread of ages, has a Be fraction more uniformly distributed in luminosity. We interpret this difference as evidence for an evolutionary enhancement of the Be phenomenon that occurs towards the end of the main sequence lifetime.
The B[e] Star MWC 84 (CI Cam)
Authors: Jaschek Carlos , Andrillat Yvette
Published: July 2016

The star MWC 84 (CI Cam) was first discovered to be an emission line object classified Bep (Merrill & Burwell, 1933), then classified as a symbiotic star and finally identified as the possible optical counterpart of the X-ray transient XTE J0421+560 (Wagner & Starrfield, 1998)

We have observed MWC 84 at the Haute Provence Observatory (CNRS) with a resolution of about 1.3 Å in 1992 (wavelength regions Hα and near infrared), 1998 and 1999 (from 4080 to 8880 Å).
Rapid Variations of Discrete Absorption Components in the spectrum of P Cygni
Authors: Israelian G.L.
Published: July 2016

The morphology and variability of spectral lines in the P Cygni high-resolution and high signal-to-noise near-UV spectra have been studied in detail over a period of few days. It is found that several Balmer lines have profiles with a complicated structure. All those lines which are well developed, but still not saturated, show two absorption components. A striking profile variability is discovered on a time-scale of from 1 to 3 days. The most dominant part of rapid variations is the drift of absorption components. It appears that there are two different kinds of components: long lived (with a characteristic time-scale of 200 days) and short-lived (time-scale of few days). The DAC phenomenon in the P Cygni stellar wind is a problems that still remains unsolved.
The Nebula Surrounding the B[e] Supergiant R4
Authors: Pasquali A. , Nota A. , Langer N. , Schulte-Ladbeck R.E. , Clampin M.
Published: July 2016

New, NTT observations of the B[e] supergiant RMC4 in the Small Magellanic Cloud show that the star is embedded in a circumstellar nebula, whose velocity structure is typical of a bipolar outflow. The nebula is kinematically associated with RMC4 and expanding at 100 km/s on average. Its diameter as computed from the spatial extension of its spectral lines is of 8.6″ which corresponds to a linear size of 2.4 pc and gives a dynamical age of 12500 yr. The line ratio [NII]λ6584/[SII]λ6717 indicates that the nebula is nitrogen enriched as it is expected for ejected nebulae. This is the first bipolar outflow detected around a well-established B[e] supergiant which also belongs to a binary system. The nebular morphology and chemistry are consistent with the picture of a binary merger in which RMC4 was composed by a close pair and a third star (the observed companion). The close pair merged into a single star (the present B[e] supergiant) and produced a circumstellar nebula to be later shaped by the ensuing B star wind (cf. Langer & Heger 1998).
Probing the Small Scale Structures around Herbig Be Stars using Hα Spectropolarimetry
Authors: Oudmaijer René D. , Drew Janet E. , Busfield Graeme
Published: July 2016

We present spectropolarimetric observations across Hα of a sample of Herbig Be objects. Roughly half of the observed Herbig Be stars show polarization changes across Hα, implying immediately that their ionized, hence inner, envelopes are not spherically symmetric. This pattern, if confirmed by observations of a larger sample, could indicate that the non-detection rate is simply a consequence of sampling randomly-oriented circumstellar disks able to scatter starlight within a few stellar radii, with as implication that the massive Herbig Be stars are still surrounded by accretion disks. In addition, we present preliminary modelling which will assist interpreting the kinematic structure of the electron-scattering region.
Optical Variability of the Be Star o And during the Period 1975–1998: Rotational Modulation or Multimodal Pulsations?
Authors: Guerrero G. , Sareyan J.P. , Alvarez M. , Chauville J. , Ferro A. Arellano , Mathias P. , Pena J. , Garciá E.
Published: July 2016

Photometric observations of o And collected from 1994 to 1998 are presented. Neither multimodal pulsations nor rotational modulation seems able to explain completely the complex light curves, but a model based on the pulsations together with some type of magnetic activity could be applicable.
Mid-term Photometric Periodic Variations in Be Stars HR 1960 and HR 2968
Authors: Carrier F. , Burki G.
Published: July 2016

The Be stars HR 1960 and HR 2968 have been monitored from 1978 to 1998 in Geneva photometry and from November 1989 to March 1993 by the Hipparcos satellite. A spectroscopic survey of these stars started in September 1998. Both stars show luminosity variations with a period of 395 d and 371 d for HR 1960 and HR 2968 respectively.
The Multiperiodicity of μ Cen (B2 IVe)
Authors: Baade D. , Rivinius Th. , Štefl S.
Published: July 2016

We re-discuss the reality of the four periods near 0.5 d and reject the claim (Balona et al., these proceedings) that μ Cen exhibits a single ∼0.66-d period caused by co-rotating clouds. The alleged 0.66-d period is not genuine but results from the simultaneous proximity of this value to the beat period between the true 0.28- and 0.5-d periods as well as to a 2-c/d alias of the 0.28-d period.
Phase Variation and NRP Modes in Southern Be Stars
Authors: Janot-Pacheco E. , Leister N.V. , de Souza A.D. , Jankov S. , Hubert A.M. , Floquet M.
Published: July 2016

ζ Ophiuchi and η Centauri are hot, rapidly rotating, southern Be stars showing multi-mode nonradial pulsations (nrp). We use high resolution, high signal-to-noise ratio spectroscopic observations of these objects to test the Telting and Schrijvers’ method (TS) of mode degree l and azimuthal order | m | estimation. In this method, these quantum numbers are calculated from the blue-to-red phase difference of the corresponding main frequency and its first harmonic, respectively. The phase differences were obtained withe the help of the Clean and Cleanest algorithms. Quantum numbers calculated with TS are compatible with those obtained with the Fourier Doppler method within the estimated errors. In the absence of other tools, the TS method can thus be used to estimate l and | m | with reasonably accuracy.
Short-term Periodicity in the Pole-on Be Star υ Cyg
Authors: Floquet M. , Neiner C. , Hubert A.M. , Janot-Pacheco E. , Leister N.V.
Published: July 2016

The pole-on Be star υ Cyg (HD 202904) displayed with Hipparcos photometry a strong long-lived outburst between 1989 and 1993. High S/N spectroscopic observations were obtained in August-September 1998. The photospheric λ6678 line is strongly perturbed by variable outer V and R emission components and is itself highly variable.

All the studied quantities (profiles, EW, radial velocity of the line centroid, V and R emission components, V/R ratio) are dominated by ν = 1.5 c/d frequency. The first harmonic (ν = 3.0 c/d) is also detected in the central part of the profile. In the nrp frame, this pair of frequencies corresponds to a low degree sectorial g-mode l = |m| = 2. Moreover mid-term variations are superimposed to short ones.
Mapping the Non-Radial Pulsations
Authors: Berdyugina S.V. , Korhonen H. , Schrijvers C. , Telting J.H.
Published: July 2016

We apply the surface imaging technique to high-resolution spectra of the rapidly rotating β Cep-type star ω1 Sco. Assuming only temperature fluctuations due to pulsations, we obtain a map of the surface corotating with the dominant pulsation mode. Prom the map we identify the dominant mode and find traces of a second pulsation mode. We conclude that the traditional surface imaging technique can be successfully used for mapping stellar non-radial pulsations.
Spectral and Light Variability of Be Star 60 Cygni
Authors: Koubský P. , Harmanec P. , Huber A.M. , Floquet M. , Kubát J. , Ballereau D. , Božić H. , Chauville J. , Holmgren D. , Yang S. , Cao H. , Eenens P. , Huang L. , Percy J.R.
Published: July 2016

The analysis of high S/N spectra and photometric data of 60 Cyg shows that: (1) Pronounced long-term variations in spectra are accompanied with light variations. (2) The medium-term variations of RV could indicate that 60 Cyg is a spectroscopic binary. (3) Two independent structures dominate the rapid variability of both spectrum and light of the star.
Light Curves of Be Stairs due to Orbiting Arcs of Matter or Prominence-Like Structures
Authors: Zorec J. , Frémat Y. , Hubert A.M.
Published: July 2016

An alternative explanation to the light variations of some Be stars observed during their Be ⇌ Be-shell phase changes is proposed in terms of orbiting or passing clouds. Discrete ejections of matter and/or the presence of orbiting clouds suggest that the circumstellar envelopes of these Be stars may be clumpy.
The Changing X-Ray Properties of γ Cas
Authors: Smith Myron A. , Robinson Richard D.
Published: July 2016

The origin of the hot X-ray emission from γ Cas has been a subject of long debate, with some authors advocating that it arises from a supposed undetected degenerate companion. Parmar et al. (1996) concluded that X-ray properties alone limited one’s ability to understand this source. Thus, Smith et al. (1998, “SRC”) obtained ≈1 day’s simultaneous X-ray and UV spectroscopic and photometric coverage with the RXTE/PCA and HST/GHRS space-borne instruments on 14-15 March 1996. The observed 2–10 keV X-ray light curve was found to have two distinct components; short duration bursts (‘shots)’ superimposed on a slowly varying background, termed the “basal” flux, which modulates on a timescales of hours. SRC found two maxima in the RXTE light curve separated by 10 hours. These features coincided with the appearance of two “dips” in the UV continuum light curve sampled near λ1400. From these light curves and other arguments, SRC concluded that γ Cas’s X-ray and UV continuum flux originated near the surface of the star and were modulated in intensity as the star rotated with a period of 1.123 days. This period was deduced by phasing of the X-ray minima obtained from our RXTE data with ASCA observations taken 10 days earlier and from comparisons of UV minima observed with the GHRS with similar minima seen in IUE observations taken two months earlier.
Spectrophotometric and Photometric Behaviours of Be Stars: the Circumstellar Envelope Formation Mechanisms
Authors: Zorec J. , Hubert A.M. , Moujtahid A.
Published: July 2016

A mechanism to create circumstellar envelopes in Be stars is proposed. The mechanism assumes a mass-loaded wind produced by ablated discrete stellar ejecta. The discrete mass ejections are suggested by the long-term spectrophotometric behaviours of Be stars and by their short and long-lived light outbursts discovered recently.
Shell Lines in Be Disks
Authors: Hanuschik R. W.
Published: July 2016

Shell lines have high diagnostic potential for the kinematical conditions in Be disks. We present here results from our long-term spectroscopic monitoring campaign of Fe II shell lines. We demonstrate that most of them are likely to arise in Keplerian disks being hydrostatically supported. There is furthermore one class of shell lines (dubbed NOACs) which does not fit into this simple scheme.
The Circumstellar Structure of the Be Shell Star ϕ Per
Authors: Hummel W. , Štefl S. , Rivinius Th.
Published: July 2016

We present phase resolved spectra of the Be binary ϕ Per. It is shown that orbital phase variations of the He I line profiles are due to a sector emission region in the circumprimary disk facing the secondary. The increasing asymmetry of Fe II emission lines indicates a density inhomogeneity in the circumprimary disk that developed after 1996.
Multiwavelength Monitoring of the Be/X-ray Binary XPersei - Evidence for Multiple Disk Structures
Authors: Roche P. , Tarasov A.E. , Lyuty V.M. , Clark J.S. , Larionov V.
Published: July 2016

We present optical photometry and high resolution optical spectra of the Be star X Persei/HD 24534, the counterpart to the X-ray pulsar 4U0352+30, obtained over the past ~10 years. These spectra show a variety of behaviour, ending with the onset of a strong V/R cycle. Observations of the He 16678 line suggest several episodes of discrete disc forming. This data forms part of a major long-term multiwavelength monitoring programme (UBVRIJHKL photometry plus optical and UV spectroscopy).
An MHD Model of Be Stars with Disks
Authors: Dudorov A. E. , Pudritz R. E.
Published: July 2016

An investigation of the formation and evolution of Be stars show that these stars could have dipolar fossil magnetic fields. This magnetic field should constrain the circumstellar magnetic disk and influence its dynamical features. For studying these effects we refine the alphamodel of accretion disks of Shakura and Sunyaev by incorporating into this model the evolution of large-scale magnetic fields. In the frame of our model we can investigate the rotational history of the star with the disk and the ionization and thermal properties of disks. We show in particular that in the magnetopause region a current sheet can form that can generate X-ray radiation.
Highly-Eccentric Be/X-ray Binaries: Evolution, Wind Rose Effect, Accretor-Propeller Luminosity Gap
Authors: Raguzova Natalya V. , Lipunov Vladimir M.
Published: July 2016

The influence of the spatial distribution of stellar wind velocities (Wind Rose effect) on the X-ray light curve of highly eccentric binaries is examined using the properties of Be disk-fed outflow. It is shown that a phase shift of the maximum X-ray luminosity is always present in the X-ray light curves. The observed X-ray light curves of some transient binaries are analysed using the developed model. We show that the Be/X-ray transients A0538–66, X0331+53 are likely to undergo transitions from the accreting neutron star regime to the propelling one. The example of evolutionary track which can lead to a formation of the Be/X-ray binary is presented. We conclude that synchronization is a very important process for Be star evolution in binary systems and calculate the critical orbital period for existence of a Be/X-ray binary.
The Evolutionary Evidence for Be/Black Hole Binaries
Authors: Raguzova Natalya V. , Lipunov Vladimir M.
Published: July 2016

Using a Monte Carlo simulation of the modern scenario of the evolution of binary systems (the “Scenario Machine”), we calculate the number of binary black holes with Be stars and their expected observational properties. So far, only two possible candidates for Be/BH binaries have been proposed among the observable sources, the superluminal source GRS 1915+105 in the Galaxy and RX J0117.6–7330 in the SMC. We obtained an evolutionary track that can lead to the formation of such systems. The modern evolutionary scenario predicts the existence of binary black holes on eccentric orbits around Be stars and such systems may be discovered in the near future.
The Evolutionary Evidence for Most Be Stars Being Paired with Hot White Dwarfs
Authors: Raguzova Natalya V.
Published: July 2016

Using the “Scenario Machine” we study the number and physical properties of binary Be stars with white dwarfs taking into account cooling of the compact object and discuss the formation of such systems. According to our calculations the number of binary systems containing a Be star paired with a white dwarf in our galaxy is very large − 46% of all Be stars formed as a result of binary evolution must have a white dwarf as companion. These white dwarfs should be very hot with a surface temperature lying in the range from 30,000 to 60,000 K.
NLTE Model Atmospheres of Irradiated Stars in B Binaries
Authors: Kubát Jiří
Published: July 2016

Model atmospheres of B stars irradiated by their companion are calculated using our model atmosphere computer code under the assumption of hydrostatic, radiative, and statistical equilibrium (NLTE). The external source of radiation (a hot white dwarf) is able to change the temperature structure of the outer atmospheric layers of B stars significantly. The changes of the temperature structure cause changes in the profiles of some lines, especially in those of hydrogen.
The X-ray Outbursts of Be/X-ray Transients
Authors: Negueruela Ignacio , Okazaki Atsuo T.
Published: July 2016

We present a new scenario for the behaviour of Be/X-ray binaries based on long-term multiwavelength monitoring and the decretion disc model. The circumstellar discs of the primaries are truncated because of the tidal and resonant effect of the neutron star. The geometry of the systems and the value of viscosity determine the presence or absence of Type I X-ray outbursts. The interaction of a strongly disturbed disc with the neutron star originates Type II X-ray and optical outbursts.
Substantial Disc Loss in the Be/X-ray Binary System A0535+26
Authors: Haigh N.J. , Coe M.J. , Steele I.A. , Fabregat J.
Published: July 2016

Infrared JHK photometry from October 1998 revealed a remarkable change in the Be/X-ray binary system A0535+26, manifesting itself as a dramatic reduction in emission from the circumstellar disc. Optical and IR spectra presented here have confirmed this disc-loss in greater detail showing radically reduced Hydrogen and Helium line emission, to a degree never before seen in this system, and only rarely in a handful of Be/X-ray binaries. Optical spectroscopy has revealed the re-appearance of a small, stable inner disc, and IR spectra/photometry show the eventual regrowth of a robust circumstellar disc resembling the pre-disc-loss state.
The Parkes Multibeam Pulsar Survey
Authors: Camilo F. , Lyne A. G. , Manchester R. N. , Bell J. F. , Kaspi V. M. , D’Amico N. , McKay N. P. F. , Crawford F. , Stairs I. H. , Morris D. J. , Sheppard D. C. , Possenti A.
Published: July 2016

The Parkes multibeam pulsar survey uses a 13-element receiver operating at a wavelength of 20 cm to survey the inner Galactic plane with remarkable sensitivity. To date we have collected and analyzed data from 45% of the survey region (|b| < 5°; 260° <l< 50°), and have discovered 440 pulsars, in addition to re-detecting 190 previously known ones. Most of the newly discovered pulsars are at great distances, as inferred from a median dispersion measure (DM) of 400 cm−3pc.
A VLA Survey for Radio Pulsars in the Galactic Center
Authors: Lazio T. Joseph W. , Cordes James M.
Published: July 2016

A radio pulsar in the Galactic center will suffer 350secondsof pulse broadening. An imaging search for compact sources is far less desensitized by angular broadening than a periodicity search is affected by pulse broadening. We have conducted an imaging survey of the GC using the VLA and have detected approximately 200 sources. Six compact, steep-spectrum sources have been identified; additional compact sources with no spectral information have also been identified. Additional observations are in progress.
High Precision Timing of PSR J0437–4715
Authors: Britton M. C. , van Straten W. , Bailes M. , Toscano M. , Manchester R. N.
Published: July 2016

Systematic effects currently dominate the timing residuals of the pulsar PSR J0437–4715. These systematics arise from transformations that occur during the propagation and detection of radio waves. The transformation properties of polarized radiation are related to the Lorentz group, and such effects may be represented using Lorentz transformations. These effects may be removed using the techniques of polarimetric self-calibration. Alternatively, an invariant profile may be formed from the polarimetric analogue of the Lorentz invariantI2–Q2–U2–V2and used for pulsar timing. Observations of PSR J0437–4715 are presented that show the consistency between these two techniques.
Millisecond Pulsars in 47 Tucanae
Authors: Freire Paulo C. , Camilo Fernando , Lorimer Duncan R. , Lyne Andrew G. , Manchester Richard N.
Published: July 2016

Recent observations of the globular cluster 47 Tuc, made with the Parkes telescope at a wavelength of 20 cm, have resulted in the discovery of nine new millisecond pulsars (MSPs), all in binary systems. The number of timing solutions available has risen from two to 14. These results will make possible a more detailed study of the cluster dynamics.
Gravitational perturbations as a source of timing noise
Authors: Rodin A. E.
Published: July 2016

In assumption that pulsar gravitationally interacts with its surroundings the relationships between the pulsar rotational and orbital parameters are derived and the solutions for PSR B1620–26 and PSR B1822–09 are presented.
Characteristics of Pulsar Radio Emission at Single-pulse Resolution
Authors: Deshpande Avinash A.
Published: July 2016

Pulsar radio emission shows remarkably rich, but complex behavior in both intensity and polarization when considered on a pulse-to-pulse basis. A large number of pulses, when averaged together, tend to approach & define stable shapes that can be considered as distinct signatures of different pulsars. Such average profiles have shapes ranging from that describable as a simple one-component profile to those suggesting as many as 9 components. The components are understood as resulting from an average of many, often narrower, intities — the subpulses —that appear within the longitude range of a given component. The pulse components are thusformedand represent statistically an intensity-weighted average pattern of the radiation received as a function of longitude. The profile mode changes recognized in many pulsars suggest that the emission profile of a given pulsar may have two quasi-stable states, with one (primary) state more probable/brighter than the other (secondary) state. There are also (often associated) polarization modes that represent polarization states that are orthogonal to each other. The complex nature of orthogonaljumpsobserved in polarization position-angle sweeps may be attributable to possible superposition of two profile/polarization modes with orthogonal polarizations.
Identification of Physical Components in Pulsar Emission
Authors: Seiradakis J.H. , Karastergiou A. , Kramer M. , Psaltis D.
Published: July 2016

We have used power spectra analysis on high frequency (1.4 GHz) data, obtained with the Effelsberg 100m radio-telescope in order to investigate the emission characteristics of pulsars. This analysis has not only revealed the prominent periodicities of the fluctuating components, but has also proven a powerful tool for identifying weak and often unresolved components and their longitudinal location within the integrated pulsar profile. Furthermore, close examination of the properties of the fluctuating components indicates physical connections between them, giving new insight to the structure of the emitting region.
A Decade of Low Frequency Pulsar Polarimetry at PRAO: a Review of the Main Results
Authors: Suleymanova Svetlana A. , Pugachev V.D.
Published: July 2016

The main results of the linear polarization measurements of pulsars done at the lowest radio frequencies 40, 60 and 103 MHz are summarized in this paper. We have analyzed 35 integrated polarization profiles and 20 statistical distribution displays and compared them with published high frequency results.
Nanoarcsecond Single-Dish Imaging of the Vela Pulsar
Authors: Macquart J.-P. , Johnston S. , Walker M. , Stinebring D.
Published: July 2016

We have measured the properties of the diffractive scintillation toward the Vela pulsar under the extremely strong scattering conditions encountered at 660 MHz. We obtain a decorrelation bandwidth ofvd= 244±4 Hz and diffractive decorrelation timescale oftdiff= 3.3±0.3s. Our measurement of the modulation indicesm= 0.87±0.003±0.05 andm= 0.93±0.03±0.05 (one For each polarization stream), are at variance with the modulation index of the Vela pulsar obtained at 2.3 GHz by Gwinn et al. (F997)ifthe deviation from a modulation index of unity is ascribed to a source size effect.
Radio Polarimetry Results for Young Southern Pulsars
Authors: Crawford Fronefield , Kaspi Victoria M. , Manchester Richard N.
Published: July 2016

We present radio polarimetry results for nine Southern pulsars. Six of the nine are young, with characteristic ages less than 100 kyr and high spin-down luminosities. All six show significant linear polarization, and we confirm a previously noticed trend in which the degree of linear polarization increases with spin-down luminosity. We have used the rotating vector model to fit the observed position angle data for PSR J1513–5908 (B1509–58). We find that a magnetic inclination angleα> 60° is excluded at the 3σlevel in the fit, and that the geometry suggested by the morphology of an apparent bipolar X-ray outflow is marginally inconsistent with a recent model of the pulsar magnetosphere.
The Mode-Separated Pulse Profiles of Pulsar Radio Emission
Authors: McKinnon Mark M. , Stinebring Daniel R.
Published: July 2016

Two modes of orthogonal polarization are generally observed in the radio emission from pulsars. Essentially all attempts to calculate the average profiles of the individual modes have assumed that the modes occur separately. We have presented evidence, however, that the modes occur simultaneously. Therefore, we believe that “mode-separated” pulse profiles which have been published to date reveal little about the polarization properties of the individual modes.

Calculating mode-separated pulse profiles for superposed orthogonal modes is complicated by the unknown polarization properties of the individual modes. However, the simplest model of pulsar radio emission which can explain the wide variety in the emission’s polarization is one in which the individual modes are completely polarized. We use our simple model to compute the average profiles of the orthogonal modes in PSR B0525+21. The total intensity of the two mode profiles resembles the overall pulse profile, and each profile is highly linearly polarized.
Pulsar Polarimetry – New Aspects at High Radio Frequencies
Authors: Hoensbroech Alexis von
Published: July 2016

Pulsar polarimetry is an important tool for the investigation of the physical processes and the environment in the magnetosphere. However, the great variety of observed polarization states and the few obvious systematics hamper a straightforward interpretation. In this paper it is shown that the polarimetric features of pulsars are much more systematic at high radio frequencies. An analysis of 116 profiles at 4.85 GHz reveals a clear correlation between the degree of polarization andĖ. Also evidence is shown for pulsars with a heavily increasing degree of circular polarization. Further, a basic concept of a simple magnetospheric propagation scenario is presented, which can account for a variety of polarimetric properties of pulsars.
A Sociological Study of the Optically Emitting Isolated Neutron Stars
Authors: Caraveo Patrizia A.
Published: July 2016

Although less than 1 % of all radio pulsars are detected at optical wavelengths, their optical emission can yield a wealth of information that is either very difficult or plainly impossible to obtain at other wavelengths.
CLYPOS: the Cananea-Ljubljana Young Pulsar Optical Survey
Authors: Carramiñana Alberto , Čadež Andrej , Alvarez César
Published: July 2016

The Cananea-Ljubljana Young Pulsar Optical Survey, or CLYPOS, is an observational study of ≳ 30 known radio pulsars, in search for pulsed optical emission. The survey is being carried out at the 2.12m telescope of the Observatorio Astrofísico Guillermo Haro, near Cananea, Sonora, using the stroboscopic camera of the University of Ljubljana. We restricted the study to young pulsars with declinationδ> −35°, prioritized in terms ofE/d2. Our strategy consists in spending two hours of observing time per pulsar, scanning the whole pulsed-phase interval three times. Further details are given below.