bluuebunny/crossref_metadata_2025 huggingface dataset:
A 330 MHz Survey for Pulsars and Supernova Remnants in M31
Authors: Gelfand Joseph D. , Joseph T. , Lazio W. , Gaensler Bryan M.
Published: July 2016

In the radio band, supernova remnants (SNRs) and pulsars are best identified at low frequencies due to their steep spectrA. Motivated by this fact, we have carried out a deep 330-MHz observation of M31 using the VLA. Achieving a sensitivity of 0.6 mJy at 6″ resolution over the entire optical disk of M31, we identified 405 distinct radio sources. While most of these are unresolved background radio galaxies, we found five SNR candidates, three pulsar wind nebula (PWN) candidates, and three pulsar candidates in our source list. The properties of these sources are discussed.
The Galactic Population and Birth Rate of Radio Pulsars
Authors: Lorimer D. R.
Published: July 2016

We review current understanding of the underlying, as opposed to the observed, pulsar population. The observed sample is heavily biased by selection effects, so that surveys see less than 10% of all potentially observable pulsars. We compare various techniques used to correct the sample for these biases. By far the most significant recent development has been the discovery of over 700 pulsars in the Parkes Multibeam (PM) survey. This new sample is far less affected by selection effects and we use it to make a preliminary analysis of the Galactic pulsar distribution, finding further evidence for a deficit of pulsars in the inner Galaxy.
New Radio Science Facilities for Compact Objects
Authors: Cordes J. M.
Published: July 2016

In a throwback to the early days in radio astronomy, new concepts for radio telescopes are being considered as next-generation facilities. The Low-Frequency Array (LOFAR) and the Square-Kilometer Array (SKA) are two particular projects that will incorporate innovations in hardware and software. Along the way to these projects, major surveys for pulsars and transients and/or follow-up pulsar timing observations will be conducted with the ALFA multibeam system at Arecibo, the Allen Telescope Array (ATA), the Extended VLA (EVLA) and with SKA prototype systems that include the European MBRACE project (Multibeam Radio Astronomy Concept Experiment) and China's FAST (500m Aperture Spherical Telescope). These projects are discussed here in the context of anticipated science drivers.
The Pulsar Birth Rate from the Parkes Multibeam Survey
Authors: Vranesevic N.
Published: July 2016

We report on calculations of the pulsar birth rate based on the results of the Parkes multibeam survey. Prom the observed sample of more than 800 pulsars, we compute the pulsar current, accounting as accurately as possible for all known selection effects. The main goal of this work is to understand the pulsar birth rate as a function of the surface dipole magnetic field strength. We show that pulsars with magnetic fields greater than 1012.5 G account for about half of the total birth rate.
Year-scale Morphological Variation of the X-ray Crab Nebula
Authors: Mori Koji , Burrows David N. , Pavlov George G. , Hester J. Jeff , Shibata Shinpei , Tsunemi Hiroshi
Published: July 2016

We present year-scale morphological variations of the Crab Nebula revealed by the Chandra X-ray Observatory. Observations have been performed about every 1.7 years over the three years from launch. The variations are clearly recognized at two sites: the torus and the southern jet. The torus, which had been steadily expanding until 1.7 years ago, now appears to have shrunk in the latest observation. Additionally, the circular structures seen to the northeast of the torus have decayed into several arcs. On the other hand, the southern jet shows the growth of its overall kinked-structure. We discuss the nature of these variations in terms of the pulsar wind nebula mechanism.
The Boomerang: A Crushed and Re-born PWN?
Authors: Kothes Roland , Uyaniker Bülent , Reich Wolfgang
Published: July 2016

We present new high radio frequency observations of the Boomerang pulsar wind nebula (PWN) made with the Effelsberg 100-m radio telescope. A comparison with low frequency data from the Canadian Galactic Plane Survey (CGPS; Taylor et al. 2003) reveals a change of the nebula's emission structure with frequency caused by a radial steepening of the radio spectrum above 5 GHz. We also find evidence that the reverse shock of the initial supernova shock wave has driven away or crushed the original PWN which might explain why the current nebula around the pulsar has such a low radio luminosity.
Central Compact Objects in Supernova Remnants
Authors: Pavlov George G. , Sanwal Divas , Teter Marcus A.
Published: July 2016

There are point-like sources in central regions of several supernova remnants which have not been detected outside the X-ray range. The X-ray spectra of these Central Compact Objects (CCOs) have thermal components with blackbody temperatures of 0.2–0.5 keV and characteristic sizes of 0.3-3 km. Most likely, the CCOs are neutron stars born in supernova explosions. We overview their observational properties, emphasizing the Chandra data, and compare them with magnetars.
Unveiling the Multi-wavelength Phenomenology of Anomalous X-ray Pulsars
Authors: Israel GianLuca , Stella Luigi , Covino Stefano , Campana Sergio , Angelini Lorella , Mignani Roberto , Mereghetti Sandro , Marconi Gianni , Perna Rosalba
Published: July 2016

During 2002–2003 the number of IR-identified counterparts to the Anomalous X-ray Pulsars (AXPs) has grown to four (4U 0142+61, IE 2259+586, IE 1048.1−5937 and RXS J170849−400910) out of the six objects (plus two candidates) known in this class. More importantly, some new common characteristics have been identified, such as IR variability, IR flattening in the broad-band energy spectrum, X-ray spectral variability as a function of pulse phase (which are not predicted by the magnetar model), and X-ray bursts (which cannot be explained in terms of standard accretion models). We present the results obtained from an extensive multi-wavelength observational campaign carried out with the NTT and CFHT for the optical/IR bands, and XMM and Chandra (plus BeppoSAX archival data) in X-rays. Based on these results and those reported in the literature, the IR-to-X-ray emission of AXPs is compared.
From Crab Pulsar to Magnetar?
Authors: Lyne A. G.
Published: July 2016

We review the evolution of the Crab pulsar's rotational history during the past 35 years. Representing 3.7% of the pulsar's age, it is possible to estimate the likely development of the magnetic field and characteristic age much better than previously. The increasing magnetic field of this pulsar and of other young pulsars, most dramatically the Vela pulsar, raises the interesting possibility that these objects might evolve into magnetars. We discuss the observational case for such a proposal, but note that the origin of these field enhancements may be associated with glitch activity. However, it is understood no better than the origin of the magnetar fields, but may be one and the same.
Discovery of Radio Emission from Two Anomalous X-ray Pulsars
Authors: Malofeev V. M. , Malov O. I. , Teplykh D. A.
Published: July 2016

The detection of pulsed radio emission and first results of the investigations from the anomalous X-ray pulsar (AXP) 1E 2259+586 and the AXP candidate RX J1308.6+2127 at the frequency 111 MHz are presented.
Out of the Chorus Line: What Makes 1E 1207.4–5209 a Unique Object?
Authors: De Luca Andrea , Caraveo Patrizia , Mereghetti Sandro , Moroni Michele , Bignami Giovanni , Mignani Roberto
Published: July 2016

The discovery of deep spectral features in the X-ray spectrum of 1E 1207.4–5209 has pushed this Isolated Neutron Star (INS) out of the chorus line, since no other INS has shown significant features in its X-ray continuum. On 2002 Aug, XMM-Newton devoted a two-orbit target-of-opportunity observation to this target, with the aim of better understanding the nature of such spectral features using much improved statistics. Indeed, the 260 ksec observation yielded 360 000 photons from 1E 1207.4–5209, allowing for a very sensitive study of the temporal and spectral behavior of this object.
Giant Pulses in Millisecond Pulsars
Authors: Joshi B. C. , Kramer M. , Lyne A. G. , McLaughlin M. A. , Stairs I. H.
Published: July 2016

Giant pulses (GPs), occasional individual pulses with an intensity 100 times the average intensity, have been detected in four pulsars to date. Their origin is not well understood, but studies suggest a connection between the strength of magnetic field at the light cylinder Blc and the existence of GPs. Here, we report on detection of significant Large Amplitude Pulses (LAPs) in two more pulsars with high values of Blc, PSRs J0218+4232 and B1957+20, observed using Giant Meterwave Radio Telescope (GMRT).
On the Giant Nano-subpulses in the Crab Pulsar
Authors: Gil J. , Melikidze George I.
Published: July 2016

Extremely short and powerful subpulses were recently detected within the giant radio pulses from the Crab pulsar. We argue that these are consistent with beaming due to the curvature of field lines, and thus with coherent curvature radiation. We also demonstrate that the observed fluxes are consistent with the emission of charged relativistic solitons, generated by means of modulational instability of the Langmuir turbulence associated with sparking discharge of the pulsar's polar gap.
Enhanced Optical Emission from the Crab Pulsar
Authors: Stappers B. W. , Shearer A.
Published: July 2016

We have detected an enhancement in the optical emission from the Crab pulsar which is correlated with the presence of the giant radio pulses. Coincident optical pulses were found to be on average 3% brighter than those coincident with normal radio pulses. This enhancement, combined with the lack of any other pulse profile changes, indicates that both the giant radio pulses and the increased optical emission are most likely linked to an increase in the electron-positron plasma density.
High-frequency Polarimetric Observations of the Crab Pulsar
Authors: Karastergiou A. , Jessner A. , Wielebinski R.
Published: July 2016

We present high quality polarimetric observations with the Effelsberg radio telescope of the Crab pulsar at 8.35 GHz using a new sensitive receiver with a very large bandwidth. We present our observations and discuss them in the context of the conclusions reached by Moffett & Hankins (1999) about the geometry and the origin of the various pulse components.
Centrifugal Acceleration in Pulsar Magnetospheres
Authors: Thomas R. M. C. , Gangadhara R. T.
Published: July 2016

We present a relativistic model of pulsar radio emission by plasma accelerated along the rotating magnetic field lines projected on to a 2D plane perpendicular to the rotation axis. We have derived the expression for the trajectory of a particle, and estimated the spectrum of radio emission by the plasma bunches. We used the parameters given by Peyman & Gangadhara (2002). The analytical expressions for the Stokes parameters are obtained, and their values compared with the observed profiles. The one sense of circular polarization, observed in many pulsars, can be explained in light of our model.
HST and VLT Observations of Pulsars and Their Environments
Authors: Mignani R. P. , De Luca A. , Caraveo P. A.
Published: July 2016

The state of the art of optical studies of isolated neutron stars (INSs) and their pulsar wind nebulae (PWNe) is reviewed. In addition, results obtained from recent HST and VLT observations are presented and discussed.
High Resolution Optics & Detector Systems for Hard X-rays
Authors: Sharma D. P. , Ramsey B. D. , Gaskin J. A. , Engelhaupt D. , Speegle C. , Apple J. , Finger M. H.
Published: July 2016

We describe the development of hard X-ray focusing optics telescopes at the National Space Science and Technology Center.
Long-term Timing of 374 Pulsars
Authors: Hobbs G. , Lyne A. , Kramer M.
Published: July 2016

We have analyzed the arrival times for 374 pulsars that have been observed for more than six years using the 76-m Lovell telescope at Jodrell Bank Observatory. Here we present a qualitative analysis of structures seen in the timing residuals.
Stars at γ-Ray Energies: the INTEGRAL Look at Stars
Authors: Montmerle Thierry
Published: July 2016

The European γ-ray satellite INTEGRAL, launched on October 17, 2002, is the successor to the highly successful American satellite Compton-GRO. Even though its main observational program focuses on “classical” high-energy sources like compact X-ray binaries or AGNs, some time is being devoted to γ-ray studies of massive stars and magnetically active late-type stars. We briefly describe here the four instruments of INTEGRAL, and summarize the ongoing stellar programs.
New Results from the SMA
Authors: M. Moran James
Published: July 2016

The Submillimeter Array (SMA) is nearing completion in “millimeter” valley just below the summit of Mauna Kea in Hawaii. Numerous astronomical observations have been undertaken in the partially transparent bands between 0.45 and 1.3 mm. The status of the instrument is described in this paper, and examples of images that have been made with the partially completed Array of the dust and gas envelopes of a high mass protostellar object (IRAS 18089—1732), a low mass young star (LkCa15), and three evolved stars (CRL 2688, V Hydrae, and IRC+10216) are presented.
Near-IR Observations of Vega-like Stars with the VLTI: β Pic, α PsA, ∊ Eri and τ Cet
Authors: Di Folco Emmanuel , Kervella Pierre , Thévenin Frédéric , Morel Pierre , Domiciano de Suza Armando , Coudé du Foresto Vincent
Published: July 2016

We have conducted K band interferometric observations of four nearby main-sequence Vega-like stars at the VLTI with very long baselines. The very high resolution allowed us to probe the innermost region of the disks, where planets are supposed to be formed. The diameters of three bright and nearby prototypes β Pictoris, Fomalhaut (α PsA) and ∊ Eridani as well as τ Ceti have been measured with VINCI, the VLTI commissioning instrument, with a high accuracy. The derived diameters were used to constrain their age with help of the evolution code CESAM. The precision achieved with VINCI allowed us to discuss the shape of their photosphere and the possible detection of warm circumstellar material within the narrow interferometric field of view.
Structures of Binary Star Coronae
Authors: S. Brickhouse Nancy
Published: July 2016

Stellar coronae in binary star systems offer both a puzzle and an opportunity. We might expect that large magnetic loop structures on close binaries, such as RS CVn systems and contact binaries, would show evidence for interactions between the stars. While some radio studies support this scenario, there is surprisingly little evidence from EUV and X-ray observations for differences between binary and single star systems. Meanwhile, the binary systems offer observational opportunities through rotational modulation and eclipses of flaring and non-flaring regions. Localizing the sources of coronal emission is key to making the magnetic connection to the underlying photosphere. We discuss the structure of stellar coronae from the perspective of studies of binary systems.
Coronae of Cool Stars
Authors: Audard M. , Drake S. A. , Güdel M. , Mewe R. , Pallavicini R. , Simon T. , Singh K. P. , Skinner S. L. , White N. E.
Published: July 2016

We present preliminary results of grating observations of YY Mensae and V824 Arae by Chandra and XMM-Newton. Spectral features are presented in the context of the emission measure distributions, the coronal abundances, and plasma electron densities. In particular, we observe a coronal N/C enhancement in YY Men believed to reflect the photospheric composition (CN cycle). Finally, we interpret line broadening in YY Men as Doppler thermal broadening in its very hot corona.
Influences of Planets on Parent Stars: Abundances
Authors: Murray Norman
Published: July 2016

The heavily cratered face of Mercury and the Moon bears mute testimony to the flux of smaller objects that bombarded the inner solar system in the first billion years after the sun formed. A significant fraction of these bodies likely struck the sun, slightly altering its surface abundances of heavy elements. Stellar pollution of this sort can be detected by looking at metallicities of carefully selected populations of stars of varying mass, e.g., in moderate age clusters, by searching for specific patterns in relative abundances in individual stars, or by looking for isotopic anomalies such as 6Li. I describe the current state of such studies.
Physical Parameters of 59 Stars with Planets
Authors: Cayrel de Strobel G.
Published: July 2016

Astrometric, kinematic, spectroscopic and internal stellar structure data of 59 out of 102, extra-solar planet stars (thereafter ESPs), as yet discovered, are herewith discussed. The remaining 43 have been discarded, because they are not yet subjected to detailed spectroscopic analyses. The assembling of true physical parameters of ESPs has been made with the help of the Hipparcos and the [Fe/H] Catalogues. The retained 59 ESPs, could be divided into three sub-samples: midly metal poor, metal normal and metal enriched ESPs. Three observational (logTeff, Mbol) diagrams for each of the metallicity groups have been constructed and interpreted with the help of theoretical HR diagrams, computed for metal-poor, metal-normal, and metal-rich internal structure models. The age of 47 evolved ESPs of the sample has been estimated from the relevant isochrones. Even if the age difference between some of the ESPs is great, (from 1 to >12 Gyr) stars as young as the Hyades (670 Myr) have not been found. ESPs are biased towards metallicities higher than solar. In this sample the number of ESPs with metallicity [Fe/H]>0 is 2.4 times the number of ESPs with [Fe/H] < 0, whereas the proportion is roughly inverted in a sample of non ESPs.
The Sun as a Star: Comparing Alpha Cen A to UV Solar Spectra
Authors: Linsky Jeffrey L. , Pagano Isabella , Valenti Jeff A. , Duncan Doug
Published: July 2016

The Space Telescope Imaging Spectrograph (STIS) obtained high resolution echelle spectra of the nearby G2 V star α Centauri A covering the entire 1133—3150 Â region with very high signal/noise. This data set provides what is probably the best approximation to the spectrum of the Sun viewed as a star, because it is a full disk spectrum with 2.6 km s—1 resolution, accurate absolute fluxes, full UV spectral coverage, high S/N, and low scattered light. In the 1140—1670 Â region we identify 671 emission lines from 37 different atoms and ions and the molecules CO and H2. We make a detailed comparison of the solar and α Cen A spectra in terms of line identification, line widths and Doppler shifts, emission measure distributions, and electron densities.
Nanoflares and the Heating of the Solar Corona
Authors: Benz Arnold O.
Published: July 2016

New observational signatures of the heating process(es) have been revealed by space missions including SoHO, TRACE, Yohkoh, and RHESSI. Evidences for heating in the quiet corona, active region loops, and the solar wind are different and must be distinguished. Prime indications come from line broadening and waves, the distribution of temperature and radiation loss in relation to height, the correlation of magnetic flux and brightness, nanoflares and other fluctuations. This review concentrates on microevents observed at coronal temperatures. The reported nanoflares in quiet regions are about 2 orders of magnitude smaller than microflares reported in active regions and exhibit less radio emission. To estimate the impact of these microevents on the corona, the effects from a localized energy release must be considered, regardless of the energy source (reconnection or waves). In particular, the coupling with the chromosphere, i.e. the back-reaction of the chromosphere on coronal energy release, has an important effect on the corona. A necessary requirement for the heating process(es) is to deposit most of the heat in the low corona, but to heat also the upper corona to even higher temperature. Finally, the heating process must be able to account for the coronae of more active stars showing coronal emissions at levels of more than 3 orders of magnitude higher than the Sun.
An Observational Test for Coronal Heating Models
Authors: van Driel-Gesztelyi Lidia , Démoulin Pascal , Mandrini Cristina H. , Harra Louise K. , Klimchuk James A.
Published: July 2016

We correlate the evolution of the mean X-ray flux, emission measure and temperature (Yohkoh SXT & BCS) with the magnetic flux density (SOHO/MDI) in active region NOAA 7978 from its birth throughout its decay, for five solar rotations. We show that these plasma parameters together with other quantities deduced from them, such as the density and the pressure, follow power-law relationships with the mean magnetic flux density (B). We derive the dependence of the mean coronal heating rate on the magnetic flux density. We use the obtained scaling laws of coronal loops in thermal equilibrium to derive observational estimates of the scaling of the coronal heating with B. These results are used to test the validity of coronal heating models. We find that models based on the dissipation of stressed, current-carrying magnetic fields are in better agreement with the observations than models that attribute coronal heating to the dissipation of MHD waves injected at the base of the corona. This confirms, with smaller error bars, previous results obtained for individual coronal loops, as well as for the global coronal emission of the Sun and cool stars.
Diagnostics of Coronal Heating in Solar Active Regions
Authors: Fludra A. , Ireland J.
Published: July 2016

We study the relationship between EUV spectral line intensities and the photospheric magnetic field in solar active regions, using magnetograms from SOHO-MDI and EUV spectra of the Fe XVI 360.8 Â line (2 × 106 K) and the O V 629.7 A line (220,000 K) from the Coronal Diagnostic Spectrometer on SOHO, recorded for several active regions. We overlay and compare spatial patterns of the O V emission and the magnetic flux concentrations, with a 4″ x 4″ spatial resolution, and search for a relationship between the local O V line intensity and the photospheric magnetic flux density in each active region. While this dependence exhibits a certain amount of scatter, it can be represented by a power law fit. The average power index from all regions is 0.7 ± 0.2. Applying static loop models, we derive the dependence of the heating rate on the magnetic flux density, Eh ∝ B0.8, and compare it to the dependence predicted by the coronal heating models.
Solar “EIT Waves” — What are They?
Authors: Harra Louise K. , Sterling Alphonse C.
Published: July 2016

There has been substantial interest in the coronal wave phenomena since its discovery several years ago using the EUV Imaging Telescope onboard SOHO (Thompson et al. 1999). One of the first explanations was that finally the coronal part of the Moreton wave had been discovered. Since then, there have been a number of results giving different explanations. We will discuss these in this paper along with the latest results on coronal waves from a spectroscopic perspective.
Linking Thin Flux Tube MHD Models to Apparent Stellar Surface Activity
Authors: Granzer T. , Strassmeier K. G.
Published: July 2016

We model thin magnetic flux tubes as they rise from the bottom of a stellar convection zone to the photosphere. On emergence they form active regions, i.e. star spots. This model was very successfully applied to the solar case, where the simulations where in agreement with the butterfly diagram, Joy's law, and Hale's law. We propose the use of a similar model to describe stellar activity in the more extreme form found on active stars. A comparison between Doppler-images of well-observed pre-MS stars and a theoretically derived probability of star-spot formation as a function of latitude is presented.
Outflows from Young Stars: Theory and Observation
Authors: Shang Hsien
Published: July 2016

Recent observations have revealed that young stellar objects are associated with jet-like structures and Herbig-Haro objects emitting at wavelengths ranging from optical lines to radio continua. These phenomena are similar in morphologies, and have mostly comparable energetics, dynamics, and kinematics. Probing such phenomena observed at various wavelengths with self-consistent physical and radiative processes arising within an inner disk-wind driven magnetocentrifugally from the circumstellar accretion disk is a challenge for confronting theory and observation of outflows. How such early outflow phase may play a role in forming planetary materials may help solve puzzles posed by meteorites. We will discuss the relevant observations, theoretical foundations for modelling approaches, magnetic structures and dynamical effects, and the connection to the early solar system.
Outflow Velocities in Polar Coronal Holes
Authors: Gabriel A. H. , Bely-Dubau F. , Lemaire P. , Antonucci E.
Published: July 2016

Observations have been carried out using the oxygen VI multiplet ratio 1032/1038 Â from SUMER on SOHO. Analysis based on the Doppler dimming method shows that the outflow velocity in polar plumes is higher than that in the interplume region, contrary to many published suggestions. The addition of UVCS data for the interplume region, leads to a conclusion that the effective oxygen ion “temperature” in the radial direction has to rise to around 14 MK over the height range 1.5 to 1.8 R⊙.
Extended Atmospheres of the M Supergiants Alpha Ori and Alpha Sco
Authors: Brown Alexander , Harper Graham M.
Published: July 2016

Multifrequency spatially-resolved radio continuum observations of the M supergiants, α Ori (M2 Iab) and α Sco (M1.5 Iab + B2.5 V), have been obtained using the VLA A array and VLA+Pie Town configurations, to study changes in the extended (i.e. scale 1 − 10 stellar radii) atmospheres of these stars and to model the conditions in their wind acceleration regions. Strong modelling constraints on the atmospheric thermal properties are derived, because the radio emission is resolved at multiple wavelengths. Changes seen in the α Ori source flux density and radio visibility data occurring on several year timescales are described, based on observations obtained in 2002 February and April and in 1996 December. The need for multicomponent models of the plasma conditions in both the warm and cool gas around α Ori is discussed. The radio properties of the α Sco system, both of the M supergiant itself and in the H II region surrounding the B-type companion, provide important tools for estimating conditions within the M supergiant's wind.
The Giant Star Ca II Ionization Problem: Mass Loss Revisited
Authors: Harper Graham M. , Brown Alexander , Ayres Thomas , Sim Stuart A.
Published: July 2016

Pioneering studies of winds from non-coronal evolved late-type stars were plagued by uncertainties in the Ca ionization balance which severely limited the accuracy of derived mass-loss rates. Here we re-examine the Ca II ionization balance in these stellar winds using FUSE spectra which reveal, for the first time, the flux from the photoionizing radiation field shortward of 1045Â. We present a FUSE 912-1185Â spectroscopic survey of evolved late-K and M stars; including the M giants α Cet (M1.5 III), γ Cru (M3.5 III), β Gru (M4.5 III), and R Dor (M8e III). Using FUSE spectra of α Tau (K5 III), supplemented with partial redistribution calculations of H Ly-α and Ly-β, together with UV and radio data, we present a study of α Tau's wind ionization balance and derive new constraints which place the mass-loss rate significantly below that suggested by the Reimers formula.
A Magnetic Betelgeuse? Numerical Simulations of Non-Linear Dynamo Action
Authors: F. Dorch S. B.
Published: July 2016

Betelgeuse is an example of a cool supergiant displaying brightness fluctuations and irregular surface structures. Simulations by Freytag, Steffen, & Dorch (2002) of the convective envelope of the star have shown that the fluctuations in the star's luminosity may be caused by giant cell convection. A related question regarding the nature of Betelgeuse and supergiants in general is whether these stars may be magnetically active. If so, that may in turn also contribute to their variability. By performing detailed numerical simulations, I find that both linear kinematic and non-linear dynamo action are possible and that the non-linear magnetic field saturates at a value somewhat below equipartition: in the linear regime there are two modes of dynamo action.
The Inner Density Cusp of Cold Dark Matter Halos
Authors: Navarro Julio F.
Published: July 2016

I report recent results of numerical simulations designed to study the inner structure of Cold Dark Matter (CDM) halos. This work confirms the proposal of Navarro, Frenk & White (NFW) that the shape of ACDM halo mass profiles differs strongly from a power law and is approximately independent of mass. the logarithmic slope of the spherically-averaged density profile, as measured by β = –d ln ρ/d ln r, decreases monotonically towards the center, becoming shallower than isothermal (β < 2) inside a characteristic radius, r–2, and shows no evidence for convergence to a well-defined asymptotic value (β0) at the center. the dark mass contained within the innermost radius resolved by the simulations places strong constraints on β0; cusps as steep as r–1.5 are clearly ruled out in our highest resolution simulations. A profile where the radial dependence of the slope is a simple power law, β(r) ∝ rα, approximates the structure of halos better than the NFW profile and so may minimize errors when extrapolating our results inward to radii not yet reliably probed by numerical simulations. We compare the spherically-averaged circular velocity (Vc) profiles to the rotation curves of low surface brightness (LSB) galaxies in the samples of de Blok et al. and Swaters et al. the Vc profiles of simulated CDM halos are generally consistent with the rotation curves of LSB galaxies, but there are also some clearly discrepant cases. This disagreement has been interpreted as excluding the presence of cusps, but it may also just reflect the difference between circular velocity and rotation speed likely to arise in gaseous disks embedded within realistic triaxial halos.
Decomposition of the Visible and Dark Matter Mass Profiles in the Einstein Ring 0047–2808
Authors: Dye Simon , Warren Steve
Published: July 2016

Using our semi-linear inversion method, we measure the mass profile of the lens galaxy in the Einstein ring system 0047–2808. The lens is modeled as a baryonic component following the observed light embedded in a generalised dark matter NFW halo. The semi-linear method makes full use of the information content in the ring image. We determine a B-band mass to light ratio for the baryons of 2.33+0.30–0.62h M⊙/LB⊙ (99% CL), accounting for 54% of the total projected mass within the Einstein radius of 1.16″. The inner logarithmic slope of the halo is found to be 0.65+0.73–0.31 (99% CL). We find that the halo is fairly well aligned with the light but has only half the ellipticity.
Rotation curve of our Galaxy and field galaxies
Authors: Russeil D. , Garrido O. , Amram P. , Marcelin M.
Published: July 2016

We present a database of galaxies rotation curve (from Hα observations), including our Galaxy.
Cold Molecular Gas as Baryonic Dark Matter
Authors: Pfenniger Daniel
Published: July 2016

We review the different cold dark gas models that have been proposed in the literature, as well as a new variant which addresses their principal stability problems by taking into account the property of molecular hydrogen to become solid or liquid below 33 K and at sufficiently high pressure. This new physical ingredient provides the possibility to stabilise cold gas globules by a core of condensed molecular hydrogen. Such loosely bound cold globules behave in a galaxy as a collisionless ensemble of matter, and form a reservoir of gas easily liberated through, e.g., UV excitation. the cold condensed cores survive the longest, of order a Gyr in the solar neighbourhood radiation field, and much longer in spiral outer HI disks.
Bars and the connection between dark and visible matter
Authors: Athanassoula E.
Published: July 2016

Isolated barred galaxies evolve by redistributing their internal angular momentum, which is emitted mainly at the inner disc resonances and absorbed mainly at the resonances in the outer disc and the halo. This causes the bar to grow stronger and its pattern speed to decrease with time. A massive, responsive halo enhances this process. I show correlations and trends between the angular momentum absorbed by the halo and the bar strength, pattern speed and morphology. It is thus possible to explain why some disc galaxies are strongly barred, while others have no bar, or only a short bar or an oval. in some cases, a bar is found also in the halo component. This “halo bar” is triaxial, but more prolate-like, is shorter than the disc bar and rotates with roughly the same pattern speed. I finally discuss whether bars can modify the density cusps found in cosmological CDM simulations of dark matter haloes.
High-resolution CO Survey of Virgo Spirals at Nobeyama — Massive Cores inferred from Central Rotation Curves
Authors: Sofue Y. , Nakanishi H. , Onodera S. , Koda J. , Kohno K.
Published: July 2016

We present the results of a high-resolution CO-line survey using the Nobeyama Millimeter-wave Array at high-angular (⋐ 2–3″) and high spectral resolutions for the 15 CO-richest Virgo spirals. We derived exact rotation curves using position-velocity diagrams by applying the iteration method. the obtained RCs rise steeply in the central 100 pc. Surface-mass-density distributions by direct deconvolution of the RCs show massive cores of ⋐ 109M⊙ within 100 pc, suggesting the existence of DM cusps in the centres. Five galaxies were found to nest single-peaked extremely high-density molecular cores, where star formation is currently suppressed by the high differential rotation. We show that the deeper is the gravitational potential, the higher is the central gas density.
Bulge Formation in Late-type Galaxies — Cuspy- vs Soft-core Dark Matter Density Profiles
Authors: Huang J.-H , Deng Z.-G , Fu Y.-N
Published: July 2016

Observational data increasingly indicate that the mergers of galaxies, even minor mergers, can trigger the formation of a set of SSCs within galaxies. the follow-up, dynamical evolution of SSCs in a configuration of dark matter (DM) dominated systems would be basically similar to what we simulated in this work. the scenario that we propose yields a series of results comparable to the relevant observations. Most notable are two points. One is that the low bulge detection rate in very late-type galaxies is in favour of soft-core DM profiles in galaxies of this kind. On the other hand, the observed young ages of nuclear clusters provide evidence supporting cuspy-core profiles. in conclusion, both the soft- and cuspy-core DM density profiles are suitable to relevant dwarf galaxies based on comparisons with observations.
Dark Matter Distribution in Nearby Galaxies
Authors: Garrido Olivia , Amram Philippe , Carignan Claude , Blais-Ouellette Sébastien , Marcelin Michel , Russeil Delphine
Published: July 2016

We present results obtained from a study of the mass distribution of 24 galaxies observed using Fabry-Pérot techniques, as part of the GHASP survey (see Russeil et al., this meeting). For each galaxy, we combined high resolution Hα rotation curves derived from 2-D velocity fields, with low resolution HI data, in order to determine accurately the inner slope of the rotation curve which strongly constrains the distribution of matter. Our work suggests the existence of a constant density core in the center of the dark halos.
The σc — Vcirc correlation in high and low surface brightness galaxies
Authors: Pizzella A. , Bontà E. Dalla , Corsini E. M. , Coccato L. , Bertola F.
Published: July 2016

We investigate the relation between the central velocity dispersion, σc, and the circular velocity, Vcirc, in galaxies. in addition to previously obtained data, we consider an observationally homogeneus sample of 52 high surface brightness and 11 low surface brightness spiral galaxies. We performed a straight line regression analysis in a linear scale, finding a good fit, also for low σc galaxies, always rejected in the previous studies. Low surface brightness galaxies seem to behave differently, showing either higher values of Vcirc or lower values of σc with respect to their high surface brightness counterparts.
A search for LSB dwarf galaxies in various environments
Authors: Roberts Sarah , Davies Jonathan , Sabatini Sabina
Published: July 2016

The varying dwarf galaxy populations in different environments pose a problem for Cold Dark Matter (CDM) hierarchical clustering models. in this paper we present results from a survey conducted in different environments to search for low surface brightness (LSB) dwarf galaxies.
Polar Ring Galaxies and the Tully-Fisher relation: implications for the dark halo shape
Authors: Arnaboldi Magda , Iodice Enrica , Bournaud Frederick , Combes Francoise , Sparke Linda S. , Van Driel Wim , Capaccioli Massimo
Published: July 2016

We have investigated the Tully-Fisher relation for Polar Ring Galaxies (PRGs), based on near infrared, optical and Hi data available for a sample of these peculiar objects. The total K-band luminosity, which mainly comes from the central host galaxy, and the measured Hi linewidth at 20% of the peak line flux density, which traces the potential in the polar plane, place most polar rings of the sample far from the Tully-Fisher relation defined for spiral galaxies, with many PRGs showing larger Hi line-widths than expected for the observed K band luminosity. This result is confirmed by a larger sample of objects, based on B-band data. This observational evidence may be related to the dark halo shape and orientation in these systems, which we study by numerical modeling of PRG formation and dynamics: the larger rotation velocities observed in PRGs can be explained by a flattened polar halo, aligned with the polar ring.
What X-rays tell us about dark matter halos
Authors: Jing Y.P.
Published: July 2016

We present a detailed non-spherical modeling of dark matter halos on the basis of a careful analysis of state-of-the art N-body simulations. the fitting formulae presented here form a complete and accurate description of the triaxial density profiles of halos in Cold Dark Matter (CDM) models. This modeling allows us to quantitatively discuss implications for shape observations of galactic and cluster halos. the predictions of the concordance ACDM model are confronted with the shape observations from the Milky Way to X-ray clusters.
Structure of the Local Galactic Magnetic Field
Authors: Rand R. J. , Kulkarni S. R.
Published: July 2016

We have modeled the local Galactic magnetic field using pulsar rotation measures (RMs), of which there are now about 200 available. The North Polar Spur has a significant effect on pulsar RMs. Using RMs of 116 pulsars nearer than 3 kpc, we find that the local field has a strength B0 = 1.6 ± 0.2 μG toward longitude lB =96° ± 4°, with a reversal of the field at a distance Dr = 600 ± 80 pc toward the inner Galaxy. Relaxing the 3 kpc distance restriction, we find that a concentric ring model with reversals is superior to a bisymmetric spiral model as a fit to the data.
Parameters of the Magnetic Field in the Local Galactic Arm Derived from Low Frequency Absorption Measurements in the Ionized Gas
Authors: Abramenkov Eugene A. , Krymkin Valery V.
Published: July 2016

Parameters of the interstellar magnetic field - the strength ratio of the regular and the isotropic component and the orientation of the regular component - have been derived in the Local Galactic arm over a scale ≤ 1000 pc in the direction of the Galactic anticentre. The results have been obtained by an independent method involving analysis of the Galactic longitude dependences of the volume density of the low frequency Galactic background. An estimate of the ratio of the arm and interarm magnetic field strengths has been made.
The Need for High Resolution for Polarization Studies of Galactic Background Radiation
Authors: Verschuur G.L. , Spoelstra T. A. Th.
Published: July 2016

Polarization data at 390 and 826 MHz were obtained with the 300-foot telescope in February 1987. A survey of selected regions of sky planned for December 1988 had to be postponed. However, our limited data at 390 MHz show that the 30′ beam detected polarization temperatures between four to six times larger than found in surveys with a 1.3 arcmin resolution. This was true in both the highly polarized region around 1=140 degrees and in the North Polar Spur where polarization structures appear to be unresolved (<0.9 pc at the distance of the spur). High resolution observations will be critical to our understanding of the interstellar magnetic field and the scale-length of depolarizing structures.
Large-Scale Galactic and Intergalactic Magnetic Fields
Authors: Fujimoto M. , Sawa T.
Published: July 2016

Large-scale axisymmetric and bisymmetric spiral (ASS and BSS) structures are found of magnetic fields in spiral galaxies by measuring the Faraday rotation of polarized radio emission. Dynamo theory is introduced to explain the field structures, and strong magnetogravitational interaction is suggested to occur between the BSS magnetic fields and spiral density waves. Up-to-date data about the rotation measures RM and redshifts z of QSOs and distant radio galaxies are given for discussing large-scale intergalactic magnetic fields.
Torus-Dynamo
Authors: Deinzer W. , Grosser H. , Schmitt D.
Published: July 2016

Accretion disks around compact objects as well as the gaseous components in galaxies often have the form of a torus. To study the structure and behaviour of magnetic fields generated in such rings, a dynamo is investigated, which is working inside a torus embedded into vacuum. The equations for the kinematic αω-dynamo are written down in toroidal coordinates (see Figure 1). Besides loss of magnetic flux by Ohmic diffusion (characterized by the magnetic diffusivity D) they describe its production by the inductive effects of differential rotation and of turbulent matter, which we have chosen as ω(r) = ω′0r and α = α0 sin θ, respectively. These equations are solved by series expansion into the exponential decay modes of slender tori, which are available in analytical form. A linear homogeneous system of equations follows for the expansion coefficients; its eigenvalues determine the time-dependence of the solutions, the dynamo modes.
Key Problems of Flat Objects Dynamo Theory and Ways of Their Solution
Authors: Krause F. , Meinel R. , Elstner D. , Rüdiger G.
Published: July 2016

The present status of galactic dynamo theory is discussed. A new concept which allows the determination of marginal dynamo numbers for axisymmetric as well as non-axisymmetric large-scale magnetic field modes in axisymmetric disks is applied to a simple galaxy model. The results obtained so far show that a preference of non-axisymmetric fields can only be expected if the α-effect is highly anisotropic and the differential rotation is not too strong. Mostly axisymmetric-spiral fields have to be expected.
Enhancement of Galactic Dynamos by Density Waves
Authors: Tosa Makoto , Chiba Masashi
Published: July 2016

We examine effects of density waves on the local galactic αω-dynamo. Oscillations of the magnetic field and the dynamo parameters due to the density wave perturbation irreversibly couple with the dynamo action to enhance the growth of the magnetic fields.
Galactic Dynamos and Density Wave Theory
Authors: Mestel L , Subramanian K
Published: July 2016

A steady density wave in the stellar background of a disk–like galaxy is supposed to force a spiral shock wave in the interstellar gas. The jump in vorticity across the shock leads to a locally enhanced helicity, and so to an α–effect which is steady but azimuth–dependent in the frame rotating with the angular velocity ω of the density wave. This is simulated by the adoption of the form for the local dynamo growth rate arising when the standard kinematic dynamo equation is treated by the thin–disk approximation (Ruzmaikin et al 1988). The global magnetic field is proportional to the function Q satisfying

where η is the turbulent resistivity (for simplicity assumed uniform) and is the laminar angular velocity of the gas in the inertial frame. We look for solutions of the form where is a global eigen-value, and the non-vanishing of couples all odd or all the even m-values. Anticipating that the strong differential rotation will ensure that in the modes with the largest growth-rate the higher-m parts are weak, the equations are truncated, leaving just a pair in q1, q-1, to describe a basically bisymmetric (m = 1) mode. Approximate treatment by the WKBJ technique suggests that a corotating growing mode (with Γ real and positive) will differ significantly from zero over the range between the points where Numerical solutions have been found for a set of illustrative parameters with corotation occurring at 6.67 kpc, and the turbulence parameters close to those in the M51 mode studied by Ruzmaikin et al which extends over = 1 kpc. Three growing corotating modes were found, the fastest extending for ~ 3 kpc, the other two for over 4 kpc. The first two grow 2-3 times faster, the third somewhat slower, than the M51 mode.
Magnetohydrodynamic Simulation of the Evolution of Large-Scale Magnetic Fields in Disk Galaxies
Authors: Bishop Robert C. , Shapiro Paul R. , Barnes Daniel C.
Published: July 2016

The amplification of a seed magnetic field by the hydrodynamic behavior of a disk galaxy is an important and challenging problem. We present our initial work on a numerical simulation of the amplification of such a field to large scales and its subsequent evolution. The computations will be carried out using a 3-D magnetohydrodynamic code.
On the Nature of Magnetohydrodynamic Turbulence in the Interstellar Medium
Authors: Fedorenko V.N.
Published: July 2016

Various mechanisms of creation of the extended spectrum of MHD turbulence in the interstellar medium are reviewed. Within the scales 1014 cm ≲ L ≲ 1019 cm the turbulence mostly consists of the ensemble of weak shock waves. At 1012 cm ≲ L ≲ 1014 cm the principle mechanism is generation of MHD waves by cosmic rays.
Interstellar Magnetohydrodynamic Waves as Revealed by Radio Astronomy
Authors: Spangler S. R.
Published: July 2016

The plasma density fluctuations responsible for interstellar scintillations occur on the same scales as interstellar magnetohydrodynamic waves (Alfvén waves), which are responsible for many important processes such as the acceleration of the cosmic rays. This suggests that these density fluctuations represent a compressive component of MHD waves, and raises the exciting possibility that radioastronomical observations can provide more or less direct measurements of interstellar microphysical processes. Extraction of MHD wave properties from the radio scattering measurements requires a sound theoretical understanding of the relationship between the magnetic field in an MHD wave and the corresponding plasma density perturbation. We present a plasma kinetic theory treatment of the density compression associated with an MHD wave field. The density perturbation may be expressed as the sum of three terms. These terms are proportional to the wave amplitude, wave intensity, and sine transform of the wave intensity, respectively. The coefficients of these three terms are functions of the plasma β, the electron-to-ion temperature ratio, and the angle of wave propagation with respect to the large scale magnetic field. This relation can serve as the basis for inferring the MHD wave field given a radio scattering measurement of the density fluctuation statistics. In an attempt to apply these ideas to the interstellar plasma turbulence, we have made VLBI angular broadening measurements of sources whose lines of sight pass close to supernova remnants. The intensity of MHD waves is expected to be high in the vicinity of the shock waves associated with supernova remnants. We do not yet have unambiguous evidence of enhanced radio wave scattering due to shock-associated MHD waves. However, we have found anomalously high scattering for the source CL4, whose line of sight passes through the Cygnus Loop.