WorldWideScience

Sample records for stars weakly magnetized

  1. The effect of an accretion disk on coherent pulsed emission from weakly magnetized neutron stars

    International Nuclear Information System (INIS)

    Asaoka, Ikuko; Hoshi, Reiun.

    1989-01-01

    Using a simple model for hot spots formed on the magnetic polar regions we calculate the X-ray pulse profiles expected from bright low-mass X-ray binaries. We assume that neutron stars in close binary systems are surrounded by accretion disks extending down in the vicinity of their surfaces. Even partial eclipses of a hot spot by the accretion disk change the coherent pulsed fraction and, in some cases, the phase of pulsations by almost 180deg. Coherent pulsations are clearly seen even for sufficiently compact model neutron stars, if the hot spots emit isotropic or fan-beam radiation. In the case of pencil-beam radiation, coherent pulsations are also seen if the cap-opening angle is less than ∼60deg, while the inclination angle is larger than 68deg. Gravitational lensing alone does not smear coherent pulsations in moderately weak magnetized neutron stars in the presence of an absorbing accretion disk. (author)

  2. A combined HST and XMM-Newton campaign for the magnetic O9.7 V star HD 54879. Constraining the weak-wind problem of massive stars

    Science.gov (United States)

    Shenar, T.; Oskinova, L. M.; Järvinen, S. P.; Luckas, P.; Hainich, R.; Todt, H.; Hubrig, S.; Sander, A. A. C.; Ilyin, I.; Hamann, W.-R.

    2017-10-01

    Context. HD 54879 (O9.7 V) is one of a dozen O-stars for which an organized atmospheric magnetic field has been detected. Despite their importance, little is known about the winds and evolution of magnetized massive stars. Aims: To gain insights into the interplay between atmospheres, winds, and magnetic fields of massive stars, we acquired UV and X-ray data of HD 54879 using the Hubble Space Telescope and the XMM-Newton satellite. In addition, 35 optical amateur spectra were secured to study the variability of HD 54879. Methods: A multiwavelength (X-ray to optical) spectral analysis is performed using the Potsdam Wolf-Rayet (PoWR) model atmosphere code and the xspec software. Results: The photospheric parameters (T∗ = 30.5 kK, log g = 4.0 [cm s-2], log L = 4.45 [L⊙]) are typical for an O9.7 V star. The microturbulent, macroturbulent, and projected rotational velocities are lower than previously suggested (ξph,vmac,vsini ≤ 4 km s-1). An initial mass of 16 M⊙ and an age of 5 Myr are inferred from evolutionary tracks. We derive a mean X-ray emitting temperature of log TX = 6.7 [K] and an X-ray luminosity of LX = 1 × 1032 erg s-1. Short- and long-scale variability is seen in the Hα line, but only a very long period of P ≈ 5 yr could be estimated. Assessing the circumstellar density of HD 54879 using UV spectra, we can roughly estimate the mass-loss rate HD 54879 would have in the absence of a magnetic field as log ṀB = 0 ≈ -9.0 [M⊙ yr-1]. The magnetic field traps the stellar wind up to the Alfvén radius rA ≳ 12 R∗, implying that its true mass-loss rate is log Ṁ ≲ -10.2 [M⊙ yr-1]. Hence, density enhancements around magnetic stars can be exploited to estimate mass-loss rates of non-magnetic stars of similar spectral types, essential for resolving the weak wind problem. Conclusions: Our study confirms that strongly magnetized stars lose little or no mass, and supplies important constraints on the weak-wind problem of massive main sequence

  3. Magnetic fields of HgMn stars

    DEFF Research Database (Denmark)

    Hubrig, S.; González, J. F.; Ilyin, I.

    2012-01-01

    Context. The frequent presence of weak magnetic fields on the surface of spotted late-B stars with HgMn peculiarity in binary systems has been controversial during the two last decades. Recent studies of magnetic fields in these stars using the least-squares deconvolution (LSD) technique have...... failed to detect magnetic fields, indicating an upper limit on the longitudinal field between 8 and 15G. In these LSD studies, assumptions were made that all spectral lines are identical in shape and can be described by a scaled mean profile. Aims. We re-analyse the available spectropolarimetric material...

  4. Surface structure of quark stars with magnetic fields

    Indian Academy of Sciences (India)

    We investigate the impact of magnetic fields on the electron distribution of the electrosphere of quark stars. For moderately strong magnetic fields of ∼ 1013 G, quantization effects are generally weak due to the large number density of electrons at surface, but can nevertheless affect the photon emission properties of quark ...

  5. Fundamental parameters of He-weak and He-strong stars

    Science.gov (United States)

    Cidale, L. S.; Arias, M. L.; Torres, A. F.; Zorec, J.; Frémat, Y.; Cruzado, A.

    2007-06-01

    Context: He-weak and He-strong stars are chemically peculiar AB objects whose He lines are anomalously weak or strong for their MK spectral type. The determination of fundamental parameters for these stars is often more complex than for normal stars due to their abundance anomalies. Aims: We discuss the determination of fundamental parameters: effective temperature, surface gravity, and visual and bolometric absolute magnitudes of He-weak and He-strong stars. We compare our values with those derived independently from methods based on photometry and model fitting. Methods: We carried out low resolution spectroscopic observations in the wavelength range 3400-4700 Å of 20 He-weak and 8 He-strong stars to determine their fundamental parameters by means of the Divan-Chalonge-Barbier (BCD) spectrophotometric system. This system is based on the measurement of the continuum energy distribution around the Balmer discontinuity (BD). For a few He-weak stars we also estimate the effective temperatures and the angular diameters by integrating absolute fluxes observed over a wide spectral range. Non-LTE model calculations are carried out to study the influence of the He/H abundance ratio on the emergent radiation of He-strong stars and on their T_eff determination. Results: We find that the effective temperatures, surface gravities and bolometric absolute magnitudes of He-weak stars estimated with the BCD system and the integrated flux method are in good agreement between each other, and they also agree with previous determinations based on several different methods. The mean discrepancy between the visual absolute magnitudes derived using the hipparcos parallaxes and the BCD values is on average ±0.3 mag for He-weak stars, while it is ±0.5 mag for He-strong stars. For He-strong stars, we note that the BCD calibration, based on stars in the solar environment, leads to overestimated values of T_eff. By means of model atmosphere calculations with enhanced He/H abundance ratios

  6. MAGNETIC FIELDS OF STARS

    OpenAIRE

    Bychkov, V. D.; Bychkova, L. V.; Madej, J.

    2008-01-01

    Now it is known about 1212 stars of the main sequence and giants (from them 610 stars - it is chemically peculiarity (CP) stars) for which direct measurements of magnetic fields were spent (Bychkov et al.,2008). Let's consider, what representations were generated about magnetic fields (MT) of stars on the basis of available observations data.

  7. First results from the LIFE project: discovery of two magnetic hot evolved stars

    Science.gov (United States)

    Martin, A. J.; Neiner, C.; Oksala, M. E.; Wade, G. A.; Keszthelyi, Z.; Fossati, L.; Marcolino, W.; Mathis, S.; Georgy, C.

    2018-04-01

    We present the initial results of the Large Impact of magnetic Fields on the Evolution of hot stars (LIFE) project. The focus of this project is the search for magnetic fields in evolved OBA giants and supergiants with visual magnitudes between 4 and 8, with the aim to investigate how the magnetic fields observed in upper main-sequence (MS) stars evolve from the MS until the late post-MS stages. In this paper, we present spectropolarimetric observations of 15 stars observed using the ESPaDOnS instrument of the Canada-France-Hawaii Telescope. For each star, we have determined the fundamental parameters and have used stellar evolution models to calculate their mass, age, and radius. Using the least-squared deconvolution technique, we have produced averaged line profiles for each star. From these profiles, we have measured the longitudinal magnetic field strength and have calculated the detection probability. We report the detection of magnetic fields in two stars of our sample: a weak field of Bl = 1.0 ± 0.2 G is detected in the post-MS A5 star 19 Aur and a stronger field of Bl = -230 ± 10 G is detected in the MS/post-MS B8/9 star HR 3042.

  8. MAGNETIC GRAIN TRAPPING AND THE HOT EXCESSES AROUND EARLY-TYPE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Rieke, G. H.; Gáspár, András; Ballering, N. P., E-mail: grieke@as.arizona.edu, E-mail: agaspar@as.arizona.edu, E-mail: ballerin@email.arizona.edu [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)

    2016-01-10

    A significant fraction of main sequence stars observed interferometrically in the near-infrared have slightly extended components that have been attributed to very hot dust. To match the spectrum appears to require the presence of large numbers of very small (<200 nm in radius) dust grains. However, particularly for the hotter stars, it has been unclear how such grains can be retained close to the star against radiation pressure force. We find that the expected weak stellar magnetic fields are sufficient to trap nm-sized dust grains in epicyclic orbits for a few weeks or longer, sufficient to account for the hot excess emission. Our models provide a natural explanation for the requirement that the hot excess dust grains be smaller than 200 nm. They also suggest that magnetic trapping is more effective for rapidly rotating stars, consistent with the average vsini measurements of stars with hot excesses being larger (at ∼2σ) than those for stars without such excesses.

  9. On the Weak-Wind Problem in Massive Stars: X-Ray Spectra Reveal a Massive Hot Wind in mu Columbae

    Science.gov (United States)

    Huenemoerder, David P.; Oskinova, Lidia M.; Ignace, Richard; Waldron, Wayne L.; Todt, Helge; Hamaguchi, Kenji; Kitamoto, Shunji

    2012-01-01

    Mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"--identified from cool wind UV/optical spectra--is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma-the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays.

  10. Destruction of a Magnetized Star

    Science.gov (United States)

    Kohler, Susanna

    2017-01-01

    What happens when a magnetized star is torn apart by the tidal forces of a supermassive black hole, in a violent process known as a tidal disruption event? Two scientists have broken new ground by simulating the disruption of stars with magnetic fields for the first time.The magnetic field configuration during a simulation of the partial disruption of a star. Top left: pre-disruption star. Bottom left: matter begins to re-accrete onto the surviving core after the partial disruption. Right: vortices form in the core as high-angular-momentum debris continues to accrete, winding up and amplifying the field. [Adapted from Guillochon McCourt 2017]What About Magnetic Fields?Magnetic fields are expected to exist in the majority of stars. Though these fields dont dominate the energy budget of a star the magnetic pressure is a million times weaker than the gas pressure in the Suns interior, for example they are the drivers of interesting activity, like the prominences and flares of our Sun.Given this, we can wonder what role stars magnetic fields might play when the stars are torn apart in tidal disruption events. Do the fields change what we observe? Are they dispersed during the disruption, or can they be amplified? Might they even be responsible for launching jets of matter from the black hole after the disruption?Star vs. Black HoleIn a recent study, James Guillochon (Harvard-Smithsonian Center for Astrophysics) and Michael McCourt (Hubble Fellow at UC Santa Barbara) have tackled these questions by performing the first simulations of tidal disruptions of stars that include magnetic fields.In their simulations, Guillochon and McCourt evolve a solar-mass star that passes close to a million-solar-mass black hole. Their simulations explore different magnetic field configurations for the star, and they consider both what happens when the star barely grazes the black hole and is only partially disrupted, as well as what happens when the black hole tears the star apart

  11. A radio survey of weak T Tauri stars in Taurus-Auriga

    International Nuclear Information System (INIS)

    O'neal, D.; Feigelson, E.D.; Mathieu, R.D.; Myers, P.C.

    1990-01-01

    A multi-epoch 5 GHz survey of candidate or confirmed weak T Tauri stars in the Taurus-Auriga molecular cloud complex was conducted with the Very Large Array. The stars were chosen from those having detectable X-ray or chromospheric emission, and weak-emission-line pre-main-sequence stars found by other means. Snapshots of 99 VLA fields containing 119 candidate stars were obtained with a sensitivity of 0.7 mJy; most fields were observed on two or three dates. Nine radio sources coincident with cataloged stars were found. One may be an RS CVn binary system; the other eight are pre-main-sequence stars. Three of the detected stars - HD 283447, V410 Tau, and FK X-ray 1 - were previously known radio sources. Five new detections are Herbig's Anon 1, Hubble 4, HDE 283572, Elias 12, and HK Tau/c. At least five of the sources are variable, and no linear or circular polarization was found. Several lines of evidence suggest that the radio-detected weak T Tauri stars are quite young, perhaps younger on average than nondetected stars. 54 refs

  12. MHD Simulations of Magnetized Stars in the Propeller Regime of Accretion

    Directory of Open Access Journals (Sweden)

    Lii Patrick

    2014-01-01

    Full Text Available Accreting magnetized stars may be in the propeller regime of disc accretion in which the angular velocity of the stellar magnetosphere exceeds that of the inner disc. In these systems, the stellar magnetosphere acts as a centrifugal barrier and inhibits matter accretion onto the rapidly rotating star. Instead, the matter accreting through the disc accumulates at the disc-magnetosphere interface where it picks up angular momentum and is ejected from the system as a wide-angled outflow which gradually collimates at larger distances from the star. If the ejection rate is lower than the accretion rate, the matter will accumulate at the boundary faster than it can be ejected; in this case, accretion onto the star proceeds through an episodic accretion instability in which the episodes of matter accumulation are followed by a brief episode of simultaneous ejection and accretion of matter onto the star. In addition to the matter dominated wind component, the propeller outflow also exhibits a well-collimated, magnetically-dominated Poynting jet which transports energy and angular momentum away from the star. The propeller mechanism may explain some of the weakly-collimated jets and winds observed around some T Tauri stars as well as the episodic variability present in their light curves. It may also explain some of the quasi-periodic variability observed in cataclysmic variables, millisecond pulsars and other magnetized stars.

  13. A search for strong, ordered magnetic fields in Herbig Ae/Be stars

    Science.gov (United States)

    Wade, G. A.; Bagnulo, S.; Drouin, D.; Landstreet, J. D.; Monin, D.

    2007-04-01

    The origin of magnetic fields in intermediate- and high-mass stars is fundamentally a mystery. Clues towards solving this basic astrophysical problem can likely be found at the pre-main-sequence (PMS) evolutionary stage. With this work, we perform the largest and most sensitive search for magnetic fields in PMS Herbig Ae/Be (HAeBe) stars. We seek to determine whether strong, ordered magnetic fields, similar to those of main-sequence Ap/Bp stars, can be detected in these objects, and if so, to determine the intensities, geometrical characteristics, and statistical incidence of such fields. 68 observations of 50 HAeBe stars have been obtained in circularly polarized light using the FORS1 spectropolarimeter at the ESO VLT. An analysis of both Balmer and metallic lines reveals the possible presence of weak longitudinal magnetic fields in photospheric lines of two HAeBe stars, HD 101412 and BF Ori. Results for two additional stars, CPD-53 295 and HD 36112, are suggestive of the presence of magnetic fields, but no firm conclusions can be drawn based on the available data. The intensity of the longitudinal fields detected in HD 101412 and BF Ori suggest that they correspond to globally ordered magnetic fields with surface intensities of order 1 kG. On the other hand, no magnetic field is detected in 4 other HAeBe stars in our sample in which magnetic fields had previously been confirmed. Monte Carlo simulations of the longitudinal field measurements of the undetected stars allow us to place an upper limit of about 300 G on the general presence of aligned magnetic dipole magnetic fields, and of about 500 G on perpendicular dipole fields. Taking into account the results of our survey and other published results, we find that the observed bulk incidence of magnetic HAeBe stars in our sample is 8-12 per cent, in good agreement with that of magnetic main-sequence stars of similar masses. We also find that the rms longitudinal field intensity of magnetically detected HAe

  14. Atmospheric Composition of Weak G Band Stars: CNO and Li Abundances

    Science.gov (United States)

    Adamczak, Jens; Lambert, David L.

    2013-03-01

    We determined the chemical composition of a large sample of weak G band stars—a rare class of G and K giants of intermediate mass with unusual abundances of C, N, and Li. We have observed 24 weak G band stars with the 2.7 m Harlan J. Smith Telescope at the McDonald Observatory and derived spectroscopic abundances for C, N, O, and Li, as well as for selected elements from Na-Eu. The results show that the atmospheres of weak G band stars are highly contaminated with CN-cycle products. The C underabundance is about a factor of 20 larger than for normal giants and the 12C/13C ratio approaches the CN-cycle equilibrium value. In addition to the striking CN-cycle signature the strong N overabundance may indicate the presence of partially ON-cycled material in the atmospheres of the weak G band stars. The exact mechanism responsible for the transport of the elements to the surface has yet to be identified but could be induced by rapid rotation of the main sequence progenitors of the stars. The unusually high Li abundances in some of the stars are an indicator for Li production by the Cameron-Fowler mechanism. A quantitative prediction of a weak G band star's Li abundance is complicated by the strong temperature sensitivity of the mechanism and its participants. In addition to the unusual abundances of CN-cycle elements and Li, we find an overabundance of Na that is in accordance with the NeNa chain running in parallel with the CN cycle. Apart from these peculiarities, the element abundances in a weak G band star's atmosphere are consistent with those of normal giants.

  15. ATMOSPHERIC COMPOSITION OF WEAK G BAND STARS: CNO AND Li ABUNDANCES

    International Nuclear Information System (INIS)

    Adamczak, Jens; Lambert, David L.

    2013-01-01

    We determined the chemical composition of a large sample of weak G band stars—a rare class of G and K giants of intermediate mass with unusual abundances of C, N, and Li. We have observed 24 weak G band stars with the 2.7 m Harlan J. Smith Telescope at the McDonald Observatory and derived spectroscopic abundances for C, N, O, and Li, as well as for selected elements from Na-Eu. The results show that the atmospheres of weak G band stars are highly contaminated with CN-cycle products. The C underabundance is about a factor of 20 larger than for normal giants and the 12 C/ 13 C ratio approaches the CN-cycle equilibrium value. In addition to the striking CN-cycle signature the strong N overabundance may indicate the presence of partially ON-cycled material in the atmospheres of the weak G band stars. The exact mechanism responsible for the transport of the elements to the surface has yet to be identified but could be induced by rapid rotation of the main sequence progenitors of the stars. The unusually high Li abundances in some of the stars are an indicator for Li production by the Cameron-Fowler mechanism. A quantitative prediction of a weak G band star's Li abundance is complicated by the strong temperature sensitivity of the mechanism and its participants. In addition to the unusual abundances of CN-cycle elements and Li, we find an overabundance of Na that is in accordance with the NeNa chain running in parallel with the CN cycle. Apart from these peculiarities, the element abundances in a weak G band star's atmosphere are consistent with those of normal giants.

  16. Relativistic stars with purely toroidal magnetic fields

    International Nuclear Information System (INIS)

    Kiuchi, Kenta; Yoshida, Shijun

    2008-01-01

    We investigate the effects of the purely toroidal magnetic field on the equilibrium structures of the relativistic stars. The basic equations for obtaining equilibrium solutions of relativistic rotating stars containing purely toroidal magnetic fields are derived for the first time. To solve these basic equations numerically, we extend the Cook-Shapiro-Teukolsky scheme for calculating relativistic rotating stars containing no magnetic field to incorporate the effects of the purely toroidal magnetic fields. By using the numerical scheme, we then calculate a large number of the equilibrium configurations for a particular distribution of the magnetic field in order to explore the equilibrium properties. We also construct the equilibrium sequences of the constant baryon mass and/or the constant magnetic flux, which model the evolution of an isolated neutron star as it loses angular momentum via the gravitational waves. Important properties of the equilibrium configurations of the magnetized stars obtained in this study are summarized as follows: (1) For the nonrotating stars, the matter distribution of the stars is prolately distorted due to the toroidal magnetic fields. (2) For the rapidly rotating stars, the shape of the stellar surface becomes oblate because of the centrifugal force. But, the matter distribution deep inside the star is sufficiently prolate for the mean matter distribution of the star to be prolate. (3) The stronger toroidal magnetic fields lead to the mass shedding of the stars at the lower angular velocity. (4) For some equilibrium sequences of the constant baryon mass and magnetic flux, the stars can spin up as they lose angular momentum.

  17. VLA observations of dwarf M flare stars and magnetic stars

    Science.gov (United States)

    Willson, R. F.; Lang, K. R.; Foster, P.

    1988-01-01

    The VLA has been used to search for 6 cm emission from 16 nearby dwarf M stars, leading to the detection of only one of them - Gliese 735. The dwarf M flare stars AD Leonis and YZ Canis Minoris were also monitored at 6 cm and 20 cm wavelength in order to study variability. Successive oppositely circularly polarized bursts were detected from AD Leo at 6 cm, suggesting the presence of magnetic fields of both magnetic polarities. An impulsive 20-cm burst from YZ CMi preceded slowly varying 6-cm emission. The VLA was also used, unsuccessfully, to search for 6-cm emission from 13 magnetic Ap stars, all of which exhibit kG magnetic fields. Although the Ap magnetic stars have strong dipolar magnetic fields, the failure to detect gyroresonant radiation suggests that these stars do not have hot, dense coronae. The quiescent microwave emission from GL 735 is probably due to nonthermal radiation, since unusually high (H = 50 kG or greater) surface magnetic fields are inferred under the assumption that the 6-cm radiation is the gyroresonant radiation of thermal electrons.

  18. HD 66051: the first eclipsing binary hosting an early-type magnetic star

    Science.gov (United States)

    Kochukhov, O.; Johnston, C.; Alecian, E.; Wade, G. A.

    2018-05-01

    Early-type magnetic stars are rarely found in close binary systems. No such objects were known in eclipsing binaries prior to this study. Here we investigated the eclipsing, spectroscopic double-lined binary HD 66051, which exhibits out-of-eclipse photometric variations suggestive of surface brightness inhomogeneities typical of early-type magnetic stars. Using a new set of high-resolution spectropolarimetric observations, we discovered a weak magnetic field on the primary and found intrinsic, element-dependent variability in its spectral lines. The magnetic field structure of the primary is dominated by a nearly axisymmetric dipolar component with a polar field strength Bd ≈ 600 G and an inclination with respect to the rotation axis of βd = 13°. A weaker quadrupolar component is also likely to be present. We combined the radial velocity measurements derived from our spectra with archival optical photometry to determine fundamental masses (3.16 and 1.75 M⊙) and radii (2.78 and 1.39 R⊙) with a 1-3% precision. We also obtained a refined estimate of the effective temperatures (13000 and 9000 K) and studied chemical abundances for both components with the help of disentangled spectra. We demonstrate that the primary component of HD 66051 is a typical late-B magnetic chemically peculiar star with a non-uniform surface chemical abundance distribution. It is not an HgMn-type star as suggested by recent studies. The secondary is a metallic-line star showing neither a strong, global magnetic field nor intrinsic spectral variability. Fundamental parameters provided by our work for this interesting system open unique possibilities for probing interior structure, studying atomic diffusion, and constraining binary star evolution.

  19. Hydromagnetic rotational braking of magnetic stars

    International Nuclear Information System (INIS)

    Fleck, R.C. Jr.

    1980-01-01

    It is suggested that the magnetic Ap stars can be rotationally decelerated to long periods by the braking action of the associated magnetic field on time scales of order 10 7 --10 10 years depending on whether the star's dipole field is aligned perpendicular or parallel to the rotation axis. Rotation includes a toroidal magnetic field in the plasma surrounding a star, and the accompanying magnetic stresses produce a net torque acting to despin the star. These results indicate that it is not necessary to postulate mass loss or mass accretion for this purely hydromagnetic braking effect

  20. The influence of hyperons and strong magnetic field in neutron star properties

    International Nuclear Information System (INIS)

    Lopes, L.L.; Menezes, D.P.

    2012-01-01

    Neutron stars are among the most exotic objects in the universe and constitute a unique laboratory to study nuclear matter above the nuclear saturation density. In this work, we study the equation of state (EoS) of the nuclear matter within a relativistic model subject to a strong magnetic field. We then apply this EoS to study and describe some of the physical characteristics of neutron stars, especially the massradius relation and chemical compositions. To study the influence of the magnetic field and the hyperons in the stellar interior, we consider altogether four solutions: two different magnetic fields to obtain a weak and a strong influence; and two configurations: a family of neutron stars formed only by protons, electrons, and neutrons and a family formed by protons, electrons, neutrons, muons, and hyperons. The limit and the validity of the results found are discussed with some care. In all cases, the particles that constitute the neutron star are in ,B equilibrium and zero total net charge. Our work indicates that the effect of a strong magnetic field has to be taken into account in the description of magnetars, mainly if we believe that there are hyperons in their interior, in which case the influence of the magnetic field can increase the mass by more than 10 %. We have also seen that although a magnetar can reach 2.48 M0, a natural explanation of why we do not know pulsars with masses above 2.0 Mo arises. We also discuss how the magnetic field affects the strangeness fraction in some standard neutron star masses, and to conclude our paper, we revisit the direct Urca process related to the cooling of the neutron stars and show how it is affected by the hyperons and the magnetic field. (author)

  1. MAGNETIC FLUX EXPULSION IN STAR FORMATION

    International Nuclear Information System (INIS)

    Zhao Bo; Li Zhiyun; Nakamura, Fumitaka; Krasnopolsky, Ruben; Shang, Hsien

    2011-01-01

    Stars form in dense cores of magnetized molecular clouds. If the magnetic flux threading the cores is dragged into the stars, the stellar field would be orders of magnitude stronger than observed. This well-known 'magnetic flux problem' demands that most of the core magnetic flux be decoupled from the matter that enters the star. We carry out the first exploration of what happens to the decoupled magnetic flux in three dimensions, using a magnetohydrodynamic (MHD) version of the ENZO adaptive mesh refinement code. The field-matter decoupling is achieved through a sink particle treatment, which is needed to follow the protostellar accretion phase of star formation. We find that the accumulation of the decoupled flux near the accreting protostar leads to a magnetic pressure buildup. The high pressure is released anisotropically along the path of least resistance. It drives a low-density expanding region in which the decoupled magnetic flux is expelled. This decoupling-enabled magnetic structure has never been seen before in three-dimensional MHD simulations of star formation. It generates a strong asymmetry in the protostellar accretion flow, potentially giving a kick to the star. In the presence of an initial core rotation, the structure presents an obstacle to the formation of a rotationally supported disk, in addition to magnetic braking, by acting as a rigid magnetic wall that prevents the rotating gas from completing a full orbit around the central object. We conclude that the decoupled magnetic flux from the stellar matter can strongly affect the protostellar collapse dynamics.

  2. Neutron stars velocities and magnetic fields

    Science.gov (United States)

    Paret, Daryel Manreza; Martinez, A. Perez; Ayala, Alejandro.; Piccinelli, G.; Sanchez, A.

    2018-01-01

    We study a model that explain neutron stars velocities due to the anisotropic emission of neutrinos. Strong magnetic fields present in neutron stars are the source of the anisotropy in the system. To compute the velocity of the neutron star we model its core as composed by strange quark matter and analice the properties of a magnetized quark gas at finite temperature and density. Specifically we have obtained the electron polarization and the specific heat of magnetized fermions as a functions of the temperature, chemical potential and magnetic field which allow us to study the velocity of the neutron star as a function of these parameters.

  3. Unveiling the Role of the Magnetic Field at the Smallest Scales of Star Formation

    Energy Technology Data Exchange (ETDEWEB)

    Hull, Charles L. H.; Mocz, Philip; Burkhart, Blakesley; Goodman, Alyssa A.; Hernquist, Lars [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Girart, Josep M. [Institut de Ciències de l’Espai (CSIC-IEEC), Campus UAB, Carrer de Can Magrans S/N, E-08193 Cerdanyola del Vallès, Catalonia (Spain); Cortés, Paulo C. [National Radio Astronomy Observatory, Charlottesville, VA 22903 (United States); Springel, Volker [Heidelberger Institut für Theoretische Studien, Schloss-Wolfsbrunnenweg 35, D-69118 Heidelberg (Germany); Li, Zhi-Yun [Department of Astronomy, University of Virginia, Charlottesville, VA 22903 (United States); Lai, Shih-Ping, E-mail: chat.hull@cfa.harvard.edu [Institute of Astronomy and Department of Physics, National Tsing Hua University, 101 Section 2 Kuang Fu Road, 30013 Hsinchu, Taiwan (China)

    2017-06-20

    We report Atacama Large Millimeter/submillimeter Array (ALMA) observations of polarized dust emission from the protostellar source Ser-emb 8 at a linear resolution of 140 au. Assuming models of dust-grain alignment hold, the observed polarization pattern gives a projected view of the magnetic field structure in this source. Contrary to expectations based on models of strongly magnetized star formation, the magnetic field in Ser-emb 8 does not exhibit an hourglass morphology. Combining the new ALMA data with previous observational studies, we can connect magnetic field structure from protostellar core (∼80,000 au) to disk (∼100 au) scales. We compare our observations with four magnetohydrodynamic gravo-turbulence simulations made with the AREPO code that have initial conditions ranging from super-Alfvénic (weakly magnetized) to sub-Alfvénic (strongly magnetized). These simulations achieve the spatial dynamic range necessary to resolve the collapse of protostars from the parsec scale of star-forming clouds down to the ∼100 au scale probed by ALMA. Only in the very strongly magnetized simulation do we see both the preservation of the field direction from cloud to disk scales and an hourglass-shaped field at <1000 au scales. We conduct an analysis of the relative orientation of the magnetic field and the density structure in both the Ser-emb 8 ALMA observations and the synthetic observations of the four AREPO simulations. We conclude that the Ser-emb 8 data are most similar to the weakly magnetized simulations, which exhibit random alignment, in contrast to the strongly magnetized simulation, where the magnetic field plays a role in shaping the density structure in the source. In the weak-field case, it is turbulence—not the magnetic field—that shapes the material that forms the protostar, highlighting the dominant role that turbulence can play across many orders of magnitude in spatial scale.

  4. Suppression of cooling by strong magnetic fields in white dwarf stars.

    Science.gov (United States)

    Valyavin, G; Shulyak, D; Wade, G A; Antonyuk, K; Zharikov, S V; Galazutdinov, G A; Plachinda, S; Bagnulo, S; Machado, L Fox; Alvarez, M; Clark, D M; Lopez, J M; Hiriart, D; Han, Inwoo; Jeon, Young-Beom; Zurita, C; Mujica, R; Burlakova, T; Szeifert, T; Burenkov, A

    2014-11-06

    Isolated cool white dwarf stars more often have strong magnetic fields than young, hotter white dwarfs, which has been a puzzle because magnetic fields are expected to decay with time but a cool surface suggests that the star is old. In addition, some white dwarfs with strong fields vary in brightness as they rotate, which has been variously attributed to surface brightness inhomogeneities similar to sunspots, chemical inhomogeneities and other magneto-optical effects. Here we describe optical observations of the brightness and magnetic field of the cool white dwarf WD 1953-011 taken over about eight years, and the results of an analysis of its surface temperature and magnetic field distribution. We find that the magnetic field suppresses atmospheric convection, leading to dark spots in the most magnetized areas. We also find that strong fields are sufficient to suppress convection over the entire surface in cool magnetic white dwarfs, which inhibits their cooling evolution relative to weakly magnetic and non-magnetic white dwarfs, making them appear younger than they truly are. This explains the long-standing mystery of why magnetic fields are more common amongst cool white dwarfs, and implies that the currently accepted ages of strongly magnetic white dwarfs are systematically too young.

  5. Residual Gas and Dust around Transition Objects and Weak T Tauri Stars

    Energy Technology Data Exchange (ETDEWEB)

    Doppmann, Greg W. [W. M. Keck Observatory, 65-1120 Mamalahoa Hwy., Kamuela, HI 96743 (United States); Najita, Joan R. [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States); Carr, John S., E-mail: gdoppmann@keck.hawaii.edu, E-mail: najita@noao.edu, E-mail: carr@nrl.navy.mil [Naval Research Laboratory, Code 7213, Washington, DC 20375 (United States)

    2017-02-20

    Residual gas in disks around young stars can spin down stars, circularize the orbits of terrestrial planets, and whisk away the dusty debris that is expected to serve as a signpost of terrestrial planet formation. We have carried out a sensitive search for residual gas and dust in the terrestrial planet region surrounding young stars ranging in age from a few to ∼10 Myr. Using high-resolution 4.7 μ m spectra of transition objects (TOs) and weak T Tauri stars, we searched for weak continuum excesses and CO fundamental emission, after making a careful correction for the stellar contribution to the observed spectrum. We find that the CO emission from TOs is weaker and located farther from the star than CO emission from nontransition T Tauri stars with similar stellar accretion rates. The difference is possibly the result of chemical and/or dynamical effects (i.e., a low CO abundance or close-in low-mass planets). The weak T Tauri stars show no CO fundamental emission down to low flux levels (5 × 10{sup −20} to 10{sup −18} W m{sup −2}). We illustrate how our results can be used to constrain the residual disk gas content in these systems and discuss their potential implications for star and planet formation.

  6. The evolution of surface magnetic fields in young solar-type stars II: the early main sequence (250-650 Myr)

    Science.gov (United States)

    Folsom, C. P.; Bouvier, J.; Petit, P.; Lèbre, A.; Amard, L.; Palacios, A.; Morin, J.; Donati, J.-F.; Vidotto, A. A.

    2018-03-01

    There is a large change in surface rotation rates of sun-like stars on the pre-main sequence and early main sequence. Since these stars have dynamo-driven magnetic fields, this implies a strong evolution of their magnetic properties over this time period. The spin-down of these stars is controlled by interactions between stellar and magnetic fields, thus magnetic evolution in turn plays an important role in rotational evolution. We present here the second part of a study investigating the evolution of large-scale surface magnetic fields in this critical time period. We observed stars in open clusters and stellar associations with known ages between 120 and 650 Myr, and used spectropolarimetry and Zeeman Doppler Imaging to characterize their large-scale magnetic field strength and geometry. We report 15 stars with magnetic detections here. These stars have masses from 0.8 to 0.95 M⊙, rotation periods from 0.326 to 10.6 d, and we find large-scale magnetic field strengths from 8.5 to 195 G with a wide range of geometries. We find a clear trend towards decreasing magnetic field strength with age, and a power law decrease in magnetic field strength with Rossby number. There is some tentative evidence for saturation of the large-scale magnetic field strength at Rossby numbers below 0.1, although the saturation point is not yet well defined. Comparing to younger classical T Tauri stars, we support the hypothesis that differences in internal structure produce large differences in observed magnetic fields, however for weak-lined T Tauri stars this is less clear.

  7. Neutron star crustal plate tectonics. I. Magnetic dipole evolution in millisecond pulsars and low-mass X-ray binaries

    International Nuclear Information System (INIS)

    Ruderman, M.

    1991-01-01

    Crust lattices in spinning-up or spinning-down neutron stars have growing shear stresses caused by neutron superfluid vortex lines pinned to lattice nuclei. For the most rapidly spinning stars, this stress will break and move the crust before vortex unpinning occurs. In spinning-down neutron stars, crustal plates will move an equatorial subduction zone in which the plates are forced into the stellar core below the crust. The opposite plate motion occurs in spinning-up stars. Magnetic fields which pass through the crust or have sources in it move with the crust. Spun-up neutron stars in accreting low-mass X-ray binaries LMXBs should then have almost axially symmetric magnetic fields. Spun-down ones with very weak magnetic fields should have external magnetic fields which enter and leave the neutron star surface only near its equator. The lowest field millisecond radiopulsars seem to be orthogonal rotators implying that they have not previously been spun-up in LMXBs but are neutron stars initially formed with periods near 0.001 s that subsequently spin down to their present periods. Accretion-induced white dwarf collapse is then the most plausible genesis for them. 29 refs

  8. Neutron stars, magnetic fields, and gravitational waves

    International Nuclear Information System (INIS)

    Lamb, F.K.

    2001-01-01

    The r-modes of rapidly spinning young neutron stars have recently attracted attention as a promising source of detectable gravitational radiation. These neutron stars are expected to have magnetic fields ∼ 10 12 G. The r-mode velocity perturbation causes differential motion of the fluid in the star; this is a kinematic effect. In addition, the radiation-reaction associated with emission of gravitational radiation by r-waves drives additional differential fluid motions; this is a dynamic effect. These differential fluid motions distort the magnetic fields of neutron stars and may therefore play an important role in determining the structure of neutron star magnetic fields. If the stellar field is ∼ 10 16 (Ω/Ω B ) G or stronger, the usual r-modes are no longer normal modes of the star; here Ω and Ω B are the angular velocities of the star and at which mass shedding occurs. Much weaker magnetic fields can prevent gravitational radiation from amplifying the r-modes or damp existing r-mode oscillations on a relatively short timescale by extracting energy from the modes faster than gravitational wave emission can pump energy into them. The onset of proton superconductivity in the cores of newly formed magnetic neutron stars typically increases the effect on the r-modes of the magnetic field in the core by many orders of magnitude. Once the core has become superconducting, magnetic fields of the order of 10 12 G or greater are usually sufficient to damp r-modes that have been excited by emission of gravitational radiation and to suppress any further emission. A rapid drop in the strength of r-mode gravitational radiation from young neutron stars may therefore signal the onset of superconductivity in the core and provide a lower bound on the strength of the magnetic field there. Hence, measurements of r-mode gravitational waves from newly formed neutron stars may provide valuable diagnostic information about magnetic field strengths, cooling processes, and the

  9. Electromagnetic fields of rotating magnetized NUT stars

    International Nuclear Information System (INIS)

    Ahmedov, B.J.; Khugaev, A.V.; Ahmedov, B.J.

    2004-01-01

    Full text: Analytic general relativistic expressions for the electromagnetic fields external to a slowly-rotating magnetized NUT star with nonvanishing gravitomagnetic charge have been presented. Solutions for the electric and magnetic fields have been found after separating the Maxwell equations in the external background spacetime of a slowly rotating NUT star into angular and radial parts in the lowest order approximation. The star is considered isolated and in vacuum, with different models for stellar magnetic field: i) monopolar magnetic field and II) dipolar magnetic field aligned with the axis of rotation. We have shown that the general relativistic corrections due to the dragging of reference frames and gravitomagnetic charge are not present in the form of the magnetic fields but emerge only in the form of the electric fields. In particular, we have shown that the frame-dragging and gravitomagnetic charge provide an additional induced electric field which is analogous to the one introduced by the rotation of the star in the flat spacetime limit

  10. Ap stars with resolved magnetically split lines: Magnetic field determinations from Stokes I and V spectra⋆

    Science.gov (United States)

    Mathys, G.

    2017-05-01

    rotation period shorter than 150 days, ⟨ B ⟩ av > 7.5 kG, while those stars with a longer period all have ⟨ B ⟩ av 100 d than in shorter period stars. The root-mean-square longitudinal fields of all the studied stars but one is less than one-third of their phased-average mean field moduli, which is consistent with the expected behaviour for fields whose geometrical structure resembles a centred dipole. However, moderate but significant departures from the latter are frequent. Crossover resulting from the correlation between the Zeeman effect and the rotation-induced Doppler effect across the stellar surface is definitely detected in stars with rotation periods of up to 130 days and possibly even up to 500 days. Weak, but formally significant crossover of constant sign, has also been observed in a number of longer period stars, which could potentially be caused by pulsation velocity gradients across the depth of the photosphere. The quadratic field is in average 1.3 times greater than the mean field modulus and both of those moments vary with similar relative amplitudes and almost in phase in most stars. Rare exceptions almost certainly have unusual field structures. The distribution of the known values and lower limits of the rotation periods of the Ap stars with magnetically resolved lines indicates that for some of them, Prot must almost certainly reach 300 yr or possibly even much higher values. Of the 43 Ap stars that we studied in detail, 22 are in binary systems. The shortest orbital period Porb of those systems is 27 days. For those non-synchronised Ap binaries for which both the rotation period and the orbital period, or meaningful lower limits thereof, are reliably determined, the distribution of the orbital periods of the systems in which the Ap star has a rotation period that is shorter than 50 days is different from its distribution for those systems in which the rotation period of the Ap star is longer, at a confidence level of 99.6%. The shortest

  11. The magnetic early B-type stars I: magnetometry and rotation

    Science.gov (United States)

    Shultz, M. E.; Wade, G. A.; Rivinius, Th; Neiner, C.; Alecian, E.; Bohlender, D.; Monin, D.; Sikora, J.; MiMeS Collaboration; BinaMIcS Collaboration

    2018-04-01

    The rotational and magnetic properties of many magnetic hot stars are poorly characterized, therefore the Magnetism in Massive Stars and Binarity and Magnetic Interactions in various classes of Stars collaborations have collected extensive high-dispersion spectropolarimetric data sets of these targets. We present longitudinal magnetic field measurements for 52 early B-type stars (B5-B0), with which we attempt to determine their rotational periods Prot. Supplemented with high-resolution spectroscopy, low-resolution Dominion Astrophysical Observatory circular spectropolarimetry, and archival Hipparcos photometry, we determined Prot for 10 stars, leaving only five stars for which Prot could not be determined. Rotational ephemerides for 14 stars were refined via comparison of new to historical magnetic measurements. The distribution of Prot is very similar to that observed for the cooler Ap/Bp stars. We also measured v sin i and vmac for all stars. Comparison to non-magnetic stars shows that v sin i is much lower for magnetic stars, an expected consequence of magnetic braking. We also find evidence that vmac is lower for magnetic stars. Least-squares deconvolution profiles extracted using single-element masks revealed widespread, systematic discrepancies in between different elements: this effect is apparent only for chemically peculiar stars, suggesting it is a consequence of chemical spots. Sinusoidal fits to H line measurements (which should be minimally affected by chemical spots), yielded evidence of surface magnetic fields more complex than simple dipoles in six stars for which this has not previously been reported; however, in all six cases, the second- and third-order amplitudes are small relative to the first-order (dipolar) amplitudes.

  12. Magnetization reversal in weak ferrimagnets and canted antiferromagnets

    International Nuclear Information System (INIS)

    Kageyama, H.; Khomskii, D.I.; Levitin, R.Z.; Markina, M.M.; Okuyama, T.; Uchimoto, T.; Vasil'ev, A.N.

    2003-01-01

    In some ferrimagnets the total magnetization vanishes at a certain compensation temperature T*. In weak magnetic fields, the magnetization can change sign at T* (the magnetization reversal). Much rarer is observation of ferrimagnetic-like response in canted antiferromagnets, where the weak ferromagnetic moment is due to the tilting of the sublattice magnetizations. The latter phenomenon was observed in nickel (II) formate dihydrate Ni(HCOO) 2 ·2H 2 O. The observed weak magnetic moment increases initially below T N =15.5 K, equals zero at T*=8.5 K and increases again at lowering temperature. The sign of the low-field magnetization at any given temperature is determined by the sample's magnetic prehistory and the signs are opposite to each other at T N

  13. SURPRISINGLY WEAK MAGNETISM ON YOUNG ACCRETING BROWN DWARFS

    International Nuclear Information System (INIS)

    Reiners, A.; Basri, G.; Christensen, U. R.

    2009-01-01

    We have measured the surface magnetic flux on four accreting young brown dwarfs and one nonaccreting young very low mass (VLM) star utilizing high-resolution spectra of absorption lines of the FeH molecule. A magnetic field of 1-2 kG had been proposed for one of the brown dwarfs, Two Micron All Sky Survey (2MASS) J1207334-393254, because of its similarities to higher mass T Tauri stars as manifested in accretion and the presence of a jet. We do not find clear evidence for a kilogauss field in any of our young brown dwarfs but do find a 2 kG field on the young VLM star. Our 3σ upper limit for the magnetic flux in 2MASS J1207334-393254 just reaches 1 kG. We estimate the magnetic field required for accretion in young brown dwarfs given the observed rotations, and find that fields of only a few hundred gauss are sufficient for magnetospheric accretion. This predicted value is less than our observed upper limit. We conclude that magnetic fields in young brown dwarfs are a factor of 5 or more lower than in young stars of about one solar mass, and in older stars with spectral types similar to our young brown dwarfs. It is interesting that, during the first few million years, the fields scale down with mass in line with what is needed for magnetospheric accretion, yet no such scaling is observed at later ages within the same effective temperature range. This scaling is opposite to the trend in rotation, with shorter rotation periods for very young accreting brown dwarfs compared with accreting solar-mass objects (and very low Rossby numbers in all cases). We speculate that in young objects a deeper intrinsic connection may exist between magnetospheric accretion and magnetic field strength, or that magnetic field generation in brown dwarfs may be less efficient than in stars. Neither of these currently has an easy physical explanation.

  14. Effects of magnetic fields on main sequence stars

    International Nuclear Information System (INIS)

    Hubbard, E.N.

    1981-01-01

    A number of effects of low to medium strength ( 2 /8π) magnetic field pressure term so that the only effect of such a field may come from its inhibiting convection in the core. Isochrones of both convective and radiative core models of 2-5 M are presented. In the deep envelope, mixing of partially nuclear processed material driven by rising and falling magnetic flux tubes may be seen. The effects of this mixing will be brought to the surface during the deep convection phase of the star's tenure as a red giant. This model is used to predict a signature for magnetic mixing based on the CNO isotope and abundance ratios. In the outer envelope the gas pressure is low enough that one might expect to see a perturbation of the stellar structure due to the magnetic field pressure itself. This perturbation is calculated under several physical models for intermediate and high mass stars and it is determined that sufficient magnetic field energy may be available in the outer envelope to expand a star by about 20% over its unperturbed radius. Finally the evidence for the existence of non-magnetic neutron stars is considered, concluding that while no non-magnetic neutron stars have ever been positively identified, there is no evidence that prevents the existence of at least as many non-magnetic as magnetic neutron stars

  15. Broad-band linear polarization and magnetic intensification in rotating magnetic stars

    International Nuclear Information System (INIS)

    Degl'Innocenti, M.L.; Calamai, G.; Degl'Innocenti, E.L.; Patriarchi, P.

    1981-01-01

    Magnetic intensification is proposed as a mechanism to explain the general features of the variable broad-band linear polarization emerging from rotating magnetic stars. This mechanism is studied in detail, and some efforts are made to investigate the wide variety of polarization diagrams that can result from it. Theoretical results are compared with direct observations of the variable magnetic star 53 Cam to determine its geometric and magnetic configuration

  16. Magnetic fields in beta Cep, SPB, and Be stars

    OpenAIRE

    Schoeller, M.; Hubrig, S.; Briquet, M.; Ilyin, I.

    2013-01-01

    Recent observational and theoretical results emphasize the potential significance of magnetic fields for structure, evolution, and environment of massive stars. Depending on their spectral and photometric behavior, the upper main-sequence B-type stars are assigned to different groups, such as beta Cep stars and slowly pulsating B (SPB) stars, He-rich and He-deficient Bp stars, Be stars, BpSi stars, HgMn stars, or normal B-type stars. All these groups are characterized by different magnetic fi...

  17. Magnetic fields of Herbig Ae/Be stars

    Directory of Open Access Journals (Sweden)

    Hubrig S.

    2014-01-01

    Full Text Available We report on the status of our spectropolarimetric studies of Herbig Ae/Be stars carried out during the last years. The magnetic field geometries of these stars, investigated with spectropolarimetric time series, can likely be described by centred dipoles with polar magnetic field strengths of several hundred Gauss. A number of Herbig Ae/Be stars with detected magnetic fields have recently been observed with X-shooter in the visible and the near-IR, as well as with the high-resolution near-IR spectrograph CRIRES. These observations are of great importance to understand the relation between the magnetic field topology and the physics of the accretion flow and the accretion disk gas emission.

  18. Theory of Disk Accretion onto Magnetic Stars

    Directory of Open Access Journals (Sweden)

    Lai Dong

    2014-01-01

    Full Text Available Disk accretion onto magnetic stars occurs in a variety of systems, including accreting neutron stars (with both high and low magnetic fields, white dwarfs, and protostars. We review some of the key physical processes in magnetosphere-disk interaction, highlighting the theoretical uncertainties. We also discuss some applications to the observations of accreting neutron star and protostellar systems, as well as possible connections to protoplanetary disks and exoplanets.

  19. Stellar magnetic activity – Star-Planet Interactions

    Directory of Open Access Journals (Sweden)

    Poppenhaeger, K.

    2015-01-01

    Full Text Available Stellar magnetic activity is an important factor in the formation and evolution of exoplanets. Magnetic phenomena like stellar flares, coronal mass ejections, and high-energy emission affect the exoplanetary atmosphere and its mass loss over time. One major question is whether the magnetic evolution of exoplanet host stars is the same as for stars without planets; tidal and magnetic interactions of a star and its close-in planets may play a role in this. Stellar magnetic activity also shapes our ability to detect exoplanets with different methods in the first place, and therefore we need to understand it properly to derive an accurate estimate of the existing exoplanet population. I will review recent theoretical and observational results, as well as outline some avenues for future progress.

  20. Rotation and magnetism in intermediate-mass stars

    Science.gov (United States)

    Quentin, Léo G.; Tout, Christopher A.

    2018-06-01

    Rotation and magnetism are increasingly recognized as important phenomena in stellar evolution. Surface magnetic fields from a few to 20 000 G have been observed and models have suggested that magnetohydrodynamic transport of angular momentum and chemical composition could explain the peculiar composition of some stars. Stellar remnants such as white dwarfs have been observed with fields from a few to more than 109 G. We investigate the origin of and the evolution, on thermal and nuclear rather than dynamical time-scales, of an averaged large-scale magnetic field throughout a star's life and its coupling to stellar rotation. Large-scale magnetic fields sustained until late stages of stellar evolution with conservation of magnetic flux could explain the very high fields observed in white dwarfs. We include these effects in the Cambridge stellar evolution code using three time-dependant advection-diffusion equations coupled to the structural and composition equations of stars to model the evolution of angular momentum and the two components of the magnetic field. We present the evolution in various cases for a 3 M_{⊙} star from the beginning to the late stages of its life. Our particular model assumes that turbulent motions, including convection, favour small-scale field at the expense of large-scale field. As a result, the large-scale field concentrates in radiative zones of the star and so is exchanged between the core and the envelope of the star as it evolves. The field is sustained until the end of the asymptotic giant branch, when it concentrates in the degenerate core.

  1. A search for magnetic fields in Lambda Bootis stars

    International Nuclear Information System (INIS)

    Bohlender, D.A.; Landstreet, J.D.

    1990-01-01

    We have searched a sample of λ Boo stars for magnetic fields similar to those observed in the magnetic Ap and Bp stars, using a Balmer-line Zeeman analyser. Apart from one dubious measurement, no fields are detected in our sample. It appears that magnetic fields of the λ Boo stars, if they exist, are significantly smaller than those found in magnetic upper main-sequence stars of similar spectral type; this conclusion is supported at about the 90 or 95 per cent confidence level by the present data. (author)

  2. Neutron star formation and the weak interaction

    International Nuclear Information System (INIS)

    Burrows, A.

    1986-01-01

    The only known direct diagnostic of the central event is its neutrino emission. The imprint of the entire internal evolution is stamped on the spectrum, mix of flavors, luminosities, and features of the accompanying neutrino burst. Detection and scrutiny of this neutrino signal will test theories concerning stellar collapse, type II supernovae, and the formation of neutron stars in ways impossible by other means. Despite the fact that an incredible 3x10 53 ergs may be emitted in neutrinos after the initiation of collapse, the very weakness of the neutrino/matter interaction that allows them to penetrate the stellar envelope and escape makes their detection at the Earth very difficult. Though neutrino astronomy is not yet a mature discipline, the physical theories of collapse have progressed to a sufficient degree that specific and detailed predictions can be made about the neutrino emissions that with future detector technology might be tested. The time seems propitious to summarize and review what is known and suspected about the neutrino signature of collapse, the potential for its detection, and how it can be used to test our ideas about the death of massive stars and the birth of neutrino stars. (orig./BBOE)

  3. Simulations of Magnetic Fields in Tidally Disrupted Stars

    Energy Technology Data Exchange (ETDEWEB)

    Guillochon, James [Harvard-Smithsonian Center for Astrophysics, The Institute for Theory and Computation, 60 Garden Street, Cambridge, MA 02138 (United States); McCourt, Michael, E-mail: jguillochon@cfa.harvard.edu [Department of Physics, University of California, Santa Barbara, CA 93106 (United States)

    2017-01-10

    We perform the first magnetohydrodynamical simulations of tidal disruptions of stars by supermassive black holes. We consider stars with both tangled and ordered magnetic fields, for both grazing and deeply disruptive encounters. When the star survives disruption, we find its magnetic field amplifies by a factor of up to 20, but see no evidence for a self-sustaining dynamo that would yield arbitrary field growth. For stars that do not survive, and within the tidal debris streams produced in partial disruptions, we find that the component of the magnetic field parallel to the direction of stretching along the debris stream only decreases slightly with time, eventually resulting in a stream where the magnetic pressure is in equipartition with the gas. Our results suggest that the returning gas in most (if not all) stellar tidal disruptions is already highly magnetized by the time it returns to the black hole.

  4. Fallback accretion onto magnetized neutron stars and the hidden magnetic field model

    International Nuclear Information System (INIS)

    Torres, A; Cerdá-Durán, P; Font, J A

    2015-01-01

    The observation of several neutron stars with relatively low values of the surface magnetic field found in supernova remnants has led in recent years to controversial interpretations. A possible explanation is the slow rotation of the proto-neutron star at birth which is unable to amplify its magnetic field to typical pulsar levels. An alternative possibility, the hidden magnetic field scenario, seems to be favoured over the previous one due to the observation of three low magnetic field magnetars. This scenario considers the accretion of the fallback of the supernova debris onto the neutron star as the responsible for the observed low magnetic field. In this work, we have studied under which conditions the magnetic field of a neutron star can be buried into the crust due to an accreting fluid. We have considered a simplified toy model in general relativity to estimate the balance between the incoming accretion flow an the magnetosphere. We conclude that the burial is possible for values of the surface magnetic field below 10 13 G. The preliminary results reported in this paper for simplified polytropic models should be confirmed using a more realistic thermodynamical setup. (paper)

  5. Observations and analysis of the photospheric magnetic fields on dwarf G, K, and M stars

    Energy Technology Data Exchange (ETDEWEB)

    Saar, S.H.

    1987-01-01

    An improved technique was developed for the analysis of magnetic broadening in stellar absorption-line profiles. Unlike previous methods, the new technique is based on a model that includes radiative-transfer effects and the full Zeeman patterns. The effects of weak blends on the profiles can be reduced by comparing identical lines in two stars of the same spectral type, one of which is chromospheric inactive. After adjusting for differences in line strength and doppler broadening, the difference profile can be modeled to determine both the fraction of the stellar surface covered by magnetic regions (f) and the mean field strength in these regions (B). Accuracies of about 20% in B and f are possible. It was found that previous Zeeman-analysis methods systematically overestimate f, especially for cooler stars, due to their neglect of line saturation and blends. The new technique were applied to two sets of high-resolution, how-noise spectra. The first set consists of 29 stars, spanning spectral types from GO to M4.5 and a broad range of rotational rates and ages. The first-ever detection was made of photospheric magnetic fields on a BY Draconis variable (EQ Vir) and a dMe flare star (AD Leo).

  6. GMC Collisions as Triggers of Star Formation. III. Density and Magnetically Regulated Star Formation

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Benjamin [National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan); Tan, Jonathan C. [Department of Physics, University of Florida, Gainesville, FL 32611 (United States); Christie, Duncan [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Nakamura, Fumitaka [National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Van Loo, Sven [School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT (United Kingdom); Collins, David, E-mail: ben.wu@nao.ac.jp [Department of Physics, Florida State University, Tallahassee, FL 32306-4350 (United States)

    2017-06-01

    We study giant molecular cloud (GMC) collisions and their ability to trigger star cluster formation. We further develop our three-dimensional magnetized, turbulent, colliding GMC simulations by implementing star formation subgrid models. Two such models are explored: (1) “Density-Regulated,” i.e., fixed efficiency per free-fall time above a set density threshold and (2) “Magnetically Regulated,” i.e., fixed efficiency per free-fall time in regions that are magnetically supercritical. Variations of parameters associated with these models are also explored. In the non-colliding simulations, the overall level of star formation is sensitive to model parameter choices that relate to effective density thresholds. In the GMC collision simulations, the final star formation rates and efficiencies are relatively independent of these parameters. Between the non-colliding and colliding cases, we compare the morphologies of the resulting star clusters, properties of star-forming gas, time evolution of the star formation rate (SFR), spatial clustering of the stars, and resulting kinematics of the stars in comparison to the natal gas. We find that typical collisions, by creating larger amounts of dense gas, trigger earlier and enhanced star formation, resulting in 10 times higher SFRs and efficiencies. The star clusters formed from GMC collisions show greater spatial substructure and more disturbed kinematics.

  7. The Fastest Rotating Pulsar: a Strange Star?

    Institute of Scientific and Technical Information of China (English)

    徐仁新; 徐轩彬; 吴鑫基

    2001-01-01

    According to the observational limits on the radius and mass, the fastest rotating pulsar (PSR 1937+21) is probably a strange star, or at least some neutron star equations of state should be ruled out, if we suggest that a dipole magnetic field is relevant to its radio emission. We presume that the millisecond pulsar is a strange star with much low mass, small radius and weak magnetic moment.

  8. An infrared diagnostic for magnetism in hot stars

    Science.gov (United States)

    Oksala, M. E.; Grunhut, J. H.; Kraus, M.; Borges Fernandes, M.; Neiner, C.; Condori, C. A. H.; Campagnolo, J. C. N.; Souza, T. B.

    2015-06-01

    Magnetospheric observational proxies are used for indirect detection of magnetic fields in hot stars in the X-ray, UV, optical, and radio wavelength ranges. To determine the viability of infrared (IR) hydrogen recombination lines as a magnetic diagnostic for these stars, we have obtained low-resolution (R~ 1200), near-IR spectra of the known magnetic B2V stars HR 5907 and HR 7355, taken with the Ohio State Infrared Imager/Spectrometer (OSIRIS) attached to the 4.1 m Southern Astrophysical Research (SOAR) Telescope. Both stars show definite variable emission features in IR hydrogen lines of the Brackett series, with similar properties as those found in optical spectra, including the derived location of the detected magnetospheric plasma. These features also have the added advantage of a lowered contribution of stellar flux at these wavelengths, making circumstellar material more easily detectable. IR diagnostics will be useful for the future study of magnetic hot stars, to detect and analyze lower-density environments, and to detect magnetic candidates in areas obscured from UV and optical observations, increasing the number of known magnetic stars to determine basic formation properties and investigate the origin of their magnetic fields. Based on observations obtained at the Southern Astrophysical Research (SOAR) telescope, which is a joint project of the Ministério da Ciência, Tecnologia, e Inovação (MCTI) da República Federativa do Brasil, the US National Optical Astronomy Observatory (NOAO), the University of North Carolina at Chapel Hill (UNC), and Michigan State University (MSU).

  9. Observational Effects of Magnetism in O Stars: Surface Nitrogen Abundances

    Science.gov (United States)

    Martins, F.; Escolano, C.; Wade, G. A.; Donati, J. F.; Bouret, J. C.

    2011-01-01

    Aims. We investigate the surface nitrogen content of the six magnetic O stars known to date as well as of the early B-type star Tau Sco.. We compare these abundances to predictions of evolutionary models to isolate the effects of magnetic field on the transport of elements in stellar interiors. Methods. We conduct a quantitative spectroscopic analysis of the ample stars with state-of-the-art atmosphere models. We rely on high signal-to-noise ratio, high resolution optical spectra obtained with ESPADONS at CFHT and NARVAL at TBL. Atmosphere models and synthetic spectra are computed with the code CMFGEN. Values of N/H together with their uncertainties are determined and compared to predictions of evolutionary models. Results. We find that the magnetic stars can be divided into two groups: one with stars displaying no N enrichment (one object); and one with stars most likely showing extra N enrichment (5 objects). For one star (Ori C) no robust conclusion can be drawn due to its young age. The star with no N enrichment is the one with the weakest magnetic field, possibly of dynamo origin. It might be a star having experienced strong magnetic braking under the condition of solid body rotation, but its rotational velocity is still relatively large. The five stars with high N content were probably slow rotators on the zero age main sequence, but they have surface N/H typical of normal O stars, indicating that the presence of a (probably fossil) magnetic field leads to extra enrichment. These stars may have a strong differential rotation inducing shear mixing. Our results shOuld be viewed as a basis on which new theoretical simulations can rely to better understand the effect of magnetism on the evolution of massive stars.

  10. Parallel Tracks as Quasi-steady States for the Magnetic Boundary Layers in Neutron-star Low-mass X-Ray Binaries

    Energy Technology Data Exchange (ETDEWEB)

    Erkut, M. Hakan [Physics Engineering Department, Faculty of Science and Letters, Istanbul Technical University, 34469, Istanbul (Turkey); Çatmabacak, Onur, E-mail: mherkut@gmail.com [Institute for Computational Sciences Y11 F74, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich (Switzerland)

    2017-11-01

    The neutron stars in low-mass X-ray binaries (LMXBs) are usually thought to be weakly magnetized objects accreting matter from their low-mass companions in the form of a disk. Albeit weak compared to those in young neutron-star systems, the neutron-star magnetospheres in LMXBs can play an important role in determining the correlations between spectral and temporal properties. Parallel tracks appearing in the kilohertz (kHz) quasi-periodic oscillation (QPO) frequency versus X-ray flux plane can be used as a tool to study the magnetosphere–disk interaction in neutron-star LMXBs. For dynamically important weak fields, the formation of a non-Keplerian magnetic boundary layer at the innermost disk truncated near the surface of the neutron star is highly likely. Such a boundary region may harbor oscillatory modes of frequencies in the kHz range. We generate parallel tracks using the boundary region model of kHz QPOs. We also present the direct application of our model to the reproduction of the observed parallel tracks of individual sources such as 4U 1608–52, 4U 1636–53, and Aql X-1. We reveal how the radial width of the boundary layer must vary in the long-term flux evolution of each source to regenerate the parallel tracks. The run of the radial width looks similar for different sources and can be fitted by a generic model function describing the average steady behavior of the boundary region over the long term. The parallel tracks then correspond to the possible quasi-steady states the source can occupy around the average trend.

  11. Gravitomagnetic effect in magnetized neutron stars

    Energy Technology Data Exchange (ETDEWEB)

    Chatterjee, Debarati [LPC/ENSICAEN, 6 Boulevard Maréchal Juin, Caen, 14050 France (France); Chakraborty, Chandrachur [Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005 India (India); Bandyopadhyay, Debades, E-mail: dchatterjee@lpccaen.in2p3.fr, E-mail: chandrachur.chakraborty@tifr.res.in, E-mail: debades.bandyopadhyay@saha.ac.in [Astroparticle Physics and Cosmology Division, Saha Institute of Nuclear Physics, HBNI, 1/AF Bidhannagar, Kolkata, 700064 India (India)

    2017-01-01

    Rotating bodies in General Relativity produce frame dragging, also known as the gravitomagnetic effect in analogy with classical electromagnetism. In this work, we study the effect of magnetic field on the gravitomagnetic effect in neutron stars with poloidal geometry, which is produced as a result of its rotation. We show that the magnetic field has a non-negligible impact on frame dragging. The maximum effect of the magnetic field appears along the polar direction, where the frame-dragging frequency decreases with increase in magnetic field, and along the equatorial direction, where its magnitude increases. For intermediate angles, the effect of the magnetic field decreases, and goes through a minimum for a particular angular value at which magnetic field has no effect on gravitomagnetism. Beyond that particular angle gravitomagnetic effect increases with increasing magnetic field. We try to identify this 'null region' for the case of magnetized neutron stars, both inside and outside, as a function of the magnetic field, and suggest a thought experiment to find the null region of a particular pulsar using the frame dragging effect.

  12. Neutron stars. [quantum mechanical processes associated with magnetic fields

    Science.gov (United States)

    Canuto, V.

    1978-01-01

    Quantum-mechanical processes associated with the presence of high magnetic fields and the effect of such fields on the evolution of neutron stars are reviewed. A technical description of the interior of a neutron star is presented. The neutron star-pulsar relation is reviewed and consideration is given to supernovae explosions, flux conservation in neutron stars, gauge-invariant derivation of the equation of state for a strongly magnetized gas, neutron beta-decay, and the stability condition for a neutron star.

  13. The Role of Magnetic Fields in Star Formation

    Science.gov (United States)

    Pipher, Judith

    2018-06-01

    The SOFIA instrument complement makes available the capability to characterize the physical properties (turbulence, dynamics, magnetic field structure and strength, gas density) of the molecular cloud filaments in which stars form.HAWC+, the newest SOFIA instrument, provides a unique opportunity to probe the complex roles that magnetic fields play in the star formation process on spatial scales intermediate to those explored by Planck (5’ scale), to those of ALMA at the smallest spatial scales (powerful tools to further our understanding of the fundamental physics of both low mass and high mass star formation, including the role that magnetic fields play in each.

  14. A weak magnetic field inhibits hippocampal neurogenesis in SD rats

    Science.gov (United States)

    Zhang, B.; Tian, L.; Cai, Y.; Pan, Y.

    2017-12-01

    Geomagnetic field is an important barrier that protects life forms on Earth from solar wind and radiation. Paleomagnetic data have well demonstrated that the strength of ancient geomagnetic field was dramatically weakened during a polarity transition. Accumulating evidence has shown that weak magnetic field exposures has serious adverse effects on the metabolism and behaviors in organisms. Hippocampal neurogenesis occurs throughout life in mammals' brains which plays a key role in brain function, and can be influenced by animals' age as well as environmental factors, but few studies have examined the response of hippocampal neurogenesis to it. In the present study, we have investigated the weak magnetic field effects on hippocampal neurogenesis of adult Sprague Dawley (SD) rats. Two types of magnetic fields were used, a weak magnetic field (≤1.3 μT) and the geomagnetic fields (51 μT).The latter is treated as a control condition. SD rats were exposure to the weak magnetic field up to 6 weeks. We measured the changes of newborn nerve cells' proliferation and survival, immature neurons, neurons and apoptosis in the dentate gyrus (DG) of hippocampus in SD rats. Results showed that, the weak magnetic field (≤1.3 μT) inhibited their neural stem cells proliferation and significantly reduced the survival of newborn nerve cells, immature neurons and neurons after 2 or 4 weeks continuous treatment (i.e. exposure to weak magnetic field). Moreover, apoptosis tests indicated the weak magnetic field can promote apoptosis of nerve cells in the hippocampus after 4 weeks treatment. Together, our new data indicate that weak magnetic field decrease adult hippocampal neurogenesis through inhibiting neural stem cells proliferation and promoting apoptosis, which provides useful experimental constraints on better understanding the mechanism of linkage between life and geomagnetic field.

  15. Magnetic fields and massive star formation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Qizhou; Keto, Eric; Ho, Paul T. P.; Ching, Tao-Chung; Chen, How-Huan [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Qiu, Keping [School of Astronomy and Space Science, Nanjing University, 22 Hankou Road, Nanjing 210093 (China); Girart, Josep M.; Juárez, Carmen [Institut de Ciències de l' Espai, (CSIC-IEEC), Campus UAB, Facultat de Ciències, C5p 2, E-08193 Bellaterra, Catalonia (Spain); Liu, Hauyu; Tang, Ya-Wen; Koch, Patrick M.; Rao, Ramprasad; Lai, Shih-Ping [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 106, Taiwan (China); Li, Zhi-Yun [Department of Astronomy, University of Virginia, P.O. Box 400325, Charlottesville, VA 22904 (United States); Frau, Pau [Observatorio Astronómico Nacional, Alfonso XII, 3 E-28014 Madrid (Spain); Li, Hua-Bai [Department of Physics, The Chinese University of Hong Kong, Hong Kong (China); Padovani, Marco [Laboratoire de Radioastronomie Millimétrique, UMR 8112 du CNRS, École Normale Supérieure et Observatoire de Paris, 24 rue Lhomond, F-75231 Paris Cedex 05 (France); Bontemps, Sylvain [OASU/LAB-UMR5804, CNRS, Université Bordeaux 1, F-33270 Floirac (France); Csengeri, Timea, E-mail: qzhang@cfa.harvard.edu [Max Planck Institute for Radioastronomy, Auf dem Hügel 69, D-53121 Bonn (Germany)

    2014-09-10

    Massive stars (M > 8 M {sub ☉}) typically form in parsec-scale molecular clumps that collapse and fragment, leading to the birth of a cluster of stellar objects. We investigate the role of magnetic fields in this process through dust polarization at 870 μm obtained with the Submillimeter Array (SMA). The SMA observations reveal polarization at scales of ≲0.1 pc. The polarization pattern in these objects ranges from ordered hour-glass configurations to more chaotic distributions. By comparing the SMA data with the single dish data at parsec scales, we found that magnetic fields at dense core scales are either aligned within 40° of or perpendicular to the parsec-scale magnetic fields. This finding indicates that magnetic fields play an important role during the collapse and fragmentation of massive molecular clumps and the formation of dense cores. We further compare magnetic fields in dense cores with the major axis of molecular outflows. Despite a limited number of outflows, we found that the outflow axis appears to be randomly oriented with respect to the magnetic field in the core. This result suggests that at the scale of accretion disks (≲ 10{sup 3} AU), angular momentum and dynamic interactions possibly due to close binary or multiple systems dominate over magnetic fields. With this unprecedentedly large sample of massive clumps, we argue on a statistical basis that magnetic fields play an important role during the formation of dense cores at spatial scales of 0.01-0.1 pc in the context of massive star and cluster star formation.

  16. Disk accretion onto magnetic T Tauri stars

    International Nuclear Information System (INIS)

    Koenigl, A.

    1991-01-01

    The dynamical and radiative consequences of disk accretion onto magnetic T Tauri stars (TTS) are examined using the Ghosh and Lamb model. It is shown that a prolonged disk accretion phase is compatible with the low rotation rates measured in these stars if they possess a kilogauss strength field that disrupts the disk at a distance of a few stellar radii from the center. It is estimated that a steady state in which the net torque exerted on the star is zero can be attained on a time scale that is shorter than the age of the youngest visible TTS. Although the disk does not develop an ordinary shear boundary layer in this case, one can account for the observed UV excess and Balmer emission in terms of the shocks that form at the bottom of the high-latitude magnetic accretion columns on the stellar surface. This picture also provides a natural explanation of some of the puzzling variability properties of stars like DF Tau and RY Lup. YY Ori stars are interpreted as magnetic TTS in which the observer's line of sight is roughly parallel to an accretion column. 37 refs

  17. Matter and Radiation in Strong Magnetic Fields of Neutron Stars

    International Nuclear Information System (INIS)

    Lai, D

    2006-01-01

    Neutron stars are found to possess magnetic fields ranging from 10 8 G to 10 15 G, much larger than achievable in terrestrial laboratories. Understanding the properties of matter and radiative transfer in strong magnetic fields is essential for the proper interpretation of various observations of magnetic neutron stars, including radio pulsars and magnetars. This paper reviews the atomic/molecular physics and condensed matter physics in strong magnetic fields, as well as recent works on modeling radiation from magnetized neutron star atmospheres/surface layers

  18. Cooling Curve of Strange Star in Strong Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    WANG Xiao-Qin; LUO Zhi-Quan

    2008-01-01

    In this paper, firstly, we investigate the neutrino emissivity from quark Urca process in strong magnetic field. Then, we discuss the heat capacity of strange stars in strong magnetic field. Finally, we give the cooling curve in strong magnetic field. In order to make a comparison, we also give the corresponding cooling curve in the case of null magnetic field. It turns out that strange stars cool faster in strong magnetic field than that without magnetic field.

  19. Magnetic inhibition of convection and the fundamental properties of low-mass stars. II. Fully convective main-sequence stars

    Energy Technology Data Exchange (ETDEWEB)

    Feiden, Gregory A. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Chaboyer, Brian, E-mail: gregory.a.feiden@gmail.com, E-mail: brian.chaboyer@dartmouth.edu [Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755 (United States)

    2014-07-01

    We examine the hypothesis that magnetic fields are inflating the radii of fully convective main-sequence stars in detached eclipsing binaries (DEBs). The magnetic Dartmouth stellar evolution code is used to analyze two systems in particular: Kepler-16 and CM Draconis. Magneto-convection is treated assuming stabilization of convection and also by assuming reductions in convective efficiency due to a turbulent dynamo. We find that magnetic stellar models are unable to reproduce the properties of inflated fully convective main-sequence stars, unless strong interior magnetic fields in excess of 10 MG are present. Validation of the magnetic field hypothesis given the current generation of magnetic stellar evolution models therefore depends critically on whether the generation and maintenance of strong interior magnetic fields is physically possible. An examination of this requirement is provided. Additionally, an analysis of previous studies invoking the influence of star spots is presented to assess the suggestion that star spots are inflating stars and biasing light curve analyses toward larger radii. From our analysis, we find that there is not yet sufficient evidence to definitively support the hypothesis that magnetic fields are responsible for the observed inflation among fully convective main-sequence stars in DEBs.

  20. Weak Hard X-Ray Emission from Two Broad Absorption Line Quasars Observed with NuStar: Compton-Thick Absorption or Intrinsic X-Ray Weakness?

    Science.gov (United States)

    Luo, B.; Brandt, W. N.; Alexander, D. M.; Harrison, F. A.; Stern, D.; Bauer, F. E.; Boggs, S. E.; Christensen, F. E.; Comastri, A.; Craig, W. W..; hide

    2013-01-01

    We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain approx. or equal to 400-600 hard X-ray (is greater than or equal to 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed N(sub H) is less than or equal to 10(exp24) cm(exp-2). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N(sub H) 7 × 10(exp 24) cm(exp-2) if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe Ka line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.

  1. WEAK HARD X-RAY EMISSION FROM TWO BROAD ABSORPTION LINE QUASARS OBSERVED WITH NuSTAR: COMPTON-THICK ABSORPTION OR INTRINSIC X-RAY WEAKNESS?

    Energy Technology Data Exchange (ETDEWEB)

    Luo, B.; Brandt, W. N. [Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States); Alexander, D. M.; Hickox, R. [Department of Physics, Durham University, South Road, Durham DH1 3LE (United Kingdom); Harrison, F. A.; Fuerst, F.; Grefenstette, B. W.; Madsen, K. K. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States); Stern, D. [Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States); Bauer, F. E. [Departamento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Boggs, S. E.; Craig, W. W. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Christensen, F. E. [DTU Space-National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark); Comastri, A. [INAF-Osservatorio Astronomico di Bologna, Via Ranzani 1, I-40127 Bologna (Italy); Fabian, A. C. [Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom); Farrah, D. [Department of Physics, Virginia Tech, Blacksburg, VA 24061 (United States); Fiore, F. [Osservatorio Astronomico di Roma, via Frascati 33, I-00040 Monteporzio Catone (Italy); Hailey, C. J. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Matt, G. [Dipartimento di Matematica e Fisica, Universita degli Studi Roma Tre, via della Vasca Navale 84, I-00146 Roma (Italy); Ogle, P. [IPAC, California Institute of Technology, Mail Code 220-6, Pasadena, CA 91125 (United States); and others

    2013-08-01

    We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of two X-ray weak broad absorption line (BAL) quasars, PG 1004+130 (radio loud) and PG 1700+518 (radio quiet). Many BAL quasars appear X-ray weak, probably due to absorption by the shielding gas between the nucleus and the accretion-disk wind. The two targets are among the optically brightest BAL quasars, yet they are known to be significantly X-ray weak at rest-frame 2-10 keV (16-120 times fainter than typical quasars). We would expect to obtain Almost-Equal-To 400-600 hard X-ray ({approx}> 10 keV) photons with NuSTAR, provided that these photons are not significantly absorbed (N{sub H} {approx}< 10{sup 24} cm{sup -2}). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain the column densities for both to be N{sub H} Almost-Equal-To 7 Multiplication-Sign 10{sup 24} cm{sup -2} if the weak hard X-ray emission is caused by obscuration from the shielding gas. We discuss a few possibilities for how PG 1004+130 could have Compton-thick shielding gas without strong Fe K{alpha} line emission; dilution from jet-linked X-ray emission is one likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place statistical constraints upon the fraction of intrinsically X-ray weak BAL quasars; this fraction is likely 17%-40%.

  2. Differential rotation in magnetic stars

    International Nuclear Information System (INIS)

    Moss, D.

    1981-01-01

    The possibility that large-scale magnetic fields in stars are the product of a contemporary dynamo situated in the convective stellar core, rather than being a fossil from an earlier stage in the history of the star, is investigated. It is demonstrated that then the envelope will almost inevitably be in a state of differential rotation. Some simple models are constructed to illustrate the magnitude of the effects on the structure of the envelope and magnetic field. It is found that, for models which are relatively rapidly rotating, a modest differential rotation at the surface of the core may increase considerably the ratio of internal to surface field, but only give rise to a small surface differential rotation. (author)

  3. Magnetic fields and dense chromospheres in dMe stars

    International Nuclear Information System (INIS)

    Mullan, D.J.

    1975-01-01

    We examine in a semi-quantitative fashion the hypothesis that dense chromospheres of dMe stars are heated by dissipation of hydromagnetic waves. We propose that dMe stars are a set of magnetic stars on the lower main sequence, with strong fields presumably generated by dynamo action in deep convective envelopes. We discuss how the combination of magnetic fields and dense chromospheres in dMe stars provides a consistent interpretation of the following features: 1) The dMe stars which are most likely to be flares stars are those with hydrogen lines in emission. However, it is proposed that in certain conditions, Balmer lines may appear in absorption, and we suggest that 'negative flares' can be explained at least in part by the occurrence of strong absorption in Hα. 2) The propagation of flare-initiated coronal waves can trigger sympathetic stellar flares. 3) Apart from flare activity, emission line strengths in dMe stars must exhibit time variations due to the emergence of new magnetic flux ropes through the stellar surface. 4) The combination of strong magnetic fields with dense chromospheres makes the Faraday rotation measure large enough to have potentially a detectable effect on polarized visible light. 5) It is suggested that grain formation occurs in starspots on dMe stars. (orig./WL) [de

  4. Magnetic fields driven by tidal mixing in radiative stars

    Science.gov (United States)

    Vidal, Jérémie; Cébron, David; Schaeffer, Nathanaël; Hollerbach, Rainer

    2018-04-01

    Stellar magnetism plays an important role in stellar evolution theory. Approximatively 10 per cent of observed main sequence (MS) and pre-main-sequence (PMS) radiative stars exhibit surface magnetic fields above the detection limit, raising the question of their origin. These stars host outer radiative envelopes, which are stably stratified. Therefore, they are assumed to be motionless in standard models of stellar structure and evolution. We focus on rapidly rotating, radiative stars which may be prone to the tidal instability, due to an orbital companion. Using direct numerical simulations in a sphere, we study the interplay between a stable stratification and the tidal instability, and assess its dynamo capability. We show that the tidal instability is triggered regardless of the strength of the stratification (Brunt-Väisälä frequency). Furthermore, the tidal instability can lead to both mixing and self-induced magnetic fields in stably stratified layers (provided that the Brunt-Väisälä frequency does not exceed the stellar spin rate in the simulations too much). The application to stars suggests that the resulting magnetic fields could be observable at the stellar surfaces. Indeed, we expect magnetic field strengths up to several Gauss. Consequently, tidally driven dynamos should be considered as a (complementary) dynamo mechanism, possibly operating in radiative MS and PMS stars hosting orbital companions. In particular, tidally driven dynamos may explain the observed magnetism of tidally deformed and rapidly rotating Vega-like stars.

  5. Roles of nuclear weak rates on the evolution of degenerate cores in stars

    Directory of Open Access Journals (Sweden)

    Suzuki Toshio

    2017-01-01

    Full Text Available Electron-capture and β-decay rates in stellar environments are evaluated with the use of new shell-model Hamiltonians for sd-shell and pf-shell nuclei as well as for nuclei belonging to the island of inversion. Important role of the nuclear weak rates on the final evolution of stellar degenerate cores is presented. The weak interaction rates for sd-shell nuclei are calculated to study nuclear Urca processes in O-Ne-Mg cores of stars with 8-10 M⊙ (solar mass and their effects on the final fate of the stars. Nucleosynthesis of iron-group elements in Type Ia supernova explosions are studied with the weak rates for pf-shell nuclei. The problem of the neutron-rich iron-group isotope over-production compared to the solar abundances is shown to be nearly solved with the use of the new rates and explosion model of slow defraglation with delayed detonation. Evaluation of the weak rates is extended to the island of inversion and the region of neutron-rich nuclei near 78Ni, where two major shells contribute to their configurations.

  6. X-RAY EMISSION FROM MAGNETIC MASSIVE STARS

    International Nuclear Information System (INIS)

    Nazé, Yaël; Petit, Véronique; Rinbrand, Melanie; Owocki, Stan; Cohen, David; Ud-Doula, Asif; Wade, Gregg A.

    2014-01-01

    Magnetically confined winds of early-type stars are expected to be sources of bright and hard X-rays. To clarify the systematics of the observed X-ray properties, we have analyzed a large series of Chandra and XMM-Newton observations, corresponding to all available exposures of known massive magnetic stars (over 100 exposures covering ∼60% of stars compiled in the catalog of Petit et al.). We show that the X-ray luminosity is strongly correlated with the stellar wind mass-loss rate, with a power-law form that is slightly steeper than linear for the majority of the less luminous, lower- M-dot B stars and flattens for the more luminous, higher- M-dot O stars. As the winds are radiatively driven, these scalings can be equivalently written as relations with the bolometric luminosity. The observed X-ray luminosities, and their trend with mass-loss rates, are well reproduced by new MHD models, although a few overluminous stars (mostly rapidly rotating objects) exist. No relation is found between other X-ray properties (plasma temperature, absorption) and stellar or magnetic parameters, contrary to expectations (e.g., higher temperature for stronger mass-loss rate). This suggests that the main driver for the plasma properties is different from the main determinant of the X-ray luminosity. Finally, variations of the X-ray hardnesses and luminosities, in phase with the stellar rotation period, are detected for some objects and they suggest that some temperature stratification exists in massive stars' magnetospheres

  7. V819 TAU: A RARE WEAK-LINED T TAURI STAR WITH A WEAK INFRARED EXCESS

    International Nuclear Information System (INIS)

    Furlan, E.; Forrest, W. J.; Manoj, P.; Kim, K. H.; Watson, Dan M.; Sargent, B. A.

    2009-01-01

    We use Spitzer data to infer that the small infrared excess of V819 Tau, a weak-lined T Tauri star in Taurus, is real and not attributable to a 'companion' 10'' to the south. We do not confirm the mid-infrared excess in HBC 427 and V410 X-ray 3, which are also non-accreting T Tauri stars in the same region; instead, for the former object, the excess arises from a red companion 9'' to the east. A single-temperature blackbody fit to the continuum excess of V819 Tau implies a dust temperature of 143 K; however, a better fit is achieved when the weak 10 and 20 μm silicate emission features are also included. We infer a disk of sub-μm silicate grains between about 1 AU and several 100 AU with a constant surface density distribution. The mid-infrared excess of V819 Tau can be successfully modeled with dust composed mostly of small amorphous olivine grains at a temperature of 85 K, and most of the excess emission is optically thin. The disk could still be primordial, but gas-poor and therefore short-lived, or already at the debris disk stage, which would make it one of the youngest debris disk systems known.

  8. Advances in the measurement of weak magnetic fields

    International Nuclear Information System (INIS)

    Li Damin; Huang Minzhe.

    1992-01-01

    The state-of-art and general features of instruments for measuring weak magnetic fields (such as the non-directional magnetometer, induced coil magnetometer, proton magnetometer, optical pumping magnetometer, flux-gate magnetometer and superconducting quantum magnetometer) are briefly described. Emphasis is laid on the development of a novel technique used in the flux-gate magnetometer and the liquid nitrogen SQUID. Typical applications of the measuring techniques for weak magnetic fields are given

  9. The period of the magnetic star HD 133 029

    International Nuclear Information System (INIS)

    Panov, K.; Schoeneich, W.

    1976-01-01

    The period of 0.741285 days for the light variability of the magnetic star HD 133 029 was obtained from UBV observations. The observations of the effective magnetic field by Babcock show variations with a period of 0.7447 days. A small change of the period and a slow change of the magnitude of this magnetic star seems to be present. (author)

  10. Effect of Weak Magnetic Field on Bacterial Growth

    Science.gov (United States)

    Masood, Samina

    Effects of weak magnetic fields are observed on the growth of various bacterial strains. Different sources of a constant magnetic field are used to demonstrate that ion transport in the nutrient broth and bacterial cellular dynamics is perturbed in the presence of weak magnetic field which affects the mobility and absorption of nutrients in cells and hence their doubling rate. The change is obvious after a few hours of exposure and keeps on increasing with time for all the observed species. The growth rate depends on the field strength and the nature of the magnetic field. The field effect varies with the shape and the structure of the bacterial cell wall as well as the concentration of nutrient broth. We closely study the growth of three species Escherichia coli, Pseudomonas aeruginosa and Staphylococcus epidermidis with the same initial concentrations at the same temperature in the same laboratory environment. Our results indicate that the weak static field of a few gauss after a few hours gives a measurable change in the growth rates of all bacterial species. This shows that the same magnetic field has different effects on different species in the same environment.

  11. Tidal Heating of Earth-like Exoplanets around M Stars: Thermal, Magnetic, and Orbital Evolutions.

    Science.gov (United States)

    Driscoll, P E; Barnes, R

    2015-09-01

    The internal thermal and magnetic evolution of rocky exoplanets is critical to their habitability. We focus on the thermal-orbital evolution of Earth-mass planets around low-mass M stars whose radiative habitable zone overlaps with the "tidal zone," where tidal dissipation is expected to be a significant heat source in the interior. We develop a thermal-orbital evolution model calibrated to Earth that couples tidal dissipation, with a temperature-dependent Maxwell rheology, to orbital circularization and migration. We illustrate thermal-orbital steady states where surface heat flow is balanced by tidal dissipation and cooling can be stalled for billions of years until circularization occurs. Orbital energy dissipated as tidal heat in the interior drives both inward migration and circularization, with a circularization time that is inversely proportional to the dissipation rate. We identify a peak in the internal dissipation rate as the mantle passes through a viscoelastic state at mantle temperatures near 1800 K. Planets orbiting a 0.1 solar-mass star within 0.07 AU circularize before 10 Gyr, independent of initial eccentricity. Once circular, these planets cool monotonically and maintain dynamos similar to that of Earth. Planets forced into eccentric orbits can experience a super-cooling of the core and rapid core solidification, inhibiting dynamo action for planets in the habitable zone. We find that tidal heating is insignificant in the habitable zone around 0.45 (or larger) solar-mass stars because tidal dissipation is a stronger function of orbital distance than stellar mass, and the habitable zone is farther from larger stars. Suppression of the planetary magnetic field exposes the atmosphere to stellar wind erosion and the surface to harmful radiation. In addition to weak magnetic fields, massive melt eruption rates and prolonged magma oceans may render eccentric planets in the habitable zone of low-mass stars inhospitable for life.

  12. Doppler-Zeeman mapping of the magnetic CP star HD 215441

    Science.gov (United States)

    Khokhlova, V. L.; Vasilchenko, D. V.; Stepanov, V. V.; Tsymbal, V. V.

    1997-07-01

    The method of Vasilchenko et al. (1996) is used to obtain a Doppler-Zeeman map of the magnetic CP star HD 215441. The magnetic field is approximated by a magnetic dipole that is arbitrarily shifted from the star center. The solution of the inverse problem yields the dipole parameters and the maps of Si, Ti, Cr, and Fe abundance anomalies; the coordinates of local magnetic vectors on the star surface are computed. A comparison of the distribution of abundance anomalies and the magnetic-field configuration reveals that in the region where the magnetic-field lines are vertical (near the magnetic pole), Si, Ti and Cr are highly deficient, while the Fe enhancement is strongest. In the regions where the magnetic-field lines are horizontal (near the magnetic equator), Si, Ti and Cr show the greatest overabundance. In these regions, the Fe abundance is also slightly enhanced and exhibits, as it were, a secondary maximum. The factors that limit the accuracy of Doppler-Zeeman mapping are reviewed.

  13. Magnetic field effects on the crust structure of neutron stars

    Science.gov (United States)

    Franzon, B.; Negreiros, R.; Schramm, S.

    2017-12-01

    We study the effects of high magnetic fields on the structure and on the geometry of the crust in neutron stars. We find that the crust geometry is substantially modified by the magnetic field inside the star. We build stationary and axis-symmetric magnetized stellar models by using well-known equations of state to describe the neutron star crust, namely, the Skyrme model for the inner crust and the Baym-Pethick-Sutherland equation of state for the outer crust. We show that the magnetic field has a dual role, contributing to the crust deformation via the electromagnetic interaction (manifested in this case as the Lorentz force) and by contributing to curvature due to the energy stored in it. We also study a direct consequence of the crust deformation due to the magnetic field: the thermal relaxation time. This quantity, which is of great importance to the thermal evolution of neutron stars, is sensitive to the crust properties, and, as such, we show that it may be strongly affected by the magnetic field.

  14. SPINDOWN OF ISOLATED NEUTRON STARS: GRAVITATIONAL WAVES OR MAGNETIC BRAKING?

    International Nuclear Information System (INIS)

    Staff, Jan E.; Jaikumar, Prashanth; Chan, Vincent; Ouyed, Rachid

    2012-01-01

    We study the spindown of isolated neutron stars from initially rapid rotation rates, driven by two factors: (1) gravitational wave emission due to r-modes and (2) magnetic braking. In the context of isolated neutron stars, we present the first study including self-consistently the magnetic damping of r-modes in the spin evolution. We track the spin evolution employing the RNS code, which accounts for the rotating structure of neutron stars for various equations of state. We find that, despite the strong damping due to the magnetic field, r-modes alter the braking rate from pure magnetic braking for B ≤ 10 13 G. For realistic values of the saturation amplitude α sat , the r-mode can also decrease the time to reach the threshold central density for quark deconfinement. Within a phenomenological model, we assess the gravitational waveform that would result from r-mode-driven spindown of a magnetized neutron star. To contrast with the persistent signal during the spindown phase, we also present a preliminary estimate of the transient gravitational wave signal from an explosive quark-hadron phase transition, which can be a signal for the deconfinement of quarks inside neutron stars.

  15. Magnetized color flavor locked state and compact stars

    CERN Document Server

    Felipe, R Gonzalez; Martinez, A Perez

    2010-01-01

    The stability of the color flavor locked phase in the presence of a strong magnetic field is investigated within the phenomenological MIT bag model, taking into account the variation of the strange quark mass, the baryon density, the magnetic field, as well as the bag and gap parameters. It is found that the minimum value of the energy per baryon in a color flavor locked state at vanishing pressure is lower than the corresponding one for unpaired magnetized strange quark matter and, as the magnetic field increases, the energy per baryon decreases. This implies that magnetized color flavor locked matter is more stable and could become the ground state inside neutron stars. The mass-radius relation for such stars is also studied.

  16. MAGNETIC FIELD MEASUREMENTS OF T TAURI STARS IN THE ORION NEBULA CLUSTER

    International Nuclear Information System (INIS)

    Hao Yang; Johns-Krull, Christopher M.

    2011-01-01

    We present an analysis of high-resolution (R ∼ 50, 000) infrared K-band echelle spectra of 14 T Tauri stars (TTSs) in the Orion Nebula Cluster. We model Zeeman broadening in three magnetically sensitive Ti I lines near 2.2 μm and consistently detect kilogauss-level magnetic fields in the stellar photospheres. The data are consistent in each case with the entire stellar surface being covered with magnetic fields, suggesting that magnetic pressure likely dominates over gas pressure in the photospheres of these stars. These very strong magnetic fields might themselves be responsible for the underproduction of X-ray emission of TTSs relative to what is expected based on main-sequence star calibrations. We combine these results with previous measurements of 14 stars in Taurus and 5 stars in the TW Hydrae association to study the potential variation of magnetic field properties during the first 10 million years of stellar evolution, finding a steady decline in total magnetic flux with age.

  17. Streams and magnetic fields in surface layers of Ap-stars

    International Nuclear Information System (INIS)

    Dolginov, A.Z.; Urpin, V.A.

    1978-01-01

    Magnetic field generation of Ap-stars is considered. It is shown that in the surface layers of Ap-stars inhomogeneity of chemical composition produces a strong magnetic field. Velocities of possible circulation of stellar matter are estimated. It is shown that circulation does not prevent the process of the magnetic field generation. It needs the order of million years, for arranging the stationary magnetic field in surface layers

  18. Weak hard X-ray emission from two broad absorption line quasars observed with NuSTAR: Compton-thick absorption or intrinsic X-ray weakness?

    DEFF Research Database (Denmark)

    Luo, B.; Brandt, W. N.; Alexander, D. M.

    2013-01-01

    are not significantly absorbed (NH ≲ 1024 cm-2). However, both BAL quasars are only detected in the softer NuSTAR bands (e.g., 4-20 keV) but not in its harder bands (e.g., 20-30 keV), suggesting that either the shielding gas is highly Compton-thick or the two targets are intrinsically X-ray weak. We constrain...... likely explanation. We also discuss the intrinsic X-ray weakness scenario based on a coronal-quenching model relevant to the shielding gas and disk wind of BAL quasars. Motivated by our NuSTAR results, we perform a Chandra stacking analysis with the Large Bright Quasar Survey BAL quasar sample and place...

  19. Mixed poloidal-toroidal magnetic configuration and surface abundance distributions of the Bp star 36 Lyn

    Science.gov (United States)

    Oksala, M. E.; Silvester, J.; Kochukhov, O.; Neiner, C.; Wade, G. A.; the MiMeS Collaboration

    2018-01-01

    Previous studies of the chemically peculiar Bp star 36 Lyn revealed a moderately strong magnetic field, circumstellar material and inhomogeneous surface abundance distributions of certain elements. We present in this paper an analysis of 33 high signal-to-noise ratio, high-resolution Stokes IV observations of 36 Lyn obtained with the Narval spectropolarimeter at the Bernard Lyot Telescope at Pic du Midi Observatory. From these data, we compute new measurements of the mean longitudinal magnetic field, Bℓ, using the multiline least-squares deconvolution (LSD) technique. A rotationally phased Bℓ curve reveals a strong magnetic field, with indications for deviation from a pure dipole field. We derive magnetic maps and chemical abundance distributions from the LSD profiles, produced using the Zeeman-Doppler imaging code INVERSLSD. Using a spherical harmonic expansion to characterize the magnetic field, we find that the harmonic energy is concentrated predominantly in the dipole mode (ℓ = 1), with significant contribution from both the poloidal and toroidal components. This toroidal field component is predicted theoretically, but not typically observed for Ap/Bp stars. Chemical abundance maps reveal a helium enhancement in a distinct region where the radial magnetic field is strong. Silicon enhancements are located in two regions, also where the radial field is stronger. Titanium and iron enhancements are slightly offset from the helium enhancements, and are located in areas where the radial field is weak, close to the magnetic equator.

  20. Assessing magnetic torques and energy fluxes in close-in star-planet systems

    OpenAIRE

    Strugarek, A

    2016-01-01

    Planets in close-in orbit interact with the magnetized wind of their hosting star. This magnetic interaction was proposed to be a source for enhanced emissions in the chromosphere of the star, and to participate in setting the migration time-scale of the close-in planet. The efficiency of the magnetic interaction is know to depend on the magnetic properties of the host star, of the planet, and on the magnetic topology of the interaction. We use a global, three-dimensional numerical model of c...

  1. Magnetic field of massive chemically peculiar stars in the Orion OB1 association

    Science.gov (United States)

    Romanyuk, I. I.; Semenko, E. A.; Kudryavtsev, D. O.; Yakunin, I. A.

    2018-01-01

    Spectropolarimetric observations of 55 chemically peculiar stars in the Orion OB1 association were obtained at the 6 m telescope of the Russian Academy of Sciences with the aim of searching for the presence of stellar magnetic fields. We found 8 new magnetic stars in addition to 20 previously known objects. The frequency of chemically peculiar A and B-type stars among normal A and B-type stars and the frequency of magnetic stars among all chemically peculiar stars decreases with age in the Orion OB1 association.

  2. ASYMMETRIC MAGNETIC RECONNECTION IN WEAKLY IONIZED CHROMOSPHERIC PLASMAS

    International Nuclear Information System (INIS)

    Murphy, Nicholas A.; Lukin, Vyacheslav S.

    2015-01-01

    Realistic models of magnetic reconnection in the solar chromosphere must take into account that the plasma is partially ionized and that plasma conditions within any two magnetic flux bundles undergoing reconnection may not be the same. Asymmetric reconnection in the chromosphere may occur when newly emerged flux interacts with pre-existing, overlying flux. We present 2.5D simulations of asymmetric reconnection in weakly ionized, reacting plasmas where the magnetic field strengths, ion and neutral densities, and temperatures are different in each upstream region. The plasma and neutral components are evolved separately to allow non-equilibrium ionization. As in previous simulations of chromospheric reconnection, the current sheet thins to the scale of the neutral–ion mean free path and the ion and neutral outflows are strongly coupled. However, the ion and neutral inflows are asymmetrically decoupled. In cases with magnetic asymmetry, a net flow of neutrals through the current sheet from the weak-field (high-density) upstream region into the strong-field upstream region results from a neutral pressure gradient. Consequently, neutrals dragged along with the outflow are more likely to originate from the weak-field region. The Hall effect leads to the development of a characteristic quadrupole magnetic field modified by asymmetry, but the X-point geometry expected during Hall reconnection does not occur. All simulations show the development of plasmoids after an initial laminar phase

  3. The STAR detector magnet subsystem

    International Nuclear Information System (INIS)

    Brown, R.L.; Etkin, A.; Foley, K.J.

    1997-01-01

    The RHIC (Relativistic Heavy Ion Collider) Accelerator currently under construction at Brookhaven National Laboratory will have large detectors at two of its six intersection regions. One of these detectors, known as STAR (Solenoidal Tracker At RHIC), weighs 1100 tons and is being built around a large solenoid magnet. The magnet is 7.32 in in diameter, 7.25 m long and utilizes three different sizes of room temperature aluminum coils. The magnet will operate with a field set from 0.25 T to 0.5 T and have a field uniformity of better than 1000 ppm over a portion of its interior region. This paper describes the magnet design, fabrication and assembly requirements and presents the current construction status

  4. Weakly damped modes in star clusters and galaxies

    Science.gov (United States)

    Weinberg, Martin D.

    1994-01-01

    A perturber may excite a coherent mode in a star cluster or galaxy. If the stellar system is stable, it is commonly assumed that such a mode will be strongly damped and therefore of little practical consequence other than redistributing momentum and energy deposited by the perturber. This paper demonstrates that this assumption is false; weakly damped modes exist and may persist long enough to have observable consequences. To do this, a method for investigating the dispersion relation for spherical stellar systems and for locating weakly damped modes in particular is developed and applied to King models of varying concentration. This leads to a following remarkable result: King models exhibit very weakly damped m = 1 modes over a wide range of concentration (0.67 less than or equal to c less than or equal to 1.5 have been examined). The predicted damping time is tens of hundreds of crossing times. This mode causes the peak density to shift from and slowly revolve about the initial center. The existence of the mode is supported by n-body simulation. Higher order modes and possible astronomical consequences are discussed. Weakly damped modes, for example, may provide a neutral explanation for observed discrepancies between density and kinematic centers in galaxies, off-center nuclei, the location of velocity cusps due to massive black holes, and both m = 1 and barlike disturbances of disks enbedded in massive halos or spheroids. Gravitational shocking may excite the m = 1 mode in globular clusters, which could modify their subsequent evolution and displace the positions of exotic remnants.

  5. Method and apparatus for measuring weak magnetic fields

    DEFF Research Database (Denmark)

    1995-01-01

    When measuring weak magnetic fields, a container containing a medium, such as a solution containing a stable radical, is placed in a polarising magnetic field, which is essentially at right angles to the field to be measured. The polarising field is interrupted rapidly, the interruption being...

  6. Radio-wavelength observations of magnetic fields on active dwarf-M, RS CVN and magnetic stars

    Energy Technology Data Exchange (ETDEWEB)

    Lang, K.R.

    1986-01-01

    The dwarf M stars YZ Canis Minoris and AD Leonis exhibit narrow band, slowly varying (hours) microwave emission that cannot be explained by conventional thermal radiation mechanisms. The dwarf M stars AD Leonis and Wolf 424 emit rapid spikes whose high brightness temperatures similarly require a nonthermal radiation process which could result from coherent mechanisms such as an electron-cyclotron maser or coherent-plasma radiation. If the electron-cyclotron maser emits at the second or third harmonic of the gyrofrequency, the coronal magnetic field strength H = 250 or 167 G and constraints on the plasma frequency imply an electron density of 6 x 10/sup 9//cm/sup 3/. Coherent-plasma radiation requires similar values of electron density but much weaker magnetic fields. Radio spikes from AD Leonis and Wolf 424 have rise times tau/sub R/ < 5 ms, indicating a linear size of L < 1.5 x 10/sup 8/ cm, or less than 0.005 of the stellar radius. Although Ap magnetic stars have strong dipole magnetic fields, they exhibit no detectable gyroresonant radiation, suggesting that these stars do not have hot, dense coronae. The binary RS CVn star UX Arietis exhibits variable emission at 6 cm wavelength on time scales ranging from 30 s to more than one hour. The shortest variation implies a linear size much less than that of the halo observed by VLBI techniques, and most probably sizes smaller than those of the component stars. The observed variations might be due to absorption by a thermal plasma located between the stars.

  7. A self-consistent study of magnetic field effects on hybrid stars

    International Nuclear Information System (INIS)

    Dexheimer, V; Franzon, B; Schramm, S

    2017-01-01

    It is understood that strong magnetic fields affect the structure of neutron stars. Nevertheless, many calculations for magnetized neutron stars are still being performed using symmetric solutions of Einstein’s equations. In this conference proceeding, we review why this is not the correct procedure and we also discuss the effects of magnetic fields on the stellar population and temperature profiles. (paper)

  8. THE HIDDEN MAGNETIC FIELD OF THE YOUNG NEUTRON STAR IN KESTEVEN 79

    International Nuclear Information System (INIS)

    Shabaltas, Natalia; Lai Dong

    2012-01-01

    Recent observations of the central compact object in the Kesteven 79 supernova remnant show that this neutron star (NS) has a weak dipole magnetic field (a few × 10 10 G) but an anomalously large (∼64%) pulse fraction in its surface X-ray emission. We explore the idea that a substantial sub-surface magnetic field exists in the NS crust, which produces diffuse hot spots on the stellar surface due to anisotropic heat conduction, and gives rise to the observed X-ray pulsation. We develop a general-purpose method, termed 'Temperature Template with Full Transport' (TTFT), that computes the synthetic pulse profile of surface X-ray emission from NSs with arbitrary magnetic field and surface temperature distributions, taking into account magnetic atmosphere opacities, beam pattern, vacuum polarization, and gravitational light bending. We show that a crustal toroidal magnetic field of order a few × 10 14 G or higher, varying smoothly across the crust, can produce sufficiently distinct surface hot spots to generate the observed pulse fraction in the Kes 79 NS. This result suggests that substantial sub-surface magnetic fields, much stronger than the 'visible' dipole fields, may be buried in the crusts of some young NSs, and such hidden magnetic fields can play an important role in their observational manifestations. The general TTFT tool we have developed can also be used for studying radiation from other magnetic NSs.

  9. X-Ray Flare Oscillations Track Plasma Sloshing along Star-disk Magnetic Tubes in the Orion Star-forming Region

    Science.gov (United States)

    Reale, Fabio; Lopez-Santiago, Javier; Flaccomio, Ettore; Petralia, Antonino; Sciortino, Salvatore

    2018-03-01

    Pulsing X-ray emission tracks the plasma “echo” traveling in an extremely long magnetic tube that flares in an Orion pre-main sequence (PMS) star. On the Sun, flares last from minutes to a few hours and the longest-lasting ones typically involve arcades of closed magnetic tubes. Long-lasting X-ray flares are observed in PMS stars. Large-amplitude (∼20%), long-period (∼3 hr) pulsations are detected in the light curve of day-long flares observed by the Advanced CCD Imaging Spectrometer on-board Chandra from PMS stars in the Orion cluster. Detailed hydrodynamic modeling of two flares observed on V772 Ori and OW Ori shows that these pulsations may track the sloshing of plasma along a single long magnetic tube, triggered by a sufficiently short (∼1 hr) heat pulse. These magnetic tubes are ≥20 solar radii long, enough to connect the star with the surrounding disk.

  10. Evolution of magnetized, differentially rotating neutron stars: Simulations in full general relativity

    International Nuclear Information System (INIS)

    Duez, Matthew D.; Liu, Yuk Tung; Shapiro, Stuart L.; Stephens, Branson C.; Shibata, Masaru

    2006-01-01

    We study the effects of magnetic fields on the evolution of differentially rotating neutron stars, which can be formed in stellar core collapse or binary neutron star coalescence. Magnetic braking and the magnetorotational instability (MRI) both act on differentially rotating stars to redistribute angular momentum. Simulations of these stars are carried out in axisymmetry using our recently developed codes which integrate the coupled Einstein-Maxwell-MHD equations. We consider stars with two different equations of state (EOS), a gamma-law EOS with Γ=2, and a more realistic hybrid EOS, and we evolve them adiabatically. Our simulations show that the fate of the star depends on its mass and spin. For initial data, we consider three categories of differentially rotating, equilibrium configurations, which we label normal, hypermassive and ultraspinning. Normal configurations have rest masses below the maximum achievable with uniform rotation, and angular momentum below the maximum for uniform rotation at the same rest mass. Hypermassive stars have rest masses exceeding the mass limit for uniform rotation. Ultraspinning stars are not hypermassive, but have angular momentum exceeding the maximum for uniform rotation at the same rest mass. We show that a normal star will evolve to a uniformly rotating equilibrium configuration. An ultraspinning star evolves to an equilibrium state consisting of a nearly uniformly rotating central core, surrounded by a differentially rotating torus with constant angular velocity along magnetic field lines, so that differential rotation ceases to wind the magnetic field. In addition, the final state is stable against the MRI, although it has differential rotation. For a hypermassive neutron star, the MHD-driven angular momentum transport leads to catastrophic collapse of the core. The resulting rotating black hole is surrounded by a hot, massive, magnetized torus undergoing quasistationary accretion, and a magnetic field collimated along

  11. Large-scale Organized Magnetic Fields in O, B and A Stars

    Science.gov (United States)

    Mathys, G.

    2009-06-01

    The status of our current knowledge of magnetic fields in stars of spectral types ranging from early F to O is reviewed. Fields with large-scale organised structure have now been detected and measured throughout this range. These fields are consistent with the oblique rotator model. In early F to late B stars, their occurrence is restricted to the subgroup of the Ap stars, which have the best studied fields among the early-type stars. Presence of fields with more complex topologies in other A and late B stars has been suggested, but is not firmly established. Magnetic fields have not been studied in a sufficient number of OB stars yet so as to establish whether they occur in all or only in some subset of these stars.

  12. Evolution of Neutron Star Magnetic Fields

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    in nuclei. The neutrons are expected to form a 3P superfluid and the protons a 1S ... crust are expected to form a lattice; the electrons are free and highly degenerate, .... the reduced magnetic fields in neutron stars processed in binaries,.

  13. Winds of Massive Magnetic Stars: Interacting Fields and Flow

    Science.gov (United States)

    Daley-Yates, S.; Stevens, I. R.

    2018-01-01

    We present results of 3D numerical simulations of magnetically confined, radiatively driven stellar winds of massive stars, conducted using the astrophysical MHD code Pluto, with a focus on understanding the rotational variability of radio and sub-mm emission. Radiative driving is implemented according to the Castor, Abbott and Klein theory of radiatively driven winds. Many magnetic massive stars posses a magnetic axis which is inclined with respect to the rotational axis. This misalignment leads to a complex wind structure as magnetic confinement, centrifugal acceleration and radiative driving act to channel the circumstellar plasma into a warped disk whose observable properties should be apparent in multiple wavelengths. This structure is analysed to calculate free-free thermal radio emission and determine the characteristic intensity maps and radio light curves.

  14. Radial modes of slowly rotating compact stars in the presence of magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Panda, N.R. [Institute of Physics, Bhubaneswar (India); Siksha ' O' Anusandhan University, Bhubaneswar (India); Mohanta, K.K. [Rairangpur College, Rairangpur, Odisha (India); Sahu, P.K. [Institute of Physics, Bhubaneswar (India)

    2016-09-15

    Compact stars are composed of very high-density hadron matter. When the matter is above nuclear matter density, then there is a chance of different phases of matter such as hadron matter to quark matter. There is a possible phase which, having the quark core surrounded by a mixed phase followed by hadronic matter, may be considered as a hybrid phase inside the stars called hybrid star (HS). The star which consists of only u, d and s quarks is called quark star (QS) and the star which has only hadronic matter is called neutron star (NS). For the equation of state (EOS) of hadronic matter, we have considered the Relativistic Mean Field (RMF) theory and we incorporated the effect of strong magnetic fields. For the EOS of the quark phase we use the simple MIT bag model. We have assumed Gaussian parametrization to make the density dependent for both bag pressure in quark matter and magnetic field. We have constructed the intermediate mixed phase by using the Glendenning conjecture. Eigenfrequencies of radial pulsations of slowly rotating magnetized compact stars (NS, QS, HS) are calculated in a general relativistic formalism given by Chandrasekhar and Friedman. We have studied the effect of central density on the square of the frequencies of the compact stars in the presence of zero and strong magnetic field. (orig.)

  15. Magnetic Fields of Neutron Stars

    Indian Academy of Sciences (India)

    Sushan Konar

    2017-09-12

    Sep 12, 2017 ... the material properties of the region where currents supporting the .... 1The evolution of magnetic field in neutron stars, in particular, the question of .... −10, 10. −9, 10. −8. M⊙/yr respec- tively. See Konar & Bhattacharya (1997) for details. Peq ≃ 1.9 ms ..... ported by a grant (SR/WOS-A/PM-1038/2014) from.

  16. Not an Oxymoron: Some X-ray Binary Pulsars with Enormous Spinup Rates Reveal Weak Magnetic Fields

    Science.gov (United States)

    Christodoulou, D. M.; Laycock, S. G. T.; Kazanas, D.

    2018-05-01

    Three high-mass X-ray binaries have been discovered recently exhibiting enormous spinup rates. Conventional accretion theory predicts extremely high surface dipolar magnetic fields that we believe are unphysical. Instead, we propose quite the opposite scenario: some of these pulsars exhibit weak magnetic fields, so much so that their magnetospheres are crushed by the weight of inflowing matter. The enormous spinup rate is achieved before inflowing matter reaches the pulsar's surface as the penetrating inner disk transfers its excess angular momentum to the receding magnetosphere which, in turn, applies a powerful spinup torque to the pulsar. This mechanism also works in reverse: it spins a pulsar down when the magnetosphere expands beyond corotation and finds itself rotating faster than the accretion disk which then exerts a powerful retarding torque to the magnetic field and to the pulsar itself. The above scenaria cannot be accommodated within the context of neutron-star accretion processes occurring near spin equilibrium, thus they constitute a step toward a new theory of extreme (far from equilibrium) accretion phenomena.

  17. Exploration of the validity of weak magnets as a suitable placebo in trials of magnetic therapy.

    Science.gov (United States)

    Greaves, C J; Harlow, T N

    2008-06-01

    To investigate whether 50 mT magnetic bracelets would be suitable as a placebo control condition for studying the pain relieving effects of higher strength magnetic bracelets in arthritis. Randomised controlled comparison between groups given either a weak 50 mT or a higher strength 180 mT magnetic bracelets to test. Four arthritis support groups in Devon, UK. One hundred sixteen people with osteoarthritis and rheumatoid arthritis. Beliefs about group allocation and expectation of benefit. There was no significant difference between groups in beliefs about allocation to the 'active magnet' group. Participants were however more likely to have an expectation of benefit (pain relief) with the higher strength magnetic bracelets. Asking about perceived group allocation is not sufficient to rule out placebo effects in trials of magnetic bracelets which use weak magnets as a control condition. There are differences in expectation of benefit between different magnet strengths.

  18. Energy flux determines magnetic field strength of planets and stars.

    Science.gov (United States)

    Christensen, Ulrich R; Holzwarth, Volkmar; Reiners, Ansgar

    2009-01-08

    The magnetic fields of Earth and Jupiter, along with those of rapidly rotating, low-mass stars, are generated by convection-driven dynamos that may operate similarly (the slowly rotating Sun generates its field through a different dynamo mechanism). The field strengths of planets and stars vary over three orders of magnitude, but the critical factor causing that variation has hitherto been unclear. Here we report an extension of a scaling law derived from geodynamo models to rapidly rotating stars that have strong density stratification. The unifying principle in the scaling law is that the energy flux available for generating the magnetic field sets the field strength. Our scaling law fits the observed field strengths of Earth, Jupiter, young contracting stars and rapidly rotating low-mass stars, despite vast differences in the physical conditions of the objects. We predict that the field strengths of rapidly rotating brown dwarfs and massive extrasolar planets are high enough to make them observable.

  19. A magnetic study of spotted UV Ceti flare stars and related late-type dwarfs

    Science.gov (United States)

    Vogt, S. S.

    1980-09-01

    A multichannel photoelectric Zeeman analyzer has been used to investigate the magnetic nature of the spotted UV Ceti flare stars. Magnetic observations were obtained on a sample of 19 program objects, of which 5 were currently spotted dKe-dMe stars, 7 were normal dK-dM stars, 7 were UV Ceti flare stars, and 1 was a possible post-T Tauri star. Contrary to most previously published observations and theoretical expectations, no magnetic fields were detected on any of these objects from either the absorption lines or the H-alpha emission line down to an observational uncertainty level of 100-160 gauss (standard deviation).

  20. Spectropolarimetry of magnetic stars. IV. The crossover effect.

    Science.gov (United States)

    Mathys, G.

    1995-01-01

    This paper is devoted to the study of the crossover effect in magnetic Ap stars. It is shown that this effect can be measured by the second order moment about their centre of the profiles of spectral lines recorded in the Stokes parameter V. The interpretation of these measurements in terms of magnetic field is developed. It is shown that one can derive from them a quantity called the mean asymmetry of the longitudinal magnetic field, which is the first moment of the component of the magnetic field along the line of sight, about the plane defined by the line of sight and the stellar rotation axis. The consistency of the determination of this quantity with that of the mean longitudinal magnetic field from measurements of wavelength shifts of lines between right and left circular polarization is demonstrated. This technique of analysis is applied to observations of a sample of 29 stars, among which 10 have a detectable crossover effect. For 8 of them, the available observational data allow the study of the variations of the asymmetry of the longitudinal field with rotation phase. In most cases, this variation is sinusoidal and essentially symmetric about 0, and it occurs in quadrature with the variation of the mean longitudinal field. A more complex behaviour is definitely observed in HD 147010 and HD 175362, where the variation of the asymmetry of the longitudinal field is better represented by the superposition of two sinusoids, one with the rotation frequency of the star, and the other with twice that frequency.

  1. Probing the extreme wind confinement of the most magnetic O star with COS spectroscopy

    Science.gov (United States)

    Petit, Veronique

    2014-10-01

    We propose to obtain phase-resolved UV spectroscopy of the recently discovered magnetic O star NGC 1624-2, which has the strongest magnetic field ever detected in a O-star, by an order of magnitude. We will use the strength and variability of the UV resonance line profiles to diagnose the density, velocity, and ionization structure of NGC 1624-2's enormous magnetosphere that results from entrapment of its stellar wind by its strong, nearly dipolar magnetic field. With this gigantic magnetosphere, NGC 1624-2 represents a new regime of extreme wind confinement that will constrain models of magnetized winds and their surface mass flux properties. A detailed understanding of such winds is necessary to study the rotational braking history of magnetic O-stars, which can shed new light on the fundamental origin of magnetism in massive, hot stars.

  2. Topological currents in neutron stars: kicks, precession, toroidal fields, and magnetic helicity

    International Nuclear Information System (INIS)

    Charbonneau, James; Zhitnitsky, Ariel

    2010-01-01

    The effects of anomalies in high density QCD are striking. We consider a direct application of one of these effects, namely topological currents, on the physics of neutron stars. All the elements required for topological currents are present in neutron stars: degenerate matter, large magnetic fields, and parity violating processes. These conditions lead to the creation of vector currents capable of carrying momentum and inducing magnetic fields. We estimate the size of these currents for many representative states of dense matter in the neutron star and argue that they could be responsible for the large proper motion of neutron stars (kicks), the toroidal magnetic field and finite magnetic helicity needed for stability of the poloidal field, and the resolution of the conflict between type-II superconductivity and precession. Though these observational effects appear unrelated, they likely originate from the same physics — they are all P-odd phenomena that stem from a topological current generated by parity violation

  3. Role of magnetic interactions in neutron stars

    Directory of Open Access Journals (Sweden)

    Adhya Souvik Priyam

    2015-01-01

    Full Text Available In this work, we present a calculation of the non-Fermi liquid correction to the specific heat of magnetized degenerate quark matter present at the core of the neutron star. The role of non-Fermi liquid corrections to the neutrino emissivity has been calculated beyond leading order. We extend our result to the evaluation of the pulsar kick velocity and cooling of the star due to such anomalous corrections and present a comparison with the simple Fermi liquid case.

  4. Gravitational waves from color-magnetic "mountains" in neutron stars.

    Science.gov (United States)

    Glampedakis, K; Jones, D I; Samuelsson, L

    2012-08-24

    Neutron stars may harbor the true ground state of matter in the form of strange quark matter. If present, this type of matter is expected to be a color superconductor, a consequence of quark pairing with respect to the color and flavor degrees of freedom. The stellar magnetic field threading the quark core becomes a color-magnetic admixture and, in the event that superconductivity is of type II, leads to the formation of color-magnetic vortices. In this Letter, we show that the volume-averaged color-magnetic vortex tension force should naturally lead to a significant degree of nonaxisymmetry in systems such as radio pulsars. We show that gravitational radiation from such color-magnetic "mountains" in young pulsars, such as the Crab and Vela, could be observable by the future Einstein Telescope, thus, becoming a probe of paired quark matter in neutron stars. The detectability threshold can be pushed up toward the sensitivity level of Advanced LIGO if we invoke an interior magnetic field about a factor ten stronger than the surface polar field.

  5. White-dwarf rotational equilibria in magnetic cataclysmic variable stars

    Energy Technology Data Exchange (ETDEWEB)

    Warner, B. (Cape Town Univ. (South Africa). Dept. of Astronomy Australian National Univ., Canberra (Australia). Dept. of Mathematics); Wickramasinghe, D.T. (Australian National Univ., Canberra (Australia). Dept. of Mathematics)

    1991-02-01

    The magnetic cataclysmic variable stars (polars, intermediate polars and DQ Her stars) are grouped about three lines in the orbital period-spin period diagram. This segregation is shown to be the consequence of competition between braking and accretion torques when combined with the effects of cyclical variations in rate of mass transfer. (author).

  6. MODELING THE RISE OF FIBRIL MAGNETIC FIELDS IN FULLY CONVECTIVE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Weber, Maria A.; Browning, Matthew K., E-mail: mweber@astro.ex.ac.uk [Department of Physics and Astronomy, University of Exeter, Stocker Road, EX4 4QL Exeter (United Kingdom)

    2016-08-20

    Many fully convective stars exhibit a wide variety of surface magnetism, including starspots and chromospheric activity. The manner by which bundles of magnetic field traverse portions of the convection zone to emerge at the stellar surface is not especially well understood. In the solar context, some insight into this process has been gleaned by regarding the magnetism as consisting partly of idealized thin flux tubes (TFTs). Here we present the results of a large set of TFT simulations in a rotating spherical domain of convective flows representative of a 0.3 M {sub ⊙} main-sequence star. This is the first study to investigate how individual flux tubes in such a star might rise under the combined influence of buoyancy, convection, and differential rotation. A time-dependent hydrodynamic convective flow field, taken from separate 3D simulations calculated with the anelastic equations, impacts the flux tube as it rises. Convective motions modulate the shape of the initially buoyant flux ring, promoting localized rising loops. Flux tubes in fully convective stars have a tendency to rise nearly parallel to the rotation axis. However, the presence of strong differential rotation allows some initially low-latitude flux tubes of moderate strength to develop rising loops that emerge in the near-equatorial region. Magnetic pumping suppresses the global rise of the flux tube most efficiently in the deeper interior and at lower latitudes. The results of these simulations aim to provide a link between dynamo-generated magnetic fields, fluid motions, and observations of starspots for fully convective stars.

  7. The Of?p stars of the Magellanic Clouds: Are they strongly magnetic?

    Science.gov (United States)

    Munoz, M.; Wade, G. A.; Nazé, Y.; Bagnulo, S.; Puls, J.

    2018-01-01

    All known Galactic Of?p stars have been shown to host strong, organized, magnetic fields. Recently, five Of?p stars have been discovered in the Magellanic Clouds. They posses photometric (Nazé et al., 2015) and spectroscopic (Walborn et al., 2015) variability compatible with the Oblique Rotator Model (ORM). However, their magnetic fields have yet to be directly detected. We have developed an algorithm allowing for the synthesis of photometric observables based on the Analytic Dynamical Magnetosphere (ADM) model by Owocki et al. (2016). We apply our model to OGLE photometry in order to constrain their magnetic geometries and surface dipole strengths. We predict that the field strengths for some of theses candidate extra-Galactic magnetic stars may be within the detection limits of the FORS2 instrument

  8. Photometric investigation of the magnetic star 53 Camelopardalis

    International Nuclear Information System (INIS)

    Muciek, M.; Gertner, J.; North, P.; Rufener, F.

    1985-01-01

    New photometric results obtained in the Geneva system are presented for the star 53 Cam. Earlier photometric results obtained in another system are used as well to show the existence of about four ''null-wavelength regions'' between 3400 and 7700 A and to draw the pseudocontinuum of this star. Assuming axisymmetry about the magnetic axis, a simple model of brightness and equivalent width distribution on the surface of the star are proposed. The distribution of the intensity of the γ 5200 depression is given and a slight inhomogeneity of the distribution of effective temperature is suggested. 28 refs., 7 figs., 4 tabs. (author)

  9. Magnetic field topology and chemical abundance distributions of the young, rapidly rotating, chemically peculiar star HR 5624

    Science.gov (United States)

    Kochukhov, O.; Silvester, J.; Bailey, J. D.; Landstreet, J. D.; Wade, G. A.

    2017-09-01

    Context. The young, rapidly rotating Bp star HR 5624 (HD 133880) shows an unusually strong non-sinusoidal variability of its longitudinal magnetic field. This behaviour was previously interpreted as the signature of an exceptionally strong, quadrupole-dominated surface magnetic field geometry. Aims: We studied the magnetic field structure and chemical abundance distributions of HR 5624 with the aim to verify the unusual quadrupolar nature of its magnetic field and to investigate correlations between the field topology and chemical spots. Methods: We analysed high-resolution, time series Stokes parameter spectra of HR 5624 with the help of a magnetic Doppler imaging inversion code based on detailed polarised radiative transfer modelling of the line profiles. Results: We refined the stellar parameters, revised the rotational period, and obtained new longitudinal magnetic field measurements. Our magnetic Doppler inversions reveal that the field structure of HR 5624 is considerably simpler and the field strength is much lower than proposed by previous studies. We find a maximum local field strength of 12 kG and a mean field strength of 4 kG, which is about a factor of three weaker than predicted by quadrupolar field models. Our model implies that overall large-scale field topology of HR 5624 is better described as a distorted, asymmetric dipole rather than an axisymmetric quadrupole. The chemical abundance maps of Mg, Si, Ti, Cr, Fe, and Nd obtained in our study are characterised by large-scale, high-contrast abundance patterns. These structures correlate weakly with the magnetic field geometry and, in particular, show no distinct element concentrations in the horizontal field regions predicted by theoretical atomic diffusion calculations. Conclusions: We conclude that the surface magnetic field topology of HR 5624 is not as unusual as previously proposed. Considering these results together with other recent magnetic mapping analyses of early-type stars suggests that

  10. Characterization of the magnetic field of the Herbig Be star HD200775

    Science.gov (United States)

    Alecian, E.; Catala, C.; Wade, G. A.; Donati, J.-F.; Petit, P.; Landstreet, J. D.; Böhm, T.; Bouret, J.-C.; Bagnulo, S.; Folsom, C.; Grunhut, J.; Silvester, J.

    2008-03-01

    The origin of the magnetic fields observed in some intermediate-mass and high-mass main-sequence stars is still a matter of vigorous debate. The favoured hypothesis is a fossil field origin, in which the observed fields are the condensed remnants of magnetic fields present in the original molecular cloud from which the stars formed. According to this theory a few per cent of the pre-main-sequence (PMS) Herbig Ae/Be star should be magnetic with a magnetic topology similar to that of main-sequence intermediate-mass stars. After our recent discovery of four magnetic Herbig stars, we have decided to study in detail one of them, HD200775, to determine if its magnetic topology is similar to that of the main-sequence magnetic stars. With this aim, we monitored this star in Stokes I and V over more than 2yr, using the new spectropolarimeters ESPaDOnS at Canada-France-Hawaii Telescope (CFHT), and Narval at Bernard Lyot Telescope (TBL). By analysing the intensity spectrum we find that HD200775 is a double-lined spectroscopic binary system, whose secondary seems similar, in temperature, to the primary. We have carefully compared the observed spectrum to a synthetic one, and we found no evidence of abundance anomalies in its spectrum. We infer the luminosity ratio of the components from the Stokes I profiles. Then, using the temperature and luminosity of HD200775 found in the literature, we estimate the age, the mass and the radius of both components from their HR diagram positions. From our measurements of the radial velocities of both stars we determine the ephemeris and the orbital parameters of the system. A Stokes V Zeeman signature is clearly visible in most of the least-squares deconvolution profiles and varies on a time-scale on the order of 1d. We have fitted the 30 profiles simultaneously, using a χ2 minimization method, with a centred and a decentred-dipole model. The best-fitting model is obtained with a reduced χ2 = 1.0 and provides a rotation period of 4

  11. A Rigidly Rotating Magnetosphere Model for the Circumstellar Environments of Magnetic OB Stars

    Science.gov (United States)

    Townsend, R.; Owocki, S.; Groote, D.

    2005-11-01

    We report on a new model for the circumstellar environments of rotating, magnetic hot stars. This model predicts the channeling of wind plasma into a corotating magnetosphere, where -- supported against gravity by centrifugal forces -- it can steadily accumulate over time. We apply the model to the B2p star σ Ori E, demonstrating that it can simultaneously reproduce the spectroscopic, photometric and magnetic variations exhibited by the star.

  12. New measurements of photospheric magnetic fields in late-type stars and emerging trends

    Science.gov (United States)

    Saar, S. H.; Linsky, J. L.

    1986-01-01

    The magnetic fields of late-type stars are measured using the method of Saar et al. (1986). The method includes radiative transfer effects and compensation for line blending; the photospheric magnetic field parameters are derived by comparing observed and theoretical line profiles using an LTE code that includes line saturation and full Zeeman pattern. The preliminary mean active region magnetic field strengths (B) and surface area coverages for 20 stars are discussed. It is observed that there is a trend of increasing B towards the cooler dwarfs stars, and the linear correlation between B and the equipartition value of the magnetic field strength suggests that the photospheric gas pressure determines the photospheric magnetic field strengths. A tendency toward larger filling factors at larger stellar angular velocities is also detected.

  13. Weak hard X-ray emission from broad absorption line quasars: evidence for intrinsic X-ray weakness

    International Nuclear Information System (INIS)

    Luo, B.; Brandt, W. N.; Scott, A. E.; Alexander, D. M.; Gandhi, P.; Stern, D.; Teng, S. H.; Arévalo, P.; Bauer, F. E.; Boggs, S. E.; Craig, W. W.; Christensen, F. E.; Comastri, A.; Farrah, D.; Hailey, C. J.; Harrison, F. A.; Koss, M.; Ogle, P.; Puccetti, S.; Saez, C.

    2014-01-01

    We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z = 0.148-1.223, are among the optically brightest and most luminous BAL quasars known at z < 1.3. However, their rest-frame ≈2 keV luminosities are 14 to >330 times weaker than expected for typical quasars. Our results from a pilot NuSTAR study of two low-redshift BAL quasars, a Chandra stacking analysis of a sample of high-redshift BAL quasars, and a NuSTAR spectral analysis of the local BAL quasar Mrk 231 have already suggested the existence of intrinsically X-ray weak BAL quasars, i.e., quasars not emitting X-rays at the level expected from their optical/UV emission. The aim of the current program is to extend the search for such extraordinary objects. Three of the six new targets are weakly detected by NuSTAR with ≲ 45 counts in the 3-24 keV band, and the other three are not detected. The hard X-ray (8-24 keV) weakness observed by NuSTAR requires Compton-thick absorption if these objects have nominal underlying X-ray emission. However, a soft stacked effective photon index (Γ eff ≈ 1.8) for this sample disfavors Compton-thick absorption in general. The uniform hard X-ray weakness observed by NuSTAR for this and the pilot samples selected with <10 keV weakness also suggests that the X-ray weakness is intrinsic in at least some of the targets. We conclude that the NuSTAR observations have likely discovered a significant population (≳ 33%) of intrinsically X-ray weak objects among the BAL quasars with significantly weak <10 keV emission. We suggest that intrinsically X-ray weak quasars might be preferentially observed as BAL quasars.

  14. MAGNETIC CYCLES IN A DYNAMO SIMULATION OF FULLY CONVECTIVE M-STAR PROXIMA CENTAURI

    Energy Technology Data Exchange (ETDEWEB)

    Yadav, Rakesh K.; Wolk, Scott J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Christensen, Ulrich R. [Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany); Poppenhaeger, Katja, E-mail: rakesh.yadav@cfa.harvard.edu [Astrophysics Research Center, Queen’s University Belfast, Belfast BT7 1NN (United Kingdom)

    2016-12-20

    The recent discovery of an Earth-like exoplanet around Proxima Centauri has shined a spot light on slowly rotating fully convective M-stars. When such stars rotate rapidly (period ≲20 days), they are known to generate very high levels of activity that is powered by a magnetic field much stronger than the solar magnetic field. Recent theoretical efforts are beginning to understand the dynamo process that generates such strong magnetic fields. However, the observational and theoretical landscape remains relatively uncharted for fully convective M-stars that rotate slowly. Here, we present an anelastic dynamo simulation designed to mimic some of the physical characteristics of Proxima Centauri, a representative case for slowly rotating fully convective M-stars. The rotating convection spontaneously generates differential rotation in the convection zone that drives coherent magnetic cycles where the axisymmetric magnetic field repeatedly changes polarity at all latitudes as time progress. The typical length of the “activity” cycle in the simulation is about nine years, in good agreement with the recently proposed activity cycle length of about seven years for Proxima Centauri. Comparing our results with earlier work, we hypothesis that the dynamo mechanism undergoes a fundamental change in nature as fully convective stars spin down with age.

  15. Magnetic massive stars as progenitors of `heavy' stellar-mass black holes

    Science.gov (United States)

    Petit, V.; Keszthelyi, Z.; MacInnis, R.; Cohen, D. H.; Townsend, R. H. D.; Wade, G. A.; Thomas, S. L.; Owocki, S. P.; Puls, J.; ud-Doula, A.

    2017-04-01

    The groundbreaking detection of gravitational waves produced by the inspiralling and coalescence of the black hole (BH) binary GW150914 confirms the existence of 'heavy' stellar-mass BHs with masses >25 M⊙. Initial characterization of the system by Abbott et al. supposes that the formation of BHs with such large masses from the evolution of single massive stars is only feasible if the wind mass-loss rates of the progenitors were greatly reduced relative to the mass-loss rates of massive stars in the Galaxy, concluding that heavy BHs must form in low-metallicity (Z ≲ 0.25-0.5 Z⊙) environments. However, strong surface magnetic fields also provide a powerful mechanism for modifying mass-loss and rotation of massive stars, independent of environmental metallicity. In this paper, we explore the hypothesis that some heavy BHs, with masses >25 M⊙ such as those inferred to compose GW150914, could be the natural end-point of evolution of magnetic massive stars in a solar-metallicity environment. Using the MESA code, we developed a new grid of single, non-rotating, solar-metallicity evolutionary models for initial zero-age main sequence masses from 40 to 80 M⊙ that include, for the first time, the quenching of the mass-loss due to a realistic dipolar surface magnetic field. The new models predict terminal-age main-sequence (TAMS) masses that are significantly greater than those from equivalent non-magnetic models, reducing the total mass lost by a strongly magnetized 80 M⊙ star during its main-sequence evolution by 20 M⊙. This corresponds approximately to the mass-loss reduction expected from an environment with metallicity Z = 1/30 Z⊙.

  16. Magnetic braking in young late-type stars. The effect of polar spots

    Science.gov (United States)

    Aibéo, A.; Ferreira, J. M.; Lima, J. J. G.

    2007-10-01

    Context: The existence of rapidly rotating cool stars in young clusters implies a reduction of angular momentum loss rate for a certain period of the star's early life. Recently, the concentration of magnetic flux near the poles of these stars has been proposed as an alternative mechanism to dynamo saturation in order to explain the saturation of angular momentum loss. Aims: In this work we study the effect of magnetic surface flux distribution on the coronal field topology and angular momentum loss rate. We investigate if magnetic flux concentration towards the pole is a reasonable alternative to dynamo saturation. Methods: We construct a 1D wind model and also apply a 2-D self-similar analytical model, to evaluate how the surface field distribution affects the angular momentum loss of the rotating star. Results: From the 1D model we find that, in a magnetically dominated low corona, the concentrated polar surface field rapidly expands to regions of low magnetic pressure resulting in a coronal field with small latitudinal variation. We also find that the angular momentum loss rate due to a uniform field or a concentrated field with equal total magnetic flux is very similar. From the 2D wind model we show that there are several relevant factors to take into account when studying the angular momentum loss from a star. In particular, we show that the inclusion of force balance across the field in a wind model is fundamental if realistic conclusions are to be drawn from the effect of non-uniform surface field distribution on magnetic braking. This model predicts that a magnetic field concentrated at high latitudes leads to larger Alfvén radii and larger braking rates than a smoother field distribution. Conclusions: From the results obtained, we argue that the magnetic surface field distribution towards the pole does not directly limit the braking efficiency of the wind.

  17. Magnetization of neutron star matter and implications in physics of soft gamma repeaters

    Energy Technology Data Exchange (ETDEWEB)

    Kondratyev, V N [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    2002-01-01

    The magnetization of neutron star matter is considered within the thermodynamic formalism. The quantization effects are demonstrated to result in sharp abrupt magnetic field dependence of nuclide magnetic moments. Accounting for inter-nuclide magnetic coupling we show that such anomalies give rise to erratic jumps in magnetotransport of neutron star crusts. The properties of such a noise are favorably compared with burst statistics of Soft Gamma Repeaters. PACS: 97.60.Jd, 21.10.Dr, 26.60.+c, 95.30.Ky. (author)

  18. Mass-radius relation for magnetized strange quark stars

    CERN Document Server

    Martinez, A Perez; Paret, D Manreza

    2010-01-01

    We review the stability of magnetized strange quark matter (MSQM) within the phenomenological MIT bag model, taking into account the variation of the relevant input parameters, namely, the strange quark mass, baryon density, magnetic field and bag parameter. A comparison with magnetized asymmetric quark matter in $\\beta$-equilibrium as well as with strange quark matter (SQM) is presented. We obtain that the energy per baryon for MSQM decreases as the magnetic field increases, and its minimum value at vanishing pressure is lower than the value found for SQM, which implies that MSQM is more stable than non-magnetized SQM. The mass-radius relation for magnetized strange quark stars is also obtained in this framework.

  19. Signatures of field induced spin polarization of neutron star matter in seismic vibrations of paramagnetic neutron star

    International Nuclear Information System (INIS)

    Bastrukov, S I; Yang, J; Podgainy, D V; Weber, F

    2003-01-01

    A macroscopic model of the dissipative magneto-elastic dynamics of viscous spin polarized nuclear matter is discussed in the context of seismic activity of a paramagnetic neutron star. The source of the magnetic field of such a star is attributed to Pauli paramagnetism of baryon matter promoted by a seed magnetic field frozen into the star in the process of gravitational collapse of a massive progenitor. Particular attention is given to the effect of shear viscosity of incompressible stellar material on the timing of non-radial torsional magneto-elastic pulsations of the star triggered by starquakes. By accentuating the fact that this kind of vibration is unique to the seismology of a paramagnetic neutron star we show that the high-frequency modes decay faster than the low-frequency modes. The obtained analytic expressions for the period and relaxation time of this mode, in which the magnetic susceptibility and viscosity enter as input parameters, are then quantified by numerical estimates for these parameters taken from early and current works on transport coefficients of dense matter. It is found that the effect of viscosity is crucial for the lifetime of magneto-torsion vibrations but it does not appreciably affect the periods of this seismic mode which fall in the realm of periods of pulsed emission of soft gamma-ray repeaters and anomalous x-ray pulsars - young super-magnetized neutron stars, radiating, according to the magnetar model, at the expense of the magnetic energy release. Finally, we present arguments that the long periodic pulsed emission of these stars in a quiescent regime of radiation can be interpreted as a manifestation of weakly damped seismic magneto-torsion vibrations exhibiting the field induced spin polarization of baryon matter

  20. Extremely weak magnetic field exposure may inhibit hippocampal neurogenesis of Sprague Dawley rats

    Science.gov (United States)

    Zhang, B.; Tian, L.; Cai, Y.; Xu, H.; Pan, Y.

    2016-12-01

    Hippocampal neurogenesis occurs throughout life in mammals brains and can be influenced by animals' age as well as environmental factors. Lines of evidences have shown that the magnetic field is an important physics environmental factor influencing many animals' growth and development, and extremely weak magnetic field exposures have been proved having serious adverse effects on the metabolism and behaviors in some animals, but few studies have examined the response of hippocampal neurogenesis to it. In the present study, we experimentally examined the extremely weak magnetic field effects on neurogenesis of the dentate gyrus (DG) of hippocampus of adult Sprague Dawley (SD) rats. Two types of magnetic fields were used, an extremely weak magnetic field (≤ 0.5μT) and the geomagnetic fields (strength 31-58μT) as controls. Thirty-two SD rats (3-weeks old) were used in this study. New cell survival in hippocampus was assessed at 0, 14, 28, and 42 days after a 7-day intraperitoneal injections of 5-bromo-2'-deoxyuridine (BrdU). Meanwhile, the amounts of immature neurons and mature neurons which are both related to hippocampal neurogenesis, as documented by labeling with doublecortin (DCX) and neuron (NeuN), respectively, were also analyzed at 0, 14, 28, and 42 days. Compared with geomagnetic field exposure groups, numbers of BrdU-, DCX-positive cells of DG of hippocampus in tested rats reduces monotonously and more rapidly after 14 days, and NeuN-positive cells significantly decreases after 28days when exposed in the extremely weak magnetic field condition. Our data suggest that the exposure to an extremely weak magnetic field may suppress the neurogenesis in DG of SD rats.

  1. Interstellar Magnetic Fields and Polarimetry of Dust Emission

    Science.gov (United States)

    Dowell, Darren

    2010-01-01

    Magnetic fields are an important ingredient in the stormy cosmos. Magnetic fields: (1) are intimately involved with winds from Active Galactic Nuclei (AGN) and stars (2) create at least some of the structures observed in the ISM (3) modulate the formation of clouds, cores, and stars within a turbulent medium (4) may be dynamically important in protostellar accretion disks (5) smooth weak shocks (C-shocks).

  2. Convection and magnetism of solar-type stars (G and K)

    International Nuclear Information System (INIS)

    Do-Cao, Olivier Long

    2013-01-01

    This thesis aims at understanding the internal dynamics of solar-type stars and the origin of their magnetism. We will explore the complex nonlinear interactions between convection, rotation and magnetism conducting both 2D (STELEM code) and 3D (ASH code) numerical simulations. This dual approach will unveil the mechanisms and key parameters behind those physical processes. While the Sun has played a central role in previous studies, this work extends our knowledge to G and K stars. This manuscript is divided into 4 parts. The first one introduces the concepts behind internal stellar dynamics, and emphasizes the dynamo effect. Accurate observations of the Sun will be compared to stellar data, allowing us to determine what is specific to the Sun and what is generic for all stars. The second part reports the results obtained with the 2D STELEM code. This code allows us to study the generation and evolution of the large scale magnetic fields on a timescale comparable to the solar cycle period (11 years), giving us insight into the underlying dynamo processes at work. We show that the current solar models cannot reproduce the observations, when applied to rapidly rotating stars, unless we consider a turbulent pumping mechanism under specific conditions. Then, we have improved these kinematic models by taking into account the large scale magnetic field feedback on the longitudinal velocity component, called the Malkus Proctor effect. The models are now able to reproduce the solar torsional oscillations and can predict how their properties evolve with rotation rate. The third part focuses on 3D numerical simulations running on massively parallel supercomputers, using the ASH code. In contrast with the previously described code, ASH explicitly resolves the full MHD equations. We have studied (hydrodynamically) how the convective properties of G and K stars change as function of mass and rotation rate, first by considering the convective envelope alone, then by taking into

  3. T Tauri stars - Wild as dust

    International Nuclear Information System (INIS)

    Bertout, C.

    1989-01-01

    T Tauri stars (TTSs), their surroundings, and their common evolution toward the main sequence are discussed. The photospheric properties of TTSs and their solar-type outer atmospheres, recent evidence for circumstellar disks around classical TTSs (CTTSs), and CTTS mass outflows are examined. TTSs are depicted as complex systems whose properties depend mostly on the initial conditions of star formation and on their rotation rates, which appear to control the magnetodynamic activity in the stars. The most exotic traits of CTTSs are primarily due to the disk and its interaction with the star, and the properties of weak-line TTSs (WTTSs) are mainly manifestations of the enhanced solar-type magnetic activity expected from their rotation rates. CTTSs are expected to become WTTSs when their disks dissipate. 217 refs

  4. Properties of a magnetic superconductor with weak magnetization-application to ErNi2B2C

    International Nuclear Information System (INIS)

    Ng, T.K.; Leung, W.T.

    2001-01-01

    Using a Ginsburg-Landau free-energy functional, we study the H-T phase diagram of a weak magnetic superconductor, where the magnetization from the magnetic component is marginal in supporting a spontaneous vortex phase. In particular, the competition between the spiral state and spontaneous vortex phase is analysed. Our theory is applied to understand the magnetic properties of ErNi 2 B 2 C. (orig.)

  5. A general nonlinear magnetomechanical model for ferromagnetic materials under a constant weak magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Shi, Pengpeng; Zheng, Xiaojing, E-mail: xjzheng@xidian.edu.cn [School of Mechano-Electronic Engineering, Xidian University, Xi' an 710071, Shaanxi (China); Jin, Ke [School of Aerospace Science and Technology, Xidian University, Xi' an 710071, Shaanxi (China)

    2016-04-14

    Weak magnetic nondestructive testing (e.g., metal magnetic memory method) concerns the magnetization variation of ferromagnetic materials due to its applied load and a weak magnetic surrounding them. One key issue on these nondestructive technologies is the magnetomechanical effect for quantitative evaluation of magnetization state from stress–strain condition. A representative phenomenological model has been proposed to explain the magnetomechanical effect by Jiles in 1995. However, the Jiles' model has some deficiencies in quantification, for instance, there is a visible difference between theoretical prediction and experimental measurements on stress–magnetization curve, especially in the compression case. Based on the thermodynamic relations and the approach law of irreversible magnetization, a nonlinear coupled model is proposed to improve the quantitative evaluation of the magnetomechanical effect. Excellent agreement has been achieved between the predictions from the present model and previous experimental results. In comparison with Jiles' model, the prediction accuracy is improved greatly by the present model, particularly for the compression case. A detailed study has also been performed to reveal the effects of initial magnetization status, cyclic loading, and demagnetization factor on the magnetomechanical effect. Our theoretical model reveals that the stable weak magnetic signals of nondestructive testing after multiple cyclic loads are attributed to the first few cycles eliminating most of the irreversible magnetization. Remarkably, the existence of demagnetization field can weaken magnetomechanical effect, therefore, significantly reduces the testing capability. This theoretical model can be adopted to quantitatively analyze magnetic memory signals, and then can be applied in weak magnetic nondestructive testing.

  6. Starquake-induced Magnetic Field and Torque Evolution in Neutron Stars

    International Nuclear Information System (INIS)

    Link, B.; Franco, L.M.; Epstein, R.I.

    1998-01-01

    The persistent increases in spin-down rate (offsets) seen to accompany glitches in the Crab and other pulsars suggest increases in the spin-down torque. We interpret these offsets as due to starquakes occurring as the star spins down and the rigid crust becomes less oblate. We study the evolution of strain in the crust, the initiation of starquakes, and possible consequences for magnetic field and torque evolution. Crust cracking occurs as equatorial material shears under the compressive forces arising from the star's decreasing circumference and as matter moves to higher latitudes along a fault inclined to the equator. A starquake is most likely to originate near one of the two points on the rotational equator farthest from the magnetic poles. The material breaks along a fault approximately aligned with the magnetic poles. We suggest that the observed offsets come about when a starquake perturbs the star's mass distribution, producing a misalignment of the angular momentum and spin axes. Subsequently, damped precession to a new rotational state increases the angle α between the rotation and magnetic axes. The resulting increase in external torque appears as a permanent increase in the spin-down rate. Repeated starquakes would continue to increase α, making the pulsar more of an orthogonal rotator. copyright copyright 1998. The American Astronomical Society

  7. Tidal and magnetic interactions in close binary stars

    International Nuclear Information System (INIS)

    Campbell, C.G.

    1983-03-01

    The thesis investigates the nature of non-synchronous motions in members of close binary stars under the influence of gravitational and magnetic fields existing in these systems, and the evolution of such motions in different classes of binaries. Largely convective stars are considered and a solution is found for the fluid flow associated with the non-synchronous rotation of such a secondary in a close binary system, taking tidal and rotational forces into account. The tidal velocity field is calculated for a low mass white dwarf secondary star in a twin - degenerate binary. It is found that the synchronisation times can be comparable to the lifetime of the binary so that some asynchronism may remain present. (U.K.)

  8. Effects of neutrino emissivity on the cooling of neutron stars in the presence of a strong magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Coelho, Eduardo Lenho, E-mail: eduardo.coelho@uva.br [Universidade Veiga de Almeida, 108 Ibituruna St., 20271-020, Rio de Janeiro (Brazil); Chiapparini, Marcelo [Instituto de Física, Universidade do Estado do Rio de Janeiro, 524 São Francisco Xavier St., 20271-020, Rio de Janeiro (Brazil); Negreiros, Rodrigo Picanço [Instituto de Física, Universidade Federal Fluminense, Gal. Milton Tavares de Souza Ave., 24210-346, Rio de Janeiro (Brazil)

    2015-12-17

    One of the most interesting kind of neutron stars are the pulsars, which are highly magnetized neutron stars with fields up to 10{sup 14} G at the surface. The strength of magnetic field in the center of a neutron star remains unknown. According to the scalar virial theorem, magnetic field in the core could be as large as 10{sup 18} G. In this work we study the influence of strong magnetic fields on the cooling of neutron stars coming from direct Urca process. Direct Urca process is an extremely efficient mechanism for cooling a neutron star after its formation. The matter is described using a relativistic mean-field model at zero temperature with eight baryons (baryon octet), electrons and muons. We obtain the relative population of each species of particles as function of baryon density for different magnetic fields. We calculate numerically the cooling of neutron stars for a parametrized magnetic field and compare the results for the case without a magnetic field.

  9. Relativistic MHD modeling of magnetized neutron stars, pulsar winds, and their nebulae

    Science.gov (United States)

    Del Zanna, L.; Pili, A. G.; Olmi, B.; Bucciantini, N.; Amato, E.

    2018-01-01

    Neutron stars are among the most fascinating astrophysical sources, being characterized by strong gravity, densities about the nuclear one or even above, and huge magnetic fields. Their observational signatures can be extremely diverse across the electromagnetic spectrum, ranging from the periodic and low-frequency signals of radio pulsars, up to the abrupt high-energy gamma-ray flares of magnetars, where energies of ∼ {10}46 {erg} are released in a few seconds. Fast-rotating and highly magnetized neutron stars are expected to launch powerful relativistic winds, whose interaction with the supernova remnants gives rise to the non-thermal emission of pulsar wind nebulae, which are known cosmic accelerators of electrons and positrons up to PeV energies. In the extreme cases of proto-magnetars (magnetic fields of ∼ {10}15 G and millisecond periods), a similar mechanism is likely to provide a viable engine for the still mysterious gamma-ray bursts. The key ingredient in all these spectacular manifestations of neutron stars is the presence of strong magnetic fields in their constituent plasma. Here we will present recent updates of a couple of state-of-the-art numerical investigations by the high-energy astrophysics group in Arcetri: a comprehensive modeling of the steady-state axisymmetric structure of rotating magnetized neutron stars in general relativity, and dynamical 3D MHD simulations of relativistic pulsar winds and their associated nebulae.

  10. The Equation of State of Neutron Star Matter in Strong Magnetic Fields

    International Nuclear Information System (INIS)

    Broderick, A.; Prakash, M.; Lattimer, J. M.

    2000-01-01

    We study the effects of very strong magnetic fields on the equation of state (EOS) in multicomponent, interacting matter by developing a covariant description for the inclusion of the anomalous magnetic moments of nucleons. For the description of neutron star matter, we employ a field-theoretical approach, which permits the study of several models that differ in their behavior at high density. Effects of Landau quantization in ultrastrong magnetic fields (B>10 14 G) lead to a reduction in the electron chemical potential and a substantial increase in the proton fraction. We find the generic result for B>10 18 G that the softening of the EOS caused by Landau quantization is overwhelmed by stiffening due to the incorporation of the anomalous magnetic moments of the nucleons. In addition, the neutrons become completely spin polarized. The inclusion of ultrastrong magnetic fields leads to a dramatic increase in the proton fraction, with consequences for the direct Urca process and neutron star cooling. The magnetization of the matter never appears to become very large, as the value of |H/B| never deviates from unity by more than a few percent. Our findings have implications for the structure of neutron stars in the presence of large frozen-in magnetic fields. (c) 2000 The American Astronomical Society

  11. The Equation of State of Neutron Star Matter in Strong Magnetic Fields

    Energy Technology Data Exchange (ETDEWEB)

    Broderick, A; Prakash, M; Lattimer, J M

    2000-07-01

    We study the effects of very strong magnetic fields on the equation of state (EOS) in multicomponent, interacting matter by developing a covariant description for the inclusion of the anomalous magnetic moments of nucleons. For the description of neutron star matter, we employ a field-theoretical approach, which permits the study of several models that differ in their behavior at high density. Effects of Landau quantization in ultrastrong magnetic fields (B>10{sup 14} G) lead to a reduction in the electron chemical potential and a substantial increase in the proton fraction. We find the generic result for B>10{sup 18} G that the softening of the EOS caused by Landau quantization is overwhelmed by stiffening due to the incorporation of the anomalous magnetic moments of the nucleons. In addition, the neutrons become completely spin polarized. The inclusion of ultrastrong magnetic fields leads to a dramatic increase in the proton fraction, with consequences for the direct Urca process and neutron star cooling. The magnetization of the matter never appears to become very large, as the value of |H/B| never deviates from unity by more than a few percent. Our findings have implications for the structure of neutron stars in the presence of large frozen-in magnetic fields. (c) 2000 The American Astronomical Society.

  12. Investigation of Condensed Media in Weak Fields by the Method of Nuclear Magnetic Resonance

    Science.gov (United States)

    Davydov, V. V.; Myazin, N. S.; Dudkin, V. I.; Velichko, E. N.

    2018-05-01

    A compact design of a rapid-response nuclear magnetic spectrometer for investigation of condensed media in weak fields is reported. As a result of investigation of different condensed media, special features of recording a nuclear magnetic resonance (NMR) signal in a weak magnetic field from a small volume of the medium under study are established. For the first time the NMR absorption spectra of condensed media in a weak field are collected. Based on the results of experimental studies, the potential of using a compact NMR-spectrometer for condensed media monitoring in a rapid response mode is determined.

  13. Influence of Weak External Magnetic Field on Amorphous and Nanocrystalline Fe-based Alloys

    Science.gov (United States)

    Degmová, J.; Sitek, J.

    2010-07-01

    Nanoperm, Hitperm and Finamet amorphous and nanocrystalline alloys were measured by Mössbauer spectrometry in a weak external magnetic field of 0.5 T. It was shown that the most sensitive parameters of Mössbauer spectra are the intensities of the 2nd and the 5th lines. Rather small changes were observed also in the case of internal magnetic field values. The spectrum of nanocrystalline Nanoperm showed the increase in A23 parameter (ratio of line intensities) from 2.4 to 3.7 and decrease of internal magnetic field from 20 to 19 T for amorphous subspectrum under the influence of magnetic field. Spectrum of nanocrystalline Finemet shown decrease in A23 parameter from 3.5 to 2.6 almost without a change in the internal magnetic field value. In the case of amorphous Nanoperm and Finemet samples, the changes are almost negligible. Hitperm alloy showed the highest sensitivity to the weak magnetic field, when the A23 parameter increased from 0.4 to 2.5 in the external magnetic fields. The A23 parameter of crystalline subspectrum increased from 2.7 to 3.8 and the value of internal magnetic field corresponding to amorphous subspectrum increased from 22 to 24 T. The behavior of nanocrystalline alloys under weak external magnetic field was analyzed within the three-level relaxation model of magnetic dynamics in an assembly of single-domain particles.

  14. Chemical spots on the surface of the strongly magnetic Herbig Ae star HD 101412

    DEFF Research Database (Denmark)

    Järvinen, S. P.; Hubrig, S.; Schöller, M.

    2016-01-01

    Due to the knowledge of the rotation period and the presence of a rather strong surface magnetic field, the sharp-lined young Herbig Ae star HD 101412 with a rotation period of 42 d has become one of the most well-studied targets among the Herbig Ae stars. High-resolution HARPS polarimetric spectra...... that is opposite to the behaviour of the other elements studied. Since classical Ap stars usually show a relationship between the magnetic field geometry and the distribution of element spots, we used in our magnetic field measurements different line samples belonging to the three elements with the most numerous...

  15. Radial oscillations of neutron stars in strong magnetic fields

    Indian Academy of Sciences (India)

    The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to ...

  16. GLOBAL GALACTIC DYNAMO DRIVEN BY COSMIC RAYS AND EXPLODING MAGNETIZED STARS

    International Nuclear Information System (INIS)

    Hanasz, Michal; Woltanski, Dominik; Kowalik, Kacper

    2009-01-01

    We report the first results of the first global galactic-scale cosmic ray (CR)-MHD simulations of CR-driven dynamo. We investigate the dynamics of magnetized interstellar medium (ISM), which is dynamically coupled with CR gas. We assume that exploding stars deposit small-scale, randomly oriented, dipolar magnetic fields into the differentially rotating ISM, together with a portion of CRs, accelerated in supernova shocks. We conduct numerical simulations with the aid of a new parallel MHD code PIERNIK. We find that the initial magnetization of galactic disks by exploding magnetized stars forms favorable conditions for the CR-driven dynamo. We demonstrate that dipolar magnetic fields supplied on small supernova remnant scales can be amplified exponentially by the CR-driven dynamo, to the present equipartition values, and transformed simultaneously to large galactic scales. The resulting magnetic field structure in an evolved galaxy appears spiral in the face-on view and reveals the so-called X-shaped structure in the edge-on view.

  17. Deflection of weakly magnetic materials by superconducting OGMS

    International Nuclear Information System (INIS)

    Boehm, J.; Gerber, R.; Fletcher, D.; Parker, M.R.

    1988-01-01

    Applications of a superconducting Open Gradient Magnetic Separator to fractional separation in air of weakly magnetic materials are presented. The dependence of particle deflection of these materials on the magnetic field strength, release location, magnetic susceptibility, particle density and other properties is investigated. The aim is to maximise the deflection of the magnetically stronger component of the feed to facilitate its separation from the particle stream round the magnet. Materials (e.g. CuSO/sub 4/, MnO/sub 2/) with chi/rho- ratios of the order of 7 x 10/sup -8/ m/sup 3//kg have been deflected. The applicability of dry magnetic separation has thus been considerably extended since up to now the separation of such materials has been restricted to High Gradient Magnetic Separation. The dependence of the separation efficiency upon the method of feeding and the influence of the residence time are studied in order to establish the optimum parameters for the recovery of the desired fraction. The experimental results are compared with predictions of a theory that is based upon novel approximative calculations of magnetic fields in which the use of elliptic integrals is avoided

  18. The [Fe(III)[Fe(III)(L1)2]3] star-type single-molecule magnet.

    Science.gov (United States)

    Saalfrank, Rolf W; Scheurer, Andreas; Bernt, Ingo; Heinemann, Frank W; Postnikov, Andrei V; Schünemann, Volker; Trautwein, Alfred X; Alam, Mohammad S; Rupp, Holger; Müller, Paul

    2006-06-21

    Star-shaped complex [Fe(III)[Fe(III)(L1)2]3] (3) was synthesized starting from N-methyldiethanolamine H2L1 (1) and ferric chloride in the presence of sodium hydride. For 3, two different high-spin iron(III) ion sites were confirmed by Mössbauer spectroscopy at 77 K. Single-crystal X-ray structure determination revealed that 3 crystallizes with four molecules of chloroform, but, with only three molecules of dichloromethane. The unit cell of 3.4CHCl3 contains the enantiomers (delta)-[(S,S)(R,R)(R,R)] and (lambda)-[(R,R)(S,S)(S,S)], whereas in case of 3.3CH2Cl2 four independent molecules, forming pairs of the enantiomers [lambda-(R,R)(R,R)(R,R)]-3 and [lambda-(S,S)(S,S)(S,S)]-3, were observed in the unit cell. According to SQUID measurements, the antiferromagnetic intramolecular coupling of the iron(III) ions in 3 results in a S = 10/2 ground state multiplet. The anisotropy is of the easy-axis type. EPR measurements enabled an accurate determination of the ligand-field splitting parameters. The ferric star 3 is a single-molecule magnet (SMM) and shows hysteretic magnetization characteristics below a blocking temperature of about 1.2 K. However, weak intermolecular couplings, mediated in a chainlike fashion via solvent molecules, have a strong influence on the magnetic properties. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were used to determine the structural and electronic properties of star-type tetranuclear iron(III) complex 3. The molecules were deposited onto highly ordered pyrolytic graphite (HOPG). Small, regular molecule clusters, two-dimensional monolayers as well as separated single molecules were observed. In our STS measurements we found a rather large contrast at the expected locations of the metal centers of the molecules. This direct addressing of the metal centers was confirmed by DFT calculations.

  19. Polarized X-Ray Emission from Magnetized Neutron Stars: Signature of Strong-Field Vacuum Polarization

    Science.gov (United States)

    Lai, Dong; Ho, Wynn C.

    2003-08-01

    In the atmospheric plasma of a strongly magnetized neutron star, vacuum polarization can induce a Mikheyev-Smirnov-Wolfenstein type resonance across which an x-ray photon may (depending on its energy) convert from one mode into the other, with significant changes in opacities and polarizations. We show that this vacuum resonance effect gives rise to a unique energy-dependent polarization signature in the surface emission from neutron stars. The detection of polarized x rays from neutron stars can provide a direct probe of strong-field quantum electrodynamics and constrain the neutron star magnetic field and geometry.

  20. Polarized x-ray emission from magnetized neutron stars: signature of strong-field vacuum polarization.

    Science.gov (United States)

    Lai, Dong; Ho, Wynn C G

    2003-08-15

    In the atmospheric plasma of a strongly magnetized neutron star, vacuum polarization can induce a Mikheyev-Smirnov-Wolfenstein type resonance across which an x-ray photon may (depending on its energy) convert from one mode into the other, with significant changes in opacities and polarizations. We show that this vacuum resonance effect gives rise to a unique energy-dependent polarization signature in the surface emission from neutron stars. The detection of polarized x rays from neutron stars can provide a direct probe of strong-field quantum electrodynamics and constrain the neutron star magnetic field and geometry.

  1. THE FRAGMENTATION OF MAGNETIZED, MASSIVE STAR-FORMING CORES WITH RADIATIVE FEEDBACK

    Energy Technology Data Exchange (ETDEWEB)

    Myers, Andrew T.; McKee, Christopher F. [Department of Physics, University of California, Berkeley, Berkeley, CA 94720 (United States); Cunningham, Andrew J. [Lawrence Livermore National Laboratory, P.O. Box 808, L-23, Livermore, CA 94550 (United States); Klein, Richard I. [Department of Astronomy, University of California, Berkeley, Berkeley, CA 94720 (United States); Krumholz, Mark R., E-mail: atmyers@berkeley.edu [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States)

    2013-04-01

    We present a set of three-dimensional, radiation-magnetohydrodynamic calculations of the gravitational collapse of massive (300 M{sub Sun }), star-forming molecular cloud cores. We show that the combined effects of magnetic fields and radiative feedback strongly suppress core fragmentation, leading to the production of single-star systems rather than small clusters. We find that the two processes are efficient at suppressing fragmentation in different regimes, with the feedback most effective in the dense, central region and the magnetic field most effective in more diffuse, outer regions. Thus, the combination of the two is much more effective at suppressing fragmentation than either one considered in isolation. Our work suggests that typical massive cores, which have mass-to-flux ratios of about 2 relative to critical, likely form a single-star system, but that cores with weaker fields may form a small star cluster. This result helps us understand why the observed relationship between the core mass function and the stellar initial mass function holds even for {approx}100 M{sub Sun} cores with many thermal Jeans masses of material. We also demonstrate that a {approx}40 AU Keplerian disk is able to form in our simulations, despite the braking effect caused by the strong magnetic field.

  2. Weak-interaction processes in stars: applications to core-collapse supernovae

    International Nuclear Information System (INIS)

    Martinez-Pinedo, G.

    2003-01-01

    The role of weak-interaction processes in core collapse and neutrino nucleosynthesis is reviewed. Recent calculations of the electron capture rates for nuclei with mass numbers A=65-112 show that, contrarily to previous assumptions, during core collapse electron capture is dominated by captures on heavy nuclei. Astrophysical simulations demonstrate that these rates have an important impact on the collapse. Neutrinos emitted by the collapsing core can interact with the overlying shells of the star producing substantial nuclear transmutations. This process known as ν-process seems to be responsible for the production of 138 La by charged current neutrino interactions with 138 Ba. The ν-process is then sensitive to the spectra of different neutrino species and to neutrino oscillations. (orig.)

  3. A neutron depolarization study of magnetic inhomogeneities in weak-link superconductors

    International Nuclear Information System (INIS)

    Zhuchenko, N.K.; Yagud, R.Z.

    1993-01-01

    Neutron depolarization measurements in the mixed state of both high-T c and low-T c weak-link superconductors have been carried out. Samples of YBCO, BSCCO, SnMo 6 S 8 and 0.5 Nb-0.5 Ti of different magnetic prehistory were analyzed at temperatures T 4.2 K under applied magnetic fields II <= 16.5 kOe. We ascribe the appearance of magnetic inhomogeneities and their hysteresis behaviour to the interaction between dipole magnetic fields (diamagnetic and paramagnetic ones) and applied magnetic fields

  4. Dynamical mass generation in QED with weak magnetic fields

    International Nuclear Information System (INIS)

    Ayala, A.; Rojas, E.; Bashir, A.; Raya, A.

    2006-01-01

    We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics in the presence of magnetic fields using Schwinger-Dyson equations. We show that, contrary to the case where the magnetic field is strong, in the weak field limit eB << m(0)2, where m(0) is the value of the dynamically generated mass in the absence of the magnetic field, masses are generated above a critical value of the coupling and that this value is the same as in the case with no magnetic field. We carry out a numerical analysis to study the magnetic field dependence of the mass function above critical coupling and show that in this regime the dynamically generated mass and the chiral condensate for the lowest Landau level increase proportionally to (eB)2

  5. On the fate of superheavy magnetic monopoles in a neutron star

    International Nuclear Information System (INIS)

    Kuzmin, V.A.; Rubakov, V.A.; AN SSSR, Moscow. Inst. Yadernykh Issledovanij)

    1983-02-01

    We propose two possible scenarios of the behaviour of superheavy magnetic monopoles in a neutron star, in which the monopole-antimonopole annihilation rate is sufficiently large to prevent the enormous heating of a neutron star due to the monopole induced neutron decays. We find that the galactic monopole flux of order 10 -16 cm -2 s -1 ster -1 can be compatible with the observational limit on the X-ray luminosity of neutron stars. (author)

  6. STAR/SVT alignment within a finite magnetic field

    International Nuclear Information System (INIS)

    Barannikova, O.Yu.; Belaga, V.V.; Ososkov, G.A.; Panebrattsev, Yu.A.; Bellweid, R.K.; Pruneau, C.A.; Wilson, W.K.

    1999-01-01

    We report on the development of SVT (Silicon Vertex Tracker) software for the purpose of the SVT and TPC (Time Projection Chamber) relative alignment as well as the internal alignment of the SVT components. The alignment procedure described complements the internal SVT alignment procedure discussed in Star Note 356. It involves track reconstruction in both the Star TPC and SVT for the calibration of the SVT geometry in the presence of a finite magnetic field. This new software has been integrated under the package SAL already running under STAR. Both the implementation and the performance of the alignment algorithm are described. We find that the current software implementation in SAL should enable a very satisfactory internal SVT alignment as well as an excellent SVT to TPC relative alignment

  7. FIRST ZEEMAN DOPPLER IMAGING OF A COOL STAR USING ALL FOUR STOKES PARAMETERS

    International Nuclear Information System (INIS)

    Rosén, L.; Kochukhov, O.; Wade, G. A.

    2015-01-01

    Magnetic fields are ubiquitous in active cool stars, but they are in general complex and weak. Current Zeeman Doppler imaging (ZDI) studies of cool star magnetic fields chiefly employ circular polarization observations because linear polarization is difficult to detect and requires a more sophisticated radiative transfer modeling to interpret. But it has been shown in previous theoretical studies, and in the observational analyses of magnetic Ap stars, that including linear polarization in the magnetic inversion process makes it possible to correctly recover many otherwise lost or misinterpreted magnetic features. We have obtained phase-resolved observations in all four Stokes parameters of the RS CVn star II Peg at two separate epochs. Here we present temperature and magnetic field maps reconstructed for this star using all four Stokes parameters. This is the very first such ZDI study of a cool active star. Our magnetic inversions reveal a highly structured magnetic field topology for both epochs. The strength of some surface features is doubled or even quadrupled when linear polarization is taken into account. The total magnetic energy of the reconstructed field map also becomes about 2.1–3.5 times higher. The overall complexity is also increased as the field energy is shifted toward higher harmonic modes when four Stokes parameters are used. As a consequence, the potential field extrapolation of the four Stokes parameter ZDI results indicates that magnetic field becomes weaker at a distance of several stellar radii due to a decrease of the large-scale field component

  8. Magnetohydrodynamics of neutron star interiors

    International Nuclear Information System (INIS)

    Easson, I.; Pethick, C.J.

    1979-01-01

    Magnetohydrodynamic equations for the charged particles in the fluid interior of a neutron star are derived from the Landau-Boltzmann kinetic equations. It is assumed that the protons are normal and the neutrons are superfluid. The dissipative processes associated with the weak interactions are shown to be negligible except in very hot neutron stars; we neglect them here. Among the topics discussed are: the influence of the neutron-proton nuclear force (Fermi liquid corrections) on the magnetohydrodynamics; the effects of the magnetic field on the pressure, viscosity, and heat conductivity tensors; the plasma equation of state; and the form of the generalized Ohm's law

  9. Weak magnetism of Aurivillius-type multiferroic thin films probed by polarized neutron reflectivity

    Science.gov (United States)

    Zhai, Xiaofang; Grutter, Alexander J.; Yun, Yu; Cui, Zhangzhang; Lu, Yalin

    2018-04-01

    Unambiguous magnetic characterization of room-temperature multiferroic materials remains challenging due in part to the difficulty of distinguishing their very weak ferromagnetism from magnetic impurity phases and other contaminants. In this study, we used polarized neutron reflectivity to probe the magnetization of B i6FeCoT i3O18 and LaB i5FeCoT i3O18 in their epitaxial thin films while eliminating a variety of impurity contributions. Our results show that LaB i5FeCoT i3O18 exhibits a magnetization of about 0.016 ±0.027 μB/Fe -Co pair at room temperature, while the B i6FeCoT i3O18 thin film only exhibits a weak magnetic moment below room temperature, with a saturation magnetization of 0.049 ±0.015 μB/Fe -Co pair at 50 K. This polarized-neutron-reflectivity study places an upper magnetization limit on the matrix material of the magnetically doped Aurivillius oxides and helps to clarify the true mechanism behind the room-temperature magnetic performance.

  10. Accurate evolutions of inspiralling and magnetized neutron stars: Equal-mass binaries

    International Nuclear Information System (INIS)

    Giacomazzo, Bruno; Rezzolla, Luciano; Baiotti, Luca

    2011-01-01

    By performing new, long and numerically accurate general-relativistic simulations of magnetized, equal-mass neutron-star binaries, we investigate the role that realistic magnetic fields may have in the evolution of these systems. In particular, we study the evolution of the magnetic fields and show that they can influence the survival of the hypermassive neutron star produced at the merger by accelerating its collapse to a black hole. We also provide evidence that, even if purely poloidal initially, the magnetic fields produced in the tori surrounding the black hole have toroidal and poloidal components of equivalent strength. When estimating the possibility that magnetic fields could have an impact on the gravitational-wave signals emitted by these systems either during the inspiral or after the merger, we conclude that for realistic magnetic-field strengths B 12 G such effects could be detected, but only marginally, by detectors such as advanced LIGO or advanced Virgo. However, magnetically induced modifications could become detectable in the case of small-mass binaries and with the development of gravitational-wave detectors, such as the Einstein Telescope, with much higher sensitivities at frequencies larger than ≅2 kHz.

  11. Magnetic fields and star formation: evidence from imaging polarimetry of the Serpens Reflection Nebula

    Energy Technology Data Exchange (ETDEWEB)

    Warren-Smith, R F; Draper, P W; Scarrott, S M

    1987-08-01

    CCD imaging of the Serpens bipolar reflection nebula shows it to be surrounded by dark material having spiral density structure. Multi-colour polarization mapping also reveals details of the surrounding magnetic field, indicating that this also has spiral structure. These observations are discussed along with current ideas about the role of magnetic fields during star formation. An interpretation involving the non-axisymmetric magnetically braked collapse of a protostellar cloud is proposed and a resulting magnetic field configuration is described which can account for the observations. Evidence is also discussed for the formation of a binary star system within the nebula, resulting from the fragmentation of a magnetized protostellar disc.

  12. An infrared diagnostic for magnetism in hot stars

    Czech Academy of Sciences Publication Activity Database

    Oksala, M.E.; Grunhut, J.H.; Kraus, Michaela; Borges Fernandes, M.; Neiner, C.; Condori, C.A.H.; Condori, J.C.; Souza, C. T.

    2015-01-01

    Roč. 578, June (2015), A112/1-A112/4 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GA14-21373S Institutional support: RVO:67985815 Keywords : stars * magnetic field * circumstellar matter Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  13. Directional Solidification Microstructure of a Ni-Based Superalloy: Influence of a Weak Transverse Magnetic Field

    Directory of Open Access Journals (Sweden)

    Xu Li

    2015-06-01

    Full Text Available A Ni-based superalloy CMSX-6 was directionally solidified at various drawing speeds (5–20 μm·s−1 and diameters (4 mm, 12 mm under a 0.5 T weak transverse magnetic field. The results show that the application of a weak transverse magnetic field significantly modified the solidification microstructure. It was found that if the drawing speed was lower than 10 μm·s−1, the magnetic field caused extensive macro-segregation in the mushy zone, and a change in the mushy zone length. The magnetic field significantly decreases the size of γ’ and the content of γ-γ’ eutectic. The formation of macro-segregation under a weak magnetic field was attributed to the interdendritic solute transport driven by the thermoelectric magnetic convection (TEMC. The γ’ phase refinement could be attributed to a decrease in nucleation activation energy owing to the magnetic field during solid phase transformation. The change of element segregation is responsible for the content decrease of γ-γ’ eutectic.

  14. Systematic Analysis of the Effects of Mode Conversion on Thermal Radiation from Neutron Stars

    Science.gov (United States)

    Yatabe, Akihiro; Yamada, Shoichi

    2017-12-01

    In this paper, we systematically calculate the polarization in soft X-rays emitted from magnetized neutron stars, which are expected to be observed by next-generation X-ray satellites. Magnetars are one of the targets for these observations. This is because thermal radiation is normally observed in the soft X-ray band, and it is thought to be linearly polarized because of different opacities for two polarization modes of photons in the magnetized atmosphere of neutron stars and the dielectric properties of the vacuum in strong magnetic fields. In their study, Taverna et al. illustrated how strong magnetic fields influence the behavior of the polarization observables for radiation propagating in vacuo without addressing a precise, physical emission model. In this paper, we pay attention to the conversion of photon polarization modes that can occur in the presence of an atmospheric layer above the neutron star surface, computing the polarization angle and fraction and systematically changing the magnetic field strength, radii of the emission region, temperature, mass, and radii of the neutron stars. We confirmed that if plasma is present, the effects of mode conversion cannot be neglected when the magnetic field is relatively weak, B∼ {10}13 {{G}}. Our results indicate that strongly magnetized (B≳ {10}14 {{G}}) neutron stars are suitable to detect polarizations, but not-so-strongly magnetized (B∼ {10}13 {{G}}) neutron stars will be the ones to confirm the mode conversion.

  15. Magnus force and inertia properties of magnetic vortices in weak ferromagnets

    International Nuclear Information System (INIS)

    Zvezdin, A.K.; Zvezdin, K.A.

    2010-01-01

    The question of the Magnus force in weak ferromagnets acting on magnetic vortices (Bloch lines), within domain boundary has been investigated and the general formula of the Magnus force has been derived. It is shown that the Magnus force is non-zero in most types domain boundaries and determined by the average sublattice magnetization, Dzyaloshinskii coupling constants and exchange interaction between the sublattices. Generalized expressions have been obtained for the effective Langrangian and Rayleigh functions in weak ferromagnets allowing for their vortex structure. The mass of a vortex was considered and the value m * ∼ 10 -14 g/cm was obtained for YFeO 3 . The dynamic bending of the domain boundary in the presence of a moving vortex has been analyzed. A formula has been obtained, which describes the dependence of the vortex velocity in a motionless domain boundary upon the magnetic-field.

  16. Accretion of matter onto highly magnetized neutron stars: Final report, July 1-September 30, 1985

    International Nuclear Information System (INIS)

    Hernquist, L.

    1986-06-01

    A final report is given of two research projects dealing with magnetic fields of neutron stars. These are the modulation of thermal x-rays from cooling neutron stars and plasma instabilities in neutron star accretion columns

  17. Energy partition, scale by scale, in magnetic Archimedes Coriolis weak wave turbulence.

    Science.gov (United States)

    Salhi, A; Baklouti, F S; Godeferd, F; Lehner, T; Cambon, C

    2017-02-01

    Magnetic Archimedes Coriolis (MAC) waves are omnipresent in several geophysical and astrophysical flows such as the solar tachocline. In the present study, we use linear spectral theory (LST) and investigate the energy partition, scale by scale, in MAC weak wave turbulence for a Boussinesq fluid. At the scale k^{-1}, the maximal frequencies of magnetic (Alfvén) waves, gravity (Archimedes) waves, and inertial (Coriolis) waves are, respectively, V_{A}k,N, and f. By using the induction potential scalar, which is a Lagrangian invariant for a diffusionless Boussinesq fluid [Salhi et al., Phys. Rev. E 85, 026301 (2012)PLEEE81539-375510.1103/PhysRevE.85.026301], we derive a dispersion relation for the three-dimensional MAC waves, generalizing previous ones including that of f-plane MHD "shallow water" waves [Schecter et al., Astrophys. J. 551, L185 (2001)AJLEEY0004-637X10.1086/320027]. A solution for the Fourier amplitude of perturbation fields (velocity, magnetic field, and density) is derived analytically considering a diffusive fluid for which both the magnetic and thermal Prandtl numbers are one. The radial spectrum of kinetic, S_{κ}(k,t), magnetic, S_{m}(k,t), and potential, S_{p}(k,t), energies is determined considering initial isotropic conditions. For magnetic Coriolis (MC) weak wave turbulence, it is shown that, at large scales such that V_{A}k/f≪1, the Alfvén ratio S_{κ}(k,t)/S_{m}(k,t) behaves like k^{-2} if the rotation axis is aligned with the magnetic field, in agreement with previous direct numerical simulations [Favier et al., Geophys. Astrophys. Fluid Dyn. (2012)] and like k^{-1} if the rotation axis is perpendicular to the magnetic field. At small scales, such that V_{A}k/f≫1, there is an equipartition of energy between magnetic and kinetic components. For magnetic Archimedes weak wave turbulence, it is demonstrated that, at large scales, such that (V_{A}k/N≪1), there is an equipartition of energy between magnetic and potential components

  18. Small-scale dynamo action during the formation of the first stars and galaxies. I. The ideal MHD limit

    NARCIS (Netherlands)

    Schleicher, D. R. G.; Banerjee, R.; Sur, S.; Arshakian, T. G.; Klessen, R. S.; Beck, R.; Spaans, M.

    We explore the amplification of magnetic seeds during the formation of the first stars and galaxies. During gravitational collapse, turbulence is created from accretion shocks, which may act to amplify weak magnetic fields in the protostellar cloud. Numerical simulations showed that such turbulence

  19. Tearing mode growth in a regime of weak magnetic shear

    International Nuclear Information System (INIS)

    Riyopoulos, S.; Hazeltine, R.D.

    1987-06-01

    The nonlinear growth for the m/n ≥ 2 resistive tearing mode is studied in case when the rational surface q(r 0 ) = m/n falls in a regime of weak magnetic shear, q'(r 0 ) ≅ 0. The island width is determined self-consistently from the nonlinear, zero-helicity component of the perturbed magnetic flux that provides the local shear. It is found that the magnetic perturbation keeps growing exponentially in the nonlinear regime on a hybrid resistive-Alfvenic time scale, while the island width and the vorticity grow on a much slower time scale. Accordingly, much faster release of magnetic energy results for modes growing near minima of hollow q profiles

  20. Thomson scattering in magnetic fields. [of white dwarf stars

    Science.gov (United States)

    Whitney, Barbara

    1989-01-01

    The equation of transfer in Thomson scattering atmospheres with magnetic fields is solved using Monte Carlo methods. Two cases, a plane parallel atmosphere with a magnetic field perpendicular to the atmosphere, and a dipole star, are investigated. The wavelength dependence of polarization from plane-parallel atmosphere is qualitatively similar to that observed in the magnetic white dwarf Grw+70 deg 8247, and the field strength determined by the calculation, 320 MG, is quantitatively similar to that determined from the line spectrum. The dipole model does not resemble the data as well as the single plane-parallel atmosphere.

  1. Slowly braked, rotating neutron stars

    Science.gov (United States)

    Sato, H.

    1975-01-01

    A slowly braked, rotating neutron star is believed to be a star which rapidly rotates, has no nebula, is nonpulsing, and has a long initial braking time of ten thousand to a million years because of a low magnetic field. Such an object might be observable as an extended weak source of infrared or radio wave radiation due to the scattering of low-frequency strong-wave photons by accelerated electrons. If these objects exist abundantly in the Galaxy, they would act as sources of relatively low-energy cosmic rays. Pulsars (rapidly braked neutron stars) are shown to have difficulties in providing an adequate amount of cosmic-ray matter, making these new sources seem necessary. The possibility that the acceleration mechanism around a slowly braked star may be not a direct acceleration by the strong wave but an acceleration due to plasma turbulence excited by the strong wave is briefly explored. It is shown that white dwarfs may also be slowly braked stars with braking times longer than 3.15 million years.

  2. NICER observations of highly magnetized neutron stars: Initial results

    Science.gov (United States)

    Enoto, Teruaki; Arzoumanian, Zaven; Gendreau, Keith C.; Nynka, Melania; Kaspi, Victoria; Harding, Alice; Guver, Tolga; Lewandowska, Natalia; Majid, Walid; Ho, Wynn C. G.; NICER Team

    2018-01-01

    The Neutron star Interior Composition Explorer (NICER) was launched on June 3, 2017, and attached to the International Space Station. The large effective area of NICER in soft X-rays makes it a powerful tool not only for its primary science objective (diagnostics of the nuclear equation state) but also for studying neutron stars of various classes. As one of the NICER science working groups, the Magnetars and Magnetospheres (M&M) team coordinates monitoring and target of opportunity (ToO) observations of magnetized neutron stars, including magnetars, high-B pulsars, X-ray dim isolated neutron stars, and young rotation-powered pulsars. The M&M working group has performed simultaneous X-ray and radio observations of the Crab and Vela pulsars, ToO observations of the active anomalous X-ray pulsar 4U 0142+61, and a monitoring campaign for the transient magnetar SGR 0501+4516. Here we summarize the current status and initial results of the M&M group.

  3. Low energy constituent quark and pion effective couplings in a weak external magnetic field

    Science.gov (United States)

    Braghin, Fábio L.

    2018-03-01

    An effective model with pions and constituent quarks in the presence of a weak external background electromagnetic field is derived by starting from a dressed one gluon exchange quark-quark interaction. By applying the auxiliary field and background field methods, the structureless pion limit is considered to extract effective pion and constituent quark couplings in the presence of a weak magnetic field. The leading terms of a large quark and gluon masses expansion are obtained by resolving effective coupling constants which turn out to depend on a weak magnetic field. Two pion field definitions are considered for that. Several relations between the effective coupling constants and parameters can be derived exactly or in the limit of very large quark mass at zero and weak constant magnetic field. Among these ratios, the Gell-Mann-Oakes-Renner and the quark level Goldberger-Treiman relations are obtained. In addition to that, in the pion sector, the leading terms of Chiral Perturbation Theory coupled to the electromagnetic field are recovered. Some numerical estimates are provided for the effective coupling constants and parameters.

  4. Atmospheric mass-loss of extrasolar planets orbiting magnetically active host stars

    Science.gov (United States)

    Lalitha, Sairam; Schmitt, J. H. M. M.; Dash, Spandan

    2018-06-01

    Magnetic stellar activity of exoplanet hosts can lead to the production of large amounts of high-energy emission, which irradiates extrasolar planets, located in the immediate vicinity of such stars. This radiation is absorbed in the planets' upper atmospheres, which consequently heat up and evaporate, possibly leading to an irradiation-induced mass-loss. We present a study of the high-energy emission in the four magnetically active planet-bearing host stars, Kepler-63, Kepler-210, WASP-19, and HAT-P-11, based on new XMM-Newton observations. We find that the X-ray luminosities of these stars are rather high with orders of magnitude above the level of the active Sun. The total XUV irradiation of these planets is expected to be stronger than that of well-studied hot Jupiters. Using the estimated XUV luminosities as the energy input to the planetary atmospheres, we obtain upper limits for the total mass- loss in these hot Jupiters.

  5. Magnetic-field-dependent microwave absorption in HgSe in weak magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Veinger, A. I., E-mail: Anatoly.Veinger@mail.ioffe.ru; Tisnek, T. V.; Kochman, I. V. [Russian Academy of Sciences, Ioffe Physical–Technical Institute (Russian Federation); Okulov, V. I. [Russian Academy of Sciences, Ural Branch, Mikheev Institute of Metal Physics (Russian Federation)

    2017-02-15

    The low-temperature magnetoresistive effect in the semiconductor HgSe:Fe in weak magnetic fields at microwave frequencies is examined. The negative and positive components of magnetoabsorption based on the magnetoresistive effect in the degenerate conduction band are analyzed. The special features of experiments carried out in the investigated frequency range are noted. The momentum and electron-energy relaxation times are determined from the experimental field and temperature dependences.

  6. Thermal generation of the magnetic field in the surface layers of massive stars

    Science.gov (United States)

    Urpin, V.

    2017-11-01

    A new magnetic field-generation mechanism based on the Nernst effect is considered in hot massive stars. This mechanism can operate in the upper atmospheres of O and B stars where departures from the LTE form a region with the inverse temperature gradient.

  7. Do weak stationary magnetic fields affect the perceived astringency of red wine?

    Directory of Open Access Journals (Sweden)

    Stephen Wesley Rowcliffe

    2018-03-01

    Full Text Available To investigate claims that products containing weak stationary magnets can reduce the astringency of tannic red wine, a double- blind randomized trial was carried out, in which 96 paired tastings were conducted of magnetized and non-magnetized samples of a young Nebbiolo. The data showed no association between reported differences in astringency and actual difference in the magnetic treatments given to the wine (χ2=0.135, degrees of freedom=1, P=0.71. This study confirms an earlier work that magnets have no observable effect on red wine.

  8. Do weak stationary magnetic fields affect the perceived astringency of red wine?

    OpenAIRE

    Stephen Wesley Rowcliffe

    2018-01-01

    To investigate claims that products containing weak stationary magnets can reduce the astringency of tannic red wine, a double- blind randomized trial was carried out, in which 96 paired tastings were conducted of magnetized and non-magnetized samples of a young Nebbiolo. The data showed no association between reported differences in astringency and actual difference in the magnetic treatments given to the wine (χ2=0.135, degrees of freedom=1, P=0.71). This study confirms an earlier work that...

  9. The magnetic field of the B1/B2V star σ Lup

    NARCIS (Netherlands)

    Henrichs, H.F.; Kolenberg, K.; Plaggenborg, B.; Marsden, S.C.; Waite, I.A.; Wade, G.A.

    2011-01-01

    The ultraviolet stellar wind lines of the photometrically periodic variable early B-type star σ Lupi were found to behave very similarly to what has been observed in known magnetic B stars, although no periodicity could be determined. AAT spectropolarimetric measurements with SEMPOL were obtained.

  10. Accretion onto magnetized neutron stars: Normal mode analysis of the interchange instability at the magnetopause

    International Nuclear Information System (INIS)

    Arons, J.; Lea, S.M.

    1976-01-01

    We describe the results of a linearized hydromagnetic stability analysis of the magnetopause of an accreting neutron star. The magnetosphere is assumed to be slowly rotating, and the plasma just outside of the magnetopause is assumed to be weakly magnetized. The plasma layer is assumed to be bounded above by a shock wave, and to be thin compared with the radius of the magnetosphere. Under these circumstances, the growing modes are shown to be localized in the direction parallel to the zero-order magnetic field. The structure of the modes is still similar to the flute mode, however. The growth rate at each magnetic latitude is lambda given by γ 2 =g/sub n/kα/sub eff/(lambda) tanh [kz/sub s/(lambda)] where g/sub n/ is the magnitude of the gravitational acceleration normal to the surface, kapprox. =vertical-barmvertical-bar/R (lambda)cos lambda, vertical-barmvertical-bar is the azimuthal mode number, R (lambda) is the radius of the magnetosphere, z/sub s/ is the height of the shock above the magnetopause, and α/sub eff/(lambda) <1 is the effective Atwood number which embodies the stabilizing effects of favorable curvature and magnetic tension. We calculate α/sub eff/(lambda), and also discuss the stabilizing effects of viscosity and of aligned flow parallel to the magnetopause

  11. Using the Seismology of Non-magnetic Chemically Peculiar Stars as ...

    Indian Academy of Sciences (India)

    stars we can infer some constraints on those mixing processes. As pulsa- tions in the ... Finally, microscopic diffusion due to gravity and radiation pressure ... complications posed by the largely unknown strength and geometry of the magnetic.

  12. Reduction of weak interaction rates in neutron stars by nucleon spin fluctuations: Degenerate case

    International Nuclear Information System (INIS)

    Raffelt, G.; Strobel, T.

    1997-01-01

    Nucleon spin fluctuations in a dense medium reduce the open-quotes naiveclose quotes values of weak interaction rates (neutrino opacities, neutrino emissivities). We extend previous studies of this effect to the degenerate case which is appropriate for neutron stars a few ten seconds after formation. If neutron-neutron interactions by a one-pion exchange potential are the dominant cause of neutron spin fluctuations, a perturbative calculation of weak interaction rates is justified for T approx-lt 3m/(4πα π 2 )∼1MeV, where m is the neutron mass and α π ∼15 the pion fine-structure constant. At higher temperatures, the application of Landau close-quote s theory of Fermi liquids is no longer justified; i.e., the neutrons cannot be viewed as simple quasiparticles in any obvious sense. copyright 1997 The American Physical Society

  13. New color-magnetic defects in dense quark matter

    Science.gov (United States)

    Haber, Alexander; Schmitt, Andreas

    2018-06-01

    Color-flavor locked (CFL) quark matter expels color-magnetic fields due to the Meissner effect. One of these fields carries an admixture of the ordinary abelian magnetic field and therefore flux tubes may form if CFL matter is exposed to a magnetic field, possibly in the interior of neutron stars or in quark stars. We employ a Ginzburg–Landau approach for three massless quark flavors, which takes into account the multi-component nature of color superconductivity. Based on the weak-coupling expressions for the Ginzburg–Landau parameters, we identify the regime where CFL is a type-II color superconductor and compute the radial profiles of different color-magnetic flux tubes. Among the configurations without baryon circulation we find a new solution that is energetically preferred over the flux tubes previously discussed in the literature in the parameter regime relevant for compact stars. Within the same setup, we also find a new defect in the 2SC phase, namely magnetic domain walls, which emerge naturally from the previously studied flux tubes if a more general ansatz for the order parameter is used. Color-magnetic defects in the interior of compact stars allow for sustained deformations of the star, potentially strong enough to produce detectable gravitational waves.

  14. Monitoring and modelling of white dwarfs with extremely weak magnetic fields. WD 2047+372 and WD 2359-434

    Science.gov (United States)

    Landstreet, J. D.; Bagnulo, S.; Valyavin, G.; Valeev, A. F.

    2017-11-01

    Magnetic fields are detected in a few percent of white dwarfs. The number of such magnetic white dwarfs known is now some hundreds. Fields range in strength from a few kG to several hundred MG. Almost all the known magnetic white dwarfs have a mean field modulus ≥1 MG. We are trying to fill a major gap in observational knowledge at the low field limit (≤200 kG) using circular spectro-polarimetry. In this paper we report the discovery and monitoring of strong, periodic magnetic variability in two previously discovered "super-weak field" magnetic white dwarfs, WD 2047+372 and WD 2359-434. WD 2047+372 has a mean longitudinal field that reverses between about -12 and + 15 kG, with a period of 0.243 d, while its mean field modulus appears nearly constant at 60 kG. The observations can be interpreted in terms of a dipolar field tilted with respect to the stellar rotation axis. WD 2359-434 always shows a weak positive longitudinal field with values between about 0 and + 12 kG, varying only weakly with stellar rotation, while the mean field modulus varies between about 50 and 100 kG. The rotation period is found to be 0.112 d using the variable shape of the Hα line core, consistent with available photometry. The field of this star appears to be much more complex than a dipole, and is probably not axisymmetric. Available photometry shows that WD 2359-434 is a light variable with an amplitude of only 0.005 mag; our own photometry shows that if WD 2047+372 is photometrically variable, the amplitude is below about 0.01 mag. These are the first models for magnetic white dwarfs with fields below about 100 kG based on magnetic measurements through the full stellar rotation. They reveal two very different magnetic surface configurations, and that, contrary to simple ohmic decay theory, WD 2359-434 has a much more complex surface field than the much younger WD 2047+372. Based, in part, on observations collected at the European Organisation for Astronomical Research in the

  15. What is the magnetic Weak Gravity Conjecture for axions

    Energy Technology Data Exchange (ETDEWEB)

    Hebecker, Arthur; Henkenjohann, Philipp [Institute for Theoretical Physics, University of Heidelberg (Germany); Witkowski, Lukas T. [APC, Universite Paris 7, CNRS/IN2P3, CEA/IRFU, Obs. de Paris, Sorbonne Paris Cite, Paris (France)

    2017-03-15

    The electric Weak Gravity Conjecture demands that axions with large decay constant f couple to light instantons. The resulting large instantonic corrections pose problems for natural inflation. We explore an alternative argument based on the magnetic Weak Gravity Conjecture for axions, which we try to make more precise. Roughly speaking, it demands that the minimally charged string coupled to the dual 2-form-field exists in the effective theory. Most naively, such large-f strings curve space too much to exist as static solutions, thus ruling out large-f axions. More conservatively, one might allow non-static string solutions to play the role of the required charged objects. In this case, topological inflation would save the superplanckian axion. Furthermore, a large-f axion may appear in the low-energy effective theory based on two subplanckian axions in the UV. The resulting effective string is a composite object built from several elementary strings and domain walls. It may or may not satisfy the magnetic Weak Gravity Conjecture depending on how strictly the latter is interpreted and on the cosmological dynamics of this composite object, which remain to be fully understood. Finally, we recall that large-field brane inflation is naively possible in the codimension-one case. We show how string-theoretic back-reaction closes this apparent loophole of large-f (non-periodic) pseudo-axions. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Dynamos in asymptotic-giant-branch stars as the origin of magnetic fields shaping planetary nebulae.

    Science.gov (United States)

    Blackman, E G; Frank, A; Markiel, J A; Thomas, J H; Van Horn, H M

    2001-01-25

    Planetary nebulae are thought to be formed when a slow wind from the progenitor giant star is overtaken by a subsequent fast wind generated as the star enters its white dwarf stage. A shock forms near the boundary between the winds, creating the relatively dense shell characteristic of a planetary nebula. A spherically symmetric wind will produce a spherically symmetric shell, yet over half of known planetary nebulae are not spherical; rather, they are elliptical or bipolar in shape. A magnetic field could launch and collimate a bipolar outflow, but the origin of such a field has hitherto been unclear, and some previous work has even suggested that a field could not be generated. Here we show that an asymptotic-giant-branch (AGB) star can indeed generate a strong magnetic field, having as its origin a dynamo at the interface between the rapidly rotating core and the more slowly rotating envelope of the star. The fields are strong enough to shape the bipolar outflows that produce the observed bipolar planetary nebulae. Magnetic braking of the stellar core during this process may also explain the puzzlingly slow rotation of most white dwarf stars.

  17. CONNECTING FLARES AND TRANSIENT MASS-LOSS EVENTS IN MAGNETICALLY ACTIVE STARS

    Energy Technology Data Exchange (ETDEWEB)

    Osten, Rachel A. [Space Telescope Science Institute 3700 San Martin Drive, Baltimore, MD 21218 (United States); Wolk, Scott J., E-mail: osten@stsci.edu [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138 (United States)

    2015-08-10

    We explore the ramification of associating the energetics of extreme magnetic reconnection events with transient mass-loss in a stellar analogy with solar eruptive events. We establish energy partitions relative to the total bolometric radiated flare energy for different observed components of stellar flares and show that there is rough agreement for these values with solar flares. We apply an equipartition between the bolometric radiated flare energy and kinetic energy in an accompanying mass ejection, seen in solar eruptive events and expected from reconnection. This allows an integrated flare rate in a particular waveband to be used to estimate the amount of associated transient mass-loss. This approach is supported by a good correspondence between observational flare signatures on high flaring rate stars and the Sun, which suggests a common physical origin. If the frequent and extreme flares that young solar-like stars and low-mass stars experience are accompanied by transient mass-loss in the form of coronal mass ejections, then the cumulative effect of this mass-loss could be large. We find that for young solar-like stars and active M dwarfs, the total mass lost due to transient magnetic eruptions could have significant impacts on disk evolution, and thus planet formation, and also exoplanet habitability.

  18. Turbulence, transport and confinement: from tokamaks to star magnetism

    International Nuclear Information System (INIS)

    Strugarek, Antoine

    2012-01-01

    This thesis is part of the general study of self-organization in hot and magnetized plasmas. We focus our work on two specific objects: stars and tokamaks. We use first principle numerical simulations to study turbulence, transport and confinement in these plasmas. The first part of this thesis introduces the main characteristics of stellar and tokamak plasmas. The reasons for studying them together are properly detailed. The second part is focused on stellar aspects. We study the interactions between the 3D turbulent motions in the solar convection zone with an internal magnetic field in the tachocline (the transition region between the instable and stable zones in the Sun). The tachocline is a very thin layer (less than five percent of the solar radius) that acts as a transport barrier of angular momentum. We show that such an internal magnetic field is not likely to explain the observed thickness of the tachocline and we give some insights on how to find alternative mechanisms to constrain it. We also explore the effect of the environment of star on its structure. We develop a methodology to study the influence of stellar wind and of the magnetic coupling of a star with its orbiting planets. We use the same methodology to analyse the magnetic interaction between a stellar wind and a planetary magnetosphere that acts as a transport barrier of matter. Then, the third part is dedicated to fusion oriented research. We present a numerical investigation on the experimental mechanisms that lead to the development of transport barriers in the plasma. These barriers are particularly important for the design of high performance fusion devices. The creation of transport barriers is obtained in turbulent first principle simulations for the very first time. The collaboration between the two scientific teams lead to the results presented in the fourth part of this thesis. An original spectral method is developed to analyse the saturation of stellar convective dynamos and of

  19. Weak Hard X-Ray Emission from Broad Absorption Line Quasars: Evidence for Intrinsic X-Ray Weakness

    DEFF Research Database (Denmark)

    Luo, B.; Brandt, W. N.; Alexander, D. M.

    2014-01-01

    We report NuSTAR observations of a sample of six X-ray weak broad absorption line (BAL) quasars. These targets, at z = 0.148-1.223, are among the optically brightest and most luminous BAL quasars known at z 330 times weaker than...... expected for typical quasars. Our results from a pilot NuSTAR study of two low-redshift BAL quasars, a Chandra stacking analysis of a sample of high-redshift BAL quasars, and a NuSTAR spectral analysis of the local BAL quasar Mrk 231 have already suggested the existence of intrinsically X-ray weak BAL...... quasars, i.e., quasars not emitting X-rays at the level expected from their optical/UV emission. The aim of the current program is to extend the search for such extraordinary objects. Three of the six new targets are weakly detected by NuSTAR with ≲ 45 counts in the 3-24 keV band, and the other three...

  20. Zero Sound in Neutron Stars with Dense Quark Matter under Strong Magnetic Fields

    DEFF Research Database (Denmark)

    Kouvaris, Christoforos

    2009-01-01

    We study a neutron star with a quark matter core under extremely strong magnetic fields. We investigate the possibility of an Urca process as a mechanism for the cooling of such a star. We found that apart from very particular cases, the Urca process cannot occur. We also study the stability...

  1. Weak correction to the muon magnetic moment in a gauge model

    International Nuclear Information System (INIS)

    Darby, D.; Grammer, G. Jr.

    1976-01-01

    The weak correction, asub(μ)sup(W), to the anomalous magnetic moment of the muon is calculated in an SU(2) x U(1) x U(1) gauge model of weak and electromagnetic interactions. The Rsub(xi) gauge is used and Ward-Takahashi identities are utilized in eliminating all xi-dependence before the loop integration is performed. asub(μ)sup(W,expt) places no constraint on the mass of one of the neutral vector mesons, which may be arbitrarily small. (Auth.)

  2. Weak ferrimagnetism, compensation point and magnetization reversal in Ni(HCOO)2x2H2O

    International Nuclear Information System (INIS)

    Kageyama, H.; Khomskii, D.I.; Levitin, R.Z.; Vasiliev, A.N.

    2003-01-01

    Nickel (II) format dihydrate Ni(HCOO) 2 x2H 2 O shows peculiar magnetic response at T N =15.5 K. The magnitude of weak magnetic moment increases initially below T N , equals zero at T*=8.5 K and increases again at lowering temperature. The sign of low field magnetization at any given temperature is determined by the sample's magnetic prehistory and the signs are opposite to each other at T N . This behavior suggests that Ni(HCOO) 2 x2H 2 O is a weak ferrimagnet and T* is a compensation point

  3. Direct URCA-processes in neutron star quark core with strong magnetic field.

    Directory of Open Access Journals (Sweden)

    Belyaev Vasily

    2017-01-01

    In evaluations, the strength of magnetic field corresponds to the case, where the quarks of medium occupy a lot of Landau levels, while the electrons are in ground Landau level. The analytical dependence of neutrino emissivity on chemical potentials of quarks and electrons, temperature and magnetic field strength is obtained and briefly discussed. The result could be important in application to a massive strongly magnetized neutron star with quark core.

  4. MAGNETIC FIELD TOPOLOGY IN LOW-MASS STARS: SPECTROPOLARIMETRIC OBSERVATIONS OF M DWARFS

    International Nuclear Information System (INIS)

    Phan-Bao, Ngoc; Lim, Jeremy; Donati, Jean-Francois; Johns-Krull, Christopher M.; MartIn, Eduardo L.

    2009-01-01

    The magnetic field topology plays an important role in the understanding of stellar magnetic activity. While it is widely accepted that the dynamo action present in low-mass partially convective stars (e.g., the Sun) results in predominantly toroidal magnetic flux, the field topology in fully convective stars (masses below ∼0.35 M sun ) is still under debate. We report here our mapping of the magnetic field topology of the M4 dwarf G 164-31 (or Gl 490B), which is expected to be fully convective, based on time series data collected from 20 hr of observations spread over three successive nights with the ESPaDOnS spectropolarimeter. Our tomographic imaging technique applied to time series of rotationally modulated circularly polarized profiles reveals an axisymmetric large-scale poloidal magnetic field on the M4 dwarf. We then apply a synthetic spectrum fitting technique for measuring the average magnetic flux on the star. The flux measured in G 164-31 is |Bf| = 3.2 ± 0.4 kG, which is significantly greater than the average value of 0.68 kG determined from the imaging technique. The difference indicates that a significant fraction of the stellar magnetic energy is stored in small-scale structures at the surface of G 164-31. Our Hα emission light curve shows evidence for rotational modulation suggesting the presence of localized structure in the chromosphere of this M dwarf. The radius of the M4 dwarf derived from the rotational period and the projected equatorial velocity is at least 30% larger than that predicted from theoretical models. We argue that this discrepancy is likely primarily due to the young nature of G 164-31 rather than primarily due to magnetic field effects, indicating that age is an important factor which should be considered in the interpretation of this observational result. We also report here our polarimetric observations of five other M dwarfs with spectral types from M0 to M4.5, three of them showing strong Zeeman signatures.

  5. Dirac’s magnetic monopole and the Kontsevich star product

    Science.gov (United States)

    Soloviev, M. A.

    2018-03-01

    We examine relationships between various quantization schemes for an electrically charged particle in the field of a magnetic monopole. Quantization maps are defined in invariant geometrical terms, appropriate to the case of nontrivial topology, and are constructed for two operator representations. In the first setting, the quantum operators act on the Hilbert space of sections of a nontrivial complex line bundle associated with the Hopf bundle, whereas the second approach uses instead a quaternionic Hilbert module of sections of a trivial quaternionic line bundle. We show that these two quantizations are naturally related by a bundle morphism and, as a consequence, induce the same phase-space star product. We obtain explicit expressions for the integral kernels of star-products corresponding to various operator orderings and calculate their asymptotic expansions up to the third order in the Planck constant \\hbar . We also show that the differential form of the magnetic Weyl product corresponding to the symmetric ordering agrees completely with the Kontsevich formula for deformation quantization of Poisson structures and can be represented by Kontsevich’s graphs.

  6. General Relativistic Radiation MHD Simulations of Supercritical Accretion onto a Magnetized Neutron Star: Modeling of Ultraluminous X-Ray Pulsars

    Energy Technology Data Exchange (ETDEWEB)

    Takahashi, Hiroyuki R. [Center for Computational Astrophysics, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Mitaka, Tokyo 181-8588 (Japan); Ohsuga, Ken, E-mail: takahashi@cfca.jp, E-mail: ken.ohsuga@nao.ac.jp [Division of Theoretical Astronomy, National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Mitaka, Tokyo 181-8588 (Japan)

    2017-08-10

    By performing 2.5-dimensional general relativistic radiation magnetohydrodynamic simulations, we demonstrate supercritical accretion onto a non-rotating, magnetized neutron star, where the magnetic field strength of dipole fields is 10{sup 10} G on the star surface. We found the supercritical accretion flow consists of two parts: the accretion columns and the truncated accretion disk. The supercritical accretion disk, which appears far from the neutron star, is truncated at around ≃3 R {sub *} ( R {sub *} = 10{sup 6} cm is the neutron star radius), where the magnetic pressure via the dipole magnetic fields balances with the radiation pressure of the disks. The angular momentum of the disk around the truncation radius is effectively transported inward through magnetic torque by dipole fields, inducing the spin up of a neutron star. The evaluated spin-up rate, ∼−10{sup −11} s s{sup −1}, is consistent with the recent observations of the ultraluminous X-ray pulsars. Within the truncation radius, the gas falls onto a neutron star along the dipole fields, which results in a formation of accretion columns onto the northern and southern hemispheres. The net accretion rate and the luminosity of the column are ≃66 L {sub Edd}/ c {sup 2} and ≲10 L {sub Edd}, where L {sub Edd} is the Eddington luminosity and c is the light speed. Our simulations support a hypothesis whereby the ultraluminous X-ray pulsars are powered by the supercritical accretion onto the magnetized neutron stars.

  7. Impact of the uncertainty in α-captures on {sup 22}Ne on the weak s-process in massive stars

    Energy Technology Data Exchange (ETDEWEB)

    Nishimura, N. [Astrophysics group, EPSAM, Keele University, Keele, ST5 1BH, UK and NuGrid Project (United Kingdom); Hirschi, R. [Astrophysics group, EPSAM, Keele University, Keele, ST5 1BH, UK and Kavli IPMU (WPI), University of Tokyo, Kashiwa, 277-8583 (Japan); Pignatari, M. [NuGrid Project and Department of Physics, University of Basel, Basel, CH-4056 (Switzerland); Herwig, F. [NuGrid Project and Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P5C2 (Canada); Beard, M. [NuGrid Project and Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States); Imbriani, G. [Dipartiment di Scienze Fisiche, Universita di Napoli Federico II, Napoli (Italy); Görres, J.; Boer, R. J. de; Wiescher, M. [Department of Physics, University of Notre Dame, Notre Dame, IN 46556 (United States)

    2014-05-02

    Massive stars at solar metallicity contribute to the production of heavy elements with atomic masses between A = 60 and A = 90 via the so-called weak s-process (which takes place during core He and shell C burning phases). Furthermore, recent studies have shown that rotation boosts the s-process production in massive stars at low metallicities, with a production that may reach the barium neutron-magic peak. These results are very sensitive to neutron source and neutron poison reaction rates. For the weak s-process, the main neutron source is the reaction {sup 22}Ne(α,n){sup 25}Mg, which is in competition with {sup 22}Ne(α,γ){sup 26}Mg. The uncertainty of both rates strongly affects the nucleosynthesis predictions from stellar model calculations. In this study, we investigate the impact of the uncertainty in α-captures on {sup 22}Ne on the s-process nucleosynthesis in massive stars both at solar and at very low metallicity. For this purpose, we post-process, with the Nugrid mppnp code, non-rotating and rotating evolutionary models 25M{sub ⊙} stars at two different metallicities: Z = Z{sub ⊙} and Z = 10{sup −5}Z{sub ⊙}, respectively. Our results show that uncertainty of {sup 22}Ne(α,n){sup 25}Mg and {sup 22}Ne(α,γ){sup 26}Mg rates have a significant impact on the final elemental production especially for metal poor rotating models. Beside uncertainties in the neutron source reactions, for fast rotating massive stars at low metallicity we revisit the impact of the neutron poisoning effect by the reaction chain {sup 16}O(n,γ){sup 17}O(α,γ){sup 21}Ne, in competition with the {sup 17}O(α,n){sup 20}Ne, recycling the neutrons captured by {sup 16}O.

  8. Magnetic field strength of a neutron-star-powered ultraluminous X-ray source

    Science.gov (United States)

    Brightman, M.; Harrison, F. A.; Fürst, F.; Middleton, M. J.; Walton, D. J.; Stern, D.; Fabian, A. C.; Heida, M.; Barret, D.; Bachetti, M.

    2018-04-01

    Ultraluminous X-ray sources (ULXs) are bright X-ray sources in nearby galaxies not associated with the central supermassive black hole. Their luminosities imply they are powered by either an extreme accretion rate onto a compact stellar remnant, or an intermediate mass ( 100-105M⊙) black hole1. Recently detected coherent pulsations coming from three bright ULXs2-5 demonstrate that some of these sources are powered by accretion onto a neutron star, implying accretion rates significantly in excess of the Eddington limit, a high degree of geometric beaming, or both. The physical challenges associated with the high implied accretion rates can be mitigated if the neutron star surface field is very high (1014 G)6, since this suppresses the electron scattering cross-section, reducing the radiation pressure that chokes off accretion for high luminosities. Surface magnetic field strengths can be determined through cyclotron resonance scattering features7,8 produced by the transition of charged particles between quantized Landau levels. Here, we present the detection at a significance of 3.8σ of an absorption line at 4.5 keV in the Chandra spectrum of a ULX in M51. This feature is likely to be a cyclotron resonance scattering feature produced by the strong magnetic field of a neutron star. Assuming scattering off electrons, the magnetic field strength is implied to be 1011 G, while protons would imply a magnetic field of B 1015 G.

  9. Feedback first: the surprisingly weak effects of magnetic fields, viscosity, conduction and metal diffusion on sub-L* galaxy formation

    Science.gov (United States)

    Su, Kung-Yi; Hopkins, Philip F.; Hayward, Christopher C.; Faucher-Giguère, Claude-André; Kereš, Dušan; Ma, Xiangcheng; Robles, Victor H.

    2017-10-01

    Using high-resolution simulations with explicit treatment of stellar feedback physics based on the FIRE (Feedback In Realistic Environments) project, we study how galaxy formation and the interstellar medium (ISM) are affected by magnetic fields, anisotropic Spitzer-Braginskii conduction and viscosity, and sub-grid metal diffusion from unresolved turbulence. We consider controlled simulations of isolated (non-cosmological) galaxies but also a limited set of cosmological 'zoom-in' simulations. Although simulations have shown significant effects from these physics with weak or absent stellar feedback, the effects are much weaker than those of stellar feedback when the latter is modelled explicitly. The additional physics have no systematic effect on galactic star formation rates (SFRs). In contrast, removing stellar feedback leads to SFRs being overpredicted by factors of ˜10-100. Without feedback, neither galactic winds nor volume-filling hot-phase gas exist, and discs tend to runaway collapse to ultra-thin scaleheights with unphysically dense clumps congregating at the galactic centre. With stellar feedback, a multi-phase, turbulent medium with galactic fountains and winds is established. At currently achievable resolutions and for the investigated halo mass range 1010-1013 M⊙, the additional physics investigated here (magnetohydrodynamic, conduction, viscosity, metal diffusion) have only weak (˜10 per cent-level) effects on regulating SFR and altering the balance of phases, outflows or the energy in ISM turbulence, consistent with simple equipartition arguments. We conclude that galactic star formation and the ISM are primarily governed by a combination of turbulence, gravitational instabilities and feedback. We add the caveat that active galactic nucleus feedback is not included in the present work.

  10. Searching for magnetic fields in 11 Wolf-Rayet stars: Analysis of circular polarization measurements from ESPaDOnS

    Energy Technology Data Exchange (ETDEWEB)

    De la Chevrotière, A.; St-Louis, N.; Moffat, A. F. J. [Centre de Recherche en Astrophysique du Québec (CRAQ), Département de physique, Université de Montréal, C.P. 6128, Succ. Centre-ville, Montréal, Québec H3C 3J7 (Canada); Collaboration: MiMeS Collaboration

    2014-02-01

    With recent detections of magnetic fields in some of their progenitor O stars, combined with known strong fields in their possible descendant neutron stars, it is natural to search for magnetic fields in Wolf-Rayet (WR) stars, despite the problems associated with the presence of winds enhanced by an order of magnitude over those of O stars. We continue our search among a sample of 11 bright WR stars following our introductory study in a previous paper of WR6 = EZ CMa using the spectropolarimeter ESPaDOnS at Canada-France-Hawaii Telescope, most of them in all four Stokes parameters. This sample includes six WN stars and five WC stars encompassing a range of spectral subclasses. Six are medium/long-period binaries and three show corotating interaction regions. We report no definite detections of a magnetic field in the winds in which the lines form (which is about the same distance from the center of the star as it is from the surface of the progenitor O star) for any of the eleven stars. Possible reasons and their implications are discussed. Nonetheless, the data show evidence supporting marginal detections for WR134, WR137, and WR138. According to the Bayesian analysis, the most probable field intensities are B {sub wind} ∼ 200, 130, and 80 G, respectively, with a 95.4% probability that the magnetic fields present in the observable parts of their stellar wind, if stronger, does not exceed B{sub wind}{sup max}∼1900 G, ∼1500 G, and ∼1500 G, respectively. In the case of non-detections, we report an average field strength upper limit of B{sub wind}{sup max}∼500 G.

  11. Massive-Star Magnetospheres: Now in 3-D!

    Science.gov (United States)

    Townsend, Richard

    Magnetic fields are unexpected in massive stars, due to the absence of a dynamo convection zone beneath their surface layers. Nevertheless, kilogauss-strength, ordered fields were detected in a small subset of these stars over three decades ago, and the intervening years have witnessed the steady expansion of this subset. A distinctive feature of magnetic massive stars is that they harbor magnetospheres --- circumstellar environments where the magnetic field interacts strongly with the star's radiation-driven wind, confining it and channelling it into energetic shocks. A wide range of observational signatures are associated with these magnetospheres, in diagnostics ranging from X-rays all the way through to radio emission. Moreover, these magnetospheres can play an important role in massive-star evolution, by amplifying angular momentum loss in the wind. Recent progress in understanding massive-star magnetospheres has largely been driven by magnetohydrodynamical (MHD) simulations. However, these have been restricted to two- dimensional axisymmetric configurations, with three-dimensional configurations possible only in certain special cases. These restrictions are limiting further progress; we therefore propose to develop completely general three-dimensional models for the magnetospheres of massive stars, on the one hand to understand their observational properties and exploit them as plasma-physics laboratories, and on the other to gain a comprehensive understanding of how they influence the evolution of their host star. For weak- and intermediate-field stars, the models will be based on 3-D MHD simulations using a modified version of the ZEUS-MP code. For strong-field stars, we will extend our existing Rigid Field Hydrodynamics (RFHD) code to handle completely arbitrary field topologies. To explore a putative 'photoionization-moderated mass loss' mechanism for massive-star magnetospheres, we will also further develop a photoionization code we have recently

  12. Helium-burning flashes on accreting neutron stars: effects of stellar mass, radius, and magnetic field

    International Nuclear Information System (INIS)

    Joss, P.C.; Li, F.K.

    1980-01-01

    We have computed the evolution of the helium-burning shell in an accreting neutron star for various values of the stellar mass (M), radius (R), and surface magnetic fields strength (B). As shown in previous work, the helium-burning shell is often unstable and undergoes thermonuclear flashes that result in the emission of X-ray bursts from the neutron-star surface. The dependence of the properties of these bursts upon the values of M and R can be described by simple scaling relations. A strong magnetic field decreases the radiative and conductive opacities and inhibits convection in the neutron-star surface layers. For B 12 gauss, these effects are unimportant; for B> or approx. =10 13 gauss, the enhancement of the electron thermal conductivity is sufficiently large to stabilize the helium-burning shell against thermonuclear flashes. For intermediate values of B, the reduced opacities increase the recurrence intervals between bursts and the energy released per burst, while the inhibition of convection increases the burst rise times to about a few seconds. If the magnetic field funnels the accreting matter onto the magnetic polar caps, the instability of the helium-burning shell will be very strongly suppressed. These results suggest that it may eventually be possible to extract information on the macroscopic properties of neutron stars from the observed features of X-ray burst sources

  13. Magnetic properties of neutron-star matter

    International Nuclear Information System (INIS)

    Chao, N.C.

    1975-01-01

    An array of qualitative and quantitative evidence is presented to the effect that neutron-star matter in its ground state is antiferromagnetic rather than ferromagnetic. The energy of pure neutron matter is evaluated as a function of spin polarization by a two-body Jastrow procedure, for densities up to five times that of ordinary nuclear matter. The anti-ferromagnetic state is energetically preferred to states with non-zero spin polarization, and lies considerably lower in energy than the ferromagnetic state. The magnetic susceptibility of the material is calculated as a function of density in the same approximation, with results which are in good agreement with independent estimates [pt

  14. Magnetic properties of neutron-star matter

    Energy Technology Data Exchange (ETDEWEB)

    Chao, N C [PERNAMBUCO UNIV., RECIFE (BRAZIL). INSTITUTO DE FISICA; CLARK, J W [WASHINGTON UNIV., ST. LOUIS, MO. (USA)

    1975-08-01

    An array of qualitative and quantitative evidence is presented to the effect that neutron-star matter in its ground state is antiferromagnetic rather than ferromagnetic. The energy of pure neutron matter is evaluated as a function of spin polarization by a two-body Jastrow procedure, for densities up to five times that of ordinary nuclear matter. The anti-ferromagnetic state is energetically preferred to states with non-zero spin polarization, and lies considerably lower in energy than the ferromagnetic state. The magnetic susceptibility of the material is calculated as a function of density in the same approximation, with results which are in good agreement with independent estimates.

  15. Magnetic cycles and rotation periods of late-type stars from photometric time series

    Science.gov (United States)

    Suárez Mascareño, A.; Rebolo, R.; González Hernández, J. I.

    2016-10-01

    Aims: We investigate the photometric modulation induced by magnetic activity cycles and study the relationship between rotation period and activity cycle(s) in late-type (FGKM) stars. Methods: We analysed light curves, spanning up to nine years, of 125 nearby stars provided by the All Sky Automated Survey (ASAS). The sample is mainly composed of low-activity, main-sequence late-A to mid-M-type stars. We performed a search for short (days) and long-term (years) periodic variations in the photometry. We modelled the light curves with combinations of sinusoids to measure the properties of these periodic signals. To provide a better statistical interpretation of our results, we complement our new results with results from previous similar works. Results: We have been able to measure long-term photometric cycles of 47 stars, out of which 39 have been derived with false alarm probabilities (FAP) of less than 0.1 per cent. Rotational modulation was also detected and rotational periods were measured in 36 stars. For 28 stars we have simultaneous measurements of activity cycles and rotational periods, 17 of which are M-type stars. We measured both photometric amplitudes and periods from sinusoidal fits. The measured cycle periods range from 2 to 14 yr with photometric amplitudes in the range of 5-20 mmag. We found that the distribution of cycle lengths for the different spectral types is similar, as the mean cycle is 9.5 yr for F-type stars, 6.7 yr for G-type stars, 8.5 yr for K-type stars, 6.0 yr for early M-type stars, and 7.1 yr for mid-M-type stars. On the other hand, the distribution of rotation periods is completely different, trending to longer periods for later type stars, from a mean rotation of 8.6 days for F-type stars to 85.4 days in mid-M-type stars. The amplitudes induced by magnetic cycles and rotation show a clear correlation. A trend of photometric amplitudes with rotation period is also outlined in the data. The amplitudes of the photometric variability

  16. Discovery of a magnetic field in the δ Scuti F2m star ρ Pup

    Science.gov (United States)

    Neiner, C.; Wade, G. A.; Sikora, J.

    2017-06-01

    ρ Pup is a δ Scuti F2 pulsator, known to host a main radial mode as well as non-radial pulsations, with chemical peculiarities typical of evolved Am stars. We present a high-precision spectropolarimetric observations of this star, obtained with ESPaDOnS at the Canada-France-Hawaii Telescope in the frame of the BRITE spectropolarimetric survey. A magnetic field is clearly detected in ρ Pup, with a longitudinal field strength below 1 G. This makes ρ Pup the second known magnetic δ Scuti discovered, after HD 188774, and a possible cool evolved counterpart of the recently discovered ultraweakly magnetic Am family.

  17. Coordinated NuSTAR and Swift observations of SU Lyncis: a hard X-ray bright symbiotic star with weak optical signatures

    Science.gov (United States)

    Lopes de Oliveira, Raimundo; Mukai, Koji; Luna, Gerardo Juan Manuel; Sokoloski, Jennifer; Nelson, Thomas; Lucy, Adrian B.

    2018-01-01

    The variable M giant SU Lyncis was recently identified as the optical counterpart of a hard, thermal X-ray source. Also considering the fact that the star displays weak high-excitation emission, it was classified as a symbiotic system purely powered by accretion without accompanying nuclear fusion. This discovery revealed the existence of a subclass of symbiotics which is "invisible" to optical surveys and thus underestimated since these surveys favour the identification of systems with more intense emission lines that arise when shell-burning is present. At the same time, this discovery opens up a new window to investigate accretion and evolution of symbiotic systems. Here we report on the X-ray and UV properties of SU Lyncis derived from simultaneous NuSTAR and Swift observations. The investigation is focused on the strong photometric variability in UV and on the X-ray spectral characterization, which is associated with a hot thermal plasma with sub-solar abundance and suffering the effects of a relatively dense local absorber. The results are discussed in the context of the accretion geometry and mass of the white dwarf, and the imposed limits to the reflection fraction.

  18. Magnetized hypermassive neutron-star collapse: a central engine for short gamma-ray bursts.

    Science.gov (United States)

    Shibata, Masaru; Duez, Matthew D; Liu, Yuk Tung; Shapiro, Stuart L; Stephens, Branson C

    2006-01-27

    A hypermassive neutron star (HMNS) is a possible transient formed after the merger of a neutron-star binary. In the latest axisymmetric magnetohydrodynamic simulations in full general relativity, we find that a magnetized HMNS undergoes "delayed" collapse to a rotating black hole (BH) as a result of angular momentum transport via magnetic braking and the magnetorotational instability. The outcome is a BH surrounded by a massive, hot torus with a collimated magnetic field. The torus accretes onto the BH at a quasisteady accretion rate [FORMULA: SEE TEXT]; the lifetime of the torus is approximately 10 ms. The torus has a temperature [FORMULA: SEE TEXT], leading to copious ([FORMULA: SEE TEXT]) thermal radiation that could trigger a fireball. Therefore, the collapse of a HMNS is a promising scenario for generating short-duration gamma-ray bursts and an accompanying burst of gravitational waves and neutrinos.

  19. Period04 FCAPT uvby Photometric Studies of Eight Magnetic CP Stars

    Science.gov (United States)

    Adelman, Saul J.; Dukes, Robert J.

    2014-06-01

    We present Four College Automated Photometric Telescope (FCAPT) differential Stromgren uvby photometry of 8 magnetic CP (mCP) stars: HD 5797 (V551 Cas), HD 26792 (DH Cam), HD 27309 (56 Tau, V724 Tau), HD 49713 (V740 Mon), HD 74521 (49 Cnc, BI Cnc), HD 120198 (84 UMa, CR UMa), HD 171263 (QU Ser), and HD 215441 (GL Lac, Babcock's star). Our data sets are larger than those of most mCP stars in the literature. These are the first FCAPT observations of HD 5797, HD 26792, HD 49713, and HD 171263. Those for the remaining four stars substantially extend published FCAPT data. The FCAPT observed some stars for a longer time range and with greater accuracy than other optical region automated photometric telescopes.Our goals were to determine very accurate periods, the u, v, b, and y amplitudes, and if there were any long period periods. In addition we wanted to compare our results with those of magnetic field measurements to help interpret the light curves.We used the Period04 computer program to analyze the light curves. This program provides errors for the derived quantities as it fits the light curve. Our derived periods of 68.046 +/- 0.008 days for HD 5797, 3.80205 +/- 0.00006 days for HD 26792, 1.56889 +/- 0.000002 days for HD 27309, 2.13536 +/- 0.00002 days for HD 49713, 7.0505 +/- 0.0001 days for HD 74521, 1.38577 +/- 0.000004 days for HD 120198, 3.9974 +/- 0.0001days for HD 171263, and 9.487792 +/- 0.00005 days for HD 215441 are refinements of the best determinations in the literature.

  20. MAGNETIC ACTIVITY CYCLES IN THE EXOPLANET HOST STAR ε ERIDANI

    International Nuclear Information System (INIS)

    Metcalfe, T. S.; Mathur, S.; Buccino, A. P.; Mauas, P. J. D.; Petrucci, R.; Brown, B. P.; Soderblom, D. R.; Henry, T. J.; Hall, J. C.; Basu, S.

    2013-01-01

    The active K2 dwarf ε Eri has been extensively characterized both as a young solar analog and more recently as an exoplanet host star. As one of the nearest and brightest stars in the sky, it provides an unparalleled opportunity to constrain stellar dynamo theory beyond the Sun. We confirm and document the 3-year magnetic activity cycle in ε Eri originally reported by Hatzes and coworkers, and we examine the archival data from previous observations spanning 45 years. The data show coexisting 3-year and 13-year periods leading into a broad activity minimum that resembles a Maunder minimum-like state, followed by the resurgence of a coherent 3-year cycle. The nearly continuous activity record suggests the simultaneous operation of two stellar dynamos with cycle periods of 2.95 ± 0.03 years and 12.7 ± 0.3 years, which, by analogy with the solar case, suggests a revised identification of the dynamo mechanisms that are responsible for the so-called 'active' and 'inactive' sequences as proposed by Böhm-Vitense. Finally, based on the observed properties of ε Eri, we argue that the rotational history of the Sun is what makes it an outlier in the context of magnetic cycles observed in other stars (as also suggested by its Li depletion), and that a Jovian-mass companion cannot be the universal explanation for the solar peculiarities.

  1. Flare stars

    International Nuclear Information System (INIS)

    Nicastro, A.J.

    1981-01-01

    The least massive, but possibly most numerous, stars in a galaxy are the dwarf M stars. It has been observed that some of these dwarfs are characterized by a short increase in brightness. These stars are called flare stars. These flare stars release a lot of energy in a short amount of time. The process producing the eruption must be energetic. The increase in light intensity can be explained by a small area rising to a much higher temperature. Solar flares are looked at to help understand the phenomenon of stellar flares. Dwarfs that flare are observed to have strong magnetic fields. Those dwarf without the strong magnetic field do not seem to flare. It is believed that these regions of strong magnetic fields are associated with star spots. Theories on the energy that power the flares are given. Astrophysicists theorize that the driving force of a stellar flare is the detachment and collapse of a loop of magnetic flux. The mass loss due to stellar flares is discussed. It is believed that stellar flares are a significant contributor to the mass of interstellar medium in the Milky Way

  2. Kinetic electromagnetic instabilities in an ITB plasma with weak magnetic shear

    Science.gov (United States)

    Chen, W.; Yu, D. L.; Ma, R. R.; Shi, P. W.; Li, Y. Y.; Shi, Z. B.; Du, H. R.; Ji, X. Q.; Jiang, M.; Yu, L. M.; Yuan, B. S.; Li, Y. G.; Yang, Z. C.; Zhong, W. L.; Qiu, Z. Y.; Ding, X. T.; Dong, J. Q.; Wang, Z. X.; Wei, H. L.; Cao, J. Y.; Song, S. D.; Song, X. M.; Liu, Yi.; Yang, Q. W.; Xu, M.; Duan, X. R.

    2018-05-01

    Kinetic Alfvén and pressure gradient driven instabilities are very common in magnetized plasmas, both in space and the laboratory. These instabilities will be easily excited by energetic particles (EPs) and/or pressure gradients in present-day fusion and future burning plasmas. This will not only cause the loss and redistribution of the EPs, but also affect plasma confinement and transport. Alfvénic ion temperature gradient (AITG) instabilities with the frequency ω_BAE<ω<ω_TAE and the toroidal mode numbers n=2{-}8 are found to be unstable in NBI internal transport barrier plasmas with weak shear and low pressure gradients, where ω_BAE and ω_TAE are the frequencies of the beta- and toroidicity-induced Alfvén eigenmodes, respectively. The measured results are consistent with the general fishbone-like dispersion relation and kinetic ballooning mode equation, and the modes become more unstable the smaller the magnetic shear is in low pressure gradient regions. The interaction between AITG activity and EPs also needs to be investigated with greater attention in fusion plasmas, such as ITER (Tomabechi and The ITER Team 1991 Nucl. Fusion 31 1135), since these fluctuations can be enhanced by weak magnetic shear and EPs.

  3. Theoretical models of highly magnetic white dwarf stars that violate the Chandrasekhar Limit

    Science.gov (United States)

    Shah, Hridaya

    2017-08-01

    Until recently, white dwarf (WD) stars were believed to be no more massive than 1.44 solar masses (M ⊙ ). This belief has been changed now with the observations of over-luminous or 'peculiar' Type la supernovae that have lead researchers to hypothesize the existence of WDs in the mass range 2.4 - 2.8 M ⊙ . This discovery also raises some doubt over the reliability of the Type Ia supernova as a standard candle. It is thought that these super-massive WDs are their most likely progenitors and that they probably have a very strong magnetic field inside them. A degenerate electron gas in a magnetic field, such as that present inside this star, will be Landau quantized. Magnetic field changes the momentum space of electrons which in turn changes their density of states (DOS) and that in turn changes the equation of state (EoS) of matter inside the star, as opposed to that without a field. When this change in the DOS is taken into account and a link between the DOS and the EoS is established, as is done in this work, I find a physical reason behind the theoretical mass-radius (M-R) relations of a super-massive WD. I start with different equations of state with at most three Landau levels occupied and then construct stellar models of magnetic WDs (MWDs) using the same. I also show the M-R relations of these stars for a particular chosen value of maximum electron Fermi energy. Once a multiple Landau level system of electrons is considered, I find that it leads to such an EoS that gives multiple branches in the MR relations. Super-massive MWDs are obtained only when the Landau level occupancy is limited to just one level and some of the mass values fall within the mass range given above.

  4. A Method to Measure the Transverse Magnetic Field and Orient the Rotational Axis of Stars

    Energy Technology Data Exchange (ETDEWEB)

    Leone, Francesco; Scalia, Cesare; Gangi, Manuele; Giarrusso, Marina [Università di Catania, Dipartimento di Fisica e Astronomia, Sezione Astrofisica, Via S. Sofia 78, I-95123 Catania (Italy); Munari, Matteo; Scuderi, Salvatore; Trigilio, Corrado [INAF—Osservatorio Astrofisico di Catania, Via S. Sofia 78, I-95123 Catania (Italy); Stift, Martin J. [Armagh Observatory, College Hill, Armagh BT61 9DG. Northern Ireland (United Kingdom)

    2017-10-20

    Direct measurements of stellar magnetic fields are based on the splitting of spectral lines into polarized Zeeman components. With a few exceptions, Zeeman signatures are hidden in data noise, and a number of methods have been developed to measure the average, over the visible stellar disk, of longitudinal components of the magnetic field. At present, faint stars are only observable via low-resolution spectropolarimetry, which is a method based on the regression of the Stokes V signal against the first derivative of Stokes I . Here, we present an extension of this method to obtain a direct measurement of the transverse component of stellar magnetic fields by the regression of high-resolution Stokes Q and U as a function of the second derivative of Stokes I . We also show that it is possible to determine the orientation in the sky of the rotation axis of a star on the basis of the periodic variability of the transverse component due to its rotation. The method is applied to data, obtained with the Catania Astrophysical Observatory Spectropolarimeter along the rotational period of the well known magnetic star β CrB.

  5. EFFECTS OF FOSSIL MAGNETIC FIELDS ON CONVECTIVE CORE DYNAMOS IN A-TYPE STARS

    International Nuclear Information System (INIS)

    Featherstone, Nicholas A.; Toomre, Juri; Browning, Matthew K.; Brun, Allan Sacha

    2009-01-01

    The vigorous magnetic dynamo action achieved within the convective cores of A-type stars may be influenced by fossil magnetic fields within their radiative envelopes. We study such effects through three-dimensional simulations that model the inner 30% by radius of a 2 M sun A-type star, capturing the convective core and a portion of the overlying radiative envelope within our computational domain. We employ the three-dimensional anelastic spherical harmonic code to model turbulent dynamics within a deep rotating spherical shell. The interaction between a fossil field and the core dynamo is examined by introducing a large-scale magnetic field into the radiative envelope of a mature A star dynamo simulation. We find that the inclusion of a twisted toroidal fossil field can lead to a remarkable transition in the core dynamo behavior. Namely, a super-equipartition state can be realized in which the magnetic energy built by dynamo action is 10-fold greater than the kinetic energy of the convection itself. Such strong-field states may suggest that the resulting Lorentz forces should seek to quench the flows, yet we have achieved super-equipartition dynamo action that persists for multiple diffusion times. This is achieved by the relative co-alignment of the flows and magnetic fields in much of the domain, along with some lateral displacements of the fastest flows from the strongest fields. Convection in the presence of such strong magnetic fields typically manifests as 4-6 cylindrical rolls aligned with the rotation axis, each possessing central axial flows that imbue the rolls with a helical nature. The roll system also possesses core-crossing flows that couple distant regions of the core. We find that the magnetic fields exhibit a comparable global topology with broad, continuous swathes of magnetic field linking opposite sides of the convective core. We have explored several poloidal and toroidal fossil field geometries, finding that a poloidal component is essential

  6. Mottled Protoplanetary Disk Ionization by Magnetically Channeled T Tauri Star Energetic Particles

    Science.gov (United States)

    Fraschetti, F.; Drake, J. J.; Cohen, O.; Garraffo, C.

    2018-02-01

    The evolution of protoplanetary disks is believed to be driven largely by angular momentum transport resulting from magnetized disk winds and turbulent viscosity. The ionization of the disk that is essential for these processes has been thought to be due to host star coronal X-rays but could also arise from energetic particles produced by coronal flares, or traveling shock waves, and advected by the stellar wind. We have performed test-particle numerical simulations of energetic protons propagating into a realistic T Tauri stellar wind, including a superposed small-scale magnetostatic turbulence. The isotropic (Kolmogorov power spectrum) turbulent component is synthesized along the individual particle trajectories. We have investigated the energy range [0.1–10] GeV, consistent with expectations from Chandra X-ray observations of large flares on T Tauri stars and recent indications by the Herschel Space Observatory of a significant contribution of energetic particles to the disk ionization of young stars. In contrast with a previous theoretical study finding a dominance of energetic particles over X-rays in the ionization throughout the disk, we find that the disk ionization is likely dominated by X-rays over much of its area, except within narrow regions where particles are channeled onto the disk by the strongly tangled and turbulent magnetic field. The radial thickness of such regions is 5 stellar radii close to the star and broadens with increasing radial distance. This likely continues out to large distances from the star (10 au or greater), where particles can be copiously advected and diffused by the turbulent wind.

  7. MAGNETIC GAMES BETWEEN A PLANET AND ITS HOST STAR: THE KEY ROLE OF TOPOLOGY

    Energy Technology Data Exchange (ETDEWEB)

    Strugarek, A. [Département de physique, Université de Montréal, C.P. 6128 Succ. Centre-Ville, Montréal, QC H3C 3J7 (Canada); Brun, A. S.; Réville, V. [Laboratoire AIM Paris-Saclay, CEA/Irfu Université Paris-Diderot CNRS/INSU, F-91191 Gif-sur-Yvette (France); Matt, S. P., E-mail: strugarek@astro.umontreal.ca [Astrophysics group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)

    2015-12-20

    Magnetic interactions between a star and a close-in planet are postulated to be a source of enhanced emissions and to play a role in the secular evolution of the orbital system. Close-in planets generally orbit in the sub-alfvénic region of the stellar wind, which leads to efficient transfers of energy and angular momentum between the star and the planet. We model the magnetic interactions occurring in close-in star–planet systems with three-dimensional, global, compressible magnetohydrodynamic numerical simulations of a planet orbiting in a self-consistent stellar wind. We focus on the cases of magnetized planets and explore three representative magnetic configurations. The Poynting flux originating from the magnetic interactions is an energy source for enhanced emissions in star–planet systems. Our results suggest a simple geometrical explanation for ubiquitous on/off enhanced emissions associated with close-in planets, and confirm that the Poynting fluxes can reach powers of the order of 10{sup 19} W. Close-in planets are also shown to migrate due to magnetic torques for sufficiently strong stellar wind magnetic fields. The topology of the interaction significantly modifies the shape of the magnetic obstacle that leads to magnetic torques. As a consequence, the torques can vary by at least an order of magnitude as the magnetic topology of the interaction varies.

  8. MAGNETIC GAMES BETWEEN A PLANET AND ITS HOST STAR: THE KEY ROLE OF TOPOLOGY

    International Nuclear Information System (INIS)

    Strugarek, A.; Brun, A. S.; Réville, V.; Matt, S. P.

    2015-01-01

    Magnetic interactions between a star and a close-in planet are postulated to be a source of enhanced emissions and to play a role in the secular evolution of the orbital system. Close-in planets generally orbit in the sub-alfvénic region of the stellar wind, which leads to efficient transfers of energy and angular momentum between the star and the planet. We model the magnetic interactions occurring in close-in star–planet systems with three-dimensional, global, compressible magnetohydrodynamic numerical simulations of a planet orbiting in a self-consistent stellar wind. We focus on the cases of magnetized planets and explore three representative magnetic configurations. The Poynting flux originating from the magnetic interactions is an energy source for enhanced emissions in star–planet systems. Our results suggest a simple geometrical explanation for ubiquitous on/off enhanced emissions associated with close-in planets, and confirm that the Poynting fluxes can reach powers of the order of 10 19 W. Close-in planets are also shown to migrate due to magnetic torques for sufficiently strong stellar wind magnetic fields. The topology of the interaction significantly modifies the shape of the magnetic obstacle that leads to magnetic torques. As a consequence, the torques can vary by at least an order of magnitude as the magnetic topology of the interaction varies

  9. Vertical Gradient Freezing Using Submerged Heater Growth With Rotation and With Weak Magnetic and Electric Fields

    National Research Council Canada - National Science Library

    Bliss, D. F; Holmes, A. M; Wang, X; Ma, N; Iseler, G. W

    2005-01-01

    ...) method utilizing a submerged heater. Electromagnetic stirring can be induced in the gallium-antimonide melt just above the crystal growth interface by applying a weak radial electric current in the melt together with a weak axial magnetic field...

  10. Accretion dynamics and polarized x-ray emission of magnetized neutron stars

    International Nuclear Information System (INIS)

    Arons, J.

    1991-01-01

    The basic ideas of accretion onto magnetized neutron stars are outlined. These are applied to a simple model of the structure of the plasma mound sitting at the magnetic poles of such as star, in which upward diffusion of photons is balanced by their downward advection. This steady flow model of the plasma's dynamical state is used to compute the emission of polarized X-rays from the optically thick, birefringent medium. The linear polarization of the continuum radiation emerging from the quasi-static mound is found to be as much as 40% at some rotation phases, but is insensitive to the geometry of the accretion flow. The role of the accretion shock, whose detailed polarimetric and spectral characteristics have yet to be calculated, is emphasized as the final determinant of the properties of the emerging X-rays. Some results describing the fully time dependent dynamics of the flow are also presented. In particular, steady flow onto a neutron star is shown to exhibit formation of ''photon bubbles,'' regions of greatly reduced plasma density filled with radiation which form and rise on millisecond time scales. The possible role of these complex structures in the flow for the formation of the emergent spectrum is briefly outlined

  11. Accretion dynamics and polarized X-ray emission of magnetized neutron stars

    Science.gov (United States)

    Arons, Jonathan

    1991-01-01

    The basic ideas of accretion onto magnetized neutron stars are outlined. These are applied to a simple model of the structure of the plasma mound sitting at the magnetic poles of such a star, in which upward diffusion of photons is balanced by their downward advection. This steady flow model of the plasma's dynamical state is used to compute the emission of polarized X-raysfrom the optically thick, birefringent medium. The linear polarization of the continuum radiation emerging from the quasi-static mound is found to be as much as 40 percent at some rotation phases, but is insensitive to the geometry of the accretion flow. The role of the accretion shock, whose detailed polarimetric and spectral characteristics have yet to be calculated, is emphasized as the final determinant of the properties of the emerging X-rays. Some results describing the fully time dependent dynamics of the flow are also presented. In particular, steady flow onto a neutron star is shown to exhibit formation of 'photon bubbles', regions of greatly reduced plasma density filled with radiation which form and rise on millisecond time scale. The possible role of these complex structures in the flow for the formation of the emergent spectrum is briefly outlined.

  12. SEARCH FOR A MAGNETIC FIELD VIA CIRCULAR POLARIZATION IN THE WOLF-RAYET STAR EZ CMa

    International Nuclear Information System (INIS)

    De la Chevrotière, A.; St-Louis, N.; Moffat, A. F. J.

    2013-01-01

    We report on the first deep, direct search for a magnetic field via the circular polarization of Zeeman splitting in a Wolf-Rayet (W-R) star. Using the highly efficient ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, we observed at three different epochs one of the best W-R candidates in the sky expected to harbor a magnetic field, the bright, highly variable WN4 star EZ CMa = WR6 = HD 50896. We looked for the characteristic circular polarization (Stokes V) pattern in strong emission lines that would arise as a consequence of a global, rotating magnetic field with a split monopole configuration. We also obtained nearly simultaneous linear polarization spectra (Stokes Q and U), which are dominated by electron scattering, most likely from a flattened wind with large-scale corotating structures. As the star rotates with a period of 3.766 days, our view of the wind changes, which in turn affects the value of the linear polarization in lines versus continuum at the ∼0.2% level. Depending on the epoch of observation, our Stokes V data were affected by significant crosstalk from Stokes Q and U to V. We removed this spurious signal from the circular polarization data and experimented with various levels of spectral binning to increase the signal-to-noise ratio of our data. In the end, no magnetic field is unambiguously detected in EZ CMa. Assuming that the star is intrinsically magnetic and harbors a split monopole configuration, we find an upper limit of B ∼ 100 G for the intensity of its field in the line-forming regions of the stellar wind.

  13. SEARCH FOR A MAGNETIC FIELD VIA CIRCULAR POLARIZATION IN THE WOLF-RAYET STAR EZ CMa

    Energy Technology Data Exchange (ETDEWEB)

    De la Chevrotiere, A.; St-Louis, N.; Moffat, A. F. J. [Departement de Physique, Universite de Montreal and Centre de Recherche en Astrophysique du Quebec (CRAQ), C. P. 6128, succ. centre-ville, Montreal (Quebec) H3C 3J7 (Canada); Collaboration: MiMeS Collaboration

    2013-02-20

    We report on the first deep, direct search for a magnetic field via the circular polarization of Zeeman splitting in a Wolf-Rayet (W-R) star. Using the highly efficient ESPaDOnS spectropolarimeter at the Canada-France-Hawaii Telescope, we observed at three different epochs one of the best W-R candidates in the sky expected to harbor a magnetic field, the bright, highly variable WN4 star EZ CMa = WR6 = HD 50896. We looked for the characteristic circular polarization (Stokes V) pattern in strong emission lines that would arise as a consequence of a global, rotating magnetic field with a split monopole configuration. We also obtained nearly simultaneous linear polarization spectra (Stokes Q and U), which are dominated by electron scattering, most likely from a flattened wind with large-scale corotating structures. As the star rotates with a period of 3.766 days, our view of the wind changes, which in turn affects the value of the linear polarization in lines versus continuum at the {approx}0.2% level. Depending on the epoch of observation, our Stokes V data were affected by significant crosstalk from Stokes Q and U to V. We removed this spurious signal from the circular polarization data and experimented with various levels of spectral binning to increase the signal-to-noise ratio of our data. In the end, no magnetic field is unambiguously detected in EZ CMa. Assuming that the star is intrinsically magnetic and harbors a split monopole configuration, we find an upper limit of B {approx} 100 G for the intensity of its field in the line-forming regions of the stellar wind.

  14. Effective Induction Heating around Strongly Magnetized Stars

    Science.gov (United States)

    Kislyakova, K. G.; Fossati, L.; Johnstone, C. P.; Noack, L.; Lüftinger, T.; Zaitsev, V. V.; Lammer, H.

    2018-05-01

    Planets that are embedded in the changing magnetic fields of their host stars can experience significant induction heating in their interiors caused by the planet’s orbital motion. For induction heating to be substantial, the planetary orbit has to be inclined with respect to the stellar rotation and dipole axes. Using WX UMa, for which the rotation and magnetic axes are aligned, as an example, we show that for close-in planets on inclined orbits, induction heating can be stronger than the tidal heating occurring inside Jupiter’s satellite Io; namely, it can generate a surface heat flux exceeding 2 W m‑2. An internal heating source of such magnitude can lead to extreme volcanic activity on the planet’s surface, possibly also to internal local magma oceans, and to the formation of a plasma torus around the star aligned with the planetary orbit. A strongly volcanically active planet would eject into space mostly SO2, which would then dissociate into oxygen and sulphur atoms. Young planets would also eject CO2. Oxygen would therefore be the major component of the torus. If the O I column density of the torus exceeds ≈1012 cm‑2, the torus could be revealed by detecting absorption signatures at the position of the strong far-ultraviolet O I triplet at about 1304 Å. We estimate that this condition is satisfied if the O I atoms in the torus escape the system at a velocity smaller than 1–10 km s‑1. These estimates are valid also for a tidally heated planet.

  15. WEAK AND COMPACT RADIO EMISSION IN EARLY HIGH-MASS STAR-FORMING REGIONS. I. VLA OBSERVATIONS

    Energy Technology Data Exchange (ETDEWEB)

    Rosero, V.; Hofner, P. [Physics Department, New Mexico Tech, 801 Leroy Pl., Socorro, NM 87801 (United States); Claussen, M. [National Radio Astronomy Observatory, 1003 Lopezville Rd., Socorro, NM 87801 (United States); Kurtz, S.; Carrasco-González, C.; Rodríguez, L. F.; Loinard, L. [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, Morelia 58090, México (Mexico); Cesaroni, R. [INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze (Italy); Araya, E. D. [Physics Department, Western Illinois University, 1 University Circle, Macomb, IL 61455 (United States); Menten, K. M.; Wyrowski, F. [Max-Planck-Institute für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn (Germany); Ellingsen, S. P. [School of Physical Sciences, University of Tasmania, Private Bag 37, Hobart, Tasmania 7001 (Australia)

    2016-12-01

    We present a high-sensitivity radio continuum survey at 6 and 1.3 cm using the Karl G. Jansky Very Large Array toward a sample of 58 high-mass star-forming regions. Our sample was chosen from dust clumps within infrared dark clouds with and without IR sources (CMC–IRs and CMCs, respectively), and hot molecular cores (HMCs), with no previous, or relatively weak radio continuum detection at the 1 mJy level. Due to the improvement in the continuum sensitivity of the Very Large Array, this survey achieved map rms levels of ∼3–10  μ Jy beam{sup −1} at sub-arcsecond angular resolution. We extracted 70 continuum sources associated with 1.2 mm dust clumps. Most sources are weak, compact, and prime candidates for high-mass protostars. Detection rates of radio sources associated with the millimeter dust clumps for CMCs, CMC–IRs, and HMCs are 6%, 53%, and 100%, respectively. This result is consistent with increasing high-mass star formation activity from CMCs to HMCs. The radio sources located within HMCs and CMC–IRs occur close to the dust clump centers, with a median offset from it of 12,000 au and 4000 au, respectively. We calculated 5–25 GHz spectral indices using power-law fits and obtained a median value of 0.5 (i.e., flux increasing with frequency), suggestive of thermal emission from ionized jets. In this paper we describe the sample, observations, and detections. The analysis and discussion will be presented in Paper II.

  16. X-rays from stars

    Science.gov (United States)

    Güdel, Manuel

    2004-07-01

    Spectroscopic studies available from Chandra and XMM-Newton play a pivotal part in the understanding of the physical processes in stellar (magnetic and non-magnetic) atmospheres. It is now routinely possible to derive densities and to study the influence of ultraviolet radiation fields, both of which can be used to infer the geometry of the radiating sources. Line profiles provide important information on bulk mass motions and attenuation by neutral matter, e.g. in stellar winds. The increased sensitivity has revealed new types of X-ray sources in systems that were thought to be unlikely places for X-rays: flaring brown dwarfs, including rather old, non-accreting objects, and terminal shocks in jets of young stars are important examples. New clues concerning the role of stellar high-energy processes in the modification of the stellar environment (ionization, spallation, etc.) contribute significantly to our understanding of the "astro-ecology" in forming planetary systems. Technological limitations are evident. The spectral resolution has not reached the level where bulk mass motions in cool stars become easily measurable. Higher resolution would also be important to perform X-ray "Doppler imaging" in order to reconstruct the 3-D distribution of the X-ray sources around a rotating star. Higher sensitivity will be required to perform high-resolution spectroscopy of weak sources such as brown dwarfs or embedded pre-main-sequence sources. A new generation of satellites such as Constellation-X or XEUS should pursue these goals.

  17. MAGNETIC ACTIVITY CYCLES IN THE EXOPLANET HOST STAR {epsilon} ERIDANI

    Energy Technology Data Exchange (ETDEWEB)

    Metcalfe, T. S.; Mathur, S. [Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301 (United States); Buccino, A. P.; Mauas, P. J. D.; Petrucci, R. [Instituto de Astronomia y Fisica del Espacio (CONICET), C.C. 67 Sucursal 28, C1428EHA-Buenos Aires (Argentina); Brown, B. P. [Department of Astronomy and Center for Magnetic Self-Organization, University of Wisconsin, Madison, WI 53706-1582 (United States); Soderblom, D. R. [Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218 (United States); Henry, T. J. [Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30302 (United States); Hall, J. C. [Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001 (United States); Basu, S. [Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520 (United States)

    2013-02-01

    The active K2 dwarf {epsilon} Eri has been extensively characterized both as a young solar analog and more recently as an exoplanet host star. As one of the nearest and brightest stars in the sky, it provides an unparalleled opportunity to constrain stellar dynamo theory beyond the Sun. We confirm and document the 3-year magnetic activity cycle in {epsilon} Eri originally reported by Hatzes and coworkers, and we examine the archival data from previous observations spanning 45 years. The data show coexisting 3-year and 13-year periods leading into a broad activity minimum that resembles a Maunder minimum-like state, followed by the resurgence of a coherent 3-year cycle. The nearly continuous activity record suggests the simultaneous operation of two stellar dynamos with cycle periods of 2.95 {+-} 0.03 years and 12.7 {+-} 0.3 years, which, by analogy with the solar case, suggests a revised identification of the dynamo mechanisms that are responsible for the so-called 'active' and 'inactive' sequences as proposed by Boehm-Vitense. Finally, based on the observed properties of {epsilon} Eri, we argue that the rotational history of the Sun is what makes it an outlier in the context of magnetic cycles observed in other stars (as also suggested by its Li depletion), and that a Jovian-mass companion cannot be the universal explanation for the solar peculiarities.

  18. THE DECAY OF A WEAK LARGE-SCALE MAGNETIC FIELD IN TWO-DIMENSIONAL TURBULENCE

    Energy Technology Data Exchange (ETDEWEB)

    Kondić, Todor; Hughes, David W.; Tobias, Steven M., E-mail: t.kondic@leeds.ac.uk [Department of Applied Mathematics, University of Leeds, Leeds LS2 9JT (United Kingdom)

    2016-06-01

    We investigate the decay of a large-scale magnetic field in the context of incompressible, two-dimensional magnetohydrodynamic turbulence. It is well established that a very weak mean field, of strength significantly below equipartition value, induces a small-scale field strong enough to inhibit the process of turbulent magnetic diffusion. In light of ever-increasing computer power, we revisit this problem to investigate fluids and magnetic Reynolds numbers that were previously inaccessible. Furthermore, by exploiting the relation between the turbulent diffusion of the magnetic potential and that of the magnetic field, we are able to calculate the turbulent magnetic diffusivity extremely accurately through the imposition of a uniform mean magnetic field. We confirm the strong dependence of the turbulent diffusivity on the product of the magnetic Reynolds number and the energy of the large-scale magnetic field. We compare our findings with various theoretical descriptions of this process.

  19. Weak nonlinear analysis of magneto–convection under magnetic field modulation

    International Nuclear Information System (INIS)

    Bhadauria, B S; Kiran, Palle

    2014-01-01

    An analytic study of heat transport in an electrically conducting fluid layer is performed under a non-uniform time-dependent magnetic field. The applied vertical magnetic field consists of two parts: a constant part and a time-dependent periodic part, which varies sinusoidally with time. A weakly nonlinear theory has been considered to investigate heat transfer in the fluid layer. The heat transfer coefficient is obtained by deriving the non-autonomous Ginzburg–Landau equation for an amplitude of convection. This amplitude of convection is derived by using NDSolve Mathematica 8, and the results are verified using Runge–Kutta–Fehlberg method. The Nusselt number is obtained in terms of various system parameters and the effect of each parameter on heat transport is reported in detail. The effect of magnetic Prandtl number Pm, amplitude of modulation δ is to enhance the heat transfer. The Chandrasekhar number Q, modulation frequency ω is to stabilize the system. Further, it is found that magnetic modulation can be used effectively in either enhancing the heat transfer or diminishing it. (paper)

  20. Magnetic fields in O-, B- and A-type stars on the main sequence

    Directory of Open Access Journals (Sweden)

    Briquet Maryline

    2015-01-01

    Full Text Available In this review, the latest observational results on magnetic fields in main-sequence stars with radiative envelopes are summarised together with the theoretical works aimed at explaining them.

  1. Equation of state and hybrid star properties with the weakly interacting light U-boson in relativistic models

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Dong-Rui; Jiang, Wei-Zhou; Wei, Si-Na; Yang, Rong-Yao [Southeast University, Department of Physics, Nanjing (China); Xiang, Qian-Fei [Chinese Academy of Sciences, Institute of High Energy Physics, Beijing (China)

    2016-05-15

    It has been a puzzle whether quarks may exist in the interior of massive neutron stars, since the hadron-quark phase transition softens the equation of state (EOS) and reduce the neutron star (NS) maximum mass very significantly. In this work, we consider the light U-boson that increases the NS maximum mass appreciably through its weak coupling to fermions. The inclusion of the U-boson may thus allow the existence of the quark degrees of freedom in the interior of large mass neutron stars. Unlike the consequence of the U-boson in hadronic matter, the stiffening role of the U-boson in the hybrid EOS is not sensitive to the choice of the hadron phase models. In addition, we have also investigated the effect of the effective QCD correction on the hybrid EOS. This correction may reduce the coupling strength of the U-boson that is needed to satisfy NS maximum mass constraint. While the inclusion of the U-boson also increases the NS radius significantly, we find that appropriate in-medium effects of the U-boson may reduce the NS radii significantly, satisfying both the NS radius and mass constraints well. (orig.)

  2. Shock-front compression of the magnetic field in the Canis Majoris R1 star-formation region

    International Nuclear Information System (INIS)

    Vrba, F.J.; Baierlein, R.; Herbst, W.; Wesleyan Univ., Middletown, CT; Van Vleck Observatory, Middletown, CT)

    1987-01-01

    Results are presented from a linear polarization survey at optical wavelengths of over 140 stars in the direction of the CMa R1 star-formation region; 26 of these are clearly associated with nebulosity within the area. The observations were obtained in order to test the argument of Herbst et al. (1978) that star formation in CMa R1 is driven by a shock wave from a nearby supernova (Herbs and Assousa, 1977 and 1978). The polarizations are found to be consistent with a simple model of the compression by a supernova-induced spherical shock front of an initially uniform interstellar magnetic field. The polarization vectors are inconsistent with a scenario of quiescent cloud collapse along magnetic-field lines. Multicolor polarimetry of the nebular stars provides evidence of grain growth toward increasing cloud optical depth, characterized by a ratio of total-to-selective extinction of R = 3.0 at E(B-V) = 0.23, increasing to R = 4.2 at E(B-V) = 0.7. 15 references

  3. Ion-collecting sphere in a stationary, weakly magnetized plasma with finite shielding length

    International Nuclear Information System (INIS)

    Patacchini, Leonardo; Hutchinson, Ian H

    2007-01-01

    Collisionless ion collection by a negatively biased stationary spherical probe in a finite shielding length plasma is investigated using the Particle in Cell code SCEPTIC, in the presence of a weak magnetic field B. The overall effect of the magnetic field is to reduce the ion current, linearly in |B| for weak enough fields, with a slope steepness increasing with the electron Debye length. The angular current distribution and space-charge buildup strongly depend on the focusing properties of the probe, hence on its potential and the plasma shielding length. In particular, it is found that the concavity of the ion collection flux distribution can reverse sign when the electron Debye length is comparable to or larger than the probe radius (λ De ∼> r p ), provided the ion temperature is much lower than the probe bias (T i p )

  4. Frequency dependence of p-mode frequency shifts induced by magnetic activity in Kepler solar-like stars

    Science.gov (United States)

    Salabert, D.; Régulo, C.; Pérez Hernández, F.; García, R. A.

    2018-04-01

    The variations of the frequencies of the low-degree acoustic oscillations in the Sun induced by magnetic activity show a dependence on radial order. The frequency shifts are observed to increase towards higher-order modes to reach a maximum of about 0.8 μHz over the 11-yr solar cycle. A comparable frequency dependence is also measured in two other main sequence solar-like stars, the F-star HD 49933, and the young 1 Gyr-old solar analog KIC 10644253, although with different amplitudes of the shifts of about 2 μHz and 0.5 μHz, respectively. Our objective here is to extend this analysis to stars with different masses, metallicities, and evolutionary stages. From an initial set of 87 Kepler solar-like oscillating stars with known individual p-mode frequencies, we identify five stars showing frequency shifts that can be considered reliable using selection criteria based on Monte Carlo simulations and on the photospheric magnetic activity proxy Sph. The frequency dependence of the frequency shifts of four of these stars could be measured for the l = 0 and l = 1 modes individually. Given the quality of the data, the results could indicate that a physical source of perturbation different from that in the Sun is dominating in this sample of solar-like stars.

  5. Helical magnetic axis configuration combined with l = 1 and weak l = -1 torsatron fields

    International Nuclear Information System (INIS)

    Kikuchi, Hitoshi; Saito, Katsunori; Gesso, Hirokazu; Shiina, Shoichi

    1989-01-01

    The superposition of a relatively weak l = -1 torsatron field on a main l = 1 torsatron field leads to the improvement of the confinement properties due to the formation of a local magnetic well, which results from the local curvature of the helical magnetic axis with a larger excursion in the major radius direction. This l±1 helical magnetic axis system has a comparatively simple, compact coil structure. Here the vacuum configuration properties of l = ±1 system are described. (author)

  6. Current bistability in a weakly coupled multi-quantum well structure: a magnetic field induced 'memory effect'

    International Nuclear Information System (INIS)

    Feu, W H M; Villas-Boas, J M; Cury, L A; Guimaraes, P S S; Vieira, G S; Tanaka, R Y; Passaro, A; Pires, M P; Landi, S M; Souza, P L

    2009-01-01

    A study of magnetotunnelling in weakly coupled multi-quantum wells reveals a new phenomenon which constitutes a kind of memory effect in the sense that the electrical resistance of the sample after application of the magnetic field is different from before and contains the information that a magnetic field was applied previously. The change in the electric field domain configuration triggered by the magnetic field was compared for two samples, one strictly periodic and another with a thicker quantum well inserted into the periodic structure. For applied biases at which two electric field domains are present in the sample, as the magnetic field is increased a succession of discontinuous reductions in the electrical resistance is observed due to the magnetic field-induced rearrangement of the electric field domains, i.e. the domain boundary jumps from well to well as the magnetic field is changed. The memory effect is revealed for the aperiodic structure as the electric field domain configuration triggered by the magnetic field remains stable after the field is reduced back to zero. This effect is related to the multi-stability in the current-voltage characteristics observed in some weakly coupled multi-quantum well structures.

  7. THE WEAK s-PROCESS IN MASSIVE STARS AND ITS DEPENDENCE ON THE NEUTRON CAPTURE CROSS SECTIONS

    International Nuclear Information System (INIS)

    Pignatari, M.; Herwig, F.; Gallino, R.; Bisterzo, S.; Heil, M.; Wiescher, M.; Kaeppeler, F.

    2010-01-01

    The slow neutron capture process in massive stars (weak s process) produces most of the s-process isotopes between iron and strontium. Neutrons are provided by the 22 Ne(α,n) 25 Mg reaction, which is activated at the end of the convective He-burning core and in the subsequent convective C-burning shell. The s-process-rich material in the supernova ejecta carries the signature of these two phases. In the past years, new measurements of neutron capture cross sections of isotopes beyond iron significantly changed the predicted weak s-process distribution. The reason is that the variation of the Maxwellian-averaged cross sections (MACS) is propagated to heavier isotopes along the s path. In the light of these results, we present updated nucleosynthesis calculations for a 25 M sun star of Population I (solar metallicity) in convective He-burning core and convective C-burning shell conditions. In comparison with previous simulations based on the Bao et al. compilation, the new measurement of neutron capture cross sections leads to an increase of s-process yields from nickel up to selenium. The variation of the cross section of one isotope along the s-process path is propagated to heavier isotopes, where the propagation efficiency is higher for low cross sections. New 74 Ge, 75 As, and 78 Se MACS result in a higher production of germanium, arsenic, and selenium, thereby reducing the s-process yields of heavier elements by propagation. Results are reported for the He core and for the C shell. In shell C-burning, the s-process nucleosynthesis is more uncertain than in the He core, due to higher MACS uncertainties at higher temperatures. We also analyze the impact of using the new lower solar abundances for CNO isotopes on the s-process predictions, where CNO is the source of 22 Ne, and we show that beyond Zn this is affecting the s-process yields more than nuclear or stellar model uncertainties considered in this paper. In particular, using the new updated initial

  8. Neutrino-heated winds from millisecond protomagnetars as sources of the weak r-process

    Science.gov (United States)

    Vlasov, Andrey D.; Metzger, Brian D.; Lippuner, Jonas; Roberts, Luke F.; Thompson, Todd A.

    2017-06-01

    We explore heavy element nucleosynthesis in neutrino-driven winds from rapidly rotating, strongly magnetized protoneutron stars ('millisecond protomagnetars') for which the magnetic dipole is aligned with the rotation axis, and the field is assumed to be a static force-free configuration. We process the protomagnetar wind trajectories calculated by Vlasov, Metzger & Thompson through the r-process nuclear reaction network SkyNet using contemporary models for the evolution of the wind electron fraction during the protoneutron star cooling phase. Although we do not find a successful second or third-peak r-process for any rotation period P, we show that protomagnetars with P ˜ 1-5 ms produce heavy element abundance distributions that extend to higher nuclear mass number than from otherwise equivalent spherical winds (with the mass fractions of some elements enhanced by factors of ≳100-1000). The heaviest elements are synthesized by outflows emerging along flux tubes that graze the closed zone and pass near the equatorial plane outside the light cylinder. Due to dependence of the nucleosynthesis pattern on the magnetic field strength and rotation rate of the protoneutron star, natural variations in these quantities between core collapse events could contribute to the observed diversity of the abundances of weak r-process nuclei in metal-poor stars. Further diversity, including possibly even a successful third-peak r-process, could be achieved for misaligned rotators with non-zero magnetic inclination with respect to the rotation axis. If protomagnetars are central engines for GRBs, their relativistic jets should contain a high-mass fraction of heavy nuclei of characteristic mass number \\bar{A}≈ 100, providing a possible source for ultrahigh energy cosmic rays comprised of heavy nuclei with an energy spectrum that extends beyond the nominal Grezin-Zatsepin-Kuzmin cut-off for protons or iron nuclei.

  9. CARINA OB STARS: X-RAY SIGNATURES OF WIND SHOCKS AND MAGNETIC FIELDS

    International Nuclear Information System (INIS)

    Gagne, Marc; Fehon, Garrett; Savoy, Michael R.; Cohen, David H.; Townsley, Leisa K.; Broos, Patrick S.; Povich, Matthew S.; Corcoran, Michael F.; Walborn, Nolan R.; Remage Evans, Nancy; Moffat, Anthony F. J.; Naze, Yael; Oskinova, Lida M.

    2011-01-01

    The Chandra Carina Complex contains 200 known O- and B-type stars. The Chandra survey detected 68 of the 70 O stars and 61 of 127 known B0-B3 stars. We have assembled a publicly available optical/X-ray database to identify OB stars that depart from the canonical L X /L bol relation or whose average X-ray temperatures exceed 1 keV. Among the single O stars with high kT we identify two candidate magnetically confined wind shock sources: Tr16-22, O8.5 V, and LS 1865, O8.5 V((f)). The O4 III(fc) star HD 93250 exhibits strong, hard, variable X-rays, suggesting that it may be a massive binary with a period of >30 days. The visual O2 If* binary HD 93129A shows soft 0.6 keV and hard 1.9 keV emission components, suggesting embedded wind shocks close to the O2 If* Aa primary and colliding wind shocks between Aa and Ab. Of the 11 known O-type spectroscopic binaries, the long orbital-period systems HD 93343, HD 93403, and QZ Car have higher shock temperatures than short-period systems such as HD 93205 and FO 15. Although the X-rays from most B stars may be produced in the coronae of unseen, low-mass pre-main-sequence companions, a dozen B stars with high L X cannot be explained by a distribution of unseen companions. One of these, SS73 24 in the Treasure Chest cluster, is a new candidate Herbig Be star.

  10. Models of large-scale magnetic fields in stellar interiors. Application to solar and ap stars

    International Nuclear Information System (INIS)

    Duez, Vincent

    2009-01-01

    Stellar astrophysics needs today new models of large-scale magnetic fields, which are observed through spectropolarimetry at the surface of Ap/Bp stars, and thought to be an explanation for the uniform rotation of the solar radiation zone, deduced from helio seismic inversions. During my PhD, I focused on describing the possible magnetic equilibria in stellar interiors. The found configurations are mixed poloidal-toroidal, and minimize the energy for a given helicity, in analogy with Taylor states encountered in spheromaks. Taking into account the self-gravity leads us to the 'non force-free' equilibria family, that will thus influence the stellar structure. I derived all the physical quantities associated with the magnetic field; then I evaluated the perturbations they induce on gravity, thermodynamic quantities as well as energetic ones, for a solar model and an Ap star. 3D MHD simulations allowed me to show that these equilibria form a first stable states family, the generalization of such states remaining an open question. It has been shown that a large-scale magnetic field confined in the solar radiation zone can induce an oblateness comparable to a high core rotation law. I also studied the secular interaction between the magnetic field, the differential rotation and the meridional circulation in the aim of implementing their effects in a next generation stellar evolution code. The influence of the magnetism on convection has also been studied. Finally, hydrodynamic processes responsible for the mixing have been compared with diffusion and a change of convection's efficiency in the case of a CoRoT star target. (author) [fr

  11. Chiral-model of weak-interaction form factors and magnetic moments of octet baryons

    International Nuclear Information System (INIS)

    Kubodera, K.; Kohyama, Y.; Tsushima, K.; Yamaguchi, T.

    1989-01-01

    For baryon spectroscopy, magnetic moments and weak interaction form factors provide valuable information, and the impressive amount of available experimental data on these quantities for the octet baryons invites detailed investigations. The authors of this paper have made extensive studies of the weak-interaction form factors and magnetic moments of the octet baryons within the framework of the volume-type cloudy-bag model (v-type CBM). The clouds of all octet mesons have been included. Furthermore, we have taken into account in a unified framework various effects that were so far only individually discussed in the literature. Thus, the gluonic effects, center-of-mass (CM0 corrections, and recoil corrections have been included). In this talk, after giving a brief summary of some salient features of the results, we discuss a very interesting application of our model to the problem of the spin content of nucleons

  12. The Destructive Birth of Massive Stars and Massive Star Clusters

    Science.gov (United States)

    Rosen, Anna; Krumholz, Mark; McKee, Christopher F.; Klein, Richard I.; Ramirez-Ruiz, Enrico

    2017-01-01

    Massive stars play an essential role in the Universe. They are rare, yet the energy and momentum they inject into the interstellar medium with their intense radiation fields dwarfs the contribution by their vastly more numerous low-mass cousins. Previous theoretical and observational studies have concluded that the feedback associated with massive stars' radiation fields is the dominant mechanism regulating massive star and massive star cluster (MSC) formation. Therefore detailed simulation of the formation of massive stars and MSCs, which host hundreds to thousands of massive stars, requires an accurate treatment of radiation. For this purpose, we have developed a new, highly accurate hybrid radiation algorithm that properly treats the absorption of the direct radiation field from stars and the re-emission and processing by interstellar dust. We use our new tool to perform a suite of three-dimensional radiation-hydrodynamic simulations of the formation of massive stars and MSCs. For individual massive stellar systems, we simulate the collapse of massive pre-stellar cores with laminar and turbulent initial conditions and properly resolve regions where we expect instabilities to grow. We find that mass is channeled to the massive stellar system via gravitational and Rayleigh-Taylor (RT) instabilities. For laminar initial conditions, proper treatment of the direct radiation field produces later onset of RT instability, but does not suppress it entirely provided the edges of the radiation-dominated bubbles are adequately resolved. RT instabilities arise immediately for turbulent pre-stellar cores because the initial turbulence seeds the instabilities. To model MSC formation, we simulate the collapse of a dense, turbulent, magnetized Mcl = 106 M⊙ molecular cloud. We find that the influence of the magnetic pressure and radiative feedback slows down star formation. Furthermore, we find that star formation is suppressed along dense filaments where the magnetic field is

  13. Precision modelling of M dwarf stars: the magnetic components of CM Draconis

    Science.gov (United States)

    MacDonald, J.; Mullan, D. J.

    2012-04-01

    The eclipsing binary CM Draconis (CM Dra) contains two nearly identical red dwarfs of spectral class dM4.5. The masses and radii of the two components have been reported with unprecedentedly small statistical errors: for M, these errors are 1 part in 260, while for R, the errors reported by Morales et al. are 1 part in 130. When compared with standard stellar models with appropriate mass and age (≈4 Gyr), the empirical results indicate that both components are discrepant from the models in the following sense: the observed stars are larger in R ('bloated'), by several standard deviations, than the models predict. The observed luminosities are also lower than the models predict. Here, we attempt at first to model the two components of CM Dra in the context of standard (non-magnetic) stellar models using a systematic array of different assumptions about helium abundances (Y), heavy element abundances (Z), opacities and mixing length parameter (α). We find no 4-Gyr-old models with plausible values of these four parameters that fit the observed L and R within the reported statistical error bars. However, CM Dra is known to contain magnetic fields, as evidenced by the occurrence of star-spots and flares. Here we ask: can inclusion of magnetic effects into stellar evolution models lead to fits of L and R within the error bars? Morales et al. have reported that the presence of polar spots results in a systematic overestimate of R by a few per cent when eclipses are interpreted with a standard code. In a star where spots cover a fraction f of the surface area, we find that the revised R and L for CM Dra A can be fitted within the error bars by varying the parameter α. The latter is often assumed to be reduced by the presence of magnetic fields, although the reduction in α as a function of B is difficult to quantify. An alternative magnetic effect, namely inhibition of the onset of convection, can be readily quantified in terms of a magnetic parameter δ≈B2/4

  14. Numerical study of rotating relativistic stars

    International Nuclear Information System (INIS)

    Wilson, J.R.

    1975-01-01

    The equations of structure for rotating stars in general relativity are presented and put in a form suitable for computer calculations. The results of equilibrium calculations for supermassive stars, neutron stars, and magnetically supported stars are reported, as are calculations of collapsing, rotating, and magnetized stars in the slowly changing gravitational field approximation. (auth)

  15. Ripple structure in degenerate electron-gas-dominated stars with intense magnetic fields

    International Nuclear Information System (INIS)

    Wilkes, J.M.

    1988-01-01

    We investigate the implications of ripple structure, i.e., the appearance of oscillating and discontinuous slopes in the thermodynamic variables of a degenerate electron gas, for models of magnetic stars dominated by such a gas. We also examine the effects in these models of the recent discovery by R.L. Ingraham that strong magnetic fields can inhibit degeneracy in an electron gas. The thesis begins with the presentation of a theory of self-gravitating fluids based upon recent work in modern continuum mechanics and thermodynamics on electromagnetic interactions in continuous media. Our theory predicts as a general result the existence of an anisotropic pressure tensor in such a fluid, which is in agreement with the one known to occur in the special case of a free-electron gas in a magnetic field. Furthermore, the theory clarifies the relation between this pressure tensor and the scalar thermodynamic pressure, and provides an unambiguous prescription for the incorporation of these and other variables, such as the magnetization, in the fluid equations of motion. We next show that under suitable assumptions the usual thermodynamic equilibrium and stability conditions for such a fluid follow from the general theory. A definition of local thermodynamic equilibrium is then introduced, and used to develop a local equilibrium statistical mechanics of ideal gases. From this we derive the equations of state for an ideal free-electron gas in a magnetic field. Finally, these equations of state are used in a simplified system of structure equations for model stars in intense magnetic fields. We find the effects of degeneracy-inhibition to be small in these simple models

  16. Extinction of photoemission of Mn-Doped ZnS nanofluid in weak magnetic field

    Science.gov (United States)

    Vu, Anh-Tuan; Bui, Hong-Van; Pham, Van-Ben; Le, Van-Hong; Hoang, Nam-Nhat

    2016-08-01

    The observation of extinction of photoluminescence of Mn-doped ZnS nanofluid under applying of weak magnetic field is reported. At a constant field of 270 Gauss and above, the exponential decays of photoluminescent intensity was observed in disregard of field direction. About 50% extinction was achieved after 30 minute magnetization and a total extinction after 1 hour. The memory effect preserved for more than 2 hours at room temperature. This extinction was observed in a system with no clear ferromagnetic behavior.

  17. Weak-field precession of nano-pillar spin-torque oscillators using MgO-based perpendicular magnetic tunnel junction

    Science.gov (United States)

    Zhang, Changxin; Fang, Bin; Wang, Bochong; Zeng, Zhongming

    2018-04-01

    This paper presents a steady auto-oscillation in a spin-torque oscillator using MgO-based magnetic tunnel junction (MTJ) with a perpendicular polarizer and a perpendicular free layer. As the injected d.c. current varied from 1.5 to 3.0 mA under a weak magnetic field of 290 Oe, the oscillation frequency decreased from 1.85 to 1.3 GHz, and the integrated power increased from 0.1 to 74 pW. A narrow linewidth down to 7 MHz corresponding to a high Q factor of 220 was achieved at 2.7 mA, which was ascribed to the spatial coherent procession of the free layer magnetization. Moreover, the oscillation frequency was quite sensitive to the applied field, about 3.07 MHz/Oe, indicating the potential applications as a weak magnetic field detector. These results suggested that the MgO-based MTJ with perpendicular magnetic easy axis could be helpful for developing spin-torque oscillators with narrow-linewidth and high sensitive.

  18. Images of gravitational and magnetic phenomena derived from two-dimensional back-projection Doppler tomography of interacting binary stars

    International Nuclear Information System (INIS)

    Richards, Mercedes T.; Cocking, Alexander S.; Fisher, John G.; Conover, Marshall J.

    2014-01-01

    We have used two-dimensional back-projection Doppler tomography as a tool to examine the influence of gravitational and magnetic phenomena in interacting binaries that undergo mass transfer from a magnetically active star onto a non-magnetic main-sequence star. This multitiered study of over 1300 time-resolved spectra of 13 Algol binaries involved calculations of the predicted dynamical behavior of the gravitational flow and the dynamics at the impact site, analysis of the velocity images constructed from tomography, and the influence on the tomograms of orbital inclination, systemic velocity, orbital coverage, and shadowing. The Hα tomograms revealed eight sources: chromospheric emission, a gas stream along the gravitational trajectory, a star-stream impact region, a bulge of absorption or emission around the mass-gaining star, a Keplerian accretion disk, an absorption zone associated with hotter gas, a disk-stream impact region, and a hot spot where the stream strikes the edge of a disk. We described several methods used to extract the physical properties of the emission sources directly from the velocity images, including S-wave analysis, the creation of simulated velocity tomograms from hydrodynamic simulations, and the use of synthetic spectra with tomography to sequentially extract the separate sources of emission from the velocity image. In summary, the tomography images have revealed results that cannot be explained solely by gravitational effects: chromospheric emission moving with the mass-losing star, a gas stream deflected from the gravitational trajectory, and alternating behavior between stream state and disk state. Our results demonstrate that magnetic effects cannot be ignored in these interacting binaries.

  19. Parallel Simulation of HGMS of Weakly Magnetic Nanoparticles in Irrotational Flow of Inviscid Fluid

    Directory of Open Access Journals (Sweden)

    Kanok Hournkumnuard

    2014-01-01

    Full Text Available The process of high gradient magnetic separation (HGMS using a microferromagnetic wire for capturing weakly magnetic nanoparticles in the irrotational flow of inviscid fluid is simulated by using parallel algorithm developed based on openMP. The two-dimensional problem of particle transport under the influences of magnetic force and fluid flow is considered in an annular domain surrounding the wire with inner radius equal to that of the wire and outer radius equal to various multiples of wire radius. The differential equations governing particle transport are solved numerically as an initial and boundary values problem by using the finite-difference method. Concentration distribution of the particles around the wire is investigated and compared with some previously reported results and shows the good agreement between them. The results show the feasibility of accumulating weakly magnetic nanoparticles in specific regions on the wire surface which is useful for applications in biomedical and environmental works. The speedup of parallel simulation ranges from 1.8 to 21 depending on the number of threads and the domain problem size as well as the number of iterations. With the nature of computing in the application and current multicore technology, it is observed that 4–8 threads are sufficient to obtain the optimized speedup.

  20. [Modulating effect of weak combined magnetic fields on duration of mealworm beetle Tenebrio molitor metamorphosis stage].

    Science.gov (United States)

    Novikov, V V; Sheĭman, I M; Iablokova, E V; Fesenko, E E

    2014-01-01

    It is shown that an exposure of pupae of the mealworm beetle Tenebrio molitor to the combined static (42 μT) and very weak alternating (250 nT) magnetic fields exerts different influence, depending on the frequency of the alternating magnetic field, on duration of metamorphosis processes in these insects. For instance, an exposure of pupae to weak combined magnetic fields, adjusted to the frequency of ion cyclotron resonance for glutaminic acid (4,4 Hz), stimulates metamorphosis process--a transitional stage from pupae to imago lasts shorter. An inhibiting effect was observed when adjusted to the frequency of ion cyclotron resonance for Ca2 (32,2 Hz). At some frequencies this effect is not seen. For instance, an exposure at a frequency of ion cyclotron resonance for K+ (16,5 Hz) exerts no noticeable effect on the duration of the pupal metamorphosis stage.

  1. Pressure dependence of the magnetic properties of various weakly ferromagnetic transition metal alloys

    International Nuclear Information System (INIS)

    Buis, N.

    1979-01-01

    A large number of experimental results are summarized obtained in an apparatus designed for the measurement of magnetization under high pressures (up to 5k bar gas pressure), at temperatures from 4.2K to room temperature and in magnetic fields up to 5.1 T. Two alloy systems studied were Zr (Fesub(1-x)Cosub(x)) 2 and Y(Fesub(x)Cosub(1-x)) 2 and no consistent picture could be deduced from the large pressure effects on the magnetization. Apparently, one cannot apply the model for weak itinerant ferromagnetism on Zr(Fesub(1-x)Cosub(x)) 2 or a simple giant moment model on Y(Fesub(x)Cosub(1-x)) 2 with small iron content, because the magnetic behaviour of both systems is too complicated. (C.F.)

  2. Eyes in the sky. Interactions between asymptotic giant branch star winds and the interstellar magnetic field

    Science.gov (United States)

    van Marle, A. J.; Cox, N. L. J.; Decin, L.

    2014-10-01

    Context. The extended circumstellar envelopes (CSEs) of evolved low-mass stars display a large variety of morphologies. Understanding the various mechanisms that give rise to these extended structures is important to trace their mass-loss history. Aims: Here, we aim to examine the role of the interstellar magnetic field in shaping the extended morphologies of slow dusty winds of asymptotic giant branch (AGB) stars in an effort to pin-point the origin of so-called eye shaped CSEs of three carbon-rich AGB stars. In addition, we seek to understand if this pre-planetary nebula (PN) shaping can be responsible for asymmetries observed in PNe. Methods: Hydrodynamical simulations are used to study the effect of typical interstellar magnetic fields on the free-expanding spherical stellar winds as they sweep up the local interstellar medium (ISM). Results: The simulations show that typical Galactic interstellar magnetic fields of 5 to 10 μG are sufficient to alter the spherical expanding shells of AGB stars to appear as the characteristic eye shape revealed by far-infrared observations. The typical sizes of the simulated eyes are in accordance with the observed physical sizes. However, the eye shapes are transient in nature. Depending on the stellar and interstellar conditions, they develop after 20 000 to 200 000 yrs and last for about 50 000 to 500 000 yrs, assuming that the star is at rest relative to the local interstellar medium. Once formed, the eye shape develops lateral outflows parallel to the magnetic field. The explosion of a PN in the centre of the eye-shaped dust shell gives rise to an asymmetrical nebula with prominent inward pointing Rayleigh-Taylor instabilities. Conclusions: Interstellar magnetic fields can clearly affect the shaping of wind-ISM interaction shells. The occurrence of the eyes is most strongly influenced by stellar space motion and ISM density. Observability of this transient phase is favoured for lines-of-sight perpendicular to the

  3. Weak electric and magnetic dipole moments of the τ lepton from azimuthal asymmetries

    International Nuclear Information System (INIS)

    Sanchez Alvaro, E.

    1997-01-01

    Measurements of the weak electric dipole moment d τ w and, for the first time, the weak magnetic dipole moment a τ w of the τ lepton using L3 detector at LEP are presented. Azimuthal asymmetries for τ→πν and τ→ρν are used to obtain these measurements. Observed asymmetries are consistent with zero, and the limits set on d τ w and a τ w are vertical stroke d τ w vertical stroke -17 e.cm and vertical stroke a τ w vertical stroke <0.014 at 95% C.L. (orig.)

  4. Be stars - Chromospheres and cool envelopes and their relation to magnetic fields

    International Nuclear Information System (INIS)

    Ringuelet, A.E.; Iglesias, M.E.

    1991-01-01

    The present paper discusses Be stars with nonexpanding cool envelopes observed at large inclination angles. It is suggested that high-ionization lines are formed in a chromosphere where the rise in temperature is partly due to dissipation of mechanical energy by braking forces, and that braking forces can be provided by a magnetic field. Further, it is shown how the same magnetic field that characterizes the chromosphere can produce an equatorial envelope (outside the chromosphere) when gravity is counterbalanced by radiation pressure and some particular conditions are fulfilled. 49 refs

  5. Transient growth of a Vlasov plasma in a weakly inhomogeneous magnetic field

    KAUST Repository

    Ratushnaya, Valeria

    2016-12-17

    We investigate the stability properties of a collisionless Vlasov plasma in a weakly inhomogeneous magnetic field using non-modal stability analysis. This is an important topic in a physics of tokamak plasma rich in various types of instabilities. We consider a thin tokamak plasma in a Maxwellian equilibrium, subjected to a small arbitrary perturbation. Within the framework of kinetic theory, we demonstrate the emergence of short time scale algebraic instabilities evolving in a stable magnetized plasma. We show that the linearized governing operator (Vlasov operator) is non-normal leading to the transient growth of the perturbations on the time scale of several plasma periods that is subsequently followed by Landau damping. We calculate the first-order distribution function and the electric field and study the dependence of the transient growth characteristics on the magnetic field strength and perturbation parameters of the system. We compare our results with uniformly magnetized plasma and field-free Vlasov plasma.

  6. Transient growth of a Vlasov plasma in a weakly inhomogeneous magnetic field

    KAUST Repository

    Ratushnaya, Valeria; Samtaney, Ravi

    2016-01-01

    We investigate the stability properties of a collisionless Vlasov plasma in a weakly inhomogeneous magnetic field using non-modal stability analysis. This is an important topic in a physics of tokamak plasma rich in various types of instabilities. We consider a thin tokamak plasma in a Maxwellian equilibrium, subjected to a small arbitrary perturbation. Within the framework of kinetic theory, we demonstrate the emergence of short time scale algebraic instabilities evolving in a stable magnetized plasma. We show that the linearized governing operator (Vlasov operator) is non-normal leading to the transient growth of the perturbations on the time scale of several plasma periods that is subsequently followed by Landau damping. We calculate the first-order distribution function and the electric field and study the dependence of the transient growth characteristics on the magnetic field strength and perturbation parameters of the system. We compare our results with uniformly magnetized plasma and field-free Vlasov plasma.

  7. GMC Collisions as Triggers of Star Formation. II. 3D Turbulent, Magnetized Simulations

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Benjamin; Tan, Jonathan C. [Department of Physics, University of Florida, Gainesville, FL 32611 (United States); Nakamura, Fumitaka [National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan); Loo, Sven Van [School of Physics and Astronomy, University of Leeds (United Kingdom); Christie, Duncan [Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States); Collins, David [Department of Physics, Florida State University, Tallahassee, FL 32306-4350 (United States)

    2017-02-01

    We investigate giant molecular cloud collisions and their ability to induce gravitational instability and thus star formation. This mechanism may be a major driver of star formation activity in galactic disks. We carry out a series of 3D, magnetohydrodynamics (MHD), adaptive mesh refinement simulations to study how cloud collisions trigger formation of dense filaments and clumps. Heating and cooling functions are implemented based on photo-dissociation region models that span the atomic-to-molecular transition and can return detailed diagnostic information. The clouds are initialized with supersonic turbulence and a range of magnetic field strengths and orientations. Collisions at various velocities and impact parameters are investigated. Comparing and contrasting colliding and non-colliding cases, we characterize morphologies of dense gas, magnetic field structure, cloud kinematic signatures, and cloud dynamics. We present key observational diagnostics of cloud collisions, especially: relative orientations between magnetic fields and density structures, like filaments; {sup 13}CO( J = 2-1), {sup 13}CO( J = 3-2), and {sup 12}CO( J = 8-7) integrated intensity maps and spectra; and cloud virial parameters. We compare these results to observed Galactic clouds.

  8. Self excitation of second harmonic ion-acoustic waves in a weakly magnetized plasma

    International Nuclear Information System (INIS)

    Tsukabayashi, I.; Yagishita, T.; Nakamura, Y.

    1994-01-01

    Electrostatic ion-acoustic waves in a weakly magnetized plasma are investigated experimentally. It is observed that finite amplitudes ion acoustic waves excite a new second harmonic wave train behind the initial ion waves excite a new second harmonic wave train behind the initial ion waves in a parallel magnetic field. The excitation of higher harmonic waves can be explained by non-linearity of finite amplitude ion-acoustic waves. The newly excited second harmonics waves satisfy a dispersion relation of the ion-acoustic waves. (author). 3 refs, 5 figs

  9. Superconducting Film Flux Transformer for a Sensor of a Weak Magnetic Field

    International Nuclear Information System (INIS)

    Ichkitidze, L; Mironyuk, A

    2012-01-01

    The object of study is a superconducting film flux transformer in the form of a square shaped loop with the tapering operative strip used in a sensor of a weak magnetic field. The magnetosensitive film element based on the giant magnetoresistance effect is overlapped with the tapering operative strip of the flux transformer; it is separated from the latter by the insulator film. It is shown that the topological nanostructuring of the operative strip of the flux transformer increases its gain factor by one or more orders of magnitude, i.e. increases its efficiency, which leads to a significant improvement of important parameters of a magnetic-field sensor.

  10. B fields in OB stars (BOB): Low-resolution FORS2 spectropolarimetry of the first sample of 50 massive stars

    NARCIS (Netherlands)

    Fossati, L.; Castro, N.; Schöller, M.; Hubrig, S.; Langer, N.; Morel, T.; Briquet, M.; Herrero, A.; Przybilla, N.; Sana, H.; Schneider, F.R.N.; de Koter, A.

    2015-01-01

    Within the context of the collaboration "B fields in OB stars" (BOB), we used the FORS2 low-resolution spectropolarimeter to search for a magnetic field in 50 massive stars, including two reference magnetic massive stars. Because of the many controversies of magnetic field detections obtained with

  11. Neutron star equilibrium configurations within a fully relativistic theory with strong, weak, electromagnetic, and gravitational interactions

    International Nuclear Information System (INIS)

    Belvedere, Riccardo; Pugliese, Daniela; Rueda, Jorge A.; Ruffini, Remo; Xue, She-Sheng

    2012-01-01

    We formulate the equations of equilibrium of neutron stars taking into account strong, weak, electromagnetic, and gravitational interactions within the framework of general relativity. The nuclear interactions are described by the exchange of the σ, ω, and ρ virtual mesons. The equilibrium conditions are given by our recently developed theoretical framework based on the Einstein–Maxwell–Thomas–Fermi equations along with the constancy of the general relativistic Fermi energies of particles, the “Klein potentials”, throughout the configuration. The equations are solved numerically in the case of zero temperatures and for selected parameterizations of the nuclear models. The solutions lead to a new structure of the star: a positively charged core at supranuclear densities surrounded by an electronic distribution of thickness ∼ℏ/(m e c)∼10 2 ℏ/(m π c) of opposite charge, as well as a neutral crust at lower densities. Inside the core there is a Coulomb potential well of depth ∼m π c 2 /e. The constancy of the Klein potentials in the transition from the core to the crust, imposes the presence of an overcritical electric field ∼(m π /m e ) 2 E c , the critical field being E c =m e 2 c 3 /(eℏ). The electron chemical potential and the density decrease, in the boundary interface, until values μ e crust e core and ρ crust core . For each central density, an entire family of core–crust interface boundaries and, correspondingly, an entire family of crusts with different mass and thickness, exist. The configuration with ρ crust =ρ drip ∼4.3×10 11 gcm −3 separates neutron stars with and without inner crust. We present here the novel neutron star mass–radius for the especial case ρ crust =ρ drip and compare and contrast it with the one obtained from the traditional Tolman–Oppenheimer–Volkoff treatment.

  12. RED DWARF DYNAMO RAISES PUZZLE OVER INTERIORS OF LOWEST-MASS STARS

    Science.gov (United States)

    2002-01-01

    NASA's Hubble Space Telescope has uncovered surprising evidence that powerful magnetic fields might exist around the lowest mass stars in the universe, which are near the threshold of stellar burning processes. 'New theories will have to be developed to explain how these strong fields are produced, since conventional models predict that these low mass red dwarfs should have very weak or no magnetic fields,' says Dr. Jeffrey Linsky of the Joint Institute for Laboratory Astrophysics (JILA) in Boulder, Colorado. 'The Hubble observations provide clear evidence that very low mass red dwarf stars must have some form of dynamo to amplify their magnetic fields.' His conclusions are based upon Hubble's detection of a high-temperature outburst, called a flare, on the surface of the extremely small, cool red dwarf star Van Biesbroeck 10 (VB10) also known as Gliese 752B. Stellar flares are caused by intense, twisted magnetic fields that accelerate and contain gasses which are much hotter than a star's surface. Explosive flares are common on the Sun and expected for stars that have internal structures similar to our Sun's. Stars as small as VB10 are predicted to have a simpler internal structure than that of the Sun and so are not expected to generate the electric currents required for magnetic fields that drive flares. Besides leading to a clearer understanding of the interior structure of the smallest red dwarf stars known, these unexpected results might possibly shed light on brown dwarf stars. A brown dwarf is a long-sought class of astronomical object that is too small to shine like a star through nuclear fusion processes, but is too large to be considered a planet. 'Since VB10 is nearly a brown dwarf, it is likely brown dwarfs also have strong magnetic fields,' says Linsky. 'Additional Hubble searches for flares are needed to confirm this prediction.' A QUARTER-MILLION DEGREE TORCH The star VB10 and its companion star Gliese 752A make up a binary system located 19 light

  13. Electromagnetic multipole fields of neutron stars

    International Nuclear Information System (INIS)

    Roberts, W.J.

    1979-01-01

    There is now indisputable evidence that some pulsars possess space velocities so high that internal asymmetries in the dynamics of their formation are strongly implied. We develop in this paper a complete formalism for the calculation of the only such mechanism that has yet been subjected to quantitative analysis: electromagnetic recoil radiation. To make the general problem tractable without doing violence to the physics, we have made the following simplifying assumptions: (1) the magnetic induction B in athin shell enclosing the surface can be satisfactorily approximated by a sum of vacuum multipole fields; (2) the star is spherical, and all parts are in good electrical contact; (3) vertical-bar Ω X r vertical-barvery-much-less-thanc everywhere within the star; and (4) the star is surrounded by a vacuum. Our qualitative conclusions hold even if these assumptions are violated, but corrections to our quantitative results required by a relaxation of our assumptions are not easily computed.Given this simple electrodynamic model of a neutron star, we solve the following problems: (1) What electric multipoles are induced by each magnetic multipole. (2) What is the general formula for the recoil produced by the projection on the rotational axis of a net linear momentum flux produced by the rotation of any two magnetic multipoles. (3) What is the set of centered multipoles that represents the field of an arbitrary off-centered multipole. We use these general results go perform a detailed analysis of the linear momentum radiated by an off-centered dipole. We find a force larger by a factor 6 than that obtained for the special case treated in the best previous calculation. In spite of this considerable increase in the computed strengrh of the effect, we still believe it to be too weak to produce the large space velocities observed for pulsars. For the mechanism to be effective, the pulsar must be born rotating near the breakup velocity

  14. Magnetic stripes and holes: Complex domain patterns in perforated films with weak perpendicular anisotropy

    Directory of Open Access Journals (Sweden)

    F. Valdés-Bango

    2017-05-01

    Full Text Available Hexagonal antidot arrays have been patterned on weak perpendicular magnetic anisotropy NdCo films by e-beam lithography and lift off. Domain structure has been characterized by Magnetic Force Microscopy at remanence. On a local length scale, of the order of stripe pattern period, domain configuration is controlled by edge effects within the stripe pattern: stripe domains meet the hole boundary at either perpendicular or parallel orientation. On a longer length scale, in-plane magnetostatic effects dominate the system: clear superdomains are observed in the patterned film with average in-plane magnetization along the easy directions of the antidot array, correlated over several antidot array cells.

  15. Magnetic stripes and holes: Complex domain patterns in perforated films with weak perpendicular anisotropy

    Science.gov (United States)

    Valdés-Bango, F.; Vélez, M.; Alvarez-Prado, L. M.; Alameda, J. M.; Martín, J. I.

    2017-05-01

    Hexagonal antidot arrays have been patterned on weak perpendicular magnetic anisotropy NdCo films by e-beam lithography and lift off. Domain structure has been characterized by Magnetic Force Microscopy at remanence. On a local length scale, of the order of stripe pattern period, domain configuration is controlled by edge effects within the stripe pattern: stripe domains meet the hole boundary at either perpendicular or parallel orientation. On a longer length scale, in-plane magnetostatic effects dominate the system: clear superdomains are observed in the patterned film with average in-plane magnetization along the easy directions of the antidot array, correlated over several antidot array cells.

  16. Zeeman effect in sulfur monoxide. A tool to probe magnetic fields in star forming regions

    Science.gov (United States)

    Cazzoli, Gabriele; Lattanzi, Valerio; Coriani, Sonia; Gauss, Jürgen; Codella, Claudio; Ramos, Andrés Asensio; Cernicharo, José; Puzzarini, Cristina

    2017-09-01

    Context. Magnetic fields play a fundamental role in star formation processes and the best method to evaluate their intensity is to measure the Zeeman effect of atomic and molecular lines. However, a direct measurement of the Zeeman spectral pattern from interstellar molecular species is challenging due to the high sensitivity and high spectral resolution required. So far, the Zeeman effect has been detected unambiguously in star forming regions for very few non-masing species, such as OH and CN. Aims: We decided to investigate the suitability of sulfur monoxide (SO), which is one of the most abundant species in star forming regions, for probing the intensity of magnetic fields via the Zeeman effect. Methods: We investigated the Zeeman effect for several rotational transitions of SO in the (sub-)mm spectral regions by using a frequency-modulated, computer-controlled spectrometer, and by applying a magnetic field parallel to the radiation propagation (I.e., perpendicular to the oscillating magnetic field of the radiation). To support the experimental determination of the g factors of SO, a systematic quantum-chemical investigation of these parameters for both SO and O2 has been carried out. Results: An effective experimental-computational strategy for providing accurate g factors as well as for identifying the rotational transitions showing the strongest Zeeman effect has been presented. Revised g factors have been obtained from a large number of SO rotational transitions between 86 and 389 GHz. In particular, the rotational transitions showing the largest Zeeman shifts are: N,J = 2, 2 ← 1, 1 (86.1 GHz), N,J = 4, 3 ← 3, 2 (159.0 GHz), N,J = 1, 1 ← 0, 1 (286.3 GHz), N,J = 2, 2 ← 1, 2 (309.5 GHz), and N,J = 2, 1 ← 1, 0 (329.4 GHz). Our investigation supports SO as a good candidate for probing magnetic fields in high-density star forming regions. The complete list of measured Zeeman components is only available at the CDS via anonymous ftp to http

  17. BANYAN. IV. Fundamental parameters of low-mass star candidates in nearby young stellar kinematic groups—isochronal age determination using magnetic evolutionary models

    Energy Technology Data Exchange (ETDEWEB)

    Malo, Lison; Doyon, René; Albert, Loïc; Lafrenière, David; Artigau, Étienne; Gagné, Jonathan [Département de physique and Observatoire du Mont-Mégantic, Université de Montréal, Montréal, QC H3C 3J7 (Canada); Feiden, Gregory A. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Riedel, Adric, E-mail: malo@cfht.hawaii.edu, E-mail: doyon@astro.umontreal.ca [Department of Astrophysics, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024 (United States)

    2014-09-01

    Based on high-resolution optical spectra obtained with ESPaDOnS at Canada-France-Hawaii Telescope, we determine fundamental parameters (T {sub eff}, R, L {sub bol}, log g, and metallicity) for 59 candidate members of nearby young kinematic groups. The candidates were identified through the BANYAN Bayesian inference method of Malo et al., which takes into account the position, proper motion, magnitude, color, radial velocity, and parallax (when available) to establish a membership probability. The derived parameters are compared to Dartmouth magnetic evolutionary models and field stars with the goal of constraining the age of our candidates. We find that, in general, low-mass stars in our sample are more luminous and have inflated radii compared to older stars, a trend expected for pre-main-sequence stars. The Dartmouth magnetic evolutionary models show a good fit to observations of field K and M stars, assuming a magnetic field strength of a few kG, as typically observed for cool stars. Using the low-mass members of the β Pictoris moving group, we have re-examined the age inconsistency problem between lithium depletion age and isochronal age (Hertzspring-Russell diagram). We find that the inclusion of the magnetic field in evolutionary models increases the isochronal age estimates for the K5V-M5V stars. Using these models and field strengths, we derive an average isochronal age between 15 and 28 Myr and we confirm a clear lithium depletion boundary from which an age of 26 ± 3 Myr is derived, consistent with previous age estimates based on this method.

  18. Anomalous magnetic and weak magnetic dipole moments of the τ lepton in the simplest little Higgs model

    Energy Technology Data Exchange (ETDEWEB)

    Arroyo-Urena, M.A.; Tavares-Velasco, G. [Benemerita Universidad Autonoma de Puebla, Facultad de Ciencias Fisico-Matematicas, Puebla, PUE (Mexico); Hernandez-Tome, G. [Benemerita Universidad Autonoma de Puebla, Facultad de Ciencias Fisico-Matematicas, Puebla, PUE (Mexico); Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional, Departamento de Fisica, Mexico City (Mexico)

    2017-04-15

    We obtain analytical expressions, both in terms of parametric integrals and Passarino-Veltman scalar functions, for the one-loop contributions to the anomalous weak magnetic dipole moment (AWMDM) of a charged lepton in the framework of the simplest little Higgs model (SLHM). Our results are general and can be useful to compute the weak properties of a charged lepton in other extensions of the standard model (SM). As a by-product we obtain generic contributions to the anomalous magnetic dipole moment (AMDM), which agree with previous results. We then study numerically the potential contributions from this model to the τ lepton AMDM and AWMDM for values of the parameter space consistent with current experimental data. It is found that they depend mainly on the energy scale f at which the global symmetry is broken and the t{sub β} parameter, whereas there is little sensitivity to a mild change in the values of other parameters of the model. While the τ AMDM is of the order of 10{sup -9}, the real (imaginary) part of its AWMDM is of the order of 10{sup -9} (10{sup -10}). These values seem to be out of the reach of the expected experimental sensitivity of future experiments. (orig.)

  19. High-entropy ejections from magnetized proto-neutron star winds: implications for heavy element nucleosynthesis

    Science.gov (United States)

    Thompson, Todd A.; ud-Doula, Asif

    2018-06-01

    Although initially thought to be promising for production of the r-process nuclei, standard models of neutrino-heated winds from proto-neutron stars (PNSs) do not reach the requisite neutron-to-seed ratio for production of the lanthanides and actinides. However, the abundance distribution created by the r-, rp-, or νp-processes in PNS winds depends sensitively on the entropy and dynamical expansion time-scale of the flow, which may be strongly affected by high magnetic fields. Here, we present results from magnetohydrodynamic simulations of non-rotating neutrino-heated PNS winds with strong dipole magnetic fields from 1014 to 1016 G, and assess their role in altering the conditions for nucleosynthesis. The strong field forms a closed zone and helmet streamer configuration at the equator, with episodic dynamical mass ejections in toroidal plasmoids. We find dramatically enhanced entropy in these regions and conditions favourable for third-peak r-process nucleosynthesis if the wind is neutron-rich. If instead the wind is proton-rich, the conditions will affect the abundances from the νp-process. We quantify the distribution of ejected matter in entropy and dynamical expansion time-scale, and the critical magnetic field strength required to affect the entropy. For B ≳1015 G, we find that ≳10-6 M⊙ and up to ˜10-5 M⊙ of high-entropy material is ejected per highly magnetized neutron star birth in the wind phase, providing a mechanism for prompt heavy element enrichment of the universe. Former binary companions identified within (magnetar-hosting) supernova remnants, the remnants themselves, and runaway stars may exhibit overabundances. We provide a comparison with a semi-analytic model of plasmoid eruption and discuss implications and extensions.

  20. Effect of weak magnetic field on the grain size of electrodeposited nickel

    International Nuclear Information System (INIS)

    Ansari, M.S.; Gul, N.

    2007-01-01

    Effect of weak magnetic field on the electro-deposition of nickel onto copper electrode has been investigated. The working conditions were optimized through adjustment of cathodic current density (CCD), deposition time, bath temperature and pH of the medium. For electro-deposition in the absence of magnetic field, the optimum conditions comprised of pH = 4.0+- 0.5, average CCD = 22.5 +- 0.5 mA cm/sup -2/ and bath temperature in the range from 25 to 30 degree C. The same conditions were maintained for the electrodeposition while applying magnetic field of 0.75 kG. The morphological features of the Ni-deposits on copper cathode were compared for the two cases. The applied magnetic field not only enhanced the amount of nickel deposition but also improved the quality of the deposit. Surface morphology of the electro-deposited nickel has been monitored using scanning electron microscopy (SEM); the preliminary investigation has shown that the grain size decreased with the applied magnetic field case. One possible explanation to this behavior is the convection flow of cations close to the electrode surface induced by the Lorentz force which also influences the ion-migration. (author)

  1. Burn out or fade away? On the X-ray and magnetic death of intermediate mass stars

    Energy Technology Data Exchange (ETDEWEB)

    Drake, Jeremy J.; Kashyap, Vinay; Günther, H. Moritz; Wright, Nicholas J. [Smithsonian Astrophysical Observatory, MS-3, 60 Garden Street, Cambridge, MA 02138 (United States); Braithwaite, Jonathan, E-mail: jdrake@cfa.harvard.edu [Argelander Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn (Germany)

    2014-05-10

    The nature of the mechanisms apparently driving X-rays from intermediate mass stars lacking strong convection zones or massive winds remains poorly understood, and the possible role of hidden, lower mass close companions is still unclear. A 20 ks Chandra HRC-I observation of HR 4796A, an 8 Myr old main sequence A0 star devoid of close stellar companions, has been used to search for a signature or remnant of magnetic activity from the Herbig Ae phase. X-rays were not detected and the X-ray luminosity upper limit was L{sub X} ≤ 1.3 × 10{sup 27} erg s{sup –1}. The result is discussed in the context of various scenarios for generating magnetic activity, including rotational shear and subsurface convection. A dynamo driven by natal differential rotation is unlikely to produce observable X rays, chiefly because of the difficulty in getting the dissipated energy up to the surface of the star. A subsurface convection layer produced by the ionization of helium could host a dynamo that should be effective throughout the main sequence but can only produce X-ray luminosities of the order 10{sup 25} erg s{sup –1}. This luminosity lies only moderately below the current detection limit for Vega. Our study supports the idea that X-ray production in Herbig Ae/Be stars is linked largely to the accretion process rather than the properties of the underlying star, and that early A stars generally decline in X-ray luminosity at least 100,000 fold in only a few million years.

  2. WHAT SETS THE INITIAL ROTATION RATES OF MASSIVE STARS?

    International Nuclear Information System (INIS)

    Rosen, Anna L.; Krumholz, Mark R.; Ramirez-Ruiz, Enrico

    2012-01-01

    The physical mechanisms that set the initial rotation rates in massive stars are a crucial unknown in current star formation theory. Observations of young, massive stars provide evidence that they form in a similar fashion to their low-mass counterparts. The magnetic coupling between a star and its accretion disk may be sufficient to spin down low-mass pre-main-sequence (PMS) stars to well below breakup at the end stage of their formation when the accretion rate is low. However, we show that these magnetic torques are insufficient to spin down massive PMS stars due to their short formation times and high accretion rates. We develop a model for the angular momentum evolution of stars over a wide range in mass, considering both magnetic and gravitational torques. We find that magnetic torques are unable to spin down either low-mass or high-mass stars during the main accretion phase, and that massive stars cannot be spun down significantly by magnetic torques during the end stage of their formation either. Spin-down occurs only if massive stars' disk lifetimes are substantially longer or their magnetic fields are much stronger than current observations suggest.

  3. CHANDRA X-RAY DETECTION OF THE ENIGMATIC FIELD STAR BP Psc

    International Nuclear Information System (INIS)

    Kastner, Joel H.; Montez, Rodolfo; Rodriguez, David; Zuckerman, B.; Perrin, Marshall D.; Grosso, Nicolas; Forveille, Thierry; Graham, James R.

    2010-01-01

    BP Psc is a remarkable emission-line field star that is orbited by a dusty disk and drives a parsec-scale system of jets. We report the detection by the Chandra X-ray Observatory of a weak X-ray point source coincident with the centroids of optical/IR and submillimeter continuum emission at BP Psc. As the star's photosphere is obscured throughout the visible and near-infrared, the Chandra X-ray source likely represents the first detection of BP Psc itself. The X-rays most likely originate with magnetic activity at BP Psc and hence can be attributed either to a stellar corona or to star-disk interactions. The log of the ratio of X-ray to bolometric luminosity, log(L X /L bol ), lies in the range -5.8 to -4.2. This is smaller than log(L X /L bol ) ratios typical of low-mass, pre-main sequence stars, but is well within the log(L X /L bol ) range observed for rapidly rotating (FK Com-type) G giant stars. Hence, the Chandra results favor an exotic model wherein the disk/jet system of BP Psc is the result of its very recently engulfing a companion star or a giant planet, as the primary star ascended the giant branch.

  4. Multi-critical points in weakly anisotropic magnetic systems

    International Nuclear Information System (INIS)

    Basten, J.A.J.

    1979-02-01

    This report starts with a rather extensive presentation of the concepts and ideas which constitute the basis of the modern theory of static critical phenomena. It is shown how at a critical point the semi-phenomenological concepts of universality and scaling are directly related to the divergence of the correlation length and how they are extended to a calculational method for critical behaviour in Wilson's Renormalization-Group (RG) approach. Subsequently the predictions of the molecular-field and RG-theories on the phase transitions and critical behaviour in weakly anisotropic antiferromagnets are treated. In a magnetic field applied along the easy axis, these materials can display an (H,T) phase diagram which contains either a bicritical point or a tetracritical point. Especially the behaviour close to these multi-critical points, as predicted by the extended-scaling theory, is discussed. (Auth.)

  5. Gravitational magnetic monopoles and Majumdar-Papapetrou stars

    International Nuclear Information System (INIS)

    Lemos, Jose P.S.; Zanchin, Vilson T.

    2006-01-01

    During the 1990s a large amount of work was dedicated to studying general relativity coupled to non-Abelian Yang-Mills type theories. Several remarkable results were accomplished. In particular, it was shown that the magnetic monopole, a solution of the Yang-Mills-Higgs equations can indeed be coupled to gravitation. For a low Higgs mass it was found that there are regular monopole solutions, and that for a sufficiently massive monopole the system develops an extremal magnetic Reissner-Nordstroem quasihorizon with all the matter fields laying inside the horizon. These latter solutions, called quasi-black holes, although nonsingular, are arbitrarily close to having a horizon, and for an external observer it becomes increasingly difficult to distinguish these from a true black hole as a critical solution is approached. However, at precisely the critical value the quasi-black hole turns into a degenerate space-time. On the other hand, for a high Higgs mass, a sufficiently massive monopole develops also a quasi-black hole, but at a critical value it turns into an extremal true horizon, now with matter fields showing up outside. One can also put a small Schwarzschild black hole inside the magnetic monopole, the configuration being an example of a non-Abelian black hole. Surprisingly, Majumdar-Papapetrou systems, Abelian systems constructed from extremal dust (pressureless matter with equal charge and energy densities), also show a resembling behavior. Previously, we have reported that one can find Majumdar-Papapetrou solutions which are everywhere nonsingular, but can be arbitrarily close of being a black hole, displaying the same quasi-black-hole behavior found in the gravitational magnetic monopole solutions. With the aim of better understanding the similarities between gravitational magnetic monopoles and Majumdar-Papapetrou systems, here we study a particular system, namely a system composed of two extremal electrically charged spherical shells (or stars

  6. LSPM J1314+1320: An Oversized Magnetic Star with Constraints on the Radio Emission Mechanism

    Energy Technology Data Exchange (ETDEWEB)

    MacDonald, James; Mullan, D. J. [Dept. Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)

    2017-07-10

    LSPM J1314+1320 (=NLTT 33370) is a binary star system consisting of two nearly identical pre-main-sequence stars of spectral type M7. The system is remarkable among ultracool dwarfs for being the most luminous radio emitter over the widest frequency range. Masses and luminosities are at first sight consistent with the system being coeval at age ∼80 Myr according to standard (nonmagnetic) evolutionary models. However, these models predict an average effective temperature of ∼2950 K, which is 180 K hotter than the empirical value. Thus, the empirical radii are oversized relative to the standard models by ≈13%. We demonstrate that magnetic stellar models can quantitatively account for the oversizing. As a check on our models, we note that the radio emission limits the surface magnetic field strengths: the limits depend on identifying the radio emission mechanism. We find that the field strengths required by our magnetic models are too strong to be consistent with gyrosynchrotron emission but are consistent with electron cyclotron maser emission.

  7. Improved methods for the measurement and analysis of stellar magnetic fields

    Science.gov (United States)

    Saar, Steven H.

    1988-01-01

    The paper presents several improved methods for the measurement of magnetic fields on cool stars which take into account simple radiative transfer effects and the exact Zeeman patterns. Using these methods, high-resolution, low-noise data can be fitted with theoretical line profiles to determine the mean magnetic field strength in stellar active regions and a model-dependent fraction of the stellar surface (filling factor) covered by these regions. Random errors in the derived field strength and filling factor are parameterized in terms of signal-to-noise ratio, wavelength, spectral resolution, stellar rotation rate, and the magnetic parameters themselves. Weak line blends, if left uncorrected, can have significant systematic effects on the derived magnetic parameters, and thus several methods are developed to compensate partially for them. The magnetic parameters determined by previous methods likely have systematic errors because of such line blends and because of line saturation effects. Other sources of systematic error are explored in detail. These sources of error currently make it difficult to determine the magnetic parameters of individual stars to better than about + or - 20 percent.

  8. Further comments on the effects of vacuum birefringence on the polarization of X-rays emitted from magnetic neutron stars

    Science.gov (United States)

    Chanan, G. A.; Novick, R.; Silver, E. H.

    1979-01-01

    The birefringence of the vacuum in the presence of strong (of the order of 1 teragauss) magnetic fields will in general affect the polarization of X-rays propagating through these fields. Two of the four Stokes parameters will vary so rapidly with wavelength as to be 'washed out' and unobservable, but the remaining two parameters will be unaffected. These results show that one conclusion of an earlier work is incorrect: Polarized X-ray emission from the surface of a magnetic neutron star will not in general be completely depolarized by the effects of vacuum birefringence. In particular, this birefringence has no effect on the linear polarization of cyclotron emission from the poles of magnetic neutron stars, and a similar result holds for synchrotron emission. More general cases of the propagation of polarized X-rays in magnetic fields are also discussed.

  9. Plunging neutron stars as origin of organised magnetic field in galactic nuclei

    Czech Academy of Sciences Publication Activity Database

    Karas, Vladimír; Kopáček, Ondřej; Kunneriath, D.; Zajaček, M.; Araudo, Anabella; Eckart, A.; Kovář, J.

    2017-01-01

    Roč. 47, č. 2 (2017), s. 124-132 ISSN 1335-1842 R&D Projects: GA ČR GA17-16287S; GA MŠk LD15061 Grant - others:COST(XE) MP1304 Institutional support: RVO:67985815 Keywords : magnetic fields * neutron stars * galactic centre Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics OBOR OECD: Astronomy (including astrophysics,space science) Impact factor: 0.336, year: 2016

  10. Particle acceleration at the magnetic poles of a neutron star

    International Nuclear Information System (INIS)

    Jones, P.B.

    1977-01-01

    The magnetic conversion of a photon in a neutron star magnetosphere near one of the magnetic poles is followed by acceleration of the electron and positron to ultra-relativistic energies. The positron moves along open magnetic flux lines to the light cylinder. The electron incident on the stellar surface produces an electromagnetic shower. Following a comment by Cheng and Ruderman (Astrophys.J.;214:598 (1977)), an order of magnitude estimate has been made of the spectrum of backward moving photons created in the electron shower. The most important source of photons is shown to be the formation of the giant dipole state in Fe 56 . Under the assumption that the surface magnetic flux density exceeds 10 12 G, the photons have, with high probability, mean free paths for magnetic conversion in the magnetosphere of 1 4 cm. An equation for the maximum acceleratin potential has been obtained in a one-dimensional model of pair creation and electron multiplication based on this photon source. The model has been applied to the phenomenon of subpulse drift in pulsars. The plasma accelerated at the magnetic pole has three components; positrons, protons and light nuclei (Z < approximately 6) formed by spallation, and iron group nuclei. Equations determining their relative fluxes have been found. The light nuclei include those with Z = 3 to 5, usually considered to be present in galactic cosmic rays only as a result of the interaction of heavier nuclei with the interstellar medium. (author)

  11. Toward a measurement of weak magnetism in {sup 6}He decay

    Energy Technology Data Exchange (ETDEWEB)

    Huyan, X.; Naviliat-Cuncic, O., E-mail: naviliat@nscl.msu.edu; Bazin, D.; Gade, A.; Hughes, M.; Liddick, S.; Minamisono, K.; Noji, S.; Paulauskas, S. V.; Simon, A. [Michigan State University, National Superconducting Cyclotron Laboratory (United States); Voytas, P. [Wittenberg University, Department of Physics (United States); Weisshaar, D. [Michigan State University, National Superconducting Cyclotron Laboratory (United States)

    2016-12-15

    Sensitive searches for exotic scalar and tensor couplings in nuclear and neutron decays involve precision measurements of the shape of the β-energy spectrum. We have performed a high statistics measurement of the β-energy spectrum in the allowed Gamow-Teller decay of {sup 6}He with the aim to first find evidence of the contribution due to the weak magnetism form factor. We review here the motivation, describe the principle of the measurement, summarize the theoretical corrections to the allowed phase space, and anticipate the expected statistical precision.

  12. Magnetization dynamics of weak stripe domains in Fe-N thin films: a multi-technique complementary approach.

    Science.gov (United States)

    Camara, Ibrahima; Tacchi, Silvia; Garnier, Louis-Charles; Eddrief, Mahmoud; Fortuna, Franck; Carlotti, Giovanni; Marangolo, Massimiliano

    2017-09-26

    The resonant eigenmodes of a nitrogen-implanted iron α'-FeN characterized by weak stripe domains are investigated by Brillouin light scattering and broadband ferromagnetic resonance experiments, assisted by micromagnetic simulations. The spectrum of the dynamic eigenmodes in the presence of the weak stripes is very rich and two different families of modes can be selectively detected using different techniques or different experimental configurations. Attention is paid to the evolution of the mode frequencies and spatial profiles under the application of an external magnetic field, of variable intensity, in the direction parallel or transverse to the stripes. The different evolution of the modes with the external magnetic field is accompanied by a distinctive spatial localization in specific regions, such as the closure domains at the surface of the stripes and the bulk domains localized in the inner part of the stripes. The complementarity of BLS and FMR techniques, based on different selection rules, is found to be a fruitful tool for the study of the wealth of localized mag-netic excitations generally found in nanostructures. © 2017 IOP Publishing Ltd.

  13. Theoretical basal Ca II fluxes for late-type stars: results from magnetic wave models with time-dependent ionization and multi-level radiation treatments

    Science.gov (United States)

    Fawzy, Diaa E.; Stȩpień, K.

    2018-03-01

    In the current study we present ab initio numerical computations of the generation and propagation of longitudinal waves in magnetic flux tubes embedded in the atmospheres of late-type stars. The interaction between convective turbulence and the magnetic structure is computed and the obtained longitudinal wave energy flux is used in a self-consistent manner to excite the small-scale magnetic flux tubes. In the current study we reduce the number of assumptions made in our previous studies by considering the full magnetic wave energy fluxes and spectra as well as time-dependent ionization (TDI) of hydrogen, employing multi-level Ca II atomic models, and taking into account departures from local thermodynamic equilibrium. Our models employ the recently confirmed value of the mixing-length parameter α=1.8. Regions with strong magnetic fields (magnetic filling factors of up to 50%) are also considered in the current study. The computed Ca II emission fluxes show a strong dependence on the magnetic filling factors, and the effect of time-dependent ionization (TDI) turns out to be very important in the atmospheres of late-type stars heated by acoustic and magnetic waves. The emitted Ca II fluxes with TDI included into the model are decreased by factors that range from 1.4 to 5.5 for G0V and M0V stars, respectively, compared to models that do not consider TDI. The results of our computations are compared with observations. Excellent agreement between the observed and predicted basal flux is obtained. The predicted trend of Ca II emission flux with magnetic filling factor and stellar surface temperature also agrees well with the observations but the calculated maximum fluxes for stars of different spectral types are about two times lower than observations. Though the longitudinal MHD waves considered here are important for chromosphere heating in high activity stars, additional heating mechanism(s) are apparently present.

  14. Discovery of new magnetic early-B stars within the MiMeS HARPSpol survey

    Czech Academy of Sciences Publication Activity Database

    Alecian, E.; Kochukhov, O.; Petit, V.; Grunhut, J.; Landstreet, J.; Oksala, Mary E.; Wade, G.A.; Hussain, G.; Neiner, C.; Bohlender, D.A.

    2014-01-01

    Roč. 567, July (2014), A28/1-A28/19 ISSN 0004-6361 R&D Projects: GA ČR(CZ) GAP209/11/1198 Institutional support: RVO:67985815 Keywords : star s * magnetic field * chemically peculiar Subject RIV: BN - Astronomy, Celestial Mechanics, Astrophysics Impact factor: 4.378, year: 2014

  15. Global low-frequency modes in weakly ionized magnetized plasmas: effects of equilibrium plasma rotation

    International Nuclear Information System (INIS)

    Sosenko, P.; Pierre, Th.; Zagorodny, A.

    2004-01-01

    The linear and non-linear properties of global low-frequency oscillations in cylindrical weakly ionized magnetized plasmas are investigated analytically for the conditions of equilibrium plasma rotation. The theoretical results are compared with the experimental observations of rotating plasmas in laboratory devices, such as Mistral and Mirabelle in France, and KIWI in Germany. (authors)

  16. Weak interactions in astrophysics and cosmology

    International Nuclear Information System (INIS)

    Taylor, R.J.

    1977-01-01

    There ar many problems in astrophysics and cosmology in which the form of the weak interactions, their strength or the number of weakly interacting particles, is very important. It is possible that astronomical observations may give some information about the weak interactions. In the conventional hot big bang cosmological theory the number of leptons with associated neutrinos influences the speed of expansion of the Universe and the chemical composition of pre-galactic matter. The strength of the weak interaction, as exemplified by the half-life of the neutron, has a similar effect. In addition, the form of the weak interactions will determine how effectively neutrino viscosity can smooth out irregularities in the early Universe. Because neutrinos have a very long mean free path, they can escape from the central region of stars whereas photons can only escape from the surface. In late stages of stellar evolution, neutrino luminosity is often believed to be much greater than photon luminosity. This can both accelerate the cooling of dying stars and influence the stages of stellar evolution leading to the onset of supernova explosions. In pre-super-novae it is even possible that very dense stellar cores can be opaque to neutrinos and that the absorption or scattering of neutrinos can cause the explosion. These results depend crucially on the form of the weak interactions, with the discovery of neutral currents being very important. Until the solar neutrino experiment has been reconciled with theory, the possible role of uncertainties in the weak interactions cannot be ignored. (author)

  17. RADIATIVELY EFFICIENT MAGNETIZED BONDI ACCRETION

    International Nuclear Information System (INIS)

    Cunningham, Andrew J.; Klein, Richard I.; McKee, Christopher F.; Krumholz, Mark R.; Teyssier, Romain

    2012-01-01

    We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion from a uniform, isothermal gas onto a resistive, stationary point mass. Only mass, not magnetic flux, accretes onto the point mass. The simulations for this study avoid complications arising from boundary conditions by keeping the boundaries far from the accreting object. Our simulations leverage adaptive refinement methodology to attain high spatial fidelity close to the accreting object. Our results are particularly relevant to the problem of star formation from a magnetized molecular cloud in which thermal energy is radiated away on timescales much shorter than the dynamical timescale. Contrary to the adiabatic case, our simulations show convergence toward a finite accretion rate in the limit in which the radius of the accreting object vanishes, regardless of magnetic field strength. For very weak magnetic fields, the accretion rate first approaches the Bondi value and then drops by a factor of ∼2 as magnetic flux builds up near the point mass. For strong magnetic fields, the steady-state accretion rate is reduced by a factor of ∼0.2 β 1/2 compared to the Bondi value, where β is the ratio of the gas pressure to the magnetic pressure. We give a simple expression for the accretion rate as a function of the magnetic field strength. Approximate analytic results are given in the Appendices for both time-dependent accretion in the limit of weak magnetic fields and steady-state accretion for the case of strong magnetic fields.

  18. RADIATIVELY EFFICIENT MAGNETIZED BONDI ACCRETION

    Energy Technology Data Exchange (ETDEWEB)

    Cunningham, Andrew J.; Klein, Richard I. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); McKee, Christopher F. [Department of Astronomy, University of California Berkeley, Berkeley, CA 94720 (United States); Krumholz, Mark R. [Department of Astronomy and Astrophysics, University of California Santa Cruz, Santa Cruz, CA 94560 (United States); Teyssier, Romain, E-mail: ajcunn@gmail.com [Service d' Astrophysique, CEA Saclay, 91191 Gif-sur-Yvette (France)

    2012-01-10

    We have carried out a numerical study of the effect of large-scale magnetic fields on the rate of accretion from a uniform, isothermal gas onto a resistive, stationary point mass. Only mass, not magnetic flux, accretes onto the point mass. The simulations for this study avoid complications arising from boundary conditions by keeping the boundaries far from the accreting object. Our simulations leverage adaptive refinement methodology to attain high spatial fidelity close to the accreting object. Our results are particularly relevant to the problem of star formation from a magnetized molecular cloud in which thermal energy is radiated away on timescales much shorter than the dynamical timescale. Contrary to the adiabatic case, our simulations show convergence toward a finite accretion rate in the limit in which the radius of the accreting object vanishes, regardless of magnetic field strength. For very weak magnetic fields, the accretion rate first approaches the Bondi value and then drops by a factor of {approx}2 as magnetic flux builds up near the point mass. For strong magnetic fields, the steady-state accretion rate is reduced by a factor of {approx}0.2 {beta}{sup 1/2} compared to the Bondi value, where {beta} is the ratio of the gas pressure to the magnetic pressure. We give a simple expression for the accretion rate as a function of the magnetic field strength. Approximate analytic results are given in the Appendices for both time-dependent accretion in the limit of weak magnetic fields and steady-state accretion for the case of strong magnetic fields.

  19. EVOLUTION OF INTERMEDIATE-MASS X-RAY BINARIES DRIVEN BY THE MAGNETIC BRAKING OF AP/BP STARS. I. ULTRACOMPACT X-RAY BINARIES

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Wen-Cong [School of Physics and Electrical Information, Shangqiu Normal University, Shangqiu 476000 (China); Podsiadlowski, Philipp, E-mail: chenwc@pku.edu.cn [Department of Physics, University of Oxford, Oxford OX1 3RH (United Kingdom)

    2016-10-20

    It is generally believed that ultracompact X-ray binaries (UCXBs) evolved from binaries consisting of a neutron star accreting from a low-mass white dwarf (WD) or helium star where mass transfer is driven by gravitational radiation. However, the standard WD evolutionary channel cannot produce the relatively long-period (40–60 minutes) UCXBs with a high time-averaged mass-transfer rate. In this work, we explore an alternative evolutionary route toward UCXBs, where the companions evolve from intermediate-mass Ap/Bp stars with an anomalously strong magnetic field (100–10,000 G). Including the magnetic braking caused by the coupling between the magnetic field and an irradiation-driven wind induced by the X-ray flux from the accreting component, we show that intermediate-mass X-ray binaries (IMXBs) can evolve into UCXBs. Using the MESA code, we have calculated evolutionary sequences for a large number of IMXBs. The simulated results indicate that, for a small wind-driving efficiency f = 10{sup −5}, the anomalous magnetic braking can drive IMXBs to an ultra-short period of 11 minutes. Comparing our simulated results with the observed parameters of 15 identified UCXBs, the anomalous magnetic braking evolutionary channel can account for the formation of seven and eight sources with f = 10{sup −3}, and 10{sup −5}, respectively. In particular, a relatively large value of f can fit three of the long-period, persistent sources with a high mass-transfer rate. Though the proportion of Ap/Bp stars in intermediate-mass stars is only 5%, the lifetime of the UCXB phase is ≳2 Gyr, producing a relatively high number of observable systems, making this an alternative evolutionary channel for the formation of UCXBs.

  20. Effects of the weak magnetic field and electron diffusion on the spatial potential and negative ion transport in the negative ion source

    International Nuclear Information System (INIS)

    Sakurabayashi, T.; Hatayama, A.; Bacal, M.

    2004-01-01

    The effects of the weak magnetic field on the negative ion (H - ) extraction in a negative ion source have been studied by means of a two-dimensional electrostatic particle simulation. A particle-in-cell model is used which simulates the motion of the charged particles in their self-consistent electric field. In addition, the effect of the electron diffusion across the weak magnetic field is taken into account by a simple random-walk model with a step length Δx per time step Δt; Δx=√(2D perpendicular )Δt)·ξ x , where D perpendicular ) and ξ x are the perpendicular diffusion coefficient and normal random numbers. Under this simple diffusion model, the electron diffusion has no significant effects on the H - transport. Most electrons are magnetized by the weak magnetic field and lost along the field line. As a result, more H - ions arrive instead of electrons in the region close to the plasma grid in order to ensure the plasma neutrality

  1. Rotational Evolution and Magnetic Field of AP Stars

    Science.gov (United States)

    Xiaojun, C.; Matsuura, O. T.

    1990-11-01

    RESUMO. Prop6e- se qLie 0 campo de estrelas Ap pode ser 9cr ado pelo mecanismo de na base clo envelope c 0 fl V C C t V 0, C t r a ri S p 0 r t a d C) p a r a a S LI p e r f C 1 e p e I a Instabllidade de boiament 0 na ase de Haya hi. Campos cibservados permit em est imar uma perda de momento durante a ase pr -Seque%nC:ia P r ri C: p a I a ci ni p a t V C I C: C) m a s C) b s e r V a nT C 5. E S t r C I a S A normals, que ro t a ao , ria0 most ram camp Os :os superficia; importantes e isto pode ac:oriteaer C LIma protoestrela evolue para Sequencia Principal em passar pela fase de Hayashi. ABSTRACT: It 5 proposed that the ma9netic field o Ap stars may be enerated by the dynamo at the base of the convective envelope, arid transported to the surface b y t h C i ri s t a b iii t y C) f b LI 0 y a n c y i n t h C H a y a s hi p h a s e. Observed surface ma9netic fields allow to estimate a 1055 of an9ular momentum during the pre-Main Sequence phase compatible with the observations. apidIy rotating normal A stars do not shciw important surface magnetic fields and this may occur if a protostar evcilves to Main Sequence skipping the Hayashi phase. Key words: HYDROMAGNETICS - STARS-PECULIAR A

  2. Cellular target of weak magnetic fields: ionic conduction along actin filaments of microvilli.

    Science.gov (United States)

    Gartzke, Joachim; Lange, Klaus

    2002-11-01

    The interaction of weak electromagnetic fields (EMF) with living cells is a most important but still unresolved biophysical problem. For this interaction, thermal and other types of noise appear to cause severe restrictions in the action of weak signals on relevant components of the cell. A recently presented general concept of regulation of ion and substrate pathways through microvilli provides a possible theoretical basis for the comprehension of physiological effects of even extremely low magnetic fields. The actin-based core of microfilaments in microvilli is proposed to represent a cellular interaction site for magnetic fields. Both the central role of F-actin in Ca2+ signaling and its polyelectrolyte nature eliciting specific ion conduction properties render the microvillar actin filament bundle an ideal interaction site for magnetic and electric fields. Ion channels at the tip of microvilli are connected with the cytoplasm by a bundle of microfilaments forming a diffusion barrier system. Because of its polyelectrolyte nature, the microfilament core of microvilli allows Ca2+ entry into the cytoplasm via nonlinear cable-like cation conduction through arrays of condensed ion clouds. The interaction of ion clouds with periodically applied EMFs and field-induced cation pumping through the cascade of potential barriers on the F-actin polyelectrolyte follows well-known physical principles of ion-magnetic field (MF) interaction and signal discrimination as described by the stochastic resonance and Brownian motor hypotheses. The proposed interaction mechanism is in accord with our present knowledge about Ca2+ signaling as the biological main target of MFs and the postulated extreme sensitivity for coherent excitation by very low field energies within specific amplitude and frequency windows. Microvillar F-actin bundles shielded by a lipid membrane appear to function like electronic integration devices for signal-to-noise enhancement; the influence of coherent signals

  3. Old and new neutron stars

    International Nuclear Information System (INIS)

    Ruderman, M.

    1984-09-01

    The youngest known radiopulsar in the rapidly spinning magnetized neutron star which powers the Crab Nebula, the remnant of the historical supernova explosion of 1054 AD. Similar neutron stars are probably born at least every few hundred years, but are less frequent than Galactic supernova explosions. They are initially sources of extreme relativistic electron and/or positron winds (approx.10 38 s -1 of 10 12 eV leptons) which greatly decrease as the neutron stars spin down to become mature pulsars. After several million years these neutron stars are no longer observed as radiopulsars, perhaps because of large magnetic field decay. However, a substantial fraction of the 10 8 old dead pulsars in the Galaxy are the most probable source for the isotropically distributed γ-ray burst detected several times per week at the earth. Some old neutron stars are spun-up by accretion from companions to be resurrected as rapidly spinning low magnetic field radiopulsars. 52 references, 6 figures, 3 tables

  4. Accreting neutron stars, black holes, and degenerate dwarf stars.

    Science.gov (United States)

    Pines, D

    1980-02-08

    During the past 8 years, extended temporal and broadband spectroscopic studies carried out by x-ray astronomical satellites have led to the identification of specific compact x-ray sources as accreting neutron stars, black holes, and degenerate dwarf stars in close binary systems. Such sources provide a unique opportunity to study matter under extreme conditions not accessible in the terrestrial laboratory. Quantitative theoretical models have been developed which demonstrate that detailed studies of these sources will lead to a greatly increased understanding of dense and superdense hadron matter, hadron superfluidity, high-temperature plasma in superstrong magnetic fields, and physical processes in strong gravitational fields. Through a combination of theory and observation such studies will make possible the determination of the mass, radius, magnetic field, and structure of neutron stars and degenerate dwarf stars and the identification of further candidate black holes, and will contribute appreciably to our understanding of the physics of accretion by compact astronomical objects.

  5. White Dwarf Stars

    OpenAIRE

    Kepler, S. O.; Romero, Alejandra Daniela; Pelisoli, Ingrid; Ourique, Gustavo

    2017-01-01

    White dwarf stars are the final stage of most stars, born single or in multiple systems. We discuss the identification, magnetic fields, and mass distribution for white dwarfs detected from spectra obtained by the Sloan Digital Sky Survey up to Data Release 13 in 2016, which lead to the increase in the number of spectroscopically identified white dwarf stars from 5000 to 39000. This number includes only white dwarf stars with log g >= 6.5 stars, i.e., excluding the Extremely Low Mass white dw...

  6. VizieR Online Data Catalog: Magnetic early B-type stars. I. (Shultz+, 2018)

    Science.gov (United States)

    Shultz, M.; Wade, G. A.; Rivinius, Th.; Neiner, C.; Alecian, E.; Bohlender, D.; Monin, D.; Sikora, J.; Mimes Collaboration; Binamics Collaboration

    2018-03-01

    Longitudinal magnetic field measurements of early B-type stars derived from 1) least-squares deconvolution profiles extracted from high-resolution spectropolarimetric data (ESPaDOnS, Narval, HARPSpol), using masks consisting of metallic lines, metallic + He lines, individual chemical elements, as well as single-line H measurements; and 2) from single-line low-resolution spectropolarimetric observations with dimaPol. (3 data files).

  7. Zeeman effect in sulfur monoxide: a tool to probe magnetic fields in star forming regions

    DEFF Research Database (Denmark)

    Cazzoli, Gabriele; Lattanzi, Valerio; Coriani, Sonia

    2017-01-01

    Context. Magnetic fields play a fundamental role in star formation processes and the best method to evaluate their intensity is to measure the Zeeman effect of atomic and molecular lines. However, a direct measurement of the Zeeman spectral pattern from interstellar molecular species is challengi...

  8. Potentially large contributions to the muon anomalous magnetic moment from weak-isosinglet squarks in E6 superstring models

    International Nuclear Information System (INIS)

    Morris, D.A.

    1988-01-01

    We examine contributions to the anomalous magnetic moment of the muon from weak-isosinglet squarks found in E 6 superstring models. We find that such contributions are up to 2 orders of magnitude larger than those previously calculated and correspondingly require smaller Yukawa couplings in order to maintain agreement with the measured muon anomalous magnetic moment

  9. Magnet design with 100-kA HTS STARS conductors for the helical fusion reactor

    Science.gov (United States)

    Yanagi, N.; Terazaki, Y.; Ito, S.; Tamura, H.; Hamaguchi, S.; Mito, T.; Hashizume, H.; Sagara, A.

    2016-12-01

    The high-temperature superconducting (HTS) option is employed for the conceptual design of the LHD-type helical fusion reactor FFHR-d1. The 100-kA-class STARS (Stacked Tapes Assembled in Rigid Structure) conductor is used for the magnet system including the continuously wound helical coils. Protection of the magnet system in case of a quench is a crucial issue and the hot-spot temperature during an emergency discharge is estimated based on the zero-dimensional and one-dimensional analyses. The number of division of the coil winding package is examined to limit the voltage generation. For cooling the HTS magnet, helium gas flow is considered and its feasibility is examined by simple analysis as a first step.

  10. Neutron Star Science with the NuSTAR

    Energy Technology Data Exchange (ETDEWEB)

    Vogel, J. K. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-10-16

    The Nuclear Spectroscopic Telescope Array (NuSTAR), launched in June 2012, helped scientists obtain for the first time a sensitive high-­energy X-­ray map of the sky with extraordinary resolution. This pioneering telescope has aided in the understanding of how stars explode and neutron stars are born. LLNL is a founding member of the NuSTAR project, with key personnel on its optics and science team. We used NuSTAR to observe and analyze the observations of different neutron star classes identified in the last decade that are still poorly understood. These studies not only help to comprehend newly discovered astrophysical phenomena and emission processes for members of the neutron star family, but also expand the utility of such observations for addressing broader questions in astrophysics and other physics disciplines. For example, neutron stars provide an excellent laboratory to study exotic and extreme phenomena, such as the equation of state of the densest matter known, the behavior of matter in extreme magnetic fields, and the effects of general relativity. At the same time, knowing their accurate populations has profound implications for understanding the life cycle of massive stars, star collapse, and overall galactic evolution.

  11. Magnetic static and scaling properties of the weak random-axis magnet (DyxY1-x)Al2

    International Nuclear Information System (INIS)

    Gehring, P.M.; Salamon, M.B.; del Moral, A.; Arnaudas, J.I.

    1990-01-01

    The effects of a random component of the magnetocrystalline anisotropy on the magnetic properties and critical behavior of polycrystalline DyAl 2 have been investigated using dc magnetic measurements. Random magnetic anisotropy (RMA) is produced by site-diluting ferromagnetic DyAl 2 with the nonmagnetic, isomorphic intermetallic YAl 2 . Dilution distorts the cubic Laves-phase unit cell because of a slight lattice mismatch thereby lowering the local crystal symmetry in a random fashion. Additional contributions to the RMA come from spin-orbit scattering by the conduction electrons. Hysteresis loops display little remanence and very small coercive fields, suggesting a weak RMA. This is consistent with estimates of the RMA strength D obtained using an approach of Chudnovsky et al. The magnetization at high temperatures (T>4T c ) is well described by a Curie-Weiss law. The paramagnetic Curie temperatures are positive, implying an average ferromagnetic exchange coupling between Dy ions, and increase with x. The paramagnetic moment shows no evidence of quenching across the series, thus confirming the well-localized nature of the 4f electronic orbitals. Low-field thermal scans of the bulk dc magnetization show no sign of a spontaneous moment for Dy concentrations 0.10≤x≤0.90, yet a sharp increase in the magnetization occurs at a temperature T c that increases with x. A ferromagnetic scaling analysis applied to the line of transitions at T c results in a surprisingly good collapse of the magnetization data. By extension of prior theoretical work of Aharony and Pytte, a direct connection can be made between pure and RMA exponents, which gives remarkable agreement with the experimental values

  12. The discovery of 13.72-min oscillations in the cool magnetic Ap star HD 217522

    International Nuclear Information System (INIS)

    Kurtz, D.W.

    1983-01-01

    The discovery is announced of oscillations with a period near 13.72 min in the cool magnetic Ap star HD 217522. 97 hr of high-speed photometric observations are presented, obtained on 18 nights spread over a time span of 74 days in 1982. The amplitude of the oscillations in HD 217522 is variable from night to night and also on a longer time-scale. A frequency analysis of the data identifies the principal frequency of oscillation to be 4.37435+-0.00014 hr -1 . Because of the complexities of the amplitude modulation of the light curve and the very low amplitude of the light variations, the data are insufficient for a complete frequency solution. This star is the seventh member of the class of rapidly oscillating Ap stars. (author)

  13. On the Use of Line Depth Ratios to Measure Starspot Properties on Magnetically Active Stars

    Science.gov (United States)

    O'Neal, Douglas

    2006-07-01

    Photometric and spectroscopic techniques have proven to be effective ways to measure the properties of dark, cool starspots on magnetically active stars. Recently, a technique was introduced using atomic line depth ratios (LDRs) to measure starspot properties. Carefully reproducing this technique using a new set of spectroscopic observations of active stars, we find that the LDR technique encounters difficulties, specifically by overestimating spot temperatures (because the atomic lines blend with titanium oxide absorption in cooler spots) and by not tightly constraining the filling factor of spots. While the use of LDRs for active star studies has great promise, we believe that these concerns need to be addressed before the technique is more widely applied. This paper includes data taken at McDonald Observatory of the University of Texas at Austin.

  14. The different origins of magnetic fields and activity in the Hertzsprung gap stars, OU Andromedae and 31 Comae

    Science.gov (United States)

    Borisova, A.; Aurière, M.; Petit, P.; Konstantinova-Antova, R.; Charbonnel, C.; Drake, N. A.

    2016-06-01

    Context. When crossing the Hertzsprung gap, intermediate-mass stars develop a convective envelope. Fast rotators on the main sequence, or Ap star descendants, are expected to become magnetic active subgiants during this evolutionary phase. Aims: We compare the surface magnetic fields and activity indicators of two active, fast rotating red giants with similar masses and spectral class but different rotation rates - OU And (Prot = 24.2 d) and 31 Com (Prot = 6.8 d) - to address the question of the origin of their magnetism and high activity. Methods: Observations were carried out with the Narval spectropolarimeter in 2008 and 2013. We used the least-squares deconvolution (LSD) technique to extract Stokes V and I profiles with high signal-to-noise ratio to detect Zeeman signatures of the magnetic field of the stars. We then provide Zeeman-Doppler imaging (ZDI), activity indicators monitoring, and a precise estimation of stellar parameters. We use state-of-the-art stellar evolutionary models, including rotation, to infer the evolutionary status of our giants, as well as their initial rotation velocity on the main sequence, and we interpret our observational results in the light of the theoretical Rossby numbers. Results: The detected magnetic field of OU Andromedae (OU And) is a strong one. Its longitudinal component Bl reaches 40 G and presents an about sinusoidal variation with reversal of the polarity. The magnetic topology of OU And is dominated by large-scale elements and is mainly poloidal with an important dipole component, as well as a significant toroidal component. The detected magnetic field of 31 Comae (31 Com) is weaker, with a magnetic map showing a more complex field geometry, and poloidal and toroidal components of equal contributions. The evolutionary models show that the progenitors of OU And and 31 Com must have been rotating at velocities that correspond to 30 and 53%, respectively, of their critical rotation velocity on the zero age main sequence

  15. Global, finite energy, weak solutions for the NLS with rough, time-dependent magnetic potentials

    Science.gov (United States)

    Antonelli, Paolo; Michelangeli, Alessandro; Scandone, Raffaele

    2018-04-01

    We prove the existence of weak solutions in the space of energy for a class of nonlinear Schrödinger equations in the presence of a external, rough, time-dependent magnetic potential. Under our assumptions, it is not possible to study the problem by means of usual arguments like resolvent techniques or Fourier integral operators, for example. We use a parabolic regularisation, and we solve the approximating Cauchy problem. This is achieved by obtaining suitable smoothing estimates for the dissipative evolution. The total mass and energy bounds allow to extend the solution globally in time. We then infer sufficient compactness properties in order to produce a global-in-time finite energy weak solution to our original problem.

  16. Flares on a Bp Star

    Science.gov (United States)

    Mullan, D. J.

    2009-09-01

    Two large X-ray flares have been reported from the direction of a magnetic B2p star (σ Ori E). Sanz-Forcada et al. have suggested that the flares did not occur on the B2p star but on a companion of late spectral type. A star which is a candidate for a late-type flare star near σ Ori E has recently been identified by Bouy et al. However, based on the properties of the flares, and based on a recent model of rotating magnetospheres, we argue that, rather than attributing the two flares to a late-type dwarf, it is a viable hypothesis that the flares were magnetic phenomena associated with the rotating magnetosphere of the B2p star itself.

  17. FLARES ON A Bp STAR

    International Nuclear Information System (INIS)

    Mullan, D. J.

    2009-01-01

    Two large X-ray flares have been reported from the direction of a magnetic B2p star (σ Ori E). Sanz-Forcada et al. have suggested that the flares did not occur on the B2p star but on a companion of late spectral type. A star which is a candidate for a late-type flare star near σ Ori E has recently been identified by Bouy et al. However, based on the properties of the flares, and based on a recent model of rotating magnetospheres, we argue that, rather than attributing the two flares to a late-type dwarf, it is a viable hypothesis that the flares were magnetic phenomena associated with the rotating magnetosphere of the B2p star itself.

  18. Low virial parameters in molecular clouds: Implications for high-mass star formation and magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Kauffmann, Jens; Pillai, Thushara [Astronomy Department, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Goldsmith, Paul F., E-mail: jens.kauffmann@astro.caltech.edu, E-mail: tpillai@astro.caltech.edu [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Boulevard, Pasadena, CA 91109 (United States)

    2013-12-20

    Whether or not molecular clouds and embedded cloud fragments are stable against collapse is of utmost importance for the study of the star formation process. Only 'supercritical' cloud fragments are able to collapse and form stars. The virial parameter α = M {sub vir}/M, which compares the virial mass to the actual mass, provides one way to gauge stability against collapse. Supercritical cloud fragments are characterized by α ≲ 2, as indicated by a comprehensive stability analysis considering perturbations in pressure and density gradients. Past research has suggested that virial parameters α ≳ 2 prevail in clouds. This would suggest that collapse toward star formation is a gradual and relatively slow process and that magnetic fields are not needed to explain the observed cloud structure. Here, we review a range of very recent observational studies that derive virial parameters <<2 and compile a catalog of 1325 virial parameter estimates. Low values of α are in particular observed for regions of high-mass star formation (HMSF). These observations may argue for a more rapid and violent evolution during collapse. This would enable 'competitive accretion' in HMSF, constrain some models of 'monolithic collapse', and might explain the absence of high-mass starless cores. Alternatively, the data could point at the presence of significant magnetic fields ∼1 mG at high gas densities. We examine to what extent the derived observational properties might be biased by observational or theoretical uncertainties. For a wide range of reasonable parameters, our conclusions appear to be robust with respect to such biases.

  19. Magnetic Hydrogen Atmosphere Models and the Neutron Star RX J1856.5-3754

    Energy Technology Data Exchange (ETDEWEB)

    Ho, Wynn C.G.; /MIT, MKI /KIPAC, Menlo Park; Kaplan, David L.; /MIT, MKI; Chang, Philip; /UC, Berkeley, Astron. Dept. /UC, Santa Barbara; van Adelsberg, Matthew; /Cornell; Potekhin, Alexander Y.; /Cornell U., Astron. Dept. /Ioffe Phys. Tech. Inst.

    2006-12-08

    RX J1856.5-3754 is one of the brightest nearby isolated neutron stars, and considerable observational resources have been devoted to it. However, current models are unable to satisfactorily explain the data. We show that our latest models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a condensed surface can fit the entire spectrum, from X-rays to optical, of RX J1856.5-3754, within the uncertainties. In our simplest model, the best-fit parameters are an interstellar column density N{sub H} {approx} 1 x 10{sup 20} cm{sup -2} and an emitting area with R{sup {infinity}} {approx} 17 km (assuming a distance to RX J1856.5-3754 of 140 pc), temperature T{sup {infinity}} {approx} 4.3 x 10{sup 5} K, gravitational redshift z{sub g} {approx} 0.22, atmospheric hydrogen column y{sub H} {approx} 1 g cm{sup -2}, and magnetic field B {approx} (3-4) x 10{sup 12} G; the values for the temperature and magnetic field indicate an effective average over the surface. We also calculate a more realistic model, which accounts for magnetic field and temperature variations over the neutron star surface as well as general relativistic effects, to determine pulsations; we find there exist viewing geometries that produce pulsations near the currently observed limits. The origin of the thin atmospheres required to fit the data is an important question, and we briefly discuss mechanisms for producing these atmospheres. Our model thus represents the most self-consistent picture to date for explaining all the observations of RX J1856.5-3754.

  20. MN Lup: X-RAYS FROM A WEAKLY ACCRETING T TAURI STAR

    International Nuclear Information System (INIS)

    Günther, H. M.; Wolk, S. J.; Wolter, U.; Robrade, J.

    2013-01-01

    Young T Tauri stars (TTS) are surrounded by an accretion disk, which over time disperses due to photoevaporation, accretion, and possibly planet formation. The accretion shock on the central star produces an UV/optical veiling continuum, line emission, and X-ray signatures. As the accretion rate decreases, the impact on the central star must change. In this article we study MN Lup, a young star where no indications of a disk are seen in IR observations. We present XMM-Newton and VLT/UVES observations, some of them taken simultaneously. The X-ray data show that MN Lup is an active star with L X /L bol close to the saturation limit. However, we find high densities (n e > 3 × 10 10 cm –3 ) in the X-ray grating spectrum. This can be well fitted using an accretion shock model with an accretion rate of 2 × 10 –11 M ☉ yr –1 . Despite the simple Hα line profile which has a broad component, but no absorption signatures as typically seen on accreting TTS, we find rotational modulation in Ca II K and in photospheric absorption lines. These line profile modulations do not clearly indicate the presence of a localized hot accretion spot on the star. In the Hα line we see a prominence in absorption about 2R * above the stellar surface—the first of its kind on a TTS. MN Lup is also the only TTS where accretion is seen, but no dust disk is detected that could fuel it. We suggest that MN Lup presents a unique and short-lived state in the disk evolution. It may have lost its dust disk only recently and is now accreting the remaining gas at a very low rate.

  1. ULX spectra revisited: Accreting, highly magnetized neutron stars as the engines of ultraluminous X-ray sources

    Science.gov (United States)

    Koliopanos, Filippos; Vasilopoulos, Georgios; Godet, Olivier; Bachetti, Matteo; Webb, Natalie A.; Barret, Didier

    2017-12-01

    Aims: In light of recent discoveries of pulsating ultraluminous X-ray sources (ULXs) and recently introduced theoretical schemes that propose neutron stars (NSs) as the central engines of ULXs, we revisit the spectra of eighteen well known ULXs, in search of indications that favour this newly emerging hypothesis. Methods: We examine the spectra from high-quality XMM-Newton and NuSTAR observations. We use a combination of elementary black body and multicolour disk black body (MCD) models, to diagnose the predictions of classic and novel theoretical models of accretion onto NSs. We re-interpret the well established spectral characteristics of ULXs in terms of accretion onto lowly or highly magnetised NSs, and explore the resulting parameter space for consistency. Results: We confirm the previously noted presence of the low-energy (≲6 keV) spectral rollover and argue that it could be interpreted as due to thermal emission. The spectra are well described by a double thermal model consisting of a "hot" (≳1 keV) and a "cool" (≲0.7 keV) multicolour black body (MCB). Under the assumption that the "cool" MCD emission originates in a disk truncated at the neutron star magnetosphere, we find that all ULXs in our sample are consistent with accretion onto a highly magnetised (B ≳ 1012 G) neutron star. We note a strong correlation between the strength of the magnetic field, the temperature of the "hot" thermal component and the total unabsorbed luminosity. Examination of the NuSTAR data supports this interpretation and also confirms the presence of a weak, high-energy (≳15 keV) tail, most likely the result of modification of the MCB emission by inverse Compton scattering. We also note that the apparent high-energy tail, may simply be the result of mismodelling of MCB emission with an atypical temperature (T) versus radius (r) gradient, using a standard MCD model with a fixed gradient of T r-0.75. Conclusions: We have offered a new and robust physical interpretation for

  2. Multi-Wavelength Polarimetry of Isolated Neutron Stars

    Directory of Open Access Journals (Sweden)

    Roberto P. Mignani

    2018-03-01

    Full Text Available Isolated neutron stars are known to be endowed with extreme magnetic fields, whose maximum intensity ranges from 10 12 – 10 15 G, which permeates their magnetospheres. Their surrounding environment is also strongly magnetized, especially in the compact nebulae powered by the relativistic wind from young neutron stars. The radiation from isolated neutron stars and their surrounding nebulae is, thus, supposed to bring a strong polarization signature. Measuring the neutron star polarization brings important information about the properties of their magnetosphere and of their highly magnetized environment. Being the most numerous class of isolated neutron stars, polarization measurements have been traditionally carried out for radio pulsars, hence in the radio band. In this review, I summarize multi-wavelength linear polarization measurements obtained at wavelengths other than radio both for pulsars and other types of isolated neutron stars and outline future perspectives with the upcoming observing facilities.

  3. Which of Kepler's Stars Flare?

    Science.gov (United States)

    Kohler, Susanna

    2017-12-01

    The habitability of distant exoplanets is dependent upon many factors one of which is the activity of their host stars. To learn about which stars are most likely to flare, a recent study examines tens of thousands of stellar flares observed by Kepler.Need for a Broader SampleArtists rendering of a flaring dwarf star. [NASAs Goddard Space Flight Center/S. Wiessinger]Most of our understanding of what causes a star to flare is based on observations of the only star near enough to examine in detail the Sun. But in learning from a sample size of one, a challenge arises: we must determine which conclusions are unique to the Sun (or Sun-like stars), and which apply to other stellar types as well.Based on observations and modeling, astronomers think that stellar flares result from the reconnection of magnetic field lines in a stars outer atmosphere, the corona. The magnetic activity is thought to be driven by a dynamo caused by motions in the stars convective zone.HR diagram of the Kepler stars, with flaring main-sequence (yellow), giant (red) and A-star (green) stars in the authors sample indicated. [Van Doorsselaere et al. 2017]To test whether these ideas are true generally, we need to understand what types of stars exhibit flares, and what stellar properties correlate with flaring activity. A team of scientists led by Tom Van Doorsselaere (KU Leuven, Belgium) has now used an enormous sample of flares observed by Kepler to explore these statistics.Intriguing TrendsVan Doorsselaere and collaborators used a new automated flare detection and characterization algorithm to search through the raw light curves from Quarter 15 of the Kepler mission, building a sample of 16,850 flares on 6,662 stars. They then used these to study the dependence of the flare occurrence rate, duration, energy, and amplitude on the stellar spectral type and rotation period.This large statistical study led the authors to several interesting conclusions, including:Flare star incidence rate as a a

  4. Method for Transformation of Weakly Magnetic Minerals (Hematite, Goethite into Strongly Magnetic Mineral (Magnetite to Improve the Efficiency of Technologies for Oxidized Iron Ores Benefication

    Directory of Open Access Journals (Sweden)

    Ponomarenko, O.

    2015-03-01

    Full Text Available A new method for relatively simple transformation of weakly magnetic minerals (goethite (α-FeOOH and hematite (α-Fe2O3 into strongly magnetic mineral (magnetite (Fe3O4 was developed. It was shown, that transformation of structure and magnetic characteristics of go ethite and hematite are realized in the presence of starch at relatively low temperatures (in the range of 300—600 °С. Obtained results open up new possibilities for development of effective technologies for oxidized iron ore beneficiation.

  5. Development and investigation of an inverse problem solution algorithm for determination of Ap stars magnetic field geometry

    International Nuclear Information System (INIS)

    Piskunov, N.E.

    1985-01-01

    Mathematical formulation of the inverse problem of determination of magnetic field geometry from the polarization profiles of spectral lines is gven. The solving algorithm is proposed. A set of model calculations has shown the effectiveness of the algorithm, the high precision of magnetic star model parameters obtained and also the advantages of the inverse problem method over the commonly used method of interpretation of effective field curves

  6. Is there a highly magnetized neutron star in GX 301-2?

    Science.gov (United States)

    Doroshenko, V.; Santangelo, A.; Suleimanov, V.; Kreykenbohm, I.; Staubert, R.; Ferrigno, C.; Klochkov, D.

    2010-06-01

    We present the results of an in-depth study of the long-period X-ray pulsar GX 301-2. Using archival data of INTEGRAL, RXTE ASM, and CGRO BATSE, we study the spectral and timing properties of the source. Comparison of our timing results with previously published work reveals a secular decay of the orbital period at a rate of ≃ - 3.25 × 10-5 d yr-1, which is an order of magnitude faster than for other known systems. We argue that this is probably result either of the apsidal motion or of gravitational coupling of the matter lost by the optical companion with the neutron star, although current observations do not allow us to distinguish between those possibilities. We also propose a model to explain the observed long pulse period. We find that a very strong magnetic field B ~ 1014 G can explain the observed pulse period in the framework of existing models for torques affecting the neutron star. We show that the apparent contradiction with the magnetic field strength BCRSF ~ 4 × 1012 G derived from the observed cyclotron line position may be resolved if the line formation region resides in a tall accretion column of height ~2.5-3 RNS. The color temperature measured from the spectrum suggests that such a column may indeed be present, and our estimates show that its height is sufficient to explain the observed cyclotron line position.

  7. Magnetic Fields Versus Gravity

    Science.gov (United States)

    Hensley, Kerry

    2018-04-01

    Deep within giant molecular clouds, hidden by dense gas and dust, stars form. Unprecedented data from the Atacama Large Millimeter/submillimeter Array (ALMA) reveal the intricate magnetic structureswoven throughout one of the most massive star-forming regions in the Milky Way.How Stars Are BornThe Horsehead Nebulasdense column of gas and dust is opaque to visible light, but this infrared image reveals the young stars hidden in the dust. [NASA/ESA/Hubble Heritage Team]Simple theory dictates that when a dense clump of molecular gas becomes massive enough that its self-gravity overwhelms the thermal pressure of the cloud, the gas collapses and forms a star. In reality, however, star formation is more complicated than a simple give and take between gravity and pressure. Thedusty molecular gas in stellar nurseries is permeated with magnetic fields, which are thought to impede the inward pull of gravity and slow the rate of star formation.How can we learn about the magnetic fields of distant objects? One way is by measuring dust polarization. An elongated dust grain will tend to align itself with its short axis parallel to the direction of the magnetic field. This systematic alignment of the dust grains along the magnetic field lines polarizes the dust grains emission perpendicular to the local magnetic field. This allows us to infer the direction of the magnetic field from the direction of polarization.Magnetic field orientations for protostars e2 and e8 derived from Submillimeter Array observations (panels a through c) and ALMA observations (panels d and e). Click to enlarge. [Adapted from Koch et al. 2018]Tracing Magnetic FieldsPatrick Koch (Academia Sinica, Taiwan) and collaborators used high-sensitivity ALMA observations of dust polarization to learn more about the magnetic field morphology of Milky Way star-forming region W51. W51 is one of the largest star-forming regions in our galaxy, home to high-mass protostars e2, e8, and North.The ALMA observations reveal

  8. Calculation of effective impedance of polycrystals in weak magnetic fields

    International Nuclear Information System (INIS)

    Kaganova, I.M.

    2006-01-01

    We present results for the effective surface impedance tensor (EIT) of polycrystals of metals in a weak uniform magnetic field H. The frequency region corresponds to the region in which the local impedance boundary conditions are applicable. We suppose that the resistivity tensor ρ ik (H) of the single crystal grains out of which the polycrystal is composed, is known up to the terms of O(H 2 ). For polycrystals of metals of arbitrary symmetry, the elements of the EIT can be calculated to the same order in H, even if the tensor ρ ik (H) is strongly anisotropic. As examples, we write down the EIT of polycrystals of (i) cubic metals (ii) metals with ellipsoidal Fermi surfaces, and (iii) metals of tetragonal symmetry whose tensor ρ ik (0) is strongly anisotropic. Although polycrystals are metals that are isotropic on average, in the presence of a uniform magnetic field the structure of the EIT is not the same as the structure of the impedance tensor of an isotropic metal with a spherical Fermi surface. The results cannot be improved either by taking into account higher powers of H, or with respect to the anisotropy of the single crystal grains

  9. Phonons and magnetic excitation correlations in weak ferromagnetic YCrO{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Yogesh; Sahoo, Satyaprakash, E-mail: satya504@gmail.com, E-mail: guptaraj@iitk.ac.in, E-mail: rkatiyar@hpcf.upr.edu; Perez, William; Katiyar, Ram S., E-mail: satya504@gmail.com, E-mail: guptaraj@iitk.ac.in, E-mail: rkatiyar@hpcf.upr.edu [Department of Physics, University of Puerto Rico, Puerto Rico 00936-8377 (United States); Mukherjee, Somdutta [Department of Physics, Indian Institute of Technology, Kanpur (India); Gupta, Rajeev, E-mail: satya504@gmail.com, E-mail: guptaraj@iitk.ac.in, E-mail: rkatiyar@hpcf.upr.edu [Department of Physics, Indian Institute of Technology, Kanpur (India); Department of Materials Science Programme, Indian Institute of Technology, Kanpur (India); Garg, Ashish [Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur (India); Chatterjee, Ratnamala [Department of Physics, Indian Institute of Technology, Delhi (India)

    2014-05-14

    Here, we report the temperature dependent Raman spectroscopic studies on orthorhombically distorted perovskite YCrO{sub 3} over a temperature range of 20–300 K. Temperature dependence of DC-magnetization measurements under field cooled and zero field cooled protocols confirmed a Néel transition at T{sub N} ∼ 142 K. Magnetization isotherms recorded at 125 K show a clear loop opening without any magnetization saturation up to 20 kOe, indicating a coexistence of antiferromagnetic (AFM) and weak ferromagnetic (WFM) phases. Estimation of exchange constants using mean-field approximation further confirm the presence of a complex magnetic phase below T{sub N}. Temperature evolution of Raman line-shape parameters of the selected modes (associated with the octahedral rotation and A(Y)-shift in the unit-cell) reveal an anomalous phonon shift near T{sub N}. An additional phonon anomaly was identified at T{sup *} ∼ 60 K, which could possibly be attributed to the change in the spin dynamics. Moreover, the positive and negative shifts in Raman frequencies between T{sub N} and T{sup *} suggest competing WFM and AFM interactions. A close match between the phonon frequency of B{sub 3g} (3)-octahedral rotation mode with the square of sublattice magnetization between T{sub N} and T{sup *} is indicative of the presence of spin-phonon coupling in multiferroic YCrO{sub 3}.

  10. Sensed presence and mystical experiences are predicted by suggestibility, not by the application of transcranial weak complex magnetic fields.

    Science.gov (United States)

    Granqvist, Pehr; Fredrikson, Mats; Unge, Patrik; Hagenfeldt, Andrea; Valind, Sven; Larhammar, Dan; Larsson, Marcus

    2005-04-29

    Transcranial magnetic stimulation (TMS) with weak (micro Tesla) complex waveform fields have been claimed to evoke the sensed presence of a sentient being in up to 80% in the general population. These findings have had a questionable neurophysiological foundation as the fields are approximately six orders of magnitude weaker than ordinary TMS fields. Also, no independent replication has been reported. To replicate and extend previous findings, we performed a double-blind experiment (N=89), with a sham-field control group. Personality characteristics indicating suggestibility (absorption, signs of abnormal temporal lobe activity, and a "new age"-lifestyle orientation) were used as predictors. Sensed presence, mystical, and other somatosensory experiences previously reported from the magnetic field stimulation were outcome measures. We found no evidence for any effects of the magnetic fields, neither in the entire group, nor in individuals high in suggestibility. Because the personality characteristics significantly predicted outcomes, suggestibility may account for previously reported effects. Our results strongly question the earlier claims of experiential effects of weak magnetic fields.

  11. The Diversity of Neutron Stars

    Science.gov (United States)

    Kaplan, David L.

    2004-12-01

    Neutron stars are invaluable tools for exploring stellar death, the physics of ultra-dense matter, and the effects of extremely strong magnetic fields. The observed population of neutron stars is dominated by the >1000 radio pulsars, but there are distinct sub-populations that, while fewer in number, can have significant impact on our understanding of the issues mentioned above. These populations are the nearby, isolated neutron stars discovered by ROSAT, and the central compact objects in supernova remnants. The studies of both of these populations have been greatly accelerated in recent years through observations with the Chandra X-ray Observatory and the XMM-Newton telescope. First, we discuss radio, optical, and X-ray observations of the nearby neutron stars aimed at determining their relation to the Galactic neutron star population and at unraveling their complex physical processes by determining the basic astronomical parameters that define the population---distances, ages, and magnetic fields---the uncertainties in which limit any attempt to derive basic physical parameters for these objects. We conclude that these sources are 1e6 year-old cooling neutron stars with magnetic fields above 1e13 Gauss. Second, we describe the hollow supernova remnant problem: why many of the supernova remnants in the Galaxy have no indication of central neutron stars. We have undertaken an X-ray census of neutron stars in a volume-limited sample of Galactic supernova remnants, and from it conclude that either many supernovae do not produce neutron stars contrary to expectation, or that neutron stars can have a wide range in cooling behavior that makes many sources disappear from the X-ray sky.

  12. Polarization variablity among Wolf-Rayet stars. IV. A complete lack of circular polarization in the optical continuum

    International Nuclear Information System (INIS)

    Robert, C.; Moffat, A.F.J.

    1989-01-01

    Quasi-simultaneous blue and red, broadband optical monitoring in linear and circular polarization and in intensity has been carried out over an interval of three weeks for several Wolf-Rayet stars that show relatively large Delta P variations in linear polarization. No significant varying Delta V component of circular polarization is detected in any of these stars. The lower upper limit Delta V/Delta P implies that the intrinsic linearly polarized light which does vary cannot be produced by electrons gyrating in a magnetic field, unless they are ultrarelativistic - a rather unlikely situation. The low mean circular polarization typically observed is probably interstellar in origin. Lack of periodicity in the observed variations of linear polarization implies that even weak magnetic field loops are unlikely to be involved in confining pockets of wind plasma. The observed linear polarization variations are related mainly to electron scattering. 25 refs

  13. Disordered nuclear pasta, magnetic field decay, and crust cooling in neutron stars

    Science.gov (United States)

    Horowitz, C. J.; Berry, D. K.; Briggs, C. M.; Caplan, M. E.; Cumming, A.; Schneider, A. S.

    2015-04-01

    Nuclear pasta, with non-spherical shapes, is expected near the base of the crust in neutron stars. Large scale molecular dynamics simulations of pasta show long lived topological defects that could increase electron scattering and reduce both the thermal and electrical conductivities. We model a possible low conductivity pasta layer by increasing an impurity parameter Qimp. Predictions of light curves for the low mass X-ray binary MXB 1659-29, assuming a large Qimp, find continued late time cooling that is consistent with Chandra observations. The electrical and thermal conductivities are likely related. Therefore observations of late time crust cooling can provide insight on the electrical conductivity and the possible decay of neutron star magnetic fields (assuming these are supported by currents in the crust). This research was supported in part by DOE Grants DE-FG02-87ER40365 (Indiana University) and DE-SC0008808 (NUCLEI SciDAC Collaboration).

  14. Dark stars: a new study of the first stars in the Universe

    International Nuclear Information System (INIS)

    Freese, Katherine; Bodenheimer, Peter; Gondolo, Paolo; Spolyar, Douglas

    2009-01-01

    We have proposed that the first phase of stellar evolution in the history of the Universe may be dark stars (DSs), powered by dark matter (DM) heating rather than by nuclear fusion. Weakly interacting massive particles, which may be their own antipartners, collect inside the first stars and annihilate to produce a heat source that can power the stars. A new stellar phase results, a DS, powered by DM annihilation as long as there is DM fuel, with lifetimes from millions to billions of years. We find that the first stars are very bright (∼10 6 L o-dot ) and cool (T surf surf > 50 000 K); hence DS should be observationally distinct from standard Pop III stars. Once the DM fuel is exhausted, the DS becomes a heavy main sequence star; these stars eventually collapse to form massive black holes that may provide seeds for supermassive black holes observed at early times as well as explanations for recent ARCADE data and for intermediate black holes.

  15. Kepler observations of the variability in B-type stars

    DEFF Research Database (Denmark)

    Balona, Luis A.; Pigulski, A.; De Cat, P.

    2011-01-01

    The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies, characteristic of slowly pulsating B (SPB) stars. Seven of these stars also show a few weak, isolated high frequencies and they could be cons...

  16. MAGNETIZATION OF CLOUD CORES AND ENVELOPES AND OTHER OBSERVATIONAL CONSEQUENCES OF RECONNECTION DIFFUSION

    International Nuclear Information System (INIS)

    Lazarian, A.; Esquivel, A.; Crutcher, R.

    2012-01-01

    Recent observational results for magnetic fields in molecular clouds reviewed by Crutcher seem to be inconsistent with the predictions of the ambipolar diffusion theory of star formation. These include the measured decrease in mass to flux ratio between envelopes and cores, the failure to detect any self-gravitating magnetically subcritical clouds, the determination of the flat probability distribution function (PDF) of the total magnetic field strengths implying that there are many clouds with very weak magnetic fields, and the observed scaling B∝ρ 2/3 that implies gravitational contraction with weak magnetic fields. We consider the problem of magnetic field evolution in turbulent molecular clouds and discuss the process of magnetic field diffusion mediated by magnetic reconnection. For this process that we termed 'reconnection diffusion', we provide a simple physical model and explain that this process is inevitable in view of the present-day understanding of MHD turbulence. We address the issue of the expected magnetization of cores and envelopes in the process of star formation and show that reconnection diffusion provides an efficient removal of magnetic flux that depends only on the properties of MHD turbulence in the core and the envelope. We show that as the amplitude of turbulence as well as the scale of turbulent motions decrease from the envelope to the core of the cloud, the diffusion of the magnetic field is faster in the envelope. As a result, the magnetic flux trapped during the collapse in the envelope is being released faster than the flux trapped in the core, resulting in much weaker fields in envelopes than in cores, as observed. We provide simple semi-analytical model calculations which support this conclusion and qualitatively agree with the observational results. Magnetic reconnection is also consistent with the lack of subcritical self-gravitating clouds, with the observed flat PDF of field strengths, and with the scaling of field strength

  17. MAGNETIZATION OF CLOUD CORES AND ENVELOPES AND OTHER OBSERVATIONAL CONSEQUENCES OF RECONNECTION DIFFUSION

    Energy Technology Data Exchange (ETDEWEB)

    Lazarian, A. [Astronomy Department, University of Wisconsin, Madison, WI 53706 (United States); Esquivel, A. [Instituto de Ciencias Nucleares, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-543, 04510 Mexico D.F. (Mexico); Crutcher, R. [Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 W. Green Street, Urbana, IL 61801 (United States)

    2012-10-01

    Recent observational results for magnetic fields in molecular clouds reviewed by Crutcher seem to be inconsistent with the predictions of the ambipolar diffusion theory of star formation. These include the measured decrease in mass to flux ratio between envelopes and cores, the failure to detect any self-gravitating magnetically subcritical clouds, the determination of the flat probability distribution function (PDF) of the total magnetic field strengths implying that there are many clouds with very weak magnetic fields, and the observed scaling B{proportional_to}{rho}{sup 2/3} that implies gravitational contraction with weak magnetic fields. We consider the problem of magnetic field evolution in turbulent molecular clouds and discuss the process of magnetic field diffusion mediated by magnetic reconnection. For this process that we termed 'reconnection diffusion', we provide a simple physical model and explain that this process is inevitable in view of the present-day understanding of MHD turbulence. We address the issue of the expected magnetization of cores and envelopes in the process of star formation and show that reconnection diffusion provides an efficient removal of magnetic flux that depends only on the properties of MHD turbulence in the core and the envelope. We show that as the amplitude of turbulence as well as the scale of turbulent motions decrease from the envelope to the core of the cloud, the diffusion of the magnetic field is faster in the envelope. As a result, the magnetic flux trapped during the collapse in the envelope is being released faster than the flux trapped in the core, resulting in much weaker fields in envelopes than in cores, as observed. We provide simple semi-analytical model calculations which support this conclusion and qualitatively agree with the observational results. Magnetic reconnection is also consistent with the lack of subcritical self-gravitating clouds, with the observed flat PDF of field strengths, and

  18. Nonlinear localized excitations in magnets with a weak exchange interaction as a soliton problem

    International Nuclear Information System (INIS)

    Gvozdikova, M.V.; Kovalev, A.S.

    1998-01-01

    The spin dynamics of soliton-like localized excitations in a discrete ferromagnet chain with an easy axis anisotropy and a weak exchange interaction is studied. The connection of these excitations with longwave magnetic solitons is discussed. The localized excitation frequency dependence on exchange interaction is found for a fixed number of spin deviation. It is shown that this dependence modifies essentially when the exchange interaction becomes comparable with an anisotropy value

  19. General Relativistic Simulations of Low-Mass Magnetized Binary Neutron Star Mergers

    Science.gov (United States)

    Giacomazzo, Bruno

    2017-01-01

    We will present general relativistic magnetohydrodynamic (GRMHD) simulations of binary neutron star (BNS) systems that produce long-lived neutron stars (NSs) after merger. While the standard scenario for short gamma-ray bursts (SGRBs) requires the formation after merger of a spinning black hole surrounded by an accretion disk, other theoretical models, such as the time-reversal scenario, predict the formation of a long-lived magnetar. The formation of a long-lived magnetar could in particular explain the X-ray plateaus that have been observed in some SGRBs. Moreover, observations of NSs with masses of 2 solar masses indicate that the equation of state of NS matter should support masses larger than that. Therefore a significant fraction of BNS mergers will produce long-lived NSs. This has important consequences both on the emission of gravitational wave signals and on their electromagnetic counterparts. We will discuss GRMHD simulations of ``low-mass'' magnetized BNS systems with different equations of state and mass ratios. We will describe the properties of their post-merger remnants and of their gravitational and electromagnetic emission.

  20. THE SPITZER c2d SURVEY OF WEAK-LINE T TAURI STARS. III. THE TRANSITION FROM PRIMORDIAL DISKS TO DEBRIS DISKS

    International Nuclear Information System (INIS)

    Wahhaj, Zahed; Cieza, Lucas; Koerner, David W.; Case, April; Stapelfeldt, Karl R.; Chapman, Nicholas; Padgett, Deborah L.; Brooke, Tim; Keller, James R.; MerIn, Bruno; Evans, Neal J.; Harvey, Paul; Sargent, Anneila; Van Dishoeck, Ewine F.; Allen, Lori; Blake, Geoff; Mundy, Lee; Myers, Philip C.

    2010-01-01

    We present 3.6 to 70 μm Spitzer photometry of 154 weak-line T Tauri stars (WTTSs) in the Chamaeleon, Lupus, Ophiuchus, and Taurus star formation regions, all of which are within 200 pc of the Sun. For a comparative study, we also include 33 classical T Tauri stars which are located in the same star-forming regions. Spitzer sensitivities allow us to robustly detect the photosphere in the IRAC bands (3.6 to 8 μm) and the 24 μm MIPS band. In the 70 μm MIPS band, we are able to detect dust emission brighter than roughly 40 times the photosphere. These observations represent the most sensitive WTTSs survey in the mid- to far-infrared to date and reveal the frequency of outer disks (r = 3-50 AU) around WTTSs. The 70 μm photometry for half the c2d WTTSs sample (the on-cloud objects), which were not included in the earlier papers in this series, those of Padgett et al. and Cieza et al., are presented here for the first time. We find a disk frequency of 19% for on-cloud WTTSs, but just 5% for off-cloud WTTSs, similar to the value reported in the earlier works. WTTSs exhibit spectral energy distributions that are quite diverse, spanning the range from optically thick to optically thin disks. Most disks become more tenuous than L disk /L * = 2 x 10 -3 in 2 Myr and more tenuous than L disk /L * = 5 x 10 -4 in 4 Myr.

  1. A non-local-thermodynamic equilibrium formulation of the transport equation for polarized light in the presence of weak magnetic fields. Doctoral thesis

    International Nuclear Information System (INIS)

    McNamara, D.J.

    1977-01-01

    The present work is motivated by the desire to better understand solar magnetism. Just as stellar astrophysics and radiative transfer have been coupled in the history of research in physics, so too has the study of radiative transfer of polarized light in magnetic fields and solar magnetism been a history of mutual growth. The Stokes parameters characterize the state of polarization of a beam of radiation. The author considers the changes in polarization, and therefore in the Stokes parameters, due to the transport of a beam through an optically thick medium in a weak magnetic field. The transport equation is derived from a general density matrix equation of motion. This allows the possibility of interference effects arising from the mixing of atomic sublevels in a weak magnetic field to be taken into account. The statistical equilibrium equations are similarly derived. Finally, the coupled system of equations is presented, and the order of magnitude of the interference effects, shown. Collisional effects are not considered. The magnitude of the interference effects in magnetic field measurements of the sun may be evaluated

  2. Escape of charged particles from a neutron star

    International Nuclear Information System (INIS)

    Pelizzari, M.A.

    1976-01-01

    The theory of particle trajectories in an axisymmetric magnetic field, formulated by C. Stormer, can be extended to cover conservative force fields as well. As such, it is an ideal tool to study the escape of charged particles from a rapidly rotating neutron star, enabling one to determine the maximum range of their trajectories in space. With the aid of this theory, it is shown that a neutron star, rotating in a vacuum with rotation and magnetic axes aligned, will not evolve a perfectly conducting magnetosphere if the neutron star is the only source of charge. The sign of charge accelerated from the equatorial regions will be magnetically trapped to a toroidal region very near the star, and the opposite sign of charge, emerging from the polar regions, will escape from the magnetosphere until a critical stellar charge is reached, after which polar charges will be electrostatically bound to the magnetosphere. This selective magnetic trapping of one sign of charge, which prevents the formation of a stellar wind, is a consequence of the magnetic field's orientation relative to the internal charge density of the neutron star

  3. APPARENT NON-COEVALITY AMONG THE STARS IN UPPER SCORPIO: RESOLVING THE PROBLEM USING A MODEL OF MAGNETIC INHIBITION OF CONVECTION

    Energy Technology Data Exchange (ETDEWEB)

    MacDonald, James; Mullan, D. J. [Dept. of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)

    2017-01-01

    Two eclipsing binaries in the USco association have recently yielded precise values of masses and radii for four low-mass members of the association. Standard evolution models would require these dM4.5–dM5 stars to have ages which are younger than those of more massive stars in the association by factors which appear (in extreme cases) to be as large as ∼3. Are the stars in the association therefore non-coeval? We suggest that the answer is no: by incorporating the effects of magnetic inhibition of convective onset, we show that the stars in USco can be restored to coevality provided the four low-mass member stars have vertical surface fields in the range 200–700 G. Fields of such magnitude have already been measured on the surface of certain solar-type stars in other young clusters.

  4. THE HERSCHEL DIGIT SURVEY OF WEAK-LINE T TAURI STARS: IMPLICATIONS FOR DISK EVOLUTION AND DISSIPATION

    International Nuclear Information System (INIS)

    Cieza, Lucas A.; Olofsson, Johan; Henning, Thomas; Harvey, Paul M.; Evans, Neal J. II; Najita, Joan; Merín, Bruno; Liebhart, Armin; Güdel, Manuel; Augereau, Jean-Charles; Pinte, Christophe

    2013-01-01

    As part of the 'Dust, Ice, and Gas In Time (DIGIT)' Herschel Open Time Key Program, we present Herschel photometry (at 70, 160, 250, 350, and 500 μm) of 31 weak-line T Tauri star (WTTS) candidates in order to investigate the evolutionary status of their circumstellar disks. Of the stars in our sample, 13 had circumstellar disks previously known from infrared observations at shorter wavelengths, while 18 of them had no previous evidence for a disk. We detect a total of 15 disks as all previously known disks are detected at one or more Herschel wavelengths and two additional disks are identified for the first time. The spectral energy distributions (SEDs) of our targets seem to trace the dissipation of the primordial disk and the transition to the debris disk regime. Of the 15 disks, 7 appear to be optically thick primordial disks, including 2 objects with SEDs indistinguishable from those of typical Classical T Tauri stars, 4 objects that have significant deficit of excess emission at all IR wavelengths, and 1 'pre-transitional' object with a known gap in the disk. Despite their previous WTTS classification, we find that the seven targets in our sample with optically thick disks show evidence for accretion. The remaining eight disks have weaker IR excesses similar to those of optically thin debris disks. Six of them are warm and show significant 24 μm Spitzer excesses, while the last two are newly identified cold debris-like disks with photospheric 24 μm fluxes, but significant excess emission at longer wavelengths. The Herschel photometry also places strong constraints on the non-detections, where systems with F 70 /F 70,* ∼> 5-15 and L disk /L * ∼> 10 –3 to 10 –4 can be ruled out. We present preliminary models for both the optically thick and optically thin disks and discuss our results in the context of the evolution and dissipation of circumstellar disks.

  5. THE HERSCHEL DIGIT SURVEY OF WEAK-LINE T TAURI STARS: IMPLICATIONS FOR DISK EVOLUTION AND DISSIPATION

    Energy Technology Data Exchange (ETDEWEB)

    Cieza, Lucas A. [Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822 (United States); Olofsson, Johan; Henning, Thomas [Max Planck Institute fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany); Harvey, Paul M.; Evans, Neal J. II [Department of Astronomy, University of Texas at Austin, 2515 Speedway, Stop C1400, Austin, TX 78712-1205 (United States); Najita, Joan [National Optical Astronomy Observatory, 950 N. Cherry Avenue, Tucson, AZ 86719 (United States); Merin, Bruno [Herschel Science Centre, European Space Astronomy Centre, ESA, P.O. Box 78, E-28691 Villanueva de la Canada, Madrid (Spain); Liebhart, Armin; Guedel, Manuel [Department of Astronomy, University of Vienna, Tuerkenschanzstr. 17, A-1180 Vienna (Austria); Augereau, Jean-Charles; Pinte, Christophe, E-mail: lcieza@ifa.hawaii.edu [UJF-Grenoble 1/CNRS-INSU, Institut de Planetologie et d' Astrophysique (IPAG) UMR 5274, BP 53, F-38041 Grenoble cedex 9 (France)

    2013-01-10

    As part of the 'Dust, Ice, and Gas In Time (DIGIT)' Herschel Open Time Key Program, we present Herschel photometry (at 70, 160, 250, 350, and 500 {mu}m) of 31 weak-line T Tauri star (WTTS) candidates in order to investigate the evolutionary status of their circumstellar disks. Of the stars in our sample, 13 had circumstellar disks previously known from infrared observations at shorter wavelengths, while 18 of them had no previous evidence for a disk. We detect a total of 15 disks as all previously known disks are detected at one or more Herschel wavelengths and two additional disks are identified for the first time. The spectral energy distributions (SEDs) of our targets seem to trace the dissipation of the primordial disk and the transition to the debris disk regime. Of the 15 disks, 7 appear to be optically thick primordial disks, including 2 objects with SEDs indistinguishable from those of typical Classical T Tauri stars, 4 objects that have significant deficit of excess emission at all IR wavelengths, and 1 'pre-transitional' object with a known gap in the disk. Despite their previous WTTS classification, we find that the seven targets in our sample with optically thick disks show evidence for accretion. The remaining eight disks have weaker IR excesses similar to those of optically thin debris disks. Six of them are warm and show significant 24 {mu}m Spitzer excesses, while the last two are newly identified cold debris-like disks with photospheric 24 {mu}m fluxes, but significant excess emission at longer wavelengths. The Herschel photometry also places strong constraints on the non-detections, where systems with F {sub 70}/F {sub 70,*} {approx}> 5-15 and L {sub disk}/L {sub *} {approx}> 10{sup -3} to 10{sup -4} can be ruled out. We present preliminary models for both the optically thick and optically thin disks and discuss our results in the context of the evolution and dissipation of circumstellar disks.

  6. ζ Oph and the weak-wind problem

    Science.gov (United States)

    Gvaramadze, V. V.; Langer, N.; Mackey, J.

    2012-11-01

    Mass-loss rate, ?, is one of the key parameters affecting evolution and observational manifestations of massive stars and their impact on the ambient medium. Despite its importance, there is a factor of ˜100 discrepancy between empirical and theoretical ? of late-type O dwarfs, the so-called weak-wind problem. In this Letter, we propose a simple novel method to constrain ? of runaway massive stars through observation of their bow shocks and Strömgren spheres, which might be of decisive importance for resolving the weak-wind problem. Using this method, we found that ? of the well-known runaway O9.5 V star ζ Oph is more than an order of magnitude higher than that derived from ultraviolet (UV) line fitting and is by a factor of 6-7 lower than those based on the theoretical recipe by Vink et al. and the Hα line. The discrepancy between ? derived by our method and that based on UV lines would be even more severe if the stellar wind is clumpy. At the same time, our estimate of ? agrees with that predicted by the moving reversing layer theory by Lucy.

  7. Ageing and memory effects in the weak random anisotropy magnets amorphous NdGdFe and HoGdFe

    International Nuclear Information System (INIS)

    Saito, Toshiaki; Emura, Ai; Hanashima, Koji

    2007-01-01

    We experimentally examined the ageing phenomena in typical weak random anisotropy magnets (weak RAMs), amorphous NdGdFe and HoGdFe, with a small ratio of the random anisotropy (D) to the ferromagnetic exchange (J) (D/J). These weak RAMs have very long average relaxation time, two or three orders longer than that of spin glasses (SGs) around the transition temperature, and also have a very large ac excitation field (h 0 ) dependence of the ac susceptibility. Measuring the imaginary part of the ac susceptibility at frequency of 0.5 Hz and h 0 of 0.3 Oe by using two temperature-change protocols, we observed the memory and rejuvenation effects as reported in SGs, but the effects are weaker in the present weak RAMs, suggesting that the picture of the hierarchical structure of the free energy space is also effective in weak RAMs as in SGs, but it may have smaller barrier heights than those of SGs

  8. POPULATION SYNTHESIS OF YOUNG ISOLATED NEUTRON STARS: THE EFFECT OF FALLBACK DISK ACCRETION AND MAGNETIC FIELD EVOLUTION

    International Nuclear Information System (INIS)

    Fu, Lei; Li, Xiang-Dong

    2013-01-01

    The spin evolution of isolated neutron stars (NSs) is dominated by their magnetic fields. The measured braking indices of young NSs show that the spin-down mechanism due to magnetic dipole radiation with constant magnetic fields is inadequate. Assuming that the NS magnetic field is buried by supernova fallback matter and re-emerges after accretion stops, we carry out a Monte Carlo simulation of the evolution of young NSs, and show that most of the pulsars have braking indices ranging from –1 to 3. The results are compatible with the observational data of NSs associated with supernova remnants. They also suggest that the initial spin periods of NSs might occupy a relatively wide range

  9. On the Origin of Sub-subgiant Stars. II. Binary Mass Transfer, Envelope Stripping, and Magnetic Activity

    Energy Technology Data Exchange (ETDEWEB)

    Leiner, Emily; Mathieu, Robert D. [Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706 (United States); Geller, Aaron M., E-mail: leiner@astro.wisc.edu [Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 (United States)

    2017-05-10

    Sub-subgiant stars (SSGs) lie to the red of the main sequence and fainter than the red giant branch in cluster color–magnitude diagrams (CMDs), a region not easily populated by standard stellar evolution pathways. While there has been speculation on what mechanisms may create these unusual stars, no well-developed theory exists to explain their origins. Here we discuss three hypotheses of SSG formation: (1) mass transfer in a binary system, (2) stripping of a subgiant’s envelope, perhaps during a dynamical encounter, and (3) reduced luminosity due to magnetic fields that lower convective efficiency and produce large starspots. Using the stellar evolution code MESA, we develop evolutionary tracks for each of these hypotheses, and compare the expected stellar and orbital properties of these models with six known SSGs in the two open clusters M67 and NGC 6791. All three of these mechanisms can create stars or binary systems in the SSG CMD domain. We also calculate the frequency with which each of these mechanisms may create SSG systems, and find that the magnetic field hypothesis is expected to create SSGs with the highest frequency in open clusters. Mass transfer and envelope stripping have lower expected formation frequencies, but may nevertheless create occasional SSGs in open clusters. They may also be important mechanisms to create SSGs in higher mass globular clusters.

  10. Solving the relativistic Rankine-Hugoniot condition in the presence of a magnetic field in the astrophysical scenario of a neutron star

    International Nuclear Information System (INIS)

    Mallick, Ritam

    2011-01-01

    The Rankine-Hugoniot condition has been solved to study phase transition in an astrophysical scenario mainly in the case of phase transition from a neutron star (NS) to a quark star (QS). The equations of state and temperature play a huge role in determining the nature of the front propagation, which brings about the phase transition in a NS. The shock jump conditions can be solved analytically, but the situation changes drastically by the inclusion of the magnetic field. High magnetic fields, which are always associated with a NS play a huge role in determining the structure and evolution of a NS. So, a magnetic field has been introduced in the shock jump condition in the de Hoffmann-Teller frame. The modified conservation condition for the perpendicular and oblique shocks is obtained in this frame. Numerical solution of the perpendicular shock has been obtained, which shows considerable deviation from the nonmagnetic case. The results show that the magnetic field helps in shock generation. It also indirectly hints at the instability of the matter and thereby the NS for very high magnetic field, implying that NSs can only support a magnetic field of some finite strength.

  11. Confinement and Isotropization of Galactic Cosmic Rays by Molecular-Cloud Magnetic Mirrors When Turbulent Scattering Is Weak

    International Nuclear Information System (INIS)

    Chandran, Benjamin D. G.

    2000-01-01

    Theoretical studies of magnetohydrodynamic (MHD) turbulence and observations of solar wind fluctuations suggest that MHD turbulence in the interstellar medium is anisotropic at small scales, with smooth variations along the background magnetic field and sharp variations perpendicular to the background field. Turbulence with this anisotropy is inefficient at scattering cosmic rays, and thus the scattering rate ν may be smaller than has been traditionally assumed in diffusion models of Galactic cosmic-ray propagation, at least for cosmic-ray energies E above 1011-1012 eV at which self-confinement is not possible. In this paper, it is shown that Galactic cosmic rays can be effectively confined through magnetic reflection by molecular clouds, even when turbulent scattering is weak. Elmegreen's quasi-fractal model of molecular-cloud structure is used to argue that a typical magnetic field line passes through a molecular cloud complex once every ∼300 pc. Once inside the complex, the field line will in most cases be focused into one or more dense clumps in which the magnetic field can be much stronger than the average field in the intercloud medium (ICM). Cosmic rays following field lines into cloud complexes are most often magnetically reflected back into the ICM, since strong-field regions act as magnetic mirrors. For a broad range of cosmic-ray energies, a cosmic ray initially following some particular field line separates from that field line sufficiently slowly that the cosmic ray can be trapped between neighboring cloud complexes for long periods of time. The suppression of cosmic-ray diffusion due to magnetic trapping is calculated in this paper with the use of phenomenological arguments, asymptotic analysis, and Monte Carlo particle simulations. Formulas for the coefficient of diffusion perpendicular to the Galactic disk are derived for several different parameter regimes within the E-ν plane. In one of these parameter regimes in which scattering is weak, it

  12. Improved Magnetic STAR Methods for Real-Time, Point-by-Point Localization of Unexploded Ordnance and Buried Mines

    Science.gov (United States)

    2008-09-01

    of magnetic UXO. The prototype STAR Sensor comprises: a) A cubic array of eight fluxgate magnetometers . b) A 24-channel data acquisition/signal...array (shaded boxes) of eight low noise Triaxial Fluxgate Magnetometers (TFM) develops 24 channels of vector B- field data. Processor hardware

  13. Magnetic starspots

    International Nuclear Information System (INIS)

    Jahn, K.; Stepien, K.

    1984-01-01

    Models of large magnetic starspots with an axisymmetric untwisted magnetic field on late type stars are discussed. It is assumed that the magnetic field reduces the efficiency of convection inside the spot. A unique relation between the stellar mass and the difference of effective temperatures of the spot and the surrounding photosphere is adopted from observations. It is equivalent to the reduction of a s (the mixing length theory parameter) inside the spot to the value 0.15 independently of the stellar mass. The surface magnetic field of large spots covering a considerable part of the stellar surface is a decreasing function of the magnetic flux. Hence a coverage of a star by magnetic regions rapidly increases as a function of the magnetic flux in a narrow range of fluxes. This behaviour can explain the Vaughan-Preston gap. Recent observations of magnetic fields on G and K type stars are in a good agreement with our predictions. 35 refs., 3 figs., 4 tabs. (author)

  14. Optical Orientation of Mn2+ Ions in GaAs in Weak Longitudinal Magnetic Fields

    Science.gov (United States)

    Akimov, I. A.; Dzhioev, R. I.; Korenev, V. L.; Kusrayev, Yu. G.; Sapega, V. F.; Yakovlev, D. R.; Bayer, M.

    2011-04-01

    We report on optical orientation of Mn2+ ions in bulk GaAs subject to weak longitudinal magnetic fields (B≤100mT). A manganese spin polarization of 25% is directly evaluated by using spin-flip Raman scattering. The dynamical Mn2+ polarization occurs due to the s-d exchange interaction with optically oriented conduction band electrons. Time-resolved photoluminescence reveals a nontrivial electron spin dynamics, where the oriented Mn2+ ions tend to stabilize the electron spins.

  15. Stellar Obliquity and Magnetic Activity of Planet-hosting Stars and Eclipsing Binaries Based on Transit Chord Correlation

    Science.gov (United States)

    Dai, Fei; Winn, Joshua N.; Berta-Thompson, Zachory; Sanchis-Ojeda, Roberto; Albrecht, Simon

    2018-04-01

    The light curve of an eclipsing system shows anomalies whenever the eclipsing body passes in front of active regions on the eclipsed star. In some cases, the pattern of anomalies can be used to determine the obliquity Ψ of the eclipsed star. Here we present a method for detecting and analyzing these patterns, based on a statistical test for correlations between the anomalies observed in a sequence of eclipses. Compared to previous methods, ours makes fewer assumptions and is easier to automate. We apply it to a sample of 64 stars with transiting planets and 24 eclipsing binaries for which precise space-based data are available, and for which there was either some indication of flux anomalies or a previously reported obliquity measurement. We were able to determine obliquities for 10 stars with hot Jupiters. In particular we found Ψ ≲ 10° for Kepler-45, which is only the second M dwarf with a measured obliquity. The other eight cases are G and K stars with low obliquities. Among the eclipsing binaries, we were able to determine obliquities in eight cases, all of which are consistent with zero. Our results also reveal some common patterns of stellar activity for magnetically active G and K stars, including persistently active longitudes.

  16. Parametrically induced low-frequency waves in weakly inhomogeneous magnetized plasmas

    International Nuclear Information System (INIS)

    Pesic, S.

    1981-01-01

    The linear dispersion relation governing the parametric interaction of a lower hybrid pump wave with a weakly-inhomogeneous current carrying hot plasma confined by a helical magnetic field is derived and solved numerically. The stability boundaries are delineated over a wide range in the k-space. The frequency and growth rate of decay instabilities are calculated for plasma parameters relevant to lower hybrid plasma heating experiments. The parametric excitation of drift waves and ion cyclotron current instabilities is discussed. In the low-density plasma region low minimum thresholds and high growth rates are obtained for the pump decay into ion cyclotron and nonresonant quasimodes. The spatial amplification of hot ion Bernstein waves and nonresonant quasimodes dominate in the plasma core (ω 0 /ωsub(LH) < 2). The presented theoretical results are in qualitative agreement with current LH plasma heating experiments. (author)

  17. A high-resolution spectropolarimetric survey of Herbig Ae/Be stars - II. Rotation

    Science.gov (United States)

    Alecian, E.; Wade, G. A.; Catala, C.; Grunhut, J. H.; Landstreet, J. D.; Böhm, T.; Folsom, C. P.; Marsden, S.

    2013-02-01

    We report the analysis of the rotational properties of our sample of Herbig Ae/Be (HAeBe) and related stars for which we have obtained high-resolution spectropolarimetric observations. Using the projected rotational velocities measured at the surface of the stars, we have calculated the angular momentum of the sample and plotted it as a function of age. We have then compared the angular momentum and the v sin i distributions of the magnetic to the non-magnetic HAeBe stars. Finally, we have predicted v sin i of the non-magnetic, non-binary (`normal') stars in our sample when they reach the zero-age main sequence (ZAMS), and compared them to various catalogues of v sin i of main-sequence stars. First, we observe that magnetic HAeBe stars are much slower rotators than normal stars, indicating that they have been more efficiently braked than the normal stars. In fact, the magnetic stars have already lost most of their angular momentum, despite their young ages (lower than 1 Myr for some of them). Secondly, our analysis suggests that the low-mass (1.5 5 M⊙) are losing angular momentum. We propose that winds, which are expected to be stronger in massive stars, are at the origin of this phenomenon.

  18. Inter-Division IV/V WG on Active OB Stars

    NARCIS (Netherlands)

    Owocki, S.; Aerts, C.; Fabregat, J.; Gies, D.; Henrichs, H.F.; McDavid, D.; Porter, J.; Rivinius, T.; Peters, G.; Stefl, S.

    2007-01-01

    Our group studies active early-type (OB) stars, with historical focus on classical Be stars, but extending in recent years to include Slowly Pulsating B-stars (SPB), Beta-Cephei stars, the strongly magnetic Bp stars, Luminous Blue Vairiable (LBV) stars, and B[e] stars. An overall goal is to

  19. ROTATION PERIODS OF OPEN-CLUSTER STARS .3.

    NARCIS (Netherlands)

    PROSSER, CF; SHETRONE, MD; DASGUPTA, A; BACKMAN, DE; LAAKSONEN, BD; BAKER, SW; MARSCHALL, LA; WHITNEY, BA; KUIJKEN, K; STAUFFER, [No Value

    We present the results from a photometric monitoring program of 15 open cluster stars and one weak-lined T Tauri star during late 1993/early 1994. Several slow rotators which are members of the Alpha Persei, Pleiades, and Hyades open clusters have been monitored and period estimates derived. Using

  20. Neutron stars: Observational diversity and evolution

    Science.gov (United States)

    Safi-Harb, S.

    2017-12-01

    Ever since the discovery of the Crab and Vela pulsars in their respective Supernova Remnants, our understanding of how neutron stars manifest themselves observationally has been dramatically shaped by the surge of discoveries and dedicated studies across the electromagnetic spectrum, particularly in the high-energy band. The growing diversity of neutron stars includes the highly magnetized neutron stars (magnetars) and the Central Compact Objects shining in X-rays and mostly lacking pulsar wind nebulae. These two subclasses of high-energy objects, however, seem to be characterized by anomalously high or anomalously low surface magnetic fields (thus dubbed as ‘magnetars’ and ‘anti-magnetars’, respectively), and have pulsar characteristic ages that are often much offset from their associated SNRs’ ages. In addition, some neutron stars act ‘schizophrenic’ in that they occasionally display properties that seem common to more than one of the defined subclasses. I review the growing diversity of neutron stars from an observational perspective, then highlight recent and on-going theoretical and observational work attempting to address this diversity, particularly in light of their magnetic field evolution, energy loss mechanisms, and supernova progenitors’ studies.

  1. X-ray sources in stars formation areas: T Tauri stars and proto-stars in the rho Ophiuchi dark cloud

    International Nuclear Information System (INIS)

    Grosso, Nicolas

    1999-01-01

    This thesis studies from large to small scales, X-ray sources in the rho Ophiuchi dark cloud. After some background on the formation of the low-mass young stars (Chapter 1), Chapter 2 takes an interest in the T Tauri star population. Chapter 3 tackles the search of the magnetic activity at the younger stage of protostar, presenting a powerful X-ray emission from an IR protostar, called YLW15, during a flare, and a quasi-periodic flare of the same source; as well as a new detection of another IR protostar in the ROSAT archives. It ends with a review of protostar detections. Some IR protostar flares show a very long increasing phase. Chapter 4 links this behaviour with a modulation by the central star rotation. The standard model of jet emission assumes that the central star rotates at the same speed that the inner edge of its accretion disk. This chapter shows that the observation of the YLW15 quasi-periodic flare suggests rather that the forming star rotates faster than its accretion disk, at the break up limit. The synchronism with the accretion disk, observed on T Tauri stars, must be reach progressively by magnetic breaking during the IR protostar stage, and more or less rapidly depending on the forming star mass. Recent studies have shown that T Tauri star X-ray emission could ionize the circumstellar disk, and play a role in the instability development, as well as stimulate the accretion. The protostar X-ray emission might be higher than the T Tauri star one, Chapter 5 presents a millimetric interferometric observation dedicated to measure this effect on YLW15. Finally, Chapter 6 reassembles conclusions and perspectives of this work. (author) [fr

  2. Improved ring potential of QED at finite temperature and in the presence of weak and strong magnetic fields

    International Nuclear Information System (INIS)

    Sadooghi, N.; Anaraki, K. Sohrabi

    2008-01-01

    Using the general structure of the vacuum polarization tensor Π μν (k 0 ,k) in the infrared (IR) limit, k 0 →0, the ring contribution to the QED effective potential at finite temperature and the nonzero magnetic field is determined beyond the static limit, (k 0 →0, k→0). The resulting ring potential is then studied in weak and strong magnetic field limits. In the weak magnetic field limit, at high temperature and for α→0, the improved ring potential consists of a term proportional to T 4 α 5/2 , in addition to the expected T 4 α 3/2 term arising from the static limit. Here, α is the fine structure constant. In the limit of the strong magnetic field, where QED dynamics is dominated by the lowest Landau level, the ring potential includes a novel term consisting of dilogarithmic function (eB)Li 2 (-(2α/π)(eB/m 2 )). Using the ring improved (one-loop) effective potential including the one-loop effective potential and ring potential in the IR limit, the dynamical chiral symmetry breaking of QED is studied at finite temperature and in the presence of the strong magnetic field. The gap equation, the dynamical mass and the critical temperature of QED in the regime of the lowest Landau level dominance are determined in the improved IR as well as in the static limit. For a given value of the magnetic field, the improved ring potential is shown to be more efficient in decreasing the critical temperature arising from the one-loop effective potential.

  3. An improved age-activity relationship for cool stars older than a gigayear

    DEFF Research Database (Denmark)

    Booth, R. S.; Poppenhaeger, K.; Watson, C. A.

    2017-01-01

    Stars with convective envelopes display magnetic activity, which decreases over time due to the magnetic braking of the star. This age dependence of magnetic activity is well studied for younger stars, but the nature of this dependence for older stars is not well understood. This is mainly because...... absolute stellar ages for older stars are hard to measure. However, relatively accurate stellar ages have recently come into reach through asteroseismology. In this work, we present X-ray luminosities, which are a measure for magnetic activity displayed by the stellar coronae, for 24 stars with well......-determined ages older than a gigayear. We find 14 stars with detectable X-ray luminosities and use these to calibrate the age-activity relationship. We find a relationship between stellar X-ray luminosity, normalized by the stellar surface area, and age that is steeper than the relationships found for younger...

  4. Investigating the Magnetospheres of Rapidly Rotating B-type Stars

    Science.gov (United States)

    Fletcher, C. L.; Petit, V.; Nazé, Y.; Wade, G. A.; Townsend, R. H.; Owocki, S. P.; Cohen, D. H.; David-Uraz, A.; Shultz, M.

    2017-11-01

    Recent spectropolarimetric surveys of bright, hot stars have found that ~10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (~kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA's XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.

  5. Investigating the origin of cyclical wind variability in hot, massive stars - I. On the dipolar magnetic field hypothesis

    NARCIS (Netherlands)

    David-Uraz, A.; Wade, G.A.; Petit, V.; ud-Doula, A.; Sundqvist, J.O.; Grunhut, J.; Schultz, M.; Neiner, C.; Alecian, E.; Henrichs, H.F.; Bouret, J.-C.

    2014-01-01

    OB stars exhibit various types of spectral variability associated with wind structures, including the apparently ubiquitous discrete absorption components (DACs). These are proposed to be caused by either magnetic fields or non-radial pulsations. In this paper, we evaluate the possible relation

  6. Development of the Facility for Transformation of Magnetic Characteristics of Weakly Magnetic Oxidized Iron Ores Related to Improvement of Technologies for Iron Ore Concentrate Production

    Directory of Open Access Journals (Sweden)

    Ponomarenko, O.M.

    2016-01-01

    Full Text Available New facility for continuous registration of iron ore magnetization depending on temperature by heating of iron ores upon reducing conditions was created. Facility allows to register the processes of transformation of weakly magnetic minerals into strongly magnetic ones under the influence of reducing agents and temperature, as well as to determine the Curie temperature of the minerals. Using created facility it was shown, that heating of goethite and hematite in the presence of 4 % of starch in the temperature range of 300—650 °С leads to significant increase of magnetization of the samples. X-Ray diffraction confirmed that under indicated conditions the structure of hematite and goethite is transformed into magnetite structure. Obtained results open up new possibilities for the development of effective technologies for oxidized iron ore beneficiation.

  7. The diversity of neutron stars: Nearby thermally emitting neutron stars and the compact central objects in supernova remnants

    Science.gov (United States)

    Kaplan, David L.

    Neutron stars are invaluable tools for exploring stellar death, the physics of ultra-dense matter, and the effects of extremely strong magnetic fields. The observed population of neutron stars is dominated by the > 1000 radio pulsars, but there are distinct sub-populations that, while fewer in number, can have significant impact on our understanding of the issues mentioned above. These populations are the nearby isolated neutron stars discovered by ROSAT, and the central compact objects in supernova remnants. The studies of both of these populations have been greatly accelerated in recent years through observations with the Chandra X-ray Observatory and the XMM-Newton telescope. First, we discuss radio, optical, and X-ray observations of the nearby neutron stars aimed at determining their relation to the Galactic neutron star population and at unraveling their complex physical processes by determining the basic astronomical parameters that define the population -- instances, ages, and magnetic fields -- the uncertainties in which limit any attempt to derive basic physical parameters for these objects. We conclude that these sources are 10^6 year-old cooling neutron stars with magnetic fields above 10^13 G. Second, we describe the hollow supernova remnant problem: why many of the supernova remnants in the Galaxy have no indication central neutron stars. We have undertaken an X-ray census of neutron stars in a volume-limited sample of Galactic supernova remnants, and from it conclude that either many supernovae do not produce neutron stars contrary to expectation, or that neutron stars can have a wide range in cooling behavior that makes many sources disappear from the X-ray sky.

  8. Gas, dust, stars, star formation, and their evolution in M 33 at giant molecular cloud scales

    Science.gov (United States)

    Komugi, Shinya; Miura, Rie E.; Kuno, Nario; Tosaki, Tomoka

    2018-04-01

    We report on a multi-parameter analysis of giant molecular clouds (GMCs) in the nearby spiral galaxy M 33. A catalog of GMCs identifed in 12CO(J = 3-2) was used to compile associated 12CO(J = 1-0), dust, stellar mass, and star formation rate. Each of the 58 GMCs are categorized by their evolutionary stage. Applying the principal component analysis on these parameters, we construct two principal components, PC1 and PC2, which retain 75% of the information from the original data set. PC1 is interpreted as expressing the total interstellar matter content, and PC2 as the total activity of star formation. Young (activity compared to intermediate-age and older clouds. Comparison of average cloud properties in different evolutionary stages imply that GMCs may be heated or grow denser and more massive via aggregation of diffuse material in their first ˜ 10 Myr. The PCA also objectively identified a set of tight relations between ISM and star formation. The ratio of the two CO lines is nearly constant, but weakly modulated by massive star formation. Dust is more strongly correlated with the star formation rate than the CO lines, supporting recent findings that dust may trace molecular gas better than CO. Stellar mass contributes weakly to the star formation rate, reminiscent of an extended form of the Schmidt-Kennicutt relation with the molecular gas term substituted by dust.

  9. NuSTAR Observation of the Symbiotic System GX 1+4

    Science.gov (United States)

    Wolff, Michael Thomas; Becker, Peter A.; Enoto, Teruaki; Pottschmidt, Katja; Wood, Kent

    2017-08-01

    We report on a NuSTAR observation of the symbiotic binary system GX 1+4. GX 1+4 is one of a small number of systems with a red giant mass donor and a magnetic neutron star in orbit around each other. The accreting pulsar in GX 1+4 has a spin period of ~150 seconds with epochs of both spin-up and spin-down. The orbital period that has not been determined. Magnetic accretion theory in such systems suggests that the neutron star has a magnetic field in the range 1013-1014 Gauss although this is not settled because no cyclotron absorption feature has been observed in the X-ray spectrum. The NuSTAR spectrum shows broad Fe-line emission near ~6.5 keV and also shows a broad power law shape detected up to ~60 keV. We analyze and discuss the NuSTAR X-ray data with particular attention to the question of what can the spectrum tell us about the structure of the accretion flow onto the neutron star and the magnetic field strength.

  10. Stellar magnetic activity and exoplanets

    Directory of Open Access Journals (Sweden)

    Vidotto A.A.

    2017-01-01

    Full Text Available It has been proposed that magnetic activity could be enhanced due to interactions between close-in massive planets and their host stars. In this article, I present a brief overview of the connection between stellar magnetic activity and exoplanets. Stellar activity can be probed in chromospheric lines, coronal emission, surface spot coverage, etc. Since these are manifestations of stellar magnetism, these measurements are often used as proxies for the magnetic field of stars. Here, instead of focusing on the magnetic proxies, I overview some recent results of magnetic field measurements using spectropolarimetric observations. Firstly, I discuss the general trends found between large-scale magnetism, stellar rotation, and coronal emission and show that magnetism seems to be correlated to the internal structure of the star. Secondly, I overview some works that show evidence that exoplanets could (or not act as to enhance the activity of their host stars.

  11. Electromagnetic activity of a pulsating paramagnetic neutron star

    International Nuclear Information System (INIS)

    Bastrukov, S.I.; Podgainy, D.V.; Yang, J.; Weber, F.

    2002-01-01

    The fact that neutron star matter possesses the capability of maintaining a highly intense magnetic field has been and still is among the most debatable issues in pulsar astrophysics. Over the years, there were several independent suggestions that the dominant source of pulsar magnetism is either the field-induced or the spontaneous magnetic polarization of the baryon material. The Pauli paramagnetism of degenerate neutron matter is one of the plausible and comprehensive mechanisms of the magnetic ordering of neutron magnetic moments, promoted by a seed magnetic field inherited by the neutron star from a massive progenitor and amplified by its implosive contraction due to the magnetic flux conservation. Adhering to this attitude and based on the equations of magnetoelastic dynamics underlying continuum mechanics of single-axis magnetic insulators, we investigate electrodynamics of a paramagnetic neutron star undergoing nonradial pulsations. We show that the suggested approach regains a recent finding of Akhiezer et al. that the spin-polarized neutron matter can transmit perturbations by low-frequency transverse magnetoelastic waves. We found that nonradial torsional magnetoelastic pulsations of a paramagnetic neutron star can serve as a powerful generator of a highly intense electric field producing the magnetospheric polarization charge whose acceleration along the open magnetic field lines leads to the synchrotron and curvature radiation. Analytic and numerical estimates for periods of nonradial torsional magnetoelastic modes are presented and are followed by a discussion of their possible manifestation in currently monitored activity of pulsars and magnetars

  12. Electro-weak theory

    International Nuclear Information System (INIS)

    Deshpande, N.G.

    1980-01-01

    By electro-weak theory is meant the unified field theory that describes both weak and electro-magnetic interactions. The development of a unified electro-weak theory is certainly the most dramatic achievement in theoretical physics to occur in the second half of this century. It puts weak interactions on the same sound theoretical footing as quantum elecrodynamics. Many theorists have contributed to this development, which culminated in the works of Glashow, Weinberg and Salam, who were jointly awarded the 1979 Nobel Prize in physics. Some of the important ideas that contributed to this development are the theory of beta decay formulated by Fermi, Parity violation suggested by Lee and Yang, and incorporated into immensely successful V-A theory of weak interactions by Sudarshan and Marshak. At the same time ideas of gauge invariance were applied to weak interaction by Schwinger, Bludman and Glashow. Weinberg and Salam then went one step further and wrote a theory that is renormalizable, i.e., all higher order corrections are finite, no mean feat for a quantum field theory. The theory had to await the development of the quark model of hadrons for its completion. A description of the electro-weak theory is given

  13. A neutron depolarization study of magnetic inhomogeneities in weak-link superconductors. Issledovanie magnitnykh neodnorodnostej v sverkhprovodnikakh so slabymi svyazyami metodom depolyarizatsii nejtronov

    Energy Technology Data Exchange (ETDEWEB)

    Zhuchenko, N K; Yagud, R Z [AN SSSR, Leningrad (Russian Federation). Inst. Yadernoj Fiziki

    1993-09-01

    Neutron depolarization measurements in the mixed state of both high-T[sub c] and low-T[sub c] weak-link superconductors have been carried out. Samples of YBCO, BSCCO, SnMo[sub 6]S[sub 8] and 0.5 Nb-0.5 Ti of different magnetic prehistory were analyzed at temperatures T 4.2 K under applied magnetic fields II <= 16.5 kOe. We ascribe the appearance of magnetic inhomogeneities and their hysteresis behaviour to the interaction between dipole magnetic fields (diamagnetic and paramagnetic ones) and applied magnetic fields.

  14. Accretion by rotating magnetic neutron stars. III. Accretion torques and period changes in pulsating X-ray sources

    International Nuclear Information System (INIS)

    Ghosh, P.; Lamb, F.K.

    1979-01-01

    We use the solutions of the two-dimensional hydromagnetic equations obtained previously to calculate the torque on a magnetic neutron star accreting from a Keplerian disk. We find that the magnetic coupling between the star and the plasma outside the inner edge of the disk is appreciable. As a result of this coupling the spin-up torque on fast rotators is substantially less than that on slow rotators; for sufficiently high stellar angular velocities or sufficiently low accretion rates this coupling dominates that de to the plasma and the magnetic field at the inner edge of the disk, braking the star's rotation even while accretion, and hence X-ray emission, continues.We apply these results to pulsating X-ray sources, and show that the observed secular spin-up rates of all the sources in which this rate has been measured can be accounted for quantitatively if one assumes that these sources are accreting from Keplerian disks and have magnetic moments approx.10 29 --10 32 gauss cm 3 . The reduction of the torque on fast rotators provides a natural explanation of the spin-up rate of Her X-1, which is much below that expected for slow rotators. We show further that a simple relation between the secular spin-up rate : P and the quantity PL/sup 3/7/ adequately represents almost all the observational data, P and L being the pulse period and the luminosity of the source, respectively. This ''universal'' relation enables one to estimate any one of the parameters P, P, and L for a given source if the other two are known. We show that the short-term period fluctuations observed in Her X-1, Cen X-3, Vela X-1, and X Per can be accounted for quite naturally as consequences of torque variations caused by fluctuations in the mass transfer rate. We also indicate how the spin-down torque at low luminosities found here may account for the paradoxical existence of a large number of long-period sources with short spin-up time scales

  15. Astrophysical evidence for weak new forces

    International Nuclear Information System (INIS)

    Burgess, C.; Cloutier, J.

    1988-01-01

    Recent observations of the orbital precession rate for eclipsing binary star systems appear to be in disagreement with the predictions of general relativity. We here analyse whether these discrepancies can be interpreted as being due to the existence of a new, long range, very weak force. We find that, with a conservative estimate of the astrophysical errors involved, the binary-star data by itself is consistent with what would be expected of a new force. The coupling and range required to fit the data can be consistent with the present limits on the existence of new forces. The strongest constraints come from recent terrestrial searches for a ''fifth force''. This analysis underlines the fact that these binary star systems are sensitive to forces whose coupling strength can be as low as 10 -5 that of gravity

  16. Magnetic Resonance Imaging of Surgical Implants Made from Weak Magnetic Materials

    Science.gov (United States)

    Gogola, D.; Krafčík, A.; Štrbák, O.; Frollo, I.

    2013-08-01

    Materials with high magnetic susceptibility cause local inhomogeneities in the main field of the magnetic resonance (MR) tomograph. These inhomogeneities lead to loss of phase coherence, and thus to a rapid loss of signal in the image. In our research we investigated inhomogeneous field of magnetic implants such as magnetic fibers, designed for inner suture during surgery. The magnetic field inhomogeneities were studied at low magnetic planar phantom, which was made from four thin strips of magnetic tape, arranged grid-wise. We optimized the properties of imaging sequences with the aim to find the best setup for magnetic fiber visualization. These fibers can be potentially exploited in surgery for internal stitches. Stitches can be visualized by the magnetic resonance imaging (MRI) method after surgery. This study shows that the imaging of magnetic implants is possible by using the low field MRI systems, without the use of complicated post processing techniques (e.g., IDEAL).

  17. What drives galactic magnetism?

    Science.gov (United States)

    Chyży, K. T.; Sridhar, S. S.; Jurusik, W.

    2017-07-01

    Aims: Magnetic fields are important ingredients of the interstellar medium. They are suspected to be maintained by dynamo processes related to star-formation activity, properties of the interstellar medium and global features of galaxies. We aim to use statistical analysis of a large number of various galaxies to probe, model, and understand relations between different galaxy properties and magnetic fields. Methods: We have compiled a sample of 55 galaxies including low-mass dwarf and Magellanic-types, normal spirals and several massive starbursts, and applied principal component analysis (PCA) and regression methods to assess the impact of various galaxy properties on the observed magnetic fields. Results: According to PCA the global galaxy parameters (like H I, H2, and dynamical mass, star formation rate (SFR), near-infrared luminosity, size, and rotational velocity) are all mutually correlated and can be reduced to a single principal component. Further PCA performed for global and intensive (not size related) properties of galaxies (such as gas density, and surface density of the star formation rate, SSFR), indicates that magnetic field strength B is connected mainly to the intensive parameters, while the global parameters have only weak relationships with B. We find that the tightest relationship of B is with SSFR, which is described by a power-law with an index of 0.33 ± 0.03. The relation is observed for galaxies with the global SFR spread over more than four orders of magnitude. Only the radio faintest dwarf galaxies deviate from this relation probably due to the inverse Compton losses of relativistic electrons or long turbulence injection timescales. The observed weaker associations of B with galaxy dynamical mass and the rotational velocity we interpret as indirect ones, resulting from the observed connection of the global SFR with the available total H2 mass in galaxies. Using our sample we constructed a diagram of B across the Hubble sequence which

  18. Enhanced collective focusing of intense neutralized ion beam pulses in the presence of weak solenoidal magnetic fields

    International Nuclear Information System (INIS)

    Dorf, Mikhail A.; Davidson, Ronald C.; Kaganovich, Igor D.; Startsev, Edward A.

    2012-01-01

    The design of ion drivers for warm dense matter and high energy density physics applications and heavy ion fusion involves transverse focusing and longitudinal compression of intense ion beams to a small spot size on the target. To facilitate the process, the compression occurs in a long drift section filled with a dense background plasma, which neutralizes the intense beam self-fields. Typically, the ion bunch charge is better neutralized than its current, and as a result a net self-pinching (magnetic) force is produced. The self-pinching effect is of particular practical importance, and is used in various ion driver designs in order to control the transverse beam envelope. In the present work we demonstrate that this radial self-focusing force can be significantly enhanced if a weak (B ∼ 100 G) solenoidal magnetic field is applied inside the neutralized drift section, thus allowing for substantially improved transport. It is shown that in contrast to magnetic self-pinching, the enhanced collective self-focusing has a radial electric field component and occurs as a result of the overcompensation of the beam charge by plasma electrons, whereas the beam current becomes well-neutralized. As the beam leaves the neutralizing drift section, additional transverse focusing can be applied. For instance, in the neutralized drift compression experiments (NDCX) a strong (several Tesla) final focus solenoid is used for this purpose. In the present analysis we propose that the tight final focus in the NDCX experiments may possibly be achieved by using a much weaker (few hundred Gauss) magnetic lens, provided the ion beam carries an equal amount of co-moving neutralizing electrons from the preceding drift section into the lens. In this case the enhanced focusing is provided by the collective electron dynamics strongly affected by a weak applied magnetic field.

  19. Extreme neutron stars from Extended Theories of Gravity

    Energy Technology Data Exchange (ETDEWEB)

    Astashenok, Artyom V. [I. Kant Baltic Federal University, Institute of Physics and Technology, Nevskogo st. 14, Kaliningrad, 236041 (Russian Federation); Capozziello, Salvatore [Dipartimento di Fisica, Università di Napoli ' ' Federico II' ' , Via Cinthia, 9, Napoli, I-80126 Italy (Italy); Odintsov, Sergei D., E-mail: artyom.art@gmail.com, E-mail: capozziello@na.infn.it, E-mail: odintsov@ieec.uab.es [Instituciò Catalana de Recerca i Estudis Avançats (ICREA), Barcelona (Spain)

    2015-01-01

    We discuss neutron stars with strong magnetic mean fields in the framework of Extended Theories of Gravity. In particular, we take into account models derived from f(R) and f(G) extensions of General Relativity where functions of the Ricci curvature invariant R and the Gauss-Bonnet invariant G are respectively considered. Dense matter in magnetic mean field, generated by magnetic properties of particles, is described by assuming a model with three meson fields and baryons octet. As result, the considerable increasing of maximal mass of neutron stars can be achieved by cubic corrections in f(R) gravity. In principle, massive stars with M > 4M{sub ☉} can be obtained. On the other hand, stable stars with high strangeness fraction (with central densities ρ{sub c} ∼ 1.5–2.0 GeV/fm{sup 3}) are possible considering quadratic corrections of f(G) gravity. The magnetic field strength in the star center is of order 6–8 × 10{sup 18} G. In general, we can say that other branches of massive neutron stars are possible considering the extra pressure contributions coming from gravity extensions. Such a feature can constitute both a probe for alternative theories and a way out to address anomalous self-gravitating compact systems.

  20. Stars the size of planets

    International Nuclear Information System (INIS)

    Whitehouse, D.

    1984-01-01

    Red dwarf stars, the faintest and smallest stars that can be seen, sometimes host flares of immense violence. The article discusses the energy of these flares in terms of mass, x-rays, brightness, variation in light output, the sun and magnetic phenomena. (U.K.)

  1. Introduction to modeling convection in planets and stars magnetic field, density stratification, rotation

    CERN Document Server

    Glatzmaier, Gary

    2013-01-01

    This book provides readers with the skills they need to write computer codes that simulate convection, internal gravity waves, and magnetic field generation in the interiors and atmospheres of rotating planets and stars. Using a teaching method perfected in the classroom, Gary Glatzmaier begins by offering a step-by-step guide on how to design codes for simulating nonlinear time-dependent thermal convection in a two-dimensional box using Fourier expansions in the horizontal direction and finite differences in the vertical direction. He then describes how to implement more efficient and accura

  2. Kepler observations of variability in B-type stars

    OpenAIRE

    Balona, L. A.; Pigulski, A.; De Cat, P.; Handler, G.; Gutierrez-Soto, J; Engelbrecht, C. A.; Frescura, F.; Briquet, M.; Cuypers, J.; Daszynska-Daszkiewicz, J.; Degroote, P.; Dukes, R. J.; Garcia, R. A.; Green, E. M.; Heber, U.

    2011-01-01

    The analysis of the light curves of 48 B-type stars observed by Kepler is presented. Among these are 15 pulsating stars, all of which show low frequencies characteristic of SPB stars. Seven of these stars also show a few weak, isolated high frequencies and they could be considered as SPB/beta Cep hybrids. In all cases the frequency spectra are quite different from what is seen from ground-based observations. We suggest that this is because most of the low frequencies are modes of high degree ...

  3. Ultraviolet energy distributions and the temperatures of peculiar B and A stars

    International Nuclear Information System (INIS)

    Adelman, S.J.; NASA, Goddard Space Flight Center, Greenbelt, MD)

    1985-01-01

    Color temperatures have been estimated by comparing ultraviolet observations of HgMn and magnetic Ap stars with those of normal stars. Ultraviolet data from the OAO-2, ANS, TD-1, and IUE satellites generally give similar results. The values for the normal stars were derived from comparison of fluxes predicted by solar-composition fully line-blanketed model atmospheres with optical region spectrophotometry. The ultraviolet temperatures of the HgMn stars cover a narrower temperature range than do their optical region values. Magnetic Ap stars with similar optical region temperatures can show substantial differences in their ultraviolet color temperatures. This may result from magnetic field configuration and abundance differences. 27 references

  4. Bats respond to very weak magnetic fields.

    Directory of Open Access Journals (Sweden)

    Lan-Xiang Tian

    Full Text Available How animals, including mammals, can respond to and utilize the direction and intensity of the Earth's magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here, the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT, despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05. Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth's magnetic field strength varied and the polarity reversed tens of times over the past fifty million years.

  5. Fermi and the Theory of Weak Interactions

    Indian Academy of Sciences (India)

    IAS Admin

    Quantum Field Theory created by Dirac and used by Fermi to describe weak ... of classical electrodynamics (from which the electric field and magnetic field can be obtained .... Universe. However, thanks to weak interactions, this can be done.

  6. A search for the age-dependency of Ap star parameters

    International Nuclear Information System (INIS)

    Ruediger, G.; Scholz, G.

    1988-01-01

    Some observational data of the sample of the magnetic chemically peculiar stars (MCP stars) are investigated statistically. For the MCP stars of spectral types later than A2 both the frequency distribution and the R · sin i-values suggest the existence of a linear relation between stellar diameter and rotation period. The MCP stars of spectral types earlier than B9 show an overpopulation of small R · sin i which may indicate the existence of a second group with smaller radius in this sample. The equatorially symmetric rotator is used as the magnetic model. With respect to its temporal behaviour the effective magnetic field is separated into dipolar and quadrupolar contribution. Both signs of the axisymmetric quadrupole moment appear with equal frequency. The dipole moment which produces the amplitude of the B eff (t) curve forms for longer periods two groups which are separated by a distinct gap. Both of the groups exhibit magnetic fields which are the stronger the greater the stellar radius is, contrary to what is expected for frozen-in fields. The dominance of magnetic curves without polarity reversal for longer-period stars is in accordance with predictions of the dynamo theory. (author)

  7. A NuSTAR survey of nearby ultraluminous infrared galaxies

    DEFF Research Database (Denmark)

    Teng, Stacy H.; Rigby, Jane R.; Stern, Daniel

    2015-01-01

    We present a Nuclear Spectroscopic Telescope Array (NuSTAR), Chandra, and XMM-Newton survey of nine of the nearest ultraluminous infrared galaxies (ULIRGs). The unprecedented sensitivity of NuSTAR at energies above 10 keV enables spectral modeling with far better precision than was previously......] line luminosity than do Seyfert 1 galaxies. We identify IRAS 08572+3915 as another candidate intrinsically X-ray weak source, similar to Mrk 231. We speculate that the X-ray weakness of IRAS 08572+3915 is related to its powerful outflow observed at other wavelengths....

  8. Expanded calculation of weak-interaction-mediated neutrino cooling rates due to 56Ni in stellar matter

    International Nuclear Information System (INIS)

    Nabi, Jameel-Un

    2010-01-01

    An accurate estimate of the neutrino cooling rates is required in order to study the various stages of stellar evolution of massive stars. Neutrino losses from proto-neutron stars play a crucial role in deciding whether these stars would be crushed into black holes or explode as supernovae. Both pure leptonic and weak-interaction processes contribute to the neutrino energy losses in stellar matter. At low temperatures and densities, the characteristics of the early phase of presupernova evolution, cooling through neutrinos produced via the weak interaction, are important. Proton-neutron quasi-particle random phase approximation (pn-QRPA) theory has recently been used with success for the calculation of stellar weak-interaction rates of fp-shell nuclide. The lepton-to-baryon ratio (Y e ) during early phases of stellar evolution of massive stars changes substantially, mainly due to electron captures on 56 Ni. The stellar matter is transparent to the neutrinos produced during the presupernova evolution of massive stars. These neutrinos escape the site and assist the stellar core in maintaining a lower entropy. Here, an expanded calculation of weak-interaction-mediated neutrino and antineutrino cooling rates due to 56 Ni in stellar matter using the pn-QRPA theory is presented. This detailed scale is appropriate for interpolation purposes and is of greater utility for simulation codes. The calculated rates are compared with earlier calculations. During the relevant temperature and density regions of stellar matter the reported rates show few differences compared with the shell model rates and might contribute in fine-tuning of the lepton-to-baryon ratio during the presupernova phases of stellar evolution of massive stars.

  9. By Draconis Stars

    Science.gov (United States)

    Bopp, Bernard W.

    An optical spectroscopic survey of dK-M stars has resulted in the discovery of several new H-alpha emission objects. Available optical data suggest these stars have a level of chromospheric activity midway between active BY Dra stars and quiet dM's. These "marginal" BY Dra stars are single objects that have rotation velocities slightly higher than that of quiet field stars but below that of active flare/BY Dra objects. The marginal BY Dra stars provide us with a class of objects rotating very near a "trigger velocity" (believed to be 5 km/s) which appears to divide active flare/BY Dra stars from quiet dM's. UV data on Mg II emission fluxes and strength of transition region features such as C IV will serve to fix activity levels in the marginal objects and determine chromosphere and transition-region heating rates. Simultaneous optical magnetic field measures will be used to explore the connection between fieldstrength/filling-factor and atmospheric heating. Comparison of these data with published information on active and quiet dM stars will yield information on the character of the stellar dynamo as it makes a transition from "low" to "high" activity.

  10. Automatic Mapping Extraction from Multiecho T2-Star Weighted Magnetic Resonance Images for Improving Morphological Evaluations in Human Brain

    Directory of Open Access Journals (Sweden)

    Shaode Yu

    2013-01-01

    Full Text Available Mapping extraction is useful in medical image analysis. Similarity coefficient mapping (SCM replaced signal response to time course in tissue similarity mapping with signal response to TE changes in multiecho T2-star weighted magnetic resonance imaging without contrast agent. Since different tissues are with different sensitivities to reference signals, a new algorithm is proposed by adding a sensitivity index to SCM. It generates two mappings. One measures relative signal strength (SSM and the other depicts fluctuation magnitude (FMM. Meanwhile, the new method is adaptive to generate a proper reference signal by maximizing the sum of contrast index (CI from SSM and FMM without manual delineation. Based on four groups of images from multiecho T2-star weighted magnetic resonance imaging, the capacity of SSM and FMM in enhancing image contrast and morphological evaluation is validated. Average contrast improvement index (CII of SSM is 1.57, 1.38, 1.34, and 1.41. Average CII of FMM is 2.42, 2.30, 2.24, and 2.35. Visual analysis of regions of interest demonstrates that SSM and FMM show better morphological structures than original images, T2-star mapping and SCM. These extracted mappings can be further applied in information fusion, signal investigation, and tissue segmentation.

  11. Constraining the neutrino magnetic dipole moment from white dwarf pulsations

    International Nuclear Information System (INIS)

    Córsico, A.H.; Althaus, L.G.; Bertolami, M.M. Miller; Kepler, S.O.; García-Berro, E.

    2014-01-01

    Pulsating white dwarf stars can be used as astrophysical laboratories to constrain the properties of weakly interacting particles. Comparing the cooling rates of these stars with the expected values from theoretical models allows us to search for additional sources of cooling due to the emission of axions, neutralinos, or neutrinos with magnetic dipole moment. In this work, we derive an upper bound to the neutrino magnetic dipole moment (μ ν ) using an estimate of the rate of period change of the pulsating DB white dwarf star PG 1351+489. We employ state-of-the-art evolutionary and pulsational codes which allow us to perform a detailed asteroseismological period fit based on fully DB white dwarf evolutionary sequences. Plasmon neutrino emission is the dominant cooling mechanism for this class of hot pulsating white dwarfs, and so it is the main contributor to the rate of change of period with time (Pidot) for the DBV class. Thus, the inclusion of an anomalous neutrino emission through a non-vanishing magnetic dipole moment in these sequences notably influences the evolutionary timescales, and also the expected pulsational properties of the DBV stars. By comparing the theoretical Pidot value with the rate of change of period with time of PG 1351+489, we assess the possible existence of additional cooling by neutrinos with magnetic dipole moment. Our models suggest the existence of some additional cooling in this pulsating DB white dwarf, consistent with a non-zero magnetic dipole moment with an upper limit of μ ν  ∼< 10 -11  μ B . This bound is somewhat less restrictive than, but still compatible with, other limits inferred from the white dwarf luminosity function or from the color-magnitude diagram of the Globular cluster M5. Further improvements of the measurement of the rate of period change of the dominant pulsation mode of PG 1351+489 will be necessary to confirm our bound

  12. Cooling of Accretion-Heated Neutron Stars

    Science.gov (United States)

    Wijnands, Rudy; Degenaar, Nathalie; Page, Dany

    2017-09-01

    We present a brief, observational review about the study of the cooling behaviour of accretion-heated neutron stars and the inferences about the neutron-star crust and core that have been obtained from these studies. Accretion of matter during outbursts can heat the crust out of thermal equilibrium with the core and after the accretion episodes are over, the crust will cool down until crust-core equilibrium is restored. We discuss the observed properties of the crust cooling sources and what has been learned about the physics of neutron-star crusts. We also briefly discuss those systems that have been observed long after their outbursts were over, i.e, during times when the crust and core are expected to be in thermal equilibrium. The surface temperature is then a direct probe for the core temperature. By comparing the expected temperatures based on estimates of the accretion history of the targets with the observed ones, the physics of neutron-star cores can be investigated. Finally, we discuss similar studies performed for strongly magnetized neutron stars in which the magnetic field might play an important role in the heating and cooling of the neutron stars.

  13. The Stability of Magnetized Rotating Plasmas with Superthermal Fields

    DEFF Research Database (Denmark)

    Pessah, Martin Elias; Psaltis, Dimitrios

    2005-01-01

    be taken fully into account. We demonstrate that the presence of a strong toroidal component in the magnetic field plays a non-trivial role. When strong fields are considered, the strength of the toroidal magnetic field not only modifies the growth rates of the unstable modes but also determines which...... modes are subject to instabilities. We find that, for rotating configurations with Keplerian laws, the magnetorotational instability is stabilized at low wavenumbers for toroidal Alfven speeds exceeding the geometric mean of the sound speed and the rotational speed. We discuss the significance of our......During the last decade it has become evident that the magnetorotational instability is at the heart of the enhanced angular momentum transport in weakly magnetized accretion disks around neutron stars and black holes. In this paper, we investigate the local linear stability of differentially...

  14. VUV Spectroscopy of the Sun as a Star

    Science.gov (United States)

    Kankelborg, Charles; Philip, Judge; Winebarger, Amy R.; Kobayashi, Ken; Smart, Roy

    2017-08-01

    We describe a new sounding rocket mission to obtain the first high resolution, high quality VUV (100-200 nm) spectrum of the Sun-as-a-star. Our immediate science goal is to understand better the processes of chromospheric and coronal heating. HST data exist for a dozen or so Sun-like stars of a quality already beyond our ability to construct a comparable sun-as-a-star UV spectrum. The solar spectrum we obtain will enable us to understand the nature of magnetic energy dissipation as a Sun-like star evolves, and the dependence of magnetic activity on stellar mass and metallicity. This poster presents the instrument design, scientific prospects, and broader impacts of the proposed mission.

  15. Pressure-induced weak ferromagnetism in uranium dioxide, UO2

    International Nuclear Information System (INIS)

    Sakai, H; Kato, H; Tokunaga, Y; Kambe, S; Walstedt, R E; Nakamura, A; Tateiwa, N; Kobayashi, T C

    2003-01-01

    The dc magnetization of insulating UO 2 under high pressure up to ∼1 GPa has been measured using a piston-cylinder cell. Pressure-induced weak ferromagnetism appeared at low pressure (∼0.2 GPa). Both the remanent magnetization and the coercive force increase as pressure increases. This weak ferromagnetism may come from spin canting or from uncompensated moments around grain boundaries

  16. Magnetic Inflation and Stellar Mass. I. Revised Parameters for the Component Stars of the Kepler Low-mass Eclipsing Binary T-Cyg1-12664

    Energy Technology Data Exchange (ETDEWEB)

    Han, Eunkyu; Muirhead, Philip S. [Department of Astronomy and Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215 (United States); Swift, Jonathan J. [The Thacher School, 5025 Thacher Road Ojai, CA 93023 (United States); Baranec, Christoph; Atkinson, Dani [Institute for Astronomy, University of Hawaiì at Mānoa, Hilo, HI 96720-2700 (United States); Law, Nicholas M. [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3255 (United States); Riddle, Reed [California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125 (United States); Mace, Gregory N. [McDonald Observatory and The University of Texas, 2515 Speedway, Stop C1400, Austin, TX 78712-1205 (United States); DeFelippis, Daniel, E-mail: eunkyuh@bu.edu [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)

    2017-09-01

    Several low-mass eclipsing binary stars show larger than expected radii for their measured mass, metallicity, and age. One proposed mechanism for this radius inflation involves inhibited internal convection and starspots caused by strong magnetic fields. One particular eclipsing binary, T-Cyg1-12664, has proven confounding to this scenario. Çakırlı et al. measured a radius for the secondary component that is twice as large as model predictions for stars with the same mass and age, but a primary mass that is consistent with predictions. Iglesias-Marzoa et al. independently measured the radii and masses of the component stars and found that the radius of the secondary is not in fact inflated with respect to models, but that the primary is, which is consistent with the inhibited convection scenario. However, in their mass determinations, Iglesias-Marzoa et al. lacked independent radial velocity measurements for the secondary component due to the star’s faintness at optical wavelengths. The secondary component is especially interesting, as its purported mass is near the transition from partially convective to a fully convective interior. In this article, we independently determined the masses and radii of the component stars of T-Cyg1-12664 using archival Kepler data and radial velocity measurements of both component stars obtained with IGRINS on the Discovery Channel Telescope and NIRSPEC and HIRES on the Keck Telescopes. We show that neither of the component stars is inflated with respect to models. Our results are broadly consistent with modern stellar evolutionary models for main-sequence M dwarf stars and do not require inhibited convection by magnetic fields to account for the stellar radii.

  17. Cyclotron Lines in Accreting Neutron Star Spectra

    Science.gov (United States)

    Wilms, Jörn; Schönherr, Gabriele; Schmid, Julia; Dauser, Thomas; Kreykenbohm, Ingo

    2009-05-01

    Cyclotron lines are formed through transitions of electrons between discrete Landau levels in the accretion columns of accreting neutron stars with strong (1012 G) magnetic fields. We summarize recent results on the formation of the spectral continuum of such systems, describe recent advances in the modeling of the lines based on a modification of the commonly used Monte Carlo approach, and discuss new results on the dependence of the measured cyclotron line energy from the luminosity of transient neutron star systems. Finally, we show that Simbol-X will be ideally suited to build and improve the observational database of accreting and strongly magnetized neutron stars.

  18. NEW EVIDENCE OF MAGNETIC INTERACTIONS BETWEEN STARS FROM THREE-DIMENSIONAL DOPPLER TOMOGRAPHY OF ALGOL BINARIES: {beta} PER AND RS VUL

    Energy Technology Data Exchange (ETDEWEB)

    Richards, Mercedes T. [Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States); Agafonov, Michail I.; Sharova, Olga I., E-mail: mrichards@astro.psu.edu, E-mail: agfn@nirfi.sci-nnov.ru, E-mail: shol@nirfi.sci-nnov.ru [Radiophysical Research Institute (NIRFI), 25/12a, Bolshaya Pecherskaya St., Nizhny Novgorod 603950 (Russian Federation)

    2012-11-20

    Time-resolved H{alpha} spectra of magnetically active interacting binaries have been used to create three-dimensional (3D) Doppler tomograms by means of the Radioastronomical Approach. This is the first 3D reconstruction of {beta} Per, with RS Vul for comparison. These 3D tomograms have revealed evidence of the mass transfer process (gas stream, circumprimary emission, localized region, absorption zone), as well as loop prominences and coronal mass ejections (CMEs) in {beta} Per and RS Vul that could not be discovered from two-dimensional tomograms alone. The gas stream in both binaries may have been deflected beyond the central plane by the donor star's magnetic field. The stream was more elongated along the predicted trajectory in RS Vul than in {beta} Per, but not as pronounced as in U CrB (stream state). The loop prominence reached maximum V{sub z} velocities of {+-}155 km s{sup -1} in RS Vul compared to {+-}120 km s{sup -1} in {beta} Per, while the CME reached a maximum V{sub z} velocity of +150 km s{sup -1} in RS Vul and +100 km s{sup -1} in {beta} Per. The 3D tomograms show that the gas flows are not symmetric relative to the central plane and are not confined to that plane, a result confirmed by recent 15 GHz VLBI radio images of {beta} Per. Both the 3D H{alpha} tomography and the VLBI radio images support an earlier prediction of the superhump phenomenon in {beta} Per: that the gas between the stars is threaded with a magnetic field even though the hot B8V mass-gaining star is not known to have a magnetic field.

  19. Landau-Zener tunneling in the presence of weak intermolecular interactions in a crystal of Mn4 single-molecule magnets

    Science.gov (United States)

    Wernsdorfer, W.; Bhaduri, S.; Vinslava, A.; Christou, G.

    2005-12-01

    A Mn4 single-molecule magnet (SMM), with a well-isolated spin ground state of S=9/2 , is used as a model system to study Landau-Zener (LZ) tunneling in the presence of weak intermolecular dipolar and exchange interactions. The anisotropy constants D and B are measured with minor hysteresis loops. A transverse field is used to tune the tunnel splitting over a large range. Using the LZ and inverse LZ method, it is shown that these interactions play an important role in the tunnel rates. Three regions are identified: (i) at small transverse fields, tunneling is dominated by single tunnel transitions, (ii) at intermediate transverse fields, the measured tunnel rates are governed by reshuffling of internal fields, and (iii) at larger transverse fields, the magnetization reversal starts to be influenced by the direct relaxation process, and many-body tunnel events may occur. The hole digging method is used to study the next-nearest-neighbor interactions. At small external fields, it is shown that magnetic ordering occurs which does not quench tunneling. An applied transverse field can increase the ordering rate. Spin-spin cross-relaxations, mediated by dipolar and weak exchange interactions, are proposed to explain additional quantum steps.

  20. MAGNETIC BRAKING AND PROTOSTELLAR DISK FORMATION: AMBIPOLAR DIFFUSION

    International Nuclear Information System (INIS)

    Mellon, Richard R.; Li Zhiyun

    2009-01-01

    It is established that the formation of rotationally supported disks during the main accretion phase of star formation is suppressed by a moderately strong magnetic field in the ideal MHD limit. Nonideal MHD effects are expected to weaken the magnetic braking, perhaps allowing the disk to reappear. We concentrate on one such effect, ambipolar diffusion, which enables the field lines to slip relative to the bulk neutral matter. We find that the slippage does not sufficiently weaken the braking to allow rotationally supported disks to form for realistic levels of cloud magnetization and cosmic ray ionization rate; in some cases, the magnetic braking is even enhanced. Only in dense cores with both exceptionally weak fields and unreasonably low ionization rate do such disks start to form in our simulations. We conclude that additional processes, such as Ohmic dissipation or Hall effect, are needed to enable disk formation. Alternatively, the disk may form at late times when the massive envelope that anchors the magnetic brake is dissipated, perhaps by a protostellar wind.

  1. Weak Localisation in Clean and Highly Disordered Graphene

    International Nuclear Information System (INIS)

    Hilke, Michael; Massicotte, Mathieu; Whiteway, Eric; Yu, Victor

    2013-01-01

    We look at the magnetic field induced weak localisation peak of graphene samples with different mobilities. At very low temperatures, low mobility samples exhibit a very broad peak as a function of the magnetic field, in contrast to higher mobility samples, where the weak localisation peak is very sharp. We analyze the experimental data in the context of the localisation length, which allows us to extract, both the localisation length and the phase coherence length of the samples, regardless of their mobilities. This analysis is made possible by the observation that the localisation length undergoes a generic weak localisation dependence with striking universal properties

  2. Magnetic Modeling of Inflated Low-mass Stars Using Interior Fields No Larger than ˜10 kG

    Science.gov (United States)

    MacDonald, James; Mullan, D. J.

    2017-11-01

    We have previously reported on models of low-mass stars in which the presence of inflated radii is ascribed to magnetic fields that impede the onset of convection. Some of our magneto-convection models have been criticized because, when they were first reported by Mullan & MacDonald, the deep interior fields were found to be very large (50-100 MG). Such large fields are now known to be untenable. For example, Browning et al. used stability arguments to suggest that interior fields in low-mass stars cannot be larger than ˜1 MG. Moreover, 3D models of turbulent stellar dynamos suggest that fields generated in low-mass interiors may be not much stronger than 10-20 kG. In the present paper, we present magneto-convective models of inflated low-mass stars in which the interior fields are not permitted to be stronger than 10 kG. These models are used to fit empirical data for 15 low-mass stars for which precise masses and radii have been measured. We show that our 10 kG magneto-convective models can replicate the empirical radii and effective temperatures for 14 of the stars. In the case of the remaining star (in the Praesepe cluster), two different solutions have been reported in the literature. We find that one of these solutions can be fitted well with our model using the nominal age of Praesepe (800 Myr). However, the second solution cannot be fitted unless the star’s age is assumed to be much younger (˜150 Myr).

  3. Weak-scale hidden sector and energy transport in fireball models of gamma-ray bursts

    International Nuclear Information System (INIS)

    Demir, Durmus A.; Mosquera Cuesta, Herman J.

    2000-12-01

    The annihilation of pairs of very weakly interacting particles in the neighborhood of gamma-ray sources is introduced here as a plausible mechanism to overcome the baryon load problem. This way we can explain how these very high energy gamma-ray bursts can be powered at the onset of very energetic events like supernovae (collapsars) explosions or coalescences of binary neutron stars. Our approach uses the weak-scale hidden sector models in which the Higgs sector of the standard model is extended to include a gauge singlet that only interacts with the Higgs particle. These particles would be produced either during the implosion of the red supergiant star core or at the aftermath of a neutron star binary merger. The whole energetics and timescales of the relativistic blast wave, the fireball, are reproduced. (author)

  4. Binary neutron star mergers and short gamma-ray bursts: Effects of magnetic field orientation, equation of state, and mass ratio

    Science.gov (United States)

    Kawamura, Takumu; Giacomazzo, Bruno; Kastaun, Wolfgang; Ciolfi, Riccardo; Endrizzi, Andrea; Baiotti, Luca; Perna, Rosalba

    2016-09-01

    We present fully general-relativistic magnetohydrodynamic simulations of the merger of binary neutron star (BNS) systems. We consider BNSs producing a hypermassive neutron star (HMNS) that collapses to a spinning black hole (BH) surrounded by a magnetized accretion disk in a few tens of ms. We investigate whether such systems may launch relativistic jets and hence power short gamma-ray bursts. We study the effects of different equations of state (EOSs), different mass ratios, and different magnetic field orientations. For all cases, we present a detailed investigation of the matter dynamics and of the magnetic field evolution, with particular attention to its global structure and possible emission of relativistic jets. The main result of this work is that we observe the formation of an organized magnetic field structure. This happens independently of EOS, mass ratio, and initial magnetic field orientation. We also show that those models that produce a longer-lived HMNS lead to a stronger magnetic field before collapse to a BH. Such larger fields make it possible, for at least one of our models, to resolve the magnetorotational instability and hence further amplify the magnetic field in the disk. However, by the end of our simulations, we do not (yet) observe a magnetically dominated funnel nor a relativistic outflow. With respect to the recent simulations of Ruiz et al. [Astrophys. J. 824, L6 (2016)], we evolve models with lower and more plausible initial magnetic field strengths and (for computational reasons) we do not evolve the accretion disk for the long time scales that seem to be required in order to see a relativistic outflow. Since all our models produce a similar ordered magnetic field structure aligned with the BH spin axis, we expect that the results found by Ruiz et al. (who only considered an equal-mass system with an ideal fluid EOS) should be general and—at least from a qualitative point of view—independent of the mass ratio, magnetic field

  5. A model explaining synchronization of neuron bioelectric frequency under weak alternating low frequency magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Moral, A. del, E-mail: delmoral@unizar.es [Laboratorio de Magnetismo, Departamento de Física de Materia Condensada and Instituto de Ciencia de Materiales, Universidad de Zaragoza and Consejo Superior de Investigaciones Científicas, 50009 Zaragoza (Spain); Laboratorio de Magnetobiología, Departamento de Anatomía e Histología, Facultad de Medicina, Universidad de Zaragoza, 50009 Zaragoza (Spain); Centro de Tecnología Biomédica, Universidad Politécnica de Madrid, 28223 Madrid (Spain); Azanza, María J., E-mail: mjazanza@unizar.es [Laboratorio de Magnetobiología, Departamento de Anatomía e Histología, Facultad de Medicina, Universidad de Zaragoza, 50009 Zaragoza (Spain); Centro de Tecnología Biomédica, Universidad Politécnica de Madrid, 28223 Madrid (Spain)

    2015-03-01

    A biomagnetic-electrical model is presented that explains rather well the experimentally observed synchronization of the bioelectric potential firing rate (“frequency”), f, of single unit neurons of Helix aspersa mollusc under the application of extremely low frequency (ELF) weak alternating (AC) magnetic fields (MF). The proposed model incorporates to our widely experimentally tested model of superdiamagnetism (SD) and Ca{sup 2+} Coulomb explosion (CE) from lipid (LP) bilayer membrane (SD–CE model), the electrical quadrupolar long range interaction between the bilayer LP membranes of synchronized neuron pairs, not considered before. The quadrupolar interaction is capable of explaining well the observed synchronization. Actual extension of our SD–CE-model shows that the neuron firing frequency field, B, dependence becomes not modified, but the bioelectric frequency is decreased and its spontaneous temperature, T, dependence is modified. A comparison of the model with synchronization experimental results of pair of neurons under weak (B{sub 0}≅0.2–15 mT) AC-MF of frequency f{sub M}=50 Hz is reported. From the deduced size of synchronized LP clusters under B, is suggested the formation of small neuron networks via the membrane lipid correlation. - Highlights: • Neuron pair synchronization under low frequency alternating (AC) magnetic field (MF). • Superdiamagnetism and Ca{sup 2+} Coulomb explosion for AC MF effect in synchronized frequency. • Membrane lipid electrical quadrupolar pair interaction as synchronization mechamism. • Good agreement of model with electrophysiological experiments on mollusc Helix neurons.

  6. A model explaining synchronization of neuron bioelectric frequency under weak alternating low frequency magnetic field

    International Nuclear Information System (INIS)

    Moral, A. del; Azanza, María J.

    2015-01-01

    A biomagnetic-electrical model is presented that explains rather well the experimentally observed synchronization of the bioelectric potential firing rate (“frequency”), f, of single unit neurons of Helix aspersa mollusc under the application of extremely low frequency (ELF) weak alternating (AC) magnetic fields (MF). The proposed model incorporates to our widely experimentally tested model of superdiamagnetism (SD) and Ca 2+ Coulomb explosion (CE) from lipid (LP) bilayer membrane (SD–CE model), the electrical quadrupolar long range interaction between the bilayer LP membranes of synchronized neuron pairs, not considered before. The quadrupolar interaction is capable of explaining well the observed synchronization. Actual extension of our SD–CE-model shows that the neuron firing frequency field, B, dependence becomes not modified, but the bioelectric frequency is decreased and its spontaneous temperature, T, dependence is modified. A comparison of the model with synchronization experimental results of pair of neurons under weak (B 0 ≅0.2–15 mT) AC-MF of frequency f M =50 Hz is reported. From the deduced size of synchronized LP clusters under B, is suggested the formation of small neuron networks via the membrane lipid correlation. - Highlights: • Neuron pair synchronization under low frequency alternating (AC) magnetic field (MF). • Superdiamagnetism and Ca 2+ Coulomb explosion for AC MF effect in synchronized frequency. • Membrane lipid electrical quadrupolar pair interaction as synchronization mechamism. • Good agreement of model with electrophysiological experiments on mollusc Helix neurons

  7. THE MASS-DEPENDENCE OF ANGULAR MOMENTUM EVOLUTION IN SUN-LIKE STARS

    International Nuclear Information System (INIS)

    Matt, Sean P.; Baraffe, Isabelle; Chabrier, Gilles; Brun, A. Sacha; Bouvier, Jérôme

    2015-01-01

    To better understand the observed distributions of the rotation rate and magnetic activity of Sun-like and low-mass stars, we derive a physically motivated scaling for the dependence of the stellar wind torque on the Rossby number. The torque also contains an empirically derived scaling with stellar mass (and radius), which provides new insight into the mass-dependence of stellar magnetic and wind properties. We demonstrate that this new formulation explains why the lowest mass stars are observed to maintain rapid rotation for much longer than solar-mass stars, and simultaneously why older populations exhibit a sequence of slowly rotating stars, in which the low-mass stars rotate more slowly than solar-mass stars. The model also reproduces some previously unexplained features in the period-mass diagram for the Kepler field, notably: the particular shape of the ''upper envelope'' of the distribution, suggesting that ∼95% of Kepler field stars with measured rotation periods are younger than ∼4 Gyr; and the shape of the ''lower envelope'', corresponding to the location where stars transition between magnetically saturated and unsaturated regimes

  8. Binding the diproton in stars: anthropic limits on the strength of gravity

    Science.gov (United States)

    Barnes, Luke A.

    2015-12-01

    We calculate the properties and investigate the stability of stars that burn via strong (and electromagnetic) interactions, and compare their properties with those that, as in our Universe, include a rate-limiting weak interaction. It has been suggested that, if the diproton were bound, stars would burn ~1018 times brighter and faster via strong interactions, resulting in a universe that would fail to support life. By considering the representative case of a star in our Universe with initially equal numbers of protons and deuterons, we find that stable, "strong-burning" stars adjust their central densities and temperatures to have familiar surface temperatures, luminosities and lifetimes. There is no "diproton disaster". In addition, strong-burning stars are stable in a much larger region of the parameter space of fundamental constants, specifically the strength of electromagnetism and gravity. The strongest anthropic bound on stars in such universes is not their stability, as is the case for stars limited by the weak interaction, but rather their lifetime. Regardless of the strength of electromagnetism, all stars burn out in mere millions of years unless the gravitational coupling constant is extremely small, αGlesssim 10-30.

  9. THE IMPACT OF THERMODYNAMICS ON GRAVITATIONAL COLLAPSE: FILAMENT FORMATION AND MAGNETIC FIELD AMPLIFICATION

    International Nuclear Information System (INIS)

    Peters, Thomas; Klessen, Ralf S.; Federrath, Christoph; Smith, Rowan J.; Schleicher, Dominik R. G.; Banerjee, Robi; Sur, Sharanya

    2012-01-01

    Stars form by the gravitational collapse of interstellar gas. The thermodynamic response of the gas can be characterized by an effective equation of state. It determines how gas heats up or cools as it gets compressed, and hence plays a key role in regulating the process of stellar birth on virtually all scales, ranging from individual star clusters up to the galaxy as a whole. We present a systematic study of the impact of thermodynamics on gravitational collapse in the context of high-redshift star formation, but argue that our findings are also relevant for present-day star formation in molecular clouds. We consider a polytropic equation of state, P = kρ Γ , with both sub-isothermal exponents Γ 1. We find significant differences between these two cases. For Γ > 1, pressure gradients slow down the contraction and lead to the formation of a virialized, turbulent core. Weak magnetic fields are strongly tangled and efficiently amplified via the small-scale turbulent dynamo on timescales corresponding to the eddy-turnover time at the viscous scale. For Γ < 1, on the other hand, pressure support is not sufficient for the formation of such a core. Gravitational contraction proceeds much more rapidly and the flow develops very strong shocks, creating a network of intersecting sheets and extended filaments. The resulting magnetic field lines are very coherent and exhibit a considerable degree of order. Nevertheless, even under these conditions we still find exponential growth of the magnetic energy density in the kinematic regime.

  10. The magnetic fields at the surface of active single G-K giants

    Science.gov (United States)

    Aurière, M.; Konstantinova-Antova, R.; Charbonnel, C.; Wade, G. A.; Tsvetkova, S.; Petit, P.; Dintrans, B.; Drake, N. A.; Decressin, T.; Lagarde, N.; Donati, J.-F.; Roudier, T.; Lignières, F.; Schröder, K.-P.; Landstreet, J. D.; Lèbre, A.; Weiss, W. W.; Zahn, J.-P.

    2015-02-01

    . Our results show that the magnetic fields of these giants are produced by a dynamo, possibly of α-ω origin since Ro is in general smaller than unity. Four stars for which the magnetic field is measured to be outstandingly strong with respect to that expected from the rotational period/magnetic field relation or their evolutionary status are interpreted as being probable descendants of magnetic Ap stars. In addition to the weak-field giant Pollux, 4 bright giants (Aldebaran, Alphard, Arcturus, η Psc) are detected with magnetic field strength at the sub-Gauss level. Besides Arcturus, these stars were not considered to be active giants before this study and are very similar in other respects to ordinary giants, with S-index indicating consistency with basal chromospheric flux. Tables 6-8 are available in electronic form at http://www.aanda.orgBased on observations obtained at the Télescope Bernard Lyot (TBL) at Observatoire du Pic du Midi, CNRS/INSU and Université de Toulouse, France, and at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, CNRS/INSU and the University of Hawaii.

  11. Limits on Self-Interacting Dark Matter from Neutron Stars

    DEFF Research Database (Denmark)

    Kouvaris, C.

    2012-01-01

    We impose new severe constraints on the self-interactions of fermionic asymmetric dark matter based on observations of nearby old neutron stars. Weakly interacting massive particle (WIMP) self-interactions mediated by Yukawa-type interactions can lower significantly the number of WIMPs necessary...... for gravitational collapse of the WIMP population accumulated in a neutron star. Even nearby neutron stars located at regions of low dark matter density can accrete a sufficient number of WIMPs that can potentially collapse, form a mini black hole, and destroy the host star. Based on this, we derive constraints...

  12. Bats Respond to Very Weak Magnetic Fields

    Science.gov (United States)

    Tian, Lan-Xiang; Pan, Yong-Xin; Metzner, Walter; Zhang, Jin-Shuo; Zhang, Bing-Fang

    2015-01-01

    How animals, including mammals, can respond to and utilize the direction and intensity of the Earth’s magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (Preversed tens of times over the past fifty million years. PMID:25922944

  13. LONG-ORBITAL-PERIOD PREPOLARS CONTAINING EARLY K-TYPE DONOR STARS. BOTTLENECK ACCRETION MECHANISM IN ACTION

    International Nuclear Information System (INIS)

    Tovmassian, G.; González–Buitrago, D.; Zharikov, S.; Reichart, D. E.; Haislip, J. B.; Ivarsen, K. M.; LaCluyze, A. P.; Moore, J. P.; Miroshnichenko, A. S.

    2016-01-01

    We studied two objects identified as cataclysmic variables (CVs) with periods exceeding the natural boundary for Roche-lobe-filling zero-age main sequence (ZAMS) secondary stars. We present observational results for V1082 Sgr with a 20.82 hr orbital period, an object that shows a low luminosity state when its flux is totally dominated by a chromospherically active K star with no signs of ongoing accretion. Frequent accretion shutoffs, together with characteristics of emission lines in a high state, indicate that this binary system is probably detached, and the accretion of matter on the magnetic white dwarf takes place through stellar wind from the active donor star via coupled magnetic fields. Its observational characteristics are surprisingly similar to V479 And, a 14.5 hr binary system. They both have early K-type stars as donor stars. We argue that, similar to the shorter-period prepolars containing M dwarfs, these are detached binaries with strong magnetic components. Their magnetic fields are coupled, allowing enhanced stellar wind from the K star to be captured and channeled through the bottleneck connecting the two stars onto the white dwarf’s magnetic pole, mimicking a magnetic CV. Hence, they become interactive binaries before they reach contact. This will help to explain an unexpected lack of systems possessing white dwarfs with strong magnetic fields among detached white+red dwarf systems

  14. LONG-ORBITAL-PERIOD PREPOLARS CONTAINING EARLY K-TYPE DONOR STARS. BOTTLENECK ACCRETION MECHANISM IN ACTION

    Energy Technology Data Exchange (ETDEWEB)

    Tovmassian, G.; González–Buitrago, D.; Zharikov, S. [Instituto de Astronomía, Universidad Nacional Autónoma de México, Apartado Postal 877, Ensenada, Baja California, 22800 México (Mexico); Reichart, D. E.; Haislip, J. B.; Ivarsen, K. M.; LaCluyze, A. P.; Moore, J. P. [Department of Physics and Astronomy, University of North Carolina at Chapel Hill, Campus Box 3255, Chapel Hill, NC 27599 (United States); Miroshnichenko, A. S., E-mail: gag@astro.unam.mx, E-mail: dgonzalez@astro.unam.mx, E-mail: zhar@astro.unam.mx [Department of Physics and Astronomy, University of North Carolina at Greensboro, Greensboro, NC 27402-6170 (United States)

    2016-03-01

    We studied two objects identified as cataclysmic variables (CVs) with periods exceeding the natural boundary for Roche-lobe-filling zero-age main sequence (ZAMS) secondary stars. We present observational results for V1082 Sgr with a 20.82 hr orbital period, an object that shows a low luminosity state when its flux is totally dominated by a chromospherically active K star with no signs of ongoing accretion. Frequent accretion shutoffs, together with characteristics of emission lines in a high state, indicate that this binary system is probably detached, and the accretion of matter on the magnetic white dwarf takes place through stellar wind from the active donor star via coupled magnetic fields. Its observational characteristics are surprisingly similar to V479 And, a 14.5 hr binary system. They both have early K-type stars as donor stars. We argue that, similar to the shorter-period prepolars containing M dwarfs, these are detached binaries with strong magnetic components. Their magnetic fields are coupled, allowing enhanced stellar wind from the K star to be captured and channeled through the bottleneck connecting the two stars onto the white dwarf’s magnetic pole, mimicking a magnetic CV. Hence, they become interactive binaries before they reach contact. This will help to explain an unexpected lack of systems possessing white dwarfs with strong magnetic fields among detached white+red dwarf systems.

  15. The heterogeneity of surfaces of magnetic Ap stars

    International Nuclear Information System (INIS)

    Hack, M.

    1977-01-01

    The observations of spectrum-variability and light-variability of Ap stars are reviewed. It is shown that these variations are interpretable as due to the changing aspect of the spotted surface as the star rotates. It is stressed that the geometry of the phenomenon is understood fairly well but the physics is very far from being understood. (Auth.)

  16. Calculation of the structural properties of a strange quark star in the presence of a strong magnetic field using a density dependent bag constant

    Institute of Scientific and Technical Information of China (English)

    Gholam Hossein Bordbar; Hajar Bahri; Fatemeh Kayanikhoo

    2012-01-01

    We have calculated the structural properties of a strange quark star with a static model in the presence of a strong magnetic field.To this end,we use the MITbag model with a density dependent bag constant.To parameterize the density dependence of the bag constant,we have used our results for the lowest order constrained variational calculation of the asymmetric nuclear matter.By calculating the equation of state of strange quark matter,we have shown that the pressure of this system increases by increasing both density and magnetic field.Finally,we have investigated the effect of density dependence of the bag constant on the structural properties of a strange quark star.

  17. Interactions between exoplanets and the winds of young stars

    Directory of Open Access Journals (Sweden)

    Vidotto A. A.

    2014-01-01

    Full Text Available The topology of the magnetic field of young stars is important not only for the investigation of magnetospheric accretion, but also responsible in shaping the large-scale structure of stellar winds, which are crucial for regulating the rotation evolution of stars. Because winds of young stars are believed to have enhanced mass-loss rates compared to those of cool, main-sequence stars, the interaction of winds with newborn exoplanets might affect the early evolution of planetary systems. This interaction can also give rise to observational signatures which could be used as a way to detect young planets, while simultaneously probing for the presence of their still elusive magnetic fields. Here, we investigate the interaction between winds of young stars and hypothetical planets. For that, we model the stellar winds by means of 3D numerical magnetohydrodynamic simulations. Although these models adopt simplified topologies of the stellar magnetic field (dipolar fields that are misaligned with the rotation axis of the star, we show that asymmetric field topologies can lead to an enhancement of the stellar wind power, resulting not only in an enhancement of angular momentum losses, but also intensifying and rotationally modulating the wind interactions with exoplanets.

  18. Theories for the winds from Wolf Rayet stars

    International Nuclear Information System (INIS)

    Cassinelli, J.P.

    1982-01-01

    The massive and fast winds of Wolf Rayet stars present a serious momentum problem for the line-driven wind theories that are commonly used to explain the fast winds of early type stars. It is perhaps possible for the winds to be driven by lines, if multiple scattering occurs and if there are a sufficient number of lines in the spectrum so that large fraction of the continuum is blocked by line opacity in the winds. Several other mechanisms are discussed, in particular two that rely on strong magnetic fields: a) Alfven wave driven wind models like those recently developed by Hartmann and MacGregor for late type supergiants and b) the ''Fast Magnetic Rotator'' model that was developed by Belcher and MacGregor for the winds from pre-main sequence stars. In either model, large magnetic fields (approximately equal to 10 4 gauss) are required to drive the massive and fast winds of Wolf Rayet stars. Smaller fields might be possible if the multiple scattering line radiation force can be relied on to provide a final acceleration to terminal velocity. (Auth.)

  19. Weak Galactic halo-Fornax dSph connection from RR Lyrae stars

    NARCIS (Netherlands)

    Fiorentino, G.; Monelli, M.; Stetson, P. B.; Bono, G.; Gallart, C.; Martínez-Vázquez, C. E.; Bernard, E. J.; Massari, D.; Braga, V. F.; Dall'Ora, M.

    2017-01-01

    Aims: For the first time accurate pulsation properties of the ancient variable stars of the Fornax dwarf spheroidal galaxy (dSph) are discussed in the broad context of galaxy formation and evolution. Methods: Homogeneous multi-band BVI optical photometry of spanning twenty years has allowed us to

  20. From clouds to cores to envelopes to disks: a multi-scale view of magnetized star formation

    Science.gov (United States)

    Hull, Charles; Plambeck, R. L.; TADPOL survey Team

    2014-01-01

    Magnetic fields are thought to play an important role in the formation of stars. However, that importance has been called into question by previous observations showing misalignment between protostellar outflows and magnetic fields (B-fields), as well as inconsistency in field morphology between 10,000 and 1000 AU scales. To investigate these inconsistencies, we used the 1.3 mm full-Stokes polarimeter — which I tested, installed, and calibrated for CARMA, a mm-wave interferometer — to map dust polarization with ~2.5" resolution toward 29 star-forming cores and 8 star-forming regions as part of the TADPOL survey. We find that a subset of the sources have consistent B-field orientations between the large 20") scales measured by single-dish submm bolometers and the small scales measured by CARMA. Those same sources also tend to have higher fractional polarizations (measured by CARMA), presumably because the B-fields are less twisted by dynamic effects. However, even in these sources, which seem to have retained the memory of the global B-field direction, the fields in the cores are misaligned with the disks and outflows in the central protostars — a key result of the TADPOL survey. Furthermore, the cores with lower polarization fractions tend to have B-fields that are perpendicular to outflows, which suggests that in these sources the B-fields have lost the memory of the larger-scale global field, and have been wrapped up by core rotation. This is an important result for disk formation theory, as it suggests that field misalignment may indeed be the solution to the magnetic braking catastrophe. Finally, we find that all sources exhibit the so-called “polarization hole” effect, where the polarization drops significantly near the total intensity peak. When this effect was seen in low-resolution single-dish maps, it was attributed to the averaging of unresolved structure in the plane of the sky. However, the higher resolution maps we present here resolve these

  1. Shear viscosity of the quark-gluon plasma in a weak magnetic field in perturbative QCD: Leading log

    Science.gov (United States)

    Li, Shiyong; Yee, Ho-Ung

    2018-03-01

    We compute the shear viscosity of two-flavor QCD plasma in an external magnetic field in perturbative QCD at leading log order, assuming that the magnetic field is weak or soft: e B ˜g4log (1 /g )T2. We work in the assumption that the magnetic field is homogeneous and static, and the electrodynamics is nondynamical in a formal limit e →0 while e B is kept fixed. We show that the shear viscosity takes a form η =η ¯(B ¯)T3/(g4log (1 /g )) with a dimensionless function η ¯(B ¯) in terms of a dimensionless variable B ¯=(e B )/(g4log (1 /g )T2). The variable B ¯ corresponds to the relative strength of the effect of cyclotron motions compared to the QCD collisions: B ¯˜lmfp/lcyclo. We provide a full numerical result for the scaled shear viscosity η ¯(B ¯).

  2. Rotation, spectral variability, magnetic geometry and magnetosphere of the Of?p star CPD -28° 2561

    OpenAIRE

    Wade, G. A.; Barba, R. H.; Grunhut, J.; Martins, F.; Petit, V.; Sundqvist, J. O.; Townsend, R. H. D.; Walborn, N. R.; Alecian, E.; Alfaro, E. J.; Maíz Apellaniz, J; Arias, Julia Ines; Gamen, Roberto Claudio; Morrell, Nidia Irene; Naze, Y.

    2017-01-01

    We report magnetic and spectroscopic observations and modelling of the Of?p star CPD −28° 2561. Using more than 75 new spectra, we have measured the equivalent width variations and examined the dynamic spectra of photospheric and wind-sensitive spectral lines. A period search results in an unambiguous 73.41 d variability period. High-resolution spectropolarimetric data analysed using least-squares deconvolution yield a Zeeman signature detected in the mean Stokes V profile corresponding to ph...

  3. Astrid-2 EMMA Magnetic Calibration

    DEFF Research Database (Denmark)

    Merayo, José M.G.; Brauer, Peter; Risbo, Torben

    1998-01-01

    The Swedish micro-satellite Astrid-2 contains a tri-axial fluxgate magnetometer with the sensor co-located with a Technical University of Denmark (DTU) star camera for absolute attitude, and extended about 0.9 m on a hinged boom. The magnetometer is part of the RIT EMMA electric and magnetic fields...... experiment built as a collaboration between the DTU, Department of Automation and the Department of Plasma Physics, The Alfvenlaboratory, Royal Institute of Technology (RIT), Stockholm. The final magnetic calibration of the Astrid-2 satellite was done at the Lovoe Magnetic Observatory under the Geological...... Survey of Sweden near Stockholm on the night of May 15.-16., 1997. The magnetic calibration and the intercalibration between the star camera and the magnetic sensor was performed by measuring the Earth's magnetic field and simultaneously observing the star sky with the camera. The rotation matrix between...

  4. Binding the diproton in stars: anthropic limits on the strength of gravity

    Energy Technology Data Exchange (ETDEWEB)

    Barnes, Luke A., E-mail: L.Barnes@physics.usyd.edu.au [Sydney Institute for Astronomy, School of Physics, A28, The University of Sydney, NSW 2006 (Australia)

    2015-12-01

    We calculate the properties and investigate the stability of stars that burn via strong (and electromagnetic) interactions, and compare their properties with those that, as in our Universe, include a rate-limiting weak interaction. It has been suggested that, if the diproton were bound, stars would burn ∼10{sup 18} times brighter and faster via strong interactions, resulting in a universe that would fail to support life. By considering the representative case of a star in our Universe with initially equal numbers of protons and deuterons, we find that stable, 'strong-burning' stars adjust their central densities and temperatures to have familiar surface temperatures, luminosities and lifetimes. There is no 'diproton disaster'. In addition, strong-burning stars are stable in a much larger region of the parameter space of fundamental constants, specifically the strength of electromagnetism and gravity. The strongest anthropic bound on stars in such universes is not their stability, as is the case for stars limited by the weak interaction, but rather their lifetime. Regardless of the strength of electromagnetism, all stars burn out in mere millions of years unless the gravitational coupling constant is extremely small, α{sub G}∼< 10{sup −30}.

  5. Binding the diproton in stars: anthropic limits on the strength of gravity

    International Nuclear Information System (INIS)

    Barnes, Luke A.

    2015-01-01

    We calculate the properties and investigate the stability of stars that burn via strong (and electromagnetic) interactions, and compare their properties with those that, as in our Universe, include a rate-limiting weak interaction. It has been suggested that, if the diproton were bound, stars would burn ∼10 18 times brighter and faster via strong interactions, resulting in a universe that would fail to support life. By considering the representative case of a star in our Universe with initially equal numbers of protons and deuterons, we find that stable, 'strong-burning' stars adjust their central densities and temperatures to have familiar surface temperatures, luminosities and lifetimes. There is no 'diproton disaster'. In addition, strong-burning stars are stable in a much larger region of the parameter space of fundamental constants, specifically the strength of electromagnetism and gravity. The strongest anthropic bound on stars in such universes is not their stability, as is the case for stars limited by the weak interaction, but rather their lifetime. Regardless of the strength of electromagnetism, all stars burn out in mere millions of years unless the gravitational coupling constant is extremely small, α G ∼< 10 −30

  6. NEAR-INFRARED PERIODIC AND OTHER VARIABLE FIELD STARS IN THE FIELD OF THE CYGNUS OB7 STAR-FORMING REGION

    Energy Technology Data Exchange (ETDEWEB)

    Wolk, Scott J.; Rice, Thomas S. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Aspin, Colin A. [Institute for Astronomy, University of Hawaii at Manoa, 640 North Aohoku Place, Hilo, HI 96720 (United States)

    2013-04-15

    We present a subset of the results of a three-season, 124 night, near-infrared monitoring campaign of the dark clouds Lynds 1003 and Lynds 1004 in the Cygnus OB7 star-forming region. In this paper, we focus on the field star population. Using three seasons of UKIRT J, H, and K-band observations spanning 1.5 years, we obtained high-quality photometry on 9200 stars down to J = 17 mag, with photometric uncertainty better than 0.04 mag. After excluding known disk-bearing stars we identify 149 variables-1.6% of the sample. Of these, about 60 are strictly periodic, with periods predominantly <2 days. We conclude this group is dominated by eclipsing binaries. A few stars have long period signals of between 20 and 60 days. About 25 stars have weak modulated signals, but it was not clear if these were periodic. Some of the stars in this group may be diskless young stellar objects with relatively large variability due to cool starspots. The remaining {approx}60 stars showed variations which appear to be purely stochastic.

  7. Using the Seismology of Non-magnetic Chemically Peculiar Stars as ...

    Indian Academy of Sciences (India)

    2016-01-27

    Jan 27, 2016 ... Chemical composition is a good tracer of the hydrodynamical processes that occur in stars as they often lead to mixing and particle transport. By comparing abundances predicted by models and those observed in stars we can infer some constraints on those mixing processes. As pulsations in the stars are ...

  8. New T Tauri stars in Chamaeleon I and Chamaeleon II

    Science.gov (United States)

    Hartigan, Patrick

    1993-01-01

    A new objective prism survey of the entire Chamaeleon I dark cloud and 2/3 of the Chamaeleon II cloud has uncovered 26 new H-alpha emission line objects that were missed by previous H-alpha plate surveys. The new H-alpha emission line objects have similar IR colors and spatial distributions to the known T Tauri stars in these dark clouds, and could represent the very low mass end of the stellar population in these clouds or an older, less active component to the usual classical T Tauri star population. The new H-alpha survey identified 70 percent of the total known Young Stellar Objects (YSOs) in Cha I, compared with 35 percent for IRAS, and 25 percent from the Einstein X-ray survey. Ten of the new objects are weak-lined stars, with H-alpha equivalent widths less than 10 A. Weak-lined T Tauri stars make up about half of the total population of young stars in the Chamaeleon I cloud, a proportion similar to the Taurus-Auriga cloud. Presented are coordinates, finding charts, and optical and IR photometry of the new emission-line objects.

  9. Magnetic fields in starspots on late-type giants

    International Nuclear Information System (INIS)

    Jahn, K.

    1985-01-01

    Computations of models of magnetic starspots on cool active giants show that the value of the magnetic intensity in spots is generally of the order of one kilogauss, although in larger spots the field can be as weak as a few hundred gauss. It is also argued, that spots on giants qualitatively differ from those on late-type dwarfs, since they cannot be too large. The largest individual spots can cover at most about one percent of a stellar hemisphere. This is in a very good agreement with earlier suggestions based on observations of spotted giants. The assumption that spots are the regions of the strongest magnetic field allows to discuss recent attempts of detection of the magnetic field on late-type giants. Polarimetric measurements most probably cannot be successful, due to a small field strength and a complex topology of the field. It is shown that even if a whole surface was covered by spots with relatively strong field, the resulting not longitudinal field would be as weak as a few gauss. Also methods independent of polarimetric measurements, based on the analysis of Zeeman broadening, generally are not sensitive enough to detect the magnetic field on giants, even in spots. λ And is discussed as an example. The comparison of models of spots computed for that stars with photometric observations suggests, that a dark region on λ And consists of hundreds of small spots (each of them smaller than about 0.1% of the hemisphere), in which the magnetic intensity cannot exceed about 900 gauss, and most probably is even smaller. 23 refs., 4 figs., 4 tabs. (author)

  10. Tidal Love Numbers of Neutron Stars

    International Nuclear Information System (INIS)

    Hinderer, Tanja

    2008-01-01

    For a variety of fully relativistic polytropic neutron star models we calculate the star's tidal Love number k 2 . Most realistic equations of state for neutron stars can be approximated as a polytrope with an effective index n ∼ 0.5-1.0. The equilibrium stellar model is obtained by numerical integration of the Tolman-Oppenheimer-Volkhov equations. We calculate the linear l = 2 static perturbations to the Schwarzschild spacetime following the method of Thorne and Campolattaro. Combining the perturbed Einstein equations into a single second-order differential equation for the perturbation to the metric coefficient g tt and matching the exterior solution to the asymptotic expansion of the metric in the star's local asymptotic rest frame gives the Love number. Our results agree well with the Newtonian results in the weak field limit. The fully relativistic values differ from the Newtonian values by up to ∼24%. The Love number is potentially measurable in gravitational wave signals from inspiralling binary neutron stars.

  11. Origin and Evolution of Magnetic Field in PMS Stars: Influence of Rotation and Structural Changes

    Energy Technology Data Exchange (ETDEWEB)

    Emeriau-Viard, Constance; Brun, Allan Sacha, E-mail: constance.emeriau@cea.fr, E-mail: sacha.brun@cea.fr [Laboratoire AIM Paris-Saclay CEA/DSM—CNRS—Université Paris Diderot, IRFU/DAp CEA Paris-Saclay, F-91191 Gif-sur-Yvette Cedex (France)

    2017-09-01

    During stellar evolution, especially in the pre-main-sequence phase, stellar structure and rotation evolve significantly, causing major changes in the dynamics and global flows of the star. We wish to assess the consequences of these changes on stellar dynamo, internal magnetic field topology, and activity level. To do so, we have performed a series of 3D HD and MHD simulations with the ASH code. We choose five different models characterized by the radius of their radiative zone following an evolutionary track computed by a 1D stellar evolution code. These models characterized stellar evolution from 1 to 50 Myr. By introducing a seed magnetic field in the fully convective model and spreading its evolved state through all four remaining cases, we observe systematic variations in the dynamical properties and magnetic field amplitude and topology of the models. The five MHD simulations develop a strong dynamo field that can reach an equipartition state between the kinetic and magnetic energies and even superequipartition levels in the faster-rotating cases. We find that the magnetic field amplitude increases as it evolves toward the zero-age main sequence. Moreover, the magnetic field topology becomes more complex, with a decreasing axisymmetric component and a nonaxisymmetric one becoming predominant. The dipolar components decrease as the rotation rate and the size of the radiative core increase. The magnetic fields possess a mixed poloidal-toroidal topology with no obvious dominant component. Moreover, the relaxation of the vestige dynamo magnetic field within the radiative core is found to satisfy MHD stability criteria. Hence, it does not experience a global reconfiguration but slowly relaxes by retaining its mixed stable poloidal-toroidal topology.

  12. A Common Origin of Magnetism from Planets to White Dwarfs

    Energy Technology Data Exchange (ETDEWEB)

    Isern, Jordi; Külebi, Baybars [Institut de Ciències de l’Espai (CSIC), Campus UAB, 08193 Cerdanyola (Spain); García-Berro, Enrique [Institut d’Estudis Espacials de Catalunya, Ed. Nexus-201, c/Gran Capità 2-4, E-08034 Barcelona (Spain); Lorén-Aguilar, Pablo [School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL (United Kingdom)

    2017-02-20

    Isolated magnetic white dwarfs have field strengths ranging from kilogauss to gigagauss. However, the origin of the magnetic field has not been hitherto elucidated. Whether these fields are fossil, hence the remnants of original weak magnetic fields amplified during the course of the evolution of their progenitor stars, or are the result of binary interactions, or, finally, they are produced by other internal physical mechanisms during the cooling of the white dwarf itself, remains a mystery. At sufficiently low temperatures, white dwarfs crystallize. Upon solidification, phase separation of its main constituents, {sup 12}C and {sup 16}O, and of the impurities left by previous evolution occurs. This process leads to the formation of a Rayleigh–Taylor unstable liquid mantle on top of a solid core. This convective region, as it occurs in solar system planets like the Earth and Jupiter, can produce a dynamo able to yield magnetic fields of strengths of up to 0.1 MG, thus providing a mechanism that could explain magnetism in single white dwarfs.

  13. Observations on the variability of linear polarization in late-type dwarf stars

    Energy Technology Data Exchange (ETDEWEB)

    Huovelin, J.; Linnaluoto, S.; Tuominen, I.; Virtanen, H.

    1989-04-01

    Broadband (UBV) linear polarimetric observations of a sample of late-type (F7-K5) dwarfs are reported. The observations include ten stars and extend over a maximum of 20 nights. Seven stars show significant temporal variability of polarization, which could be interpreted as rotational modulation due to slowly varying magnetic regions. Magnetic intensification in saturated Zeeman sensitive absorption lines is suggested as the dominant effect connecting linear polarization with magnetic activity in the most active single late-type dwarfs, while the wavelength dependence in the less active stars could also be due to a combination of Rayleigh and Thomson scattering.

  14. The first detection on Wolf-Rayet stars in M31

    International Nuclear Information System (INIS)

    Shara, M.M.; Moffat, A.F.J.

    1982-01-01

    A search to continuum magnitude B approximately equal to 21.5 (Msub(B) approximately equal to -3) using a narrow band filter at lambda4670A and a wide B-band filter has revealed 21 Wolf-Rayet star candidates in about half the giant Sb galaxy M31. Some weak-line WR stars, particularly WN subtypes, may have escaped detection. These numbers are compatible with the total number of luminous (i.e. massive) stars in M31. Eighteen of twenty confirmed candidate stars in M31 lie in the direction of OB associations in the ring of prominent star formation 5-16 kpc from the center. (Auth.)

  15. The Ca II resonance lines in M dwarf stars without H-alpha emission

    Energy Technology Data Exchange (ETDEWEB)

    Giampapa, M.S.; Cram, L.E.; Wild, W.J. (National Solar Observatory, Tucson, AZ (USA) Sydney Univ. (Australia) Arizona Univ., Tucson (USA))

    1989-10-01

    Spectra of the Ca II H and K lines in a sample of 31 M dwarf stars without H-alpha emission are used to calculate chromospheric K line radiative losses, F(k), and to study the joint response of Ca II K and H-alpha to chromospheric heating in dwarf M stars. It is suggested that the poor correlation found in the equivalent width - log F(K) diagram may be due either to radial segregation of the H-alpha and K line forming regions or to lateral inhomogeneities in the chromospheres. The results confirm the existence of dM stars with weak H-alpha absorption and K line emission only slightly weaker than that of the dMe stars, and show that dM stars with weak H-alpha but kinematics and metallicities representative of the young disk population belong to a class characterized by a comparatively high degree of chromospheric activity. 32 refs.

  16. Negative magnetoresistance in perpendicular of the superlattices axis weak magnetic field at scattering of impurity ions

    International Nuclear Information System (INIS)

    Askerov, B. M.; Figarova, R.; Guseynov, G.I.

    2012-01-01

    Full Text : The transverse magnetoresistance in superlattices with the cosine dispersion law of conduction electrons in a case, when a weak magnetic field in plane of layer at scattering of the charge carriers of impurity ions has been studied. It has been shown that in a quasi-two-dimensional case the magnetoresistance was positive, while in a quasi-three-dimensional case can become negative depending of a degree of mini-band filling. Such behavior of magnetoresistance, apparently, has been related to presence in a mini-band of region with the negative effective mass

  17. Magnetized Converging Flows toward the Hot Core in the Intermediate/High-mass Star-forming Region NGC 6334 V

    International Nuclear Information System (INIS)

    Juárez, Carmen; Girart, Josep M.; Zamora-Avilés, Manuel; Palau, Aina; Ballesteros-Paredes, Javier; Tang, Ya-Wen; Koch, Patrick M.; Liu, Hauyu Baobab; Zhang, Qizhou; Qiu, Keping

    2017-01-01

    We present Submillimeter Array (SMA) observations at 345 GHz toward the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern toward the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km s −1 , converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with magnetohydrodynamic simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (∼0.1 pc) of NGC 6334 V toward the higher-density hot core region (∼0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity.

  18. Magnetic study of weakly contaminated forest soils

    Czech Academy of Sciences Publication Activity Database

    Kapička, Aleš; Jordanova, Neli; Petrovský, Eduard; Podrázský, V.

    2003-01-01

    Roč. 148, 1/4 (2003), s. 31-44 ISSN 0049-6979 R&D Projects: GA AV ČR IAA3012905 Institutional research plan: CEZ:AV0Z3012916 Keywords : anthropogenic ferrimagnetics * environmental magnetism * soil pollution Subject RIV: DE - Earth Magnetism, Geodesy, Geography Impact factor: 0.883, year: 2003

  19. Biological effects due to weak magnetic fields on plants

    Science.gov (United States)

    Belyavskaya, N.

    In the evolution process, living organisms have experienced the action of the Earth's magnetic field (MF) that is a natural component of our environment. It is known that a galactic MF induction does not exceed 0.1 nT, since investigations of weak magnetic field (WMF) effects on biological systems have attracted attention of biologists due to planning long-term space flights to other planets where the magnetizing force is near 10-5 Oe. However, the role of WMF and its influence on organisms' functioning are still insufficiently investigated. A large number of experiments with seedlings of different plant species placed in WMF has found that the growth of their primary roots is inhibited during the early terms of germination in comparison with control. The proliferation activity and cell reproduction are reduced in meristem of plant roots under WMF application. The prolongation of total cell reproductive cycle is registered due to the expansion of G phase in1 different plant species as well as of G phase in flax and lentil roots along with2 relative stability of time parameters of other phases of cell cycle. In plant cells exposed to WMF, the decrease in functional activity of genome at early prereplicate period is shown. WMF causes the intensification in the processes of proteins' synthesis and break-up in plant roots. Qualitative and quantitative changes in protein spectrum in growing and differentiated cells of plant roots exposed to WMF are revealed. At ultrastructural level, there are observed such ultrastructural peculiarities as changes in distribution of condensed chromatin and nucleolus compactization in nuclei, noticeable accumulation of lipid bodies, development of a lytic compartment (vacuoles, cytosegresomes and paramural bodies), and reduction of phytoferritin in plastids in meristem cells of pea roots exposed to WMF. Mitochondria are the most sensitive organelle to WMF application: their size and relative volume in cells increase, matrix is electron

  20. A spin-down mechanism for accreting neutron stars

    International Nuclear Information System (INIS)

    Illarionov, A.F.; AN SSSR, Moscow. Fizicheskij Inst.); Kompaneets, D.A.

    1990-01-01

    We propose a new spin-down mechanism for accreting neutron stars that explains the existence of a number of long-period (p≅100-1000 s) X-ray pulsars in wide binaries with OB-stars. The spin-down is a result of efficient angular momentum transfer from the rotating magnetosphere of the accreting star to an outflowing stream of magnetized matter. The outflow is formed within a limited solid angle, and the outflow rate is less than the accretion rate. The outflow formation is connected with the anisotropy and intensity of the hard X-ray emission of the neutron star. X-rays from the pulsar heat through Compton scattering the accreting matter anisotropically. The heated matter has a lower density than the surrounding accreting matter and flows up by the action of the buoyancy force. We find the criterion for the outflow to form deep in the accretion flow (i.e., close to the neutron star magnetosphere). The neutron star loses angular momentum when the outflow forms so deep as to capture the magnetic field lines from the rotating magnetosphere. The balance between angular momentum gain by accreting gas and loss by outflowing matter takes place at a particular value of the period of the spinning neutron star. (orig.)

  1. Magnetic Excitations in Weakly Coupled Spin Dimers and Chains Material Cu2Fe2Ge4O13

    International Nuclear Information System (INIS)

    Masuda, Takatsugu; Zheludev, Andrey I.; Sales, Brian C.; Imai, S.; Uchinokura, K.; Park, S.

    2005-01-01

    Magnetic excitations in a weakly coupled spin dimers and chains compound Cu 2 Fe 2 Ge 4 O 13 are measured by inelastic neutron scattering. Both structure factors and dipsersion of low-energy excitations up to 10 meV energy transfer are well described by a semiclassical spin wave theory involving interacting Fe 3+ (S=5/2) chains. Additional dispersionsless excitations are observed at higher energies, at ℎω=24 meV, and associated with singlet-triplet transitions within Cu 2+ dimers. Both types of excitations can be understood by treating weak interactions between the Cu 2+ and Fe 3+ subsystems at the level of the mean-field random phase approximation. However, this simple model fails to account for the measured temperature dependence of the 24 meV mode.

  2. Multipolar electromagnetic fields around neutron stars: general-relativistic vacuum solutions

    Science.gov (United States)

    Pétri, J.

    2017-12-01

    Magnetic fields inside and around neutron stars are at the heart of pulsar magnetospheric activity. Strong magnetic fields are responsible for quantum effects, an essential ingredient to produce leptonic pairs and the subsequent broad-band radiation. The variety of electromagnetic field topologies could lead to the observed diversity of neutron star classes. Thus, it is important to include multipolar components to a presumably dominant dipolar magnetic field. Exact analytical solutions for these multipoles in Newtonian gravity have been computed in recent literature. However, flat space-time is not adequate to describe physics in the immediate surroundings of neutron stars. We generalize the multipole expressions to the strong gravity regime by using a slowly rotating metric approximation such as the one expected around neutron stars. Approximate formulae for the electromagnetic field including frame dragging are computed from which we estimate the Poynting flux and the braking index. Corrections to leading order in compactness and spin parameter are presented. As far as spin-down luminosity is concerned, it is shown that frame dragging remains irrelevant. For high-order multipoles starting from the quadrupole, the electric part can radiate more efficiently than the magnetic part. Both analytical and numerical tools are employed.

  3. Supernovae theory: study of electro-weak processes during gravitational collapse of massive stars

    International Nuclear Information System (INIS)

    Fantina, A.F.

    2010-01-01

    The physics of supernova requires the understanding of both the complex hydrodynamical phenomena (such as transfer of energy, neutrino transport, shock) as well as the microphysics related to the dense and hot matter. In the framework of type II Supernovae theory, currently most of numerical simulations that simulate the supernova core collapse up to the formation and propagation of the shock wave fail to reproduce the observed explosion of the outer layers of massive stars. The reason for that could be due both to hydrodynamical phenomena such as rotation, convection, and general relativity, and to some micro-physical processes involved in the picture and not yet completely understood. The aim of this work is to investigate some of these micro-physical inputs, namely the electro-weak processes, that play a crucial role during the gravitational collapse and to analyse their effects by means of hydrodynamical simulations. Among nuclear processes which occur in core-collapse supernova, the most important electro-weak process taking place during the collapse is the electron capture; it occurs both on free protons and on protons bound in nuclei. This capture is essential to determine the evolution of the lepton fraction of the core during the neutronization phase. It affects the efficiency of the bounce and, as a consequence, the strength of the shock wave. Moreover, both the equation of state of supernova matter and electron capture rates in nuclei are modified by the effective mass of nucleons in nuclei, induced by many-body correlations in the dense medium, and its temperature dependence. In the first part of the thesis, a nuclear model aimed at studying the nuclear effective mass is presented. We show how we have included in a energy density functional (EDF) approach a surface-peaked nucleon effective mass to mimic some effects beyond Hartree-Fock. We have added a term to the Skyrme functional, in order to reproduce the enhancement of the effective mass at the

  4. The twinkling of stars

    International Nuclear Information System (INIS)

    Jakeman, E.; Parry, G.; Pike, E.R.; Pusey, P.N.

    1978-01-01

    This article collects together some of the main ideas and experimental results on the twinkling of stars. Statistical methods are used to characterise the features of the scintillation and to investigate the ways in which these depend on the zenith angle of the star, the bandwidth of the light and various other parameters. Some new results are included which demonstrate the advantages of using photon counting methods in experiments on stellar scintillation. Since the twinkling of stars is a consequence of the turbulence in the Earth's magnetic atmosphere then measurements can be used to deduce some features of the structure of the turbulence. Some of the experiments designed to do this are discussed and the results reported. (author)

  5. Dark matter, neutron stars, and strange quark matter.

    Science.gov (United States)

    Perez-Garcia, M Angeles; Silk, Joseph; Stone, Jirina R

    2010-10-01

    We show that self-annihilating weakly interacting massive particle (WIMP) dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star into a strange star. We use an energy estimate for the long-lived strangelet based on the Fermi-gas model combined with the MIT bag model to set a new limit on the possible values of the WIMP mass that can be especially relevant for subdominant species of massive neutralinos.

  6. Neutron star kicks and asymmetric supernovae

    International Nuclear Information System (INIS)

    Lai, D.

    2001-01-01

    Observational advances over the last decade have left little doubt that neutron stars received a large kick velocity (of order a few hundred to a thousand km s -1 ) at birth. The physical origin of the kicks and the related supernova asymmetry is one of the central unsolved mysteries of supernova research. We review the physics of different kick mechanisms, including hydrodynamically driven, neutrino - magnetic field driven, and electromagnetically driven kicks. The viabilities of the different kick mechanisms are directly related to the other key parameters characterizing nascent neutron stars, such as the initial magnetic field and the initial spin. Recent observational constraints on kick mechanisms are also discussed. (orig.)

  7. THE UNREASONABLE WEAKNESS OF R -PROCESS COSMIC RAYS IN THE NEUTRON-STAR-MERGER NUCLEOSYNTHESIS SCENARIO

    Energy Technology Data Exchange (ETDEWEB)

    Kyutoku, Koutarou [Interdisciplinary Theoretical Science (iTHES) Research Group, RIKEN, Wako, Saitama 351-0198 (Japan); Ioka, Kunihito, E-mail: koutarou.kyutoku@riken.jp [Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, 606-8502 (Japan)

    2016-08-10

    We reach the robust conclusion that, by combining the observed cosmic rays of r -process elements with the fact that the velocity of the neutron-star-merger ejecta is much higher than that of the supernova ejecta, either (1) the reverse shock in the neutron-star-merger ejecta is a very inefficient accelerator that converts less than 0.003% of the ejecta kinetic energy to the cosmic-ray energy or (2) the neutron star merger is not the origin of the Galactic r -process elements. We also find that the acceleration efficiency should be less than 0.1% for the reverse shock of the supernova ejecta with observed cosmic rays lighter than the iron.

  8. SPIN EVOLUTION OF ACCRETING YOUNG STARS. II. EFFECT OF ACCRETION-POWERED STELLAR WINDS

    International Nuclear Information System (INIS)

    Matt, Sean P.; Pinzón, Giovanni; Greene, Thomas P.; Pudritz, Ralph E.

    2012-01-01

    We present a model for the rotational evolution of a young, solar-mass star interacting magnetically with an accretion disk. As in a previous paper (Paper I), the model includes changes in the star's mass and radius as it descends the Hayashi track, a decreasing accretion rate, and a prescription for the angular momentum transfer between the star and disk. Paper I concluded that, for the relatively strong magnetic coupling expected in real systems, additional processes are necessary to explain the existence of slowly rotating pre-main-sequence stars. In the present paper, we extend the stellar spin model to include the effect of a spin-down torque that arises from an accretion-powered stellar wind (APSW). For a range of magnetic field strengths, accretion rates, initial spin rates, and mass outflow rates, the modeled stars exhibit rotation periods within the range of 1-10 days in the age range of 1-3 Myr. This range coincides with the bulk of the observed rotation periods, with the slow rotators corresponding to stars with the lowest accretion rates, strongest magnetic fields, and/or highest stellar wind mass outflow rates. We also make a direct, quantitative comparison between the APSW scenario and the two types of disk-locking models (namely, the X-wind and Ghosh and Lamb type models) and identify some remaining theoretical issues for understanding young star spins.

  9. Magnetic collapse of a neutron gas: Can magnetars indeed be formed?

    International Nuclear Information System (INIS)

    Martinez, A. Perez; Rojas, H. Perez; Cuesta, H.J.M.

    2003-01-01

    A relativistic degenerate neutron gas in equilibrium with a background of electrons and protons in a magnetic field exerts its pressure anisotropically, having a smaller value perpendicular to than along the magnetic field. For critical fields the magnetic pressure may produce the vanishing of the equatorial pressure of the neutron gas. Taking this as a model for neutron stars, the outcome could be a transverse collapse of the star. This fixes a limit to the fields to be observable in stable neutron star pulsars as a function of their density. The final structure left over after the implosion might be a mixed phase of nucleons and a meson condensate, a strange star, or a highly distorted black hole or black ''cigar'', but not a magnetar, if viewed as a superstrongly magnetized neutron star. However, we do not exclude the possibility of superstrong magnetic fields arising in supernova explosions which lead directly to strange stars. In other words, if any magnetars exist, they cannot be neutron stars. (orig.)

  10. Using He I λ10830 to Diagnose Mass Flows Around Herbig Ae/Be Stars

    Science.gov (United States)

    Cauley, Paul W.; Johns-Krull, Christopher M.

    2015-01-01

    The pre-main sequence Herbig Ae/Be stars (HAEBES) are the intermediate mass cousins of the low mass T Tauri stars (TTSs). However, it is not clear that the same accretion and mass outflow mechanisms operate identically in both mass regimes. Classical TTSs (CTTSs) accrete material from their disks along stellar magnetic field lines in a scenario called magnetospheric accretion. Magnetospheric accretion requires a strong stellar dipole field in order to truncate the inner gas disk. These fields are either absent or very weak on a large majority of HAEBES, challenging the view that magnetospheric accretion is the dominant accretion mechanism. If magnetospheric accretion does not operate similarly around HAEBES as it does around CTTSs, then strong magnetocentrifugal outflows, which are directly linked to accretion and are ubiquitous around CTTSs, may be driven less efficiently from HAEBE systems. Here we present high resolution spectroscopic observations of the He I λ10830 line in a sample of 48 HAEBES. He I λ10830 is an excellent tracer of both mass infall and outflow which is directly manifested as red and blue-shifted absorption in the profile morphologies. These features, among others, are common in our sample. The occurrence of both red and blue-shifted absorption profiles is less frequent, however, than is found in CTTSs. Statistical contingency tests confirm this difference at a significant level. In addition, we find strong evidence for smaller disk truncation radii in the objects displaying red-shifted absorption profiles. This is expected for HAEBES experiencing magnetospheric accretion based on their large rotation rates and weak magnetic field strengths. Finally, the low incidence of blue-shifted absorption in our sample compared to CTTSs and the complete lack of simultaneous red and blue-shifted absorption features suggests that magnetospheric accretion in HAEBES is less efficient at driving strong outflows. The stellar wind-like outflows that are

  11. Effective magnetic moment of neutrinos in strong magnetic fields

    International Nuclear Information System (INIS)

    Perez M, A.; Perez R, H.; Masood, S.S.; Gaitan, R.; Rodriguez R, S.

    2002-01-01

    In this paper we compute the effective magnetic moment of neutrinos propagating in dense high magnetized medium. Taking typical values of magnetic field and densities of astrophysical objects (such as the cores of supernovae and neutron stars) we obtain an effective type of dipole magnetic moment in agreement with astrophysical and cosmological bounds. (Author)

  12. Electron surfing acceleration by the electron two-stream instability in a weak magnetic field

    International Nuclear Information System (INIS)

    Dieckmann, M E; Shukla, P K

    2006-01-01

    The thermalization of relativistically flowing colliding plasmas is not well understood. The transition layer, in which both plasmas interact and thermalize, is wide and highly structured and the instabilities in this layer may yield non-thermal particle distributions and shock-less energy dissipation. The objective in this work is to explore the ability of an electron two-stream instability for thermalizing a plasma beam that moves at the mildly relativistic speed 0.3c through weakly magnetized plasma and to identify the resulting particle distributions. It is demonstrated here with particle-in-cell simulations that the electron two-stream instability leads to waves that propagate within a wide angular range relative to the flow velocity. The waves are thus not planar, as required for efficient electron surfing acceleration (ESA). The short lifetime of the waves implies, however, only weak modifications of the ESA by the oblique modes, since the waves are sufficiently homogeneous. The ion (proton) beams are not modulated, which would be required to extract some of their energy. The instability can thus heat the electrons significantly, but it fails to accelerate them to relativistic energies and it cannot form a shock layer by thermalizing the protons, at least not for the system and the resolved timescales considered here

  13. Electron surfing acceleration by the electron two-stream instability in a weak magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Dieckmann, M E; Shukla, P K [Institut fuer Theoretische Physik IV, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

    2006-10-15

    The thermalization of relativistically flowing colliding plasmas is not well understood. The transition layer, in which both plasmas interact and thermalize, is wide and highly structured and the instabilities in this layer may yield non-thermal particle distributions and shock-less energy dissipation. The objective in this work is to explore the ability of an electron two-stream instability for thermalizing a plasma beam that moves at the mildly relativistic speed 0.3c through weakly magnetized plasma and to identify the resulting particle distributions. It is demonstrated here with particle-in-cell simulations that the electron two-stream instability leads to waves that propagate within a wide angular range relative to the flow velocity. The waves are thus not planar, as required for efficient electron surfing acceleration (ESA). The short lifetime of the waves implies, however, only weak modifications of the ESA by the oblique modes, since the waves are sufficiently homogeneous. The ion (proton) beams are not modulated, which would be required to extract some of their energy. The instability can thus heat the electrons significantly, but it fails to accelerate them to relativistic energies and it cannot form a shock layer by thermalizing the protons, at least not for the system and the resolved timescales considered here.

  14. Maser Emission from Gravitational States on Isolated Neutron Stars

    Science.gov (United States)

    Tepliakov, Nikita V.; Vovk, Tatiana A.; Rukhlenko, Ivan D.; Rozhdestvensky, Yuri V.

    2018-04-01

    Despite years of research on neutron stars, the source of their radio emission is still under debate. Here we propose a new coherent mechanism of pulsar radio emission based on transitions between gravitational states of electrons confined above the pulsar atmosphere. Our mechanism assumes that the coherent radiation is generated upon the electric and magnetic dipole transitions of electrons falling onto the polar caps of the pulsar, and predicts that this radiation occurs at radio frequencies—in full agreement with the observed emission spectra. We show that while the linearly polarized electric dipole radiation propagates parallel to the neutron star surface and has a fan-shape angular spectrum, the magnetic dipole emission comes from the magnetic poles of the pulsar in the form of two narrow beams and is elliptically polarized due to the spin–orbit coupling of electrons confined by the magnetic field. By explaining the main observables of the pulsar radio emission, the proposed mechanism indicates that gravitational quantum confinement plays an essential role in the physics of neutron stars.

  15. Degenerate stars. XII - Recognition of hot nondegenerates

    Science.gov (United States)

    Greenstein, J. L.

    1980-12-01

    Fifty-one newly observed degenerate stars and 14 nondegenerates include 13 faint red stars, most of which do not show any lines except DF, Gr 554. Hot subdwarfs and an X-ray source are discussed along with the problem of low-resolution spectroscopic classification of dense hot stars. The multichannel spectrum of the carbon-rich magnetic star LP 790-29 is examined by fitting the undisturbed parts of the spectrum to a black body of 7625 K by the least squares method; the Swan bands absorb 600 A of the spectrum assuming that the blocked radiation is redistributed in the observed region.

  16. Gamma ray bursts from comet neutron star magnetosphere interaction, field twisting and Eparallel formation

    International Nuclear Information System (INIS)

    Colgate, S.A.

    1990-01-01

    Consider the problem of a comet in a collision trajectory with a magnetized neutron star. The question addressed in this paper is whether the comet interacts strongly enough with a magnetic field such as to capture at a large radius or whether in general the comet will escape a magnetized neutron star. 6 refs., 4 figs

  17. Weak coupling polaron and Landau-Zener scenario: Qubits modeling

    Science.gov (United States)

    Jipdi, M. N.; Tchoffo, M.; Fokou, I. F.; Fai, L. C.; Ateuafack, M. E.

    2017-06-01

    The paper presents a weak coupling polaron in a spherical dot with magnetic impurities and investigates conditions for which the system mimics a qubit. Particularly, the work focuses on the Landau-Zener (LZ) scenario undergone by the polaron and derives transition coefficients (transition probabilities) as well as selection rules for polaron's transitions. It is proven that, the magnetic impurities drive the polaron to a two-state superposition leading to a qubit structure. We also showed that the symmetry deficiency induced by the magnetic impurities (strong magnetic field) yields to the banishment of transition coefficients with non-stacking states. However, the transition coefficients revived for large confinement frequency (or weak magnetic field) with the orbital quantum numbers escorting transitions. The polaron is then shown to map a qubit independently of the number of relevant states with the transition coefficients lifted as LZ probabilities and given as a function of the electron-phonon coupling constant (Fröhlich constant).

  18. Spectrophotometry of peculiar B and A stars. XVIII - The helium rich variable stars HR 1890, Sigma Orionis E, and HD 37776

    Science.gov (United States)

    Adelman, S. J.; Pyper, D. M.

    1985-01-01

    Optical region spectrophotometry at 3300-7850 A has been obtained for three helium rich stars, HR 1890, Sigma Ori E, and HD 37776, of the Orion OB1 Association. New uvby-beta photometry of HR 1890 and HD 37776 as well as published data are also used to investigate the variability of these stars. A new period of 1.53862 days was determined for HD 37776. For all three stars H-beta varies in antiphase with strong He I lines. The spectrophotometric bandpass containing the strong He I line at 4471 A varies in phase with the R index of Pedersen and Thomsen (1977). Evidence is found for weak absorption features which appear to be an extension of the 5200 A feature seen in cooler CP stars.

  19. Magnetic-flux dynamics of high-Tc superconductors in weak magnetic fields

    DEFF Research Database (Denmark)

    Il’ichev, E. V.; Jacobsen, Claus Schelde

    1994-01-01

    Aspects of magnetic-flux dynamics in different types of samples of the high-temperature superconductor YBa2Cu3Ox have been investigated in magnetic fields below 1 Oe and at 77 K. The experiments were carried out in an arrangement including a field coil, a flat sample perpendicular to the field...

  20. An upper bound on Q-star masses

    International Nuclear Information System (INIS)

    Hochron, D.R.; Selipsky, S.B.

    1992-06-01

    Q-stars (the gravitational generalization of Q-balls, strongly bound bulk matter that an appear in field theories of strongly interacting hadrons) are the only known impact objects consistent with the known bulk structure of nuclei and chiral symmetry that evade the Rhoades-Ruffini upper bound of 3.2M circle-dot . Generic bounds are quite weak: M Q-star circle-dot . If, however, we assume that the 1.558 ms pulsar is a Q-star, equilibrium. A stability criteria of rotating fluids place a much stronger upper bound of M c ≤ 5.3M circle-dot on such models under certain special assumptions. This has important implications for heavy compact objects such as Cygnus X-1

  1. Electromagnetic damping of neutron star oscillations

    International Nuclear Information System (INIS)

    McDermott, P.N.; Savedoff, M.P.; Van Horn, H.M.; Zweibel, E.G.; Hansen, C.J.

    1984-01-01

    Nonradial pulsations of a neutron star with a strong dipole magnetic field cause emission of electromagnetic radiation. Here we compute the power radiated to vacuum by neutron star g-mode pulsations and by torsional oscillations of the neutron star crust. For the low-order quadrupole fluid g-modes we have considered, we find electromagnetic damping to be considerably more effective than gravitational radiation. For example, a 0.5 M/sub sun/ neutron star with a core temperature approx.10 7 K has a g 1 -mode period of 371 ms; for this mode were find the electromagnetic damping time to be tau/sub FM/approx.0.3 s, assuming the surface magnetic field strength of the neutron star to be B 0 approx.10 12 gauss. This is considerably less than the corresponding gravitational radiation time tau/sub GR/approx.3 x 10 17 yr. For dipole g-mode oscillations, there is no gravitational radiation, but electromagnetic damping and ohmic dissipation are efficient damping mechanisms. For dipole torsional oscillations, we find that electromagnetic damping again dominates, with tau/sub EM/approx.5 yr. Among the cases we have studied, quadrupole torsional oscillations appear to be dominated by gravitational radiation damping, with tau/sub GR/approx.10 4 yr, as compared with tau/sub EM/approx.2 x 10 7 yr

  2. On the Pressure of a Neutron Gas Interacting with the Non-Uniform Magnetic Field of a Neutron Star

    Science.gov (United States)

    Skobelev, V. V.

    2018-04-01

    On the basis of simple arguments, practically not going beyond the scope of an undergraduate course in general physics, we estimate the additional pressure (at zero temperature) of degenerate neutron matter due to its interaction with the non-uniform magnetic field of a neutron star. This work has methodological and possibly scientific value as an intuitive application of the content of such a course to a solution of topical problems of astrophysics.

  3. Demonstrating the Likely Neutron Star Nature of Five M31 Globular Cluster Sources with Swift-NuSTAR Spectroscopy

    Science.gov (United States)

    Maccarone, Thomas J.; Yukita, Mihoko; Hornschemeier, Ann; Lehmer, Bret D.; Antoniou, Vallia; Ptak, Andrew; Wik, Daniel R.; Zezas, Andreas; Boyd, Padi; Kennea, Jamie; hide

    2016-01-01

    We present the results of a joint Swift-NuSTAR spectroscopy campaign on M31. We focus on the five brightest globular cluster X-ray sources in our fields. Two of these had previously been argued to be black hole candidates on the basis of apparent hard-state spectra at luminosities above those for which neutron stars are in hard states. We show that these two sources are likely to be Z-sources (i.e. low magnetic field neutron stars accreting near their Eddington limits), or perhaps bright atoll sources (low magnetic field neutron stars which are just a bit fainter than this level) on the basis of simultaneous Swift and NuSTAR spectra which cover a broader range of energies. These new observations reveal spectral curvature above 6-8 keV that would be hard to detect without the broader energy coverage the NuSTAR data provide relative to Chandra and XMM-Newton. We show that the other three sources are also likely to be bright neutron star X-ray binaries, rather than black hole X-ray binaries. We discuss why it should already have been realized that it was unlikely that these objects were black holes on the basis of their being persistent sources, and we re-examine past work which suggested that tidal capture products would be persistently bright X-ray emitters. We discuss how this problem is likely due to neglecting disc winds in older work that predict which systems will be persistent and which will be transient.

  4. On Fallback Disks around Young Neutron Stars

    Science.gov (United States)

    Alpar, M. Ali; Ertan, Ü.; Erkut, M. H.

    2006-08-01

    Some bound matter in the form of a fallback disk may be an initial parameter of isolated neutron stars at birth, which, along with the initial rotation rate and dipole (and higher multipole) magnetic moments, determines the evolution of neutron stars and the categories into which they fall. This talk reviews the possibilities of fallback disk models in explaining properties of isolated neutron stars of different categories. Recent observations of a fallback disk and observational limits on fallback disks will also be discussed.

  5. Dark matter that can form dark stars

    International Nuclear Information System (INIS)

    Gondolo, Paolo; Huh, Ji-Haeng; Kim, Hyung Do; Scopel, Stefano

    2010-01-01

    The first stars to form in the Universe may be powered by the annihilation of weakly interacting dark matter particles. These so-called dark stars, if observed, may give us a clue about the nature of dark matter. Here we examine which models for particle dark matter satisfy the conditions for the formation of dark stars. We find that in general models with thermal dark matter lead to the formation of dark stars, with few notable exceptions: heavy neutralinos in the presence of coannihilations, annihilations that are resonant at dark matter freeze-out but not in dark stars, some models of neutrinophilic dark matter annihilating into neutrinos only and lighter than about 50 GeV. In particular, we find that a thermal DM candidate in standard Cosmology always forms a dark star as long as its mass is heavier than ≅ 50 GeV and the thermal average of its annihilation cross section is the same at the decoupling temperature and during the dark star formation, as for instance in the case of an annihilation cross section with a non-vanishing s-wave contribution

  6. Magnetic Resonance Imaging with a Weak Albumin Binding Contrast Agent can Reveal Additional Endo leaks in Patients with an Enlarging Aneurysm after EVAR

    NARCIS (Netherlands)

    Habets, J.; Zandvoort, H. J. A.; Moll, F. L.; Bartels, L. W.; Vonken, E. P. A.; van Herwaarden, J. A.; Leiner, T.

    WHAT THIS PAPER ADDS In patients with enlarging aneurysms of unknown origin after endovascular aneurysm repair, magnetic resonance imaging (MRI) with a weak albumin binding contrast agent has additional diagnostic value for both the detection and determination of the origin of the endoleak.

  7. Detection of a weak ring current in a nonaromatic porphyrin nanoring using magnetic circular dichroism.

    Science.gov (United States)

    Kowalska, Patrycja; Peeks, Martin D; Roliński, Tomasz; Anderson, Harry L; Waluk, Jacek

    2017-12-13

    We compare the absorption and magnetic circular dichroism (MCD) spectra of a series of porphyrin oligomers - dimer, tetramer, and hexamer - bound in a linear or cyclic fashion. The MCD signal is extremely weak for low energy transitions in the linear oligomers, but it is amplified when the cyclic porphyrin hexamer binds a template, restricting rotational freedom. The appearance of Faraday A terms in the MCD spectra demonstrates the presence of a magnetic moment, and thus, uncompensated electronic current. The value of the excited state magnetic moment estimated from the A term is very low compared with those of monomeric porphyrins, which confirms the nonaromatic character of the cyclic array and the lack of a global ring current in the ground state of the neutral nanoring. DFT calculations predict the absorption and MCD patterns reasonably well, but fail to reproduce the MCD sign inversion observed in substituted monomeric zinc porphyrins ("soft" chromophores). Interestingly, a correct sign pattern is predicted by INDO/S calculations. Analysis of the MCD spectra of the monomeric porphyrin unit allowed us to distinguish between two close-lying lowest energy transitions, which some previous assignments placed further apart. The present results prove the usefulness of MCD not only for deconvolution and assignment of electronic transitions, but also as a sensitive tool for detecting electronic ring currents.

  8. The strongest magnetic fields in the universe

    CERN Document Server

    Balogh, A; Falanga, M; Lyutikov, M; Mereghetti, S; Piran, T; Treumann, RA

    2016-01-01

    This volume extends the ISSI series on magnetic fields in the Universe into the domain of what are by far the strongest fields in the Universe, and stronger than any field that could be produced on Earth. The chapters describe the magnetic fields in non-degenerate strongly magnetized stars, degenerate stars (such as white dwarfs and neutron stars), exotic members called magnetars, and in their environments, as well as magnetic fields in the environments of black holes. These strong fields have a profound effect on the behavior of matter, visible in particular in highly variable processes like radiation in all known wavelengths, including Gamma-Ray bursts. The generation and structure of such strong magnetic fields and effects on the environment are also described.

  9. Neutron star in the presence of strong magnetic field

    Indian Academy of Sciences (India)

    thereby giving the idea that compact stars might contain deconfined and chirally restored quark matter in them. Recently [1], the mass measurement of mil- lisecond pulsar PSR J1614-2230 has set a new robust mass limit for compact stars to be. M = 1.97 ± 0.04M⊙. This value, together with the mass of pulsar J1903+0327 ...

  10. Tessellated permanent magnet circuits for flow-through, open gradient separations of weakly magnetic materials

    Energy Technology Data Exchange (ETDEWEB)

    Moore, Lee R. [Department of Biomedical Engineering, Cleveland Clinic, 9500 Euclid Ave., Cleveland OH 44195 (United States); Williams, P. Stephen [Cambrian Technologies, Inc., Cleveland, OH (United States); Chalmers, Jeffrey J. [William G. Lowrie Department of Chemical and Biomedical Engineering, The Ohio State University, Columbus 151 W. Woodruff Avenue, OH 43210 (United States); Zborowski, Maciej, E-mail: zborowm@ccf.org [Department of Biomedical Engineering, Cleveland Clinic, 9500 Euclid Ave., Cleveland OH 44195 (United States)

    2017-04-01

    Emerging microfluidic-based cell assays favor label-free red blood cell (RBC) depletion. Magnetic separation of RBC is possible because of the paramagnetism of deoxygenated hemoglobin but the process is slow for open-gradient field configurations. In order to increase the throughput, periodic arrangements of the unit magnets were considered, consisting of commercially available Nd-Fe-B permanent magnets and soft steel flux return pieces. The magnet design is uniquely suitable for multiplexing by magnet tessellation, here meaning the tiling of the magnet assembly cross-sectional plane by periodic repetition of the magnet and the flow channel shapes. The periodic pattern of magnet magnetizations allows a reduction of the magnetic material per channel with minimal distortion of the field cylindrical symmetry inside the magnet apertures. A number of such magnet patterns are investigated for separator performance, size and economy with the goal of designing an open-gradient magnetic separator capable of reducing the RBC number concentration a hundred-fold in 1 mL whole blood per hour. - Highlights: • Simple geometry of commercial, off-the-shelf NdFeB magnet blocks is amenable to generate high fields and open gradients. • Periodic pattern of permanent magnet blocks (tessellation) reduces the number of blocks per separation channel and improves the efficiency of separator design. • Split-flow lateral transport thin (SPLITT) fractionation model predicts 100-fold reduction of red blood cells from 1 mL whole blood sample in 1 h, suitable for laboratory medicine applications.

  11. Tessellated permanent magnet circuits for flow-through, open gradient separations of weakly magnetic materials

    International Nuclear Information System (INIS)

    Moore, Lee R.; Williams, P. Stephen; Chalmers, Jeffrey J.; Zborowski, Maciej

    2017-01-01

    Emerging microfluidic-based cell assays favor label-free red blood cell (RBC) depletion. Magnetic separation of RBC is possible because of the paramagnetism of deoxygenated hemoglobin but the process is slow for open-gradient field configurations. In order to increase the throughput, periodic arrangements of the unit magnets were considered, consisting of commercially available Nd-Fe-B permanent magnets and soft steel flux return pieces. The magnet design is uniquely suitable for multiplexing by magnet tessellation, here meaning the tiling of the magnet assembly cross-sectional plane by periodic repetition of the magnet and the flow channel shapes. The periodic pattern of magnet magnetizations allows a reduction of the magnetic material per channel with minimal distortion of the field cylindrical symmetry inside the magnet apertures. A number of such magnet patterns are investigated for separator performance, size and economy with the goal of designing an open-gradient magnetic separator capable of reducing the RBC number concentration a hundred-fold in 1 mL whole blood per hour. - Highlights: • Simple geometry of commercial, off-the-shelf NdFeB magnet blocks is amenable to generate high fields and open gradients. • Periodic pattern of permanent magnet blocks (tessellation) reduces the number of blocks per separation channel and improves the efficiency of separator design. • Split-flow lateral transport thin (SPLITT) fractionation model predicts 100-fold reduction of red blood cells from 1 mL whole blood sample in 1 h, suitable for laboratory medicine applications.

  12. Magnetized Converging Flows toward the Hot Core in the Intermediate/High-mass Star-forming Region NGC 6334 V

    Energy Technology Data Exchange (ETDEWEB)

    Juárez, Carmen; Girart, Josep M. [Institut de Ciències de l’Espai, (CSIC-IEEC), Campus UAB, Carrer de Can Magrans, S/N, E-08193 Cerdanyola del Vallès, Catalonia (Spain); Zamora-Avilés, Manuel; Palau, Aina; Ballesteros-Paredes, Javier [Instituto de Radioastronomía y Astrofísica, Universidad Nacional Autónoma de México, P.O. Box 3-72, 58090, Morelia, Michoacán (Mexico); Tang, Ya-Wen; Koch, Patrick M.; Liu, Hauyu Baobab [Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei, 10617, Taiwan (China); Zhang, Qizhou [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Qiu, Keping, E-mail: juarez@ice.cat [School of Astronomy and Space Science, Nanjing University, 163 Xianlin Avenue, Nanjing 210023 (China)

    2017-07-20

    We present Submillimeter Array (SMA) observations at 345 GHz toward the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern toward the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km s{sup −1}, converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with magnetohydrodynamic simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (∼0.1 pc) of NGC 6334 V toward the higher-density hot core region (∼0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity.

  13. Simulation of weak and strong Langmuir collapse regimes

    International Nuclear Information System (INIS)

    Hadzievski, L.R.; Skoric, M.M.; Kono, M.; Sato, T.

    1998-01-01

    In order to check the validity of the self-similar solutions and the existence of weak and strong collapse regimes, direct two dimensional simulation of the time evolution of a Langmuir soliton instability is performed. Simulation is based on the Zakharov model of strong Langmuir turbulence in a weakly magnetized plasma accounting for the full ion dynamics. For parameters considered, agreement with self-similar dynamics of the weak collapse type is found with no evidence of the strong Langmuir collapse. (author)

  14. SPECTROPOLARIMETRY OF THE CLASSICAL T TAURI STAR BP TAU

    International Nuclear Information System (INIS)

    Chen, Wei; Johns-Krull, Christopher M.

    2013-01-01

    We implement a least-squares deconvolution (LSD) code to study magnetic fields on cool stars. We first apply our code to high-resolution optical echelle spectra of 53 Cam (a magnetic Ap star) and three well-studied cool stars (Arcturus, 61 Cyg A, and ξ Boo A) as well as the Sun (by observing the asteroid Vesta) as tests of the code and the instrumentation. Our analysis is based on several hundred photospheric lines spanning the wavelength range 5000 Å to 9000 Å. We then apply our LSD code to six nights of data on the Classical T Tauri Star BP Tau. A maximum longitudinal field of 370 ± 80 G is detected from the photospheric lines on BP Tau. A 1.8 kG dipole tilted at 129° with respect to the rotation axis and a 1.4 kG octupole tilted at 104° with respect to the rotation axis, both with a filling factor of 0.25, best fit our LSD Stokes V profiles. Measurements of several emission lines (He I 5876 Å, Ca II 8498 Å, and 8542 Å) show the presence of strong magnetic fields in the line formation regions of these lines, which are believed to be the base of the accretion footpoints. The field strength measured from these lines shows night-to-night variability consistent with rotation of the star

  15. SPECTROPOLARIMETRY OF THE CLASSICAL T TAURI STAR BP TAU

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Wei; Johns-Krull, Christopher M., E-mail: wc2@rice.edu, E-mail: cmj@rice.edu [Department of Physics and Astronomy, Rice University, Houston, TX 77005 (United States)

    2013-10-20

    We implement a least-squares deconvolution (LSD) code to study magnetic fields on cool stars. We first apply our code to high-resolution optical echelle spectra of 53 Cam (a magnetic Ap star) and three well-studied cool stars (Arcturus, 61 Cyg A, and ξ Boo A) as well as the Sun (by observing the asteroid Vesta) as tests of the code and the instrumentation. Our analysis is based on several hundred photospheric lines spanning the wavelength range 5000 Å to 9000 Å. We then apply our LSD code to six nights of data on the Classical T Tauri Star BP Tau. A maximum longitudinal field of 370 ± 80 G is detected from the photospheric lines on BP Tau. A 1.8 kG dipole tilted at 129° with respect to the rotation axis and a 1.4 kG octupole tilted at 104° with respect to the rotation axis, both with a filling factor of 0.25, best fit our LSD Stokes V profiles. Measurements of several emission lines (He I 5876 Å, Ca II 8498 Å, and 8542 Å) show the presence of strong magnetic fields in the line formation regions of these lines, which are believed to be the base of the accretion footpoints. The field strength measured from these lines shows night-to-night variability consistent with rotation of the star.

  16. Gravitational waves from neutron stars and asteroseismology

    Science.gov (United States)

    Ho, Wynn C. G.

    2018-05-01

    Neutron stars are born in the supernova explosion of massive stars. Neutron stars rotate as stably as atomic clocks and possess densities exceeding that of atomic nuclei and magnetic fields millions to billions of times stronger than those created in laboratories on the Earth. The physical properties of neutron stars are determined by many areas of fundamental physics, and detection of gravitational waves can provide invaluable insights into our understanding of these areas. Here, we describe some of the physics and astrophysics of neutron stars and how traditional electromagnetic wave observations provide clues to the sorts of gravitational waves we expect from these stars. We pay particular attention to neutron star fluid oscillations, examining their impact on electromagnetic and gravitational wave observations when these stars are in a wide binary or isolated system, then during binary inspiral right before merger, and finally at times soon after merger. This article is part of a discussion meeting issue `The promises of gravitational-wave astronomy'.

  17. Gravitational waves from neutron stars and asteroseismology.

    Science.gov (United States)

    Ho, Wynn C G

    2018-05-28

    Neutron stars are born in the supernova explosion of massive stars. Neutron stars rotate as stably as atomic clocks and possess densities exceeding that of atomic nuclei and magnetic fields millions to billions of times stronger than those created in laboratories on the Earth. The physical properties of neutron stars are determined by many areas of fundamental physics, and detection of gravitational waves can provide invaluable insights into our understanding of these areas. Here, we describe some of the physics and astrophysics of neutron stars and how traditional electromagnetic wave observations provide clues to the sorts of gravitational waves we expect from these stars. We pay particular attention to neutron star fluid oscillations, examining their impact on electromagnetic and gravitational wave observations when these stars are in a wide binary or isolated system, then during binary inspiral right before merger, and finally at times soon after merger.This article is part of a discussion meeting issue 'The promises of gravitational-wave astronomy'. © 2018 The Author(s).

  18. Dispersion functions for weakly relativistic magnetized plasmas in inhomogeneous magnetic field

    International Nuclear Information System (INIS)

    Gaelzer, R.; Schneider, R.S.; Ziebell, L.F.

    1995-01-01

    The study of wave propagation and absorption inhomogeneous plasmas can be made by using a formulation in which the dielectric properties of the plasma are described by an effective dielectric tensor which incorporates inhomogeneity effects, inserted into a dispersion relation which is formally the same as that of an homogeneous plasma. We have recently utilized this formalism in the study of electron cyclotron absorption in inhomogeneous media, both in the case of homogeneous magnetic field and in the case of inhomogeneous magnetic field. In the present paper we resume the study of the case with inhomogeneous magnetic field, in order to introduce a generalized dispersion function useful for the case of a Maxwellian plasma, and discuss some of its properties. (author). 10 refs

  19. A radial velocity survey of extremely hydrogen-deficient stars

    International Nuclear Information System (INIS)

    Jeffery, C.S.; Kiel Univ.; Drilling, J.S.; Heber, U.

    1987-01-01

    A radial velocity survey of hot extremely hydrogen-deficient stars has been carried out in order to search for possible binaries. The survey found three stars to have large velocity variations. Of these, two are known hydrogen-deficient binaries and one, HDE 320156 (= LSS 4300), is a suspected binary. HDE 320156 (= LSS 4300) is therefore confirmed to be a single-lined spectroscopic hydrogen-deficient binary. The hydrogen-deficient binary stars all show weak C-lines. The remaining stars in the sample are C-strong extreme-helium (EHe) stars and did not show large-amplitude velocity variations. Small-amplitude radial velocity variations known to be present amongst the EHe stars are largely undetected. Evidence for variability is, however, present in the known variable V2076 Oph (HD 160641) and in LS IV - 1 0 2 with amplitudes between 10 and 20 km s -1 . (author)

  20. Einstein Observatory coronal temperatures of late-type stars

    Science.gov (United States)

    Schmitt, J. H. M. M.; Collura, A.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.

    1990-01-01

    The results are presented of a survey of the coronal temperatures of late-type stars using the Einstein Observatory IPC. The spectral analysis shows that the frequently found one- and two-temperature descriptions are mainly influenced by the SNR of the data and that models using continuous emission measure distributions can provide equally adequate and physically more meaningful and more plausible descriptions. Intrinsic differences in differential emission measure distributions are found for four groups of stars. M dwarfs generally show evidence for high-temperature gas in conjunction with lower-temperature material, while main-sequence stars of types F and G have the high-temperature component either absent or very weak. Very hot coronae without the lower-temperature component appearing in dwarf stars are evident in most of the giant stars studied. RS CVn systems show evidence for extremely hot coronae, sometimes with no accompanying lower-temperature material.

  1. NuSTAR and swift observations of the fast rotating magnetized white dwarf AE Aquarii

    DEFF Research Database (Denmark)

    Kitaguchi, Takao; An, Hongjun; Beloborodov, Andrei M.

    2014-01-01

    AE Aquarii is a cataclysmic variable with the fastest known rotating magnetized white dwarf (P-spin = 33.08 s). Compared to many intermediate polars, AE Aquarii shows a soft X-ray spectrum with a very low luminosity (L-X similar to 10(31) erg s(-1)). We have analyzed overlapping observations...... of this system with the NuSTAR and the Swift X-ray observatories in 2012 September. We find the 0.5-30 keV spectra to be well fitted by either an optically thin thermal plasma model with three temperatures of 0.75(-0.45)(+0.18), 2.29(-0.82)(+0.96), and 9.33(-2.18)(+6.07) keV, or an optically thin thermal plasma...

  2. Extending the Sensitivity of Paleomagnetic Techniques: Magnetostratigraphy of Weakly- Magnetized, Organic-Rich Black Limestone from the Permian of Japan

    Science.gov (United States)

    Kirschvink, J. L.; Isozaki, Y.

    2007-12-01

    Despite their importance for biostratigraphy, bituminous, organic-rich limestone has rarely yielded reliable paleomagnetic results, principally due to the weak magnetization levels encountered; NRMs for such samples often start with moments below 10-10Am2 (10-7 emu), and they become unmeasurable or unstable rapidly upon demagnetization. Recently, we have developed a fairly simple and inexpensive automation system for standard paleomagnetic and rock magnetic measurements that has the additional benefit of using an extremely low-noise sample holder. A vacuum pick-and-put system holds samples at the end a thin-walled quartz-glass tube, moving them between a measurement queue and the sense region of a vertically-aligned superconducting rock magnetometer. The system minimizes the amount of extraneous material introduced into the magnetometer's sense region. With frequent cleaning in strong acid, the glass holder system is capable of reliably measuring samples with moments below 1 pAm2 (10-9 emu), on a DC-SQuID magnetometer system with stable instrument noise of a few hundred fAm2. Signal averaging and clean-lab handling techniques are often needed to achieve this sensitivity, however. To test this system, we collected a series of densely-spaced samples for magnetostratigraphy from two sections in the Middle-Late Permian limestone at Kamura in Kyushu, Japan, which is the remnant of lagoonal sediments formed on an oceanic island atoll (Isozaki et al., 2007). According to fusulinids, the Saraito section spans Wordian time, which should be near the end of the Kiaman Reversed superchron. Similarly, strata at the Kamura section cover late Capitanian to early Wuchiapingian time, which should display a shift from predominantly Normal to Reversed magnetization. Raman spectroscopy suggests no appreciable heating. NRM intensities of the samples range generally between 10-10 and 10-11 Am2, with little change in the vectors either upon low-temperature cycling or alternating

  3. The Case of the Missing Cyanogen-rich AGB Stars in Galactic Globular Clusters

    DEFF Research Database (Denmark)

    Campbell, S. W.; Yong, D.; Wylie-de Boer, E. C.

    2012-01-01

    The handful of available observations of AGB stars in Galactic Globular Clusters suggest that the GC AGB populations are dominated by cyanogen-weak stars (eg. Norris et al. 1981; Sneden et al. 2000). This contrasts strongly with the distributions on the RGB (and other) populations, which generall...

  4. Calculation of the form of an equilibrium poloidal magnetic field contained in a polytropic star

    International Nuclear Information System (INIS)

    Brundrit, G.B.; Miketinac, M.J.

    1976-01-01

    This program is designed to integrate the exact equations which determine the distribution of the density of a self-gravitating, axisymmetric polytrope of infinite conductivity containing a poloidal magnetic field. In addition, other properties of an equilibrium configuration such as mass, volume and radius are calculated. The program can also provide at very small extra cost the rates of change of the density with respect to changes of the polytropic index n and the parameter lambda which characterizes the poloidal magnetic field. Mathematically, the problem can be formulated as a boundary value problem for three coupled equations, two of which are second order, non-linear, two-dimensional partial differential equations. The solution is obtained numerically by an adaptation of the Stoeckl's finite difference-finite expansion method. In fact, the present program is a major modification of the program TOROID. The numerical scheme developed in the program is valid for all polytropes whose polytropic index n is greater than or equal to one. The other parameter of the theory, lambda, is unrestricted, i.e. the program permits the study of stars whose matnetic energy is a 'sizeable' percentage of their gravitational energy. Also, the program, with minor modifications, could be used for calculating equilibrium configurations of (a) (uniformly or non-uniformly) rotating polytropes pervaded by poloidal magnetic fields or (b) (rotation) polytropes containing poloidal magnetic fields. However, the greatest use of the present program is expected to arise in attempts to construct equilibrium configurations of polytropes containing mixed poloidal toroidal magnetic fields. (Auth.)

  5. Simulations of extragalactic magnetic fields and of their observables

    Science.gov (United States)

    Vazza, F.; Brüggen, M.; Gheller, C.; Hackstein, S.; Wittor, D.; Hinz, P. M.

    2017-12-01

    The origin of extragalactic magnetic fields is still poorly understood. Based on a dedicated suite of cosmological magneto-hydrodynamical simulations with the ENZO code we have performed a survey of different models that may have caused present-day magnetic fields in galaxies and galaxy clusters. The outcomes of these models differ in cluster outskirts, filaments, sheets and voids and we use these simulations to find observational signatures of magnetogenesis. With these simulations, we predict the signal of extragalactic magnetic fields in radio observations of synchrotron emission from the cosmic web, in Faraday rotation, in the propagation of ultra high energy cosmic rays, in the polarized signal from fast radio bursts at cosmological distance and in spectra of distant blazars. In general, primordial scenarios in which present-day magnetic fields originate from the amplification of weak (⩽nG ) uniform seed fields result in more homogeneous and relatively easier to observe magnetic fields than astrophysical scenarios, in which present-day fields are the product of feedback processes triggered by stars and active galaxies. In the near future the best evidence for the origin of cosmic magnetic fields will most likely come from a combination of synchrotron emission and Faraday rotation observed at the periphery of large-scale structures.

  6. Weakly interacting massive particles and stellar structure

    International Nuclear Information System (INIS)

    Bouquet, A.

    1988-01-01

    The existence of weakly interacting massive particles (WIMPs) may solve both the dark matter problem and the solar neutrino problem. Such particles affect the energy transport in the stellar cores and change the stellar structure. We present the results of an analytic approximation to compute these effects in a self-consistent way. These results can be applied to many different stars, but we focus on the decrease of the 8 B neutrino flux in the case of the Sun

  7. Production of gamma ray bursts from asymmetric core combustion of magnetized young neutron stars

    Science.gov (United States)

    de Gouveia dal Pino, E. M.; Lugones, G.; Horvath, J. E.; Ghezzi, C. R.

    2005-09-01

    Many works in the past have explored the idea that the conversion of hadronic matter into strange quark matter in neutron stars may be an energy source for GRBs (see references in Lugones et al. 2002, Lugones and Horvath 2003). These models addressed essentially spherically symmetric conversions of the whole neutron star rendering isotropic gamma emission. Accumulating observational evidence suggests that at least ''long'' GRBs are strongly asymmetric, jet-like outflows. The ''short'' burst subclass is not obviously asymmetric, and they may actually be spherically symmetric if the sources are close enough. A new potentially important feature recently recognized (Lugones et al. 2002) is that if a conversion to strange quark matter actually begins near the center of a neutron star, the presence of a magnetic field with intensity B ˜ 1013 G (see also Ghezi, de Gouveia Dal Pino & Horvath 2004) will originate a prompt collimated gamma emission, which may be observed as a short, beamed GRB after the recovery of a fraction of the neutrino energy via ν {barν} → e+e- → γγ. The calculations show that the neutrino luminosity is ˜ 1053 erg/sec and that the e+e- luminosity is about two orders of magnitude smaller ( tet{Lugones2002grb}). We find that 90 % of the e+e- pairs are injected inside small cylinders located just above the polar caps (with radius δ and height 0.4 R) in a timescale of τi ≃ 0.2 s almost independently of the initial temperature. This provides an interesting suitable explanation for the inner engine of short gamma ray bursts.

  8. Radio-emission of pre-main sequence stars of the Rho Ophiuchi cloud: observations and interpretation

    International Nuclear Information System (INIS)

    Andre, P.

    1987-11-01

    Observations of the radio continuum emission of a young star population have been made at VLA on the whole molecular cloud Rho Ophiuchi, one of the closest site of star formation. A dozen of stellar sources have been detected. Radio emission of some identified objects seems to have a magnetic nature and be produced by gyrosynchrotron mechanism. In particular, one of the sources shows a radio radiation circularly polarized; two other stars have a radiation strongly variable probably due to magnetic eruptions more important than those detected in X radiation. More generally, radio observations select probably a specific population of young stars characterized by magnetic field presence extended on several stellar radii and by absence of dense circumstellar environment. Spatial distribution of these objects suggest, they are younger than most of the pre-main sequence stars [fr

  9. Measuring the rotation periods of 4-10 Myr T-Tauri stars in the Orion OB1 association

    Science.gov (United States)

    Karim, Md Tanveer; Stassun, Keivan; Briceno, Cesar; Vivas, Kathy; Raetz, Stefanie; Calvet, Nuria; Mateu, Cecilia; Downes, Juan Jose; Hernandez, Jesus; Neuhäuser, Ralph; Mugrauer, Markus; Takahashi, Hidenori; Tachihara, Kengo; Chini, Rolf; YETI

    2016-01-01

    Most existing studies of young stellar populations have focused on the youngest (Investigaciones de Astronomía-Quest Equatorial Survey Team (CIDA-QUEST), the Young Exoplanet Transit Initiative (YETI) and from a Kitt Peak National Observatory (KPNO) campaign. We investigated stellar rotation periods according to the type of stars (Classical or Weak-lined T-Tauri stars) and their locations, to look for population-wide trends. We detected 563 periodic variables and 1411 non-periodic variables by investigating the light curves of these stars. We find that ~ 30% of Weak-line T-Tauri stars (WTTS) and ~ 20% of Classical T-Tauri stars (CTTS) are periodic. Though we did not find any noticeable difference in rotation period between CTTS and WTTS, our study does show a change in the overall rotation periods of stars 4-10 Myr old, consistent with predictions of angular momentum evolution models, an important constraint for theoretical models for an age range for which no similar data existed.

  10. Effects of weak magnetic fields on post-implantation damage in superconducting oxides

    International Nuclear Information System (INIS)

    Khait, Y.L.

    1996-01-01

    Experimentally verifiable effects of weak permanent magnetic fields (PMF's) acting during ion implantation in high-T c superconducting (HTSC) materials at T∼300 K on post-implantation damage (PID) and material parameters are considered. The presence of PMF's of H∼10 3 Oe during ion implantation can enlarge substantially the PID in HTSC materials implanted with ions of moderate energies (e.g. 200-400 keV) and dosage (10 11- 10 12 cm -3 ) at room temperature. The PMF-induced increase in the radiation damage causes the corresponding enhancement in the material resistivity R and reduction in the critical current j cir (measured after the cooling of the HTSC material down to T (L) c after the ion implantation). This is an extension of the PMF effects found experimentally (and explained theoretically) in semiconductors in our previous work. The experimentally verifiable PMF effects on the defect (atomic) migration and radiation damage is a generic consequence of the kinetic electron-related theory of atomic rate processes in solids. The theory links the PMF effects with electron transitions occurring in the nanometer vicinity of atoms overcoming energy barriers which affect exponentially rates of atomic (defect) diffusion. The magnetic field can enhance the number of downward electron transitions that accompany atomic (defect) jumps over energy barriers and synchronize with the jumps. This enhances exponentially the rates of defect migration out of thermal spikes that prevents the defects from fast recombination, and thus, the PMF increases the PID and changes correspondingly R and j cir . (orig.)

  11. Black hole variability and the star formation-active galactic nucleus connection: Do all star-forming galaxies host an active galactic nucleus?

    International Nuclear Information System (INIS)

    Hickox, Ryan C.; Chen, Chien-Ting J.; Civano, Francesca M.; Hainline, Kevin N.; Mullaney, James R.; Alexander, David M.; Goulding, Andy D.

    2014-01-01

    We investigate the effect of active galactic nucleus (AGN) variability on the observed connection between star formation and black hole accretion in extragalactic surveys. Recent studies have reported relatively weak correlations between observed AGN luminosities and the properties of AGN hosts, which has been interpreted to imply that there is no direct connection between AGN activity and star formation. However, AGNs may be expected to vary significantly on a wide range of timescales (from hours to Myr) that are far shorter than the typical timescale for star formation (≳100 Myr). This variability can have important consequences for observed correlations. We present a simple model in which all star-forming galaxies host an AGN when averaged over ∼100 Myr timescales, with long-term average AGN accretion rates that are perfectly correlated with the star formation rate (SFR). We show that reasonable prescriptions for AGN variability reproduce the observed weak correlations between SFR and L AGN in typical AGN host galaxies, as well as the general trends in the observed AGN luminosity functions, merger fractions, and measurements of the average AGN luminosity as a function of SFR. These results imply that there may be a tight connection between AGN activity and SFR over galaxy evolution timescales, and that the apparent similarities in rest-frame colors, merger rates, and clustering of AGNs compared to 'inactive' galaxies may be due primarily to AGN variability. The results provide motivation for future deep, wide extragalactic surveys that can measure the distribution of AGN accretion rates as a function of SFR.

  12. Interstellar clouds and the formation of stars

    Energy Technology Data Exchange (ETDEWEB)

    Alfven, H; Carlqvist, P [Kungliga Tekniska Hoegskolan, Stockholm (Sweden). Institutionen foer Plasmafysik

    1978-05-01

    Part I gives a survey of the drastic revision of cosmic plasma physics which is precipitated by the exploration of the magnetosphere through in situ measurements. The 'pseudo-plasma formalism', which until now has almost completely dominated theoretical astrophysics, must be replaced by an experimentally based approach involving the introduction of a number of neglected plasma phenomena, such as electric double layers, critical velocity, and pinch effect. The general belief that star light is the main ionizer is shown to be doubtful; hydromagnetic conversion of gravitational and kinetic energy may often be much more important. In Part II the revised plasma physics is applied to dark clouds and star formation. Magnetic fields do not necessarily counteract the contraction of a cloud; they may just as well 'pinch' the cloud. Magnetic compression may be the main mechanism for forming interstellar clouds and keeping them together. Part III treats the formation of stars in a dusty cosmic plasma cloud. Star formation is due to an instability, but it is very unlikely that it has anything to do with the Jeans instability. A reasonable mechanism is that the sedimentation of 'dust' (including solid bodies of different size) is triggering off a gravitationally assisted accretion. A 'stellesimal' accretion analogous to the planetesimal accretion leads to the formation of a star surrounded by a very low density hollow in the cloud. Matter falling in from the cloud towards the star is the raw material for the formation of planets and satellites.

  13. ABOUT EXOBIOLOGY: THE CASE FOR DWARF K STARS

    Energy Technology Data Exchange (ETDEWEB)

    Cuntz, M. [Department of Physics, University of Texas at Arlington, Arlington, TX 76019 (United States); Guinan, E. F., E-mail: cuntz@uta.edu, E-mail: edward.guinan@villanova.edu [Department of Astrophysics and Planetary Science, Villanova University, Villanova, PA 19085 (United States)

    2016-08-10

    One of the most fundamental topics of exobiology concerns the identification of stars with environments consistent with life. Although it is believed that most types of main-sequence stars might be able to support life, particularly extremophiles, special requirements appear to be necessary for the development and sustainability of advanced life forms. From our study, orange main-sequence stars, ranging from spectral type late-G to mid-K (with a maximum at early K), are most promising. Our analysis considers a variety of aspects, including (1) the frequency of the various types of stars, (2) the speed of stellar evolution in their lifetimes, (3) the size of the stellar climatological habitable zones (CLI-HZs), (4) the strengths and persistence of their magnetic-dynamo-generated X-ray–UV emissions, and (5) the frequency and severity of flares, including superflares; both (4) and (5) greatly reduce the suitability of red dwarfs to host life-bearing planets. The various phenomena show pronounced dependencies on the stellar key parameters such as effective temperature and mass, permitting the assessment of the astrobiological significance of various types of stars. Thus, we developed a “Habitable-Planetary-Real-Estate Parameter” (HabPREP) that provides a measure for stars that are most suitable for planets with life. Early K stars are found to have the highest HabPREP values, indicating that they may be “Goldilocks” stars for life-hosting planets. Red dwarfs are numerous, with long lifetimes, but their narrow CLI-HZs and hazards from magnetic activity make them less suitable for hosting exolife. Moreover, we provide X-ray–far-UV irradiances for G0 V–M5 V stars over a wide range of ages.

  14. ABOUT EXOBIOLOGY: THE CASE FOR DWARF K STARS

    International Nuclear Information System (INIS)

    Cuntz, M.; Guinan, E. F.

    2016-01-01

    One of the most fundamental topics of exobiology concerns the identification of stars with environments consistent with life. Although it is believed that most types of main-sequence stars might be able to support life, particularly extremophiles, special requirements appear to be necessary for the development and sustainability of advanced life forms. From our study, orange main-sequence stars, ranging from spectral type late-G to mid-K (with a maximum at early K), are most promising. Our analysis considers a variety of aspects, including (1) the frequency of the various types of stars, (2) the speed of stellar evolution in their lifetimes, (3) the size of the stellar climatological habitable zones (CLI-HZs), (4) the strengths and persistence of their magnetic-dynamo-generated X-ray–UV emissions, and (5) the frequency and severity of flares, including superflares; both (4) and (5) greatly reduce the suitability of red dwarfs to host life-bearing planets. The various phenomena show pronounced dependencies on the stellar key parameters such as effective temperature and mass, permitting the assessment of the astrobiological significance of various types of stars. Thus, we developed a “Habitable-Planetary-Real-Estate Parameter” (HabPREP) that provides a measure for stars that are most suitable for planets with life. Early K stars are found to have the highest HabPREP values, indicating that they may be “Goldilocks” stars for life-hosting planets. Red dwarfs are numerous, with long lifetimes, but their narrow CLI-HZs and hazards from magnetic activity make them less suitable for hosting exolife. Moreover, we provide X-ray–far-UV irradiances for G0 V–M5 V stars over a wide range of ages.

  15. Chromospheric and Transition Region Emission Properties of G, K, and M dwarf Exoplanet Host Stars

    Science.gov (United States)

    France, Kevin; Arulanantham, Nicole; Fossati, Luca; Lanza, A. F.; Linsky, Jeffrey L.; Redfield, Seth; Loyd, Robert; Schneider, Christian

    2018-01-01

    Exoplanet magnetic fields have proven notoriously hard to detect, despite theoretical predictions of substantial magnetic field strengths on close-in extrasolar giant planets. It has been suggested that stellar and planetary magnetic field interactions can manifest as enhanced stellar activity relative to nominal age-rotation-activity relationships for main sequence stars or enhanced activity on stars hosting short-period massive planets. In a recent study of M and K dwarf exoplanet host stars, we demonstrated a significant correlation between the relative luminosity in high-temperature stellar emission lines (L(ion)/L_Bol) and the “star-planet interaction strength”, M_plan/a_plan. Here, we expand on that work with a survey of G, K, and M dwarf exoplanet host stars obtained in two recent far-ultraviolet spectroscopic programs with the Hubble Space Telescope. We have measured the relative luminosities of stellar lines C II, Si III, Si IV, and N V (formation temperatures from 30,000 – 150,000 K) in a sample of ~60 exoplanet host stars and an additional ~40 dwarf stars without known planets. We present results on star-planet interaction signals as a function of spectral type and line formation temperature, as well as a statistical comparison of stars with and without planets.

  16. A new Be star in an open cluster - NGC 6871-8

    Science.gov (United States)

    Grigsby, James A.; Morrison, Nancy D.

    1988-01-01

    Spectroscopic observations of H-alpha show that star eight in the open cluster NGC 6871 is a previously-undiscovered Be star. The H-alpha profile was observed to vary from clear emission to pure absorption over a period of ten days; later observations over a five-day interval show weak emission along with asymmetries and filling in of the profile.

  17. Short-Period Binary Stars: Observations, Analyses, and Results

    CERN Document Server

    Milone, Eugene F; Hobill, David W

    2008-01-01

    Short-period binaries run the gamut from widely separated stars to black-hole pairs; in between are systems that include neutron stars and white dwarfs, and partially evolved systems such as tidally distorted and over-contact systems. These objects represent stages of evolution of binary stars, and their degrees of separation provide critical clues to how their evolutionary paths differ from that of single stars. The widest and least distorted systems provide astronomers with the essential precise data needed to study all stars: mass and radius. The interactions of binary star components, on the other hand, provide a natural laboratory to observe how the matter in these stars behaves under different and often varying physical conditions. Thus, cataclysmic variables with and without overpoweringly strong magnetic fields, and stars with densities from that found in the Sun to the degenerate matter of white dwarfs and the ultra-compact states of neutron stars and black holes are all discussed. The extensive inde...

  18. Coronal rain in magnetic bipolar weak fields

    Science.gov (United States)

    Xia, C.; Keppens, R.; Fang, X.

    2017-07-01

    Aims: We intend to investigate the underlying physics for the coronal rain phenomenon in a representative bipolar magnetic field, including the formation and the dynamics of coronal rain blobs. Methods: With the MPI-AMRVAC code, we performed three dimensional radiative magnetohydrodynamic (MHD) simulation with strong heating localized on footpoints of magnetic loops after a relaxation to quiet solar atmosphere. Results: Progressive cooling and in-situ condensation starts at the loop top due to radiative thermal instability. The first large-scale condensation on the loop top suffers Rayleigh-Taylor instability and becomes fragmented into smaller blobs. The blobs fall vertically dragging magnetic loops until they reach low-β regions and start to fall along the loops from loop top to loop footpoints. A statistic study of the coronal rain blobs finds that small blobs with masses of less than 1010 g dominate the population. When blobs fall to lower regions along the magnetic loops, they are stretched and develop a non-uniform velocity pattern with an anti-parallel shearing pattern seen to develop along the central axis of the blobs. Synthetic images of simulated coronal rain with Solar Dynamics Observatory Atmospheric Imaging Assembly well resemble real observations presenting dark falling clumps in hot channels and bright rain blobs in a cool channel. We also find density inhomogeneities during a coronal rain "shower", which reflects the observed multi-stranded nature of coronal rain. Movies associated to Figs. 3 and 7 are available at http://www.aanda.org

  19. Observational constraints on neutron star masses and radii

    Energy Technology Data Exchange (ETDEWEB)

    Coleman Miller, M. [University of Maryland, Department of Astronomy and Joint Space-Science Institute, College Park, MD (United States); Lamb, Frederick K. [University of Illinois at Urbana-Champaign, Center for Theoretical Astrophysics and Department of Physics, Urbana, IL (United States); University of Illinois at Urbana-Champaign, Department of Astronomy, Urbana, IL (United States)

    2016-03-15

    Precise and reliable measurements of the masses and radii of neutron stars with a variety of masses would provide valuable guidance for improving models of the properties of cold matter with densities above the saturation density of nuclear matter. Several different approaches for measuring the masses and radii of neutron stars have been tried or proposed, including analyzing the X-ray fluxes and spectra of the emission from neutron stars in quiescent low-mass X-ray binary systems and thermonuclear burst sources; fitting the energy-dependent X-ray waveforms of rotation-powered millisecond pulsars, burst oscillations with millisecond periods, and accretion-powered millisecond pulsars; and modeling the gravitational radiation waveforms of coalescing double neutron star and neutron star - black hole binary systems. We describe the strengths and weaknesses of these approaches, most of which currently have substantial systematic errors, and discuss the prospects for decreasing the systematic errors in each method. (orig.)

  20. On the theory of group generation of stars

    Science.gov (United States)

    Zhilyayev, B. Y.; Porfiryev, V. V.; Shulman, L. M.

    1973-01-01

    The hypothesis proposed is that topology of a rotating gaseous cloud can be variable in the contraction process. Due to rotation an originally spherical cloud is transformed into a toroidal body. The contraction of a thin torus is considered with different suppositions on cooling the gas. In the determined time the torus will become gravitationally unstable. The excitation of Jeans' waves is shown to result in the disintegration of the torus into fragments. The number of the fragments and their mass distributions are calculated. The proposed hypothesis on toroidal stages in stellar evolution can remove some difficulties in the theory of structure and evolution of stars, such as absence of limitary stars, distribution of rotation velocities of early-type stars, origin of poloidal magnetic fields and decline rotators with the magnetic axis orthogonal to the axis of rotation.

  1. Global helioseismology (WP4.1): From the Sun to the stars & solar analogs

    Science.gov (United States)

    García, Rafael A.

    2017-10-01

    Sun-as-a star observations put our star as a reference for stellar observations. Here, I review the activities in which the SPACEINN global seismology team (Working Package WP4.1) has worked during the past 3 years. In particular, we will explain the new deliverables available on the SPACEINN seismic+ portal. Moreover, special attention will be given to surface dynamics (rotation and magnetic fields). After characterizing the rotation and the magnetic properties of around 300 solar-like stars and defining proper metrics for that, we use their seismic properties to characterize 18 solar analogues for which we study their surface magnetic and seismic properties. This allows us to put the Sun into context compared to its siblings.

  2. Strange exotic states and compact stars

    International Nuclear Information System (INIS)

    Sagert, Irina; Wietoska, Mirjam; Schaffner-Bielich, Juergen

    2006-01-01

    We discuss the possible appearance of strange exotic multi-quark states in the interiors of neutron stars and signals for the existence of strange quark matter in the cores of compact stars. We show how the in-medium properties of possible pentaquark states are constrained by pulsar mass measurements. The possibility of generating the observed large pulsar kick velocities by asymmetric emission of neutrinos from strange quark matter in magnetic fields is outlined

  3. A radio-pulsing white dwarf binary star.

    Science.gov (United States)

    Marsh, T R; Gänsicke, B T; Hümmerich, S; Hambsch, F-J; Bernhard, K; Lloyd, C; Breedt, E; Stanway, E R; Steeghs, D T; Parsons, S G; Toloza, O; Schreiber, M R; Jonker, P G; van Roestel, J; Kupfer, T; Pala, A F; Dhillon, V S; Hardy, L K; Littlefair, S P; Aungwerojwit, A; Arjyotha, S; Koester, D; Bochinski, J J; Haswell, C A; Frank, P; Wheatley, P J

    2016-09-15

    White dwarfs are compact stars, similar in size to Earth but approximately 200,000 times more massive. Isolated white dwarfs emit most of their power from ultraviolet to near-infrared wavelengths, but when in close orbits with less dense stars, white dwarfs can strip material from their companions and the resulting mass transfer can generate atomic line and X-ray emission, as well as near- and mid-infrared radiation if the white dwarf is magnetic. However, even in binaries, white dwarfs are rarely detected at far-infrared or radio frequencies. Here we report the discovery of a white dwarf/cool star binary that emits from X-ray to radio wavelengths. The star, AR Scorpii (henceforth AR Sco), was classified in the early 1970s as a δ-Scuti star, a common variety of periodic variable star. Our observations reveal instead a 3.56-hour period close binary, pulsing in brightness on a period of 1.97 minutes. The pulses are so intense that AR Sco's optical flux can increase by a factor of four within 30 seconds, and they are also detectable at radio frequencies. They reflect the spin of a magnetic white dwarf, which we find to be slowing down on a 10 7 -year timescale. The spin-down power is an order of magnitude larger than that seen in electromagnetic radiation, which, together with an absence of obvious signs of accretion, suggests that AR Sco is primarily spin-powered. Although the pulsations are driven by the white dwarf's spin, they mainly originate from the cool star. AR Sco's broadband spectrum is characteristic of synchrotron radiation, requiring relativistic electrons. These must either originate from near the white dwarf or be generated in situ at the M star through direct interaction with the white dwarf's magnetosphere.

  4. Iron Kα line of Proca stars

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Tianling; Zhou, Menglei; Bambi, Cosimo [Center for Field Theory and Particle Physics and Department of Physics, Fudan University, 220 Handan Road, 200433 Shanghai (China); Herdeiro, Carlos A.R.; Radu, Eugen, E-mail: 14307110042@fudan.edu.cn, E-mail: mlzhou13@fudan.edu.cn, E-mail: bambi@fudan.edu.cn, E-mail: herdeiro@ua.pt, E-mail: eugen.radu@ua.pt [Departamento de Física da Universidade de Aveiro and Center for Research and Development in Mathematics and Applications (CIDMA), Campus de Santiago, 3810-183 Aveiro (Portugal)

    2017-08-01

    X-ray reflection spectroscopy can be a powerful tool to test the nature of astrophysical black holes. Extending previous work on Kerr black holes with scalar hair [1] and on boson stars [2], here we study whether astrophysical black hole candidates may be horizonless, self-gravitating, vector Bose-Einstein condensates, known as Proca stars [3]. We find that observations with current X-ray missions can only provide weak constraints and rule out solely Proca stars with low compactness. There are two reasons. First, at the moment we do not know the geometry of the corona, and therefore the uncertainty in the emissivity profile limits the ability to constrain the background metric. Second, the photon number count is low even in the case of a bright black hole binary, and we cannot have a precise measurement of the spectrum.

  5. Doppler-Zeeman Mapping of the Rapidly Rotating Magnetic CP Star HD37776

    Science.gov (United States)

    Khokhlova, V. L.; Vasilchenko, D. V.; Stepanov, V. V.; Romanyuk, I. I.

    2000-03-01

    We present the results of our analysis of magnetic-field configuration and abundance anomalies on the surface of the rapidly rotating, chemically peculiar helium-strong variable B2 V star HD37776 with unresolved Zeeman components of spectral lines. Simultaneous inversion of the observed Stokes I and V profiles, which realizes the method of Doppler-Zeeman mapping (Vasilchenko et al. 1996), has been applied for the first time. Spectroscopic observations were carried out with the Main stellar spectrograph of the 6-m Special Astrophysical Observatory telescope equipped with a Zeeman analyzer and a CCD array, which allowed spectra in right- and left-hand circularly polarized light to be taken simultaneously at a signal-to-noise ratio S/N > 200 (Romanyuk et al. 1999). The profile width of winged spectral lines (reaching 5 A) is determined by Zeeman line splitting; however, the observed Zeeman components are blurred and unresolved because of the rapid stellar rotation. When solving the inverse problem, we sought for the magnetic-field configuration in the form of a combination of arbitrarily oriented dipole, quadrupole, and octupole placed at the stellar center. The observed Stokes I and V profiles for eight spectral lines of He, OII, AlIII, SiIII, and FeIII averaged over the visible stellar surface were used as input data. We constructed a model of the magnetic field from the condition of coincidence of magnetic maps obtained from different lines of different chemical elements and from the condition of a minimum profile residual. This model is a combination of centered coaxial dipole and quadrupole with the dominant quadrupole component at 30 deg < i < 50 deg, beta = 40 deg, and a maximum surface field strength H_s = 60 kG. A comparison of our abundance maps with the field configuration shows that the He concentration is at a maximum in the regions of maximum radial field, while the maximum concentrations of O, Al, Si, and Fe coincide with the regions of maximum

  6. Magneto–Thermal Evolution of Neutron Stars with Emphasis to ...

    Indian Academy of Sciences (India)

    The magnetic and thermal evolution of neutron stars is a very complex process with many non-linear interactions. For a decent understanding of neutron star physics, these evolutions cannot be considered isolated. A brief overview is presented, which describes the main magneto–thermal interactions that determine the fate ...

  7. Hot subluminous stars: Highlights from the MUCHFUSS and Kepler missions

    Directory of Open Access Journals (Sweden)

    Geier S.

    2013-03-01

    Full Text Available Research into hot subdwarf stars is progressing rapidly. We present recent important discoveries. First we review the knowledge about magnetic fields in hot subdwarfs and highlight the first detection of a highly-magnetic, helium-rich sdO star. We briefly summarize recent discoveries based on Kepler light curves and finally introduce the closest known sdB+WD binary discovered by the MUCHFUSS project and discuss its relevance as a progenitor of a double-detonation type Ia supernova.

  8. ROTATION AND MAGNETIC ACTIVITY IN A SAMPLE OF M-DWARFS

    International Nuclear Information System (INIS)

    Browning, Matthew K.; Basri, Gibor; Marcy, Geoffrey W.; Zhang Jiahao; West, Andrew A.

    2010-01-01

    We have analyzed the rotational broadening and chromospheric activity in a sample of 123 M-dwarfs, using spectra taken at the W.M. Keck Observatory as part of the California Planet Search program. We find that only seven of these stars are rotating more rapidly than our detection threshold of v sin i ∼ 2.5 km s -1 . Rotation appears to be more common in stars later than M3 than in the M0-M2.5 mass range: we estimate that less than 10% of early-M stars are detectably rotating, whereas roughly a third of those later than M4 show signs of rotation. These findings lend support to the view that rotational braking becomes less effective in fully convective stars. By measuring the equivalent widths of the Ca II H and K lines for the stars in our sample, and converting these to approximate L Ca /L bol measurements, we also provide constraints on the connection between rotation and magnetic activity. Measurable rotation is a sufficient, but not necessary condition for activity in our sample: all the detectable rotators show strong Ca II emission, but so too do a small number of non-rotating stars, which we presume may lie at high inclination angles relative to our line of sight. Our data are consistent with a 'saturation-type' rotation-activity relationship, with activity roughly independent of rotation above a threshold velocity of less than 6 km s -1 . We also find weak evidence for a 'gap' in L Ca /L bol between a highly active population of stars, which typically are detected as rotators, and another much less active group.

  9. The Mysterious Dimmings of the T Tauri Star V1334 Tau

    International Nuclear Information System (INIS)

    Rodriguez, Joseph E.; Zhou, George; Cargile, Phillip A.; Relles, Howard M.; Latham, David W.; Eastman, Jason; Bieryla, Allyson; Esquerdo, Gilbert A.; Berlind, Perry; Calkins, Michael L.; Vanderburg, Andrew; Stevens, Daniel J.; Osborn, Hugh P.; Shappee, Benjamin J.; Reed, Phillip A.; Lund, Michael B.; Stassun, Keivan G.; Gaidos, Eric; Ansdell, Megan; Siverd, Robert J.

    2017-01-01

    We present the discovery of two extended ∼0.12 mag dimming events of the weak-lined T Tauri star V1334. The start of the first event was missed but came to an end in late 2003, and the second began in 2009 February, and continues as of 2016 November. Since the egress of the current event has not yet been observed, it suggests a period of >13 years if this event is periodic. Spectroscopic observations suggest the presence of a small inner disk, although the spectral energy distribution shows no infrared excess. We explore the possibility that the dimming events are caused by an orbiting body (e.g., a disk warp or dust trap), enhanced disk winds, hydrodynamical fluctuations of the inner disk, or a significant increase in the magnetic field flux at the surface of the star. We also find a ∼0.32 day periodic photometric signal that persists throughout the 2009 dimming which appears to not be due to ellipsoidal variations from a close stellar companion. High-precision photometric observations of V1334 Tau during K2 campaign 13, combined with simultaneous photometric and spectroscopic observations from the ground, will provide crucial information about the photometric variability and its origin.

  10. The Mysterious Dimmings of the T Tauri Star V1334 Tau

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez, Joseph E.; Zhou, George; Cargile, Phillip A.; Relles, Howard M.; Latham, David W.; Eastman, Jason; Bieryla, Allyson; Esquerdo, Gilbert A.; Berlind, Perry; Calkins, Michael L.; Vanderburg, Andrew [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Stevens, Daniel J. [Department of Astronomy, The Ohio State University, Columbus, OH 43210 (United States); Osborn, Hugh P. [Department of Physics, University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL (United Kingdom); Shappee, Benjamin J. [Carnegie Observatories, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Reed, Phillip A. [Department of Physical Sciences, Kutztown University, Kutztown, PA 19530 (United States); Lund, Michael B.; Stassun, Keivan G. [Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 (United States); Gaidos, Eric [Department of Geology and Geophysics, University of Hawai‘i at Mnoa, Honolulu, HI 96822 (United States); Ansdell, Megan [Institute for Astronomy, University of Hawai‘i at Manoa, Honolulu, HI 96822 (United States); Siverd, Robert J. [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Santa Barbara, CA 93117 (United States); and others

    2017-02-20

    We present the discovery of two extended ∼0.12 mag dimming events of the weak-lined T Tauri star V1334. The start of the first event was missed but came to an end in late 2003, and the second began in 2009 February, and continues as of 2016 November. Since the egress of the current event has not yet been observed, it suggests a period of >13 years if this event is periodic. Spectroscopic observations suggest the presence of a small inner disk, although the spectral energy distribution shows no infrared excess. We explore the possibility that the dimming events are caused by an orbiting body (e.g., a disk warp or dust trap), enhanced disk winds, hydrodynamical fluctuations of the inner disk, or a significant increase in the magnetic field flux at the surface of the star. We also find a ∼0.32 day periodic photometric signal that persists throughout the 2009 dimming which appears to not be due to ellipsoidal variations from a close stellar companion. High-precision photometric observations of V1334 Tau during K2 campaign 13, combined with simultaneous photometric and spectroscopic observations from the ground, will provide crucial information about the photometric variability and its origin.

  11. The G+M eclipsing binary V530 Orionis: a stringent test of magnetic stellar evolution models for low-mass stars

    Energy Technology Data Exchange (ETDEWEB)

    Torres, Guillermo [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Lacy, Claud H. Sandberg [Department of Physics, University of Arkansas, Fayetteville, AR 72701 (United States); Pavlovski, Krešimir [Department of Physics, Faculty of Science, University of Zagreb, Bijenicka cesta 32, 10000 Zagreb (Croatia); Feiden, Gregory A. [Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala (Sweden); Sabby, Jeffrey A. [Physics Department, Southern Illinois University Edwardsville, Edwardsville, IL 62026 (United States); Bruntt, Hans [Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C (Denmark); Clausen, Jens Viggo, E-mail: gtorres@cfa.harvard.edu [Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, DK-2100 Copenhagen Ø (Denmark)

    2014-12-10

    We report extensive photometric and spectroscopic observations of the 6.1 day period, G+M-type detached double-lined eclipsing binary V530 Ori, an important new benchmark system for testing stellar evolution models for low-mass stars. We determine accurate masses and radii for the components with errors of 0.7% and 1.3%, as follows: M {sub A} = 1.0038 ± 0.0066 M {sub ☉}, M {sub B} = 0.5955 ± 0.0022 M {sub ☉}, R {sub A} = 0.980 ± 0.013 R {sub ☉}, and R {sub B} = 0.5873 ± 0.0067 R {sub ☉}. The effective temperatures are 5890 ± 100 K (G1 V) and 3880 ± 120 K (M1 V), respectively. A detailed chemical analysis probing more than 20 elements in the primary spectrum shows the system to have a slightly subsolar abundance, with [Fe/H] = –0.12 ± 0.08. A comparison with theory reveals that standard models underpredict the radius and overpredict the temperature of the secondary, as has been found previously for other M dwarfs. On the other hand, models from the Dartmouth series incorporating magnetic fields are able to match the observations of the secondary star at the same age as the primary (∼3 Gyr) with a surface field strength of 2.1 ± 0.4 kG when using a rotational dynamo prescription, or 1.3 ± 0.4 kG with a turbulent dynamo approach, not far from our empirical estimate for this star of 0.83 ± 0.65 kG. The observations are most consistent with magnetic fields playing only a small role in changing the global properties of the primary. The V530 Ori system thus provides an important demonstration that recent advances in modeling appear to be on the right track to explain the long-standing problem of radius inflation and temperature suppression in low-mass stars.

  12. Turbulent Magnetic Relaxation in Pulsar Wind Nebulae

    Science.gov (United States)

    Zrake, Jonathan; Arons, Jonathan

    2017-09-01

    We present a model for magnetic energy dissipation in a pulsar wind nebula. A better understanding of this process is required to assess the likelihood that certain astrophysical transients may be powered by the spin-down of a “millisecond magnetar.” Examples include superluminous supernovae, gamma-ray bursts, and anticipated electromagnetic counterparts to gravitational wave detections of binary neutron star coalescence. Our model leverages recent progress in the theory of turbulent magnetic relaxation to specify a dissipative closure of the stationary magnetohydrodynamic (MHD) wind equations, yielding predictions of the magnetic energy dissipation rate throughout the nebula. Synchrotron losses are self-consistently treated. To demonstrate the model’s efficacy, we show that it can reproduce many features of the Crab Nebula, including its expansion speed, radiative efficiency, peak photon energy, and mean magnetic field strength. Unlike ideal MHD models of the Crab (which lead to the so-called σ-problem), our model accounts for the transition from ultra to weakly magnetized plasma flow and for the associated heating of relativistic electrons. We discuss how the predicted heating rates may be utilized to improve upon models of particle transport and acceleration in pulsar wind nebulae. We also discuss implications for the Crab Nebula’s γ-ray flares, and point out potential modifications to models of astrophysical transients invoking the spin-down of a millisecond magnetar.

  13. Turbulent Magnetic Relaxation in Pulsar Wind Nebulae

    Energy Technology Data Exchange (ETDEWEB)

    Zrake, Jonathan [Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, SLAC National Accelerator Laboratory, Menlo Park, CA 94025 (United States); Arons, Jonathan [Astronomy Department and Theoretical Astrophysics Center, University of California, Berkeley, 601 Campbell Hall, Berkeley, CA 94720 (United States)

    2017-09-20

    We present a model for magnetic energy dissipation in a pulsar wind nebula. A better understanding of this process is required to assess the likelihood that certain astrophysical transients may be powered by the spin-down of a “millisecond magnetar.” Examples include superluminous supernovae, gamma-ray bursts, and anticipated electromagnetic counterparts to gravitational wave detections of binary neutron star coalescence. Our model leverages recent progress in the theory of turbulent magnetic relaxation to specify a dissipative closure of the stationary magnetohydrodynamic (MHD) wind equations, yielding predictions of the magnetic energy dissipation rate throughout the nebula. Synchrotron losses are self-consistently treated. To demonstrate the model’s efficacy, we show that it can reproduce many features of the Crab Nebula, including its expansion speed, radiative efficiency, peak photon energy, and mean magnetic field strength. Unlike ideal MHD models of the Crab (which lead to the so-called σ -problem), our model accounts for the transition from ultra to weakly magnetized plasma flow and for the associated heating of relativistic electrons. We discuss how the predicted heating rates may be utilized to improve upon models of particle transport and acceleration in pulsar wind nebulae. We also discuss implications for the Crab Nebula’s γ -ray flares, and point out potential modifications to models of astrophysical transients invoking the spin-down of a millisecond magnetar.

  14. Another Possibility for Boyajian's Star

    Science.gov (United States)

    Kohler, Susanna

    2017-07-01

    The unusual light curve of the star KIC 8462852, also known as Tabbys star or Boyajians star, has puzzled us since its discovery last year. A new study now explores whether the stars missing flux is due to internal blockage rather than something outside of the star.Mysterious DipsMost explanations for the flux dips of Boyajians star rely on external factors, like this illustrated swarm of comets. [NASA/JPL-Caltech]Boyajians star shows unusual episodes of dimming in its light curve by as much as 20%, each lasting a few to tens of days and separated by periods of typically hundreds of days. In addition, archival observations show that it has gradually faded by roughly 15% over the span of the last hundred years. What could be causing both the sporadic flux dips and the long-term fading of this odd star?Explanations thus far have varied from mundane to extreme. Alien megastructures, pieces of smashed planets or comets orbiting the star, and intervening interstellar medium have all been proposed as possible explanations but these require some object external to the star. A new study by researcher Peter Foukal proposes an alternative: what if the source of the flux obstruction is the star itself?Analogy to the SunDecades ago, researchers discovered that our own stars total flux isnt as constant as we thought. When magnetic dark spots on the Suns surface block the heat transport, the Suns luminosity dips slightly. The diverted heat is redistributed in the Suns interior, becoming stored as a very small global heating and expansion of the convective envelope. When the blocking starspot is removed, the Sun appears slightly brighter than it did originally. Its luminosity then gradually relaxes, decaying back to its original value.Model of a stars flux after a 1,000-km starspot is inserted at time t = 0 and removed at time t = ts at a depth of 10,000 km in the convective zone. The stars luminosity dips, then becomes brighter than originally, and then gradually decays. [Foukal

  15. Magnetic Fields in the Interstellar Medium

    Science.gov (United States)

    Clark, Susan

    2017-01-01

    The Milky Way is magnetized. Invisible magnetic fields thread the Galaxy on all scales and play a vital but still poorly understood role in regulating flows of gas in the interstellar medium and the formation of stars. I will present highlights from my thesis work on magnetic fields in the diffuse interstellar gas and in accretion disks. At high Galactic latitudes, diffuse neutral hydrogen is organized into an intricate network of slender linear features. I will show that these neutral hydrogen “fibers” are extremely well aligned with the ambient magnetic field as traced by both starlight polarization (Clark et al. 2014) and Planck 353 GHz polarized dust emission (Clark et al. 2015). The structure of the neutral interstellar medium is more tightly coupled to the magnetic field than previously known. Because the orientation of neutral hydrogen is an independent predictor of the local dust polarization angle, our work provides a new tool in the search for inflationary gravitational wave B-mode polarization in the cosmic microwave background, which is currently limited by dust foreground contamination. Magnetic fields also drive accretion in astrophysical disks via the magnetorotational instability (MRI). I analytically derive the behavior of this instability in the weakly nonlinear regime and show that the saturated state of the instability depends on the geometry of the background magnetic field. The analytical model describes the behavior of the MRI in a Taylor-Couette flow, a set-up used by experimentalists in the ongoing quest to observe MRI in the laboratory (Clark & Oishi 2016a, 2016b).

  16. Quasiclassical approach to the weak levitation of extended states in the quantum Hall effect

    International Nuclear Information System (INIS)

    Fogler, M.M.

    1998-01-01

    The two-dimensional motion of a charged particle in a random potential and a transverse magnetic field is believed to be delocalized only at discrete energies E N . In strong fields there is a small positive deviation of E N from the center of the Nth Landau level, which is referred to as the open-quotes weak levitationclose quotes of the extended state. I calculate the size of the weak levitation effect for the case of a smooth random potential rederiving earlier results of Haldane and Yang [Phys. Rev. Lett. 78, 298 (1997)] and extending their approach to lower magnetic fields. I find that as the magnetic field decreases, this effect remains weak down to the lowest field B min where such a quasiclassical approach is still justified. Moreover, in the immediate vicinity of B min the weak levitation becomes additionally suppressed. This indicates that the open-quotes strong levitationclose quotes expected at yet even lower magnetic fields must be of a completely different origin. copyright 1998 The American Physical Society

  17. Angular momentum transfer in primordial discs and the rotation of the first stars

    Science.gov (United States)

    Hirano, Shingo; Bromm, Volker

    2018-05-01

    We investigate the rotation velocity of the first stars by modelling the angular momentum transfer in the primordial accretion disc. Assessing the impact of magnetic braking, we consider the transition in angular momentum transport mode at the Alfvén radius, from the dynamically dominated free-fall accretion to the magnetically dominated solid-body one. The accreting protostar at the centre of the primordial star-forming cloud rotates with close to breakup speed in the case without magnetic fields. Considering a physically motivated model for small-scale turbulent dynamo amplification, we find that stellar rotation speed quickly declines if a large fraction of the initial turbulent energy is converted to magnetic energy (≳ 0.14). Alternatively, if the dynamo process were inefficient, for amplification due to flux freezing, stars would become slow rotators if the pre-galactic magnetic field strength is above a critical value, ≃10-8.2 G, evaluated at a scale of nH = 1 cm-3, which is significantly higher than plausible cosmological seed values (˜10-15 G). Because of the rapid decline of the stellar rotational speed over a narrow range in model parameters, the first stars encounter a bimodal fate: rapid rotation at almost the breakup level, or the near absence of any rotation.

  18. CARBON NEUTRON STAR ATMOSPHERES

    International Nuclear Information System (INIS)

    Suleimanov, V. F.; Klochkov, D.; Werner, K.; Pavlov, G. G.

    2014-01-01

    The accuracy of measuring the basic parameters of neutron stars is limited in particular by uncertainties in the chemical composition of their atmospheres. For example, the atmospheres of thermally emitting neutron stars in supernova remnants might have exotic chemical compositions, and for one of them, the neutron star in Cas A, a pure carbon atmosphere has recently been suggested by Ho and Heinke. To test this composition for other similar sources, a publicly available detailed grid of the carbon model atmosphere spectra is needed. We have computed this grid using the standard local thermodynamic equilibrium approximation and assuming that the magnetic field does not exceed 10 8  G. The opacities and pressure ionization effects are calculated using the Opacity Project approach. We describe the properties of our models and investigate the impact of the adopted assumptions and approximations on the emergent spectra

  19. Extended I-Love relations for slowly rotating neutron stars

    Science.gov (United States)

    Gagnon-Bischoff, Jérémie; Green, Stephen R.; Landry, Philippe; Ortiz, Néstor

    2018-03-01

    Observations of gravitational waves from inspiralling neutron star binaries—such as GW170817—can be used to constrain the nuclear equation of state by placing bounds on stellar tidal deformability. For slowly rotating neutron stars, the response to a weak quadrupolar tidal field is characterized by four internal-structure-dependent constants called "Love numbers." The tidal Love numbers k2el and k2mag measure the tides raised by the gravitoelectric and gravitomagnetic components of the applied field, and the rotational-tidal Love numbers fo and ko measure those raised by couplings between the applied field and the neutron star spin. In this work, we compute these four Love numbers for perfect fluid neutron stars with realistic equations of state. We discover (nearly) equation-of-state independent relations between the rotational-tidal Love numbers and the moment of inertia, thereby extending the scope of I-Love-Q universality. We find that similar relations hold among the tidal and rotational-tidal Love numbers. These relations extend the applications of I-Love universality in gravitational-wave astronomy. As our findings differ from those reported in the literature, we derive general formulas for the rotational-tidal Love numbers in post-Newtonian theory and confirm numerically that they agree with our general-relativistic computations in the weak-field limit.

  20. Constraining weakly interacting slim particles with a massive star and in the laboratory

    International Nuclear Information System (INIS)

    Seggern, Jan Eike von

    2014-01-01

    This doctoral thesis is devoted to constraining the allowed parameter space of weakly interacting slim particles (WISPs). WISPs are predicted by many extensions of the Standard Model of Particle Physics (SM): The Peccei-Quinn solution of the strong CP-problem of quantum chromo dynamics requires the existence of an axion; some embeddings of the SM into string theories predict a large number of axion-like particles (ALPs), the so called axi-verse, and hidden photons (HPs). Cosmological and astrophysical observables are sensitive to the existence of WISPs. Measurements of these observables allow to constrain the allowed WISP parameter space. In addition dedicated laboratory based experiments exist. Although the parameter space excluded by these experiments is generally smaller than the regions excluded by measurements of cosmological or astrophysical observables, the results from these experiment are valuable complements to these measurements because they are less model dependent. In this thesis, I present my work that helps to constrain the WISP parameter space in two ways: First, the existence of ALPs implies their production in stellar cores. The oscillation of ALPs with photons in the galactic magnetic field (GMF) suggest an X-ray flux from red supergiant (RSG) stars. RSGs are expected to emit no X-rays if ALPs do not exist. An upper limit for the X-ray count rate from the nearby RSG α-Ori (Betelgeuse) is estimated from observations of α-Ori with the Chandra X-ray Telescope. The interior of α-Ori is modelled with the ''Evolve ZAMS'' code. Based on this, the corresponding ALP production rate is calculated. Using current estimates of the value of the regular component of the GMF, the resulting X-ray flux density at Earth from ALP-photon oscillations and the corresponding count rates with the Chandra instruments are calculated. Comparison of this estimate with the upper limit from the Chandra measurements allows to exclude values of the ALP-photon coupling above 2