Core Rotation Research Articles

On the frequency bifurcations of the MHD startup modes in NSTX

The observed bifurcations of the low frequency (<50 kHz) and low toroidal periodicity (n < 5) magnetohydrodynamic (MHD) activity often present in the initial part of the National Spherical Tokamak Experiment (NSTX) discharges can be explained by the evolution of the radial profile of the safety factor (q=rBϕ/RBθ) crossing multiple rational surfaces in the core. Important performance limiting instability mechanisms in the NSTX spherical tokamak are often linked to low frequency and low-n MHD activity. They are quite common in long-pulse NSTX plasmas. They can be present at the beginning of the plasma current flat-top, at the end of the discharge or during the whole duration, and they have been observed to deleteriously impact performance over a wide range of q95. An interesting feature observed in some NSTX discharges is the presence of a bifurcation in the frequency of the low n modes, as low as n = 1, that have frequencies comparable to the plasma core rotation divided by n. Equilibrium reconstructions constrained by magnetic diagnostics data and motional stark effect pitch angle radial profiles suggest that the observed bifurcations are linked to a fast evolving minimum value of q. 3D non-linear resistive MHD simulations show that these modes are ideal and exist as non-resonant before the correspondent rational surface enters the plasma.

Dynamical galactic effects induced by solitonic vortex structure in bosonic dark matter

The nature of dark matter (DM) remains one of the unsolved mysteries of modern physics. An intriguing possibility is to assume that DM consists of ultralight bosonic particles in the Bose–Einstein condensate (BEC) state. We study stationary DM structures by using the system of the Gross–Pitaevskii and Poisson equations, including the effective temperature effect with parameters chosen to describe the Milky Way galaxy. We have investigated DM structure with BEC core and isothermal envelope. We compare the spherically symmetric and vortex core states, which allows us to analyze the impact of the core vorticity on the halo density, velocity distribution, and, therefore, its gravitational field. Gravitational field calculation is done in the gravitoelectromagnetism approach to include the impact of the core rotation, which induces a gravimagnetic field. As a result, the halo with a vortex core is characterized by smaller orbital velocity in the galactic disk region in comparison with the non-rotating halo. It is found that the core vorticity produces gravimagnetic perturbation of celestial body dynamics, which can modify the circular trajectories.

A 10-Year Follow-up Survey of Psychiatry Resident Education in Consultation-Liaison Psychiatry.

In 2010, the Academy of Consultation-Liaison (then Academy of Psychosomatic Medicine) surveyed US residency programs to understand training in consultation-liaison (CL) psychiatry, leading to recommendations in 2014. Since then, residency training in CL has evolved in the context of competing training demands, increased prioritization of electives, and reactions to coronavirus2019. To determine the current state of residency training in CL across the United States, including the structure of core and elective resident rotations in CL, attending physician staffing, presence of fellows and other trainees, didactic curriculum, and impact of coronavirus2019. Members of the Academy of Consultation-Liaison Residency Education Subcommittee designed and piloted an 81-question survey tool that was sent to program directors of 269 US general psychiatry training programs for voluntary completion. One hundred three of 269 programs responded to the survey, yielding a response rate of 38.3%. Responding programs were larger and more likely to have a CL fellowship than nonresponding programs. Of the 103 responding programs, 82.5% have more than the minimally required time on CL, with 46.6% reporting an increase in total CL time in the past decade. Since 2010, 18.4% of responding programs changed the placement of the CL rotation, with 43.7% now adherent to the 2014 Academy of Psychosomatic Medicine recommendation to include core CL training in the second half of residency. Thirty-five percent of responding programs require residents to rotate on more than 1 CL service, and 19.4% have a required outpatient CL component. Faculty full-time equivalent varies widely. Of all services included, 33.8% report that all CL faculty are board-certified in CL psychiatry, whereas 18.7% have no board-certified faculty. Of the 103 responding programs, 36.9% offer a CL fellowship, but 31.1% report no residency graduates pursuing CL fellowships in the past 5 years. Of the included programs, 77.7% have a formal CL curriculum for residents, with 34.0% reporting a separate didactic series during the CL rotation. Among the responding programs, the amount of time spent on core CL rotations has increased in the past decade, but programs have also shifted CL training earlier in the course of residency. Residency programs are increasingly challenged to provide an optimal CL experience, and updated guidance from Academy of Consultation-Liaison may be appreciated.

Asteroseismology of evolved stars to constrain the internal transport of angular momentum

Context. Asteroseismic measurements of the internal rotation rate in evolved stars pointed to a lack of angular momentum (AM) transport in stellar evolution models. Several physical processes in addition to hydrodynamical ones were proposed as candidates for the missing mechanism. Nonetheless, no current candidate can satisfy all the constraints provided by asteroseismology. Aims. We revisit the role of a candidate process whose efficiency scales with the contrast between the rotation rate of the core and the surface. This process was proposed in previous works to be related to the azimuthal magneto-rotational instability. Methods. We computed stellar evolution models of low- and intermediate-mass stars with the parametric formulation of AM transport proposed in previous works for this instability until the end of the core-helium burning for low- and intermediate-mass stars, and compare our results to the latest asteroseismic constraints available in the post-main sequence phase. Results. Both hydrogen-shell-burning stars in the red-giant branch and core-helium-burning stars of low- and intermediate-mass in the mass range 1 M⊙ ≲ M ≲ 2.5 M⊙ can be simultaneously reproduced by this kind of parametrisation. Conclusions. Given the current constraints from asteroseismology, the core rotation rate of post-main sequence stars seems to be well explained by a process whose efficiency is regulated by the internal degree of differential rotation in radiative zones.

The Proceduralization of Hominin Knapping Skill: Memorizing Different Lithic Technologies

Reconstructing the technical and cognitive abilities of past hominins requires an understanding of how skills like stone toolmaking were learned and transmitted. We ask how much of the variability in the uptake of knapping skill is due to the characteristics of the knapping sequences themselves? Fundamental to skill acquisition is proceduralization, the process whereby skilful tasks are converted from declarative memories (consciously memorized facts and events) into procedural memories (sub-consciously memorized actions) via repetitive practice. From knapping footage, we time and encode each action involved in discoidal, handaxe, Levallois and prismatic blade production. The structure and complexity of these reduction sequences were quantified using k-mer analysis and Markov chains. The amount of time spent on tasks and the pattern of core rotations revealed portions of these reduction sequences that are predisposed to being converted into procedural memories. We observed two major pathways to achieve this proceduralization: either a repetitive or a predictable sequence of core rotations. Later Acheulean handaxes and Levallois knapping involved a predictable platform selection sequence, while prismatic blade knapping involved a repetitive exploitation of platforms. Technologies and the portions of their reduction sequence that lend themselves to proceduralization probably facilitated the more rapid uptake of stone toolmaking skill.

Mode Mixing and Rotational Splittings. II. Reconciling Different Approaches to Mode Coupling

In the mixed-mode asteroseismology of subgiants and red giants, the coupling between the p- and g-mode cavities must be understood well in order to derive localized estimates of interior rotation from measurements of mode multiplet rotational splittings. There exist now two different descriptions of this coupling: one based on an asymptotic quantization condition, and the other arising from the coupling matrices associated with “acoustic molecular orbitals.” We examine the analytic properties of both, and derive closed-form expressions for various quantities—such as the period-stretching function τ—which previously had to be solved for numerically. Using these, we reconcile both formulations for the first time, deriving relations by which quantities in each formulation may be translated to and interpreted within the other. This yields an information criterion for whether a given configuration of mixed modes may meaningfully constrain the parameters of the asymptotic construction, which is likely not satisfied by the majority of first-ascent red giant stars in our observational sample. Since this construction has been already used to make rotational measurements of such red giants, we examine—through a hare-and-hounds exercise—whether, and how, such limitations affect these existing measurements. While averaged estimates of core rotation seem fairly robust, template-matching using the asymptotic construction has difficulty reliably assigning rotational splittings to individual multiplets, or estimating the mixing fractions ζ of the most p-dominated mixed modes, where such estimates are most needed. We finally discuss implications for extending the two-zone model of radial differential rotation, e.g., via rotational inversions, with these methods.

Constraining the rotation profile in a low-luminosity subgiant with a surface rotation measurement

ABSTRACT Rotationally induced mode splitting frequencies of low-luminosity subgiants suggest that angular momentum transport mechanisms are 1–2 orders of magnitude more efficient in these stars than predicted by theory. Constraints on the rotation profile of low-luminosity subgiants could be used to identify the dominant mechanism for angular momentum transport. We develop a forward model for the rotation profile given observed rotational splittings, assuming a step-like rotation profile. We identify a consistent degeneracy between the position of the profile discontinuity and the surface rotation rate. We perform mock experiments that show the discontinuity position can be better constrained with a prior on the surface rotation rate, which is informed by star spot modulations. We finally apply this approach to KIC 12508433, a well-studied low-luminosity subgiant, as an example case. With the observed surface rotation prior, we obtain a factor of 2 increase in precision of the position of strong rotation gradient. We recover the literature values of the core and surface rotation rates and find the highest support for a discontinuity in the radiative zone. Auxiliary measurements of surface rotation could substantially improve inferences on the rotation profile of low-luminosity subgiants with already available data.

Isotope effects on intrinsic rotation in hydrogen, deuterium and tritium plasmas

The isotope effect on intrinsic rotation was studied at the Joint European Torus (JET) tokamak. With the unique capability of JET to operate with tritium (T), for the first time, experiments in hydrogen (H), deuterium (D) and T in Ohmic plasmas were compared. Two rotation reversals per isotope type are observed in plasma density scans spanning the linear and the saturated Ohmic confinement regimes. A clear isotope mass dependence is observed at the higher densities. The magnitude of the core rotation was found to depend on isotope mass, with stronger co-current rotation observed in H. Change on intrinsic rotation characteristics coexist with a stronger thermal energy confinement in T.

Disruption of fungal hyphae suppressed litter-derived C retention in soil and N translocation to plants under drought-stressed temperate grassland

Litter decomposition often represents the largest carbon (C) and nitrogen (N) input into the soil and thereby supports soil nutrition cycling function. Common mycelial networks (CMNs) can promote soil C and N trades during the litter decomposition process. However, the degree to which this promotion depends on abiotic variables, such as drought, remains unresolved. Importantly, the influence of soil fungi mycelium on the turnover of litter-derived C and N could weaken under drought if disrupts fungal hyphae. Here, we used plant litter of stable isotope dual-labeling (13C and 15N), experimental drought (ambient, 30%, 50%, or 70% growing season precipitation reductions), and physical disruption to soil fungal hyphae (via soil core rotation) to investigate decomposition dynamics along the soil-plant-atmosphere continuum in a temperate grassland. On average, drought significantly slowed plant litter decomposition by up to 31.8%, but undisrupted fungal hyphae accelerated litter decomposition by up to 31.7% and promoted the release of C and N from plant litter. The intactness of fungal hyphae would have divergent effects on the allocation of litter-derived C and N during decomposition under drought conditions. Intact soil fungal hyphae contributed about 47% of litter-derived C transfer into soil microbial biomass after litter decomposition, but no significant effects in the soil, plant aboveground, or CO2 emissions, compared to hyphae disruption treatment. Undisrupted hyphae promoted approx. 82% of the turnover of litter-derived N from soil to plant and reduced content of litter-derived N in soil and N2O emission compared to hyphae disruption. We conclude that intact networks of soil fungal hyphae are essential to maintaining litter decomposition processes under drought conditions in temperate grassland ecosystems because the fungi promote releases of carbon and nitrogen from plant litter that facilitate carbon and nitrogen cycling.

Measurement of alternating and rotational magnetostrictions of Non-oriented silicon steel sheets

Extensive numerical analyses and experimental tests have shown that while major regions of magnetic cores in electromagnetic devices, such as transformers and rotating electric machines, are dominated by the alternating magnetic fields, the rotating magnetic fields exist in the corner joints of multi-phase transformers and the yoke area behind the teeth of rotating electric machines. These magnetic fields cause core losses due to hysteresis and eddy currents, mechanical vibration and acoustic noises due to magnetostriction. Many studies have been reported in the literature on alternating and rotational core losses and alternating magnetostriction, but not so much on rotational magnetostriction, especially in non-oriented (NO) silicon steel sheets. The vibration and noise caused by rotational magnetostriction are much higher than those caused by alternating magnetostriction. This paper reports the development of a magnetostriction measurement system consisting of a 2D symmetrical single sheet tester (SST) and resistance strain gauges. The selection considerations of resistance strain gauges are summarized. The alternating and rotational magnetostriction characteristics of a NO silicon steel, B35A300 (0.35 mm), are measured. Because the rotating magnetic field in the stator is not always ideally circular but more often elliptical, the magnetostriction under elliptical magnetizations with different axis ratios is also measured. The magnetostriction anisotropy of the NO steel sheet is observed and analyzed. The elongation and contraction under alternating, circular and elliptical rotating magnetizations with different axis ratios are discussed. The results can provide data support for calculating and designing multi-phase transformers and rotating electric machines under different types of magnetizations. The research can provide theoretical and practical guidance for mitigating mechanical vibration and acoustic noise caused by magnetostriction.

Integration of Veterans Affairs Medical Centers Into Neurosurgical Residency Programs.

Veterans Affairs (VA) medical centers serve as a unique training environment for US residency programs. In this study, we aim to explore the scope and details of VA integration into neurosurgery resident training. We used data from the Accreditation Council for Graduate Medical Education database to provide an overview of neurosurgery training programs with an active VA affiliation and developed a multi-institutional survey to gather information related to rotation design, operative volume, expectations, and core training values. Of the 116 neurosurgery residency programs, 40 have an active affiliation with a VA medical center (34%). Residents most frequently rotated at the VA during their third postgraduate year, with an average rotation length of 7.5 months (range 2-21). Nearly all programs reported a weekly mix of clinic and operative days (96%), with residents longitudinally following patients throughout their rotations. Attending neurosurgeons from VA-affiliated programs reported operative experience (100%), independent decision-making (89%), and continuity of care (81%) as core values of VA neurosurgery rotations. Surgical volume varied between programs with an average of 13.4 ± 6.4 (SD) cases per month per rotating resident. A significant portion of neurosurgery residency programs in the United States incorporate VA rotations into resident training. Although rotation details vary from program-to-program, shared values include a strong operative experience, independent decision-making, and continuity of care. This analysis provides a comprehensive assessment of VA rotation structure across the country, which is valuable for programs considering implementing a VA rotation into their training program or modifying an existing rotation.

Rotational modulation in A and F stars: magnetic stellar spots or convective core rotation?

ABSTRACT The Kepler mission revealed a plethora of stellar variability in the light curves of many stars, some associated with magnetic activity or stellar oscillations. In this work, we analyse the periodic signal in 162 intermediate-mass stars, interpreted as Rossby modes and rotational modulation – the so-called hump and spike feature. We investigate whether the rotational modulation (spike) is due to stellar spots caused by magnetic fields or due to Overstable Convective (OsC) modes resonantly exciting g modes, with frequencies corresponding to the convective core rotation rate. Assuming that the spikes are created by magnetic spots at the stellar surface, we recover the amplitudes of the magnetic fields, which are in good agreement with theoretical predictions. Our data show a clear anticorrelation between the spike amplitudes and stellar mass and possibly a correlation with stellar age, consistent with the dynamo-generated magnetic fields theory in (sub)-surface convective layers. Investigating the harmonic behaviour, we find that for 125 stars neither of the two possible explanations can be excluded. While our results suggest that the dynamo-generated magnetic field scenario is more likely to explain the spike feature, we assess further work is needed to distinguish between the two scenarios. One method for ruling out one of the two explanations is to directly observe magnetic fields in hump and spike stars. Another would be to impose additional constraints through detailed modelling of our stars, regarding the rotation requirement in the OsC mode scenario or the presence of a convective-core (stellar age).

20 s Cadence TESS Photometry of HR 8799

We analyzed 20 s cadence Transiting Exoplanet Survey Satellite time-series photometry of the exoplanet host star HR 8799 collected in Sector 56. The amplitude spectrum shows Gamma Doradus (γ Dor) pulsations consistent with previous space-based photometry from MOST. Assuming that HR 8799 is a representative of γ Dor stars in the Kepler sample, the dominant dipole mode at 1.98 cycles day−1 implies a core rotation period of ∼0.7 day, which combined with and stellar radius measurements would result in a preliminary stellar inclination of ∼28° assuming rigid rotation. We find no significant residual photometric variation after removing the pulsation signal aside from a ∼9 days trend that is likely a systematic effect or an artifact from performing aggressive frequency subtraction in the presence of red noise.

ON THE STRESS WAVE IN THE EARTH'S BODY DUE TO DIFFERENTIAL ROTATION OF THE MANTLE AND CORE

Seismic energy generated as a result of elastic deformation of tectonic plates or blocks of rocks is realized by unloading at deformations exceeding the ultimate strength of rocks. The currently generally accepted earthquake source models are essentially local and are not able to establish a connection between seismic activity and some geophysical phenomena on a planetary scale. One of the features of seismicity is the recurrence of strong earthquakes in one place after a certain time interval. The purpose of this work is to study the influence of differential rotation of the solid core and mantle on seismic processes. It has now been established that the rate of rotation of the solid core exceeds the rate of rotation of the mantle. In relative motion, the solid core makes one revolution presumably in 200–400 years. Earlier, based on this, an explanation was proposed for long-period variations in the length of the day. In this paper, on a simple mechanical model, it is shown that the differential rotation of the elastic mantle and the solid core of an ellipsoidal shape generates a stress wave in the Earth's body. The idea of a stress wave is qualitatively new in the physical description of a seismic process. To demonstrate this effect, a solution is given to the problem of deformation of an elastic spherical shell interacting with a dumbbell-shaped solid body rotating in its cavity. When solving the problem, the apparatus of spherical vectors was used. The stress distribution of the spherical layer inside the shell is constructed and the areas of greatest risk are identified. It is shown that taking into account the differential rotation leads to the migration of the zones of greatest risk with a period equal to half the period of a complete rotation of the dumbbell relative to the shell (100–200 years). The results of the work can be useful in studying the relationship between seismicity and planetary rotation regimes.

Assessing Medical Students' Attitudes and Knowledge Regarding LGBTQ Health Needs Across the United States.

The lesbian, gay, bisexual, transgender, and queer/questioning (LGBTQ) community experiences health disparities. It is thus imperative that medical trainees receive training in the care of LGBTQ community. The objective of this study was to identify gaps in knowledge and comfort among medical school students in providing care for the LGBTQ community. An online survey was administered to medical students at 3 institutions in the United States from December 2020 to March 2021. Using a Likert scale, the survey assessed attitudes, comfort, and knowledge in providing care for the LGBTQ community. The survey included questions for each specific LGBTQ population. Results were quantified using descriptive and stratified analyses, and an exploratory factor analysis was used to calculate attitude summary measure (ASM) scores. A total knowledge score was calculated, with higher values indicating greater knowledge. Among the 300 medical students who completed the survey, the majority were female (55.7%), White (54.7%), and heterosexual (64.3%). The majority of medical students felt comfortable (strongly agree/agree) participating in the care of lesbian (94.3%), gay (96.0%), and bisexual (96.3%) patients; this percentage dropped to 82.3% for non-binary and 71.3% for transgender patients. Only 27.0% of medical students reported confidence in their knowledge of health needs of transgender patients. LGBTQ self-identification, percent of core rotations completed in school, region of country, and friends and/or family who are part of the LGBTQ community were significantly associated with various ASM scores. Knowledge questions yielded high percentages of "neutral" responses, and medical students who identified as LGBTQ had significantly higher total knowledge scores. Overall, the surveyed medical students feel comfortable and willing to provide care for LGBTQ persons. But, there is limited knowledge about specific LGBTQ health needs. More education and training in the needs of transgender and non-binary patients, in particular, is indicated.

Darcy flow and heat transfer of nanoliquid within a porous annulus with incorporating magnetic terms

Current investigation was carried out to analyze the treatment of nanomaterial within a domain which experienced magnetic force. Outer rhombus wall is cold and the inner circle has uniform heat flux and due to these conditions, carrier fluid rotates counterclockwise. Darcy law was used for simulation and Joule heating was neglected in equations. Influences of parameters were discussed in plots and contours and CVFEM has been employed to reach such outputs. Rotational core becomes stronger with the rise of Ra while opposite results have been accomplished with the soar of Ha. In cases with higher values of shape factor, Nu has higher values and a similar trend is reported for Rd. Moreover, Nu experiences 30% reduction when Ha augments. This negative impact becomes more sensible when radiation terms are added in equations. Inclusion of nano powders has a favorable impact on Nu although it has a negative impact on temperature gradient.

Rapid decline in the lightcurves of luminous supernovae by jet-driven bipolar explosions

ABSTRACT We calculate the lightcurves of jet-driven bipolar core collapse supernova (CCSN) explosions into a bipolar circumstellar matter (CSM) and show that an equatorial observer finds the lightcurves to possess a rapid, and even an abrupt drop. The scenario that might lead to such an explosive morphology is a common envelope evolution (CEE), where shortly before the CCSN explosion the red-supergiant progenitor interacts with a more compact companion that spirals-in and spins-up the core. The companion can be a main sequence star, a neutron star, or a black hole. The binary interaction ejects a shell through an intensive wind and the CEE ejects a denser gas in the equatorial plane. We assume that the companion accretes mass and launches jets. We conduct three-dimensional (3D) hydrodynamical simulations where we launch weak jets, the shaping jets, into the dense shell and show that the interaction forms a bipolar CSM. As a result of the rapid pre-collapse core rotation jets drive the CCSN explosion. We simulate the interaction of the jets with the bipolar CSM and use a simple scheme to calculate the lightcurves. We show that the abrupt drop in the lightcurve of an observer not too close to the polar directions can account for the lightcurve of the hydrogen poor luminous supernova (LSN) SN 2018don.

Improved asteroseismic inversions for red-giant surface rotation rates

Context. Asteroseismic observations of internal stellar rotation have indicated a substantial lack of angular momentum transport in theoretical models of subgiant and red-giant stars. Accurate core and surface rotation rate measurements are therefore needed to constrain the internal transport processes included in the models. Aims. We eliminate substantial systematic errors of asteroseismic surface rotation rates found in previous studies. Methods. We propose a new objective function for the optimally localised averages method of rotational inversions for red-giant stars, which results in more accurate envelope rotation rate estimates obtained from the same data. We use synthetic observations from stellar models across a range of evolutionary stages and masses to demonstrate the improvement. Results. We find that our new inversion technique allows us to obtain estimates of the surface rotation rate that are independent of the core rotation. For a star at the base of the red-giant branch, we reduce the systematic error from about 20% to a value close to 0, assuming constant envelope rotation. We also show the equivalence between this method and the method of linearised rotational splittings. Conclusions. Our new rotational inversion method substantially reduces the systematic errors of red-giant surface rotation rates. In combination with independent measures of the surface rotation rate, this will allow better constraints to be set on the internal rotation profile. This will be a very important probe for further constraining the internal angular momentum transport along the lower part of the red-giant branch.

A new scenario for magnetar formation: Tayler-Spruit dynamo in a proto-neutron star spun up by fallback

Magnetars are isolated young neutron stars characterised by the most intense magnetic fields known in the Universe, which power a wide variety of high-energy emissions from giant flares to fast radio bursts. The origin of their magnetic field is still a challenging question. In situ magnetic field amplification by dynamo action could potentially generate ultra-strong magnetic fields in fast-rotating progenitors. However, it is unclear whether the fraction of progenitors harbouring fast core rotation is sufficient to explain the entire magnetar population. To address this point, we propose a new scenario for magnetar formation involving a slowly rotating progenitor, in which a slow-rotating proto-neutron star is spun up by the supernova fallback. We argue that this can trigger the development of the Tayler-Spruit dynamo while other dynamo processes are disfavoured. Using the findings of previous studies of this dynamo and simulation results characterising the supernova fallback, we derive equations modelling the coupled evolution of the proto-neutron star rotation and magnetic field. Their time integration for different accreted masses is successfully compared with analytical estimates of the amplification timescales and saturation value of the magnetic field. We find that the magnetic field is amplified within 20 − 40 s after the core bounce, and that the radial magnetic field saturates at intensities between ∼1013 and 1015 G, therefore spanning the full range of a magnetar’s dipolar magnetic fields. The toroidal magnetic field is predicted to be a factor of 10–100 times stronger, lying between ∼1015 and 3 × 1016 G. We also compare the saturation mechanisms proposed respectively by H.C. Spruit and J. Fuller, showing that magnetar-like magnetic fields can be generated for a neutron star spun up to rotation periods of ≲8 ms and ≲28 ms, corresponding to accreted masses of ≳ 4 × 10−2 M⊙ and ≳ 1.1 × 10−2 M⊙, respectively. Therefore, our results suggest that magnetars can be formed from slow-rotating progenitors for accreted masses compatible with recent supernova simulations and leading to plausible initial rotation periods of the proto-neutron star.

The spins of stripped B stars support magnetic internal angular momentum transport

In order to predict the spins of stellar remnants we need to understand the evolution of the internal rotation of stars, and to identify at which stage the rotation of the contracting cores of evolved stars decouples from their expanding envelopes. The donor stars of mass transferring binaries lose almost their entire envelope and may thus offer a direct view on their core rotation. After the mass transfer event they contract and fade rapidly, although they are well observable when caught in the short-lived B-star phase. The B-type primary of the galactic binary system LB-1, which was originally suggested to contain a massive black hole, is nicely explained as a stripped star accompanied by a fainter Be star. The narrow absorption lines in the primary’s spectrum signify extremely slow rotation, atypical of B-type main-sequence stars. Here we investigate the evolution of mass donors in generic grids of detailed binary evolution models, where both stars include differential rotation, internal angular momentum transport, and spin-orbit coupling. Whereas the mass gainers are typically spun-up during the mass transfer, we find that the spins of the stripped donor models depend sensitively on the employed mechanism for internal angular momentum transport. Purely hydrodynamic transport cannot explain the observed slow rotation, while models including magnetic angular momentum transport are able to reproduce the observed rotation of LB-1 and similar stars, independent of the initial rotation rate. In such models the spin of the white dwarfs that emerge at the end of the evolution is independent of the mass stripping. We find evidence that the mass transfer in LB-1 was moderately non-conservative.