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When a rotating neutron star loses angular momentum, the reduction in the centrifugal force makes it contract. This perturbs each fluid element, raising the local pressure and originating deviations from beta equilibrium that enhance the neutrino emissivity and produce thermal energy. This mechanism is named rotochemical heating and has previously been studied for neutron stars of non-superfluid matter, finding that they reach a quasi-steady state in which the rate that the spin-down modifies the equilibrium concentrations is the same to that of the neutrino reactions restoring the equilibrium. On the other hand, the neutron star interior is believed to contain superfluid nucleons, which affect the thermal evolution of the star by suppressing the neutrino reactions and the specific heat, and opening new Cooper pairing reactions. In this work we describe the thermal effects of Cooper pairing with spatially uniform energy gaps of neutrons and protons on rotochemical heating in millisecond pulsars (MSPs) when only modified Urca reactions are allowed. We find that the chemical imbalances grow up to a value close to the energy gaps, which is higher than the one of the nonsuperfluid case. Therefore, the surface temperatures predicted with Cooper pairing are higher and explain the recent measurement of MSP J0437–4715. [ABSTRACT FROM AUTHOR]

The thermal emission detected from the millisecond pulsar J0437-4715 is not explained by standard cooling models of neutron stars without a heating mechanism. We investigated three heating mechanisms controlled by the rotational braking of the pulsar: breaking of the solid crust, superfluid vortex creep, and non-equilibrium reactions (“rotochemical heating”). We find that the crust cracking mechanism does not produce detectable heating. Given the dependence of the heating mechanisms on spin-down parameters, which leads to different temperatures for different pulsars, we study the thermal evolution for two types of pulsars: young, slowly rotating “classical” pulsars and old, fast rotating millisecond pulsars (MSPs). We find that the rotochemical heating and vortex creep mechanism can be important both for classical pulsars and MSPs. [ABSTRACT FROM AUTHOR]

Stellar radiation zones are stable strongly stratified rotating magnetic regions. The buoyancy force, the Coriolis acceleration and the Lorentz force are thus ruling the gravity waves dynamics. In this work, we examine the behaviour of these waves in stellar interiors and we show how the approximations assumed in the non-magnetic case (for gravito-inertial waves) can be generalized. [ABSTRACT FROM AUTHOR]

The discovery of transiting extrasolar planets has enabled us to do a number of interesting studies. Transit photometry reveals the radius and the orbital inclination of transiting planets, which allows us to learn the true mass and density of the respective planets by the combined information from radial velocity (RV) measurements. In addition, follow-up observations of transiting planets, looking at such things as secondary eclipses, transit timing variations, transmission spectroscopy, and the Rossiter-McLaughlin effect, provide us information about their dayside temperatures, unseen bodies in systems, planetary atmospheres, and the obliquity of planetary orbits. Such observational information, which will provide us a greater understanding of extrasolar planets, is available only for transiting planets. Here, I briefly summarize what we can learn from transiting planets and introduce previous studies. [ABSTRACT FROM AUTHOR]

Today, the generation of magnetic fields in solar-type stars and its relation to activity and rotation can coherently be explained, although it is certainly not understood in its entirety. Rotation facilitates the generation of magnetic flux that couples to the stellar wind, slowing down the star. There are still many open questions, particularly at early phases (young age), and at very low mass. It is vexing that rotational braking becomes inefficient at the threshold to fully convective interiors, although no threshold in magnetic activity is seen, and the generation of large scale magnetic fields is still possible for fully convective stars. This article briefly outlines our current understanding of the rotation-magnetic field relation. [ABSTRACT FROM AUTHOR]

Rotational studies at different ages and masses are important for constraining the angular momentum evolution of young stellar objects (YSO). Of particular interest are the rotational studies of very low mass (VLM) stars and brown dwarfs (BDs), because few rotational periods are known in that mass range. We aim to extend these studies well down into the substellar regime, providing for the first time information on rotational periods for a large sample of VLM stars and BDs. This extensive rotational period study of YSOs in the 1 Myr old Orion Nebula Cluster (ONC) is based on a deep photometric monitoring campaign using the Wide Field Imager (WFI) camera on the ESO/MPG 2.2 m telescope on La Silla, Chile. Time series data with about 95 data points were taken over 19 nights. Accurate I-band photometry of 2908 stars was obtained within a magnitude range between 13 and 21 mag, i.e. three magnitudes deeper than the previous studies in the ONC ([11]). Two different power spectral analysis techniques were used to search for periodic variability. In addition, the χ2 variability test was used for the detection of irregular variables. We measured rotational periods of 487 objects with estimated masses between 0.5 M⊙ and 0.015 M⊙, 124 of which are BD candidates. This is by far the most extensive and complete rotational period data set for young VLM stars and BDs. Besides the periodic variables, 808 objects show strong non-periodic (i.e. irregular) brightness variations. We studied the dependence of the period distribution on the magnitude (mass) and variability level and compared the found period distribution with that of higher-mass objects in the ONC ([11]) and with the rotational data set existing for the twice as old cluster NGC 2264 ([18]). We found that substellar objects rotate on average faster than the VLM stars, a trend which was already observed for higher mass stars. In addition, we found a clear dependence of the rotational periods on position within the field. Objects located inside the so-called Rcluster rotate on average slower, which can be explained by an age spread in the ONC, with a somewhat younger central region. The results of a comparison between the period distributions of the ONC and NGC 2264 strongly favours this hypothesis. Interesting correlations between rotational period and variability level were also found in both clusters, probably explained by different magnetic field topologies. [ABSTRACT FROM AUTHOR]

We present here the first results of a spectropolarimetric analysis of a small sample (∼20) of active stars ranging from spectral type M0 to M8, which are either fully-convective or possess a very small radiative core. This study aims at providing new constraints on dynamo processes in fully-convective stars. Results for stars with spectral types M0–M4—i.e. with masses above or just below the full convection threshold (≃0.35 M⊙)—are presented. Tomographic imaging techniques allow us to reconstruct the surface magnetic topologies from the rotationally modulated time-series of circularly polarised profiles. We find strong differences between partly and fully convective stars concerning magnetic field topology and characteristic scales, and differential rotation. Our results suggest that magnetic field generation in fully convective stars relies on different dynamo processes than those acting in the Sun and other partly convective stars, in agreement with theoretical expectations. [ABSTRACT FROM AUTHOR]

Proto-planetary and transitional disks which are detected in scattered light provide a critical test of the interpretation of circumstellar disks based on the IR spectral energy distribution (SED) alone. The disk inclination to the line-of-sight, outter radius, and surface brightness (SB) maps or radial SB distributions provided by spatially resolved imaging remove most of the degeneracies inherent in fitting IR SEDs without such observational constraints. We have imaged the disk of SAO 206462 (HD 135344 B) in 1.1 and 1.6 μm scattered light with HST/NICMOS and can trace the essentially face-on disk out to 1.05”. The cavity detected in sub-mm observations lies entirely under the NICMOS coronagraphic spot, a result consistent with the SED fitting if the star is at d = 140 pc. The SED had previously been classified as a Meeus Group I SED and interpreted as arising in a flared disk. Neither the 1.1 nor the 1.6 μm radial surface brightness profiles are consistent with a flared disk. A FUSE FUV spectrum demonstrates the presence of excess light in this system, confirming the accretion rate estimated from Brγ. Collectively, these data strengthen the interpretation of this system as a transitional disk. [ABSTRACT FROM AUTHOR]

We present first results from a multi-object spectroscopy campaign in IC2602, the Hyades, the Pleiades, and the Coma cluster using VLT/FLAMES. We analysed the data for radial velocity, rotational velocity (v sin i), and Hα-activity. Here, we highlight three aspects of this study in the context of rotational braking and the rotation-activity relationship among low mass stars. Finally we discuss the cluster membership of sources in IC2602. [ABSTRACT FROM AUTHOR]

We have obtained rotation periods for 95 stars in the young open cluster NGC 2362 (t∼5 Myr, d∼1.5 kpc) and find periods ranging from P<1 day to P∼14 days. These periods have been combined with flux measurements from archival Spitzer/IRAC images to examine the role disk-locking may play at this age. [ABSTRACT FROM AUTHOR]

Using numerical simulations of magnetized stellar winds, we carry out a parameter study to find the dependence of the stellar wind torque on observable parameters. We find that the power-law dependencies of the torque on parameters is significantly different than what has been used in all spin evolution models to date. [ABSTRACT FROM AUTHOR]

Using the FLAMES multi-object spectrometric facility of the 8.2 m VLT/UT2, we have obtained high-resolution spectra of 100 young, low and intermediate mass pre-main-sequence stars in the Orion Nebula Cluster. The X-ray properties of all our targets are comprehensively characterised in the Chandra Orion Ultradeep Project (COUP). We have used synthetic model spectra to determine effective surface temperatures (Teff), radial velocities (vrad), projected rotational velocities (v sin i) and measures of the Hα emission (EW). The high-resolution spectra also show that several targets previously treated as single stars in the literature are double-lined spectroscopic binaries. We study the relationship between rotation and X-ray luminosity for our targets and find a suggestion of inhibited X-ray emission in the most rapid rotators. We will show the dependence of X-ray luminosity as a function of stellar rotation and mass, and outline the implications of these results for dynamo activity in pre-main sequence stars. [ABSTRACT FROM AUTHOR]

Rotation is a key parameter in the evolution of stars. From 1 Myr (the age of the ONC) to 4.5 Gyr (the age of the Sun), solar-like stars lose about 1–2 orders of specific angular momentum. The main agents for this rotational braking are believed to be star-disk interaction and magnetically powered stellar winds. Over the last decade, the observational fundament to probe the stellar spindown has dramatically improved. Significant progress has been made in exploring the underlying physical causes of the rotational braking. Parameterized models combining the effects of star-disk interaction, winds, and pre-main sequence contraction are able to reproduce the main features of the rotational data for stars spanning more than 3 orders of magnitude in age. This has allowed us to constrain stellar ages based on the rotation rates (‘gyrochronology’). One main challenge for future work is to extend this type of analysis to the substellar mass range, where the rotational database is still sparse. More theoretical and observational work is required to explore the physics of the braking processes, aiming to explain rotational evolution from first principles. In this review for Cool Stars 15, I will summarize the status quo and the recent developments in the field. [ABSTRACT FROM AUTHOR]

We have examined the relationship between rotation and activity in 14 late-type (M6–M7) M dwarfs, using high resolution spectra taken at the Keck Observatory and flux-calibrated spectra from the Sloan Digital Sky Survey. Most are inactive at a spectral type where Hα emission has previously seen to be very common. We used the cross-correlation technique to quantify the rotational broadening; six of the stars in our sample have v sin i>=3.5 kms-1. Three of these stars do not exhibit Hα emission, despite rotating at velocities where previous work has observed strong levels of magnetic field and stellar activity. Our results suggest that rotation and activity in late-type M dwarfs may not always be linked, and open several addtional possibilities including a rotation dependant activity threshold, or a Maunder-minimum phenomenon in fully convective stars. [ABSTRACT FROM AUTHOR]

The dustiest known main-sequence star, BD +20 307, is actually a double-lined binary with a period of 3.4202 days and a circular orbit. The system is also metal poor with [Fe/H] = -0.4. The components are late-F and early-G dwarfs and have a mass ratio of 1.07. The photometric period of about 3.5 days indicates that the components are synchronously rotating. The metal poor, binary nature invalidates the idea that the object is a very young single star with a warm planet-making dust disk. Instead, the metal poor nature of the system and the lithium abundances of the components argue that the system is likely several billion years old, and so the dust disk results from the recent collision of two planetary mass rocky objects. Thus, BD +20 307 may well be the first known system with planets orbiting a close binary star. [ABSTRACT FROM AUTHOR]

The RACE-OC project, standing for Rotation and Activity Evolution in Open Clusters, is a long-term project aimed at studying the evolution of rotation and magnetic activity of late-type members of stellar open clusters. Magnetic fields play a fundamental role in altering the rotational properties of late-type stars. They are responsible, e.g., for angular momentum loss in the wind or its redistribution in the stellar interior. Magnetic fields in late-type stars and their related phenomena, such as photospheric cool spots and bright faculae, chromospheric plages, and X-ray emission, in turn depend on the stellar rotation which controls the efficiency of the hydromagnetic dynamo. Thus, the evolution of angular momentum and magnetic activity offer complementary approaches to understanding the mechanisms by which rotation and magnetic fields influence each other in late-type stars. [ABSTRACT FROM AUTHOR]

Intermittent accreting millisecond X-ray pulsars are an exciting new type of sources. Their pulsations appear and disappear either on timescales of hundreds of seconds or on timescales of days. The study of these sources add new observational constraints to present models that explain the presence or not of pulsations in neutron star LMXBs. In this paper we present preliminary results on spectral and aperiodic variability studies of all intermittent AMSPs, with a particular focus on the comparison between pulsating and non pulsating periods. [ABSTRACT FROM AUTHOR]

The key contribution of the discovery of nuclear-powered pulsations from the accretion-powered millisecond pulsars (AMPs) has been the establishment of burst oscillation frequency as a reliable proxy for stellar spin rate. This has doubled the sample of rapidly-rotating accreting neutron stars and revealed the unexpected absence of any stars rotating near the break-up limit. The resulting ‘braking problem’ is now a major concern for theorists, particularly given the possible role of gravitational wave emission in limiting spin. This, however, is not the only area where burst oscillations from the AMPs are having an impact. Burst oscillation timing is developing into a promising technique for verifying the level of spin variability in the AMPs (a topic of considerable debate). These sources also provide unique input to our efforts to understand the still-elusive burst oscillation mechanism. This is because they are the only stars where we can reliably gauge the role of uneven fuel deposition and, of course, the magnetic field. [ABSTRACT FROM AUTHOR]

The primary concern of this contribution is that accreting millisecond pulsars (AMXPs) show a much larger amount of information than is commonly believed. The three questions to be addressed are: 1. Is the apparent spin torque observed in AMXPs real ? 2. Why do we see correlations and anti-correlations between fractional amplitudes and timing residuals in some AMXPs ? 3. Why the timing residuals, the lightcurve and the 1Hz QPO in SAX J1808.4—3658 are related ? [ABSTRACT FROM AUTHOR]

We present a comprehensive timing study of the 2.5 ms pulsar SAX J1808.4—3658, a soft X-ray transient with a recurrence time of roughly 2 years. Using data from the Rossi X-ray Timing Explorer, we construct a phase-connected pulse timing solution for each of four observed outbursts during 1998–2005. We measure a long-term spin down with better than 6σ confidence. The rate is (-5.6±2.0)×10-16 Hz s-1, with most of the change occurring during quiescence, and most likely is due to the magnetic dipole torques from a B = 1.5×108 G field. We also find that the 2 hr binary orbital period is increasing at a rate of (3.5±0.2)×10-12 s s-1, although it is unclear whether this change reflects secular evolution or short-term variability. [ABSTRACT FROM AUTHOR]

Very massive primordial stars (140 M⊙⊙) are suggested to end their lives as pair-instability supernovae. Such an event can be traced by a typical chemical signature in low metallicity stars, but at the present time, this signature is lacking in the extremely metal-poor stars we are able to observe. Does it mean that those very massive objects did not form, contrarily to the primordial star formation scenarios? Could they avoid this tragical fate? We explore the effects of rotation, anisotropic mass loss and magnetic fields on the core size of a very massive Population III model, in order to check if its mass is sufficiently modified to prevent the pair instability. We obtain that a Population III model of 150 M⊙ with υ/υcrit = 0.56 computed with the inclusion of wind anisotropy and Tayler-Spruit dynamo avoids the pair instability explosion. [ABSTRACT FROM AUTHOR]

Recent observations by XMM-Newton detected rotational pulsations in the total brightness and spectrum of several neutron stars. To properly interpret the data, accurate modeling of neutron star emission is necessary. Detailed analysis of the shape and strength of the rotational variations allows a measurement of the surface composition and magnetic field, as well as constrains the nuclear equation of state. We discuss our models of the spectra and light curves of two of the most observed neutron stars, RX J1856.5–3754 and 1E 1207.4–5209, and discuss some implications of our results and the direction of future work. [ABSTRACT FROM AUTHOR]

We study the nature of non-axisymmetric dynamical instabilities in differentially rotating stars with both linear eigenmode analysis and hydrodynamic simulations in Newtonian gravity. We especially investigate the following three types of instability; the one-armed spiral instability, the low T/|W| bar instability, and the high T/|W| bar instability, where T is the rotational kinetic energy and W is the gravitational potential energy. The nature of the dynamical instabilities is clarified by using a canonical angular momentum as a diagnostic. We find that the one-armed spiral and the low T/|W| bar instabilities occur around the corotation radius, and they grow through the inflow of canonical angular momentum around the corotation radius. The result is a clear contrast to that of a classical dynamical bar instability in high T/|W|. We also discuss the feature of gravitational waves generated from these three types of instability. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The currently favored scenario for the progenitor evolution of Type Ia supernovae (SNe Ia) presumes that white dwarfs in close binary systems grow to the Chandrasekhar limit via mass accretion from their non-degenerate companions. However, the accreted hydrogen and/or helium usually participate thermally unstable or even violent nuclear reactions in a geometrically confined region, due to the compactness of the white dwarf. Since shell flashes induced by the thermal instability might induce significant loss of mass, efficient mass increase of white dwarfs by hydrogen and/or helium accretion has been seriously questioned. A good understanding of the stability of thermonuclear shell sources is therefore crucial in order to investigate the evolution of accreting white dwarfs as SNe Ia progenitors. Here, we present a quantitative criterion for the thermal stability of thermonuclear shell sources, and discuss the effects of rotation on the stability of helium shell burning in helium accreting CO white dwarfs with M ≈ 10-7...10-6 M⊙ yr-1. In particular, we show that, if the effects of rotation are properly considered, helium shell sources are significantly stabilized, which might increase the likelihood for accreting white dwarfs to grow to the Chandrasekhar limit. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Several works have recently shown that there is an important extra line-broadening (usually called macroturbulence) affecting the spectra of O and B Supergiants that adds to stellar rotation. So far, the only (very recent) physical explanation for the appearance of macroturbulence relates to oscillations. This is a plausible explanation, but no direct evidence confirming its validity has been presented yet. We recently started an observational project to obtain constraints on the time-scales of variability associated to this extra line-broadening and its possible origin. Our observational strategy consists of the study of a well selected group of O and B stars, for which we obtain time series of high-quality spectra. We present some preliminary results from our first campaign with FIES@NOT2.5 m. [ABSTRACT FROM AUTHOR]

The present work focuses on the discussion of the λ Bootis nature of the multiperiodic δ Scuti star HD 192640 (29 Cyg), through a comprehensive asteroseismic modelling. Some of the most recent asteroseismic tools are used to check whether the observed low metallicity is internal, i.e., intrinsic, present throughout the star, or due to superficial processes as accretion, diffusive settling, radiative levitation, mass loss, etc. The modelling method includes: 1) effects of rotation on equilibrium models, on the adiabatic oscillation spectrum, and its influence in multicolour observables, 2) non-adiabatic stability of radial and non-radial modes, 3) inclusion of the atmosphere-pulsation interaction for a more accurate multicolour mode identification. The analysis performed reveals that the models fulfilling all the constraints are those in the middle of the Main Sequence, with sub-solar metallicity, except for some other unlikely possibilities. Therefore this study does not support the idea of the λ Bootis stars being ZAMS or Pre-MS stars interacting with their primordial cloud of gas and dust, but suggests the explanation of their nature as sub-metallic MS objects. Nevertheless, more accurate multicolour photometric observations are required for a more conclusive study using the procedure presented here, since the observational errors are too large for a definitive rejection of any of the possible explanations. [ABSTRACT FROM AUTHOR]

The deconfinement phase transition will lead to the release of latent heat during spins down of neutron stars if the transition is the first-order one. We have investigated the thermal evolution of neutron stars undergoing such deconfinement phase transition. The results show that neutron stars may be heated to higher temperature. This feature could be particularly interesting for high temperature of low-magnetic field millisecond pulsar at late stage. [ABSTRACT FROM AUTHOR]

When a rotating neutron star loses angular momentum, the reduction of the centrifugal force makes it contract. This perturbs each fluid element, raising the local pressure and originating deviations from beta equilibrium, inducing reactions that release heat (rotochemical heating). This effect has previously been studied by Fernández and Reisenegger for neutron stars of non-superfluid matter and by Petrovich and Reisenegger for superfluid matter, finding that the system in both cases reaches a quasi-steady state, corresponding to a partial equilibration between compression, due to the loss of angular momentum, and reactions that try to restore the equilibrium. However, Petrovich and Reisenegger assumes a constant value of the superfluid energy gap, whereas theoretical models predict density-dependent gap amplitudes, and therefore gaps that depend on the location in the star. In this work, we try to discriminate between several proposed gap models, comparing predicted surface temperatures to the value measured for the nearest millisecond pulsar, J0437-4715. [ABSTRACT FROM AUTHOR]

We continue the pulsar magnetosphere calculations of Contopoulos, Kazanas and Fendt. The assumptions of the model are listed and illustrated. Different grids from 30×30 up to 150×150 are used, though high resolution is not so important for determining the source function if only an appropriate convergence scheme is used (substantially different from the approach, to be published elsewhere). We compactify the physical space to carry out integration on a finite grid. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]