Posts Tagged surface temperature

Recent Postings from surface temperature

Thermal properties of Rhea's Poles: Evidence for a Meter-Deep Unconsolidated Subsurface Layer

Cassini's Composite Infrared Spectrometer (CIRS) observed both of Rhea's polar regions during two flybys on 2013/03/09 and 2015/02/10. The results show Rhea's southern winter pole is one of the coldest places directly observed in our solar system: temperatures of 25.4+/-7.4 K and 24.7+/-6.8 K are inferred. The surface temperature of the northern summer pole is warmer: 66.6+/-0.6 K. Assuming the surface thermophysical properties of both polar regions are comparable then these temperatures can be considered a summer and winter seasonal temperature constraint for the polar region. These observations provide solar longitude coverage at 133 deg and 313 deg for the summer and winter poles respectively, with additional winter temperature constraint at 337 deg. Seasonal models with bolometric albedos of 0.70-0.74 and thermal inertias of 1-46 MKS can provide adequate fits to these temperature constraints. Both these albedo and thermal inertia values agree (within error) with those previously observed on both Rhea's leading and trailing hemispheres. Investigating the seasonal temperature change of Rhea's surface is particularly important, as the seasonal wave is sensitive to deeper surface temperatures (~10cm to m) than the more commonly reported diurnal wave (<1cm). The low thermal inertia derived here implies that Rhea's polar surfaces are highly porous even at great depths. Analysis of a CIRS 10 to 600 cm-1 stare observation, taken between 16:22:33 and 16:23:26 UT on 2013/03/09 centered on 71.7 W, 58.7 S provides the first analysis of a thermal emissivity spectrum on Rhea. The results show a flat emissivity spectrum with negligible emissivity features. A few possible explanations exist for this flat emissivity spectrum, but the most likely for Rhea is that the surface is both highly porous and composed of small particles (less than approximately 50 um).

In hot water: effects of temperature-dependent interiors on the radii of water-rich super-Earths

Observational advancements are leading to increasingly precise measurements of super-Earth masses and radii. Such measurements are used in internal structure models to constrain interior compositions of super-Earths. It is now critically important to quantify the effect of various model assumptions on the predicted radii. In particular, models often neglect thermal effects, a choice justified by noting that the thermal expansion of a solid Earth-like planet is small. However, the thermal effects for water-rich interiors may be significant. We have systematically explored the extent to which thermal effects can influence the radii of water-rich super-Earths over a wide range of masses, surface temperatures, surface pressures and water mass fractions. We developed temperature-dependent internal structure models of water-rich super-Earths that include a comprehensive temperature-dependent water equation of state. We found that thermal effects induce significant changes in their radii. For example, for super-Earths with 10 per cent water by mass, the radius increases by up to 0.5$\,$R$_\oplus$ when the surface temperature is increased from 300 to 1000$\,$K, assuming a surface pressure of 100$\,$bar and an adiabatic temperature gradient in the water layer. The increase is even larger at lower surface pressures and/or higher surface temperatures, while changing the water fraction makes only a marginal difference. These effects are comparable to current super-Earth radial measurement errors, which can be better than 0.1$\,$R$_\oplus$. It is therefore important to ensure that the thermal behaviour of water is taken into account when interpreting super-Earth radii using internal structure models.

Seismology of Rapidly Rotating Accreting White Dwarfs

A number of White Dwarfs (WDs) in cataclysmic binaries have shown brightness variations consistent with non-radial oscillations as observed in isolated WDs. A few objects have been well-characterized with photometric campaigns in the hopes of gleaning information about the mass, spin, and possibly internal structural characteristics. The novel aspect of this work is the possiblity to measure or constrain the interior structure and spin rate of WDs which have spent gigayears accreting material from their companion, undergoing thousands of nova outbursts in the process. In addition, variations in the surface temperature affect the site of mode driving, and provide unique and challenging tests for mode driving theories previously applied to isolated WD's. Having undergone long-term accretion, these WDs are expected to have been spun up. Spin periods in the range 60-100 seconds have been measured by other means for two objects, GW Lib and V455 And. Compared to typical mode frequencies, the spin frequency may be similar or higher, and the Coriolis force can no longer be treated as a small perturbation on the fluid motions. We present the results of a non-perturbative calculation of the normal modes of these WDs, using interior thermal structures appropriate to accreting systems. This includes a discussion of the surface brightness distributions, which are strongly modified from the non-rotating case. Using the measured spin period of approximately 100 seconds, we show that the observed pulsations from GW Lib are consistent with the three lowest azimuthal order rotationally modified modes that have the highest frequency in the stellar frame. The high frequencies are needed for the convective driving, but are then apparently shifted to lower frequencies by a combination of their pattern motion and the WD rotation.

Near infrared spectroscopy of M dwarfs. III. Carbon and oxygen abundances in late M dwarfs including the dusty rapid rotator 2MASSI J1835379+325954

Carbon and oxygen abundances of eight late M dwarfs are determined based on the near IR spectra of medium resolution. Seven objects with T_eff above 2600K are analyzed with the dust-free models. The M8.5 dwarf 2MASSI J1835379+325954 whose T_eff is 2275K is analyzed by the dusty model, in which the surface temperature is higher by about 600K due to the blanketing effect of the dust, and C and O abundances are higher by 0.25 and 0.15dex, respectively, compared to the analysis by the dust-free model. Once dust forms in the photosphere, the dust works as a kind of thermostat and temperatures of the surface layers remain nearly the same as the condensation temperatures of the dust grains. For this reason, the temperatures of the surface layers of the dusty dwarfs are not sensitive to the fundamental parameters including T_eff. Also, 2MASS J1835379 +325954 is a rapid rotator, for which its EWs are thought to remain unchanged by the rotational broadening. This is, however, true only when the true continuum is well defined. Otherwise, the pseudo-continuum level depends on the rotational velocity and hence the EWs as well. For this reason, the derived abundances depend on the rotational velocity assumed: For the values of V_rot*sin(i)=37.6 and 44.0km/s available in the literature, the derived C and O abundances differ by 0.23 and 0.14dex, respectively, and we find that the higher value provides a better account of the observed spectrum. The resulting C and O abundances in our late M dwarfs show no systematic difference from our results for the early and middle M dwarfs, and confirm the higher O/C ratio at the lower metallicity. In late M dwarfs, CO and H2O remain as excellent abundance indicators of C and O, respectively, except for additional uncertainty due to the complexity associated with the dust formation in the latest M dwarfs.

Hydrodynamical wind on vertically self-gravitating ADAFs in the presence of toroidal magnetic field

We present the effect of a hydrodynamical wind on the structure and the surface temperature of a vertically self-gravitating magnetized ADAFs using self-similar solutions. Also a model for an axisymmetric, steady-state, vertically self-gravitating hot accretion flow threaded by a toroidal magnetic field has been formulated. The model is based on $\alpha-$prescription for turbulence viscosity. It is found that the thickness and radial velocity of the disc are reduced significantly as wind gets stronger. In particular, the solutions indicated that the wind and advection have the same effects on the structure of the disc. We also find that in the optically thin ADAF becomes hotter by including the wind parameter and the self-gravity parameter.

Thermal Conductivity Of Rubble Piles

Rubble piles are a common feature of solar system bodies. They are composed of monolithic elements of ice or rock bound by gravity. Voids occupy a significant fraction of the volume of a rubble pile. They can exist up to pressure $P\approx \epsy\mu$, where $\epsy$ is the monolithic material's yield strain and $\mu$ its rigidity. At low $P$, contacts between neighboring elements are confined to a small fraction of their surface areas. As a result, the effective thermal conductivity of a rubble pile, $\kcon\approx k(P/(\epsy\mu))^{1/2}$, can be orders of magnitude smaller than, $k$, the thermal conductivity of its monolithic elements. In a fluid-free environment, only radiation can transfer energy across voids. It contributes an additional component, $\krad=16\ell\sigma T^3/3$, to the total effective conductivity, $\keff=\kcon +\krad$. Here $\ell$, the inverse of the opacity per unit volume, is of order the size of the elements and voids. An important distinction between $\kcon$ and $\krad$ is that the former is independent of the size of the elements whereas the latter is proportional to it. Our expression for $\keff$ provides a good fit to the depth dependence of thermal conductivity in the top $140\,\mathrm{cm}$ of the lunar regolith. It also offers a good starting point for detailed modeling of thermal inertias for asteroids and satellites. Measurement of the response of surface temperature to variable insolation is a valuable diagnostic of a regolith. There is an opportunity for careful experiments under controlled laboratory conditions to test models of thermal conductivity such as the one we outline.

Formation of Massive Primordial Stars: Intermittent UV Feedback with Episodic Mass Accretion

We present coupled stellar evolution (SE) and 3D radiation-hydrodynamic (RHD) simulations of the evolution of primordial protostars, their immediate environment, and the dynamic accretion history under the influence of stellar ionizing and dissociating UV feedback. Our coupled SE-RHD calculations result in a wide diversity of final stellar masses covering $10~M_\odot \lesssim M_* \lesssim 10^3~M_\odot$. The formation of very massive ($\gtrsim 250~M_\odot$) stars is possible under weak UV feedback, whereas ordinary massive (a few $\times 10~M_\odot$) stars form when UV feedback can efficiently halt the accretion. Weak UV feedback occurs in cases of variable accretion, in particular when repeated short accretion bursts temporarily exceed $0.01~M_\odot~{\rm yr}^{-1}$, causing the protostar to inflate. In the bloated state, the protostar has low surface temperature and UV feedback is suppressed until the star eventually contracts, on a thermal adjustment timescale, to create an HII region. If the delay time between successive accretion bursts is sufficiently short, the protostar remains bloated for extended periods, initiating at most only short periods of UV feedback. Disk fragmentation does not necessarily reduce the final stellar mass. Quite the contrary, we find that disk fragmentation enhances episodic accretion as many fragments migrate inward and are accreted onto the star, thus allowing continued stellar mass growth under conditions of intermittent UV feedback. Our results suggest that, together with a number of ordinary massive stars, very massive stars can occur in significant numbers in the early universe. This may explain the recently reported peculiar abundance pattern of a Galactic metal-poor star, possibly the observational signature of very massive precursor primordial stars.

Entropy Product Formula for spinning BTZ Black Hole [Cross-Listing]

We investigate the thermodynamic properties of inner and outer horizons in the background of spinning BTZ(Ba\~{n}ados,Teitelboim and Zanelli) black hole. We compute the \emph{horizon radii product, the entropy product, the surface temperature product, the Komar energy product and the specific heat product} for both the horizons. We observe that the entropy product is \emph{universal}(mass-independent), whereas the surface temperature product, Komar energy product and specific heat product are \emph{not universal} because they all depends on mass parameter. We also show that the \emph{First law} of black hole thermodynamics and \emph {Smarr-Gibbs-Duhem } relations hold for inner horizon as well as outer horizon. The Christodoulou-Ruffini mass formula is derived for both the horizons. We further study the \emph{stability} of such black hole by computing the specific heat for both the horizons. It has been observed that under certain condition the black hole possesses \emph{second order phase transition}.

Evolution of an Early Titan Atmosphere: Comment

Escape of an early atmosphere from Titan, during which time NH3 could be converted by photolysis into the present N2 dominated atmosphere, is an important problem in planetary science. Recently Gilliam and Lerman (2014) estimated escape driven by the surface temperature and pressure, which we show gave loss rates that are orders of magnitude too large. Their model, related to Jeans escape from an isothermal atmosphere, was used to show that escape driven only by surface heating would deplete the atmospheric inventory of N for a suggested Titan accretion temperature of ~355 K. Therefore, they concluded that the accretion temperature must be lower in order to retain the present Titan atmosphere. Here we show that the near surface atmospheric temperature is essentially irrelevant for determining the atmospheric loss rate from Titan and that escape is predominantly driven by solar heating of the upper atmosphere. We also give a rough estimate of the escape rate in the early solar system (~10^4 kg/s) consistent with an inventory of nitrogen being available over the time period suggested by Atreya et al. (1978) for conversion of NH3 into N2.

Atmospheric Escape by Magnetically Driven Wind from Gaseous Planets II --Effects of Magnetic Diffusion--

We investigate roles of Alfvenic waves in the weakly-ionized atmosphere of hot Jupiters by carrying out non-ideal magnetohydrodynamic (MHD) simulations with Ohmic diffusion in one-dimensional magnetic flux tubes. Turbulence at the surface excites Alfven waves and they propagate upward to drive hot (~ 10^4 K) outflows. The magnetic diffusion plays an important role in the dissipation of the Alfvenic waves in the weakly ionized atmosphere of hot Jupiters. The mass-loss rate of the spontaneously driven planetary wind is considerably reduced, in comparison with that obtained from ideal MHD simulations because the Alfvenic waves are severely damped at low altitudes in the atmosphere, whereas the wave heating is still important in the heating of the upper atmosphere. Dependence on the surface temperature, planetary radius, and velocity dispersion at the surface is also investigated. We find an inversion phenomenon of the transmitted wave energy flux; the energy flux carried by Alfven waves in the upper atmosphere has a nonmonotonic correlation with the input energy flux from the surface in a certain range of the surface temperature because the resistivity is determined by the global physical properties of the atmosphere in a complicated manner. We also point out that the heating and mass loss are expected only in limited zones if the open magnetic field is confined in the limited regions.

Infrared Variability from Circumbinary Disc Temperature Modulations

The temperature of a circumbinary disc edge should undulate due to variations in illumination as a function of binary orbital phase. We explore circumbinary disc temperature variations as a source of broad-band infrared light curve variability. Approximating the wall of a circumbinary disc edge as a wide optically thick cylinder with surface temperature dependent on its illumination, we find that a binary comprised of 1 M$_\odot$ and 0.5 M$_\odot$ pre-main sequence stars in a $\sim$15.5 day period, would exhibit the largest amplitude variations of $\sim$9% at 3.77 and 4.68 {\mu}m as seen by a distant observer. The amplitude of variations and shape of the light curve is sensitive to the luminosity and mass ratios of the stars in the binary, the radius of the circumbinary disc clearing, the binary separation, and the orbital inclination. The light curve variations are smooth and very red with a non-sinusoidal shape for most of the parameter space explored. Possible morphologies include a single peak with a flat region, two peaks of different heights or a single dip.

A versatile numerical method for obtaining structures of rapidly rotating baroclinic stars: self-consistent and systematic solutions with shellular-type rotation [Replacement]

This paper develops a novel numerical method for obtaining structures of rapidly rotating stars based on a self-consistent field scheme. The solution is obtained iteratively. Both rapidly rotating barotropic and baroclinic equilibrium states are calculated self-consistently using this method. Two types of rotating baroclinic stars are investigated by changing the isentropic surfaces inside the star. Solution sequences of these are calculated systematically and critical rotation models beyond which no rotating equilibrium state exists are also obtained. All of these rotating baroclinic stars satisfy necessarily the Bjerknes-Rosseland rules. Self-consistent solutions of baro-clinic stars with shellular-type rotation are successfully obtained where the isentropic surfaces are oblate and the surface temperature is hotter at the poles than at the equator if it is assumed that the star is an ideal gas star. These are the first self-consistent and systematic solutions of rapidly rotating baroclinic stars with shellular-type rotations. Since they satisfy the stability criterion due to their rapid rotation, these rotating baroclinic stars would be dynamically stable. This novel numerical method and the solutions of the rapidly rotating baroclinic stars will be useful for investigating stellar evolution with rapid rotations.

Testing the Early Mars H2-CO2 Greenhouse Hypothesis with a 1-D Photochemical Model

A recent study by Ramirez et al. (2014) demonstrated that an atmosphere with 1.3-4 bar of CO2 and H2O, in addition to 5-20% H2, could have raised the mean annual and global surface temperature of early Mars above the freezing point of water. Such warm temperatures appear necessary to generate the rainfall (or snowfall) amounts required to carve the ancient martian valleys. Here, we use our best estimates for early martian outgassing rates, along with a 1-D photochemical model, to assess the conversion efficiency of CO, CH4, and H2S to CO2, SO2, and H2. Our outgassing estimates assume that Mars was actively recycling volatiles between its crust and interior, as Earth does today. H2 production from serpentinization and deposition of banded iron-formations is also considered. Under these assumptions, maintaining an H2 concentration of ~1-2% by volume is achievable, but reaching 5% H2 requires additional H2 sources or a slowing of the hydrogen escape rate below the diffusion limit. If the early martian atmosphere was indeed H2-rich, we might be able to see evidence of this in the rock record. The hypothesis proposed here is consistent with new data from the Curiosity Rover, which show evidence for a long-lived lake in Gale Crater near Mt. Sharp. It is also consistent with measured oxygen fugacities of martian meteorites, which show evidence for progressive mantle oxidation over time.

Thermodynamic Product Formula for Ho\v{r}ava Lifshitz Black Hole

We examine the thermodynamic properties of inner and outer horizons in the background of Ho\v{r}ava Lifshitz black hole. We compute the \emph{horizon radii product, the surface area product, the entropy product, the surface temperature product, the Komar energy product and the specific heat product} for both the horizons of said black hole. We show that surface area product, entropy product and irreducible mass product are \emph{universal} quantities, whereas the surface temperature product, Komar energy product and specific heat product are \emph{not universal} quantities because they all are depends on mass parameter. We also observe that the \emph{First law} of black hole thermodynamics and \emph {Smarr-Gibbs-Duhem } relations do not hold for this black hole. The underlying reason behind this failure due to the scale invariance of the coupling constant. We further derive the \emph{Smarr mass formula} and \emph{Christodolou-Ruffini mass formula} for such black hole spacetime. Moreover we study the stability of such black hole by computing the specific heat for both the horizons. It has been observed that under certain condition the black hole possesses second order phase transition.

Thermodynamic Product Formula for Ho\v{r}ava Lifshitz Black Hole [Cross-Listing]

We examine the thermodynamic properties of inner and outer horizons in the background of Ho\v{r}ava Lifshitz black hole. We compute the \emph{horizon radii product, the surface area product, the entropy product, the surface temperature product, the Komar energy product and the specific heat product} for both the horizons of said black hole. We show that surface area product, entropy product and irreducible mass product are \emph{universal} quantities, whereas the surface temperature product, Komar energy product and specific heat product are \emph{not universal} quantities because they all are depends on mass parameter. We also observe that the \emph{First law} of black hole thermodynamics and \emph {Smarr-Gibbs-Duhem } relations do not hold for this black hole. The underlying reason behind this failure due to the scale invariance of the coupling constant. We further derive the \emph{Smarr mass formula} and \emph{Christodolou-Ruffini mass formula} for such black hole spacetime. Moreover we study the stability of such black hole by computing the specific heat for both the horizons. It has been observed that under certain condition the black hole possesses second order phase transition.

Characterizing the Habitable Zones of Exoplanetary Systems with a Large Ultraviolet/Visible/Near-IR Space Observatory

Understanding the surface and atmospheric conditions of Earth-size, rocky planets in the habitable zones (HZs) of low-mass stars is currently one of the greatest astronomical endeavors. Knowledge of the planetary effective surface temperature alone is insufficient to accurately interpret biosignature gases when they are observed in the coming decades. The UV stellar spectrum drives and regulates the upper atmospheric heating and chemistry on Earth-like planets, is critical to the definition and interpretation of biosignature gases, and may even produce false-positives in our search for biologic activity. This white paper briefly describes the scientific motivation for panchromatic observations of exoplanetary systems as a whole (star and planet), argues that a future NASA UV/Vis/near-IR space observatory is well-suited to carry out this work, and describes technology development goals that can be achieved in the next decade to support the development of a UV/Vis/near-IR flagship mission in the 2020s.

Modeling the surface temperature of Earth-like planets

We introduce a novel Earth-like planet surface temperature model (ESTM) for habitability studies based on the spatial-temporal distribution of planetary surface temperatures. The ESTM adopts a surface Energy Balance Model complemented by: radiative-convective atmospheric column calculations, a set of physically-based parameterizations of meridional transport, and descriptions of surface and cloud properties more refined than in standard EBMs. The parameterization is valid for rotating terrestrial planets with shallow atmospheres and moderate values of axis obliquity (epsilon >= 45^o). Comparison with a 3D model of atmospheric dynamics from the literature shows that the equator-to-pole temperature differences predicted by the two models agree within ~5K when the rotation rate, insolation, surface pressure and planet radius are varied in the intervals 0.5 <= Omega/Omega_o <= 2, 0.75 <= S/S_o <= 1.25, 0.3 <= p/(1 bar) <= 10, and 0.5 <= R/R_o <= 2, respectively. The ESTM has an extremely low computational cost and can be used when the planetary parameters are scarcely known (as for most exoplanets) and/or whenever many runs for different parameter configurations are needed. Model simulations of a test-case exoplanet (Kepler-62e) indicate that an uncertainty in surface pressure within the range expected for terrestrial planets may impact the mean temperature by ~60 K. Within the limits of validity of the ESTM, the impact of surface pressure is larger than that predicted by uncertainties in rotation rate, axis obliquity, and ocean fractions. We discuss the possibility of performing a statistical ranking of planetary habitability taking advantage of the flexibility of the ESTM.

Doppler Imaging of LQ Hya for 1998-2002

We study the spot distribution on the surface of LQ~Hya during the observing seasons October 1998 -- November 2002. We look for persistent active longitudes, trends in the level of spot activity and compare to photometric data, specifically to the derived time epochs of the lightcurve minima. We apply the Doppler Imaging technique on photospheric spectral lines using an inversion code to retrieve images of the surface temperature. We present new temperature maps using multiple spectral lines for a total of 7 seasons. We calculate spot coverage fractions from each map, and as a result we find a general trend that is interpreted to be an indication of a spot cycle. There is a minimum during the observing season of March 1999. After this the activity increases until November 2000, followed by a general decrease in activity again. We find no evidence for active longitudes persisting over multiple observing seasons. The spot activity appears to be concentrated to two latitude regions. The high latitude spots are particularly strong when the spot coverage is at a maximum. Using the currently accepted rotation period, we find spot structures to show a trend in the phase-time plot, indicative of a need for a longer period. We conclude that the long-term activity of LQ~Hya is more chaotic than that of some magnetically active binary stars analyzed with similar methods, but still with clear indications of an activity cycle.

Seismic Sounding of Convection in the Sun

Our Sun, primarily composed of ionized hydrogen and helium, has a surface temperature of 5777~K and a radius $R_\odot \approx 696,000$ km. In the outer $R_\odot/3$, energy transport is accomplished primarily by convection. Using typical convective velocities $u\sim100\,\rm{m\,s^{-1}}$ and kinematic viscosities of order $10^{-4}$ m$^{2}$s$^{-1}$, we obtain a Reynolds number $Re \sim 10^{14}$. Convection is thus turbulent, causing a vast range of scales to be excited. The Prandtl number, $Pr$, of the convecting fluid is very low, of order $10^{-7}$\,--\,$10^{-4}$, so that the Rayleigh number ($\sim Re^2 Pr$) is on the order of $10^{21}\,-\,10^{24}$. Solar convection thus lies in extraordinary regime of dynamical parameters, highly untypical of fluid flows on Earth. Convective processes in the Sun drive global fluid circulations and magnetic fields, which in turn affect its visible outer layers ("solar activity") and, more broadly, the heliosphere ("space weather"). The precise determination of the depth of solar convection zone, departures from adiabaticity of the temperature gradient, and the internal rotation rate as a function of latitude and depth are among the seminal contributions of helioseismology towards understanding convection in the Sun. Contemporary helioseismology, which is focused on inferring the properties of three-dimensional convective features, suggests that transport velocities are substantially smaller than theoretical predictions. Furthermore, helioseismology provides important constraints on the anisotropic Reynolds stresses that control the global dynamics of the solar convection zone. This review discusses the state of our understanding of convection in the Sun, with a focus on helioseismic diagnostics. We present our considerations with the interests of fluid dynamicists in mind.

Gravitational collapse, shear-free anisotropic radiating star [Replacement]

We present a class of exact solutions of Einstein field equations for a shear-free spherically symmetric anisotropic fluid undergoing radial heat flow. The interior metric fulfilled all the relevant physical and thermodynamic conditions and matched with Vaidya exterior metric over the boundary. Initially the interior solutions represent a static configuration of dissipative fluid which then gradually starts evolving into radiating collapse. The apparent luminosity observed by the distant observer at rest at infinity and the effective surface temperature are zero in remote past at the instance when collapse begins and at the stage when collapsing configuration reach the horizon of the black hole.

Gravitational collapse, shear-free anisotropic radiating star [Replacement]

We present a class of exact solutions of Einstein field equations for a shear-free spherically symmetric anisotropic fluid undergoing radial heat flow. The interior metric fulfilled all the relevant physical and thermodynamic conditions and matched with Vaidya exterior metric over the boundary. Initially the interior solutions represent a static configuration of dissipative fluid which then gradually starts evolving into radiating collapse. The apparent luminosity observed by the distant observer at rest at infinity and the effective surface temperature are zero in remote past at the instance when collapse begins and at the stage when collapsing configuration reach the horizon of the black hole.

Gravitational collapse, shear-free anisotropic radiating star [Replacement]

We present a class of exact solutions of Einstein field equations for a shear-free spherically symmetric anisotropic fluid undergoing radial heat flow. The interior metric fulfilled all the relevant physical and thermodynamic conditions and matched with Vaidya exterior metric over the boundary. Initially the interior solutions represent a static configuration of dissipative fluid which then gradually starts evolving into radiating collapse. The apparent luminosity observed by the distant observer at rest at infinity and the effective surface temperature are zero in remote past at the instance when collapse begins and at the stage when collapsing configuration reach the horizon of the black hole.

Gravitational collapse, shear-free anisotropic radiating star

We present a class of exact solutions of Einstein field equations for a shear-free spherically symmetric anisotropic fluid undergoing radial heat flow. The interior metric fulfilled all the relevant physical and thermodynamic conditions and matched with Vaidya exterior metric over the boundary. Initially the interior solutions represent a static configuration of dissipative fluid which then gradually starts evolving into radiating collapse. The apparent luminosity observed by the distant observer at rest at infinity and the effective surface temperature are zero in remote past at the instance when collapse begins and at the stage when collapsing configuration reach the horizon of the black hole.

Viscoelastic Models of Tidally Heated Exomoons

Tidal heating of exomoons may play a key role in their habitability, since the elevated temperature can melt the ice on the body even without significant solar radiation. The possibility of life is intensely studied on Solar System moons such as Europa or Enceladus, where the surface ice layer covers tidally heated water ocean. Tidal forces may be even stronger in extrasolar systems, depending on the properties of the moon and its orbit. For studying the tidally heated surface temperature of exomoons, we used a viscoelastic model for the first time. This model is more realistic than the widely used, so-called fixed Q models, because it takes into account the temperature dependency of the tidal heat flux, and the melting of the inner material. With the use of this model we introduced the circumplanetary Tidal Temperate Zone (TTZ), that strongly depends on the orbital period of the moon, and less on its radius. We compared the results with the fixed Q model and investigated the statistical volume of the TTZ using both models. We have found that the viscoelastic model predicts 2.8 times more exomoons in the TTZ with orbital periods between 0.1 and 3.5 days than the fixed Q model for plausible distributions of physical and orbital parameters. The viscoelastic model gives more promising results in terms of habitability, because the inner melting of the body moderates the surface temperature, acting like a thermostat.

Mapping the Surface of the Magnetar 1E 1048.1-5937 in Outburst and Quiescence Through Phase Resolved X-ray Spectroscopy

We model the pulse profiles and the phase resolved spectra of the anomalous X-ray pulsar 1E 1048.1-5937 obtained with XMM-Newton to map its surface temperature distribution during an active and a quiescent epoch. We develop and apply a model that takes into account the relevant physical and geometrical effects on the neutron star surface, magnetosphere, and spacetime. Using this model, we determine the observables at infinity as a function of pulse phase for different numbers and sizes of hot spots on the surface. We show that the pulse profiles extracted from both observations can be modeled with a single hot spot and an antipodal cool component. The size of the hot spot changes from $\approx 80^{\circ}$ in 2007, 3 months after the onset of a dramatic flux increase, to $\approx 30^{\circ}$ during the quiescent observation in 2011, when the pulsed fraction returned to the pre-outburst $\approx$ 65\% level. For the 2007 observation, we also find that a model consisting of a single 0.4 keV hot spot with a magnetic field strength of $1.8 \times 10^{14}$ G accounts for the spectra obtained at three different pulse phases but under predicts the flux at the pulse minimum, where the contribution to the emission from the cooler component is non-negligible. The inferred temperature of the spot stays approximately constant between different pulse phases, in agreement with a uniform temperature, single hot spot model. These results suggest that the emitting area grows significantly during outbursts but returns to its persistent and significantly smaller size within a few year timescale.

Improving a pavement-watering method on the basis of pavement surface temperature measurements [Replacement]

Pavement-watering has been studied since the 1990's and is currently considered a promising tool for urban heat island reduction and climate change adaptation. However, possible future water resource availability problems require that water consumption be optimized. Although pavement heat flux can be studied to improve pavement-watering methods (frequency and water consumption), these measurements are costly and require invasive construction work to install appropriate sensors in a dense urban environment. Therefore, we analyzed infrared camera measurements of pavement surface temperatures in search of alternative information relevant to this goal. Firstly, surface temperature reductions of up to 4{\textdegree}C during shading and 13{\textdegree}C during insolation were found. Secondly, the infrared camera successfully detected temperature spikes indicative of surface drying and can therefore be used to optimize the watering frequency. Measurements made every 5 min or less are recommended to minimize relevant data loss. Finally, if the water retaining capacity of the studied pavement is known, optimization of total water consumption is possible on the sole basis of surface temperature measurements.

Could the Earth's surface Ultraviolet irradiance be blamed for the global warming? A new effect may exist

Whether natural factors could interpret the rise of the Earth's surface temperature is still controversial. Though numerous recent researches have reported apparent correlations between solar activity and the Earth's climate, solar activity has encountered a big problem when describing the rapid global warming after 1970s. Our investigation shows the good positive correlations between the Earth's surface Ultraviolet irradiance (280-400 nm) and the Earth's surface temperature both in temporal and spatial variations by analyzing the global surface Ultraviolet irradiance (280-400 nm) and global surface temperature data from 1980-1999. The rise of CO$_2$ cannot interpret the good positive correlations, and we could even get an opposite result to the good correlations when employing the rise of CO$_2$ to describe the relation between them. Based on the good positive correlations, we suggest a new effect, named "Highly Excited Water Vapor" (HEWV) effect, which can interpret how the Sun influences the Earth's surface temperature reasonably, including the rapid warming after 1970s.

Lithium enrichment on the single active K1-giant DI Piscium -- Possible joint origin of differential rotation and Li enrichment

We investigate the surface spot activity of the rapidly rotating, lithium-rich active single K-giant DI Psc to measure the surface differential rotation and understand the mechanisms behind the Li-enrichment. Doppler imaging was applied to recover the surface temperature distribution of DI Psc in two subsequent rotational cycles using the individual mapping lines Ca I 6439, Fe I 6430, Fe I 6421 and Li I 6708. Surface differential rotation was derived by cross-correlation of the subsequent maps. Difference maps are produced to study the uniformity of Li-enrichment on the surface. These maps are compared with the rotational modulation of the Li I 6708 line equivalent width. Doppler images obtained for the Ca and Fe mapping lines agree well and reveal strong polar spottedness, as well as cool features at lower latitudes. Cross-correlating the consecutive maps yields antisolar differential rotation with shear coefficient -0.083 +- 0.021. The difference of the average and the Li maps indicates that the lithium abundance is non-activity related. There is also a significant rotational modulation of the Li equivalent width.

Creation of magnetic spots at the neutron star surface

According to the partially screened gap scenario, an efficient electron-positron pair creation, a general precondition of radio-pulsar activity, relies on the existence of magnetic spots, i.e., local concentrations of strong and small scale magnetic field structures at the surface of neutron stars. They have a strong impact on the surface temperature, which is potentially observable. Here we reinforce the idea that such magnetic spots can be formed by extracting magnetic energy from the toroidal field that resides in deep crustal layers, via Hall drift. We study and discuss the magneto-thermal evolution of qualitatively different neutron star models and initial magnetic field configurations that lead to the creation of magnetic spots. We find that magnetic spots can be created on a timescale of $10^4$ years with magnetic field strengths $\gtrsim 5\times 10^{13}$ G, provided almost the whole magnetic energy is stored in its toroidal component, and that the conductivity in the inner crust is not too large. The lifetime of the magnetic spots is at least $\sim$one million of years, being longer if the initial field permeates both core and crust.

Doppler Probe of Accretion onto a T Tauri star

The YY Ori stars are T Tauri stars with prominent time-variable redshifted absorption components that flank certain emission lines. One of the brightest in this class is S CrA, a visual double star. We have obtained a series of high-resolution spectra of the two components during four nights with the UVES spectrograph at the Very Large Telescope. We followed the spectral changes occurring in S CrA to derive the physical structure of the accreting gas. We found that both stars are very similar with regard to surface temperature, radius, and mass. Variable redshifted absorption components are particularly prominent in the SE component. During one night, this star developed a spectrum unique among the T Tauri stars: extremely strong and broad redshifted absorption components appeared in many lines of neutral and ionized metals, in addition to those of hydrogen and helium. The absorption depths of cooler, low ionization lines peak at low velocities - while more highly ionized lines have peak absorption depths at high velocities. The different line profiles indicate that the temperature and density of the accretion stream increase as material approaches the star. We derive the physical conditions of the flow at several points along the accretion funnel directly from the spectrum of the infalling gas. We estimated mass accretion rates of about 10^(-7) solar masses per year, which is similar to that derived from the relation based on the strength of H alpha emission line. This is the first time the density and temperature distributions in accretion flows around a T Tauri star have been inferred from observations. Compared with predictions from standard models of accretion in T Tauri stars, which assume a dipole stellar magnetic field, we obtained higher densities and a steeper temperature rise toward the star.

Doppler Probe of Accretion onto a T Tauri star [Replacement]

The YY Ori stars are T Tauri stars with prominent time-variable redshifted absorption components that flank certain emission lines. One of the brightest in this class is S CrA, a visual double star. We have obtained a series of high-resolution spectra of the two components during four nights with the UVES spectrograph at the Very Large Telescope. We followed the spectral changes occurring in S CrA to derive the physical structure of the accreting gas. We found that both stars are very similar with regard to surface temperature, radius, and mass. Variable redshifted absorption components are particularly prominent in the SE component. During one night, this star developed a spectrum unique among the T Tauri stars: extremely strong and broad redshifted absorption components appeared in many lines of neutral and ionized metals, in addition to those of hydrogen and helium. The absorption depths of cooler, low ionization lines peak at low velocities - while more highly ionized lines have peak absorption depths at high velocities. The different line profiles indicate that the temperature and density of the accretion stream increase as material approaches the star. We derive the physical conditions of the flow at several points along the accretion funnel directly from the spectrum of the infalling gas. We estimated mass accretion rates of about 10^(-7) solar masses per year, which is similar to that derived from the relation based on the strength of H alpha emission line. This is the first time the density and temperature distributions in accretion flows around a T Tauri star have been inferred from observations. Compared with predictions from standard models of accretion in T Tauri stars, which assume a dipole stellar magnetic field, we obtained higher densities and a steeper temperature rise toward the star.

Spectral features in isolated neutron stars induced by inhomogeneous surface temperatures

The thermal X-ray spectra of several isolated neutron stars display deviations from a pure blackbody. The accurate physical interpretation of these spectral features bears profound implications for our understanding of the atmospheric composition, magnetic field strength and topology, and equation of state of dense matter. With specific details varying from source to source, common explanations for the features have ranged from atomic transitions in the magnetized atmospheres or condensed surface, to cyclotron lines generated in a hot ionized layer near the surface. Here we quantitatively evaluate the X-ray spectral distortions induced by inhomogeneous temperature distributions of the neutron star surface. To this aim, we explore several surface temperature distributions, we simulate their corresponding general relativistic X-ray spectra (assuming an isotropic, blackbody emission), and fit the latter with a single blackbody model. We find that, in some cases, the presence of a spurious 'spectral line' is required at a high significance level in order to obtain statistically acceptable fits, with central energy and equivalent width similar to the values typically observed. We also perform a fit to a specific object, RX J0806.4-4123, finding several surface temperature distributions able to model the observed spectrum. The explored effect is unlikely to work in all sources with detected lines, but in some cases it can indeed be responsible for the appearance of such lines. Our results enforce the idea that surface temperature anisotropy can be an important factor that should be considered and explored also in combination with more sophisticated emission models like atmospheres.

Axion mass limit from observations of the neutron star in Cassiopeia A

Direct Chandra observations of a surface temperature of isolated neutron star in Cassiopeia A (Cas A NS) and its cooling scenario which has been recently simultaneously suggested by several scientific groups put stringent constraints on poorly known properties of the superfluid neutron star core. We use these unique data and well-defined cooling scenario to constrain the upper limit on the axion mass, $m_{a}\lesssim 0.007\,\text{eV}$, assuming that the axion energy losses produce no noticeable modification of the temperature profile of the Cas A NS.

Axion mass limit from observations of the neutron star in Cassiopeia A [Replacement]

Direct Chandra observations of a surface temperature of isolated neutron star in Cassiopeia A (Cas A NS) and its cooling scenario which has been recently simultaneously suggested by several scientific teams put stringent constraints on poorly known properties of the superfluid neutron star core. It was found also that the thermal energy losses from Cas A NS are approximately twice more intensive than it can be explained by the neutrino emission. We use these unique data and well-defined cooling scenario to estimate the strength of KSVZ axion interactions with neutrons. We speculate that enlarged energy losses occur owing to emission of axions from superfluid core of the neutron star. If the axion and neutrino losses are comparable we find $c_{n}^{2}m_{a}^{2}\sim 5.7\times 10^{-6}\,\text{eV}^2$, where $m_{a}$ is the axion mass, and $c_{n}$ is the effective Peccei-Quinn charge of the neutron. (Given the QCD uncertainties of the hadronic axion models, the dimensionless constant $c_{n}$ could range from $-0.05$ to $ 0.14$.)

Axion mass limit from observations of the neutron star in Cassiopeia A [Replacement]

Direct Chandra observations of a surface temperature of isolated neutron star in Cassiopeia A (Cas A NS) and its cooling scenario which has been recently simultaneously suggested by several scientific teams put stringent constraints on poorly known properties of the superfluid neutron star core. It was found also that the thermal energy losses from Cas A NS are approximately twice more intensive than it can be explained by the neutrino emission. We use these unique data and well-defined cooling scenario to estimate the strength of KSVZ axion interactions with neutrons. We speculate that enlarged energy losses occur owing to emission of axions from superfluid core of the neutron star. If the axion and neutrino losses are comparable we find $c_{n}^{2}m_{a}^{2}\sim 5.7\times 10^{-6}\,\text{eV}^2$, where $m_{a}$ is the axion mass, and $c_{n}$ is the effective Peccei-Quinn charge of the neutron. (Given the QCD uncertainties of the hadronic axion models, the dimensionless constant $c_{n}$ could range from $-0.05$ to $ 0.14$.)

Warming early Mars with CO2 and H2

The presence of valleys on ancient terrains of Mars suggest that liquid water flowed on the martian surface 3.8 billion years ago or before. The above-freezing temperatures required to explain valley formation could have been transient, in response to frequent large meteorite impacts on early Mars, or they could have been caused by long-lived greenhouse warming. Climate models that consider only the greenhouse gases carbon dioxide and water vapor have been unable to recreate warm surface conditions, given the lower solar luminosity at that time. Here we use a one-dimensional climate model to demonstrate that an atmosphere containing 1.3-4 bar of CO2 and water vapor, along with 5 to 20 percent H2, could have raised the mean surface temperature of early Mars above the freezing point of water. Vigorous volcanic outgassing from a highly reduced early martian mantle is expected to provide sufficient atmospheric H2 and CO2, the latter from the photochemical oxidation of outgassed CH4 and CO, to form a CO2-H2 greenhouse. Such a dense early martian atmosphere is consistent with independent estimates of surface pressure based on cratering data.

Superflare occurrence and energies on G, K and M type stars

Kepler data from G, K and M type stars are used to study conditions that lead to superflares of energies above $10^{34} {\rm erg}$. From the 117661 included stars, 795 show superflares with a total of 6830 such events. We study if parameters, like the surface temperature or the rotation rate, have any effect on the superflare occurrence rate or energy. For slowly rotating stars we find a quadratic increase of the mean occurrence rate with the rotation rate up to a critical point, after which the rate decreases linearly. Motivated by standard dynamo theory, we study the behavior of the relative starspot coverage, approximated as the relative brightness variation. For faster rotating stars, an increased fraction of stars shows higher spot coverage, which leads to higher superflare rates. A turbulent dynamo is used to study the dependence of the Ohmic dissipation as a proxy of the flare energy on the differential rotation or shear rate. The resulting statistics of the dissipation energy as a function of dynamo number is similar to the observed flare statistics as a function of the inverse Rossby number and shows similarly strong fluctuations. This supports the idea that superflares might well be possible for solar-type G stars.

Efficient diffusive mechanisms of O atoms at very low temperatures on surfaces of astrophysical interest

At the low temperatures of interstellar dust grains, it is well established that surface chemistry proceeds via diffusive mechanisms of H atoms weakly bound (physisorbed) to the surface. Until recently, however, it was unknown whether atoms heavier than hydrogen could diffuse rapidly enough on interstellar grains to react with other accreted species. In addition, models still require simple reduction as well as oxidation reactions to occur on grains to explain the abundances of various molecules. In this paper we investigate O-atom diffusion and reactivity on a variety of astrophysically relevant surfaces (water ice of three different morphologies, silicate, and graphite) in the 6.5 - 25 K temperature range. Experimental values were used to derive a diffusion law that emphasizes that O atoms diffuse by quantum mechanical tunnelling at temperatures as low as 6.5 K. The rate of diffusion on each surface, based on modelling results, were calculated and an empirical law is given as a function of the surface temperature. Relative diffusion rates are k_H2Oice > k_sil > k_graph >> k_expected. The implications of an efficient O-atom diffusion over astrophysically relevant time-scales are discussed. Our findings show that O atoms can scan any available reaction partners (e.g., either another H atom, if available, or a surface radical like O or OH) at a faster rate than that of accretion. Also, as dense clouds mature H2 becomes far more abundant than H and the O/H ratio grows, the reactivity of O atoms on grains is such that O becomes one of the dominant reactive partners together with H.

Oxygen diffusion and reactivity at low temperature on bare amorphous olivine-type silicate

The mobility of O atoms at very low temperatures is not generally taken into account, despite O diffusion would add to a series of processes leading to the observed rich molecular diversity in space. We present a study of the mobility and reactivity of O atoms on an amorphous silicate surface. Our results are in the form of RAIRS and temperature-programmed desorption spectra of O2 and O3 produced via two pathways: O + O and O2 + O, investigated in a submonolayer regime and in the range of temperature between 6.5 and 30 K. All the experiments show that ozone is formed efficiently on silicate at any surface temperature between 6.5 and 30 K. The derived upper limit for the activation barriers of O + O and O2 + O reactions is 150 K/kb. Ozone formation at low temperatures indicates that fast diffusion of O atoms is at play even at 6.5 K. Through a series of rate equations included in our model, we also address the reaction mechanisms and show that neither the Eley Rideal nor the Hot atom mechanisms alone can explain the experimental values. The rate of diffusion of O atoms, based on modeling results, is much higher than the one generally expected, and the diffusive process proceeds via the Langmuir-Hinshelwood mechanism enhanced by tunnelling. In fact, quantum effects turn out to be a key factor that cannot be neglected in our simulations. Astrophysically, efficient O3 formation on interstellar dust grains would imply the presence of huge reservoirs of oxygen atoms. Since O3 is a reservoir of elementary oxygen, and also of OH via its hydrogenation, it could explain the observed concomitance of CO2 and H2O in the ices.

Evidence of two different types of short term solar modulation of regional surface temperature and cloud

Recent work indicates that 27 day variations in cosmic ray flux during 2007 2009 are phase locked to 27 day variations in cloud and surface temperature at Shetland. Here we extend the study to other regions including Central England, US and Australia and to several other annual intervals that exhibit strong 27 day variation in cosmic ray flux and sunspot area. Band pass filtering was used to obtain 27 day components of daily maximum temperature in each region and 27 day components of cloud variation were determined, in Australia only, from solar exposure records. When cosmic ray flux is the dominant influence phase locked variations in surface temperature occur in each of the regions with, however, in phase or anti phase variation in different regions. Similar phase locking of 27 day variation in surface temperature to sunspot area variation occurs when sunspot activity is the dominant influence with indications that changes from in phase to anti phase variation are linked to flipping of sunspot activity from one active longitude to another. The 27 day component of cloud in Australia was phase locked to the 27 day component of temperature in Central England in two of the intervals studied, 1997 and 2005, indicating the global nature of the connection between solar disturbance and the lower atmosphere. It was observed that very large swings in 27 day temperature components are often correlated with 27 day variation in solar activity.

Origin and Loss of nebula-captured hydrogen envelopes from "sub"- to "super-Earths" in the habitable zone of Sun-like stars

We investigate the origin and loss of captured hydrogen envelopes from protoplanets between `sub-Earth'-like bodies of 0.1$M_{\oplus}$ up to `super-Earths' with 5$M_{\oplus}$ in the HZ of a Sun like G star, assuming their rocky cores had formed before the nebula dissipated. We model the gravitational accumulation of nebula gas around a core as a function of protoplanetary luminosity during accretion and calculate the resulting surface temperature by solving the hydrostatic structure equations for the protoplanetary nebula. Depending on nebular properties and resulting luminosities, for planetary bodies of 0.1--1$M_{\oplus}$ we obtain hydrogen envelopes with masses between $\sim 2.5\times 10^{19}$--$1.5\times 10^{26}$ g. For `super-Earths' with masses between 2--5$M_{\oplus}$ hydrogen envelopes within the mass range of $\sim 7.5\times 10^{23}$--$1.5\times 10^{28}$ g can be captured. To study the escape of these hydrogen-dominated protoatmospheres, we apply a hydrodynamic upper atmosphere model and calculate the loss rates due to the heating by the high XUV flux of the young star. Our results indicate that under most nebula conditions `sub-Earth' and Earth-mass planets can lose their envelopes by thermal escape during the first $100$ Myr after the disk dissipated. However, if a nebula has a low dust depletion factor or low accretion rates resulting in low protoplanetary luminosities, it is possible that even protoplanets with Earth-mass cores may keep their hydrogen envelopes during their whole lifetime. In contrast to lower mass protoplanets, `super-Earths' accumulate a huge amount of nebula gas and lose only tiny fractions of their primordial envelopes. Our results agree with the fact that Venus, Earth, and Mars are not surrounded by dense hydrogen envelopes, as well as with the recent discoveries of low density `super-Earths' that most likely could not get rid of their protoatmospheres.

The outflows accelerated by the magnetic fields and radiation force of accretion disks

The inner region of a luminous accretion disk is radiation pressure dominated. We estimate the surface temperature of a radiation pressure dominated accretion disk, \Theta=(c_s/r\Omega_K)^2<<(H/r)^2, which is significantly lower than that of a gas pressure dominated disk, \Theta (H/r)^2. This means that the outflow can be launched magnetically from the photosphere of the radiation pressure dominate disk only if the effective potential barrier along the magnetic field line is extremely shallow or no potential barrier is present. For the latter case, the slow sonic point in the outflow may probably be in the disk, which leads to a slow circular dense flow above the disk. This implies that hot gas (probably in the corona) is necessary for launching a jet from the radiation pressure dominated disk, which provides a natural explanation on the observational evidence that the relativistic jets are related to hot plasma in some X-ray binaries and active galactic nuclei. We investigate the outflows accelerated from the hot corona above the disk by the magnetic field and radiation force of the accretion disk. We find that, with the help of the radiation force, the mass loss rate in the outflow is high, which leads to a slow outflow. This may be the reason why the jets in radio-loud narrow-line Seyfert galaxies are in general mild relativistic compared with those in blazars.

The outflows accelerated by the magnetic fields and radiation force of accretion disks [Replacement]

The inner region of a luminous accretion disk is radiation pressure dominated. We estimate the surface temperature of a radiation pressure dominated accretion disk, \Theta=(c_s/r\Omega_K)^2<<(H/r)^2, which is significantly lower than that of a gas pressure dominated disk, \Theta (H/r)^2. This means that the outflow can be launched magnetically from the photosphere of the radiation pressure dominate disk only if the effective potential barrier along the magnetic field line is extremely shallow or no potential barrier is present. For the latter case, the slow sonic point in the outflow may probably be in the disk, which leads to a slow circular dense flow above the disk. This implies that hot gas (probably in the corona) is necessary for launching a jet from the radiation pressure dominated disk, which provides a natural explanation on the observational evidence that the relativistic jets are related to hot plasma in some X-ray binaries and active galactic nuclei. We investigate the outflows accelerated from the hot corona above the disk by the magnetic field and radiation force of the accretion disk. We find that, with the help of the radiation force, the mass loss rate in the outflow is high, which leads to a slow outflow. This may be the reason why the jets in radio-loud narrow-line Seyfert galaxies are in general mild relativistic compared with those in blazars.

Line driven winds and the UV turnover in AGN accretion discs

AGN SEDs generally show a turnover at lambda 1000A, implying a maximal accretion disc (AD) temperature of T_max~50,000K. Massive O stars display a similar T_max, associated with a sharp rise in a line driven mass loss Mdot_wind with increasing surface temperature. AGN AD are also characterized by similar surface gravity to massive O stars. The Mdot_wind of O stars reaches ~10^-5 Msun/year. Since the surface area of AGN AD can be 10^6 larger, the implied Mdot_wind in AGN AD can reach the accretion rate Mdot. A rise to Mdot_wind Mdot towards the AD center may therefore set a similar cap of T_max~50,000K. To explore this idea, we solve the radial structure of an AD with a mass loss term, and calculate the implied AD emission using the mass loss term derived from observations of O stars. We find that Mdot_wind becomes comparable to Mdot typically at a few 10s of GM/c^2. Thus, the standard thin AD solution is effectively truncated well outside the innermost stable orbit. The calculated AD SED shows the observed turnover at lambda~1000A, which is weakly dependent on the AGN luminosity and black hole mass. The AD SED is generally independent of the black hole spin, due to the large truncation radius. However, a cold AD (low Mdot, high black hole mass) is predicted to be windless, and thus its SED should be sensitive to the black hole spin. The accreted gas may form a hot thick disc with a low radiative efficiency inside the truncation radius, or a strong line driven outflow, depending on its ionization state.

Line driven winds and the UV turnover in AGN accretion discs [Replacement]

AGN SEDs generally show a turnover at lambda 1000A, implying a maximal accretion disc (AD) temperature of T_max~50,000K. Massive O stars display a similar T_max, associated with a sharp rise in a line driven mass loss Mdot_wind with increasing surface temperature. AGN AD are also characterized by similar surface gravity to massive O stars. The Mdot_wind of O stars reaches ~10^-5 Msun/year. Since the surface area of AGN AD can be 10^6 larger, the implied Mdot_wind in AGN AD can reach the accretion rate Mdot. A rise to Mdot_wind Mdot towards the AD center may therefore set a similar cap of T_max~50,000K. To explore this idea, we solve the radial structure of an AD with a mass loss term, and calculate the implied AD emission using the mass loss term derived from observations of O stars. We find that Mdot_wind becomes comparable to Mdot typically at a few 10s of GM/c^2. Thus, the standard thin AD solution is effectively truncated well outside the innermost stable orbit. The calculated AD SED shows the observed turnover at lambda~1000A, which is weakly dependent on the AGN luminosity and black hole mass. The AD SED is generally independent of the black hole spin, due to the large truncation radius. However, a cold AD (low Mdot, high black hole mass) is predicted to be windless, and thus its SED should be sensitive to the black hole spin. The accreted gas may form a hot thick disc with a low radiative efficiency inside the truncation radius, or a strong line driven outflow, depending on its ionization state.

On the semi-annual, 27 day, variation in geomagnetic activity, cloud cover and surface temperature

We develop a basic model of the time variation of geomagnetic activity and show that the model predicts, with decreasing levels of exactitude, the time variation of the ~27 day period components of geomagnetic aa index, cloud cover and surface temperature during several years near solar cycle minima. We interpret this as indicating that there is a connection between the ~27 day variation of geomagnetic activity and the ~27 day variations of cloud cover and surface temperature with the decreasing correlations between model variation and aa index, cloud cover and surface temperature variation due to delays and phase shifts between the three variables some of which are obvious, such as the 180 degree seasonal phase shift between cloud cover and surface temperature, and others less certain. We find that, while the components of cloud cover and surface temperature influenced by geomagnetic activity amount to, on average, about 20% of the overall variations, the influence may be several times higher during the semi-annual maxima in geomagnetic activity that occur around the equinoxes.

Nuclear medium cooling scenario in the light of new Cas A cooling data and the 2 M_sun pulsar mass measurements [Replacement]

Recently, Elshamounty et al. performed a reanalysis of the surface temperature of the neutron star in the supernova remnant Cassiopeia A on the basis of Chandra data measured during last decade, and added a new data point. We show that all reliably known temperature data of neutron stars including those belonging to Cassiopea A can be comfortably explained in our "nuclear medium cooling" scenario of neutron stars. The cooling rates account for medium-modified one-pion exchange in dense matter, polarization effects in the pair-breaking-formation processes operating on superfluid neutrons and protons paired in the 1S_0 state, and other relevant processes. The emissivity of the pair-breaking-formation process in the 3P_2 state is a tiny quantity within our scenario. Crucial for a successful description of the Cassiopeia A cooling proves to be the thermal conductivity from both, the electrons and nucleons, being reduced by medium effects. Moreover, we exploit an EoS which stiffens at high densities due to an excluded volume effect and is capable of describing a maximum mass of 2.1 M_sun, thus including the recent measurements of PSR J1614-2230 and PSR J0348+0432.

Limits on Quaoar's Atmosphere

Here we present high cadence photometry taken by the Acquisition Camera on Gemini South, of a close passage by the $\sim540$ km radius Kuiper Belt Object, (50000) Quaoar, of a r'=20.2 background star. Observations before and after the event show that the apparent impact parameter of the event was $0.019\pm0.004$", corresponding to a close approach of $580\pm120$ km to the centre of Quaoar. No signatures of occultation by either Quaoar's limb or its potential atmosphere are detectable in the relative photometry of Quaoar and the target star, which were unresolved during closest approach. From this photometry we are able to put constraints on any potential atmosphere Quaoar might have. Using a Markov chain Monte Carlo and likelihood approach, we place pressure upper limits on sublimation supported, isothermal atmospheres of pure N$_2$, CO, and CH$_4$. For N$_2$ and CO, the upper limit surface pressures are 1 and 0.7 $\mu{bar}$ respectively. The surface temperature required for such low sublimation pressures is $\sim33$ K, much lower than Quaoar's mean temperature of $\sim44$ K measured by others. We conclude that Quaoar cannot have an isothermal N$_2$ or CO atmosphere. We cannot eliminate the possibility of a CH$_4$ atmosphere, but place upper surface pressure and mean temperature limits of $\sim138$ nbar and $\sim44$ K respectively.

The cooling of the Cassiopeia A neutron star as a probe of the nuclear symmetry energy and nuclear pasta [Replacement]

X-ray observations of the neutron star in the Cas A supernova remnant over the past decade suggest the star is undergoing a rapid drop in surface temperature of $\approx$ $2-5.5\%$. One explanation suggests the rapid cooling is triggered by the onset of neutron superfluidity in the core of the star, causing enhanced neutrino emission from neutron Cooper pair breaking and formation (PBF). Using consistent neutron star crust and core equations of state (EOSs) and compositions, we explore the sensitivity of this interpretation to the density dependence of the symmetry energy $L$ of the EOS used, and to the presence of enhanced neutrino cooling in the bubble phases of crustal "nuclear pasta". Modeling cooling over a conservative range of neutron star masses and envelope compositions, we find $L\lesssim70$ MeV, competitive with terrestrial experimental constraints and other astrophysical observations. For masses near the most likely mass of $M\gtrsim 1.65 M_{\odot}$, the constraint becomes more restrictive $35\lesssim L\lesssim 55$ MeV. The inclusion of the bubble cooling processes decreases the cooling rate of the star during the PBF phase, matching the observed rate only when $L\lesssim45$ MeV, taking all masses into consideration, corresponding to neutron star radii $\lesssim 11$km.

The cooling of the Cassiopeia A neutron star as a probe of the nuclear symmetry energy and nuclear pasta

X-ray observations of the neutron star in the Cas A supernova remnant over the past decade suggest the star is undergoing rapid cooling, with a drop in surface temperature of $\approx$ 2-5.5%. One of the leading explanations suggests the rapid cooling is triggered by the onset of neutron superfluidity in the core of the star, causing enhanced neutrino emission from neutron Cooper pair breaking and formation (PBF). Using consistent neutron star crust and core equations of state (EOSs) and compositions, we explore the sensitivity of this interpretation to the density dependence of the symmetry energy $L$ of the EOS used, and to the presence of enhanced neutrino cooling in the bubble phases of crustal "nuclear pasta". Using a conservative range of possible neutron star masses and envelope compositions, we find $L\lesssim70$ MeV, competitive with constraints from terrestrial experimental constraints and other astrophysical observations. If one demands that $M\gtrsim 1.4 M_{\odot}$, the constraint becomes more restrictive $L\lesssim55$ MeV. Finally, the inclusion of the bubble cooling processes decreases the cooling rate of the star during the PBF phase, allowing observations only when $L\lesssim45$ MeV (35 MeV) for all masses ($M\gtrsim 1.4 M_{\odot}$) corresponding to neutron star radii $\lesssim 11$km.

 

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