On the time scale of energy transport in the sun

It is pointed out that the time scale of energy transport in the Sun is the Kelvin–Helmholtz time scale, of order 3×10⁷ years, roughly 100 times longer than the photon-diffusion time estimated by Mitalas and Sills (1992). The difference corresponds to a factor U _gas/U _rad, the ratio of thermal energy density to radiation energy density. Thus the heat transport, even when mediated by photons, is slowed down by the large heat capacity of the star. A numerical example calculation is presented.     

The gross energy balance of solar active regions

According to Parker's earlier articles in this journal the photospheric temperature is lower in sunspots than elsewhere because of increased outflow of mechanical energy, rather than inhibited inflow from the convective zone. In this case the atmosphere above the spot group receives an excess supply of energy that must equal the deficiency in radiative power output of the spot group compared with the normal photosphere. The extra power supplied to the atmosphere was then assumed to be lost by radiation. On 26 November 1973 the active region McMath 12628 was studied with sufficient precision to test for this equality. It is shown that the atmosphere did not radiate and almost certainly did not receive, more than a very small part of the missing flux of the spot group. This result is an important constraint on the plausible theories of sunspot formation.     

Meridional energy balance of Jupiter

The meridional energy balance of Jupiter is calculated from high spatial resolution observations by the Voyager 1 infrared spectrometer and radiometer. On a hemispheric scale Jupiter radiates thermal energy to space approximately uniform with latitude while solar energy absorption varies approximately as the solar angle. This implies internal adjustment to the solar energy with a larger contribution poleward of ±45° than in the equatorial zone. The internal flux is modulated by the major visible features of the zone and belt system but, unlike the hemispheric scale where increased internal flux is correlated with decreased solar absorption, on smaller scales the inverse occurs. The energy balance is very likely to be controlled by dynamics, but the relative influence of the upper atmosphere and the interior is not yet clear. Models have been proposed that would explain the pole-to-equator variation in the thermal emission and it is suggested that the smaller scale variations may be the result of forced convective circulation.     

Neutral corpuscular energy flux by charge-transfer collisions in the vicinity of the sun

Charge-transfer collisions between solar-wind protons and neutral interstellar hydrogen in the vicinity of the sun have been considered. Due to the focusing effect of the sun's gravitational field interstellar particles entering the solar system in free flights produce a specific density distribution in the circumsolar space. On their way from the sun to the orbit of the earth solar protons will therefore generate fast neutrals by collisions with neutral hydrogen. Depending on the position at its orbit the earth will be hit by these fast neutrals which will come down directly into the thermosphere and will produce temperature and density increases. It is shown that the corpuscular energy flux connected with these fast neutrals will have a semi-annually varying profile along the earth's orbit. Interstellar particle densities of about 5 cm^–3 at infinity would produce energy fluxes of the order of 0.1 erg/cm² sec. Assuming a specific proper motion of interstellar matter surrounding the solar system we obtain a neutral corpuscular energy flux having nearly the same shape and phase as the wellknown semi-annual effect in atmospheric temperatures and densities. Collision-generated, fast neutrals reaching the earth could therefore possibly give an explanation of this effect.Mitteilungen der Astronomischen Institute Bonn, Nr. 102.     

Force and energy balance in the transition region network

Two-dimensional numerical models of the solar transition region are calculated using an inverse coordinates method which attains pressure equilibrium between the network magnetic field and the external comparatively field-free gas. If A(y, z) is the magnetic potential (a scalar in 2D), which is constant on field lines, the method involves interchanging dependent and independent variables to obtain a quasi-linear PDE for y(A, z), which is solved iteratively. The advantage of this approach is that magnetic field lines, including any magnetic interface, become coordinate lines, thereby simplifying the energy equation and free boundary problem. In order to examine the effects of self-consistent geometry on the thermal structure of the transition region network, we calculate four models. The energy balance includes the effects of radiation, conduction, and enthalpy flux. It is confirmed that the lower branch of the emission measure curve cannot be explained within the single fluxtube model if the classical Spitzer thermal conductivity is used. However, by including a turbulent thermal conductivity as proposed by Cally (1990a), transition region models are obtained for which the resulting emission measure curves exhibit the correct behaviour, including the observed turn-up below about 200 000 K. In summary, the broad conclusions of previous non-turbulent 2D models are confirmed, but most importantly, the turbulent conductivity hypothesis tested in 1D by Cally is shown to produce excellent agreement with observations in the more realistic geometry.     

The roles of particle precipitation and Joule heating in the energy balance of the Jovian thermosphere

Order of magnitude calculations have been carried out to compare particle precipitation and Joule heating with solar radiation as sources of energy in the Jovian thermosphere. Calculations based on a detailed atomic cross section approach to energy deposition show that the efficiency of conversion of energetic particle precipitation energy into thermal energy is 0.33, larger than on Earth. This emphasizes the role of particle precipitation heating, which may serve as a source for gravity waves. In contrast to the terrestrial case, Joule heating is found to be of only minor significance in the Jovian atmosphere.     

The paradox of the scale-free discs

Scale-free discs have no preferred length or time-scale. The question has been raised whether such discs have a continuum of unstable linear modes or perhaps no unstable modes at all. We resolve this paradox by analysing the particular case of a gaseous, isentropic disc with a completely flat rotation curve (the Mestel disc) exactly . The heart of the matter is this: what are the correct boundary conditions to impose at the origin or central cusp? We argue that the linear stability problem is ill-posed and that similar ambiguities may afflict general disc models with power-law central cusps. From any finite radius, waves reach the origin after finite time but with logarithmically divergent phase. Instabilities exist, but their pattern speeds depend upon an undetermined phase with which waves are reflected from the origin. For any definite choice of this phase, there is an infinite but discrete set of growing modes. The ratio of growth rate to pattern speed is independent of the central phase. This ratio is derived in closed form for non-self-gravitating normal modes and is shown to agree with approximate results obtained from the shearing sheet in the short-wavelength limit. This provides the first exact, analytically solved stability analysis for a differentially rotating disc. For self-gravitating normal modes, the ratio of growth rate to pattern is found numerically by solving recurrence relations in Mellin-transform space.     

The far ultraviolet spectrum of the sun

Predictions of solar flux and limb darkening calculated from the Utrecht Reference Model, the Mutschlecner model, and the Bilderberg Continuum Atmosphere are compared with the rocket ultraviolet observations. The calculations employ recent experimental and theoretical determinations of metallic photo-ionization cross-sections. The spectral region between the continuous absorption edge from the first excited level of silicon at 1680 Å and the ground-state absorption edge at 1525 Å proves particularly significant for an investigation of the solar temperature minimum. The analysis indicates that the solar temperature minimum is relatively broad and flat, having a nearly constant temperature over somewhat more than a scale height, and that the chromospheric rise occurs just above 5000 = 10^–4 or so. Within the assumptions of the present models, a satisfactory interpretation of the ultraviolet spectrum can be reached with a temperature minimum of 4600° ± 100 °K.     

The 22-year cycle of the sun

The 22-yr solar cycle is being explained as due to a spin-aligned magnetic quadrupole frozen into the (radiative) core. Differential rotation of the poorly conducting convection zone gives rise to flux winding and to an alternating dominance, near the surface, of one of the two constituent dipoles. Equatorial superrotation and polar subrotation are stabilized by the same magnetic flux that transfers angular momentum from the (radiative) core to the (escaping) solar wind. The time- and radius-dependent magnetic torque is also responsible for the rigid and twisting oscillations of a thin surface layer, and for the relative velocities of different tracers.     

Facular excess radiation and the energy balance of solar active regions

Plage areas and intensities derived from CaII K spectroheliograms are used as a proxy for the facular irradiance excess of solar active regions for the period 19 August to 4 September 1980. Using a calibration method proposed by Vrnak et al. (1991), the photospheric facular index (PFI) with constant facular contrastC _p = 0.018 is replaced by a variableC _p , depending on the plage brightness. A sgnificant increase ofC _p from 0.015 to 0.025 is found for plage areas varying from a few to approx. 6 · 10³ millionths hemispheres.Combining the facular irradiance excess with sunspot deficits (as determined for the same period by Steinegger et al. 1990) yields good aggrement with the irradiance variations measured by ACRIM I, using a center-to-limb variation ofC _p according to Chapman and Meyer (1986). The ratio of facular excess to sunspot deficit (integrated over solid angle 2) decreases from values of 1.5 to 2 for regions with sunspot areas below 100 millionths hemispheres to 0.2 for sunspots of areas > 1000 millionths hemispheres,     

The surface energy balance at the Huygens landing site and the moist surface conditions on Titan

The Huygens Probe provided a wealth of data concerning the atmosphere of Titan. It also provided tantalizing evidence of a small amount of surface liquid. We have developed a detailed surface energy balance for the Probe landing site. We find that the daily averaged non-radiative fluxes at the surface are 0.7 W m^?2, much larger than the global average value predicted by McKay et al. (1991) of 0.037 W m^?2. Considering the moist surface, the methane and ethane detected by the Probe from the surface is consistent with a ternary liquid of ethane, methane, and nitrogen present on the surface with mole fractions of methane, ethane, and nitrogen of 0.44, 0.34, and 0.22, respectively, and a total mass load of ～0.05 kg m^?2. If this liquid is included in the surface energy balance, only a small fraction of the non-radiative energy is due to latent heat release (～10^?3 W m^?2). If the amount of atmospheric ethane is less than 0.6×10^?5, the surface liquid is most likely evaporating over timescales of 5 Titan days, and the moist surface is probably a remnant of a recent precipitation event. If the surface liquid mass loading is increased to 0.5 kg m^?2, then the liquid lifetime increases to ～56 Titan days. Our modeling results indicate a dew cycle is unlikely, given that even when the diurnal variation of liquid is in equilibrium, the diurnal mass variation is only 3% of the total liquid. If we assume a high atmospheric mixing ratio of ethane (>0.6×10^?5), the precipitation of liquid is large (38 cm/Titan year for an ethane mixing ratio of 2×10^?5). Such a flux is many orders of magnitude in excess of the photochemical production rate of ethane.     

The relation between hot and cool loops

In order to study the origin of the hot (3 MK) corona above active regions, we compare Yohkoh/SXT X-ray images, which represent a broad temperature range above 2.5 MK, with TRACE EUV coronal images whose primary sensitivities are in the 1–2 MK range. Nearly simultaneous X-ray and EUV snapshots show that there are loops that appear similar in these images of different temperature sensitivities, but they are not exactly cospatial with each other. A significant difference is noted in the active region core, where bright loops are seen in X-ray images but not in EUV images, reflecting their high (5 MK) temperatures. In SXT time-sequence images, these loops are found to undergo repetitive minor brightenings, suggestive of their flare-like origin. This is consistent with the absence of the EUV counterparts of the X-ray loops in TRACE time-sequence images at earlier and later times. We need to revisit the validity of the assumption that coronal loops are steady.     

The mass and luminosity of cool dwarf stars

A new empirical mass-luminosity relation for Main-Sequence. stars in the range –0.6相似文献   

The O VI emission from the sun

The ionization equilibrium of oxygen is calculated for various temperatures. A peculiarity in the dielectronic recombination leads to a considerable fraction of Ovi in the corona. Thus, the Ovi lines may be emitted from the corona rather than the transition region.     

The diameter of the sun at decameter wavelengths

Using observations obtained with the Clark Lake radioheliograph we determined the diameter of the Sun in the decameter wavelength range. Both equatorial and polar diameters increase with decreasing frequency, as D=Af . The eccentricity of the brightness distribution appears to remain constant in the frequency range (30–74 MHz) in good agreement with the optical results in a corresponding height range. The smaller size of the polar diameter is attributed to coronal holes covering the poles during the period of our observations, while streamers were observed at the equator most of the time.     

The distribution of interstellar extinction near the sun

Photometric data inuvbyß system from 3713 stars is used to map the distribution of colour excesses up to 500 parsec from the Sun, producing diagrams for a series of layers aligned with the galactic plane. Individual clouds are detected, with a mean diameter of 6 parsecs, while cloud complexes have a mean diameter of 100 pc. From the maps it seems that the interstellar medium near the Sun presents regions of non-negligible extinction, while the Sun itself is enbedded in a diffuse cloud, or slightly off its border. The large scatter in the distribution ofE(b-) is confirmed, with a mean extinction ofA _v=0 _. ^m 38 up to 500 pc.     

The sun and exoplanets: The solitude of man

Solar pulsations with a period of P ₀ = 9600.606(12) were discovered in 1974. A more recent discovery is that planetary distances in the solar system are subject to spatial resonance with the parameter L ₀ ?? cP ₀ ?? 9600 ls and that the P ₀ pulsation itself has cosmological significance (coherent cosmic oscillation, or the pace of absolute time of the universe; c is the speed of light). As of June 2011, 552 extrasolar planets have been discovered. Statistical analysis shows that the distribution of the semimajor axes of alien planets does not have L ₀ resonance. Moreover, it appears to have no resonance at all. This frustrates the 20th-century hopes for the existence of extraterrestrial civilizations and possible contact with them. They are simply not there. This explanation of the Fermi paradox, or the Great Silence, appears to rest on the triumph of the anthropic principle, which has been successfully implemented by nature within our planetary system. This leads to a vision whereby the cosmos seems to be created specially for us. The scale L ₀ indicates that the sun is a special quantum object, where L ₀ is a wave function parameter that is not subject to the rational principles of the classical world, but rather follows a peculiar, quantum logic.     

The cool surfaces of binary near-Earth asteroids

Here we show results from thermal-infrared observations of km-sized binary near-Earth asteroids (NEAs). We combine previously published thermal properties for NEAs with newly derived values for three binary NEAs. The η value derived from the near-Earth asteroid thermal model (NEATM) for each object is then used to estimate an average thermal inertia for the population of binary NEAs and compared against similar estimates for the population of non-binaries. We find that these objects have, in general, surface temperatures cooler than the average values for non-binary NEAs as suggested by elevated η values. We discuss how this may be evidence of higher-than-average surface thermal inertia. This latter physical parameter is a sensitive indicator of the presence or absence of regolith: bodies covered with fine regolith, such as the Earth’s moon, have low thermal inertia, whereas a surface with little or no regolith displays high thermal inertia. Our results are suggestive of a binary formation mechanism capable of altering surface properties, possibly removing regolith: an obvious candidate is the YORP effect.We present also newly determined sizes and geometric visible albedos derived from thermal-infrared observations of three binary NEAs: (5381) Sekhmet, (153591) 2001 SN₂₆₃, and (164121) 2003 YT₁. The diameters of these asteroids are 1.41 ± 0.21 km, 1.56 ± 0.31 km, and 2.63 ± 0.40 km, respectively. Their albedos are 0.23 ± 0.13, 0.24 ± 0.16, and 0.048 ± 0.015, respectively.