Can Solar System observations tell us something about the cosmological constant?

In this note we show that the latest determinations of the residual Mercury's perihelion advance, obtained by accounting for almost all known Newtonian and post-Newtonian orbital effects, yields only very broad constraints on the cosmological constant. Indeed, from \delta\dot\omega=-0.0036 + - 0.0050 arcseconds per century one gets -2 10^-34 km^-2 < Lambda < 4 10^-35 km^-2. The currently accepted value for Lambda, obtained from many independent cosmological and large-scale measurements, amounts to almost 10^-46 km^-2.Comment: Latex2e, 4 pages, 2 table, no figures, 11 references. Table 2 added, typos in the units of Lambda correcte

Методи машинного навчання в задачі класифікації зірок за їх спостережуваними параметрами

Класифікація зірок за їх спостережуваними параметрами є однією з головних задач астрономії. Вона дозволяє науковцям вивчати історію формування та еволюції галактик, встановлювати закономірності розподілу матерії у космосі, та передбачення подальшого розвитку всесвіту. На сьогоднішній день, завдяки сучасним астрономічним обсерваторіям та космічним місіям, людство може спостерігати мільярди зірок

Exploring the Temporal Variation of the Solar Quadrupole Moment J 2

Recently, Rozelot & Eren pointed out that the first solar gravitational moment ( J _2 ) might exhibit a temporal variation. The suggested explanation is through the temporal variation of the solar rotation with latitude. This issue is deeper developed due to an accurate knowledge of the long-term variations in solar differential rotation regarding solar activity. Here we analyze solar cycles 12–24, investigating the long-term temporal variations in solar differential rotation. It is shown that J _2 exhibits a net modulation over the 13 studied cycles of ≈(89.6 ± 0.1) yr, with a peak-to-peak amplitude of ≈0.1 × 10 ^−7 for a reference value of 2.07 × 10 ^−7 ). Moreover, J _2 exhibits a positive linear trend in the period of minima solar activity (sunspot number up to around 40) and a marked declining trend in the period of maxima (sunspot number above 50). In absolute magnitude, the mean value of J _2 is more significant during periods of minimum than in periods of maximum. These findings are based on observational results that are not free of errors and can be refined further by considering torsional oscillations for example. They are comforted by identifying a periodic variation of the J _2 term evidenced through the analysis of the perihelion precession of planetary orbits either deduced from ephemerides or computed in the solar equatorial coordinate system instead of the ecliptic coordinate one usually used

Editorial. The Solar Cycle

International audienc

Influence of the UTLS region on the astrolabes solar signal measurement

International audienceRegular measurements of the Sun's diameter have been obtained by means of solar astrolabes for several decades. However, the variations found from those measurements are still very controversial, and the results implying changes in the solar radius are not conclusive. Since the quality of the measurements cannot be doubted, it is necessary to wonder what they are actually observing. We show here that some refraction effects, neglected so far, must be taken into account. Then, if the lower atmospheric layers merely add high-frequency noise (validated by the measured Fried parameter), we show here that the mid- to long-term variations take root in the upper troposphere - lower stratosphere region. Hence, the annual means of the Sun's apparent radius, measured at Calern (France) and Santiago (Chile), are linearly correlated with the geopotential height at 50-100 mb with correlation coefficients of -0.66 and 0.62, respectively, the opposite signs being the signature of the symmetry of the two hemispheres, North and South. In addition, the measurement dispersion is correlated with the variance of the wind speed above each observatory. Thus, it appears that the solar signal is amplified by the mechanisms dwelling in this interface zone between the lower stratosphere and the upper troposphere. Because these amplification mechanisms are unknown, it is difficult to extract pure solar information from the astrolabe signals, especially in sites where the seeing is less than 14-16 cm

Joint Discussion 17 Highlights of recent progress in the seismology of the Sun and Sun-like stars

International audienceThe seismology and physics of localized structures beneath the surface of the Sun takes on a special significance with the completion in 2006 of a solar cycle of observations by the ground-based Global Oscillation Network Group (GONG) and by the instruments on board the Solar and Heliospheric Observatory (SOHO). Of course, the spatially unresolved Birmingham Solar Oscillation Network (BiSON) has been observing for even longer. At the same time, the testing of models of stellar structure moves into high gear with the extension of deep probes from the Sun to other solar-like stars and other multi-mode pulsators, with ever-improving observations made from the ground, the success of the MOST satellite, and the recently launched CoRoT satellite. Here we report the current state of the two closely related and rapidly developing fields of helio- and asteroseimology