Characterization of terrestrial exoplanets based on the phase curves and albedos of Mercury, Venus and Mars

The empirically derived phase curves of terrestrial planets strongly distinguish between airless Mercury, cloud-covered Venus, and the intermediate case of Mars. The function for Mercury is steeply peaked near phase angle zero due to powerful backscattering from its surface, while that for Venus has 100 times less contrast and exhibits a brightness excess near 170° due to Mie scattering from droplets in the atmosphere. The phase curve of Mars falls between those of Mercury and Venus, and there are variations in luminosity due to the planet’s rotation, seasons, and atmospheric states. The phase function and geometric albedo of the Earth are estimated from published albedos values. The curves for Mercury, Venus and Mars are compared to that of the Earth as well as theoretical phase functions for giant planets. The parameters of these different phase functions can be used to characterize exoplanets.     

Opposition effect of Trojan asteroids

CCD-photometry of three Jupiter Trojan asteroids were carried out to study their opposition effect. We obtained well-sampled magnitude–phase curves for (588) Achilles, (884) Priamus, and (1143) Odysseus in the maximal attainable phase angle range down to 0.1–0.2°. The magnitude–phase relations have a linear behavior in all observed range of phase angles and do not show any non-linear opposition brightening. We have not found any confident differences between phase slopes measured in B, V and R bands. The values of the measured phase slopes of Trojans are different from available data for Centaurs. They are within the range of phase slopes measured for some low-albedo main belt asteroids, also exhibit a linear behavior down to small phase angles. An absence of non-linear opposition brightening puts constraints on the surface properties of the studied objects, assuming very dark surfaces where single scattering plays dominating role.We also determined the rotation periods, amplitudes, the values of color indexes B–V and V–R, and the absolute magnitudes of these asteroids.     

Voyager disk-integrated photometry of Io

Voyager full-disk images of Io, available at solar phase angle of α = 2?29° and 101?159°, allow comparisons of the satellite's near-opposition photometric behavior with Earth-based results and the determination of the phase curve out to very high phase angles. The near-opposition data were reduced iteratively for self-consistent phase and rotation curves in each Voyager filter; the resulting phase coefficients, geometric albedos, and rotational lightcurves are consistent with Earth-based findings, except for a previously noted tendency for Voyager to yield somewhat redder spectral information. The derived near-opposition phase coefficients, ranging between 0.016 and 0.024 mag/ deg, decrease with increasing wavelength, a trend weakly noted in some Earth-based observations. The full, α = 2?159° phase curves allow the first direct determination of the phase integral of Io at several wavelengths: q rises from ≈0.7 in the ultraviolet to ≈0.8 in the orange. Combination of the Voyager phase integrals with Earth-based albedo information leads to a best estimate of the bolometric Bond albedo of 0.50 ± 0.10, a value consistent with, but slightly below, previous estimates.     

The phase ratios of the color index: Mapping of two regions of the near side of the Moon

From the ground-based colorimetry performed for two surface regions of the near side of the Moon, images of the phase ratio of the color index C(600 nm/470 nm) have been built for the phase angles between 2° and 95°. It has been found that for phase angles smaller than α ∼ 40°–50°, the color index of the highlands grows with the phase quicker than that of the mare regions. For larger phase angles, α > 50°, a reverse situation is observed. The laboratory data on the spectrophotometry of the lunar samples confirm the peculiarities found in the phase dependence of color. The influence of multiple scattering on the phase dependence of the color of the mare and highland regions of the Moon are discussed.     

Entropy change and phase transitions in an expanding Universe

The work compiles a correlated study of a gravitational quasi equilibrium thermodynamic approach for establishing and signifying a unique behavior of the cosmological entropy and phase transitions in an expanding Universe. On the basis of prescribed boundary conditions for the cluster temperature a relation for the intra‐cluster medium (ICM) of galaxy clusters has been derived. A more productive and signifying approach of the correlation functions used for galaxy clustering phenomena shows a unique behavior of the entropy change where a phenomenon known as the gravitational phase transition occurs. This unique behavior occurs with a symmetry breaking from mild clustering to low clustering and from mild clustering to high clustering which differs from a normal symmetry breaking in material sciences. We also derive results for the specific latent heat associated with the phase transitions of 3.20 T_c and 0.55 T_c for the mildly clustered phase to the low clustered phase and from the mildly clustered phase to the highly clustered phase, respectively. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Long-term longitudinal asymmetries in sunspot activity: Difference between the ascending and descending phase of the solar cycle

We study the longitudinal distribution of sunspot activity in 1917–1995 using vector sums of sunspot areas. The vector sum of sunspots of one solar rotation gives a total vector whose amplitude characterizes the size of longitudinal asymmetry and whose phase describes the location of the momentarily dominating longitude. We find that when the phase distributions are calculated separately for the ascending phase and maximum (AM) on the one hand and for the declining phase and minimum (DM) on the other hand, they behave differently and depict broad maxima around roughly opposite longitudes. While the maximum of the phase distribution for the AM period is found around the Carrington longitude of 180°, the maximum for the DM period is at the longitude of about 0°. This difference can be seen in both solar hemispheres, but it is more pronounced in the southern hemisphere where the phase distribution has a particularly clear pattern. No other division of data into two intervals leads to similar systematic differences.     

Synchronization of Sunspot Numbers and Sunspot Areas

Sunspot activity is usually described by either sunspot numbers or sunspot areas. The smoothed monthly mean sunspot numbers (SNs) and the smoothed monthly mean areas (SAs) in the time interval from November 1874 to September 2007 are used to analyze their phase synchronization. Both the linear method (fast Fourier transform) and some nonlinear approaches (continuous wavelet transform, cross-wavelet transform, wavelet coherence, cross-recurrence plot, and line of synchronization) are utilized to show the phase relation between the two series. There is a high level of phase synchronization between SNs and SAs, but the phase synchronization is detected only in their low-frequency components, corresponding to time scales of about 7 to 12 years. Their high-frequency components show a noisy behavior with strong phase mixing. Coherent phase variables should exist only for a frequency band with periodicities around the dominating 11-year cycle for SNs and SAs. There are some small phase differences between them. SNs lag SAs during most of the considered time interval, and they are in general more asynchronous around the minimum and maximum times of a cycle than at the ascending and descending phases.     

一种时频信号相位补偿方法

为消除信号产生器内温度变化对信号相位的影响,提出了一种恒温控制和实时相位调整相结合的方法。在这种方法中,除恒温控制外,基于对信号产生器内部温度、相位测量值变化率、设备调相分辨率和相位波动指标等的分析研究,合理计算实时相位调整关键参数,进行实时相位调整,有效地减小信号产生器内部温度变化引起的相位波动,提高了输出端信号相位的一致性和稳定性。     

The photometric functions of Phobos and Deimos I. Disc-integrated photometry

We have used the integrated brightnesses from Mariner 9 high-resolution images to determine the large phase angle (20° to 80°) phase curves of Phobos and Deimos. The derived phase coefficients are β = 0.032 ± 0.001 mag/deg for Phobos and β = 0.030 ± 0.001 mag/deg for Deimos, while the corresponding phase integrals are q_Phobos = 0.52 and q_Deimos = 0.57. The predicted intrinsic phase coefficients of the surface material are β_i = 0.019 mag/deg and β_i = 0.017 mag/deg for Phobos and Deimos, respectively. The phase curves, phase coefficients and phase integrals are typical of objects whose surface layers are dark and intricate in texture, and are consistent with the presence of a regolith on both satellites. The relative reflectance of Deimos to Phobos is 1.15±0.10. The presence of several bright patches on Deimos could account for this slight difference in average reflectance.     

Monochromatic intensity measurements of selected areas of lunar surface for possible investigations

Absolute photoelectric intensity measurements of 104 selected lunar regions are given in five interference filters 4035 Å, 4765 Å, 5538 Å, 6692 Å and 7922 Å. Among these regions, eighteen lunar regions have been measured repeatedly for several phase angles between +86° and ?43°. They include observations made very close to the full Moon. A catalogue has been compiled to serve as a basin for possible investigations of colour contrasts of lunar grounds, variation of the ratio of reflectivity with wavelengths and phase angles for morphological studies. The study can be extended for the brightness phase variation, opposition effect and radiance factors at zero phase in five colours.     

Solar phase curves and phase integrals for the leading and trailing hemispheres of Iapetus from the Cassini Visual Infrared Mapping Spectrometer

We performed photometry of Cassini Visual Infrared Mapping Spectrometer observations of Iapetus to produce the first phase integrals calculated directly from solar phase curves of Iapetus for the leading hemisphere and to estimate the phase integrals for the trailing hemisphere. We also explored the phase integral dependence on wavelength and geometric albedo. The extreme dichotomy of the brightness of the leading and trailing sides of Iapetus is reflected in their phase integrals. Our phase integrals, which are lower than the results of Morrison et al. (Morrison, D., Jones, T.J., Cruikshank, D.P., Murphy, R.E. [1975]. Icarus 24, 157-171) and Squyres et al. (Squyres, S.W., Buratti, B.J., Veverka, J., Sagan, C. [1984]. Icarus 59, 426-435), have profound implications on the energy balance and volatile transport on this icy satellite.     

The Relative Phase Asynchronization between Sunspot Numbers and Polar Faculae

The monthly sunspot numbers compiled by Temmer et al. and the monthly polar faculae from observations of the National Astronomical Observatory of Japan, for the interval of March 1954 to March 1996, are used to investigate the phase relationship between polar faculae and sunspot activity for total solar disk and for both hemispheres in solar cycles 19, 20, 21 and 22. We found that (1) the polar faculae begin earlier than sunspot activity, and the phase difference exhibits a consistent behaviour for different hemispheres in each of the solar cycles, implying that this phenomenon should not be regarded as a stochastic fluctuation; (2) the inverse correlation between polar faculae and sunspot numbers is not only a long-term behaviour, but also exists in short time range; (3) the polar faculae show leads of about 50–71 months relative to sunspot numbers, and the phase difference between them varies with solar cycle; (4) the phase difference value in the northern hemisphere differs from that in the southern hemisphere in a solar cycle, which means that phase difference also existed between the two hemispheres. Moreover, the phase difference between the two hemispheres exhibits a periodical behaviour. Our results seem to support the finding of Hiremath (2010).     

Coronal Mass Ejections Associated with Slow Long Duration Flares

It is well known that there is a temporal relationship between coronal mass ejections (CMEs) and associated flares. The duration of the acceleration phase is related to the duration of the rise phase of a flare. We investigate CMEs associated with slow long duration events (LDEs), i.e. flares with the long rising phase. We determined the relationships between flares and CMEs and analyzed the CME kinematics in detail. The parameters of the flares (GOES flux, duration of the rising phase) show strong correlations with the CME parameters (velocity, acceleration during main acceleration phase, and duration of the CME acceleration phase). These correlations confirm the strong relation between slow LDEs and CMEs. We also analyzed the relation between the parameters of the CMEs, i.e. a velocity, an acceleration during the main acceleration phase, a duration of the acceleration phase, and a height of a CME at the end of the acceleration phase. The CMEs associated with the slow LDEs are characterized by high velocity during the propagation phase, with the median equal to 1423 km?s^?1. In half of the analyzed cases, the main acceleration was low (a<300 m?s^?2), which suggests that the high velocity is caused by the prolonged acceleration phase (the median for the duration of the acceleration phase is equal 90 minutes). The CMEs were accelerated up to several solar radii (with the median ≈?7 R _⊙), which is much higher than in typical impulsive CMEs. Therefore, slow LDEs may potentially precede extremely strong geomagnetic storms. The analysis of slow LDEs and associated CMEs may give important information for developing more accurate space-weather forecasts, especially for extreme events.     

O(S) excitation mechanism and atmospheric tides

There are two mechanisms which can account for the oxygen green line emission at 100 km Altitude, namely the Chapman and Barth mechanisms. Theoretical results and experimental data are used in order to discriminate which of these predominates in the atmosphere. In particular we have used an important new test which consists in comparing the phase of the mean diurnal variation of the green line intensity with the phase of the tide responsible for this variation. This is a powerful test because the phase of the green line variation calculated from the tidal phase has a very weak dependence on the atmospheric model used. Our conclusion is that in the atmosphere the Chapman mechanism predominates.     

Asteroid photometric and polarimetric phase curves: empirical interpretation

A method for interpretation of asteroid phase curves, based on empirical modeling and laboratory measurements, is outlined and preliminary results are presented. A linear-exponential function is used to describe the opposition peaks and negative polarization surges of various asteroids and laboratory samples and a statistical algorithm is used in parameter estimation. The linear-exponential function describes well the phase curves, but dense phase angle coverage, particularly at small phase angles must be obtained to improve the results. Major emphasis should also be put on laboratory study: with an extensive library of laboratory measurements, a stronger connection between the phase curve properties and surface characteristics is possible.     

Preflare characteristics of active regions observed in soft X-rays

X-ray images from the AS&E telescope on Skylab are used to investigate coronal conditions in solar active regions during the 20-min periods preceding the X-ray onsets of small flares. The preflare or precursor phase is defined as a phase with a characteristic length or time scale significantly different from that of the rise phase. We show that there is no observational evidence of a requirement for a coronal preflare heating phase with a time scale longer than 2 min for small flares characterized by one or two loops. In 18 out of 25 cases the flaring X-ray structure was not the brightest feature in the preflare active region. The electron densities are estimated for preflare loops.     

Asteroid observations at low phase angles. I. 50 Virginia, 91 Aegina and 102 Miriam

We present observations of magnitude-phase dependences of three low-albedo asteroids down to phase angles of 0.1–0.2°. Data were obtained during 40 nights from 1994 to 1995 within the joint observational program at ESO and Kharkiv Astronomical Observatories with the aim to reach as low phase angles as possible. All three low-albedo asteroids may display a small nonlinear increase in magnitude-phase dependence at subdegree phase angles. The phase curves of 50 Virginia and 102 Miriam are poorly approximated by the HG function. Rotation periods of the asteroids were also determined: 14.310±0.010 hours for 50 Virginia, 6.030±0.001 h for 91 Aegina and 15.789± 0.003 h for 102 Miriam.     

Open issues on the synthesis of evolved stellar populations at ultraviolet wavelengths

This paper deals with five-dimensional black hole solutions in (a) Einstein-Maxwell-Gauss-Bonnet theory with a cosmological constant and (b) Einstein-Yang-Mills-Gauss-Bonnet theory for spherically symmetric space time. In both the cases the possibility of phase transition is examined and it is analyzed whether the phase transition is a Hawking-Page type phase transition or not.     

Low phase angle effects in photometry of trans-neptunian objects: 20000 Varuna and 19308 (1996 TO66)

We present the results of photometric observations of trans-neptunian object 20000 Varuna, which were obtained during 7 nights in November 2004-February 2005. The analysis of new and available photometric observations of Varuna reveals a pronounced opposition surge at phase angles less than 0.1 deg with amplitude of 0.2 mag relatively to the extrapolation of the linear part of magnitude-phase dependence to zero phase angle. The opposition surge of Varuna is markedly different from that of dark asteroids while quite typical for moderate albedo Solar System bodies. We find an indication of variations of the scattering properties over Varuna's surface that could result in an increase of the lightcurve amplitude toward zero phase angle. It is shown that a similar phase effect can be responsible for lightcurve changes found for TNO 19308 (1996 TO₆₆) in 1997-1999.