Reflected light from 3D exoplanetary atmospheres and simulation of HD 209458b

We present radiation transfer models that demonstrate that reflected light levels from 3D exoplanetary atmospheres can be more than 50 per cent lower than those predicted by models of homogeneous or smooth atmospheres. Compared to smooth models, 3D atmospheres enable starlight to penetrate to larger depths resulting in a decreased probability for the photons to scatter back out of the atmosphere before being absorbed. The increased depth of penetration of starlight in a 3D medium is a well-known result from theoretical studies of molecular clouds and planetary atmospheres. For the first time we study the reflectivity of 3D atmospheres as a possible explanation for the apparent low geometric albedos inferred for extrasolar planetary atmospheres. Our models indicate that 3D atmospheric structure may be an important contributing factor to the non-detections of scattered light from exoplanetary atmospheres. We investigate the self-shadowing radiation transfer effects of patchy cloud cover in 3D scattered light simulations of the atmosphere of HD 209458b. We find that, for a generic planet, geometric albedos can be as high as 0.45 in some limited situations, but that in general the geometric albedo is much lower. We conclude with some explanations on why extrasolar planets are likely dark at optical wavelengths.     

Ionization fraction in the thermosphere of the exoplanet HD 209458b

Dissociation and ionization of hydrogen molecules and ionization of hydrogen atoms due to extreme UV radiation from the parent star are accompanied by the formation of a concurrent photoelectron flux with excess kinetic energy. These dissociation and ionization processes are the main source of atomic and molecular ions in the thermospheres of extrasolar planets, such as the “hot Jupiter” HD 209458b. The ionization processes are the most important part of contemporary aeronomic models of planetary atmospheres in the Solar System and extrasolar systems (Johnson et al., 2008; Yelle et al., 2008). We estimate the contribution of the dissociation and ionization processes due to the stellar UV radiation and the concurrent photoelectron flux to the formation of extended ionospheres around extrasolar giant planets. As opposed to models of other researchers, we calculated the ionization rates due to the concurrent photo-electron flux for the first time. It is established that, in contrast to a widely used parametrization of the photoelectron contribution (Cecchi-Pestellini et al., 2006; 2009), the rate of secondary ionization due to the photoelectrons depends appreciably on the altitude, approaching the photoionization rate in the lower layers of the thermosphere. The calculated ionization rate in the thermosphere of the extrasolar giant planet (EGP) orbiting close to its parent star is a necessary link when modeling an aeronomic model and estimating the rate of the EGP atmospheric loss.     

Detection of Planetary Transits of the Star HD 209458 in the Hipparcos Data Set

A search of the Hipparcos satellite photometry data for the star HD 209458 reveals evidence for a planetary transit signature consistent with the planetary properties reported by Henry et al. and Charbonneau et al. and allows further refinement of the planet's orbital period. The long time baseline (about 2926 days or 830 periods) from the best Hipparcos transit-like event to the latest transit reported by Henry et al. for the night of 1999 November 15 (UT) allows for an orbital period determination of 3.524736 days with an uncertainty of 0.000045 days (3.9 s). The transit events observed by Charbonneau et al. fall at the interim times expected to within the errors of this newly derived period. A series of statistical tests was performed to assess the likelihood of these events occurring by chance. This was crucial given the ill-conditioned problem presented by the sparse sampling of the light curve and the non-Gaussian distribution of the points. Monte Carlo simulations using bootstrap methods with the actual Hipparcos HD 209458 data set indicate that the transit-like signals of the depth observed would only be produced by chance in 21 out of 1 million trials. The transit durations and depths obtained from the Hipparcos data are also consistent with those determined by Charbonneau et al. and Henry et al. within the limitations of the sampling intervals and photometric precision of the Hipparcos data.     

Suprathermal hydrogen produced by the dissociation of molecular hydrogen in the extended atmosphere of exoplanet HD 209458b

The ionization and dissociation of molecular hydrogen by the ultraviolet (UV) radiation of the parent star lead to the formation of hydrogen atoms with an excess of kinetic energy and, thus, are an important source of suprathermal hydrogen atoms in the upper atmosphere of exoplanet HD 209458b. Contemporary aeronomical models did not investigate these processes because they assumed the fast local thermalization of the hot atoms of hydrogen by elastic collisions. However, the kinetics and transfer of these atoms were not calculated in detail, because they require the solving of the Boltzmann equation for a nonthermal atom population. This work estimates the effect of the UV radiation of the parent star and the accompanying photocleacton flux on the production of the suprathermal fraction of atomic hydrogen in the H₂ → H transition region. We also consider the formation of the escaping flux of Hatoms created by this effect in the upper atmosphere of HD 209458b. We calculate the production rate and energy spectrum of the hydrogen atoms with excess kinetic energy during the dissociation of H₂. Using the numerical stochastic model created by Shematovich (2004) for a hot planetary corona, we investigate the molecular-scale kinetics and transfer of suprathermal hydrogen atoms in the upper atmosphere and the emergent flux of atoms evaporating from the atmosphere. The latter is estimated as 3.4 × 10¹² cm⁻² s⁻¹ for a moderate stellar activity level of UV radiation, which leads to a planetary atmosphere evaporation rate of 3.4 × 10⁹ g s⁻¹ due to the process of the dissociation of H₂. This estimate is close to the observational value of ∼10¹⁰ g s⁻¹ for the rate of atmospheric loss of HD 209458b.     

Nature of Quiet Sun Oscillations Using Data from the Hinode, TRACE, and SOHO Spacecraft

We study the nature of quiet-Sun oscillations using multi-wavelength observations from TRACE, Hinode, and SOHO. The aim is to investigate the existence of propagating waves in the solar chromosphere and the transition region by analyzing the statistical distribution of power in different locations, e.g. in bright magnetic (network), bright non-magnetic and dark non-magnetic (inter-network) regions, separately. We use Fourier power and phase-difference techniques combined with a wavelet analysis. Two-dimensional Fourier power maps were constructed in the period bands 2??C?4?minutes, 4??C?6?minutes, 6??C?15?minutes, and beyond 15?minutes. We detect the presence of long-period oscillations with periods between?15 and 30?minutes in bright magnetic regions. These oscillations were detected from the chromosphere to the transition region. The Fourier power maps show that short-period powers are mainly concentrated in dark regions whereas long-period powers are concentrated in bright magnetic regions. This is the first report of long-period waves in quiet-Sun network regions. We suggest that the observed propagating oscillations are due to magnetoacoustic waves, which can be important for the heating of the solar atmosphere.     

Detection Capability Evaluation of Lunar Mineralogical Spectrometer:Results from Ground Experimental Data

The Chang’E-6 mission will first land on the far side of the moon and bring lunar samples back. As a hyperspectral imager aboard the Chang’E-6 lander, the Lunar Mineralogical Spectrometer(LMS), will achieve the goal of spectral detection and mineral composition analysis in the sampling area, and the data of LMS will also be compared with the results of the returned sample laboratory measurements. Visible and near-infrared hyperspectral remote sensing is an effective tool for lunar minerals ident...     

Secondary radio eclipse of the transiting planet HD 189733 b: an upper limit at 307–347 MHz

We report the first attempt to observe the secondary eclipse of a transiting extra-solar planet at radio wavelengths. We observed HD 189733 b with the Robert C. Byrd Green Bank Telescope of the National Radio Astronomy Observatory (NRAO) over about 5.5 h before, during and after secondary eclipse, at frequencies of 307–347 MHz. In this frequency range, we determine the 3σ upper limit to the flux density to be 81 mJy. The data are consistent with no eclipse or a marginal reduction in flux at the time of secondary eclipse in all subsets of our bandwidth; the strongest signal is an apparent eclipse at the 2σ level in the 335.2–339.3 MHz region. Our observed upper limit is close to theoretical predictions of the flux density of cyclotron-maser radiation from the planet.     

On the Nature and Redshift Evolution of DLA Galaxies

We extend our spiral galaxy models, which successfully describe nearby template spectra as well as the redshift evolution of CFRS and HDF spirals, to include – in a chemically consistent way – the redshift evolution of a series of individual elements. Comparison with observed DLA abundances shows that DLAs might well be the progenitors of present-day spiral types Sa through Sd. Our models bridge the gap between high redshift DLA and nearby spiral HII region abundances. The slow redshift evolution of DLA abundances is a natural consequence of the long SF timescales for discs, the scatter at any redshift reflects the range of SF timescales from early to late spiral types. We claim that, while at high redshift all spiral progenitor types seem to give rise to DLA absorption, towards low redshifts, the early-type spirals seem to drop out of DLA samples due to low gas and/or high metal and dust content. Model implications for the spectrophotometric properties of the DLA galaxy population are discussed in the context of campaigns for the optical identifications of DLA galaxies both at low and high redshift. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the mass and distance of the Quasi-Stellar Object 3C 273

For the QSO 3C 273 we derive, on the basis of two different theoretical models, expressions for a lower limit to the mass of the QSO, as a function of its distance. We conclude that an appreciable gravitational redshift component is consistent with the observational data only if the QSO mass is at least Galactic in magnitude. The setting of an independent upper limit to the QSO massM10¹⁰ M could indicate that the QSO redshift is predominantly cosmological in nature.     

On the Collision Nature of Two Coronal Mass Ejections: A Review

Observational and numerical studies have shown that the kinematic characteristics of two or more coronal mass ejections (CMEs) may change significantly after a CME collision. The collision of CMEs can have a different nature, i.e. inelastic, elastic, and superelastic processes, depending on their initial kinematic characteristics. In this article, we first review the existing definitions of collision types including Newton’s classical definition, the energy definition, Poisson’s definition, and Stronge’s definition, of which the first two were used in the studies of CME–CME collisions. Then, we review the recent research progresses on the nature of CME–CME collisions with the focus on which CME kinematic properties affect the collision nature. It is shown that observational analysis and numerical simulations can both yield an inelastic, perfectly inelastic, merging-like collision, or a high possibility of a superelastic collision. Meanwhile, previous studies based on a 3D collision picture suggested that a low approaching speed of two CMEs is favorable for a superelastic nature. Since CMEs are an expanding magnetized plasma structure, the CME collision process is quite complex, and we discuss this complexity. Moreover, the models used in both observational and numerical studies contain many limitations. All of the previous studies on collisions have not shown the separation of two colliding CMEs after a collision. Therefore the collision between CMEs cannot be considered as an ideal process in the context of a classical Newtonian definition. In addition, many factors are not considered in either observational analysis or numerical studies, e.g. CME-driven shocks and magnetic reconnections. Owing to the complexity of the CME collision process, a more detailed and in-depth observational analysis and simulation work are needed to fully understand the CME collision process.     

On the Nature of Jets from a Main Sequence Companion at the Onset of Common Envelope Evolution

I consider a flow structure by which main sequence companions that enter a common envelope evolution(CEE)with giant stars might launch jets even when the accreted gas has a sub-Keplerian specific angular momentum. I first show that after a main sequence star enters the envelope of a giant star the specific angular momentum of the accreted gas is sub-Keplerian but still sufficiently large for the accreted gas to avoid two conical-like openings along the two opposite polar directions. I suggest th...     

Comparison of Star Formation Rate Estimates from Hα, FIR and Radio Data

We use three indicators of massive star formation, H_α, FIR and non-thermal radio luminosities, to compare estimates of the star formation rate (SFR) for a sample of 34 spiral galaxies. To adjust the SFR values obtained from these indicators, we considered the slope, α, and/or the upper mass limit M _up of the initial mass function (IMF) as free parameters. The best agreement between the indicators is found for M _up≈ 60-100 M⊙ and α ≈–3.1 at the high-mass end of the IMF (M>10 M⊙.Parallelwith the SFR we also estimated the FIR excess X _FIR, defined as the fraction of the observed FIR not directly related to young massive stars. X _FIR is found to be well correlated with types of spiral galaxies and their colours (B-V): the redder a galaxy, the higher its FIR excess. We conclude that for any parameters of the IMF the observed FIR flux of early-type spiral galaxies needs an additional source of energy apart from massive star radiation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Absolute Calibration of the Clementine UVVIS Data: Comparison with Ground-Based Observation of the Moon

Calibrated Clementine images of the Moon and data from Pieters's absolutized spectrophotometric catalog are compared. The scales of these two photometric systems are shown to differ greatly: the albedo of the lunar surface at a phase angle of 6° determined from the Clementine data turns out to be a factor of 2.5 higher than that inferred from ground-based photometry. The fact that the lunar-soil samples from the Apollo 16 landing site used for absolute calibration of the Clementine data are not representative may be responsible for the differences between the scales. Maps are constructed (for wavelengths of 0.42, 0.75, and 0.95 m), which reproduce the distribution of the ratio of the brightnesses determined from telescopic images of the visible lunar hemisphere and from the corresponding Clementine mosaics. The comparison shows fairly good agreement in the details. On the average, the differences are about 10%. The streakiness of the Clementine mosaics are clearly seen in the maps, which is attributable to a low quality of the photometric joining of the data from two one-month imaging series.     

On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode (Invited Review)

A major, albeit serendipitous, discovery of the SOlar and Heliospheric Observatory mission was the observation by the Extreme Ultraviolet Telescope (EIT) of large-scale extreme ultraviolet (EUV) intensity fronts propagating over a significant fraction of the Sun??s surface. These so-called EIT or EUV waves are associated with eruptive phenomena and have been studied intensely. However, their wave nature has been challenged by non-wave (or pseudo-wave) interpretations and the subject remains under debate. A string of recent solar missions has provided a wealth of detailed EUV observations of these waves bringing us closer to resolving the question of their nature. With this review, we gather the current state-of-the-art knowledge in the field and synthesize it into a picture of an EUV wave driven by the lateral expansion of the CME. This picture can account for both wave and pseudo-wave interpretations of the observations, thus resolving the controversy over the nature of EUV waves to a large degree but not completely. We close with a discussion on several remaining open questions in the field of EUV waves research.     

Comparison of the composition of the Tempel 1 ejecta to the dust in Comet C/Hale-Bopp 1995 O1 and YSO HD 100546

Spitzer Infrared Spectrograph observations of the Deep Impact experiment in July 2005 have created a new paradigm for understanding the infrared spectroscopy of primitive solar nebular (PSN) material—the ejecta spectrum is the most detailed ever observed in cometary material. Here we take the composition model for the material excavated from Comet 9P/Tempel 1's interior and successfully apply it to Infrared Space Observatory spectra of material emitted from Comet C/1995 O1 (Hale-Bopp) and the circumstellar material found around the young stellar object HD 100546. Comparison of our results with analyses of the cometary material returned by the Stardust spacecraft from Comet 81P/Wild 2, the in situ Halley flyby measurements, and the Deep Impact data return provides a fundamental cross-check for the spectral decomposition models presented here. We find similar emission signatures due to silicates, carbonates, phyllosilicates, water ice, amorphous carbon, and sulfides in the two ISO-observed systems but there are significant differences as well. Compared to Tempel 1, no Fe-rich olivines and few crystalline pyroxenes are found in Hale-Bopp and HD 100546. The YSO also lacks amorphous olivine, while being super-rich in amorphous pyroxene. All three systems show substantial emission due to polycyclic aromatic hydrocarbons. The silicate and PAH material in Hale-Bopp is clearly less processed than in Tempel 1, indicating an earlier age of formation for Hale-Bopp. The observed material around HD 100546 is located ∼13 AU from the central source, and demonstrates an unusual composition due to either a very different, non-solar starting mix of silicates or due to disk material processing during formation of the interior disk cavity and planet(s) in the system.