EChOSim: The Exoplanet Characterisation Observatory software simulator

EChOSim is the end-to-end time-domain simulator of the Exoplanet Characterisation Observatory (EChO) space mission. EChOSim has been developed to assess the capability of the EChO mission concept to detect and characterise the atmospheres of transiting exoplanets. Here we discuss the details of the EChOSim implementation and describe the models used to represent the instrument and to simulate the detection. Software simulators have assumed a central role in the design of new instrumentation and in assessing the level of systematics affecting the measurements of existing experiments. Thanks to its high modularity, EChOSim can simulate basic aspects of several existing and proposed spectrometers including instruments on the Hubble Space Telescope and Spitzer, ground-based and balloon-borne experiments. A discussion of different uses of EChOSim is given, including examples of simulations performed to assess the EChO mission.     

A refractory inclusion with solar oxygen isotopes and the rarity of such objects in the meteorite record

NASA's Genesis mission revealed that the Sun is enriched in ¹⁶O compared to the Earth and Mars (the Sun's Δ¹⁷O, defined as δ¹⁷O–0.52×δ¹⁸O, is –28.4 ± 3.6‰; McKeegan et al. 2011). Materials as ¹⁶O‐rich as the Sun are extremely rare in the meteorite record. Here, we describe a Ca‐Al‐rich inclusion (CAI) from a CM chondrite that is as ¹⁶O‐enriched as the Sun (Δ¹⁷O = –29.1 ± 0.7‰). This CAI also has large nucleosynthetic anomalies in ⁴⁸Ca and ⁵⁰Ti (δ‐values are –8.1 ± 3.3 and –11.7 ± 2.4‰, respectively) and shows no clear evidence for incorporation of live ²⁶Al; (²⁶Al/²⁷Al)₀ = (0.03 ± 0.11) × 10^–5. Due to their anomalous isotopic characteristics, the rare CAIs consistent with the Genesis value could be among the first materials that formed in the solar system. In contrast to the CAI studied here, the majority of CAIs formed in or interacted with a reservoir characterized by a Δ¹⁷O value near –23.5‰. Combined with ²⁶Al‐²⁶Mg systematics, the oxygen isotopic compositions of FUN (fractionation and unidentified nuclear effects), UN, and normal CAIs suggest that nebular conditions were favorable for solids to inherit this value for an extended period of time. Many later‐formed materials, such as chondrules, planetesimals, and terrestrial planets, formed in reservoirs with Δ¹⁷O near 0‰. The distribution could be easier to explain if the common CAI value of –23.5‰, which is consistent with the Genesis value within 3σ, represented the average composition of the protoplanetary disk.     

First results from the Gauribidanur Radio heliograph

Observations of the Sun at two frequencies (51 and 77 MHz) using the East-West arm of the Gauribidanur Radio heliograph are presented.     

Photospheric Magnetic Field: Relationship Between North–South Asymmetry and Flux Imbalance

Photospheric magnetic fields were studied using the Kitt Peak synoptic maps for 1976?–?2003. Only strong magnetic fields (B>100 G) of the equatorial region were taken into account. The north–south asymmetry of the magnetic fluxes was considered as well as the imbalance between positive and negative fluxes. The north–south asymmetry displays a regular alternation of the dominant hemisphere during the solar cycle: the northern hemisphere dominated in the ascending phase, the southern one in the descending phase during Solar Cycles 21?–?23. The sign of the imbalance did not change during the 11 years from one polar-field reversal to the next and always coincided with the sign of the Sun’s polar magnetic field in the northern hemisphere. The dominant sign of leading sunspots in one of the hemispheres determines the sign of the magnetic-flux imbalance. The sign of the north–south asymmetry of the magnetic fluxes and the sign of the imbalance of the positive and the negative fluxes are related to the quarter of the 22-year magnetic cycle where the magnetic configuration of the Sun remains constant (from the minimum where the sunspot sign changes according to Hale’s law to the magnetic-field reversal and from the reversal to the minimum). The sign of the north–south asymmetry for the time interval considered was determined by the phase of the 11-year cycle (before or after the reversal); the sign of the imbalance of the positive and the negative fluxes depends on both the phase of the 11-year cycle and on the parity of the solar cycle. The results obtained demonstrate the connection of the magnetic fields in active regions with the Sun’s polar magnetic field in the northern hemisphere.     

3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum

Measurement of the coronal magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employed STEREO/COR1 data obtained during a deep minimum of solar activity in February 2008 (Carrington Rotation CR 2066) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 R_⊙ using a tomography method. With this, we qualitatively deduced structures of the coronal magnetic field. The 3D electron-density analysis is complemented by the 3D STEREO/EUVI emissivity in the 195 Å band obtained by tomography for the same CR. A global 3D MHD model of the solar corona was used to relate the reconstructed 3D density and emissivity to open/closed magnetic-field structures. We show that the density-maximum locations can serve as an indicator of current-sheet position, while the locations of the density-gradient maximum can be a reliable indicator of coronal-hole boundaries. We find that the magnetic-field configuration during CR 2066 has a tendency to become radially open at heliocentric distances greater than 2.5 R_⊙. We also find that the potential-field model with a fixed source surface is inconsistent with the boundaries between the regions with open and closed magnetic-field structures. This indicates that the assumption of the potential nature of the coronal global magnetic field is not satisfied even during the deep solar minimum. Results of our 3D density reconstruction will help to constrain solar coronal-field models and test the accuracy of the magnetic-field approximations for coronal modeling.     

High-Resolution Optical Spectroscopy of the Post-AGB Supergiant V340 Ser ( $${\mathbf{=}}$$ IRAS 17279 $$\mathbf{-}$$ 1119)

Astronomy Letters - Evidence of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser ( $${=}$$ IRAS 17279 $$-$$ 1119)...     

On the periodical structures in populations of galaxies and of clusters of galaxies

Analysing the distribution of the redshift of clusters of galaxies, obtained from the catalogue of SCHMIDT (1986), two already known periodical structures were confirmed and both periods were extended by a number of periods — approximately by two times (We elucidated 5 new periods in the first structure and 4 in the second.). The statistical significance of these structures was estimated to 0.01 in the first case and to 0.02 in the second one. Particularly, the second structure may be the largest known object in the Universe (about 900 Mpc at H = 75 km s^-1 Mpc^-1). These results agree with the predictions of the axion-dominated early Universe. In addition, we discovered periodical structures of an another type — in luminosity functions of galaxies, which are members of rich clusters. Bei der Analyse des Katalogs von SCHMIDT (1986) wurden zwei periodische Strukturen in den Verteilungen der Rotverschiebungen von Galaxienhaufen festgestellt. In den beiden Strukturen wurden 5 bzw. 4 neue Perioden beobachtet, weshalb sich die Periodenzahl in jeder der beiden Strukturen etwa verdoppelt hat. Die statistische Signifikanzen dieser Strukturen wurden zu 0.01 und 0.02 abgeschätzt. Möglicherweise entspricht die zweite Struktur dem größten bekannten Objekt des Weltalls (etwa 900 Mpc bei H = 75 km s^-1 Mpc^-1). Diese Resultate stützen die Theorie eines axiondominierten frühen Universums. Außerdem wurden weitere periodische Strukturen in der Leuchtkraftfunktion von Galaxien aus reichen Galaxien-haufen entdeckt.