AzTEC millimetre survey of the COSMOS field – I. Data reduction and source catalogue

We present a 1.1 mm wavelength imaging survey covering 0.3 deg² in the COSMOS field. These data, obtained with the AzTEC continuum camera on the James Clerk Maxwell Telescope, were centred on a prominent large-scale structure overdensity which includes a rich X-ray cluster at z ≈ 0.73. A total of 50 mm-galaxy candidates, with a significance ranging from 3.5 to 8.5σ, are extracted from the central 0.15 deg² area which has a uniform sensitivity of ∼1.3 mJy beam⁻¹. 16 sources are detected with S/N ≥ 4.5, where the expected false-detection rate is zero, of which a surprisingly large number (9) have intrinsic (deboosted) fluxes ≥5 mJy at 1.1 mm. Assuming the emission is dominated by radiation from dust, heated by a massive population of young, optically obscured stars, then these bright AzTEC sources have far-infrared luminosities  >6 × 10¹² L_⊙  and star formation rates  >1100 M_⊙ yr⁻¹  . Two of these nine bright AzTEC sources are found towards the extreme peripheral region of the X-ray cluster, whilst the remainder are distributed across the larger scale overdensity. We describe the AzTEC data reduction pipeline, the source-extraction algorithm, and the characterization of the source catalogue, including the completeness, flux deboosting correction, false-detection rate and the source positional uncertainty, through an extensive set of Monte Carlo simulations. We conclude with a preliminary comparison, via a stacked analysis, of the overlapping MIPS 24-μm data and radio data with this AzTEC map of the COSMOS field.     

On bridges B(pL, qS) around triangular libration points

When μ is smaller than Routh’s critical value μ ₁ = 0.03852 . . . , two planar Lyapunov families around triangular libration points exist, with the names of long and short period families. There are periodic families which we call bridges connecting these two Lyapunov families. With μ increasing from 0 to 1, how these bridges evolve was studied. The interval (0,1) was divided into six subintervals (0, μ ₅), (μ ₅, μ ₄), (μ ₄, μ ₃), (μ ₃, μ ₂), (μ ₂, μ ₁), (μ ₁, 1), and in each subinterval the families B(pL, qS) were studied, along with the families B(qS, qS′). Especially in the interval (μ ₂, μ ₁), the conclusion that the bridges B(qS, qS′) do not exist was obtained. Connections between the short period family and the bridges B(kS, (k + 1)S) were also studied. With these studies, the structure of the web of periodic families around triangular libration points was enriched.     

Variability of Extended Bipolar Regions

Using NSO/Kitt Peak synoptic charts from 1975 to 2003, we group the main solar magnetic fields into two categories: one for active regions (ARs) and the other for extended bipolar regions (EBRs). Comparing them, we find that there exist three typical characteristics in the variability of EBRs: First, there exists a correlation between ARs and EBRs. The phase of EBR flux has a delay nearly two CRs. Second, we find that the EBR flux has two prominent periods at 1.79 years and 3.21 years. The 1.79-year period seems to only belong to large-scale magnetic features. Lastly, the North – South asymmetry of EBR flux is not very significant on a time scale of one solar cycle. However, during solar maxima, its dominance is found to shift from one hemisphere to the other.     

Periodicities in Global Mean TEC from GNSS Observations

As an important measurement parameter, global total electron content (TEC) is appropriate for the study of the Sun–Earth connection. In this paper, the wavelet technique is employed to investigate the periodicities in global mean TEC during 1995–2008. Analysis results show several remarkable components (including 27-day, semiannual and annual cycles) existing in global mean TEC with obvious time-variable characteristics, besides 11-year cycle. After analyzing sunspot numbers and solar extreme ultra-violet (EUV) radiation variations during this time period, except for semiannual variations, close correlation between global mean TEC and solar variations is found, especially, a strong resemblance of the 27-day fluctuation exists in global mean TEC, sunspot and solar EUV radiation variations.     

Structural evolution of the 40 km wide Araguainha impact structure,central Brazil

Abstract— The 40 km wide Araguainha structure in central Brazil is a shallowly eroded impact crater that presents unique insights into the final stages of complex crater formation. The dominant structural features preserved at Araguainha relate directly to the centripetal movement of the target rocks during the collapse of the transient cavity. Slumping of the transient cavity walls resulted in inward‐verging inclined folds and a km‐scale anticline in the outer ring of the structure. The folding stage was followed by radial and concentric faulting, with downward displacement of kilometer‐scale blocks around the crater rim. The central uplift records evidence for km‐scale upward movement of crystalline basement rocks from the transient cavity floor, and lateral moment of sedimentary target rocks detached from the cavity walls. Much of the structural grain in the central uplift relates to structural stacking of km‐scale thrust sheets of sedimentary strata onto the core of crystalline basement rocks. Outward‐plunging radial folds indicate tangential oblate shortening of the strata during the imbrication of the thrust sheets. Each individual sheet records an early stage of folding and thickening due to non‐coaxial strains, shortly before sheet imbrication. We attribute this folding and thickening phase to the kilometer‐scale inward movement of the target strata from the transient cavity walls to the central uplift. The outer parts of the central uplift record additional outward movement of the target rocks, possibly related to the collapse of the central uplift. An inner ring structure at 10–12 km from the crater center marks the extent of the deformation related to the outward movement of the target rocks.     

RR Pic (1925): a Chandra X-ray view

We present the Chandra ACIS-S3 data of the old classical nova RR Pic (1925). The source has a count rate of 0.067 ± 0.002 count s⁻¹ in the 0.3–5.0 keV energy range. We detect the orbital period of the underlying binary system in the X-ray wavelengths. We also find that the neutral hydrogen column density differs for orbital minimum and orbital maximum spectra with values  0.25^+0.23_−0.18× 10²²  and  0.64^+0.13_−0.14× 10²² cm⁻²  at 3σ confidence level. The X-ray spectrum of RR Pic can be represented by a composite model of bremsstrahlung with a photoelectric absorption, two absorption lines centered around 1.1–1.4 keV and five Gaussian lines centered at emission lines around 0.3–1.1 keV corresponding to various transitions of S, N, O, C, Ne and Fe. The bremsstrahlung temperature derived from the fits ranges from 0.99 to 1.60 keV and the unabsorbed X-ray flux is found to be  2.5^+0.4_−1.2× 10⁻¹³ erg  cm⁻² s⁻¹  in the 0.3–5.0 keV range with a luminosity of 1.1 ± 0.2  10³¹ erg s⁻¹  at 600 pc. We also detect excess emission in the spectrum possibly originating from the reverse shock in the ejecta. A fit with a cooling flow plasma emission model shows enhanced abundances of He, C, N, O and Ne in the X-ray emitting region indicating existence of diffusive mixing.     

Solar Radio Spikes in 2.6 – 3.8 GHz during the 13 December 2006 Event

On 13 December 2006, some unusual radio bursts in the range 2.6?–?3.8 GHz were observed during an X3.4 flare/CME event from 02:30 to 04:30 UT in active region NOAA 10930 (S06W27) with the digital spectrometers of the National Astronomical Observatories of China (NAOC). During this event many spikes were detected with the high temporal resolution of 8 ms and high frequency resolution of 10 MHz. Many of them were found to have complex structures associated with other radio burst types. The new observational features may reflect certain emission signatures of the electron acceleration site. In this paper, we present the results of the analysis of the new observational features of the complex spikes. According to the observed properties of the spikes, we identify five classes. Their observational parameters, such as duration, bandwidth, and relative bandwidth, were determined. Most spikes had negative polarization, but spikes with positive polarization were observed during a short time interval and were identified as a separate class. Based on the analysis of observations with Hinode/SOT (Solar Optical Telescope) we suggest that the sources of the spikes with opposite polarizations were different. Combined observations of spikes and fiber bursts are used to estimate the magnetic field strength in the source.     

Molecular line profiles as diagnostics of protostellar collapse: modelling the 'blue asymmetry' in inside-out infall

The evolution of star-forming core analogues undergoing inside-out collapse is studied with a multipoint chemodynamical model which self-consistently computes the abundance distribution of chemical species in the core. For several collapse periods the output chemistry of infalling tracer species such as HCO⁺, CS and N₂H⁺ is then coupled to an accelerated Λ-iteration radiative transfer code, which predicts the emerging molecular line profiles using two different input gas/dust temperature distributions. We investigate the sensitivity of the predicted spectral line profiles and line asymmetry ratios to the core temperature distribution, the time-dependent model chemistry, as well as to ad hoc abundance distributions. The line asymmetry is found to be strongly dependent on the adopted chemical abundance distribution. In general, models with a warm central region show higher values of blue asymmetry in optically thick HCO⁺ and CS lines than models with a starless core temperature profile. We find that in the formal context of Shu-type inside-out infall, and in the absence of rotation or outflows, the relative blue asymmetry of certain HCO⁺ and CS transitions is a function of time and, subject to the foregoing caveats, can act as a collapse chronometer. The sensitivity of simulated HCO⁺ line profiles to linear radial variations, subsonic or supersonic, of the internal turbulence field is investigated in the separate case of static cores.