Late-time photometry of two nearby type II-P supernovae： 2004dj and 2004et

We present late-time photometry for two bright type II-P supernovae （SNe） 2004dj and 2004et, extending over 400 d after the explosion, which are measured with a set of intermediate-band filters that have the advantage of tracing the strength variations of some spectral features. Although these two SNe II-P exhibit similar photometric evolution at earlier times, they diverge during the nebular phase. SN 2004dj shows a slow late-time decline rate with - 0.7 ±0.1 mag （100d）^-1 during the period ranging from t ≈ 200 - 300 d after the explosion, while SN 2004et shows a much faster decline rate at a comparable phase, e.g., 1.3 ± 0.1 mag （100d）^-1. The steeper decay rate seen in SN 2004et is likely due to dust formation in the explosion ejecta. Based on intermediate-band photometry, we derived the evolution of the feature lines [e.g., Hα] of SNe 2004dj and 2004et which are similar in flux at comparable phases but perhaps with significantly different decay rates. The origin of the observed variations in the continuum and the feature lines is briefly discussed.     

The C/O ratio of He-accreting carbon-oxygen white dwarfs and type Ⅰa supernovae

Type Ⅰa supernovae (SNe Ⅰa) are thermonuclear explosions of carbon-oxygen white dwarfs (CO WDs),and are believed to be excellent cosmological distance indicator...     

Disparity between Hα and Hβ in SN 2008 in: Inhomogeneous external layers of type IIP supernovae?

We study disparity between Hα and Hβ in early spectra of the type IIP supernova SN 2008in. The point is that these lines cannot be described simultaneously in a spherically-symmetric model with the smooth density distribution. It is shown that an assumption of a clumpy structure of external layers of the envelope resolves the problem. We obtain estimates of the velocity at the inner border of the inhomogeneous zone (≈6100 km s^?1), the filing factor of inhomogeneities (≤0.5), and the mass of the inhomogeneous layers (～0.03 M _⊙). The amplitude of flux fluctuations in the early spectrum of Hα (ΔF/F ～ 10^?2) imposes a constraint on the size of inhomogeneities (≤200 km s^?1). A detection of fluctuations in the early Hα of type IIP supernovae might become an observational test of the inhomogeneous structure of their envelopes. We propose also the indirect test of the clumpy structure of external layers: the study of properties of the initial radiation outburst due to the shock breakout. The inhomogeneous structure of external layers of type IIP supernovae could be an outcome of density perturbations and density inversion in outer convective layers of presupernova red supergiant.     

Photometric study of two β Lyr-type binaries: DD Aqr and RR Lep

This paper presents detailed analysis of photometric observations of two eclipsing binary systems, DD Aqr and RR Lep. The V light curve of the neglected binary star DD Aqr from the All Sky Automated Survey was solved for the first time. The 1982–1987 UBV light curves of RR Lep from Vyas and Abhyankar (1989) were re-analysed. The final solutions give these two β Lyr-type binary stars as having near contact configurations in which the secondary components almost fill their Roche limiting lobes. Using O-C residuals formed by the updated minima times, orbital period changes of the systems were analysed. The O-C diagram of DD Aqr displays a cyclic variation, while that of RR Lep shows a quasi-sinusoidal variation superimposed on a downward parabolic form. The parabolic variation, which suggests a secular orbital period decrease in RR Lep, was interpreted in terms of the combined effect of mass transfer and loss. The cyclic O-C variations were interpreted in terms of the light travel time effect due to unseen components in these two systems. The absolute parameters of the components of the systems were estimated, and their present evolutionary status is also discussed.     

Radio-continuum study of the nearby sculptor group galaxies. Part 3: NGC 7793 at λ=12.2, 6 and 3 cm

We re-examine a series of archived centimetre radio-continuum observations (λ=16, 6 and 3 cm) focusing on NGC?7793 using the Australia Telescope Compact Array. These new images are both very sensitive (σ=0.011 mJy/beam) and feature reasonably high angular resolution (down to <3″). Using these images, a total of 76 discrete radio sources are identified, of which 57 have been classified. We also studied the radio component of the micro-quasar NGC7793-S26 which shows two distinct regions of somewhat steep spectral index (α) between ?0.3 and ?0.7.     

CALLISTO facilities in Peru: spectrometer commissioning and observations of type Ⅲ solar radio bursts

The Astrophysics Directorate of CONIDA has installed two radio spectrometer stations belonging to the e-CALLISTO network in Lima, Peru. Given their strategic location near the Equator, it is possible to observe the Sun evenly throughout the whole year. The receiver located at Pucusana, nearby the capital city of Lima, took data from October 2014 until August 2016 in the metric and decimetric bands looking for radio bursts. During this period, this e-CALLISTO detector was unique in its time-zone coverage. To asses the suitability of the sites and the performance of the antennas, we analyzed the radio ambient background and measured their radiation pattern and beamwidth. To demonstrate the capabilities of the facilities for studying solar dynamics in these radio frequencies, we have selected and analyzed type Ⅲ Solar Radio Bursts. The study of this kind of burst helps to understand the electron beams traversing the solar corona and the solar atmospheric density. We have characterized the most common radio bursts with the following mean values: a negative drift rate of –25.8 ± 3.7 MHz s~(-1), a duration of 2.6 ± 0.3 s and 35 MHz bandwidth in the frequency range of 114 to 174 MHz. In addition, for some events, it was possible to calculate a global frequency drift which on average was 0.4 ± 0.1 MHz s~(-1).     

Spatially resolved methane band photometry of Jupiter: I. Absolute reflectivity and center-to-limb variations in the 6190-, 7250-, and 8900-Å bands

Spatially resolved measurements of Jupiter's absolute reflectivity in methane bands at 6190, 7250, and 8900 Å and nearby continuum regions are presented. The data were obtained with a 400 × 400 pixel charge-coupled device (CCD) at the 1.54-m Catalina telescope near Tucson, Arizona. Jupiter was imaged on the CCD through narrow-band interference filters. Photometric standard stars were also measured. Calibration data were obtained to remove instrumental effects. Uncertainty in the absolute reflectivity is ±8%. Uncertainty in the relative (across the disk) reflectivity is 1 or 2%. Uncertainty in the geomtry is ±1 pixel (0.22 arcsec) for centering and ±1% in scale. Intensity and scattering geometry are tabulated for points across 10 axisymmetric cloud bands and the Great Red Spot. Because of their high spatial, photometric, and time resolution, these data provide strong constraints on models of the Jovian cloud structure.     

Radio-continuum study of the nearby Sculptor group Galaxies. Part 2: NGC 55 at λ=20, 13, 6 and 3 cm

A series of new radio-continuum (λ=20, 13, 6 and 3 cm) mosaic images focused on the NGC 55 galactic system were produced using archived observational data from the Australia Telescope Compact Array. These new images are both very sensitive (down to rms=33 μJy) and feature high angular resolution (down to <4″). Using these newly created images, 66 previously unidentified discrete sources are identified. Of these sources, 46 were classified as background sources, 11 as H?ii regions and 6 as supernova remnant candidates. This relatively low number of SNR candidates detected coupled with the low number of large H?ii regions is consistent with the estimated low star formation rate of the galaxy at 0.06 M _⊙?year^?1. Our spectral index map shows that the core of galaxy appears to have a shallow spectral index between α=?0.2 and ?0.4. This indicates that the core of the galaxy is a region of high thermal radiation output.     

Dynamics of two satellites in the 2/1 Mean–Motion resonance: application to the case of Enceladus and Dione

The dynamics of a pair of satellites similar to Enceladus–Dione is investigated with a two-degrees-of-freedom model written in the domain of the planar general three-body problem. Using surfaces of section and spectral analysis methods, we study the phase space of the system in terms of several parameters, including the most recent data. A detailed study of the main possible regimes of motion is presented, and in particular we show that, besides the two separated resonances, the phase space is replete of secondary resonances.     

In search of infall motion in molecular clumps Ⅱ: HCO~+(1-0) and HCN(1-0)observations toward a sub-sample of infall candidates

Gravitational accretion accumulates the original mass.This process is crucial for us to understand the initial phases of star formation.Using the specific infall profiles in optically thick and thin lines,we searched the clumps with infall motion from the Milky Way Imaging Scroll Painting(MWISP) CO data in previous work.In this study,we selected 133 sources as a sub-sample for further research and identification.The excitation temperatures of these sources are between 7.0 and 38.5 K,while the H_2 column densities are between 10~(21) and 10~(23) cm~(-2).We have observed optically thick lines HCO~+(1-0) and HCN(1-0) using the DLH 13.7-m telescope,and found 56 sources with a blue profile and no red profile in these two lines,which are likely to have infall motions,with a detection rate of 42%.This suggests that using CO data to restrict the sample can effectively improve the infall detection rate.Among these confirmed infall sources are 43 associated with Class O/I young stellar objects(YSOs),and 13 which are not.These 13 sources are probably associated with the sources in the earlier evolutionary stage.In comparison,the confirmed sources that are associated with Class O/I YSOs have higher excitation temperatures and column densities,while the other sources are colder and have lower column densities.Most infall velocities of the sources that we confirmed are between 10~(-1) to 10~0 km s~(-1),which is consistent with previous studies.