J. R. Liu

Charge-exchange X-ray emission of nearby star-forming galaxies

Properties of hot gas outflows from galaxies are generally me asured from associated Xray line emission assuming that it represents atomic transi tions in thermally excited hot gas. X-ray line emission, however, can also arise from the charge exchange between highly ionised ions and neutral species. The Kα triplet of He-like ions can be used as a powerful diagnostic, because the charge exchange X-ray emission (CXE) favours the inter-combination and forbidden lines, while the thermal emission favours the resonance line. We analyse the O VII triplet of a sample of nine nearby star-forming galaxies observed by the XMM-Newton reflection grating spectrometers. For most galaxies, the forbidden li nes are comparable to or stronger than the resonance lines, which is in contrast to the thermal prediction. For NGC 253, M51, M83, M61, NGC 4631, and the Antennae galaxy, the observed line ratios are consistent with the ratio of the CXE; for M94 and NGC 2903, the observed ratios indicate multiple origins; for M82, different regions show different line ratios, also indicating multiple origins. We dis cuss other possible mechanisms that can produce a relatively strong forbidden line, such as a collisional non-equilibrium-ionization recombining/ionizing plasma, which are not favoured. These results suggest that the CXE may be a common process and contribute a significant fraction of the soft X-ray line emission for galaxies with massive star formation.

Re-determination of Phoebe's orbit

In order to improve the orbit of Phoebe, the ninth satellite of the Saturnian system, 101 new observations were made by our research team in 2003, using a CCD detector of large size (2048×2048 pixels) mounted on the 1.56 m astrometric reflector at the Sheshan Station of Shanghai Astronomical Observatory. We fitted a numerical integration of its orbit to all of the collected Earth-based astrometric observations from 1904 to 2003, including the newest precise data sets from Qiao & Tang and from Peng et al. A new set of initial conditions of Phoebe has been obtained, leading to an improved orbit of this satellite.

Astrometry of five major Uranian satellites in 1995-1997 ?

At the oppositions of 1995-1997, a total of 122 CCD frames were taken on the 1.56 m astrometric telescope at the Sheshan station, yielding 864 positions of the major Uranian satellites. The calibration of the images was carried out using a least-squares iterative program by fitting to the well-known orbits of the brighter moons of Uranus, based on the modern theory GUST86 and an ephemeris produced by numerical integration. The residuals lay between 0: 00 03 and 0: 00 05 for each of the inter-satellite positions, except for the innermost and faintest satellite Miranda, whose residuals exceeded 0: 08 due to the proximity of Uranus. No significant systematic errors were found when using satellites themselves for determining calibration parameters. The largest residual in the comparison between GUST86 and the numerical integration was about 0: 00 01.

Two-year monitoring of intra-day variability of quasar 1156+295 at 4.8 GHz

Aims. The quasar 1156+295 (4C +29.45) is one of the targets in the Urumqi monitoring program which aimed to search for evidence of annual modulation in the timescales of intra-day variable (IDV) sources.

Radio and optical intra-day variability observations of five blazars

We carried out a pilot campaign of radio and optical band intra-day variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287, B0925+504 and BL Lacertae) on 2015 December 18-21 by using the radio telescope in Effelsberg (Germany) and several optical telescopes in Asia, Europe and America. After calibration, the light curves from both 5 GHz radio band and the optical R band were obtained, although the data were not smoothly sampled over the sampling period of about four days. We tentatively analyse the amplitudes and time-scales of the variabilities, and any possible periodicity. The blazars vary significantly in the radio (except 3C66A and BL Lacertae with only marginal variations) and optical bands on intra-and inter-day time-scales, and the source B0925+504 exhibits a strong quasi-periodic radio variability. No significant correlation between the radio-and optical-band variability appears in the five sources, which we attribute to the radio IDV being dominated by interstellar scintillation whereas the optical variability comes from the source itself. However, the radio and optical-band variations appear to be weakly correlated in some sources and should be investigated based on well-sampled data from future observations.

On the soft X-ray emission of M82

We present a spatial analysis of the soft X-ray and Hα emissions from the outflow of the starburst galaxy M82. We find that the two emissions are tightly correlated on various scales. The O VII triplet of M82, as resolved by X-ray grating observations of XMM-Newton, is dominated by the forbidden line, inconsistent with the thermal prediction. The O VII triplet also shows some spatial variations. We discuss three possible explanations for the observed O VII triplet, including the charge exchange at interfaces between the hot outflow and neutral cool gas, a collisional non-equilibrium-ionization recombining plasma, and resonance scattering (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fe K lines in the nuclear region of M82

We study the spatial distribution of the Fe 6.4 and 6.7 keV lines in the nuclear region of M82 using the Chandraarchival data with a total exposure time of 500 ks. The deep exposure provides a significant detection of the Fe 6.4 keV line. Both t he Fe 6.4 and 6.7 keV lines are diffuse emissions with similar spatial extent, but their morpho logy do not exactly follow each other. Assuming a thermal collisional-ionization-equili brium (CIE) model, the fitted temperatures are around 5− 6 keV and the Fe abundances are about 0.4− 0.6 solar value. We also analyse the spectrum of a point source, which shows a strong Fe 6.7 keV line and is likely a supernova remnant or a superbubble. The fitted Fe abundance o f the point source is 1.7 solar value. It implies that part of the iron may be depleted from th e X-ray emitting gases. If this is a representative case of the Fe enrichment, a mild mass-loading of a factor of 3 will make the Fe abundance of the point source in agreement with that of the hot gas, which then implies that most of the hard X-ray continuum (2− 8 keV) of M82 has a thermal origin. In addition, the Fe 6.4 keV line is consistent with the fluorescence emissi on irradiated by the hard photons from nuclear point sources.