RFI measurements and mitigation for FAST

Radio Frequency Interference(RFI)mitigation is essential for supporting the science output of Five-hundred-meter Aperture Spherical radio Telescope(FAST)due to its high sensitivity.In order to protect FAST from RFI,an Electromagnetic Compatibility(EMC)study has been carried out and the operation of a Radio Quiet Zone(RQZ)is ongoing.RFI measurements of the telescope instruments and monitoring of the active radio services outside the site have revealed the radiation properties of the RFI sources.Based on the measurement results and theoretical analysis,various EMC methods have been implemented for the telescope to decrease the RFIs.Meanwhile,the main RFI sources in the FAST RQZ,such as mobile stations,broadcast stations and navigation instruments,have been identified,and the technical measures have been adopted to protect the quiet radio environment around the site.The early science outputs of FAST have demonstrated the efficiency of RFI mitigation methods.     

Chinese Journal of Astronomy and Astrophysics Instructions for Authors

The Chinese Journal of Astronomy and Astrophysics (ChJAA) publishes original research papers and reviews on all branches of astronomy and astrophysics. Reviews are by invitation only. Important new results that require rapid publication can be submitted as a Letter (letters must be restricted in length to 5 printed pages).     

Chinese Journal of Astronomy and Astrophysics Instructions for Authors

The Chinese Journal of Astronomy and Astrophysics (CJAA) publishes original researchpapers and reviews on all branches of astronomy and astrophysics. Reviews are by invitationonly. Important new results that require rapid published can be submitted as a Letter.Authors who submit a paper are expected to be able to certify that the paper is originalwork, has not been published before and is not being considered for publication elsewhere.Papers should be written in grammatical English: author…     

Correlation between X-ray and γ-ray for Fermi blazars

Using γ-ray band data detected by Fermi Large Area Telescope (LAT) and X-ray band data for 78 blazars, we find a medium correlation between X-ray flux and γ-ray flux in all states. A medium correlation is also found between X-ray (1 keV) mean spectral index α _x and γ-ray mean spectral index α _γ for BL Lacertae objects (BL Lacs), and there is no correlation for Flat Spectrum Radio Quasars (FSRQs). From these results, we suggest that the most likely radiation mechanism for the high energy gamma-rays would be synchrotron self-Compton (SSC), and that the gamma-ray emission mechanism may be somewhat different for BL Lacs and FSRQs.     

GOLD’s coating and testing facilities for ISSIS-WSO

The interaction between Ricci scalar curvature and the baryon number current, dynamically breaks CPT in an expanding universe and leads to baryon asymmetry. Using this kind of interaction and study the gravitational baryogenesis in the Bianchi type I universe. We find out the effect of anisotropy of the universe on the baryon asymmetry for the case which the equation of state parameter, ω, varies with time.     

Chinese Journal of Astronomy and Astrophysics Instructions for Authors

The Chinese Journal of Astronomy and Astrophysics (ChJAA) publishes original research papers and reviews on all branches of astronomy and astrophysics. Reviews are by invitation only. Important new results that require rapid publication can be submitted as a Letter (letters must be restricted in length to 5 printed pages).Authors who submit a paper are expected to be able to certify that the paper is original work, has not been published before and is not being considered for publication elsewhere.Papers should be written in grammatical English: authors who have doubts about this should ask a knowledgeable colleague to read a draft critically.     

Chinese Journal of Astronomy and Astrophysics Instructions for Authors

The Chinese Journal of Astronomy and Astrophysics (ChJAA) publishes original researchpapers and reviews on all branches of astronomy and astrophysics. Reviews are by invitationonly. Importaat new results that require raPid publication can be submitted as a Letter (lettersmust be restricted in length to 5 prillted pages).Authors who submit a paper are expected to be able to certify that the paper is originalwork, has not been published before and is not being considered for publication else…     

Searching for Variable Stars in and around Open Clusters

We present a snapshot of our recent results of a variable star survey in 1 degree fields around three open clusters: NGC 188, NGC 7789 and M67. A total number of 39 variable stars are newly discovered, including 22 W UMa stars, 10 EA (Algol) type binaries, one RR-lyr and one RRd pulsator, and five unclassified variables.     

The time and frequency standard system for FAST receivers

This paper reports on the time and frequency standard system for the Five-hundred meter Aperture Spherical radio Telescope(FAST),including the system design,stability measurements and pulsar timing observations.The stability and drift rate of the frequency standard are calculated using 1-year monitoring data.The UTC-NIM Disciplined Oscillator(NIMDO)system improves the system time accuracy and stability to the level of 5 ns.Pulsar timing observations were carried out for several months.The weighted RMS of timing residuals reaches the level of less than 3.0μs.     

Absolute measurements and computed values for Martian irradiance between 10.5 and 12.5 μm

The combination of seasonal and orbital changes in Martian insolation result in complex latitude dependent surface temperature variations that effect the total radiance of the planet as seen from the earth. These surface temperature variations have been calculated, based upon a computer simulation of the thermal environment of the planet. The temperature variations are then integrated to yield the total radiance of the planet as seen from the earth as a function of time. The absolute radiance of Mars was measured on April 4, 1971, with a balloon-borne radiometer system operating in the wavelength range between 10.5 and 12.5 μm. The average brightness temperature of the Mars disk determined from these measurements was 254°K with a 1 σ error of 4°K.     

Ganymede crater dimensions – Implications for central peak and central pit formation and development

The morphology of impact craters on the icy Galilean satellites differs from craters on rocky bodies. The differences are thought due to the relative weakness of ice and the possible presence of sub-surface water layers. Digital elevation models constructed from Galileo images were used to measure a range of dimensions of craters on the dark and bright terrains of Ganymede. Measurements were made from multiple profiles across each crater, so that natural variation in crater dimensions could be assessed and averaged scaling trends constructed. The additional depth, slope and volume information reported in this work has enabled study of central peak formation and development, and allowed a quantitative assessment of the various theories for central pit formation. We note a possible difference in the size-morphology progression between small craters on icy and silicate bodies, where central peaks occur in small craters before there is any slumping of the crater rim, which is the opposite to the observed sequence on the Moon. Conversely, our crater dimension analyses suggest that the size-morphology progression of large lunar craters from central peak to peak-ring is mirrored on Ganymede, but that the peak-ring is subsequently modified to a central pit morphology. Pit formation may occur via the collapse of surface material into a void left by the gradual release of impact-induced volatiles or the drainage of impact melt into sub-crater fractures.     

Steps Towards a Fully Automated Classification and Redshiftmeasurement Pipeline for LAMOST Spectra. I. Continuum level and wavelength estimation for galaxies

1 INTRoDUCTIONThere are aiready several wide-field multi-fiber spectrograPhic surveys in various stages ofdevelopment, most notably the stellar popu1ation, galaxy and QSO suxveys using the 2dF faciLity as described by Lewis et al. (1998) and the Sloan Digital Sky Survey (SDSS) aJs summarizedby York et al. (2000), both of which are already underway, and those surveys planning to usethe 6dF facility as described by Wason et al. (2000) and the LAMOST facility as outllnedby Wang et a…     

The beaming effect and γ-ray emission for Fermi blazars

We study the γ-ray luminosity and beaming effect for Fermi blazars.Our results are as follows.(i) There are significant correlations between γ-ray luminosity and radio core luminosity,and between γ-ray luminosity and R_v,which suggests that the γ-ray emissions have a strong beaming effect,(ⅱ) Using the L_(ext)/M_(abs) as an indicator of environment effects,we find that there is no significant correlation betweenγ-ray luminosity and L_(ext)/M_(abs) for all sources when we remove the effect of redshift.Flat spectrum radio quasars considered alone also do not show a significant correlation,but BL Lacertae objects(BL Lacs) still show a significant correlation when we remove the effect of redshift.These results suggest that the γ-ray emission may be affected by the environment on a kiloparsec scale for BL Lacs.     

AVIATR—Aerial Vehicle for In-situ and Airborne Titan Reconnaissance

We describe a mission concept for a stand-alone Titan airplane mission: Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVIATR). With independent delivery and direct-to-Earth communications, AVIATR could contribute to Titan science either alone or as part of a sustained Titan Exploration Program. As a focused mission, AVIATR as we have envisioned it would concentrate on the science that an airplane can do best: exploration of Titan??s global diversity. We focus on surface geology/hydrology and lower-atmospheric structure and dynamics. With a carefully chosen set of seven instruments??2 near-IR cameras, 1 near-IR spectrometer, a RADAR altimeter, an atmospheric structure suite, a haze sensor, and a raindrop detector??AVIATR could accomplish a significant subset of the scientific objectives of the aerial element of flagship studies. The AVIATR spacecraft stack is composed of a Space Vehicle (SV) for cruise, an Entry Vehicle (EV) for entry and descent, and the Air Vehicle (AV) to fly in Titan??s atmosphere. Using an Earth-Jupiter gravity assist trajectory delivers the spacecraft to Titan in 7.5 years, after which the AVIATR AV would operate for a 1-Earth-year nominal mission. We propose a novel ??gravity battery?? climb-then-glide strategy to store energy for optimal use during telecommunications sessions. We would optimize our science by using the flexibility of the airplane platform, generating context data and stereo pairs by flying and banking the AV instead of using gimbaled cameras. AVIATR would climb up to 14?km altitude and descend down to 3.5?km altitude once per Earth day, allowing for repeated atmospheric structure and wind measurements all over the globe. An initial Team-X run at JPL priced the AVIATR mission at FY10 $715M based on the rules stipulated in the recent Discovery announcement of opportunity. Hence we find that a standalone Titan airplane mission can achieve important science building on Cassini??s discoveries and can likely do so within a New Frontiers budget.     

A simulation package—SASAL for X-ray and EUV spectroscopy of astrophysical and laboratory plasmas

For the laboratory astrophysics community,those spectroscopic modeling codes extensively used in astronomy,e.g.Chianti,AtomDB,Cloudy and Xstar,cannot be directly applied to analyzing laboratory measurements due to their discrepancies from astrophysical cases.For example,plasma from an electron beam ion trap has an electron energy distribution that follows a Gaussian profile,instead of a Maxwellian one.The laboratory miniature for a compact object produced by a laser-driven implosion shows a departure from equilibrium,that often occurs in celestial objects,so we setup a spectral analysis system for astrophysical and laboratory(sasal) plasmas to act as a bridge between them,which benefits the laboratory astrophysical community.     

Deep radio occultations and “evolute flashes”; their characteristics and utility for planetary studies

Radio occultation studies of the structure of planetary atmospheres have generally involved relatively shallow penetration of the spacecraft behind the limb of the planet in the plane of the sky. Current radio link sensitivities allow detection of the radio signals at all occultation depths, whenever the planet-spacecraft distance is sufficiently large for the refraction to occur at atmospheric heights where microwave absorption is not too large. Voyager 1 at Jupiter and Voyager 2 at Saturn will pass almost directly behind the planets as viewed from the Earth. Thus they will pass through the caustics that corresponds to the focal line of a spherical planet, expanded by oblateness into a surface approximating a four-cusp cylinder. In the plane of the sky, the projection of this surface approximates the evolute of the planet's limb. As the spacecraft passes behind the planet with its antenna tracking the occulting limb, the strength of the radio signals received on Earth will at first decrease due to defocusing in the atmosphere, but then increase as the evolute is approached, because of the focusing caused by limb curvature. Inside the evolute there are four simultaneous signal paths over four limb positions. If we neglect absorption, focused signals for an instant could become orders of magnitude stronger than for the unocculted spacecraft. Measurements of the frequency and intensity of deep occultation signals, and of the timing and character of these “evolute flashes”, could provide information on atmospheric absorption, turbulence, and structure, and on details of the shape of the atmosphere at the focusing limbs as affected, for example, by planetary gravitational moments, rotation, and zonal winds. Such observations will be attempted with Voyager and potentially could be very fruitful in the Pioneer Venus and Galileo (Jupiter) orbiting missions.     

Brightness of the Coronal Green Line and Prediction for Activity Cycles 23 and 24

Cyclic variations of the mean semi-annual intensities I of the coronal green line 530.3 nm are compared with the mean semi-annual variations of the Wolf numbers W during the period of 1943–1999 (activity cycles 18–23). The values of I in the equatorial zone proved to correlate much better with the Wolf numbers in a following cycle than in a given one (the correlation coefficient r is 0.86 and 0.755, respectively). Such increase of the correlation coefficient with a shift by one cycle differs in different phases of the cycle, being the largest at the ascending branch. The regularities revealed make it possible to predict the behaviour of W in the following cycle on the basis of intensities of the coronal green line in the preceding cycle. We predict the maximum semi-annual W in cycle 23 to be 110–122 and the epoch of minimum between cycles 23 and 24 to take place at 2006–2007. A slow increase of I in the current cycle 23 permits us to forecast a low-Wolf-number cycle 24 with the maximum W50 at 2010–2011. A scheme is proposed on the permanent transformation of the coronal magnetic fields of different scales explaining the found phenomenon.     

A New Formulation for General Relativistic Force-Free Electrodynamics and Its Applications

We formulate the general relativistic force-free electrodynamics in a new 3 ＋ 1 language. In this formulation, when we have properly defined electric and magnetic fields, the covariant Maxwell equations could be cast in the traditional form with new vacuum constitutive constraint equations. The fundamental equation governing a stationary, axisymmetric force-free black hole magnetosphere is derived using this formulation which recasts the Grad-Shafranov equation in a simpler way. Compared to the classic 3＋1 system of Thorne and MacDonald, the new system of 3＋1 equations is more suitable for numerical use for it keeps the hyperbolic structure of the electrodynamics and avoids the singularity at the event horizon. This formulation could be readily extended to non-relativistic limit and find applications in fiat spacetime. We investigate its application to disk wind, black hole magnetosphere and solar physics in both fiat and curved spacetime.     

Modelling, design and diagnostics for a photoionised plasma experiment

Photoionised plasmas are common in astrophysical environments and new high resolution spectra from such sources have been recorded in recent years by the Chandra and XMM-Newton satellites. These provide a wealth of spectroscopic information and have motivated recent efforts aimed at obtaining a detailed understanding of the atomic-kinetic and radiative characteristics of photoionised plasmas. The Z-pinch facility at the Sandia National Laboratories is the most powerful terrestrial source of X-rays and provides an opportunity to produce photoionised plasmas in a well characterised radiation environment. We present modelling work and experimental design considerations for a forthcoming experiment at Sandia in which X-rays from a collapsing Z-pinch will be used to photoionise low density neon contained in a gas cell. View factor calculations were used to evaluate the radiation environment at the gas cell; the hydrodynamic characteristics of the gas cell were examined using the Helios-CR code, in particular looking at the heating, temperature and ionisation of the neon and the absorption of radiation. Emission and absorption spectra were also computed, giving estimates of spectra likely to be observed experimentally.     

Asteroseismology and the degeneracy of model solutions for subgiant stars

Stellar evolutionary models are essential for the determination of stellar masses and ages. Several parameters can be used to characterize the structure of subgiant stars. Amongst others we can find: the helium and metal abundances, mixing length and core overshooting. In many cases, these parameters are scaled taking into account the solar values. Yet, the universality of such scalings has been put to question. As shown here, by allowing some freedom to these parameters we end up with a degeneracy of model solutions. This puts serious limitations on the determination of mass and age. Asteroseismology may provide a valuable help to break such a degeneracy. This is illustrated with an application to the subgiant star μ Her.