Mutual strategy of search for CETI call signals

A strategy of search for call signals from extraterrestrial intelligence (ETI) is suggested, assuming a mutual desire to communicate.Angular convergence leads to the principle of natural beacons—the directions to the most conspicuous objects of the Universe. On the time axis convergence leads to synchronization of transmission by the observed occurence of Nova (Supernova). Every star receives according to a schedule of the first contract with every other star. An example of a schedule is given, stimulated by Nova Cygni 1975. The schedule conception imposes heavy demands on the precision of astrometry. Fixed and statistical components of the schedule are considered. A small angular vicinity of Nova Cygni 1975 is a potential source of signals from ETI during the next 20–40 years. The Earth must transmit call signals on the day of observation of maximum Nova outburst toward the stars located within a small angular vicinity of the direction antipodal to the Nova. A systematic analysis allows the removal from call signals of the most dangerous anthropomorphims: the type of modulation, the rate of transmission, the codes (languages). It leads to physicomathematical call signals in the form of a product of the physical constant, φ_H, and maematical ones $\text{(π, 2π, 2}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{, 1/π,…)}$. The precision in the received frequency, πφ_H, of monochromatic oscillation is the criterion of intelligence.     

A milky way search strategy for extraterrestial intelligence

It is assumed that the density of sites of technical civilizations emitting suitable signals (whether purposeful or unintentional) is proportional to the stellar density at any location in our Galaxy, as modeled by Bahcall and Soneira (1980, Astrophys. J. Suppl. Ser.44, 73–110). A wide variety of possible radio luminosity functionsφ(L)for these civilizations is then assumed and for each the number of detectable signals per square degree over the sky is calculated. It has been found that most detectable signals occur at galactic latitudes of 10° or less and longitudes within 90° of the galactic center, a region which covers only 9% of the entire sky. This result holds for a wide range ofφ(L) types, including Gaussian distributions and power law functions with slopes less than 2.5, or any combination of these. The Milky Way is much less preffered, but still advantageous, for cases of steep power law functions (slopes greater than 2.5) or Gaussian functions with mean luminosities so low that any existing civilizations can only be detected at small distances(<0.5 kpc). The only cases where low galactic latitudes are not advantageous are (1) for frequencies of operation less than 600 MHz where the deleterious effects on signal-to-noise ratios of the natural galactic background emission become dominant, and (2) in searches for narrowband(<1 Hz) signals at frequencies less than 2 GHz where significant interstellar broadening of signals occurs over distances of? 10 kpc. Furthermore, all of the above results have broader applicability: they are equally valid for searches for any type of natural radio phenomenon if its probability of occurence is proportional to stellar density. Therefore, for a nontargeted search, a Milky Way strategy which concentrates on the inner galactic plane is preferred. The factor of 10 in time saved over an all-sky survey can then be used for, say, increased sensitivity or a survey of nearby galaxies. For a targeted search, rather than searching the nearestn solar-like stars, time is more profitably spent, for example, on the very nearest0.1n stars plus the next nearest0.9n stars which are also within 10° of the galactic plane. This picks up the Milky Way background while only sacrificing a factor of 2 in the average distance to the target stars.     

A search strategy for finding extraterrestrial radio beacons

The Principle of Anti-Cryptography, together with our knowledge of the structure and properties of the universe, lead to the suggestion that extraterrestrial radio beacons will transmit continuously and omnidirectionally, using binary sense-switched circular polarization modulation. The expected frequency of transmission is the rest frequency of hydrogen, relative to the galactic center. Probable signaling rates are within two orders of magnitude of one second. Methods of implementing the strategy are suggested, from both the receiving and transmitting viewpoints.     

A new observational strategy in search for solar g-modes

The aim of the present work is the detection of solar g-modes, by means of a new observational strategy based on the exploitation of their spatial and temporal properties. The basic data, obtained at the Observatorio del Teide in 1993, consists of daily solar velocity measurements taken continuously and sequentially at six different and symmetric positions on the solar disk. By correlating the time series resulting from the reduction process, from different solar disk positions and considering the geometrical properties of different modes (l,m) on the Sun's surface, some of these can be selectively eliminated or enhanced. Moreover, the main spectral features present in the resulting power spectra must have precise phase relations if they correspond to global solar g-modes. The severe constraints established by the above properties have been applied to the best observed series (summer 1993). As a result, a discrete series of peaks have been selected that fulfill all the imposed conditions and which can therefore be interpreted as being of solar origin.     

利用光纤进行高精度时间传递

介绍了一种利用光纤电视信道传递时间和频率的初步方案,对闭环时延的测定作了阐述,还讨论了采用扩频技术的副载波复用系统进行双向时间传递的方法.     

Optical monitoring of the quasar 4C 38.41

The results of a photometric monitoring of the quasar 4C 38.41, performed at the optical R and B bands in 2002 February–March, are presented. With a 60/90 cm Schmidt telescope at the Xinglong station of the National Astronomical Observatories of China, we observed the source exhibiting amplitude variations of up to 0.78 mag in both bands during the whole campaign. Intraday and even intranight variations are detected as well. A typical variability time-scale of about 36 d is derived from our 2-month observations at the optical bands, which is identical to that found at a radio wavelength of 92 cm, suggesting a common origin for the variations in 4C 38.41 from optical to radio bands.     

Optical monitoring of quasars – I. Variability

We present an analysis of quasar variability from data collected during a photometric monitoring of 50 objects carried out at CNPq/Laboratório Nacional de Astrofísicá, Brazil, between 1993 March and 1996 July. A distinctive feature of this survey is its photometric accuracy, ∼0.02  V  mag, achieved through differential photometry with CCD detectors, which allows the detection of faint levels of variability. We find that the relative variability, δ σ L , observed in the V band is anticorrelated with both luminosity and redshift, although we have no means of discovering the dominant relation, given the strong coupling between luminosity and redshift for the objects in our sample. We introduce a model for the dependence of quasar variability on frequency that is consistent with multiwavelength observations of the nuclear variability of the Seyfert galaxy NGC 4151. We show that correcting the observed variability for this effect slightly increases the significance of the trends of variability with luminosity and redshift. Assuming that variability depends only on the luminosity, we show that the corrected variability is anticorrelated with luminosity and is in good agreement with predictions of a simple Poissonian model. The energy derived for the hypothetical pulses, ∼10⁵⁰ erg, agrees well with those obtained in other studies. We also find that the radio-loud objects in our sample tend to be more variable than the radio-quiet ones, for all luminosities and redshifts.     

Optical multi-color monitoring of OJ 287 from 2006 to 2012

We present our optical multi-color monitoring of the BL Lac object OJ 287 from January 2006to December 2012 in the V,R and I bands.A relatively active state in OJ 287 has been found over all monitored epochs,among which the variations of average magnitude in V/R/I bands were measured with ?V=1.956 mag,?R=2.067 mag and ?I=2.115 mag,respectively.No reliable intraday variability is detected,but possible variability is detected on 16 nights.Their relative variation amplitudes fall into the range between 1% and 8%,with the majority between 2% and 4%.No time lags have been detected,but strong correlations exist among light curves in the three wavebands.The bluer-when-brighter trend is dominant over intraday timescales,which supports the shock-in-jet model.When combining with additional V/R band data obtained from SMARTS and the Steward Observatory,we also find a bluer-when-brighter trend over a long-term timescale.Some possible periods of 513,176,36,30,26,17 and 14 d are found in all time-series data sets from 2006 to 2017.Possible explanations about these periods are given.     

Optical monitoring and intra-day variabilities of BL Lac Objects OJ 287

Using the 1.26 m National Astronomical Observatory-Guangzhou University Infrared/Optical Telescope(NGT),we monitor one BL Lac object,OJ 287.For this source,we obtain 15 094 gri observations(4900 at g band,5184 at r band and 5010 at i band) in 155 nights from 2014 December 13 to 2019 March15.Based on the upper observations,we obtain the following results.(1) The total variation amplitude is ～ 2.3 mag.(2) There are intra-day variabilities(IDVs).The IDV timescales(△T) are in the range from 7.69 min(Δm=0.06 ± 0.02 mag) to 371.09 min(Δm=0.26 ± 0.04 mag).(3) There are strong correlations between ΔT and Δm,△m=(2.91 ± 0.66) × 10~(-4)ΔT+(0.08 ± 0.009),with r=0.52,p=5.33 × 10~(-5).(4) There are intra-day periods in this source,with the period P≈94 min on 2017 December 10.When we supplement the observations from the literature,we can obtain that the long-term period is about 12.02 ± 0.41 yr.(5) The spectral properties of OJ 287 show the bluer-when-brighter behavior,whatever state the source is at.     

Optical observations of the Be/X‐ray transient system KS 1947+300

ROTSE‐IIId observations of the Be/X‐ray transient system KS 1947+300 obtained between September 2004 and December 2005 make it possible to study the correlation between optical and X‐ray activity. The optical outburst of 0.1 mag was accompanied by an increase of the X‐ray flux in the 2004 observations. A strong correlation between the optical and X‐ray light curves suggests that the neutron star directly accretes from the outflowing material of the Be star. The nearly zero time lag between X‐ray and optical light curves suggests a heating of the disk of Be star by X‐rays. No optical brightening and X‐ray enhancement was seen in the 2005 observations. There is no indication of an orbital modulation in the optical light curve. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical studies of the X-ray transient XTE J2123−058 – I. Photometry

We present optical photometry of the X-ray transient XTE J2123−058, obtained in 1998 July–October. The light curves are strongly modulated on the 5.95-h orbital period, and exhibit dramatic changes in amplitude and form during the decline. We used synthetic models, which include the effect of partial eclipses and X-ray heating effects, to estimate the system parameters, and we constrain the binary inclination to be i =73°±4. The model is successful in reproducing the light curves at different stages of the decay by requiring the accretion disc to become smaller and thinner by 30 per cent as the system fades by 1.7 mag in the optical. From August 26 the system reaches quiescence with a mean magnitude of R =21.7±0.1 and our data are consistent with the optical variability being dominated by the ellipsoidal modulation of the companion.     

Optical interferometric observations of a transient event of 1986 March 13 in the coma of Comet Halley

During the recent apparition of Comet Halley in 1985-86 a transient ionic event in the form of a blob of H₂ O⁺ emission was recorded in thecoma at ～ 0^h UT on 1986 March 13. Observations were carried out using a special IHW filter for H₂ O⁺ emission at 7000 å/175 å, a 35 cm telescope, a Fabry-Perot interferometer and an image intensifier camera from Gurushikhar, Mt Abu. (24?39’N,72? 47’E). A Fabry-Perot inter-ferogram in Ha taken a few minutes later at the same location reveals strong hydrogen emission (Hα) associated with the blob. The velocity field in the blob is structured with relative velocities upto ～ 35km s^?1. The event is interpreted as arising due to the sector boundary crossing of the interplanetary magnetic field by the comet     

Optical studies of the X-ray transient XTE J2123–058 – II. Phase-resolved spectroscopy

We present time-resolved spectroscopy of the soft X-ray transient XTE J2123–058 in outburst. A useful spectral coverage of 3700–6700 Å was achieved spanning two orbits of the binary, with single-epoch coverage extending to ∼9000 Å. The optical spectrum approximates a steep blue power law, consistent with emission on the Rayleigh–Jeans tail of a hot blackbody spectrum. The strongest spectral lines are He  ii 4686 Å and C  iii /N  iii 4640 Å (Bowen blend) in emission. Their relative strengths suggest that XTE J2123–058 was formed in the Galactic plane, not in the halo. Other weak emission lines of He  ii and C  iv are present, and Balmer lines show a complex structure, blended with He  ii . He  ii 4686-Å profiles show a complex multiple S-wave structure, with the strongest component appearing at low velocities in the lower-left quadrant of a Doppler tomogram. H α shows transient absorption between phases 0.35 and 0.55. Both of these effects appear to be analogous to similar behaviour in SW Sex type cataclysmic variables. We therefore consider whether the spectral line behaviour of XTE J2123–058 can be explained by the same models invoked for those systems.