Research Activity in 2000

Cosmology

Chen Jiansheng,Zhang Haotong and Xue Suijian et al. continued to take the multi-object fiber spectra for some selected BATC fields. A dedicated data reduction produced several hundred spectra of various kinds of objects, among which, the spectra with higher S/N ratios were used for checking the reliability of the SED classification approach developed based on BATC photometric system. That is a preliminary positive result, however, more tight quantitative conclusions will still await more high quality observations. In addition, the international cooperation programigh Redshift Survey between Chinese, Russian and Armenian astronomers, initiated by Chen Jiansheng et al. in 1999, has achieved much progress. The relevant terminal instruments, such as focal reducer SCORPIO (14'x14') and Faint Object Spectral Camera for Byurakan 2.6m telescope (Byu FOSC) as well as a new type CCD controller, were successful in testing on the telescope. The first scientific light is expected to come out in August 2001. The imaging system will be able to achieve a limiting magnitude of 25.0 in R band with one-hour exposure under the typical weather conditions with 2" seeing.

Deng Zugan worked mainly on two topics: 1) He made extensive analyses of large-scale structure with the discrete wavelet transformations as to explore the dependence of galaxy's morphology stratification on the scale and to get the relation of galaxy formation bias and scale. With the discrete wavelet transformations he also discussed the selection of galaxy clusters and the characters of their abundances and distributions. Furthermore he investigated the possibility of removing the degeneracy of cosmological parameters in using wavelet analysis. 2) With the newest sample got as he could as possible he analyzed the character of galaxy's distribution on very large-scale as mainly to explore the typical scale of the large-scale structure and the stratification or bias of galaxies on very large- scale. Meanwhile he collaborated with others in studying infrared spectra of galaxies, morphology and X-ray character, especially the X-ray character of Mkr273.

Active Galactic Nuclei

Cao Xinwu et al. performed a statistic analysis on a sample of radio-loud quasars and found that the extended radio emission of the jet is a good indicator of jet power. They calculated the profiles of thermal X-ray line emissions from Advection Dominated Accretion Flows (ADAFs). Some important physical quantities of ADAFs can be inferred from the observed thermal X-ray line profiles.

In 2000, Fan Junhui et al. mainly concentrated on discussions of the variability properties of blazars, including the long-term variation, the searching of long-term period of variability in the light curve of blazars, the estimation of the central black hole mass of gamma-ray loud blazar, the optical photometry of gamma-ray loud blazars, and the correlation between the gamma-ray and the emission lines. They found that there are possible 4.16- and 7.0-year periods in the light curve of PKS 2155-304. An optical data base was provided for radio selected BL Lacertae objects, based on which long-term periods, which are found to be in the range of 1.3 to 17 years, were searched for about a dozen of objects. The mass of about 106 times of the solar mass of a central black hole was estimated for PKS 0235+164 based on the short-term timescale. The correlation between the gamma-ray radiation and the emission lines more favors the SSC model than the EC model. In October of 2000, they observed a sample of gamma-ray loud blazars with the 70-cm telescope at Abstumani Observatory of Georgia.

Wang Jianmin worked in 2000 mainly on three topics: 1) To set up an intrinsic constraint on TeV emission from blazars, he calculated the reflected synchrotron component by clouds in broad line region, then calculated the pair opacity due to interaction between the reflected synchrotron photon and high energy photons from inverse Compton. He found that the reflected synchrotron strongly limits the TeV photons. He also predicted the preferred candidates

of TeV blazars. 2) He suggested the observational consequences of ejected blob from optically thin advection-dominated accretion flow in blazars. It is found that the high-energy recombination emission lines and non-thermal flares will be observed if there is blob ejection from nucleus. 3) He studied the detailed profiles of emission lines from a relativistic jet (outflow) around black hole and found that the profile is sensitive to the velocity distribution of jet (outflow), emissivity law, viewing angle, and the spin of black hole. He suggests the profile may be powerful tool to probe the formation of relativistic jet (outflow) from accretion disk.

Yuan Feng did two pieces of work in this year. ADAF model is widely assumed to describe the compact radio source Sgr A* located at the center of our Galaxy and nearby giant elliptical galaxies such as M87. However, the radio observations designed to test this idea indicated that the predicted radio flux is two or three orders of magnitude higher than observations, although its X-ray prediction is correct. He proposed jet-included ADAF model to solve this problem. The second work is that he found a new accretion disk model. There are three models up to date, namely the standard thin disk, the slim disk and ADAF. Among them ADAF is the only one hot disk. Because of its low radiation efficiency and corresponding low accretion rate, this model can only interpret the low luminosity systems. His new model corresponds to mass accretion rate higher than the critical rate of ADAF, and the efficiency is also higher compared to ADAF. Therefore, it promisingly interprets high luminosity systems such as the high and very high states of the galactic X-ray sources and narrow line Seyfert galaxy.

Galaxies

Chang Ruixiang et al. adopted the star formation law presented by Efstathiou (2000) in the two-component chemical evolution model for Milky Way disk. To explore the influence of different gas-infall forms on the evolution of Galactic disk, they compared predictions of four different models with observations. Their results show that whether infall timescale varies with radius or not largely influences the disk evolution. The "inside-out" model predicts that the total mass density of the disk can still be roughly expressed as exponential, but its scale length increases with time. Moreover, The star formation law adopted in this work depends more strongly on gas surface density than that in Chang et al (1999). It has large effects on star formation and gas evolution history of the whole disk.

Ma Jun made CCD spectrophotometry of star clusters in the nearby spiral galaxy M33, detected by Chandar, Bianchi, & Ford, using the images obtained with the 60/90 cm Schmidt Telescope of Beijing Astronomical

Observatory and 13 intermediate-band filters from 3800 to 10000 A. The observations covered the whole area of M33 with a total integration of 32.75 hours from September 23, 1995 to August 28, 2000, which provided a multi-color map of M33 in 1.7挕?.7'. By aperture photometry, he obtained the spectral energy distributions (SEDs) of these star clusters. Using theoretical stellar population synthesis models, he also obtained the distributions of age and metallicity of the star clusters, which were formed continuously from 3×106 ― 1010 years, and have a large span of metallicity from Z=0.0004 to Z=0.05.

Wu Hong performed deep surface photometry of the edge-on galaxy NGC 4565 using the long exposure images of BATC. The vertical profile of this galaxy can reach as far as 30kpc to a limit surface magnitude of 29 farther and deeper than those of previous works. A two-dimension model was used to fit the observed profiles of the galaxy. The model includes three components (thin disk, thick disk and power-law halo) and total twelve free parameters. The best fitted parameters were obtained according to the method of minimum χ2. The parameters of both disks agree with those of previous works. They found that the density luminosity of halo decreases as r--3.88, excluding the existence of the possible luminous halo.

Zhou Xu continued working in project of BATC survey together with his colleagues of BATC group. In observations they improved the observing system and the quality of the observational data. They have completed a manual of observational methods and the training program of observers. In the same time the BATC data accumulation and the scientific research work both were much progressing. In cooperation with Russian astronomers, they have made follow-up observations 2 times so far with the Russian 6m telescope. The results confirmed the reliability of the BATC survey for special objects. Together with Japanese Astronomers, they studied galaxy cluster Abell566 and the study of the second cluster Abell2634 is going on. They continued to make HH object survey and found some new HH objects. In studying nearby galaxies, they began to study stellar populations of the nearby face-on galaxy M33 and the luminosity profile of the edge-on galaxy NGC4565. With the BATC photometric system, the discovering program of minor planets is still going on and the research work of minor planets started. They also made identification and study of X-ray sources in a BATC survey region.

Zou Zhenlong and Han Jinlin discussed the physical background of the unified scaling law in spiral galaxies, and qualitatively got the power index of the empirical relation among the luminosity L, radius R, and the rotation velocity V. L ? (VR)α with ?=4/3,consistent with the observation value 1.3.They also discussed the possible causes for the data dispersion on the plane in 3-dimensional space of these parameters,and found that the relation L ? V2R can fit new I band data best.

Stellar Physics

Deng Licai In the year 2000 worked as follows: 1) Teaching the course of "Stellar structure and evolution" for graduate students in the whole year; 2) Doing research work on stellar evolution and open clusters. Searching for variable stars around open clusters in NGC 188 has been carried out and a few new variable stars were discovered. In order to put such a work on a more solid base, he did theoretical surveys of instability domains on the HR diagram, new definitions for Beta Cephei and Delta Scuti instability strips were given in a series of papers (collaborating with Prof Xiong, D.R.). New models for massive stars with high mass loss rate have been worked out based on the new observational results and pulsational models. Studies on young stellar populations would be made using such models.

Zhang Huawei completed high resolution and high signal to noise ratio observations and data reductions of very metal-poor stars. Abundances of 17 elements were determined by combining atmosphere model calculations and line analyses. Kinematical parameters were calculated based on Hipparcos satellite data. Abundances of elements were discussed as functions of metallicities and kinematics. Chemical abundances of nearby star HD131023 were determined. Some heavy elements were found to be overabundant relative the Sun.

Zhang Bo et al. studied wind mass accretion and orbital parameters' variation in barium stars system. Considering higher power terms of orbital eccentricity e, the equations of wind mass accretion and orbital parameters' variation were reduced in condition of the conservation of total angular momentum instead of the tangential momentum. Subsequently, for the extrinsic AGB stars, the wind mass accretion and orbital parameters' variation were calculated. The calculating results show that, the barium stars with longer orbital period than 1600 days may be formed by wind accretion, and those with shorter period than 600 days can become cataclysmic binaries. So the observations of the heavy elemental overabundances and the orbital parameters of Ba stars can be interpreted, and the orbital periods' lower limit 600 days of the extrinsic S stars can be interpreted. During the evolution of binary system, the system widens as it loses mass and the orbital period increases, while orbital eccentricity remains nearly constant, which can explain the observed properties of the orbital parameters in Ba stars .

High Energy Astrophysics

Qiao Guojun et al. continued the study of radiation mechanism of radio pulsars and paid attention to finding any possible differences between neutron stars and strange stars and to theories and observations of anomalous X-ray pulsars. For radiation mechanisms of radio pulsars, they paid much attention to finding a theory, which can be consistent with observations as more as possible. They also tried to find a way to get some limitations for parameters in the theory from observations. He cooperated with Dr. Xu R.X. and Dr. Zhang Bing to pay attention to finding any possible differences between neutron stars and strange stars from observations of radio pulsars, anomalous X-ray pulsars and soft gamma-ray repeaters.

Wu Xinji et al. made pulsar's observations using the 25m radio telescope of UAO (Urumqi Astronomical Observatory) and did research work of the pulsar's candidates and the geometry asymmetry of mean pulse profile of pulsar. The main observations used the 25m radio telescope of UAO. The regular timing observations at 18cm for 74 pulsars were carried out once every 7~14 days. The new data of locations, periods, period derivatives, timing noise and flux density of such pulsars were obtained. A glitch of Crab pulsar on July 15 was detected. The scintillation observations for 8 strong pulsars using the 128 frequency channels were made to study the proper motion of pulsars. The new receiver system of 49cm and the system for simultaneity observations at both 49cm and 92cm were built, and the observational experiments went well. The regular timing observations for 18 pulsars at 92cm and 49cm have been proceeding and the data of long-term variation of flux density have been obtained. The new mode change of the mean pulse profile of PSR B0329+54 at 49cm was found.

Xu Renxin et al. continued the study of pulsar radio emission. They explored the possibility and the implications of the idea that pulsars are born as strange stars, and proposed that strange stars are very likely to have crusts with very small mass of about 10^{-15} M⊙ but bare polar caps almost throughout their lifetimes if strange stars are produced during supernova explosions. They also investigated the dynamo-originated magnetic fields of proto-strange stars.

Wu Xuebing worked on accretion disk related problems at Max-Plank-Institute for Astrophysics during this year. He explained the quasi-periodic oscillations (QPOs) observed in neutron star X-ray binaries according to the transition layer model of accretion disks. Considering the viscosity effects and three-dimensional perturbations, he improved the accretion disk oscillation model and adopted it to account for the high frequency QPOs in X-ray binaries and their correlation with the low frequency QPOs. Using accretion disk model, he estimated the accretion rates of some AGNs and quasars with recently well-measured black hole masses and studied the correlation between accretion rates and multi-band luminosities. He also discussed the physics connection between the central accretion disks and the host galaxies of these AGNs.

Xue Suijian collaborated with other BATC members, Zhou X., Jiang Z.J., Wu H., Ma J. and Chen J.S. et al., performed optical identifications of faint ROSAT X-ray sources in a one-square-degree region of T329 of BATC sky survey based on multi-color CCD imaging observations made for the T329 utilizing BAO 60/90 cm Schmidt telescope with 15 intermediate-band filters covering the wavelength range from 3360 to 9745 Angstrom. A SED-based object classification algorithm was developed and used in finding the most promising optical counterparts within each of X-ray error circles. Complete identifications of the X-ray sources, in particular to pick up quasars and other type of AGN objects, aim at achieving a well defined X-ray selected AGN sample for further studies as well as to address the question: what's the selecting efficiencies of X-ray and UVX methods used in AGN surveys compared to each other method.

Star Formation

On the basis of the searching for the dense cores of molecular clouds with optical thin lines 13CO J=1-0, surveys for dynamic characters of the corresponding regions with easily excited CO J=1-0 line were made on the 13.7m telescope of PMO (Purple Mountain Observatory) at Qinghai Station by Wu Yuefang at al. of "Star Formation Group." CO J=1-0 spectra were obtained for about 200 sources. With parameters of emission intensity, velocity and line widths, the evolutionary states of the clouds and the activities of young stellar objects were examined. They obtained 79 candidates of high velocity bipolar outflows. Four new outflows were discovered. Another 12 sources are in identifications with mapping. Combining IRAS, TMASS and maser data, the properties of the associated sources and possible driving mechanism were investigated.

With the Collaboration of Gornergrat observatory of Koln University, 10 sources were mapped with sub-millimeter line of CO J=3-2, among which three are outflows. In TMC-2A, two rotation cores with opposite direction were found. The properties of outflows measured with high J level line and CO J=1-0 line were compared to explore the substance of outflow.

With the collaboration of Astronomy Group of BAO (Beijing Astronomical Observatory), the star formation in interaction Galaxy Arp299 was examined. Using 2.16m telescope of BAO at Xinglong Station, two dimension Hα spectra were obtained within the system region. Dynamic structure and star formation active regions were obtained. The data are in further study. They analyzed the properties of exciting sources of about 400 HH objects. Frequency distribution, emission intensity and color characteristics were obtained. With the statistic results, some driving sources of new HH objects were identified. The results could also be applied to search for new HH objects.For using the ISO data to examine the dense gas-dust regions and young celestial objects, they installed IDL platform which now is in further adjusting.

Mao Xinjie devoted his effort to the research of temperature structure in dark molecular clouds B5 and suggested a theoretical model to explain the temperature rise on the cloud edge (Mao, 2000). He assumes: 1) The cloud is spherical with uniform number density, and there is a core in its central region; 2) The cloud rotates as a rigid body with angular velocity in z-direction, and the magnetic field lines thread the sphere parallel to the z-axis as well; 3) The dark cloud is a weakly ionized plasma system. To maintain the magnetic field in the cloud the currents J must not be equal to zero, but very small that (Vi ≈ Ve) is estimated based on Ampere law ??????J?c, therefore the neutrals and ions make up a 2-fluid MHD system. Because of ambipolar diffusion and the dissipation of the rotational energy of the cloud, the cloud potential is converted into thermal energy, which leads to the edge temperature rising.

Solar Physics

Wang Jingxiu and Zhang Jun initiated a new working direction - studies of global coronal mass ejection (CME) with the emphasis on the identification of CME source regions, associated magnetic evolutions and the physical process of CME initiation. The coronal mass ejections are different from either solar or stellar flares, in which the localized solar atmosphere is heated to very high temperature and shows enhanced radiation, or from collimated astrophysical jets. CMEs are instabilities of large or global scale of solar magnetic fields and ejections of huge amount of magnetized plasma into the interplanetary space in the form of magnetic clouds. Their analogue in other astrophysical subjects has not been clearly identified. Zhang and Wang have their preliminary results published in Geophys.Res. Lett. and Astrophys.J.Lett., and presented in IAU symposium No.203, a few more papers are under refereeing by Astrophys.J., Sol. Phys.and J.Geophys.Res..

Asteroids

Zhu Jin made photometric and spectral observations of the Near-Earth-Asteroid 2000 DP107 with the 0.6/0.9-m Schmidt telescope and 2.16-m reflector of BAO. The work of this field will be supported by the National Natural Science Foundation of China from next year, and some graduate students and more observation time will be involved.