查看更多>>摘要：I reminisce on my early life in Section 1;on my education in Sections 2 and 3;on the years at Princeton as a research astronomer in Section 4;on the years on the faculty at Chicago in Section 5;on research on Diffuse Interstellar Bands(DIBs)in Section 6;on construction of the 3.5 m telescope at Apache Point Observatory(APO)in Section 7;on work on the Sloan Digital Sky Survey(SDSS)in Section 8;on work in public education in Chicago in Section 9;and on my travels in Section 10.My main science research is of an observational nature,concerning Galactic and intergalactic interstellar gas.Highlights for me included my work on the orbiting telescope Copernicus,including the discovery of interstellar deuterium;early observations of absorption associated with five-times ionized oxygen;and discoveries concerning the phases of gas in the local interstellar medium,based on previously unobservable interstellar UV spectral lines.With other instruments and collaborations,I extended interstellar UV studies to the intergalactic cool gas using quasi-stellar object QSO absorption lines redshifted to the optical part of the spectrum;provided a better definition of the emission and morphological character of the source of absorption lines in QSO spectra;and pursued the identification of the unidentified DIBs.For several of these topics,extensive collaborations with many scientists were essential over many years.The conclusions developed slowly,as I moved from being a graduate student at Chicago,to a research scientist position at Princeton and then to a faculty position at Chicago.At each stage of life,I was exposed to new technologies adaptable to my science and to subsequent projects.From high school days,I encountered several management opportunities which were formative.I have been extremely fortunate both in scientific mentors I had and in experimental opportunities I encountered.
查看更多>>摘要：This paper investigates the spin-up of a mass-accreting star in a close binary system passing through the first stage of mass exchange in the Hertzsprung gap.Inside an accreting star,angular momentum is carried by meridional circulation and shear turbulence.The circulation carries part of the angular momentum of the accreted layers to the accretor's surface.The greater the rate of arrival of angular momentum in the accretor is,the greater this part.It is assumed that this part of the angular momentum can be removed by the disk further from the accretor.If the angular momentum in the matter entering the accretor is more than half the Keplerian value,then the angular momentum obtained by the accretor during mass exchange stage does not depend on the rate of arrival of angular momentum.The accretor may have the characteristics of a Be-star immediately after the end of mass exchange.
查看更多>>摘要：Reviewing the empirical and theoretical parameter relationships between various parameters is a good way to understand more about contact binary systems.In this investigation,two-dimensional(2D)relationships for P-Mv(system),P-L1,2,M1,2-L1,2,and q-Lratio were revisited.The sample used is related to 118 contact binary systems with an orbital period shorter than 0.6 days whose absolute parameters were estimated based on the Gaia Data Release 3 parallax.We reviewed previous studies on 2D relationships and updated six parameter relationships.Therefore,Markov chain Monte Carlo and Machine Learning methods were used,and the outcomes were compared.We selected 22 contact binary systems from eight previous studies for comparison,which had light curve solutions using spectroscopic data.The results show that the systems are in good agreement with the results of this study.
查看更多>>摘要：Aiming at improving the survey efficiency of the Wide Field Survey Telescope,we have developed a basic scheduling strategy that takes into account the telescope characteristics,observing conditions,and weather conditions at the Lenghu site.The sky area is divided into rectangular regions,referred to as"tiles,"with a size of 2°577 × 2°.634 slightly smaller than the focal area of the mosaic CCDs.These tiles are continuously filled in annulars parallel to the equator.The brightness of the sky background,which varies with the moon phase and distance from the moon,plays a significant role in determining the accessible survey fields.Approximately 50 connected tiles are grouped into one block for observation.To optimize the survey schedule,we perform simulations by taking into account the length of exposures,data readout,telescope slewing,and all relevant observing conditions.We utilize the Greedy Algorithm for scheduling optimization.Additionally,we propose a dedicated dithering pattern to cover the gaps between CCDs and the four corners of the mosaic CCD array,which are located outside of the 3° field of view.This dithering pattern helps to achieve relatively uniform exposure maps for the final survey outputs.
查看更多>>摘要：Polycyclic aromatic hydrocarbons(PAHs),PANHs,and peptoids dust spectral calculations from the interstellar medium(ISM)are important for dust observations and theory.Our goal is to calculate the radiation spectrum of spherical PAHs dust clusters in a vacuum containing ionized and applied in the presence of an electric field.We propose a new simple computational model to calculate the size of three-dimensional spherical dust clusters formed by different initial dust structures.By the Vienna Ab-initio Simulation Package code,the density functional theory with the generalized approximation was used to calculate the electron density gradient and obtain the radiation spectrum of dust.When the radius of spherical dust clusters is～[0.009-0.042]μm,the dust radiation spectrum agrees well with the Z=0.02 mMMP stellar spectra,and the PAHs radiation spectrum of NGC 4676 at wavelengths of(0-5]μm and(5-10]μm,respectively.In the ionized state,the N-PAH,C10H9N,2(C4H 4)1+,and peptoids 4(CHON),(C8H10N2O5)1+ dust clusters at 3.3 μm,while the 2(C22H21N3O 2)1+,4(CHON)dust clusters at 5.2 μm have obvious peaks.There is a characteristic of part of PAHs and peptoids clusters radiation at the near-infrared wavelength of 2 μm.However,especially after applying an electric field to the dust,the emission spectrum of the dust increases significantly in the radiation wavelength range[3-10]μm.Consequently,the dust clusters of PAHs,PANHs,and peptoids of the radius size～[0.009-0.042]μm are likely to exist in the ISM.
查看更多>>摘要：Very low frequency(VLF)signals are propagated between the ground-ionosphere.Multimode interference will cause the phase to show oscillatory changes with distance while propagating at night,leading to abnormalities in the received VLF signal.This study uses the VLF signal received in Qingdao City,Shandong Province,from the Russian Alpha navigation system to explore the multimode interference problem of VLF signal propagation.The characteristics of the effect of multimode interference phenomena on the phase are analyzed according to the variation of the phase of the VLF signal.However,the phase of VLF signals will also be affected by the X-ray and energetic particles that are released during the eruption of solar flares,therefore the two phenomena are studied in this work.It is concluded that the X-ray will not affect the phase of VLF signals at night,but the energetic particles will affect the phase change,and the influence of energetic particles should be excluded in the study of multimode interference phenomena.Using VLF signals for navigation positioning in degraded or unavailable GPS conditions is of great practical significance for VLF navigation systems as it can avoid the influence of multimode interference and improve positioning accuracy.
查看更多>>摘要：Seeing is an important index to evaluate the quality of an astronomical site.To estimate seeing at the Muztagh-Ata site with height and time quantitatively,the European Centre for Medium-Range Weather Forecasts reanalysis database(ERA5)is used.Seeing calculated from ERA5 is compared consistently with the Differential Image Motion Monitor seeing at the height of 12 m.Results show that seeing decays exponentially with height at the Muztagh-Ata site.Seeing decays the fastest in fall in 2021 and most slowly with height in summer.The seeing condition is better in fall than in summer.The median value of seeing at 12 m is 0.89 arcsec,the maximum value is 1.21 arcsec in August and the minimum is 0.66 arcsec in October.The median value of seeing at 12 m is 0.72 arcsec in the nighttime and l.08 arcsec in the daytime.Seeing is a combination of annual and about biannual variations with the same phase as temperature and wind speed indicating that seeing variation with time is influenced by temperature and wind speed.The Richardson number Ri is used to analyze the atmospheric stability and the variations of seeing are consistent with Ri between layers.These quantitative results can provide an important reference for a telescopic observation strategy.
查看更多>>摘要：Star-forming processes strongly influence the ISM chemistry.Nowadays,many high-quality databases are available at millimeter wavelengths.Using them,it is possible to carry out studies that review and deepen previous results.If these studies involve large samples of sources,it is preferred to use direct tools to study the molecular gas.With the aim of testing these tools such as the use of the HCN/HNC ratio as a thermometer,and the use of H13CO+,HC3N,N2H+and C2H as"chemical clocks,"we present a molecular line study toward 55 sources representing massive young stellar objects at different evolutionary stages:infrared dark clouds(IRDCs),high-mass protostellar objects(HMPOs),hot molecular cores(HMCs)and ultracompact H Ⅱ regions.We found that the use of the HCN/HNC ratio as a universal thermometer in the ISM should be taken with care because the HCN optical depth is a big issue that can affect the method.Hence,this tool should be utilized only after a careful analysis of the HCN spectrum,checking that no line,neither the main nor the hyperfine ones,presents absorption features.We point out that the analysis of the emission of H13CO+,HC3N,N2H+and C2H could be useful to trace and distinguish regions among IRDCs,HMPOs and HMCs.The molecular line widths of these four species increase from the IRDC to the HMC stage,which can be a consequence of the gas dynamics related to the star-forming processes taking place in the molecular clumps.Our results not only contribute with more statistics,acting as a probe of such chemical tools,useful to obtain information in large samples of sources,but also complement previous works through the analysis of other types of sources.
查看更多>>摘要：Cross-matching is a key technique to achieve fusion of multi-band astronomical catalogs.Due to different equipment such as various astronomical telescopes,the existence of measurement errors,and proper motions of the celestial bodies,the same celestial object will have different positions in different catalogs,making it difficult to integrate multi-band or full-band astronomical data.In this study,we propose an online cross-matching method based on pseudo-spherical indexing techniques and develop a service combining with high performance computing system(Taurus)to improve cross-matching efficiency,which is designed for the Data Center of Xinjiang Astronomical Observatory.Specifically,we use Quad Tree Cube to divide the spherical blocks of the celestial object and map the 2D space composed of R.A.and decl.to 1D space and achieve correspondence between real celestial objects and spherical patches.Finally,we verify the performance of the service using Gaia 3 and PPMXL catalogs.Meanwhile,we send the matching results to VO tools-Topcat and Aladin respectively to get visual results.The experimental results show that the service effectively solves the speed bottleneck problem of cross-matching caused by frequent I/O,and significantly improves the retrieval and matching speed of massive astronomical data.
查看更多>>摘要：A significant excess of the stellar mass density at high redshift has been discovered from the early data release of James Webb Space Telescope(JWST),and it may require a high star formation efficiency.However,this will lead to large number density of ionizing photons in the epoch of reionization(EoR),so that the reionization history will be changed,which can arise tension with the current EoR observations.Warm dark matter(WDM),via the free streaming effect,can suppress the formation of small-scale structure as well as low-mass galaxies.This provides an effective way to decrease the ionizing photons when considering a large star formation efficiency in high-z massive galaxies without altering the cosmic reionization history.On the other hand,the constraints on the properties of WDM can be derived from the JWST observations.In this work,we study WDM as a possible solution to reconcile the JWST stellar mass density of high-z massive galaxies and reionization history.We find that,the JWST high-z comoving cumulative stellar mass density alone has no significant preference for either CDM or WDM model.But using the observational data of other stellar mass density measurements and reionization history,we obtain that the WDM particle mass with mW=0.51+0.22-0.12 keV and star formation efficiency parameter f0*＞0.39 in 2σ confidence level can match both the JWST high-z comoving cumulative stellar mass density and the reionization history.
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