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Astronomical seeing and ground-level optical turbulence at Delingha observatory on the northern Tibetan Plateau

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 2023年第3期525卷 3236-3247页

作者： Zhu, Liming Zhang, Hanjiu Zhang, Liang Duan, Xuefeng Lu, Xinying Liu, Ying Li, Xuebin Sun, Gang Weng, Ningquan Chinese Acad Sci Anhui Inst Opt & Fine Mech Key Lab Atmospher Opt HFIPS Hefei 230031 Peoples R China Univ Sci & Technol China Grad Sch Sci Isl Branch Hefei 230026 Peoples R China Adv Laser Technol Lab Anhui Prov Hefei 230037 Peoples R China Univ Sci & Technol China Sch Environm Sci & Optoelect Technol Hefei 230026 Peoples R China

This paper presents a comprehensive site survey of the Delingha site on the northern Tibetan Plateau from 2012 to 2014. In this campaign, we investigated 24 h continuous astronomical seeing, meteorological properties, and C-n(2) in the ground layer (GL). The results show that the median seeing is 3.46 arcsec during the day and 1.80 arcsec during the night. The best nighttime seeing occurs in summer (1.66 arcsec), while the worst occurs in autumn (1.96 arcsec). Seeing exhibits obvious diurnal behaviour, with the worst seeing occurring around mid-day (11:00 to 14:00, Beijing time), and the best seeing just before sunset (18:00 to 20:00, Beijing time). Moreover, the Delingha site has good meteorological properties for astronomical observations during the measurement period, especially the low median wind speed (2.8 m s (-1)) and great temperature inversion (day: -0.3 K, night: 0.6 K). As for the vertical distribution of C-n(2) , the exponential h (-0.46) dependence of C-n(2) varying with height in the GL is also obtained, and its power index is significantly related to the seasons. Furthermore, we calculated the contribution of optical turbulence in the GL to the whole atmosphere. Turbulence within the GL contributes significantly in summer, and its contribution can reach more than 35 per cent. Finally, we present the complete dependence analysis of seeing on meteorological parameters at the Delingha site. The results show that the best seeing tends to occur when the temperature inversion is sufficiently large, but the dependence of seeing on wind speed is not significant.

关键词： turbulence atmospheric effects method: data analysis site testing

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Optical turbulence forecasts at short time-scales using an autoregressive method at the Very Large Telescope

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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 2023年第3期523卷 3487-3502页

作者： Masciadri, E. Turchi, A. Fini, L. INAF Osservatorio Astrofis Arcetri Largo Enr Fermi 5 I-50125 Florence Italy

In this study we demonstrate that we can provide forecasts of all the main astroclimatic parameters (seeing, wavefront coherence time, isoplanatic angle, and ground-layer fraction) on time-scales of 1 and 2 h (the most critical ones for the service mode) with a root-mean-square error (RMSE) that is smaller than or, at worst, comparable to the instrumental uncertainty (i.e. the standard deviation between instrument estimates). The seeing RMSE is 0.08 arcsec. Results are achieved thank to the use of the autoregressive method (AR) in our automatic forecast system and the study is applied to the Very Large Telescope (VLT). The AR method is a hybrid method taking into account forecasts of a non-hydrostatical mesoscale model jointly with real-time observations made in situ. We demonstrate that the AR method allows an improvement in forecast performance of roughly a factor of three or more with respect to the standard forecasts at a long time-scale (beginning of the afternoon for the coming night), depending on the parameter and the time-scale (1 and 2 h). The AR method also allows roughly a factor of two gain with respect to prediction by persistence. We also show that the AR method provides significantly better performance than a random-forest machine-learning algorithm. An extended analysis of the AR performance is provided following different strategies. Results achieved in this study are therefore very promising and tell us that we can provide real assistance to the service mode of the VLT instrumentation supported by adaptive optics systems.

关键词： turbulence atmospheric effects instrumentation: high angular resolution method: data analysis methods: numerical site testing

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Solar eclipses observed worldwide in the first half of the 15th century and ?T determined from multiply observed eclipses

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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 2023年第6期75卷 1013-1029页

作者： Tanikawa, Kiyotaka Soma, Mitsuru Simmonds, Ockie Iwahashi, Kiyomi Natl Astron Observ Japan 2-21-1 Osawa Mitaka Tokyo 1818588 Japan Soc Maori Astron Res & Tradit C-O Prof Pauline Harris 13 Buckley Grove Paraparaumu 5032 New Zealand Kokugakuin Univ 4-10-28 HigashiShibuya Ku Tokyo 1508440 Japan

The main purpose of the present paper is to list all the solar eclipses which took place in the first half of the 15th century, to list all the available records of observation of these eclipses, and, by using the multiply observed or contemporaneously observed solar eclipses, to determine Delta T for a few periods of the first half of the 15th century. We make the table using solar eclipse records from East Asia (China, Korea, and Japan), India, West Asia, and Europe, though the table is not perfect because the compilation of records is not complete in some of the relevant areas. We evaluate the reliability of the Chinese records of solar eclipses. The Chinese official history book, the Mingshi, records visible eclipses, while it does not record invisible eclipses. A simple analysis shows that the reliability of the book is 97%. The marginally observable eclipses in China are useful for us to determine Delta T. We briefly consider the Maori eclipse observed in 1409. We extract the multiply observed eclipses and check whether these are useful for determining the value of Delta T. Finally, with newly added records of solar eclipses, we re-determine the value range of Delta T during the years 1431-1433 (see Tanikawa et al. 2019, in Proc. 5th Symposium on Historical Astronomical Records and Modern Science), and add a new Delta T in the year 1445.

关键词： eclipses history and philosophy of astronomy method: data analysis time

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Surface Rotation of LAMOST-Kepler Li-rich Giant Stars

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Chinese Astronomy and Astrophysics 2021年第1期45卷 45-57页

作者： Ming-hao, D.U. Shao-lan, B.I. Jian-rong, S.H.I. Hong-liang, Y.A.N. Department of Astronomy Beijing Normal University Beijing 100875 National Astronomical Observatories Chinese Academy of Sciences Beijing 100101 School of Astronomy and Space Science University of Chinese Academy of Sciences Beijing 100049

The years-long high-precision photometric data observed by Kepler satellite combining with huge amount of spectra observed by LAMOST provide a great opportunity to study the relations between surface rotation and lithium abundance of li-rich giants. In this study, we cross match the Kepler data with li-rich giants catalog from LAMOST, and obtain 619 common sources. Then we measure 36 rotation periods from the full set of 295 li-rich giants with good data quality which consists of two sub-samples. The rotation periods of 14 stars was extracted from 205 stars with evolutionary stages determined using asteroseismology, including 11 core helium-burning stars (HeBs), 2 red giant branch stars (RGBs), and 1 unclassified star. All the super lithium-rich giant stars (A(Li)>3.3 dex) are HeBs in our sample. The remaining 90 giants do not have evolutionary stages confirmed, and in this sub-sample, 22 giants have their rotation period measured. The rotation detection rate of the former sub-sample is 6.8%, which is significantly higher than the detection rate of a large giant sample in previous studies (2.08%). With the surface rotation period measured, we confirm the relation between stellar rotation and lithium enrichment of giants. Meanwhile, we find that the less Li-enriched stars have a relatively dispersed distribution of rotation periods, and the giants with a high Li enrichment is concentrated on the rapidly rotating area, which is consistent with earlier studies. The present work also shows a jump at A(Li)≈3.3 dex in the relation between rotation period and Li abundance that coincidently is the boundary between Li-rich giants and super Li-rich giants which may indicate the different mechanisms. The rotation periods of super Li-rich giants become shorter as the lithium enrichment increases. This correlation provides an evidence for the rotational induced extra-mixing mechanism responsible for Li enrichment of giants. © 2021

关键词： method: data analysis Stars: abundance stars: chemically peculiar Stars: rotation

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On the detection of stellar differential rotation based on the Fourier transform of spectral line profiles

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PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 2020年第1期72卷 10-1-10-18页

作者： Takeda, Yoichi Natl Astron Observ Japan 2-21-1 Osawa Mitaka Tokyo 1818588 Japan Grad Univ Adv Studies SOKENDAI 2-21-1 Osawa Mitaka Tokyo 1818588 Japan

It is known that stellar differential rotation can be detected by analyzing the Fourier transform of spectral line profiles, since the ratio of the first and second zero frequencies is a useful indicator. This approach essentially relies on the conventional formulation that the observed flux profile is expressible as a convolution of the rotational broadening function and the intrinsic profile, which implicitly assumes that the local intensity profile does not change over the disk. Although this postulation is unrealistic in the strict sense, how the result is affected by this approximation is still unclear. With the aim of examining this problem, flux profiles of several test lines (showing different center-to-limb variations) were simulated using a model atmosphere corresponding to a mid-F dwarf by integrating the intensity profiles for various combinations of v(e) sin i (projected rotational velocity), alpha (differential degree), and i (inclination angle), and their Fourier transforms were computed to check whether the zeros are detected at the predicted positions or not. For this comparison a large grid of standard rotational broadening functions and their transforms/zeros were also calculated. It turned out that the situation depends critically on v(e)sin i: In the case of v(e) sin i greater than or similar to 20 km s(-1), where rotational broadening is predominant over other line broadening velocities (typically several km s(-1)), the first/second zeros of the transform are confirmed almost at the expected positions. In contrast, deviations begin to appear as v(e) sin i is lowered, and the zero features of the transform are totally different from those expected at v(e) sin i as low as -10 km s(-1), which means that the classical formulation is no longer valid. Accordingly, while the zero-frequency approach is safely applicable to studying differential rotation in the former broader-line case, it would be difficult to practice for the latter sharp-line case.

关键词： line: profiles method: data analysis stars: rotation stars: solar-type

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A new method of determining brightness and size of cometary nuclei

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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 2020年第3期492卷 4175-4188页

作者： Paradowski, Mieczyslaw Leszek Marie Curie Sklodowska Univ Inst Phys Pl M Curie Sklodowskiej 1 PL-20031 Lublin Poland

This paper presents a new method of determining the brightness and size of cometary nuclei that has been applied to the following 32 observed comets: 2P/Encke, 29P/Schwassmann-Wachmann 1, 102P/Shoemaker 1, 103P/Hartley 2, 168P/Hergenrother, 189P/NEAT, 260P/McNaught, 315P/LONEOS, P/2012 NJ (La Saga), P/2013 J2 (McNaught), C/2006 S3 (LONEOS), C/2009 P1 (Garradd), C/2010 S1 (LINEAR), C/2010 X1 (Elenin), C/2011 J2 (LINEAR), C/2011 L4 (PANSTARRS), C/2011 W3 (Lovejoy), C/2012 F6 (Lemmon), C/2012 J1 (Catalina), C/2012 K1 (PANSTARRS), C/2012 S1 (ISON), C/2013 R1 (Lovejoy), C/2013 US10 (Catalina), C/2014 B1 (Schwartz), C/2014 E2 (Jacques), C/2014 Q2 (Lovejoy), C/2015 F4 (Jacques), C/2015 V2 (Johnson), C/2015 ER61 (PANSTARRS), C/2015 VL62 (Lemmon-Yeung-PANSTARRS), C/2016 A8 (LINEAR), and C/2017 O1 (ASASSN). The method consists in fitting the exponential decay function to the measured coma brightness in the aperture radius range from 0.5 to 2 pixels, and extrapolating this function to 0 pixels to obtain nuclear brightness. The R-band absolute nuclear magnitude R-N(1, 1, 0), and the logarithm of the nucleus diameter D-N expressed in kilometres, follow a linear dependence with the absolute total visual magnitude H. This dependence is of the form R-N(1, 1, 0) = 12.5943 + 0.648H, and log D-N [km] = 1.2415 - 0.13H. Comet 2P/Encke does not fit this dependence due to its high nuclear density of 800 kg m(-3) (Sosa & Fernandez 2009). The mean bulk density of the observed comets (except 2P/Encke) is 453 +/- 29 kg m(-3). The accuracy of the method in determining the brightness of comet nuclei at a level of 1 sigma is 8 per cent.

关键词： method: data analysis techniques: photometric comets: general

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Lifting the Veil on Ultra Metal-Poor Stars in the Outermost Halo

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Proceedings of the International Astronomical Union 2018年第S334期13卷 389-390页

作者： Jinmi Yoon Devin D. Whitten Timothy C. Beers Vinicius M. Placco Young Sun Lee Sarah Dietz Dmitrii Gudin Kaitlin C. Rasmussen Department of Physics University of Notre Dame Notre Dame IN USA email: jinmi.yoon@nd.edu JINA Center for the Evolution of the Elements Notre Dame IN USA Department of Astronomy & Space Science Chungnam National Univ. Daejeon South Korea

The study of extremely metal-poor (EMP; [Fe/H] <−3.0) and ultra metal-poor (UMP; [Fe/H] <−4.0) stars is crucial for better understanding first-star nucleosynthesis and constraining the initial mass function in the early Universe. However, UMP stars discovered in the past 25 years only number ~25. A few recent theoretical studies have pointed out that there is likely to exist large numbers of EMP and UMP stars in the periphery of the Galactic halo, at distances exceeding 30-50 kpc. We present identifications of several new EMP/UMP stars and introduce a survey to expedite discovering hundreds to thousands of EMP/UMP stars in the outermost halo (as well as in the local volume) over the next few years, which could revolutionize chemical-evolution studies of the Galaxy.

关键词： General: nucleosynthesis method: data analysis Galaxy: halo stars: abundances

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Multifractal properties of solar filaments and sunspots numbers

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NEW ASTRONOMY 2015年 38卷 1-10页

作者： Wu, Nan Li, Qi-Xiu Zou, Peng Chongqing Univ Dept Phys Chongqing 400044 Peoples R China Chinese Acad Sci Purple Mt Observ Key Lab Dark Matter & Space Astron Nanjing 210008 Jiangsu Peoples R China

We analyze multifractal properties of low (LLSFNs;= 50 degrees), full-disk (FDSFNs;0 degrees similar to 90 degrees) solar filament numbers (SFNs) and international sunspot numbers (ISNs) by estimating characteristic p... 详细信息

We analyze multifractal properties of low (LLSFNs;< 50 degrees), high (HISFNs;>= 50 degrees), full-disk (FDSFNs;0 degrees similar to 90 degrees) solar filament numbers (SFNs) and international sunspot numbers (ISNs) by estimating characteristic parameters (alpha(0), Delta(alpha), spectrum skewness) off (alpha) singularity spectrum. We find that the SFNs and ISNs have multifractal nature. The obtained alpha(0) and Delta(alpha) indicate that long-term behaviour of the solar filaments is more complex than that of the sunspots and the high-latitude filaments is the most complex in long-term behaviour. The spectrum skewnesses manifest that the ISNs display well symmetrical distribution in singularity strengths, whereas the SFNs are dominated by low singularity strengths, which means that the long-term behaviour of sunspots has homogenous structures and the filaments display averagely small fluctuations in amplitude. To detect the origin of their multifractality, we decompose the raw data of ISNs and SFNs: smoothed data represent similar to 11-year cyclic activities and detrended data represent accidental activities. We also calculate their f(alpha) spectra, respectively. We find that the similar to 11-year cyclic activities of filaments and sunspots tend to be a monofractal and display a bit predominance of low singularity strengths. Their accidental activities have the most complex behaviour than the raw and smoothed data. The accidental activities are dominated by high singularity strengths showing averagely large fluctuations in amplitude. Furthermore, multifractal properties from alpha(0) and Delta(alpha) of the accidental activities have the same features as that of raw data. We think that the similar to 11-year periodic activity determines global fluctuations, while the accidental activities rule local complexity. (C) 2014 Elsevier B.V. All rights reserved.

关键词： Sun: sunspots Sun: filaments method: data analysis

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A new test of uniformity for object orientations in astronomy

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Proceedings of the International Astronomical Union 2015年第S306期10卷 276-278页

作者： Pelgrims, V. IFPA AGO Dept. University of Liège Allée du 6 Août 17 Liège B4000 Belgium

We briefly present a new coordinate-invariant statistical test dedicated to the study of the orientations of transverse quantities of non-uniformly distributed sources on the celestial sphere. These quantities can be ... 详细信息

关键词： method: data analysis method: statistics polarization quasars: general

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Reconstructing light curves from HXMT imaging observations

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Proceedings of the International Astronomical Union 2015年第S306期10卷 355-358页

作者： Huo, Zhuo-Xi Zhang, Juan Li, Yi-Ming Zhou, Jian-Feng Tsinghua University Beijing 100084 China Institute of High Energy Physics Chinese Academy of Sciences Beijing 100049 China

The Hard X-ray Modulation Telescope (HXMT) is a Chinese space telescope mission. It is scheduled for launch in 2015. The telescope will perform an all-sky survey in hard X-ray band (1 - 250 keV), a series of deep imaging observations of small sky regions as well as pointed observations. In this work we present a conceptual method to reconstruct light curves from HXMT imaging observation directly, in order to monitor time-varying objects such as GRB, AXP and SGR in hard X-ray band with HXMT imaging observations. © International Astronomical Union 2015.

关键词： method: data analysis techniques: image processing X-rays: time-varying objects

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