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Slit-Modulation Imaging method for Detecting Any Periodic Structural Change in Interferometric data

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN 2008年第6期60卷 1371-1386页

作者： Miyoshi, Makoto Natl Inst Nat Sci Natl Astron Observ Japan Mitaka Tokyo 1818588 Japan

We propose a slit-modulation imaging (SMI) method, a new imaging technique for detecting shorter periodic structural changes of interferometric data. Using simulations with artificial visibility data, we show that the SMI method is highly effective in detecting periodic change patterns, of which period is shorter than the observing time span, of interferometric data.

关键词： method: data analysis method: synthesis imaging techniques: interferometric

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

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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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On the importance of background subtraction in the analysis of coronal loops observed with TRACE (Research Note)

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ASTRONOMY & ASTROPHYSICS 2010年第1期515卷 A7-1-A7-7页

作者： Terzo, S. Reale, F. Univ Palermo Dipartimento Sci Fis & Astron I-90123 Palermo Italy INAF Osservatorio Astron Palermo I-90134 Palermo Italy

Aims. Using TRACE coronal observations, we compare the analysis and diagnostics of coronal loop after subtracting the background with two different and independent methods. methods. We analyze sequences of images in the 171 angstrom and 195 angstrom filter bands of TRACE. One background subtraction method consists of considering background values obtained by interpolating between concentric strips around the analyzed loop. Another involves a pixel-to-pixel subtraction of the final image after the loop has completely faded out, used by Reale and Ciaravella. Results. We compare the emission distributions along the loop obtained with the two methods and find that they differ considerably. We also find differences in the related filter ratio and temperature profiles. In particular, the pixel-to-pixel subtraction leads to coherent diagnostics of a cooling loop. After applying the other type of subtraction, the diagnostics are much less clear. Conclusions. The background subtraction should be treated with care when analyzing a loop. The pixel-to-pixel subtraction appears to be more reliable, but its application is not always possible. Subtraction by means of interpolation between surrounding regions can produce higher systematic errors, because of intersecting structures and the large amount of subtracted emission in TRACE observations.

关键词： Sun: corona Sun: X-rays, gamma rays method: data analysis

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MOSE: operational forecast of the optical turbulence and atmospheric parameters at European Southern Observatory ground-based sites - I. Overview and vertical stratification of atmospheric parameters at 0-20 km

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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 2013年第3期436卷 1968-1985页

作者： Masciadri, E. Lascaux, F. Fini, L. INAF Osservatorio Astrofis Arcetri I-50125 Florence Italy

We present an overview of the MOSE (MOdelling ESO Sites) project that aims to prove the feasibility of the forecast of the classical atmospheric parameters (wind-speed intensity and direction, temperature, relative humidity) and the optical turbulence (C-N(2) profiles and the most relevant integrated astroclimatic parameters derived from C-N(2);i.e. the seeing epsilon, the isoplanatic angle theta(0) and the wavefront coherence time tau(0)) above the two European Southern Observatory ground-based sites of Cerro Paranal and Cerro Armazones. The final outcome of the study is to investigate the opportunity to implement an automatic system for the forecast of these parameters at these sites. In this paper, we present results related to the meso-nh model ability in reconstructing the vertical stratification of the atmospheric parameters along 20 km above the ground. The very satisfactory performances shown by the model in reconstructing most of these parameters (and, in particular, the wind speed) make this tool of investigation the most suitable to be used in astronomical observatories to support Adaptive Optics facilities and to calculate the temporal evolution of the wind speed and the wavefront coherence time at whatever temporal sampling. A further great advantage of this solution is that such estimates can be available in advance (of the order of some hours) with respect to the time of interest.

关键词： turbulence atmospheric effects balloons method: data analysis methods: numerical site testing

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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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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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Iris: An extensible application for building and analyzing spectral energy distributions

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ASTRONOMY AND COMPUTING 2014年 7-8卷 81-94页

作者： Laurino, O. Budynkiewicz, J. D'Abrusco, R. Bonaventura, N. Busko, I. Cresitello-Dittmar, M. Doe, S. M. Ebert, R. Evans, J. D. Norris, P. Pevunova, O. Refsdal, B. Thomas, B. Thompson, R. Smithsonian Astrophys Observ Cambridge MA 02138 USA Space Telescope Sci Inst Baltimore MD 21218 USA Infrared Proc & Anal Ctr Pasadena CA 91125 USA Natl Opt Astron Observ Tucson AZ 85719 USA

Iris is an extensible application that provides astronomers with a user-friendly interface capable of ingesting broad-band data from many different sources in order to build, explore, and model spectral energy distributions (SEDs). Iris takes advantage of the standards defined by the International Virtual Observatory Alliance, but hides the technicalities of such standards by implementing different layers of abstraction on top of them. Such intermediate layers provide hooks that users and developers can exploit in order to extend the capabilities provided by Iris. For instance, custom Python models can be combined in arbitrary ways with the Iris built-in models or with other custom functions. As such, Iris offers a platform for the development and integration of SED data, services, and applications, either from the user's system or from the web. In this paper we describe the built-in features provided by Iris for building and analyzing SEDs. We also explore in some detail the Iris framework and software development kit, showing how astronomers and software developers can plug their code into an integrated SED analysis environment. (C) 2014 Elsevier B.V. All rights reserved.

关键词： data abstraction method: data analysis Object-oriented programming Software frameworks Spectral energy distribution Virtual observatory tools

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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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Towards a fast, model-independent Cosmic Microwave Background bispectrum estimator

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STATISTICAL methodOLOGY 2012年第1-2期9卷 71-84页

作者： Pires, S. Plaszczynski, S. Lavabre, A. CEA DSM CNRS Univ Paris Diderot AIM IRFU SEDI SAP Serv AstrophysCEA Saclay F-91191 Gif Sur Yvette France Univ Paris 11 LAL CNRS UMR8607 IN2P3 Orsay France

The measurements of the statistical properties of the Cosmic Microwave Background (CMB) fluctuations enable us to probe the physics of the very early Universe especially at the epoch of inflation. A particular interest lays on the detection of the non-Gaussianity of the CMB as it can constrain the current proposed models of inflation and structure formation, or possibly point out new models. The current approach to measure the degree of non-Gaussianity of the CMB is to estimate a single parameter f(NL)(local) which is highly model-dependent. The bispectrum is a natural and widely studied tool for measuring the non-Gaussianity in a model-independent way. This paper sets the grounds for a full CMB bispectrum estimator based on the decomposition of the sphere onto projected patches. The mean bispectrum estimated this way can be calculated quickly and is model-independent. This approach is very flexible, allowing exclusion of some patches in the processing or consideration of just a specific region of the sphere. (C) 2011 Elsevier B.V. All rights reserved.

关键词： Cosmology: CMB method: data analysis

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