In a collaboration of the German Astrophysical Virtual Observatory (GAVO) and AstroGrid-D, the German Astronomy Community Grid (GACG), we provide a VO service for the access and the calculation of stellar synthetic energy distributions (SEDs) based on static as well as expanding non-LTE model atmospheres.
At three levels, a VO user may directly compare observed and theoretical SEDs: The easiest and fastest way is to use pre-calculated SEDs from the GAVO database. For individual objects, grids of model atmospheres and SEDs can be calculated on the compute resources of AstroGrid-D within reasonable wallclock time. Experienced VO users may even create own atomic-data files for a more detailed analyses.
Spectral Analyses Of The Hottest White Dwarfs: Grids Of Spectral Energy Distributions For Extremely Hot, Compact Stars In The Framework Of The Virtual Observatory
Binary and multiple stars have long provided an effective empirical method of testing stellar formation and evolution theories. In particular, the existence of wide binary systems (separations $>$20,000 au) is particularly challenging to binary formation models as their physical separations are beyond the typical size of a collapsing cloud core ($\sim$5,000$-$10,000 au). We mined the recently published Gaia-DR2 catalog to identify bright comoving systems in the five-dimensional space (sky position, parallax, and proper motion). We identified 3,741 comoving binary and multiple stellar candidate…
Using Virtual Observatory tools, we cross-matched the Carlsberg Meridian 14 and the 2MASS Point Source catalogs to select candidate nearby bright M dwarfs distributed over ~ 25,000 deg^2. Here, we present reconnaissance low-resolution optical spectra for 27 candidates that were observed with the Intermediate Dispersion Spectrograph at the 2.5m Isaac Newton Telescope (R ~ 1600). We derived spectral types from a new spectral index, R, which measures the ratio of fluxes at 7485-7015 A and 7120-7150 A. We also used VOSA, a Virtual Observatory tool for spectral energy distribution fitting, to deriv…
We present a catalogue of 73,221 white dwarf candidates extracted from the astrometric and photometric data of the recently published Gaia DR2 catalogue. White dwarfs were selected from the Gaia Hertzsprung-Russell diagram with the aid of the most updated population synthesis simulator. Our analysis shows that Gaia has virtually identified all white dwarfs within 100 pc from the Sun. Hence, our sub-population of 8,555 white dwarfs within this distance limit and the colour range considered, $-\,0.52<(G_{\rm BP}-G_{\rm RP})<0.80$, is the largest and most complete volume-limited sample of such ob…
In this contribution we report the current stage of the MOLecular Dissociation (MOL-D) database which is a web service within the Serbian virtual observatory (SerVO) and node within Virtual Atomic and Molecular Data Center (VAMDC). MOL-D is an atomic and molecular (A&M) database devoted to the modelling of stellar atmospheres, laboratory plasmas, industrial plasmas etc. The initial stage of development was done at the end of 2014, when the service for data connected with hydrogen and helium molecular ions was done. In the next stage of the development of MOL-D, we include new cross-sections an…
The virtual observatory service TheoSSA: Establishing a database of synthetic stellar flux standards. II. NLTE spectral analysis of the OB-type subdwarf Feige 110
The German Astrophysical Virtual Observatory (GAVO) developed the registered service TheoSSA (theoretical stellar spectra access) and the supporting registered VO tool TMAW (Tuebingen Model-Atmosphere WWW interface). These allow individual spectral analyses of hot, compact stars with state-of-the-art non-local thermodynamical equilibrium (NLTE) stellar-atmosphere models that presently consider opacities of the elements H, He, C, N, O, Ne, Na, and Mg, without requiring detailed knowledge about the involved background codes and procedures. Presently, TheoSSA provides easy access to about 150000 …
The frequency of multiple systems and their properties are key constraints of stellar formation and evolution. Formation mechanisms of very low-mass (VLM) objects are still under considerable debate and an accurate assessment of their multiplicity and orbital properties are essential for constraining current theoretical models. Taking advantage of the Virtual Observatory capabilities, we looked for comoving low and VLM binary (or multiple) systems using the Large Area Survey of the UKIDSS LAS DR10, SDSS DR9, and the 2MASS Catalogues. Other catalogues (WISE, GLIMPSE, SuperCosmos ...) were used …
Recent massive sky surveys in different bandwidths are providing new opportunities to modern astronomy. The Virtual Observatory (VO) represents the adequate framework to handle the huge amount of information available and filter out data according to specific requirements. In this work, we applied a selection strategy to find new, uncatalogued hot subdwarfs making use of VO tools. We used large area catalogues (GALEX, SDSS, SuperCosmos, 2MASS) to retrieve photometric and astrometric information of stellar objects. To these objects, we applied colour and proper motion filters, together with an …
The virtual observatory service TheoSSA: Establishing a database of synthetic stellar flux standards. I. NLTE spectral analysis of the DA-type white dwarf G 191-B2B
Stellar synthetic spectroscopy in the Virtual Observatory era
参数包括在VO大网格的合成光谱完全覆盖HR图。一个明显的需要是在所有红移的人口合成。理论光谱还具有预测特殊行为的能力，这些行为可能在观察到的光谱中未被注意到，或导致错误的结论。一个有趣的例子是极端贫金属恒星中的Ca II H & K线。在富碳大气中，H & K线相对于连续谱变得更弱，这将导致低估金属丰度。实际发生的是连续谱的位移，这在绝对通量合成光谱中很明显，但在观测到的连续归一化光谱中看不到。图书馆的合成光谱的描述，以及用于计算它们的代码。对通过VO提供这些库的问题以及必要的输入数据，即行列表和模型大气，作了一些评论。
In this paper we report a search for vanishing sources in POSS I red images using Virtual Observatory archives, tools and services. The search, conducted in the framework of the VASCO project, aims at finding POSS I (red) sources not present in recent catalogues like Pan-STARRS DR2 (limiting magnitude r=21.4) or Gaia EDR3 (limiting magnitude G=21). We found 298 165 sources visible only in POSS I plates, out of which 288 770 had a crossmatch within 5 arcsec in other archives (mainly in the infrared), 189 were classified as asteroids, 35 as variable objects, 3 592 as artefacts from the compariso…
Ultracool dwarfs encompass a wide variety of compact stellar-like objects with spectra classified as late-M, L, T and Y. Most of them have been discovered using wide-field imaging surveys. The Virtual Observatory has proven to be of great utility to efficiently exploit these astronomical resources. We aim to validate a Virtual Observatory methodology designed to discover and characterize ultracool dwarfs in deep extragalactic surveys like ALHAMBRA and COSMOS. Three complementary searches based on parallaxes, proper motions and colours, respectively were carried out. A total of 897 candidate ul…
This tutorial is devoted to extending an existing catalogue with data taken elsewhere, either from CDS Vizier or Simbad database. As an example, we used the so-called 'Spectroscopic Survey of Stars in the Solar Neighborhood' (aka. S4N, Allende Prieto et al. 2004) in order to retrieve all objects with available data for the set of fundamental stellar parameters effective temperature, surface gravity and metallicity. Then for each object in this dataset we query Simbad database to retrieve the projected rotational velocity. This combines Vizier and Simbad queries made using Python astroquery mod…
The estimation of the binary fraction of hot subdwarfs is key to shed light on the different evolution scenarios proposed to explain the loss of the hydrogen envelope during the red giant branch phase. In this paper we analyse the spectral energy distribution of the hot subdwarfs included in a recent and comprehensive catalogue with the aim of identifying companions. Our methodology shows a performance superior to the photometric criteria used in that study, identifying 202 objects wrongly classified as binaries according to their spectral energy distributions, and finding 269 new binaries. Ou…
The nature and physical properties of asteroids, in particular those orbiting in the near-Earth space, are of scientific interest and practical importance. Exoplanet surveys can be excellent resources to detect asteroids, both already known and new objects. This is due their similar observing requirements: large fields of view, long sequences, and short cadence. If the targeted fields are not located far from the ecliptic, many asteroids will cross occasionally the field of view. We present two complementary methodologies to identify asteroids serendipitously observed in large-area astronomica…
The aim of the project is to identify wide common proper motion companions to a sample of spectroscopically confirmed M and L metal-poor dwarfs (also known as subdwarfs) to investigate the impact of metallicity on the binary fraction of low-mass metal-poor binaries and to improve the determination of their metallicity from the higher-mass binary. We made use of Virtual Observatory tools and large-scale public surveys to look in Gaia for common proper motion companions to a well-defined sample of ultracool subdwarfs with spectral types later than M5 and metallicities below or equal to $-$0.5 de…
The heterogeneity of papers dealing with the discovery and characterization of exoplanets makes every attempt to maintain a uniform exoplanet catalog almost impossible. Four sources currently available online (NASA Exoplanet Archive, Exoplanet Orbit Database, Exoplanet Encyclopaedia, and Open Exoplanet Catalogue) are commonly used by the community, but they can hardly be compared, due to discrepancies in notations and selection criteria. Exo-MerCat is a Python code that collects and selects the most precise measurement for all interesting planetary and orbital parameters contained in the four …
Ca II K Spectral Study of an Emerging Flux Region using Domeless Solar Telescope in Hida Observatory
与飞田天文台和Hinode卫星合作对一个新兴通量区进行了观测。由飞田天文台的圆顶太阳望远镜拍摄的连续的Ca II K光谱日像图。Hinode观察到新兴的通量区域与Ca II H和Fe I斯托克斯IQUV过滤图。在这项研究中，详细的动力学和时间演化的磁通量出现的观测研究。这一事件首先是在光球磁场信号中探测到的。3分钟后，检测到暗区的水平扩展。在水平膨胀后7 min，色球层高度上出现了最大上升速度为2.1km/s的环。观测到的从光球层到上色球层的出射磁通量的动力学与以前的模拟工作的结果是一致的。我们的观测证实了弱磁场下磁通管的逐渐上升阶段。
Archives of Photographic PLates for Astronomical USE (APPLAUSE) Digitisation of astronomical plates and their integration into the International Virtual Observatory
Recent data from the Auger Observatory on low energy secondary cosmic ray particles are analyzed to study temporal correlations together with data on the daily sunspot numbers and neutron monitor data. Standard spectral analysis demonstrates that the available data shows 1/f^β fluctuations with β approximately 1 in the low frequency range. All data behave like Brownian fluctuations in the high frequency range. The existence of long-range correlations in the data was confirmed by detrended fluctuation analysis. The real data confirmed the correlation between the scaling exponent of the detrende…
New ultracool subdwarfs identified in large-scale surveys using Virtual Observatory tools: Part I: UKIDSS LAS DR5 vs SDSS DR7
该项目的目的是提高我们对低质量和低金属丰度群体的认识，以调查金属丰度对恒星（和亚恒星）质量函数的影响。我们提出了一个光度和自行搜索的结果，旨在发掘超冷次矮星在大规模的调查。我们采用并结合了UKIDSS LAS DR 5和SDSS DR 7，并补充了来自2 MASS、DENIS和SuperCOSMOS的辅助数据。SDSS DR 7与UKIDSS LAS DR 5的搜索共返回了32个超冷亚矮星候选者，只有两个在文献中被认为是亚矮星。在600和1000 nm之间的光学范围内对27个候选物进行了光谱跟踪。我们确认了20颗光谱类型晚于M5的次矮星、极端次矮星或超次矮星，成功率约为60%。在这20个新的次矮星中，我们发现了2个早期的L次矮星，它们很可能位于100 pc以内，我们建议将它们作为未来搜索的模板，因为它们是它们子类的第一个例子。另外7个源是太阳金属丰度M矮星，光谱类型在M4和M7之间，没有H α发射，表明它们是古老的M矮星。剩下的5颗候选星还没有后续的光谱观测，只有1颗在修正了自行后仍然是真正的超冷亚矮星。我们根据当前的分类方案分配光谱类型，并在可能的情况下测量它们的径向速度。利用有限数量的具有三角形半径的次矮星，我们估计新的次矮星的距离在90到600之间。我们提供了两颗亚矮星的WISE中红外测光结果，并讨论了它们的颜色。最后，我们估计了超冷次矮星表面密度的下限，其数量级比太阳金属丰…
Flares and CMEs can have deleterious effects on their surroundings: they can erode atmospheres of orbiting planets over time and also have high importance in stellar evolution. Most of the CME detections in the literature are single events found serendipitously sparse for statistical investigation. We aimed to gather a large amount of spectral data of M-dwarfs to drastically increase the number of known events to make statistical analysis possible in order to study the properties of potential stellar CMEs. Using archive data we investigated asymmetric features of Balmer-lines, that could indic…
The third data release of Gaia has provided low resolution spectra for ~100,000 white dwarfs (WDs) that, together with the excellent photometry and astrometry, represent an unrivalled benchmark for the study of this population. In this work, we first built a highly-complete volume-limited sample consisting in 12,718 WDs within 100 pc from the Sun. The use of VOSA tool allowed us to perform an automated fitting of their spectral energy distributions to different atmospheric models. In particular, the use of spectrally derived J-PAS photometry from Gaia spectra led to the classification of DA an…
Ultracool dwarfs (UCDs) are objects with spectral types equal or later than M7. Most of them have been discovered using wide-field imaging surveys. The Virtual Observatory (VO) has proven to be of great utility to efficiently exploit these astronomical resources. We aim to validate a VO methodology designed to discover and characterize UCDs in the J-PLUS photometric survey. J-PLUS is a multiband survey carried out with the wide angle T80Cam optical camera mounted on the 0.83-m telescope JAST/T80 in the Observatorio Astrofísico de Javalambre. In this work we make use of the Internal Data Releas…
University of Michigan（密歇根大学）；NASA GSFC（美国国家航空航天局戈达德太空飞行中心）；NorthWest Research Associates（西北研究协会）；Lockheed Martin Solar and Astrophysics Laboratory（洛克希德·马丁太阳与天体物理实验室）；Stanford University（斯坦福大学）
Both NASA's Solar Dynamics Observatory (SDO) and the JAXA/NASA Hinode mission include spectropolarimetric instruments designed to measure the photospheric magnetic field. SDO's Helioseismic and Magnetic Imager (HMI) emphasizes full-disk high-cadence and good spatial resolution data acquisition while Hinode's Solar Optical Telescope Spectro-Polarimeter (SOT-SP) focuses on high spatial resolution and spectral sampling at the cost of a limited field of view and slower temporal cadence. This work introduces a deep-learning system named SynthIA (Synthetic Inversion Approximation), that can enhance …
Ultracool dwarfs (UCDs) comprise the lowest mass members of the stellar population and brown dwarfs, from M7 V to cooler objects with L, T, and Y spectral types. Most of them have been discovered using wide-field imaging surveys, for which the Virtual Observatory (VO) has proven to be of great utility. We aim to perform a search for UCDs in the entire Javalambre Photometric Local Universe Survey (J-PLUS) second data release (2176 deg$^2$) following a VO methodology. We also explore the ability to reproduce this search with a purely machine learning (ML)-based methodology that relies solely on …
Multi-Application Solar Telescope (MAST) is a 50 cm off-axis Gregorian telescope and started operational recently at Udaipur Solar Observatory (USO). For understanding the evolution and dynamics of solar magnetic and velocity fields, an imaging spectropolarimeter is being developed as one of the back-end instruments of MAST. This system consists of a narrow-band filter and a polarimeter. Polarimeter includes a linear polarizer and two sets of Liquid Crystal Variable Retarders (LCVRs). The instrument is intended for the simultaneous observations in the spectral lines 617.3 nm and 854.2 nm, whic…
