Membership, binarity and accretion among very low-mass stars and brown dwarfs of the σ Orionis cluster     

M. J. Kenyon  R. D. Jeffries  Tim Naylor  J. M. Oliveira  P. F. L. Maxted 《Monthly notices of the Royal Astronomical Society》2005,356(1):89-106

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Observational studies of early-type binary stars: MP Centauri     

Dirk Terrell  Ulisse Munari  Toma&#; Zwitter  George Wolf 《Monthly notices of the Royal Astronomical Society》2005,360(2):583-586

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Spectroscopic binaries near the North Galactic Pole paper 14: HD 118234     

R. F. Griffin 《Journal of Astrophysics and Astronomy》1988,9(2):75-78

Photoelectric radial-velocity measurements show that the Seventh-magnitude star HD 118234 is a spectroscopic binary in a very eccentric 59-day orbit.  相似文献   

The sun‐as‐a‐star solar spectrum     

A.A. Pevtsov  L. Bertello  A.R. Marble 《Astronomische Nachrichten》2014,335(1):21-26

The Sun is the only star for which individual surface features can be observed directly. For other stars, the properties of starspots, stellar rotation, stellar flares, etc, are derived indirectly via variation of star‐integrated spectral line profiles or their luminosity measurements. Solar disk‐integrated and disk‐resolved observations allow for investigations of the contribution of individual solar disk features to sun‐as‐a‐star spectra. Here, we provide a brief overview of three sun‐as‐a‐star programs, currently in operation, and describe recent improvements in observations and data reduction for the Integrated Sunlight Spectrometer (ISS), one of three instruments comprising the Synoptic Optical Long‐term Investigations of the Sun (SOLIS) system. Next, we discuss studies employing sun‐as‐a‐star observations (including Ca II K line as proxy for total unsigned magnetic flux and 2800 MHz radio flux) as well as the effects of flares on solar disk‐integrated spectra. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Estimating stellar atmospheric parameters based on Lasso features     

Chuan-Xing Liu  Pei-Ai Zhang  Yu Lu 《中国天文和天体物理学报》2014,(4):423-432

With the rapid development of large scale sky surveys like the Sloan Digital Sky Survey （SDSS）, GAIA and LAMOST （Guoshoujing telescope）, stellar spectra can be obtained on an ever-increasing scale. Therefore, it is necessary to estimate stel- lar atmospheric parameters such as Teff, log g and [Fe/H] automatically to achieve the scientific goals and make full use of the potential value of these observations. Feature selection plays a key role in the automatic measurement of atmospheric parameters. We propose to use the least absolute shrinkage selection operator （Lasso） algorithm to select features from stellar spectra. Feature selection can reduce redundancy in spectra, alleviate the influence of noise, improve calculation speed and enhance the robustness of the estimation system. Based on the extracted features, stellar atmospheric param- eters are estimated by the support vector regression model. Three typical schemes are evaluated on spectral data from both the ELODIE library and SDSS. Experimental results show the potential performance to a certain degree. In addition, results show that our method is stable when applied to different spectra.  相似文献   

Note on the orbit of the magnetic star 53 Cam     

L. Oetken 《Astronomische Nachrichten》1989,310(3):213-215

Ausgehend von den bekannten spektroskopischen Bahnelementen von 53 Cam wurden die Positionen des Begleiters für die Zeiten der Speckle-Beobachtungen berechnet und mit den beobachteten Positionen verglichen. Bei Berücksichtigung der Doppeldeutigkeit in der Speckle-Interferometrie lassen sich die Beobachtungen mäßig gut darstellen bei einer Neigung von näherungsweise 45° zwischen Bahn- und Tangentialebene.  相似文献   

Magnetic field measurements of ϵ Eridani from Zeeman broadening     

L. T. Lehmann  A. Künstler  T. A. Carroll  K. G. Strassmeier 《Astronomische Nachrichten》2015,336(3):258-265

We present new magnetic field measurements of the K2 main‐sequence star ϵ Eri based on principal components analysis (PCA) line‐profile reconstructions. The aim of this paper is to quantify the surface‐averaged magnetic field and search for possible variations. A total of 338 optical échelle spectra from our robotic telescope facility STELLA with a spectral resolution of 55 000 were available for analysis. This time‐series was used to search for the small line‐profile variations due to a surface magnetic field with the help of a PCA. Evidence for a spatial and temporal inhomogeneous magnetic field distribution is presented. The mean, surface averaged, magnetic field strength was found tobe 〈B〉 = 186 ± 47 G in good agreement with previous Zeeman‐broadening measurements. Clear short‐term variations of the surface averaged magnetic field of up to few tens Gauss were detected together with evidence for a three‐year cycle in the surface‐averaged magnetic field of ϵ Eri. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Doppler tomography of cataclysmic variables     

L. Morales‐Rueda 《Astronomische Nachrichten》2004,325(3):193-196

The study of cataclysmic variables (CVs), and in particular of the evolution of their accretion discs throughout their different brightness states, has benefited largely from the use of indirect imaging techniques. I report on the latest results obtained from Doppler tomography of CVs concentrating mainly on results published since the 2000 Astrotomography meeting in Brussels. Emphasis is given to the spiral structures found in the accretion discs of some CVs, to the evolution of these structures throughout quiescence and outburst, and to our search for them in more systems. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

The sulfur species in hot rocky exoplanet atmospheres     

L. J. Janssen  P. Woitke  O. Herbort  M. Min  K. L. Chubb  Ch. Helling  L. Carone 《Astronomische Nachrichten》2023,344(10):e20230075

The first JWST observations of hot Jupiters showed an unexpected detection of SO ${}_2$ in their hydrogen-rich atmospheres. We investigate how much sulfur can be expected in the atmospheres of rocky exoplanets and which sulfur molecules can be expected to be most abundant and detectable by transmission spectroscopy. We run thermochemical equilibrium models at the crust–atmosphere interface, considering surface temperatures 500–5000 K, surface pressures 1–100 bar, and various sets of element abundances based on common rock compositions. Between 1000 and 2000 K, we find gaseous sulfur concentrations of up to 25% above the rock in our models. SO ${}_2$, SO, H ${}_2$S, and S ${}_2$ are by far the most abundant sulfur molecules. SO ${}_2$ shows potentially detectable features in transmission spectra at about 4 $\mu$m, between 7 and 8 $\mu$m, and beyond 15 $\mu$m. In contrast, the sometimes abundant H ${}_2$S molecule is difficult to detect in these spectra, which are mostly dominated by H ${}_2$O and CO ${}_2$. Although the molecule PS only occurs with concentrations ppm, it can cause a strong absorption feature between 0.3 and 0.65 $\mu$m in some of our models for high surface pressures. The detection of sulfur molecules would enable a better characterization of the planetary surface.  相似文献