scholarly journals Speckle Interferometry of Double Stars from the Southern Hemisphere

1995 ◽  
Vol 166 ◽  
pp. 392-392
Author(s):  
E. Horch ◽  
W. F. Van Altena ◽  
T. M. Girard ◽  
C. E. López ◽  
O. Franz
Keyword(s):  
Southern Hemisphere ◽  
Main Sequence ◽  
Speckle Interferometry ◽  
Double Star ◽  
Lower Portion ◽  
Stanford University ◽  
Imaging Device ◽  
Double Stars ◽  
Microchannel Array

We have started a new program of double star observations in the southern hemisphere which utilizes the technique of speckle interferometry. Observations are made using the Stanford University speckle interferometer on the 76-cm reflector at the Cesco Observatory at El Leoncito, Argentina (jointly run by Universidad Nacional de San Juan and Yale Southern Observatory), although we will also have access to larger aperture telescopes. The Stanford system, formerly used at Lick Observatory, is on long term loan to us from Dr. Gethyn Timothy and features a multi-anode microchannel array (MAMA) detector as the imaging device. This new program of double star research will help alleviate the continuing problem of fewer speckle observations in the southern hemisphere. In combination with other data such as the eyepiece interferometer measures of Finsen and Hipparcos parallaxes, it should also eventually contribute to a better understanding of the lower portion of the main sequence mass-luminosity relation.

scholarly journals Dynamical investigations of the multiple stars

2017 ◽  
Vol 26 (1) ◽  
Author(s):  
Olga V. Kiyaeva ◽  
Roman Ya. Zhuchkov
Keyword(s):  
High Precision ◽  
Orbital Period ◽  
Triple System ◽  
Main Sequence ◽  
Double Star ◽  
Multiple Stars ◽  
Ccd Observations ◽  
Triple Star

AbstractTwo multiple stars - the quadruple star - Bootis (ADS 9173) and the triple star T Taury were investigated. The visual double star - Bootiswas studied on the basis of the Pulkovo 26-inch refractor observations 1982-2013. An invisible satellite of the component A was discovered due to long-term uniform series of observations. Its orbital period is 20 ± 2 years. The known invisible satellite of the component B with near 5 years period was confirmed due to high precision CCD observations. The astrometric orbits of the both components were calculated. The orbits of inner and outer pairs of the pre-main sequence binary T Taury were calculated on the basis of high precision observations by the VLT and on the Keck II Telescope. This weakly hierarchical triple system is stable with probability more than 70%.

scholarly journals Binarity of Hipparcos Main Sequence Survey Stars

2001 ◽  
Vol 200 ◽  
pp. 64-68 ◽  
Author(s):  
Carl F. Quist ◽  
Lennart Lindegren
Keyword(s):  
Main Sequence ◽  
Double Star ◽  
Double Stars ◽  
Hipparcos Catalogue ◽  
Total Multiplicity

Hipparcos observations of double stars, mainly A and F primaries, are modelled in order to check the statistics of double-star solutions in the Hipparcos Catalogue and to set quantitative limits on binary distributions. The number of companions per primary is estimated to 0.25 ± 0.05 for semi-major axes from 1 to 10 AU, and to 0.43 ± 0.20 for the range 10–100 AU. The total multiplicity found is between 0.9 and 1.2.

scholarly journals Detection and Measurement of Double Stars with HIPPARCOS: Provisional Results from NDAC

1992 ◽  
Vol 135 ◽  
pp. 412-420
Author(s):  
S. Söderhjelm ◽  
L. Lindegren ◽  
F. Van Leeuwen ◽  
D.W. Evans
Keyword(s):  
Data Analysis ◽  
Case History ◽  
Speckle Interferometry ◽  
Single Step ◽  
Double Star ◽  
Double Stars ◽  
Early Results ◽  
Reduction Methods ◽  
Small Parts ◽  
Provisional Data

AbstractThe HIPPARCOS satellite observes 118,000 stars from a predefined list. Some 10% of these are known doubles or multiples, and another 2—3% may ultimately be found to be non-single with separations above 0″.l and magnitude–differences below 4–5. This paper describes briefly the special reduction methods used by NDAC (Northern Data Analysis Consortium) for treating these non-singles. A key feature is the use of the main reduction results to calibrate and collect the data for individual doubles in ‘case history files’. This enables a global solution of both absolute and relative parameters for a double to be carried out in a single step. Using provisional data tapes covering small parts of a 14-month interval, tests have been made of major parts of the double star reductions. These early results are compared with independent HIPPARCOS data and with ground–based speckle interferometry.

scholarly journals SUSI’s Potential for Double Star Research

1992 ◽  
Vol 135 ◽  
pp. 521-526
Author(s):  
John Davis
Keyword(s):  
Angular Resolution ◽  
Double Star ◽  
Double Stars ◽  
Stellar Interferometer ◽  
New Instrument

AbstractThe Sydney University Stellar Interferometer (SUSI) is currently undergoing commissioning and will soon commence its astronomical program in which observations of double stars will form a major component. With its 640-m long North–South array of input siderostats, the new instrument will have unprecedented angular resolution.

scholarly journals Long-Term and Seasonal Trends in Global Wave Height Extremes Derived from ERA-5 Reanalysis Data

2020 ◽  
Vol 8 (12) ◽  
pp. 1015
Author(s):  
Alicia Takbash ◽  
Ian R. Young
Keyword(s):  
Southern Hemisphere ◽  
Wave Height ◽  
Significant Wave Height ◽  
Reanalysis Data ◽  
Extreme Value Analysis ◽  
Winter Storms ◽  
Value Analysis ◽  
Weather Forecasts ◽  
Significant Wave

A non-stationary extreme value analysis of 41 years (1979–2019) of global ERA5 (European Centre for Medium-Range Weather Forecasts Reanalysis) significant wave height data is undertaken to investigate trends in the values of 100-year significant wave height, Hs100. The analysis shows that there has been a statistically significant increase in the value of Hs100 over large regions of the Southern Hemisphere. There have also been smaller decreases in Hs100 in the Northern Hemisphere, although the related trends are generally not statistically significant. The increases in the Southern Hemisphere are a result of an increase in either the frequency or intensity of winter storms, particularly in the Southern Ocean.

scholarly journals Nonstationarity in Southern Hemisphere Climate Variability Associated with the Seasonal Breakdown of the Stratospheric Polar Vortex

2017 ◽  
Vol 30 (18) ◽  
pp. 7125-7139 ◽  
Author(s):  
Nicholas J. Byrne ◽  
Theodore G. Shepherd ◽  
Tim Woollings ◽  
R. Alan Plumb
Keyword(s):  
Climate Variability ◽  
Southern Hemisphere ◽  
Seasonal Cycle ◽  
Vortex Breakdown ◽  
Polar Vortex ◽  
Reanalysis Data ◽  
Early Summer ◽  
Stratospheric Polar Vortex ◽  
Time Symmetry

Abstract Statistical models of climate generally regard climate variability as anomalies about a climatological seasonal cycle, which are treated as a stationary stochastic process plus a long-term seasonally dependent trend. However, the climate system has deterministic aspects apart from the climatological seasonal cycle and long-term trends, and the assumption of stationary statistics is only an approximation. The variability of the Southern Hemisphere zonal-mean circulation in the period encompassing late spring and summer is an important climate phenomenon and has been the subject of numerous studies. It is shown here, using reanalysis data, that this variability is rendered highly nonstationary by the organizing influence of the seasonal breakdown of the stratospheric polar vortex, which breaks time symmetry. It is argued that the zonal-mean tropospheric circulation variability during this period is best viewed as interannual variability in the transition between the springtime and summertime regimes induced by variability in the vortex breakdown. In particular, the apparent long-term poleward jet shift during the early-summer season can be more simply understood as a delay in the equatorward shift associated with this regime transition. The implications of such a perspective for various open questions are discussed.

scholarly journals Progress in semi-empirical modelling of main-sequence stellar chromospheres

1996 ◽  
Vol 176 ◽  
pp. 547-555
Author(s):  
E.R. Houdebine
Keyword(s):  
Main Sequence ◽  
Radiation Transfer ◽  
Research Programme ◽  
Significant Progress ◽  
Wave Dissipation ◽  
Empirical Modelling ◽  
Spectral Signatures ◽  
Outer Atmosphere ◽  
Semi Empirical

We present the results of a long term research programme on the outer atmospheres of main-sequence dwarfs. Combining NLTE-radiation transfer calculations with high resolution spectroscopic observations have led to significant progress in understanding chromospheric physical properties and spectral signatures. We emphasize that in order to unravel the extremely complex physics of the outer atmosphere and its energy source, magnetic field and acoustic wave dissipation, one must isolate the influence of all stellar parameters.

scholarly journals Long-term Prescription? Digital Surveillance is Here to Stay

2021 ◽  
Vol 56 (4) ◽  
pp. 105-118
Author(s):  
Žilvinas Švedkauskas ◽  
Ahmed Maati
Keyword(s):  
Public Health ◽  
The State ◽  
Digital Data ◽  
Stanford University ◽  
Digital Surveillance ◽  
Complex Relationships ◽  
The Impact ◽  
Everyday Communication

An emerging literature has shown concerns about the impact of the pandemic on the proliferation of digital surveillance. Contributing to these debates, in this paper we demonstrate how the pandemic facilitates digital surveillance in three ways: (1) By shifting everyday communication to digital means it contributes to the generation of extensive amounts of data susceptible to surveillance. (2) It motivates the development of new digital surveillance tools. (3) The pandemic serves as a perfect justification for governments to prolong digital surveillance. We provide empirical anecdotes for these three effects by examining reports by the Global Digital Policy Incubator at Stanford University. Building on our argument, we conclude that we might be on the verge of a dangerous normalization of digital surveillance. Thus, we call on scholars to consider the full effects of public health crises on politics and suggest scrutinizing sources of digital data and the complex relationships between the state, corporate actors, and the sub-contractors behind digital surveillance.

scholarly journals Zoom fatigue wśród nastolatków

2021 ◽  
pp. 167-178
Author(s):  
Ewa Pudłowska
Keyword(s):  
Distance Learning ◽  
School Psychologist ◽  
Social Phenomenon ◽  
Stanford University ◽  
Social Changes ◽  
Negative Effects ◽  
Long Distance ◽  
School Activities ◽  
The Impact

The aim of this study is to analyze a new social phenomenon that appeared during the SARS-CoV-2 pandemic, i.e. zoom fatigue. Zoom fatigue is the result of fatigue from long-term conferences, which can also be related to long-term school lessons during distance learning. The main considerations will focus on teenagers, namely on the impact of zoom fatigue on teenagers in Polish schools and on observation of students from technical secondary schools by a school psychologist. This paper, based on the results of research conducted at Stanford University and by Social Changes, is also an attempt to answer the questions: what risks may arise from the phenomenon of zoom fatigue and the threat posed by distance learning for teenagers in the era of Covid-19. It will also attempt to answer the question of how to help students cope with the fatigue of long distance school activities and find ways to help teens deal with isolation and the negative effects of zoom fatigue and find ways to overcome zoom fatigue.

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