Stellar Surface Magnetoconvection as a Source of Astrophysical Noise. III. Sun-as-a-Star Simulations and Optimal Noise Diagnostics

Abstract Space astrometry now permits accurate determinations of stellar radial motion, without using spectroscopy. Although the feasibility of deducing astrometric radial velocities from geometric projection effects was realized already by Schlesinger (1917), only with Hipparcos has it become practical. Such a program has now been carried out for the moving clusters of Ursa Major, Hyades, and Coma Berenices. Realized inaccuracies reach about 300 m/s (Dravins et al. 1997). Discrepancies between astrometric and spectroscopic radial velocities reveal effects (other than stellar motion) that affect wavelength positions of spectral lines. Such are caused by stellar surface convection, and by gravitational redshifts. A parallel program (Gullberg & Dravins 1997) is analyzing high-precision spectroscopic radial velocities for different spectral lines in these stars, using the ELODIE radial-velocity instrument atHaute-Provence.

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Can complex T Tauri star light curves be modelled with star-spots?

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3347 ◽

2020 ◽

Vol 500 (1) ◽

pp. 1366-1379

Author(s):

C Koen

Keyword(s):

Ridge Regression ◽

Young Stars ◽

Light Curves ◽

Stellar Surface ◽

Tauri Star ◽

T Tauri ◽

Almost All

ABSTRACT ‘Transiting Exoplanet Survey Satellite’ photometry of 10 young stars with very complex periodic light curves is considered. Previous findings that these cannot be due to dark surface spots are re-evaluated by allowing arbitrarily shaped areas on the stellar surface to have sub-photospheric fluxes. This is done by approximating flux integrals by sums over surface elements. The unknown ratios of spot to photospheric fluxes are determined by lasso or ridge regression procedures. It is found that almost all light curves can be modelled very accurately in this way. The usual, if rarely stated, caveat applies – star-spot models presented in the paper are not unique.

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Optical transient from an explosion close to the stellar surface

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2590 ◽

2019 ◽

Vol 490 (1) ◽

pp. 312-318 ◽

Cited By ~ 1

Author(s):

Almog Yalinewich ◽

Christopher D Matzner

Keyword(s):

Stellar Surface ◽

Hydrodynamic Evolution ◽

New Generation ◽

Optical Surveys ◽

Optical Transient

ABSTRACT We study the hydrodynamic evolution of an explosion close to the stellar surface, and give predictions for the radiation from such an event. We show that such an event will give rise to a multiwavelength transient. We apply this model to describe a precursor burst to the peculiar supernova iPTF14hls, which occurred in 1954, 60 yr before the supernova. We propose that the new generation of optical surveys might detect similar transients, and that they can be used to identify supernova progenitors well before the explosion.

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Doppler imaging of stellar surface structure

Astronomy and Astrophysics ◽

10.1051/0004-6361:20031538 ◽

2003 ◽

Vol 411 (3) ◽

pp. 595-604 ◽

Cited By ~ 28

Author(s):

K. G. Strassmeier ◽

T. Pichler ◽

M. Weber ◽

T. Granzer

Keyword(s):

Surface Structure ◽

Stellar Surface ◽

Doppler Imaging

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Tuning Pulsation Modes with Stellar Interferometry

International Astronomical Union Colloquium ◽

10.1017/s025292110001592x ◽

2002 ◽

Vol 185 ◽

pp. 170-171

Author(s):

A. Domiciano de Souza ◽

F. Vakili ◽

S. Jankov ◽

E. Janot-Pacheco

Keyword(s):

Brightness Distribution ◽

Stellar Surface ◽

Radial Pulsation ◽

Surface Imaging ◽

Stellar Rotation ◽

Fourier Plane ◽

Stellar Interferometry ◽

High Degree ◽

Multi Mode

AbstractStellar interferometry represents a qualitative jump toward stellar surface imaging. We propose a method that tunes and filters out high degree non-radial pulsation (NRP) modes from the Fourier plane associated to the stellar brightness distribution. The proposed method can be applied to continuum flux, slow stellar rotation and high degree multi mode NRP stars.

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X-Ray Diffraction and Barkhausen Noise Diagnostics of Thick Welds Prepared by Metal Active Gas and Laser Welding

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.827.113 ◽

2016 ◽

Vol 827 ◽

pp. 113-116 ◽

Cited By ~ 1

Author(s):

Kamil Kolařík ◽

Nikolaj Ganev ◽

Karel Trojan ◽

Ondřej Řídký ◽

Lukáš Zuzánek ◽

...

Keyword(s):

Noise Analysis ◽

Real Structure ◽

Barkhausen Noise ◽

X Ray Diffraction ◽

X Ray ◽

Structure Changes ◽

Rs Analysis ◽

Noise Diagnostics ◽

Non Destructive ◽

Power Diode

Non-destructive methods for detection and measurement of residual stresses (RS) have been increasingly used in the last few years. The paper outlines the capability of Barkhausen noise analysis (BNA) for evaluation of real structure changes and RS on cross-section of welds due to welding of ferromagnetic plates compared with X-ray diffraction (XRD). The purpose of this study is to evaluate the RS distribution of specimens joined using by high power diode laser and metal active gas (MAG) welding that can be used for quantitative analysis of macro and micro level RS separately. The principal advantages of BNA over XRD as a tool for RS analysis and real structure characterisation are that it is mobile, faster with more facile carrying out and hence BNA is frequently used for continuous monitoring of RS in industrial processes.

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Stellar Surface Convection, Line Asymmetries, and Wavelength Shifts

International Astronomical Union Colloquium ◽

10.1017/s0252921100048661 ◽

1999 ◽

Vol 170 ◽

pp. 268-277 ◽

Cited By ~ 5

Author(s):

Dainis Dravins

Keyword(s):

Adaptive Optics ◽

Temporal Variability ◽

Stellar Surface ◽

Time Variability ◽

The Sun ◽

Atmospheric Physics ◽

Spatially Resolved ◽

Activity Cycles ◽

To Come ◽

Surface Convection

AbstractWavelength positions of photospheric absorption lines may be affected by surface convection (stellar granulation). Asymmetries and wavelength shifts originate from correlated velocity and brightness patterns: rising (blueshifted) elements are hot (bright), and convective blueshifts result from a larger contribution of such blueshifted photons than of redshifted ones from the sinking and cooler (darker) gas. For the Sun, the effect is around 300 m s−1, expected to increase in F-type stars, and in giants. Magnetic fields affect convection and induce lineshift variations over stellar activity cycles. A sufficient measuring precision reveals also the temporal variability of line wavelengths (due to the evolution of granules on the stellar surface). A major future development to come from adaptive optics and optical interferometry will be the study of wavelength variations across spatially resolved stars, together with their spatially resolved time variability. Thus, precise radial velocities should soon open up new vistas in stellar atmospheric physics.

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Diagnostics of Advanced Power Intensive Power Sources Based on the Acoustic Spectroscopy Method

Herald of the Bauman Moscow State Technical University Series Natural Sciences ◽

10.18698/1812-3368-2021-6-121-127 ◽

2021 ◽

pp. 121-127

Author(s):

E.M. Petrenko ◽

V.A. Semenova

Keyword(s):

High Reliability ◽

Methodological Approach ◽

Spectral Characteristics ◽

Experimental Studies ◽

Mechanical Action ◽

Mean Value ◽

Spectroscopy Method ◽

Power Sources ◽

Acoustic Spectroscopy ◽

Noise Diagnostics

Objective of this article is to develop a method for lithium chemical current sources diagnostics, which would ensure high reliability in assessing their technical state (primarily, the discharge degree) close to potentially achievable introduction of the acoustic spectroscopy method. Today, microcalorimetric studies and methods of impedance and noise spectroscopy make it possible to predict the lithium chemical current sources service life. However, implementation of the microcalorimetric studies result requires a lot of time accompanied by using stationary and large-size equipment, which is practically impossible in the autonomous conditions. Application of the impedance spectroscopy method provides satisfactory results only with high degrees of discharge. In the range of 0--30 %, it is very difficult to determine the discharge degree, since noticeable alteration in the correlate within its deviation from the mean value is missing. In this regard, it is proposed in order to provide diagnostics of the lithium chemical current sources in the region of initial degrees of discharge to introduce the noise diagnostics method. In order to increase reliability of the diagnostic estimates, it is advisable to use acoustic spectroscopy as a physically independent method in diagnosing the state of lithium chemical current sources. Results of the preliminary measurements analysis confirm the prospects of using the acoustic spectroscopy method in assessing the current state of primary lithium chemical current sources. Experimental studies of the lithium chemical current sources response to acoustic (mechanical) action made it possible to determine a set of parameters characterizing the proposed methodological approach. This provided a possibility to search for correlation dependences of the lithium chemical current sources spectral characteristics on the degree of their discharge. This makes it possible to use the method of acoustic spectroscopy in prompt and reliable diagnostics of the primary current sources in the region of low discharge degrees

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