The Angular Diameter and Fundamental Parameters of Sirius A

AbstractThe Sydney University Stellar Interferometer (SUSI) has been used to make a new determination of the angular diameter of Sirius A. The observations were made at an effective wavelength of 694.1 nm and the new value for the limb-darkened angular diameter is 6.048 ± 0.040 mas (± 0.66%). This new result is compared with previous measurements and is found to be in excellent agreement with a conventionally calibrated measurement made with the European Southern Observatory's Very Large Telescope Interferometer (VLTI) at 2.176 μm (but not with a second globally calibrated VLTI measurement). A weighted mean of the SUSI and first VLTI results gives the limb-darkened angular diameter of Sirius A as 6.041 ± 0.017 mas (± 0.28%). Combination with the Hipparcos parallax gives the radius equal to 1.713 ± 0.009 R⊙. The bolometric flux has been determined from published photometry and spectrophotometry and, combined with the angular diameter, yields the emergent flux at the stellar surface equal to (5.32 ± 0.14) × 108 W m−2 and the effective temperature equal to 9845 ± 64 K. The luminosity is 24.7 ± 0.7 L⊙.

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First results from MFOSC-P: low-resolution optical spectroscopy of a sample of M dwarfs within 100 parsecs

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa163 ◽

2020 ◽

Vol 492 (4) ◽

pp. 5844-5852 ◽

Cited By ~ 1

Author(s):

A S Rajpurohit ◽

Vipin Kumar ◽

Mudit K Srivastava ◽

F Allard ◽

D Homeier ◽

...

Keyword(s):

Effective Temperature ◽

Spectral Synthesis ◽

Surface Gravity ◽

Low Resolution ◽

M Dwarfs ◽

Physical Research Laboratory ◽

Fundamental Parameters ◽

Faint Object ◽

First Results

ABSTRACT Mt Abu Faint Object Spectrograph and Camera (MFOSC-P) is an in-house-developed instrument for the Physical Research Laboratory (PRL) 1.2 m telescope at Mt Abu, India, commissioned in 2019 February. Here we present the first science results derived from the low-resolution spectroscopy programme of a sample of M dwarfs carried out during the commissioning run of MFOSC-P between 2019 February and June. M dwarfs carry great significance for exoplanet searches in the habitable zone and are among the promising candidates for the observatory’s several ongoing observational campaigns. Determination of their accurate atmospheric properties and fundamental parameters is essential to constrain both their atmospheric and evolutionary models. In this study, we provide a low-resolution (R ∼ 500) spectroscopic catalogue of 80 bright M dwarfs (J < 10) and classify them using their optical spectra. We have also performed spectral synthesis and χ2 minimization techniques to determine their fundamental parameters regarding effective temperature and surface gravity by comparing the observed spectra with the most recent BT-Settl synthetic spectra. The spectral type of M dwarfs in our sample ranges from M0 to M5. The derived effective temperature and surface gravity range from 4000–3000 K and 4.5–5.5 dex, respectively. In most of the cases, the derived spectral types are in good agreement with previously assigned photometric classifications.

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The Determination of Angular Diameters of Stars

Highlights of Astronomy ◽

10.1017/s1539299600000812 ◽

1971 ◽

Vol 2 ◽

pp. 713-720

Author(s):

John Davis

Keyword(s):

Effective Temperature ◽

Binary Systems ◽

Spectral Energy Distribution ◽

Stellar Atmospheres ◽

Angular Diameter ◽

Effective Temperatures ◽

The Absolute ◽

Limb Darkening ◽

Angular Diameters

Ideally the determination of the angular diameter of a star would include the measurement of the distribution of intensity across the stellar disc. However, direct methods of measuring angular diameters have so far lacked adequate ‘signal to noise’ ratio to measure the intensity distribution and it has been the custom, in the first instance, to express the measured angular diameter in terms of the angular diameter of the equivalent uniform disc (θUD). Subsequent use of the angular diameter involves the assumption of a limb-darkening law and the application of an appropriate correction to θUD to find the ‘true’ angular diameter (θLD) of the star (e.g. Hanbury Brown et al., 1967). In this article we will discuss the determination of θUD for single stars and we will not refer further to the more difficult problems of determining intensity distributions involving limb-darkening and rotational effects and of measuring the angular parameters of binary systems.By itself the angular diameter of a star has no intrinsic value but when it is combined with other observational data it enables basic physical properties of the star to be determined. It is then possible to make a direct comparison of the observed properties of the star with the predictions of theoretical models of stellar atmospheres and interiors. For example, the combination of an angular diameter with the absolute monochromatic flux received from the star (ƒν), corrected for interstellar extinction, yields the absolute emergent flux at the stellar surface (). If the spectral energy distribution for the star is known it can be calibrated absolutely by and hence the effective temperature (Te) of the star can be found (this is equivalent to knowing the bolometric correction for the star and using it with the angular diameter to find Te). In addition to leading to the determination of Te, the absolute surface flux distribution may be compared directly with the predicted flux distributions for theoretical model stellar atmospheres (e.g. Davis and Webb, 1970). For O and early B. type stars a large fraction of the emergent flux is in the far ultra-violet and the effective temperatures cannot be determined from the, at present, incomplete empirical flux curves. In these cases it is possible to obtain an estimate of the effective temperatures by using the values of to calibrate a grid of model atmospheres which have Te as a parameter. In this way, by measuring the angular diameters of stars of different spectral types, it is possible to establish an effective temperature scale.

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Photometric and Spectrophotometric Data Required for the SUSI Programme

International Astronomical Union Colloquium ◽

10.1017/s0252921100007466 ◽

1993 ◽

Vol 136 ◽

pp. 120-124

Author(s):

R.R. Shobbrook

Keyword(s):

Light Curve ◽

Binary Stars ◽

Current Phase ◽

Orbital Inclination ◽

Fundamental Parameters ◽

Pulsating Stars ◽

Stellar Interferometer ◽

Spectrophotometric Data ◽

Angular Diameters

The Sydney University Stellar Interferometer, SUSI, a modern version of a Michelson stellar interferometer, will be capable of measuring the angular diameters of stars down to V ≈ 8.0, for all spectral types. The resolution of the 640 m baseline — <0.1 milliarcsec at optical wavelengths — includes reasonable sample sizes of all spectral types and luminosity classes to this magnitude limit.The angular diameter data require complementary photometric, spectrophotometric and also spectroscopic data for the determination of fundamental parameters of single and multiple stars. This paper discusses the accuracy required of these data for some of the main problems to be tackled by SUSI. A selection of the programmes planned for this unique instrument is listed below, where the need for complementary data is also indicated.• The measurement of the changes of angular diameters of Cepheids and other pulsating stars such as Mira variables. Comparison with the linear changes determined from radial velocity curves will enable their distances and luminosities to be determined by an essentially geometric method.• The measurement of the angular sizes of the orbits and of one or both components of spectroscopic binary stars. This effectively makes them ‘visual’ binaries so that the orbital inclination, i, may be determined. When these data are combined with the velocity curve solutions which include (mass)sin3i and (semi – majoraxis)sin i, we may determine masses and linear radii of one or both components and also the distances to the systems. Also, the light curve of an eclipsing binary provides information on the ellipticities and radii of the components and on the eccentricity of the orbit — information which may be used to aid the analysis of the SUSI data. In addition, the determination of the light curve (some bright systems have not been observed for up to one or two decades) is the quickest method of finding the current phase of its orbit.• The establishment of the total-flux-based temperature scale of all spectral types and luminosity classes from O to M. This requires accurate photometry and spectrophotometry over as wide a wavelength range as possible; it therefore also requires observations from space observatories, as was also necessary for the analysis using the Narrabri intensity interferometer data (Code et al., 1976).• The measurement of diameters of stars with shells or extended atmospheres, such as Be and Wolf Rayet stars, at different wavelengths — in particular, in the emission lines.

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The Apparent Size of Rapidly Rotating Stars

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000010705 ◽

1968 ◽

Vol 1 (3) ◽

pp. 85-86

Author(s):

I.D. Johnston ◽

N.C. Wareing

Keyword(s):

Effective Temperature ◽

Apparent Size ◽

Angular Diameter ◽

Rotating Stars ◽

Intensity Correlation ◽

Stellar Interferometer ◽

Axis Of Rotation ◽

The Earth ◽

Rapidly Rotating Stars ◽

Uniform Disk

The stellar interferometer at Narrabri Observatory measures the angular diameter of hot, bright stars. It does this by matching the observed intensity correlation from two detectors, as a function of separation between the detectors, with that from a uniform disk (see Hanbury Brown et al.). When this measurement is taken in conjunction with experimental determinations of the monochromatic flux received at the Earth, the effective temperature of the star, Te, can be determined. However, if the star being observed is rotating rapidly, comparison with a uniform disk is of doubtful validity. Owing to its rotation the shape of the star will be distorted, and its effective temperature will vary over the surface (being apparently hotter at the poles). Therefore the measured angular diameter of the star will be different, and will change with the orientation of the star’s axis of rotation in the sky.

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Uses of Very Large Telescopes for Galaxy Research

International Astronomical Union Colloquium ◽

10.1017/s0252921100108802 ◽

1984 ◽

Vol 79 ◽

pp. 703-711 ◽

Cited By ~ 3

Author(s):

M.-H. Ulrich

Keyword(s):

Elliptical Galaxies ◽

Point Sources ◽

High Spectral Resolution ◽

Large Field ◽

Large Telescope ◽

Quasar Spectra ◽

Very Large Telescope ◽

Large Telescopes ◽

Field Imaging

SummaryMany areas of extragalactic research will greatly benefit from observations with a very large telescope. We concentrate, here, on four of them as illustrative examples:First we briefly discuss the study of the absorption lines in quasar spectra.In the second section we suggest the possibility of doing serendipity large field imaging during high spectral resolution exposures on point sources.In sections 3 and 4 we discuss two topics which have long been recognized as important drivers for the construction of very large telescopes, the determination of the nature of the missing mass, and the study of elliptical galaxies.

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Gravity darkening in stars with surface differential rotation

Astronomy and Astrophysics ◽

10.1051/0004-6361/201730818 ◽

2017 ◽

Vol 606 ◽

pp. A32 ◽

Cited By ~ 7

Author(s):

J. Zorec ◽

M. Rieutord ◽

F. Espinosa Lara ◽

Y. Frémat ◽

A. Domiciano de Souza ◽

...

Keyword(s):

Differential Rotation ◽

Effective Temperature ◽

Rotational Velocity ◽

Viewing Angle ◽

Rotating Stars ◽

Stellar Rotation ◽

Fundamental Parameters ◽

Effective Gravity ◽

Unique Interpretation

Context. The interpretation of stellar apparent fundamental parameters (viewing-angle dependent) requires that they be treated consistently with the characteristics of their surface rotation law. Aims. We aim to develop a model to determine the distribution of the effective temperature and gravity, which explicitly depend on the surface differential rotation law and on the concomitant stellar external geometry. Methods. The basic assumptions in this model are: a) the external stellar layers are in radiative equilibrium; b) the emergent bolometric flux is anti-parallel with the effective gravity; c) the angular velocity in the surface obeys relations like Ω(θ) = Ωo [ 1 + αΥ(θ,k) ] where Υ(θ,k) = coskθ or sinkθ, and where (α,k) are free parameters. Results. The effective temperature varies with co-latitude θ, with amplitudes that depend on the differential-rotation law through the surface effective gravity and the gravity-darkening function (GDF). Although the derived expressions can be treated numerically, for some low integer values of k, analytical forms of the integral of characteristic curves, on which the determination of the GDF relies, are obtained. The effects of the quantities (η,α,k) (η = ratio between centrifugal and gravitational accelerations at the equator) on the determination of the Vsini parameter and on the gravity-darkening exponent are studied. Depending on the values of (η,α,k) the velocity V in the derived Vsini may strongly deviate from the equatorial rotational velocity. It is shown that the von Zeipel’s-like gravity-darkening exponent β1 depends on all parameters (η,α,k) and that its value also depends on the viewing-angle i. Hence, there no unique interpretation of this exponent determined empirically in terms of (i,α). Conclusions. We stress that the data on rotating stars should be analyzed by taking into account the rotational effects through the GDF, by assuming k = 2 as a first approximation. Instead of the classic pair (η,β1), it would be more useful to determine the quantities (η,α,i) to characterize stellar rotation.

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Constraints on HD 113337 fundamental parameters and planetary system

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935494 ◽

2019 ◽

Vol 627 ◽

pp. A44

Author(s):

S. Borgniet ◽

K. Perraut ◽

K. Su ◽

M. Bonnefoy ◽

P. Delorme ◽

...

Keyword(s):

Effective Temperature ◽

Main Sequence ◽

Giant Planet ◽

Parameter Analysis ◽

Angular Diameter ◽

Fundamental Parameter ◽

Infrared Excess ◽

Fundamental Parameters ◽

Complementary Techniques ◽

Interesting System

Context. HD 113337 is a main-sequence F6V field star more massive than the Sun. This star hosts one confirmed giant planet and possibly a second candidate, detected by radial velocities (RVs). The star also hosts a cold debris disc detected through the presence of an infrared excess, making it an interesting system to explore. Aims. We aim to bring new constraints on the star’s fundamental parameters, debris disc properties, and planetary companion(s) by combining complementary techniques. Methods. We used the VEGA interferometer on the CHARA array to measure the angular diameter of HD 113337. We derived its linear radius using the parallax from the Gaia Second Data Release. We computed the bolometric flux to derive its effective temperature and luminosity, and we estimated its mass and age using evolutionary tracks. Then, we used Herschel images to partially resolve the outer debris disc and estimate its extension and inclination. Next, we acquired high-contrast images of HD 113337 with the LBTI to probe the ~10–80 au separation range. Finally, we combined the deduced contrast maps with previous RVs of the star using the MESS2 software to bring upper mass limits on possible companions at all separations up to 80 au. We took advantage of the constraints on the age and inclination brought by fundamental parameter analysis and disc imaging, respectively, for this analysis. Results. We derive a limb-darkened angular diameter of 0.386 ± 0.009 mas that converts into a linear radius of 1.50 ± 0.04 R⊙ for HD 113337. The fundamental parameter analysis leads to an effective temperature of 6774 ± 125 K and to two possible age solutions: one young within 14–21 Myr and one old within 0.8–1.7 Gyr. We partially resolve the known outer debris disc and model its emission. Our best solution corresponds to a radius of 85 ± 20 au, an extension of 30 ± 20 au, and an inclination within 10–30° for the outer disc. The combination of imaging contrast limits, published RV, and age and inclination solutions allows us to derive a first possible estimation of the true masses of the planetary companions: ~7−2+4 MJup for HD 113337 b (confirmed companion) and ~16−3+10 MJup for HD 113337 c (candidate companion). We also constrain possible additional companions at larger separations.

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Sorption of Se (IV) from aqueous solutions with subsequent determination by X-ray fluorescence analysis

Industrial laboratory Diagnostics of materials ◽

10.26896/1028-6861-2020-86-10-5-9 ◽

2020 ◽

Vol 86 (10) ◽

pp. 5-9

Author(s):

D. G. Filatova ◽

A. A. Arkhipenko ◽

M. A. Statkus ◽

V. V. Es’kina ◽

V. B. Baranovskaya ◽

...

Keyword(s):

Inductively Coupled Plasma ◽

Fluorescence Analysis ◽

Standard Samples ◽

Phase Contact Time ◽

Sorbent Phase ◽

X Ray ◽

Fundamental Parameters ◽

Inductively Coupled ◽

Subsequent Determination

An approach to sorptive separation of Se (IV) from solutions on a novel S,N-containing sorbent with subsequent determination of the analyte in the sorbent phase by micro-x-ray fluorescence method is presented. The sorbent copolymethylenesulfide-N-alkyl-methylenamine (CMA) was synthesized using «snake in the cage» procedure and proven to be stable in acid solutions. Conditions for quantitative extraction of Se (IV) were determined: sorption in 5 M HCl or 0.05 M HNO3 solutions when heated to 60°C, phase contact time being 1 h. The residual selenium content in the solution was determined by inductively coupled plasma mass spectrometry (ICP-MS) using 82Se isotope. The absence of selenium losses is proved and the mechanism of sorption interaction under specified conditions is proposed. The method of micro-x-ray fluorescence analysis (micro-RFA) with mapping revealed a uniform distribution of selenium on the sorbent surface. The possibility of determining selenium in the sorbent phase by micro-RFA is shown. When comparing the obtained results with the results of calculations by the method of fundamental parameters, it is shown the necessity of using standard samples of sorbates to obtain correct results of RFA determination of selenium in the sorbent phase.

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