scholarly journals The Effective Temperature Determination

1995 ◽  
Vol 10 ◽  
pp. 395-398
Author(s):  
Roger Cayrel
Keyword(s):  
Effective Temperature ◽  
Stellar Atmosphere ◽  
Angular Diameter ◽  
Stellar Disk ◽  
Basic Method ◽  
Stellar Diameters ◽  
F Stars ◽  
Subgiant Stars ◽  
Limb Darkening ◽  
Current Accuracy

The content of my oral contribution has been reduced here to a guide to the recent litterature on the subject.The effective temperature of a star can be obtained directly by measuring the total flux received on earth from it, and its angular diameter. In principle interferometrie methods could determine both the limb-darkening law of the stellar disk and the angular diameter of the disk. In practice, in order to obtain a decent accuracy on the angular diameter, interferometrie methods have so far borrowed the limb-darkening law from stellar atmosphere theory, in order to concentrate all the observational information on a single parameter. The total number of stellar diameters and effective temperatures obtained by this basic method remains very small (about 30 stars) and concerns exclusively giant or subgiant stars. The reader is invited to look at the following references and those therein (Di Benedetto 1993, Mozurkewich et al. 1991, Alonso et al. 1994). Smalley and Dworetsky (A&A in press) have reinvestigated the old Code et al. (1976) calibration with more recent spatial UV data, for B, A, and F stars, and have found no significant changes. The accuracy of the basic method is at the best of the order of 1.5 %, and there is a deep need for more data, and for doubling the current accuracy. Actually there is a strong effort for developping interferometry both from the ground (ESO VLTI, USNO astrometric interferometer) andfrom space (OSI project, Colavita et al. 1993; GAIA project at ESA). So there is hope for a not to far future.

The Determination of Angular Diameters of Stars

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.

scholarly journals Interferometric Fringe Visibility Null as a Function of Spatial Frequency: A Probe of Stellar Atmospheres

2019 ◽  
Vol 08 (04) ◽  
pp. 1950012
Author(s):  
J. T. Armstrong ◽  
A. M. Jorgensen ◽  
D. Mozurkewich ◽  
H. R. Neilson ◽  
E. K. Baines ◽  
...  
Keyword(s):  
Spatial Frequency ◽  
Angular Size ◽  
Brightness Distribution ◽  
Stellar Atmosphere ◽  
Stellar Atmospheres ◽  
Stellar Disk ◽  
Baseline Length ◽  
Fringe Visibility ◽  
Multiple Wavelengths ◽  
Limb Darkening

We introduce an observational tool based on visibility nulls in optical spectro-interferometry fringe data to probe the structure of stellar atmospheres. In a preliminary demonstration, we use both Navy Precision Optical Interferometer (NPOI) data and stellar atmosphere models to show that this tool can be used, for example, to investigate limb darkening. Using bootstrapping with either multiple linked baselines or multiple wavelengths in optical and infrared spectro-interferometric observations of stars makes it possible to measure the spatial frequency [Formula: see text] at which the real part of the fringe visibility [Formula: see text] vanishes. That spatial frequency is determined by [Formula: see text], where [Formula: see text] is the projected baseline length, and [Formula: see text] is the wavelength at which the null is observed. Since [Formula: see text] changes with the Earth’s rotation, [Formula: see text] also changes. If [Formula: see text] is constant with wavelength, [Formula: see text] varies in direct proportion to [Formula: see text]. Any departure from that proportionality indicates that the brightness distribution across the stellar disk varies with wavelength via variations in limb darkening, in the angular size of the disk, or both. In this paper, we introduce the use of variations of [Formula: see text] with [Formula: see text] as a means of probing the structure of stellar atmospheres. Using the equivalent uniform disk diameter [Formula: see text], given by [Formula: see text], as a convenient and intuitive parameterization of [Formula: see text], we demonstrate this concept by using model atmospheres to calculate the brightness distribution for [Formula: see text] Ophiuchi and to predict [Formula: see text], and then comparing the predictions to coherently averaged data from observations taken with the NPOI.

scholarly journals Project VeSElkA : Preliminary results for CP stars recently observed with ESPaDOnS

2014 ◽  
Vol 9 (S307) ◽  
pp. 381-382
Author(s):  
Viktor Khalack ◽  
Francis LeBlanc
Keyword(s):  
Effective Temperature ◽  
Stellar Atmosphere ◽  
Balmer Line ◽  
Line Profiles ◽  
Chemically Peculiar ◽  
Peculiar Stars ◽  
First Results ◽  
Chemically Peculiar Stars ◽  
The Phoenix ◽  
Temperature Surface

AbstractWe present the first results for the estimation of gravity and effective temperature of poorly studied chemically peculiar stars recently observed with the spectropolarimeter ESPaDOnS at CFHT in the frame of the VeSElkA (Vertical Stratification of Elements Abundance) project. A grid of theoretical stellar atmosphere models with the corresponding fluxes has been calculated using the PHOENIX code. We have used these fluxes to fit Balmer line profiles employing the code FITSB2 that produces estimates of the effective temperature, surface gravity and radial velocity for each star.

scholarly journals Direct Observations of the Heterogeneity of Supergiant Disks

1977 ◽  
Vol 4 (2) ◽  
pp. 405-405
Author(s):  
J. W. Harvey ◽  
C. R. Lynds ◽  
S. P. Worden
Keyword(s):  
Signal To Noise Ratio ◽  
Atmospheric Dispersion ◽  
Stellar Atmosphere ◽  
High Magnification ◽  
Specific Technique ◽  
Signal To Noise ◽  
Speckle Imaging ◽  
Direct Observations ◽  
Good Signal ◽  
Limb Darkening

Resolved images of the disks of the largest stars observed with the largest telescopes can be constructed using the class of techniques called speckle imaging. The observations must be made with narrow passbands (~ 10 nm), short exposures (~ 20 ms) compensation for atmospheric dispersion, high magnification and good signal-to-noise ratio. One specific technique applied to a Ori (Lynds et al., 1976) shows slight but apparently real differences in the images of the disk corresponding to low and high opacity in the stellar atmosphere which we interpret as due to temperature differences. There are also significant differences in the star’s diameter and/or limb darkening at the two different opacity wavelengths.

The Absolute Flux Distribution of Sirius

1970 ◽  
Vol 1 (8) ◽  
pp. 378-379 ◽  
Author(s):  
J. Davis ◽  
R. J. Webb
Keyword(s):  
Effective Temperature ◽  
Flux Distribution ◽  
Model Atmosphere ◽  
Angular Diameter ◽  
Sufficient Data ◽  
Absolute Flux ◽  
Stringent Test ◽  
Net Flux ◽  
The Absolute

The angular diameter of a star, combined with observed stellar fluxes in absolute units, allows the absolute fluxes emitted at the surface of the star to be calculated and thus provides a stringent test of model atmosphere predictions. Furthermore, if the flux distribution is observed at all wavelengths contributing significantly to the net flux, an empirical effective temperature can be found. Sufficient data are now available for Sirius (αCMa) to be studied in this way.

scholarly journals Fundamental effective temperature measurements for eclipsing binary stars – I. Development of the method and application to AI Phoenicis

2020 ◽  
Vol 497 (3) ◽  
pp. 2899-2909
Author(s):  
N J Miller ◽  
P F L Maxted ◽  
B Smalley
Keyword(s):  
Effective Temperature ◽  
Binary Stars ◽  
Zero Point ◽  
Stellar Atmosphere ◽  
Eclipsing Binaries ◽  
Dwarf Stars ◽  
Eclipsing Binary ◽  
Eclipsing Binary Stars ◽  
Effective Temperatures ◽  
Photometric Measurements

ABSTRACT Stars with accurate and precise effective temperature (Teff) measurements are needed to test stellar atmosphere models and calibrate empirical methods to determine Teff. There are few standard stars currently available to calibrate temperature indicators for dwarf stars. Gaia parallaxes now make it possible, in principle, to measure Teff for many dwarf stars in eclipsing binaries. We aim to develop a method that uses high-precision measurements of detached eclipsing binary stars, Gaia parallaxes, and multiwavelength photometry to obtain accurate and precise fundamental effective temperatures that can be used to establish a set of benchmark stars. We select the well-studied binary AI Phoenicis to test our method, since it has very precise absolute parameters and extensive archival photometry. The method uses the stellar radii and parallax for stars in eclipsing binaries. We use a Bayesian approach to obtain the integrated bolometric fluxes for the two stars from observed magnitudes, colours, and flux ratios. The fundamental effective temperature of two stars in AI Phoenicis are 6199 ± 22 K for the F7 V component and 5094 ± 16 K for the K0 IV component. The zero-point error in the flux scale leads to a systematic error of only 0.2 per cent (≈ 11 K) in Teff. We find that these results are robust against the details of the analysis, such as the choice of model spectra. Our method can be applied to eclipsing binary stars with radius, parallax, and photometric measurements across a range of wavelengths. Stars with fundamental effective temperatures determined with this method can be used as benchmarks in future surveys.

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