Determination Of Effective Temperature Research Articles

Determination of effective temperatures for an extended sample of dwarfs and subdwarfs (F0-K5)

We have applied the InfraRed Flux Method (IRFM) to a sample of 475 dwarfs and subdwarfs in order to derive their effective temperatures with a mean accuracy of about 1.5%. We have used the new homogeneous grid of theoretical model atmosphere flux distributions developed by Kurucz (1991, 1993) for the application of the IRFM. The atmospheric parameters of the stars cover, roughly, the ranges: 3500 K 8000 K; -3.5 ≤ [Fe/H] ; 3.5 ≤ log(g) . The monocromatic infrared fluxes at the continuum, and the bolometric fluxes are derived using recent results, which satisfy the accuracy requeriments of the work. Photometric calibrations have been revised and applied to estimate metallicities, although direct spectroscopic determinations were preferred when available. The adopted infrared absolute flux calibration, based on direct optical measurements of angular stellar diameters, sets the effective temperatures determined using the IRFM on the same scale than those obtained by direct methods. We derive three temperatures, TJ, TH and TK, for each star using the monochromatic fluxes at different infrared wavelengths in the photometric bands J, H, and K. They show good consistency over 4000 K, and no trend with wavelength may be appreciated. We provide a detailed description of the steps followed for the application of the IRFM, as well as the sources of the errors associated to the different inputs of the method, and their transmission into the final temperatures. We also provide comparison with previous works.

Medium-Resolution Near-Infrared (2.15-2.35 micron) Spectroscopy of Late-Type Main-Sequence Stars

We present an atlas of moderate resolution (λ/Δλ∼1380) 2.15-2.35 μm spectra of 33 luminosity class V stars of spectral type F3 to M6 in the MK classification system. We find that the equivalent widths of several spectral features vary significantly with temperature and typically allow effective temperature determination accurate to approximately ±350 K.

Characterization and magnetic behavior of cobalt(II) and gadolinium(III) polyacrylates

AbstractThe characterization and magnetic behavior of Co(II) and Gd(III) polyacrylates prepared by organic gelation synthesis have been studied. Gd(III)‐polyacrylate shows a higher thermal stability due to stronger ionic interactions. IR spectra of both compounds reveal that carboxylate groups and water molecules exist in the coordination sphere with various forms of complexation. The samples are x‐ray amorphous and have complex structures with the randomly distributing metal atoms along the PAA chain. The a.c. susceptibility measurements between 4.2 K and 250 K indicated a low temperature magnetic ordering. Annealing the samples at 160°C for 48 h result in the appearance of a spin‐glass behavior in the in‐phase and out‐of‐phase susceptibility curves. The presence of different sizes and shapes of clusters, however, precludes the determination of effective magnetic moments and Curie temperatures. © 1995 John Wiley & Sons, Inc.

First 2.2 micrometer results from the IOTA interferometer

We present the first infrared fringe visibility measurements made with the Infrared Optical Telescope Array on Mt. Hopkins. Effective temperatures are derived for RX Boo, RS Cnc, and Beta Peg. RX Boo is the coolest small-amplitude variable giant star to have an effective temperature determination. We compare the size of its photosphere at infrared wavelengths with the sizes of its SiO and H20 radio emission regions. We also discuss initial performance parameters for the interferometer.

Technique for obtaining visibility amplitudes from atmospherically disturbed interferograms

We describe the general data-reduction techniques that we developed to deal with stellar interferograms. The techniques that we describe here were used to obtain the fundamental visibility data from raw Earth-scanned interferograms obtained with the infrared Michelson array stellar interferometer. The reduced visibility data have resulted in new direct angular diameter measurements and effective temperature determinations for α Her, α Ori, and Mira. These astrophysical results were previously published. We point out that the data-reduction techniques described here are completely general in the sense that they can be used to reduce the data from any stellar interferometer that records the temporal data stream as the fringe packet is swept by the detectors.

Determination of the effective temperatures OF B, A, and F stars of luminosity classes III–V from the slope of the spectrum in the Balmer continuum

A new method is proposed for the determination of effective temperatures, which is based on the linear relationship between the slope of the spectrum in the Balmer continuum and the effective temperatures for B, A, and F stars of luminosity classes III–V. Comparison of the effective temperatures found by this method and those found by other authors shows no systematic differences in the stellar temperatures.

The effective temperatures of Am stars from the infrared flux method

The Blackwell & Shallis infrared flux method (IRFM) is applied to the determination of effective temperatures of metallic-line (Am) stars. Since many Am stars are metal-rich spectroscopic binaries, the effects of metal abundance and binary companions on the IRFM are discussed. A modification to the IRFM is presented which allows explicitly for the effects of a companion star. This new method is applied to the determination of T eff for the classical Am star 63 Tau. After making due allowance for the effects of the companion, the IRFM gives a T eff in good agreement with that obtained using other techniques

Analytic approximations to the 2-60 microns infrared continua for standard calibration stars - With application to the calibration of spectroscopy and photometry, and the determination of effective temperature and angular size from IR measurements

view Abstract Citations (74) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Analytical Approximations to the 2-60micron Infrared Continua for Standard Calibration Stars: With Applications to the Calibration of Spectroscopy and Photometry, and the Determination of Effective Temperature and Angular Size From IR Measurements Engelke, C. W. Abstract Convenient two-parameter analytic expressions approximating the long-wavelength (2-60 μm) infrared continua expected from over a dozen stellar calibration standards are derived. These analytic spectral functions are based on the implicit scaling of a semiempirical solar atmospheric temperature profile to differing effective temperatures, a procedure believed to be theoretically valid for stars with effective temperature lower than 6000 K. The generalized result is written in the form of a Planck function with a brightness temperature that is a function of both observing wavelength and effective temperature. This function is then fit to the best empirical flux data available on the individual standard stars. The resulting spectral curves are nearly as simple to use as straight blackbody approximations, but are consistent with actual infrared measurements and stellar theory. Though intended primarily for calibration applications where continuous spectral distributions must be estimated, the process of fitting to empirical data also produces estimates of effective temperature and angular diameter for cool stars which correlate very well with results obtained by other means (to within a few percent). This suggests that such fitting of the theoretical curve to infrared data could also be useful as a technique for studying the properties of these stars themselves (similar to the presently used infrared flux method of Blackwell et al. 1990). The estimated probable error in absolute flux values generated using these fits is about ±3% below 10 μm, growing to ±5% in the vicinity of 25 μm and 6% at 60 μm. On average, monochromatic stellar fluxes obtained using the fits are the same as those obtained using the standard IRAS photometry and calibration except for a +1% bias (at 12, 25 and 60 μm) (Beichmann et al. 1988). Average short-wavelength monochromatic fluxes differ from the calibrations of Campins et al. (1985) by about - 1% at 2.22 μm, and + 1% at 3.54 μm. Relative flux ratios computed using the continua approximations for a variety of stars agree with relative photometry on those stars to within the given measurement accuracies (±1% to ±2%) indicating that the relative errors in the predictions themselves are probably 1% or better. Only for the star alpha Boo does the predicted flux relative to other stars show evidence of departing significantly from the actual measured value; an apparent 3%-4% deep depression near 20 μm is indicated relative to the computed continuum. Recalibration of 2-5.5 μm spectroscopy from Strecker et al. 1979, is demonstrated, showing that one can extract information on molecular absorption bands observed in giant stars by dividing out the underlying continua. Using the spectral fitting functions, a smoothed system of expected photometric magnitudes is generated for hypothetical narrow passbands centered at 2.2, 3.5, 4.8, 11, 22, and 60 μm. This facilitates rapid calibration of results reported in magnitudes in standard K, L, M, N, and Q bands. In such applications substitution of this fit-derived flux estimate at the effective wavelength of each band for the individual empirical estimates presently available should provide a way of getting the best calibration of photometry in any one band based on a combination of the available measurements in all bands. This is clearly advantageous even when continua are not needed explicitly. Publication: The Astronomical Journal Pub Date: September 1992 DOI: 10.1086/116314 Bibcode: 1992AJ....104.1248E Keywords: Astronomical Photometry; Calibrating; Infrared Astronomy; Reference Stars; Stellar Spectrophotometry; Stellar Temperature; Atmospheric Temperature; Brightness Temperature; Instrument Compensation; Solar Atmosphere; Temperature Profiles; Astronomy; INFRARED: STARS; TECHNIQUES: SPECTROSCOPIC full text sources ADS | data products SIMBAD (20)

Preparation, structure, dynamics, and energetics of amorphous silicon: A molecular-dynamics study.

The preparation of amorphous silicon by molecular-dynamics simulations employing the Stillinger-Weber Si potential, via direct slow cooling from the melt, is described. It is shown that previous failures to obtain amorphous Si using these interaction potentials are of kinetic origin, i.e., related to the quench rate employed. The amorphous silicon sample which we prepared exhibits structural and dynamical properties in good agreement with available experimental data for the static structure factor and phonon density of states. Detailed analyses of the structure, including distributions of bond and dihedral angles and ring statistics, and energetics, including the determination of effective temperatures for n-fold-coordinated atoms (n=3--5) and estimates of the formation energy of coordination defects (i.e., n\ensuremath{\ne}4) are presented. The lack of medium-range order, measured via correlation between dihedral angles associated with adjacent bonds, is discussed.

Theoretical colours and isochrones for some Hubble Space Telescope colour systems

We present a grid of synthetic surface brightness magnitudes for 21 of the Hubble Space Telescope Wide Field Camera (WFC) pass-bands. The magnitudes are calculated from a new set of synthetic spectra for effective temperatures in the range 4000 to 7250 K, logarithmic surface gravities typical of dwarfs and sub-giants, and for metallicities from solar to one thousandth of the solar metallicity. We also present the absolute magnitudes in these 21 pass-bands for a set of globular cluster isochrones with different helium abundances, metallicities, oxygen abundances and ages. The isochrones were taken from VandenBerg & Bell (1985), Bell & VandenBerg (1987), Hesser et al. (1987) and McClure et al. (1987), who originally published them for the Cousins VRI, Johnson UBV, Strömgren and Thuan–Gunn photometric systems. We have investigated the effects of two different laws of interstellar reddening on the colours and magnitudes. We discuss different sets of broad and intermediate bandwidth WFC colours and their usefulness and efficiency for determining ages and metallicities for globular clusters. One set of filters may be used to form a four colour system, like the Strömgren uvby system, which promises to be more sensitive than the uvby system for determination of effective temperatures and luminosities, and about as sensitive for finding stellar metallicities. We present transformations from the 21 WFC pass-bands to Johnson UBV, Cousins VRI, Strömgren uvby and Thuan–Gunn uvgr systems, and discuss the WFC calibration observations of Harris et al. (1988) who used a ground based observational system simulating observations with the WFC. Finally, in an appendix, the synthetic spectra are tested against photometry and spectral scans for a number of well known F and G dwarfs. The blue and ultraviolet fluxes of the model spectra are seen to be too great compared to the observations. These differences are very likely to be caused by a lack of sufficient atomic and molecular data for line blanketing calculations in these spectra regions, a problem under further study.

Determination of effective temperatures of the accretion disks in symbiotic stars

The conditions of the excitation of ultraviolet emission lines in symbiotic stars-triple systems with white dwarf and nebular clouds are examined. A new method is suggested for the determination of effective temperatureT* of the accretion disk around of white dwarf, which is based on the balance between the summary intensitiesEe=ΣEi of ultraviolet emission lines, escaped by nebular cloud, and a definite part of the energy of black-body radiation of accretion disk in the region shorter from the some wavelengthλ0. This condition brings us to the formula (9) which is used for the determination of the temperatureT* and radiusrn of nebular cloud around the symbiotic system. It is shown that practically in all casesλ0=180 A=const. The results of the application of this method in relation to the five symbiotic triple-star systems are presented in Tables III and IV.

Grids for the determination of effective temperature and surface gravity of B, A and F stars using uvby β photometry

Comparaison des couleurs synthetiques et des indices de photometrie uvbyβ calcules pour des atmospheres stellaires modeles avec les couleurs et indices observes pour des etoiles B, A et F dont on connait T eff et log g

Measuring Stars with High Angular Resolution: Current Status and Future Prospects

The current state of knowledge of angular diameters of stars is reviewed and, based on this review and the requirements for the determination of surface fluxes, effective temperatures, radii and masses, targets of sensitivity, angular resolution and accuracy for future programs of stellar angular diameter measurements are established. Long baseline interferometry is the only technique with the potential to meet all the targets. The necessary improvements in sensitivity, angular resolution and accuracy are promised by the approach adopted in the modern Michelson stellar interferometer under development at the University of Sydney and the prototype instrument, which is currently nearing completion, is briefly described to illustrate how the atmospheric and mechanical problems which have inhibited the development of amplitude interferometry may be overcome using modern technology. This program together with the developments taking place at CERGA lead to the conclusion that the prospects for contributions by high angular resolution measurements to the determination of fundamental stellar quantities during the next decade are excellent.

Hot Subluminous Stars

Extensive mass loss is observed for hot subluminous stars, through P Cygni lines in the ultraviolet. This persists in some sub-dwarf 0 stars, but is generally not observed in white dwarfs. The ultraviolet provides determination of effective temperatures. Among nine sdO’s, the maximum temperature reported is definitely below 60, 000 K; an object at 100, 000 K would be distinguishable. The sdO’s show a wide variety of line strengths, notably in N V, C IV and Si TV, as well as He II. One halo sdB is reported as rich in peculiar elements; it shows anomalous N V for its temperature. The comparison of effective temperatures of white dwarfs observed from space and from the ground gives excellent agreement. The hottest white dwarfs are near 60, 000 K, although one (helium-rich) reaches 80, 000 K. Another helium-rich close binary probably has an accretion disk; it is the only white dwarf to show the expanding shell of N V, C IV, Si IV characteristic of some subdwarfs. Two magnetic white dwarfs have been observed; one has strong unidentifiable features and the smallest known radius.

Stellar model chromospheres. VIII - 70 Ophiuchi A /K0 V/ and Epsilon Eridani /K2 V/

view Abstract Citations (57) References (28) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar model chromospheres. VIII. 70 Ophiuchi A (K0 V) and epsilon Eridani (K2 V). Kelch, W. L. Abstract Model atmospheres for the late-type active-chromosphere dwarf stars 70 Oph A and Epsilon Eri are computed from high-resolution Ca II K line profiles as well as Mg II h and k line fluxes. A method is used which determines a plane-parallel homogeneous hydrostatic-equilibrium model of the upper photosphere and chromosphere which differs from theoretical models by lacking the constraint of radiative equilibrium (RE). The determinations of surface gravities, metallicities, and effective temperatures are discussed, and the computational methods, model atoms, atomic data, and observations are described. Temperature distributions for the two stars are plotted and compared with RE models for the adopted effective temperatures and gravities. The previously investigated T min/T eff vs. T eff relation is extended to Epsilon Eri and 70 Oph A, observed and computed Ca II K and Mg II h and k integrated emission fluxes are compared, and full tabulations are given for the proposed models. It is suggested that if less than half the observed Mg II flux for the two stars is lost in noise, the difference between an active-chromosphere star and a quiet-chromosphere star lies in the lower-chromospheric temperature gradient. Publication: The Astrophysical Journal Pub Date: June 1978 DOI: 10.1086/156212 Bibcode: 1978ApJ...222..931K Keywords: Chromosphere; Dwarf Stars; Late Stars; Stellar Atmospheres; Stellar Models; Stellar Spectra; Binary Stars; H Lines; K Lines; Line Spectra; Metallic Stars; Photoionization; Photosphere; Spectrum Analysis; Stellar Mass; Stellar Temperature; Temperature Distribution; Astrophysics; Line Profiles:Stellar Chromospheres; Stellar Chromospheres: Models full text sources ADS | data products SIMBAD (2) Related Materials (12) Part 1: 1973ApJ...180..473L Part 2: 1974ApJ...192...93A Part 3: 1975ApJ...200..660A Part 4: 1975ApJ...201..212A Part 5: 1976ApJ...210..199A Part 6: 1978ApJ...220..619L Part 7: 1978ApJ...220..962K Part 9: 1979ApJ...229..700K Part 10: 1979ApJS...41...47L Part 11: 1979ApJS...41..481L Part 12: 1981ApJ...246..502G Part 13: 1982ApJ...258..740G

The Position of Central Stars in the Hertzsprung-Russell Diagram

The determination of total luminosity and effective temperature recently reported on sometimes (but not always) differ in a substantial way from the determination of these quantities from Hell Zanstra method. For example, differences in luminosity exceeding a factor of 10 have been noted. The resultant effect on the Hertzsprung-Russell diagram is presented and discussed. (Paper will appear in Astronomy and Astrophysics.)

18. Model Atmospheres for Hydrogen-Deficient White Dwarfs

The determination of atmospheric parameters for non-DA white dwarfs is investigated with the computed helium-rich model atmospheres by Bues (1970). Only poor predictions are possible from UBV colors alone for DB and DC stars. From uvby colors a determination of effective temperature is possible within 1000 K. Profiles of lines in different parts of the spectrum are necessary for better results.A deficiency of metal abundances for the cooler non-DA stars is obtained.

A Study of the Eclipsing Binary Beta Aurigae

Photoelectric spectrum scans and abundance analyses for effective temperature and surface gravity determination of eclipsing binary system beta Auriga

Determination of effective vibrational temperature for the BaO A1Σ- X1Σ-system in a carbon arc

The “effective” vibrational temperature for the A 1Σ- X 1Σ system of BaO excited in a carbon arc has been determined. Peak intensities of a large number of band heads were measured with a self-recording microphotometer. By plotting ∑ υ″ logI υ′,υ″ em v 4 against G'( v') with v' = 0, 1, 2, 3, 4, the slope of the line was determined from which the “effective” vibrationale temperature has been calculated. Allowance has been made for weak bands, by calculating their intensities theoretically where they could not be measured. Vibrational temperatures have also been calculated according to Nichollos' method. (15)

Determination of Effective Oil Temperature in a Transformer

It has shown in this paper that: 1. The effective oil temperature and the thermal time constant of each winding, as well as the winding temperature at instant of shutdown, can be determined from the resistance-time data taken immediately after the shutdown of a heat run on a transformer. 2. The average oil temperature as determined in accordance with the Test Code checks, within limits of test accuracy, the effective oil temperature determined by the resistance-time data methods described in this paper. 3. The effective oil temperature for each individual winding may not necessarily be the same value. This indicates that such factors as size of ventilation ducts, relative position of the windings to each other and to the core, and the division of loss in the transformner, may affect the temperature of the oil which effectively cools each individual winding.