Paper Abstracts

Arribas S., Roger C.M. (1989 A&A 215, 305)

Abstract

From a new set of infrared photometry we have derived the effective temperatures with a 3% error for a sample of low main sequence stars with spectroscopic determinations of their metal content. This has been used to extend the previous (B-V), Teff, [Fe/H] empirical calibrations for population I up to 4000K as well as to analyse the influence of some limitations of previous works. The agreement with the empirical calibration of Arribas and Martinez Roger (1988) is very good for almost the complete tenperature and metallicity range. Only for Teff lower than 5000 K and the lowest metallicities, that calibration does not reproduce the observed behaviour. Comparison with theoretical models shows that for solar abundance they are predicting exceedingly blue colours. Particularly in the new range analyzed (4000K < Teff < 5000K) the differences with the VandenBerg and Bell (1985) calibration can be as large as 0.09 mag. The new Buser and Kurucz (1988) models show better agreement. In both models the effect of metallicity in colours is underestimated. The possible influence of metallicity on the (V-K): Teff relation has also been investigated and was found to be about 30 K/dex for this spectral range.

These results support the suggestion of Magain (1987) that opacity at the ultraviolet is larger than that considered by the current atmosphere models for late type stars.

Balona L.A. (1984, MNRAS 211, 973)

Abstract

Using the Kurucz model atmospheres as a guide, we calibrate effective temperatures and bolometric corrections for early-type stars in terms of the Stromgren co and beta indices. These are placed on an empirical scale by adjusting the zero points for best agreement with measurements by Code et al. The form of the mass calibration is determined from evolutionary calculations and the zero point adjusted for best agreement with empirical determinations. A mass discrepancy problem arises when these masses are compared with those determined from model atmospheres.

Balona L.A. (1994, NMNRAS 268, 119)

Abstract

We discuss the determination of effective temperature, bolometric correction and surface gravity using Stromgren indices. We use synthetic colours to define the functional relationship over a wide range of surface gravity, and calibrate the relationship by means of stars with well-determined effective temperatures and surface gravities. The calibrations are presented as interpolation formulae, valid for O-F stars. We find that the latest evolutionary computations predict masses that agree with those from detached eclipsing binaries to within 7 per cent. We discuss the position of the zero-age main sequence from the models relative to that observed in two young open clusters. There is a serious discrepancy between the surface gravity calculated from model atmospheres and from evolutionary models.

Carney B.W. (1977, ApJ 233, 211)

Abstract

The relation between stellar ultraviolet excesses and abundances is reexamined with the aid of new data and an investigation is made of the accuracy of previous analyses. A high-resolution echellogram of the subdwarf HD 201891 is analysed to illustrate some of the problems. Generally, the earliest and latest analytical techniques yield consistent results for dwarfs. New UBV data yield normalized ultraviolet excesses, d(U-B)0.6, which are compared to abundances to produce a graphical relation that may be used to estimate [FE/H] to 0.2 dex. given UBV colors accuracte to 0.01 mag. The relation suggests a possible discontinuity between the halo and old-disk stars.

Claria J.J.,Piatti A.E. (1994, PASP )

Abstract

A revised effective temperature calibration for the DDO photometric system is presented. Recently published photometric and spectroscopic observations of field and open cluster G and K stars allow a better definition of the solar-abundance fiducial relation in the DDO Co(45-48) vs Co(42-45) diagram. The ability of the DDO system to assing MK spectral types to G and K giants is demonstrated. The new DDO effective temperature calibration reproduces satisfactorily the infrared temperature scale of Bell and Gustafsson (1989). It is shown that Osborn's (1979) calibration underestimates the effective temperatures of K giants by ~ 170 K and those of late-type dwarfs by ~ 150 K.

Cramer N., Maeder A. (1979, A&A 78, 305)

Abstract

Based on colour differences measuring the Balmer jump, but with different sensitivity to the accumulated effets of hydrogen and H- and K-lines, a method of luminosity and Teff calibration for B-type stars is established in the Geneva system. The references for calibration rest on star cluster distances properly adjusted to the Hyades modulus and on Code's et al. (1976) effective temperatures based on measurements of angular stellar diameters and absolute UV, visible and IR fluxes. The calibration is essentially independent of interstellar reddening and it allows a clear recognition of stellar perculiarities. The effects of unresolved binaries and rotation are also considered and a comparison with uvby beta results is made.

Geisler D. (1986, PASP 98, 762)

Abstract

Washington photometry is presented for a number of late-type giants with Fe abundances in the range -4.5< [Fe/H]< -0.5. The new data more than double the sample of such stars available with both accurate photometry and high-resolution abundance determinations. This permits a much-improved reexamination of the sensitivity of the Washington system to Fe and CN/CH abundances. New empirical calibrations of the two abundance indices, delta(M-T1) and delta (C-M), are presented. The Fe abundance sensitivity of the delta(M-T1) index is very limited for stars more metal-poor than [Fe/H]~ -1. The delta(C-M) index, however, is very sensitive to Fe abundance throughout the entire range of known stellar abundance. Indeed, the Fe abundance sensitivity of the delta(C-M) index is comparable to or exceeds that of all other photometric or low-resolution spectroscopic abundance indices at all metallicities. In view of the very broad bands employed by the Washington system, the delta(C-M) index offers, for many purposes, the best choice for an efficient, accurate, and sensitive abundance index for normal late-type giants. The system should prove to be very useful for investigation of abundances in extragalactic system using a CCD.

The ability of the system to detect anomalous CN/CH strengths is also investigated via observations of a number of giants in the globular clusters 47 Tuc and M4 with a variety of known CN and CH strengths. The delta(C-M) index is found to be much more sensitive to Fe abundance than CN or CH strength. The system cam differentiate CN- or CH-strong giants from normal giants, but not consistently, and is most effective for giants more metal-rich than 0.1 solar.

The new calibrations yield [Fe/H] = -0.85 = 0.1 for 47 Tuc. This intermediate values is in good agreement with most recent determinations and further weakens the evidence for a significantly lower Fe abundance, since the original value of -1.25 was used by Pilachowski, Canterna, and Wallerstein to support their controversial echelle result.

Geisler D., Claria J.J., Minniti D. (1991, AJ 102, 1836)

Abstract

A revised metal abundance calibration for the Washington photometric system is presented which represents a significant improvement over previous calibrations in several respects. First, new observations of a number of field and open cluster giants allow a much more precise definition of the solar-abundance fiducial relation in the two-color diagrams from which the abundance-sensitive delta indices are derived. Second, observations of a large sample of globular cluster giants clearly demonstrate, and allow correction for, an unsuspected decrease in metallicity sensitivity for cooler giants. Third, a new abundance index, C-T1, and a new temperature index, M-T2, are introduced. The M-T2 color provides a much broader baseline than the T1-T2 color and is thus much less susceptible to photometric errors in determining abundance. Fourth, the total sample of field and cluster giants now available with Fe abundances derived from high dispersion spectroscopy is substantially larger than available previously, leading to a more extensive and accurate calibration. Various combinations of abundance and temperature indices are investigated. Metal abundance calibrations are presented for five such combinations over the range from [Fe/H] = +0.5 to -4, indicating that each is capable of deriving abundance to ~0.15 dex. The abundance indices vary by ~1 mag over this metallicity range. We confirm that the Washington system offers a unique combination of efficiency and accuracy for determining metallicity in late-type giants over the full range of stellar abundances, although the system loses sensitivity for the coolest metal-poor stars. Metallicities determined from the calibration are given for some 50 open and globular clusters with previously Washington photometry. The abundance scale established here for globular clusters is in good agreement with that of Zinn [ApJ, 293, 424 (1985)] and with that of Janes [ApJS, 39, 135 (1979)] for open clusters. Finally, comprehensive reddening and photometric error estimates are derived, as well as abundance sensitivities, and the suitability of the different indices to abundance determinations under various conditions are discussed. Under most circumstances, especially for CCD applications where substantial photometric errors may be present due to, e.g., aperture correction uncertainties, the best abundance index is the C-M color, using M-T2 as the temperature index. Thus, in many applications it is only necessary to observe in three filters, excluding T1 observations.

Gray R.O. (1991, A&A 252, 237)

Abstract

This paper is the second in a series of papers which derives an empirical calibration of the Stromgren uvby beta photometric system for the A, F and early G supergiants. This paper considers the F and early G supergiants. A calibration which gives the intrinsic colour (b-y)o in terms of a temperature parameter, [m1] and a gravity parameter delta [c1] is derived. This calibration is subjected to tests to determine the presence of systematic errors. It is also used to derive colour excesses for a set of classical Cepheid variable stars, which are compared to other estimates in the literature. Finally, the (b-y)o index is calibrated against the effective temperatures of Luck & Bond (1989), and the sensitivity of the calibration to metal abundance is discussed.

Gray R.O. (1992, A&A 265, 704)

Abstract

This paper, the third in a series, deals with calibration of Stromgren photometry for the A and early F supergiants. We derive a gravity parameter, delta G, which can be used to separate photometrically supergiants of different luminosity classes. delta G is used in conjunction with [m1] to derive a simple calibration which gives the intrinsic colour, (b-y)o of the supergiant. This calibration is tested and compared with other reddening estimates for A and F supergiants in the literature. Finally, we derive a semi-empirical effective temperature calibration for the A and F supergiants.

Janes K.A. (1975, ApJ 29, 161)

Abstract

DDO intermediate-band photometry of 1200 G and K stars is used to derive procedures to estimate the anomalous cyanogen strength and the absolute visual magnitude of a G or K giant star. As expected, the CN-strength index, delta CN, is correlated with [Fe/H], but the development of the absolute magnitude calibration leads to several interesting results: The DDO absolute magnitudes, plus published radial velocities and proper motions, are used to calculate space velocities for 799 giants. The Z velocities (perpendicular to the galactic plane) show the expected correlation with delta CN, and the extreme CN-weak stars have high velocities in the plane. In addition, the kinematics suggest that there is an actual galactic gradient in the mean value of delta CN among K giants. This gradient is probably the result of a radial gradient in the nitrogen abundance in the galactic plane.

Kobi D., North P. (1990, A&AS 85, 999)

Abstract

A new, semi-empirical calibration of the d, m2 and B2-V1 parameters of Geneva photometry is given, which allows to estimate Te, log g and [Fe/H] of A4 V-III to G5 V stars. The calibration is based on Kurucz's grid of atmosphere models, corrected by means of fundamental stars. Recent evolutionary tracks for stars witgh a metal content Z = 0.02 are used to calibrate the d vs B2-V1 diagram in term of mass for solar-composition stars.

Lub J., Pel J.W. (1977, A&A 54, 137)

Abstract

In this paper we discuss the properties of the Walraven VBLUW photometric system, in use at the Leiden Southern Station. A careful analysis of the standard star observations of different observing seasons shows that colour changes as small as 0.01 on a timescale of a few years are detectable. The variation of the early standard stars is largest in (B-U), the Balmer jump index. Special attention is paid to the stability of the photometric passbands, and a new determination of the filter profiles is given. The stable and accurate definition of the passbands is an important feature of the VBLUW photometer, which is particularly valuable for the comparison of observed stars with theoretical colours. The properties of the VBLUW system with respect to atmospheric extinction and interstellar reddening are discussed, and it is shown that the colour-terms in the extinction and reddening corrections are sufficiently small to be neglected. For the colour excesses we adopt: E(B-V)/E(V-B)=0.64; E(U-W)/E(V-B)=0.45; E(B-L)/E(V-B)=0.43. Theoretical colours are derived from a grid of model atmosphere fluxes computed by Kurucz (1975), and the application of the VBLUW photometry to the classification of stars of spectral type A to G is discussed. A three-dimensional classification in terms of temperature, effective gravity and heavy element abundance appears to be possible in this spectral range. We find that below Te=8000 K the VBLUW photometry is more than twice as sensitive to differences in heavy element abundance as is the Stromgren uvby system. The tables at the end of this paper give numerical data for the computed theoretical colours. We also give VBLUW photometry for 148 bright stars of known M.K. spectral type, and for 54 Hyades stars. The photometric properties and theoretical colours discussed in this paper will be the strating point for the interpretation of a large body of VBLUW data on Cepheids and RR Lyrae variables.

Janes K.A. (1977, PASP 89, 576)

Abstract

A method is described for deriving the interstellar reddening and (B-V)o value of a single K-giant star from DDO photometry. For Population I stars, the method works well and is independent of composition. It does not work, however, for Population II stars.

Napiwotzki R., et al. (1993, AA 268, 653)

Abstract

The determination of stellar temperatures and surface gravities by means of the Stromgren photometric system is examined in the region. We used a sample of stars with independently derived temperature and gravities. We compare our results with Castelli (1991) and present new temperature calibrations for normal stars ([u-b],(b-y)o, and Johnson (B-V)o) and for Ap stars ([u-b] and [c1]).

The use of integrated fluxes and especially the infrared flux method (IRFM) for determining stellar temperatures is discussed. SDurface gravities of B and A stars, derived by fitting theoretical profiles to the Balmer lines, are used to check the calibrations.

North P., Nicolet B. (1990, AA 228, 78)

Abstract

A new, semi-empirical calibration of the two reddening free parameters X and Y of Geneva photometry in terms of effective temperature and gravity is proposed. The calibration is based on Kurucz's grid of atmosphere models and on a set of fundamental stars; it is valid for main sequence stars with Te > 10'000K. Theoretical evolutionary tracks were then used to calibrate the Y vs X diagram in terms of stellar mass, for M > 2.5-3.0 M.

Olsen E.H. (1988, AA 189, 173)

Abstract

Several calibrations of Stromgren uvby-beta photometry with respect to the intrinsic colour (b-y)o exist for F-type stars. These calibration are complementary, since they are valid for different ranges of heavy element abundance. A new comprehensive intrinsic colour calibration is presented. It is valid for all F0-G2 stars of luminosity classes III-V, except possibly the most extreme population II stars. The calibration is based on 1231 stars. The rms scatter around the calibration is 0.009 (one star).

Paltoglu G., Bell R.A> (1994, MNRAS 268, 793)

Abstract

Synthetic colours have been calculated for the Washington photometry system from a grid of synthetic spectra. The grid of spectra covers a range in Teff, log g and abundance appropriate for Population I and II dwarfs and giants. We also examine the effects of C and N abundance variations on the colours of the giants. We compare the model colours with observations of field dwarfs and giants compiled from the literature, as well as published cluster giant branch photometry. We find that our dwarf models match the observed disc dwarf sequence very well in the (C - M) versus (T1 - T2) and (M - T1) versus (T1 - T2) colour planes, while our solar-abundance giant branch grid and isochrones are a good fit to the disc giant sequence. Our metal-poor isochrones are systematically too red when compared with globular cluster giant branches; this may be due to the parameters chosen for the computation of the isochrones. A comparison of the effects of abundance and gravity on the indices (T1 - T2) and (M - T2), used for estimating Teff, suggests that the latter should be the index of choice. Neither (C - M) nor (M - T1) is found to be particularly sensitive to variations in [C/Fe] or [N/Fe] if the abundances are anticorrelated. At solar abundance, however, (C - M), (M - T1) and (T1 - T2) are strongly affected if the abundances are not anticorrelated. We confirm empirical suggestions that (C - M) and (C - T1), are the best abundance indicators. The model colours for the gravity indicator (M - 51) match the observed sequences very well. This index is useful for estimating both gravity and abundance. It may be particularly useful for estimating the abundance of highly reddened open and globular clusters.

Piatti A.E., Claria J.J. (1993, J.Ap.A. 14, 145)

Abstract

Serveral arguments that justify establishing a revised abundance calibration for DDO photometry of population I red giants are presented. The components of the blanketing vector in the DDO C(45-48) vs C(42-45) diagram are determined for late-type dwarfs and giants. We have redefined the DDO cyanogen anomaly and calibrated it against metallicity. The sample of field giants now available with abundances derived from high dispersion spectroscopy is substantially larger than previously available, leading to a more accurate abundance calibration. Iso-abundance lines in the C(41-42) vs C(42-45) diagram have been determined for population I G and K giants and an iterative method for deriving abundance of these stars is described. We show that the new DDO abundance are in very good agreement with those derived from high dispersion spectroscopy.The new method improves by about 0.1 dex the DDO abundances derived for early G and/or late K giants, with respect to the delta CN method of Janes (1975).

Schuster W.J., Nissen P.E. (1989, A&A 221, 65)

Abstract

The uvby beta photometry of 711 hight-velocity and metal-poor stars by Schuster and Nissen (1988, Paper I) has been used to derive new (b-y)o - beta and [Fe/H] calibrations. The interstellare color excess, E(b-y), can be determined with a standard deviation of 0.01 for beta values down to 2.55. The standard deviation of [Fe/H] increases from about 0.15 dex at [Fe/H]~-0.5 to about 0.30 dex at [Fe/H]~-2.5. The calibrations are particularly useful for metal-poor, late-F and G stars, and will be used to study the age-metallicity-kinematic relations of halo and old disk population stars. The error of E(b-y) for unresolved binary stars is shown to be negligible whereas the error of [Fe/H] is of the order of +0.10 to + 0.25 dex. Errors in beta due to radial velocity shifts of the H Beta line are shown to be negligible for the particular set of beta observations in Paper I. The derived reddenings and metallicities for stars from Paper I agree very well with data from the survey of proper motions stars by Laird et al. (1988) for the large majority of the 132 stars in common between the two works. However, about 10% of the stars have significant differences in the derived reddenings, which lead to differences in [Fe/H] of typically +0.40 dex. The [Fe/H] values for stars in Paper I do not agree particularly well with the [Fe/H] values of Sandage and Fouts (1987). From a comparison of data for 258 stars in common the standard deviation of the [Fe/H] values of Sandage and Fouts is estimated to be 0.35 dex. This error should be taken into account when deriving the intrinsic relations between kinematical parameters and metallicity from the data of Sandage and Fouts.

Smalley B., Dworetsky M.M. (1995, A&A 293, 446)

Abstract

We present an investigation into the determination of fundamental values of Tefff and log g. A re-evaluation of the fundamental values of T eff determined by Code et al. (1976) using modern flux measurements is presented, but there are no significant changes. A determination of fundamental values of Tefff for four binary systems with fundamental log g value has been performed. Medium-resolution Hbeta profiles of the fundamental stars have been obtained and compared to theoretical profiles in order to provide estimates of the parameters that have not been obtained in a fundamenta manner. We have calculated a table of synthetic beta indices which explicitly include the effects of metal-line blocking. We find that these beta indices are in good agreement with the photometric values. A comparison of theoretical uvby colours is also presented, and found to be in very good agreement with the photometric colours.

Straizys V., et al. (1993, Baltic AStr. 2, 326)

Abstract

Colour indices and reddening-free Q-parameters in the Vilnius photometric system of B-type stars of all luminosities and A-supergiants are calibrated in terms of effective temperature and surface gravity, using synthetic spectra of the newest Kurucz model atmospheres. The calibration is verified by comparing the photometrically determined effective temperatures and surfaces gravities with the most accurate spectroscopic data. Satisfactory agreement has been found, proving the accuray of the calibration within +0.02 to +0.05 dex in log Te and +0.2 to +0.3 dex in log g.

Tautvaisiene G., Lazauskaite R. (1993, Baltic Astr. 2, 256)

Abstract

A new semi-empirical surface gravity calibration of the intrinsic colour indices U-P and U-X of the Vilnius photometric system is presented. It is applicable for giants of all metallicities with temperatures from 4200K to 5500K and log g from 0.5 dex to 3.0 dex. The standard deviation of the observed minus predicted log g residuals is about +0.3dex. The U-P colour index is found to be a very good surface gravity indicator, and it can be used for for log g determination even when other atmospheric parameters (temperature and metallicity) are poorly known. The main atmospheric parameters for 93 red metal-deficient giants are determined from colour indices of the Vilnius system and compared with the evolutionary isochrones.

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Last update: 7 Novembre 1995