Arribas S., Roger C.M. (1989 A&A 215, 305)
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)
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)
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)
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
Claria J.J.,Piatti A.E. (1994, PASP )
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)
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
Geisler D. (1986, PASP 98, 762)
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)
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)
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)
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)
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.
- A revision is necessay in the Wilson-Bappu calibration of K-line absolute
magnitudes, Mv (K).
- No correlation is found between delta CN and Mv
(K), which implies that there is no metallicity-dependence in Mv (K).
- The new calibration yields a Hyades distance modulus (m-M)=3.22 mag.
Kobi D., North P. (1990, A&AS 85, 999)
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)
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)
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)
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
North P., Nicolet B. (1990, AA 228, 78)
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)
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)
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)
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)
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)
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
Straizys V., et al. (1993, Baltic AStr. 2, 326)
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)
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.
Last update: 7 Novembre 1995