DDO Paper Abstracts
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.
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.
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.
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).
Last update: 7 Novembre 1995