Robert F. Wing

Synthetic Spectra and Color-Temperature Relations of M Giants

As part of a project to model the integrated spectra and colors of elliptical galaxies through evolutionary synthesis, we have refined our synthetic spectrum calculations of M giants. After critically assessing three effective temperature scales for M giants, we adopted the relation of Dyck et al. for our models. Using empirical spectra of field M giants as a guide, we then calculated MARCS stellar atmosphere models and SSG synthetic spectra of these cool stars, adjusting the band absorption oscillator strengths of the TiO bands to better reproduce the observational data. The resulting synthetic spectra are found to be in very good agreement with the K-band spectra of stars of the appropriate spectral type taken from Kleinmann & Hall as well. Spectral types estimated from the strengths of the TiO bands and the depth of the band head of CO near 2.3 μm quantitatively confirm that the synthetic spectra are good representations of those of field M giants. The broadband colors of the models match the field relations of K and early-M giants very well; for late-M giants, differences between the field star and synthetic colors are probably caused by the omission of spectral lines of VO and H2O in the spectrum synthesis calculations. Here, we present four grids of K-band bolometric corrections and colors—Johnson U-V and B-V, Cousins V-R and V-I, Johnson-Glass V-K, J-K, and H-K, and CIT/CTIO V-K, J-K, H-K, and CO—for models having 3000 K ≤ Teff ≤ 4000 K and -0.5 ≤ log g ≤ 1.5. These grids, which have [Fe/H] = +0.25, 0.0, -0.5, and -1.0, extend and supplement the color-temperature relations of hotter stars presented in a companion paper.

Outer layers of a carbon star: The view from the Hubble Space Telescope

To advance our understanding of the relationship between stellar chromospheres and mass loss, which is a common property of carbon stars and other asymptotic giant branch stars, we have obtained ultraviolet spectra of the nearby N-type carbon star UU Aur using the Hubble Space Telescope (HST). In this paper we describe the HST observations, identify spectral features in both absorption and emission, and attempt to infer the velocity field in the chromosphere, upper troposphere, and circumstellar envelope from spectral line shifts. A mechanism for producing fluoresced emission to explain a previously unobserved emission line is proposed. Some related ground-based observations are also described.

Red supergiants in the southern Milky Way. I : Search and classification techniques

A detailed description of a continuing survey for distant, cool supergiants near the galactic plane in the southern hemisphere is presented. Candidate stars are found on near-infrared objective-prism plates, and confirming observations are made with near-infrared narrow-band photometry and medium-resolution CCD spectroscopy. The fluxes of 36 southern and equatorial standard stars for the eight-color narrowband system are given. It is shown how stars are classified in temperature and luminosity type and how the photometry is used to derive distances and reddening

THE SPECTRAL TYPE AND INFRARED BRIGHTNESS OF R DORADUS

The southern semiregular variable R Doradus has been classified M8.0 on the basis of narrow-band photoelectric measurements in the near infrared. It is one of the brightest stars in the infrared and the brightest star visually to have such a late spectral type. Key words: spectral type - infrared photometry - late-type star

THE RADIAL VELOCITY OF RGO 153, A CARBON STAR IN THE FIELD OF Ω CENTAURI

The radial velocity of RGO 153, one of three carbon stars that have been found in the field of the globular cluster CL) Cen, differs by more than 250 km sec-1 from the mean cluster velocity, indicating that the star is not a physical member of the cluster. Key words: globular cluster - carbon star - radial velocity

New S Stars Found in a Southern Galactic Plane Survey

Based upon the presence of bands of ZrO and LaO, four new S stars have been identified. They were found among more than 700 red spectrograms of cool stars in a survey of the southern Galactic plane.

Photometric Properties of Peculiar Red Giants

Four quite different kinds of information are commonly obtained through photometric observations: (1) magnitudes and colors on various systems; (2) energy distributions, leading to estimates of effective temperature, tests of model atmospheres, and the detection of companions or circumstellar shells; (3) spectroscopic data from narrow-band photometry of strong spectral features; and (4) light curves of variable stars. The photometric properties of the peculiar red giants — the cool carbon and S-type stars, and the warmer R-type carbon stars, CH stars, barium stars, and related objects — are reviewed with emphasis on what can be learned from each of these kinds of photometric data.

Color Temperatures of Red Giants and their Relation to the Effective Temperature

Color temperatures of red giant stars can be calibrated in terms of effective temperature if the colors are measured at wavelengths of minimal discrete absorption and nearly equal continuous opacity. The problem, of selecting suitable wavelengths in the complex spectra of M stars is discussed; measurements in the near infrared are recommended for early M stars, and the inclusion of a measurement at 4.00 µm is very helpful for stars later than about M5. Color temperatures based on infrared continuum points appear to confirm the new scale of effective temperatures derived by Ridgway et al., in that line-blanketed models of those effective temperatures are able to reproduce the observed color temperatures. A program of direct measurements of absolute infrared monochromatic fluxes is now in progress.

On the Use of Photometry in Spectral Classification

We discuss the applicability of photoelectric photometry to the classification of stellar spectra. A distinction is made between “photometric” classifications, which depend upon correlations between photometric colors and spectral type, and true “spectral” classifications, which can be obtained photometrically if based upon reddening-free indices of the strengths of appropriate spectral features. Examples are given of the use of wide-band and intermediate-band photometry to measure intrinsic spectral characteristics of stars. One narrow-band photometric system – the writer’s eight-color system of TiO/CN classification photometry – is discussed in detail because it does provide true spectral classifications for stars of type M. Results from the eight-color system are compared to MK classifications as regards sensitivity, accuracy, and range of applicability.

Standardization of the Solar‐Neighborhood Main Sequence for Spectral Types K4 to M6

We have selected a set of nearby stars suitable for use in defining the solar‐neighborhood main sequence from type K4 V to M6 V. The chosen stars have excellent photometry, spectral classifications on a consistent scale, and smooth distributions in color and molecular band strength. They also have high‐quality parallax measurements which show them to lie near the mean main sequence as defined by a larger sample of stars. High‐velocity stars, subdwarfs, and other peculiar types have been avoided, as have close visual binaries which may be difficult to observe separately. We show color‐magnitude diagrams for the selected standard stars and for a larger set of stars for which the same data are available.