Colors Of Stellar Populations Research Articles

Fitting formulae for the effects of binary interactions on lick indices and colors of stellar populations

More than about 50% of stars are in binaries, but most stellar population studies take single star stellar population (ssSSP) models, which do not take binary interactions into account. In fact, the integrated peculiarities of ssSSPs are different from those of stellar populations with binary interactions (bsSSPs). Therefore, it is necessary to investigate the effects of binary interactions on the Lick indices and colors of populations in detail. We show some formulae for calculating the difference between the Lick indices and colors of bsSSPs, and those of ssSSPs. Twenty-five Lick indices and 12 colors are studied in this work. The results can be conveniently used for calculating the effects of binary interactions on stellar population studies and for adding the effects of binary interactions into present ssSSP models. The electronic data and fortran procedures in the paper can be obtained on request from the authors.

How Binary Interactions Affect Spectral Stellar Population Synthesis

Single-star stellar population (ssSSP) models are usually used for spectral stellar population studies. However, more than 50% of stars are in binaries and evolve differently from single stars. This suggests that the effects of binary interactions should be considered when modeling the stellar populations of galaxies and star clusters. Via a rapid spectral stellar population synthesis model, we give detailed studies of the effects of binary interactions on the Lick indices and colors of stellar populations and on the determination of the stellar ages and metallicities of populations. Our results show that binary interactions make stellar populations less luminous and bluer, with larger age-sensitive Lick indices (H beta) and smaller metallicity-sensitive indices (e. g., Mg b, Fe5270, and Fe5335) compared to ssSSPs. It also shows that when ssSSP models are used to determine the ages and metallicities of stellar populations, smaller ages or metallicities are obtained when using two line indices (H beta and [MgFe]) or two colors (e. g., u - R and R - K), respectively. Some relations for linking the stellar population parameters obtained by ssSSPs to those obtained by binary-star stellar populations (bsSSPs) are presented in this work. This can help us get some absolute values for stellar population parameters and is useful for absolute studies. However, it is found that the relative luminosity-weighted stellar ages and metallicities obtained via ssSSPs and bsSSPs are similar. This suggests that ssSSPs can be used for most spectral stellar population studies, except in some special cases.

Testing Population Synthesis Models with Globular Cluster Colors.

We have measured an extensive set of UBVRIJHK colors for M31 globular clusters. We compare the predicted simple stellar population colors of three population synthesis models to the intrinsic colors of Galactic and M31 globular clusters. The best-fitting models fit the cluster colors very well: the weighted mean color offsets are all smaller than 0.05 mag. The most significant offsets between model and data are in the U and B passbands; these are not unexpected and are likely caused by problems with the spectral libraries used by the models. The metal-rich clusters (&sqbl0;Fe&solm0;H&sqbr0; greater, similar-0.8) are best fit by young (8 Gyr) models, while the metal-poor clusters are best fit by older (12-16 Gyr) models. If this range of globular cluster ages is correct, it implies that conditions for cluster formation must have existed for a substantial fraction of the galaxies' lifetimes.

M31 Globular Clusters: Colors and Metallicities

We present a new catalog of photometric and spectroscopic data on M31 globular clusters (GCs). The catalog includes new optical and near-infrared photometry for a substantial fraction of the 435 clusters and cluster candidates. We use these data to determine the reddening and intrinsic colors of individual clusters, and we find that the extinction laws in the Galaxy and M31 are not significantly different. There are significant (up to 0.2 mag in V-K) offsets between the clusters' intrinsic colors and simple stellar population colors predicted by population synthesis models; we suggest that these are due to systematic errors in the models. The distributions of M31 clusters' metallicities and metallicity-sensitive colors are bimodal, with peaks at [Fe/H] ≈ -1.4 and -0.6. The distribution of V-I is often bimodal in elliptical galaxies' globular cluster systems, but it is not sensitive enough to metallicity to show bimodality in M31 and Galactic cluster systems. The radial distribution and kinematics of the two M31 metallicity groups imply that they are analogs of the Galactic halo and disk/bulge cluster systems. The globular clusters in M31 have a small radial metallicity gradient, suggesting that some dissipation occurred during the formation of the globular cluster system. The lack of correlation between cluster luminosity and metallicity in M31 GCs shows that self-enrichment is not important in GC formation.

A search for candidate light echoes: Photometry of supernova environments

Supernova (SN) light echoes could be a powerful tool for determining distances to galaxies geometrically, Sparks (1994). In this paper we present CCD photometry of the environments of 64 historical supernovae, the rst results of a program designed to search for light echoes from these SNe. We commonly nd patches of optical emission at, or close to, the sites of the supernovae. The color distribution of these patches is broad, and generally consistent with stellar population colors, possibly with some reddening. However there are in addition patches with both unusu- ally red and unusually blue colors. We expect light echoes to be blue, and while none of the objects are quite as blue in V R as the known light echo of SN 1991T, there are features that are unusually blue and we identify these as candidate light echoes for follow-on observations.

THE CONTROLLING PARAMETERS OF THE INTEGRATED FLUX OF A STELLAR POPULATION

ABSTRACT Stellar evolutionary isochrones are coupled with mostly theoretical flux distributions of stars in order to predict the flux distributions and colors of stellar populations as a function of population age and metallicity. Twenty one empirical indices of absorption feature strengths are measured for ensembles of stars of differing ages, temperatures, and metallicities. These indices are expressed as polynomials in stellar temperature, surface gravity, and metallicity, and are applied to the population models to predict index strengths as a function of population age and metallicity. Checks are made against stellar observations. The model predictions are compared to measured indices of elliptical galaxies. The logarithmic ratio [Me/Fe] (which is zero for a scaled solar ratio) is shown to be greater than that of the most metal-rich stars in the solar neighborhood in giant elliptical galaxies. Since [Mg/Fe] is probably near zero for metal-rich stars, [Mg/Fe] appears to be greater than zero in giant ellipticals, but not in smaller, M32-class, ellipticals. This behavior is probably mirrored in Na and NC indices, suggesting that all light elements are relatively enhanced in giant ellipticals, on average. If this is true, the nucleosynthetic history of giant ellipticals must differ from that of smaller ellipticals. Surface brightness fluctuation magnitudes are predicted. Models agree with the empirical I-band calibration, giving extragalactic distances which may be good to 10% for galaxies well-measured in two passbands. Qualitative agreement is also reached in fluctuation color-color diagrams and color-index diagrams. A fluctuation magnitude which is independent of color probably exists between Cousins I and Johnson J. The model colors, magnitudes, mass-to-light ratios, spectral indices, and fluctuation magnitudes are tabulated. Four specific theorems follow from this work. First, the stellar populations of ellipticals are controlled by at least three parameters, and these parameters are most likely mean heavy element abundance, mean light element abundance, and mean age. Second, if Delta-age/Delta-Z = 3/2 for two populations, they will appear almost identical in most indices. The few exceptional indices include H-Beta and the G band, which provide the best age sensitivity, and several Fe blends which are roughly twice as sensitive to metallicity as any previously used index assuming the absence of abundance ratio differences. Third, of the controlling parameters of a population, Z is dominant, followed by age, IMF, and Y. For the present, uncertainties in stellar evolution have the same magnitude as the effects of IMF and Y on population indices. Finally, because of the similar effects of age and metallicity on absorption features, the spectra of old populations are sensitive to changes in some elemental abundance ratios (like [Mg/Fe]), implying that these ratios can be quantitatively measured when appropriate models become available.

Stellar population synthesis revisited

view Abstract Citations (335) References (66) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar Population Synthesis Revisited Charlot, Stephane ; Bruzual A, Gustavo Abstract The isochrone synthesis method is introduced as a population synthesis method for galaxies. The method permits accurate distributions of stars in the theoretical color-magnitude diagram to be computed for any stellar population and thereby circumvent the problems faced by earlier techniques. A set of evolutionary tracks extending from the ZAMS up to the beginning of the white-dwarf cooling sequence is compiled to optimize the models. Comparison of model predictions with observational data leads to the conclusion that the isochrone synthesis can reproduce the observed colors of stellar populations of ages from a few tens of millions of yr to a Hubble time. Publication: The Astrophysical Journal Pub Date: January 1991 DOI: 10.1086/169608 Bibcode: 1991ApJ...367..126C Keywords: Astronomical Photometry; Asymptotic Giant Branch Stars; Color-Magnitude Diagram; Galactic Evolution; Stellar Evolution; Star Clusters; Stellar Color; Stellar Models; Ubv Spectra; Astrophysics; GALAXIES: EVOLUTION; GALAXIES: PHOTOMETRY; GALAXIES: STELLAR CONTENT; STARS: EVOLUTION full text sources ADS | data products SIMBAD (1)

Imaging and spectroscopic studies of the interacting system Markarian 171

view Abstract Citations (17) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Imaging and Spectroscopic Studies of the Interacting System Markarian 171 Friedman, Scott D. ; Cohen, Ross D. ; Jones, B. ; Smith, Harding E. ; Stein, W. A. Abstract V, R, and I broadband CCD images, as well as H-alpha spectroscopic observations of Markarian 171, are presented. Two apparently interacting dust-enshrouded galaxies exhibit relatively normal V-R, V-I galactic stellar-population colors in their outer regions, and spatially extended H-alpha emission. However, the dereddened colors imply a hot stellar population. The dual characteristics of narrow H-alpha lines and spatially extended H-alpha emission clearly distinguish this type of activity from that associated with the compact central regions of active galactic nuclei and QSOs. Apparently, in the case of Mk 171 the interaction has induced star formation throughout a significant fraction of the galaxy (kiloparsecs) - not just in the immediate vicinity of the nucleus (parsecs). A peculiar stellar population of hot stars associated with a knot of weak H-alpha emission appears spatially separate from the other emission-line regions. It is possible that this stellar knot is a severed remnant attributable to the gravitational interaction between the two galaxies. Publication: The Astronomical Journal Pub Date: December 1987 DOI: 10.1086/114581 Bibcode: 1987AJ.....94.1480F Keywords: Astronomical Spectroscopy; Charge Coupled Devices; Emission Spectra; Gravitational Effects; H Alpha Line; Markarian Galaxies; Hot Stars; Spectral Energy Distribution; Star Distribution; Stellar Color; Astronomy; RADIO SOURCES: GALAXIES full text sources ADS | data products SIMBAD (7) NED (5)