NH and Mg Index Trends in Elliptical Galaxies

We examine the spectrum in the vicinity of the NH3360 index of Davidge & Clark (1994), which was defined to measure the NH absorption around 3360 \AA and which shows almost no trend with velocity dispersion (Toloba et al. 2009), unlike other N- sensitive indices, which show a strong trend (Graves et al. 2007). Computing the effect of individual elements on the integrated spectrum with synthetic stellar population integrated spectra, we find that, while being well correlated with nitrogen abundance, NH3360 is almost equally well anti-correlated with Mg abundance. This prompts the definition of two new indices, Mg3334, which is mostly sensitive to magnesium, and NH3375, which is mostly sensitive to nitrogen. Rather surprisingly, we find that the new NH3375 index shows a trend versus optical absorption feature indices that is as shallow as the NH3360 index. We hypothesize that the lack of a strong index trend in these near-UV indices is due to the presence of an old metal-poor component of the galactic population. Comparison of observed index trends and those predicted by models shows that a modest fraction of an old, metal-poor stellar population could easily account for the observed flat trend in these near-UV indices, while still allowing substantial N abundance increase in the larger galaxies.Comment: 19 pages, 6 figures, 6 table

A Library of Lick/IDS Indices for Binary Stellar Populations

Using EPS we present 13 refined Lick/IDS absorption-line indices for an extensive set of instantaneous-burst binary stellar populations (BSPs) at high resolution (0.3 \AA) of various age and metallicity (1-15Gyr, 0.004-0.03), and 38 indices at intermediate resolution (3 \AA). These indices are obtained by two methods: (1) obtain them by using the empirical fitting functions (FFs method); (2) measure them directly from the synthetic spectra (DC method). Together with our previous paper a database of Lick/IDS spectral absorption-line indices for BSPs at high and intermediate resolutions is provided. This set of indices includes 21 indices of Worthey et al., four Balmer indices defined by Worthey & Ottaviani and 13 indices with the new passband definitions of Trager et al. The full set of synthetic indices and the integrated pseudo-continuum are listed in the Appendix, which is only available online or from our website (http://www.ast9. com/), or on request from the first author. Moreover, the ISEDs can be obtained from our website. We compare the synthetic Lick/IDS indices obtained by FFs method and those by DC method, and find that the discrepancies are significant: Ca4455 (index 6), Fe4668 (8), Mg_b (13), Fe5709 (17), NaD (19), TiO_1 (20) and TiO_2 (21, except for Z=0.02) in the W94 system, Ca4455^T (6^T), C_2 4668^T (8^T), NaD^T (19^T), TiO_1^T (20^T) and TiO_2^T (21^T, except for Z=0.02) in the T98 system obtained by DC method are less (bluer) than the corresponding ones obtained by FFs method for all metallicities. Ca4227 (index 3), Fe5782 (18),Ca4227^T (3^T) and Fe5782^T (18^T) are greater at Z=0.03 and become to be bluer at Z=0.004, Fe5709^T (17^T) index is less at Z=0.03 and becomes to be redder at Z=0.004 than the corresponding ones obtained by FFs method.Comment: 16 pages, 2 figures, to be published in MNRA

Line-of-sight velocity distribution corrections for Lick/IDS indices of early-type galaxies

We investigate line-of-sight velocity distribution (LOSVD) corrections for absorption line-strength indices of early-type galaxies in the Lick/IDS system. This system is often used to estimate basic stellar population parameters such as luminosity weighted ages and metallicities. Using single stellar population model spectral energy distributions by Vazdekis (1999) we find that the LOSVD corrections are largely insensitive to changes in the stellar populations for old galaxies (age >3 Gyr). Only the Lick/IDS Balmer series indices show an appreciable effect, which is on the order of the correction itself. Furthermore, we investigate the sensitivity of the LOSVD corrections to non-Gaussian LOSVDs. In this case the LOSVD can be described by a Gauss-Hermite series and it is shown that typical values of h_3 and h_4 observed in early-type galaxies can lead to significant modifications of the LOSVD corrections and thus to changes in the derived luminosity weighted ages and metallicities. A new, simple parameterisation for the LOSVD corrections, taking into account the h_3 and h_4 terms, is proposed and calibrations given for a subset of the Lick/IDS indices and two additional indices applicable to old (>3 Gyr) stellar populations.Comment: 10 pages, 8 figures, accepted by A&

Spectral Indices of Stars at Super-solar Regime

We derived Lick narrow-band indices for 139 candidate super metal-rich stars of different luminosity class previously studied in Malagnini et al. (2000). Indices include Iron Fe50, Fe52, Fe53, and Magnesium Mgb and Mg2 features. By comparing observations with Kurucz' synthetic model atmospheres, no evidence is found for non-standard Mg vs. Fe relative abundance (i.e. [Mg/Fe]~ 0, on the average, for our sample). A comparison with the Worthey et al.(1994) and Buzzoni et al.(1992, 1994) fitting function predictions for [Fe/H] > 0 is performed and briefly discussed.Comment: 4 pages, 3 figures; proceedings of "New Quests in Stellar Astrophysics: The link between Stars and Cosmology", 26-30 March, 2001, Puerto Vallarta, Mexico, eds. M. Chavez, A. Bressan, A. Buzzoni & D. Mayya, to be published by the Kluwer Academic Publisher

The G Dwarf Problem Exists in Other Galaxies

Stellar population models with abundance distributions determined from the analytic Simple model of chemical evolution fail to match observations of the nuclei of bulge-dominated galaxies in three respects. First, the spectral energy distribution in the mid-ultraviolet range 2000 < lam < 2400 exceeds observation by ~ 0.6 mag. Most of that excess is due to metal-poor main sequence stars. Second, the models do not reproduce metal-sensitive optical absorption features that arise mainly from red giant stars. Third, the strength of a Ca II index sensitive to hot stars does not jibe with the predicted number of A-type horizontal branch stars. The number of metal poor stars in galaxies is at least a factor of two less than predicted by the Simple model, exactly similar to the ``G Dwarf problem'' in the solar cylinder. Observations at larger radii in local group galaxies indicate that the paucity of metal poor stars applies globally, rather than only in the nuclei. Because of the dominance of metal rich stars, primordial galaxies will have a plentiful dust supply early in their star formation history, and thus will probably have weak Lyman-alpha emission, as is apparently observed. We confirm that early-type galaxies cannot have been formed exclusively from mergers of small all-stellar subsystems, a result already established by dynamical simulations. The constraint of peaked abundance distributions will limit future chemical evolution models. It will also make age estimates for the stellar populations in early type galaxies and bulges more secure.Comment: 14 pages, LaTeX includes 3 postscript figures. Uses AAS LaTeX v 4.0 and times.sty. Accepted for publication in the Astronomical Journal. Postscript available at http://shemesh.gsfc.nasa.gov/~dorman/Ben.htm

Emission Corrections for Hydrogen Features of the Graves et. al 2007 Sloan Digital Sky Survey Averages of Early Type, Non-liner Galaxies

For purposes of stellar population analysis, emission corrections for Balmer series indices on the Lick index system in Sloan Digital Sky Survey (SDSS) stacked quiescent galaxy spectra are derived, along with corrections for continuum shape and gross stellar content, as a function of the Mg $b$ Lick index strength. These corrections are obtained by comparing the observed Lick index measurements of the SDSS with new observed measurements of 13 Virgo Cluster galaxies, and checked with model grids. From the H$\alpha$ Mg $b$ diagram a linear correction for the observed measurement is constructed using best fit trend lines. Corrections for H$\beta$, H$\gamma$ and H$\delta$ are constructed using stellar population models to predict continuum shape changes as a function of Mg $b$ and Balmer series emission intensities typical of H{\sc II} regions. The corrections themselves are fairly secure, but the interpretation for H$\delta$ and H$\gamma$ indices is complicated by the fact that the H$\delta$ and H$\gamma$ indices are sensitive to elemental abundances other than hydrogen

On the Anomalous Balmer Line Strengths in Globular Clusters

Spectral feature index diagrams with integrated globular clusters and simple stellar population models often show that some clusters have weak H beta, so weak that even the oldest models cannot match the observed feature depths. In this work, we rule out the possibility that abundance mixture effects are responsible for the weak indices unless such changes operate to cool the entire isochrone. We discuss this result in the context of other explanations, including horizontal branch morphology, blue straggler populations, and nebular or stellar emission fill-in, finding a preference for flaring in M giants as an explanation for the H beta anomaly.Comment: Submitted to the A

Advanced prediction technique for the low speed aerodynamics of V/STOL aircraft. Volume 1: Technical discussion

The V/STOL Aircraft Propulsive Effects (VAPE) computerized prediction method is evaluated. The program analyzes viscous effects, various jet, inlet, and Short TakeOff and Landing (STOL) models, and examines the aerodynamic configurations of V/STOL aircraft