Isochrones of M67 with an Expanded Set of Parameters

We create isochrones of M67 using the Yale Rotating Stellar Evolution Code. In addition to metallicity, parameters that are traditionally held fixed, such as the mixing length parameter and initial helium abundance, also vary. The amount of convective overshoot is also changed in different sets of isochrones. Models are constructed both with and without diffusion. From the resulting isochrones that fit the cluster, the age range is between 3.6 and 4.8 Gyr and the distance is between 755 and 868 pc. We also confirm Michaud et al. (2004) claim that M67 can be fit without overshoot if diffusion is included.Comment: 4 pages, 3 figures, to appear in the proceedings of the joint TASC2/KASC9/SPACEINN/HELAS8 conference "Seismology of the Sun and the Distant Stars 2016

Star Formation in the NGC 5846 Group of Galaxies

Environmental interactions in groups and clusters of galaxies are thought to alter the evolution of member galaxies. The goal of this research was to analyze gas and star formation properties of galaxies in the NGC 5846 group. A sample of group galaxies was observed at CTIO (Cerro Tololo Inter-American Observatory in Chile) and KPNO (Kitt Peak National Observatory) using broadband red (R) and narrowband hydrogen emission line (Hα) filters. The images were reduced and analyzed to extract star formation rates and distributions. Neutral hydrogen data from the Arecibo Legacy Fast ALFA (ALFALFA) survey were used to measure the cold neutral gas content, which provides the raw material for star formation. The amounts and extents of star formation in the sample galaxies are compared as a function of cold gas content, galaxy type, and position in the group and compared to those of galaxies located in other environments. Of the NGC 5846 galaxies sampled using the wide-field MOSAIC camera at KPNO, 32% had Hα emission detected. The star-forming galaxies in the NGC 5846 group show a range of star formation rates, with a number that have lower mean star formation rates and gas content compared to isolated galaxies, but also a few that show enhanced star formation. Truncated star formation similar to that of galaxies in the Virgo Cluster is seen in several NGC 5846 galaxies. These results indicate the possibility of environmental interactions in this intermediate density group environment

Changing the νmax⁡\nu_{\max} Scaling Relation: The Need For a Mean Molecular Weight Term

The scaling relations that relate the average asteroseismic parameters $\Delta \nu$ and $\nu_{\max}$ to the global properties of stars are used quite extensively to determine stellar properties. While the $\Delta \nu$ scaling relation has been examined carefully and the deviations from the relation have been well documented, the $\nu_{\max}$ scaling relation has not been examined as extensively. In this paper we examine the $\nu_{\max}$ scaling relation using a set of stellar models constructed to have a wide range of mass, metallicity, and age. We find that as with $\Delta \nu$, $\nu_{\max}$ does not follow the simple scaling relation. The most visible deviation is because of a mean molecular weight term and a $\Gamma_1$ term that are commonly ignored. The remaining deviation is more difficult to address. We find that the influence of the scaling relation errors on asteroseismically derived values of $\log g$ are well within uncertainties. The influence of the errors on mass and radius estimates is small for main sequence and subgiants, but can be quite large for red giants.Comment: 15 pages, 14 figures, accepted for publication in Ap

Spatial and Electronic Correlations in the PE545 Light-Harvesting Complex

The recent discovery of long-lasting quantum coherence effects in photosynthetic pigment-protein complexes has challenged our view of the role that protein motions play in light-harvesting processes. Several groups have suggested that correlated fluctuations involving the pigments site energies and couplings could be at the origin of such unexpected behavior. Here we combine molecular dynamics simulations with quantum mechanics/molecular mechanics calculations to analyze the degree of correlated fluctuations in the PE545 complex of Rhodomonas sp. strain CS24. We find that correlations between the motions of the chromophores, which are significantly assisted by the water solvent, do not translate into appreciable site energy correlations but do lead to significant cross-correlations of energies and couplings. Such behavior, not observed in a recent study on the Fenna-Mathews-Olson complex, seems to provide phycobiliproteins with an additional fundamental mechanism to control quantum coherence and light-harvesting efficiency compared with chlorophyll-containing complexes

Towards an ab initio description of the optical spectra of light-harvesting antennae: application to the CP29 complex of photosystem II.

Only going beyond the static crystal picture through molecular dynamics simulations can a realistic excitonic picture of the light-harvesting complex CP29 be obtained using a multiscale polarizable QM/MM approach

Geometry Optimization in Polarizable QM/MM Models: The Induced Dipole Formulation

We present the mathematical derivation and the computational implementation of the analytical geometry derivatives for a polarizable QM/MM model (QM/MMPol). In the adopted QM/MMPol model, the focused part is treated at QM level of theory, while the remaining part (the environment) is described classically as a set of fixed charges and induced dipoles. The implementation is performed within the ONIOM procedure, resulting in a polarizable embedding scheme, which can be applied to solvated and embedded systems and combined with different polarizable force fields available in the literature. Two test cases characterized by strong hydrogen-bond and dipole-dipole interactions, respectively, are used to validate the method with respect to the nonpolarizable one. Finally, an application to geometry optimization of the chromophore of Rhodopsin is presented to investigate the impact of including mutual polarization between the QM and the classical parts in conjugated systems

Investigating the Metallicity-Mixing Length Relation

Stellar models typically use the mixing length approximation as a way to implement convection in a simplified manner. While conventionally the value of the mixing length parameter, $\alpha$, used is the solar calibrated value, many studies have shown that other values of $\alpha$ are needed to properly model stars. This uncertainty in the value of the mixing length parameter is a major source of error in stellar models and isochrones. Using asteroseismic data, we determine the value of the mixing length parameter required to properly model a set of about 450 stars ranging in $\log g$, $T_{\mathrm{eff}}$, and $\mathrm{[Fe/H]}$. The relationship between the value of $\alpha$ required and the properties of the star is then investigated. For Eddington atmosphere, non-diffusion models, we find that the value of $\alpha$ can be approximated by a linear model, in the form of $\alpha/\alpha_{\odot}=5.426 -0.101 \log (g) -1.071 \log (T_{\mathrm{eff}}) + 0.437 (\mathrm{[Fe/H]})$. This process is repeated using a variety of model physics as well as compared to previous studies and results from 3D convective simulations.Comment: 20 pages, 17 figures, accepted for publication in Ap

Molecular basis of the exciton-phonon interactions in the PE545 light-harvesting complex

Long-lived quantum coherences observed in several photosynthetic pigment-protein complexes at low and at room temperatures have generated a heated debate over the impact that the coupling of electronic excitations to molecular vibrations of the relevant actors (pigments, proteins and solvents) has on the excitation energy transfer process. In this work, we use a combined MD and QM/MMPol strategy to investigate the exciton-phonon interactions in the PE545 light-harvesting complex by computing the spectral densities for each pigment and analyzing their consequences in the exciton dynamics. Insights into the origin of relevant peaks, as well as their differences among individual pigments, are provided by correlating them with normal modes obtained from a quasi-harmonic analysis of the motions sampled by the pigments in the complex. Our results indicate that both the protein and the solvent significantly modulate the intramolecular vibrations of the pigments thus playing an important role in promoting or suppressing certain exciton-phonon interactions. We also find that these low-frequency features are largely smoothed out when the spectral density is averaged over the complex, something difficult to avoid in experiments that underscores the need to combine theory and experiment to understand the origin of quantum coherence in photosynthetic light-harvesting

Asteroseismology of the Hyades with K2: first detection of main-sequence solar-like oscillations in an open cluster

The Hyades open cluster was targeted during Campaign 4 (C4) of the NASA K2 mission, and short-cadence data were collected on a number of cool main-sequence stars. Here, we report results on two F-type stars that show detectable oscillations of a quality that allows asteroseismic analyses to be performed. These are the first ever detections of solar-like oscillations in main-sequence stars in an open cluster.Comment: 12 pages, 8 figures, 2 tables; accepted for publication in MNRA