This is the first of a series of papers presenting the Modules for Experiments in Stellar Astrophysics (MESA) Isochrones and Stellar Tracks (MIST) project, a new comprehensive set of stellar evolutionary tracks and isochrones computed using MESA, a state-of-the-art open-source 1D stellar evolution package. In this work, we present models with solar-scaled abundance ratios covering a wide range of ages (5 ≤ log(Age) [yr] ≤ 10.3), masses (0.1 ≤ M/M ≤ 300), and metallicities (−2.0 ≤ [Z/H] ≤ 0.5). The models are self-consistently and continuously evolved from the pre-main sequence (PMS) to the end of hydrogen burning, the white dwarf cooling sequence, or the end of carbon burning, depending on the initial mass. We also provide a grid of models evolved from the PMS to the end of core helium burning for −4.0 ≤ [Z/H] < −2.0. We showcase extensive comparisons with observational constraints as well as with some of the most widely used existing models in the literature. The evolutionary tracks and isochrones can be downloaded from the project website at http://waps.cfa.harvard.edu/MIST/.We import the nuclear reaction rates directly from the JINA REACLIB database, 9 a compilation of the latest reaction rates in the literature (Cyburt et al. 2010). For example, the 15 N(p,α) 12 C reaction rate comes from Angulo et al. (1999), while the triple-α reaction rate comes from Fynbo et al. (2005). We use the JINA reaction rates for p-p chains, cold and hot CNO cycles, triple-α process, α-capture up to 32 S, Ne-Na and Mg-Al cycles, and C/O burning. We adopt the mesa_49.net nuclear network in MESA.The nuclear network tracks and solves for the abundances of the following 52 species: n, 1 H, 2 H

We measure star formation rates of ~50,000 optically-selected galaxies in the local universe (z~0.1), spanning a range from gas-rich dwarfs to massive ellipticals. We obtain dust-corrected SFRs by fitting the GALEX (UV) and SDSS (optical) photometry to a library of population synthesis models that include dust attenuation. For star-forming galaxies, our UV-based SFRs compare remarkably well with those derived from SDSS H alpha. Deviations from perfect agreement between these two methods are due to differences in the dust attenuation estimates. In contrast to H alpha, UV provides reliable SFRs for galaxies with weak or no H alpha emission, and where H alpha is contaminated with an emission from an AGN. We use full-SED SFRs to calibrate a simple prescription that uses GALEX UV magnitudes to produce good SFRs for normal star-forming galaxies. The specific SFR is considered as a function of stellar mass for (1) star-forming galaxies with no AGN, (2) those hosting an AGN, and for (3) galaxies without H alpha emission. We find that the three have distinct star formation histories, with AGN lying intermediate between the star-forming and the quiescent galaxies. Normal star forming galaxies (without an AGN) lie on a relatively narrow linear sequence. Remarkably, galaxies hosting a strong AGN appear to represent the massive continuation of this sequence. Weak AGN, while also massive, have lower SFR, sometimes extending to the realm of quiescent galaxies. We propose an evolutionary sequence for massive galaxies that smoothly connects normal star-forming galaxies to quiescent (red sequence) galaxies via strong and weak AGN. We confirm that some galaxies with no H alpha emission show signs of SF in the UV. We derive a UV-based cosmic SFR density at z=0.1 with smaller total error than previous measurements (abridged).Comment: Accepted for publication in ApJ (Special GALEX Supplement issue - Dec 2007). v2: Typo in Eq. 2 correcte

We combine Hα emission-line and infrared continuum measurements of two samples of nearby galaxies to derive dust attenuation-corrected star formation rates (SFRs). We use a simple energy balance based method that has been applied previously to HII regions in the Spitzer Infrared Nearby Galaxies Survey (SINGS), and extend the methodology to integrated measurements of galaxies. We find that our composite Hα + IR based SFRs are in excellent agreement with attenuation-corrected SFRs derived from integrated spectrophotometry, over the full range of SFRs (0.01 -80 M ⊙ yr −1 ) and attenuations (0 -2.5 mag) studied. We find that the combination of Hα and total infrared luminosities provides the most robust SFR measurements, but combinations of Hα measurements with monochromatic luminosities at 24 µm and 8 µm perform nearly as well. The calibrations differ significantly from those obtained for HII regions (Calzetti et al. 2007), with the difference attributable to a more evolved population of stars heating the dust. Our results are consistent with a significant component of diffuse dust (the 'IR cirrus' component) that is heated by a non-star-forming -2population. The same methodology can be applied to [O II]λ3727 emissionline measurements, and the radio continuum fluxes of galaxies can be applied in place of IR fluxes when the latter are not available. We assess the precision and systematic reliability of all of these composite methods.-4 -The advent of large sets of multi-wavelength observations of nearby galaxies now provides us with the opportunity to derive attenuation-corrected Hα and UV continuum luminosities of galaxies by combining these fluxes with various components of the IR emission. Moreover the availability of integrated optical spectra (and in some cases Pa α maps) of the same galaxies allows us to derive additional attenuation estimates, and test the precision and systematic reliability of the respective attenuation-corrected SFR measurements.The Spitzer Infrared Nearby Galaxies Survey (SINGS; Kennicutt et al. 2003) offers an ideal dataset for testing and calibrating such multi-wavelength SFR estimators. The survey includes imaging of a diverse sample of 75 galaxies within 30 Mpc, with wavelength coverage extending from the UV to the radio, including ultraviolet imaging at 150 and 230 nm, Hα, and 7 infrared wavelengths over 3.6 -160 µm. In addition, drift-scanned spectra over the wavelength range 3600 -6900Å are available, which complement matching infrared spectra over the range 10 -40 µm. We first applied these data to calibrate and test the combined use of Hα and 24 µm infrared fluxes of individual HII regions to derive attenuation-corrected emission-line fluxes (Calzetti et al. 2007, hereafter denoted C07;Kennicutt et al. 2007;Prescott et al. 2007). These studies revealed that the Spitzer 24 µm sources were highly correlated in position and flux with those of optical HII region counterparts. Kennicutt et al. (2007) and C07 found that the ratio of 24 µm to Hα fluxes yielded attenuation-corrected Hα lum...

We present new calibrations of far-ultraviolet (FUV) attenuation as derived from the total infrared to FUV luminosity ratio (IRX) and the FUV-NUV color. We find that the IRX-corrected FUV luminosities are tightly and linearly correlated with the attenuation-corrected Hα luminosities (as measured from the Balmer decrement), with a rms scatter of ±0.09 dex. The ratios of these attenuation-corrected FUV to Hα luminosities are consistent with evolutionary synthesis model predictions, assuming a constant star formation rate over 100 Myr, solar metallicity and either a Salpeter or a Kroupa IMF with lower and upper mass limits of 0.1 and 100M ⊙ . The IRX-corrected FUV to Balmer-corrected Hα luminosity ratios do not show any trend with other galactic properties over the ranges covered by our sample objects. In contrast, FUV attenuation derived from the FUV-NUV color (UV spectral slope) show much larger random and systematic uncertainties. When compared to either Balmercorrected Hα luminosities or IRX-corrected FUV luminosities the color-corrected FUV luminosities show ∼ 2.5 times larger rms scatter, and systematic nonlinear deviations as functions of luminosity and other parameters. Linear combinations of 25µm and 1.4GHz radio continuum luminosities with the observed FUV luminosities are also well correlated with the Balmer-corrected Hα luminosities. These results provide useful prescriptions for deriving attenuation-corrected star

Using a complete sample of ∼300 star-forming galaxies within 11 Mpc of the Milky Way, we evaluate the consistency between star formation rates (SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum and Hα nebular emission, assuming standard conversion recipes in which the SFR scales linearly with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders of magnitude, down to ultra-low activities on the order of ∼10 −4 M yr −1 . The data are drawn from the 11 Mpc Hα and Ultraviolet Galaxy Survey (11HUGS), which has obtained Hα fluxes from ground-based narrowband imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies (SFR ∼ 1 M yr −1 ), our results are consistent with previous work which has shown that FUV SFRs tend to be lower than Hα SFRs before accounting for internal dust attenuation, but that there is relative consistency between the two tracers after proper corrections are applied. However, a puzzle is encountered at the faint end of the luminosity function. As lower luminosity dwarf galaxies, roughly less active than the Small Magellanic Cloud, are examined, Hα tends to increasingly underpredict the total SFR relative to the FUV. The trend is evident prior to corrections for dust attenuation, which affects the FUV more than the nebular Hα emission, so this general conclusion is robust to the effects of dust. Although past studies have suggested similar trends, this is the first time this effect is probed with a statistical sample for galaxies with SFR 0.1 M yr −1 . By SFR ∼ 0.003 M yr −1 , the average Hα-to-FUV flux ratio is lower than expected by a factor of two, and at the lowest SFRs probed, the ratio exhibits an order of magnitude discrepancy for the handful of galaxies that remain in the sample. A range of standard explanations does not appear to be able to fully account for the magnitude of the systematic. Some recent work has argued for a stellar initial mass function which is deficient in high-mass stars in dwarf and low surface brightness galaxies, and we also consider this scenario. Under the assumption that the FUV traces the SFR in dwarf galaxies more robustly, the prescription relating Hα luminosity to SFR is re-calibrated for use in the low SFR regime when FUV data are not available.