Realistic ionizing fluxes for young stellar populations from 0.05 to 2 Z

By Linda J. Smith, R. Norris, P. Crowther. 2002

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We present a new grid of ionizing fluxes for O and Wolf‐Rayet (W‐R) stars for use with evolutionary synthesis codes and single-star H II region analyses. A total of 230 expanding, non-LTE, line-blanketed model atmospheres have been calculated for five metallicities (0.05, 0.2, 0.4, 1 and 2 Z� ) using the WM-BASIC code of Pauldrach, Hoffmann & Lennon for O stars and the CMFGEN code of Hillier & Miller for W‐R stars. The stellar wind parameters are scaled with metallicity for both O and W‐R stars. We compare the ionizing fluxes of the new models with the CoStar models of Schaerer & de Koter and the pure helium W‐R models of Schmutz, Leitherer & Gruenwald. We find significant differences, particularly above 54 eV, where the emergent flux is determined by the wind density as a function of metallicity. The new models have lower ionizing fluxes in the He I continuum with important implications for nebular line ratios. We incorporate the new models into the evolutionary synthesis code STARBURST99 and compare the ionizing outputs for an instantaneous burst and continuous star formation with the work of Schaerer & Vacca (SV98), and Leitherer et al. The changes in the output ionizing fluxes as a function of age are dramatic. We find that, in contrast to previous studies, nebular He II λ4686 will be at, or just below, the detection limit in low metallicity starbursts during

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c24cec7ba07d9164c2a7f99281d5360d75debb57

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Citations in the corpus

EXTRAGALACTIC CHEMICAL ABUNDANCES: DO H ii REGIONS AND YOUNG STARS TELL THE SAME STORY? THE CASE OF THE SPIRAL GALAXY NGC 300 (2009, background): “Population synthesis models that include line-blanketed atmospheres for O stars and an improved treatment of the ionizing output of W-R stars are able to reproduce the empirical radiation softening (Smith et al. 2002).”
A CLASS I AND CLASS II CH3OH MASER SURVEY OF EGOs FROM THE GLIMPSE SURVEY (2009, unknown): “5 (Smith et al. 2002).”
Nebular Continuum and Line Emission in Stellar Population Synthesis Models (2016, methodology): “The Wolf–Rayet (WR) stellar spectra are from M. Ng et al. (2017, private communication) using WMBasic (Pauldrach et al. 2001), and the O-star spectra are from Smith et al. (2002) using CMFGEN (Hillier & Lanz 2001).”
The chemical composition of metal-poor emission-line galaxies in the Data Release 3 of the Sloan Digital Sky Survey (2005, methodology): “These sequences are defined as in Stasińska & Izotov (2003), but have been recomputed with the new atomic data, and with an input radiation field computed with Starburst 99 (Leitherer et al. , 1999) using the stellar model atmospheres described in Smith et al. (2002).”
SPITZER SAGE INFRARED PHOTOMETRY OF MASSIVE STARS IN THE LARGE MAGELLANIC CLOUD (2009, methodology): “Generic CMFGEN models (Smith et al. 2002) are shown for the other four WR stars: a WN 85 kK model for BAT99-1 (WN3b) and a WN 45 kK model for the remaining WNL stars, all of which show excess above that predicted by the models.”
TOWARD A UNIFICATION OF STAR FORMATION RATE DETERMINATIONS IN THE MILKY WAY AND OTHER GALAXIES (2011, methodology): “We stress that these systematic issues are not mutually exclusive, and we cannot rule out additional contributions from the O star models themselves (Smith et al. 2002; Martins et al. 2005) and runaway O stars.”
Star Formation in the Milky Way and Nearby Galaxies (2012, methodology): “These have been estimated by several authors using evolutionary synthesis models (e.g., Smith et al. 2002; Raiter et al. 2010), but the precise dependences are sensitive to the details of the input stellar models, in particular how effects of stellar rotation are modelled.”
Modeling the Pan-Spectral Energy Distribution of Starburst Galaxies. IV. The Controlling Parameters of the Starburst SED (2007, methodology): “A detailed description of latest stellar atmospheres and stellar evolution physics used within the code are given in Smith et al. (2002) and Vázquez & Leitherer (2005).”
Grids of model spectra for WN stars, ready for use (2004, result): “We compared these numbers with the WN model series published by Smith et al. (2002).”
Binary Population and Spectral Synthesis Version 2.1: Construction, Observational Verification, and New Results (2017, methodology): “1 models, we have created new WM-BASIC (Pauldrach et al. 1998) models based upon the grid determined by Smith et al. (2002).”
Stellar and wind properties of massive stars in the central parsec of the Galaxy (2006, methodology): “…ionisation flux delivered by this population we used the following approach: for the WC9 stars not analysed here, we adopted the ionising fluxes of Smith et al. (2002) using their model WC number 3; for the 2 Ofpe/WN9 stars IRS16NE and IRS16SW, we adopted the parameters of IRS16C; for the WN7…”
Fitting the integrated spectral energy distributions of galaxies (2010, background): “…tracks, stellar libraries have improved significantly in recent years, with both fully theoretical (e.g. Kurucz 1992; Westera et al. 2002; Smith et al. 2002; Coelho et al. 2005; Martins et al. 2005; Lançon et al. 2007) and empirical, e.g. STELIB (Le Borgne et al. 2003), MILES…”
A new calibration of stellar parameters of Galactic O stars (2005, methodology): “Smith et al. (2002) computed new ionisation fluxes for O stars using WM-BASIC (Pauldrach et al. 2001).”