J/AJ/109/2503 J/AJ/109/2503 Synthesis model in HII regions. II. Y D Mayya Astron. J. 109 2503 1995 1995AJ....109.2503M H II regions Models, evolutionary Tables 3, 4, and 5 are given. Each table has been split into three parts, a, b, and c, where each part includes derived quantities for Initial Mass Functions (IMF) defined by slope, lower cutoff (M_l_), and upper cutoff (M_u_), as follows: part a: slope = 2.5, M_l_ = 1, M_u_ = 60 part b: slope = 3.5, M_l_ = 1, M_u_ = 30 part c: slope = 1.0, M_l_ = 1, M_u_ = 120 Tabulated quantities are smoothed over a period of 0.5Myr to suppress the short term fluctuations on the computer quantities. For the continuous star-formation model, constant star-formation rate (SFR) is assumed in computations of the tabulated quantities. Table 5 give the ages of the young and old bursts for the two-burst models. A stellar population synthesis model, suitable for comparison with Giant Extragalactic H II Regions (GEHRs), is constructed incorporating the recent developments in modeling stellar evolution by Maeder and co-workers and stellar atmospheres by Kurucz. A number of quantities suitable for comparison with broadband data of GEHRs in visible and near-infrared parts of the spectrum are synthesized in addition to the hydrogen and helium ionizing photon production rates at solar metallicities, for three scenarios of star formation - (i) instantaneous burst (IB); (ii) continuous star formation (CSF); and (iii) two bursts of star formation, with the older burst rich in red supergiants. For the IB case, evolution of color indexes shows three distinct phases - an initial steady blue phase, followed by a red bump (5-15Myr) and another steady phase with color indexes intermediate to the earlier two phases. CSF color indexes asymptotically reach peak values at ~10Myr, never reaching the reddest IB color indexes. Ionizing photon production rate falls off by an order of magnitude in 6Myr for IB, whereas it almost remains constant for the CSF model. Two-burst models with burst separations ~10Myr have properties of both IB and CSF, simultaneously producing the red IB color indexes and high ionizing photon rate, making such regions easily distinguishable using optical observations. Flat IMFs result in bluest color indexes when the massive stars are on the main sequence and reddest color indexes during the red supergiant phase of the evolving massive stars. Errors on the computed quantities due to the statistical uncertainties inherent in the process of star formation become negligible for cluster masses in excess of 10^5 M_{sun}_. Our GEHR spectra in the range 200nm to 3um are found to be in good agreement with the computations of Mas-Hesse & Kunth (1991A&AS...88..399M)

Age Age of the cluster Myr M/L Ratio of total mass to bolometric lum. solMass/solLum M/Lv Ratio of total mass to visual luminosity solMass/solLum NLy Lyman continuum photon production rate per unit mass of the cluster ph/s/solMass fHe Fraction of hydrogen ionizing photons which are capable of ionizing helium --- Phi/Lb Ratio of expected Hbeta to blue band luminosity number=1 Lyman continuum photon rate N_L_ is also expressed in units or expected Hbeta luminosity {phi} from a nebula at 10,000K, and defined as: {phi}=4.78x10^-13^N_L_. {phi} in this equation has dimensions or erg/s/M_{sun}_, and N_L_ in ph/s/M_{sun}_. --- B-V B-V color index mag V-R V-R color index mag V-I V-I color index mag J-H J-H color index mag H-K H-K color index mag V-K V-K color index mag WHb Hbeta equivalent width number=2 Equivalent widths assuming a gas temperature of 10,000K. 0.1nm WHa Halpha equivalent width number=2 Equivalent widths assuming a gas temperature of 10,000K. 0.1nm T(yng) Age of the younger burst Myr T(old) Age of the older burst Myr M/L Ratio of total mass to bolometric lum. solMass/solLum M/Lv Ratio of total mass to visual luminosity solMass/solLum NLy Lyman continuum photon production rate per unit mass of the cluster ph/s/solMass fHe Fraction of hydrogen ionizing photons which are capable of ionizing helium --- Phi/Lb Ratio of expected Hbeta to blue band lum.(1) --- B-V B-V color index mag V-R V-R color index mag V-I V-I color index mag J-H J-H color index mag H-K H-K color index mag V-K V-K color index mag WHb Hbeta emission line equivalent width number=2 Equivalent widths assuming a gas temperature of 10,000K. 0.1nm WHa Halpha emission line equivalent width number=2 Equivalent widths assuming a gas temperature of 10,000K. 0.1nm CDS 1996Jan09AAS CD-ROM series, Vol. 5, 1995 Lee Brotzman [ADS] 19-Jul-1995 J_AJ_109_2503.xml