This investigation presents a set of transformations to Johnson BÀV, Cousins VÀR, and Cousins VÀI, as well as bolometric corrections to V, for [Fe/H] = À3, À2, À1, À0.5, 0.0, and +0.3 and, in each case, values of log g from À0.5 to 5.0 for 3000 K T eff 5500 K and from 2.0 to 5.0 for 6000 K T eff 40,000 K. These transformations employ the predictions from Kurucz model atmospheres at high temperatures (T eff ! 8000 K) and from MARCS model atmospheres at intermediate temperatures (from 7000 K down to a temperature in the range 4000 K T eff 5500 K, depending on [Fe/H], where adjustments to satisfy observational constraints become necessary). Thus, theoretical color-T eff relations are used exclusively down to a minimum temperature that is cooler than the temperatures of turnoff stars in open and globular star clusters. To better represent the color transformations obeyed by cool stars (down to 3000 K), corrections to the synthetic transformations have been determined from a careful consideration of observations for a few globular clusters (M92, M68, and 47 Tucanae), the color-magnitude diagrams (CMDs) of several open clusters (M67, the Pleiades, the Hyades, and NGC 6791), the CMDs and mass-luminosity diagram for solar neighborhood stars having good distance measurements from Hipparcos, empirical (BÀV )-T eff and (VÀK)-T eff relations, and color-color diagrams for field giants. The semiempirical color transformations that have been produced as a result of our analysis are also compared with several others that have been published in recent years: some of the deficiencies of the latter are revealed.

SN 2007od exhibits characteristics that have rarely been seen in a Type IIP supernova (SN). Optical V-band photometry reveals a very steep brightness decline between the plateau and nebular phases of ∼4.5 mag, likely due to SN 2007od containing a low mass of 56 Ni. The optical spectra show an evolution from normal Type IIP with broad Hα emission, to a complex, four-component Hα emission profile exhibiting asymmetries caused by dust extinction after day 232. This is similar to the spectral evolution of the Type IIn SN 1998S, although no early-time narrow (∼200 km s −1 ) Hα component was present in SN 2007od. In both SNe, the intermediate-width Hα emission components are thought to arise in the interaction between the ejecta and its circumstellar medium (CSM). SN 2007od also shows a mid-infrared excess due to new dust. The evolution of the Hα profile and the presence of the mid-IR excess provide strong evidence that SN 2007od formed new dust before day 232. Late-time observations reveal a flattening of the visible light curve. This flattening is a strong indication of the presence of a light echo, which likely accounts for much of the broad, underlying Hα component seen at late times. We believe that the multi-peaked Hα emission is consistent with the interaction of the ejecta with a circumstellar ring or torus (for the inner components at ±1500 km s −1 ) and a single blob or cloud of circumstellar material out of the plane of the CSM ring (for the outer component at −5000 km s −1 ). The most probable location for the formation of new dust is in the cool dense shell created by the interaction between the expanding ejecta and its CSM. Monte Carlo radiative transfer modeling of the dust emission from SN 2007od implies that up to ∼4 × 10 −4 M of new dust has formed. This is similar to the amounts of dust formed in other core-collapse supernovae such as SNe 1999em, 2004et, and 2006jc.

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SN 2010jl was an extremely bright, Type IIn SNe which showed a significant IR excess no later than 90 days after explosion. We have obtained Spitzer 3.6 and 4.5 µm and JHK observations of SN 2010jl ∼90 days post explosion. Little to no reddening in the host galaxy indicated that the circumstellar material lost from the progenitor must lie in a torus inclined out of the plane of the sky. The likely cause of the high mid-IR flux is the reprocessing of the initial flash of the SN by pre-existing circumstellar dust. Using a 3D Monte Carlo Radiative Transfer code, we have estimated that between 0.03-0.35 M ⊙ of dust exists in a circumstellar torus around the SN located 6 × 10 17 cm away from the SN and inclined between 60-80 • to the plane of the sky. On day 90, we are only seeing the illumination of approximately 5% of this torus, and expect to see an elevated IR flux from this material up until day ∼ 450. It is likely this dust was created in an LBV-like mass loss event of more than 3 M ⊙ , which is large but consistent with other LBV progenitors such as η Carinae.

A new grid of theoretical color indices for the Strömgren uvby photometric system has been derived from MARCS model atmospheres and SSG synthetic spectra for cool dwarf and giant stars having À3:0 ½Fe=H þ0:5 and 3000 T eA 8000 K. At warmer temperatures (i.e., 8000 < T eA 40; 000 K), this grid has been supplemented with the synthetic uvby colors from recent Kurucz atmospheric models without overshooting (Castelli, Gratton, & Kurucz, published in 1997). Our transformations appear to reproduce the observed colors of extremely metal-poor turnoff and giant stars: the various uvby color-magnitude diagrams (CMDs) for the ½Fe=H $ À2:2 globular cluster M92 can be matched exceedingly well down to M V % 6 by the same isochrone that provides a very good fit to published BV data (see Paper I), on the assumption of the same distance and reddening. Due to a number of assumptions made in the synthetic color calculations, however, our color-T eff relations for cool stars fail to provide a suitable match to the uvby photometry of both cluster and field stars having ½Fe=H > À2:0. To overcome this problem, the theoretical indices at intermediate and high metallicities have been corrected using a set of color calibrations based on field stars having well-determined distances from Hipparcos, accurate T eff estimates from the infrared flux method, and spectroscopic [Fe/H] values. In contrast with Paper I, star clusters played only a minor role in this analysis in that they provided a supplementary constraint on the color corrections for cool dwarf stars with T eA 5500 K. They were mainly used to test the color-T eff relations and, encouragingly, isochrones that employ the transformations derived in this study are able to reproduce the observed CMDs (involving uÀv, vÀb, and bÀy colors) for a number of open and globular clusters (including M67, the Hyades, and 47 Tuc) rather well. Moreover, our interpretations of such data are very similar, if not identical, with those given in Paper I from a consideration of BV(RI ) C observations for the same clusters-which provides a compelling argument in support of the color-T eff relations that are reported in both studies. In the present investigation, we have also analyzed the observed Strömgren photometry for the classic Population II subdwarfs, compared our ''final'' (bÀy)-T eff relationship with those derived empirically in a number of recent studies and examined in some detail the dependence of the m 1 index on [Fe/ H].