Stellar Mass Maps for S4G

We present stellar mass maps for the S4G sample based on imaging at 3.6 μm that we correct for the presence of non-stellar emission using an ICA technique. Our dust-free images can be readily converted into stellar mass maps, and this important legacy dataset will be made public through IRSA.

The S4G view of stellar mass, mid-IR dust, and evolved, intermediate-age stars in nearby galaxies

With deep imaging at 3.6 and 4.5 μm where the light in nearby galaxies is dominated by old stars, the Spitzer Survey of Stellar Structure in Nearby Galaxies (S4G) promises to be the ultimate inventory of stellar mass and structure in the local universe. We present results from a novel technique that makes it possible to fully exploit the information contained in these images, pertaining not only to the stellar light (and, ultimately, mass distribution), but also the nature and distribution of the mid-IR dust and the properties of evolved, intermediate age stars (e.g. in AGB-dominated star clusters). We apply Independent Component Analysis (ICA) to the 3.6 and 4.5 μm bands to separate the light from the old stars from the secondary non-stellar (i.e. PAH and hot dust) sources of emission, which are identified via comparison to the non-stellar emission imaged at 8 μm. Then, within the context of age and mass estimation at high z, we extract optical-to-mid-IR SEDs for a sample of ICA-identified AGB-dominated clusters to constrain the typically uncertain fractional contribution of AGB light to the total stellar emission in (rest-frame) NIR bands.

Spectral analyses of late–type [WC] central stars: element abundances of N, Ne and Si

The optical spectra of [WC] central stars of the latest subtypes ([WC11], [WC12]) exhibit not only stellar emission lines of hydrogen (in some cases), helium, carbon and oxygen, but also features of nitrogen (N ii, N iii), neon (Ne i), magnesium (Mg ii), aluminium (Al iii), silicon (Si iii, Si iv) and iron (Fe iii). Some of these features are also visible in the peculiar [WC9]–type object SwSt 1 which has a lower final wind velocity and a smaller wind density than normal [WC9] stars.

Quantitative classification of [WC] nuclei of Planetary Nebulae

We have carried out spectral classification of 65 [WC] stars, using spectra obtained at ESO in 1994-1995 with a spectral resolution of 1500 and high signal to noise ratio. We quantify the visual classification, by using the line ratios of CIII, CIV, OV, OVI in the 530-580 nm range, correlated with the blue CIII - IV lines. We measured the total strength of the above emission lines and derived the ratios of the emission line strengths. Using the stellar emission line ratios we classified about 32 CSPN as [WC] and about 30 as WELS which show only relatively weak CIV 5806 and CIV 4650 and He II 4686 stellar emission lines. The presence of CIV 5806 and the absence of CIII 5696 the WELS appear to belong to the [WC3] type. However the OV lines are very weak or absent. Some stars are reclassified, and 4 stars are found in the [WC5-7] gap. We classified 34 CSPN as [WC]. The [WC2] CSPN NGC 2867 and PB 6 show narrow and weak He II 5412 absorption feature. Based on the relative strengths of the stellar emission features NGC 2867 [WC 2], PB 6 [WC2] and M1-61 [WC4] appear to be related to WELS (Weak Emission Line Central Stars of Planetary Nebulae). The observed spectral characteristics of the central stars of these PN suggest that they are related to [WC] - PG 1159 type of objects.