Wednesday Colloquium



CLOUDY Workshop



"Searching for Y dwarfs at the faint limits of WISE"

Mariusz Gromadzki (Universidad de Valparaíso, Chile)

WISE mission, which was designed to detect the coolest objects, has lead to a breakthrough in the brown dwarfs research. It has found plenty of late T dwarfs and identified first Y dwarfs. We have explored the WISE All-Sky database applying various selection criteria to obtain sample of W2-only detected and low signal-to-noise (S/N≥8) late T and Y dwarf candidates. Spurious sources were removed using database selection criteria defined through analysis of a control sample comprising isolated point-like non-variable non-moving sources from the SDSS. We perform J-band photometric follow-up on 4-8m class telescopes to prove the high proper motion and low temperature of these objects. The low resolution near-IR spectroscopy of the best candidates has confirmed a few late T dwarfs (>T8) and one Y dwarf. Here we will present summary of ground based photometric and spectroscopic follow-up of the candidates.


"Can Novae Make Supernovae? Surprising Connections between Erupting Stars"

Michael Shara (American Museum of Natural History)

Classical novae and supernovae were long thought to be completely separate astrophysical phenomena. This is no longer true; at least some supernovae may have symbiotic nova precursors. I?ll review the current state of knowledge of the temporal evolution of the white dwarfs in novae, and the Tree of Death of Supernovae. These will help illuminate the still-controversial but ultimately testable, hypothesized connection between novae and supernovae.


"Chemical abundances of giants in the S-type symbiotic systems. Clues for the enrichment with Titanium and Zirconium"

Cezary Gałan (NCAC, Warsaw)

The elemental abundances of symbiotic giants are essential to address the role of chemical composition in the evolution of symbiotic binaries, to map their parent population, and to trace their mass transfer history. However, the number of symbiotic giants with fairly well determined photospheric composition is still insufficient for statistical considerations. Until quite recently photospheric chemical compositions were known for few only cases of red giants in the S-type symbiotic systems. In the recent studies we have increased this number by several times, up to nearly 30 giants, making it possible to perform a first attempt of statistical analysis. Our chemical composition measurements were performed with use of high-resolution (R ∼ 50 000), high signalto- noise (S/N), near-IR spectra. Spectrum synthesis analysis employing standard local thermal equilibrium (LTE) and atmosphere models was used to obtain photospheric abundances of CNO and elements around the iron peak (Sc, Ti, Fe, and Ni). Our analysis revealed metallicities distributed in a wide range: from significantly sub-solar to slightly super-solar in several cases, with the largest representation around solar and slightly sub-solar metallicity. The enrichment in 14N isotope found in all these objects, indicates that the giants have experienced the first dredge-up, what is confirmed also by the low 12C/13C ratio, always whenever its measurement was possible. We found that the relative abundance [Ti/Fe] is large in both, the red and the yellow symbiotic systems, what suggests it can be an intrinsic characteristic of all symbiotic giants. It will also be discussed on the s-process enhancement observed in some of these objects, manifesting mainly by Zirconium enrichment, what possibly may be the case of roughly a half of our sample of giants in the S-type symbiotic systems.