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Post Info TOPIC: DY Centauri
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RE: DY Centauri
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Title: On the binary helium star DY Centauri: Chemical composition and evolutionary state
Author: Gajendra Pandey (1), N. Kameswara Rao (1), C. Simon Jeffery (2), David L. Lambert (3) ((1) IIA Bangalore, (2) Armagh Observatory UK, (3) UT Austin Texas)

DY Cen has shown a steady fading of its visual light by about 1 magnitude in the last 40 years suggesting a secular increase in its effective temperature. We have conducted non-LTE and LTE abundance analyses to determine the star's effective temperature, surface gravity, and chemical composition using high-resolution spectra obtained over two decades. The derived stellar parameters for three epochs suggest that DY Cen has evolved at a constant luminosity and has become hotter by about 5000 K in 23 years. We show that the derived abundances remain unchanged for the three epochs. The derived abundances of the key elements, including F and Ne, are as observed for the extreme helium stars resulting from a merger of an He white dwarf with a C-O white dwarf. Thus, DY Cen by chemical composition appears to be also a product of a merger of two white dwarfs. This appearance seems to be at odds with the recent suggestion that DY Cen is a single-lined spectroscopic binary.

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Blobrana


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Title: The hot R Coronae Borealis star DY Centauri is a binary
Authors: N. Kameswara Rao, David L. Lambert, D. A. Garcia-Hernandez, C. Simon Jeffery, Vincent M. Woolf, Barbara McArthur

The remarkable hot R Coronae Borealis star DY Cen is revealed to be the first and only binary system to be found among the R Coronae Borealis (RCB) stars and their likely relatives, including the Extreme Helium stars and the hydrogen-deficient carbon stars. Radial velocity determinations from 1982-2010 have shown DY Cen is a single-lined spectroscopic binary in an eccentric orbit with a period of 39.67 days. It is also one of the hottest and most H-rich member of the class of RCB stars. The system may have evolved from a common-envelope to its current form.

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Blobrana


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Title: High-resolution optical spectroscopy of DY Cen: diffuse interstellar bands in a proto-fullerene circumstellar environment?
Authors: D. A. Garcia-Hernandez, N. Kameswara Rao, David L. Lambert

We search high-resolution and high-quality VLT/UVES optical spectra of the hot R Coronae Borealis (RCB) star DY Cen for electronic transitions of the C60 molecule and diffuse interstellar bands (DIBs). We report the non-detection of the strongest C60 electronic transitions (e.g., those at ~3760, 3980, and 4024 A). Absence of C60 absorption bands may support recent laboratory results, which show that the ~7.0, 8.5, 17.4, and 18.8 um emission features seen in DY Cen - and other similar objects with PAH-like dominated IR spectra - are attributable to proto-fullerenes or fullerene precursors rather than to C60. DIBs towards DY Cen are normal for its reddening; the only exception is the DIB at 6284 A (possibly also the 7223A DIB) that is found to be unusually strong. We also report the detection of a new broad (FWHM~2 A) and unidentified feature centred at ~4000 A. We suggest that this new band may be related to the circumstellar proto-fullerenes seen at infrared wavelengths.

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