Browsing by Subject "stars: carbon"

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Discovery of SiCSi in IRC+10216: A Missing Link Between Gas and Dust Carriers of SiC Bonds
(2015-06) Cernicharo, J.; McCarthy, M. C.; Gottlieb, C. A.; Agundez, M.; Prieto, L. V.; Baraban, J. H.; Changala, P. B.; Guelin, M.; Kahane, C.; Martin-Drumel, M. A.; Patel, N. A.; Reilly, N. J.; Stanton, J. F.; Quintana-Lacaci, G.; Thorwirth, S.; Young, K. H.; Stanton, J. F.
We report the discovery in space of a disilicon species, SiCSi, from observations between 80 and 350 GHz with the IRAM 30 m radio telescope. Owing to the close coordination between laboratory experiments and astrophysics, 112 lines have now been detected in the carbon-rich star CW Leo. The derived frequencies yield improved rotational and centrifugal distortion constants up to sixth order. From the line profiles and interferometric maps with the Submillimeter Array, the bulk of the SiCSi emission arises from a region of 6. in radius. The derived abundance is comparable to that of SiC2. As expected from chemical equilibrium calculations, SiCSi and SiC2 are the most abundant species harboring a Si-C bond in the dust Formation zone and certainly both play a key role in the Formation of SiC dust grains.
Do Hydrogen-Deficient Carbon Stars Have Winds?
(2009-06) Geballe, T. R.; Rao, N. Kameswara; Clayton, Geoffrey C.; Rao, N. Kameswara
We present high resolution spectra of the five known hydrogen-deficient carbon (HdC) stars in the vicinity of the 10830 angstrom line of neutral helium. In R Coronae Borealis (RCB) stars the He I line is known to be strong and broad, often with a P Cygni profile, and must be formed in the powerful winds of those stars. RCB stars have similar chemical abundances as HdC stars and also share greatly enhanced O-18 abundances with them, indicating a common origin for these two classes of stars, which has been suggested to be white dwarf mergers. A narrow He I absorption line may be present in the hotter HdC stars, but no line is seen in the cooler stars, and no evidence for a wind is found in any of them. The presence of wind lines in the RCB stars is strongly correlated with dust formation episodes so the absence of wind lines in the HdC stars, which do not make dust, is as expected.
Improved Line Data for the Swan System (Cc)-C-12-C-13 Isotopologue
(2014-03) Ram, Ram S.; Brooke, James S. A.; Bernath, Peter F.; Sneden, Christopher; Lucatello, Sara; Sneden, Christopher
We present new, accurate predictions for rotational line positions, excitation energies, and transition probabilities of the (CC)-C-12-C-13 isotopologue Swan d(3)Pi-a(3)Pi system 0-0, 0-1, 0-2, 1-0, 1-1, 1-2, 2-0, 2-1, and 2-2 vibrational bands. The line positions and energy levels were predicted through new analyses of published laboratory data for the (CC)-C-12-C-13 lines. Transition probabilities were derived from recent computations of transition dipole moments and related quantities. The (CC)-C-12-C-13 line data were combined with similar data for C-12(2), reported in a companion paper, and applied to produce synthetic spectra of carbon-rich metal-poor stars that have strong C-2 Swan bands. The matches between synthesized and observed spectra were used to estimate band head positions for a few of the (CC)-C-12-C-13 vibrational bands and to verify that the new computed line data match observed spectra. The much weaker C-2 lines of the bright red giant Arcturus were also synthesized in the band head regions.
Line Lists for the A(2)Pi-X-2 Sigma(+) (Red) and B-2 Sigma(+)-X-2 Sigma(+) (Violet) Systems of Cn, (Cn)-C-13-N-14, and (Cn)-C-12-N-15, and Application To Astronomical Spectra
(2014-10) Sneden, Christopher; Lucatello, Sara; Ram, Ram S.; Brooke, James S. A.; Bernath, Peter; Sneden, Christopher
New red and violet system line lists for the CN isotopologues (CN)-C-13-N-14 and (CN)-C-12-N-15 have been generated. These new transition data are combined with those previously derived for (CN)-C-12-N-14, and applied to the determination of CNO abundances in the solar photosphere and in four red giant stars: Arcturus, the bright, very low-metallicity star HD 122563, and the carbon-enhanced metal-poor stars HD 196944 and HD 201626. When both red and violet system lines are detectable in a star, their derived N abundances are in good agreement. The mean N abundances determined in this work are also generally in accord with published values.
Neutron-Capture Nucleosynthesis In The First Stars*
(2014-04) Roederer, Ian U.; Preston, George W.; Thompson, Ian B.; Shectman, Stephen A.; Sneden, Christopher; Sneden, Christopher
Recent studies suggest that metal-poor stars enhanced in carbon but containing low levels of neutron-capture elements may have been among the first to incorporate the nucleosynthesis products of the first generation of stars. We have observed 16 stars with enhanced carbon or nitrogen using the MIKE Spectrograph on the Magellan Telescopes at Las Campanas Observatory and the Tull Spectrograph on the Smith Telescope at McDonald Observatory. We present radial velocities, stellar parameters, and detailed abundance patterns for these stars. Strontium, yttrium, zirconium, barium, europium, ytterbium, and other heavy elements are detected. In four stars, these heavy elements appear to have originated in some form of r-process nucleosynthesis. In one star, a partial s-process origin is possible. The origin of the heavy elements in the rest of the sample cannot be determined unambiguously. The presence of elements heavier than the iron group offers further evidence that zero-metallicity rapidly rotating massive stars and pair instability supernovae did not contribute substantial amounts of neutron-capture elements to the regions where the stars in our sample formed. If the carbon-or nitrogen-enhanced metal-poor stars with low levels of neutron-capture elements were enriched by products of zero-metallicity supernovae only, then the presence of these heavy elements indicates that at least one form of neutron-capture reaction operated in some of the first stars.