Abstract
Carbon-deficient red giants (CDRGs) are a rare class of peculiar red giants, also called "weak G-band" or "weak CH" stars. Their atmospheric compositions show depleted carbon, a low isotopic ratio, and an overabundance of nitrogen, indicating that the material at the surface has undergone CN-cycle hydrogen burning. I present Strömgren uvby photometry of nearly all known CDRGs. Barium stars, having an enhanced carbon abundance, exhibit the "Bond-Neff effect" - a broad depression in their energy distributions at ∼4000 Å, recently confirmed to be due to the CH molecule. This gives Ba ii stars unusually low Strömgren c 1 photometric indices. I show that CDRGs, lacking CH absorption, exhibit an "anti-Bond-Neff effect" - higher c 1 indices than normal red giants. Using precise parallaxes from Gaia DR2, I plot CDRGs in the color-magnitude diagram (CMD) and compare them with theoretical evolution tracks. Most CDRGs lie in a fairly tight clump in the CMD, indicating initial masses in the range ∼2-3.5, M⊙, if they have evolved as single stars. It is unclear whether they are stars that have just reached the base of the red-giant branch and the first dredge-up of CN-processed material, or are more highly evolved helium-burning stars in the red-giant clump. About 10% of CDRGs have higher masses of ∼4-4.5, M&odot:, and exhibit unusually high rotational velocities. I show that CDRGs lie at systematically larger distances from the Galactic plane than normal giants, possibly indicating a role of binary mass transfer and mergers. CDRGs continue to present a major puzzle for our understanding of stellar evolution.
Original language | English (US) |
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Article number | 12 |
Journal | Astrophysical Journal |
Volume | 887 |
Issue number | 1 |
DOIs | |
State | Published - Dec 10 2019 |
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- Space and Planetary Science
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Carbon-deficient Red Giants. / Bond, Howard E.
In: Astrophysical Journal, Vol. 887, No. 1, 12, 10.12.2019.Research output: Contribution to journal › Article › peer-review
TY - JOUR
T1 - Carbon-deficient Red Giants
AU - Bond, Howard E.
N1 - Funding Information: Howard E. Bond Howard E. Bond Department of Astronomy & Astrophysics, Pennsylvania State University, University Park, PA 16802, USA Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA Visiting astronomer, Cerro Tololo Inter-American Observatory and Kitt Peak National Observatory, National Optical Astronomy Observatory, which are operated by the Association of Universities for Research in Astronomy under a cooperative agreement with the National Science Foundation. Howard E. Bond 2019-12-10 2019-12-05 09:33:50 cgi/release: Article released bin/incoming: New from .zip Penn State University Grant return of overhead funds yes Carbon-deficient red giants (CDRGs) are a rare class of peculiar red giants, also called “weak G-band” or “weak CH” stars. Their atmospheric compositions show depleted carbon, a low isotopic ratio, and an overabundance of nitrogen, indicating that the material at the surface has undergone CN-cycle hydrogen burning. I present Str�mgren uvby photometry of nearly all known CDRGs. Barium stars, having an enhanced carbon abundance, exhibit the “Bond–Neff effect”—a broad depression in their energy distributions at ∼4000�Å, recently confirmed to be due to the CH molecule. This gives Ba ii stars unusually low Str�mgren c 1 photometric indices. I show that CDRGs, lacking CH absorption, exhibit an “anti-Bond–Neff effect”—higher c 1 indices than normal red giants. Using precise parallaxes from Gaia DR2, I plot CDRGs in the color–magnitude diagram (CMD) and compare them with theoretical evolution tracks. Most CDRGs lie in a fairly tight clump in the CMD, indicating initial masses in the range ∼2– , if they have evolved as single stars. It is unclear whether they are stars that have just reached the base of the red-giant branch and the first dredge-up of CN-processed material, or are more highly evolved helium-burning stars in the red-giant clump. About 10% of CDRGs have higher masses of ∼4– , and exhibit unusually high rotational velocities. I show that CDRGs lie at systematically larger distances from the Galactic plane than normal giants, possibly indicating a role of binary mass transfer and mergers. CDRGs continue to present a major puzzle for our understanding of stellar evolution. � 2019. The American Astronomical Society. All rights reserved. Adamczak J. and Lambert D. L. 2013 ApJ 765 155 (AL13) 10.1088/0004-637X/765/2/155 Adamczak J. and Lambert D. L. ApJ 0004-637X 765 2 155 2013 155 Adams W. S., Joy A. H., Humason M. L. et al 1935 ApJ 81 187 10.1086/143628 Adams W. S., Joy A. H., Humason M. 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PY - 2019/12/10
Y1 - 2019/12/10
N2 - Carbon-deficient red giants (CDRGs) are a rare class of peculiar red giants, also called "weak G-band" or "weak CH" stars. Their atmospheric compositions show depleted carbon, a low isotopic ratio, and an overabundance of nitrogen, indicating that the material at the surface has undergone CN-cycle hydrogen burning. I present Strömgren uvby photometry of nearly all known CDRGs. Barium stars, having an enhanced carbon abundance, exhibit the "Bond-Neff effect" - a broad depression in their energy distributions at ∼4000 Å, recently confirmed to be due to the CH molecule. This gives Ba ii stars unusually low Strömgren c 1 photometric indices. I show that CDRGs, lacking CH absorption, exhibit an "anti-Bond-Neff effect" - higher c 1 indices than normal red giants. Using precise parallaxes from Gaia DR2, I plot CDRGs in the color-magnitude diagram (CMD) and compare them with theoretical evolution tracks. Most CDRGs lie in a fairly tight clump in the CMD, indicating initial masses in the range ∼2-3.5, M⊙, if they have evolved as single stars. It is unclear whether they are stars that have just reached the base of the red-giant branch and the first dredge-up of CN-processed material, or are more highly evolved helium-burning stars in the red-giant clump. About 10% of CDRGs have higher masses of ∼4-4.5, M&odot:, and exhibit unusually high rotational velocities. I show that CDRGs lie at systematically larger distances from the Galactic plane than normal giants, possibly indicating a role of binary mass transfer and mergers. CDRGs continue to present a major puzzle for our understanding of stellar evolution.
AB - Carbon-deficient red giants (CDRGs) are a rare class of peculiar red giants, also called "weak G-band" or "weak CH" stars. Their atmospheric compositions show depleted carbon, a low isotopic ratio, and an overabundance of nitrogen, indicating that the material at the surface has undergone CN-cycle hydrogen burning. I present Strömgren uvby photometry of nearly all known CDRGs. Barium stars, having an enhanced carbon abundance, exhibit the "Bond-Neff effect" - a broad depression in their energy distributions at ∼4000 Å, recently confirmed to be due to the CH molecule. This gives Ba ii stars unusually low Strömgren c 1 photometric indices. I show that CDRGs, lacking CH absorption, exhibit an "anti-Bond-Neff effect" - higher c 1 indices than normal red giants. Using precise parallaxes from Gaia DR2, I plot CDRGs in the color-magnitude diagram (CMD) and compare them with theoretical evolution tracks. Most CDRGs lie in a fairly tight clump in the CMD, indicating initial masses in the range ∼2-3.5, M⊙, if they have evolved as single stars. It is unclear whether they are stars that have just reached the base of the red-giant branch and the first dredge-up of CN-processed material, or are more highly evolved helium-burning stars in the red-giant clump. About 10% of CDRGs have higher masses of ∼4-4.5, M&odot:, and exhibit unusually high rotational velocities. I show that CDRGs lie at systematically larger distances from the Galactic plane than normal giants, possibly indicating a role of binary mass transfer and mergers. CDRGs continue to present a major puzzle for our understanding of stellar evolution.
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U2 - 10.3847/1538-4357/ab4e13
DO - 10.3847/1538-4357/ab4e13
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AN - SCOPUS:85077321276
VL - 887
JO - Astrophysical Journal
JF - Astrophysical Journal
SN - 0004-637X
IS - 1
M1 - 12
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