| Name: | Sunayana Maben |
| Affiliation: | National Astronomical Observatories, Chinese Academy of Sciences |
| Conference ID : | ASI2024_909 |
| Title : | Investigation of the 70-year-old weak G-band puzzle: carbon-deficient red clump stars are likely merger products |
| Authors : | Sunayana Maben, Bharat Kumar Yerra, Bacham Eswar Reddy, Simon W. Campbell, Gang Zhao |
| Authors Affiliation: | 1 Sunayana Maben, Gang Zhao Affiliation (National Astronomical Observatories, Chinese Academy of Sciences, Beijing -100101, China)
2 Sunayana Maben, Bharat Kumar Yerra, Bacham Eswar Reddy Affiliation (Indian Institute of Astrophysics, Bangalore -560034, India)
3 Simon W. Campbell Affiliation (Monash University, Clayton - 3800, Australia) |
| Mode of Presentation: | Oral |
| Abstract Category : | Stars, Interstellar Medium, and Astrochemistry in Milky Way |
| Abstract : | The weak G-band stars, or carbon-deficient red giants (CDGs), are a rare class of chemically peculiar G and K giants whose low-resolution spectra show very weak or absent G-band absorption of the CH molecule at 4300 Å. High-resolution spectroscopic studies showed that their carbon abundances are under-abundant by about a factor of 20 compared to normal giants, and their nitrogen abundances are enhanced. Almost 70 years after Bidelman's discovery, the number of CDGs in the literature is just 44, and the origin of carbon deficiency remains a puzzle. In this study, we initiated a systematic search for CDGs in large spectroscopic databases, which in turn increased their number in the literature by more than a factor of 3. Survey results conclude that CDGs are rare (<<1% of giants; Maben et al. 2023a). We aimed to better characterize the CDGs by using asteroseismology combined with spectroscopy and astrometry. We identified 15 new CDGs in the Kepler field and found that our CDGs are almost exclusively in the red clump phase (Maben et al. 2023b). Asteroseismic masses revealed that our CDGs are primarily low-mass stars (M ≲ 2 Msun), in contrast to previous studies that suggested they are intermediate mass (2.5–5.0 Msun) based on HRD. The demarcations in chemical patterns and luminosities led us to split them into three groups. We concluded that a merger of a helium white dwarf with a red giant branch star is the most likely scenario for the two groups of over-luminous stars. For the normal-luminosity CDGs, we could not distinguish between core He-flash pollution or lower-mass merger scenarios. The strong bias towards CDGs being Li-rich giants suggests they may be related in some way, so formation scenarios for the CDGs may also apply to the Li-rich giant population (and vice-versa). |
