Identification of a Class of Low-mass Asymptotic Giant Branch Stars Struggling to Become Carbon Stars in the Magellanic Clouds
Abstract
We have identified a new class of Asymptotic Giant Branch (AGB) stars in the Small and Large Magellanic Clouds (SMC/LMC) using optical to infrared photometry, light curves, and optical spectroscopy. The strong dust production and long-period pulsations of these stars indicate that they are at the very end of their AGB evolution. Period-mass-radius relations for the fundamental-mode pulsators give median current stellar masses of 1.14{M}⊙ in the LMC and 0.94{M}⊙ in the SMC (with dispersions of 0.21 and 0.18 {M}⊙ , respectively), and models suggest initial masses of <1.5 {M}⊙ and <1.25 {M}⊙ , respectively. This new class of stars includes both O-rich and C-rich chemistries, placing the limit where dredge-up allows carbon star production below these masses. A high fraction of the brightest among them should show S star characteristics indicative of atmospheric C/O ≈ 1, and many will form O-rich dust prior to their C-rich phase. These stars can be separated from their less-evolved counterparts by their characteristically red J-[8] colors.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2015
- DOI:
- arXiv:
- arXiv:1507.07003
- Bibcode:
- 2015ApJ...810..116B
- Keywords:
-
- infrared: stars;
- Magellanic Clouds;
- stars: AGB and post-AGB;
- stars: low-mass;
- stars: variables: general;
- stars: winds;
- outflows;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 16 pages, 18 figures, accepted for publication in ApJ