USAAAO 2026, I кръг — Задача 28
USAAAO 2026 - First Round · 9 февруари 2026 г.
Problem writers
Problem writers: Srihari (Hari) Balaji, Vincent Bian, Ferdinand, Hagan Hensley, Elizabeth Lee, Joe McCarty, Lucas Pinheiro, Feodor Yevtushenko
Условие
Below is an HR diagram for a globular cluster from Gaia DR3 data:
The figure has labeled regions: “A”, “B”, “C”, and “D”. 1) Identify the region where stars undergo hydrogen burning in their cores. 2) Identify the region where stars experience Helium flash.
(a) 1. Region A; 2. Region B
(b) 1. Region A; 2. Region C
(c) 1. Region B; 2. Region C
(d) 1. Region B; 2. Region D
(e) 1. Region C; 2. Region D
Отговори
- B
Решение
Solution: For the labeled regions:
(1) Region A is the Main Sequence phase, where stars undergo hydrogen fusion in their core.
(2) Region B is the Red Giant Branch, where stars undergo hydrogen burning in their shell. (No burning in their core)
(3) Region C is the tip of the Red Giant Branch, and for low-mass stars, they typically experience Helium flash here. The Helium flash indicates the first time of Helium burning in the core of low-mass stars.
(4) Region D is the Horizontal Branch, where stars undergo helium fusion in their core and hydrogen shell burning.
So, region A and C is the most appropriate.
Answer: B
Оригинал в Архива: usaaao_first_exam_2026.pdf · официални решения: usaaao_first_exam_solutions_2026.pdf