Thành phần của Mặt Trời gồm hydro (khoảng 74% khối lượng, hay 92% thể tích), heli (khoảng 24% khối lượng, 7% thể tích), và một lượng nhỏ các nguyên tố khác, gồm sắt, nickel, oxy, silic, lưu huỳnh, magiê, carbon, neon, canxi, và crom.[ | Do Active Regions Modify Oscillation Frequencies 377 few tiles with positive frequency shifts that have no counterparts in the MAI image implying a weaker agreement. To estimate how well we can associate the locations of active regions as locations of frequency shifts we calculate the Pearson s correlation coefficient rp between the shifts and MAI for each of the three ring-days. These are found to be and and and for CR 2009 and 2058 respectively and confirms that the correlation between shifts and the surface magnetic activity during the two activity periods are significantly different. This result is consistent with the recent findings inferred from global modes Jain et al. 2009 . Thus the argument that the solar-cycle variations in the global mode frequencies are due to global averaging of the local effect of active regions Hindman et al. 2001 is only partially supported by our analysis. We believe that the weak component of the magnetic field for example ubiquitous horizontal field or turbulent field must be taken into account to fully explain the frequency shifts particularly during the minimal-activity phase of the solar cycle. Acknowledgment We thank John Leibacher for a critical reading of the manuscript. This research was supported in part by NASA grants NNG 05HL41I and NNG 08EI54I. This work utilizes data obtained by the Global Oscillation Network Group program managed by the National Solar Observatory which is operated by AURA Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory High Altitude Observatory Learmonth Solar Observatory Udaipur Solar Observatory Instituto de Astrofisica de Canarias and Cerro Tololo Interamerican Observatory. This work also utilizes 96min magnetograms from SOI MDI on board Solar and Heliospheric Observatory SOHO . SOHO is a project of international cooperation between ESA and NASA. References .
