Research

Solar and Stellar Astrophysics

Description

Stellar Physics

LINK TO YY ISOCHRONES

 

The study of stellar evolution is a speciality of the Yale stellar physics group. The group develops and maintain codes to study stellar evolution in which the input physics is regularly updated. In response to observational advances in stellar populations and nucleosynthesis, on going work extends the parameter space of the Yale-Yonsei grid of evolutionary tracks.

The stellar physics group has, in the last few years, also been involved in theoretical simulations of 3D radiation hydrodynamics to understand the physics of turbulent convection in the atmospheres of the sun and sun-like stars. One of the goals is to predict the depth and structure of convective envelopes, and the effective sizes of convective cores, which are two major uncertainties in calculating stellar evolutionary tracks and lifetimes.

Recent 3D simulations have also revealed striking differences in the dynamics of granulation in the sun and in the F-star Procyon A, the details of which can now be analysed with the help of the space asteroseismic data from the MOST mission (see below).

Yale astrophysicists are also involved in several theoretical projects of asteroseismology, i.e. the study of stellar interiors using oscillations. Two space missions dedicated to observations of stellar oscillations, MOST (Microvariability and Oscillations of STars) and COROT (Convection, ROTation and planetary transits), have recently been launched, to be followed by NASA's Kepler mission in 2009. Yale astrophysicists are involved in the interpretation of current space data

Solar Physics

There are two basic types of solar physics research done at Yale, one to study the Sun in order to understand it and perhaps apply what we learn to other stars, and the second is to study the effects the Sun has on Earth. A key to understanding the Sun (and its effect on Earth) is to understand how the Sun changes with time, i.e., solar variability, and that is the current focus of solar research at Yale.

Studying Solar Variability

The study of solar variability at Yale involves using two techniques, helioseismic inversions and modelling. Helioseismology is the study of the Sun using data on solar oscillations. Solar oscillations provide a unique window into the Sun and these can be used to build up a picture of the interior of the Sun which is normally hidden to us. Information about these oscillations have been successfully used in the past to reconstruct the structure of the Sun from the core to the surface. These have also been used to determine the rotation of the solar interior. Since the frequencies of these oscillations change with time, these can be used to probe changes that occur inside the star. Changes in solar dynamics have been observed clearly. It is more difficult to observe changes in solar structure, and that is the focus of study here. A related issue that is studied here is the sub-surface structure of solar active regions.

We use data from GONG and MDI projects and shall exploit data from the upcoming Solar Dynamics Observatory (SDO). Prof. Basu is a Co-Investigator of the mission.

Our ultimate aim is to try and determine the magnetic field structures that can cause the changes we see. The modelling efforts are described in the section on solar-terrestrial effects.

Solar-Terrestrial Effects

Research on Solar-Terrestrial effects done here used to involve forecasting the magnitude of the activity cycle, its effect on the atmosphere of the Earth, specifically in terms of the lifetime of low Earth orbiting satellites, etc. However, the current research emphasis is in understanding the solar component of global warming. In turn, this involves deciphering the physics of the engine that drives solar variability, an essential element for explaining past changes, and forecasting future ones. This work involves the development of complex models of the solar interior, and testing them with appropriate space-based observations. The group has developed a 2D numerical code of the solar structure that includes the effects of magnetic fields, turbulence, and rotation. The models will be calibrated with observations made by the PICARD satellite, to be launched in Spring 2009, as well as helioseismic data. Prof. Sofia is one of the Co-Investigators of PICARD and shall have preferential access to the data.

Image Credits: (header) NASA, ESA, J. Hester and A. Loll (Arizona State University)

Yale University

© 2014 Yale University. All Rights Reserved.

Members

Group Members

Sarbani Basu

Professor, Astronomy

Web Site | Please visit my homepage

E-mail |

Phone | (203) 432-3028

Fax | (203) 432-5048

Sabatino Sofia

Professor, Astronomy

Web Site | Please visit my homepage

E-mail |

Phone | N/A

Fax | (203) 432-5048

Pierre Demarque

Munson Professor Emeritus of Natural Philosophy and Astronomy

Web Site | Please visit my homepage

E-mail |

Phone | (203) 432-3024

Fax | (203) 432-5048

Linghuai Li

Associate Research Scientist

E-mail |

Phone | (203) 436-8848

Fax | (203) 432-5048

Frank Robinson

Research Scientist Geology & Geophysics; Assistant in Instruction Astronomy

Web Site | Please visit my homepage

E-mail |

Phone | (203) 432-7128

Charles Baldner

Graduate Student

E-mail |

Phone | (203) 432-3029

Fax | (203) 432-5048

Lisa Esch

Graduate Student

E-mail |

Phone | (203) 432-3031

Fax | (203) 432-5048

Joel Tanner

Graduate Student

E-mail |

Phone | (203) 432-5774

Fax | (203) 432-5048

Yale University

© 2014 Yale University. All Rights Reserved.