Found 2 talks width keyword variable stars

The "Asteroid Terrestrial-impact Last Alert System" (ATLAS) is funded by NASA to find dangerous asteroids before they strike the Earth. It has operated from two Hawaii sites since 2015 and will very soon have South Africa and Chile sites to cover the entire visible sky every night four times to a limiting magnitude of m~19.5 per exposure. The process of finding asteroids leads to auxiliary data products along the way including accurate photometry of all stars in the sky and detection of flares and transients.  I will describe ATLAS, how we approach our NASA mission to find NEOs, how ATLAS fits in with other ongoing or planned surveys, some of the data products that are available now, and the many new scientific opportunities that are emerging and waiting to be exploited.  Time will be reserved at the end of the talk for some real time demonstrations: audience participation is encouraged.  References include 2018PASP..130f4505T, our public web page at fallingstar.com and fallingstar.com/weather/ to see our current fisheye and webcam views at all four sites.

Zoom link: https://rediris.zoom.us/j/82241288569?pwd=QmtUWkNoRHNvYlk3dWJhRCtCdE1RQT0

Meeting ID: 822 4128 8569
Passcode: 776606

Youtube: https://youtu.be/Ax-70hAibow

To study the extended atmosphere of evolved stars such as Mira-type variables, spectropolarimetry is an innovative tool. For many kinds of stars, it has been used to measure global magnetic fields through circular polarization and the Zeeman effect. However, linear polarization has seldom been used in the past years even though phenomena such as scattering and the Hanle effect can definitely be studied as well, as it is done in solar physics. In this presentation, I am going to describe original results coming from a spectropolarimetric survey of Mira stars with NARVAL@TBL. Such results concern spectral lines like the Balmer lines of hydrogen and calcium lines. More specifically, I will focus on linear polarization and link this polarization to the propagation of the hypersonic radiative shock wave which is typical of Miras' atmospheres. In general, these environements are very dynamical and scattering in an aspherical atmosphere and velocity gradients can induce a strong linear polarization, likely to be further affected by weak magnetic fields. This analysis is very inspired of what is already done with solar spectra. In addition to that, I am going to present exclusive results about the first detection of a surface magnetic field in a Mira star and explain how the shock wave can impact this field. This work is likely to lead to collaborations with other disciplines such as interferometry (geometry of the scattering environement and characterization of the shock) and radio-astronomy (study of the polarization of masers).