Wednesday Colloquium


"Cepheids in the far side of the Milky Way from the VVV survey"

Gergely Hajdu (NCAC, Warsaw)

The structure of the far side of the Milky Way's disk has not been charted until very recently, due to the severe extinction caused by interstellar dust in the Galactic plane. In order to do so, we have conducted a census of distant Classical and Type II Cepheid variables along the Galactic plane in the VISTA Variables in the Vía Láctea (VVV) survey. Zero-point calibration issues of VVV survey products forced us to revise them, after which the photometry could finally be leveraged to its fullest potential. We have searched the recalibrated VVV Ks-band time series of the Galactic plane area for Cepheid variables, which have been classified using a convolutional neural network, revealing 640 Classical and over 500 Type II Cepheids. The Type II Cepheids were used to probe the near-IR extinction law, as well as the structure of the ancient Galactic inner bulge. Similarly, the Classical Cepheids are used to trace the distribution of the young stellar component of the far Galactic disk.





"How electron-positron pair plasma fills pulsar magnetosphere, heats NS surface, and generates radio emission."

Andrey Timokhin (Uniwersytet Zielonogórski)

I give an overview of recent pulsar magnetosphere models emphasizing the importance of pair plasma generation. I discuss how much pair plasma can be produced in pair cascades and what it means for the physics of Pulsar Wind Nebulae. Relativistic particles accelerated in pair formation zones heat the neutron star surface, I demonstrate that the temperatures of pulsar polar caps predicted in the frame of modern pair cascade models agree with observations quite well. I also present a novel robust mechanism for the direct generation of coherent radio emission in pair discharges and discuss its implications.


"Twenty Years of Science with the Chandra X-ray Observatory"

Aneta Siemiginowska (CfA, Harvard University)

X-ray emission traces signatures of energetic and violent events associated with formation and evolution of all structures in the universe. Studies of X-ray sky are relatively recent, as the first X-ray cosmic sources were detected only sixty years ago, while the optical sky has been known to humans since the beginning of life. Over the past two decades, our view of the X-ray universe has been significantly improved thanks to the NASA’s Chandra X-ray Observatory. Chandra, with its extremely sharp X-ray vision enabled by large-area, sub-arcsecond mirrors, has revolutionized our understanding of the high-energy sky. It has brought many important astrophysical processes into focus for the first time and has comprised a key component of our multiwavelength view of the Universe. In this talk I will give a broad overview of the science enabled with Chandra and focus on a handful of the exciting results, including breakthrough discoveries on the births and deaths of stars, the cosmic growth of black holes, and the formation and evolution of galaxies and clusters. I will conclude with a look toward the future of high-resolution X-ray observatories.