Finding Cosmic Inflation

Main Colloquium
Prof. Eiichiro Komatsu
SCHEDULED
Max-Planck-Institut für Astrophysik, Garching

The cosmic microwave background (CMB) research told us a remarkable story: the structure we see in our Universe such as galaxies, stars, planets, and eventually ourselves originated from tiny quantum fluctuations generated in the early Universe. With the WMAP we have confirmed many of the key predictions of inflation including flatness and statistical homogeneity of our Universe, Gaussianity and adiabaticity of primordial density fluctuations, and a small but non-zero deviation from the scale-invariant spectrum of density fluctuations. Yet, the extraordinary claim requires extraordinary evidence. The last prediction of inflation that is yet to be confirmed is the existence of primordial gravitational waves whose wavelength can be as big as billions of light years. To this end we have proposed to JAXA a new satellite mission called LiteBIRD, whose primary scientific goal is to find signatures of gravitational waves in the polarisation of the CMB. In this presentation we describe the current state of affairs regarding our understanding of the early Universe, physics of polarisation of CMB, the LiteBIRD proposal, as well as a sub-mm telescope in Chile called CCAT-p that we are currently building.

HCN emission in circumstellar envelopes of carbon-rich AGB stars

Master Colloquium
Manali Jeste
SCHEDULED
Max-Planck-Institut für Radioastronomie

Low- and intermediate-mass stars, after moving past the Horizontal Branch in the Hertzsprung-Russell diagram, reach the Asymptotic Giant Branch (AGB) where they start the final parts of their lives. AGB objects have a carbon-oxygen core at the center of helium- and hydrogen-burning shells and are surrounded by a circumstellar envelope (CSE). The star becomes carbon-rich when the abundance ratio of carbon to oxygen, C/O, becomes higher than 1 due to the third dredge-up mechanism. AGB stars contribute substantially to the molecular enrichment of the interstellar medium. HCN is one of the most abundant carbon-bearing molecules found in the atmospheres and CSEs of these stars. For this study, we observed a total of 16 carbon-rich AGB stars using the APEX telescope in the J = 2-1 to 4-3 transitions of HCN and combined this data set with archival Herschel telescope data (J = 6-5 to 13-12 transitions). In addition to lines from the ground state, we detected rotational lines from various vibrationally excited levels of HCN, which trace the innermost hot regions of the CSE. Until now, the only AGB star for which such multi-transition HCN data sets have been discussed is the nearby, high mass-loss object IRC+10216. We have analyzed the HCN data for all the 16 sources and investigated the excitation conditions (temperature and column densities) in detail, for 3 of them, namely CRL-3068, II Lup, and IRC+10216. In the future, we plan to model HCN emission in AGB stars by combining our data with spatial information obtained with ALMA. [Referees: Prof. Karl Menten, Prof. Pavel Kroupa]

Enabling charge particle astronomy with Galactic magnetic tomography

Lunch Colloquium
Dr. Vasiliki Pavlidou
SCHEDULED
Department of Physics, University of Crete

The sources of the highest-energy particles in the Universe remain an unresolved mystery. The reason is that charged-particle astronomy is severely complicated by magnetic deflections. I will discuss a radically new approach to charged-particle astronomy: constructing a 3-dimensional map of local Galactic magnetic field measurements, primarily through optopolarimetric magnetic tomography, and backtracking the paths that UHECR traverse through the Galaxy before reaching us, to improve agreement between their (corrected) arrival directions and the location of their sources on the sky. Effectively, this technique aims to improve the charged-particle point-spread-function by a factor of several, boosting the sensitivity to individual sources by a similar factor, and allowing us to probe the cosmic-ray composition at the highest energies without reference to the development of extensive air showers in the atmosphere. This approach is becoming possible for the first time thanks to two experimental breakthroughs: the unparalleled wealth of stellar distances that the Gaia mission is in the process of providing; and recent advances in optopolarimetry of point sources that make possible systematic large-area surveys of stars. This technique would act multiplicatively on the return from current and future cosmic-ray observatories, ground- and space-based.

Hearing the 3D shape of Musca molecular cloud

Main Colloquium
Prof. Konstantinos Tassis
SCHEDULED
Department of Physics, University of Crete and Institute of Astronomy, FORTH, Greece

Dust continuum and molecular observations of the low column density parts of molecular clouds have revealed the presence of elongated structures which appear to be well aligned with the magnetic field. These so-called striations are remarkably ordered structures in otherwise chaotic-looking clouds. They encode information revealing the properties of their parent clouds. We have demonstrated that magnetosonic waves, ubiquitous in molecular clouds, are the most probable cause of striations, since they are the only mechanism that can reproduce quantitatively their observed properties. If indeed striations are the interstellar ripples caused by the passage of magnetosonic waves, then profound consequences are implied for their ability to reveal hidden, important information about molecular clouds. I will present a specific example: striations in the Musca molecular cloud are found to encode normal modes of the cloud's global magnetosonic vibrations, allowing the reconstruction of its 3D shape.