Gina Panopoulou's research group

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Up-to-date list of Gina's publications can be found on the NASA ADS webpage at this location.

Contents

A new compilation of stellar polarization catalogs

Stellar polarization is a unique tool for mapping the Galactic magnetic field and understanding the properties of interstellar dust. Despite their importance, stellar polarimetry measurements are sparse and difficult to find. Observations are conducted by different investigators, with different instruments and are made available in many separate publications. To enable a more widespread accessibility of optical polarimetry for studies of the interstellar medium, we compiled a new catalog of stellar polarization measurements. The data are gathered into a single, homogeneous format from 81 separate publications, representing a community effort of two decades. We combine this invaluable dataset with stellar distances from the Gaia mission, enabling new 3D studies of the magnetized ISM.

Figure 1: The number of stars per square degree with measured optical polarization in our new dataset of starlight polarimetry. This is the most complete dataset to date of optical polarimetry, spanning data collected over two decades.

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Improved CMB foreground modeling

The Galactic magnetic field interacts with interstellar dust and cosmic rays and produces broadband emission from radio to infrared wavelengths. This emission is polarized and acts as a confusing foreground to light from the early Universe, known as the Cosmic Microwave Background (CMB). To study the pristine light of the CMB, we must accurately model and subtract the signal from our Milky Way. A large effort is underway to improve such models by incorporating 3D information about the ISM and its magnetic field.

Figure 3: A map of the number of dusty ISM clouds along the line of sight measured using HI spectra in the BICEP/Keck field.

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Understanding ISM dust properties

Combining measurements of polarized dust emission with those of starlight polarization, we can learn about the physics of dust grains in the ISM.

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Optopolarimetric mapping of molecular clouds

The ISM contains clouds, mainly made up of molecular hydrogen, that are the sites where stars form. The details of this formation process are a subject of active academic research. One aspect of this process is the influence of the magnetic field on the structure and evolution of these clouds. We study this by measuring the polarization of starlight, which reveals the orientation of the magnetic field in molecular clouds. With enough measurements, one can construct a map of the magnetic field as seen on the plane of the sky. Figure 1 shows a map of the magnetic field orientation (red lines) in the Polaris Flare molecular cloud, made using the RoboPol polarimeter at the Skinakas observatory in Greece. The magnetic field structure can be compared to the intricate filamentary morphology of the cloud, seen through the Herschel space telescope in the far infrared, to learn about the influence of the magnetic field on cloud structure. The Polaris Flare polarization data are publicly available.

Figure 4: Optical polarization segments from RoboPol overlaid on the Polaris Flare dust emission image (Herschel @ 250 microns).

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Morphology & kinematics of filamentary structures in molecular clouds

Through observations of the emission from dust in molecular clouds, the Herschel Space Telescope revealed that cloud material is organized in a network of filamentary structures. The properties of these structures are very interesting, as they can help us understand how they form and evolve.

Another interesting aspect of the process leading to star formation is the manner in which gas moves inside a cloud, a motion that is highly complex (turbulent). One can use emission line data from molecules like CO, which exist in minuscule fractions in molecular clouds, to trace one of the 3 components of the gas velocity, the component that lies along the line of sight. Gina has used such radio data from the NRAO taken in the region of the Taurus molecular cloud, to study the kinematics of filamentary structures. Gina developed FilTER, a code for extracting the properties of these filaments.

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