Astrophysics Reserch

My scientific research focuses on observational star formation and molecular clouds.


Image: Artist impression of the birth of a star. With submillimeter instruments, it is possible to penetrate the surrounding dust of a forming star. While matter accretes on the protostar, bipolar jets and molecular outflows erupt on both sides. Image credit: NASA/JPL-Caltech.

The query of where we come from or how our Solar System formed are ancient questions. During human history, many different types of people including philosophers, religious leaders, and scientists have tried to come up with different suggestions to address these questions. Today, even with our advanced engineering tools and our improved scientific methods, we are still trying to find at least some clues. Especially after the invention of radio astronomy in the 1930s by Karl Jansky and the detection of the first molecule –the methylidyne radical (CH)– in the interstellar medium in 1937 by optical absorption lines (Swings & Rosenfeld 1937, McKellar 1940), a lot of progress has been made during the course of time. Many new molecules have been discovered in a variety of astronomical sources, which span a large range of conditions.

Molecules

The interstellar medium (ISM) consists of ∼99% of gas and 1% dust by mass. Approximately 90% of this gas is in the form of H or H , 8% in He and ~1-2% is heavier elements by number. More than 170 different molecular species have been detected in various interstellar and circumstellar media from nearby objects to distant galaxies. About 50 of those molecules contain 6 or more atoms and are called complex molecules. Deep inside molecular clouds, most of the carbon is in the form of CO and the hydrogen is in the form of H2.

Herschel [NII] survey in the Galactic Plane


Far infrared and sub-/millimeter atomic & ionic fine structure and molecular rotational lines are powerful tracers of star formation on both Galactic and extragalactic scales.
Although CO lines trace cool to moderately warm molecular gas, ionized carbon [CII] produces the strongest lines which arise from almost all reasonably warm (T >50 K) parts of the ISM. However, [CII] alone cannot distinguish highly ionized gas from weakly ionized gas.
[NII] plays a significant role in star formation as it is produced only in ionized regions; in [HII] regions as well as diffuse ionized gas. The ionization potential of nitrogen (14.5 eV) is greater than that of hydrogen (13.6 eV), therefore the ionized nitrogen [NII] lines reflect the effects of massive stars, with possible enhancement from X-ray and shock heating from the surroundings.

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Filaments in Taurus Molecular Cloud


Many fundamental questions on how stars form now seem to come down to the question of how dense cores form out of the larger filamentary structures. In recent years, there has been tremendous progress on the observational side with the Spitzer Space Telescope and the Herschel Space Observatory carrying out large surveys of nearby star-forming regions, whereas theoretical studies use ever more powerful computers to produce simulations that can be compared with data. In spite of these new observational techniques and instruments, however, a number of fundamental questions still remain. In particular, the entire question of the efficiency of star formation and what sets the initial mass function now seems to come down to the question of how material gets collected from the diffuse gas into molecular clouds, and how these clouds subsequently form filaments and dense cores out of which new stars form. What is the origin of filamentary structures? Are they still accreting material from the larger surroundings?


Searching for Oxygen in a forming star


Oxygen is the third most abundant element in the Universe after hydrogen and helium, but it is still unclear what the main gas-phase reservoir is in dense molecular clouds. It is important to search for O2 in order to understand the origin of this and other vital molecules for life that are chemically related, such as H2O.

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Water and CO in low-mass star-forming regions


Most studies concentrated on the cold gas and dust -as probed by low-J CO lines (J≤3)-, however, in my research, we follow the warm gas -as probed by higher-J CO lines (J≥6)- which is much more diagnostic of the energetic processes that shape these deeply embedded sources. Our main question is the quantification and location of the gas that is heated in the protostellar envelope via various processes. In addition, the abundance structure of CO is investigated. Data on high-J CO was obtained by the Herschel Guaranteed Time Key Project, WISH "Water in Star-forming regions with Herschel" (PI: Ewine van Dishoeck) together with observations from JCMT and APEX.

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