Beobachtungen mit dem IRAM-Teleskop
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In September 2018, we conducted an observation campaign using the IRTF (Infrared Telescope Facility) telescope in Hawaii. With its 3-meter primary mirror, combined with the TEXES instrument we used, it offers high spectral resolution in the mid-infrared range. Along with several other telescopes, the IRTF is located on Mauna Kea at an elevation of 4,200 meters. It was originally built in 1979 to support the Voyager missions and is now operated by the University of Hawaii on behalf of NASA.
What were we looking for?
As part of the measurement campaign, researchers searched for the molecules titanium oxide (TiO) and titanium dioxide (TiO₂) in the envelopes of aging stars. These and other metal-bearing molecules serve as the “seeds” for the formation of cosmic dust. These dust grains, which can be as small as a few micrometers, are of great interest to astronomers because chemical reactions take place on their surfaces that make the formation of larger molecules in the very thin interstellar medium possible in the first place. For example, most of the water found on Earth was likely formed on cosmic dust grains.
Where does cosmic dust come from?
The source of the dust is aging stars: Toward the end of their lives, some of them slowly shed their outer layers. Due to their high temperature, these layers initially consist only of atoms; however, as they move farther away, they cool down, and small, metal-containing molecules begin to form. As this process continues, more and more atoms accumulate on these condensation nuclei until they reach the size of dust grains.
Despite the significant role dust particles play in the chemistry of the interstellar medium, the exact conditions under which they form remain unknown to this day.
What sources did we examine?
To investigate this, we searched for TiO and TiO₂ in the atmospheres of two aging stars: The first star is VY Canis Majoris in the constellation "Canis Major"—an oxygen-rich red supergiant that is slowly shedding its outer layers and has thus already formed a large dust cloud around itself. At 1,500 solar radii, it is one of the largest known stars in the Milky Way.
The other star is Mira A—a red giant in the constellation Cetus that, together with the white dwarf Mira B, forms a binary star system. Mira A is about 400 times larger than the Sun; it is a so-called variable star and gives its name to the class of Mira stars. The dust envelope it ejects is attracted to Mira B and forms a disk around it.
Based on our measurements of the infrared spectra of the stellar envelopes, we aim to gain insights into the conditions—such as temperature and pressure—under which titanium oxides and other small metal-containing molecules begin to condense. We hope to gain a better understanding of the “starting point” of dust formation in space. These measurements were made possible only by the prior characterization of the corresponding infrared spectra in our laboratory.