JpGU-AGU Joint Meeting 2020

Presentation information

[J] Oral

P (Space and Planetary Sciences ) » P-CG Complex & General

[P-CG27] Origin and evolution of materials in space

convener:Hideko Nomura(Division of Science, National Astronomical Observatory of Japan), Takafumi Ootsubo(Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency), Hitoshi Miura(Graduate School of Natural Sciences, Department of Information and Basic Science, Nagoya City University), Aki Takigawa(Department of Earth and Planetary Science, The University of Tokyo)

[PCG27-10] X-ray induced chemistry for water and related molecules in low-mass protostar envelopes

*Shota Notsu1,2, Ewine van Dishoeck1,3, Catherine Walsh4, Arthur Bosman5, Hideko Nomura6 (1.Leiden Observatory, Faculty of Science, Leiden University, 2.Star and Planet Formation Laboratory, RIKEN Cluster for Pioneering Research, 3.Max Planck Institute for Extraterrestrial Physics, 4.School of Physics and Astronomy, University of Leeds, 5.Department of Astronomy, University of Michigan, 6.Division of Science, National Astronomical Observatory of Japan)

Keywords:astrochemistry, molecules, protostars, snowline, water, X-ray

Water has been used to study dynamical properties of star-forming regions, and it is also one of key molecules in chemical evolutions. Recent water line observations toward several low-mass protostars suggested low water abundances in the inner warm envelopes. Water destruction by strong X-ray fluxes may influence in these regions, but detailed processes, including molecules holding oxygen instead, have not yet understood.

In our study, we calculated the chemical evolutions of low-mass Class 0 protostar envelopes using the detailed gas-grain chemical reaction network including X-ray induced chemical reactions, and investigated the dependences of water and related molecule’s abundances on X-ray radiation fields.

If the central protostars have higher X-ray luminosities (LX>1030 erg s−1), water gas abundances become higher (up tp x(H2O)~10−8−10−7) just outside the water snowline (T<100 K), compared with the values (x(H2O)∼10−10) in the cases of lower X-ray luminosities (LX<1030 erg s−1). Inside the water snowline (T>100 K), in the cases of lower X-ray luminosities, water gas molecules maintain the high abundances of 10-4, and they are considered to be the dominant oxygen carrier with CO. On the other hand, in the cases of higher X-ray luminosities, water gas abundances become much smaller just inside the water snowline (T∼100−250 K, below to x(H2O)∼10−8−10−7) and in the innermost hot regions (T∼250 K, x(H2O)∼10−6). In these cases, molecular and atomic oxygen abundances reach around 10−4 within the water snowline. In addition, some other water related molecules, such as HCO+ and CH3OH, are also affected by X-ray radiation fields. These X-ray effects are larger in the envelope models with lower number densities. Current and future molecular line observations for protostars (e.g., ALMA) will access the regions where such X-ray induced chemistry is important.