Molecular emission in the disk around DM Tauri reveals complex chemical processes

Observations of the protoplanetary disk surrounding the star DM Tauri reveal how specific molecules are distributed near the disk midplane. By studying N2H+ and DCO+ ions, researchers identified distinct patterns of emission that highlight the influence of external ultraviolet radiation and cosmic rays on the chemical environment where planets begin to form.

Star system: DM Tauri | Distance from the Sun: 470 light years

Planets emerge from the dense, flat regions of gas and dust known as protoplanetary disks that surround young stars. By investigating the chemical conditions in the disk around DM Tauri, researchers can better understand the environment that influences planetary evolution. This study focuses on the distribution of two specific molecular ions, N2H+ and DCO+, which serve as chemical markers for the conditions found in these distant rotating disks.

To map these molecules, the team used the Atacama Large Millimeter/submillimeter Array, commonly known as ALMA. This telescope allows for precise measurements of the radial profiles of these ions. The observations revealed that DCO+ is concentrated toward the center with a dip in intensity at 120 astronomical units, while N2H+ shows a central drop and a peak near 100 astronomical units. Both molecules were detected as far out as 400 astronomical units from the star.

The findings indicate that standard models based on carbon monoxide parameters cannot fully explain the emission observed in the outer regions of the disk. This extended emission suggests that increased ultraviolet light and higher rates of ionization from cosmic rays and X-rays play a significant role. These energetic processes lead to the release of trapped gases like carbon monoxide and nitrogen into the disk, which subsequently alters the chemistry of the entire region.

Key findings
DCO+ emission peaks at the center with a notable depression near 120 astronomical units.
N2H+ emission displays a central depression and reaches a peak intensity near 100 astronomical units.
Both molecules exhibit extended emission spanning out to 400 astronomical units from the central star.
Increased external ultraviolet penetration and higher ionization rates best explain the chemical patterns observed in the outer disk.
The presence of these ions is influenced by a combination of CO snowline locations, ionization levels, and carbon monoxide depletion.

Scientific study

Peering into the Midplane of the DM Tau Disk using N2H+ and DCO+ (external link)