Tracking Methanol Maser Rings Around Young Stars

Methanol Masers are important markers found in areas where massive stars are being born. These masers emit radio waves at a frequency of 6.7 GHz and can provide valuable information about the Gas Movements around young stars. This study focuses on a specific type of structure formed by these masers, known as Rings. By studying how these masers move, we can learn more about the processes occurring near forming stars.

#The Importance of Methanol Maser Rings

Methanol masers are typically located in regions where young stars are forming, especially those that are larger than eight times the mass of the Sun. These stars are often difficult to observe because they are far away and shrouded in dust. However, the 6.7 GHz methanol masers can give us insights into the velocity and movement of gas in their vicinity. Understanding how these masers behave and move can help us better understand the environment and conditions where these massive stars are born.

#Objectives of the Study

The primary goal of this investigation is to analyze the rings formed by methanol masers and to measure their movements accurately over time. We are particularly interested in whether the masers are moving inward toward the center of the ring, outward away from the center, or if they show some sort of rotation. By examining these motions, we can infer the dynamics of gas around newly forming stars.

#Methodology

Our research utilized a very sensitive technique known as Very Long Baseline Interferometry (VLBI), which allows us to observe these masers with a high level of precision. This technique has been used over multiple observations spanning several years to track the movements of the masers. We focused on a sample of sources that showed little variation in their methanol emissions.

We observed five key targets: G23.20700.377, G23.38900.185, G28.81700.365, G31.04700.356, and G31.58100.077. For one of these sources, G23.65700.127, we included it in our study for comparison due to its circular shape.

#Observations and Data Collection

The observations were made over three key periods from 2004 to 2015 using the European VLBI Network. Data was collected from various radio antennas. Each observation lasted about nine hours, and during this time, we aimed to improve the quality of our measurements by using advanced calibration techniques.

To determine the positions of the maser spots, we analyzed the collected data and used statistical methods to fit models to the distributions of maser emissions. This allowed us to obtain precise measurements of their movements.

#Results and Findings

From the data we collected, we noted that the majority of the maser spots in our sample moved outward from the center of the rings. This outward motion suggests a pattern of expansion rather than an inward collapse toward the center.

The Velocities measured ranged from about 0.5 km/s to 13 km/s. Specifically, G23.20700.377 and G23.38900.185 exhibited notable expansion, and we observed how the size of the elliptical shape fitting the maser distribution grew over time. This indicates that the gas surrounding these stars is indeed moving outward.

Despite the general stability in the overall structure of the masers, we also noted that the intensity of individual maser spots varied over the observation periods. This variability suggests some form of instability within the clouds of gas emitting the masers.

#Detailed Findings for Each Source

1. G23.20700.377: The analysis revealed that the majority of maser cloudlets are moving outward. We identified a total of 218, 219, and 250 maser spots across the three observation years. The average proper motion for these cloudlets ranged from 1.2 km/s to 11.6 km/s.

2. G23.38900.185: Similar results were found here, with the majority of maser spots exhibiting linear motions and expanding outward. The velocities ranged from 0.5 km/s to 16.1 km/s.

3. G23.65700.127: This source showed a nearly circular distribution of maser spots. The masers also moved outward with similar velocity patterns as seen in the other sources.

4. G28.81700.365: This source presented fewer maser spots, but the outward motions were still evident, with velocities noted between 1.6 km/s and 13.0 km/s.

5. G31.04700.356: Analyzing this source involved examining individual maser spots due to its complex structure. Velocities ranged from 0.7 km/s to 7.1 km/s, and we noted significant changes in the intensity of the maser emissions over time.

6. G31.58100.077: This target showed some uncertainty with its Proper Motions, suggesting possible rotation. The velocities reached as high as 5.5 km/s. Accurate interpretation of this target's behaviors remains a challenge and requires future study.

#Discussion

The movement patterns observed in the methanol masers provide critical insights into the behavior of gas surrounding massive stars. The overall outward movement from the centers of the rings aligns with the idea that these masers are part of an expanding structure, possibly related to the young stars they surround.

In most of the sources studied, the masers did not appear to be falling inward but rather expanding outward, suggesting that the energy and dynamics in these regions are complex and fluid. The observed variability in intensity over time further reinforces the idea that these environments are not static.

It is essential to compare these results to other studies and observations of massive star-forming regions. Previous studies have also suggested similar patterns, but this study allowed for a more detailed analysis of the proper motions, especially with the long observation times that provided high-quality data.

#Future Research Directions

Given the results obtained, future investigations should focus on more sources with similar methanol maser emissions to build a more comprehensive picture of the gas dynamics around massive stars. Additional observations using different techniques, such as infrared and thermal mapping, can complement the data gathered from the VLBI observations.

Understanding the connection between methanol masers and young stars is crucial for interpreting how these stars evolve and interact with their environment. More extensive studies involving thermal tracers will help clarify whether the observed maser rings correlate with outflows or accreting discs around young stars.

By exploring these connections, we can enhance our understanding of stellar formation processes and the role methanol masers play in them. The dynamics of the gas surrounding massive stars remain an exciting field of study with many unanswered questions.

#Conclusion

This study highlights the significance of 6.7 GHz methanol maser emissions in investigating the dynamics of star-forming regions. The observation of outward motions of maser cloudlets indicates a coherent expansion process, suggesting dynamic interactions in the gas surrounding massive young stars.

Variations in individual maser intensities hint at underlying instability, prompting further questions regarding the nature and behavior of these gas clouds. Continued observation and research into such phenomena will illuminate the complexities of star formation and the evolution of massive stars as they come to life in the cosmos.