Observations of an Ongoing FU Orionis Event in VdBH 221

During their early development, young stars, known as Young Stellar Objects (YSOs), gain most of their mass in bursts. One rare phenomenon among these is the FU Orionis-type outburst, or FUOr event. These events are crucial for studying how young stars behave during their mass accumulation stages. In this article, we will discuss a specific case of an ongoing outburst in a young open cluster called VdBH 221, focusing on its characteristics and implications for our knowledge of star formation.

#What Are FU Orionis Events?

FUOr events are powerful bursts of Brightness seen in young stars. They typically exhibit significant increases in brightness, often greater than 5 magnitudes in optical light. These events are not common; they occur roughly once every 10,000 to 100,000 years per star, with only a handful confirmed so far. Most FUOr Outbursts share common features: high brightness and long-lasting effects, which can last for decades to centuries. This distinguishes them from shorter, less intense events.

Recently, researchers have detected these explosive behaviors in a variety of stars at different stages of development, particularly in embedded stars. There are several theories for what causes these bursts, including gravitational changes, thermal instability, and interactions with neighboring stars or planets.

#Recent Findings in VdBH 221

In our investigation, we focused on a young star in the VdBH 221 cluster that is currently undergoing an outburst. This star was observed to have a brightness increase of 6.3 magnitudes, indicating a strong eruptive phase. The star has shown various changes in brightness across different wavelengths of light, providing insight into its physical properties and composition.

The outburst observed has a high luminosity peak and a remarkable rate of Mass Accretion. The data gathered includes pre-outburst measurements and subsequent changes, including the brightness before and after the burst.

#Key Observations

To understand more about this outburst, we looked at various forms of data. Photometric observations help measure brightness over time, while spectral data reveal properties of the star's atmosphere and surroundings. We observed a significant delay of about 100 days between the peak brightness in optical and infrared light, which suggests that the instability starts from a deeper part of the star's surrounding disc and moves outward.

The light from this star is similar to that of other FUOr stars, indicating that it has a bright accretion disc that helps it shine. These observations can provide clues about how materials move toward the star and how the star changes through this process.

#What Is a Spectral Energy Distribution?

Spectral energy distribution, or SED, is a way to show how much light a star emits at different wavelengths. By analyzing the SED of our target star before and during its outburst, we can infer its temperature and other physical properties. The SED during the outburst suggested that the star had a lower mass and was experiencing some amount of light-blocking dust.

The star's brightness and temperature before the burst indicated that it was a low-mass YSO, consistent with other stars in its cluster. The unique features observed in the spectrum during the outburst resemble other known FUOr stars, reinforcing our classification of it as a young object.

#Stages of the Outburst

The outburst can be divided into several stages:

1. Pre-outburst Stage: Before any increase in brightness, we establish a baseline for the star's brightness.
2. Rising Stage: This happens when the brightness begins to increase sharply, which we observed beginning in late 2013.
3. Peak Stage: The star reaches its highest brightness, indicating significant changes in its physical characteristics.
4. Decaying Stage: After the peak, the brightness starts to decline, although our observations suggest it still holds considerable brightness.

#Observational Techniques

To capture these changes, we used various telescopes and imaging techniques. Our observations spanned multiple years and included both optical and infrared data. The data showed how the target star’s brightness changed over time.

In 2021 and 2022, we collected data using advanced infrared imagers and telescopes. These allowed us to capture different wavelengths of light and gather more information about the star’s behavior.

We also analyzed archival data from missions like Gaia, which provides critical information about the star's distance and motions. This data plays an essential role in understanding the overall environment around the star.

#Understanding Light Curves

Light curves are graphical representations of a star's brightness over time. By analyzing these light curves, we can identify patterns and changes in brightness. For instance, we noted that the star showed a rapid brightness increase during the rising stage and a comparatively slower decline afterward.

These patterns hint at the physical processes happening inside and around the star's accretion disc. By studying the light curves, we can explore the mechanisms driving the outburst and their implications for star formation.

#Implications for Star Formation

The behavior exhibited by this young star in the VdBH 221 cluster is key for understanding how stars form and evolve. The significant mass accretion rates observed during this outburst indicate that the star is still gathering material, which is crucial for its growth.

Understanding these outburst events helps us learn more about the conditions that create stars. Each new observation reinforces or challenges existing theories about star formation and the roles played by different environmental factors.

#Conclusion

The ongoing outburst of the young star in the VdBH 221 cluster presents a rich opportunity to understand the dynamics of star formation. Through a combination of photometric and spectral data, we've been able to characterize the behavior of this star during its eruptive phase.

The rarity of FUOr events makes this an exciting study, providing insight into how young stars evolve and accumulate mass. Continued observations are essential to unpack the complexities of these phenomena, and the results will aid our understanding of young stellar objects and their pathways in the cosmos.

As we gather more data and refine our techniques, we hope to paint a clearer picture of how stars like our target evolve and what drives their dramatic outbursts.