The Identification of 93 Day Periodic Photometric Variability for YSO YLW 16A

Abstract: Periodic variability in young stellar objects (YSOs) offers indirect evidence for an active dynamical mechanism. Starspots, accretion, stellar companions, and disk veiling can contribute to the photometric variability of YSOs. As part of an ongoing study of the Rho Oph star forming region, we report the discovery of 92.6 day periodic variations for the Class I YSO YLW 16A, observed over a period of three years. A SED model was fit to available photometric data for the object. We propose a triple-system with an inner binary with a period of 93 days eclipsed by a warped circum-binary disk. The nature of the secondary is unconstrained and could be stellar or sub-stellar. We report the discovery of a tertiary companion at a projected separation of ~40 AU that could account for the circum-binary disk warp. This light curve and model is similar to the model we proposed for WL 4 in previous work. Understanding these systems may lead to insights about the nature of stellar evolution and planetary formation, and provide valuable benchmarks for future theoretical modeling and near- and mid-infrared synoptic surveys of YSOs.

• The paper identifies a 92.6-day photometric periodicity in YSO YLW 16A, proposing it is a disk-eclipsing system with a third body affecting a warped circum-binary disk.
• The study uses long-term photometric data, SED fitting, and NACO imaging to support the eclipsing disk model and discount other mechanisms like starspots or accretion variability.
• These findings suggest systems like YLW 16A might represent a new class of disk-eclipsing YSOs, providing benchmarks for understanding star formation and disk dynamics.

An Analysis of Periodic Photometric Variability in Young Stellar Object YLW 16A

The study presented in the paper "The Identification of 93 Day Periodic Photometric Variability for YSO YLW 16A" provides an in-depth examination of the photometric variability in young stellar object (YSO) YLW 16A, located in the $\rho$ Ophiuchus star-forming region. This research exploits long-term synoptic data to unravel complex stellar behavior and proposes new insights into the dynamical interactions in young stellar systems.

Key Contributions

One of the central findings of this research is the identification of a 92.6-day periodic variability in the YSO YLW 16A, which is hypothesized to be a Class I protostar. The periodicity observed, over a period extending to three years, strongly suggests a dynamical system in operation, potentially involving a multi-star configuration with a circumstellar disk.

The paper proposes that YLW 16A is likely part of a previously unidentified class of disk-eclipsing YSOs, similar to systems like WL 4, KH-15D, and CHS 7797. This involves an eclipsing mechanism facilitated by a third body in the system, which interacts with a circum-binary disk, potentially warped due to gravitational interactions. The discovery of a tertiary companion at a projected separation of approximately 40 AU aligns with these observations. The proposed model also draws on spectral energy distribution (SED) fitting to support the existence of this complex stellar arrangement.

Results and Observational Evidence

The observations suggest that the photometric variability is not easily attributed to traditional mechanisms such as starspots or accretion variability, which typically manifest over shorter timescales. Instead, the SED analysis, bolstered by photometry across various IR bands, indicates that eclipses or shadowing events related to the circum-binary disk could be influencing the observed periodicity. The NACO imagery substantiates these claims by revealing a visual binary structure with components likely interacting under gravitational influence, encouraging the notion of a warped disk scenario.

Additionally, the SED models fitted for YLW 16A exhibit a stellar component largely affected by extinction, with a substantial infrared excess in both bright and faint states indicating significant circumstellar material.

Implications and Future Directions

The findings from this study bear significant implications for understanding the formation and evolution of stellar systems, particularly with respect to the dynamics of circumstellar disks and their role in planetary formation. The research posits that systems like YLW 16A could be more common than previously identified, providing potentially critical benchmarks for future theoretical models and infrared observational campaigns.

This research opens several avenues for future work. Observations focusing on radial velocity monitoring and further high-resolution imaging could offer greater clarity on the role of the third companion and help disentangle the various components of the system. The upcoming synoptic surveys are well-placed to discover more such systems and validate the proposed model's applicability across different contexts.

In summary, the research contributes to the critical understanding of periodic variability in young stellar objects and highlights the importance of multi-wavelength and long-term monitoring in studying young, dynamic systems. The identification of YLW 16A as part of a fascinating category of eclipsing YSOs underscores the complex nature of star and planet formation processes in their early stages.