Young Stellar Objects in the Gould Belt

Abstract: We present the full catalog of Young Stellar Objects (YSOs) identified in the 18 molecular clouds surveyed by the Spitzer Space Telescope "cores to disks" (c2d) and "Gould Belt" (GB) Legacy surveys. Using standard techniques developed by the c2d project, we identify 3239 candidate YSOs in the 18 clouds, 2966 of which survive visual inspection and form our final catalog of YSOs in the Gould Belt. We compile extinction corrected SEDs for all 2966 YSOs and calculate and tabulate the infrared spectral index, bolometric luminosity, and bolometric temperature for each object. We find that 326 (11%), 210 (7%), 1248 (42%), and 1182 (40%) are classified as Class 0+I, Flat-spectrum, Class II, and Class III, respectively, and show that the Class III sample suffers from an overall contamination rate by background AGB stars between 25% and 90%. Adopting standard assumptions, we derive durations of 0.40-0.78 Myr for Class 0+I YSOs and 0.26-0.50 Myr for Flat-spectrum YSOs, where the ranges encompass uncertainties in the adopted assumptions. Including information from (sub)millimeter wavelengths, one-third of the Class 0+I sample is classified as Class 0, leading to durations of 0.13-0.26 Myr (Class 0) and 0.27-0.52 Myr (Class I). We revisit infrared color-color diagrams used in the literature to classify YSOs and propose minor revisions to classification boundaries in these diagrams. Finally, we show that the bolometric temperature is a poor discriminator between Class II and Class III YSOs.

• The paper presents a robust census of 3239 candidate YSOs, with 2966 visually confirmed from Spitzer’s c2d and Gould Belt surveys.
• It classifies YSOs into evolutionary Classes 0+I, Flat-spectrum, II, and III, highlighting significant AGB star contamination in Class III identifications.
• The study refines protostellar lifetimes—0.40–0.78 Myr for Class 0+I and 0.26–0.50 Myr for Flat-spectrum objects—and calls for improved infrared diagnostic methods.

Young Stellar Objects in the Gould Belt: An Analytical Overview

The paper, authored by Dunham et al., offers a comprehensive census of Young Stellar Objects (YSOs) within the molecular clouds surveyed by the Spitzer Space Telescope's "cores to disks" (c2d) and "Gould Belt" (GB) Legacy surveys. This research focuses on 18 molecular clouds and presents a significant YSO catalog to the astronomical community, contributing to a deeper understanding of star formation processes within 500 parsecs of the Sun, particularly in the Gould Belt.

The authors implemented a methodology based on established protocols from the c2d project to identify a total of 3239 candidate YSOs from the surveyed clouds, of which 2966 passed a rigorous visual inspection process to form the final YSO catalog. The cataloged YSOs have their Spectral Energy Distributions (SEDs) compiled and corrected for extinction, allowing for the calculation of key parameters such as the infrared spectral index, bolometric luminosity ($L_{bol}$), and bolometric temperature ($T_{bol}$).

Findings and Classifications

The study classifies the YSOs into the standard evolutionary Classes: Class 0+I, Flat-spectrum, Class II, and Class III, utilizing the extinction-corrected infrared spectral index. The breakdown is as follows: 11% of YSOs are Class 0+I, 7% are Flat-spectrum, 42% are Class II, and 40% are Class III. Notably, the Class III sample is affected by substantial contamination (25% to 90%) by background AGB stars, which is a critical consideration for analyses dependent on accurate YSO classification.

Classifications reveal that traditional mid-infrared data are insufficient to distinguish between Class 0 and I objects, emphasizing the need for comprehensive SEDs. This has significant implications for future studies aiming to delineate early star formation stages, highlighting the intricate overlap of SED Classes where full SED data are not available.

Timescales and Durations

Utilizing benchmark durations for Class II sources, the paper derives approximate durations of $0.40-0.78$ Myr for Class 0+I YSOs and $0.26-0.50$ Myr for Flat-spectrum YSOs, aligning with existing literature on protostar lifetimes. Furthermore, with additional submillimeter/millimeter wavelength data indicating one-third of Class 0+I YSOs are Class 0, the corresponding durations are refined to $0.13-0.26$ Myr for Class 0 and $0.27-0.52$ Myr for Class I YSOs. These findings underscore the transient and dynamic nature of early star development stages and the variability inherent across different molecular cloud environments.

Revisions to Classification Schemes

The authors critically evaluate existing infrared classification color-color diagrams, proposing adjacency-based refinement of classification boundaries. This nuanced approach increases the precision and utility of these diagrams for categorizing YSOs, especially when insufficient photometric data span hampers definitive SED construction.

Ground Implications and Future Directions

The implications of this paper stretch across both observational and theoretical domains. Observational refinement of classifications and durations can bridge comparative studies within different star-forming regions, thus enriching models of stellar evolution. Theoretical astrosphere models can assimilate these refined classifications and timescales to improve simulations of stellar feedback mechanisms and their broader galactic impact.

Future research is envisaged to reconcile these findings with parallel surveys of Taurus and Orion molecular clouds, a synergy which promises to advance the collective understanding of solar neighborhood star formation comprehensively. The ongoing challenge is to further clarify the extent of Class III contamination and to fuse Spitzer data with Herschel and SCUBA-2 survey results, yielding a more holistic embrace of infrared and submillimeter to millimeter perspectives on early stellar evolution.