Embedded Young Stellar Clusters

Summary

Young stellar objects in the Perseus, Orion, and NGC 2264 star forming regions.

Finding Targets

An object whose APOGEE_TARGET2 value includes one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS-III bitmasks to learn how to use these values to identify objects in this ancillary target program.

Description

Measuring stellar kinematics in star forming regions enables critical tests of theories that
describe the formation and early evolution of stars, planets, and stellar clusters. The velocities of
young stars can reveal if/how the dynamics of star forming regions influence protostellar mass accretion, the evolution of circumstellar disks, and the structure and ultimate fate of stellar clusters. Similarly, spectroscopically identified binaries provide important tests for pre-main sequence (PMS) evolutionary tracks and help identify how the binary population evolves with age and environment. The INfrared Survey of Young Nebulous Clusters (IN-SYNC) ancillary science project utilizes APOGEE’s unique ability to obtain high-resolution NIR spectroscopy for hundreds of sources in a single field to study the dynamics and stellar populations of young clusters.

Primary contacts

Other contacts

Michiel Cottaar, Michael Meyer, Jonathan Foster, Nicola Da Rio, Kevin Flaherty

Target Selection Details

Perseus

Young stellar objects in Perseus were observed in each of two APOGEE fields, placed such that they provide optimal coverage of Perseus’ sub-clusters, IC 348 and NGC 1333, while still spanning the full extent of the Perseus Molecular Cloud. A catalog of potential young stellar objects in Perseus was constructed from:

• mid-infrared excess sources identified by the cores-to-discs (c2d) Spitzer survey team across all of Perseus (Jorgensen et al. 2006; Rebull et al. 2007)
• candidate or confirmed IC 348 members, selected via broad-band photometry and/or X-ray observations, and often confirmed spectroscopically (e.g. Luhman et al. 1998; Luhman 1999; Preibisch & Zinnecker 2001; Preibisch et al. 2003; Luhman et al. 2003, 2005; Muench et al. 2003, 2007, priv. communication)

This catalog of likely Perseus members appears highly complete: Muench et al. 2007 find that their catalog include more than 80% of IC 348 members with H < 16, a finding verified by our independent analysis of 2MASS source counts in the region (see Figure 2, Cottaar et al. 2014). Observations of the Perseus fields were designed to maximize the completeness of the IN-SYNC sample, particularly for sources with 8 < H < 12.5. For these brighter sources, APOGEE's 71.5' fiber collision limit presents the primary obstacle to obtaining a complete sample of cluster members in a single visit, particularly in the densest portions of IC 348 and NGC 1333. Constructing and observing multiple designs for each field mitigated these fiber collisions, however, maximizing the completeness of each cluster sample while also sampling multiple epochs for uncrowded sources, providing some opportunity to identify spectroscopic binaries. The high priority targets in each cluster (i.e., 8 < H < 12.5) were further sorted according to their extinction-corrected H0 magnitudes (with brighter ones at higher priority) to ensure that the survey is as complete as possible for higher mass stars. Once fibers had been allocated as evenly as possible across all visits to all accessible targets with H < 12.5, additional cluster members with H > 12.5 were assigned to all designs for that field, ensuring the maximal S/N possible for these faint targets.

Orion

The sample of targets for the IN-SYNC Orion dataset is based on the 2MASS catalog. Sources with H<12.5 mag have been restricted within a bent stripe approximately 6x1 degrees in the sky, following the distribution of YSOs in the Orion A region from Megeath et al. (2012). Five different field centers were defined, following the YSO densities along the region, with a total of 15 designs. For each design, targets were selected among all the available sources based on an iterative Monte Carlo procedure that sought to maximize target counts while respecting relative priorities for different targets. The target priorities are calculated from several factors:

1. to encourage coverage in the crowded regions, priorities are increased as a function of the local density of candidate sources;
2. to increase the number of targeted sources faster than the number of epochs for individual sources, a star already targeted in an existing design was de-prioritized in future designs, less so if faint (H>11.5);
3. known cluster members with available stellar parameters from the literature (Da Rio et al. 2010, 2012; Fang et al. 2009, 2013; Hsu et al 2012, 2013) have priorities increased over non-members or sources with unknown memberships; and
4. stars with no available stellar parameters but with IR excess detected by Spitzer (Megeath et al. 2012) have priorities increased over sources with neither stellar parameters nor detected IR excess.

Using this procedure, a total of 2697 individual sources were targeted. Of these, 684 are observed in more than 1 epoch, 1403 have available stellar parameters from the literature, and 1403 have Spitzer IR excess.

NGC 2264

To test the RV precision that APOGEE could achieve for pre-main sequence stars with significant accretion variability and/or large magnetic spots, 115 candidate NGC 2264 members were selected for APOGEE observations on the basis of:

• optical and/or IR variability identified via CoRoT & Spitzer monitoring of NGC 2264 (Cody et al. 2014)
• IRAC colors consistent with Class I/II YSOs (Sung et al. 2009)
• X-ray and/or Halpha emission consistent with Class III YSOs (Dahm et al. 2007, Sung et al. 2008)

To provide as many observations of each target as possible, and thus provide the richest dataset for examining the RV precision that APOGEE can obtain for pre-main sequence stars, the same set of 115 IN-SYNC targets were observed in each of 6 visits to the APOGEE field containing NGC 2264 (i.e., 203+00).

REFERENCES

Megeath+2012
Da Rio et al. 2010, 2012, Fang et al. 2009, 2013, Hsu et al 2012, 2013