The OCCAM Survey

The Open Cluster Chemical Abundance and Mapping (OCCAM) Survey

The OCCAM survey goals are to create a high confidence catalog of cluster age, distance, reddening, abundances based on uniform data, and utilize this sample to make marked improvements to the detailed chemical measurement of the Milky Way disk that will inform models of galaxy evolution.

The OCCAM survey will utilize large, uniform, well-calibrated surveys as its basis, starting with IR photometry from the Two Micron All-Sky Survey (2MASS; Skrutskie et al. 2006), the Spitzer/IRAC-based Galactic Legacy Infrared Mid-Plane Survey Extraordinaire programs (GLIMPSE-1, -2, -3D, 360; Benjamin et al. 2003), and the Wide-field Infrared Survey Explorer (WISE; Wright et al. 2010), combined with spectroscopy from the SDSS/APOGEE survey. APOGEE will provide high precision radial velocities (RVs), stellar parameters (Teff, log g, [M/H], [C/M], [N/M], [α/M]), and detailed abundances for individual elements (Fe, C, N, O, Al, Si, Ca, Ni, Na, S, Ti, Mn, K). These data sets will also be combined with new precision astrometric surveys as they come available (e.g., Pan-STARRS and Gaia; Kaiser et al. 2010; Casertano et al. 1996).

The OCCAM Project also includes optical high resolution follow-up of APOGEE stars to obtain Neutron capture (r- and s- process) abundances, led by TCU students.

OCCAM I: Local Galactic Metallicity Gradient with APOGEE Using SDSS DR10 (Frinchaboy et al. 2013)
Chemical abundance gradients from open clusters in the Milky Way disk: Results from the APOGEE survey (Cunha et al. 2016)
OCCAM II: Precision Cluster Abundances for APOGEE using SDSS DR14 (Donor et al. 2018)
     SDSS-IV OCCAM II Value-Added Catalog (VAC)
OCCAM III: r- and s- Process Abundances for APOGEE Calibration Clusters (O'Connell et al., submitted)
OCCAM IV: Abundances for 126 Open Clusters using SDSS/APOGEE DR16 (Donor et al. 2020)
     SDSS-IV OCCAM IV Value-Added Catalog (VAC)
OCCAM V: Chemical Abundances of CTIO/Hydra Clusters using The Cannon (Ray et al., 2022)
OCCAM VI: Galactic Chemical Gradient Analysis from APOGEE DR17 (Myers et al., in press)
     SDSS-IV OCCAM VI Value-Added Catalog (VAC)
OCCAM VII: APOGEE DR17 [C/N]-Age Calibration (Spoo et al., 2022)

This work is supported by NSF AAG grants AST-1311835 & AST-1715662.

Star Cluster Membership Analysis

We present the sample and methods being used by the survey to determine membership for the few-star sampling for most clusters as observed by the SDSS/APOGEE. To determine cluster membership, we have combined the APOGEE sample with additional data sets and are using the three-dimensional kinematical membership analysis from Frinchaboy & Majewski (2008) to derive membership probabilities for each star. We are adding additional membership criteria based on APOGEE stellar parameters (e.g., Teff, log g, Abundances) to this formulation, as these are now available from the APOGEE data. We are currently working on verification of the membership method using the DR 14 (APOGEE-1 + early APOGEE-2) and DR16 samples, and including an extension of the method by incorporation of proper motion and distance data from the ESA Gaia mission.

This part of the OCCAM project is being led by Dr. John Donor and Dr. Peter Frinchaboy.

Galactic Abundance Analysis

Metallicity gradients provide strong constraints for understanding the chemical evolution of the Galaxy. Using observations from the APOGEE survey with chemical abundances were derived automatically by the ASPCAP pipeline, we find significant gradients for most-elements. Our results are not at odds with the possibility that metallicity ([Fe/H]) gradients are steeper in the inner disk (R_GC ~7 - 14 kpc) and flat towards the outer disk. The open cluster sample studied spans a significant range in age. When breaking the sample into age bins, there is clear indication that the younger open clusters has a flatter metallicity gradient when compared with the gradients obtained from older open clusters.

This part of the OCCAM project is being led by Dr. John Donor, Dr. Peter Frinchaboy, Dr. Katia Cunha (ON, Brazil).

Neutron Capture Follow-up

The high-resolution (R=22,500), near-infrared (H-band) APOGEE survey allows for cluster membership probability determination and analysis of light and iron-peak elements. Neutron capture elements, however, prove to be elusive in the IR region covered by APOGEE. In an effort to fully study detailed Galactic chemical evolution, we conducted a high resolution (R~60,000) spectroscopic abundance analysis of neutron capture elements for OCCAM clusters in the optical regime to complement the APOGEE results. We present results for ten open clusters using data obtained at McDonald Observatory with the 2.1m Otto Struve telescope and Sandiford Echelle Spectrograph. We see abundance trends for Ba II, La II and Eu II that are consistent with Galactic abundance patterns for these elements. Ce II appears to be slightly enhanced in all program stars with a median value of ~0.1 dex and a spread of 0.5 dex for the entire sample.

This part of the OCCAM project is led by Dr. Julia O'Connell and Natalie Myers