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Gemini High Resolution Optical SpecTrograph (GHOST)

GHOST is the newest high-resolution (R ~ 50,000 - 75,000) spectrograph for Gemini-S that covers the entire optical wavelength range (360-1060 nm).  I was involved in commissioning GHOST as well as helping develop its data reduction pipeline, GHOSTDR.

Image credit:  J. Pazder / McConnachie et al. 2024


Most of my research is done with APOGEE, the Apache Point Observatory Galactic Evolution Experiment.  APOGEE is a high-resolution near-Infrared spectroscopic survey of stars in and around the Milky Way, allowing it to measure radial velocities, stellar parameters and chemical abundances for many elemental species in these stars.

Image credit:  D. Whelan/G. Zasowski


One Galaxy, Lots of Data

I use surveys like APOGEE to gain a better understanding of our Galaxy and its past. Because modern surveys measure many properties for hundreds of thousands to millions of stars, much of my work revolves around handling these large data sets and how to best visualize their high dimensionality.

Image credit:  C. Hayes

The Milky Way's Accreted Halo in APOGEE

One of the ways I have used APOGEE is to study the metal-poor stars that it observed. This revealed that metal-poor stars in our Galaxy are divided into two chemically and kinematically distinct populations.  One of these populations appears to be related to the thick disk, whereas the other appears to be a considerable population of accreted halo stars. See also the recent dynamics study of these stars from Mackereth et al. 2018.

Image credit:  Hayes et al. 2018a


Disk-like Chemistry of TriAnd

Triangulum-Andromeda (TriAnd) is a stellar overdensity seen toward the outer disk of the Milky Way about 20 kpc away from the sun. Recently using the chemical abundances of TriAnd stars observed by APOGEE we have shown that TriAnd appears to be an extension of the Milky Way disk that has been perturbed to significantly below the disk midplane.

Image credit:  Modified from Hayes et al. 2018b

Chemical Gradients along the Sgr Tidal Stream

With 6D phase space information from Gaia DR2 and APOGEE, along with chemistry from APOGEE, we identified the largest sample of Sgr stream stars with high resolution spectroscopy.  We discovered that there are metallicity and chemical gradients along the Sgr stream - implying that Sgr had internal chemical gradients before being disrupted.

Image credit:  Modified from Hayes et al. 2020

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