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Staff Record
Photo of Sarah Martell
Senior Lecturer

Sarah Martell

[p]: 

+61 2 9385 6694

[f]: 

+61 2 9385 6060

Role(s): 

co-Project Scientist for the GALAH (Galactic Archaeology with HERMES) survey
Steering Committee Chair, Astronomical Society of Australia chapter for Early-Career Researchers

Education: 

  • 2008: PhD Astronomy & Astrophysics, University of California Santa Cruz, USA
  • 2001: BS Astronomy, University of Washington, USA
  • 2001: BS Physics, University of Washington, USA

Research Interests: 

My research

My main research focus is on "Galactic archaeology" - unwinding the present-day orbits and chemical compositions of stars in the Milky Way to study the processes at work early in Galactic history. I am one of two Project Scientists for the GALAH (Galactic Archaeology with HERMES) survey, which began in late 2013. Over a five-year observing program, we will use the HERMES spectrograph, together with the 2dF 400-fiber positioner, to take high-resolution spectra of 1 million stars in the Milky Way's disk and halo from the Anglo-Australian Telescope. We will determine abundances of up to 29 important chemical elements for each star, and plan to use this unprecedented data set to identify stars that originally formed together. Combining this with the precise positions and distances the ESA Gaia spacecraft will measure for all of our stars, we will study the history of star formation, chemical evolution, migration and minor mergers in the Galaxy.

In other work, I use moderate-resolution spectroscopy from Keck Observatory, Lick Observatory and the Very Large Telescope to study the compositions of stars in globular clusters, some of the oldest stars in the Milky Way, and to compare them to star clusters in nearby dwarf galaxies. Since globular cluster stars formed at the very beginning of our galaxy's lifetime, we can use their properties to reconstruct the early history of the Milky Way. Roughly half of the stars in globular clusters have an unusual abundance pattern in the "light" elements (carbon, nitrogen, oxygen, sodium, magnesium and aluminum), indicating that star formation in clusters in the early Galaxy happened quickly and involved recycling material between subsequent generations of stars.

Comparing the abundance patterns in Galactic globular clusters with the patterns in star clusters in nearby dwarf galaxies illuminates the ways in which the large-scale galactic environment affects star formation, and comparing old globular clusters to intermediate-age clusters allows investigation of the ways that cluster formation has changed between the early Universe and the present day. Star clusters that are forming now are quite different from what we think the early phases of globular clusters were like: less massive, generally located in the disks of galaxies, and not able to recycle material into multiple generations. This implies that there has been significant evolution between the early Universe and the present day in the way that star clusters are formed, and also that individual globular clusters have evolved strongly over that same time period.

Student projects

  • GALAH data exploration: Build tools to help classify and search the large and growing dataset from the GALAH (Galactic Archaeology with HERMES) survey. Any level of programming experience welcome.
  • Rare stars in the Galaxy: Search for stars that have migrated from star clusters into the Galactic halo, or have captured material from a binary companion, using spectroscopy from the AAOmega Evolution of Galactic Structure survey.
  • Star clusters and stellar abundances: A star's chemical abundance pattern is a record of where and when it formed. Investigate the differences between stars in clusters that are young and old, in the Milky Way and in nearby dwarf galaxies, to explore the effect of environment and time on star clusters.

You can find more information about these and other available research projects in the School of Physics on the Research Projects page.

Honours, Awards and Memberships: 

Awards

  • 2014 DECRA (Discovery Early Career Researcher Award) Fellowship (Australia)
  • 2010 MPIA-ZAH Ernst Patzer Prize for excellent publication by an early-career researcher in Heidelberg (Germany)

 

Invited talks

  • "Understanding globular cluster formation using halo stars", 2017, "Globular Cluster Systems and their host Galaxies", Sexten, Italy
  • "Multiple populations in the era of large surveys", 2016, "Multiple Populations in Globular Clusters: Where do we stand?", Sexten, Italy
  • "Introduction to the GALAH Survey", 2015, Southern Cross Conference Series VIII, "Multiwavelength Dissection of Galaxies", Sydney, Australia
  • "Future of large ground-based spectroscopic surveys", 2015, IAU Symposium 314, "Young Stars & Planets Near the Sun", Atlanta, Georgia, USA
  • "The GALAH Survey: Overview and Science Goals", 2015, "Multi-Object Spectroscopy in the Next Decade", La Palma, Spain
  • "Galactic Archaeology and the GALAH Survey", 2014, Australian Institute of Physics Congress, Canberra, Australia
  • "The GALAH survey: an overview", 2014, Astronomical Society of Australia Annual Scientific Meeting, Sydney, Australia
  • "Globular clusters and halo formation", 2014, "Great Barriers in Galactic Archaeology II", Palm Cove, Australia
  • "Globular cluster stars in the halo field", 2013, GREAT-ESF workshop "The World of Clusters", Padova, Italy
  • "Globular Cluster Contributions to Galactic Halo Assembly", 2012, XXVIII Internationa Astronomical Union Symposium, Beijing, China
  • "Light-Element Abundance Variations in Globular Clusters", 2010, Astronomische Gesellschaft General Assembly, Bonn, Germany

 

Memberships

  • 2014-present, Steering Committee for Gemini Observatory Gen4#3 instrument development
  • 2014-2015, Australian member of the Gemini Observatory Science and Technology Advisory Committee
  • 2014-2015, member ex officio of the Optical Telescopes Advisory Committee
  • 2013-present, Steering Committee for the Astronomical Society of Australia Early Career Researchers chapter
  • 2011-present, Member of the Astronomical Society of Australia
  • 2009-present, International Affiliate of the American Astronomical Society

Selected Publications: 

Papers on survey science

  1. "The Tenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Apache Point Observatory Galactic Evolution Experiment", Astrophysical Journal Supplement 2014, Ahn, C P and 237 coauthors
  2. "Calibrations of Atmospheric Parameters Obtained from the First Year of SDSS-III APOGEE Observations", Astrophysical Journal 2013, Meszaros, S and 27 coauthors
  3. "The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey", Astrophysical Journal Supplement 2012, Ahn, C P and 235 coauthors

 

Papers on Galactic archaeology

  1. "CN Anomalies in the Halo System and the Origin of Globular Clusters in the Milky Way", Astrophysical Journal 2013, Carollo, D, Martell, S L, Beers, T C and Freeman, K C
  2. "Building the Galactic halo from globular clusters: evidence from chemically unusual red giants", Astronomy & Astrophysics 2011, Martell, S L, Smolinski, J P, Beers, T C and Lee, Y S
  3. "Light-element abundance variations in the Milky Way halo", Astronomy & Astrophysics 2010, Martell, S L and Grebel, E K

 

Papers on stellar structure and abundances

  1. "Lithium-rich field giants in the Sloan Digital Sky Survey", Monthly Notices of the Royal Astronomical Society 2013, Martell, S L and Shetrone, M D
  2. "Cyanogen in NGC 1851 Red Giant Branch and Asymptotic Giant Branch Stars: Quadrimodal Distributions", Astrophysical Journal 2012, Campbell, S W and 9 coauthors
  3. "A Survey of CN and CH Variations in Galactic Globular Clusters from Sloan Digital Sky Survey Spectroscopy", Astronomical Journal 2011, Smolinski, J P, Martell, S L, Beers, T C and Grebel, E K
  4. "Light-element abundance variations in globular clusters", Astronomische Nachrichten 2011, Martell, S L
  5. "Light-element Abundance Variations at Low Metallicity: The Globular Cluster NGC 5466", Astronomical Journal 2010, Shetrone, M D, Martell, S L and 5 coauthors