About

Graeme H Smith is a Professor and Astronomer in the Astronomy & Astrophysics Department within the Physical & Biological Sciences Division at UC Santa Cruz. His research primarily focuses on the properties of red giant stars within the Milky Way galaxy, including their physical evolution, chromospheric activity, and mass loss. He investigates what these stars can reveal about the chemical enrichment history of the Galaxy, with particular attention to abundance differences among stars within globular clusters. His work on these ancient stellar systems, which formed during the early stages of the Galaxy's chemical enrichment, aims to understand the origin of element abundance variations such as carbon, nitrogen, and oxygen among stars in the same cluster. This research provides insights into the early environment of the Galactic halo and processes like deep mixing within the interiors of red giants. Dr. Smith earned his Ph.D. in 1983 from the Australian National University and his B.Sc. in 1978 from the same institution. He is associated with the UC Observatories and can be contacted via phone at 831-459-2907 or email at ghsmith@ucsc.edu or graeme@ucolick.org.

Research topics

• Astronomy
• Physics
• Astrophysics
• Mathematics
• Statistics

Selected publications

• A Color–Magnitude Diagram in the DDO Photometric System

  Research Notes of the AAS · 2025-09-11 · 1 citations

  articleOpen access1st authorCorresponding

  Abstract A signature two-color diagram of the DDO photometric system plots C (45–48), which is sensitive to surface gravity for cool stars, versus C (42–45), which correlates with effective temperature. The extent to which this two-color diagram mimics a Hertzsprung–Russell diagram is explored. To this end, a color–magnitude diagram (CMD) that plots an absolute magnitude M 48 versus color C (42–45) is presented for a sample of field stars for which high-precision DDO photometry and Gaia DR3 parallaxes are available. Such a DDO CMD has seen little use to date.

  PublisherDOI

• Old and Metal-rich G Stars

  Research Notes of the AAS · 2025-07-09

  articleOpen access1st authorCorresponding

  Abstract Planetary systems of very old G stars could provide meaningful comparisons with the solar system. They may even have provided environments with the potential to harbor early exobiology within the Galaxy. It is within these contexts that attention is drawn to a selection of G stars for which there are indications of ages and metallicities significantly greater than solar. A significant fraction of these stars have been included in radial velocity exoplanet searches. Six are known to host orbiting gas giant planets. All warrant further investigation for exoplanets.

  PublisherDOI

• H <i>α</i> Emission among Evolved FGKM Stars: A Compendium from the Literature

  The Astronomical Journal · 2025-11-17

  articleOpen access1st authorCorresponding

  Abstract Emission in the wings of the H α line among late-type giant stars occurs as a consequence of conditions in their chromospheres. Data from the literature have been used to document the incidence of H α emission among Population I giant stars as a function of position in various color–magnitude diagrams (CMDs), including infrared versions that plot <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> </mml:math> versus ( J − K s ) and ( V − K s ). Population I and metal-poor Population II red giants are compared with regard to certain characteristics of H α emission. In the case of stars with emission, both observed photometry and photometry corrected for interstellar reddening are considered. Population I and II giants having H α emission are found to share a number of phenomena: (a) they occupy similar regions of the visual and infrared CMDs; (b) the emission in the blue and red wings is often of unequal strength, suggestive of mass motions in the chromosphere; (c) there are indications of time variability for a few stars that have been observed on multiple occasions; (d) red giants of both Population I and II having H α emission are often long-period or semiregular variables; and (e) a subset of them, but by no means all, evince circumstellar dust. While some giants with H α emission are pulsating red variables that have formed dusty circumstellar envelopes, others may be in prior phases of evolution where pulsations have commenced, which is restructuring the chromosphere and producing outflows, but has not yet generated the conditions needed for dust formation at higher circumstellar altitudes.

  PublisherDOI

• Edward S. Holden and the Bands of Neptune

  Research Notes of the AAS · 2025-03-27

  articleOpen access1st authorCorresponding

  Abstract Reports of visual sightings of bands on Neptune made by E. S. Holden and J. M. Schaeberle at Lick Observatory are described. Holden’s logbooks record that in 1888 September and October bands were discerned on the Neptunian disk and noted on seven nights. A summary of the logbook entries are given in this note, since they do not appear to have been previously published.

  PublisherDOI

• Inferences Regarding a Stellar Metallicity Distribution Following a Single Primordial Chemical Enrichment Event

  Research Notes of the AAS · 2024-03-05

  articleOpen access1st authorCorresponding

  Abstract An idealized scenario is presented according to which a power-law distribution in metallicity might have characterized the first metal-poor stars. The scenario assumes an initial synthesis of heavy elements within a first source of metals, followed by a subsequent ejection of these metals and their dilution within a metal-free gas environment.

  PublisherOA PDFDOI

• Chemical Evolution via Dilution of an Initial Reservoir of Heavy Elements

  Research Notes of the AAS · 2024-06-25

  articleOpen access1st authorCorresponding

  Abstract As a possible analog to the type of environment that might have produced the first low-mass metal-containing stars, a model is outlined in which a reservoir of gas containing the first metals begins forming stars upon an inflow of metal-free gas from a surrounding environment. The mass of gas in the reservoir is assumed to initially increase, reach a maximum, and then follow an exponential decline. The stellar metallicity distribution brought about is an example of chemical evolution via dilution of an initial source of metals.

  PublisherOA PDFDOI

• Christian Huygens and William Derham and 18th Century Precursors to the Habitable Zone

  Research Notes of the AAS · 2024-09-25

  articleOpen access1st authorCorresponding

  Abstract Both Christian Huygens and William Derham expressed ideas that are prescient to the concept of a circumstellar habitable zone: liquid water is a precondition for life, there is a region within the solar system within which liquid surface water can exist upon planets, the stars are suns around which planetary systems should be common, these extrasolar planetary systems may include habitable worlds. Although neither author explicitly developed the phraseology of an exoplanetary habitable zone based upon liquid water, such a concept would follow from their writings.

  PublisherDOI

• OH and H₂O Maser Activities Among Long-period Variables

  Research Notes of the AAS · 2024-07-24

  articleOpen accessSenior authorCorresponding

  Abstract The distribution within an infrared color–magnitude diagram of variable red giants known to have circumstellar masers is reported. Stars with H 2 O-maser sources occur within a color and period domain of ( J − K s ) &gt; 1.15 and P &gt; 199 days, respectively, often in the absence of OH masers. By contrast, OH masers are mostly detected among cooler red giants with ( J − K s ) &gt; 1.35 and P &gt; 316 days, and can coexist with H 2 O-maser sources. The results suggest that red giants must evolve to absolute magnitudes brighter than <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:msub> <mml:mrow> <mml:mi>K</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mo>−</mml:mo> <mml:mn>6.8</mml:mn> </mml:math> prior to enabling H 2 O-maser emission, and possibly expand beyond a certain size before triggering OH masers.

  PublisherDOI

• A Comparison of Publication Counts for Four Ultraviolet Explorer Observatories

  Research Notes of the AAS · 2024-12-23

  articleOpen access1st authorCorresponding

  Abstract Publication counts for four space-based ultraviolet observatories are compared: International Ultraviolet Explorer (IUE), Extreme Ultraviolet Explorer, Far Ultraviolet Spectroscopic Explorer (FUSE), and Galaxy Evolution Explorer (GALEX). The first three show rapid rises to either a sharp or broad maximum. Over the peak period for IUE the papers tend to be concentrated upon data from that mission specifically. Maxima are followed by declines of various duration, after which papers based upon multiple space-based observatories have lead to extended relevancy for each mission, particularly in the case of FUSE. By contrast, papers that incorporate data from GALEX have yet to evince a turn-over. As with FUSE, there is a pronounced trend for results from the GALEX mission to have been incorporated into multi-mission papers.

  PublisherDOI

• OH Emission Among Mira Variables in Color–Magnitude and Period–Magnitude Diagrams

  Research Notes of the AAS · 2023-06-06 · 1 citations

  articleOpen access1st authorCorresponding

  Abstract Infrared absolute-magnitude versus color diagrams have been derived for long-period Mira variables with and without OH-maser emission through the use of Gaia DR3 parallaxes and two samples of stars drawn from the literature. The OH-emitting Miras are mostly consistent with ( J − K s ) &gt; 1.4, an average absolute K s magnitude of around −7.6, and pulsation periods greater than 316 days.

  PublisherDOI

Recent grants

• Collaborative Research: On the Origin of Abundance Inhomogeneities in Globular Clusters

  NSF · $329k · 2009–2015

• Studying Stellar Evolution and Galactic Halo Formation with Globular Cluster Abundance Inhomogeneities

  NSF · $207k · 2004–2010

• Exploring the Solar Neighborhood with the GALEX All Sky Survey

  NSF · $98k · 2015–2021

Frequent coauthors

• Michael M. Briley

  56 shared

• J. E. Hesser

  40 shared

• R. A. Bell

  35 shared

• A. K. Dupree

  Center for Astrophysics Harvard & Smithsonian

  29 shared

• Matthew Shetrone

  21 shared

• Jay Strader

  14 shared

• Robert P. Kraft

  Center for Astrophysics Harvard & Smithsonian

  12 shared

• Sarah L. Martell

  11 shared