Brian Chaboyer

Dartmouth College

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Ata Sarajedini

University of Florida

Aaron Dotter

Dartmouth College

Nathaniel Paust

Whitman College

V. F. Braga

Astronomical Observatory of Rome

M. Dall’Ora

Astronomical Observatory of Capodimonte

M. Fabrizio

Astronomical Observatory of Rome

M. Marengo

Florida State University

C. K. Gilligan

Dartmouth College

Gregory A. Feiden

University of North Georgia

G. Bono

University of Rome Tor Vergata

Cooperative Institutions

Max Planck Society

Max Planck Institute for Astronomy

California Institute of Technology

National Institute for Astrophysics

Blue Planet (Norway)

Cerro Tololo Inter-American Observatory

Space Telescope Science Institute

The Ohio State University

U.S. National Science Foundation

University of Warsaw

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The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters without PreviousHubble Space TelescopePhotometry

The Astronomical Journal (2007)

Ata Sarajedini L. R. Bedin Brian Chaboyer Aaron Dotter M. H. Siegel

We present the first results of a large Advanced Camera for Surveys (ACS) survey of Galactic globular clusters. This Hubble Space Telescope (HST) Treasury project is designed to obtain photometry with S/N (signal-to-noise ratio) ≳10 for main-sequence stars with masses ≳0.2 M⊙ in a sample of globulars using the ACS Wide Field Channel. Here we focus on clusters without previous HST imaging data. These include NGC 5466, NGC 6779, NGC 5053, NGC 6144, Palomar 2, E3, Lyngå 7, Palomar 1, and NGC 6366. Our color-magnitude diagrams (CMDs) extend reliably from the horizontal branch to as much as 7 mag fainter than the main-sequence turnoff and represent the deepest CMDs published to date for these clusters. Using fiducial sequences for three standard clusters (M92, NGC 6752, and 47 Tuc) with well-known metallicities and distances, we perform main-sequence fitting on the target clusters in order to obtain estimates of their distances and reddenings. These comparisons, along with fitting the cluster main sequences to theoretical isochrones, yield ages for the target clusters. We find that the majority of the clusters have ages that are consistent with the standard clusters at their metallicities. The exceptions are E3, which appears ∼2 Gyr younger than 47 Tuc, and Pal 1, which could be as much as 8 Gyr younger than 47 Tuc.

Hubble sequence

10.1086/511979

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Citations (465)

The Evolution of the Lithium Abundances of Solar-Type Stars.V. K Dwarfs in the Hyades

The Astronomical Journal (1995)

David R. Soderblom B. F. Jones J. R. Stauffer Brian Chaboyer

We have observed a dozen Hyades K dwarfs at high resolution and high signal to noise to see if they show a spread in their Li abundances like the spread seen among Pleiades K dwarfs. We cannot detect a Li feature in these stars, but we see no differences in their spectra at the Li 6708 Å feature that exceed 2 mÅ. This suggests the Hyades K dwarfs lack the spread in Li seen in Pleiades K dwarfs, indicating a different history of Li depletion.

10.1086/117556

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Citations (29)

The Physics of Semiconvection and Implications for Horizontal Branch Evolution

American Astronomical Society Meeting Abstracts (1994)

Scott A. Grossman Brian Chaboyer

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The seismic structure of the Sun from GONG

Symposium - International Astronomical Union (1997)

E. Anderson H. M. Antia Sarbani Basu Brian Chaboyer S. M. Chitre

This paper is an interim report of our inferences about the hydrostatic structure of the Sun, following the first report of the GONG team in Science (Gough et al. , 1996). That work confirms that the spherically averaged structure of the Sun is more or less in agreement with current standard solar models. However, there remain some significant deviations which we regard as important clues to the existence of dynamical phenomena which are not taken into account in standard solar modelling.

Interim

Hydrostatic equilibrium

10.1017/s0074180900061106

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Citations (1)

Erratum: “High-resolution Spectroscopic Abundances of Red Giant Branch Stars in NGC 6584 and NGC 7099” (2018, ApJ, 856, 130)

The Astrophysical Journal (2019)

Erin M. O’Malley Brian Chaboyer A. Y. Kniazev

Red giant

Red-giant branch

Asymptotic giant branch

Hubble sequence

10.3847/1538-4357/aafafc

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RGB Luminosity Functions for M2, M3, and M14

American Astronomical Society Meeting Abstracts #217 (2011)

Nathaniel Paust Brian Chaboyer

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Absolute Photometry of RR Lyrae Stars in the LMC

NOAO Proposal (2006)

Andrea Kunder Brian Chaboyer

RR Lyrae variable

Variable star

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MAGNETIC INHIBITION OF CONVECTION AND THE FUNDAMENTAL PROPERTIES OF LOW-MASS STARS. I. STARS WITH A RADIATIVE CORE

The Astrophysical Journal (2013)

Gregory A. Feiden Brian Chaboyer

Magnetic fields are hypothesized to inflate the radii of low-mass stars---defined as less massive than 0.8$M_\odot$---in detached eclipsing binaries (DEBs). We investigate this hypothesis using the recently introduced magnetic Dartmouth stellar evolution code. In particular, we focus on stars thought to have a radiative core and convective outer envelope by studying in detail three individual DEBs: UV Psc, YY Gem, and CU Cnc. The results suggest that the stabilization of thermal convection by a magnetic field is a plausible explanation for the observed model-radius discrepancies. However, surface magnetic field strengths required by the models are significantly stronger than those estimated from the observed coronal X-ray emission. Agreement between model predicted surface magnetic field strengths and those inferred from X-ray observations can be found by assuming that the magnetic field sources its energy from convection. This approach makes the transport of heat by convection less efficient and is akin to reduced convective mixing length methods used in other studies. Predictions for the metallicity and magnetic field strengths of the aforementioned systems are reported. We also develop an expression relating a reduction in the convective mixing length to a magnetic field strength in units of the equipartition value. Our results are compared with those from previous investigations to incorporate magnetic fields to explain the low-mass DEB radius inflation. Finally, we explore how the effects of magnetic fields might affect mass determinations using asteroseismic data and the implication of magnetic fields on exoplanet studies.

Field strength

Radiation zone

10.1088/0004-637x/779/2/183

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Citations (101)

Correlations between Ca II H&K Emission and the Gaia M dwarf Gap

arXiv (Cornell University) (2024)

Emily M. Boudreaux Aylin García Soto Brian Chaboyer

The Gaia M dwarf gap, also known as the Jao Gap, is a novel feature discovered in the Gaia DR2 G vs. BP-RP color magnitude diagram. This gap represents a 17 percent decrease in stellar density in a thin magnitude band around the convective transition mass ($\sim 0.35 M_{\odot}$) on the main sequence. Previous work has demonstrated a paucity of Hydrogen Alpha emission coincident with the G magnitude of the Jao Gap in the solar neighborhood. The exact mechanism which results in this paucity is as of yet unknown; however, the authors of the originating paper suggest that it may be the result of complex variations to a star's magnetic topology driven by the Jao Gap's characteristic formation and breakdown of stars' radiative transition zones. We present a follow up investigating another widely used magnetic activity metric, Calcium II H\&K emission. Ca II H\&K activity appears to share a similar anomalous behavior as H$\alpha$ does near the Jao Gap magnitude. We observe an increase in star-to-star variation of magnetic activity near the Jao Gap. We present a toy model of a stars magnetic field evolution which demonstrates that this increase may be due to stochastic disruptions to the magnetic field originating from the periodic mixing events characteristic of the convective kissing instabilities which drive the formation of the Jao Gap.

10.48550/arxiv.2402.14984

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The Absolute Age of NGC 3201 derived from Detached Eclipsing Binaries and the Hess Diagram

arXiv (Cornell University) (2024)

Jiaqi Ying Brian Chaboyer Wenxin Du

We estimate the absolute age of the globular cluster NGC 3201 using $10,000$ sets of theoretical isochrones constructed through Monte Carlo simulation using the Dartmouth Stellar Evolution Program. These isochrones take into consideration of uncertainty introduced by the choice of stellar evolution parameters. We fit isochrones with 3 detached eclipsing binaries and obtained an age independent of distance. We also fit isochrones with differential reddening corrected HST photometry data utilizing two different Hess diagram based fitting methods. Results from 3 different methods analyzing 2 different types of data agree to within $1 \sigma$, and we find the absolute age of NGC 3201 $= 11.85 \pm 0.74$ Gyr. We also perform variable importance analysis to study the uncertainty contribution from individual parameters and we find the distance is the dominance source of uncertainty in photometry based analysis while total metallicity, Helium abundance, $\alpha$-element abundance, mixing length, and treatment of helium diffusion are important source of uncertainties for all 3 methods.

Absolute magnitude

10.48550/arxiv.2406.12206

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