Deep Optical Photometry of Six Fields in the Andromeda Galaxy (2009)
Brown, Thomas M., Smith, Ed, Ferguson, Henry C., Guhathakurta, Puragra, Kalirai, Jason S., Kimble, Randy A., ...
Using the Advanced Camera for Surveys on the Hubble Space Telescope, we have obtained deep optical images reaching well below the oldest main sequence turnoff in six fields of the Andromeda Galaxy....
The Extended Star Formation History of the Andromeda Spheroid at 35 Kpc on the Minor Axis (2008)
Brown, Thomas M., Beaton, Rachael, Chiba, Masashi, Ferguson, Henry C., Gilbert, Karoline M., Guhathakurta, Puragra, ...
Using the HST ACS, we have obtained deep optical images reaching well below the oldest main sequence turnoff in fields on the southeast minor-axis of the Andromeda Galaxy, 35 kpc from the nucleus....
The Dearth of UV-Bright Stars in M32: Implications for Stellar Evolution Theory (2008)
Brown, Thomas M., Smith, Ed, Ferguson, Henry C., Sweigart, Allen V., Kimble, Randy A., Bowers, Charles W.
Using the Space Telescope Imaging Spectrograph on the Hubble Space Telescope, we have obtained deep far-ultraviolet images of the compact elliptical galaxy M32. When combined with earlier...
Brown, Thomas M., Smith, Ed, Ferguson, Henry C., Guhathakurta, Puragra, Kalirai, Jasonjot S., Rich, R. Michael, ...
Using the HST ACS, we have obtained deep optical images of a southeast minor-axis field in the Andromeda Galaxy, 21 kpc from the nucleus. In both star counts and metallicity, this field represents a...
Brown, Thomas M., Smith, Ed, Ferguson, Henry C., Rich, R. Michael, Guhathakurta, Puragra, Renzini, Alvio, ...
Using the Advanced Camera for Surveys on the Hubble Space Telescope, we have obtained deep optical images reaching stars well below the oldest main sequence turnoff in the spheroid, tidal stream, and...
Brown, Thomas M., Smith, Ed, Guhathakurta, Puragra, Rich, R. Michael, Ferguson, Henry C., Renzini, Alvio, ...
We present a color-magnitude diagram (CMD) for a field in the giant tidal stream of the Andromeda galaxy (M31). These observations, taken with the Advanced Camera for Surveys on the Hubble Space...
Stellar Cluster Fiducial Sequences with the Advanced Camera for Surveys (2005)
Brown, Thomas M., Ferguson, Henry C., Smith, Ed, Guhathakurta, Puragra, Kimble, Randy A., Sweigart, Allen V., ...
We present color-magnitude diagrams of five Galactic globular clusters and one Galactic open cluster spanning a wide range of metallicity (-2.1 < [Fe/H] < +0.3), as observed in the F606W (broad V)...
Age Constraints for an M31 Globular Cluster from Main Sequence Photometry (2004)
Brown, Thomas M., Ferguson, Henry C., Smith, Ed, Kimble, Randy A., Sweigart, Allen V., Renzini, Alvio, ...
We present a color-magnitude diagram (CMD) of the globular cluster SKHB-312 in the Andromeda galaxy (M31), obtained with the Advanced Camera for Surveys on the Hubble Space Telescope. The cluster was...
RR Lyrae Stars in the Andromeda Halo from Deep Imaging with the Advanced Camera for Surveys (2004)
Brown, Thomas M., Ferguson, Henry C., Smith, Ed, Kimble, Randy A., Sweigart, Allen V., Renzini, Alvio, ...
We present a complete census of RR Lyrae stars in a halo field of the Andromeda galaxy. These deep observations, taken as part of a program to measure the star formation history in the halo, spanned...
Evidence for Flash Mixing in He-rich sdB Stars (2003)
Sweigart, Allen V., Lanz, Thierry, Brown, Thomas M., Hubeny, Ivan, Landsman, Wayne B.
We present FUSE spectra of three He-rich sdB stars. Two of these stars, PG1544+488 and JL87, reveal extremely strong C III lines, suggesting that they have mixed triple-alpha carbon from the deep...
Flash Mixing on the White Dwarf Cooling Curve: FUSE Observations of three He-rich sdB Stars (2003)
Lanz, Thierry, Brown, Thomas M., Sweigart, Allen V., Hubeny, Ivan, Landsman, Wayne B.
We present FUSE spectra of 3 He-rich sdB stars. Two of these stars, PG1544+488 and JL87, reveal extremely strong C III lines at 977 and 1176A, while the carbon lines are quite weak in the third star,...
HST Snaphot Study of Variable Stars in Globular Clusters: Inner Region of NGC 6441 (2003)
Pritzl, Barton J., Smith, Horace A., Stetson, Peter B., Catelan, Marcio, Sweigart, Allen V., Layden, Andrew C., ...
[Abridged] We present the results of a Hubble Space Telescope snapshot program to survey the inner region of the globular cluster NGC 6441 for its variable stars. A total of 57 variable stars was...
Brown, Thomas M., Ferguson, Henry C., Smith, Ed, Kimble, Randy A., Sweigart, Allen V., Renzini, Alvio, ...
We present a color-magnitude diagram (CMD) for a minor-axis field in the halo of the Andromeda galaxy (M31), 51 arcmin (11 kpc) from the nucleus. These observations, taken with the Advanced Camera...
A New Formation Mechanism for the Hottest Horizontal-Branch Stars (2002)
Sweigart, Allen V., Brown, Thomas M., Lanz, Thierry, Landsman, Wayne B., Hubeny, Ivan
Stars with very large mass loss on the red-giant branch can undergo the helium flash while descending the white-dwarf cooling curve. Under these conditions the flash convection zone will mix the...
Using M32 to Study Rapid Phases of Stellar Evolution (2002)
Brown, Thomas M., Ferguson, Henry C., Sweigart, Allen V., Kimble, Randy A., Bowers, Charles W.
The compact elliptical galaxy M32 offers a unique testing ground for theories of stellar evolution. Because of its proximity, solar-blind UV observations can resolve the hot evolved stars in its...
Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6388 (2002)
Pritzl, Barton J., Smith, Horace A., Catelan, Marcio, Sweigart, Allen V.
We have undertaken a search for variable stars in the metal-rich globular cluster NGC 6388 using time-series BV photometry. Twenty-eight new variables were found in this survey, increasing the total...
The Origin of Hot Subluminous Horizontal-Branch Stars in Omega Centauri and NGC 2808 (2002)
Sweigart, Allen V., Brown, Thomas M., Lanz, Thierry, Landsman, Wayne B., Hubeny, Ivan
Hot subluminous stars lying up to 0.7 mag below the extreme horizontal branch (EHB) are found in the UV color-magnitude diagrams of omega Cen and NGC 2808. Such stars are unexplained by canonical HB...
Brown, Thomas M., Sweigart, Allen V., Lanz, Thierry, Landsman, Wayne B., Hubeny, Ivan
We present a UV CMD spanning the hot horizontal branch (HB), blue straggler, and white dwarf populations of the globular cluster NGC 2808. These data were obtained with the Space Telescope Imaging...
Variable Stars in the Unusual, Metal-Rich Globular Cluster NGC 6441 (2001)
Pritzl, Barton J., Smith, Horace A., Catelan, Marcio, Sweigart, Allen V.
We have undertaken a search for variable stars in the metal-rich globular cluster NGC 6441 using time-series BV photometry. The total number of variables found near NGC 6441 has been increased to...
Horizontal Branch Models as a Test of Mixing on the RGB (2001)
We discuss the impact of mixing and rotation along the red-giant branch (RGB) on the properties of horizontal-branch (HB) stars with emphasis on two problems: the nature of the unexpected blue HB...
RR Lyrae Stars in NGC 6388 and NGC 6441: A New Oosterhoff Group? (1999)
Pritzl, Barton, Smith, Horace A., Catelan, Marcio, Sweigart, Allen V.
NGC 6388 and NGC 6441 are anomalies among Galactic globular clusters in that they cannot be readily place into either Oosterhoff group I or Oosterhoff group II despite their significant numbers of RR...
Synthetic Spectra and Color-Temperature Relations of M Giants (1999)
Houdashelt, Mark L., Bell, Roger A., Sweigart, Allen V., Wing, Robert F.
As part of a project to model the integrated spectra and colors of elliptical galaxies through evolutionary synthesis, we have refined our synthetic spectrum calculations of M giants. After...
Improved Color-Temperature Relations and Bolometric Corrections for Cool Stars (1999)
Houdashelt, Mark L., Bell, Roger A., Sweigart, Allen V.
We present new grids of colors and bolometric corrections for F-K stars having 4000 K < Teff < 6500 K, 0.0 < log g < 4.5 and -3.0 < [Fe/H] < 0.0. A companion paper extends these calculations into the...
Radiation-Pressure Ejection of Planetary Nebulae in Asymptotic-Giant- Branch Stars (1999)
We have investigated the possibility that radiation pressure might trigger planetary nebula (PN) ejection during helium-shell flashes in asymptotic- giant-branch (AGB) stars. We find that the outward...
Detection and Photometry of Hot Horizontal Branch Stars in the Core of M32 (1999)
Brown, Thomas M., Bowers, Charles W., Kimble, Randy A., Sweigart, Allen V., Ferguson, Henry C.
We present the deepest near-UV image of M32 to date, which for the first time resolves hot HB stars in an elliptical galaxy. Given the near-solar metallicity of M32, much larger than that of globular...
Gravonuclear Instabilities in Post-Horizontal-Branch Stars (1999)
Sweigart, Allen V., Lattanzio, John C., Gray, James P., Tout, Christopher A.
We investigate the gravonuclear instabilities reported by Bono et al. (1997a,b) during the onset of helium-shell burning at the end of the horizontal-branch (HB) phase. These instabilities are...
The Second-Parameter Effect in Metal-Rich Globular Clusters (1999)
Recent Hubble Space Telescope (HST) observations by Rich et al. (1997) have shown that the metal-rich globular clusters (GCs) NGC 6388 and NGC 6441 exhibit a pronounced 2nd parameter effect....
Hot stellar population synthesis from the UV spectrum: the globular cluster M79 (NGC 1904) (1999)
Vink, Jorick S., Heap, Sara R., Sweigart, Allen V., Lanz, Thierry, Hubeny, Ivan
We have analyzed the far UV-spectrum of the globular cluster M79. We show that the nearly Gaussian mass distribution of zero-age horizontal-branch stars, as derived by Dixon et al.(1996), is able to...
Proton-Capture Nucleosynthesis in Globular Cluster Red Giant Stars (1997)
Cavallo, Robert M., Sweigart, Allen V., Bell, Roger A.
We follow the static abundance profiles of the C, N, O, Ne, Na, Mg, and Al isotopes around the hydrogen-burning shell (H shell) of globular cluster red-giant-branch (RGB) stellar models in order to...
The Production of Sodium and Aluminum in Globular Cluster Red Giant Stars (1996)
Cavallo, Robert M., Sweigart, Allen V., Bell, Roger A.
We study the production of Na and Al around the hydrogen shell of two red-giant sequences of different metallicity in order to explain the abundance variations seen in globular cluster stars in a...