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Articles 1 - 30 of 31
Full-Text Articles in Stars, Interstellar Medium and the Galaxy
Ccd Photometry Of The Classic Second-Parameter Globular Clusters M3 And M13, Soo-Chang Rey, Suk-Jin Yoon, Young-Wook Lee, Brian Chaboyer, Ata Sarajedini
Ccd Photometry Of The Classic Second-Parameter Globular Clusters M3 And M13, Soo-Chang Rey, Suk-Jin Yoon, Young-Wook Lee, Brian Chaboyer, Ata Sarajedini
Dartmouth Scholarship
We present high-precision V, B-V color-magnitude diagrams (CMDs) for the classic second-parameter globular clusters M3 and M13 from wide-field, deep CCD photometry. The data for the two clusters were obtained during the same photometric nights with the same instrument, allowing us to determine accurate relative ages. Based on a differential comparison of the CMDs using the Δ(B-V) method, an age difference of 1.7 ± 0.7 Gyr is obtained between these two clusters. We compare this result with our updated horizontal-branch (HB) population models, which confirm that the observed age difference can produce the …
Chromospherically Active Stars. Xx. The Giant Single-Lined Binary Hd 161570, Francis C. Fekel, Gregory W. Henry, Stephen M. Henry
Chromospherically Active Stars. Xx. The Giant Single-Lined Binary Hd 161570, Francis C. Fekel, Gregory W. Henry, Stephen M. Henry
Information Systems and Engineering Management Research Publications
Spectroscopy of HD 161570 shows it to be a single-lined spectroscopic binary with a period of 45.623 days and a nearly circular orbit. The primary star has spectral type G7 III, and the secondary is most likely a G or K dwarf. A high-resolution spectrum of the 3950 Å region confirms that the primary has Ca II H and K emission lines. The logarithm of the giant's lithium abundance is less than 0.9, indicating that it is not lithium-rich. From photometric observations covering six seasons, we detected periodic short-term light variability with an amplitude ranging from 0.02 to 0.04 mag. …
A New System Of Parallel Isolated Nonthermal Filaments Near The Galactic Center: Evidence For A Local Magnetic Field Gradient, Ted N. La Rosa, Joseph W. Lazio, Nasir E. Kassim
A New System Of Parallel Isolated Nonthermal Filaments Near The Galactic Center: Evidence For A Local Magnetic Field Gradient, Ted N. La Rosa, Joseph W. Lazio, Nasir E. Kassim
Faculty and Research Publications
We report the discovery of a system of isolated nonthermal filaments approximately 0fdg5 northwest (75 pc in projection) of Sgr A. Unlike other isolated nonthermal filaments which show subfilamentation, braiding of subfilaments, and flaring at their ends, these filaments are simple linear structures and more closely resemble the parallel bundled filaments in the Galactic center radio arc. However, the most unusual feature of these filaments is that the 20/90 cm spectral index uniformly decreases as a function of length, in contrast to all other nonthermal filaments in the Galactic center. This spectral gradient may not be due to simple particle …
Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Et Al.
Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Et Al.
Publications
We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (Teff, log g, and [Fe/H]) for Galactic F- and G-type stars. The ANNs are fed with medium-resolution (Δλ ~ 1-2 Å) non-flux-calibrated spectroscopic observations. From a sample of 279 stars with previous high-resolution determinations of metallicity and a set of (external) estimates of temperature and surface gravity, our ANNs are able to predict Teff with an accuracy of σ(Teff) = 135-150 K over the range 4250 ≤ Teff ≤ 6500 K, log g with an accuracy …
Hubble Space Telescope Wfpc2 Imaging Of Cassiopeia A, R. A. Fesen, J. A. Morse, R. A. Chevalier, K. J. Borkowski, C. L. Gerardy
Hubble Space Telescope Wfpc2 Imaging Of Cassiopeia A, R. A. Fesen, J. A. Morse, R. A. Chevalier, K. J. Borkowski, C. L. Gerardy
Dartmouth Scholarship
The young galactic supernova remnant Cassiopeia A was imaged with Wide Field Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope through filters selected to capture the complete velocity range of the remnant's main shell in several emission lines. The primary lines detected, along with the specific WFPC2 filters used, were [O III] λλ4959, 5007 (F450W), [N II] λ6583 (F658N), [S II] λλ6716, 6731 + [O II] λλ7319, 7330 + [O I] λλ6300, 6364 (F675W), and [S III] λλ9069, 9532 (F850LP). About three-quarters of the remnant's 4' diameter main shell was imaged with all four filters in three WFPC2 pointings, …
Comparison Of Stellar Angular Diameters From The Npoi, The Mark Iii Optical Interferometer, And The Infrared Flux Method, Tyler E. Nordgren, Jeffrey J. Sudol, D. Mozurkewich
Comparison Of Stellar Angular Diameters From The Npoi, The Mark Iii Optical Interferometer, And The Infrared Flux Method, Tyler E. Nordgren, Jeffrey J. Sudol, D. Mozurkewich
Physics & Engineering Faculty Publications
No abstract provided.
The Cataclysmic Variable Cw 1045+525: A Secondary-Dominated Dwarf Nova?, C. Tappert, J. R. Thorstensen, W. H. Fenton, N. Bennert
The Cataclysmic Variable Cw 1045+525: A Secondary-Dominated Dwarf Nova?, C. Tappert, J. R. Thorstensen, W. H. Fenton, N. Bennert
Dartmouth Scholarship
We present spectroscopic and photometric observations of the cataclysmic variable CW 1045+525. Both the optical spectrum and the photometric lightcurve show a strong contribution of a K5V–M0V secondary. We derive an orbital period Porb = 0.271278(1) d by measuring the radial velocities of the absorption lines of the secondary. The period and spectral type of the secondary suggest a distance of 350–700 pc. There is evidence for additional sources of line- and continuum emission, but no direct evidence of an accretion disc. We discuss several scenarios for the nature of CW 1045+525 on the basis of our results, finding a …
Spectroscopy And Orbital Periods Of Four Cataclysmic Variable Stars, John R. Thorstensen, Cynthia J. Taylor
Spectroscopy And Orbital Periods Of Four Cataclysmic Variable Stars, John R. Thorstensen, Cynthia J. Taylor
Dartmouth Scholarship
We present spectroscopy and orbital periods Porb of four relatively little-studied cataclysmic variable stars. The stars and their periods are: AF Cam, Porb = 0.324(1) d (the daily cycle count is slightly ambiguous); V2069 Cyg (= RX J2123.7+4217), 0.311683(2) d; PG 0935+075, 0.1868(3) d; and KUV 03580+0614, 0.1495(6) d. V2069 Cyg and KUV 03580+0614 both show He iiλ4686 emission comparable in strength to Hβ. V2069 Cyg appears to be a luminous nova-like variable, and the strong He ii suggests it may be an intermediate polar. The period of KUV 03580+0614 is similar to members …
Spectral Energy Distribution Signatures Of Jovian Planets Around White Dwarf Stars., R. Ignace
Spectral Energy Distribution Signatures Of Jovian Planets Around White Dwarf Stars., R. Ignace
Richard Ignace
The problem of detecting Jovian-sized planets orbiting white dwarf stars is considered. Significant IR excesses result from warm Jupiters orbiting a white dwarf of Teff = 10,000 K at a distance of ~103 white dwarf radii (corresponding to ~102 Jupiter radii or a few tenths of an AU) with an orbital period of ~100 days. Such a planet will have a 10 µm flux density at its Wien peak that is comparable to the emission of the white dwarf at that wavelength. Although the white dwarf is much hotter than the planet, the planet will have peak …
Line Forces In Keplerian Circumstellar Disks And Precession Of Nearly Circular Orbits., K. G. Gayley, R. Ignace, S. P. Owocki
Line Forces In Keplerian Circumstellar Disks And Precession Of Nearly Circular Orbits., K. G. Gayley, R. Ignace, S. P. Owocki
Richard Ignace
We examine the effects of optically thick line forces on orbiting circumstellar disks, such as occur around Be stars. For radially streaming radiation, line forces are only effective if there is a strong radial velocity gradient, as occurs, for example, in a line-driven stellar wind. However, within an orbiting disk, the radial shear of the azimuthal velocity leads to strong line-of-sight velocity velocity gradients along nonradial directions. As such, in the proximity of a stellar surface extending over a substantial cone angle, the nonradial stellar radiation can impart a significant line force, even in the case of purely circular orbits. …
Terminal Speeds And Ion Fractions From [Caiv] 3.207 Μm In Three Single Wn Stars., Richard Ignace
Terminal Speeds And Ion Fractions From [Caiv] 3.207 Μm In Three Single Wn Stars., Richard Ignace
Richard Ignace
We report on the forbidden emission lines of [CaIV] at 3.207 μm and [NeIII] at 15.56 μm based on Infrared Space Observatory observations. The data set consists of three single Wolf-Rayet stars (WR 1, WR 134, and WR 136) and three binary systems (WR 11, WR 146, and WR 147). For the single stars, only the [CaIV] line was observed. Our primary objectives are to determine the wind terminal speed from the emission-line widths, derive ion number fractions, and discuss the relation between emission profile shapes and wind flow geometry. Compared to previous determinations of the terminal speed, we find …
The Nature Of [Ar Iii]-Bright Knots In The Crab Nebula, Emily L. Schaller, Robert A. Fesen
The Nature Of [Ar Iii]-Bright Knots In The Crab Nebula, Emily L. Schaller, Robert A. Fesen
Dartmouth Scholarship
The kinematic and morphological properties of a string of [Ar III] bright knots in the CrabNebula are examined using 1994 – 1999 HST WFPC-2 images of the remnant. We find that five southern [Ar III] bright knots exhibit ordinary radial motions away from the nebula’s center of expansion with magnitudes consistent with their projected radial displacements. This result does not support the suggestion by MacAlpine et al. (1994) that these knots might be moving rapidly away from the Crab pulsar due to a collimated wind. The HST images also do not show that the [Ar III] knots have unusual morphologies …
Chromospherically Active Stars. Xix. A Reexamination Of The Variability Of Hd 10909=Uv Fornacis, Francis C. Fekel, Gregory W. Henry, Keinon Brooks, Douglas S. Hall
Chromospherically Active Stars. Xix. A Reexamination Of The Variability Of Hd 10909=Uv Fornacis, Francis C. Fekel, Gregory W. Henry, Keinon Brooks, Douglas S. Hall
Information Systems and Engineering Management Research Publications
We have obtained new spectroscopy and photometry of the K0 IV, chromospherically active, single-lined spectroscopic binary HD 10909. Those observations show that the previously reported orbital and light variability periods are incorrect. HD 10909 has an orbital period of 30.1067 days and an eccentricity of 0.499. Its rotation period of 64.1 days is more than twice as long as its orbital period. The primary is situated near the base of the first-ascent red giant branch. Thus, its asynchronous rotation is likely the result of its recent evolution through the Hertzsprung gap, combined with its relatively long orbital period and high …
Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Carlos Allende Prieto, Timothy C. Beers, Christopher Sneden, Et Al.
Three-Dimensional Spectral Classification Of Low-Metallicity Stars Using Artificial Neural Networks, Shawn Snider, Ted Von Hippel, Carlos Allende Prieto, Timothy C. Beers, Christopher Sneden, Et Al.
Publications
We explore the application of artificial neural networks (ANNs) for the estimation of atmospheric parameters (Teff, log g, and [Fe/H]) for Galactic F- and G-type stars. The ANNs are fed with medium-resolution (Δλ ~ 1-2 Å) non-flux-calibrated spectroscopic observations. From a sample of 279 stars with previous high-resolution determinations of metallicity and a set of (external) estimates of temperature and surface gravity, our ANNs are able to predict Teff with an accuracy of σ(Teff) = 135-150 K over the range 4250 ≤ Teff ≤ 6500 K, log g with an accuracy of σ(log …
Stellar Pollution In The Solar Neighborhood, N. Murray, B. Chaboyer, P. Arras, B. Hansen, R. W. Noyes
Stellar Pollution In The Solar Neighborhood, N. Murray, B. Chaboyer, P. Arras, B. Hansen, R. W. Noyes
Dartmouth Scholarship
We study spectroscopically determined iron abundances of 640 solar-type stars to search for the signature of accreted iron-rich material. We find that the metallicity [Fe/H] of a subset of 466 main-sequence stars, when plotted as a function of stellar mass, mimics the pattern seen in lithium abundances in open clusters. Using Monte Carlo models, we find that, on average, these stars appear to have accreted ~0.5 M⊕ of iron while on the main-sequence. A consistency check is provided by a much smaller sample of 19 stars in the Hertzsprung gap, which are slightly evolved and the convection zones of …
X‐Ray–Emitting Groups In The Infall Region Of Abell 2199, K. Rines, A. Mahdavi, M. J. Geller, A. Diaferio, J. J. Mohr, G. Wegner
X‐Ray–Emitting Groups In The Infall Region Of Abell 2199, K. Rines, A. Mahdavi, M. J. Geller, A. Diaferio, J. J. Mohr, G. Wegner
Dartmouth Scholarship
Using a large redshift survey covering 95 deg2, we demonstrate that the infall region of Abell 2199 contains Abell 2197, one or two X-ray-emitting groups, and up to five additional groups identified in redshift surveys. Our survey shows that the X-ray-emitting systems, located at projected radii of 14, 19, and 51 (2.2, 3.1, and 8.0 h-1 Mpc), are connected kinematically to A2199. A2197 is itself an optically rich cluster; its weak X-ray emission suggests that it is much less massive than A2199. The absence of a sharp peak in the infall pattern at the position of A2197 supports this …
The Expansion Center And Dynamical Age Of The Galactic Supernova Remnant Cassiopeia A, John R. Thorstensen, Robert A. Fesen, Sidney Van Den Bergh
The Expansion Center And Dynamical Age Of The Galactic Supernova Remnant Cassiopeia A, John R. Thorstensen, Robert A. Fesen, Sidney Van Den Bergh
Dartmouth Scholarship
We present proper motions for 21 bright main shell and 17 faint, higher velocity, outer ejecta knots in the Cas A supernova remnant and use them to derive new estimates for the remnant's expansion center and age. Our study included 1951–1976 Palomar 5 m prime focus plates, 1988–1999 CCD images from the KPNO 4 m and MDM 2.4 m telescopes, and 1999 HST WFPC2 images. Measurable positions covered a 23 to 41 yr time span for most knots, with a few outer knots followed for almost 48 yr. We derive an expansion center of α(J2000) = 23h23m …
Modelling X-Ray Variability In The Structured Atmospheres Of Hot Stars., L. M. Oskinova, R. Ignace, J. C. Brown, J. P. Cassinelli
Modelling X-Ray Variability In The Structured Atmospheres Of Hot Stars., L. M. Oskinova, R. Ignace, J. C. Brown, J. P. Cassinelli
Richard Ignace
We describe X-ray production in the atmospheres of hot, early-type stars in the framework of a "stochastic shock model". The extended envelope of a star is assumed to possess numerous X-ray emitting "hot" zones that are produced by shocks and embedded in the ambient "cold" medium in dynamical equilibrium. It is shown that the apparent lack of X-ray variability on short (similar to hours) timescales do not contradict a shock model for X-ray production. The character of the X-ray variability is found to depend on the frequency with which hot zones are generated, the cool wind opacity to X-rays, and …
A Search For Previously Unrecognized Metal-Poor Subdwarfs In The Hipparcos Astrometric Catalogue, I. N. Reid, F. Van Wyk, F. Marang, G. Roberts, D. Kilkenny, S. Mahoney
A Search For Previously Unrecognized Metal-Poor Subdwarfs In The Hipparcos Astrometric Catalogue, I. N. Reid, F. Van Wyk, F. Marang, G. Roberts, D. Kilkenny, S. Mahoney
Dartmouth Scholarship
We have identified 317 stars included in the Hipparcos astrometric catalogue that have parallaxes measured to a precision of better than 15 per cent, and the location of which in the (MV,(B−V)T) diagram implies a metallicity comparable to or less than that of the intermediate‐abundance globular cluster M5. We have undertaken an extensive literature search to locate Strömgren, Johnson/Cousins and Walraven photometry for over 120 stars. In addition, we present new UBV(RI)C photometry of 201 of these candidate halo stars, together with similar data for a further 14 known metal‐poor subdwarfs. These …
Infrared Spectroscopy Of Symbiotic Stars. Iii. First Orbits For Three S-Type Systems, Francis C. Fekel, Kenneth H. Hinkle, Richard Joyce, Michael F. Skrutskie
Infrared Spectroscopy Of Symbiotic Stars. Iii. First Orbits For Three S-Type Systems, Francis C. Fekel, Kenneth H. Hinkle, Richard Joyce, Michael F. Skrutskie
Information Systems and Engineering Management Research Publications
Infrared radial velocities have been used to derive the first well-determined orbital elements for the cool giants of three symbiotic systems, BF Cyg, V1329 Cyg, and V343 Ser=AS 289. Periods found for BF Cyg and V1329 Cyg from the radial velocity data are in good agreement with periods previously determined for their light variations, and the orbits are circular. Masses for the components of BF Cyg and V1329 Cyg were determined by combining our orbital elements for the cool giants with elements for their hot stars. BF Cyg and V1329 Cyg are shown to be detached binary systems. The third …
0920+3517_Nir_Spex, Maria Teresa Ruiz
Hubble Space Telescope Images Of The Ultraluminous Supernova Remnant Complex In Ngc 6946, William P. Blair, Robert A. Fesen, Eric M. Schlegel
Hubble Space Telescope Images Of The Ultraluminous Supernova Remnant Complex In Ngc 6946, William P. Blair, Robert A. Fesen, Eric M. Schlegel
Dartmouth Scholarship
We present Hubble Space Telescope (HST) narrow-passband Hα and [S II] images and broadband continuum images of the region around an extremely luminous optical and X-ray supernova remnant complex in the spiral galaxy NGC 6946. These images, obtained with the PC1 CCD of the Wide Field Planetary Camera 2, show a circular, limb-brightened shell of diameter 035 [9 d/(5.1 Mpc) pc] superposed on the edge of a larger, lower surface brightness elliptical shell (14 × 08, or 34 pc × 20 pc). The HST images allow us to see that the [S II] : Hα ratio remains …
Theoretical Profile Shapes For Optically Thin X-Ray Emission Lines From Spherical Stellar Winds., R. Ignace
Theoretical Profile Shapes For Optically Thin X-Ray Emission Lines From Spherical Stellar Winds., R. Ignace
Richard Ignace
One of the major outstanding problems in hot star wind theory is an understanding of the observed X-ray emissions from the early-type B, O, and Wolf-Rayet (WR) stars. The latest X-ray satellites Chandra and XMM-Newton are providing key new observations of resolved emission profiles to advance that understanding. This study presents a derivation of the expected emission-line profiles, assuming optically thin line emission and spherical symmetry, with a proper treatment of the attenuation of X-rays by the dense cool wind component. Examples of line profile variability for a narrow outflowing shell are presented. Then the case of embedded hot gas …
A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion
A Determination Of The Local Density Of White Dwarf Stars, J. B. Holberg, Terry D. Oswalt, E. M. Sion
Publications
The most recent version of the Catalog of Spectroscopically Identified White Dwarfs lists 2249 white dwarf stars. Among these stars are 109 white dwarfs that have either reliable trigonometric parallaxes or color-based distance moduli that place them at a distance within 20 pc of the Sun. Most of these nearby white dwarfs are isolated stars, but 28 (25% of the sample) are in binary systems, including such well-known systems as Sirius A/B and Procyon A/B. There are also three double degenerate systems in this sample of the local white dwarf population. The sample of local white dwarfs is largely complete …
Starbursts Versus Truncated Star Formation In Nearby Clusters Of Galaxies, James A. Rose, Alejandro E. E. Gaba, Nelson Caldwell, Brian Chaboyer
Starbursts Versus Truncated Star Formation In Nearby Clusters Of Galaxies, James A. Rose, Alejandro E. E. Gaba, Nelson Caldwell, Brian Chaboyer
Dartmouth Scholarship
We present long-slit spectroscopy, B - and R -bandpass imaging, and 21 cm observations of a sample of early-type galaxies in nearby clusters, which are known to be either in a star-forming phase or to have had star formation that recently terminated. From the long-slit spectra, obtained with the Blanco 4 m telescope, we ‹nd that emission lines in the star-forming cluster galaxies are signi‹cantly more centrally concentrated than in a sample of ‹eld galaxies. The broadband imaging reveals that two currently starforming early-type galaxies in the Pegasus I cluster have blue nuclei, again indicating that recent star formation has …
The Hanle Effect As A Diagnostic Of Magnetic Fields In Stellar Envelopes Iii. Including The Finite Star Depolarization Effect., R. Ignace
Richard Ignace
The Hanle effect is a relatively new magnetic diagnostic in stellar astrophysics. Although a substantial literature exists for applications of the Hanle effect in solar studies, the Hanle effect is only a fledgling subject in stellar astrophysics, with previous work focusing on simplistic cases to isolate the magnetic effects on polarized resonance scattering line profiles. In particular, applications to stars have treated the star as a point source of illumination. This paper carries the work forward by considering the consequences of finite stellar size for the line polarization. An approach based on intensity moments is derived. For optically thin line …
The Long-Period Orbit Of The Dwarf Nova V630 Cassiopeiae, J. A. Orosz, J. R. Thorstensen, R. K. Honeycutt
The Long-Period Orbit Of The Dwarf Nova V630 Cassiopeiae, J. A. Orosz, J. R. Thorstensen, R. K. Honeycutt
Dartmouth Scholarship
We present extensive spectroscopy and photometry of the dwarf nova V630 Cassiopeiae. A late-type (K4-5) absorption spectrum is easily detectable, from which we derive the orbital parameters. We find a spectroscopic period of P=2.56387 +/- (4 times 10^{-5}) days and a semiamplitude of K_2=132.9 +/- 4.0 km/s. The resulting mass function, which is a firm lower limit on the mass of the white dwarf, is then f(M)=0.624 +/- 0.056 solar masses. The secondary star is a ``stripped giant'', and using relations between the core mass and the luminosity and the core mass and the radius we derive a lower limit …
10 New Γ Doradus And Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel, Anthony B. Kaye, Ann Kaul
10 New Γ Doradus And Δ Scuti Stars, Gregory W. Henry, Francis C. Fekel, Anthony B. Kaye, Ann Kaul
Information Systems and Engineering Management Research Publications
We present high-resolution spectroscopy and precision photometry of five new γ Doradus and five new δ Scuti variables. The five new γ Doradus variables substantially increase the number of confirmed stars of this class. All 10 stars fall in the spectral class range F0–F2, but they are cleanly separated into two groups by their luminosity and photometric periods. However, the period gap between the γ Doradus and δ Scuti stars is becoming very narrow since we confirm that HD 155154 is a γ Doradus star with the shortest periods reported to date (the shortest of its four periods is ∼0.312 …
White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, J. Allyn Smith, I. Neill Reid, Edward M. Sion
White Dwarfs In Common Proper Motion Binary Systems: Mass Distribution And Kinematics, Nicole M. Silvestri, Terry D. Oswalt, Matt A. Wood, J. Allyn Smith, I. Neill Reid, Edward M. Sion
Publications
We present the mass distribution, gravitational redshifts, radial velocities, and space motions of white dwarf stars in common proper motion binary systems. The mass distribution we derive for the 41 DA white dwarfs in this study has a mean of 0.68 ± 0.04 MꙨ. This distribution has a slightly higher mean and larger dispersion than most previous white dwarf studies. We hypothesize that this is due to a higher fraction of cool (average Teff ̴ 10,000 K), hence old, white dwarfs in our sample. Our results indicate that samples made up of predominantly cool, old white dwarf stars …
White Dwarfs In Open Clusters: New Tests Of Stellar Evolution And The Age Of The Galaxy, Ted Von Hippel
White Dwarfs In Open Clusters: New Tests Of Stellar Evolution And The Age Of The Galaxy, Ted Von Hippel
Publications
White dwarf cooling theory and very deep observations in star clusters provide a new tool to test stellar evolution theory and time scales. In particular, white dwarf cooling theory is now testing the degree of enhanced core mixing in stars with turnoff ages of 1 to 2 Gyr. More generally, I show the good overall agreement between white dwarf and modern isochrone ages over the range 0.1 to 4 Gyr.