Ted von Hippel
Embry-Riddle Aeronautical University, Physical Sciences, Faculty Member
Research Interests: Science, Mars, Multidisciplinary, Exobiology, Fossils, and 4 moreBacteria, Iron, Oxides, and Meteoroids
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The stellar populations of low surface brightness (LSB) galaxies tend to be quite blue. This has been attributed to a variety of causes, including a late formation epoch, a great age but gradual evolution, or even a variable IMF. So far,... more
The stellar populations of low surface brightness (LSB) galaxies tend to be quite blue. This has been attributed to a variety of causes, including a late formation epoch, a great age but gradual evolution, or even a variable IMF. So far, there are few constraints other than colors, which are notoriously degenerate. To date there are no continuum spectra for
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... French, RG; Hill, RE; Hiriart, D.; Holtzman, JA; Howell, RR; Jennings, DE; Massey, P.; Matthews, KY; Miko, LR; Millis, RL; Nicholson ... We obtained lightcurves from Red Buttes Observatory in Laramie WY (I), Lick Observatory (H),... more
... French, RG; Hill, RE; Hiriart, D.; Holtzman, JA; Howell, RR; Jennings, DE; Massey, P.; Matthews, KY; Miko, LR; Millis, RL; Nicholson ... We obtained lightcurves from Red Buttes Observatory in Laramie WY (I), Lick Observatory (H), Lowell Observatory (R, I, H), Palomar Observatory (I ...
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Despite the efforts of Hipparcos, the RR Lyrae (RRL) absolute magnitude calibration, M_V(RR), remains uncertain at a level that critically compromises these stars' use as standard candles. This uncertainty propagates into globular... more
Despite the efforts of Hipparcos, the RR Lyrae (RRL) absolute magnitude calibration, M_V(RR), remains uncertain at a level that critically compromises these stars' use as standard candles. This uncertainty propagates into globular cluster ages, Galactic formation scenarios, limits on the age of the Universe, and estimates of the Hubble Constant. A promising new technique is to calibrate M_V(RR) in several nearby globulars whose distances have been accurately determined by white dwarf sequence fitting. NGC 3201 is one of two globulars on which this technique is best employed, yet no high-quality photometry is published for the RRL in NGC 3201. We obtained B,V,I photometry of these stars in 1999A using YALO, but the IR leg of ANDICAM was delayed. We now propose to complete the project by obtaining K-band time-series photometry of the cluster.
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ABSTRACT
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We propose to obtain JHK photometry of 50 spectroscopically confirmed new cool white dwarfs, including 5 ultra-cool white dwarf candidates (T_eff<=4000 K), to determine temperatures, bolometric luminosities, and compositions for these... more
We propose to obtain JHK photometry of 50 spectroscopically confirmed new cool white dwarfs, including 5 ultra-cool white dwarf candidates (T_eff<=4000 K), to determine temperatures, bolometric luminosities, and compositions for these stars. Our follow- up spectroscopy of high proper motion objects in the Sloan Digital Sky Survey yielded a large number of new cool white dwarfs which are suitable for constructing an improved white dwarf luminosity function. This luminosity function will ultimately resolve the controversies, based for the most part on small number statistics, of the age of the Galactic disk. The detailed shape of the white dwarf luminosity function will also allow us to constrain the interior physics of cooling white dwarfs and place white dwarf cosmochronometry on a firmer foundation. We have already begun an observing campaign at the IRTF and Gemini-N (2005B). With the Gemini-NIRI, we propose to complete our program by obtaining the infrared photometry of the coolest white dwarfs in the Galactic disk that are intrinsically faint and need 8m class telescope observations. These observations will also improve our understanding of collisionally-induced absorption and other unrecognized opacities in cool white dwarf atmospheres.
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We present new observations of the white dwarf G 29-38 with the Spitzer Space Telescope. We detected a strong silicate emission feature, whose shape can be explained by a mixture of amorphous olivine and a small amount of forsterite. The... more
We present new observations of the white dwarf G 29-38 with the Spitzer Space Telescope. We detected a strong silicate emission feature, whose shape can be explained by a mixture of amorphous olivine and a small amount of forsterite. The spectral energy distribution also requires amorphous carbon to explain the hot continuum. The properties of this cloud suggest a relatively
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We have begun a survey of 130 white dwarfs (WDs) with Spitzer to search for infrared photometric anomalies caused by faint companions and disks. We propose follow-up photometry and spectroscopy of a few interesting objects uncovered so... more
We have begun a survey of 130 white dwarfs (WDs) with Spitzer to search for infrared photometric anomalies caused by faint companions and disks. We propose follow-up photometry and spectroscopy of a few interesting objects uncovered so far that show signs of either novel absorption features or of hosting planets or disks. The novel absorption features appear in the coolest white dwarfs we surveyed; using white dwarfs to derive the age of the Galaxy demands understanding them. A few warmer white dwarfs with normal photospheres display excesses at 4.5 and/or 8 microns, signposts of giant planets or dust disks, respectively. This study holds an opportunity to take the first mid-infrared spectrum of an extrasolar planet.
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We propose to derive [Fe/H] values of four moderately old open clusters, NGC 2360, NGC 2477, NGC 2660, and NGC 3960, using Hydra on the CTIO Blanco 4-m telescope. This information will be used in conjunction with multicolor photometric... more
We propose to derive [Fe/H] values of four moderately old open clusters, NGC 2360, NGC 2477, NGC 2660, and NGC 3960, using Hydra on the CTIO Blanco 4-m telescope. This information will be used in conjunction with multicolor photometric data from HST, as well as newly proposed CTIO 0.9m photometry, to derive ages from the cluster white dwarfs but also from the main sequence turn off. Precise metallicities for these clusters will allow us to break parameter degeneracies in the color- magnitude diagram between metallicity, distance, and reddening, in order to obtain more precise values for the cluster parameters, specifically age. This is part of our ongoing effort to use open clusters to calibrate ages obtained from main sequence evolution theory and white dwarf cooling theory.
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We performed a Spitzer/IRAC survey of 18 nearby cool white dwarfs in Cycle 1 and 2 in order to explore their flux distributions in the mid-infrared. Surprisingly, we discovered significant flux deficits in Spitzer observations of five... more
We performed a Spitzer/IRAC survey of 18 nearby cool white dwarfs in Cycle 1 and 2 in order to explore their flux distributions in the mid-infrared. Surprisingly, we discovered significant flux deficits in Spitzer observations of five hydrogen-rich white dwarfs cooler than 6000 K. These mid-infrared flux deficits are not predicted by state-of-the-art white dwarf models including current treatments of
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In the last two years a hand-full of white dwarfs (WDs) with circumstellar debris disks have been discovered. The debris disks are either left over from the late stages of stellar evolution or are the result of tidally disrupted asteroids... more
In the last two years a hand-full of white dwarfs (WDs) with circumstellar debris disks have been discovered. The debris disks are either left over from the late stages of stellar evolution or are the result of tidally disrupted asteroids or comets, and are thus signposts of planetary systems. Our team has been investigating the properties of these debris disks
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Submitted to the Annals of Applied Statistics ... STATISTICAL ANALYSIS OF STELLAR EVOLUTION: ONLINE SUPPLEMENT ... By David A. van Dyk ∗ , Steven DeGennaro, Nathan Stein, William H. Jefferys, and Ted von Hippell ... University of... more
Submitted to the Annals of Applied Statistics ... STATISTICAL ANALYSIS OF STELLAR EVOLUTION: ONLINE SUPPLEMENT ... By David A. van Dyk ∗ , Steven DeGennaro, Nathan Stein, William H. Jefferys, and Ted von Hippell ... University of California, Irvine, ...
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Certain modes in the hot ZZ Ceti stars (HDAVs) exhibit extreme pulsational stability; their periods have been observed to show a slow increase, which is theoretically accounted for by evolutionary cooling of the star. These modes are... more
Certain modes in the hot ZZ Ceti stars (HDAVs) exhibit extreme pulsational stability; their periods have been observed to show a slow increase, which is theoretically accounted for by evolutionary cooling of the star. These modes are super-stable, more stable than atomic clocks and most pulsars; they will lose one cycle in a few billion years. We have begun a
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Open clusters provide the ideal environment for the calibration of the ages determined from main sequence evolution theory (via cluster isochrones) and those determined from white dwarf cooling theory. Additionally, it provides the unique... more
Open clusters provide the ideal environment for the calibration of the ages determined from main sequence evolution theory (via cluster isochrones) and those determined from white dwarf cooling theory. Additionally, it provides the unique opportunity to directly compare and refine our understanding of both theories. Because the coolest cluster white dwarfs are faint, they require observations made with large telescopes
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We describe our on-going wide-field proper motion survey for ancient white dwarfs (WDs) that we are conducting with the Steward Observatory Bok Telescope and its prime focus imaging camera. To date we have observed over 1000 square... more
We describe our on-going wide-field proper motion survey for ancient white dwarfs (WDs) that we are conducting with the Steward Observatory Bok Telescope and its prime focus imaging camera. To date we have observed over 1000 square degrees in the r-band to r 21. We match this astrometry to the Sloan Digital Sky Survey astrometry and photometry to produce a
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White dwarf cooling sequences represent one of the few ways in which we can determine ages of Galactic components such as the disk, the halo, and globular star clusters. These age measurements rely heavily on theoretical cooling models,... more
White dwarf cooling sequences represent one of the few ways in which we can determine ages of Galactic components such as the disk, the halo, and globular star clusters. These age measurements rely heavily on theoretical cooling models, many of which disagree by as much as a few gigayears for the coolest white dwarfs. Further, observations of the white dwarf sequence in the super metal-rich open cluster NGC 6791 have found evidence for two white dwarf cooling sequences; the debate over the interpretation of these two populations is unsettled. We have undertaken a study of the white dwarf sequence of the solar-metallicity, 7-Gyr old open cluster NGC 188 in order to address the white dwarf model uncertainties and to see if the cooling sequence of NGC 6791 is unique. We present initial results of deep HST WFPC2 imaging of NGC 188 and discuss the implications of its white dwarf population.
A deep, wide-area proper motion survey is currently underway with the prime focus imaging camera on the Steward Observatory Bok Telescope and the CCD mosaic camera on the United States Naval Observatory Flagstaff Station 1.3m Telescope.... more
A deep, wide-area proper motion survey is currently underway with the prime focus imaging camera on the Steward Observatory Bok Telescope and the CCD mosaic camera on the United States Naval Observatory Flagstaff Station 1.3m Telescope. The sky footprint of the Sloan Digital Sky Survey (SDSS) is being reimaged in r to a depth of r = 21. These new observations are then matched to the SDSS catalog, yielding proper motions with errors at the faint limit of the survey of roughly 20-30 mas/yr (for a typical epoch difference of 5 years). To date, 2800 square degrees of sky have been imaged. The primary goal of the survey is to generate greatly increased samples of cool disk white dwarfs, as well as thick disk and halo white dwarfs, with which to better constrain the star formation history of the disk, thick disk, and halo.
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ABSTRACT The first of a planned series of workshops for secondary school science teachers was conducted at McDonald Observatory in 2005. In preparation for the workshop, new instructional materials on white dwarfs and the age of our... more
ABSTRACT The first of a planned series of workshops for secondary school science teachers was conducted at McDonald Observatory in 2005. In preparation for the workshop, new instructional materials on white dwarfs and the age of our Galaxy were prepared and pilot-tested. Thirteen teachers from Arizona, Delaware, and Texas performed these standards-aligned activities at the workshop in preparation for using them within their own classrooms. During four nights of observing, the participants made CCD-images at the 0.8-m telescope and reduced the data with personal computers using easily available image reduction software. Working in teams, they created a color-magnitude diagram for an open cluster and found several white dwarf candidates within the cluster. With guidance, they used the work of the White Dwarf Luminosity Function Collaboration, which fostered this workshop, to estimate the age of the Galaxy. The workshop included tours of other observatory facilities, practical exercises with small telescopes, and time to reflect on their own teaching practices. Evaluation on the workshop and the use of the instructional materials is continuing. Support from the National Science Foundation (AST 0307315), National Science FoundationsDistinguished Teaching Scholars Program (DUE-0306557), and The National Aeronautics and Space Administration under an Education and Public Outreach supplement to Grant/Contract/Agreement No. NAG5-13070 issued through the Office of Space Science is gratefully acknowledged.
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ABSTRACT We present a Bayesian analysis of 130 SDSS cool white dwarfs with optical and infrared photometry, a subset of which also has trigonometric parallax measurements. Instead of a step-wise progression of fitting a temperature, mass,... more
ABSTRACT We present a Bayesian analysis of 130 SDSS cool white dwarfs with optical and infrared photometry, a subset of which also has trigonometric parallax measurements. Instead of a step-wise progression of fitting a temperature, mass, and age for each star (as is done in previous studies), we employ a Bayesian analysis to simultaneously and self-consistently fit model atmospheres, white dwarf evolutionary models, initial-final mass relation, and precursor main-sequence ages to derive posterior age distributions. We fully incorporate the non-Gaussian nature of stellar evolution in this analysis. The goal of our study is to mine the age information available in these and other cool white dwarfs in order to better understand the details of how the different models affect age determinations of white dwarfs.
ABSTRACT The recent realization that many globular clusters host multiple populations has not only challenged our conception of what globular clusters actually are, but has also thoroughly challenged the statistical techniques we use to... more
ABSTRACT The recent realization that many globular clusters host multiple populations has not only challenged our conception of what globular clusters actually are, but has also thoroughly challenged the statistical techniques we use to analyze these systems. This modern discovery is driven by superb data from the Hubble Space Telescope and its newest instruments. Interpreting these data requires precisely applying modern stellar evolution and atmosphere models. Yet, while the quality of the data is orders of magnitude better than the single-channel photometer and photographic plate data of the 1960&#39;s and the current stellar evolution models vastly surpass the models and hardware of that epoch, research groups are still hampered by data fitting techniques that have hardly progressed over the last half century. I will describe a new Bayesian software suite for deriving parameters for single stellar populations and our first forays into multiple stellar populations. Our Bayesian technique yields better precision in the ages, distances, etc. for stars and clusters, provides a fuller understanding of errors and correlations among the derived parameters, and allows us to attack a range of problems in stellar evolution in a statistically consistent manner for the first time. We gratefully acknowledge support from NASA under grant 10-ADAP10-0076.