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Articles 151 - 180 of 211

Full-Text Articles in Stars, Interstellar Medium and the Galaxy

The White Dwarf Luminosity Function From Sloan Digital Sky Survey Imaging Data, Hugh C. Harris, Jeffrey A. Munn, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Ted Von Hippel, Stephen E. Levine, David G. Monet, Daniel J. Eisenstein, S. J. Kleinman, T. S. Metcalfe, Atsuko Nikka, D. E. Winget, J. Brinkmann, Masataka Fukugita, G. R. Knapp, Robert H. Lupton, J. Allyn Smith, Donald P. Schneider Jan 2006

The White Dwarf Luminosity Function From Sloan Digital Sky Survey Imaging Data, Hugh C. Harris, Jeffrey A. Munn, Mukremin Kilic, James W. Liebert, Kurtis A. Williams, Ted Von Hippel, Stephen E. Levine, David G. Monet, Daniel J. Eisenstein, S. J. Kleinman, T. S. Metcalfe, Atsuko Nikka, D. E. Winget, J. Brinkmann, Masataka Fukugita, G. R. Knapp, Robert H. Lupton, J. Allyn Smith, Donald P. Schneider

Publications

A sample of white dwarfs is selected from the Sloan Digital Sky Survey (SDSS) Data Release 3 using their reduced proper motions, based on improved proper motions from combined SDSS and USNO-B data. Numerous SDSS and follow-up spectra (Kilic and coworkers) are used to quantify completeness and contamination of the sample; kinematicsmodels are used to understand and correct for velocity-dependent selection biases.A luminosity function is constructed covering the range 7 < Mbol < 16, and its sensitivity to various assumptions and selection limits is discussed. The white dwarf luminosity function based on 6000 stars is remarkably smooth and rises nearly monotonically to Mbol=15.3. It then drops abruptly, although the small number of low-luminosity stars in the sample and their unknown atmospheric composition prevent quantitative conclusions about this decline. Stars …

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Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Jeffrey A. Munn, Hugh C. Harris, James W. Liebert, Ted Von Hippel, Kurtis A. Williams, Travis S. Metcalfe, D. E. Winget, Stephen E. Levine Jan 2006

Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Jeffrey A. Munn, Hugh C. Harris, James W. Liebert, Ted Von Hippel, Kurtis A. Williams, Travis S. Metcalfe, D. E. Winget, Stephen E. Levine

Publications

A reduced proper motion diagram utilizing Sloan Digital Sky Survey (SDSS) photometry and astrometry and USNO-B plate astrometry is used to separate cool white dwarf candidates from metal-weak, high-velocity, mainsequence Population II stars (subdwarfs) in the SDSS Data Release 2 imaging area. Follow-up spectroscopy using the Hobby-Eberly Telescope, the MMT, and the McDonald 2.7 m telescope is used to demonstrate that the white dwarf and subdwarf loci separate cleanly in the reduced proper motion diagram and that the contamination by subdwarfs is small near the cool white dwarf locus. This enables large, statistically complete samples of white dwarfs, particularly the …

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The Dust Cloud Around The White Dwarf G29-38, William T. Reach, Ted Von Hippel, Et Al. Dec 2005

The Dust Cloud Around The White Dwarf G29-38, William T. Reach, Ted Von Hippel, Et Al.

Publications

We present new observations of the white dwarf G29-38 with the camera (4.5 and 8 μm), photometer (24 μm), and spectrograph (5.5-14 μm) of the Spitzer Space Telescope. This star has an exceptionally large infrared excess, amounting to 3% of the bolometric luminosity. The spectral energy distribution (SED) has a continuum peak around 4.5 μm and a 9-11 μm emission feature 1.25 times brighter than the continuum. A mixture of amorphous olivine and a small amount of forsterite in an emitting region 1-5 R☉ from the star can reproduce the shape of the 9-11 μm feature. The SED …

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A Multisite Photometric Campaign On The Pre-Main-Sequence ₰ Delta Scuti Pulsator Ip Per, V. Ripepi, T. D. Oswalt, S. Bernabei, M. Marconi, Et Al. Dec 2005

A Multisite Photometric Campaign On The Pre-Main-Sequence ₰ Delta Scuti Pulsator Ip Per, V. Ripepi, T. D. Oswalt, S. Bernabei, M. Marconi, Et Al.

Publications

We present the results of a photometric multisite campaign on the δ Scuti Pre-Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 190 h of observations over 38 nights. Present data confirms the multiperiodic nature of this star and leads to the identification of at least nine pulsational frequencies. Comparison with the predictions of linear non-adiabatic radial pulsation models allowed us to identify only five of the nine observed frequencies, and to constrain the position of IP Per in the HR diagram. The latter is in good agreement with the empirical determination …

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Measuring The Evolution Of The Most Stable Optical Clock G 117-B15a, S. O. Kepler, Ted Von Hippel, Et Al. Dec 2005

Measuring The Evolution Of The Most Stable Optical Clock G 117-B15a, S. O. Kepler, Ted Von Hippel, Et Al.

Publications

We report our measurement of the rate of change of period with time () for the 215 s periodicity in the pulsating white dwarf G 117-B15A, the most stable optical clock known. After 31 years of observations, we have finally obtained a 4 σ measurement observed = (4.27 ± 0.80) × 10-15 s s-1. Taking into account the proper-motion effect of proper = (7.0 ± 2.0) × 10-16s s-1, we obtain a rate of change of period with time of = (3.57 ± 0.82) × 10-15 s s-1. This value is consistent with the cooling rate in our white dwarf …

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Faint Blue Objects In The Hubble Deep Field–South Revealed: White Dwarfs, Subdwarfs, And Quasars, Mukremin Kilic, Ted Von Hippel, Et Al. Nov 2005

Faint Blue Objects In The Hubble Deep Field–South Revealed: White Dwarfs, Subdwarfs, And Quasars, Mukremin Kilic, Ted Von Hippel, Et Al.

Publications

We explore the nature of the faint blue objects in the Hubble Deep Field–South. We have derived proper motions for the point sources in the Hubble Deep Field–South using a 3 yr baseline. Combining our proper-motion measurements with spectral energy distribution fitting enabled us to identify four quasars and 42 stars, including three white dwarf candidates. Two of these white dwarf candidates, HDF-S 1444 and 895, are found to display significant proper motion, 21:1±7:9 and 34:9 ± 8:0 mas yr -1, and are consistent with being thick-disk or halo white dwarfs located at ̴2 kpc. The other faint …

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Excess Infrared Radiation From The Massive Daz White Dwarf Gd 362: A Debris Disk?, Mukremin Kilic, Ted Von Hippel, Et Al. Oct 2005

Excess Infrared Radiation From The Massive Daz White Dwarf Gd 362: A Debris Disk?, Mukremin Kilic, Ted Von Hippel, Et Al.

Publications

We report the discovery of excess K-band radiation from the massive DAZ white dwarf star GD 362. Combining infrared photometric and spectroscopic observations, we show that the excess radiation cannot be explained by a stellar or substellar companion, and is likely to be caused by a debris disk. This would be only the second such system known, discovered 18 years after G29-38, the only single white dwarf currently known to be orbited by circumstellar dust. Both of these systems favor a model with accretion from a surrounding debris disk to explain the metal abundances observed in DAZ white dwarfs. …

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Deep Photometry Of The Globular Cluster M5: Distance Estimates From White Dwarf And Main-Sequence Stars, Andrew C. Layden, Ted Von Hippel, Et Al. Oct 2005

Deep Photometry Of The Globular Cluster M5: Distance Estimates From White Dwarf And Main-Sequence Stars, Andrew C. Layden, Ted Von Hippel, Et Al.

Publications

We present deep VI photometry of stars in the globular cluster M5 (NGC 5904) based on images taken with the Hubble Space Telescope. The resulting color-magnitude diagram reaches below V ≈27 mag, revealing the upper 2–3 mag of the white dwarf cooling sequence and main-sequence stars 8 mag and more below the turnoff. We fit the main sequence to subdwarfs of known parallax to obtain a true distance modulus of (m ̶ M )0 = 14:45 ± 0:11 mag. A second distance estimate based on fitting the cluster white dwarf sequence to field white dwarfs with known parallax …

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Where Are The Magnetic White Dwarfs With Detached, Nondegenerate Companions?, James W. Liebert, Dayal T. Wickramsinghe, Gary D. Schmidt, Nicole M. Silvestri, T. D. Oswalt, Et Al. May 2005

Where Are The Magnetic White Dwarfs With Detached, Nondegenerate Companions?, James W. Liebert, Dayal T. Wickramsinghe, Gary D. Schmidt, Nicole M. Silvestri, T. D. Oswalt, Et Al.

Publications

The Sloan Digital Sky Survey has already more than doubled the sample of white dwarfs with spectral classifications, the subset with detached M dwarf companions, and the subset of magnetic white dwarfs. In the course of assessing these new discoveries, we have noticed a curious, unexpected property of the total lists of magnetic white dwarfs and of white dwarf plus main-sequence binaries: there appears to be virtually zero overlap between the two samples! No confirmed magnetic white dwarf has yet been found in such a pairing with a main-sequence star. The same statement can be made for the samples of …

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From Young And Hot To Old And Cold: Comparing White Dwarf Cooling Theory To Main-Sequence Stellar Evolution In Open Clusters, Ted Von Hippel Mar 2005

From Young And Hot To Old And Cold: Comparing White Dwarf Cooling Theory To Main-Sequence Stellar Evolution In Open Clusters, Ted Von Hippel

Publications

I explore the current ability of both white dwarf cooling theory and main-sequence stellar evolution theory to accurately determine stellar population ages by comparing ages derived using both techniques for open clusters ranging from 0.1 to 4 Gyr. I find good agreement between white dwarf and main-sequence evolutionary ages over the entire age range currently available for study. I also find that directly comparing main-sequence turnoff ages to white dwarf ages is only weakly sensitive to realistic levels of errors in cluster distance, metallicity, and reddening. Additional detailed comparisons between white dwarf and main-sequence ages have tremendous potential to refine …

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The Chromospheric Activity And Ages Of M Dwarf Stars In Wide Binary Systems, Nicole M. Silvesteri, T. D. Oswalt, Suzanne L. Hawley Feb 2005

The Chromospheric Activity And Ages Of M Dwarf Stars In Wide Binary Systems, Nicole M. Silvesteri, T. D. Oswalt, Suzanne L. Hawley

Publications

We investigate the relationship between age and chromospheric activity for 139 M dwarf stars in wide binary systems with white dwarf companions. The age of each system is determined from the cooling age of its white dwarf component. The current limit for activity-age relations found for M dwarfs in open clusters is 4 Gyr. Our unique approach to finding ages for M stars allows for the exploration of this relationship at ages older than 4 Gyr. The general trend of stars remaining active for a longer time at later spectral type is confirmed. However, our larger sample and greater age …

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The Initial-Final Mass Relationship: Spectroscopy Of White Dwarfs In Ngc 2099 (M37), Jasonjot Singh Kalirai, Ted Von Hippel, Et Al. Dec 2004

The Initial-Final Mass Relationship: Spectroscopy Of White Dwarfs In Ngc 2099 (M37), Jasonjot Singh Kalirai, Ted Von Hippel, Et Al.

Publications

We present new observations of very faint white dwarfs (WDs) in the rich open star cluster NGC 2099 (M37). Following deep, wide-field imaging of the cluster using the Canada-France-Hawaii Telescope, we have now obtained spectroscopic observations of candidate WDs using both the Gemini Multi-Object Spectrograph on Gemini North and the Low-Resolution Imaging Spectrometer on Keck. Of our 24 WD candidates (all fainter than V = 22.4), 21 are spectroscopically confirmed to be bona fide WDs, four or five of which are most likely field objects. Fitting 18 of the 21 WD spectra with model atmospheres, we find that most WDs …

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The White Dwarf Luminosity Function: The Shape Of Things To Come, Ted Von Hippel, M. Kilie, J. Munn, K. Williams, J. Libert, D. E. Winget, T. S. Metcalfe, Et Al. Oct 2004

The White Dwarf Luminosity Function: The Shape Of Things To Come, Ted Von Hippel, M. Kilie, J. Munn, K. Williams, J. Libert, D. E. Winget, T. S. Metcalfe, Et Al.

Publications

We describe a new survey for cool white dwarfs that supplements Sloan Digital Sky Survey photometry with USNO proper motions and followup spectroscopy. To date we have discovered and spectroscopically confirmed 80 new moderate temperature and cool white dwarfs. We have also found a handful of high-velocity white dwarfs and we expect a sizable fraction of these to be thick disk or possibly halo objects. Our survey is designed to find 104 new white dwarfs, although only 60 will be among the faintest white dwarfs (MV 16), where most of the age-sensitivity resides. We discuss an extension of our survey …

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Photometric Identification Of Cool White Dwarfs, M. Kilic, D. E. Winget, Ted Von Hippel, C. F. Claver Oct 2004

Photometric Identification Of Cool White Dwarfs, M. Kilic, D. E. Winget, Ted Von Hippel, C. F. Claver

Publications

We investigate the use of a narrowband DDO51 filter for photometric identification of cool white dwarfs. We report photometric observations of 30 known cool white dwarfs with temperatures ranging from 10,000 K down to very cool temperatures (3500 K). Follow-up spectroscopic observations of a sample of objects selected using this filter and our photometric observations show that DDO51 filter photometry can help select cool white dwarf candidates for follow-up multiobject spectroscopy by rejecting 65% of main-sequence stars with the same broadband colors as the cool white dwarfs. This technique is not selective enough to efficiently feed single-object spectrographs. We present …

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Redefining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, Et Al. Sep 2004

Redefining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, Et Al.

Publications

We use the new ZZ Ceti stars (hydrogen-atmosphere white dwarf variables; DAVs) discovered within the Sloan Digital Sky Survey (Mukadam et al. 2004) to redefine the empirical ZZ Ceti instability strip. This is the first time since the discovery of white dwarf variables in 1968 that we have a homogeneous set of spectra acquired using the same instrument on the same telescope, and with consistent data reductions, for a statistically significant sample of ZZ Ceti stars. The homogeneity of the spectra reduces the scatter in the spectroscopic temperatures, and we find a narrow instability strip of width ~950 K, from …

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Book Review: Sky Vistas: Astronomy For Binoculars And Richestfield Telescopes, T. D. Oswalt Sep 2004

Book Review: Sky Vistas: Astronomy For Binoculars And Richestfield Telescopes, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Sky Vistas : Astronomy for Binoculars and Richestfield Telescopes by Craig Crossen and Gerald Rhemann Springer, 2004 279p, 3211008519 $69.95

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Proper Motion Objects In The Hubble Deep Field, M. Kilic, Ted Von Hippel, Et Al. Jul 2004

Proper Motion Objects In The Hubble Deep Field, M. Kilic, Ted Von Hippel, Et Al.

Publications

Using the deepest and finest resolution images of the universe acquired with the Hubble Space Telescope and a similar image taken 7 yr later for the Great Observatories Origins Deep Survey, we have derived proper motions for the point sources in the Hubble Deep Field–North. Two faint blue objects, HDF 2234 and HDF 3072, are found to display significant proper motion, 10:0 ± 2:5 and 15:5 ± 3:8 mas yr¯1. Photometric distances and tangential velocities for these stars are consistent with disk white dwarfs located at ~500 pc. The faint blue objects analyzed by Ibata et al. and Mendez & …

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Thirty-Five New Pulsating Da White Dwarf Stars, Anjum S. Mukadam, Ted Von Hippel, Et Al. Jun 2004

Thirty-Five New Pulsating Da White Dwarf Stars, Anjum S. Mukadam, Ted Von Hippel, Et Al.

Publications

We present 35 new pulsating DA (hydrogen atmosphere) white dwarf stars discovered from the Sloan Digital Sky Survey (SDSS) and the Hamburg Quasar Survey (HQS). We have acquired high-speed time series photometry of preselected DA white dwarfs with a prime focus CCD photometer on the 2.1 m telescope at McDonald Observatory over 15 months. We selected these stars on the basis of prior photometric and spectroscopic observations by the SDSS and HQS. For the homogeneous SDSS sample, we achieve a success rate of 80% for finding new variables at a detection threshold of 0.1%-0.3%. With 35 newly discovered DA variable …

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Re-Defining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, D. E. Winget,, M. H. Montgomery May 2004

Re-Defining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, D. E. Winget,, M. H. Montgomery

Publications

We use the new ZZ Ceti stars (hydrogen atmosphere white dwarf variables; DAVs) discovered within the Sloan Digital Sky Survey (Mukadam et al. 2004) to re-define the empirical ZZ Ceti instability strip. This is the first time since the discovery of white dwarf variables in 1968 that we have a homogeneous set of spectra acquired using the same instrument on the same telescope, and with con- sistent data reductions, for a statistically significant sample of ZZ Ceti stars. The homogeneity of the spectra reduces the scatter in the spectroscopic temperatures and we find a narrow instability strip of width ∼ …

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Spectroscopic And Photometric Analysis Of Hs 1136+6646: A Hot Young Dao+K7 V Post-Common-Envelope, Pre-Cataclysmic Variable Binary, D. K. Sing, Terry D. Oswalt, J. B. Holberg, M. R. Burleigh, S. A. Good, Et Al. May 2004

Spectroscopic And Photometric Analysis Of Hs 1136+6646: A Hot Young Dao+K7 V Post-Common-Envelope, Pre-Cataclysmic Variable Binary, D. K. Sing, Terry D. Oswalt, J. B. Holberg, M. R. Burleigh, S. A. Good, Et Al.

Publications

Extensive photometric and spectroscopic observations have been obtained for HS 1136+6646. The observations reveal a newly formed post–common-envelope binary system containing a hot ~DAO.5 primary and a highly irradiated secondary. HS 1136+6646 is the most extreme example yet of a class of short-period hot H-rich white dwarfs with K–M companion systems such as V471 Tau and Feige 24. HS 1136+6646 is a double-line spectroscopic binary showing emission lines of H i, He ii, C ii, Ca ii, and Mg ii, due in part to irradiation of the K7 V secondary by the hot white dwarf. Echelle spectra reveal the hydrogen …

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Using Optical And Near-Infrared Photometry To Test Macho Lens Candidates, Ted Von Hippel, Et Al. Oct 2003

Using Optical And Near-Infrared Photometry To Test Macho Lens Candidates, Ted Von Hippel, Et Al.

Publications

We obtained new VLT/ISAAC H-band observations for five MACHO LMC source stars and adjacent LMC field regions. After combining our near-IR photometry with Hubble Space Telescope/PC BVRI optical photometry, we compared the MACHO objects to the adjacent field stars in a variety of color-magnitude and color-color diagrams. These diagnostic diagrams were chosen to be sensitive to our hypothesis that at least some of the MACHO lenses were foreground Galactic disk or thick-disk M dwarfs. For the five lensed objects we studied, our hypothesis could be ruled out for main-sequence lens masses ≥0.1 M☉ for distances out to …

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Constraining The Evolution Of Zz Ceti, Anjum S. Mukadam, S. O. Kepler, D. E. Nather, M. Kilic, F. Mullally, T. Von Hippel, S. J. Kleinman, A. Nitta, J. A. Guzik, P. A. Bradley, J. Matthews, K. Sekiguchi, D. J. Sullivan, T. Sullivan, R. R. Shobbrook, P. Birch, X. J. Jiang, D. W. Xu, S. Joshi, B. N. Ashoka, P. Ibbetson, E. Leibowitz, E. O. Ofek, E. G. Meištas, R. Janulis, R. D. Ališauskas, R. Kalytis, G. Handler, D. Kilkenny, D. O'Donoghue, D. W. Kurtz, M. Müller, P. Moskalik, W. Ogloza, S. Zola, J. Krzesiński, F. Johnannessen, J. M. Gonzalez-Perez, J. E. Solheim, R. Silvotti, S. Bernabei, G. Vauclair, N. Dolez, J. N. Fu, M. Chevreton, M. Manteiga, O. Suárez, A. Ulla, M. S. Cunha, T. S. Metcalfe, A. Kanaan, L. Fraga, A. F. M. Costa, O. Giovannini, G. Fontaine, P. Bergeron, M. S. O'Brien, D. Sanwal, M. A. Wood, T. J. Ahrens, N. Silvestri, E. W. Klumpe, S. D. Kawaler, R. Riddle, M. D. Reed, T. K. Watson Sep 2003

Constraining The Evolution Of Zz Ceti, Anjum S. Mukadam, S. O. Kepler, D. E. Nather, M. Kilic, F. Mullally, T. Von Hippel, S. J. Kleinman, A. Nitta, J. A. Guzik, P. A. Bradley, J. Matthews, K. Sekiguchi, D. J. Sullivan, T. Sullivan, R. R. Shobbrook, P. Birch, X. J. Jiang, D. W. Xu, S. Joshi, B. N. Ashoka, P. Ibbetson, E. Leibowitz, E. O. Ofek, E. G. Meištas, R. Janulis, R. D. Ališauskas, R. Kalytis, G. Handler, D. Kilkenny, D. O'Donoghue, D. W. Kurtz, M. Müller, P. Moskalik, W. Ogloza, S. Zola, J. Krzesiński, F. Johnannessen, J. M. Gonzalez-Perez, J. E. Solheim, R. Silvotti, S. Bernabei, G. Vauclair, N. Dolez, J. N. Fu, M. Chevreton, M. Manteiga, O. Suárez, A. Ulla, M. S. Cunha, T. S. Metcalfe, A. Kanaan, L. Fraga, A. F. M. Costa, O. Giovannini, G. Fontaine, P. Bergeron, M. S. O'Brien, D. Sanwal, M. A. Wood, T. J. Ahrens, N. Silvestri, E. W. Klumpe, S. D. Kawaler, R. Riddle, M. D. Reed, T. K. Watson

Publications

We report our analysis of the stability of pulsation periods in the DAV star (pulsating hydrogen atmosphere white dwarf) ZZ Ceti, also called R548. On the basis of observations that span 31 years, we conclude that the period 213.13 s observed in ZZ Ceti drifts at a rate dP/dt ≤ (5:5 ± 1:9) x 10-15 s s-1, after correcting for proper motion. Our results are consistent with previous Ṗ values for this mode and an improvement over them because of the larger time base. The characteristic stability timescale implied for the pulsation period is …

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Book Review: Observer's Guide To Stellar Evolution: The Birth, Life, And Death Of Stars, T. D. Oswalt Sep 2003

Book Review: Observer's Guide To Stellar Evolution: The Birth, Life, And Death Of Stars, T. D. Oswalt

Publications

This document is Dr. Oswalt’s review of Observer's Guide to Stellar Evolution : the Birth, Life, and Death of Stars by Mike Inglis. Springer, 2003 236p, 1-85233-465-7 $44.95

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Multisite Observations Of The Pms Δ Delta Scuti Star V351 Ori, V. Ripepi, Terry D. Oswalt, M. Marconi, S. Bernabei, Et Al. Jun 2003

Multisite Observations Of The Pms Δ Delta Scuti Star V351 Ori, V. Ripepi, Terry D. Oswalt, M. Marconi, S. Bernabei, Et Al.

Publications

We present the results of multisite observations spanning two years on the pre–main-sequence (PMS) star V351 Ori. A total of around 180 hours of observations over 29 nights have been collected, allowing us to measure five different periodicities, most likely related to the Scuti variability of V351 Ori. Comparison with the predictions of linear nonadiabatic radial pulsation models put stringent constraints on the stellar parameters and indicate that the distance to V351 Ori is intermediate between the lower limit measured by Hipparcos (210 pc) and that of the Orion Nebula (450 pc). However, radial pulsation models are unable to reproduce …

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Intergalactic Globular Clusters, Michael J. West, Ted Von Hippel, Patrick Cote, Henry C. Ferguson, Michael D. Gregg, Andres Jordan, Ronald O. Marzke, Nial R. Tanvir Jan 2003

Intergalactic Globular Clusters, Michael J. West, Ted Von Hippel, Patrick Cote, Henry C. Ferguson, Michael D. Gregg, Andres Jordan, Ronald O. Marzke, Nial R. Tanvir

Publications

We confirm and extend our previous detection of a popula- tion of intergalactic globular clusters in Abell 1185, and report the first discovery of an intergalactic globular cluster in the nearby Virgo cluster of galaxies. The numbers, colors and luminosities of these objects can place constraints on their origin, which in turn may yield new insights to the evolution of galaxies in dense environments.

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Search For Oxygen In Cool Dq White Dwarf Atmospheres, M. Kilic, Ted Von Hippel, D. E. Winget, D. F. Lester, D. Saumon Sep 2002

Search For Oxygen In Cool Dq White Dwarf Atmospheres, M. Kilic, Ted Von Hippel, D. E. Winget, D. F. Lester, D. Saumon

Publications

The existence of carbon in cool He white dwarf (WD) atmospheres has been known for a relatively long time[5]. The presence of carbon in these atmospheres is explained by convective dredge up of interior carbon [6]. Pelletier et al. (1986) presented the first detailed calculations of this process and showed that carbon diffuses upwards from the core into the base of the He-rich envelope where it can be dredged up by a surface convection zone. As the temperature of the star decreases, more carbon diffuses upward, and the base of convection zone moves deeper into the star, further enriching the …

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Identification Of Cool White Dwarfs In The Noao Deep Wide-Field Survey, M. Kilic, Don E. Winget, T. Von Hippel, C.F. Claver Sep 2002

Identification Of Cool White Dwarfs In The Noao Deep Wide-Field Survey, M. Kilic, Don E. Winget, T. Von Hippel, C.F. Claver

Publications

The chronology of star formation is recorded in the white dwarf luminosity function (WDLF). White dwarf (WD) structure implies a relatively simple connection between WD luminosity and age. First attempts to exploit WDs as chronometers [3,4,6] showed that the WDLF was a map of the history of star formation in the disk, and a significant shortfall of low-luminosity degenerates–the inevitable consequence of the finite age of the disk. The shortfall near log(L/L⊙)≈−4.5 implies a disk age of 6.5–9.5 Gyr [2]. The WDLF from wide common proper motion binaries [5] does not show the shortfall seen by Liebert et al. (1988). …

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Wiyn Open Cluster Study. Xi. Wiyn 3.5 Meter Deep Photometry Of M35 (Ngc 2168), Ted Von Hippel, Aaron Steinhauer, Ata Sarajedini, Constantine P. Deliyannis Sep 2002

Wiyn Open Cluster Study. Xi. Wiyn 3.5 Meter Deep Photometry Of M35 (Ngc 2168), Ted Von Hippel, Aaron Steinhauer, Ata Sarajedini, Constantine P. Deliyannis

Publications

We present deep BVI observations of the core of M35 and a nearby comparison field obtained at the WIYN 3.5 m telescope under excellent seeing conditions. These observations probe to V > 26 and display the lower main sequence in BV and VI CMDs down to V = 23.3 and 24.6, respectively. At these faint magnitudes the background Galactic field stars are far more numerous than the cluster stars, yet by using a smoothing technique and CMD density distribution subtraction we are able to recover the cluster fiducial main sequence and luminosity function to V = 24.6. We find the location …

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Automated Stellar Spectral Classification And Parameterization For The Masses, Ted Von Hippel, Carlos Allende Prieto, Chris Sneden Aug 2002

Automated Stellar Spectral Classification And Parameterization For The Masses, Ted Von Hippel, Carlos Allende Prieto, Chris Sneden

Publications

Stellar spectroscopic classification has been successfully automated by a number of groups. Automated classification and parameterization work best when applied to a homogeneous data set, and thus these techniques primarily have been developed for and applied to large surveys. While most ongoing large spectroscopic surveys target extragalactic objects, many stellar spectra have been and will be obtained. We briefly summarize past work on automated classification and parameterization, with emphasis on the work done in our group. Accurate automated classification in the spectral type domain and parameterization in the temperature domain have been relatively easy. Automated parameterization in the metallicity domain, …

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Metal Abundances And Kinematics Of Bright Metal-Poor Giants Selected From The Lse Survey: Implications For The Metal-Weak Thick Disk, Timothy C. Beers, John S. Drilling, Silvia Rossi, Masashi Chiba, Jaehyon Rhee, Birgit Fṻhrmeister, John E. Norris, Ted Von Hippel Aug 2002

Metal Abundances And Kinematics Of Bright Metal-Poor Giants Selected From The Lse Survey: Implications For The Metal-Weak Thick Disk, Timothy C. Beers, John S. Drilling, Silvia Rossi, Masashi Chiba, Jaehyon Rhee, Birgit Fṻhrmeister, John E. Norris, Ted Von Hippel

Publications

We report medium-resolution (1–2A ˚ ) spectroscopy and broadband (UBV) photometry for a sample of 39 bright stars (the majority of which are likely to be giants) selected as metal-deficient candidates from an objective-prism survey concentrating on Galactic latitudes below |b| = 30, the Luminous Stars Extension (LSE) survey of Drilling & Bergeron. Although the primary purpose of the LSE survey was to select OB stars (hence the concentration on low latitudes), the small number of bright metal-deficient giant candidates noted during this survey provide interesting information on the metal-weak thick disk (MWTD) population. Metal abundance estimates are obtained from …

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