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Articles 31 - 60 of 92
Full-Text Articles in Astrophysics and Astronomy
The Initial-Final Mass Relation Among White Dwarfs In Wide Binaries, Jingkun Zhao, T. D. Oswalt, Lee Anne Wilson, Qian Wang, Gang Zhao
The Initial-Final Mass Relation Among White Dwarfs In Wide Binaries, Jingkun Zhao, T. D. Oswalt, Lee Anne Wilson, Qian Wang, Gang Zhao
Aerospace, Physics, and Space Science Faculty Publications
We present the initial–final mass relation derived from 10 white dwarfs in wide binaries that consist of a main-sequence star and a white dwarf. The temperature and gravity of each white dwarf were measured by fitting theoretical model atmospheres to the observed spectrum using a χ2 fitting algorithm. The cooling time and mass were obtained using theoretical cooling tracks. The total age of each binary was estimated from the chromospheric activity of its main-sequence component to an uncertainty of about 0.17 dex in log t. The difference between the total age and white dwarf cooling time is taken as the …
Observational Constraints On The Degenerate Mass-Radius Relation, J. B. Holberg, Terry D. Oswalt, M. A. Barstow
Observational Constraints On The Degenerate Mass-Radius Relation, J. B. Holberg, Terry D. Oswalt, M. A. Barstow
Publications
The white dwarf mass–radius relationship is fundamental to modern astrophysics. It is central to routine estimation of DA white dwarf masses derived from spectroscopic temperatures and gravities. It is also the basis for observational determinations of the white dwarf initial–final-mass relation. Nevertheless, definitive and detailed observational confirmations of the mass–radius relation (MRR) remain elusive owing to a lack of sufficiently accurate white dwarf masses and radii. Current best estimates of masses and radii allow only broad conclusions about the expected inverse relation between masses and radii in degenerate stars. In this paper, we examine a restricted set of 12 DA …
The Initial–Final Mass Relation Among White Dwarfs In Wide Binaries, J. K. Zhao, T. D. Oswalt, L. A. Willson, Q. Wang, G. Zhao
The Initial–Final Mass Relation Among White Dwarfs In Wide Binaries, J. K. Zhao, T. D. Oswalt, L. A. Willson, Q. Wang, G. Zhao
Publications
We present the initial–final mass relation derived from 10 white dwarfs in wide binaries that consist of a main-sequence star and a white dwarf. The temperature and gravity of each white dwarf were measured by fitting theoretical model atmospheres to the observed spectrum using a χ2 fitting algorithm. The cooling time and mass were obtained using theoretical cooling tracks. The total age of each binary was estimated from the chromospheric activity of its main-sequence component to an uncertainty of about 0.17 dex in log t. The difference between the total age and white dwarf cooling time is taken …
The Hubble Space Telescope * Cluster Supernova Survey. Ii. The Type Ia Supernova Rate In High-Redshift Galaxy Clusters, K Barbary, G Aldering, R Amanullah, M Brodwin, N Connolly, Ks Dawson, M Doi, P Eisenhardt, L Faccioli, V Fadeyev, Hk Fakhouri, As Fruchter, D G. Gilbank, Md Gladders, G Goldhaber, A Goobar, T Hattori, E Hsiao, Xiaosheng Huang, Y Ihara, K Kashikawa, B Koester, K Konishi, M Kowalski, C Lidman, L Lubin, J Meyers, T Morokuma, T Oda, N Panagia, S Perlmutter, M Postman, P Ripoche, P Rosati, D Rubin, Dj Schlegel, Al Spadafora, Sa Stanford, M Strovink, N Suzuki, N Takanashi, K Tokita, N Yasuda
The Hubble Space Telescope * Cluster Supernova Survey. Ii. The Type Ia Supernova Rate In High-Redshift Galaxy Clusters, K Barbary, G Aldering, R Amanullah, M Brodwin, N Connolly, Ks Dawson, M Doi, P Eisenhardt, L Faccioli, V Fadeyev, Hk Fakhouri, As Fruchter, D G. Gilbank, Md Gladders, G Goldhaber, A Goobar, T Hattori, E Hsiao, Xiaosheng Huang, Y Ihara, K Kashikawa, B Koester, K Konishi, M Kowalski, C Lidman, L Lubin, J Meyers, T Morokuma, T Oda, N Panagia, S Perlmutter, M Postman, P Ripoche, P Rosati, D Rubin, Dj Schlegel, Al Spadafora, Sa Stanford, M Strovink, N Suzuki, N Takanashi, K Tokita, N Yasuda
Physics and Astronomy
We report a measurement of the Type Ia supernova (SN Ia) rate in galaxy clusters at 0.9 < z < 1.46 from the Hubble Space Telescope Cluster Supernova Survey. This is the first cluster SN Ia rate measurement with detected z > 0.9 SNe. Finding 8 ± 1 cluster SNe Ia, we determine an SN Ia rate of 0.50+0.23 –0.19 (stat) +0.10 –0.09 (sys) h 2 70 SNuB (SNuB ≡ 10–12 SNe L –1 ☉, B yr–1). In units of stellar mass, this translates to 0.36+0.16 –0.13 (stat) +0.07 –0.06 (sys) h 2 70 SNuM (SNuM ≡ 10–12 SNe M –1 ☉ yr–1). This represents a …
Orbital Separation Amplification In Fragile Binaries With Evolved Components, K. B. Johnston, Terry D. Oswalt
Orbital Separation Amplification In Fragile Binaries With Evolved Components, K. B. Johnston, Terry D. Oswalt
Publications
The secular stellar mass-loss causes an amplification of the orbital separation in fragile, common proper motion, binary systems with separations of the order of 1000 A.U. In these systems, companions evolve as two independent coeval stars as they experience negligible mutual tidal interactions or mass transfer. We present models for how post-main sequence mass-loss statistically distorts the frequency distribution of separations in fragile binaries. These models demonstrate the expected increase in orbital seapration resulting from stellar mass-loss, as well as a perturbation of associated orbital parameters. Comparisons between our models and observations resulting from the Luyten survey of wide visual …
The 25 Parsec Local White Dwarf Population, Jerry B. Holberg, Terry D. Oswalt, Edward M. Sion, George P. Mccook
The 25 Parsec Local White Dwarf Population, Jerry B. Holberg, Terry D. Oswalt, Edward M. Sion, George P. Mccook
Publications
We have extended our detailed survey of the local white dwarf population from 20 pc to 25 pc, effectively doubling the sample volume, which now includes 232 stars. In the process new stars within 20 pc have been added, a more uniform set of distance estimates as well as improved spectral and binary classifications are available. The present 25 pc sample is estimated to be about 68% complete (the corresponding 20 pc sample is now 86% complete). The space density of white dwarfs is unchanged at 4.8 ± 0.5 x 10-3 pc-3. This new study includes a white dwarf mass …
The White Dwarf Age Of Nfc 2477, Elizabeth J. Jeffery, Ted Von Hippel, Et Al.
The White Dwarf Age Of Nfc 2477, Elizabeth J. Jeffery, Ted Von Hippel, Et Al.
Publications
We present deep photometric observations of the open cluster NGC 2477 using HST/WFPC2. By identifying seven cluster white dwarf candidates, we present an analysis of the white dwarf age of this cluster, using both the traditional method of fitting isochrones to the white dwarf cooling sequence, and by employing a new Bayesian statistical technique that has been developed by our group. This new method performs an objective, simultaneous model fit of the cluster and stellar parameters (namely, age, metallicity, distance, reddening, as well as individual stellar masses, mass ratios, and cluster membership) to the photometry. Based on this analysis, …
The Chromospheric Activity, Age, Metallicity, And Space Motions Of 36 Wide Binaries, J. K. Zhao, T. D. Oswalt, M. Rudkin, G. Zhao, Y. Q. Chen
The Chromospheric Activity, Age, Metallicity, And Space Motions Of 36 Wide Binaries, J. K. Zhao, T. D. Oswalt, M. Rudkin, G. Zhao, Y. Q. Chen
Publications
We present the chromospheric activity (CA) levels, metallicities, and full space motions for 41 F, G, K, and M dwarf stars in 36 wide binary systems. Thirty-one of the binaries contain a white dwarf (WD) component. In such binaries, the total age can be estimated by adding the cooling age of the WD to an estimate of the progenitor’s main-sequence lifetime. To better understand how CA correlates to stellar age, 14 cluster member stars were also observed. Our observations demonstrate for the first time that, in general, CA decays with age from 50 Myr to at least 8 Gyr for …
A Selection Of Hot Subluminous Stars In The Galex Survey – I. Correlation With The Guide Star Catalog, S. Vennes, A. Kawka, P. Nemeth
A Selection Of Hot Subluminous Stars In The Galex Survey – I. Correlation With The Guide Star Catalog, S. Vennes, A. Kawka, P. Nemeth
Aerospace, Physics, and Space Science Faculty Publications
We assembled a catalogue of bright, hot subdwarf and white dwarf stars extracted from a joint ultraviolet, optical and infrared source list. The selection is secured using colour criteria that correlate well with effective temperatures Teff≳ 12 000 K. We built a NUV− V versus V − J diagram for ≳60 000 bright sources using the Galaxy Evolution Explorer (GALEX) NUV magnitude (NUV < 14), the associated Guide Star Catalog (GSC2.3.2) photographic quick-V magnitude and the Two-Micron All-Sky Survey J and H magnitudes. This distillation process delivered a catalogue of ≈700 sources with NUV− V < 0.5 comprising ∼160 known hot subdwarf stars and another ∼60 known white dwarf stars. A reduced proper-motion diagram built using the proper-motion measurements extracted from the Naval Observatory Merged Astrometric Dataset allowed us to identify an additional ∼120 new hot subdwarf candidates and ∼10 hot white dwarf candidates. We present a spectroscopic study of a subset of 52 subdwarfs, 48 of them analysed here for the first time, and with nine objects brighter than V ∼ 12. …
The Structure Of X-Ray Emissions Fromtriggered Lightning Leadersmeasured By A Pinhole-Type X-Ray Camera, M. M. Schaal, J. R. Dwyer, S. Arabshahi, E. S. Cramer, R. J. Lucia, N. Y. Liu, H. K. Rassoul, D. M. Smith, J. W. Matten, A. G. Reid, J. D. Hill, D. M. Jordan, M. A. Uman
The Structure Of X-Ray Emissions Fromtriggered Lightning Leadersmeasured By A Pinhole-Type X-Ray Camera, M. M. Schaal, J. R. Dwyer, S. Arabshahi, E. S. Cramer, R. J. Lucia, N. Y. Liu, H. K. Rassoul, D. M. Smith, J. W. Matten, A. G. Reid, J. D. Hill, D. M. Jordan, M. A. Uman
Aerospace, Physics, and Space Science Faculty Publications
We investigate the structure of X-ray emissions from downward triggered lightning leaders using a pinhole-type X-ray camera (XCAM) located at the International Center for Lightning Research and Testing. This study builds on the work of Dwyer et al. (2011), which reported results from XCAM data from the 2010 summer lightning season. Additional details regarding the 2010 data are reported here. During the 2011 summer lightning season, the XCAM recorded 12 out of 17 leaders, 5 of which show downward leader propagation. Of those five leaders, one dart-stepped leader and two chaotic dart leaders are the focus of this paper. These …
Spitzer 24Μm Survey For Dust Disks Around Hot White Dwarfs, You-Hua Chu, Kate Y.L. Su, Jana Bilikova, Robert A. Gruendl, Orsola De Marco, Martin A. Guerrero, Adria Updike, Kevin Volk, Thomas Rauch
Spitzer 24Μm Survey For Dust Disks Around Hot White Dwarfs, You-Hua Chu, Kate Y.L. Su, Jana Bilikova, Robert A. Gruendl, Orsola De Marco, Martin A. Guerrero, Adria Updike, Kevin Volk, Thomas Rauch
Arts & Sciences Faculty Publications
No abstract provided.
A Detailed Model Atmosphere Analysis Of Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Ted Von Hippel, Et Al.
A Detailed Model Atmosphere Analysis Of Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We present optical spectroscopy and near-infrared photometry of 126 cool white dwarfs (WDs) in the Sloan Digital Sky Survey (SDSS). Our sample includes high proper motion targets selected using the SDSS and USNO-B astrometry and a dozen previously known ultracool WD candidates. Our optical spectroscopic observations demonstrate that a clean selection of large samples of cool WDs in the SDSS (and the SkyMapper, Pan-STARRS, and the Large Synoptic Survey Telescope data sets) is possible using a reduced proper motion diagram and a tangential velocity cut-off (depending on the proper motion accuracy) of 30 km s–1. Our near-infrared observations reveal eight …
Visitors From The Halo: 11 Gyr Old White Dwarfs In The Solar Neighborhood, Mukremin Kilic, Ted Von Hippel, Et Al.
Visitors From The Halo: 11 Gyr Old White Dwarfs In The Solar Neighborhood, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We report the discovery of three nearby old halo white dwarf (WD) candidates in the Sloan Digital Sky Survey (SDSS), including two stars in a common proper motion binary system. These candidates are selected from our 2800deg2 proper motion survey on the Bok and U.S. Naval Observatory Flagstaff Station 1.3 m telescopes, and they display proper motions of 0˝.4-0˝.5 yr¯1. Follow-up MMT spectroscopy and near-infrared photometry demonstrate that all three objects are hydrogen-dominated atmosphere WDs with T eff ≈ 3700-4100 K. For average mass WDs, these temperature estimates correspond to cooling ages of 9-10 Gyr, distances of 70-80 pc, and …
Pulsational Mapping Of Calcium Across The Surface Of A White Dwarf, Susan E. Thompson, Ted Von Hippel, Et Al.
Pulsational Mapping Of Calcium Across The Surface Of A White Dwarf, Susan E. Thompson, Ted Von Hippel, Et Al.
Publications
We constrain the distribution of calcium across the surface of the white dwarf star G29-38 by combining time-series spectroscopy from Gemini-North with global time-series photometry from the Whole Earth Telescope. G29-38 is actively accreting metals from a known debris disk. Since the metals sink significantly faster than they mix across the surface, any inhomogeneity in the accretion process will appear as an inhomogeneity of the metals on the surface of the star. We measure the flux amplitudes and the calcium equivalent width amplitudes for two large pulsations excited on G29-38 in 2008. The ratio of these amplitudes best fits a …
The White Dwarfs Within 20 Parsecs Of The Sun: Kinematics And Statistics, Edward M. Sion, J. B. Holberg, Terry D. Oswalt, George P. Mccook, Richard Wasatonic
The White Dwarfs Within 20 Parsecs Of The Sun: Kinematics And Statistics, Edward M. Sion, J. B. Holberg, Terry D. Oswalt, George P. Mccook, Richard Wasatonic
Publications
We present the kinematical properties, distribution of spectroscopic subtypes, and stellar population subcomponents of the white dwarfs within 20 pc of the Sun.We find no convincing evidence of halo white dwarfs in the total 20 pc sample of 129 white dwarfs nor is there convincing evidence of genuine thick disk subcomponent members within 20 parsecs. Virtually, the entire 20 pc sample likely belongs to the thin disk. The total DA to non-DA ratio of the 20 pc sample is 1.6, a manifestation of deepening envelope convection which transforms DA stars with sufficiently thin H surface layers into non-DAs. The addition …
A Near-Infrared Spectroscopic Survey Of Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Piotr M. Kowalski, Ted Von Hippel
A Near-Infrared Spectroscopic Survey Of Cool White Dwarfs In The Sloan Digital Sky Survey, Mukremin Kilic, Piotr M. Kowalski, Ted Von Hippel
Publications
We present near-infrared photometric observations of 15 and spectroscopic observations of 38 cool white dwarfs (WDs). This is the largest near-infrared spectroscopic survey of cool WDs to date. Combining the Sloan Digital Sky Survey photometry and our near-infrared data, we perform a detailed model atmosphere analysis. The spectral energy distributions of our objects are explained fairly well by model atmospheres with temperatures ranging from 6300 K down to 4200 K. Two WDs show significant absorption in the infrared, and are best explained with mixed H/He atmosphere models. Based on the up-to-date model atmosphere calculations by Kowalski & Saumon, we find …
Spitzer Observations Of The Oldest White Dwarfs In The Solar Neighborhood, Mukremin Kilic, Ted Von Hippel, Et Al.
Spitzer Observations Of The Oldest White Dwarfs In The Solar Neighborhood, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We present Spitzer 5-15 μm spectroscopy of one cool white dwarf and 3.6-8 μm photometry of 51 cool white dwarfs with T eff < 6000 K. The majority of our targets have accurate BVRIJHKphotometry and trigonometric parallax measurements available, which enables us to perform a detailed model atmosphere analysis using their optical, near- and mid-infrared photometry with state-of-the-art model atmospheres. We demonstrate that the optical and infrared spectral energy distributions of cool white dwarfs are well reproduced by our grid of models. Our best-fit models are consistent with the observations within 5% in all filters except the IRAC 8 μm band, which has the lowest signal-to-noise ratio photometry. Excluding …
Inverting Color–Magnitude Diagrams To Access Precise Star Cluster Parameters: A New White Dwarf Age For The Hyades, Steven Degennaro, Ted Von Hippel, Et Al.
Inverting Color–Magnitude Diagrams To Access Precise Star Cluster Parameters: A New White Dwarf Age For The Hyades, Steven Degennaro, Ted Von Hippel, Et Al.
Publications
We have extended our Bayesian modeling of stellar clusters—which uses main-sequence stellar evolution models, a mapping between initial masses and white dwarf (WD) masses, WD cooling models, and WD atmospheres—to include binary stars, field stars, and two additional main-sequence stellar evolution models. As a critical test of our Bayesian modeling technique, we apply it to Hyades UBV photometry, with membership priors based on proper motions and radial velocities, where available. Under the assumption of a particular set of WD cooling models and atmosphere models, we estimate the age of the Hyades based on cooling WDs to be 648 ± 45 …
The Dust Cloud Around The White Dwarf G 29-38. Ii. Spectrum From 5 To 40 Μm And Mid-Infrared Photometric Variability, William T. Reach, Ted Von Hippel, Et Al.
The Dust Cloud Around The White Dwarf G 29-38. Ii. Spectrum From 5 To 40 Μm And Mid-Infrared Photometric Variability, William T. Reach, Ted Von Hippel, Et Al.
Publications
We model the mineralogy and distribution of dust around the white dwarf G29-39 using the infrared spectrum from 1 to 35 μm. The spectral model for G29-38 dust combines a wide range of materials based on spectral studies of comets and debris disks. In order of their contribution to the mid-infrared emission, the most abundant minerals around G29-38 are amorphous carbon (λ < 8 μm), amorphous and crystalline silicates (5-40 μm), water ice (10-15 and 23-35 μm), and metal sulfides (18-28 μm). The amorphous C can be equivalently replaced by other materials (like metallic Fe) with featureless infrared spectra. The best-fitting crystalline silicate is Fe-rich pyroxene. In order to absorb enough starlight to power the observed emission, the disk must either be much thinner than the stellar radius (so that it can be heated from above and below) or it must have an opening angle wider than 2°. A "moderately optically thick" torus model fits well if the dust extends inward to 50 times the white dwarf radius, all grains hotter than 1100 K are vaporized, the optical depth from the star through the disk is τ∥ = 5, and the radial density profile ∝r –2.7; the total mass of this model disk is 2 × 1019 g. A physically thin (less than the white dwarf radius) and optically thick disk can contribute to the near-infrared continuum only; such a disk cannot …
Constraining The Surface Inhomogeneity And Settling Times Of Metals On Accreting White Dwarfs, Michael H. Montgomery, S.E. Thompson, Ted Von Hippel
Constraining The Surface Inhomogeneity And Settling Times Of Metals On Accreting White Dwarfs, Michael H. Montgomery, S.E. Thompson, Ted Von Hippel
Publications
Due to the short settling times of metals in DA white dwarf atmospheres, any white dwarfs with photospheric metals must be actively accreting. It is therefore natural to expect that the metals may not be deposited uniformly on the surface of the star. We present calculations showing how the temperature variations associated with white dwarf pulsations lead to an observable diagnostic of the surface metal distribution, and we show what constraints current data sets are able to provide. We also investigate the effect that time-variable accretion has on the metal abundances of different species, and we show how this can …
The First Mid-Infrared Spectra Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.
The First Mid-Infrared Spectra Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We present the first mid-infrared spectra of two cool white dwarfs obtained with the Spitzer Space Telescope. We also present 3.5–8 μ m photometry for 19 cool white dwarfs with 5000 K ≤Teff ≤ 9000 K. We perform a detailed model atmosphere analysis of these white dwarfs by fitting their UBVRIJHK and Spitzer photometry with state-of-the-art model atmospheres, and demonstrate that the optical and infrared spectral energy distributions of cool white dwarfs are well reproduced by our grid of models. Our mid-infrared photometry and 7.5-14.5 μm spectrum of WD 0018–267 are consistent with a Teff = 5720 …
A New Look At The Local White Dwarf Population, J. B. Holberg, E. M. Sion, Terry D. Oswalt, G. P. Mccook, S. Foran, John P. Subasavage
A New Look At The Local White Dwarf Population, J. B. Holberg, E. M. Sion, Terry D. Oswalt, G. P. Mccook, S. Foran, John P. Subasavage
Publications
We have conducted a detailed new survey of the local population of white dwarfs lying within 20 pc of the Sun. A new revised catalog of local white dwarfs containing 122 entries (126 individual degenerate stars) is presented. This list contains 27 white dwarfs not included in a previous list from 2002, as well as new and recently published trigonometric parallaxes. In several cases new members of the local white dwarf population have come to light through accurate photometric distance estimates. In addition, a suspected new double degenerate system (WD 0423+120) has been identified. The 20 pc sample is currently …
De Canum Venaticorum: A Bright, Eclipsing Red Dwarf–White Dwarf Binary, E. J. M. Van Den Besselaar, R. Greimel, L. Morales-Rueda, G. Nelemans, J. R. Thorstensen
De Canum Venaticorum: A Bright, Eclipsing Red Dwarf–White Dwarf Binary, E. J. M. Van Den Besselaar, R. Greimel, L. Morales-Rueda, G. Nelemans, J. R. Thorstensen
Dartmouth Scholarship
Close white dwarf - red dwarf binaries must have gone through a common-envelope phase during their evolution. DE CVn is a detached white dwarf - red dwarf binary with a relatively short (~8.7 hours) orbital period. Its brightness and the presence of eclipses makes this system ideal for a more detailed study. From a study of photometric and spectroscopic observations of DE CVn we derive the system parameters which we discuss in the frame work of common-envelope evolution. Photometric observations of the eclipses are used to determine an accurate ephemeris. From a model fit to an average low-resolution spectrum of …
White Dwarf Luminosity And Mass Functions From Sloan Digital Sky Survey Spectra, Steven Degennaro, Ted Von Hippel, D. E. Winget, S. O. Kepler, Atsuko Nitta, Detlev Koester, Leandro Althaus
White Dwarf Luminosity And Mass Functions From Sloan Digital Sky Survey Spectra, Steven Degennaro, Ted Von Hippel, D. E. Winget, S. O. Kepler, Atsuko Nitta, Detlev Koester, Leandro Althaus
Publications
We present the first phase in our ongoing work to use Sloan Digital Sky Survey (SDSS) data to create separate white dwarf (WD) luminosity functions (LFs) for two or more different mass ranges. In this paper, we determine the completeness of the SDSS spectroscopic WD sample by comparing a proper-motion selected sample of WDs from SDSS imaging data with a large catalog of spectroscopically determined WDs. We derive a selection probability as a function of a single color (g − i) and apparent magnitude (g) that covers the range −1.0 < g − i < 0.2 and 15 < g < 19.5. We address the observed upturn in log g for WDs with Teff 12,000 K and offer arguments that the problem is limited to the line profiles and is not present in the continuum. We offer an empirical method of removing the upturn, recovering a reasonable mass function for WDs with Teff < 12,000 K. Finally we present a WD LF with nearly an order of magnitude (3358) more spectroscopically confirmed WDs than any previous work.
A Spitzer White Dwarf Infrared Survey, F. Mullally, Ted Von Hippel, Et Al.
A Spitzer White Dwarf Infrared Survey, F. Mullally, Ted Von Hippel, Et Al.
Publications
We present mid-infrared photometry of 124 white dwarf stars with the Spitzer Space Telescope. Objects were observed simultaneously at 4.5 and 8.0 μm with sensitivities better than 0.1 mJy. This data set can be used to test models of white dwarf atmospheres in a new wavelength regime, as well as to search for planetary companions and debris disks.
The New Class Of Dusty Daz White Dwarfs, Ted Von Hippel, Et Al.
The New Class Of Dusty Daz White Dwarfs, Ted Von Hippel, Et Al.
Publications
Our mid-infrared survey of 124 white dwarfs with the Spitzer Space Telescope and the IRAC imager has revealed an infrared excess associated with the white dwarf WD 2115-560 naturally explained by circumstellar dust. This object is the fourth white dwarf observed to have circumstellar dust. All four are DAZ white dwarfs, i.e., they have both photospheric Balmer lines and photospheric metal lines. We discuss these four objects as a class, which we abbreviate "DAZd," where the "d" stands for "dust." Using an optically thick, geometrically thin disk model analogous to Saturn's rings, we find that the inner disk edges are …
Lp 133-373: A New Chromospherically Active Eclipsing Dme Binary With A Distant, Cool White Dwarf Companion, T. R. Vaccaro, M. Rudkin, A. Kawka, S. Vennes, Terry D. Oswalt, Et Al.
Lp 133-373: A New Chromospherically Active Eclipsing Dme Binary With A Distant, Cool White Dwarf Companion, T. R. Vaccaro, M. Rudkin, A. Kawka, S. Vennes, Terry D. Oswalt, Et Al.
Publications
We report the discovery of the partially eclipsing binary LP 133-373. Nearly identical eclipses along with observed photometric colors and spectroscopy indicate that it is a pair of chromospherically active dM4 stars in a circular 1.6 day orbit. Light and velocity curve modeling to our differential photometry and velocity data show that each star has a mass and radius of 0:340 ± 0:014 MꙨ and 0:33 ± 0:02 RꙨ. The binary is itself part of a common proper motion pair with LP 133-374, a cool DC or possible DA white dwarf with a mass of 0.49Y0.82 M …
Lp133-373 A New Chromospherically Active Eclipsing Dme Binary With A Distant, Cool White Dwarf Companion, T. R. Vaccaro, T. D. Oswalt, M. Rudkin, Adela Kawka, Stephane Vennes, Et Al.
Lp133-373 A New Chromospherically Active Eclipsing Dme Binary With A Distant, Cool White Dwarf Companion, T. R. Vaccaro, T. D. Oswalt, M. Rudkin, Adela Kawka, Stephane Vennes, Et Al.
Publications
We report the discovery of the partially eclipsing binary LP 133-373. Nearly identical eclipses along with observed photometric colors and spectroscopy indicate that it is a pair of chromospherically active dM4 stars in a circular 1.6 day orbit. Light and velocity curve modeling to our differential photometry and velocity data show that each star has a mass and radius of 0.340 ± 0.014 M☉ and 0.33 ± 0.02 R☉. The binary is itself part of a common proper motion pair with LP 133-374, a cool DC or possible DA white dwarf with a mass of 0.49-0.82 M☉, …
Discovery Of Photospheric Calcium Line-Strength Variations In The Dazd White Dwarf G29-38, Ted Von Hippel, Susan E. Thompson
Discovery Of Photospheric Calcium Line-Strength Variations In The Dazd White Dwarf G29-38, Ted Von Hippel, Susan E. Thompson
Publications
Metals in the photospheres of white dwarfs with Teff between 12,000 and 25,000 K should gravitationally settle out of these atmospheres in 1 ̶ 2 weeks. Temporal variations in the line strengths of these metals could provide a direct measurement of episodic metal accretion. Using archival VLT and Keck spectroscopy, we find evidence that the DAZd white dwarf G29-38 shows significant changes in its Ca П K line strength. At the two best-observed epochs, we find that the Ca line equivalent width (EW) = 165 ̶ 4 mǺ (in 1996.885) and 280 ± 8 mǺ (in 1999.653), which is …
New Techniques To Determine Ages Of Open Clusters Using White Dwarfs, E. J. Jeffery, Ted Von Hippel, Et Al.
New Techniques To Determine Ages Of Open Clusters Using White Dwarfs, E. J. Jeffery, Ted Von Hippel, Et Al.
Publications
Currently there are two main techniques for independently determining the ages of stellar populations: main-sequence evolution theory (via cluster isochrones) and white dwarf cooling theory. Open clusters provide the ideal environment for the calibration of these two clocks. Because current techniques to derive cluster ages from white dwarfs are observationally challenging, we discuss the feasibility of determining white dwarf ages from the brighter white dwarfs alone. This would eliminate the requirement of observing the coolest (i.e., faintest) white dwarfs. We discuss our method for testing this new idea, as well as the required photometric precision and prior constraints on metallicity, …