Open Access. Powered by Scholars. Published by Universities.®
Stars, Interstellar Medium and the Galaxy Commons™
Open Access. Powered by Scholars. Published by Universities.®
- Discipline
-
- Physical Processes (14)
- Cosmology, Relativity, and Gravity (12)
- The Sun and the Solar System (12)
- Instrumentation (10)
- External Galaxies (9)
-
- Other Astrophysics and Astronomy (8)
- Applied Mathematics (3)
- Engineering Physics (2)
- Numerical Analysis and Computation (2)
- Physics (2)
- Aerospace Engineering (1)
- Applied Statistics (1)
- Arts and Humanities (1)
- Atmospheric Sciences (1)
- Computer Sciences (1)
- Data Science (1)
- Engineering (1)
- Numerical Analysis and Scientific Computing (1)
- Oceanography and Atmospheric Sciences and Meteorology (1)
- Optics (1)
- Other Physical Sciences and Mathematics (1)
- Photography (1)
- Probability (1)
- Statistics and Probability (1)
- Keyword
-
- White dwarfs (67)
- Stars: evolution (17)
- Astronomy (12)
- X-rays (10)
- Astronautics (9)
-
- Stars: oscillations (9)
- Neutron stars (8)
- Science (8)
- Technology (8)
- Binaries (7)
- Circumstellar matter (7)
- Galaxy: stellar content (7)
- Mass function (7)
- Open clusters and associations: general (7)
- Techniques: photometric (7)
- Techniques: spectroscopic (7)
- Galaxy: halo (6)
- Infrared: stars (6)
- Methods: data analysis (6)
- Pulsars (6)
- Stars: activity (6)
- Stars: statistics (6)
- Accretion (5)
- Accretion disks (5)
- Binary stars (5)
- Globular clusters: general (5)
- Stars (5)
- Stars: atmospheres (5)
- Stars: fundamental parameters (5)
- Stars: luminosity function (5)
- Publication Year
- Publication
- Publication Type
- File Type
Articles 121 - 150 of 211
Full-Text Articles in Stars, Interstellar Medium and the Galaxy
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 …
Book Review: Clocks In The Sky: The Story Of Pulsars, T. D. Oswalt
Book Review: Clocks In The Sky: The Story Of Pulsars, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Clocks in the Sky: The Story of Pulsars by Geoff McNamara, Springer/Praxis, 2008 190p, 9780387765600 $29.95.
Multisite Photometry Of The Pulsating Herbig Ae Star V346 Ori, S. Bernabei, Terry D. Oswalt, V. Ripepi, A. Ruoppo, Et Al.
Multisite Photometry Of The Pulsating Herbig Ae Star V346 Ori, S. Bernabei, Terry D. Oswalt, V. Ripepi, A. Ruoppo, Et Al.
Publications
The study of pulsation in Pre--Main--Sequence intermediate-mass stars represents an important tool for deriving information on fundamental stellar parameters and internal structure, as well as for testing current theoretical models. Interest in this class of variable stars has significantly increased during the last decade and about 30 members are presently known in the literature. AIMS: We have constructed the frequency spectrum of the oscillations in V346 Ori. We apply asteroseismic tools to these data to estimate the intrinsic parameters (mass, luminosity, effective temperature) of V346 Ori and to obtain information on its internal structure. METHODS: CCD time series photometry in …
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 …
Statistical Analysis Of Stellar Evolution, David A. Van Dyk, Ted Von Hippel, Steven Degenarro, Nathan Stein, William Jefferys
Statistical Analysis Of Stellar Evolution, David A. Van Dyk, Ted Von Hippel, Steven Degenarro, Nathan Stein, William Jefferys
Publications
Color-Magnitude Diagrams (CMDs) are plots that compare the magnitudes (luminosities) of stars in different wavelengths of light (colors). High nonlinear correlations among the mass, color, and surface temperature of newly formed stars induce a long narrow curved point cloud in a CMD known as the main sequence. Aging stars form new CMD groups of red giants and white dwarfs. The physical processes that govern this evolution can be described with mathematical models and explored using complex computer models. These calculations are designed to predict the plotted magnitudes as a function of parameters of scientific interest, such as stellar age, mass, …
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 …
Book Review: Guide To Observing Deep-Sky Objects: A Complete Global Resource For Astronomers, T. D. Oswalt
Book Review: Guide To Observing Deep-Sky Objects: A Complete Global Resource For Astronomers, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Guide to Observing Deep-Sky Objects : a Complete Global Resource for Astronomers by Jeff A. Farinacci. Springer, 2007 189p, 9780387728506 $29.95
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 …
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.
Wide-Field Survey Of Globular Clusters In M31. I. A Catalog Of New Clusters, Sang Chul Kim, Myung Gyoon Lee, Doug Geisler, Ata Sarajedini, Hong Soo Park, Ho Seong Hwang, William E. Harris, Juan C. Seguel, Ted Von Hippel
Wide-Field Survey Of Globular Clusters In M31. I. A Catalog Of New Clusters, Sang Chul Kim, Myung Gyoon Lee, Doug Geisler, Ata Sarajedini, Hong Soo Park, Ho Seong Hwang, William E. Harris, Juan C. Seguel, Ted Von Hippel
Publications
We present the result of a wide-field survey of globular clusters (GCs) in M31 covering a 3o x 3o field centered on M31.We have searched for GCs on CCD images taken with Washington CMT1 filters at the KPNO 0.9 m telescope using the following steps: (1) inspection of morphological parameters given by the SExtractor package such as stellarity, full width at half-maximum, and ellipticity; (2) consulting the spectral types and radial velocities obtained from spectra taken with the Hydra spectrograph at the WIYN 3.5 m telescope; and (3) visual inspection of the images of each object. We …
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 …
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☉, …
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 …
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, …
The Metallicity Distribution Of Intracluster Stars In Virgo, Benjamin F. Willaims, Ted Von Hippel, Et Al.
The Metallicity Distribution Of Intracluster Stars In Virgo, Benjamin F. Willaims, Ted Von Hippel, Et Al.
Publications
We have used the Hubble Space Telescope's Advanced Camera for Surveys (ACS) to detect and measure ~5300 stars in a single intracluster field in the Virgo Cluster. By performing F606W and F814W photometry on these stars, we have determined their metallicity distribution function and constrained the types of stars present in this portion of Virgo's intracluster space. Based on the small number of stars detected that were brighter than the red giant branch (RGB) tip, we suggest that in this region, Virgo's intracluster stars are mostly old (10 Gyr). Through analysis of the RGB stars themselves, we determine that …
The Resolved Stellar Populations Of A Dwarf Spheroidal Galaxy In The Virgo Cluster, Patrick R. Durell, Ted Von Hippel, Et Al.
The Resolved Stellar Populations Of A Dwarf Spheroidal Galaxy In The Virgo Cluster, Patrick R. Durell, Ted Von Hippel, Et Al.
Publications
We report on the discovery of a faint (MV ~ -10.6 ± 0.2) dwarf spheroidal galaxy on deep F606W and F814W Hubble Space Telescope images of a Virgo intracluster field. The galaxy is easily resolved in our images, as our color magnitude diagram (CMD) extends 1 magnitude beyond the tip of the red giant branch (RGB). Thus, it is the deepest CMD for a small dwarf galaxy inside a cluster environment. Using the colors of the RGB stars, we derive a metal abundance for the dwarf of [M/H] = -2.3 ± 0.3 and show that the metallicity dispersion …
Virgo’S Intracluster Globular Clusters As Seen By The Advanced Camera For Surveys, Benjamin F. Williams, Robin Ciardullo, Ted Von Hippel, Et Al.
Virgo’S Intracluster Globular Clusters As Seen By The Advanced Camera For Surveys, Benjamin F. Williams, Robin Ciardullo, Ted Von Hippel, Et Al.
Publications
We report the discovery of four candidate intracluster globular clusters (IGCs) in a single deepHST ACS field of the Virgo Cluster. We show that each cluster is roughly spherical, has a magnitude near the peak of the Virgo globular cluster luminosity function, has a radial profile that is best fitted by a King model, and is surrounded by an excess of point sources that have the colors and magnitudes of cluster red giant stars. Despite the fact that two of our IGC candidates have integrated colors redder than the mean of the M87 globular cluster system, we propose that …
Spitzer White Dwarf Planet Limits, F. Mullally, Ted Von Hippel, D. E. Winget
Spitzer White Dwarf Planet Limits, F. Mullally, Ted Von Hippel, D. E. Winget
Publications
We present preliminary limits on the presence of planets around white dwarf stars using the IRAC photometer on the Spitzer space telescope. Planets emit strongly in the mid-infrared which allows their presence to be detected as an excess at these wavelengths. We place limits of 5 MJ for 8 stars assuming ages of 1 Gyr, and 10 MJ for 23 stars.We describe our survey, present our results and comment on approaches to improve our methodology.
Debris Disks Around White Dwarfs: The Daz Connection, Mukremin Kilic, Ted Von Hippel, Et Al.
Debris Disks Around White Dwarfs: The Daz Connection, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We present near-infrared spectroscopic observations of 20 previously known DAZ white dwarfs obtained at the NASA Infrared Telescope Facility. Two of these white dwarfs (G29-38 and GD 362) are known to display significant K-band excesses due to circumstellar debris disks. Here we report the discovery of excess K-band radiation from another DAZ white dwarf WD0408041 (GD56). Using 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 warm debris disk. Our observations strengthen the connection between the debris disk phenomena and the observed …
Inverting Color-Magnitude Diagrams To Access Precise Star Cluster Parameters: A Bayesian Approach, Ted Von Hippel, Et Al.
Inverting Color-Magnitude Diagrams To Access Precise Star Cluster Parameters: A Bayesian Approach, Ted Von Hippel, Et Al.
Publications
We demonstrate a new Bayesian technique to invert color-magnitude diagrams of main-sequence and white dwarf stars to reveal the underlying cluster properties of age, distance, metallicity, and line-of-sight absorption, as well as individual stellar masses. The advantages our technique has over traditional analyses of color-magnitude diagrams are objectivity, precision, and explicit dependence on prior knowledge of cluster parameters. Within the confines of a given set of often-used models of stellar evolution, a single mapping of initial to final masses, and white dwarf cooling, and assuming photometric errors that one could reasonably achieve with the Hubble Space Telescope, our technique …
Lp 400-22, A Very Low Mass And High-Velocity White Dwarf, Adela Kawka, Stephane Vennes, Terry D. Oswalt, J. Allyn Smith, Nicole M. Silvestri
Lp 400-22, A Very Low Mass And High-Velocity White Dwarf, Adela Kawka, Stephane Vennes, Terry D. Oswalt, J. Allyn Smith, Nicole M. Silvestri
Publications
We report the identification of LP 400-22 (WD 2234 + 222) as a very low mass and high-velocity white dwarf. The ultraviolet GALEX and optical photometric colors and a spectral line analysis of LP 400-22 show this star to have an effective temperature of 11,080 ± 140 K and a surface gravity of log g p 6.32 ± 0.08. Therefore, this is a helium-core white dwarf with a mass of 0.17 MꙨ. The tangential velocity of this white dwarf is 414 ± 43 km s-1, making it one of the fastest moving white dwarfs known. We …
The Mystery Deepens: Spitzer Observations Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.
The Mystery Deepens: Spitzer Observations Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We present 4.5 and 8 µm photometric observations of 18 cool white dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate that four white dwarfs with Teᶠᶠ < 6000 K show slightly depressed mid-infrared fluxes relative to white dwarf models. In addition, another white dwarf with a peculiar optical and near-infrared spectral energy distribution (LHS 1126) is found to display significant flux deficits in Spitzer observations. These mid-infrared flux deficits are not predicted by the current white dwarf models including collision-induced absorption due to molecular hydrogen. We postulate that either the collision-induced absorption calculations are incomplete or there are other unrecognized physical processes occurring in cool white dwarf atmospheres. The spectral energy distribution of LHS 1126 surprisingly fits a Rayleigh-Jeans spectrum in the infrared, mimicking a hot white dwarf with effective temperature well in excess of 105 K. This implies that the source of this flux deficit is probably not molecular absorption but some other process.