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Articles 31 - 60 of 182
Full-Text Articles in Stars, Interstellar Medium and the Galaxy
Redefining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, Et Al.
Redefining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, Et Al.
Ted von Hippel
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 …
Re-Defining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, D. E. Winget,, M. H. Montgomery
Re-Defining The Empirical Zz Ceti Instability Strip, Anjum S. Mukadam, Ted Von Hippel, D. E. Winget,, M. H. Montgomery
Ted von Hippel
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 ∼ …
Measuring The Evolutionary Rate Of Cooling Of Zz Ceti, Anjum S. Mukadam, Ted Von Hippel, Et Al.
Measuring The Evolutionary Rate Of Cooling Of Zz Ceti, Anjum S. Mukadam, Ted Von Hippel, Et Al.
Ted von Hippel
We have finally measured the evolutionary rate of cooling of the pulsating hydrogen atmosphere (DA) white dwarf ZZ Ceti (Ross 548), as reflected by the drift rate of the 213.13260694 s period. Using 41 yr of time-series photometry from 1970 November to 2012 January, we determine the rate of change of this period with time to be dP/dt = (5.2 ± 1.4) × 10–15 s s–1 employing the O – C method and (5.45 ± 0.79) × 10–15 s s–1 using a direct nonlinear least squares fit to the entire lightcurve. We adopt the dP/dt obtained …
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
Ted von Hippel
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.
Physical Parameterization Of Stellar Spectra: The Neural Network Approach, Coryn A.L. Bailer-Jones, Ted Von Hippel, Mike Irwin, Gerard Gilmore
Physical Parameterization Of Stellar Spectra: The Neural Network Approach, Coryn A.L. Bailer-Jones, Ted Von Hippel, Mike Irwin, Gerard Gilmore
Ted von Hippel
We present a technique which employs artificial neural networks to produce physical parameters for stellar spectra. A neural network is trained on a set of synthetic optical stellar spectra to give physical parameters (e.g. Teff, log g, [M/H]). The network is then used to produce physical parameters for real, observed spectra. Our neural networks are trained on a set of 155 synthetic spectra, generated using the spectrum program written by Gray (Gray & Corbally 1994, Gray & Arlt 1996). Once trained, the neural network is used to yield Teff for over 5000 B–K spectra extracted from a set of photographic …
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.
Ted von Hippel
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 …
Proper Motion Objects In The Hubble Deep Field, M. Kilic, Ted Von Hippel, Et Al.
Proper Motion Objects In The Hubble Deep Field, M. Kilic, Ted Von Hippel, Et Al.
Ted von Hippel
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 & …
Search For Oxygen In Cool Dq White Dwarf Atmospheres, M. Kilic, Ted Von Hippel, D. E. Winget, D. F. Lester, D. Saumon
Search For Oxygen In Cool Dq White Dwarf Atmospheres, M. Kilic, Ted Von Hippel, D. E. Winget, D. F. Lester, D. Saumon
Ted von Hippel
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 …
Moving Objects In The Hubble Ultra Deep Field, Mukremin Kilic, Alexandros Gianninas, Ted Von Hippel
Moving Objects In The Hubble Ultra Deep Field, Mukremin Kilic, Alexandros Gianninas, Ted Von Hippel
Ted von Hippel
We identify proper motion objects in the Hubble Ultra Deep Field (UDF) using the optical data from the original UDF program in 2004 and the near-infrared data from the 128 orbit UDF 2012 campaign. There are 12 sources brighter than I = 27 mag that display >3σ significant proper motions. We do not find any proper motion objects fainter than this magnitude limit. Combining optical and near-infrared photometry, we model the spectral energy distribution of each point-source using stellar templates and state-of-the-art white dwarf models. For I ≤ 27 mag, we identify 23 stars with K0-M6 spectral types and two …
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.
Ted von Hippel
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 …
Semi-Automated Extraction Of Digital Objective Prism Spectra, Coryn A.L. Bailer-Jones, Ted Von Hippel, Mike Irwin
Semi-Automated Extraction Of Digital Objective Prism Spectra, Coryn A.L. Bailer-Jones, Ted Von Hippel, Mike Irwin
Ted von Hippel
We describe a method for the extraction of spectra from high dispersion objective prism plates. Our method is a catalogue driven plate solution approach, making use of the Right Ascension and Declination coordinates for the target objects. In contrast to existing methods of photographic plate reduction, we digitize the entire plate and extract spectra off-line. This approach has the advantages that it can be applied to CCD objective prism images, and spectra can be re-extracted (or additional spectra extracted) without having to re-scan the plate. After a brief initial interactive period, the subsequent reduction procedure is completely automatic, resulting in …
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
Ted von Hippel
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 Bayesian Approach To Deriving Ages Of Individual Field White Dwarfs, Erin M. O'Malley, Ted Von Hippel, David A. Van Dyk
A Bayesian Approach To Deriving Ages Of Individual Field White Dwarfs, Erin M. O'Malley, Ted Von Hippel, David A. Van Dyk
Ted von Hippel
We apply a self-consistent and robust Bayesian statistical approach to determine the ages, distances, and zero-age main sequence (ZAMS) masses of 28 field DA white dwarfs (WDs) with ages of approximately 4-8 Gyr. Our technique requires only quality optical and near-infrared photometry to derive ages with <15% uncertainties, generally with little sensitivity to our choice of modern initial-final mass relation. We find that age, distance, and ZAMS mass are correlated in a manner that is too complex to be captured by traditional error propagation techniques. We further find that the posterior distributions of age are often asymmetric, indicating that the standard approach to deriving WD ages can yield misleading results.
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
Ted von Hippel
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 …
Wiyn Open Cluster Study Xi: Wiyn1 3.5m Deep Photometry Of M35 (Ngc 2168), Ted Von Hippel, Aaron Steinhauer, Ata Sarajedini, Constantine P. Deliyannis
Wiyn Open Cluster Study Xi: Wiyn1 3.5m Deep Photometry Of M35 (Ngc 2168), Ted Von Hippel, Aaron Steinhauer, Ata Sarajedini, Constantine P. Deliyannis
Ted von Hippel
We present deep BV I observations of the core of M35 and a nearby comparison field obtained at the WIYN 3.5m telescope under excellent seeing conditions. These observations probe to V > 26, and display the lower main sequence in BV and V I 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 …
Wiyn Open Cluster Study. Ii. Ubvri Ccd Photometry Of The Open Cluster Ngc 188, Ata Sarajedini, Ted Von Hippel, Vera Kozhurina-Platais, Pierre Demarque
Wiyn Open Cluster Study. Ii. Ubvri Ccd Photometry Of The Open Cluster Ngc 188, Ata Sarajedini, Ted Von Hippel, Vera Kozhurina-Platais, Pierre Demarque
Ted von Hippel
We present high-precision UBVRI CCD photometry of the old open cluster NGC 188. Our color-magnitude diagram extends from near the red giant branch tip to as faint as ~5 mag below the main-sequence turnoff. From an analysis of these data along with published photometry for M67, we draw the following conclusions: (1) From the UBV two-color diagram, we find a reddening of E(B ̶ V) = 0.04 ± 0.02 for M67 and E(B ̶ V) = 0.09 ± 0.02 for NGC 188. (2) Based on main-sequence fitting to solar abundance isochrones, the distance moduli …
Main Sequence Masses And Radii From Gravitational Redshifts, Ted Von Hippel
Main Sequence Masses And Radii From Gravitational Redshifts, Ted Von Hippel
Ted von Hippel
Modern instrumentation makes it possible to measure the mass to radius ratio for main sequence stars in open clusters from gravitational redshifts. For stars where independent information is available for either the mass or the radius, this application of general relativity directly determines the other quantity. Applicable examples are: 1) measuring the radii of solar metallicity main sequence stars for which the mass - luminosity relation is well known, 2) measuring the radii for stars where model atmospheres can be used to determine the surface gravity (the mass to radius squared ratio), 3) refining the mass - radius relation for …
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.
Ted von Hippel
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 …
Magnetospherically-Trapped Dust And A Possible Model For The Unusual Transits At Wd1145+017, J. Farihi, Ted Von Hippel, J. E. Pringle
Magnetospherically-Trapped Dust And A Possible Model For The Unusual Transits At Wd1145+017, J. Farihi, Ted Von Hippel, J. E. Pringle
Ted von Hippel
The rapidly evolving dust and gas extinction observed towardsWD1145+017 has opened a real-time window onto the mechanisms for destruction-accretion of planetary bodies onto white dwarf stars, and has served to underline the importance of considering the dynamics of dust particles around such objects. Here it is argued that the interaction between (charged) dust grains and the stellar magnetic field is an important ingredient in understanding the physical distribution of infrared emitting particles in the vicinity of such white dwarfs. These ideas are used to suggest a possible model for WD 1145+017 in which the unusual transit shapes are caused by …
Identification Of Cool White Dwarfs In The Noao Deep Wide-Field Survey, M. Kilic, Don E. Winget, T. Von Hippel, C.F. Claver
Identification Of Cool White Dwarfs In The Noao Deep Wide-Field Survey, M. Kilic, Don E. Winget, T. Von Hippel, C.F. Claver
Ted von Hippel
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). …
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
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
Ted von Hippel
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.
Dust Production And Depletion In Evolved Planetary Systems, J. Farihi, Ted Von Hippel, Rik Van Lieshout, P.W. Cauley, Erik Dennihy, Et Al.
Dust Production And Depletion In Evolved Planetary Systems, J. Farihi, Ted Von Hippel, Rik Van Lieshout, P.W. Cauley, Erik Dennihy, Et Al.
Ted von Hippel
The infrared dust emission from the white dwarf GD 56 is found to rise and fall by 20 per cent peak-to-peak over 11.2 yr, and is consistent with ongoing dust production and depletion. It is hypothesized that the dust is produced via collisions associated with an evolving dust disc, temporarily increasing the emitting surface of warm debris, and is subsequently destroyed or assimilated within a few years. The variations are consistent with debris that does not change temperature, indicating that dust is produced and depleted within a fixed range of orbital radii. Gas produced in collisions may rapidly re-condense onto …
From Young And Hot To Old And Cold: Comparing White Dwarf Cooling Theory To Main-Sequence Stellar Evolution In Open Clusters, Ted Von Hippel
From Young And Hot To Old And Cold: Comparing White Dwarf Cooling Theory To Main-Sequence Stellar Evolution In Open Clusters, Ted Von Hippel
Ted von Hippel
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 …
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.
Ted von Hippel
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 …
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
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
Ted von Hippel
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 …
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
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
Ted von Hippel
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 …
Contribution Of White Dwarfs To Cluster Masses, Ted Von Hippel
Contribution Of White Dwarfs To Cluster Masses, Ted Von Hippel
Ted von Hippel
I have undertaken a literature search through 1997 July 31 of white dwarfs (WDs) in open and globular clusters. I have tried to make a careful evaluation in each case of the likelihood that the object is a WD and that it is a cluster member. The results are presented for 13 open clusters and 11 globular clusters. Currently there are 36 single WDs and Ðve WDs in binaries known among the open clusters, and 340 single WDs and 11 WDs in binaries known among the globular clusters. From these data, I have calculated WD mass fractions for four open …
Bayesian Investigation Of Isochrone Consistency Using The Old Open Cluster Ngc 188, Shane Hills, Ted Von Hippel, Stéphane Courteau, Aaron M. Geller
Bayesian Investigation Of Isochrone Consistency Using The Old Open Cluster Ngc 188, Shane Hills, Ted Von Hippel, Stéphane Courteau, Aaron M. Geller
Ted von Hippel
This paper provides a detailed comparison of the differences in parameters derived for a star cluster from its color– magnitude diagrams (CMDs) depending on the filters and models used. We examine the consistency and reliability of fitting three widely used stellar evolution models to 15 combinations of optical and near-IR photometry for the old open cluster NGC 188. The optical filter response curves match those of theoretical systems and are thus not the source of fit inconsistencies. NGC 188 is ideally suited to this study thanks to a wide variety of high-quality photometry and available proper motions and radial velocities …
Bayesian Hierarchical Modelling Of Initial-Final Mass Relations Across Star Clusters, Shijing Si, David A. Van Dyk, Ted Von Hippel, Elliot Robinson, Elizabeth Jeffery, David C. Stenning
Bayesian Hierarchical Modelling Of Initial-Final Mass Relations Across Star Clusters, Shijing Si, David A. Van Dyk, Ted Von Hippel, Elliot Robinson, Elizabeth Jeffery, David C. Stenning
Ted von Hippel
The initial-final mass relation (IFMR) of white dwarfs (WDs) plays an important role in stellar evolution. To derive precise estimates of IFMRs and explore how they may vary among star clusters, we propose a Bayesian hierarchical model that pools photometric data from multiple star clusters. After performing a simulation study to show the benefits of the Bayesian hierarchical model, we apply this model to five star clusters: the Hyades, M67, NGC 188, NGC 2168, and NGC 2477, leading to reasonable and consistent estimates of IFMRs for these clusters. We illustrate how a cluster-specific analysis of NGC 188 using its own …
Bayesian Analysis For Stellar Evolution With Nine Parameters (Base-9): User's Manual, Ted Von Hippel, Elliot Robinson, Elizabeth Jeffery, Rachel Wagner-Kaiser, Steven Degennaro, Nathan Stein, David Stenning, William H. Jefferys, David Van Dyk
Bayesian Analysis For Stellar Evolution With Nine Parameters (Base-9): User's Manual, Ted Von Hippel, Elliot Robinson, Elizabeth Jeffery, Rachel Wagner-Kaiser, Steven Degennaro, Nathan Stein, David Stenning, William H. Jefferys, David Van Dyk
Ted von Hippel
BASE-9 is a Bayesian software suite that recovers star cluster and stellar parameters from photometry. BASE-9 is useful for analyzing single-age, single-metallicity star clusters, binaries, or single stars, and for simulating such systems. BASE-9 uses Markov chain Monte Carlo and brute-force numerical integration techniques to estimate the posterior probability distributions for the age, metallicity, helium abundance, distance modulus, and line-of-sight absorption for a cluster, and the mass, binary mass ratio, and cluster membership probability for every stellar object. BASE-9 is provided as open source code on a version-controlled web server. The executables are also available as Amazon Elastic Compute Cloud …