I. Hubeny

The University of Arizona, Tucson, Arizona, United States

Are you I. Hubeny?

Claim your profile

Publications (305)883.19 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: We present a series of systematic abundance measurements for 89 hydrogen atmosphere (DA-type) white dwarfs with temperatures spanning 16000-77000K drawn from the FUSE spectral archive. This is the largest study to date of white dwarfs where radiative forces are significant, exceeding our earlier work, based mainly on IUE and HST data, by a factor three. Using heavy element blanketed non-LTE stellar atmosphere calculations, we have addressed the heavy element abundance patterns making completely objective measurements of abundance values and their error ranges using a \c{hi}2 fitting technique. We are able to establish the broad range of abundances seen in a given temperature range and establish the incidence of stars which appear, in the optical, to be atmospherically devoid of any material other than H. We compare the observed abundances to predictions of radiative levitation calculations, revealing little agreement. We propose that the supply of heavy elements is accreted from external sources rather than being intrinsic to the star. These elements are then retained in the white dwarf atmospheres by radiative levitation, a model that can explain both the diversity of measured abundances for stars of similar temperature and gravity, including cases with apparently pure H envelopes, and the presence of photospheric metals at temperatures where radiative levitation is no longer effective.
    02/2014;
  • [show abstract] [hide abstract]
    ABSTRACT: This paper extends synthetic photometry to components of binary star systems. The paper demonstrates accurate recovery of single star photometric properties for four photometric standards, Vega, Sirius, GD153, and HD209458, ranging over the HR diagram, when their model synthetic spectra are placed in fictitious binary systems and subjected to synthetic photometry processing. Techniques for photometric distance determination have been validated for all four photometric standards.
    The Astronomical Journal 08/2013; 146(3):68. · 4.97 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: We study the evolution, rotation, and surface abundances of O-type dwarfs in the Small Magellanic Cloud. We analyzed the UV and optical spectra of twenty-three objects and derived photospheric and wind properties. The observed binary fraction of the sample is ~ 26%, which is compatible with more systematic studies, if one considers that the actual binary fraction is potentially larger owing to low-luminosity companions and that the sample excluded obvious spectroscopic binaries. The location of the fastest rotators in the H-R diagram indicates that these could be several Myr old. The offset in the position of these fast rotators compared with the other stars confirms the predictions of evolutionary models that fast-rotating stars tend to evolve more vertically in the H-R diagram. Only one star of luminosity-class Vz, expected to best characterize extreme youth, is located on the ZAMS, the other two stars are more evolved. The distribution of nitrogen abundance of O and B stars suggests that the mechanisms responsible for the chemical enrichment of slowly rotating massive stars depends only weakly on the star's mass. We confirm that the group of slowly rotating N-rich stars is not reproduced by the evolutionary tracks. Our results call for stronger mixing in the models to explain the range of observed N abundances. All stars have an N/C ratio as a function of stellar luminosity that matches the predictions of the stellar evolution models well. More massive stars have a higher N/C ratio than the less massive stars. Faster rotators show on average a higher N/C ratio than slower rotators. The N/O versus N/C ratios agree qualitatively well with those of stellar evolution models. The only discrepant behavior is observed for the youngest two stars of the sample, which both show very strong signs of mixing, which is unexpected for their evolutionary status.
    Astronomy and Astrophysics 04/2013; · 5.08 Impact Factor
  • L. Ibgui, I. Hubeny, T. Lanz, C. Stehlé
    [show abstract] [hide abstract]
    ABSTRACT: We describe the implementation in our generic three-dimensional radiative transfer code, IRIS, of an algorithm that allows the modeling of periodic infinite media. We show how this algorithm has been validated by comparison with well-established 1D plane-parallel models. A particularly interesting astrophysical application will be the calculation of synthetic spectra of the fully three-dimensional solar atmosphere.
    12/2012;
  • [show abstract] [hide abstract]
    ABSTRACT: We show preliminary results of our numerical simulations of laboratory experiments of radiative shocks. Such experiments aim at understanding accretion shocks in young stellar objects. Three-dimensional non-stationary radiation hydrodynamics calculations were performed with the code HERACLES. X-UV spectra were then generated with the new three-dimensional radiative transfer code IRIS.
    12/2012;
  • Source
    L. Ibgui, I. Hubeny, T. Lanz, C. Stehlé
    [show abstract] [hide abstract]
    ABSTRACT: We present IRIS, a new generic three-dimensional (3D) spectral radiative transfer code that generates synthetic spectra, or images. It can be used as a diagnostic tool for comparison with astrophysical observations or laboratory astrophysics experiments. We have developed a 3D short-characteristic solver that works with a 3D nonuniform Cartesian grid. We have implemented a piecewise cubic, locally monotonic, interpolation technique that dramatically reduces the numerical diffusion effect. The code takes into account the velocity gradient effect resulting in gradual Doppler shifts of photon frequencies and subsequent alterations of spectral line profiles. It can also handle periodic boundary conditions. This first version of the code assumes Local Thermodynamic Equilibrium (LTE) and no scattering. The opacities and source functions are specified by the user. In the near future, the capabilities of IRIS will be extended to allow for non-LTE and scattering modeling. IRIS has been validated through a number of tests. We provide the results for the most relevant ones, in particular a searchlight beam test, a comparison with a 1D plane-parallel model, and a test of the velocity gradient effect. IRIS is a generic code to address a wide variety of astrophysical issues applied to different objects or structures, such as accretion shocks, jets in young stellar objects, stellar atmospheres, exoplanet atmospheres, accretion disks, rotating stellar winds, cosmological structures. It can also be applied to model laboratory astrophysics experiments, such as radiative shocks produced with high power lasers.
    Astronomy and Astrophysics 11/2012; · 5.08 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: We present an online catalog containing spectra and supporting information for cataclysmic variables that have been observed with the Far Ultraviolet Spectroscopic Explorer (FUSE). For each object in the catalog we list some of the basic system parameters such as (RA,Dec), period, inclination, white dwarf mass, as well as information on the available FUSE spectra: data ID, observation date and time, and exposure time. In addition, we provide parameters needed for the analysis of the FUSE spectra such as the reddening E(B-V), distance, and state (high, low, intermediate) of the system at the time it was observed. For some of these spectra we have carried out model fits to the continuum with synthetic stellar and/or disk spectra using the codes TLUSTY and SYNSPEC. We provide the parameters obtained from these model fits; this includes the white dwarf temperature, gravity, projected rotational velocity and elemental abundances of C, Si, S and N, together with the disk mass accretion rate, the resulting inclination and model-derived distance (when unknown). For each object one or more figures are provided (as gif files) with line identification and model fit(s) when available. The FUSE spectra as well as the synthetic spectra are directly available for download as ascii tables. References are provided for each object as well as for the model fits. In this article we present 36 objects, and additional ones will be added to the online catalog in the future. In addition to cataclysmic variables, we also include a few related objects, such as a wind accreting white dwarf, a pre-cataclysmic variable and some symbiotics.
    The Astrophysical Journal Supplement Series 10/2012; 203:29. · 16.24 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: The BINSYN program suite is a collection of programs for analysis of binary star systems with or without an optically thick accretion disk. BINSYN produces synthetic spectra of individual binary star components plus a synthetic spectrum of the system. If the system includes an accretion disk, BINSYN also produces a separate synthetic spectrum of the disk face and rim. A system routine convolves the synthetic spectra with filter profiles of several photometric standards to produce absolute synthetic photometry output. The package generates synthetic light curves and determines an optimized solution for system parameters.
    Astrophysics Source Code Library. 07/2012;
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: The importance to stellar evolution of understanding the metal abundances in hot white dwarfs is well known. Previous work has found the hot DA white dwarfs REJ 1032+532, REJ 1614-085 and GD 659 to have highly abundant, stratified photospheric nitrogen, due to the narrow absorption-line profiles of the far-ultraviolet (FUV) N V doublet and the lack of extreme-ultraviolet (EUV) continuum absorption. A preliminary analysis of the extremely narrow, deep line profiles of the photospheric metal absorption features of PG 0948+534 suggested a similar photospheric metal configuration. However, other studies have found that REJ 1032+532, REJ 1614-085 and GD 659 can be well described by homogeneous models, with nitrogen abundances more in keeping with those of white dwarfs with higher effective temperatures. Here, a re-analysis of the nitrogen absorption features seen in REJ 1032+532, REJ 1614-085 and GD 659 is presented, with the aim of better understanding the structure of these stars, to test which models better represent the observed data and apply the results to the line profiles seen in PG 0948+534. A degeneracy is seen in the modelling of the nitrogen absorption-line profiles of REJ 1032+532, REJ 1614-085 and GD 659, with low-abundance, homogeneously distributed nitrogen models most likely being a better representation of the observed data. In PG 0948+534, no such degeneracy is seen, and the enigmatically deep line profiles could not be modelled satisfactorily.
    Monthly Notices of the Royal Astronomical Society 04/2012; 421(4):3222-3228. · 5.52 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: I. Hubeny Today, the discussion will be open to the general audience. In Sessions C, D, and E, we have talked about models and modelling techniques so I expect the discussion will focus on these topics.
    Proceedings of the International Astronomical Union 04/2012; 7(S282):341-348.
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: I. Hubeny Welcome to the last panel meeting. We invite general comments either from the audience or from the panelists. V. Trimble Well, Mercedes started us with a vocabulary item and I think I would like to end with a vocabulary item. When they were first discovered, we called them `extra solar system planets' which was descriptive and fine, but it's just rather cumbersome. At some point they became `extra solar planets.' Now I have never seen a planet inside the Sun. And therefore `extrasolar' is not a good descriptor. `Exoplanets' is OK, but now that there are so many of them that perhaps they are simply `the planets.' When you want to specialize to ours, you could say `solar system planets.' Think how much ink it would save.
    Proceedings of the International Astronomical Union 04/2012; 7(S282):551-553.
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: M. Richards: Several talks today have expressed fuzzy boundaries to describe the objects called ``stars.'' Is the following classification correct? Are stars restricted to objects that have masses greater than 0.089 solar masses and begin making energy with hydrogen burning? Do we include the stellar remnants: the white dwarfs and neturon stars? Do we include the brown dwarfs because they burn lithium or deuterium. We know that planets are not in this group since they have no energy production.
    Proceedings of the International Astronomical Union 04/2012; 7(S282):145-152.
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: I. Hubeny Does anyone from the panel have a theme question to start with today? V. Trimble It's another one-liner: From an active galaxy meeting many years ago when people talked about spiral structure. I was reminded by Dr. Rucinski's talk of Lodewijk Woltjer's remark: ``The larger our ignorance, the stronger the magnetic field.''
    Proceedings of the International Astronomical Union 04/2012; 7(S282):501-506.
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: Blue hook stars are a class of subluminous extreme horizontal branch stars that were discovered in UV images of the massive globular clusters omega Cen and NGC 2808. These stars occupy a region of the HR diagram that is unexplained by canonical stellar evolution theory. Using new theoretical evolutionary and atmospheric models, we have shown that the blue hook stars are very likely the progeny of stars that undergo extensive internal mixing during a late helium-core flash on the white dwarf cooling curve. This "flash mixing" produces hotter-than-normal EHB stars with atmospheres significantly enhanced in helium and carbon. The larger bolometric correction, combined with the decrease in hydrogen opacity, makes these stars appear subluminous in the optical and UV. Flash mixing is more likely to occur in stars born with a high helium abundance, due to their lower mass at the main sequence turnoff. For this reason, the phenomenon is more common in those massive globular clusters that show evidence for secondary populations enhanced in helium. However, a high helium abundance does not, by itself, explain the presence of blue hook stars in massive globular clusters. Here, we present new observational evidence for flash mixing, using recent HST observations. These include UV color-magnitude diagrams of six massive globular clusters and far-UV spectroscopy of hot subdwarfs in one of these clusters (NGC 2808).
    01/2012;
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: [Abridged] We present new HST FUV spectroscopy of 24 hot evolved stars in NGC2808, a massive globular cluster with a large population of "blue-hook" (BHk) stars. The BHk stars are found in UV color-magnitude diagrams of the most massive globular clusters, where they fall at luminosities immediately below the hot end of the horizontal branch (HB), in a region of the HR diagram unexplained by canonical stellar evolution theory. Using new evolutionary and atmospheric models, we have shown that these subluminous HB stars are very likely the progeny of stars that undergo extensive internal mixing during a late He-core flash on the white dwarf cooling curve. This flash mixing leads to hotter temperatures and an enormous enhancement of the surface He and C; these hotter temperatures, together with the decrease in H opacity shortward of the Lyman limit, make the BHk stars brighter in the EUV while appearing subluminous in the UV and optical. Our FUV spectroscopy demonstrates that, relative to normal HB stars at the same color, the BHk stars of NGC2808 are hotter and greatly enhanced in He and C, thus providing unambiguous evidence of flash mixing. Although the C abundance in the BHk stars is orders of magnitude larger than that in the normal HB stars, the C abundance in both the BHk and normal HB stars appears to be affected by gravitational settling. The variations seen in Si and the Fe-peak elements also indicate that atmospheric diffusion is at play in our sample, with all of our hot subdwarfs at 25,000 to 50,000 K exhibiting large enhancements of the Fe-peak elements. The hottest subdwarfs in our BHk sample may be pulsators, given that they fall in the temperature range of newly-discovered pulsating subdwarfs in omega Cen. In addition to the normal hot HB and BHk stars, we obtain spectra of 5 blue HB stars, a post-HB star, and 3 unclassified stars with unusually blue UV colors.
    The Astrophysical Journal 01/2012; 748(2). · 6.73 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: The BINSYN program suite, a collection of programs for analysis of binary star systems with or without an optically thick accretion disk, is available for download from a wiki. This article describes the package, including download instructions. BINSYN produces synthetic spectra of individual binary star components plus a synthetic spectrum of the system. If the system includes an accretion disk, BINSYN also produces a separate synthetic spectrum of the disk face and rim. A system routine convolves the synthetic spectra with filter profiles of several photometric standards to produce absolute synthetic photometry output. The package generates synthetic light curves and determines an optimized solution for system parameters. This article includes illustrative literature references that have used the suite, including mass transfer rates in several cataclysmic binary systems.
    Publications of the Astronomical Society of the Pacific 01/2012; 124(918):885-894. · 3.69 Impact Factor
  • L. Ibgui, I. Hubeny, T. Lanz, C. Stehlé
    [show abstract] [hide abstract]
    ABSTRACT: We have developed a generic three-dimensional radiative transfer code, SPEC3D, aimed at post-processing 3D radiation magnetohydrodynamics simulations. SPEC3D solves the monochromatic 3D radiative transfer equation. The numerical approach and the major features of the code are presented. The wide range of applications includes the modeling of a number of astrophysical objects and structures, such as accretion shocks around young stellar objects, stellar and exoplanets atmospheres, cosmological structures, but also the modeling of laboratory astrophysics experiments such as magnetohydrodynamics jets and radiative shocks.
    12/2011;
  • Source
    J. Budaj, I. Hubeny, A. Burrows
    [show abstract] [hide abstract]
    ABSTRACT: The internal heat loss, or cooling, of a planet determines its structure and evolution. We study the effects of irradiation, metallicity of the atmosphere, heat redistribution, stratospheres, and the depth where the heat redistribution takes place on the atmospheric structure, the core entropy, and subsequently on the cooling of the interior of the planet. We address in a consistent fashion the coupling between the day and the night sides of a planet by means of model atmosphere calculations with heat redistribution. We assume that strong convection leads to the same entropy on the day and night sides and that gravity is the same on both hemispheres. We argue that the core cooling rates from the two hemispheres of a strongly irradiated planet may not be the same and that the difference depends on several important parameters. If the day-night heat redistribution is very efficient or if it takes place at the large optical depth, then the day-side and the night-side cooling may be comparable. However, if the day-night heat transport is not efficient or if it takes place at a shallow optical depth then there can be a large difference between the day- and the night-side cooling and the night side will cool more efficiently. If stellar irradiation becomes stronger, e.g. owing to stellar evolution or migration, cooling from both the day and the night sides is reduced. Enhanced metallicity of the atmosphere would act as an added "blanket" and reduces both the day- and the night-side cooling. However, a stratosphere on the planetary day side can enhance day-side cooling since its opacity acts as a "sunshade" that screens the stellar irradiation. These effects may also influence the well-known gravity darkening and bolometric albedo effects in interacting binaries, especially for strongly irradiated cold components.
    Astronomy and Astrophysics 11/2011; · 5.08 Impact Factor
  • Source
    K. Cunha, I. Hubeny, T. Lanz
    [show abstract] [hide abstract]
    ABSTRACT: We present non-LTE oxygen abundances for a sample of B stars in the Orion association. The abundance calculations included non-LTE line formation and used fully blanketed non-LTE model atmospheres. The stellar parameters were the same as adopted in the previous study by Cunha & Lambert (1994). We find that the young Orion stars in this sample of 10 stars are described by a single oxygen abundance with an average value of A(O)=8.78 and a small dispersion of +/- 0.05 dex, which is of the order of the uncertainties in the analysis. This average oxygen abundance compares well with the average oxygen abundance obtained previously in Cunha & Lambert (1994): A(O) = 8.72 +/- 0.13 although this earlier study, based upon non-blanketed model atmospheres in LTE, displayed larger scatter. Small scatter of chemical abundances in Orion B stars had also been found in our previous studies for neon and argon; all based on the same effective temperature scale. The derived oxygen abundance distribution for the Orion association compares well with other results for the oxygen abundance in the solar neighborhood.
    10/2011;
  • Ivan Hubeny, Thierry Lanz
    [show abstract] [hide abstract]
    ABSTRACT: TLUSTY is a user-oriented package written in FORTRAN77 for modeling stellar atmospheres and accretion disks and wide range of spectroscopic diagnostics. In the program's maximum configuration, the user may start from scratch and calculate a model atmosphere of a chosen degree of complexity, and end with a synthetic spectrum in a wavelength region of interest for an arbitrary stellar rotation and an arbitrary instrumental profile. The user may also model the vertical structure of annuli of an accretion disk.
    Astrophysics Source Code Library. 09/2011;

Publication Stats

2k Citations
883.19 Total Impact Points

Institutions

  • 1999–2013
    • The University of Arizona
      • Department of Astronomy
      Tucson, Arizona, United States
  • 1997–2009
    • Universities Space Research Association
      Houston, Texas, United States
  • 2003–2008
    • National Optical Astronomy Observatory
      Tucson, Arizona, United States
  • 2007
    • New Mexico State University
      Las Cruces, New Mexico, United States
  • 1995–2005
    • Columbia University
      • Columbia Astrophysics Laboratory
      New York City, New York, United States
  • 2002–2004
    • University of Maryland, College Park
      • Department of Astronomy
      Maryland, United States
    • University of Sydney
      Sydney, New South Wales, Australia
    • University of Texas at Austin
      Austin, Texas, United States
    • Loyola University Maryland
      Baltimore, Maryland, United States
  • 2001
    • University of Hawaiʻi at Hilo
      Hilo, Hawaii, United States