Ivan Hubeny

BINSYN: A publicly available program for simulating spectra and light curves of binary systems with or without accretion disks

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.

Theory and modeling of stellar atmospheres

I will briefly outline basic concepts of the stellar atmospheres theory. After summarizing basic structural equations describing a stellar atmospheres, an emphasis is given to describing efficient numerical methods developed to deal with the stellar atmosphere problem, namely the method of complete linearization ant its recent variants, and the whole class of methods known by name Accelerated Lambda Iteration. In the next part of the lectures I will briefly summarize existing computer codes, with an emphasis on our code TLUSTY, and list some of the most useful grids of model atmospheres that are publicly available. Next, I will show how the model atmospheres and synthetic spectra are used in quantitative stellar spectroscopy in order to determine basic stellar parameters and chemical abundances. Finally, I will briefly describe an application of model atmosphere theory and models to related objects, such as accretion disks around various accretors, and atmospheres of substellar‐mass objects—extrasolar gia...

From Complete Linearization to ALI and Beyond

Starting with the ground‐breaking work of Dimitri Mihalas and Larry Auer in the late 1960’s and early 1970’s, the progress in our ability to model and understand stellar atmospheres has been enormous. Here I briefly describe some efficient algorithms that were developed and applied to numerical simulations. An emphasis is given to efficient variants of the original Complete Linearization scheme, and to the methods that use the Accelerated Lambda Iteration and related methods.

Non-LTE Abundances in OB stars: Preliminary Results for 5 Stars in the Outer Galactic Disk

The aim of this study is to analyse and determine elemental abundances for a large sample of distant B stars in the outer Galactic disk in order to constrain the chemical distribution of the Galactic disk and models of chemical evolution of the Galaxy. Here, we present preliminary results on a few stars along with the adopted methodology based on securing simultaneous O and Si ionization equilibria with consistent NLTE model atmospheres. The chemical distribution of B stars in the outer Galactic disk is presently poorly probed, based on only a few abundance results for B distant stars (e.g., Daflon et al. 2004). In order to enlarge the number of studied stars and to better represent the chemical distribution of the outer Galactic disk, we obtained high-resolution echelle spectra for a sample of 136 OB stars located towards the Galactic anti-center using the MIKE spectrograph on the 6.5m Magellan Clay telescope. A subsample of 50 sharp-lined B stars has been selected for the abundance analysis. High resolution, high signal-to-noise spectra of 3 well studied main-sequence B stars (HD 61068, HD 63922 and HD 74575) were added to the sample in order to test our adopted methodology. We use an iterative method to obtain simultaneously the stellar parameters (effective temperature (Teff), surface gravity (logg), microturbulence, and abundances of Si and O) based on non-LTE synthesis of H, He, Si, and O profiles. The synthetic spectra are computed using SYNSPEC (Hubeny & Lanz 2011), which interpolates in a grid of non-LTE model atmospheres computed with TLUSTY (Hubeny & Lanz 1995) and detailed atomic models of O (69, 219 and 41 levels for O I, II and III, respectively) and Si (70, 122 and 53 levels for Si II, III and IV, respectively). The adopted method, based on Hunter et al. (2007), consists of the following steps: (a) Initial values for the stellar parameters are set from the stellar spectral type. (b) Ionization balance of Si II/III/IV and/or O I/II/III provides Teff and abundances of Si and O. (c) logg is obtained from fits of the pressure broadened wings of the Balmer lines Hα, Hβ and Hγ. (d) Microturbulence is defined by requiring that the Si III line abundances are inde- pendent of the line strength (equivalent width).

Day-night side cooling of a strongly irradiated giant planet

The internal heat loss or cooling of a planet determines its structure and evolution. We address in a consistent fashion the coupling between the day and the night sides by means of model atmosphere calculations with heat redistribution. We assume that a strong convection leads to the same entropy on the day and night side and that the gravity is the same on both hemispheres. We argue that the core cooling rate 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 effective, or if it takes place at a large optical depth, then the day-side and the night-side cooling may be comparable. However, if the day-night heat transport is not effective, or if it takes place at a shallow optical depth, then there can be a big difference between the day-side and the night-side cooling and the night side may cool more effectively. If the stellar irradiation gets stronger e.g. due to the stellar evolution or migration, this will reduce both the day and the night side cooling. Enhanced metallicity in the atmosphere acts as a “blanket” and reduces both the day- and the night-side cooling. However, the stratosphere on the day side of the planet can enhance the day-side cooling since its opacity acts as a “shield” which screens the stellar irradiation. These results might affect the well known gravity darkening and bolometric albedo effects in interacting binaries, especially for strongly irradiated cold objects.

Basic tools for modeling stellar and planetary atmospheres

Most popular computer codes for calculating model stellar and planetary atmospheres are briefly reviewed. A particular emphasis is devoted to our universal computer program Tlusty (model stellar atmospheres and accretion disks), CoolTlusty (a variant of Tlusty for computing model atmospheres of substellar-mass objects such as giant planets and brown dwarfs), and Synspec (an associated spectrum synthesis code). We show the highlights of actual applications of these codes which include extensive grids of fully line-blanketed non-LTE model atmospheres of O and B stars, and grids of model atmospheres of extrasolar giant planets and L and T dwarfs.

Quantitative Analysis of the Spectra of Early B Stars with Ultrasharp Lines

We present selected results from an investigation that is currently underway to determine the abundances of light and Fe group elements in early B stars and assess the extent to which contemporary NLTE and LTE models represent their atmospheres. Spectral data of B stars that display ultrasharp lines, obtained with HST, FUSE, and the KPNO Coude Feed Telescope, are compared with computations from TLUSTY/SYNSPEC and SYNTHE. The B stars include the abundance standards ι Her (B3V), HR 1886 (B1V), and HR 1887 (B0.5V).