Bradford B. Behr

The Masses and Evolutionary State of the Stars in the Dwarf Nova SS Cygni

The dwarf nova SS Cygni is a close binary star consisting of a K star transferring mass to a white dwarf by way of an accretion disk. We have obtained new spectroscopic observations of SS Cyg. Fits of synthetic spectra for Roche lobe-filling stars to the absorption-line spectrum of the K star yield the amplitude of the K stars radial velocity curve and the mass ratio, KK = 162.5 ± 1.0 km s-1 and q = MK/MWD = 0.685 ± 0.015. The fits also show that the accretion disk and white dwarf contribute a fraction f = 0.535 ± 0.075 of the total flux at 5500 A. Taking the weighted average of our results with previously published results obtained using similar techniques, we find KK = 163.7 ± 0.7 km s-1 and q = 0.683 ± 0.012. The orbital light curve of SS Cyg shows an ellipsoidal variation diluted by light from the disk and white dwarf. From an analysis of the ellipsoidal variations, we limit the orbital inclination to the range 45° ≤ i ≤ 56°. The derived masses of the K star and white dwarf are MK = 0.55 ± 0.13 M☉ and MWD = 0.81 ± 0.19 M☉, where the uncertainties are dominated by systematic errors in the orbital inclination. The K star in SS Cyg is 10%-50% larger than an unevolved star with the same mass and thus does not follow the mass-radius relation for zero-age main-sequence stars, nor does it follow the ZAMS mass-spectral type relation. Its mass and spectral type are, however, consistent with models in which the core hydrogen has been significantly depleted.

STELLAR ASTROPHYSICS WITH A DISPERSED FOURIER TRANSFORM SPECTROGRAPH. I. INSTRUMENT DESCRIPTION AND ORBITS OF SINGLE-LINED SPECTROSCOPIC BINARIES

We have designed and constructed a second-generation version of the dispersed Fourier transform spectrograph, or dFTS. This instrument combines a spectral interferometer with a dispersive spectrograph to provide high-accuracy, high-resolution optical spectra of stellar targets. The new version, dFTS2, is based upon the design of our prototype, with several modifications to improve the system throughput and performance. We deployed dFTS2 to the Steward Observatory 2.3 m Bok Telescope from 2007 June to 2008 June, and undertook an observing program on spectroscopic binary stars, with the goal of constraining the velocity amplitude K of the binary orbits with 0.1% accuracy, a significant improvement over most of the orbits reported in the literature. We present results for radial velocity reference stars and orbit solutions for single-lined spectroscopic binaries.

Initial Results from the USNO Dispersed Fourier Transform Spectrograph

We have designed and constructed a ‘‘dispersed Fourier transform spectrometer’’ (dFTS), consisting of a conventionalFTSfollowedbyagratingspectrometer.Bycombiningthesetwodevices,wenegateasubstantialfraction of the sensitivity disadvantage of a conventional FTS for high-resolution, broadband, optical spectroscopy, while preserving many of the advantages inherent to interferometric spectrometers. In addition, we have implemented a simple and inexpensive laser metrology system, which enables very precise calibration of the interferometer wavelength scale. The fusion of interferometric and dispersive technologies with a laser metrology system yields an instrument well suited to stellar spectroscopy, velocimetry,and extrasolar planet detection, which is competitive with existing high-resolution, high-accuracy stellar spectrometers. In this paper we describe the design of our prototype dFTS,explain the algorithmwe use to efficiently reconstruct a broadbandspectrum from a sequence of narrowband interferograms, and present initial observations and resulting velocimetry of stellar targets. Subject headingg binaries: spectroscopic — instrumentation: interferometers — instrumentation: spectrographs — planetary systems — techniques: interferometric

A new high-resolution, high-throughput spectrometer: first experience as applied to Raman spectroscopy

The classic trade-off between resolution and throughput in a dispersive spectrometer is overcome using virtual slit technology. An optimized spectrometer designed from the ground up to incorporate a virtual slit is experimentally demonstrated by Raman experiments.

The Origins Billions Star Survey: Galactic Explorer

The Origins Billions Star Survey is a mission concept addressing the astrophysics of extrasolar planets, Galactic structure, the Galactic halo and tidal streams, the Local Group and local supercluster of galaxies, dark matter, star formation, open clusters, the solar system, and the celestial reference frame by determining the position, parallax, and proper motion, as well as photometry, for billions of stars down to 23rd visual magnitude. It is capable of surveying the entire celestial sphere or dwelling on a star field by varying the cadence of observations. The missions ability to measure objects fainter than 17th magnitude allows a large number of extragalactic compact objects to be observed, making the astrometric measurements absolute. The project mission accuracy is comparable to Gaia for a survey mission. Improved accuracy can be achieved by dwelling on a particular star field or by using the Gaia positions at 14th magnitude to improve the positions of objects at the 18th–23rd visual magnitudes.

In-depth performance analysis of the HyperFlux spectrometer

Tornado Spectral Systems introduced the HyperFluxTM spectrometer to the market in early 2012. The Hyper- Flux is the world’s first HTVS (high-throughput virtual slit) enabled spectrometer and is able to achieve much greater system flux compared to slit-based spectrometers. Since the HyperFlux’s debut extensive studies into the manufacturability, stability, and detector electronic performance have been performed and are presented in this paper. A generalized quantitative approach to spectrometer comparison by using a clearly-defined Quality Factor is presented at the end of the paper.

High-performance hyperspectral imaging using virtual slit optics

Tornado Spectral Systems (TSS) has developed High Throughput Virtual Slit (HTVS) technology that improves the performance of spectrometers by factors of several while maintaining system size. In the simplest configuration, the HTVS allows optical designers to remove the lossy slit from a spectrometer, greatly increasing throughput without a loss of resolution. This is especially useful in many standoff applications, where every photon matters. TSS has tested multiple configurations of HTVS spectral sensing and spectral imaging technology, including standoff sensing, point scan imaging, long-slit pushbroom imaging and similar configurations. The HTVS throughput-resolution advantage allows us to increase scanning speed, decrease system size, decrease aperture, decrease source intensity requirements or some combination of all four. HTVS technology expands the realm of viable spectral imaging applications. We discuss the applicability of this technology to spectral imaging and standoff sensing and present experimental results from several prototype and production spectrometers.

Simultaneous High-Resolution and High-Throughput Spectrometer Design Based on Virtual Slit Technology

The classic trade-off between resolution and throughput in a dispersive spectrometer is eliminated using virtual slit technology. An optimized spectrometer incorporating a virtual slit designed from the ground up is experimentally demonstrated.

Fundamental performance improvement to dispersive spectrograph based imaging technologies

Dispersive-based spectrometers may be qualified by their spectral resolving power and their throughput efficiency. A device known as a virtual slit is able to improve the resolving power by factors of several with a minimal loss in throughput, thereby fundamentally improving the quality of the spectrometer. A virtual slit was built and incorporated into a low performing spectrometer (R ~ 300) and was shown to increase the performance without a significant loss in signal. The operation and description of virtual slits is also given. High-performance, lowlight, and high-speed imaging instruments based on a dispersive-type spectrometer see the greatest impact from a virtual slit. The impact of a virtual slit on spectral domain optical coherence tomography (SD-OCT) is shown to improve the imaging quality substantially.

STELLAR ASTROPHYSICS WITH A DISPERSED FOURIER TRANSFORM SPECTROGRAPH. II. ORBITS OF DOUBLE-LINED SPECTROSCOPIC BINARIES

We present orbital parameters for six double-lined spectroscopic binaries (ι Pegasi, ω Draconis, 12 Bootis, V1143 Cygni, β Aurigae, and Mizar A) and two double-lined triple star systems (κ Pegasi and η Virginis). The orbital fits are based upon high-precision radial velocity (RV) observations made with a dispersed Fourier Transform Spectrograph, or dFTS, a new instrument that combines interferometric and dispersive elements. For some of the double-lined binaries with known inclination angles, the quality of our RV data permits us to determine the masses M 1 and M 2 of the stellar components with relative errors as small as 0.2%.