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The Hobby-Eberly Telescope (HET) Dark Energy Experiment (HETDEX) is undertaking a blind wide-field low-resolution spectroscopic survey of 540 square degrees of sky to identify and derive redshifts for a million Lyman-alpha emitting galaxies (LAEs) in the redshift range 1.9 < z < 3.5. The ultimate goal is to measure the expansion rate of the Universe at this epoch, to sharply constrain cosmological parameters and thus the nature of dark energy. A major multi-year wide field upgrade (WFU) of the HET was completed in 2016 that substantially increased the field of view to 22 arcminutes diameter and the pupil to 10 meters, by replacing the optical corrector, tracker, and prime focus instrument package and by developing a new telescope control system. The new, wide-field HET now feeds the Visible Integral-field Replicable Unit Spectrograph (VIRUS), a new low-resolution integral field spectrograph (LRS2), and the Habitable Zone Planet Finder (HPF), a precision near-infrared radial velocity spectrograph. VIRUS consists of 156 identical spectrographs fed by almost 35,000 fibers in 78 integral field units arrayed at the focus of the upgraded HET. VIRUS operates in a bandpass of 3500-5500 Angstroms with resolving power R~800. VIRUS is the first example of large scale replication applied to instrumentation in optical astronomy to achieve spectroscopic surveys of very large areas of sky. This paper presents technical details of the HET WFU and VIRUS, as flowed-down from the HETDEX science requirements, along with experience from commissioning this major telescope upgrade and the innovative instrumentation suite for HETDEX., 65 pages, 25 figures, published in the Astronomical Journal; replaced with final published version

We present far-ultraviolet (905 -- 1182 A), time-series spectroscopy of the eclipsing, novalike cataclysmic variable, UX UMa, acquired with FUSE. The time-averaged spectrum is complex and is dominated by overlapping spectral features. The most prominent features are emission lines of CIII, NIII}, NIV, and OVI. They are broad (FWHM >= 1800 km/s) and double-peaked with a central absorption at zero velocity. During eclipse, the spectrum is simpler: the emission lines remain bright, but the absorption components of the lines and the weaker features between the emission lines disappear entirely, leaving a flat continuum. This behavior is also evident in GHRS (1149 -- 1660 A) spectra that we retrieved from the HST archive. The FUV spectra show flickering on time scales of several minutes. The flickering is seen primarily in the continuum and/or the weaker lines rather than in the prominent emission lines. The orbital light curve has a dip in the FUV flux between orbital phases 0.45 -- 0.65, similar to a pre-eclipse dip detected in HST observations. The EWs of the line absorption features decrease during the dip. We have detected a systematic wavelength shift of spectral features on the orbital period, but with a phase lag of ~ 20 degrees, a phenomenon that has been reported at optical wavelengths. We discuss the implications of our results in the context of models of an accretion disk with a chromosphere between the disk and the extended wind. Finally, we note that the observed FUV flux is too low to be consistent with the temperature and radius of the WD derived by Baptista et al. (1995), suggesting that their remaining binary parameters, including a mass ratio of 1, ought to be viewed with skepticism. Comment: 24 pages, 10 figures; prepared using emulateapj5.sty. To appear in the Astrophysical Journal

Outflows in the form of fast winds from the accretion disk appear in nearly all high accretion rate cataclysmic variables (CVs), both novalikes (NLs) and dwarf novae in outburst (DN). The primary signatures of CV winds are broad, blueshifted absorption features and P Cygni profiles that appear in the ionized metal lines of lower inclination systems and the broad emission lines that appear in eclipsing systems. Much progress has been made in our understanding of the structure and behavior of CV outflows based on data obtained with X-ray, EUV, and UV telescopes and the kinematical models developed to fit the observations. Our current picture of CV outflows is that they are bipolar, rotating winds driven off the accretion disk primarily by radiative line driving from disk, boundary layer, and white dwarf radiation. Other mechanical forces may play a role in the formation of CV winds. The winds are highly turbulent and show complex vertical and azimuthal structure. Future work will focus on determining the physical, thermal and ionization structure of the winds and probing the mechanisms that govern wind formation and behavior., Comment: 11 pages, to appear in The astrophysics of cataclysmic variables and related objects, ASP Conf. Ser., eds. J.M. Hameury and J.P. Lasota

We present far-ultraviolet (905 -- 1182 A), time-series spectroscopy of the eclipsing, novalike cataclysmic variable, UX UMa, acquired with FUSE. The time-averaged spectrum is complex and is dominated by overlapping spectral features. The most prominent features are emission lines of CIII, NIII}, NIV, and OVI. They are broad (FWHM >= 1800 km/s) and double-peaked with a central absorption at zero velocity. During eclipse, the spectrum is simpler: the emission lines remain bright, but the absorption components of the lines and the weaker features between the emission lines disappear entirely, leaving a flat continuum. This behavior is also evident in GHRS (1149 -- 1660 A) spectra that we retrieved from the HST archive. The FUV spectra show flickering on time scales of several minutes. The flickering is seen primarily in the continuum and/or the weaker lines rather than in the prominent emission lines. The orbital light curve has a dip in the FUV flux between orbital phases 0.45 -- 0.65, similar to a pre-eclipse dip detected in HST observations. The EWs of the line absorption features decrease during the dip. We have detected a systematic wavelength shift of spectral features on the orbital period, but with a phase lag of ~ 20 degrees, a phenomenon that has been reported at optical wavelengths. We discuss the implications of our results in the context of models of an accretion disk with a chromosphere between the disk and the extended wind. Finally, we note that the observed FUV flux is too low to be consistent with the temperature and radius of the WD derived by Baptista et al. (1995), suggesting that their remaining binary parameters, including a mass ratio of 1, ought to be viewed with skepticism., 24 pages, 10 figures; prepared using emulateapj5.sty. To appear in the Astrophysical Journal

Far ultraviolet (FUV) observations are excellent probes of the inner accretion disk, disk outflows, and the mass-accumulating white dwarf in cataclysmic variables. Here we study the contrasting behavior of two canonical dwarf novae in outburst by presenting FUSE FUV (904 -- 1187 A) spectroscopy of U Gem and SS Cyg. We observed each system four times during a single outburst. The outburst peak and early decline spectra of SS Cyg are well fit by models of a steady-state accretion disk and a biconical wind. A broad, blueshifted OVI wind-formed absorption line is the only strong spectral feature. In late outburst decline, OVI and CIII lines are seen as broad emission features and the continuum has flattened. In U Gem, the continua of the optical outburst plateau spectra are plausibly fit by accretion disk model spectra. The spectra also show numerous narrow, low-velocity absorption lines that do not originate in the inner accretion disk. We discuss the line spectra in the context of partial absorption of the FUV continuum by low-velocity, vertically-extended material located at large disk radii. The late outburst decline spectrum of U Gem is dominated by the white dwarf. WD model fits confirm the sub-solar C and super-solar N abundances found in earlier studies., Comment: 10 pages, 3 figures. To appear in "The Physics of Cataclysmic Variables and Related Objects", ASP Conf. Ser., eds. B.T. Gaensicke, K. Beuermann, K. Reinsch Replaced 10/03/2001 to correct typos