Spectroscopic Observations of Twenty-one Faint Cataclysmic Variables Candidates

We provide the first minimum light spectroscopic observations for 21 previously known or suspected faint cataclysmic variable candidates. The sources were selected from the Downes et al. (2001) living edition catalog and the identified candidates have minimum light magnitudes of V~18-22. We confirm 15 of the candidates to be cataclysmic variables.Comment: 10 pages, 4 figures, accepted by A&

ST/STIS Spectroscopy of the White Dwarfs in the Short-Period Dwarf Novae LL And and EF Peg

We present new HST/STIS observations of the short-period dwarf novae LL And and EF Peg during deep quiescence. We fit stellar models to the UV spectra and use optical and IR observations to determine the physical parameters of the whitedwarfs in the systems, the distances to the binaries, and the properties of thesecondary stars. Both white dwarfs are relatively cool, having T_{eff} near 15000K, and consistent with a mass of 0.6 M-sun. The white dwarf in LL And appears to be of solar abundance or slightly lower while that in EF Peg is near 0.1-0.3 solar. LL And is found to be 760 pc away while EF Peg is closer at 380 pc. EF Peg appears to have an ~M5V secondary star, consistent with that expected for its orbital period, while the secondary object in LL And remains a mystery.Comment: Accepted in Ap

The Densities of Planets in Multiple Stellar Systems

We analyze the effect of companion stars on the bulk density of 29 planets orbiting 15 stars in the Kepler field. These stars have at least one stellar companion within 2", and the planets have measured masses and radii, allowing an estimate of their bulk density. The transit dilution by the companion star requires the planet radii to be revised upward, even if the planet orbits the primary star; as a consequence, the planetary bulk density decreases. We find that, if planets orbited a faint companion star, they would be more volatile-rich, and in several cases their densities would become unrealistically low, requiring large, inflated atmospheres or unusually large mass fractions in a H/He envelope. In addition, for planets detected in radial velocity data, the primary star has to be the host. We can exclude 14 planets from orbiting the companion star; the remaining 15 planets in seven planetary systems could orbit either the primary or the secondary star, and for five of these planets the decrease in density would be substantial even if they orbited the primary, since the companion is of almost equal brightness as the primary. Substantial follow-up work is required in order to accurately determine the radii of transiting planets. Of particular interest are small, rocky planets that may be habitable; a lower mean density might imply a more volatile-rich composition. Reliable radii, masses, and thus bulk densities will allow us to identify which small planets are truly Earth-like.Comment: Accepted by AJ; 22 page

Fringe Science: Defringing CCD Images with Neon Lamp Flat Fields

Fringing in CCD images is troublesome from the aspect of photometric quality and image flatness in the final reduced product. Additionally, defringing during calibration requires the inefficient use of time during the night to collect and produce a "supersky" fringe frame. The fringe pattern observed in a CCD image for a given near-IR filter is dominated by small thickness variations across the detector with a second order effect caused by the wavelength extent of the emission lines within the bandpass which produce the interference pattern. We show that essentially any set of emission lines which generally match the wavelength coverage of the night sky emission lines within a bandpass will produce an identical fringe pattern. We present an easy, inexpensive, and efficient method which uses a neon lamp as a flat field source and produces high S/N fringe frames to use for defringing an image during the calibration process.Comment: accepted to PAS

Paraxial ray optics cloaking

Despite much interest and progress in optical spatial cloaking, a three-dimensional (3D), transmitting, continuously multidirectional cloak in the visible regime has not yet been demonstrated. Here we experimentally demonstrate such a cloak using ray optics, albeit with some edge effects. Our device requires no new materials, uses isotropic off-the-shelf optics, scales easily to cloak arbitrarily large objects, and is as broadband as the choice of optical material, all of which have been challenges for current cloaking schemes. In addition, we provide a concise formalism that quantifies and produces perfect optical cloaks in the small-angle (`paraxial') limit

Paraxial full-field cloaking

We complete the `paraxial' (small-angle) ray optics cloaking formalism presented previously [Choi and Howell, Opt. Express 22, 29465 (2014)], by extending it to the full-field of light. Omnidirectionality is then the only relaxed parameter of what may be considered an ideal, broadband, field cloak. We show that an isotropic plate of uniform thickness, with appropriately designed refractive index and dispersion, can match the phase over the whole visible spectrum. Our results support the fundamental limits on cloaking for broadband vs. omnidirectionality, and provide insights into when anisotropy may be required