Publications of the Astronomical Society of the Pacific

Kim, Chulhee; Yushchenko, A. V.; Kim, S.-L.; Jeon, Y.-B.; Kim, Chun-Hwey

doi: 10.1086/665943pmid: N/A

High-resolution spectroscopic observation was carried out to find the chemical composition of BE Lyn. The abundances of 25 chemical elements from carbon to neodymium were found. The deficiency of iron appeared to be equal to Δ log N(Fe) = -0.26 ± 0.08 with respect to the solar metallicity, and the abundances of other elements were mainly undersolar. Only nitrogen, sodium, aluminum, and sulfur showed overabundances near 0.2–0.3 dex. The abundance pattern showed no clear signs of accretion or mass transfer events. It is not possible to exclude the classification of BE Lyn as a SX Phe–type star with slightly undersolar abundances of chemical elements. In addition, new differential time-series observations of BE Lyn were secured using V filters, and seven new times of light maximum were identified. We collected 162 times of light maximum from the literature, unpublished data, and an open database, and we proceeded to investigate the pulsational properties of BE Lyn. All five harmonic frequencies were identified using the Fourier decomposition method.

Williamon, Richard M.; Sowell, James R.

doi: 10.1086/665677pmid: N/A

YY Cet is a 10.5 mag semidetached variable with a 19 hr orbital period. The Wilson-Devinney program is used to simultaneously solve two new sets of UBV light curves together with preexisting photometry and single-line radial velocity measurements . The system has the lower-mass component completely filling its Roche lobe. The resulting masses are M1 = 1.78 ± 0.19 M⊙ and M2 = 0.92 ± 0.10 M⊙, and the radii are R1 = 2.08 ± 0.08 R⊙ and R2 = 1.62 ± 0.06 R⊙. Its computed distance is 534 ± 28 pc. Light- and velocity-curve parameters, orbital elements, and absolute dimensions are presented. A study of published TOM observations indicates that the period changed around 1999.

Turnbull, Margaret C.; Glassman, Tiffany; Roberge, Aki; Cash, Webster; Noecker, Charley; Lo, Amy; Mason, Brian; Oakley, Phil; Bally, John

doi: 10.1086/666325pmid: N/A

As part of NASA’s mission to explore habitable planets orbiting nearby stars, this article explores the detection and characterization capabilities of a 4 m space telescope plus 50 m starshade located at the Earth-Sun L2 point, known as the New Worlds Observer (NWO). Our calculations include the true spectral types and distribution of stars on the sky, an iterative target selection protocol designed to maximize efficiency based on prior detections, and realistic mission constraints. We conduct simulated observing runs for a wide range in exozodiacal background levels (ε = 1–100 times the local zodi brightness) and overall prevalence of Earth-like terrestrial planets (η⊕ = 0.1–1). We find that even without any return visits, the NWO baseline architecture (IWA = 65 mas, limiting FPB = 4 × 10-11) can achieve a 95% probability of detecting and spectrally characterizing at least one habitable Earth-like planet and an expectation value of ∼3 planets found, within the mission lifetime and ΔV budgets, even in the worst-case scenario (η⊕ = 0.1 and ε = 100 zodis for every target). This achievement requires about 1 yr of integration time spread over the 5 yr mission, leaving the remainder of the telescope time for UV-NIR general astrophysics. Cost and technical feasibility considerations point to a “sweet spot” in starshade design near a 50 m starshade effective diameter, with 12 or 16 petals, at a distance of 70,000–100,000 km from the telescope.

Meddi, F.; Ambrosino, F.; Nesci, R.; Rossi, C.; Sclavi, S.; Bruni, I.; Ruggieri, A.; Sestito, S.

doi: 10.1086/665925pmid: N/A

The realization of low-cost instruments with high technical performance is a goal that deserves some efforts in an epoch of fast technological developments; indeed, such instruments can be easily reproduced and therefore allow new research programs to be opened in several observatories. We realized a fast optical photometer based on the SiPM technology, using commercially available modules. Using low-cost components, we have developed a custom electronic chain to extract the signal produced by a commercial MPPC module produced by Hamamatsu Photonics, in order to obtain submillisecond sampling of the light curve of astronomical sources (typically, pulsars). In the early 2011 February, we observed the Crab pulsar with the Cassini telescope with our prototype photometer, deriving its period and power spectrum and the shape of its light curve, in very good agreement with the results obtained in the past with other instruments.

Ingraham, P.; Doyon, R.; Lafrenière, D.; Beaulieu, M.

doi: 10.1086/665954pmid: N/A

The scanning capability of a tunable filter represents an attractive option for performing high-contrast observations through spectral differential imaging (SDI), a speckle-attenuation technique widely used by current ground-based, high-contrast imaging instruments. The performance of such a tunable filter is illustrated through the Tunable Filter Imager (TFI), which used to be part of the science instrument complement of the James Webb Space Telescope (JWST). TFI features a low-order Fabry-Perot etalon enabling imaging spectroscopy at an average resolution of 100 in the 1.5 to 5 μm range. TFI also includes a high-contrast imaging mode featuring a Lyot coronagraph aided by SDI. TFI’s on-sky performance is determined by performing an end-to-end Fresnel propagation of the telescope and instrument using the measured wavefront error maps of TFI’s optical elements and the theoretical wavefront error maps of the optical telescope assembly. Using this simulation, we determine that SDI offers an improvement in contrast ranging from a factor of ∼7 to ∼100, depending on the instrument’s configuration. We present the companion detection capability using both the coronagraphic and noncoronagraphic modes of TFI and demonstrate the characterization capability using the HR 8799 and Fomalhaut systems. The performance of roll subtraction is also determined and compared with that of SDI. We also present the SDI capability of the Near-Infrared Imager and Slitless Spectrograph, the science instrument module to replace TFI in the JWST Fine Guidance Sensor.

Andersen, David R.; Jackson, Kate J.; Blain, Célia; Bradley, Colin; Correia, Carlos; Ito, Meguru; Lardière, Olivier; Véran, Jean-Pierre

doi: 10.1086/665924pmid: N/A

RAVEN will be a Multi-Object Adaptive Optics (MOAO) technology and science demonstrator on the Subaru telescope. The baseline design calls for three natural guide star (NGS) wavefront sensors (WFS) and two science pickoff arms that will patrol a ∼2′ diameter field of regard (FOR). Sky coverage is an important consideration, because RAVEN is both a technical and science demonstrator. Early-stage simulation of RAVEN’s performance is critical in establishing that the key science requirement can be met. That is, 30% of the energy of an unresolved point-spread function (PSF) be ensquared within a 140 mas slit using existing WFS camera and deformable mirror (DM) technology. The system was simulated with two independent modeling tools, MAOS and OOMAO, which were in excellent agreement. It was established that RAVEN will be an order 10 × 10 adaptive optics (AO) system by examining the tradeoffs between performance, sky coverage, and WFS field of view. The 30% ensquared-energy (EE) requirement will be met with three NGSs and will exceed 40% if the Subaru Laser Guide Star (LGS) is used on-axis (assuming median image quality). This is also true for NGSs as faint as mR = 14.5.

Nakaya, Hidehiko

doi: 10.1086/666056pmid: N/A

A general-purpose CCD readout electronics has been developed for use with the instruments installed on the Subaru telescope. The readout performance of the electronics itself was precisely evaluated. The readout noise measures ∼12 μV rms around the readout speed in the 1.0 V full-scale signal range, which is equivalent to 2.4 e- of the readout noise in the 200,000 e- full-well capacity with the output sensitivity of a CCD. The readout noise falls to ∼1 μV rms at slower readout speeds, which is equivalent to as well. The linearity is throughout almost the entire signal range within the 0.1% linearity error. The gain drift relative to temperature change of the correlated-double-sampling (CDS) circuit and the remnant signal are also measured. The low power consumption readout circuit is designed for mosaic CCD cameras equipped with multiple outputs. The two optical instruments of the Subaru telescope have been using this CCD readout electronics, which achieves the CCD limited readout performance.

Giordano, Christophe; Vernin, Jean; Chadid, Merieme; Aristidi, Eric; Agabi, Abdelkrim; Trinquet, Hervé

doi: 10.1086/665667pmid: N/A

We present observations made in 2006 with the single-star SCIDAR (SSS) at Dome C in Antarctica, allowing us to determine optical turbulence and velocity V(h) profiles from ice levels up to about 25 km above sea level (a.s.l.). SSS is a 16 inch telescope placed on an equatorial mount that continuously tracks the Canopus star. About 90,000 individual profiles are analyzed from March to September, where surface-layer contribution to seeing can be separated from the rest of the atmosphere. Medians of high angular resolution parameters relevant to astronomy are statistically studied, such as seeing (1.0′′), isoplanatic angle (6.9′′), and wavefront coherence time (3.4 ms). For a telescope placed above the turbulent surface layer, superb conditions are encountered (medians of seeing better than 0.3′′, isoplanatic angle better than 6.9′′, and coherence time larger than 10 ms). Astronomical conditions are twice as good at the beginning of the night, with ε0 ≈ 0.5′′, θ0 ≈ 11.5′′, and τ0 ≈ 15 ms. SSS wind-velocity profiles are consistent with National Oceanic and Atmospheric Administration analysis up to 17 km (a.s.l.), within a error bar. Coherence étendue (which is a combination of ε0, θ0, and τ0), well adapted to adaptive optics performances, is likely 4 times better at Dome C than at the already-known observatories such as Mauna Kea or ORM.

Fernández Fernández, Javier; Chou, Dean-Yi; Pan, Yen-Chen; Wang, Li-Hang

doi: 10.1086/665926pmid: N/A

We developed a method to improve the conventional differential photometry by using many auxiliary stars to reduce noise in the reference light curve, which is used to calibrate the light curve of the target star. The data used in this study are taken with the Taiwan Automated Telescope network. The light curves of two δ Scuti, HD 163032 and V830 Her, are shown here as examples. The results are compared with four other methods: conventional differential photometry; ensemble photometry; the method of Tamuz, Mazeh, & Zucker; and trend filtering algorithm. The light curve computed with our method is smoother than the other four methods, while preserving the pulsational signals. The mode frequencies determined from the light curve from our method also has a higher S/N and lower error in comparison with other methods.

Han, Xuhui

doi: 10.1086/665734pmid: N/A