Publications of the Astronomical Society of the Pacific

Liu, Jinzhong; Zhang, Yu

doi: 10.1086/675721pmid: N/A

The phase of inspiral of double compact objects (DCOs: NS + WD, NS + NS, BH + NS, and BH + BH binaries) in the disk field population of the Galaxy provides a potential source in the frequency range from 10-4 to 0.1 Hz, which can be detected by the European New Gravitational Observatory (NGO: eLISA is derived from the previous LISA proposal) project. In this frequency range, much stronger gravitational wave (GW) radiation can be obtained from DCO sources because they possess more mass than other compact binaries (e.g., close double white dwarfs). In this study, we aim to calculate the gravitational wave signals from the resolvable DCO sources in the Galaxy using a binary population synthesis approach, and determine physical properties of these binaries using Monte Carlo simulations. Combining the sensitivity curve of the eLISA detector and a confusion-limited noise floor of close double white dwarfs, we find that only a handful of DCO sources can be detected by the eLISA detector. The detectable number of DCO sources reaches 160; in the context of low-frequency eLISA observations we find that the number of NS + WD, NS + NS, BH + NS, and BH + BH objects are 132, 16, 3, and 6, respectively.

Sabogal, B. E.; García-Varela, A.; Mennickent, R. E.

doi: 10.1086/675972pmid: N/A

We present the result of a search for southern Galactic Be star candidates within the group of miscellaneous variables of the ASAS-2 catalog of variable stars, using statistical, morphological, photometric, and color criteria. This search lead us to obtain a catalog of 213 new Be star candidates. The I-band light curves of these candidates show outbursts (Type-1 stars) only in 9% of the sample, and stochastic variations (Type-4 stars) in 91% of the sample. We do not find stars showing clear high and low states (Type-2 stars) or showing outbursts and high and low states simultaneously (Type-1/Type-2 stars). Our sample of southern Galactic Be star candidates provide valuable new bright targets for high resolution spectroscopic studies with small/medium size telescopes.

Fruth, T.; Cabrera, J.; Csizmadia, Sz.; Dreyer, C.; Eigmüller, P.; Erikson, A.; Kabath, P.; Pasternacki, T.; Rauer, H.; Titz-Weider, R.; Abe, L.; Agabi, A.; Gonçalves, I.; Guillot, T.; Mékarnia, D.; Rivet, J.-P.; Crouzet, N.;

Biesiadzinski, Tomasz; Lorenzon, Wolfgang; Schubnell, Michael; Tarlé, Gregory; Weaverdyck, Curtis

doi: 10.1086/675735pmid: N/A

A study was performed to investigate the experimental conditions and systematic uncertainties that need to be considered in order to precisely characterize quantum efficiency (QE). Measurements were performed on a HAWAII-2RG1.7 μm detector but the methodology of characterization is applicable to other detectors as well and may be useful in characterization of detectors used in future ground and space based surveys. For this study the detector QE as a function of illumination intensity, total integrated signal, and temperature was measured. A 3% relative systematic uncertainty on the measured QE value was achieved at wavelengths longer than 800 nm but the total uncertainty in the determination of absolute QE is dominated by the uncertainty in the conversion gain, which adds an additional 3.4% scale uncertainty. It was found that the measured detector QE depends on illumination intensity and that temperature dependence of QE can, at least in part, be attributed to reciprocity failure. Well-chosen detector bias voltages can reduce integrated signal nonlinearity.

Mieda, Etsuko; Wright, Shelley A.; Larkin, James E.; Graham, James R.; Adkins, Sean M.; Lyke, James E.; Campbell, Randy D.; Maire, Jérôme; Do, Tuan; Gordon, Jacob

doi: 10.1086/675784pmid: N/A

Zanutta, Alessio; Landoni, Marco; Bianco, Andrea; Tomasella, Lina; Benetti, Stefano; Giro, Enrico

doi: 10.1086/675806pmid: N/A

The spectroscopic studies of near-infrared emission arising from supernovae allow the derivation of crucial quantities that could better characterise physical conditions of the expanding gas, such as the CaII IR HVF spectral feature. For this reason, it is mandatory to have diffractive optical elements (DOEs) with a spectral coverage in the range 8000–10000 Å (for low-z sources) combined with a reasonable signal-to-noise ratio (S/N) and medium-low resolution. In order to cope with all of those requirements, we developed a volume phase holographic grating (VPHG) based on an innovative photosensitive material, developed by Bayer Material Science. We demonstrated the capabilities of this new DOE through observation of SN 2013fj as a case study at the Asiago Copernico Telescope, where an AFOSC spectrograph is available.

Oshiyama, Fumika; Murakami, Naoshi; Guyon, Olivier; Martinache, Frantz; Baba, Naoshi; Matsuo, Taro; Nishikawa, Jun; Tamura, Motohide

doi: 10.1086/675807pmid: N/A

Focal-plane phase-mask coronagraphs, such as eight-octant phase-mask coronagraphs (8OPM), are one of the most promising tools for high contrast observations. However, coronagraphic performance would be degraded when combined with a centrally-obscured telescope. We propose pupil-remapping optics for removing the shade of a secondary mirror to generate a clear, circular pupil for the phase-mask coronagraph. First, we show the design of the pupil-remapping optics, called central-obscuration removal plates (CRPs). Next, we report laboratory experiments on the 8OPM coronagraph using manufactured CRPs. We also evaluate off-axis point-spread functions via both laboratory experiments and numerical simulations. Finally, we evaluate, via numerical simulations, limiting factors for coronagraphic performance, such as phase aberrations introduced by the CRPs, the effect of Fresnel diffraction, and chromatic behavior. The numerical simulations suggest that the phase aberrations could be a dominant limiting factor of the achievable contrast in the current laboratory experiments.

Li, Changwei; Zhang, Sijiong

doi: 10.1086/675973pmid: N/A

Online co-phasing of segmented telescopes by dual-wavelength digital holography is proposed. Two digital holograms (one hologram per wavelength) are employed to get the phase of the segmented telescope for a longer synthetic wavelength by the digital holographic approach. The holograms are recorded by a high-speed CCD camera using the point-diffraction Mach-Zehnder interferometer. By fitting the plane for the synthetic wavelength phase in each segment of the telescope, the coefficients of piston and tip/tilt for each segment can be acquired. To test the feasibility of the proposed method, two simulated telescopes with 37 hexagonal segments are taken as examples to examine co-phasing segmented telescopes by digital holography when atmospheric turbulence and detection noises exist. Numerical simulations show that the dual-wavelength digital holographic approach for co-phasing of segmented telescopes is feasible and highly accurate and robust.

Bernstein, Gary M.; Gruen, Daniel

doi: 10.1086/675812pmid: N/A

When simulating sky images, one often takes a galaxy image F(x) defined by a set of pixelized samples and an interpolation kernel, and then wants to produce a new sampled image representing this galaxy as it would appear with a different point-spread function, a rotation, shearing, or magnification, and/or a different pixel scale. These operations are sometimes only possible, or most efficiently executed, as resamplings of the Fourier transform of the image onto a u-space grid that differs from the one produced by a discrete Fourier transform (DFT) of the samples. In some applications, it is essential that the resampled image be accurate to better than one part in 103, so in this paper, we first use standard Fourier techniques to show that Fourier-domain interpolation with a wrapped sinc function yields the exact value of in terms of the input samples and kernel. This operation scales with image dimension as N4 and can be prohibitively slow, so we next investigate the errors accrued from approximating the sinc function with a compact kernel. We show that these approximations produce a multiplicative error plus a pair of ghost images (in each dimension) in the simulated image. Standard Lanczos or cubic interpolators, when applied in Fourier domain, produce unacceptable artifacts. We find that errors less than one part in 103 can be obtained by (1) fourfold zero-padding of the original image before executing the x → u DFT, followed by (2) resampling to the desired u-grid using a six-point, piecewise-quintic interpolant that we design expressly to minimize the ghosts, then (3) executing the DFT back to x-domain.

Dey, Arjun; Valdes, Francisco

doi: 10.1086/675808pmid: N/A

We analyze several thousand archival images from the NOAO Science Archive obtained over a five year period (2006–2011) using the MOSAIC cameras on the Kitt Peak National Observatory 4 m Mayall and Cerro Tololo Inter-American Observatory 4 m Blanco telescopes in order to investigate the delivered image quality (DIQ). We fit the resulting point spread functions with Moffat functions and find that the profiles can be approximated by Moffat profiles with β ≈ 3.5. We analyze the DIQ distributions and investigate their dependence on various observational, environmental, and temporal variables. We find that the DIQ of the MOSAIC cameras is similar at both sites. The Mayall data show no significant variation of DIQ with wavelength, but the Blanco data show a gradual rise of DIQ toward shorter wavelengths. The DIQ shows little variation with elevation for zenith distance < 50° (airmass ≲1.6). The modal value of the DIQ distribution is larger for longer exposure time images, suggesting that improvements in the guiding, tracking, mirror support, and/or focus control may improve the DIQ. The DIQ also degrades when the mirror temperature deviates from the ambient temperature by more than ± 1°. Better thermal control of the mirror and focus will likely improve the DIQ.