Publications of the Astronomical Society of the Pacific

Napoli, Vanessa J.; McSwain, M. Virginia; Boyer, Amber N. Marsh; Roettenbacher, Rachael M.

doi: 10.1086/662692pmid: N/A

The recently discovered γ-ray binary 1FGL J1018.6–5856 has a proposed optical/NIR counterpart 2MASS 10185560–5856459. We present Strömgren photometry of this star to investigate its photometric variability and measure the reddening and distance to the system. We find that the γ-ray binary has E(B - V) = 1.34 ± 0.04 and . While E(B - V) is consistent with X-ray observations of the neutral hydrogen column density, the distance is somewhat closer than some previous authors have suggested.

Morales, Miguel F.

doi: 10.1086/663092pmid: N/A

Proposed 21 cm cosmology observatories for studying the epoch of reionization (z ≈ 6–15) and dark energy (z ≈ 0–6) envision compact arrays with tens of thousands of antenna elements. Fully correlating this many elements is computationally expensive using traditional XF or FX correlators and has led some groups to reconsider direct imaging/FFT correlators. In this article we develop a variation of the direct imaging correlator that we call the MOFF correlator. The MOFF correlator shares the computational advantages of a direct imaging correlator, while avoiding a number of its shortcomings. In particular, the MOFF correlator makes no constraints on the antenna arrangement or type; provides a fully calibrated output image, including wide-field polarimetry and noncoplanar baseline effects; and can be orders of magnitude more efficient than XF or FX correlators for compact radio cosmology arrays.

Mann, Andrew W.; Gaidos, Eric; Aldering, Greg

doi: 10.1086/662640pmid: N/A

We demonstrate ground-based submillimagnitude (< 10-3) photometry of widely separated bright stars using snapshot CCD imaging. We routinely achieved this photometric precision by (1) choosing nearby comparison stars of a similar magnitude and spectral type, (2) defocusing the telescope to allow high signal (>107 e-) to be acquired in a single integration, (3) pointing the telescope so that all stellar images fall on the same detector pixels, and (4) using a region of the CCD detector that is free of nonlinear or aberrant pixels. We describe semiautomated observations with the Supernova Integrated Field Spectrograph (SNIFS) on the University of Hawaii 2.2 m telescope on Mauna Kea, with which we achieved photometric precision as good as 5.2 × 10-4(0.56 mmag) with a 5 minute cadence over a 2 hr interval. In one experiment, we monitored eight stars, each separated by several degrees, and achieved submillimagnitude precision with a cadence (per star) of ∼17 minutes. Our snapshot technique is suitable for automated searches for planetary transits among multiple bright stars.

Ruelas-Mayorga, A.; Sánchez, L. J.; Olivares, J.; Allen, C.; Poveda, A.; Costero, R.; Nigoche-Netro, A.

doi: 10.1086/662952pmid: N/A

We present a theoretical analysis of the measuring algorithm we use when applying the diffracto-astrometry technique to Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) saturated stellar images. Theoretical point-spread functions (PSFs) were generated using the Tiny Tim software for the four CCDs in the WFPC2 and for some of the available filters. These images were then measured with our diffracto-astrometry measuring algorithm using only their diffraction pattern, and positions for the simulated PSFs on each generated CCD frame were obtained. The measuring algorithm recovers the original positions reasonably well (± 0.1 to ± 0.4 pixels). However, slight deviations from the original values are observed. These also vary with position over the entire surface of the CCD. We adjust the difference between the real and the measured positions with a quadratic function of the coordinates. The transformation coefficients also present a slight correlation with the filter effective wavelength. Application of these transformation coefficients allows us to determine the position of a stellar image with a precision of a few hundredths of a pixel.

Blake, Cullen H.; Shaw, Margaret M.

doi: 10.1086/662980pmid: N/A

Modeling molecular absorption by Earth’s atmosphere is important for a wide range of astronomical observations, including broadband NIR photometry and high-resolution NIR spectroscopy. Using a line-by-line radiative transfer approach, we calculate theoretical transmission spectra in the deep red optical (700 < λ < 1050 nm) for Apache Point Observatory. In this region the spectrum is dominated by H2O, which is known to be highly variable in concentration on short timescales. We fit our telluric models to high-resolution observations of A stars and estimate the relative optical depth of H2O absorption under a wide range of observing conditions. We compare these optical depth estimates with simultaneous measurements of precipitable water vapor (PWV) based on data from a Global Positioning System (GPS) receiver located at Apache Point. We find that measured PWV correlates strongly with the scaling of H2O absorption lines in our spectra, indicating that GPS-based PWV measurements combined with atmospheric models may be a powerful tool for the real-time estimation of total molecular absorption in broad NIR bands. Using photometric measurements from the Sloan Digital Sky Survey (SDSS) DR8 database we demonstrate that PWV biases the calibrated r - z colors and z-band fluxes of mid-M stars, but not mid-G stars. While this effect is small compared with other sources of noise in the SDSS z-band observations, future surveys like the Large Synoptic Survey Telescope aim for higher precision and will need to take time-variable molecular transmission into account for the global calibration of NIR measurements of objects having strong spectral features at these wavelengths. Empirical calibrations based on PWV may be immediately applicable to ongoing efforts to make millimagnitude differential measurements of M stars to detect transiting exoplanets.

Wu, Zhen-Yu; Ma, Jun; Zhou, Xu

doi: 10.1086/663093pmid: N/A

Using a sample of 117,053 quasars identified in the PPMXL Catalogue, the systematic errors of the proper motions in the PPMXL Catalogue are estimated independently as -2.0 and -2.1 mas yr-1 in μα cos δ and μδ, respectively. For objects with SDSS r magnitude between 16.0 and 21.0 mag and SDSS g - r color between -0.4 and 1.2, there is no obvious magnitude and color dependence in the systematic errors of the proper motions in the PPMXL Catalogue. The random errors of the proper motions in the PPMXL Catalogue change from ∼4.0 to ∼8.0 mas yr-1, along with the increase of the magnitude of the objects. No color dependence in the random errors of the proper motions in the PPMXL Catalogue is found. There is obvious right-ascension α dependence of the systematic errors in both components of the proper motions in the PPMXL Catalogue. For quasars with declination δ > 0, the systematic errors of μδ in the PPMXL Catalogue increase linearly with δ with a slope of 0.07 mas yr-1 deg-1. For comparison, using a subsample of quasars identified in both the PPMXL and SDSS DR7 catalogs, the systematic errors of the USNO-SDSS proper motions in the SDSS DR7 Catalogue are derived as 0.9 and 0.5 mas yr-1 in μα cos δ and μδ, respectively. There is no obvious magnitude, color, and α dependence in the systematic errors of the USNO-SDSS proper motions. For quasars with declination δ > 0, the systematic errors of μδ in the SDSS DR7 Catalogue increase linearly with δ with a slope of 0.03. The random errors of the USNO-SDSS proper motions change from ∼2.5 to ∼6.0 mas yr-1, along with the change of the magnitude and color of the objects. Combining the 2MASS or SDSS observation data can significantly reduce the systematic errors of the proper motions in the initial photographic catalog.

Yamauchi, Chisato

doi: 10.1086/663234pmid: N/A

We develop a software kit called “2MASS Catalog Server Kit” to easily construct a high-performance database server for the 2MASS Point Source Catalog (includes 470,992,970 objects) and several all-sky catalogs. Users can perform fast radial search and rectangular search using provided stored functions in SQL similar to SDSS SkyServer. Our software kit utilizes open-source RDBMS, and therefore any astronomers and developers can install our kit on their personal computers for research, observation, etc. Out kit is tuned for optimal coordinate search performance. We implement an effective radial search using an orthogonal coordinate system, which does not need any techniques that depend on HTM or HEALpix. Applying the xyz coordinate system to the database index, we can easily implement a system of fast radial search for relatively small (less than several million rows) catalogs. To enable high-speed search of huge catalogs on RDBMS, we apply three additional techniques: table partitioning, composite expression index, and optimization in stored functions. As a result, we obtain satisfactory performance of radial search for the 2MASS catalog. Our system can also perform fast rectangular search. It is implemented using techniques similar to those applied for radial search. Our way of implementation enables a compact system and will give important hints for a low-cost development of other huge catalog databases.

Vernin, Jean; Muñoz-Tuñón, Casiana; Sarazin, Marc; Vazquez Ramió, Héctor; Varela, Antonia M.; Trinquet, Hervé; Miguel Delgado, José; Jiménez Fuensalida, Jesús; Reyes, Marcos; Benhida, Abdelmajid; Benkhaldoun, Zouhair; García Lambas, Diego; Hach, Youssef; Lazrek, M.; Lombardi, Gianluca; Navarrete, Julio; Recabarren, Pablo; Renzi, Victor; Sabil, Mohammed; Vrech, Rubén

doi: 10.1086/662995pmid: N/A

The site for the future European Extremely Large Telescope (E-ELT) is already known to be Armazones, near Paranal (Chile). The selection was based on a variety of considerations, with an important one being the quality of the atmosphere for the astronomy planned for the ELT. We present an overview of the characterization of the atmospheric parameters of candidate sites, making use of standard procedures and instruments as carried out within the Framework Programme VI (FP6) of the European Union. We have achieved full characterization of the selected sites for the parameters considered. Further details on adaptive optics results and climatology will be the subject of two forthcoming articles. A summary of the results of the FP6 site-testing campaigns at the different sites is provided.