Publications of the Astronomical Society of the Pacific

Deng, Xin-Fa; He, Ji-Zhou; Hu, Ping; Ma, Xin-sheng

doi: 10.1086/597820pmid: N/A

From the volume-limited main galaxy sample of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6), we construct three galaxy samples with different g-r colors and perform comparative studies of clustering properties among them. It is found that the redder galaxies preferentially inhabit the dense groups and clusters.

Branch, David; Dang, Leeann Chau; Baron, E.

doi: 10.1086/597788pmid: N/A

A comparative study of optical spectra of Type Ia supernovae (SNe Ia) is extended, in light of new data. The discussion is framed in terms of the four groups defined in previous papers of this series: core normal (CN), broad line (BL), cool (CL), and shallow silicon (SS). Emerging features of the SN Ia spectroscopic diversity include evidence (1) that extreme CL SN 1991bg–likes are not a physically distinct subgroup and (2) for the existence of a substantial number of SN 1999aa–like SSs that are very similar to each other and distinguishable from CN even as late as 3 weeks after maximum light. SN 1999aa–likes may be relatively numerous yet not a physically distinct subgroup. The efficacy of quantitative spectroscopic subclassification of SNe Ia based on the equivalent widths of absorption features near 5750 Å and 6100 Å near maximum light is discussed. The absolute-magnitude dispersion of a small sample of CNs is no larger than the characteristic absolute-magnitude uncertainty.

Abt, Helmut A.

doi: 10.1086/597789pmid: N/A

Assuming that binaries are formed in three-body interactions in clusters, we wonder whether the process continues after the stars reach the main sequence. We considered the 233 binaries with known orbital elements that are main-sequence members in 69 open clusters, and looked for changes (presumably decreases) in separations or periods and eccentricities. We found none that are statistically significant, indicating that most binaries are fully formed by the time that their primaries reach the main sequence.

Fu, J. N.; Zha, Q.; Zhang, Y. P.; Chen, L.; Poon, H.; Marak, K.; Boonyarak, C.; Khokhuntod, P.; Su, J.; Li, Y.; Zhang, C.; Jiang, S. Y.

doi: 10.1086/597829pmid: N/A

We present 83 new times of maximum light of the SX Phoenicis (SX Phe) star DY Pegasi (DY Peg), based mainly on our new time-series photometric observations from the years 2004–2008. Together with the times of maximum light in the literature, a comprehensive study of the O - C diagram with the data spanning over seven decades leads to a new general ephemeris formula and the determination of a new value of the updated period 0.072926187( ± 3)d. The available times of maximum light can be well modeled with either a triple linear fit, or a fit concerning a continuously increasing period change combined with the light-time effect of an orbital motion. On the contrary, the decreasing period hypothesis suggested by some previous investigators appears to be rejected. The frequency analyses of the data collected in 2004 and 2006 provide the radial pulsation frequency 13.713 c d-1 and its four harmonics. However, although extra powers were present around the reported secondary frequency 17.8 c d-1 in the Fourier transformations of the new data sets, its signal-to-noise ratios were too low to detect this frequency.

Enya, K.; Kataza, H.; Bierden, P.

doi: 10.1086/598171pmid: N/A

We present our first results on the development and evaluation of a cryogenic deformable mirror (DM) based on Micro Electro Mechanical Systems (MEMS) technology. A MEMS silicon-based DM chip with 32 channels, in which each channel is 300 μm × 300 μm in size, was mounted on a silicon substrate in order to minimize distortion and prevent it from being permanently damaged by thermal stresses introduced by cooling. The silicon substrate was oxidized to obtain electric insulation and had a metal fan-out pattern on the surface. For cryogenic tests, we constructed a measurement system consisting of a Fizeau interferometer, a cryostat cooled by liquid N2, zooming optics, electric drivers. The surface of the mirror at 95 K deformed in response to the application of a voltage, and no significant difference was found between the deformation at 95 K and that at room temperature. The power dissipation by the cryogenic DM was also measured, and we suggest that this is small enough for it to be used in a space cryogenic telescope. The properties of the DM remained unchanged after five cycles of vacuum pumping, cooling, warming, and venting. We conclude that fabricating cryogenic DMs employing MEMS technology is a promising approach. Therefore, we intend to develop a more sophisticated device for actual use, and to look for potential applications including the Space Infrared Telescope for Cosmology & Astrophysics (SPICA), and other missions.

Kurita, M.; Sato, S.; Noda, N.

doi: 10.1086/598223pmid: N/A

We have developed a transportable, lightweight telescope mount. It is capable of carrying a primary mirror of up to 2.5 m in diameter, but is only 7 m high and weighs 5 tons, approximately one-fifth the weight of a conventional telescope. We measured the pointing and the tracking accuracies to be better than 3″ and 0″.5 for 10 minutes, for pointing and tracking, respectively. We have demonstrated that the telescope is readily transportable while retaining sufficient accuracy for astronomical observations.

Robishaw, Timothy; Heiles, Carl

doi: 10.1086/597985pmid: N/A

We use observational data to show that 21 cm line profiles measured with the Green Bank Telescope (GBT) are subject to significant inaccuracies. These include ∼10% errors in the calibrated gain and significant contribution from distant sidelobes. In addition, there are ∼60% variations between the GBT and Leiden/Argentine/Bonn 21 cm line profile intensities, which probably occur because of the high main-beam efficiency of the GBT. Stokes V profiles from the GBT contain inaccuracies that are related to the distant sidelobes. We illustrate these problems, define physically-motivated components for the sidelobes, and provide numerical results showing the inaccuracies. We provide a correction scheme for Stokes I 21 cm line profiles that is fairly successful, and provide some rule-of-thumb comments concerning the accuracy of Stokes V profiles.

Steinbring, Eric; Cuillandre, Jean-Charles; Magnier, Eugene

doi: 10.1086/597766pmid: N/A

Nighttime sky-transparency statistics on Mauna Kea are reported based on data from the Canada-France-Hawaii Telescope SkyProbe monitor. We focus on the period beginning with the start of MegaCam wide-field optical imager operations in 2003 and continuing for almost three years. Skies were clear enough to observe on 76% of those nights; attenuations were less than 0.2 mag up to 60% of the time. An empirical model of cloud attenuation and duration is presented allowing us to further characterize the photometric conditions. This is a good fit to the SkyProbe data and indicates that Mauna Kea skies are truly photometric (without clouds) an average of 56% of the time, with moderate seasonal variation. Continuous monitoring of transparency during the night is necessary to overcome fluctuations in attenuation due to thin clouds.

Stothers, Richard B.

doi: 10.1086/598224pmid: N/A

Observed increases of stellar extinction after the two largest recent volcanic eruptions (El Chichón 1982 and Pinatubo 1991) are compiled here from published sources and compared with space-based measurements of stratospheric aerosol optical depth. Hemispheric and global annual mean optical depths following the two eruptions show close agreement between the two methods, if allowance is made for the fact that the stellar extinction data refer only to midlatitudes.