Elemental Abundance Analyses with DAO Spectrograms. XXXVIII. The SB2 Stars HR 104 (A2 V) and θ Aql (B9.5 III)Adelman, Saul J.; Yüce, Kutluay; Gulliver, Austin F.
doi: 10.1086/682075pmid: N/A
The study of the elemental abundances of double-lined spectroscopic binaries should provide information on the chemical differentiation of a once uniform prestellar nebula. To determine the effective temperatures and surface gravities of the primary and secondary stellar components of HR 104 and θ Aql, we used parameters derived from their orbital analyses and the requirement of equal abundances derived from Fe I and Fe II lines. For constraints we had optical region spectrophotometry for θ Aql and the large equivalent width ratios for the many spectral metal lines which were produced in both stellar atmospheres for HR 104. Since the primary stars were much brighter than the secondary stars, the abundances are considerably better determined for the primary stars. For HR 104 A we found Teff = 9875 K, log g = 4.26, and ξ = 1.7 km s-1; for HR 104 B Teff = 7200 K, log g = 4.26, and ξ = 0.6 km s-1; for θ Aql A Teff = 10400 K, log = 3.63, and ξ = 0.3 km s-1; and for θ Aql B Teff = 10250 K, log = 4.20, and ξ = 1.9 km s-1. The abundances of HR 104 A, HR 104 B, and θ Aql A are best described as the solar pattern. Those of θ Aql B suggest a weak nonmagnetic CP star pattern. While there is no trace of the Hg II 3984 line for θ Aql, the most extreme observed abundance anomalies for the secondary are those of Ca, V, Mn, and Ni. Further study of this hot marginal Am star could provide insights into the origin of the nonsolar chemical abundances.
First Scientific VLBI Observations Using New Zealand 30 Meter Radio Telescope WARK30MPetrov, L.; Natusch, T.; Weston, S.; McCallum, J.; Ellingsen, S.; Gulyaev, S.
doi: 10.1086/681965pmid: N/A
We report the results of a successful 24 hr 6.7 GHz VLBI experiment using the 30-m radio telescope wark30m near Warkworth, New Zealand, recently converted from a radio telecommunications antenna, and two radio telescopes located in Australia: Hobart 26-m and Ceduna 30-m. The geocentric position of wark30m is determined with a 100 mm uncertainty for the vertical component and 10 mm for the horizontal components. We report correlated flux densities at 6.7 GHz of 175 radio sources associated with Fermi γ-ray sources. A parsec-scale emission from the radio source 1031-837 is detected, and its association with the γ-ray object 2FGL J1032.9-8401 is established with a high likelihood ratio. We conclude that the new Pacific area radio telescope wark30m is ready to operate for scientific projects.
Identification of Potential Sites for Astronomical Observations in Northern South AmericaPinzón, G.; González, D.; Hernández, J.
doi: 10.1086/682025pmid: N/A
In this study, we describe an innovative method to determine potential sites for optical and infrared astronomical observations in the Andes region of northern South America. The method computes the clear-sky fraction (CSF) from Geostationary Observational Environmental Satellite (GOES) data for the years 2008–2012 through a comparison with temperatures obtained from long-term records of weather stations and atmospheric temperature profiles from radiosonde. Criteria for sky clearance were established for two infrared GOES channels in order to determine potential sites in the Andes region of northern South America. The method was validated using the reported observed hours at the Observatorio Nacional de Llano del Hato in Venezuela. Separate CSF percentages were computed for dry and rainy seasons for both photometric and spectroscopic night qualities. Twelve sites with 5-year averages of CSF for spectroscopic nights larger than 30% during the dry seasons were found to be suitable for astronomical observations. The best site with (220 ± 42) spectroscopic clear nights per year is located in the Andes of Venezuela (70°28′48″W, 9°5′60″N) at an altitude of 3480 m. Lower quality regions were found in Sierra Nevada de Santamarta and Serranía del Perijá with (126 ± 34) and (111 ± 27) clear nights per year, respectively. Sites over the Andes are identified in Norte de Santander with (107 ± 23) and in the north-east part of Boyacá with a mean of (94 ± 13) clear nights per year. Two sites at low latitude located in Ecuador with more than 100 clear nights per year and with similar seasonal CSF percentages were also identified. Five-year evolution suggests a possible correlation between the lowest percentages observed during the rainy seasons of 2010 and 2011 with positive values of the Southern Oscillation Index.
A Search for Optical Laser Emission Using Keck HIRESWe dedicate this work to the memory of Charles H. Townes, inventor of the laser and pioneer of opt ...Tellis, Nathaniel K.; Marcy, Geoffrey W.
doi: 10.1086/681966pmid: N/A
We present a search for laser emissions coming from point sources in the vicinity of 2796 stars, including 1368 Kepler objects-of-interest (KOIs) that host one or more exoplanets. We search for extremely narrow emission lines in the wavelength region between 3640 and 7890 Å using the Keck 10 m telescope and spectroscopy with high-resolution (λ/Δλ = 60,000). Laser-emission lines coming from nonnatural sources are distinguished from natural astrophysical sources by being monochromatic and coming from an unresolved point in space. We search for laser emissions located 2–7″ from the 2796 target stars. The detectability of laser emissions is limited by Poisson statistics of the photons and scattered light, yielding a detection threshold flux of ∼1 photons m-2 min-1 for typical Kepler stars and ∼1 00 photons m-2 min-1 for solar-type stars within 100 lt-yr. Diffraction-limited lasers having a 10 m aperture can be detected from 100 lt-yr away if their power exceeds 90 W, and from 1000 lt-yr away (Kepler planets), if their power exceeds 1 kW (from lasers located 60–200 AU, and 2000–7000 AU from the nearby and Kepler stars, respectively). We did not find any such laser emission coming from any of the 2796 target stars. We discuss the implications for the search for extraterrestrial intelligence (SETI).
A Practical Deconvolution Computation Algorithm to Extract 1D Spectra from 2D Images of Optical Fiber SpectroscopyGuangwei, Li; Haotong, Zhang; Zhongrui, Bai
doi: 10.1086/682052pmid: N/A
Bolton & Schlegel presented a promising deconvolution method to extract one-dimensional (1D) spectra from a two-dimensional (2D) optical fiber spectral CCD (charge-coupled device) image. The method could eliminate the PSF (point-spread function) difference between fibers, extract spectra to the photo noise level, as well as improve the resolution. But the method is limited by its huge computation requirement and thus can not be implemented in actual data reduction. In this article, we develop a practical computation method to solve the computation problem. The new computation method can deconvolve a 2D fiber spectral image of any size with actual PSFs, which may vary with positions. Our method does not require large amounts of memory and can extract a 4 k × 4 k noise-free CCD image with 250 fibers in 2 hr. To make our method more practical, we further consider the influence of noise, which is thought to be an intrinsic ill-posed problem in deconvolution algorithms. We modify our method with a Tikhonov regularization item to depress the method induced noise. We do a series of simulations to test how our method performs under more real situations with Poisson noise and extreme cross talk. Compared with the results of traditional extraction methods, i.e., the Aperture Extraction Method and the Profile Fitting Method, our method has the least residual and influence by cross talk. For the noise-added image, the computation speed does not depend very much on fiber distance, the signal-to-noise ratio converges in 2–4 iterations, and the computation times are about 3.5 hr for the extreme fiber distance and about 2 hr for nonextreme cases. A better balance between the computation time and result precision could be achieved by setting the precision threshold similar to the noise level. Finally, we apply our method to real LAMOST (Large sky Area Multi-Object fiber Spectroscopic Telescope; a.k.a. Guo Shou Jing Telescope) data. We find that the 1D spectrum extracted by our method has both higher signal-to-noise ratio and resolution than the traditional methods, but there are still some suspicious weak features, possibly caused by the method around the strong emission lines. As we have demonstrated, our deconvolution method has solved the computation problem and progressed in dealing with the noise influence. Multifiber spectra extracted by our method will have higher resolution and signal-to-noise ratio, and thus will provide more accurate information (such as higher radial velocity and metallicity measurement accuracy in stellar physics) to astronomers than traditional methods.
The rvfit Code: A Detailed Adaptive Simulated Annealing Code for Fitting Binaries and Exoplanets Radial VelocitiesIglesias-Marzoa, Ramón; López-Morales, Mercedes; Jesús Arévalo Morales, María
doi: 10.1086/682056pmid: N/A
The fitting of radial velocity curves is a frequent procedure in binary star and exoplanet research. In the majority of cases, the fitting routines need to be fed with a set of initial parameter values and priors from which to begin the computations and their results can be affected by local minima. We present a new code, the rvfit code, for fitting radial velocities of stellar binaries and exoplanets using an adaptive simulated annealing (ASA) global minimization method, which quickly converges to a global solution minimum without the need to provide preliminary parameter values. We show the performance of the code using both synthetic and real datasets: double-lined binaries, single-lined binaries, and exoplanet systems. In all examples, the Keplerian orbital parameters fitted by the rvfit code and their computed uncertainties are compared with literature solutions. Finally, we provide the source code, with a working example and a detailed description of how to use it.