Publications of the Astronomical Society of the Pacific

Martell, Sarah L.; Smith, Graeme H.; Briley, Michael M.

doi: 10.1086/590457pmid: N/A

Spectral indices are useful tools for quantifying the strengths of features in moderate-resolution spectra and relating them to intrinsic stellar parameters. This paper focuses on the 4300 Å CH G-band, a classic example of a feature interpreted through use of spectral indices. G-band index definitions, as applied to globular clusters of different metallicity, abound in the literature, and transformations between the various systems, or comparisons between different authors’ work, are difficult and not always useful. We present a method for formulating an optimized G-band index, using a large grid of synthetic spectra. To make our new index a reliable measure of carbon abundance, we minimize its dependence on [N/Fe] and simultaneously maximize its sensitivity to [C/Fe]. We present a definition for the new index S2(CH), along with estimates of the errors inherent in using it for [C/Fe] determination, and conclude that it is valid for use with spectra of bright globular cluster red giants over a large range in , [C/Fe], and [N/Fe].

Shahbaz, T.; Watson, C. A.; Zurita, C.; Villaver, E.; Hernandez-Peralta, H.

doi: 10.1086/590505pmid: N/A

We present a detailed optical study of the ultracompact X-ray binary 4U 0614+091. We have used 63 hr of time-resolved optical photometry taken with three different telescopes (IAC80, NOT, and SPM) to search for optical modulations. The power spectra of each data set reveals sinusoidal modulations with different periods, which are not always present. The strongest modulation has a period of 51.3 minutes, a semiamplitude of 4.6 mmag, and is present in the IAC80 data. The SPM and NOT data show periods of 42 minutes and 64 minutes, respectively, but with much weaker amplitudes, 2.6 mmag and 1.3 mmag, respectively. These modulations arise from either X-ray irradiation of the inner face of the secondary star and/or a superhump modulation from the accretion disk, or quasi-periodic modulations in the accretion disk. It is unclear whether these periods/quasi-periodic modulations are related to the orbital period; however, the strongest period of 51.3 minutes is close to earlier tentative orbital periods. Further observations taken over a long baseline are encouraged.

Rauer, Heike; Fruth, Thomas; Erikson, Anders

doi: 10.1086/590519pmid: N/A

The detection of transiting extrasolar planets requires high-photometric quality and long-duration photometric stellar time series. In this paper, we investigate the advantages provided by the Antarctic observing platform Dome C for planet transit detections during its long winter period, which allows for relatively long uninterrupted time series. Our calculations include limiting effects due to the Sun and Moon, cloud coverage, and the effect of reduced photometric quality for high extinction of target fields. We compare the potential for long time series from Dome C with a single site in Chile, a three-site low-latitude network as well as combinations of Dome C with Chile and the network, respectively. Dome C is one of the prime astronomical sites on Earth for obtaining uninterrupted long-duration observations in terms of prospects for a high observational duty cycle. The duty cycle of a project can, however, be significantly improved by integrating Dome C into a network of sites.

Blake, Cullen H.; Bloom, Joshua S.; Latham, David W.; Szentgyorgyi, Andrew H.; Skrutskie, Michael F.; Falco, Emilio E.; Starr, Dan S.

doi: 10.1086/590506pmid: N/A

Stars of late-M and L spectral types, collectively known as ultracool dwarfs (UCDs), may be excellent targets for searches for extrasolar planets. Owing to their small radii, the signal from an Earth-size planet transiting a UCD is, in principle, readily detectable. We present results from a study designed to evaluate the feasibility of using precise near-infrared (NIR) photometry to detect terrestrial extrasolar planets orbiting UCDs. We used the Peters Automated Infrared Imaging Telescope (PAIRITEL) to observe a sample of 13 UCDs over a period of 10 months. We consider several important systematic effects in NIR differential photometry and develop techniques for generating photometry with a precision of 0.01 mag and long-term stability. We simulate the planet detection efficiency of an extended campaign to monitor a large sample of UCDs with PAIRITEL. We find that both a targeted campaign with a single telescope lasting several years and a campaign making use of a network of telescopes distributed in longitude could provide significant sensitivity to terrestrial planets orbiting UCDs, potentially in the habitable zone.

Peter, D.; Feldt, M.; Dorner, B.; Henning, T.; Hippler, S.; Aceituno, J.

doi: 10.1086/590479pmid: N/A

The concept of pyramid wavefront sensors (PWFSs) has been around about a decade by now. However there is still a great lack of characterizing measurements that allow the best operation of such a system under real life conditions at an astronomical telescope. In this article we, therefore, investigate the behavior and robustness of the pyramid infrared wavefront sensor PYRAMIR mounted at the 3.5 m telescope at the Calar Alto Observatory under the influence of different error sources both intrinsic to the sensor and arising in the preceding optical system. The intrinsic errors include diffraction effects on the pyramid edges and detector readout noise. The external imperfections consist of a Gaussian profile in the intensity distribution in the pupil plane during calibration, the effect of an optically resolved reference source, and noncommon-path aberrations. We investigated the effect of three differently sized reference sources on the calibration of the PWFS. For the noncommon-path aberrations the quality of the response of the system is quantified in terms of modal cross talk and aliasing. We investigate the special behavior of the system regarding tip-tilt control. From our measurements we derive the method to optimize the calibration procedure and the setup of a PWFS adaptive optics (AO) system. We also calculate the total wavefront error arising from aliasing, modal cross talk, measurement error, and fitting error in order to optimize the number of calibrated modes for on-sky operations. These measurements result in a prediction of on-sky performance for various conditions.

Ramsey, L. W.; Barnes, J.; Redman, S. L.; Jones, H. R. A.; Wolszczan, A.; Bongiorno, S.; Engel, L.; Jenkins, J.

doi: 10.1086/591233pmid: N/A

We have designed and tested an in-plane echelle spectrograph configured to investigate precision radial velocities from ground-based near-infrared observations. The spectrograph operates across the spectral range of 0.9–1.7 μm at a spectral resolution of R = 50,000, and uses a liquid nitrogen-cooled HAWAII 1 K detector. Repeated measurements of the Earth’s rotation via integrated sunlight with two different instrument arrangements in the near-infrared Y band have produced radial velocities with ∼10 m s-1 rms over a period of several hours. The most recent instrument configuration has achieved an unbinned rms of 7 m s-1 and suggests that infrared radial velocity precisions may be able to approach those achieved at optical wavelengths.

Suzuki, Toyoaki; Kaneda, Hidehiro; Matsuura, Shuji; Shirahata, Mai; Nakagawa, Takao; Doi, Yasuo; Onaka, Takashi; Hibi, Yasunori; Kawada, Hiroshi Shibai Mitsunobu

doi: 10.1086/591291pmid: N/A

AKARI, the Japanese infrared astronomical satellite, was launched on 2006 February 21 (UT) and put into a sun-synchronous polar orbit at an altitude of 700 km. Cosmic radiations, particularly protons in the South Atlantic Anomaly (SAA), were expected to affect the performance of the stressed Ge:Ga array far-infrared detector on board AKARI. One of the influences is the radioactivation of the detector housing; γ-rays from the radioactivated detector housing interact with Ge:Ga elements, producing spikes (so-called glitches) in the electric outputs of the detector. Prior to the launch, we performed a 100 MeV proton-beam irradiation test for an engineering model of the stressed Ge:Ga array, which simulated the SAA passage. In the test, we observed glitches in the detector output that were due to the radioactivation of the detector housing. By investigating the test data, we have computed the glitch rate of the flight array detector expected in the AKARI orbit, including its change with time from the launch to the end of the AKARI mission. After the launch of AKARI, we have compared the performance observed in the orbit to that predicted by the proton-beam test. The glitch rate really changed with time after the launch; we have found that the in-orbit behavior is consistent with the prediction.

Mahmud, Naved; Anderson, Jay

doi: 10.1086/591290pmid: N/A

We explore the possibility of using resolved background galaxies to measure accurate absolute proper motions with the Hubble Space Telescope. Because galaxies are not point sources, we cannot use stellar point-spread functions (PSFs) to measure their positions. Rather, we must develop a template for each galaxy that can be used to measure a consistent position for it in each exposure at each epoch. We find that there are enough measurable galaxies in a 1200-s exposure in F606W and F775W to define an astrometric reference frame to better than 0.02 WFC pixel (1 mas). There are, however, some limitations. For example, observations taken at different orientations may suffer from the fact that the PSF is asymmetric, which can induce apparent shifts in the positions of stars and galaxies when the field is rotated relative to the PSF. This is present at the 0.03-pixel level. Nonetheless, being able to measure absolute proper motions relative to background galaxies will open up some interesting possibilities for targeted observations and pencil-beam surveys. This investigation uses the Ultra Deep Field, but the concept could work for any deep field that has extragalactic sources and dithered observations.

Manzato, P.; Pietrinferni, A.; Gasparo, F.; Taffoni, G.; Cordier, D.

doi: 10.1086/591294pmid: N/A

In the first part of this work we describe a new relational database (DB) created for storing metadata of stellar evolution models for a large range of masses and initial chemical compositions, which allows searching for data by scientific quantities and useful parameters. These data users can access the DB and might select a good catalog of evolutionary tracks and/or isochrones for making scientific studies and comparison with observational data. We also present a new Web portal where users can download scientific data of interest. This work has been conduced within the Italian Theoretical Virtual Observatory (ITVO) project, which aims to register these theoretical data under the Virtual Observatory standard and provide a set of standard tools able to visualize and analyze observational and also theoretical data. In the second part of the work we describe the link between the Grid infrastructure and the Virtual Observatory services as delineated by G. Taffoni and colleagues in 2006 and by F. Pasian and colleagues in 2008.

Costa, A.; Manzato, P.; Becciani, U.; Comparato, M.; Costa, V.; Gasparo, F.; Gheller, C.; Grillo, A.; Molinaro, M.; Pasian, F.; Taffoni, G.

doi: 10.1086/591285pmid: N/A

In order to offer an intuitive but effective access to a growing number of cosmological simulations, we have developed the Italian Theoretical Virtual Observatory project (ITVO), as described by Pasian and colleagues in 2006. In this work we describe two Web portals as two ways to access and share complex data coming from numerical astrophysical simulations. We present a set of Web services aimed at offering services such as Simple Numeric Access (ProtocolSNAPSimple Numeric Access Protocol), as described by Gheller and colleagues in 2006, and Randomizers dealing with different data formats. The Web services technology allows us to run a particular task (a SNAP job, for instance) close to its data, avoiding an expensive data transfer.