Publications of the Astronomical Society of the Pacific

Davidge, T. J.; Carrasco, Eleazar R.; Winge, Claudia; Pessev, Peter; Neichel, Benoit; Vidal, Fabrice; Rigaut, Francois

doi: 10.1086/673379pmid: N/A

The photometric properties of main sequence (MS) and pre-main sequence (PMS) stars in the young cluster Haffner 16 are examined using images recorded with the Gemini South Adaptive Optics Imager (GSAOI) and corrected for atmospheric blurring by the Gemini Multi-Conjugate Adapative Optics System (GeMS). A rich population of PMS stars is identified, and comparisons with isochrones suggest an age ≲10 Myr, assuming a distance modulus of 13.5 (D = 5 kpc). This age is consistent with that estimated from the lower cutoff of the MS on the K-band luminosity function and is ∼2 Myr younger than the age found from bright MS stars at visible wavelengths. When compared with the solar neighborhood, Haffner 16 is roughly a factor of 2 deficient in objects with subsolar masses. PMS objects in the cluster are also more uniformly distributed on the sky than bright MS stars. It is suggested that Haffner 16 is dynamically evolved and that it is shedding protostars with subsolar masses. Young low mass clusters like Haffner 16 are one possible source of PMS stars in the field. The cluster will probably evolve on time scales of ∼100–1000 Myr into a diffuse moving group with a mass function that is very different from that which prevailed early in its life.

Levato, Hugo; Grosso, Mónica

doi: 10.1086/673401pmid: N/A

We have measured the projected rotational velocities of 1023 southern B stars listed in the Bright Star Catalog (BSC) and calibrated them against the 1975 Slettebak et al. system. We joined the sample with the 1091 mostly northern stars of the BSC whose projected rotational velocities were determined in the same way. There were 387 stars in common and with the sample of 1727 B type stars we found that the published values of V sin i for B dwarfs in the BSC average 30% higher than those derived using Slettebak et al. standards. Only 1.8% of the stars have projected rotational velocities larger than 300 km s-1 and 0.2% have V sin i larger than 350 km s-1. The mean projected rotational velocity is only 25% of break-up, implying that impending break-up is not a significant factor in reducing rotational velocities. We have found with the largest sample used up to now that the distribution in V for all B-type stars on the main sequence is bimodal.

Samec, Ronald G.; Kring, James D.; Faulkner, Danny R.; Van Hamme, W.

doi: 10.1086/673474pmid: N/A

DK And is a Sonneberg variable, first classified as an RR Lyrae type-C. It was reclassified in 2006 as a totally eclipsing W Ursae Majoris variable with a period of 0.49 d. We present complete BVRI are light curves, a period study, and a simultaneous BVRI light-curve solution. The period study, covering some 73 years, reveals a 4-sigma-level quadratic ephemeris. Our light curves shows a time of constant light in the secondary eclipse of 28 minutes making this a totally eclipsing, A-type W UMa system. The depths of eclipses are only about 0.5 mag in V due to the fairly extreme fill-out. The light curve solution reveals a component temperature difference of ∼300 K, fairly high for such variables, and an inclination of 82.5°. Although the variable is near F2V type, it shows definite dark spot activity (31° radius spot). High fill-out binarity evidently induces the convective envelopes responsible for this activity.

Bendek, Eduardo A.; Guyon, Olivier; Ammons, S. Mark; Belikov, Ruslan

doi: 10.1086/673373pmid: N/A

Astrometry is a promising exoplanet detection and characterization technique that can detect earth-size exoplanets if submicroarcsecond precision is achieved. However, instrumentation available today can only reach in the order of 102 microarcseconds, mainly limited by long-term dynamic distortions on wide-field observations. To overcome this problem, we propose the implementation of a diffractive pupil, which has an array of microscopic dots imprinted on the primary mirror coating. The dots create diffractive spikes on the focal plane that are used to calibrate image plane distortions that degrade the astrometric measurement precision. This astrometry technique can be utilized simultaneously with coronagraphy for exhaustive characterization of exoplanets (mass, spectra, orbit). We designed and built an astrometry laboratory to validate the diffractive pupil ability to calibrate distortions and stabilize wide-field astrometric measurements over time. We achieved a precision of 0.0123 px, which represents 42% of the 0.0288 px stability measured for this setup before the calibration. On sky units, this result is equivalent to 3.42 × 10-3λ/D that corresponds to 150 μas for a 2.4 m telescope at 500 nm wavelength. Also, at large field angles the distortion error was reduced by a factor of 5 when the calibration was used, proving its effectiveness for large field of view. We present an astrometry error budget here to explain the source of the residual error observed when the diffractive pupil calibration is used.

Colavita, M. M.; Wizinowich, P. L.; Akeson, R. L.; Ragland, S.; Woillez, J. M.; Millan-Gabet, R.; Serabyn, E.; Abajian, M.; Acton, D. S.; Appleby, E.; Beletic, J. W.; Beichman, C. A.; Bell, J.; Berkey, B. C.; Berlin, J.; Boden, A. F.; Booth, A. J.;

Wang, Jian; Liu, Jia-jing; Tang, Peng-yi; Luo, Ming-cheng; Wu, Wen-qing; Zhang, Guang-yu; Jin, Ge; Deng, Xiao-chao

doi: 10.1086/673492pmid: N/A

The control system is an essential and important part of an astronomical telescope. For large telescopes, an efficient control system is vital for successful observations. In this paper, an exhaustive study of generic models of control systems for large telescopes and a wide range of their common requirements are presented. This paper also discusses a basic hierarchical structure, workflow model, and telescope control model based on object-oriented analysis, as well as the main data flow model of a general purpose telescope. After analysis of these models, a layered and orthogonal architecture, which has a wide range of adaptability, is proposed. The design of a concrete architecture based on the message bus, which is used in the LAMOST (Large Sky Area Multi-Object Fiber Spectroscopy Telescope) project and FAST (The Five-Hundred-Meter Aperture Spherical Radio Telescope) project, is discussed. The design of the control systems proposed in this paper can serve as a useful reference in the construction of large telescopes.

Marshall, J. L.; DePoy, D. L.

doi: 10.1086/673440pmid: N/A

We describe the flattening of scientific CCD imaging data using a dome flat-field system. The system uses light emitting diodes (LEDs) to illuminate a carefully constructed dome flat-field screen. LEDs have several advantages over more traditional illumination sources: they are available in a wide range of output wavelengths, are inexpensive, have a very long source lifetime, and are straightforward to control digitally. The circular dome screen is made of a material with Lambertian scattering properties that efficiently reflects light of a wide range of wavelengths and incident angles. In this paper, we compare flat fields obtained using this system with two types of traditionally-constructed flat fields: twilight sky flats and nighttime sky flats. Using photometric standard stars as illumination sources, we test the quality of each flat field by applying it to a set of standard star observations. We find that the dome flat-field system produces flat fields that are superior to twilight or nighttime sky flats, particularly for photometric calibration. We note that a ratio of the twilight sky flat to the nighttime sky flat is flat to within the expected uncertainty; but since both of these flat fields are inferior to the dome flat, this common test is not an appropriate metric for testing a flat field. Rather, the only feasible and correct method for determining the appropriateness of a flat field is to use standard stars to measure the reproducibility of known magnitudes across the detector.

doi: 10.1086/674078pmid: N/A