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STATISTICAL PROPERTIES OF GALACTIC δ SCUTI STARS: REVISITED
Chang, S.-W.,Protopapas, P.,Kim, D.-W.,Byun, Y.-I. American Institute of Physics 2013 The Astronomical journal Vol.145 No.5
<P>We present statistical characteristics of 1578 δ Scuti stars including nearby field stars and cluster member stars within the Milky Way. We obtained 46% of these stars (718 stars) from work by Rodríguez and collected the remaining 54% of stars (860 stars) from other literature. We updated the entries with the latest information of sky coordinates, color, rotational velocity, spectral type, period, amplitude, and binarity. The majority of our sample is well characterized in terms of typical period range (0.02-0.25 days), pulsation amplitudes (<0.5 mag), and spectral types (A-F type). Given this list of δ Scuti stars, we examined relations between their physical properties (i.e., periods, amplitudes, spectral types, and rotational velocities) for field stars and cluster members, and confirmed that the correlations of properties are not significantly different from those reported in Rodríguez's work. All the δ Scuti stars are cross-matched with several X-ray and UV catalogs, resulting in 27 X-ray and 41 UV-only counterparts. These counterparts are interesting targets for further study because of their uniqueness in showing δ Scuti-type variability and X-ray/UV emission at the same time. The compiled catalog can be accessed through the Web interface http://stardb.yonsei.ac.kr/DeltaScuti.</P>
Kim, D.-W.,Protopapas, P.,Alcock, C.,Byun, Y.-I.,Kyeong, J.,Lee, B.-C.,Wright, N. J.,Axelrod, T.,Bianco, F. B.,Chen, W.-P.,Coehlo, N. K.,Cook, K. H.,Dave, R.,King, S.-K.,Lee, T.,Lehner, M. J.,Lin, H.- American Institute of Physics 2010 The Astronomical journal Vol.139 No.2
<P>We analyzed data accumulated during 2005 and 2006 by the Taiwan-American Occultation Survey (TAOS) in order to detect short-period variable stars (periods of <img entity='lsim' SRC='http://ej.iop.org/icons/Entities/lsim.gif' ALT='lsim' ALIGN='BASELINE' />1 hr) such as δ Scuti. TAOS is designed for the detection of stellar occultation by small-size Kuiper Belt Objects and is operating four 50 cm telescopes at an effective cadence of 5 Hz. The four telescopes simultaneously monitor the same patch of the sky in order to reduce false positives. To detect short-period variables, we used the fast Fourier transform algorithm (FFT) in as much as the data points in TAOS light curves are evenly spaced. Using FFT, we found 41 short-period variables with amplitudes smaller than a few hundredths of a magnitude and periods of about an hour, which suggest that they are low-amplitude δ Scuti stars. The light curves of TAOS δ Scuti stars are accessible online at the Time Series Center Web site (http://timemachine.iic.harvard.edu).</P>
Detrending time series for astronomical variability surveys
Kim, Dae-Won,Protopapas, Pavlos,Alcock, Charles,Byun, Yong-Ik,Bianco, Federica B. Blackwell Publishing Ltd 2009 Monthly notices of the Royal Astronomical Society Vol.397 No.1
<P>ABSTRACT</P><P>We present a detrending algorithm for the removal of trends in time series. Trends in time series could be caused by various systematic and random noise sources such as cloud passages, changes of airmass, telescope vibration, CCD noise or defects of photometry. Those trends undermine the intrinsic signals of stars and should be removed. We determine the trends from subsets of stars that are highly correlated among themselves. These subsets are selected based on a hierarchical tree clustering algorithm. A bottom-up merging algorithm based on the departure from normal distribution in the correlation is developed to identify subsets, which we call clusters. After identification of clusters, we determine a trend per cluster by weighted sum of normalized light curves. We then use quadratic programming to detrend all individual light curves based on these determined trends. Experimental results with synthetic light curves containing artificial trends and events are presented. Results from other detrending methods are also compared. The developed algorithm can be applied to time series for trend removal in both narrow and wide field astronomy.</P>
Kim, Dae-Won,Protopapas, Pavlos,Byun, Yong-Ik,Alcock, Charles,Khardon, Roni,Trichas, Markos IOP Publishing 2011 The Astrophysical journal Vol.735 No.2
<P>We present a new quasi-stellar object (QSO) selection algorithm using a Support Vector Machine, a supervised classification method, on a set of extracted time series features including period, amplitude, color, and autocorrelation value. We train a model that separates QSOs from variable stars, non-variable stars, and microlensing events using 58 known QSOs, 1629 variable stars, and 4288 non-variables in the MAssive Compact Halo Object (MACHO) database as a training set. To estimate the efficiency and the accuracy of the model, we perform a cross-validation test using the training set. The test shows that the model correctly identifies similar to 80% of known QSOs with a 25% false-positive rate. The majority of the false positives are Be stars. We applied the trained model to the MACHO Large Magellanic Cloud (LMC) data set, which consists of 40 million light curves, and found 1620 QSO candidates. During the selection none of the 33,242 known MACHO variables were misclassified as QSO candidates. In order to estimate the true false-positive rate, we crossmatched the candidates with astronomical catalogs including the Spitzer Surveying the Agents of a Galaxy's Evolution LMC catalog and a few X-ray catalogs. The results further suggest that the majority of the candidates, more than 70%, are QSOs.</P>
Ishioka, R.,Wang, S.-Y.,Zhang, Z.-W.,Lehner, M. J.,Alcock, C.,Axelrod, T.,Bianco, F. B.,Byun, Y.-I.,Chen, W. P.,Cook, K. H.,Kim, D.-W.,King, S.-K.,Lee, T.,Marshall, S. L.,Protopapas, P.,Rice, J. A.,Sc American Institute of Physics 2014 The Astronomical journal Vol.147 No.4
<P>The Taiwanese-American Occultation Survey project is designed for the detection of stellar occultations by small-size Kuiper Belt Objects, and it has monitored selected fields along the ecliptic plane by using four telescopes with a 3 deg<SUP>2</SUP> field of view on the sky since 2005. We have analyzed data accumulated during 2005-2012 to detect variable stars. Sixteen fields with observations of more than 100 epochs were examined. We recovered 85 variables among a total of 158 known variable stars in these 16 fields. Most of the unrecovered variables are located in the fields observed less frequently. We also detected 58 variable stars which are not listed in the International Variable Star Index of the American Association of Variable Star Observers. These variable stars are classified as 3 RR Lyrae, 4 Cepheid, 1 δ Scuti, 5 Mira, 15 semi-regular, and 27 eclipsing binaries based on the periodicity and the profile of the light curves.</P>
( Efrosini Protopapa ) 大韓舞踊學會 2012 대한무용학회논문집 Vol.70 No.2
In recent debates on the development of practice-led research, discussions have often focused on the relationship between the different modes of doing that the researcher-practitioner engages with, which often include collaborative practice and interdisciplinary activities. Within this context, this paper sets out to explore certain principles of performance that emerged, as part of the creative process and the performances of the solo work Umm… I… and uh… [revisited], but also through reflections that I shared with performer-collaborator Susanna Recchia when the project was completed. It unfolds collaborative choreographic research through the articulation of the ``performance principles`` of the work. Such principles are discussed as that which causes and sustains a certain kind of shared thinking between choreographer and performer, in a piece whereby the performer is given by the choreographer a series of written instructions or prompts that form the ``performance score``. My practice is therefore presented here not only as multi-layered and complex in terms of its process, but also as shared amongst artists, while Recchia in particular is staged as a parallel researcher with her own reflections on practice. Given that the main focus of this practice-led research concerns the performer`s relation to space, what follows is a meditation on a series of tasks through which a space for practising choreographic thought in writing is created. The tasks are four: ``Go horizontal``. ``Mark out the territory``. ``Create a miniature``. ``Find the new beauty``. Through them I propose not a style or way of choreographing, but a way of approaching the stage and therefore a way of opening out possibilities, a way of imagining and preserving what I am exploring as the space of the dance possible, in practice.