119230126
The TAOS Project Stellar Variability II. Detection of 15 Variable Stars
The Taiwanese-American Occultation Survey (TAOS) project has collected more than a billion photometric measurements since 2005 January. These sky survey data-covering timescales from a fraction of a second to a few hundred days-are a useful source to study stellar variability. A total of 167 star fields, mostly along the ecliptic plane, have been selected for photometric monitoring with the TAOS telescopes. This paper presents our initial analysis of a search for periodic variable stars from the time-series TAOS data on one particular TAOS field, No. 151 (RA = 17$^{\rm h}30^{\rm m}6\fs$67, Dec = 27\degr17\arcmin 30\arcsec, J2000), which had been observed over 47 epochs in 2005. A total of 81 candidate variables are identified in the 3 square degree field, with magnitudes in the range 8 < R < 16. On the basis of the periodicity and shape of the lightcurves, 29 variables, 15 of which were previously unknown, are classified as RR Lyrae, Cepheid, delta Scuti, SX Phonencis, semi-regular and eclipsing binaries.
9262984
Bunch Tracing by Bunch by Bunch Measurement System in HLS
In this paper, we introduce a bunch tracing system which is based on a bunch-by-bunch (BxB) measurement system in Hefei Light Source (HLS), and present the analysis of the experiment results. Using an in-phase gate signal and a double balance mixer to control an external trigger of ADC, we test the reliability of the BxB system. By this system, we can trace all marked bunches in a set time slot or in manual burst mode. We can record all bunches’ data during the injection, ramping, wiggler excitation and normal operation, and provide a powerful facility for machine study.
39289464
HLS Turn-by-Turn System and its Application
Measurement principles and analysis of Turn-by-Turn beam position monitor system at Hefei Light Source (HLS) are presented in this paper. In emphases, several typical applications are presented here, which include the commissioning of upgraded injection system on HLS storage, monitoring of transientν transientν transientν transientν transientν transientν transientν transientν transientν transientν and damping time of storage ring, beam instability in injection, as well as experiments of low frequency feedback system. Precise analyses of experimental results offer some conclusions, which are consistent with theoretical expectations. The system plays an important role in study of beam instability and improvement of machine performance.
43173006
The TAOS Project: Statistical Analysis of Multi-Telescope Time Series Data
The Taiwanese-American Occultation Survey (TAOS) monitors fields of up to ~1000 stars at 5 Hz simultaneously with four small telescopes to detect occultation events from small (~1 km) Kuiper Belt Objects (KBOs). The survey presents a number of challenges, in particular the fact that the occultation events we are searching for are extremely rare and are typically manifested as slight flux drops for only one or two consecutive time series measurements. We have developed a statistical analysis technique to search the multi-telescope data set for simultaneous flux drops which provides a robust false-positive rejection and calculation of event significance. In this article, we describe in detail this statistical technique and its application to the TAOS data set.
102339817
BUNCH-BY-BUNCH ONLINE DIAGNOSTICS AT HLS
The design goal for the bunch-by-bunch analogue transverse feedback system at the Hefei Light Source (HLS) is to cure the transverse coupled bunch instabilities. The prototype implemented bunch-by-bunch feedback in 2006. Then we changed the circuit and replaced some components by ones of higher performance in order to get better effect. Diagnostic techniques are important tools to determine instabilities and to confirm the performance of the feedback systems. In addition to transverse feedback this system can provide online beam diagnostics and analysis in transverse and longitudinal directions. The diagnostic functions can record the response of every bunch while the feedback system manipulates the beam. The experimental results are presented. INTRODUCTION The HLS is a facility dedicated to synchrotron radiation. Its electron storage ring, with a circumference of 66 meters, operates with 45 bunches in 204.035MHz Radio Frequency (RF), and contains 31 BPMs. Each BPM has a four-button type pick-ups mounted in a skew of 45°. A 200MeV injection beam from linac and transport line ramps to 800MeV and operates at 200300mA in the HLS storage ring. A multi-cycle multi-turn injection system is used for current accumulation. A wiggler is available in the HLS. There are three operating states: injection (200MeV), 800MeV Optics-Normal, and 800MeV Optics-Wiggler. A bunch-by-bunch transverse feedback system has been under commissioning at HLS, and it is introduced in this paper. The transverse prototype implemented bunchby-bunch feedback in 2006. In order to get better effect, then we replaced some components by ones of higher performance, such as the strip line feedback kicker, the optical fibre notch filter. We moved the 3-tap filter in front of the hybrid network and add DC offset in the circuit to gain better signal to noise ratio. In addition to transverse feedback this system can provide online beam diagnostics and analysis in transverse and longitudinal directions. The diagnostic functions can record the response of every bunch while the feedback system manipulates the beam. Some phenomena observed are presented, as well as the feedback experimental results. THE FEEDBACK SYSTEM Prototype The bunch-by-bunch analogue transverse feedback system at HLS consists of 2 signal detectors (pickups), a RF front-end, a signal processing, a frequency doubling circuit, a vectors operation and control module, 2 Notch Filters, 4 RF amplifiers and a kicker. An overview of it is in [1]. We use double balance mixers (DBM) to substitute for the attenuators and phase shifters. This new method can simplify the system. It supports a range of 360 degree phase adjusting the feedback signal by vector computation. The signal can be controlled as either a feedback signal or an exciting signal arbitrarily. In order to test the prototype serial experiments were performed on timing, phasing, and powering of the feedback signal with the old 73cm general kicker. This system also works well in 800MeV operation [1].
14412863
First Results From The Taiwanese-American Occultation Survey (TAOS)
Results from the first 2 years of data from the Taiwanese-American Occultation Survey (TAOS) are presented. Stars have been monitored photometrically at 4 or 5 Hz to search for occultations by small (~3 km) Kuiper Belt objects (KBOs). No statistically significant events were found, allowing us to present an upper bound to the size distribution of KBOs with diameters 0.5 km < D < 28 km.
14223783
A CHANDRA STUDY OF THE ROSETTE STAR-FORMING COMPLEX. II. CLUSTERS IN THE ROSETTE MOLECULAR CLOUD
We explore here the young stellar populations in the Rosette Molecular Cloud (RMC) region with high spatial resolution X-ray images from the Chandra X-ray Observatory, which are effective in locating weak-lined T Tauri stars as well as disk-bearing young stars. A total of 395 X-ray point sources are detected, 299 of which (76%) have an optical or near-infrared (NIR) counterpart identified from deep FLAMINGOS images. From X-ray and mass sensitivity limits, we infer a total population of ~1700 young stars in the survey region. Based on smoothed stellar surface density maps, we investigate the spatial distribution of the X-ray sources and define three distinctive structures and substructures within them. Structures B and C are associated with previously known embedded IR clusters, while structure A is a new X-ray-identified unobscured cluster. A high-mass protostar RMCX #89 = IRAS 06306+0437 and its associated sparse cluster are studied. The different subregions are not coeval but do not show a simple spatial-age pattern. Disk fractions vary between subregions and are generally 20% of the total stellar population inferred from the X-ray survey. The data are consistent with speculations that triggered star formation around the H II region is present in the RMC, but do not support a simple sequential triggering process through the cloud interior. While a significant fraction of young stars are located in a distributed population throughout the RMC region, it is not clear if they originated in clustered environments.
118446261
ON THE X-RAY BALDWIN EFFECT IN ACTIVE GALACTIC NUCLEI OBSERVED BY THE CHANDRA HIGH-ENERGY GRATING
Using Chandra high-energy grating (HEG) observations of 32 active galactic nuclei (AGNs), we present a systematic study of the X-ray Baldwin effect (XBE; i.e., the anti-correlation between the narrow Fe Kα line equivalent width (EW) and X-ray continuum luminosity for AGN samples) with the highest spectral resolution currently available. We have previously reported an anti-correlation with EW∝L –0.22 2-10 keV in an HEG sample, and the correlation is much weaker after averaging multiple observations of individual AGNs (EW∝L –0.13 2-10 keV). This indicates that rapid variation in the X-ray continuum plays an important role in producing the XBE, and such an effect should also be visible in individual AGNs. In this Letter, by normalizing the line EWs and continuum luminosities to the time-averaged values for each AGN in our sample with multiple HEG observations, we find a strong anti-correlation between EW and LX (EW/EW∝(L/L)–0.82 ± 0.10), consistent with the XBE expected in an individual AGN if the narrow line flux remains constant while the continuum varies. This is first observational evidence that the Fe Kα line flux in a large sample of AGNs lacks a corresponding response to the continuum variation, supporting the fact that the narrow Fe-K line emission originates from a region far from the nucleus. We then performed Monte Carlo simulations to address whether the global XBE can be produced by X-ray continuum variation solely, and found that such an interpretation of the XBE cannot be ruled out statistically. One should thus be very cautious before drawing any scientific conclusion based on an observed XBE.
59359011
THE SEARCH FOR LOW-MASS COMPANIONS OF B STARS IN THE CARINA NEBULA CLUSTER TRUMPLER 16*
We have developed lists of likely B3-A0 stars (called "late B" stars) in the young cluster Trumpler 16. The following criteria were used: location within 3' of η Car, an appropriate V and B - V combination, and proper motion (where available). Color and magnitude cuts have been made assuming an E(B - V) = 0.55 mag +/- 0.1, which is a good approximation close to the center of Trumpler 16. These lists have been cross-correlated with X-ray sources found in the Chandra Carina Complex Project. Previous studies have shown that only very rarely (if at all) do late main-sequence B stars produce X-rays. We present evidence that the X-ray-detected sources are binaries with low-mass companions, since stars less massive than 1.4 M☉ are strong X-ray sources at the age of the cluster. Both the median X-ray energies and X-ray luminosities of these sources are in good agreement with values for typical low-mass coronal X-ray sources. We find that 39% of the late B stars based on a list with proper motions have low-mass companions. Similarly, 32% of a sample without proper motions have low-mass companions. We discuss the X-ray detection completeness. These results on low-mass companions of intermediate-mass stars are complementary to spectroscopic and interferometric results and probe new parameter space of low-mass companions at all separations. They do not support a steeply rising distribution of mass ratios to low masses for intermediate-mass (5 M☉) primaries, such as would be found by random pairing from the initial mass function.
3138066
The eighth data release of the Sloan Digital Sky Survey: first data from SDSS-III
The Sloan Digital Sky Survey (SDSS) started a new phase in 2008 August, with new instrumentation and new surveys focused on Galactic structure and chemical evolution, measurements of the baryon oscillation feature in the clustering of galaxies and the quasar Lyα forest, and a radial velocity search for planets around ~8000 stars. This paper describes the first data release of SDSS-III (and the eighth counting from the beginning of the SDSS). The release includes five-band imaging of roughly 5200 deg2 in the southern Galactic cap, bringing the total footprint of the SDSS imaging to 14,555 deg2, or over a third of the Celestial Sphere. All the imaging data have been reprocessed with an improved sky-subtraction algorithm and a final, self-consistent photometric recalibration and flat-field determination. This release also includes all data from the second phase of the Sloan Extension for Galactic Understanding and Exploration (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars at both high and low Galactic latitudes. All the more than half a million stellar spectra obtained with the SDSS spectrograph have been reprocessed through an improved stellar parameter pipeline, which has better determination of metallicity for high-metallicity stars.
119213652
Production of $B_c$ or $\bar{B}_c$ meson and its excited states via $\bar{t}$ quark or $t$ quark decays
The production of (bc)-quarkonium (B{sub c} meson and its excited states) or (cb)-quarkonium (B{sub c} meson and its excited states) via top quark t or top antiquark t decays, t{yields}(bc)+c+W{sup +} or t{yields}(cb)+c+W{sup -}, respectively, is studied within the framework of NRQCD. In addition to the production of the two color-singlet S-wave states |(bc)({sup 1}S{sub 0}){sub 1}> or |(cb)({sup 1}S{sub 0}){sub 1}> and |(bc)({sup 3}S{sub 1}){sub 1}> or |(cb)({sup 3}S{sub 1}){sub 1}>, the production of the P-wave excited (bc) or (cb) states, i.e. the four color-singlet P-wave states |(bc)({sup 1}P{sub 1}){sub 1}> or |(cb)({sup 1}P{sub 1}){sub 1}>, and (bc)({sup 3}P{sub J}){sub 1}> or (cb)({sup 3}P{sub J}){sub 1}> (with J=(1,2,3)), is also studied. According to the velocity scaling rule of NRQCD, for the production of P-wave excited states the contributions from the two color-octet components |(bc)({sup 1}S{sub 0}){sub 8}> or |(cb)({sup 1}S{sub 0}){sub 8}> and |(bc)({sup 3}S{sub 1}){sub 8}> or |(cb)({sup 3}S{sub 1}){sub 8}> are also taken into account. We quantitatively discuss the possibility and the advantages in experimental studies of B{sub c} or B{sub c} meson and its excited states via the indirect production at LHC in high luminosity runs and at LHC possible upgraded versions such as SLHC, DLHC,more » TLHC, etc. in the future.« less