The TAIWAN-AMERICAN OCCULTATION SURVEY PROJECT STELLAR VARIABILITY. I. DETECTION OF LOW-AMPLITUDE Δ SCUTI STARS

Kim, Dae Won; Protopapas, Pavlos; Alcock, Charles; Byun, Yong Ik; Kyeong, Jaemann; Lee, B.-C.; Wright, N. J.; Axelrod, T. S.; Bianco, Federica; Chen, W.-P.; Coehlo, N. K.; Cook, K. H.; Dave, R.; King, S. K.; Lee, T.; Lehner, M. J.; Lin, H. C.; Marshall, Stuart; Porrata, R.; Rice, John A.; Schwamb, Megan E.; Wang, J.-H.; Wang, S.-Y.; Wen, C. Y.; Zhang, Z.-W.

doi:10.1088/0004-6256/139/2/757

Cited by 8 publications

(1 citation statement)

References 43 publications

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“…In many cases, however, missing data occur when no photometric measurements are available for some stars in a given observed frame. These missing data can be simply replaced by means, medians, or the values from the interpolation of adjacent data points in each light curve (e.g., Kovács et al 2005;Kim et al 2010). Although using the replaced value is the easiest way to reconstruct the light curve to be analyzed, it is not appropriate if the time separation between two subsequent observations is too large.…”

Section: Removal Of Temporal Systematics Bymentioning

confidence: 99%

A New Method for Robust High-Precision Time-Series Photometry From Well-Sampled Images: Application to Archival MMT/Megacam Observations of the Open Cluster M37

Chang¹,

Byun²,

Hartman³

2015

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We introduce new methods for robust high-precision photometry from well-sampled images of a non-crowded field with a strongly varying point-spread function. For this work, we used archival imaging data of the open cluster M37 taken by MMT 6.5m telescope. We find that the archival light curves from the original image subtraction procedure exhibit many unusual outliers, and more than 20% of data get rejected by the simple filtering algorithm adopted by early analysis. In order to achieve better photometric precisions and also to utilize all available data, the entire imaging database was re-analyzed with our time-series photometry technique (Multi-aperture Indexing Photometry) and a set of sophisticated calibration procedures. The merit of this approach is as follows: we find an optimal aperture for each star with a maximum signal-to-noise ratio, and also treat peculiar situations where photometry returns misleading information with more optimal photometric index. We also adopt photometric de-trending based on a hierarchical clustering method, which is a very useful tool in removing systematics from light curves. Our method removes systematic variations that are shared by light curves of nearby stars, while true variabilities are preserved. Consequently, our method utilizes nearly 100% of available data and reduce the rms scatter several times smaller than archival light curves for brighter stars. This new data set gives a rare opportunity to explore different types of variability of short (∼minutes) and long (∼1 month) time scales in open cluster stars.

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Section: Removal Of Temporal Systematics Bymentioning

confidence: 99%

A New Method for Robust High-Precision Time-Series Photometry From Well-Sampled Images: Application to Archival MMT/Megacam Observations of the Open Cluster M37

Chang¹,

Byun²,

Hartman³

2015

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The active CGCG 077-102 NED02 galaxy within the Abell 2063 galaxy cluster

Adami,

Parra Ramos,

Harry

et al. 2023

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Context. Within the framework of investigating the link between the central super massive black holes in the cores of galaxies and the galaxies themselves, we detected a variable X-ray source in the center of CGCG 077-102 NED02, which is a member of the CGCG 077-102 galaxy pair within the Abell 2063 cluster of galaxies. Aims. Our goal is to combine X-ray and optical data to demonstrate that this object harbors an active super massive black hole in its core, and to relate this to the dynamical status of the galaxy pair within the Abell 2063 cluster. Methods. We used Chandra and XMM-Newton archival data to derive the X-ray spectral shape and variability. We also obtained optical spectroscopy to detect the expected emission lines that are typically found in active galactic nuclei. Finally, we used public ZTF imaging data to investigate the optical variability. Results. There is no evidence of multiple X-ray sources or extended components within CGCG 077-102 NED02. Single X-ray spectral models fit the source well. We detect significant, nonrandom inter-observation 0.5–10 keV X-ray flux variabilities, for observations separated by ∼4 days for short-term variations and by up to ∼700 days for long-term variations. Optical spectroscopy points toward a passive galaxy for CGCG 077-102 NED01 and a Seyfert for CGCG 077-102 NED02. The classification of CGCG 077-102 NED02 is also consistent with its X-ray luminosity of over 1042 erg s−1. We do not detect short-term variability in the optical ZTF light curves. However, we find a significant long-term stochastic variability in the g-band that can be well described by the damped random walk model with a best-fit characteristic damping timescale of τDRW = 30−12+28 days. Finally, the CGCG 077-102 galaxy pair is deeply embedded within the Abell 2063 potential, with a long enough history within this massive structure to have been affected by the influence of this cluster for a long time. Conclusions. Our observations point toward a moderately massive black hole in the center of CGCG 077-102 NED02 of ∼106 M⊙. As compared to another similar pair in the literature, CGCG 077-102 NED02 is not heavily obscured, perhaps because of the surrounding intracluster medium ram-pressure stripping.

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The Taiwanese-American Occultation Survey Project Stellar Variability. Ii. Detection of 15 Variable Stars

Mondal

Lin

Chen

et al. 2010

The Astronomical Journal

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The Taiwanese-American Occultation Survey (TAOS) project has collected more than a billion photometric measurements since 2005 January. These sky survey datacovering 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 timeseries TAOS data on one particular TAOS field, No. 151 (RA = 17 h 30 m 6. s 67, Dec = 27 • 17 ′ 30 ′′ , 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, δ Scuti, SX Phonencis, semi-regular and eclipsing binaries.

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The TAIWAN-AMERICAN OCCULTATION SURVEY PROJECT STELLAR VARIABILITY. I. DETECTION OF LOW-AMPLITUDE Δ SCUTI STARS

Cited by 8 publications

References 43 publications

A New Method for Robust High-Precision Time-Series Photometry From Well-Sampled Images: Application to Archival MMT/Megacam Observations of the Open Cluster M37

A New Method for Robust High-Precision Time-Series Photometry From Well-Sampled Images: Application to Archival MMT/Megacam Observations of the Open Cluster M37

The active CGCG 077-102 NED02 galaxy within the Abell 2063 galaxy cluster

The Taiwanese-American Occultation Survey Project Stellar Variability. Ii. Detection of 15 Variable Stars

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