Stochastic Modeling Handbook for Optical AGN VariabilityMoreno, Jackeline; Vogeley, Michael S.; Richards, Gordon T.; Yu, Weixiang
doi: 10.1088/1538-3873/ab1597pmid: N/A
This work develops application techniques for stochastic modeling of Active Galactic Nuclei (AGNs) variability as a probe of accretion disk physics. Stochastic models, specifically Continuous Auto-Regressive Moving Average (CARMA) models, characterize light curves with a perturbation spectrum and an Impulse-Response function, which crucially provides an interpretation for variability timescales. CARMA timescales are not physical but rather, they describe correlation structure and ordered information in stochastic processes. We begin this tutorial by reviewing discrete auto-regressive and moving-average processes, we bridge these components to their continuous analogs, and lastly we investigate the significance of CARMA timescales, obtained by modeling a light curve in the time domain, in relation to the shape of the power spectrum (PSD) and structure function. We determine that higher order CARMA models, for example the Damped Harmonic Oscillator (DHO or CARMA(2, 1)) are more sensitive to deviations from a single-slope power-law description of AGN variability; unlike Damped Random Walks (DRW or CAR(1)) where the PSD slope is fixed, the DHO slope is not. Higher complexity stochastic models than the DRW capture additional covariance in data and output additional characteristic timescales that probe the driving mechanisms of variability. We provide code using Kali software to generate simulations of diverse complexity stochastic light curves. We also provide a heuristic discussion of aliasing effects in ground-based cadences and the importance of light curve length in regards to uncertainty and limitations in timescale estimation.
The Classifications of Double Neutron Stars and their Correlations with the Binary Orbital ParametersYang, Yi-Yan; Zhang, Cheng-Min; Li, Di; Chen, Li; Linghu, Rong-Feng; Zhi, Qi-Jun
doi: 10.1088/1538-3873/ab00capmid: N/A
The statistical distribution of the total mass of 14 double neutron star (DNS) systems (out of 18 pairs observed) is found to be very narrow, with the average and standard deviation as 2.65 ± 0.03 M⊙. For the seven pairs of DNSs with the precisely measured masses of the recycled NSs (first formed) and their non-recycled companions (second formed), their masses are homogeneously distributed as 1.38 ± 0.02 M⊙ and 1.29 ± 0.02 M⊙, respectively. It is shown by the Anderson–Darling and Mann–Whitney–Wilcoxon tests that the first-born NSs share a same distribution, which should be formed by the supernova explosion; however, the second-formed NSs have the different statistical origins, which can be ascribed to three formation mechanisms after the further investigations of their orbital parameters and mass values, for instance, supernova explosion (e.g., PSR B1913+16), electron capture (e.g., PSR J0737-3039B), and ultra-stripped cores in close-orbit systems (e.g., PSR J1411+2551). In addition, by means of Fisher’s discriminant method, through simulation of the two groups of DNS samples that originated from electron-capture supernova and core-collapse supernova, we obtained the linear discriminant equation (e = −4.5Porb(day) + 1.1) between the eccentricity and orbital period, which can divide the DNSs into two groups involved in NS formed by electron-capture supernova (core-collapse supernova) without (with) kick.
Pulsations of the SX Phe Star BL CamelopardalisZong, Peng; Esamdin, Ali; Fu, Jian Ning; Niu, Hu Biao; Feng, Guo Jie; Yang, Tao Zhi; Bai, Chun Hai; Zhang, Yu; Liu, Jin Zhong
doi: 10.1088/1538-3873/ab0a1apmid: N/A
We carried out photometric observations of the SX Phe star BL Cam in 2014, 2017, and 2018 using Nanshan 1-m telescope. In addition to the dominated frequency of 25.5790 (3) cd−1 and its two harmonics, an independent frequency of 25.247 (2) cd−1, which is a nonradial mode frequency, was detected from the data in 2014. A total of 123 new times of light maxima were determined from our light curves in the three years, which, together with that published in the literature, were used to analyze the O−C diagram. The change rate of the main period was derived as (1/P)(dP/dt) = −2.39 (8) × 10−8 yr−1, which is lower than that published in previous literature. A periodical change with a period of 14.01 (9) yr was found in the residuals of the O−C curve fitting. If it was caused by the light-time effect, BL Cam should be a binary system. The mass of the companion was restricted as low as that of a brown dwarf. No evidence of the triple system suggested by previous authors was shown in our analysis.
The Oxyometer: A Novel Instrument Concept for Characterizing Exoplanet AtmospheresBaker, Ashley D.; Blake, Cullen H.; Halverson, Sam
doi: 10.1088/1538-3873/ab04b4pmid: N/A
With the Transiting Exoplanet Survey Satellite (TESS) and ground-based surveys searching for rocky exoplanets around cooler, nearby stars, the number of Earth-sized exoplanets that are well suited for atmospheric follow-up studies will increase significantly. For atmospheric characterization, the James Webb Space Telescope will only be able to target a small fraction of the most interesting systems, and the usefulness of ground-based observatories will remain limited by a range of effects related to Earth’s atmosphere. Here, we explore a new method for ground-based exoplanet atmospheric characterization that relies on simultaneous, differential, ultra-narrow-band photometry. The instrument uses a narrow-band interference filter and an optical design that enables simultaneous observing over two 0.3 nm wide bands spaced 1 nm apart. We consider the capabilities of this instrument in the case where one band is centered on an oxygen-free continuum region while the other band overlaps the 760 nm oxygen bandhead in the transmission spectrum of the exoplanet, which can be accessible from Earth in systems with large negative line-of-sight velocities. We find that M9 and M4 dwarfs that meet this radial velocity requirement will be the easiest targets but must be nearby (<8 pc) and will require the largest upcoming Extremely Large Telescopes. The oxyometer instrument design is simple and versatile and could be adapted to enable the study of a wide range of atmospheric species. We demonstrate this by building a prototype oxyometer and present its design and a detection of a 50 ppm simulated transit signal in the laboratory. We also present data from an on-sky test of a prototype oxyometer, demonstrating the ease of use of the compact instrument design.
The digest2 NEO Classification CodeKeys, Sonia; Vereš, Peter; Payne, Matthew J.; Holman, Matthew J.; Jedicke, Robert; Williams, Gareth V.; Spahr, Tim; Asher, David J.; Hergenrother, Carl
doi: 10.1088/1538-3873/ab1157pmid: N/A
We describe the software package, a fast, short-arc orbit classifier for small solar system bodies. The algorithm has been serving the community for more than 13 yr. The code provides a score, , which represents a pseudo-probability that a tracklet belongs to a given solar system orbit type. is primarily used as a classifier for Near-Earth Object (NEO) candidates, to identify those to be prioritized for follow-up observation. We describe the historical development of and demonstrate its use on real and synthetic data. We find that can accurately and precisely distinguish NEOs from non-NEOs. At the time of detection, 14% of NEO tracklets and 98.5% of non-NEOs tracklets have below the critical value of of our simulated NEOs achieved the maximum and 99.6% of NEOs achieved at least once during the simulated 10-year timeframe. We demonstrate that varies as a function of time, rate of motion, magnitude and sky-plane location, and show that NEOs tend to have lower at low Solar elongations close to the ecliptic. We use our findings to recommend future development directions for the code.
The DESI Fiber View Camera SystemBaltay, C.; Rabinowitz, D.; Besuner, R.; Casetti, D.; Emmet, W.; Fagrelius, P.; Girard, T.; Heetderks, H.; Lampton, M.; Lathem, A.; Levi, M.; Padmanabhan, N.; Silber, J.
doi: 10.1088/1538-3873/ab15c2pmid: N/A
The Dark Energy Spectroscopic Instrument (DESI) is a 5000 fiber multi-object spectrometer now being installed at the prime focus of the 4 m Mayall telescope at Kitt Peak. Using DESI to measure ∼35 million galaxy redshifts and using the Baryon Acoustic Oscillation (BAO) technique to measure distances, the results will probe the nature of the recently discovered mysterious component of our universe called dark energy. Computer controlled robotic positioners move the 120 μm diameter fibers to positions of galaxies whose location on the sky have been obtained in a previous target selection imaging survey. To achieve good throughput the fibers should be centered on the target position to within 3 μm. The robotic positioners however are only capable of a 50 μm precision on their first move. To achieve the desired precision, the Fiber View Camera (FVC) system has been implemented. The FVC, located near the hole in the primary mirror of the Mayall telescope, has been designed to take an exposure of the focal plane, located at the prime focus some 12 m above the FVC, after the robotic positioners have completed their first move. The FVC is intended to measure the fiber locations with a precision of 3 μm and issue a set of fiber coordinate corrections for the second move correcting the fiber positions by the robotic positioners. Tests show that after two iterations better than 99% of the fibers will be in their intended location to within the desired precision. This paper describes the design of the FVC system, the R&D program preceding the final design, and the tests that have been carried out to demonstrate that the FVC can achieve the required precision.
Finding the Needle in a Haystack: Detrending Photometric Timeseries Data of Strictly Periodic Astrophysical ObjectsPrša, Andrej; Zhang, Moses; Wells, Mark
doi: 10.1088/1538-3873/ab0f41pmid: N/A
Light curves of astrophysical objects frequently contain strictly periodic signals. In such cases, we can use that property to aid the detrending algorithm to fully disentangle an unknown periodic signal and an unknown baseline signal with no power at that period. The periodic signal is modeled as a discrete probability distribution function (pdf), while the baseline signal is modeled as a residual timeseries. Those two components are disentangled by minimizing the total variation (length) of the residual timeseries with regard to the per-bin pdf fluxes. We demonstrate the use of the algorithm on a synthetic case, on the eclipsing binary KIC 3953981 and on the eccentric ellipsoidal variable KIC 3547874. We further discuss the parameters and the limitations of the algorithm and speculate on the two most common use cases: detrending the periodic signal of interest and measuring the dependence of instrumental response on controlled instrumental variables. A more sophisticated version of the algorithm is released as open source on github and available via pip.