Publications of the Astronomical Society of the Pacific

Zhang, Jun; Hao, Yun Cai; Wang, Li; Long, Ye

doi: 10.1088/1538-3873/128/961/035003pmid: N/A

To collect star transits data qualified for in-orbit calibration, this study derives the full error constraints to limit star tracker's influential error sources and computes their error boundaries from a theoretical perspective. The full constraints, including not only the minimum variance estimation of position but also the error bound prediction of scale and intensity of Gaussian-shaped starspots, are studied based on the Cramér–Rao Lower Bound (CRLB) theorem. By imposing these constraints on motion, drift in focal length, and other factors, their boundaries could be determined before launch. Therefore, the in-orbit correction accuracy is expected to be close to CRLB through suitable implementation of these constraints. The correctness of the theoretical position error of motion is demonstrated by the data-fitting procedure against test results of star tracker on dynamic performance. The simulation result shows that the drift in focal length can generate an error with the same magnitude as detector noise and thus might be the dominant error source when star tracker is working under stationary circumstance. Using the accuracy performance of some typical star trackers, this study shows that the CRLB constraint may be very effective to estimate the overall position error of a starspot or one axis, valuable data that can be used for online calibration. The overall position uncertainty analysis shows that a weighted method can be employed for calibration, a process where star data can be given a weight in inverse proportion to the CRLB value.

Smitka, Michael T.; Brown, Peter J.; Kuin, Paul; Suntzeff, Nicholas B.

doi: 10.1088/1538-3873/128/961/034501pmid: N/A

We present a new technique of decontaminating Swift Ultraviolet/Optical Telescope grism spectra for transient objects. We describe the template image requirements and image processing steps necessary to successfully implement the empirical decontamination technique. We demonstrate the accuracy of the flux and wavelength calibrations for decontaminated spectra by comparing a spectrum of SN 2011fe with a well-calibrated, long-slit ultraviolet spectrum from the Hubble Space Telescope’s Space Telescope Imaging Spectrograph. We also show how the decontamination removes spurious emission lines from spectra of iPTF14bdn that otherwise could be misinterpreted as coming from the supernova. The software that implements this technique is briefly discussed and is made available to the community.

Du, Changde; Luo, Ali; Yang, Haifeng; Hou, Wen; Guo, Yanxin

doi: 10.1088/1538-3873/128/961/034502pmid: N/A

One of the most important aims of astronomical data mining is to systematically search for specific rare objects in a massive spectral data set, given a small fraction of identified samples with the same type. Most existing methods are mainly based on binary classification, which usually suffers from incompleteness when there are too few known samples. Rank-based methods could provide good solutions for such cases. After investigating several algorithms, a method combining a bipartite ranking model with bootstrap aggregating techniques was developed in this paper. The method was applied while searching for carbon stars in the spectral data of Sloan Digital Sky Survey Data Release 10 and compared with several other popular methods used for data mining. Experimental results validate that the proposed method is not only the most effective but also the least time-consuming technique among its competitors when searching for rare spectra in a large but unlabeled data set.

Zhang, M.; Bakos, G. Á.; Penev, K.; Csubry, Z.; Hartman, J. D.; Bhatti, W.; Val-Borro, M. de

doi: 10.1088/1538-3873/128/961/035001pmid: N/A

Ground-based exoplanet surveys such as SuperWASP, HAT Network of Telescopes (HATNet), and KELT have discovered close to two hundred transiting extrasolar planets in the past several years. The strategy of these surveys is to look at a large field of view and measure the brightnesses of its bright stars to around half a percent per point precision, which is adequate for detecting hot Jupiters. Typically, these surveys use CCD detectors to achieve high precision photometry. These CCDS, however, are expensive relative to other consumer-grade optical imaging devices, such as digital single-lens reflex cameras (DSLRs). We look at the possibility of using a DSLR camera for precision photometry. Specifically, we used a Canon EOS 60D camera that records light in three colors simultaneously. The DSLR was integrated into the HATNet survey and collected observations for a month, after which photometry was extracted for 6600 stars in a selected stellar field. We found that the DSLR achieves a best-case median absolute deviation of 4.6 mmag per 180 s exposure when the DSLR color channels are combined, and 1000 stars are measured to better than 10 mmag (1%). Also, we achieve 10 mmag or better photometry in the individual colors. This is good enough to detect transiting hot Jupiters. We performed a candidate search on all stars and found four candidates, one of which is KELT-3b, the only known transiting hot Jupiter in our selected field. We conclude that the Canon 60D is a cheap, lightweight device capable of useful photometry in multiple colors.

Mendikoa, Iñigo; Sánchez-Lavega, Agustín; Pérez-Hoyos, Santiago; Hueso, Ricardo; Rojas, José Félix; Aceituno, Jesús; Aceituno, Francisco; Murga, Gaizka; Bilbao, Lander De; García-Melendo, Enrique

doi: 10.1088/1538-3873/128/961/035002

Tovmassian, Gagik; Hernandez, Mercedes-Stephania; Ochoa, Jose Luis; Ernenwein, Jean-Pierre; Mandat, Dusan; Pech, Miroslav; Frayn, Ilse Plauchu; Colorado, Enrique; Murillo, Jose Manuel; Ceseña, Urania; Garcia, Benjamin; H. Lee, William; Bulik, Tomasz; Garczarczyk, Markus;

Kruk, Jeffrey W.; Xapsos, Michael A.; Armani, Nerses; Stauffer, Craig; Hirata, Christopher M.

doi: 10.1088/1538-3873/128/961/035005pmid: N/A

Geosynchronous orbits are appealing for solar or astrophysical observatories because they permit continuous data downlink at high rates. The radiation environment in these orbits presents unique challenges, however. This paper describes both the characteristics of the radiation environment in geosynchronous orbit and the mechanisms by which this radiation generates backgrounds in photon detectors. Shielding considerations are described, and a preliminary shielding design for the proposed Wide-Field InfraRed Survey Telescope observatory is presented as a reference for future space telescope concept studies that consider a geosynchronous orbit.