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تسجيل مستخدم جديدFinding, characterizing and classifying variable sources in multi-epoch sky surveys: QSOs and RR Lyrae in PS1 3$pi$ data
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In area and depth, the Pan-STARRS1 (PS1) 3$pi$ survey is unique among many-epoch, multi-band surveys and has enormous potential for all-sky identification of variable sources. PS1 has observed the sky typically seven times in each of its five bands ($grizy$) over 3.5 years, but unlike SDSS not simultaneously across the bands. Here we develop a new approach for quantifying statistical properties of non-simultaneous, sparse, multi-color lightcurves through light-curve structure functions, effectively turning PS1 into a $sim 35$-epoch survey. We use this approach to estimate variability amplitudes and timescales $(omega_r, tau)$ for all point-sources brighter than $r_{mathrm{P1}}=21.5$ mag in the survey. With PS1 data on SDSS Stripe 82 as ``ground truth, we use a Random Forest Classifier to identify QSOs and RR Lyrae based on their variability and their mean PS1 and WISE colors. We find that, aside from the Galactic plane, QSO and RR Lyrae samples of purity $sim$75% and completeness $sim$92% can be selected. On this basis we have identified a sample of $sim 1,000,000$ QSO candidates, as well as an unprecedentedly large and deep sample of $sim$150,000 RR Lyrae candidates with distances from $sim$10 kpc to $sim$120 kpc. Within the Draco dwarf spheroidal, we demonstrate a distance precision of 6% for RR Lyrae candidates. We provide a catalog of all likely variable point sources and likely QSOs in PS1, a total of $25.8times 10^6$ sources.
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RR Lyrae stars may be the best practical tracers of Galactic halo (sub-)structure and kinematics. The PanSTARRS1 (PS1) $3pi$ survey offers multi-band, multi-epoch, precise photometry across much of the sky, but a robust identification of RR Lyrae sta
rs in this data set poses a challenge, given PS1s sparse, asynchronous multi-band light curves ($lesssim 12$ epochs in each of five bands, taken over a 4.5-year period). We present a novel template fitting technique that uses well-defined and physically motivated multi-band light curves of RR Lyrae stars, and demonstrate that we get accurate period estimates, precise to 2~sec in $>80%$ of cases. We augment these light curve fits with other {em features} from photometric time-series and provide them to progressively more detailed machine-learned classification models. From these models we are able to select the widest ($3/4$ of the sky) and deepest (reaching 120 kpc) sample of RR Lyrae stars to date. The PS1 sample of $sim 45,000$ RRab stars is pure (90%), and complete (80% at 80 kpc) at high galactic latitudes. It also provides distances precise to 3%, measured with newly derived period-luminosity relations for optical/near-infrared PS1 bands. With the addition of proper motions from {em Gaia} and radial velocity measurements from multi-object spectroscopic surveys, we expect the PS1 sample of RR Lyrae stars to become the premier source for studying the structure, kinematics, and the gravitational potential of the Galactic halo. The techniques presented in this study should translate well to other sparse, multi-band data sets, such as those produced by the Dark Energy Survey and the upcoming Large Synoptic Survey Telescope Galactic plane sub-survey.
The second Gaia data release is expected to contain data products from about 22 months of observation. Based on these data, we aim to provide an advance publication of a full-sky Gaia map of RR Lyrae stars. Although comprehensive, these data still co
ntain a significant fraction of sources which are insufficiently sampled for Fourier series decomposition of the periodic light variations. The challenges in the identification of RR Lyrae candidates with (much) fewer than 20 field-of-view transits are described. General considerations of the results, their limitations, and interpretation are presented together with prospects for improvement in subsequent Gaia data releases.
We present a comprehensive and precise description of the Sagittarius (Sgr) stellar streams 3D geometry as traced by its old stellar population. This analysis draws on the sample of ${sim}44,000$ RR Lyrae (RRab) stars from the Pan-STARRS1 (PS1) 3$pi$
survey (Hernitschek et al. 2016,Sesar et al. 2017b), which is ${sim}80%$ complete and ${sim}90%$ pure within 80~kpc, and extends to ${gtrsim} 120$~kpc with a distance precision of ${sim} 3%$. A projection of RR Lyrae stars within $|tilde{B}|_{odot}<9^circ$ of the Sgr streams orbital plane reveals the morphology of both the leading and the trailing arms at very high contrast, across much of the sky. In particular, the map traces the stream near-contiguously through the distant apocenters. We fit a simple model for the mean distance and line-of-sight depth of the Sgr stream as a function of the orbital plane angle $tilde{Lambda}_{odot}$, along with a power-law background-model for the field stars. This modeling results in estimates of the mean stream distance precise to ${sim}1%$ and it resolves the streams line-of-sight depth. These improved geometric constraints can serve as new constraints for dynamical stream models.
We present new spatial models and distance estimates for globular clusters (GC) and dwarf spheroidals (dSphs) orbiting our Galaxy based on RR Lyrae (RRab) stars in the Pan-STARRS1 (PS1) 3$pi$ survey. Using the PS1 sample of RRab stars from Sesar et a
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We present an update of a spectroscopic follow-up survey at low-resolution of a large number of RR Lyrae halo overdensity candidates found in the southern sky. The substructure candidates were identified in the RR Lyrae catalog of Torrealba et al. (2
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