Search Publications
A Machine-learning-based Investigation of the Open Cluster M67
Gao, Xinhua
In this paper, we use a machine-learning method, random forest (RF), to identify reliable members of the old (4 Gyr) open cluster M67 based on the high-precision astrometry and photometry taken from the second Gaia data release (Gaia-DR2). The RF method is used to calculate membership probabilities of 71,117 stars within 2.°5 of the cluster center…
Onset of the Magnetic Explosion in Solar Polar Coronal X-Ray Jets
Panesar, Navdeep K.; Moore, Ronald L.; Sterling, Alphonse C.
We follow up on the Sterling et al. discovery that nearly all polar coronal X-ray jets are made by an explosive eruption of a closed magnetic field carrying a miniature filament in its core. In the same X-ray and EUV movies used by Sterling et al., we examine the onset and growth of the driving magnetic explosion in 15 of the 20 jets that they stu…
The Magellan Evolution of Galaxies Spectroscopic and Ultraviolet Reference Atlas (MegaSaura). II. Stacked Spectra
Dahle, H.; Rigby, J. R.; Bayliss, M. B. +8 more
We stack the rest-frame ultraviolet spectra of N = 14 highly magnified gravitationally lensed galaxies at redshifts 1.6< z< 3.6. The resulting new composite spans 900< {λ }{rest}< 3000 Å, with a peak signal-to-noise ratio (S/N) of 103 per spectral resolution element (∼100 km s-1). It is the highest S/N, highest sp…
Two Transient X-Ray Quasi-periodic Oscillations Separated by an Intermediate State in 1H 0707-495
Zhang, Peng; Zhang, Peng-fei; Yan, Jing-zhi +3 more
In the narrow-line Seyfert 1 galaxy 1H 0707-495, recently a transient quasi-periodic oscillation (QPO) signal with a frequency of ∼ 2.6× {10}-4 Hz has been detected at a high statistical significance. Here, we reanalyze the same set of XMM-Newton data observed on 2008 February 4 with the weighted-wavelet Z-transform method. In addition …
An X-Ray Imaging Survey of Quasar Jets: The Complete Survey
Birkinshaw, M.; Worrall, D. M.; Schwartz, D. A. +8 more
We present Chandra X-ray imaging of a flux-limited sample of flat spectrum radio-emitting quasars with jet-like structure. X-rays are detected from 59% of 56 jets. No counter-jets were detected. The core spectra are fitted by power-law spectra with a photon index Γ x , whose distribution is consistent with a normal distribution, with a …
Modulation of Galactic Cosmic Rays in the Inner Heliosphere over Solar Cycles
Qin, G.; Shen, Z. -N.
The 11- and 22-year modulation of galactic cosmic rays (GCRs) in the inner heliosphere is studied using a numerical model developed by Qin and Shen in 2017. Based on the numerical solutions of Parker’s transport equations, the model incorporates a modified Parker heliospheric magnetic field, a locally static time-delayed heliosphere, and a time-de…
The HST Large Programme on ω Centauri. III. Absolute Proper Motion
Milone, Antonino P.; Anderson, Jay; van der Marel, Roeland P. +11 more
In this paper, we report a new estimate of the absolute proper motion (PM) of the globular cluster NGC 5139 (ω Cen) as part of the HST large program GO-14118+14662. We analyzed a field 17 arcmin southwest of the center of ω Cen and computed PMs with epoch spans of ∼15.1 years. We employed 45 background galaxies to link our relative PMs to an absol…
The Near-infrared Tip of the Red Giant Branch. I. A Calibration in the Isolated Dwarf Galaxy IC 1613
Madore, Barry F.; Freedman, Wendy L.; Beaton, Rachael L. +8 more
Based on observations from the FourStar near-infrared camera on the 6.5 m Baade-Magellan telescope at Las Campanas, Chile, we present calibrations of the JHK luminosities of stars defining the tip of the red giant branch (TRGB) in the halo of the Local Group dwarf galaxy IC 1613. We employ metallicity-independent (rectified) T-band magnitudes—cons…
The NuSTAR Extragalactic Surveys: X-Ray Spectroscopic Analysis of the Bright Hard-band Selected Sample
Harrison, F. A.; Stern, D.; Alexander, D. M. +23 more
We discuss the spectral analysis of a sample of 63 active galactic nuclei (AGN) detected above a limiting flux of S(8{--}24 {keV})=7× {10}-14 {erg} {{{s}}}-1 {{cm}}-2 in the multi-tiered NuSTAR extragalactic survey program. The sources span a redshift range z=0{--}2.1 (median < z> =0.58). The spectral analysi…
No Surviving Companion in Kepler's Supernova
Damiani, Francesco; Ruiz-Lapuente, Pilar; Galbany, Lluís +5 more
We have surveyed Kepler’s supernova remnant in search of the companion star of the explosion. We have gone as deep as 2.6 L ⊙ in all stars within 20% of the radius of the remnant. We use FLAMES at the VLT-UT2 telescope to obtain high-resolution spectra of the stellar candidates selected from Hubble Space Telescope (HST) images. The resu…