Search Publications
Prominence Eruptions and Coronal Mass Ejection: A Statistical Study Using Microwave Observations
Howard, R. A.; Gopalswamy, N.; Shibasaki, K. +3 more
We present the results of a statistical study of a large number of solar prominence events (PEs) observed by the Nobeyama Radioheliograph. We studied the association rate, relative timing, and spatial correspondence between PEs and coronal mass ejections (CMEs). We classified the PEs as radial and transverse, depending on whether the prominence mo…
Evidence for the Formation of a Large-Scale Current Sheet in a Solar Flare
Holman, Gordon D.; Sui, Linhui
We present X-ray evidence for the formation of a large-scale current sheet in a flare observed by the Ramaty High-Energy Solar Spectroscopic Imager on 2002 April 15. The flare occurred on the northwest limb, showing a cusp-shaped flare loop in the rise phase. When the impulsive rise in hard X-rays (>25 keV) began, the cusp part of the coronal s…
Detection of Nine M8.0-L0.5 Binaries: The Very Low Mass Binary Population and Its Implications for Brown Dwarf and Very Low Mass Star Formation
Close, Laird M.; Biller, Beth; Siegler, Nick +1 more
Use of the highly sensitive Hokupa'a/Gemini curvature wave front sensor has allowed direct adaptive optics (AO) guiding on very low mass (VLM) stars with SpT = M8.0-L0.5. A survey of 39 such objects detected nine VLM binaries (seven of which were discovered for the first time to be binaries). Most of these systems are tight (separation <5 AU) a…
Accretion onto the Supermassive Black Hole in M87
Fabian, Andrew C.; Allen, Steven W.; Wilson, Andrew S. +2 more
Chandra X-ray observations of the giant elliptical galaxy M87 resolve the thermal state of the hot interstellar medium into the accretion (Bondi) radius of its central 3×109Msolar black hole. We measure the X-ray gas temperature and density profiles and calculate the Bondi accretion rate, MBondi~0.1Msolar
X-Ray Spectroscopic Evidence for Intermediate-Mass Black Holes: Cool Accretion Disks in Two Ultraluminous X-Ray Sources
Fabian, A. C.; Miller, J. M.; Fabbiano, G. +1 more
We have analyzed an XMM-Newton observation of the nearby spiral galaxy NGC 1313, which contains two ``ultraluminous'' X-ray (ULX) sources. We measure isotropic luminosities of LX=2.0×1040 ergs s-1 and LX=6.6×1039 ergs s-1 for NGC 1313 X-1 and X-2 (0.2-10.0 keV, assuming a distance o…
A 3×109 Msolar Black Hole in the Quasar SDSS J1148+5251 at z=6.41
Willott, Chris J.; Jarvis, Matt J.; McLure, Ross J.
We present near-infrared H- and K-band spectra of the z=6.41 quasar SDSS J114816.64+525150.3. The spectrum reveals a broad Mg II λ2799 emission line with an FWHM of 6000 km s-1. From the peak wavelength of this emission line, we obtain a more accurate redshift than is possible from the published optical spectrum and determine a redshift…
A Massive X-Ray Outflow from the Quasar PDS 456
O'Brien, P. T.; Reeves, J. N.; Ward, M. J.
We report on XMM-Newton spectroscopic observations of the luminous radio-quiet quasar PDS 456. The hard X-ray spectrum of PDS 456 shows a deep absorption trough (constituting 50% of the continuum) at energies above 7 keV in the quasar rest frame, which can be attributed to a series of blueshifted K-shell absorption edges due to highly ionized iron…
Quantitative Spectroscopy of O Stars at Low Metallicity: O Dwarfs in NGC 346
Bouret, J. -C.; Hillier, D. J.; Lennon, D. J. +5 more
We present the results of a detailed analysis of the properties of dwarf O-type stars in a metal-poor environment. High-resolution, high-quality ultraviolet and optical spectra of six O-type stars in the H II region NGC 346 have been obtained from a spectroscopic survey of O stars in the SMC. Stellar parameters and chemical abundances have been de…
X-Ray Fluctuation Power Spectral Densities of Seyfert 1 Galaxies
McHardy, I.; Nandra, K.; Vaughan, S. +11 more
By combining complementary monitoring observations spanning long, medium, and short timescales, we have constructed power spectral densities (PSDs) of six Seyfert 1 galaxies. These PSDs span >~4 orders of magnitude in temporal frequency, sampling variations on timescales ranging from tens of minutes to over a year. In at least four cases, the P…
A Planetary Companion to γ Cephei A
Cochran, William D.; Endl, Michael; Hatzes, Artie P. +5 more
We report on the detection of a planetary companion in orbit around the primary star of the binary system γ Cephei. High-precision radial velocity measurements using four independent data sets spanning the time interval 1981-2002 reveal long-lived residual radial velocity variations superposed on the binary orbit that are coherent in phase and amp…