Search Publications

Lithium Abundance in Solar-type Stars with Low Chromospheric Activity: Application to the Search for Maunder Minimum Analogs

Tytler, David; Lubin, Dan; Kirkman, David

We use measurements of lithium abundance to examine the evolutionary history of stars frequently believed to be in a Maunder minimum (MM) state due to their low chromospheric activity. In a sample whose main-sequence membership has been verified using Hipparcos parallax data, we find that stars with very low chromospheric activity log R'_HK

The Extended X-ray Nebula of PSR J1420-6048

Romani, Roger W.; Van Etten, Adam

The vicinity of the unidentified EGRET source 3EG J1420-6038 has undergone extensive study in the search for counterparts, revealing the energetic young pulsar PSR J1420-6048 and its surrounding wind nebula as a likely candidate for at least part of the emission from this bright and extended gamma-ray source. We report on new Suzaku observations o…

The Galaxy Alignment Effect in Abell 1689: Evolution, Radial, and Luminosity Dependence

De Propris, Roberto; Bañados, Eduardo; West, Michael J. +1 more

We measure alignments on scales of 1 Mpc h ^-1 ₇₁ for galaxies in Abell 1689 (z = 0.18) from an existing Hubble Space Telescope mosaic. We find evidence of galaxy alignment in the inner 500 h ^-1 ₇₁ kpc. The alignment appears to be stronger toward the center and is mostly present among the fainter galaxies…

Occultation of the Quiescent Emission from Sgr A* by IR Flares

Dowell, C. D.; Yusef-Zadeh, F.; Wardle, M. +2 more

We have investigated the nature of flare emission from Sgr A* during multi-wavelength observations of this source that took place in 2004, 2005, and 2006. We present evidence for dimming of submillimeter and radio flux during the peak of near-IR flares. This suggests that the variability of Sgr A* across its wavelength spectrum is phenomenological…

Differential Proper-motion Study of the Circumstellar Dust Shell of the Enigmatic Object, HD 179821

Ueta, Toshiya; Ferguson, Brian A.

HD 179821 is an enigmatic evolved star that possesses characteristics of both a post-asymptotic giant branch (post-AGB) star and a yellow hypergiant, and there has been no evidence that unambiguously defines its nature. These two hypotheses are products of an indeterminate distance, presumed to be 1 kpc or 6 kpc. We have obtained the two-epoch Hub…

New Fe VIII Line Identifications using Observations of the Quiet Sun

Young, P. R.; Landi, E.

In this work, we study Fe VIII lines emitted in the 1000-1200 Å wavelength range that originate from levels that also emit transitions observed in the 190-200 Å wavelength range. The intensity ratios between such lines depend on atomic physics parameters only and not on the physical parameters of the emitting plasma: they are excellent tools to ve…

Suzaku Observations of the Galactic Center Microquasar 1E 1740.7-2942

Miller, Jon M.; Reynolds, Mark T.

We present two Suzaku observations of the Galactic center microquasar 1E 1740.7-2942 separated by approximately 700 days. The source was observed on both occasions after a transition to the spectrally hard state. Significant emission from 1E 1740.7-2942 is detected out to an energy of 300 keV, with no spectral break or turnover evident in the data…

On the Estimate of Magnetic Non-potentiality of Sunspots Derived Using Hinode SOT/SP Observations: Effect of Polarimetric Noise

Gosain, Sanjay; Tiwari, Sanjiv Kumar; Venkatakrishnan, P.

The accuracy of Milne-Eddington (ME) inversions, used to retrieve the magnetic field vector, depends upon the signal-to-noise ratio (S/N) of the spectro-polarimetric observations. The S/N in real observations varies from pixel to pixel; therefore the accuracy of the field vector also varies over the map. The aim of this work is to study the effect…

SN 2010U: A Luminous Nova in NGC 4214

Humphreys, Roberta M.; Stanek, K. Z.; Kochanek, Christopher S. +12 more

The luminosity, light curve, post-maximum spectrum, and lack of a progenitor on deep pre-outburst images suggest that SN 2010U was a luminous, fast nova. Its outburst magnitude is consistent with that for a fast nova using the maximum magnitude-rate of decline relationship for classical novae.

Some of the data presented in this Letter were ob…

X-ray Observation of AM Herculis in a Very Low State with Suzaku

Mukai, K.; Bamba, A.; Terada, Y. +3 more

The X-ray observation of AM Herculis (AM Her) in a very low state was performed with Suzaku in 2008 October. One flare event with a timescale of ~3700 s was detected at the X-ray luminosity of 6.0 × 10²⁹ erg s^-1 in the 0.5-10 keV band at the assumed distance of 91 pc. The X-ray spectrum is represented by a thermal plasma emis…