Search Publications
Quasi-periodic Pulsations in a Solar Microwave Burst
Kundu, M. R.; White, S. M.; Grechnev, V. V.
Quasi-periodic pulsations in solar flares can provide important information on physical conditions in flaring regions. In this paper, we study a microwave burst that showed deep quasi-periodic pulsations. The most dramatic feature of this event has been discussed by Asai and coworkers. In the second of four bursts during the flare, strongly modula…
Balmer Lines as Diagnostics of Physical Conditions in Active Galactic Nuclei Broad Emission Line Regions
Popović, L. Č.
Using a well-known method for laboratory plasma diagnostics, the Boltzmann plot, we discuss the physical properties in the broad-line regions (BLRs) of active galactic nuclei (AGNs). We apply the Boltzmann plot method to Balmer lines on a sample of 14 AGNs and find that it may indicate the existence of ``case B'' recombination or partial local the…
Discovery of a Tight Brown Dwarf Companion to theLow-Mass Star LHS 2397a
Close, Laird M.; Siegler, Nick; Freed, Melanie
Using the adaptive optics system, Hokupa`a, at Gemini North, we have directly imaged a companion around the UKIRT faint standard M8 star LHS 2397a (FS 129) at a separation of 2.96 AU. Near-infrared photometry of the companion has shown it to be an L7.5 brown dwarf and confirmed the spectral type of the primary to be M8. We also derive a substellar…
The X-Ray Spectrum of the Seyfert I Galaxy Markarian 766: Dusty Warm Absorber or Relativistic Emission Lines?
Maraschi, L.; Behar, E.; Page, M. J. +10 more
Competing models for broad spectral features in the soft X-ray spectrum of the Seyfert I galaxy Mrk 766 are tested against data from a 130 ks XMM-Newton observation. A model including relativistically broadened Lyα emission lines of O VIII, N VII, and C VI is a better fit to 0.3-2 keV XMM RGS data than a dusty warm absorber. Moreover, the measured…
Soft X-Ray Excess Emission in Clusters of Galaxies Observed with XMM-Newton
Bonamente, M.; Lumb, D.; Nevalainen, J. +1 more
We present results on the spectroscopic analysis of XMM-Newton EPIC data of the central 0.5 h-150 Mpc regions of the clusters of galaxies Coma, A1795, and A3112. The temperature of the hot intracluster gas as determined by modeling the 2-7 keV PN and MOS data is consistent with that inferred from the Fe XXV/Fe XXVI line ratio…
Space Telescope Imaging Spectrograph Survey of Far-Ultraviolet Coronal Forbidden Lines in Late-Type Stars
Ayres, Thomas R.; Redfield, Seth; Harper, Graham M. +4 more
We describe an extensive search with the Space Telescope Imaging Spectrograph (STIS) for ultraviolet coronal (T>106 K) forbidden lines in a sample of 29 F-M dwarfs, giants, and supergiants. Measuring coronal lines in the 1150-1700 Å band with STIS has important advantages of superior velocity resolution and an absolute wavelength cal…
The Physical Parameters, Excitation, and Chemistry of the Rim, Jets, and Knots of the Planetary Nebula NGC 7009
Corradi, Romano L. M.; Gonçalves, Denise R.; Mampaso, Antonio +1 more
We present long-slit optical spectra along the major axis of the planetary nebula NGC 7009. These data allow us to discuss the physical, excitation, and chemical properties of all the morphological components of the nebula, including its remarkable systems of knots and jets. The main results of this analysis are the following: (1) the electron tem…
A SCUBA Galaxy in the Protocluster around 53W002 at z=2.4
Ivison, R. J.; Smail, Ian; Motohara, K. +4 more
We analyze an 850 µm Submillimetre Common-User Bolometer Array (SCUBA) map of the environment of the z=2.39 radio galaxy 53W002, which has been shown to reside in an overdensity of Lyα-detected galaxies. We identify four luminous submillimeter sources within a 2.3‧ (1.2 Mpc at z=2.39) diameter area around the radio galaxy (which itself is a …
Searching for z~=6 Objects with the Hubble Space Telescope Advanced Camera for Surveys: Preliminary Analysis of a Deep Parallel Field
Yan, Haojing; Windhorst, Rogier A.; Cohen, Seth H.
Recent results suggest that z~=6 marks the end of the reionization era. A large sample of objects at z~=6, therefore, will be of enormous importance, as it will enable us to observationally determine the exact epoch of the reionization and the sources that are responsible for it. With the Hubble Space Telescope Advanced Camera for Surveys (ACS) co…
Emission-Line Galaxies in the STIS Parallel Survey. II. Star Formation Density
Gardner, Jonathan P.; Teplitz, Harry I.; Rhodes, Jason +2 more
We present the luminosity function of [O II]-emitting galaxies at a median redshift of z=0.9, as measured in the deep spectroscopic data in the STIS Parallel Survey (SPS). The luminosity function shows strong evolution from the local value, as expected. By using random lines of sight, the SPS measurement complements previous deep single-field stud…