Search Publications

Rotating Nuclear Rings and Extreme Starbursts in Ultraluminous Galaxies

Downes, D.; Solomon, P. M.

New CO interferometer data show that the molecular gas in infrared ultraluminous galaxies is in rotating nuclear disks or rings. The CO maps yield disk radii, kinematic major axes, rotation speeds, enclosed dynamical masses, and gas masses. The CO brightness temperatures, the double-peaked CO line profiles, the limits on thermal continuum flux fro…

What Powers Ultraluminous IRAS Galaxies?

Lutz, D.; Genzel, R.; Sturm, E. +9 more

We present an ISO SWS and ISOPHOT-S, mid-infrared spectroscopic survey of 15 ultraluminous IRAS galaxies (L_IR >= 10¹² L_⊙). We combine the survey results with a detailed case study, based on arcsecond resolution, near-IR, and millimeter imaging spectroscopy, of one of the sample galaxies (UGC 5101). We compare th…

Are Gamma-Ray Bursts in Star-Forming Regions?

Paczyński, Bohdan

The optical afterglow of the gamma-ray burst GRB 970508 (z=0.835) was a few hundred times more luminous than any supernova. Therefore, the name ``hypernova'' is proposed for the whole GRB/afterglow event.

There is tentative evidence that the GRBs 970228, 970508, and 970828 were close to star-forming regions. If this case is strengthened with …

Helioseismic Studies of Differential Rotation in the Solar Envelope by the Solar Oscillations Investigation Using the Michelson Doppler Imager

Kosovichev, A. G.; Hoeksema, J. T.; Scherrer, P. H. +21 more

The splitting of the frequencies of the global resonant acoustic modes of the Sun by large-scale flows and rotation permits study of the variation of angular velocity Ω with both radius and latitude within the turbulent convection zone and the deeper radiative interior. The nearly uninterrupted Doppler imaging observations, provided by the Solar O…

Supernova Limits on the Cosmic Equation of State

Filippenko, Alexei V.; Riess, Adam G.; Tonry, John +18 more

We use Type Ia supernovae studied by the High-z Supernova Search Team to constrain the properties of an energy component that may have contributed to accelerating the cosmic expansion. We find that for a flat geometry the equation-of-state parameter for the unknown component, α_x = P_x/ρ_x, must be less than -0.55 (95…

Constraints on Cosmological Models from Hubble Space Telescope Observations of High-z Supernovae

Spyromilio, J.; Diercks, A.; Schmidt, B. P. +18 more

We have coordinated Hubble Space Telescope (HST) photometry with ground-based discovery for three supernovae: Type Ia supernovae near z~0.5 (SN 1997ce, SN 1997cj) and a third event at z=0.97 (SN 1997ck). The superb spatial resolution of HST separates each supernova from its host galaxy and leads to good precision in the light curves. We use these …

The Evolution of Early-Type Galaxies in Distant Clusters

Dickinson, Mark; Eisenhardt, Peter R.; Stanford, S. A.

We present results from an optical-infrared photometric study of early-type (E+S0) galaxies in 19 galaxy clusters out to z = 0.9. The galaxy sample is selected on the basis of morphologies determined from Hubble Space Telescope (HST) WFPC2 images and is photometrically defined in the K band in order to minimize redshift-dependent selection biases.…

Star Formation in R136: A Cluster of O3 Stars Revealed by Hubble Space Telescope Spectroscopy

Massey, Philip; Hunter, Deidre A.

The R136 cluster in 30 Doradus is the prototype ``super star cluster,'' and the only example sufficiently close that its massive star content can be studied directly. We have used the Hubble Space Telescope to obtain spectra of 65 of the bluest, most luminous stars in R136 and find that the majority of these stars are of type O3, the hottest, most…

UVCS/SOHO Empirical Determinations of Anisotropic Velocity Distributions in the Solar Corona

Romoli, M.; Raymond, J. C.; Naletto, G. +28 more

We present a self-consistent empirical model for several plasma parameters of a polar coronal hole near solar minimum, derived from observations with the Solar and Heliospheric Observatory Ultraviolet Coronagraph Spectrometer. The model describes the radial distribution of density for electrons, H⁰, and O⁵⁺ and the outflow ve…

Photoevaporation of Disks and Clumps by Nearby Massive Stars: Application to Disk Destruction in the Orion Nebula

Johnstone, Doug; Bally, John; Hollenbach, David

We present a model for the photoevaporation of circumstellar disks or dense clumps of gas by an external source of ultraviolet radiation. Our model includes the thermal and dynamic effects of 6-13.6 eV far-ultraviolet (FUV) photons and Lyman continuum EUV photons incident upon disks or clumps idealized as spheres of radius r_d and enclos…