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The Physical Basis of Luminosity Classification in the Late A-, F-, and Early G-Type Stars. II. Basic Parameters of Program Stars and the Role of Microturbulence
Gray, R. O.; Graham, P. W.; Hoyt, S. R.
Paper I of this series presented precise MK spectral types for 372 late A-, F-, and early G-type stars with the aim of understanding the nature of luminosity classification on the MK spectral classification system for this range of spectral types. In this paper, a multidimensional downhill simplex technique is introduced to determine the basic par…
The Globular Cluster System in the Outer Regions of NGC 4472
Zepf, Stephen E.; Rhode, Katherine L.
We have undertaken a study of the globular cluster (GC) systems of a large sample of elliptical and spiral galaxies in order to test specific predictions of galaxy formation models. Here we present results for the first elliptical in the study, the giant Virgo cluster galaxy NGC 4472 (M49). The galaxy was observed in three filters (BVR) using the …
Discovery of X-rays from the protostellar outflow object HH2
Maeda, Yoshitomo; Bally, John; Feigelson, Eric D. +3 more
Herbig-Haro (HH) objects have been known for 50 years to be luminous condensations of gas in star-forming regions, but their underlying physical nature is still being elucidated. Previously suggested models encompass newborn stars, stellar winds clashing with nebular material, dense pockets of interstellar gas excited by shocks from outflows, and …
Luminous Compact Galaxies at Intermediate Redshifts: Progenitors of Bulges of Massive Spirals?
Infante, Leopoldo; Hammer, François; Thuan, Trinh X. +2 more
VLT spectra of 14 luminous compact galaxies (LCGs) reveal strong metallic absorption-line systems as well as narrow and intense emission lines. Their gas extinction is found to be large (AV~1.5 mag), leading to an upward revision of their star formation rate (SFR) to an average value of ~40 Msolar yr-1. Large extin…
High-Resolution Near-Infrared Images and Models of the Circumstellar Disk in HH 30
Schneider, Glenn; Rieke, Marcia; Wood, Kenneth +6 more
We present Hubble Space Telescope near-infrared camera and multiobject spectrometer observations of the reflection nebulosity associated with the T Tauri star HH 30. The images show the scattered-light pattern characteristic of a highly inclined, optically thick disk with a prominent dust lane whose width decreases with increasing wavelength. The …
Temporal evolution of the electric field accelerating electrons away from the auroral ionosphere
Balogh, A.; André, M.; Buchert, S. +10 more
The bright night-time aurorae that are visible to the unaided eye are caused by electrons accelerated towards Earth by an upward-pointing electric field. On adjacent geomagnetic field lines the reverse process occurs: a downward-pointing electric field accelerates electrons away from Earth. Such magnetic-field-aligned electric fields in the collis…
NICMOS Observations of High-Redshift Radio Galaxies: Witnessing the Formation of Bright Elliptical Galaxies?
Pentericci, L.; Fosbury, R.; Röttgering, H. J. A. +3 more
We present the results of a near-infrared imaging program of a sample of 19 radio galaxies with redshift between 1.7 and 3.2, using the NICMOS Camera 2 on the Hubble Space Telescope (HST). The galaxies were observed in H band, which, for 18 of the 19 targets, samples the rest-frame optical emission longward of the 4000 Å break. For many sources th…
Prominence fine structures in a magnetic equilibrium: Two-dimensional models with multilevel radiative transfer
Heinzel, P.; Anzer, U.
In this paper we construct theoretical models for vertical prominence threads which are in magnetohydrostatic (MHS) equilibrium. These models are fully two-dimensional (2D) and take the form of vertically infinite threads hanging in a horizontal magnetic field. A typical example of such a 2D magnetic-dip structure is shown for the case when the ce…
Hubble Space Telescope Spectroscopy of V471 Tauri: Oversized K Star, Paradoxical White Dwarf
Bond, Howard E.; Sion, Edward M.; O'Brien, M. Sean
We have used the Goddard High Resolution Spectrograph on board the Hubble Space Telescope to obtain Lyα spectra of the hot white dwarf (WD) component of the short-period eclipsing DA+dK2 precataclysmic binary V471 Tauri, a member of the Hyades star cluster. Radial velocities of the WD were determined from eight post-COSTAR spectra obtained near th…
Observational Constraints on Coronal Heating Models Using Coronal Diagnostics Spectrometer and Soft X-Ray Telescope Data
Schmelz, J. T.; Scopes, R. T.; Cirtain, J. W. +2 more
We have constructed a multithermal differential emission measure distribution for several pixels along a relatively isolated coronal loop on the southwest limb of the solar disk using spectral line data from the Solar and Heliospheric Observatory coronal diagnostics spectrometer (CDS) and broadband data from the Yohkoh soft X-ray telescope. The te…