Search Publications
Cloning Hubble Deep Fields. II. Models for Evolution by Bright Galaxy Image Transformation
Broadhurst, Tom; Bouwens, Rychard; Silk, Joseph
In a companion paper, we outlined a methodology for generating parameter-free, model-independent ``no-evolution'' fields of faint galaxy images, demonstrating the need for significant evolution in the Hubble Deep Field (HDF) at faint magnitudes. Here we incorporate evolution into our procedure, by transforming the input bright galaxy images with r…
The Physical Characteristics of the Small-Scale Interstellar Structure toward µ Crucis
Meyer, David M.; Blades, J. C.; Lauroesch, J. T. +1 more
We present Hubble Space Telescope Goddard High Resolution Spectrograph echelle observations of multiple interstellar lines of C I, Mg I, Cr II, and Zn II toward both stars in the µ Crucis binary system. Despite large differences in the profiles of the neutral species, no significant variations between the stars are seen in the Cr II and Zn I…
Pulsation in lambda Bootis stars
Strassmeier, K. G.; Handler, G.; Garrido, R. +7 more
In this paper we present a further step in applying asteroseismic techniques to the group of lambda Bootis stars which can be characterized as nonmagnetic A to F-type Population I dwarfs with significant (surface) underabundances of Fe-peak elements. Since no conclusive theory explaining the origin of the observed abundance anomalies exists, an ex…
Hubble Space Telescope Imaging of the Mass-losing Supergiant VY Canis Majoris
Kastner, Joel H.; Weintraub, David A.
The highly luminous M supergiant VY CMa is a massive star that appears to be in its final death throes, losing mass at high rate en route to exploding as a supernova. Subarcsecond-resolution optical images of VY CMa, obtained with the Faint Object Camera (FOC) aboard the Hubble Space Telescope, vividly demonstrate that mass loss from VY CMa is hig…
Ultraviolet Spectroscopy of the Quasar Pair LB 9605, LB 9612 with the Hubble Space Telescope: Evolution in the Size of the Lyα Absorbers?
Weymann, Ray J.; Foltz, Craig B.; Impey, Chris D. +1 more
Ultraviolet spectroscopy has been obtained with the faint object spectrograph of the Hubble Space Telescope in the Lyα forest of the quasar pair, LB 9605 (zem = 1.834) and LB 9612 (zem = 1.898), in order to measure the size of the Lyα absorbers. The quasars are separated by 1.65 arcmin on the sky corresponding to a proper sep…
On the determination of absolute magnitude zero-points from HIPPARCOS parallaxes
Koen, Chris; Laney, Dave
The period-luminosity (PL) relation zero-point determination from Hipparcos trigonometric parallaxes of Cepheids is contentious. It is shown that the method used by Feast & Catchpole is equivalent to a standard minimization of sum of squares, and that it is free of Lutz-Kelker bias. The same technique is applied to RR Lyrae and field HB star d…
Evolution of Population II stars
Caputo, Filippina
The current knowledge of the evolution of Population II stars, as observed in galactic halos and globular clusters, is outlined. The recent theoretical results provided by an improved physical understanding of the stars are reported, with a particular emphasis upon those stellar evolutionary phases which are the keystones of the interpretation of …
Globular Cluster Photometry with the Hubble Space Telescope. VII. Color Gradients and Blue Stragglers in the Central Region of M30 from Wide Field Planetary Camera 2 Observations
Schneider, Donald P.; Yanny, Brian; Bahcall, John N. +2 more
We present F555W (V), F439W (B), and F336W (U) photometry of 9507 stars in the central 2' of the dense, post-core-collapse cluster M30 (NGC 7099) derived from Hubble Space Telescope Wide Field Planetary Camera 2 images. These data are used to study the mix of stellar populations in the central region of the cluster. Forty-eight blue straggler star…
Comparison of Prominences in Hα and He II 304 Å
Wang, Haimin; Chae, Jongchul; Gurman, Joseph B. +1 more
In this letter, we bring attention to prominences which show different morphology in Hα and He ii 304 Å, as observed simultaneously by BBSO and EIT on board SOHO. Those two lines have been thought to represent similar chromospheric structures although they are formed at significantly different temperatures. We give two examples representing two ki…
Evidence for multiple ejecta: April 7-11, 1997, ISTP Sun-Earth connection event
Reiner, M.; Delaboudinière, J. -P.; Bougeret, J. -L. +12 more
Evidence is presented that the enhanced geomagnetic activity, on April 10-11, 1997, was caused by one of two ejecta that left the Sun at ≈ 14 UT on April 7. This ejecta was not directly detected at the Earth. The evidence for this interpretation is based on WIND spacecraft observations in the solar wind (SW). It is consistent with: (i) measured ve…