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Comparison between Predicted and Empirical ΔVbumpHB in Galactic Globular Clusters
Salaris, M.; Zoccali, M.; Bono, G. +2 more
We present observational estimates of ΔVbumpHB in a sample of 28 galactic globular clusters (GGCs) observed by the Hubble Space Telescope. The photometric accuracy and the sizable number of stars measured in each cluster allowed us to single out the red giant branch bump both in metal-poor and in metal-rich GGCs. Empirical va…
Detection of the Red Giant Branch Stars in M82 Using the Hubble Space Telescope
Madore, Barry F.; Sakai, Shoko
We present color-magnitude diagrams and luminosity functions of stars in two halo regions of the irregular galaxy in M82, based on F555W and F814W photometry taken with the Hubble Space Telescope (HST) and Wide Field Planetary Camera 2. The I-band luminosity function shows a sudden jump at I~23.95 mag, which is identified as the tip of the red gia…
Calibration of the Thickness of the Solar Tachocline
Gough, D. O.; Elliott, J. R.
Material circulation in the solar tachocline mixes the tachocline material with the convection zone, which causes the sound speed in and immediately beneath the tachocline to exceed what one would expect from current standard solar models. Calibration against a helioseismic determination of the sound speed from SOI/MDI data of a sequence of solar …
Hubble Space Telescope Fine Guidance Sensor Astrometric Parallaxesfor Three Dwarf Novae: SS Aurigae, SS Cygni, and U Geminorum
Harrison, Thomas E.; Benedict, G. F.; Szkody, Paula +4 more
We report astrometric parallaxes for three well-known dwarf novae obtained using the Fine Guidance Sensors on the Hubble Space Telescope (HST). We found a parallax for SS Aurigae of π=5.00+/-0.64 mas, for SS Cygni we found π=6.02+/-0.46 mas, and for U Geminorum we obtained π=10.37+/-0.50 mas. These represent the first true trigonometric parallaxes…
Infrared Spectroscopy of NGC 4151: Probing the Obscured Ionizing Active Galactic Nucleus Continuum
Lutz, Dieter; Netzer, Hagai; Alexander, Tal +3 more
The Infrared Space Observatory (ISO) Short-Wavelength Spectrometer4 (SWS) infrared spectroscopic observations of the nucleus of Seyfert galaxy NGC 4151, which are described in a companion paper, are used in conjunction with a compilation of UV to IR narrow emission line data to determine the spectral shape of the obscured extreme-UV continuum that…
The Host Galaxy of GRB 990123
Piro, L.; Frontera, F.; Harrison, F. A. +20 more
We present deep images of the field of GRB 990123 obtained in a broadband UV/visible bandpass with the Hubble Space Telescope (HST) and deep near-infrared images obtained with the Keck I 10 m telescope. The HST image reveals that the optical transient (OT) is offset by 0.67" (5.8 kpc in projection) from an extended, apparently interacting galaxy. …
Faint, Moving Objects in the Hubble Deep Field: Components of the Dark Halo?
Ibata, Rodrigo A.; Gilliland, Ronald L.; Richer, Harvey B. +1 more
The deepest optical image of the sky, the Hubble Deep Field, obtained with the Hubble Space Telescope in 1995 December, has been compared to a similar image taken in 1997 December. Two very faint, blue, isolated, and unresolved objects are found to display a substantial apparent proper motion, 23+/-5 and 26+/-5 mas yr-1 a further three …
Filament Eruptions near Emerging Bipoles
Sheeley, N. R., Jr.; Wang, Y. -M.
It has been suggested in previous studies that quiescent prominences and filaments erupt preferentially in the vicinity of emerging magnetic flux. We describe three such filament eruptions observed during 1998 with the Extreme-ultraviolet Imaging Telescope on the Solar and Heliospheric Observatory. Comparison with magnetograms and with potential f…
The Interaction of New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23
Kosovichev, A. G.; Benevolenskaya, E. E.; Hoeksema, J. T. +1 more
The 11 yr cycle of solar activity follows Hale's law by reversing the magnetic polarity of leading and following sunspots in bipolar regions during the minima of activity. In the 1996-1997 solar minimum, most solar activity emerged in narrow longitudinal zones--``active longitudes'' but over a range in latitude. Investigating the distribution of s…
Hubble Space Telescope Observations of the Oldest Star Clusters in the Large Magellanic Cloud
Somerville, Rachel S.; Stetson, Peter B.; Bolte, Michael +2 more
We present V, V-I color-magnitude diagrams (CMDs) for three old star clusters in the Large Magellanic Cloud (LMC): NGC 1466, NGC 2257, and Hodge 11. Our data extend ~3 mag below the main-sequence turnoff, allowing us to determine accurate relative ages and the blue straggler frequencies. Based on a differential comparison of the CMDs, any age diff…