Search Publications
Constraints on the Hubble constant from observations of the brightest red-giant stars in a Virgo-cluster galaxy
Harris, William E.; Durrell, Patrick R.; Pierce, Michael J. +1 more
The nearest large groups of elliptical galaxies, in the Virgo and Fornax clusters, play a central role in determinations of the Hubble constant, H0, and hence the cosmological rate of expansion. Because the relative distances between these two clusters and more remote clusters are well known, absolute distance determinations to Virgo an…
Discovery of Associated Absorption LInes in an X-Ray Warm Absorber: Hubble Space Telescope Observations of PG 1114+445
Elvis, Martin; Wilkes, Belinda; Mathur, Smitha
The unified picture of X-ray/UV absorbers offers a unique opportunity to probe the nuclear environment of active galactic nuclei. To test the unified absorber scenario and to understand the physical properties of the absorber, we obtained the first UV spectrum of PG 1114+445 using the Hubble Space Telescope (HST) Faint Object Spectrograph. PG 1114…
HST WFPC2/Hα Imagery of the Nebula M1-67: A Clumpy LBV Wind Imprinting Itself on the Nebular Structure?
Moffat, Anthony F. J.; Joncas, Gilles; Grosdidier, Yves +1 more
With the Hubble Space Telescope's Wide Field Planetary Camera 2 we have obtained a deep, Hα image of the relatively young ejection-type nebula M1-67 around the runaway Population I Wolf-Rayet star WR 124 (WN 8). This image shows a wealth of complex detail, some of which have never been seen before in such a nebula. In particular, large arcs of neb…
The Coma Berenices star cluster and its moving group
Soubiran, C.; Odenkirchen, M.; Colin, J.
We report on the analysis of astrometric and photometric data from Hipparcos, Tycho and the ACT catalogue in a 1200 sq. degree field around the nearby open star cluster in Coma Berenices and infer the characteristic features of this cluster. From a sample of 51 kinematic members we derive the cluster's distance, size and spatial structure as well …
High Minor Ion Outflow Speeds in the Inner Corona and Observed Ion Charge States in Interplanetary Space
Esser, Ruth; Brickhouse, Nancy S.; Edgar, Richard J.
Flow speeds recently derived from chromospheric/transition region and coronal observations indicate that the solar wind acceleration process takes place at heights in the solar atmosphere much lower than previously imagined. Doppler-dimming observations of the O VI λ1032 and λ1037 spectral lines show that this is not only true for the background e…
HIPPARCOS photometry of 24 variable massive stars (alpha Cygni variables)
van Leeuwen, F.; van Genderen, A. M.; Zegelaar, I.
The photometric variability of 24 alpha Cyg variables, i.e. variable super-and hypergiants, observed by the Hipparcos satellite is described. Three of the selected stars are situated in the SMC, 12 in the LMC and the remaining 9 in the Galactic plane. Four of them are hot S Dor-type variables, or LBVs (luminous blue variables) and two are possible…
Echoes from an irradiated disc in GRO J1655-40
Horne, Keith; O'Brien, K.; Chen, W. +2 more
We demonstrate correlated rapid variability between the optical/UV and X-ray emission for the first time in a soft X-ray transient, GRO J1655-40: Hubble Space Telescope (HST) light curves show similar features to those seen by the Rossi X-ray Timing Explorer (RXTE), but with mean delay of up to 10-20s. We interpret the correlations as the result o…
Power-Law Decays in the Optical Counterparts of GRB 970228 and GRB 970508
Kouveliotou, C.; van Paradijs, J.; McClintock, J. E. +7 more
We report on RC- and K-band observations of the optical counterpart to GRB 970508 with the Fred Lawrence Whipple Observatory (FLWO) 1.2 m telescope. Eleven RC-band observations were obtained on 1997 May 12, and three on May 14. The counterpart clearly faded between the two nights. On May 12 there was no evidence for variabili…
Origin and production of C(^1D) atoms in cometary comae
Feldman, P. D.; Festou, M. C.; Tozzi, G. P.
The abundance of carbon atoms in the metastable (1) D state near the cometary nucleus provides an important diagnostic of one of the principal sources of carbon in the cometary coma. This quantity may be determined in two independent ways: measurement of (1) D -(1) P fluorescence at 1931 Angstroms and by prompt emission of the (1) D -(3) P doublet…
New study of the quasi-molecular Lyman alpha satellites due to H-H and H-H(+) collisions
Gerbaldi, M.; Allard, N. F.; Kielkopf, J. +2 more
We present new theoretical calculations of the total profile of the atomic hydrogen Lyman alpha spectral line perturbed by collisions with neutral hydrogen atoms and protons. The variation of the radiative dipole moment during the collision is taken into account. This leads to an increase in the amplitude of the main spectral line satellites and t…