Search Publications
Hubble Space Telescope Imagery and Canada-France-Hawaii Telescope Fabry-Perot Two-dimensional Spectroscopy in Hα of the Ejected Nebula M1-67: Turbulent Status
Moffat, Anthony F. J.; Joncas, Gilles; Grosdidier, Yves +2 more
Bright circumstellar nebulae around massive stars are potentially useful to derive time-dependent mass-loss rates and hence constrain the evolution of the central stars. A key case in this context is the relatively young ejection-type nebula M1-67 around the runaway Population I Wolf-Rayet star WR 124 (=209 BAC), which exhibits a WN 8 spectrum. Wi…
Multiwavelength Studies of Hercules X-1 during Short High and Anomalous Low States: On-again, Off-again
McCray, R.; O'Brien, K.; Boroson, B. +4 more
We present results from multiwavelength observations of the Hercules X-1 system during a short high state (SHS) and during an anomalous low state (ALS). The magnitude of deviation from spin-up appears to be positively correlated with duration of the ALS. Such a correlation is consistent with an interpretation of the ALS in terms of a change in mas…
The Metal-rich Globular Cluster NGC 6553: Observations with WFPC2, STIS, and NICMOS
Tanvir, Nial; Gilmore, Gerard; Santiago, Basilio +4 more
We present a Hubble Space Telescope study of the metal-rich globular cluster NGC 6553 using WFPC2, NICMOS, and STIS. Our primary motivation is to calibrate the STIS broadband LP magnitude against V555 and I814 magnitudes for stars of known metallicity and absolute (visual) magnitude, for application to our study of LMC globul…
HST observations of the LMC compact \ion{H}{ II} region N 11A
Schaerer, D.; Heydari-Malayeri, M.; Charmandaris, V. +3 more
We present a study of the LMC compact H ii region N 11A using Hubble Space Telescope imaging observations which resolve N 11A and reveal its unknown nebular and stellar features. The presence of a sharp ionization front extending over more than 4'' (1 pc) and fine structure filaments as well as larger loops indicate an environment typical of massi…
A Mid-Infrared Spectral Survey of Galactic Wolf-Rayet Stars
Houck, J. R.; Smith, J. D. T.
We present 8-13 µm spectra at resolution R~600 of 29 northern Galactic Wolf-Rayet stars, including the first ever reported mid-infrared (MIR) spectrum for many. Among the subtypes of the stars studied were 14 WC, 13 WN, 1 WN/WC, and an additional reclassified WN. Lines of He I and He II, along with fine-structure lines of Ne II and S IV, are…
Near-Infrared Photometry of Globular Clusters NGC 6287 and NGC 6341 (M92): The Formation of the Galactic Halo
Stetson, Peter B.; Lee, Jae-Woo; Carney, Bruce W. +1 more
We present Hubble Space Telescope (HST) Near Infrared Camera and Multi-Object Spectrometer (NICMOS) camera 3 photometry of the inner halo globular cluster NGC 6287 and the intermediate halo globular cluster NGC 6341 (M92). Our photometric measurements range from the lower red giant branch to ~3 mag below the main-sequence turnoff, allowing us to d…
Modelling of explosive events in the solar transition region in a 2D environment. II. Various MHD experiments
Doyle, J. G.; Erdélyi, R.; Galsgaard, K. +1 more
We examine the response of various physical environments representing the solar atmosphere to a magnetic reconnection event. The reconnection is driven by a localized increase of the magnetic diffusivity in the current concentration formed between two magnetic fluxes of opposite polarity. The time dependent evolution is then followed by numericall…
On the wavelength drift of spectral features from structured hot star winds
Hamann, W. -R.; Oskinova, L. M.; Brown, J. C. +1 more
Spectral lines formed in stellar winds from OB stars are observed to exhibit profile variations. Discrete Absorption Components (DACs) show a remarkably slow wavelength drift with time. In a straightforward interpretation, this is in sharp contradiction to the steep velocity law predicted by the radiation-driven wind theory, and by semi-empirical …
Optical Identification of the X-Ray Burster in the Globular Cluster NGC 1851
Anderson, Scott F.; Margon, Bruce; Deutsch, Eric W. +2 more
We have obtained exposures of the field of X0512-401 in the globular cluster NGC 1851, in X-rays with the Chandra X-Ray Observatory, and in the far-UV with the Hubble Space Telescope. We derive an accurate new X-ray position (within ~1") for X0512-401, which enables us to confirm that the only plausible candidate for the optical/UV counterpart is …
Search for Evidence of Alpha-Particle Beams during a Solar Flare Observed by the Coronal Diagnostic Spectrometer aboard the Solar and Heliospheric Observatory
Brosius, Jeffrey W.
We observed NOAA Active Region 9090 (N13°, W39°) with the Coronal Diagnostic Spectrometer (CDS) and the Extreme-Ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory spacecraft between 18:17 and 21:09 UT on 2000 July 24 to search for evidence of alpha-particle beams during solar flares. Theoretically, an alpha-particle …