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Supernova 1954J (Variable 12) in NGC 2403 Unmasked
Van Dyk, Schuyler D.; Filippenko, Alexei V.; Challis, Peter M. +2 more
We have confirmed that the precursor star of the unusual supernova 1954J (also known as Variable 12) in NGC 2403 survived what appears to have been a superoutburst, similar to the 1843 Great Eruption of η Carinae in the Galaxy. The apparent survivor has changed little in brightness and color over the last 8 years, and a Keck spectrum reveals chara…
Homogeneous Photometry. V. The Globular Cluster NGC 4147
Catelan, M.; Stetson, Peter B.; Smith, Horace A.
New BVRI broadband photometry and astrometry are presented for the globular cluster NGC 4147, based upon measurements derived from 524 ground-based CCD images mostly either donated by colleagues or retrieved from public archives. We have also reanalyzed five exposures of the cluster obtained with WFPC2 on the Hubble Space Telescope in the F439W an…
A Cross-Calibration between Tycho-2 Photometry and Hubble Space Telescope Spectrophotometry
Maíz-Apellániz, J.
By analyzing a well-calibrated sample of 256 stars observed with both Hipparcos and HST, I show that Tycho-2 photometry and HST spectrophotometry are accurate and stable enough to obtain a precise cross-calibration. Based on this analysis, I obtain the following photometric zero points with respect to Vega for Tycho-2: 0.020+/-0.001 (BT…
Faint BVRI Photometric Sequences in Selected Fields
Saha, A.; Dolphin, A. E.; Thim, F. +1 more
The results from work done to extend the Johnson-Cousins BVRI photometric standard sequence to faint levels of V~21 mag in compact fields is presented. Such calibration and extension of sequences is necessary to fill a calibration gap if reliable photometry from modest aperture telescopes in space (e.g., the Hubble Space Telescope) or terrestrial …
A Revised Geometry for the Magnetic Wind of θ1 Orionis C
Smith, Myron A.; Fullerton, Alex W.
The star θ1 Orionis C (O6-7 V) is often cited as a hot analog of Bp variables, because its optical and UV line and X-ray continuum fluxes modulate over the magnetic/rotational period. In this circumstance, one expects emission and absorption components of the UV resonance lines to vary as a flattened magnetosphere corotates with the sta…
Filaments as Possible Signatures of Magnetic Field Structure in Planetary Nebulae
Huggins, P. J.; Manley, S. P.
We draw attention to the extreme filamentary structures seen in high-resolution optical images of certain planetary nebulae. We determine the physical properties of the filaments in the nebulae IC 418, NGC 3132, and NGC 6537, and based on their large length-to-width ratios, longitudinal coherence, and morphology, we suggest that they may be signat…
Theoretical Isochrones with Extinction in the K Band
Lee, Myung Gyoon; Figer, Donald F.; Kim, Sungsoo S. +1 more
We calculate theoretical isochrones in a consistent way for five filters (K, K', Ks, F205W, and F222M) in the atmospheric window between 1.9 and 2.5 µm using the Padova stellar evolutionary models by Girardi et al. Even when displayed in the same Vega magnitude system, the near-infrared colors of the same isochrone can …
Lifting the Iron Curtain: Toward an Understanding of the Iron Stars XX Oph and AS 325
Howell, Steve B.; Cool, Richard J.; Peña, Maria +2 more
We present new optical, near-infrared, and archival ultraviolet observations of XX Ophiuchi and AS 325, two proposed ``iron'' stars. These unusual stars have optical spectra dominated by emission lines arising from hydrogen, as well as ionized metals such as iron, chromium, and titanium. Both stars have been classified as ``iron'' stars, and a num…
Magnetic White Dwarfs in the Two Micron All Sky Survey: A Search for Candidate Binary Systems
Hoard, D. W.; Wachter, Stefanie; Howell, S. B. +2 more
Our understanding of the formation and evolution of magnetic cataclysmic variables from initially detached, post-common-envelope binary stars containing a magnetic white dwarf and a main-sequence star is currently poorly constrained, due to the lack of observational identification of the progenitor systems. Very few potential pre-cataclysmic varia…
Characterizing the Adaptive Optics Off-Axis Point-Spread Function. II. Methods for Use in Laser Guide Star Observations
Faber, S. M.; Gates, E. L.; Macintosh, B. A. +2 more
Most current astronomical adaptive optics (AO) systems rely on the availability of a bright star to measure the distortion of the incoming wave front. Replacing the guide star with an artificial laser beacon alleviates this dependency on bright stars and therefore increases sky coverage, but it does not eliminate another serious problem for AO obs…