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XMM-Newton and Very Large Array Observations of the Variable Wolf-Rayet Star EZ Canis Majoris: Evidence for a Close Companion?
Skinner, Stephen L.; Zhekov, Svetozar A.; Güdel, Manuel +1 more
We present new X-ray and radio observations of the Wolf-Rayet star EZ CMa (HD 50896) obtained with XMM-Newton and the Very Large Array (VLA). This WN4 star exhibits optical and UV variability at a period of 3.765 days whose cause is unknown. Binarity may be responsible, but the existence of a companion has not been proven. The radio spectral energ…
Coronal Loop Heating by Random Energy Releases
Erdélyi, Robert; Mendoza-Briceño, César A.; Di G. Sigalotti, Leonardo
It was suggested by Parker that the solar corona is heated by numerous small localized events called nanoflares. High-resolution satellites (the Solar and Heliospheric Observatory and Transition Region and Coronal Explorer [TRACE]) have shown a kind of very small scale activity at transition region temperatures (i.e., explosive events, microflares…
Hubble Space Telescope Observations of the Cometary Blue Compact Dwarf Galaxy UGC 4483: A Relatively Young Galaxy?
Thuan, Trinh X.; Izotov, Yuri I.
We present V and I photometry of the resolved stars in the cometary blue compact dwarf galaxy UGC 4483 using Hubble Space Telescope Wide Field Planetary Camera 2 images. The resulting I versus V-I color-magnitude diagram (CMD) reaches limiting magnitudes V=27.5 mag and I=26.5 mag for photometric errors less than 0.2 mag. It reveals not only a youn…
Inversion of the Internal Solar Rotation Rate
Eff-Darwich, A.; Korzennik, S. G.; Jiménez-Reyes, S. J.
Accurate determination of the rotation rate in the inner radiative zone (0.2<r/Rsolar<0.5) of the Sun from helioseismic observations requires rotational frequency splittings of exceptional quality. Indeed, only the very low degree modes are sensitive to the dynamics of the deep interior. Low- and intermediate-degree splittings hav…
The Local Interstellar Ultraviolet Radiation Field
Henry, Richard Conn
I have used the Hipparcos Input Catalogue, together with Kurucz model stellar atmospheres and information on the strength of the interstellar extinction, to create a model of the expected intensity and spectral distribution of the local interstellar ultraviolet radiation field, under various assumptions concerning the albedo a of the interstellar …
Gemini Multi-Object Spectrograph Observations of SCUBA Galaxies behind A851
Ivison, R. J.; Smail, Ian; Morrison, G. E. +3 more
We have identified counterparts to two submillimeter (submm) sources, SMM J09429+4659 and SMM J09431+4700, seen through the core of the z=0.41 cluster A851. We employ deep 1.4 GHz observations and the far-infrared/radio correlation to refine the submm positions and then optical and near-infrared imaging to locate their counterparts. We identify an…
Neon Abundances in the H II Regions of M33
Willner, S. P.; Nelson-Patel, K.
We present neon abundances for 25 H II regions of M33, measured from line profiles of the mid-infrared transitions of [Ne II] and [Ne III] taken with the Infrared Space Observatory Short-Wavelength Spectrometer. The distribution of neon abundances as a function of galactocentric radius is best described as a step, -0.15 dex relative to the solar n…
Embedded Star Formation in the Eagle Nebula
Smith, Bradford A.; Hester, J. Jeff; Thompson, Rodger I.
M16 (=NGC 6611), the Eagle Nebula, is a well-studied region of star formation and the source of a widely recognized Hubble Space Telescope (HST) image. High spatial resolution infrared observations with the Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) on HST reveal the detailed morphology of two embedded star formation regions that …
The Nascent Bipolar Nebula Surrounding the Carbon-rich Variable CIT 6: Transition to Axisymmetry
Hines, Dean C.; Schmidt, Gary D.; Swift, Seth
CIT 6 is a luminous carbon star currently evolving off the asymptotic giant branch into a tiny proto-planetary nebula. The star is surrounded by a thick dust shell that reprocesses much of the photospheric radiation, making it one of the brightest infrared sources in the sky. Spacecraft imaging at optical and near-IR wavelengths demonstrates that …
The Stellar Populations of the Cetus Dwarf Spheroidal Galaxy
Sarajedini, A.; Dolphin, A. E.; Grebel, E. K. +7 more
We present Hubble Space Telescope Wide Field Planetary Camera 2 photometry in the V and I passbands of the recently discovered Local Group dwarf spheroidal galaxy in Cetus. Our color-magnitude diagram extends from above the first-ascent red giant branch (RGB) tip to approximately half a magnitude below the horizontal branch (HB). Given a reddening…