Search Publications
An Empirical Test of the Mg II λ1240 Doublet Branching Ratio and Oscillator Strength
Sofia, Ulysses J.; Howk, J. Christopher; Fabian, Dirk
We empirically confirm the theoretical branching ratio and oscillator strength for the weak Mg II 3s-4p doublet at 1240 Å as determined by Theodosiou & Federman. We use the independent methods of apparent optical depth analysis for the sight lines toward µ Col, γ Ara, and ρ Leo and profile component fitting for the sight line toward &mic…
Far infrared spectroscopy of FU Ori objects. ISO-LWS observations
Liseau, R.; White, G. J.; Benedettini, M. +12 more
We present the results of the first spectrophotometric observations of a sample of FU Ori objects obtained with the Long Wavelength Spectrometer (LWS) on board the Infrared Space Observatory (ISO). The [OI] (63 mu m) and the [CII] (158 mu m) lines are commonly observed in all spectra (both ON and OFF source). The observational novelty is the prese…
Mechanisms for dynamic coronal mass supply via evaporative solar ``micro-events''
Güdel, M.; Krucker, S.; Benz, A. O. +1 more
The idea that the corona is at least in part supplied by chromospheric evaporation in loop ``micro-events" is quantified in terms of the power requirements of evaporation mechanisms, using recent analyses of data on such events in high temperature EUV lines from the SoHO EIT instrument. Estimates are derived for the pre-event and event values of l…
On Deriving Distances from Cepheids Using the Hubble Space Telescope
Saha, A.; Labhardt, Lukas; Prosser, Charles
In this paper we examine the methodology of obtaining Cepheid-based distances to galaxies from image data obtained with the Wide Field Planetary Camera (WFPC2) on the Hubble Space Telescope. We identify the sources of error and how these propagate to the derived distances for the particular method utilizing the modified DoPHOT program for photomet…
Globular Clusters in the DE,N Galaxy NGC 3115 DW1: New Insights from Spectroscopy and Hubble Space Telescope Photometry
Brodie, Jean P.; Kissler-Patig, Markus; Puzia, Thomas H. +1 more
The properties of globular clusters in dwarf galaxies are key to understanding the formation of globular cluster systems and in particular in verifying scenarios in which globular cluster systems of larger galaxies formed (at least partly) from the accretion of dwarf galaxies. Here, we revisit the globular cluster system of the dE,N galaxy NGC 311…
On the existence of differences in luminosity between horizontal branch stars in globular clusters and in the field
Clementini, G.; Carretta, E.; Gratton, R. G.
The discrepancy between a long distance-scale derived from Hipparcos-based distances to globular clusters via main-sequence fitting to local subdwarfs, and a short distance-scale derived from the absolute magnitude of field RR Lyraes via statistical parallaxes and the Baade-Wesselink method could be accounted for whether an intrinsic difference of…
The ISO spectroscopic view of the HH 24-26 region
White, G. J.; Benedettini, M.; Lorenzetti, D. +6 more
We report the results of an investigation, performed with the ISO spectrometers (LWS and SWS), on the star forming region associated with the Herbig-Haro objects HH 24-25 and 26. Low-resolution LWS spectra (45-197 mu m) were observed towards the HH24MMS, HH25MMS and HH26IR sources as well as the HH26IR outflow. In addition, SWS scans of the pure H…
The Stellar Content of the Halo of NGC 5907 from Deep Hubble Space Telescope NICMOS Imaging
Zepf, Stephen E.; Graham, James R.; Sackett, Penny D. +2 more
We present H-band images obtained with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) of a field 75" (5 kpc) above the plane of the disk of the edge-on spiral galaxy NGC 5907. Ground-based observations have shown that NGC 5907 has a luminous halo with a shallow radial profile between 4 and 8 kpc that roughly traces the dark matter…
Magnetic field gradient and flare: study of a small flare in NOAA 8038
Mathew, Shibu K.; Ambastha, Ashok
Active region NOAA 8038 was observed from 10 to 13 May, 1997 using the USO solar video magnetograph. During this period, the active region was mostly inactive, and gave rise to only a single notable flare of 1N/C1.3 class on May 12, 1997/04:45 UT. The flare occurred in a weak field location, but new emerging fluxes were observed prior to the flare…
Characteristics of quiet Sun cell and network brightenings
Phillips, K. J. H.; Harra, L. K.; Gallagher, P. T.
Extreme ultraviolet observations of the quiet Sun are made with the Coronal Diagnostic Spectrometer (cds) on board the Solar and Heliospheric Observatory (soho). It has been previously noted that frequent transition region brightenings occur in both the bright network and dark cell regions. Analysing 1125 events, we determined the characteristics …