Search Publications
Are Heating Events in the Quiet Solar Corona Small Flares? Multiwavelength Observations of Individual Events
Krucker, Säm; Benz, Arnold O.
Temporary enhancements of the coronal emission measure in a quiet region have been shown to constitute a significant energy input. Here some relatively large events are studied for simultaneous brightenings in transition region lines and in radio emission. Associated emissions are discussed and tested for characteristics known from full-sized impu…
The Black Hole in IC 1459 from Hubble Space Telescope Observations of the Ionized Gas Disk
van der Marel, Roeland P.; de Zeeuw, P. Tim; Carollo, C. Marcella +1 more
The peculiar elliptical galaxy IC 1459 (MV=-21.19, D=16.5 h-1 Mpc) has a fast counterrotating stellar core, stellar shells and ripples, a blue nuclear point source, and strong radio core emission. We present results of a detailed Hubble Space Telescope study of IC 1459, and in particular its central gas disk, aimed at constra…
Two K Giants with Supermeteoritic Lithium Abundances: HDE 233517 and HD 9746
Henry, Gregory W.; Fekel, Francis C.; Uitenbroek, Han +1 more
Two unusual Li-rich K giants, HDE 233517 and HD 9746, have been studied. Optical spectroscopy and photometry have been obtained to determine the fundamental parameters of HDE 233517, a single K2 III with an extremely large infrared excess. The spectra yield Teff=4475 K, logg=2.25, [Fe/H]=-0.37, vsini=17.6 km s-1, and a non-LT…
Hubble Space Telescope imaging and ground-based spectroscopy of old nova shells - I. FH Ser, V533 Her, BT Mon, DK Lac and V476 Cyg
O'Brien, T. J.; Gill, C. D.
In this paper we report on the first five out of eleven observations in our programme of Hubble Space Telescope (HST) imaging of old nova shells. We present new WFPC2 images of the shells around FH Ser and V533 Her taken in the F656N (Hα+[Nii]) filter. We also show long-slit spectra taken using the William Herschel Telescope on La Palma for these …
α Centauri AB
Guenther, D. B.; Demarque, P.
Detailed models of α Centauri A and B based on the Hipparcos, Yale, and Söderhjelm parallaxes are compared. The consequences of the uncertainty in mass, luminosity, surface temperature, and composition on the structure and the p-mode pulsation spectrum of the models are presented. All of the models were constructed using the most current stellar s…
Two Groups of Nearly Coeval Star Clusters in the Small Magellanic Cloud
Fall, S. Michael; Rich, R. Michael; Zurek, David +1 more
We report new photometry and main-sequence turnoff ages for seven populous star clusters in the SMC with MV<-6 and age greater than 1 Gyr, using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope. In contrast to the accepted picture, these clusters appear to have formed in two brief intervals, the oldest 8+/-2 Gyr …
Transformations between the Theoretical and Observational Planes in the Hubble Space Telescope NICMOS and WFPC2 Photometric Systems
Leitherer, Claus; Origlia, Livia
Color-temperature relations and bolometric corrections in the Hubble Space Telescope (HST) Near Infrared Camera and Multi-Object Spectrometer F1110W, F160W, and F222M and the Wide Field Planetary Camera 2 F439W, F555W, and F814W photometric systems, using two different sets of model atmospheres, have been derived. This database of homogeneous, sel…
The Relative Age of the Thin and Thick Galactic Disks
Chaboyer, Brian; Liu, Wilson M.
We determine the relative ages of the open cluster NGC 188 and selected Hipparcos field stars by isochrone fitting and compare them to the age of the thick-disk globular cluster 47 Tuc. The best-fit age for NGC 188 was determined to be 6.5+/-1.0 Gyr. The solar-metallicity Hipparcos field stars yielded a slightly older thin-disk age, 7.5+/-0.7 Gyr.…
The distance to the nearest star-forming clouds: MBM12 and MBM20
Neuhäuser, R.; Alcalá, J. M.; Covino, E. +2 more
We present high-resolution spectra (R ~ 49,000) of stars that have parallax measurements from the Hipparcos satellite and are projected along the line of sight to the two nearest known star forming clouds to the Sun: MBM12 and MBM20. The spectra were obtained with the FOCES Echelle Spectrograph at the 2.2 meter telescope in Calar Alto, Spain and t…
A New Look at Carbon Abundances in Planetary Nebulae. IV. Implications for Stellar Nucleosynthesis
Henry, R. B. C.; Kwitter, K. B.; Bates, J. A.
This paper is the fourth and final report on a project designed to study carbon abundances in a sample of planetary nebulae representing a broad range in progenitor mass and metallicity. We present newly acquired optical spectrophotometric data for three Galactic planetary nebulae, IC 418, NGC 2392, and NGC 3242, and combine them with UV data from…