Search Publications
Revision and Calibration of MK Luminosity Classes for Cool Giants by HIPPARCOS Parallaxes
Keenan, Philip C.; Barnbaum, Cecilia
The Hipparcos parallaxes of cool giants are utilized in two ways in this paper. First, a plot of reduced parallaxes of stars brighter than 6.5, as a function of spectral type, for the first time separates members of the clump from stars in the main giant ridge. A slight modification of the MK luminosity standards has been made so that luminosity c…
Statistical parallaxes and kinematical parameters of classical Cepheids and young star clusters
Dambis, A. K.; Rastorguev, A. S.; Glushkova, E. V. +1 more
The statistical-parallax method is applied for the first time to space velocities of 270 classical Cepheids with proper motions adopted from HIPPARCOS (1997) and TRC (Hog et al. 1998) catalogs and distances based on the period-luminosity relation by Berdnikov et al. (1996). The distance scale of short-period Cepheids (with periods less than 9 days…
Circumstellar matter around M-giants in symbiotic binaries: SY MUSCAE and RW Hydrae
Schmutz, W.; Nussbaumer, H.; Schild, H. +1 more
For the eclipsing symbiotic binary system SY Mus we present evidence for an asymmetric density distribution around the M-giant. We obtain this result from an improved orbital solution. We determine a revised orbital period of P=625.0+/- 0.5 d from UV eclipse observations and a re-analysis of the visual light curve. Based on new radial velocity obs…
Spectroscopic, photometric, and polarimetric study of the Herbig AE candidate HD 36112
Miroshnichenko, A. S.; Savanov, I. S.; Pogodin, M. A. +6 more
We describe observations of the Herbig Ae candidate HD 36112 including high-resolution spectroscopy of photospheric and circumstellar lines, multi-colour photometry and polarimetry. These observations reveal that many features of the observational appearance of HD 36112 are similar to those of `classical' Herbig Ae stars. Among these are: the far …
On the formation of it warm molecular layers
Woitke, P.; Helling, Ch.; Winters, J. M. +1 more
The levitation of the outer atmospheres of AGB stars by pulsations is proposed as possible mechanism to form ``warm molecular layers''. We compare the amounts of CO, H_2O, CO_2 and SO_2 molecules found in an oxygen-rich dynamical model atmosphere with the values derived from recent ISO observations. In the model, the molecules are present in a lay…
Microwave and Extreme Ultraviolet Observations of Solar Polar Regions
Nindos, A.; Kundu, M. R.; White, S. M. +3 more
The poles of the Sun are brighter than the rest of the quiet Sun's emission in a limited range of radio frequencies from 17 GHz to 87 GHz. We have studied microwave images of the quiet Sun made with the Nobeyama radioheliograph at 17 GHz. They show that the so-called polar-cap brightening consists of two components: a diffuse component of 1500 K e…
The Radial and Angular Variation of the Electron Density in the Solar Corona
Mathioudakis, M.; Keenan, F. P.; Phillips, K. J. H. +2 more
We derive, for the first time, electron densities as a function of both radius (R) and position angle (θ) for the southwest quadrant of the off-limb corona, using the density-sensitive Si IX λ349.9/λ341.9 and Si X λ356.0/λ347.7 extreme-ultraviolet line ratios. The observations were made with the coronal diagnostic spectrometer on board the Solar a…
New insight into transition region dynamics via SUMER observations and numerical modelling
Doyle, J. G.; Erdélyi, R.; Sarro, L. M. +1 more
We explore the idea that the occurrence of nano-flares in a magnetic loop around the O vi formation temperature could explain the observed red-shift of mid-low transition region lines as well as the blue-shift observed in low coronal lines (T > 6x 105\ K). Observations are compared to numerical simulations of the response of the sola…
ISOCAM observations of the RCrA star formation region
Prusti, T.; Perault, M.; Olofsson, G. +16 more
The results of an ISOCAM survey of the RCrA star formation region are presented. The survey was carried out in two broad-band filters, LW2 (5-8.5 mu m) and LW3 (12-18 mu m). Although it was not possible to map the densest, central region due to saturation problems, 21 sources were identified which showed mid-IR excesses. Most of these sources have…
The Ultraviolet Peak of the Energy Distribution in 3C 273: Evidence for an Accretion Disk and Hot Corona around a Massive Black Hole
Kriss, Gerard A.; Zheng, Wei; Davidsen, Arthur F. +1 more
We present absolutely calibrated far-ultraviolet spectrophotometry of the quasar 3C 273 covering the 900-1800 Å range. Our ~3 Å resolution spectra were obtained with the Hopkins Ultraviolet Telescope (HUT) during the Astro-1 mission in 1990 December and during the Astro-2 mission in 1995 March. Both spectra exhibit a change in slope near the Lyman…