Search Publications
Fine structure of the red giant clump from HIPPARCOS data, and distance determinations based on its mean magnitude
Salaris, Maurizio; Girardi, Leo; Groenewegen, Martin A. T. +1 more
The I-band brightness M_I of clump stars is a possible distance indicator for stellar populations. Investigations have shown that M_I is almost insensitive to the V-I colour within the clump. Based on this, it was assumed that M_I was insensitive to age and composition of the stellar population and therefore an ideal standard candle, which could b…
A new analysis of the red giant branch `tip' distance scale and the value of the Hubble constant
Salaris, Maurizio; Cassisi, Santi
The theoretical evaluations of the red giant branch tip (TRGB) luminosity presented previously by Salaris & Cassisi are extended to higher metallicities, and compared with analogous independent results recently published. The present sets of stellar models agree quite well in the determination of the TRGB brightness. Relations between TRGB bol…
Solar internal rotation rate and the latitudinal variation of the tachocline
Basu, Sarbani; Antia, H. M.; Chitre, S. M.
A new set of accurately measured frequencies of solar oscillations is used to infer the rotation rate inside the Sun, as a function of radial distance as well as latitude. We have adopted a regularized least-squares technique with iterative refinement for both 1.5D inversion, using the splitting coefficients, and 2D inversion using individual m sp…
ΔY/ΔZ from fine structure in the main sequence based on Hipparcos parallaxes
Pagel, B. E. J.; Portinari, L.
The slope ΔY/ΔZ is a quantity of interest in relation to stellar evolution, the initial mass function and the determination of the primordial helium abundance. In this paper we estimate ΔY/ΔZ from fine structure in the main sequence of nearby stars from Hipparcos data for stars with Z<=Zsolar. We find a value of about 3, which is consistent wit…
HST images of a galaxy group at z=2.81, and the sizes of damped Lyalpha galaxies
Møller, P.; Warren, S. J.
We present Hubble Space Telescope (HST) WFPC2 observations in three bands (F450W=B, F467M and F814W=I) of a group of three galaxies at z=2.8 discovered in a ground-based narrow-band search for Lyalphaemission near the z=2.8 quasar PKS 0528-250. One of the galaxies is a damped Lyalpha(DLA) absorber and these observations bear on the relation betwee…
The dynamical evolution of stellar superclusters
Kroupa, Pavel
Recent images taken with the Hubble Space Telescope (HST) of the interacting disc galaxies NGC 4038/4039 (the Antennae) reveal clusters of many dozens and possibly hundreds of young compact massive star clusters within projected regions spanning about 100 to 500 pc. It is shown here that a large fraction of the individual star clusters merge withi…
The z=2.72 galaxy cB58: a gravitational fold arc lensed by the cluster MS1512+36
Saglia, R. P.; Bender, Ralf; Seitz, Stella +3 more
Using HST WFPC2 V- and R-band data of the z=0.37 cluster MS 1512+36, we show that the z=2.72 `protogalaxy' cB58 is not extraordinarily luminous intrinsically but lensed into a gravitational fold arc by the cluster. The arc has a surface- brightness-weighted axis ratio of 1:7, is marginally resolved in width and about 3 arcsec long. Its counterimag…
X-ray and soft gamma-ray spectra of broad-line radio galaxies
Zdziarski, Andrzej A.; Madejski, Greg M.; Johnson, W. Neil +2 more
We study X-ray and soft gamma-ray spectral properties of nearby broad-line radio galaxies (BLRGs) using data from GingaASCA, OSSE and EXOSAT. The X-ray spectra are well fitted by an intrinsic power-law continuum with an energy index of alpha~0.7, moderately absorbed by a cold medium. In addition, the Ginga spectra show fluorescent Fe Kalpha lines …
Effects of errors in the solar radius on helioseismic inferences
Basu, Sarbani
Frequencies of intermediate-degree f modes of the Sun seem to indicate that the solar radius is smaller than what is normally used in constructing solar models. We investigate the possible consequences of an error in radius on results for solar structure obtained using helioseismic inversions. It is shown that solar sound speed will be overestimat…
The distances to the X-ray binaries LSI +61 deg 303 and A0535+262
Coe, M. J.; Steele, I. A.; Negueruela, I. +1 more
Chevalier & Ilovaisky use Hipparcos data to show that the X-ray binary systems LSI+61 deg 303 and A0535+262 are a factor of 10 closer (i.e. d~ few hundred pc) than previously thought (d~kpc). We present high-quality CCD spectra of the systems, and conclude that the spectral types, reddening and absolute magnitudes of these objects are strongly…