Engineering topics

Bahcall, J. N.

Publications and source records attributed to Bahcall, J. N..

At least 55 records · Page 3

All sources NASA NTRS DOE OSTI

NASA NTRS1976

Search for X-ray emission from globular clusters using Uhuru data

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Ulmer, M. P.↗

NASA NTRS1976

Status of the study of ellipsoidal light variations in 3U 0900-40

Estimates of system parameters and component masses are reviewed. The mass for the X-ray source in 3U0900-40 is found. The importance of determining the X-ray eclipse duration in binary systems is explained. A list of important observations for testing and utilizing the standard picture is presented.

Avni, Y.↗

NASA NTRS1976

Is the local supercluster a physical association

A quantitative measure of the degree of concentration of a sample of galaxies toward any great circle is described and applied to the Shapley-Ames and de Vaucouleurs catalogs of bright galaxies as well as to computer-simulated catalogs of galaxies. It is found that the observed distribution can be explained as the combined result of obscuration by our Galaxy, purely local clustering on angular scales of less than about 10 deg, and our proximity to a rather large and populous cluster, the Virgo cluster. In order for this interpretation to be correct, the Virgo cluster must have a mean angular radius of the order of or greater than 15 deg. This interpretation is supported by recent measurements which do not indicate any large inhomogeneities in the motions of nearby galaxy clusters and which show that the mean recessional velocity of the Virgo cluster is consistent with a uniform Hubble expansion. If the present interpretation is correct, it may be possible to determine the Hubble constant directly from measurements of individual distance indicators (such as H II regions and the brightest stars) with distance moduli less than about 32.

Bahcall, J. N.↗

NASA NTRS1975

Optical studies of 10 high galactic latitude X-ray sources

Optical studies are reported for a representative sample of 10 unidentified high galactic latitude X-ray sources that are north of declination minus 25 deg and that have 3U error boxes less than or of the order of 0.5 square degrees. The source 3U 1410-03 is identified with a peculiar emission-line spiral galaxy, NGC 5506, and a distance group 4 rich cluster of galaxies, Abell 2142, is suggested as a possible identification for 3U 1555+27. It is shown that very few of the unidentified high galactic latitude sources are quasi-stellar sources brighter than 17.5 mag, although one possible X-ray quasar, NAB 0137-01, is reported.

Bahcall, J. N.↗

NASA NTRS1973

Radio stars and X-ray sources.

Limits on the X-ray emission from the known radio stars that can be studied with Uhuru are of interest because of the possible association between X-ray binaries and radio star binaries, and because limits or measurements of the X-ray fluxes can help determine the source of the radio emission. It is shown that if, for the moment, HDE226868 is ignored, none of the radio stars was detected as an X-ray source. It appears that there are two types of radio binary stars, one which is a strong X-ray source and one which is not.

Bahcall, J. N.↗

NASA NTRS1972

The estimation of masses of individual galaxies in clusters of galaxies.

Three different methods of estimating masses are discussed. The 'density method' is based on the analysis of the density distribution of galaxies around the object whose mass is to be found. The 'bound-galaxy method' gives estimates of the mass of a double, triple, or quadruple system from analysis of the orbital motion of the components. The 'virial method' utilizes the formulas derived for the second method to obtain estimates of the virial-theorem masses of whole clusters, and thus to obtain upper limits on the mass of an individual galaxy in a cluster. The analytic formulas are developed and compared with computer experiments, and some applications are given.

Wolf, R. A.↗

NASA NTRS1972

On identifying new kinds of astronomical objects.

The evidence for a new compact X-ray object claimed by the Berkeley group of Margon et al (1971) is called into question by Princeton critics on grounds of inadequate statistical analysis. The presented rebuttal of the Berkeley group upholds the correctness of their analytical procedure, but concedes the need for further observations.

Bahcall, J. N.↗

NASA NTRS1971