Engineering topics

Walterbos, R. A. M.

Publications and source records attributed to Walterbos, R. A. M..

6 records

NASA NTRS1994

X-ray emission from the edge-on spiral galaxy NGC 4631

This grant supported research of the X-ray emission from the disk and halo of the edge-on spiral galaxy NGC 4631, using data from the ROSAT satellite. The data were obtained on the basis of a proposal submitted by the PI, which was highly ranked in the peer review. It is a pleasure to say that the goals of the project, imaging and spectroscopy of hot gas in the disk and halo of a vigorously star forming galaxy, have been achieved. The results of the project have been submitted for publication, and are in press. A list of the publications is included.

Walterbos, R. A. M.↗

NASA NTRS1993

An atlas of supernova remnant candidates in Messier 31

Narrow-band CCD imagery in H-alpha and forbidden SII of a large fraction of the spiral arms in the Northeast half of Messier 31 has been used to isolate a sample of 52 'forbidden-line' SNR candidates for which the integrated ratio forbidden SII:H-alpha is greater than 0.5. An atlas of images in these emission lines, red optical continuum, and 1465 MHz radio continuum is presented, together with the tabulated integral properties of these sources. Assessing the completeness of the sample yields a crude estimate of the massive supernova rate (due to stars more massive than 7 solar masses) of 1 in 80 yr. The range of measured luminosities in both H-alpha and radio continuum is fully consistent with those found for 'forbidden-line' SNR in Messier 33, the LMC, and the Galaxy. With the inclusion of our candidates the number of extragalactic SNRs (with well-known distances) now exceeds the number of known galactic SNRs.

Braun, R.↗

NASA NTRS1993

A radio continuum survey of edge-on spiral galaxies at 90 cm

Accurate spectral indices of the radio emission from both the thin disk and thick disk or halo components are critical to understanding the propagation mechanisms of electrons within spiral galaxies. The spectral indices give information of relative importance of diffusion and synchrotron energy loss in the propagation of electrons in the disk. Our goal of this survey is to locate a larger sample of spiral galaxies that exhibit halo phenomena so that a statistical analysis will be possible.

Heikkila, B.↗

NASA NTRS1992

The interstellar medium of M31. III - Narrow-band imagery in H alpha and (SII)

Deep CCD imagery in H alpha and (SII) is presented of the major spiral arms of M31 with particular attention given to the data reduction and the analysis of the (SII)/H alpha flux ratios. A diffuse ionized gas noted in the images is analyzed which shows higher (SII)/H alpha ratios, and 967 discrete nebulae are listed with gray-scale images, finding charts, and absolute fluxes. The differential H-alpha luminosity function is found to have a slope of -0.95 for brighter objects and flattens out below a critical level. The curve is shown to correspond to the point at which single-star ionization accounts for the H alpha luminosities and is consistent with previous observations. The catalog of objects and fluxes is the largest existing sample of this type, and the unresolved objects in the sample are considered to be planetary nebulae.

Walterbos, R. A. M.↗

NASA NTRS1991

Diffuse ionized gas in nearby Galaxies

We discuss the distribution and spectral characteristics of diffuse ionized gas in nearby galaxies. The diffuse gas has been mapped in both edge-on and more face-on galaxies providing information on the radial and vertical distributions. Emission from diffuse ionized gas is strongest around star forming regions. The vertical distribution appears related to the radio continuum thick-disk emission. We also briefly discuss ionization mechanisms and the connection between star formation characteristics and morphology of the interstellar medium.

Walterbos, R. A. M.↗

NASA NTRS1988

An optical study of stars and dust in the Andromeda galaxy

The distribution of light in M 31 is characterized on the basis of the UBVR surface photometry reported by Walterbos and Kennicutt (1987). The results of the data analysis are presented in extensive graphs, maps, and tables and discussed in detail, considering the outer disk regions, the decomposition into bulge and disk, the global disk and bulge colors, and dust and gas in two spiral arms. Principal findings examined include: (1) position-angle changes at radial distances beyond about 18 kpc (consistent with SW disk warping); (2) a bulge profile well described by an r exp 1/4 power law; (3) a bulge contribution to total light of about 40 percent; (4) increasing blueness in the outer disk (color gradient 0.02 mag/kpc in B-R); (5) an extinction law similar to that for the Galaxy; and (6) a significant correlation between dust and H I distributions.

Walterbos, R. A. M.↗