Engineering topics

Margon, Bruce

Publications and source records attributed to Margon, Bruce.

24 records · Page 2

NASA NTRS1988

An exceptionally bright, compact starburst nucleus

Observations are reported of a remarkably bright (V about 13) starburst nucleus, 0833 + 652, which has been detected at radio, infrared, optical, ultraviolet, and X-ray wavelengths. Despite an observed flux at each of these wavelengths which is comparable to that of NGC 7714, often considered the 'prototypical' example of the starburst phenomenon, 0833 + 652 appears to be a previously uncataloged object. Its ease of detectability throughout the electromagnetic spectrum should make it useful for a variety of problems in the study of compact emission-line galaxies.

Margon, Bruce↗

NASA NTRS1987

The low-luminosity X-ray sources in Omega Centauri

UBV observations of three X-ray sources in Omega Cen (sources A, D, and E of Hertz and Grindlay, 1983), obtained with a CCD detector on the 4-m telescope at CTIO in February and August 1985, are reported. The results are presented in images, graphs, and tables and characterized in detail. No optical cataclysmic variable candidates are found down to V = 24.5 mag, corresponding to M(V) = 10.6 in the cluster. It is inferred that these low-luminosity sources, located outside the globular cluster, may be superposed unrelated objects rather than close mass-exchange binaries.

Margon, Bruce↗

NASA NTRS1987

Observations made with the International Ultraviolet Explorer

Observations were made with the International Ultraviolet Explorer of two quite diverse astronomical objects. The first is an extremely ultraviolet excess star projected near the globular cluster M5. The second is a previously unrecognized but very bright starburst galaxy. Each of these objects is discussed in detail.

Margon, Bruce↗

NASA NTRS1987

An X-ray-selected white dwarf of intermediate luminosity

Spectrophotometric observations of a previously uncataloged 17th magnitude hot DA white dwarf are reported. Simple models can reproduce the visible spectrum if the star has log g = 8.0 + or - 0.5 and T(eff) = 22,500 + or - 2000 K. The implied distance is about 200 pc. It is plausible that photospheric emission from this star is responsible for the observed X-ray source. Identification of this object with the X-ray source would imply a photosphere free of traces of helium inferred in other X-ray-emitting DAs, and would support previous suggestions that current DA model atmospheres are in need of revision at X-ray wavelengths.

Margon, Bruce↗

NASA NTRS1987

The X-ray properties of high-redshift quasi-stellar objects

Sensitive X-ray information is presented for about 90 previously uncataloged high-redshift, optically selected QSOs. Two high-redshift subsets of this larger data base are emphasized: (1) a 'complete' sample of 37 objects with z = 1.8 - 3.0, and B of 19.5 or less and (2) a sample of 78 QSOs that span a narrow range in redshift and optical luminosity. From the complete sample, it is inferred that such QSOs contribute less than 3 percent to the diffuse X-ray background (XRB), and that the contribution of all QSOs with B of 19.5 or less to the XRB is 21 + or - 8 percent. For the narrow sample, it is found that the mean X-ray to optical luminosity ratio is characterized by alpha(eff)ox = 1.50 + or - 0.03. A variety of new, model-independent, empirical evidence is presented that the primary dependence of alpha(ox) is on optical luminosity rather than redshift. It is concluded that QSOs can supply as much as 70 percent of the XRB, with the typical contributor a moderate redshift QSO with B of roughly 19-21.

Anderson, Scott F.↗

NASA NTRS1986

Spectroscopy of six X-ray-selected BL Lacertae candidates

Results of a continuing program aimed at extending the small list of X-ray-selected BL Lac objects are reported. High-quality spectra have been obtained of six faint blue objects that lie within the positional error boxes of X-ray sources discovered serendipitously by the Einstein Observatory. Three of the objects are found to be previously uncataloged low-red-shift quasi-stellar objects, including one formerly suggested as BL Lac candidate. Two are faint galactic stars, while the final object has a featureless spectrum, and thus remains a candidate. Although X-ray selection may ultimately be an effective means of discovering faint BL Lac objects, such sources are evidently rare at the X-ray flux levels attainable by the Einstein Observatory.

Margon, Bruce↗