Journal Articles

Is 1308+326 A BL Lacertae object or a quasar?

GABUZDA, D. C., KOLLGAARD, R. I., ROBERTS, D. H., WARDLE, J. F. C.
Astrophysical Journal, Part 1, vol. 410, no. 1, p. 39-43.

Abstract: The active galaxy 1308+326 (z = 0.996) has been classified as a BL Lacertae object because of its nearly featureless optical continuum and high and variable polarization. New VLBI polarization images of 1308+326, however, show both VLBI polarization structure and tentative superluminal motions that are characteristic of quasars rather than BL Lacertae objects. These data strongly suggest that this source is simply a quasar with emission lines of small equivalent width. We discuss the possibility that the optical continuum is enhanced by microlensing in a foreground galaxy, as suggested by Stickel et al.

Radio constraints on the nature of BL Lacertae objects and their parent population

KOLLGAARD, R. I., WARDLE, J. F. C., ROBERTS, D. H., GABUZDA, D. C.
Astronomical Journal, vol. 104, no. 5, p. 1687-1705.

Abstract: 5 GHz VLA observations of 17 BL Lac objects with bright radio cores at both high and low resolution are reported. Extended emission is detected around most objects. None of the sources observed at low resolution show evidence of giant halos on the scale of tens of arcmin. In general, the sources with the most luminous extended emission exhibit FR II characteristics in both morphology and polarization, and less luminous sources exhibit FR I characteristics. Thus, the parent population of the BL Lac objects contains both FR I and FR II radio sources. No BL Lac objects are found that clearly exhibit quasarlike polarization at milliarcsec resolution. This argues against the view that the more luminous BL Lac objects are simply an extension of the quasar/OVV population, or that most BL Lac objects are gravitationally microlensed images of distant quasars. Other properties are generally consistent with the view the BL Lac objects are normal radio galaxies whose jets make a small angle to the line of sight.

High-precision VLBI astrometry of the radio-emitting star Sigma CrB - A step in linking the Hipparcos and extragalactic reference frames

LESTRADE, JEAN-FRANCOIS, PHILLIPS, ROBERT B., PRESTON, ROBERT A., GABUZDA, DENISE C.
Astronomy and Astrophysics, vol. 258, no. 1, p. 112-115.

Abstract: VLBI observations of the optically bright radio-emitting star Sigma Coronae Borealis (Sigma CrB) have yielded its position relative to an angularly nearby quasar, its annual proper motion and its trigonometric parallax with formal uncertainties slightly better than 0.2 milliarcsec. This is the first result of the VLBI astrometric program we are conducting on 11 radio stars similar to Sigma CrB. We plan to obtain comparable results for all stars when enough epochs of observations are acquired. These stars will be used to astrometrically link the Hipparcos and VLBI extragalactic reference frames.

A highly sensitive radio survey of symbiotic stars at 3.6 centimeters

SEAQUIST, E. R., KROGULEC, M., TAYLOR, A. R.
Astrophysical Journal, Part 1, vol. 410, no. 1, p. 260-274.

Abstract: Results of a new highly sensitive radio survey of about 100 symbiotic stars at 3.6 cm are reported. The survey has led to the detection of about half of all the symbiotic stars searched, effectively doubling the number of known radio detections. The analysis shows that the radio emission is correlated strongly with emission in the mid-IR (12 and 25 microns) and less strongly with IR emission at both shorter and longer wavelengths. A comparison between the radio and UV continua (1300 A) indicates that the ionized nebula in nearly all symbiotic stars is optically thick and/or density bounded. In particular, there is evidence that S-types are more optically thick in the radio wavelength range than D-types.

ROSAT survey observations of OB and OBe stars

MEURS, E. J. A., PITERS, A. J. M., POLS, O. R., WATERS, L. B. F. M., COTE, J., VAN KERKWIJK, M. H., VAN PARADIJS, J., BURKI, G., TAYLOR, A. R., DE MARTINO, D.
Astronomy and Astrophysics, vol. 265, no. 2, p. L41-L44.

Abstract: We present preliminary results of the X-ray part of an extensive multiwavelength study of bright OB- and OBe-type stars, aimed at finding evidence for the existence of white-dwarf companions to Be stars. After analysis of 75 percent of the ROSAT all-sky survey, X-ray emission is detected from 129 out of 1026 OB stars in the Bright Star Catalogue, 10 of which are OBe-type stars. However, no indications for white-dwarf companions could yet be found. The ROSAT X-ray luminosities range from 10 exp -8 to 10 exp -4 times the bolometric luminosities, for both OB and OBe stars. We notice that Beta Cep stars have a softer X-ray spectrum than normal early-type B stars. The X-ray emission in O and early type B stars appears consistent with the generally accepted idea of originating from shocks in radiatively driven winds. For later type B stars the situation is less clear: one possibility is chromospheric emission from late-type companions.

Resolution of the circumstellar gas around the Be star Psi Persei

DOUGHERTY, S. M., TAYLOR, A. R.
Nature, vol. 359, no. 6398, p. 808-810.

Abstract: The VLA has been used to resolve the circumstellar envelope of the Be star Psi Persei at 15 GHz, and it is found that its radio emission comes from a nonspherical distribution of thermally radiating gas. The radio-emitting region has a major axis of 111 +/- 16 mas and is unresolved, with a 3 sigma upper limit of 68 mas, along its minor axis. The observations confirm the proposal by Struve (1931) that equatorially enhanced circumstellar plasma distributions are the source of Be star emission.

Intrinsic IR Colours of Normal B-type Stars Using the Geneva Visual and ESO IR Photometric Systems

Dougherty, S.M., Cramer, N., van Kerkwijk, M.H., Taylor, A.R., and Waters, L.B.F.M.
Astronomy and Astrophysics, 273, 503 - 508, 1993.

Abstract: We present analysis of IR and visual observations of bright, normal B-type stars to derive colour-colour relationships between the visual and IR wavelength regions. The reddening-free parameters X and Y of the Geneva photometric system (Cramer & Maeder 1979) allow the calculation of precise colour excesses at visual wavelengths and de-reddened observations. We find well-defined linear relationships between the intrinsic [B - V]_0 and [V - m_lambda]_0 colours, where m_lambda is the intrinsic near-IR magnitude at the ESO IR J,H,K,L passbands and the IRAS 12 micrometre passband. We show that the derived visual-IR colour-colour relationships are in good agreement with those of Johnson (1966) yet are bluer than the relationships derived by Koornneef (1983b). We attribute this to the fact that Koornneef did not account for interstellar reddening. The [V - 12micrometre] colour relationship is also in good agreement with that of Waters et al. (1987). Theoretical colours derived from Kurucz (1979) model atmospheres of B-type stars are also in good agreement with the near-IR passbands. However, the Kurucz models fail to reproduce the L band and 12 micrometre magnitudes of B stars by about 8 - 12% as also found by previous authors. The results of this work will be used in a study of the properties of the near-IR excess emission in Be stars.

Papers Published in Conference Proceedings

The Difference Between Be Stars and Shell Stars from H Emission

Chen, H. and Taylor, A.R.
IAU Symposium 162, Cotte d'Azur, France.,1993.

IR-Radio Spectral Indices for Be Stars

Chen, H., Taylor, A.R., Dougherty, S.M. and Waters, L.B.F.M.
IAU Symposium 162, Cotte d'Azur, France.,1993.

Identification of IR Variable Be Stars

Dougerhty, S.M. and Taylor, A.R.
IAU Symposium 162, Cotte d'Azur, France.,1993.

Radio Imaging of the Be Star ? Persei

Dougerhty, S.M. and Taylor, A.R.
IAU Symposium 162, Cotte d'Azur, France.,1993.

Space VLBI User Assistance Software

I. Fejes, D.Murphy, R. Taylor, V. Yakimov, G. Young
Presented at the URSI/IAU Symposium on VLBI Technology:Progress and Future Observational Possibilities. September 6-10, 1993, Kyoto, Japan.
eds. T.Sasao, S.Manabe, O.Kameya and M.Inoue.
Terra Scientific Publishing Co., pp. 59-69

Space VLBI Polarization Observations

Gabuzda, D.C. and Taylor, A.R.
Presented at the URSI/IAU Symposium on VLBI Technology:Progress and Future Observational Possibilities. September 6-10, 1993, Kyoto, Japan.
eds. T.Sasao, S.Manabe, O.Kameya and M.Inoue.
Terra Scientific Publishing Co., pp.54-58

Space VLBI Simulations

Murphy, D.W., Yakimov, V., Kobayashi, H., Taylor, A.R. and Fejes, I.
Presented at the URSI/IAU Symposium on VLBI Technology:Progress and Future Observational Possibilities. September 6-10, 1993, Kyoto, Japan.
eds. T.Sasao, S.Manabe, O.Kameya and M.Inoue.
Terra Scientific Publishing Co., pp.34-38

Papers presented at conferences (not included in conference proceedings)

Near-IR Variability of Be Stars

Taylor, A.R. and Dougherty, S.M.
1993 Canadian Astronomical Society Meeting, Victoria.

Simultaneous X-ray and Radio Observations of the Binary Star LSI+61 303

Gregory, P.C., Taylor, A.R., Kenny, H.T. and Young,.G.
1993 Canadian Astronomical Society Meeting, Victoria.

The Structure of the Circumstellar Envelope of the Be star ? Persei at Large Radii

Dougherty, S.M. and Taylor, A.R.
1993

VLBI Observations of the X-ray Binary System LSI+61 303

Peracaula, M., Gabuzda, D.C. and Taylor, A.R.
1993 Canadian Astronomical Society Meeting, Victoria.

The Westerbork 327 MHz Galactic Plane Survey

van Leeuwen, J., Taylor, A.R., and Goss, W.M.
1993 Canadian Astronomical Society Meeting, Victoria.

Prepared by:

Glen Young;
young@bear.ras.ucalgary.ca

Bill Scott;
bill@ras.ucalgary.ca