July 1999 arXiv papers — page 25

P. Giommi, M. T. Menna, P. Padovani

We have assembled a multi-frequency database by cross-correlating the NVSS catalog of radio sources with the RASSBSC list of soft X-ray sources, obtaining optical magnitude estimates from the Palomar and UK Schmidt surveys as provided by the APM and COSMOS on-line services. By exploiting the nearly unique broad-band properties of High-Energy Peaked (HBL) BL

J. R. Herrnstein, J. M. Moran, L. J. Greenhill, P. J. Diamond

The water maser in the mildly active nucleus in the nearby galaxy NGC4258 traces a thin, nearly edge-on, subparsec-scale Keplerian disk. Using the technique of very long baseline interferometry, we have detected the proper motions of these masers as they sweep in front of the central black hole at an orbital velocity of about 1100 km/s. The average maser pro

N. R. Tanvir, A. Boyle

We present V and I_c CCD photometry for 40 LMC Cepheids at 1 to 3 epochs. This represents a significant increase in the number of LMC Cepheids with $I$-band data, and, as we show, is a useful addition to the sample which can be used to calibrate the period--luminosity relations in these important bands.

A. C. Quillen, A. Alonso-Herrero, M. J. Rieke, G. H. Rieke

We present NICMOS imaging of broad band and molecular hydrogen emission in Seyfert galaxies. In 6 of 10 Seyferts we detect resolved or extended emission in the 1-0 S(1) 2.121 or 1-0 S(3) 1.9570 micron molecular hydrogen lines. We did not detect emission in the most distant galaxy or in the 2 Seyfert 1 galaxies in our sample because of the luminosity of the n

Knox S. Long

Using the Hopkins Ultraviolet Telescope and Hubble Space Telescope, observers have now obtained UV spectra with sufficient signal to noise and resolution to allow quantitative spectroscopic analyses of the WDs in several DNe. In the ``cleanest'' DNe, such as U Gem, the observations are allowing the basic physical parameters of the WD -- temperature,

C. M. Canosa, D. M. Worrall, M. J. Hardcastle, M. Birkinshaw

We present an analysis of X-ray data, taken with ROSAT, for a well defined sample of low-power radio galaxies from the Bologna B2 catalogue. Where possible, the HRI has been used in order to take advantage of the higher spatial resolution provided by this instrument. A variety of models are fitted to radial profiles in order to separate the resolved and unre

Agostino Martinelli, Francesca Matteucci

In this paper we present a method to solve the G-dwarf problem in the frame-work of analytical models (based on the instantaneous recycling approximation, IRA). We consider a one-zone closed model without inflows or outflows. We suppose a time-dependent Initial Mass Function (IMF) and we find an integral-differential equation which must be satisfied in order

D. Barrado y Navascues, J. R. Stauffer, B. M. Patten

We have obtained new photometry and intermediate resolution ($Δλ= 2.7$ Å ) spectra of 19 of these objects (14.9 $\le$ $I_c$ $\le$ 17.5) in order to confirm cluster membership. We identify 15 of our targets as likely cluster members based on their $VRI$ photometry, spectral types, radial velocity, and H$α$ emission strengths. Higher S/N spectra were obtained

A. D'Ercole, F. Brighenti

We study, through 2D hydrodynamical simulations, the feedback of a starburst on the ISM of typical gas rich dwarf galaxies. The main goal is to address the circulation of the ISM and metals following the starburst. We assume a single-phase rotating ISM in equilibrium in the galactic potential generated by a stellar disk and a spherical dark halo. The starbur

N. Ageorges, J. R. Walsh

The process of data taking, reduction and calibration of near-infrared imaging polarimetry data taken with the ESO Adaptive Optics System ADONIS is described. The ADONIS polarimetric facility is provided by a rotating wire grid polarizer. Images were taken at increments of 22.5 degrees of polarizer rotation from 0 to 180 degrees, over-sampling the polarizati

Patrick Cote, Mario Mateo, Edward Olszewski, Kem Cook

The High Resolution Echelle Spectrometer on the Keck I telescope has been used to measure nine radial velocities having a median precision of 2 km/s for seven red giants belonging to the isolated dwarf spheroidal galaxy Andromeda II. We find a weighted mean radial velocity of -188+/-3 km/s and a central velocity dispersion of 9.3+/-2.7 km/s. There may be evi

Hsiao-Wen Chen, Kenneth M. Lanzetta, Sebastian Pascarelle

We present a new spectrum extraction technique which employs optimal weights for the spectral extraction, deblends the overlapping spectra, determines the precise sky background, and takes into account correlations between errors correctly for STIS slitless observations. We obtained roughly 250 optimally extracted spectra in a deep STIS field as well as self

Tomonori Totani

The extreme energetics of the gamma-ray burst (GRB) 990123 has revealed that some of GRBs emit quite a large amount of energy, and total energy release from GRBs seems to change from burst to burst by a factor of 10^{2-3} as E_{gamma, iso} \sim 10^{52-55} erg, where E_{gamma, iso} is the observed GRB energy when radiation is isotropic. If all GRBs are trigge