Deep Imaging of AX J2019+112: The Luminosity of a ``Dark Cluster''

in Astrophysical Journal (1999), 527

We detect a distant cluster of galaxies centered on the QSO lens and luminous X-ray source AX J2019+112, a.k.a. the ``Dark Cluster.'' Using deep V and I Keck images and wide-field K[SUB]s[/SUB] imaging ... [more ▼]

We detect a distant cluster of galaxies centered on the QSO lens and luminous X-ray source AX J2019+112, a.k.a. the ``Dark Cluster.'' Using deep V and I Keck images and wide-field K[SUB]s[/SUB] imaging from the New Technology Telescope (NTT), a tight red sequence of galaxies is identified within a radius of 0.2 h[SUP]-1[/SUP] Mpc of the known z=1.01 elliptical lensing galaxy. The sequence, which includes the central elliptical galaxy, has a slope in good agreement with the model predictions of Kodama et al. for z~1. We estimate the integrated rest-frame luminosity of the cluster to be L[SUB]V[/SUB]>=3.2x10[SUP]11[/SUP] h[SUP]-2[/SUP] L[SUB]solar[/SUB] (after accounting for significant extinction at the low latitude of this field), more than an order of magnitude higher than previous estimates. The central region of the cluster is deconvolved using the technique of Magain, Courbin, & Sohy, revealing a thick central arc coincident with an extended radio source. All the observed lensing features are readily explained by differential magnification of a radio-loud active galactic nucleus by a shallow elliptical potential. The QSO must lie just outside the diamond caustic, producing two images; the arc is a highly magnified image formed from a region close to the center of the host galaxy, projecting inside the caustic. The mass-to-light ratio within an aperture of 0.4 h[SUP]-1[/SUP] Mpc is M[SUB]X[/SUB]/L[SUB]V[/SUB]=224[SUP]+112[/SUP][SUB]- 78[/SUB]h(M/L[SUB]V[/SUB])[SUB]solar[/SUB], using the X-ray temperature. The strong lens model yields a compatible value, M/L[SUB]V[/SUB]=372[SUP]+94[/SUP][SUB]- 94[/SUB]h(M/L[SUB]V[/SUB])[SUB]solar[/SUB], whereas an independent weak-lensing analysis sets an upper limit of M/L[SUB]V[/SUB]<520h(M/L[SUB]V[/SUB])[SUB]solar[/SUB], typical of massive clusters. [less ▲]

The Interacting Early-Type Binary BD +40°4220 (V729 Cyg): Modeling the Colliding Winds Region

in Astrophysical Journal (1999), 517

We present an analysis of an extensive set of spectroscopic observations of the mysterious early-type binary BD +40 deg4220. A new orbital solution is derived from the radial velocities of the absorption ... [more ▼]

We present an analysis of an extensive set of spectroscopic observations of the mysterious early-type binary BD +40 deg4220. A new orbital solution is derived from the radial velocities of the absorption lines. We confirm that the secondary star is highly overluminous for its mass. The absorption lines of both components display phase-locked profile variations, with some of the secondary's lines going into emission between phi=0.20 and phi=0.55. A detailed investigation of the profile variability of the He II lambda4686 emission line reveals that the pattern of variability of this line is very stable. We show that part of the He II lambda4686 emission is produced in the wind interaction region between the stars. Most of the emission lines in the visual spectrum of BD +40 deg4220 display variations that are reminiscent of those observed on the He II lambda4686 line, pointing toward a similar origin. We present numerical simulations of emission-line profiles in a colliding winds binary, showing that an important part of the variability observed in BD +40 deg4220 can be explained by a colliding winds phenomenon. The properties of the wind interaction region can be accounted for if we assume that the secondary star is an evolved object, most probably some kind of Ofpe/WN9 transition star, with a mass loss rate of ~5.5x10^-6 M_solar yr^-1. We finally discuss the fundamental parameters of the binary, concluding that mass transfer must have played a crucial role in the evolution of this system. [less ▲]

Image Deconvolution of the Radio Ring PKS 1830-211

in Astrophysical Journal (1998), 499

New high-quality Keck and ESO images of PKS 1830-211 are presented. By applying a powerful new deconvolution algorithm to these optical and infrared data, both images of the flat spectrum core of the ... [more ▼]

New high-quality Keck and ESO images of PKS 1830-211 are presented. By applying a powerful new deconvolution algorithm to these optical and infrared data, both images of the flat spectrum core of the radio source have been identified. An extended source is also detected in the optical images which is consistent with the expected location of the lensing galaxy. The source counterparts are very red at I-K~7 , which suggests strong Galactic absorption with additional absorption by the lensing galaxy at z=0.885 and is consistent with the detection of high-redshift molecules in the lens. [less ▲]

Deconvolution with Correct Sampling

in Astrophysical Journal (1998), 494

A new method for improving the resolution of astronomical images is presented. It is based on the principle that sampled data cannot be fully deconvolved without violating the sampling theorem. Thus, the ... [more ▼]

A new method for improving the resolution of astronomical images is presented. It is based on the principle that sampled data cannot be fully deconvolved without violating the sampling theorem. Thus, the sampled image should be deconvolved not by the total point-spread function but by a narrower function chosen so that the resolution of the deconvolved image is compatible with the adopted sampling. Our deconvolution method gives results that are, in at least some cases, superior to those of other commonly used techniques: in particular, it does not produce ringing around point sources superposed on a smooth background. Moreover, it allows researchers to perform accurate astrometry and photometry of crowded fields. These improvements are a consequence of both the correct treatment of sampling and the recognition that the most probable astronomical image is not a flat one. The method is also well adapted to the optimal combination of different images of the same object, as can be obtained, e.g., from infrared observations or via adaptive optics techniques. [less ▲]

HST spectra of the Jovian ultraviolet aurora: Search for heavy ion precipitation

in Astrophysical Journal (1998), 507(2), 955-967

Ultraviolet spectra using Hubble Space Telescope sampled between 1250 and 1680 Angstrom, at spectral resolution less than or equal to 0.57 Angstrom are reported for characteristically bright regions of ... [more ▼]

Ultraviolet spectra using Hubble Space Telescope sampled between 1250 and 1680 Angstrom, at spectral resolution less than or equal to 0.57 Angstrom are reported for characteristically bright regions of Jupiter's morning and afternoon northern aurora. Several observed spectra exhibit sharply enhanced resolution. We interpret this as bright auroral emission foreshortened on the morning limb with a maximum intensity at least as high as 2000 kR. We have searched for evidence that the primary precipitating particles exciting the aurora include the heavy ions known to exist in Jupiter's plasma torus and magnetosphere. We have also searched for such ambient heavy ions and neutrals at rest in the auroral ionosphere, the end products of previous precipitation, excited by the auroral cascade. We argue that primary emission would be characterized by a dramatically Doppler-broadened (similar to 10-15 Angstrom) and redshifted line profile resulting from the cascade process and the angle between the line of sight and the magnetic field lines in the atmosphere. In contrast, ambient emission would be distinguished by narrow emission lines. We have modeled the theoretical sulfur and oxygen line shapes for ion precipitation and conclude that electron precipitation is responsible for most of the H-2 emissions. O ions contributed <13% of the precipitating energy flux, and S ions contributed < 50%. This dominance suggests that field-aligned magnetospheric currents are more important than energetization of energetic ions and subsequent scattering by plasma waves as a mechanism for generating the Jovian aurora. We set an upper limit over our spectra of 35-43 R to the emission from ambient oxygen and sulfur ions and their neutrals, except that for the S II 1256 triplet, the upper limit for the nominally brightest line, at 1260 Angstrom, is 74 R. Hence, we find no evidence for the accumulation of sulfur in the auroral ionosphere. A single narrow emission line from an unidentified ambient specie near 1254 Angstrom may be detected at the 4 sigma level, introducing the possibility of complex auroral aeronomy. Differences were observed in the auroral spectral hydrocarbon absorption at different locations, which cannot be interpreted without ambiguity between auroral and atmospheric structural causes. We have found that the brighter emission in an auroral sector consistently shows more spectral hydrocarbon absorption than the dimmer emission. We suggest two alternative physical explanations for this phenomenon. [less ▲]

Optical Spectroscopy of EZ Canis Majoris: Indication for Large-Scale Structures in a Wolf-Rayet Wind

in Astrophysical Journal (1997), 482

We have carried out optical spectroscopy of the Wolf-Rayet star EZ CMa during 20 consecutive nights in 1995 January in support of the IUE Mega-project. In parallel with this optical spectroscopy, we also ... [more ▼]

We have carried out optical spectroscopy of the Wolf-Rayet star EZ CMa during 20 consecutive nights in 1995 January in support of the IUE Mega-project. In parallel with this optical spectroscopy, we also monitored EZ CMa using narrowband photometry. The light curve was found to be remarkably stable when folded with the P=3.77 day period, and it had a peak-to-valley amplitude of 0.1 mag. The P Cygni absorption components of He I lambda 3889 and He I lambda 5876 display a similar global pattern of variability as was found for the simultaneously acquired UV profiles. The strengthening of the P Cygni absorption component of these transitions is associated with the maximum of the continuum flux. Conversely, the absorption trough of N V lambda 4604 gradually disappears as the star brightens. Although the emission parts of the lines are variable at different levels, they all show the same pattern of variability, which consists of phase-dependent shifts of extra emission components superposed on the profiles. A strong correlation is found between the continuum-light level and the equivalent width of most transitions. The line skewness and the full-width at half-maximum show a daily recurrence timescale, reflecting the light curve changes. We have addressed in a rigorous statistical way the significance of the variations by calculating the "temporal variance spectrum." For any given line, we found enhanced variability at some velocities, although the whole profile displays a statistically significant level of variability. Arguments against a compact companion as the cause of the observed periodic variability are presented. Instead, our observations strongly support the suggestion in the IUE Mega analysis that the atypical level of variability results from the rotation of a structured wind. We propose that the wind variability of EZ CMa is triggered by photospheric activity, or that the wind is controlled by a large-scale magnetic field. [less ▲]

Hydrodynamic simulations of galaxy formation .2. Photoionization and the formation of low-mass galaxies

in Astrophysical Journal (1996), 465(2), 608-616

Photoionization by the high-redshift ultraviolet radiation background heats low- density gas before it falls into dark matter potential wells, and it eliminates the neutral hydrogen and singly ionized ... [more ▼]

Photoionization by the high-redshift ultraviolet radiation background heats low- density gas before it falls into dark matter potential wells, and it eliminates the neutral hydrogen and singly ionized helium that dominate cooling of primordial gas at temperatures of 10(4)-10(5) K. We investigate the influence of photoionization on galaxy formation using high-resolution simulations with a one-dimensional, spherically symmetric, Lagrangian hydrodynamics/gravity code. We find that the presence of a photoionizing background suppresses the formation of galaxies with circular velocities v(circ) less than or similar to 30 km s(-1) and substantially reduces the mass of cooled baryons in systems with circular velocities up to v(circ) similar to 50 km s(-1). Above v(circ) similar to 75 km s(-1), photoionization has no significant effect. Photoionization exerts its influence primarily by heating gas before collapse; the elimination of line cooling processes is less important. We discuss the implications of these results for hierarchical theories of galaxy formation. [less ▲]

Hubble Space Telescope Goddard high-resolution spectrograph H2 rotational spectra of Jupiter's aurora

in Astrophysical Journal (1994), 430

We have observed the emission spectrum from Jupiter's north auroral atmosphere with 0.57 A spectral resolution over 1204-1241 A. Bright emissions have been detected from 50 deg to 60 deg latitude at ... [more ▼]

We have observed the emission spectrum from Jupiter's north auroral atmosphere with 0.57 A spectral resolution over 1204-1241 A. Bright emissions have been detected from 50 deg to 60 deg latitude at locations consistent with 6 to 30 R [SUB]J[/SUB] auroral ovals, with much fainter emissions away form the auroral ovals. The emission spectrum is well fitted by both laboratory spectra and theoretical models of optically thin electron excited H2, with added Doppler-broadened Lyman Alpha emission. The observed Lyman Alpha emission wings extend more than 1 A from line center and appear correlated in strength with the H2 brightness. Individual rotational lines in the H2 Werner band system are resolved, allowing a determination of the H2 rotational temperature at the altitude of the emission. We derive best-fit temperatures from 400-450 to 700-750 K, with the auroral emission layer temperature changing either across the auroral oval or over several days' time. These observations demonstrate for the first time the ability to measure the observed rapid H2 temperature variations across Jupiter's auroral atmosphere. [less ▲]

HIGH-RESOLUTION SPECTRA OF JUPITER NORTHERN AURORAL ULTRAVIOLET EMISSION WITH THE HUBBLE-SPACE-TELESCOPE

in Astrophysical Journal (1994), 421(2), 816-827

The first spectroscopic observations of planetary aurora with the HST are reported. These include spectral regions centered on the H-2 Lyman and Werner bands of a region of Jupiter's northern aurora. The ... [more ▼]

The first spectroscopic observations of planetary aurora with the HST are reported. These include spectral regions centered on the H-2 Lyman and Werner bands of a region of Jupiter's northern aurora. The observations were made with the Goddard High Resolution Spectrograph (GHRS) using the Large Science Aperture as part of a campaign to study Jupiter at the time of the Ulysses flyby. The individual rotational-vibrational bands are resolved and the observed emissions are essentially all from H-2. A rotational-vibrational temperature for H-2 of 530 +/- 100 K is derived, a value significantly less than the 850-1100 K reported for Jovian H-3(+) in the near-infrared but consistent with the temperature reported for fundamental-band quadrupole H-2 emission. Comparison with the Faint Object Camera (FOC) images shows that the observed region was not one of the hot spots of the aurora. The results are interpreted in terms of electron impact excitation of H-2 from secondary particles generated by primaries precipitating into Jupiter's atmosphere from the magnetosphere. In the region of the aurora observed, the homopause level is found to be significantly hotter but not necessarily higher than observed at nonauroral latitudes. The equatorial H-2 dayglow spectrum was also detected; its intensity was 3.2 kR or 13% of the strength of the observed auroral emission. [less ▲]

New f values in C I and the CNO Abundances in the Sun

in Astrophysical Journal (1993), 412