Richard J. Rudy

A refined “standard” thermal model for asteroids based on observations of 1 Ceres and 2 Pallas

Abstract We present ground-based thermal infrared observations of asteroids 1 Ceres and 2 Pallas made over a period of 2 years. By analysing these data in light of the recently determined occultation diameter of Ceres (933–945 km) and Pallas (538 km) and their known small-amplitude lightcurves, we have determined a new value for the infrared beaming parameter used in the “standard” thermal emission model for asteroids. The new value is significantly lower than that previously used, and when applied in the reduction of thermal infrared observations of other asteroids, should yield model diameters that are closer to actual diameters. In our formulation, we also incorporate the recently adopted IAU magnitude convention for asteroids, which uses the zero-phase magnitudes (including the opposition effect) the same as is used for satellites.

Infrared spectra of protostars - Composition of the dust shells

Nearly complete 2 to 13 ..mu..m spectra are presented for 13 compact infrared sources associated with molecular clouds, as well as partial spectra of six additional objects. The spectra resemble blackbodies with superposed absorption features from 2.8 to 3.5 ..mu..m, at 6.0 and 6.8 ..mu..m, and in the silicate band centered near 9.7 ..mu..m. Correlations among the features are studied in an attempt to confirm possible identifications. A good correlation between the deepest part of the absorption at 3.1 ..mu..m, its long wavelength wing, and the 6.0 ..mu..m features suggests that all may be due to large amorphous water ice particles. The relatively poor correlation between the 3.4 and 6.8 ..mu..m optical depths adds no evidence to support the suggestion that these bands may be due to CH bonds.

Variability of Disk Emission in Pre-main-sequence and Related Stars. I. HD 31648 and HD 163296: Isolated Herbig Ae Stars Driving Herbig-Haro Flows

Infrared photometry and spectroscopy covering a time span of a quarter-century are presented for HD 31648 (MWC 480) and HD 163296 (MWC 275). Both are isolated Herbig Ae stars that exhibit signs of active accretion, including driving bipolar flows with embedded Herbig-Haro (HH) objects. HD 163296 was found to be relatively quiescent photometrically in its inner disk region, with the exception of a major increase in emitted flux in a broad wavelength region centered near 3 μm in 2002. In contrast, HD 31648 has exhibited sporadic changes in the entire 3-13 μm region throughout this span of time. In both stars, the changes in the 1-5 μm flux indicate structural changes in the region of the disk near the dust sublimation zone, possibly causing its distance from the star to vary with time. Repeated thermal cycling through this region will result in the preferential survival of large grains, and an increase in the degree of crystallinity. The variability observed in these objects has important consequences for the interpretation of other types of observations. For example, source variability will compromise models based on interferometry measurements unless the interferometry observations are accompanied by nearly simultaneous photometric data.

The Transitional Stripped-Envelope SN 2008ax: Spectral Evolution and Evidence for Large Asphericity

Supernova (SN) 2008ax in NGC 4490 was discovered within hours after shock breakout, presenting the rare opportunity to study a core-collapse SN beginning with the initial envelope-cooling phase immediately following shock breakout. We present an extensive sequence of optical and near-infrared spectra, as well as three epochs of optical spectropolarimetry. Our initial spectra, taken two days after shock breakout, are dominated by hydrogen Balmer lines at high velocity. However, by maximum light, He I lines dominated the optical and near-infrared spectra, which closely resembled those of normal Type Ib supernovae (SNe Ib) such as SN 1999ex. This spectroscopic transition defines Type IIb SNe, but the strong similarity of SN 2008ax to normal SNe Ib beginning near maximum light, including an absorption feature near 6270 A due to Hα at high velocities, suggests that many objects classified as SNe Ib in the literature may have ejected similar amounts of hydrogen as SN 2008ax, roughly a few × 0.01 M ☉. Only the unusually early discovery of SN 2008ax allowed us to observe the spectroscopic signatures of the hydrogen-rich outer ejecta. Early-time spectropolarimetry (six and nine days after shock breakout) revealed strong line polarization modulations of 3.4% across Hα, indicating the presence of large asphericities in the outer ejecta and possibly that the spectrum of SN 2008ax could be dependent on the viewing angle. After removal of interstellar polarization, the continuum shares a common polarization angle with the hydrogen, helium, and oxygen lines, while the calcium and iron absorptions are oriented at different angles. This is clear evidence of deviations from axisymmetry even in the outer ejecta. Intrinsic continuum polarization of 0.64% only nine days after shock breakout shows that the outer layers of the ejecta were quite aspherical. A single epoch of late-time spectropolarimetry as well as the shapes of the nebular line profiles demonstrate that asphericities extended from the outermost layers all the way down to the center of this core-collapse SN. SN 2008ax may in some ways be an extragalactic analog of the explosion giving rise to Cassiopeia A, which has recently been determined to be a remnant of an SN IIb.

Star formation in Seyfert galaxies

An analysis of the IRAS data for a sample of classical (optically selected) Seyfert galaxies is presented. The IRAS fluxes at 25 micron, 60 micron, and 100 micron are found to be uncorrelated or only very weakly correlated with the UV/Optical continuum flux and the near and mid IR flux at 3.5 and 10 microns. To investigate the possibility that star formation accounts for the far IR flux, the IRAS measurements for the Seyfert galaxies are compared to IRAS observations of a sample of normal spiral galaxies, and a sample of Starburst galaxies. It is shown that the far IR luminosities and far IR colors of Seyfert galaxies are indistinguishable from those of the Starburst galaxies. Besides, normal galaxies are an order of magnitude less luminous than both the Seyfert and the Starburst galaxies. This indicates that star formation produces the bulk of the far infrared emission in Seyfert galaxies.

0.8-2.5 Micron Spectroscopy of Nova Ophiuchi 1998*

We report 0.8-2.5 μm spectroscopy of the very fast Nova Ophiuchi 1998 from June 19 and 22 to October 2.15 1998 UT. On the first night the Paschen and Brackett emission lines dominated the spectrum, although He I 1.0830 μm was the strongest single line present and He II was very weak. There were also broad, symmetric emission wings underlying the H I and He I lines with FWHM of about 10,000 km s-1. Three nights later the rapid evolution of the nova to higher excitation conditions was evident from the much stronger He II lines which had increased by a factor of 4 relative to the hydrogen lines. The C III line at 0.9710 μm also appeared the second night, a line that we have heretofore seen only in Wolf-Rayet stars and which almost certainly indicates an overabundance of carbon. The broad emission wings were also present. About 110 days later on October 2.15 UT, the emission lines were very weak (5%-15% of the continuum) and only a few Paschen features and lines of He II were present. At no time during our observations was there any evidence of a long-wavelength upturn indicative of thermal emission from dust. The continuum magnitudes on the dates of observation at J (1.25 microns) were 9.4, 10.9 to 15.0, respectively. The optical decline of 0.37 mag day-1 makes this nova one of the fastest ever seen. Model fits of the broad lines profiles suggest that they originate in an optically thin, spherically expanding shell. The line ratios from the narrow components deviate significantly from case B values and seem to come from an optically thick (τ = 10-100 at line center in Paα), high-density (ne ~ 1011 cm-3) gas at around 10,000 K.

0.8-13 Micron Spectroscopy of V838 Monocerotis and a Model for Its Emission

Abstract : We report on the results of a number of infrared spectra (0.8-2.5, 2.1-4.6, and 3-14 microns) of V838 Monocerotis, taken from a short time after discovery in 2002 January to about 14 months later, in early 2003. The spectrum evolved dramatically, changing from a quasi-photospheric stellar spectrum with weak atomic emission lines (some with P Cygni profiles) to one showing a wide range of deep absorption features indicative of a cool, extended atmosphere with a circumstellar dust shell. The early spectra showed lines of s-process elements, such as Sr II and Ba I. The later spectra showed absorption by gaseous H2O, CO, AlO, TiO, SiO, SO2, OH, VO, and SH, as well as a complex of emission near 10 microns reminiscent of silicate emission, with a central absorbing feature at 10:3 microns. Thus, V838 Mon appears to be oxygen-rich. A simple, spherically symmetric model of the system involving a central star with a two-component expanding circumstellar shell is presented that is able to explain the major molecular features and spectral energy distribution in the objects late stages. The derived shell mass and distance are 0.04 M(circle dot solar) and 9.2 kpc, respectively.

INFRARED FABRY-PEROT IMAGING OF M82 (Fe II) EMISSION. II. TRACING EXTRAGALACTIC SUPERNOVA REMNANTS

We report high spatial and spectral resolution [Fe II] 1.644 ?m Fabry-Perot imaging observations of M82. We present extinction-corrected [Fe II] images and discuss the nature of compact [Fe II] emission regions revealed by these new data. We conclude that these [Fe II] sources trace a population of supernova remnants in M82 that are substantially older than those revealed previously on 6 cm radiographs. In addition, we find that M82 contains a distributed [Fe II] emission component that is extended along the southern minor axis and that accounts for 90% of the galaxys [Fe II] luminosity. We interpret this extended emission as tracing disk material entrained in a super wind that has broken out of the galactic disk to the south. We find that the [Fe II]/Br? line ratio throughout M82 correlates with the age of the starburst as reflected by the color of the photospheric emission from the galaxys stars. This correlation suggests that the [Fe II] emission regions in M82 are colocated with a post-main-sequence stellar population. The engineering details of our Fabry-Perot imaging methodology are also discussed.

Near-infrared [Fe II] emission of M82 supernova remnants : implications for tracing the supernova content of galaxies

Near-infrared [Fe II] and Paβ spectra of two young supernova remnants and one H II region within the central 15 kpc of M 82 are reported. Comparison of these spectra reveal a [Fe II]/Paβ ratio similar to that observed in Galactic supernova remnants and H II regions, and show that the [Fe II] background emission in M 82 has local maxima at the position of the supernova remnants observed in the radio continuum.

Near-Infrared Spectrophotometry and the CO Emission in V2274 Cygni (Nova Cygni 2001 No. 1)

Infrared spectroscopy of V2274 Cygni (=Nova Cygni 2001 No. 1) is presented for two widely separated epochs, 17 and 370 days after discovery. In addition to the Paschen and Brackett series of H I, the early-time spectrum shows strong emission lines of C I and N I, fluorescently excited lines of O I, and emission from the first overtone of carbon monoxide. Because the initial data were probably acquired no more than 18 days after outburst, CO molecule formation occurred remarkably quickly in the dense, cool, carbon and oxygen rich ejecta. Rapid formation was also seen in NQ Vul, V842 Cen, and V705 Cas, three other novae in which first-overtone CO emission has been detected. Formation of the CO molecule may occur chemically in a process that requires H2 as a precursor or directly through radiative association. The overtone emission of V2274 Cyg indicates a temperature of ~2500 K. The vibrational levels show no obvious departures from thermal equilibrium, which may indicate high optical depths in the fundamental. A large 13C/12C ratio (0.83 ± 0.3) is also indicated by the observations, consistent with the fast CNO burning expected in novae explosions. By the time of the second epoch observations, the emission lines of the neutral C, N, and O had disappeared. He I λ10830 was the dominant emission feature in the spectrum. In addition to the hydrogen lines, recombination features of He II were also strong. The common nebular lines of [S III] were seen but only two coronal line, [S VIII] λ9911 and [Si VI] λ19645, were detected. The CO emission had disappeared, but a strong thermal dust component was present. The interstellar reddening for the system was found to be E(B-V) = 1.3. This extinction, together with the absolute magnitude derived from the rate of decline of the light curve, suggest a distance of ~10.8 kpc. This places V2274 Cyg well out of the Galactic plane. The small number of novae with spectroscopic detections of carbon monoxide all have prominent C I lines, moderate speed classes and ejection velocities, exhibit marked dust formation events, and result from an explosion on a CO-type white dwarf. Based on these similarities, the spectrum of V2274 is proposed as a likely near-infrared spectral template for other novae that display carbon monoxide emission.