arXiv subjects

C. E. Woodward

Publications and source records attributed to C. E. Woodward.

81 records · Page 5Linked to original sources

arXiv2006

Infrared observations of the 2006 outburst of the recurrent nova RS Ophiuchi: the early phase

We present infrared spectroscopy of the recurrent nova RS Ophiuchi, obtained 11.81, 20.75 and 55.71 days following its 2006 eruption. The spectra are dominated by hydrogen recombination lines, together with HeI, OI and OII lines; the electron temperature of ~10^4 K implied by the recombination spectrum suggests that we are seeing primarily the wind of the red giant, ionized by the ultraviolet flash when RS Oph erupted. However, strong coronal emission lines (i.e. emission from fine structure transitions in ions having high ionization potential) are present in the last spectrum. These imply a temperature of 930000K for the coronal gas; this is in line with x-ray observations of the 2006 eruption. The emission line widths decrease with time in a way that is consistent with the shock model for the x-ray emission.

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arXiv2006

The Spitzer IRS view of V4334 Sgr (Sakurai's Object)

We present an observation of the very late thermal pulse object V4334 Sgr (Sakurai's Object) with the Infrared Spectrometer (IRS) on the Spitzer Space Telescope. The emission from 5-38 microns is dominated by the still-cooling dust shell. A number of features are seen in absorption against the dust shell, which we attribute to HCN and polyyne molecules. We use these features to determine the 12C/13C ratio for the absorbing gas to be ~ 3.2 (+3.2,-1.6}; this implies that, despite the H-content of the molecules, the hydrocarbon-bearing gas must have originated in material produced in the very late thermal pulse. We see no evidence of emission lines, despite the recently-reported optical and radio observations that suggest the effective temperature of the stellar remnant is rising.

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arXiv2006

Mapping and Mass Measurement of the Cold Dust in NGC 205 with Spitzer

We present observations at 3.6, 4.5, 5.8, 8, 24, 70 & 160um of NGC 205, the dwarf elliptical companion of M31, obtained with the Spitzer Space Telescope. The point sources subtracted images at 8 and 24um display a complex and fragmented infrared emission coming from both very small dust particles and larger grains. The extended dust emission is spatially concentrated in three main emission regions, seen at all wavelengths from 8 to 160um. These regions lie approximately along NGC 205's semi-major axis and range from ~100 to 300 pc in size. Based on our mid-to-far infrared flux density measurements alone, we derive a total dust mass estimate of the order of 3.2e4 solar masses, mainly at a temperature of ~20K. The gas mass associated with this component matches the predicted mass returned by the dying stars from the last burst of star formation in NGC 205 (~0.5 Gyr ago). Analysis of the Spitzer data combined with previous 1.1mm observations over a small central region or "Core'' (18" diameter), suggest the presence of very cold (~12K) dust and a dust mass about sixteen times higher than is estimated from the Spitzer measurements alone. Assuming a gas to dust mass ratio of 100, these two datasets, i.e.with and without the millimeter observations, suggest a total gas mass range of 3.2e6 to 5e7 solar masses.

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arXiv2006

Spitzer 4.5 micron Luminosity-Metallicity and Mass-Metallicity Relations for Nearby Dwarf Irregular Galaxies

For a sample of 25 dwarf irregular galaxies with distances D < 5 Mpc and measured oxygen abundances, we present results derived from stellar masses and galaxy luminosities from near-infrared imaging with IRAC on the Spitzer Space Telescope. We have constructed the appropriate luminosity-metallicity (L-Z) and mass-metallicity (M-Z) relations, and compared these relations with their corresponding relations from the Sloan Digital Sky Survey (SDSS). We obtain the following results. 1. The dispersion in the near-infrared L-Z relation is reduced with respect to the dispersion in the optical L-Z relation, which agrees with expectations for reduced variations of stellar mass-to-light ratios at longer wavelengths compared to optical wavelengths. 2. The dispersion in the optical L-Z relation is similar over approximately 11 mag in optical luminosity. 3. With our constructed M-Z relation, we have extended the SDSS M-Z relation to lower masses by about 2.5 dex in stellar mass. 4. The dispersion in the M-Z relation appears to be comparable over a range of 5.5 dex in stellar mass.

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arXiv2006

M33's Variable A -- A Hypergiant Star More Than 35 Years in Eruption

Variable A in M33 is a member of a rare class of highly luminous, evolved stars near the upper luminosity boundary that show sudden and dramatic shifts in apparent temperature due to the formation of optically thick winds in high mass loss episodes. Recent optical and infrared spectroscopy and imaging reveal that its ``eruption'' begun in $\sim$1950 has ended, {\it lasting $\approx$ 45 yrs}. Our current observations show major changes in its wind from a cool, dense envelope to a much warmer state surrounded by low density gas with rare emission lines of Ca II, [Ca II] and K I. Its spectral energy distribution has unexpectedly changed, especially at the long wavelengths, with a significant decrease in its apparent flux, while the star remains optically obscured. We conclude that much of its radiation is now escaping out of our line of sight. We attribute this to the changing structure and distribution of its circumstellar ejecta corresponding to the altered state of its wind as the star recovers from a high mass loss event.

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arXiv2003

A Chandra LETGS observation of V4743 Sagittarius: A Super Soft X-ray Source and a Violently Variable Light Curve

V4743 Sgr (Nova Sgr 2002 No. 3) was discovered on 20 September 2002. We obtained a 5ks ACIS-S spectrum in November 2002 and found that the nova was faint in X-rays. We then obtained a 25ks CHANDRA LETGS observation on 19 March 2003. By this time, it had evolved into the Super Soft X-ray phase exhibiting a continuous spectrum with deep absorption features. The light curve from the observation showed large amplitude oscillations with a period of 1325s (22min) followed by a decline in total count rate after ~13ks of observations. The count rate dropped from ~40cts/s to practically zero within ~6ks and stayed low for the rest of the observation (~6ks). The spectral hardness ratio changed from maxima to minima in correlation with the oscillations, and then became significantly softer during the decay. Strong H-like and He-like lines of oxygen, nitrogen, and carbon were found in absorption during the bright phase, indicating temperatures between 1-2MK, but they were shifted in wavelength corresponding to a Doppler velocity of -2400km/s. The spectrum obtained after the decline in count rate showed emission lines of CVI, NVI, and NVII suggesting that we were seeing expanding gas ejected during the outburst, probably originating from CNO-cycled material. An XMM-Newton ToO observation, obtained on 4 April 2003 and a later LETGS observation from 18 July 2003 also showed oscillations, but with smaller amplitudes.

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arXiv2003

The Early Ultraviolet Evolution of the ONeMg Nova V382 Velorum 1999

We present a multiwavelength study of the ONeMg Galactic nova V382 Velorum 1999 using HST/STIS and FUSE ultraviolet spectra and comparisons with published groundbased optical spectra. We find a close match to the basic phenomenology of another well-studied ONeMg nova, V1974 Cygni (Nova Cygni 1992), in particular to the spectral development through the start of the nebular phase. Following an ``iron curtain'' phase, the nova proceeded through a stage of P Cygni line profiles on all important resonance lines, as in many ONeMg novae and unlike the CO class. Emergent emission lines displayed considerable structure, as seen in V1974 Cyg, indicating fragmentation of the ejecta at the earliest stages of the outburst. Analysis and modeling of our ultraviolet spectra suggest that 4 - 5 $\times$ 10$^{-4}$M$_{\odot}$ of material was ejected and that the distance to the nova is $\simeq 2.5$ kpc. Relative to solar values, we find the following abundances: He = 1.0, C = 0.6$\pm$0.3, N = 17$\pm$4, O = 3.4$\pm$0.3, Ne = 17$\pm$3, Mg = 2.6$\pm$0.1, Al = 21$\pm$2, and Si = 0.5$\pm$0.3. Finally, we briefly draw comparisons with Nova LMC 2000, another ONeMg nova, for which similar data were obtained with HST and FUSE.

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arXiv2002

Dust and molecules in the Local Group galaxy NGC 6822. III. The first-ranked HII region complex Hubble V

We present maps of the first-ranked HII region complex Hubble V in the metal-poor Local Group dwarf galaxy NGC 6822 in the first four transitions of CO, the 158 micron transition of C+, the 21-cm line of HI, the Pa-beta line of HII, and the continuum at 21 cm and 2.2 micron wavelengths. We have also determined various integrated intensities, notably of HCO+ and near-IR H2 emission. Although Hubble X is located in a region of relatively strong HI emission, our mapping failed to reveal any significant CO emission from it. The relatively small CO cloud complex associated with Hubble V is comparable in size to the ionized HII region. The CO clouds are hot (Tkin) = 150 K) and have high molecular gas densities (n(H2) = 10**4 cm**-3) Molecular hydrogen probably extends well beyond the CO boundaries. C+ column densities are more than an order of magnitude higher than those of CO. The total mass of the complex is about 10**6 M(sun) and molecular gas account for more than half of this. The complex is excited by luminous stars reddened or obscured at visual, but apparent at near-infrared wavelengths. The total embedded stellar mass may account for about 10% of the total mass, and the mass of ionized gas for half of that. Hubble V illustrates that modest star formation efficiencies may be associated with high CO destruction efficiencies in low-metallicity objects. The analysis of the Hubble V photon-dominated region (PDR) confirms in an independent manner the high value of the CO-to-H2 conversion factor X found earlier, characteristic of starforming low-metallicity regions.

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arXiv1996

The Near-infrared Spectrum of the Brown Dwarf Gliese 229B

A medium resolution 1.0-2.5um spectrum of the brown dwarf, Gliese 229B has been obtained using CGS4 on UKIRT. In addition to the broad spectral structure seen in earlier low resolution observations, the new spectrum reveals a large number of absorption lines, many of which can be identified with water vapor. Water and methane are both shown to be strong absorbers in the near-infrared spectrum of the object. Several spectral features in Gl 229B that are attributable to methane match ones seen in reflection in the giant outer planets and, in particular, Titan.

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