arXiv subjects

M. T. Rushton

Publications and source records attributed to M. T. Rushton.

26 records · Page 2Linked to original sources

arXiv2008

Sakurai's Object: characterising the near-infrared CO ejecta between 2003 and 2007

We present observations of Sakurai's Object obtained at 1-5um between 2003 and 2007. By fitting a radiative transfer model to an echelle spectrum of CO fundamental absorption features around 4.7um, we determine the excitation conditions in the line-forming region. We find 12C/13C~3.5, consistent with CO originating in ejecta processed by the very late thermal pulse, rather than in the pre-existing planetary nebula. We demonstrate the existence of 2.2e-6<M<2.7e-6 Msun of CO ejecta outside the dust, forming a high-velocity wind of 500+/-80 km/s. We find evidence for significant weakening of the CO band and cooling of the dust around the central star between 2003 and 2005. The gas and dust temperatures are implausibly high for stellar radiation to be the sole contributor.

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arXiv2008

How peculiar is the "peculiar variable" DZ Crucis (Nova Cru 2003)?

The variable star DZ Cru was thought to be a nova when it was discovered in eruption in 2003 August. This explanation was later challenged, however, when the first spectra of the object were reported. We present near infrared spectroscopy of DZ Cru obtained at the New Technology Telescope on 3 occasions, starting 1.5 years after outburst, with the aim of establishing the nature of the object. The spectra display H I, O I, [N I] emission lines, together with He I P Cygni lines superposed on a dust continuum. These observations suggest the "peculiar variable in Crux'' is a classical nova.

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arXiv2007

Infrared spectroscopy of carbon monoxide in V838 Mon during 2002--2006

We report spectra of the overtone and fundamental bands of CO in the eruptive variable V838 Mon, which trace the recent evolution of the star and allow its ejecta to be characterized. The data were obtained at the United Kingdom Infrared Telescope on fourteen nights from 2002 January, shortly after the first outburst of the star, to 2006 April. Although the near-infrared stellar spectrum superficially resembled a cool supergiant after both the first and third of its outbursts in 2002, its infrared "photosphere" at that time consisted of highly blueshifted gas that was moving outward from the original stellar surface. A spectrum obtained during the third outburst reveals a remarkable combination of emission and absorption in the CO first overtone bands. The most recent observations show a composite spectrum that includes a stellar-like photosphere at a temperature similar to that seen just after the initial outburst, but at a radial velocity redshifted by 15 km/s relative to the stellar velocity determined from SiO maser emission, suggesting that the atmosphere is now contracting. Three shell components, corresponding to expansion velocities of 15, 85, and 145 km/s, also are present, but absorption is seen at all expansion velocities out to 200km/s. Weak absorption features of fundamental band lines of 13CO have been detected. However, the large uncertainty in the value of [12C/13C] does not constrain the evolutionary status of the progenitor.

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arXiv2006

The properties of V838 Mon in 2002 November

We present the results of modelling the 0.45--1 micron spectral energy distribution of V838 Mon for 2002 November. Synthetic spectra were calculated using the NextGen model atmospheres of Hauschildt et al. (1999), which incorporate line lists for H2O, TiO, CrH, FeH, CO, and MgH, as well as the VALD atomic line list. Fits to the observed spectra show that, in 2002 November, the effective temperature of V838 Mon was approximately 2000 +/-100 K. Our theoretical spectra show a comparatively weak dependence on log g. Preliminary analysis of the hot star observed together with V838 Mon shows it to be a normal B3V dwarf.

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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

Infrared observations of V838 Mon

We describe the results of fitting simple spherically symmetric models to the first overtone CO and AlO A-X (2-0) bands in V838 Mon. We find that the temperature and column of both CO and AlO systematically decline over the period 2002 October - 2005 February and that an additional, hotter and denser, component is present from 2005 January. We also describe the results of an observation of the star and its light echo at 850micron. We do not detect the `infrared' echo at these wavelength, and place an upper limit of 3x10^7 cm^-2 on the column of grains.

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arXiv2006

Circumstellar discs in the young sigma Orionis cluster

We present new K- and L'-band imaging observations for members of the young (3-5 Myr) sigma Orionis cluster, obtained with UIST at UKIRT. We determine (K-L') colour excesses with respect to the photospheres, finding evidence for warm circumstellar dust around 27 out of 83 cluster members that have masses between 0.04 Msun and 1.0 Msun. This indicates a circumstellar disc frequency of at least (33 +/- 6)% for this cluster, consistent with previous determinations from smaller samples (Oliveira et al. 2004) and also consistent with the 3 Myr disc half-life suggested by Haisch et al. (2001). There is marginal evidence that the disc frequency declines towards lower masses, but the data are also consistent with no mass-dependence at all. There is no evidence for spatial segregation of objects with and without circumstellar discs.

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arXiv2005

Infall and SiO emission in V838 Mon

We present moderate and high resolution infrared spectroscopy of the peculiar eruptive variable V838 Mon, which underwent a series of remarkable outbursts in early 2002. During the period covered by our observations, 2002 December-2003 December, the near-infrared spectrum continued to show many of the characteristics of a very cool supergiant. However, throughout this period the spectrum also revealed strong and variable SiO first overtone emission, and Paschen Beta emission. The 2003 December spectrum contained a series of Ti I lines with inverse P Cygni profiles. This is clear evidence that some material is falling inward towards the star.

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