M. T. Rushton

Circumstellar discs in the young σ Orionis cluster

We present new K- and L � -band imaging observations for members of the young (3‐5 Myr) σ Orionis cluster, obtained at the United Kingdom Infrared Telescope (UKIRT) with the UKIRT 1‐5 micron Imager Spectrometer (UIST). 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 and 1.0 M� . This indicates a circumstellar disc frequency of at least (33 ± 6) per cent for this cluster, consistent with previous determinations from smaller samples and also consistent with the 3-Myr disc half-life suggested by Haisch et al. 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.

The Spitzer Infrared Spectrometer 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 μm 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 12 C/ 13 C ratio for the absorbing gas to be ∼3.2 +3.2; 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.

Infall and SiO emission in V838 Mon

ABSTRACT We present moderate and high resolution infrared spectroscopyof the peculiar eruptivevariable V838 Mon, which underwent a series of remarkable outbursts in early 2002.During the period covered by our observations, 2002 December–2003 December, thenear-infrared spectrum continued to show many of the characteristics of a very coolsupergiant. However, throughout this period the spectrum also revealed strong andvariable SiO first overtone emission, and Paβ emission. The 2003 December spectrumcontained a series of Tiilines with inverse P Cygni profiles. This is clear evidence thatsome material is falling inward towards the star.Key words: stars: individual: V838 Mon 1 INTRODUCTIONThe multiple outburst episode of V838 Mon inearly 2002 has been well documented (Munari et al.2002; Kimeswenger et al. 2002; Crause et al. 2003;Banerjee & Ashok 2002; Wisniewski et al. 2003;Rushton et al. 2005). The object was first detected inoutburst on 2002 January 6 (V max = 10) (Brown et al.2002), and subsequent outbursts developed in 2002 February(V

Search for molecular emission from V838 Monocerotis

We present a search for 1 2 CO and SiO emission in V838 Mon. We derive upper limits on the 1 2 CO and SiO emission, and on the total mass of the circumstellar material. Using an excitation temperature of 1000 K, and a likely distance of 6 kpc, the non-detection of 1 2 CO emission leads to a 3σ upper limit on the mass of gas around the central star to be 10 - 2 M O ..

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.

The properties of V838 Monocerotis in 2002 November

We present the results of modelling the 0.45-1 μm spectral energy distribution of V838 Mon for 2002 November. Synthetic spectra were calculated using the NextGen model atmospheres of Hauschildt et al. (1999, ApJ, 512, 377), which incorporate line lists for H 2 O, 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.

Infrared observations of the recurrent nova T Pyxidis: ancient dust basks in the warm glow of the 2011 outburst

We present Spitzer Space Telescope and Herschel Space Observatory infrared observations of the recurrent nova T Pyx during its 2011 eruption, complemented by ground-base optical-infrared photometry. We find that the eruption has heated dust in the pre-existing nebulosity associated with T Pyx. This is most likely interstellar dust swept up by T Pyx – either during previous eruptions or by a wind – rather than the accumulation of dust produced during eruptions.

Infrared observations of the recurrent nova T Pyxidis: ancient dust basks in the warm glow of the 2011 outburst★: IR observations of T Pyx

We present Spitzer Space Telescope and Herschel Space Observatory infrared observations of the recurrent nova T Pyx during its 2011 eruption, complemented by ground-base optical-infrared photometry. We find that the eruption has heated dust in the pre-existing nebulosity associated with T Pyx. This is most likely interstellar dust swept up by T Pyx – either during previous eruptions or by a wind – rather than the accumulation of dust produced during eruptions.