arXiv subjects

J. Bailey

Publications and source records attributed to J. Bailey.

44 records · Page 3Linked to original sources

arXiv2008

Beyond the Iron Peak: r- and s-process Elemental Abundances in Stars with Planets

We present elemental abundances of 118 stars (28 of which are known extrasolar planetary host stars) observed as part of the Anglo-Australian Planet Search. Abundances of O, Mg, Cr, Y, Zr, Ba, Nd and Eu (along with previously published abundances for C and Si) are presented. This study is one of the first to specifically examine planetary host stars for the heavy elements produced by neutron capture reactions. We find that the host stars are chemically different to both the standard solar abundance and non-host stars in all elements studied, with enrichments over non-host stars ranging from 0.06 dex (for O) to 0.11 dex (for Cr and Y). Such abundance trends are in agreement with other previous studies of field stars and lead us to conclude that the chemical anomalies observed in planetary host stars are the result of normal galactic chemical evolution processes. Based on this observation, we conclude that the observed chemical traits of planetary host stars are primordial in origin, coming from the original nebula and not from a ``pollution'' process occurring during or after formation and that planet formation occurs naturally with the evolution of stellar material.

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arXiv2006

Near Infrared Polarization Images of the Orion Nebula

Wide-field (~8' x 8') and deep near-infrared (JHKs bands) polarization images of the Orion nebulae (IRNe) around young stellar objects (YSOs), both massive and low-mass. We found the IRNe around both IRc2 and BN to be very extensive, suggesting that there might be two extended (>0.7 pc) bipolar/monopolar IRNe in these sources. We discovered at least 13 smaller-scale (~0.01-0.1 pc) IRNe around less-massive YSOs including the famous source theta^2 Ori C. We also suggest the presence of many unresolved (<690 AU) systems around low-mass YSOs and young brown dwarfs showing possible intrinsic polarizations. Wide-field infrared polarimetry is thus demonstrated to be a powerful technique in revealing IRNe and hence potential disk/outflow systems among high-mass to substellar YSOs.

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arXiv2006

Subaru IR Echelle Spectroscopy of Herbig-Haro Driving Sources I. H_2 and [Fe II] Emission

We present infrared echelle spectroscopy of three Herbig-Haro (HH) driving sources (SVS 13, B5-IRS 1 and HH 34 IRS) using Subaru-IRCS. The large diameter of the telescope and wide spectral coverage of the spectrograph allowed us to detect several H_2 and [Fe II] lines in the H- and K-bands. These include H_2 lines arising from v=1-3 and J=1-11, and [Fe II] lines with upper level energies of E/k=1.1-2.7x10^4 K. For all objects the outflow is found to have two velocity components: (1) a high-velocity (-70 to -130 km s^-1) component (HVC), seen in [Fe II] or H_2 emission and associated with a collimated jet; and (2) a low-velocity (-10 to -30 km s^-1) component (LVC), which is seen in H_2 emission only and is spatially more compact. Such a kinematic structure resembles optical forbidden emission line outflows associated with classical T Tauri stars, whereas the presence of H_2 emission reflects the low-excitation nature of the outflowing gas close to these protostars. The observed H_2 flux ratios indicate a temperature of 2-3x10^3 K, and a gas density of 10^5 cm^-3 or more, supporting shocks as the heating mechanism. B5-IRS 1 exhibits faint extended emission associated with the H_2-LVC, in which the radial velocity slowly increases with distance from the protostar (by ~20 km s^-1 at ~500 AU). This is explained as warm molecular gas entrained by an unseen wide-angled wind. The [Fe II] flux ratios indicate electron densities to be ~10^4 cm^-3 or greater, similar to forbidden line outflows associated with classical T Tauri stars. Finally the kinematic structure of the [Fe II] emission associated with the base of the B5-IRS 1 and HH 34 IRS outflows is shown to support disk-wind models.

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arXiv2005

On the Detection of Artefacts in Spectro-astrometry

We demonstrate that artificial bipolar structure can be detected using spectro-astrometry when the point spread function (PSF) of a point source suffers distortion in a relatively wide slit. Spectro-astrometry is a technique which allows us to probe the spatial structure of astronomical sources on milliarcsecond scales making it possible to detect close binaries and to study the geometry and kinematics of outflowing gas on scales much smaller than the seeing or the diffraction limit of the telescope. It is demonstrated that distortion of the PSF, caused by tracking errors of the telescope or unstable active optics during an exposure can induce artificial signals which may be misinterpreted as a real-astrometric signal. Using simulations we show that these may be minimised by using a narrow slit relative to the seeing. Spectra should be obtained at anti-parallel slit position angles (eg. 0 and 180 degrees) for comparison in order to allow artificial signatures to be identified.

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arXiv2003

Detection of a warm molecular wind in DG Tauri

We detect near-infrared H2 emission in DG Tau using the Infrared Camera and Spectrograph (IRCS) on the 8.2-m SUBARU telescope. The spectra obtained along the jet axis show that the centroidal position of the 1-0 S(1) emission is offset by 0.2" from the star towards the jet, while those obtained perpendicular to the jet axis show a marginal extension, indicating that the emission line region has a typical width of ~0.6". Their line profiles show a peak velocity of ~15 km s^-1 blueshifted from the systemic velocity. These results indicate that the emission originates from a warm molecular wind with a flow length and width of ~40 and ~80 AU, respectively. The line flux ratios I_{1-0 S(0)}/I_{1-0 S(1)} and an upper limit for I_{2-1 S(1)}/I_{1-0 S(1)}) suggest that the flow is thermalized at a temperature of ~2000 K, and is likely heated by shocks or ambipolar diffusion. The observed velocity and spatial extension suggest that the H2 and forbidden line emission originate from different components of the same flow, i.e., a fast and partially ionised component near the axis and a slow molecular component surrounding it. Such a flow geometry agrees with model predictions of magneto-centrifugal driven winds.

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arXiv2002

GRB 011121: A Massive Star Progenitor

Of the cosmological gamma-ray bursts, GRB 011121 has the lowest redshift, z=0.36. More importantly, the multi-color excess in the afterglow detected in the Hubble Space Telescope (HST) light curves is compelling observational evidence for an underlying supernova. Here we present near-infrared and radio observations of the afterglow. We undertake a comprehensive modeling of these observations and those reported in the literature and find good evidence favoring a wind-fed circumburst medium. In detail, we infer the progenitor had a mass loss rate of Mdot ~ 10^-7 / v_w3 Mo/yr where v_w3 is the speed of the wind from the progenitor in units of 10^3 km/s. This mass loss rate is similar to that inferred for the progenitor of SN 1998bw which has been associated with GRB 980425. Our data, taken in conjunction with the HST results of Bloom et al. (2002), provide a consistent picture: the long duration GRB 011121 had a massive star progenitor which exploded as a supernova at about the same time as the GRB event.

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arXiv2002

HeI 1.083 micron emission and absorption in DG Tau: line excitation in jet, hot wind, and accretion flow

We present long-slit spectroscopy and spectro-astrometry of HeI 1.083 micron emission in the T Tauri star, DG Tau. We identify three components in the HeI feature: (1) a blueshifted emission component atv -200 km s^-1, (2) a bright emission component at zero-velocity with a FWZI of ~500 km s^-1, and (3) a blueshifted absorption feature at velocities between -250 and -500 km s^-1. The position and velocity of the blueshifted HeI emission coincide with a high-velocity component (HVC) of the [FeII] 1.257 micron emission, which arises from a jet within an arcsecond of the star. The presence of such a high excitation line (excitation energy ~ 20 eV) within the jet supports the scenario of shock heating. The bright HeI component does not show any spatial extension, and it is likely to arise from magnetospheric accretion columns. The blueshifted absorption shows greater velocities than that in H-alpha, suggesting that these absorption features arise from the accelerating wind close to the star.

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arXiv2001

Circumstellar structure of RU Lupi down to au scales

We have used the technique of spectro-astrometry to study the milli-arcsecond scale structure of the emission lines in the T Tauri star RU Lupi. The wings of the H-alpha emission are found to be displaced from the star towards the south-west (blue wing) and north-east (red wing) with angular scales of 20-30 milli-arcsecs. This structure is consistent with a bipolar outflow from the star. From a study of the variability of the intensity and position spectra we argue that a combination of magnetically-driven bipolar outflow and accreting gas contribute to the H-alpha emission. On the other hand, the [OI] and [SII] emission are displaced from the star to the south-west but at much larger distances than the H-alpha, hundreds of milli-arcsecs for the high-velocity component (HVC) and down to 30 milli-arcsecs for the low-velocity components (LVC). The presence of both red-shifted and blue-shifted outflows in H-alpha but only a blue-shifted outflow in the forbidden lines can be explained if the disc obscures the red-shifted forbidden line outflow, but a disc gap with outer radius 3-4 au allows the red-shifted H-alpha to be seen. This gap could be induced by an unseen companion.

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