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Register a new userGomezs Hamburger (IRAS 18059-3211): A pre main-sequence A-type star
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Added by
Valentin Bujarrabal
Publication date
2008
fields
Physics
and research's language is
English
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We study the nature of Gomezs Hamburger (IRAS 18059-3211), a nebula that has been proposed to be a post-AGB object. Such a classification is not confirmed; instead, we argue that it will be a key object in the study of disks rotating around young stars. We present high resolution SMA maps of CO J=2--1 in Gomezs Hamburger. The data are analyzed by means of a code that simulates the emission of a nebula showing a variety of physical conditions and kinematics. Our observations clearly show that the CO emitting gas in Gomezs Hamburger forms a spectacular disk in keplerian rotation. Model calculations undoubtly confirm this result. The central (mainly stellar) mass is found to be high, ~ 4 Mo for a distance of 500 pc. The mass and (relatively low) luminosity of the source are, independent of the assumed distance, very different from those possible in evolved stars. Gomezs Hamburger is probably a transitional object between the pre-MS and MS phases, still showing interstellar material around the central star or stellar system.
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Unraveling the 3D physical structure, the temperature and density distribution, of protoplanetary discs is an essential step if we are to confront simulations of embedded planets or dynamical instabilities. In this paper we focus on Submillimeter Array observations of the edge-on source, Gomezs Hamburger, believed to host an over-density hypothesised to be a product of gravitational instability in the disc, GoHam b. We demonstrate that, by leveraging the well characterised rotation of a Keplerian disc to deproject observations of molecular lines in position-position-velocity space into disc-centric coordinates, we are able to map out the emission distribution in the (r, z) plane and (x, y, z) space. We show that 12CO traces an elevated layer of $z,/,r sim 0.3$, while 13CO traces deeper in the disc at $z,/,r lesssim 0.2$. We localize emission associated with GoHam b, finding it at deprojected radius of approximately 500 au and at polar angle of +- 30 degrees from the disc major axis. At the spatial resolution of $sim 1.5^{primeprime}$, GoHam b is spatially unresolved, with an upper limit to its radius of $<190$~au.
Planets are thought to form in the gas and dust disks around young stars. In particular, it has been proposed that giant planets can form through the gravitational instability of massive extended disks around intermediate-mass stars. However, we still lack direct observations to constrain this mechanism. We have spatially resolved the 8.6 and 11.2 $mu$m emission of a massive protoplanetary disk seen edge on around an A star, Gomezs Hamburger (GoHam), using VISIR at the Very Large Telescope. A compact region situated at a projected distance of $350pm50$ AU south of the central star is found to have a reduced emission.This asymmetry is fully consistent with the presence of a cold density structure, or clump, identified in earlier CO observations, and we derive physical characteristics consistent with those observations: a mass of 0.8-11.4 Jupiter masses (for a dust-to-gas mass ratio of 0.01), a radius of about 10$^2$ astronomical units, and a local density of about $10^{7}$ cm$^{-3}$. Based on this evidence, we argue that this clump, which we call GoHam b, is a promising candidate for a young protoplanet formed by gravitational instability that might be representative of the precursors of massive planets observed around A stars, such as HR 8799 or Beta pictoris. More detailed studies at high angular resolution are needed to better constrain the physical properties of this object to confirm this proposal.
We report the detection of V1298 Tau b, a warm Jupiter-sized planet ($R_P$ = 0.91 $pm$ 0.05~ $R_mathrm{Jup}$, $P = 24.1$ days) transiting a young solar analog with an estimated age of 23 million years. The star and its planet belong to Group 29, a young association in the foreground of the Taurus-Auriga star-forming region. While hot Jupiters have been previously reported around young stars, those planets are non-transiting and near-term atmospheric characterization is not feasible. The V1298 Tau system is a compelling target for follow-up study through transmission spectroscopy and Doppler tomography owing to the transit depth (0.5%), host star brightness ($K_s$ = 8.1 mag), and rapid stellar rotation ($vsin{i}$ = 23 kms). Although the planet is Jupiter-sized, its mass is presently unknown due to high-amplitude radial velocity jitter. Nevertheless, V1298 Tau b may help constrain formation scenarios for at least one class of close-in exoplanets, providing a window into the nascent evolution of planetary interiors and atmospheres.
We present time series observations of intermediate mass PMS stars belonging to the young star cluster IC 348. The new data reveal that a young member of the cluster, H254, undergoes periodic light variations with delta Scuti-like characteristics. This occurrence provides an unambiguous evidence confirming the prediction that intermediate-mass pre-main sequence (PMS) stars should experience this transient instability during their approach to the main-sequence. On the basis of the measured frequency f=7.406 c/d, we are able to constrain the intrinsic stellar parameters of H254 by means of linear, non adiabatic, radial pulsation models. The range of the resulting luminosity and effective temperature permitted by the models is narrower than the observational values. In particular, the pulsation analysis allows to derive an independent estimate of the distance to IC 348 of about 320 pc. Further observations could either confirm the monoperiodic nature of H254 or reveal the presence of other frequencies.
We present the first maps of the surface magnetic fields of a pre-main sequence binary system. Spectropolarimetric observations of the young, 18 Myr, HD 155555 (V824 Ara, G5IV + K0IV) system were obtained at the Anglo-Australian Telescope in 2004 and 2007. Both datasets are analysed using a new binary Zeeman Doppler imaging (ZDI) code. This allows us to simultaneously model the contribution of each component to the observed circularly polarised spectra. Stellar brightness maps are also produced for HD 155555 and compared to previous Doppler images. Our radial magnetic maps reveal a complex surface magnetic topology with mixed polarities at all latitudes. We find rings of azimuthal field on both stars, most of which are found to be non-axisymmetric with the stellar rotational axis. We also examine the field strength and the relative fraction of magnetic energy stored in the radial and azimuthal field components at both epochs. A marked weakening of the field strength of the secondary star is observed between the 2004 and 2007 epochs. This is accompanied by an apparent shift in the location of magnetic energy from the azimuthal to radial field. We suggest that this could be indicative of a magnetic activity cycle. We use the radial magnetic maps to extrapolate the coronal field (by assuming a potential field) for each star individually - at present ignoring any possible interaction. The secondary star is found to exhibit an extreme tilt (~75 deg) of its large scale magnetic field to that of its rotation axis for both epochs. The field complexity that is apparent in the surface maps persists out to a significant fraction of the binary separation. Any interaction between the fields of the two stars is therefore likely to be complex also. Modelling this would require a full binary field extrapolation.
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