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Register a new userSubmillimeter Observations of the Young Low-Mass Object IRAS 04158+2805
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We present high spatial resolution Submillimeter Array observations and supplementary single-dish photometry of the molecular gas and dust around IRAS 04158+2805, a young source with spectral type M5-M6 in the Taurus star-forming region. A bright, highly elongated dust structure that extends 8 (~1120 AU) in diameter is revealed in a 883 micron thermal continuum image. This emission geometry is in good agreement with optical observations that show a similar structure in absorption, aligned perpendicular to bipolar scattered light nebulae. However, the interferometric data also clearly demonstrate that the submillimeter continuum emission is not centrally concentrated, but rather appears to have a toroidal geometry with substantially lower intensities inside a radius of ~250-300 AU. Spatially resolved emission from the CO J=3-2 transition exhibits a velocity gradient along the major axis of the dust structure. If this kinematic pattern is interpreted as the signature of rotation around a central object, a relatively low mass is inferred (M_star = 0.3 M_sun, with a ~50% uncertainty). We discuss several possible explanations for the observed gas and dust environment around IRAS 04158+2805, including a flattened envelope with an outflow cavity and a large circumbinary ring. This source offers unique views of the gas and dust environment surrounding a young low-mass stellar system. Its properties are generally not commensurate with formation scenarios for such low-mass objects that rely on dynamical ejection, but rather confirms that a single mechanism - molecular cloud core collapse and fragmentation - can produce stars over a wide range of stellar masses (at least an order of magnitude).
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We present a study of the circumstellar environment of IRAS 04158+2805 based on multi-wavelength observations and models. Images in the optical and near-infrared, a polarisation map in the optical, and mid-infrared spectra were obtained with VLT-FORS1, CFHT-IR, and Spitzer-IRS. Additionally we used an X-ray spectrum observed with Chandra. We interpret the observations in terms of a central star surrounded by an axisymmetric circumstellar disc, but without an envelope, to test the validity of this simple geometry. We estimate the structural properties of the disc and its gas and dust content. We modelled the dust disc with a 3D continuum radiative transfer code, MCFOST, based on a Monte-Carlo method that provides synthetic scattered light images and polarisation maps, as well as spectral energy distributions. We find that the disc images and spectral energy distribution narrowly constrain many of the disc model parameters, such as a total dust mass of 1.0-1.75x10^-4 sollar masses and an inclination of 62-63 degrees. The maximum grain size required to fit all available data is of the order of 1.6-2.8 microns although the upper end of this range is loosely constrained. The observed optical polarisation map is reproduced well by the same disc model, suggesting that the geometry we find is adequate and the optical properties are representative of the visible dust content. We compare the inferred dust column density to the gas column density derived from the X-ray spectrum and find a gas-to-dust ratio along the line of sight that is consistent with the ISM value. To our knowledge, this measurement is the first to directly compare dust and gas column densities in a protoplanetary disc.
IRAS~04158+2805 has long been thought to be a very low mass T-Tauri star (VLMS) surrounded by a nearly edge-on, extremely large disc. Recent observations revealed that this source hosts a binary surrounded by an extended circumbinary disc with a central dust cavity. In this paper, we combine ALMA multi-wavelength observations of continuum and $^{12}$CO line emission, with H$alpha$ imaging and Keck astrometric measures of the binary to develop a coherent dynamical model of this system. The system features an azimuthal asymmetry detected at the western edge of the cavity in Band~7 observations and a wiggling outflow. Dust emission in ALMA Band 4 from the proximity of the individual stars suggests the presence of marginally resolved circumstellar discs. We estimate the binary orbital parameters from the measured arc of the orbit from Keck and ALMA astrometry. We further constrain these estimates using considerations from binary-disc interaction theory. We finally perform three SPH gas + dust simulations based on the theoretical constraints; we post-process the hydrodynamic output using radiative transfer Monte Carlo methods and directly compare the models with observations. Our results suggest that a highly eccentric $esim 0.5textrm{--}0.7$ equal mass binary, with a semi-major axis of $sim 55$ au, and small/moderate orbital plane vs. circumbinary disc inclination $thetalesssim 30^circ$ provides a good match with observations. A dust mass of $sim 1.5times 10^{-4} {rm M_odot}$ best reproduces the flux in Band 7 continuum observations. Synthetic CO line emission maps qualitatively capture both the emission from the central region and the non-Keplerian nature of the gas motion in the binary proximity.
We present results of submillimeter observations of a low-mass young stellar objects (YSOs) condensation in the Cederblad 110 region of the Chamaeleon I dark cloud with Atacama Submillimeter Telescope Experiment. Our HCO+(J=4-3) map reveals a dense molecular gas with an extent of ~ 0.1 pc, which is a complex of two envelopes associated with class I sources Ced110 IRS4 and IRS11 and a very young object Cha-MMS1. The other two class I sources in this region, IRS6 and NIR89, are located outside the clump and have no extended HCO+ emission. HCO+ abundance is calculated to be 2.6 x 10^{-10} for MMS1 and 3.4 x 10^{-9} for IRS4, which are comparable to the reported value for other young sources. Bipolar outflows from IRS4 and IRS6 are detected in our 12CO(J=3-2) map. The outflow from IRS4 seems to collide with Cha-MMS1. The outflow has enough momentum to affect gas motion in MMS1, although no sign has been detected to indicate that a triggered star formation has occurred.
We present a complete low-resolution (R~100) near-infrared spectrum of the substellar object GY11, member of the rho-Ophiuchi young association. The object is remarkable because of its low estimated mass and age and because it is associated with a mid-infrared source, an indication of a surrounding dusty disk. Based on the comparison of our spectrum with similar spectra of field M-dwarfs and atmospheric models, we obtain revised estimates of the spectral type, effective temperature and luminosity of the central object. These parameters are used to place the object on a Hertzprung-Russell diagram and to compare with the prediction of pre-main sequence evolutionary models. Our analysis suggests that the central object has a very low mass, probably below the deuterium burning limit and in the range 8-12MJupiter, and a young age, less than 1Myr. The infrared excess is shown to be consistent with the emission of a flared, irradiated disk similar to those found in more massive brown dwarf and TTauri systems. This result suggests that substellar objects, even the so-called isolated planetary mass objects, found in young stellar associations are produced in a similar fashion as stars, by core contraction and gravitational collapse.
BVRIJHK photometry, Spitzer-GLIMPSE photometry and HK band spectroscopy were used to study the stellar content of IRAS 19343+2026, a (proto)star/cluster candidate, located close to the Galactic plane. The data suggest that IRAS 19343+2026 is a rich cluster associated with a massive protostar of 7.6 Msol with an age of ~ 10^5 yr. Three point sources in the vicinity of the far-infrared (FIR) peak are also found to be early B type stars. The remaining (predominantly low mass) members of the cluster are best represented by a 1 - 3 Myr pre-main-sequence (PMS) population. HK band spectra of two bright and five faint point sources in the cluster confirm that the results obtained from the photometry are good representations of their young stellar object (YSO) nature. Thus, IRAS 19343+2026 is a young cluster with at least four early B-type stars classified as young (10^4 - 10^5 yr), that are surrounded by a somewhat older (1 - 3 Myr) population of low mass YSOs. Together, these results argue for a scenario in which low mass stars form prior to massive stars in a cluster forming environment. We compute the Initial Mass Function (IMF) for this cluster using the K-band luminosity function; the slope of the IMF is shallower than predicted by the Salpeters mass function. The cluster mass, Mtot, is estimated to be in the range ~ 307 Msol (from the data completeness limit) - 585 Msol (extrapolated down to the brown dwarf limit, assuming a certain IMF).
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