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Register a new userHigh Resolution Spectroscopy of [NeII] Emission from AA Tau and GM Aur
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We present high resolution (R=80,000) spectroscopy of [NeII] emission from two young stars, GM Aur and AA Tau, which have moderate to high inclinations. The emission from both sources appears centered near the stellar velocity and is broader than the [NeII] emission measured previously for the face-on disk system TW Hya. These properties are consistent with a disk origin for the [NeII] emission we detect, with disk rotation (rather than photoevaporation or turbulence in a hot disk atmosphere) playing the dominant role in the origin of the line width. In the non-face-on systems, the [NeII] emission is narrower than the CO fundamental emission from the same sources. If the widths of both diagnostics are dominated by Keplerian rotation, this suggests that the [NeII] emission arises from larger disk radii on average than does the CO emission. The equivalent width of the [NeII] emission we detect is less than that of the spectrally unresolved [NeII] feature in the Spitzer spectra of the same sources. Variability in the [NeII] emission or the mid-infrared continuum, a spatially extended [NeII] component, or a very (spectrally) broad [NeII] component might account for the difference in the equivalent widths.
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Millimeter-wavelength polarization measurements offer a promising method for probing the geometry of magnetic fields in circumstellar disks. Single dish observations and theoretical work have hinted that magnetic field geometries might be predominantly toroidal, and that disks should exhibit millimeter polarization fractions of 2-3%. While subsequent work has not confirmed these high polarization fractions, either the wavelength of observation or the target sources differed from the original observations. Here we present new polarimetric observations of three nearby circumstellar disks at 2 resolution with the Submillimeter Array (SMA) and the Combined Array for Research in Millimeter Astronomy (CARMA). We reobserve GM Aur and DG Tau, the systems in which millimeter polarization detections have been claimed. Despite higher resolution and sensitivity at wavelengths similar to the previous observations, the new observations do not show significant polarization. We also add observations of a new HAeBe system, MWC 480. These observations demonstrate that a very low (<0.5%) polarization fraction is probably common at large (>100 AU) scales in bright circumstellar disks. We suggest that high-resolution observations may be worthwhile to probe magnetic field structure on linear distances smaller than the disk scale height, as well as in regions closer to the star that may have larger MRI-induced magnetic field strengths.
Constraining the spatial and thermal structure of the gaseous component of circumstellar disks is crucial to understand star and planet formation. Models predict that the [Ne II] line at 12.81 {mu}m detected in young stellar objects with Spitzer traces disk gas and its response to high energy radiation, but such [Ne II] emission may also originate in shocks within powerful outflows. To distinguish between these potential origins for mid-infrared [Ne II] emission and to constrain disk models, we observed 32 young stellar objects using the high resolution (R~30000) mid-infrared spectrograph VISIR at the VLT. We detected the 12.81 {mu}m [Ne II] line in 12 objects, tripling the number of detections of this line in young stellar objects with high spatial and spectral resolution spectrographs. We obtain the following main results: a) In Class I objects the [Ne II] emission observed from Spitzer is mainly due to gas at a distance of more than 20-40 AU from the star, where neon is, most likely, ionized by shocks due to protostellar outflows. b) In transition and pre-transition disks, most of the emission is confined to the inner disk, within 20-40 AU from the central star. c) Detailed analysis of line profiles indicates that, in transition and pre-transition disks, the line is slightly blue-shifted (2-12 km s{^-1}) with respect to the stellar velocity, and the line width is directly correlated with the disk inclination, as expected if the emission is due to a disk wind. d) Models of EUV/X-ray irradiated disks reproduce well the observed relation between the line width and the disk inclination, but underestimate the blue-shift of the line.
We measured the $12.8mu$m [NeII] line in the dwarf starburst galaxy He 2-10 with the high-resolution spectrometer TeXeS on the NASA IRTF. The data cube has diffraction-limited spatial resolution $sim1^{primeprime}$ and total velocity resolution including thermal broadening of $sim5$km/s. This makes it possible to compare the kinematics of individual star-forming clumps and molecular clouds in the three dimensions of space and velocity, and allows us to determine star formation efficiencies. The kinematics of the ionized gas confirm that the starburst contains multiple dense clusters. From the $M/R$ of the clusters and the $simeq30-40$% star formation efficiencies the clusters are likely to be bound and long lived, like globulars. Non-gravitational features in the line profiles show how the ionized gas flows through the ambient molecular material, as well as a narrow velocity feature which we identify with the interface of the HII region and a cold dense clump. These data offer an unprecedented view of the interaction of embedded HII regions with their environment.
We report the first detailed chemical abundances for 5 globular clusters (GCs) in M31 from high-resolution (R ~ 25,000) spectroscopy of their integrated light. These GCs are the first in a larger set of clusters observed as part of an ongoing project to study the formation history of M31 and its globular cluster population. The data presented here were obtained with the HIRES echelle spectrograph on the Keck I telescope, and are analyzed using a new integrated light spectra analysis method that we have developed. In these clusters, we measure abundances for Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Y, and Ba, ages >10 Gyrs, and a range in [Fe/H] of -0.9 to -2.2. As is typical of Milky Way GCs, we find these M31 GCs to be enhanced in the alpha-elements Ca, Si, and Ti relative to Fe. We also find [Mg/Fe] to be low relative to other [alpha/Fe], and [Al/Fe] to be enhanced in the integrated light abundances. These results imply that abundances of Mg, Al (and likely O, Na) recovered from integrated light do display the inter- and intra-cluster abundance variations seen in individual Milky Way GC stars, and that special care should be taken in the future in interpreting low or high resolution integrated light abundances of globular clusters that are based on Mg-dominated absorption features. Fe-peak and the neutron-capture elements Ba and Y also follow Milky Way abundance trends. We also present high-precision velocity dispersion measurements for all 5 M31 GCs, as well as independent constraints on the reddening toward the clusters from our analysis.
We present a detailed analysis of the XMM-Newton RGS high resolution X-ray spectra of the Seyfert 2 galaxy, Mrk573. This analysis is complemented by the study of the Chandra image, and its comparison to optical (HST) and radio (VLA) data. The soft X-ray emission is mainly due to gas photoionised by the central AGN, as indicated by the detection of radiative recombination continua from OVII and OVIII, as well as by the prominence of the OVII forbidden line. This result is confirmed by the best fit obtained with a self-consistent CLOUDY photoionisation model. However, a collisionally excited component is also required, in order to reproduce the FeXVII lines, accounting for about 1/3 of the total luminosity in the 15-26 A band. Once adopted the same model in the Chandra ACIS data, another photoionised component, with higher ionisation parameter, is needed to take into account emission from higher Z metals. The broadband ACIS spectrum also confirms the Compton-thick nature of the source. The imaging analysis shows the close morphological correspondence between the soft X-ray and the [OIII] emission. The radio emission appears much more compact, although clearly aligned with the narrow line region. The collisional phase of the soft X-ray emission may be due to starburst, requiring a star formation rate of $simeq5-9$ M$_odot$ yr$^{-1}$, but there is no clear evidence of this kind of activity from other wavelengths. On the other hand, it may be related to the radio ejecta, responsible for the heating of the plasma interacting with the outflow, but the estimated pressure of the hot gas is much larger than the pressure of the radio jets, assuming equipartition and under reasonable physical parameters.
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