Comparison of high-latitude line-of-sight ozone column density with derived ozone fields and the effects of horizontal inhomogeneity

International audienceExtensive ozone measurements were made during the second SAGE III Ozone Loss and Validation Experiment (SOLVE II). We compare high-latitude line-of-sight (LOS) slant column ozone measurements from the NASA DC-8 to ozone simulated by forward integration of measurement-derived ozone fields constructed both with and without the assumption of horizontal homogeneity. The average bias and rms error of the simulations assuming homogeneity are relatively small (?6 and 10%, respectively) in comparison to the LOS measurements. The comparison improves significantly (?2% bias; 8% rms error) using forward integrations of three-dimensional proxy ozone fields reconstructed from potential vorticity-O3 correlations. The comparisons provide additional verification of the proxy fields and quantify the influence of large-scale ozone inhomogeneity. The spatial inhomogeneity of the atmosphere is a source of error in the retrieval of trace gas vertical profiles and column abundance from LOS measurements, as well as a complicating factor in intercomparisons that include LOS measurements at large solar zenith angles

Magellanic Cloud Periphery Carbon Stars IV: The SMC

The kinematics of 150 carbon stars observed at moderate dispersion on the periphery of the Small Magellanic Cloud are compared with the motions of neutral hydrogen and early type stars in the Inter-Cloud region. The distribution of radial velocities implies a configuration of these stars as a sheet inclined at 73+/-4 degrees to the plane of the sky. The near side, to the South, is dominated by a stellar component; to the North, the far side contains fewer carbon stars, and is dominated by the neutral gas. The upper velocity envelope of the stars is closely the same as that of the gas. This configuration is shown to be consistent with the known extension of the SMC along the line of sight, and is attributed to a tidally induced disruption of the SMC that originated in a close encounter with the LMC some 0.3 to 0.4 Gyr ago. The dearth of gas on the near side of the sheet is attributed to ablation processes akin to those inferred by Weiner & Williams (1996) to collisional excitation of the leading edges of Magellanic Stream clouds. Comparison with pre LMC/SMC encounter kinematic data of Hardy, Suntzeff, & Azzopardi (1989) of carbon stars, with data of stars formed after the encounter, of Maurice et al. (1989), and Mathewson et al. (a986, 1988) leaves little doubt that forces other than gravity play a role in the dynamics of the H I.Comment: 30 pages; 7 figures, latex compiled, 1 table; to appear in AJ (June 2000

Superbubble evolution including the star-forming clouds: Is it possible to reconcile LMC observations with model predictions?

Here we present a possible solution to the apparent discrepancy between the observed properties of LMC bubbles and the standard, constant density bubble model. A two-dimensional model of a wind-driven bubble expanding from a flattened giant molecular cloud is examined. We conclude that the expansion velocities derived from spherically symmetric models are not always applicable to elongated young bubbles seen almost face-on due to the LMC orientation. In addition, an observational test to differentiate between spherical and elongated bubbles seen face-on is discussed.Comment: 25 pages, 7 figures, accepted to ApJ (September, 1999 issue

Spitzer IRAC Low Surface Brightness Observations of the Virgo Cluster

We present 3.6 and 4.5 micron Spitzer IRAC imaging over 0.77 square degrees at the Virgo cluster core for the purpose of understanding the formation mechanisms of the low surface brightness intracluster light features. Instrumental and astrophysical backgrounds that are hundreds of times higher than the signal were carefully characterized and removed. We examine both intracluster light plumes as well as the outer halo of the giant elliptical M87. For two intracluster light plumes, we use optical colors to constrain their ages to be greater than 3 & 5 Gyr, respectively. Upper limits on the IRAC fluxes constrain the upper limits to the masses, and optical detections constrain the lower limits to the masses. In this first measurement of mass of intracluster light plumes we find masses in the range of 5.5 x 10^8 - 4.5 x 10^9 and 2.1 x 10^8 - 1.5 x 10^9 solar masses for the two plumes for which we have coverage. Given their expected short lifetimes, and a constant production rate for these types of streams, integrated over Virgo's lifetime, they can account for the total ICL content of the cluster implying that we do not need to invoke ICL formation mechanisms other than gravitational mechanisms leading to bright plumes. We also examined the outer halo of the giant elliptical M87. The color profile from the inner to outer halo of M87 (160 Kpc) is consistent with either a flat or optically blue gradient, where a blue gradient could be due to younger or lower metallicity stars at larger radii. The similarity of the age predicted by both the infrared and optical colors (> few Gyr) indicates that the optical measurements are not strongly affected by dust extinction.Comment: 16 pages including appendix, 9 figures, ApJ accepte

Metal Abundances in the Magellanic Stream

We report on the first metallicity determination for gas in the Magellanic Stream, using archival HST GHRS data for the background targets Fairall 9, III Zw 2, and NGC 7469. For Fairall 9, using two subsequent HST revisits and new Parkes Multibeam Narrowband observations, we have unequivocally detected the MSI HI component of the Stream (near its head) in SII1250,1253 yielding a metallicity of [SII/H]=-0.55+/-0.06(r)+/-0.2(s), consistent with either an SMC or LMC origin and with the earlier upper limit set by Lu et al. (1994). We also detect the saturated SiII1260 line, but set only a lower limit of [SiII/H]>-1.5. We present serendipitous detections of the Stream, seen in MgII2796,2803 absorption with column densities of (0.5-1)x10^13 cm^-2 toward the Seyfert galaxies III Zw 2 and NGC 7469. These latter sightlines probe gas near the tip of the Stream (80 deg down-Stream of Fairall 9). For III Zw 2, the lack of an accurate HI column density and the uncertain MgIII ionization correction limits the degree to which we can constrain [Mg/H]; a lower limit of [MgII/HI]>-1.3 was found. For NGC 7469, an accurate HI column density determination exists, but the extant FOS spectrum limits the quality of the MgII column density determination, and we conclude that [MgII/HI]>-1.5. Ionization corrections associated with MgIII and HII suggest that the corresponding [Mg/H] may range lower by 0.3-1.0 dex. However, an upward revision of 0.5-1.0 dex would be expected under the assumption that the Stream exhibits a dust depletion pattern similar to that seen in the Magellanic Clouds. Remaining uncertainties do not allow us to differentiate between an LMC versus SMC origin to the Stream gas.Comment: 30 pages, 8 figures, LaTeX (aaspp4), also available at http://casa.colorado.edu/~bgibson/publications.html, accepted for publication in The Astronomical Journa

Magellanic Cloud Structure from Near-IR Surveys II: Star Count Maps and the Intrinsic Elongation of the LMC

I construct a near-IR star count map of the LMC and demonstrate, using the viewing angles derived in Paper I, that the LMC is intrinsically elongated. I argue that this is due to the tidal force from the Milky Way. The near-IR data from the 2MASS and DENIS surveys are used to create a star count map of RGB and AGB stars, which is interpreted through ellipse fitting. The radial number density profile is approximately exponential with a scale-length 1.3-1.5 kpc. However, there is an excess density at large radii that may be due to the tidal effect of the Milky Way. The position angle and ellipticity profile converge to PA_maj = 189.3 +/- 1.4 degrees and epsilon = 0.199 +/- 0.008 for r > 5 deg. At large radii there is a drift of the center of the star count contours towards the near side of the plane, which can be undrestood as due to viewing perspective. The fact that PA_maj differes from the line of nodes position angle Theta = 122.5 +/- 8.3 (cf. Paper I) indicates that the LMC disk is not circular, but has an intrinsic ellipticity of 0.31. The LMC is elongated in the general direction of the Galactic center, and is elongated perpendicular to the Magellanic Stream and the velocity vector of the LMC center of mass. This suggests that the elongation of the LMC has been induced by the tidal force of the Milky Way. The position angle of the line of nodes differs from the position angle Theta_max of the line of maximum line of sight velocity gradient: Theta_max - Theta = 20-60 degrees. This could be due to: (a) streaming along non-circular orbits in the elongated disk; (b) uncertainties in the transverse motion of the LMC center of mass; (c) precession and nutation of the LMC disk as it orbits the Milky Way (expected on theoretical grounds). [Abridged]Comment: Astronomical Journal, in press. 34 pages, LaTeX, with 7 PostScript figures. Contains minor revisions with respect to previously posted version. Check out http://www.stsci.edu/~marel/lmc.html for a large scale (23x21 degree) stellar number-density image of the LMC constructed from RGB and AGB stars in the 2MASS and DENIS surveys. The paper is available with higher resolution color figures from http://www.stsci.edu/~marel/abstracts/abs_R32.htm

Expectations of the transition to secondary school in children with developmental language disorder and low language ability

Background A successful transition from primary to secondary school for typically developing (TD) children is associated with academic and psychosocial outcomes. Children with developmental language disorder (DLD) tend to have pervasive needs in both of these domains, yet little is known about their experience of this transition. We have no information concerning the transition for children with low language (LL). Aim (1) To explore the expectations of the transition to primary school for children with DLD, children with LL proficiency, and their TD peers; (2) to examine the predictors of transition concerns for each group. Sample Children aged 10–11 in the final year of primary school with DLD (n = 30), LL (n = 29), or TD (n = 48) were recruited from eight UK primary schools in the summer term. Methods A battery of standardized language and psychosocial assessments, including the School Concerns Questionnaire (SCQ; Rice et al. British Journal of Educational Psychology, 81, 2011, 244), was administered. Results The TD group had significantly lower levels of school concern than DLD and LL groups while DLD and LL groups did not significantly differ. Scholastic competence predicted overall concerns of children with DLD; social competence predicted TD overall concerns; and no variables predicted overall concerns of children with LL. Exploration of school concern subfactors highlighted the importance of emotion recognition for all groups and social competence for children with LL. Conclusions Results indicate that school provision to facilitate a successful transition may most usefully target different areas depending on pupils’ language level