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Register a new userCaII K observations of QSOs in the line-of-sight to the Magellanic Bridge
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We describe medium-resolution spectroscopic observations taken with the ESO Multi-Mode Instrument in the CaII K line (3933.661 Angstroms) towards 7 QSOs located in the line-of-sight to the Magellanic Bridge. At a spectral resolution R = 6,000, five of the sightlines have a signal-to-noise ratio of 20 or higher. Definite Ca absorption due to Bridge material is detected towards 3 objects, with probable detection towards two other sightlines. Gas-phase CaII K Bridge and Milky Way abundances or lower limits for the all sightlines are estimated by the use of Parkes 21-cm HI emission line data. These data only have a spatial resolution of 14 arcminutes compared with the optical observations which have milli-arcsecond resolution. With this caveat, for the three objects with sound CaII K detections, we find that the ionic abundance of CaII K relative to HI, A=log(N(CaK)/N(HI)) for low-velocity Galactic gas ranges from -8.3 to -8.8 dex, with HI column densities varying from 3-6x10^20 cm^-2. For Magellanic Bridge gas, the values of A are 0.5 dex higher, ranging from -7.8 to -8.2 dex, with N(HI)=1-5x10^20 cm^-2. Higher values of A correspond to lower values of N(HI), although numbers are small. For the sightline towards B0251--675, the Bridge gas has two different velocities, and in only one of these is CaII K tentatively detected, perhaps indicating gas of a different origin or present-day characteristics (such as dust content), although this conclusion is uncertain and there is the possibility that one of the components could be related to the Magellanic Stream. Higher signal-to-noise CaII K data and higher resolution HI data are required to determine whether A changes with N(HI) over the Bridge and if the implied difference in the metalicity of the two Bridge components towards B0251-675 is real.
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We report a detection of far ultraviolet absorption from the supernova remnant SNR 0057 - 7226 in the Small Magellanic Cloud (SMC). The absorption is seen in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of the LBV/WR star HD 5980. Absorption from O VI 1032 and C III 977 is seen at a velocity of +300 km/s with respect to the Galactic absorption lines, +170 km/s with respect to the SMC absorption. The O VI 1038 line is contaminated by H_2 absorption, but is present. These lines are not seen in the FUSE spectrum of Sk80, only ~1 (~17 pc) away from HD 5980. No blue-shifted O VI 1032 absorption from the SNR is seen in the FUSE spectrum. The O VI 1032 line in the SNR is well described by a Gaussian with FWHM=75 km/s. We find log N(O VI)=14.33-14.43, which is roughly 50% of the rest of the O VI column in the SMC (excluding the SNR) and greater than the O VI column in the Milky Way halo along this sight line. The N(C IV)/N(O VI) ratio for the SNR absorption is in the range of 0.12-0.17, similar to the value seen in the Milky Way disk, and lower than the halo value, supporting models in which SNRs produce the highly ionized gas close to the plane of the Galaxy, while other mechanisms occur in the halo. The N(C IV)/N(O VI) ratio is also lower than the SMC ratio along this sight line, suggesting that other mechanisms contribute to the creation of the global hot ionized medium in the SMC. The O VI, C IV, and Si IV apparent column density profiles suggest the presence of a multi-phase shell followed by a region of higher temperature gas.
We used the red clump stars from the Optical Gravitational Lensing Experiment (OGLE II) survey and the the Magellanic Cloud Photometric Survey (MCPS), to estimate the line of sight depth. The observed dispersion in the magnitude and colour distribution of red clump stars is used to estimate the line of sight depth, after correcting for the contribution due to other effects. This dispersion due to depth, has a range from minimum dispersion that can be estimated, to 0.46 mag (a depth of 500 pc to 10.44 Kpc), in the LMC. In the case of SMC, the dispersion ranges from minimum dispersion to 0.35 magnitude (a depth of 665 pc to 9.53 Kpc). The thickness profile of LMC bar indicates that it is flared. The average depth in the bar region is 4.0$pm$1.4 kpc. The halo of the LMC (using RR Lyrea stars) is found to have larger depth compared to the disk/bar, which supports the presence of inner halo for the LMC. The large depth estimated for the LMC bar and the disk suggests that the LMC might have had minor mergers. In the case of SMC, the bar depth (4.90$pm$1.23 Kpc) and the disk depth (4.23$pm$1.48 Kpc) are found to be within the standard deviations. We find evidence for increase in depth near the optical center (up to 9 kpc). On the other hand, the estimated depth for the halo (RR Lyrea stars) and disk (RC stars) for the bar region of the SMC is found to be similar. Thus, increased depth and enhanced stellar as well as HI density near the optical center suggests that the SMC may have a bulge.
High-resolution HST ultra-violet spectra for five B-type stars in the Magellanic Bridge and in the Large and Small Magellanic Clouds have been analysed to estimate their iron abundances. Those for the Clouds are lower than estimates obtained from late-type stars or the optical lines in B-type stars by approximately 0.5 dex. This may be due to systematic errors possibly arising from non-LTE effects or from errors in the atomic data as similar low Fe abundances having previously been reported from the analysis of the ultra-violet spectra of Galactic early-type stars. The iron abundance estimates for all three Bridge targets appear to be significantly lower than those found for the SMC and LMC by approximately -0.5 dex and -0.8 dex respectively and these differential results should not be affected by any systematic errors present in the absolute abundance estimates. These differential iron abundance estimates are consistent with the underabundances for C, N, O, Mg and Si of approximately -1.1 dex relative to our Galaxy previously found in our Bridge targets. The implications of these very low metal abundances for the Magellanic Bridge are discussed in terms of metal deficient material being stripped from the SMC.
We present an analysis of the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of HD141569A, a transitional object known to possess a circumstellar disk. We observe two components of gas at widely different temperatures along the line of sight. We detect cold H2, which is thermalized up to J=2 at a kinetic temperature of 51K. Such low temperatures are typical of the diffuse interstellar medium. Since the line of sight to HD141569A does not pass through its disk, it appears that we are observing the cold H2 in a low extinction envelope associated with the high Galactic latitude dark cloud complex L134N, which is in the same direction and at nearly the same distance as HD141569A. The column densities of the higher J-levels of H2 suggest the presence of warm gas along the line of sight. The excitation conditions do not seem to be consistent with what is generally observed in diffuse interstellar clouds. The observed radial velocity of the gas implies that the UV spectral lines we observe are likely interstellar in origin rather than circumstellar, although our absorption line study does not definitely rule out the possibility that the warm gas is close to the star. The discovery of such warm gas along the line of sight may provide evidence for turbulent phenomena in the dark cloud L134N.
We present results from two statistical analyses applied to an neutral hydrogen (HI) dataset of the nearby tidal bridge in the Magellanic System. Primarily, analyses of the Spatial Power Spectrum suggest that the Magellanic Bridge, historically considered to be a single contiguous feature, may in fact be a projection of two kinematically and morphologically distinct structures. The southern and more obviously turbulent parts appear to show structure organized similarly to the adjacent Small Magellanic Cloud (SMC), while the northern regions are shown to be relatively deficient in large scale power. The extent of modification to the spatial power index by the velocity fluctuations is also highly variant across these parts of the Bridge. We find again that the northern part appears distinct from the southern part and from the SMC, in that the power spectrum is significantly more affected by slower velocity perturbations. We also probe the rate of spectral variation of the HI by measuring the Spectral Correlation Function over selected regions. The results from this analysis highlight a tendency for the HI spectra within the bright parts of the Bridge to have a more persistent correlation in the E-W direction than in the N-S direction. These results are considered to be quantitative evidence for the tidal processes which are thought to have been active throughout the evolution of the Magellanic Bridge
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