Early-type stars observed in the ESO UVES Paranal Observatory Project - V. Time-variable interstellar absorption
arXiv:1506.01348 · doi:10.1093/mnras/stv945
Abstract
The structure and properties of the diffuse interstellar medium (ISM) on small scales, sub-au to 1 pc, are poorly understood. We compare interstellar absorption-lines, observed towards a selection of O- and B-type stars at two or more epochs, to search for variations over time caused by the transverse motion of each star combined with changes in the structure in the foreground ISM. Two sets of data were used: 83 VLT- UVES spectra with approximately 6 yr between epochs and 21 McDonald observatory 2.7m telescope echelle spectra with 6 - 20 yr between epochs, over a range of scales from 0 - 360 au. The interstellar absorption-lines observed at the two epochs were subtracted and searched for any residuals due to changes in the foreground ISM. Of the 104 sightlines investigated with typically five or more components in Na I D, possible temporal variation was identified in five UVES spectra (six components), in Ca II, Ca I and/or Na I absorption-lines. The variations detected range from 7\% to a factor of 3.6 in column density. No variation was found in any other interstellar species. Most sightlines show no variation, with 3σ upper limits to changes of the order 0.1 - 0.3 dex in Ca II and Na I. These variations observed imply that fine-scale structure is present in the ISM, but at the resolution available in this study, is not very common at visible wavelengths. A determination of the electron densities and lower limits to the total number density of a sample of the sightlines implies that there is no striking difference between these parameters in sightlines with, and sightlines without, varying components.
19 pages, 11 figures, accepted for publication in MNRAS
References in corpus (11)
- The High Angular Resolution Multiplicity of Massive Stars
- Evolutionary state of magnetic chemically peculiar stars
- Detailed maps of interstellar clouds in front of omega Centauri: Small-scale structures in the Galactic Disc-Halo interface
- Small-scale structure in the interstellar medium: time-varying interstellar absorption towards κ Velorum
- Monitoring the Variable Interstellar Absorption toward HD 219188 with HST/STIS
- Tiny scale opacity fluctuations from VLBA, MERLIN and VLA observations of HI absorption toward 3C 138
- Spatial Variations in Galactic H I Structure on AU-Scales Toward 3C 147 Observed with the Very Long Baseline Array
- Spatial and Temporal Variations in Interstellar Absorption toward HD 72127AB
- Redshifted emission lines and radiative recombination continuum from the Wolf-Rayet binary theta Muscae: evidence for a triplet system?
- Helium stratification in HD 145792: a new Helium strong star
- Observations towards early-type stars in the ESO-POP survey: II -- searches for intermediate and high velocity clouds