We study how diffuse interstellar bands (DIBs) measured toward distance-distributed target stars can be used to locate dense interstellar (IS) clouds in the Galaxy and probe a line-of-sight (LOS) kinematical structure, a potential useful tool when ga
seous absorption lines are saturated or not available in the spectral range. Cool target stars are numerous enough for this purpose. We have devised automated DIB fitting methods appropriate to cool star spectra and multiple IS components. The data is fitted with a combination of a synthetic stellar spectrum, a synthetic telluric transmission, and empirical DIB profiles. In parallel, stellar distances and extinctions are estimated self-consistently by means of a 2D Bayesian method, from spectroscopically-derived stellar parameters and photometric data. We have analyzed Gaia-ESO Survey (GES) and previously recorded spectra that probe between $sim$ 2 and 10 kpc long LOS in five different regions of the Milky Way. Depending on the observed spectral intervals, we extracted one or more of the following DIBs: $lambdalambda$ 6283.8, 6613.6 and 8620.4. For each field, we compared the DIB strengths with the Bayesian distances and extinctions, and the DIB Doppler velocities with the HI emission spectra. For all fields, the DIB strength and the target extinction are well correlated. In case of targets widely distributed in distance, marked steps in DIBs and extinction radial distance profiles match with each other and broadly correspond to the expected locations of spiral arms. For all fields, the DIB velocity structure agrees with HI emission spectra and all detected DIBs correspond to strong NaI lines. This illustrates how DIBs can be used to locate the Galactic interstellar gas and to study its kinematics at the kpc scale.
As a follow-up of a recent study, we challenge the claim that the flow of interstellar helium through the solar system has changed substantially over the last decades. We argue that only the IBEX-Lo 2009-2010 measurements are discrepant with older co
nsensus values. Then we show that the probability of the claimed variations of longitude and velocity are highly unlikely (about 1 per cent), in view of the absence of change in latitude and absence of change in the (flow velocity, flow longitude) relation, while random values would be expected. Finally, we report other independent studies showing the stability of Helium flow and the Hydrogen flow over the years 1996-2012, consistent with the seventies earlier determinations of the interstellar flow.
Inversion of interstellar gas or dust columns measured along the path to stars distributed in distance and direction allows reconstructing the distribution of interstellar matter (ISM) in 3D. A low resolution IS dust map based on the reddening of 23,
000 stars illustrates the potential of future maps. It reveals the location of the main IS clouds within $sim$1kpc and, owing to biases towards weakly reddened targets, regions devoid of IS matter. It traces the Local Bubble and neighboring cavities, including a giant, $geq$1000 pc long cavity located beyond the so-called $beta$CMa tunnel, bordered by the main constituents of the Gould belt (GB), the rotating and expanding ring of clouds and young stars, inclined by $sim$ 20$^{circ}$ to the galactic plane. From comparison with diffuse X-ray background and absorption data it appears that the giant cavity is filled with warm, ionized and dust-poor gas in addition to million K gas. This set of structures must reflect the main events that occurred in the past. It has been suggested that the Cretaceus-Tertiary mass extinction may be due to a gamma-ray burst (GRB) in the massive globular cluster (GC) 47 Tuc during its close encounter with the Sun $sim$70 Myrs ago. Given the mass, speed and size of 47 Tuc, wherever it crossed the Galactic plane it must have produced at the crossing site significant dynamical effects on the disk stars and IS clouds, and triggered star formation. Interestingly, first-order estimates suggest that the GB dynamics and age could match the consequences of the cluster crossing. Additionally, the giant ionized, dust-free cavity could be related to an intense flux of hard radiation, and dust-gas decoupling after the burst could explain the high variability and pattern of the D/H ratio in the nearby gaseous ISM. Future Gaia data should confirm or dismiss this hypothesis.
We update two kinds of results obtained with the SWAN instrument on board SOHO. First, we use H cell data recorded in 2001 and derive the H flow direction in the same way we performed the study at solar minimum. We compare with the Helium flow and do
ing so we correct for the coordinate system change between the Ulysses and SOHO mission. The deflection plane we obtain is compatible with the previous result within error bars, confirming the predominant role of the interstellar magnetic field. Secondly, we extend the derivation of solar wind ionization temporal evolution as a function of heliolatitude. The pattern for the present solar minimum is strikingly different from the previous minimum, with a much wider slow solar wind equatorial belt which persists until at least 2008. Comparing with synoptic LASCO/C2 electron densities we infer from a preliminary study that the acceleration of the high speed solar wind occurs at a higher altitude during this minimum, a change expansion models should be able to explain.
3D maps of the ISM can be used to locate not only IS clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae. We compare our 3D maps of the IS dust to the ROSAT diffuse X-ray background maps. In the Plane, there
is a good correspondence between the locations and extents of the mapped nearby cavities and the 0.25 keV background emission distribution, showing that most of these nearby cavities contribute to this soft X-ray emission. Assuming a constant dust to gas ratio and homogeneous 1MK hot gas filling the cavities, we modeled in a simple way the 0.25 keV surface brightness along the Galactic plane as seen from the Sun, taking into account the absorption by the mapped clouds. The data-model comparison favors the existence of hot gas in the Local Bubble (LB). The average mean pressure in the local cavities is found to be on the order of about 10,000 cm-3K, in agreement with previous studies. The model overestimates the emission from the huge cavities in the 3rd quadrant. Using CaII absorption data, we show that the dust to CaII ratio is very small in this region, implying the presence of a large quantity of lower temperature (non-X-ray emitting) ionized gas, explaining at least part of the discrepancy. In the meridian plane, the two main brightness enhancements coincide well with the chimneys connecting the LB to the halo. No nearby cavity is found towards the bright North Polar Spur (NPS) at high latitude. We searched in the maps for the source regions of the 0.75 keV enhancements in the 4th and 1st quadrants. Tunnels and cavities are found to coincide with the main bright areas, however no tunnel nor cavity is found to match the low-latitude, brightest part of the NPS. In addition, the comparison between the maps and published spectra do not favor the nearby cavities located within about 200pc as potential source regions for the NPS.
