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.
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.
We present high resolution (R = 60,000) measurements of the NaI D1 and D2 (5890 A) and CaII K (3933 A) interstellar absorption line profiles recorded towards several post-AGB stars located within the M13 and M15 globular clusters, supplemented with a
lower resolution spectrum of the CaII K-line observed in absorption towards an Ofpe/WN9 star in the central region of the M33 galaxy. The normalized interstellar absorption profiles have been fit with cloud component velocities, doppler widths and column densities in order to investigate the kinematics and physical conditions of the neutral and partially ionized gas observed along each sight-line. Our CaII observations towards M13 have revealed 4 absorption components that can be identified with galactic Intermediate Velocity Clouds (IVCs) spanning the -50 > Vlsr > -80 km/s range. The NaI/CaII ratio for these IVCs is<0.3, which characterizes the gas as being warm (T=1000 K) and partially ionized. Similar observations towards two stars within M15 have revealed absorption due to a galactic IVC at Vlsr=+65 km/s. This IVC is revealed to have considerable velocity structure, requiring at least 3 cloud components to fit the observed NaI and CaII profiles. CaII K-line observations of a sight-line towards the center of the M33 galaxy have revealed at least 10 cloud components. A cloud at Vlsr=-130 km/s is either an IVC associated with the M33 galaxy occurring at +45 km/s with respect to the M33 local standard of rest, or it is a newly discovered HVC associated with our own Galaxy. In addition, 4 clouds have been discovered in the -165 > Vlsr > -205 km/s range. Three of these clouds are identified with the disk gas of M33, whereas a component at - 203 km/s could be IVC gas in the surrounding halo of M33.
We present calculations of the heliospheric SWCX emission spectra and their contributions in the ROSAT 1/4 keV band. We compare our results with the soft X-ray diffuse background (SXRB) emission detected in front of 378 identified shadowing regions d
uring the ROSAT All-Sky Survey (Snowden et al. 2000). This foreground component is principally attributed to the hot gas of the so-called Local Bubble (LB), an irregularly shaped cavity of ~50-150 pc around the Sun, which is supposed to contain ~10^6 K plasma. Our results suggest that the SWCX emission from the heliosphere is bright enough to account for most of the foreground emission towards the majority of low galactic latitude directions, where the LB is the least extended. In a large part of directions with galactic latitude above 30deg the heliospheric SWCX intensity is significantly smaller than the measured one. However, the SWCX R2/R1 band ratio differs slightly from the data in the galactic center direction, and more significantly in the galactic anti-centre direction where the observed ratio is the smallest. Assuming that both SWCX and hot gas emission are present and their relative contributions vary with direction, we tested a series of thermal plasma spectra for temperatures ranging from 10^5 to 10^6.5 K and searched for a combination of SWCX spectra and thermal emission matching the observed intensities and band ratios, while simultaneously being compatible with O VI emission measurements. In the frame of collisional equilibrium models and for solar abundances, the range we derive for hot gas temperature and emission measure cannot reproduce the Wisconsin C/B band ratio. We emphasize the need for additional atomic data, describing consistently EUV and X-ray photon spectra of the charge-exchange emission of heavier solar wind ions.
The origin of the observed variability of the gas-phase D/H ratio in the local interstellar medium is still debated, and in particular the role of deuterium depletion onto dust grains. Here we extend the study of the relationship between deuterium an
d titanium, a refractory species and tracer of elemental depletion, and explore other relationships. We have acquired high resolution spectra for nine early-type stars using the VLT/UVES spectrograph, and detected the absorption lines of interstellar TiII. Using a weighted orthogonal distance regression (ODR) code and a special method to treat non symmetric errors, we compare the TiII columns with the corresponding HI, DI and also OI columns. We perform in parallel the same comparisons for available FeII data. We find a significant correlation between TiII/HI and D/H in our data set, and, when combined with published results, we confirm and better constrain a previously published trend and extend it to low HI columns. We exclude uncertainties in HI and OI columns as the main contributor to the derived metals-deuterium correlations by showing that the TiII/HI ratio is positively correlated with DI/OI. We find a similar correlation between FeII/HI and DI/OI.The TiII gradients are similar or slightly smaller than for FeII, while one would expect larger variations on the basis of the higher condensation temperature of titanium. However we argue that ionisation effects introduce biases that affect iron and not titanium and may explain the gradient similarity. We find a less significant negative correlation between the TiII/DI ratio and the hydrogen column, possibly a sign of different evaporation of D and metals according to the cloud properties.
We study the 0.57 keV (O VII triplet) and 0.65 keV (O VIII) diffuse emission generated by charge transfer collisions between solar wind (SW) oxygen ions and interstellar H and He neutral atoms in the inner Heliosphere. These lines which dominate the
0.3-1.0 keV energy interval are also produced by hot gas in the galactic halo (GH) and possibly the Local Interstellar Bubble (LB). We developed a time-dependent model of the SW Charge-Exchange (SWCX) X-ray emission, based on the localization of the SW Parker spiral at each instant. We include input SW conditions affecting three selected fields, as well as shadowing targets observed with XMM-Newton, Chandra and Suzaku and calculate X-ray emission fot O VII and O VIII lines. We determine SWCX contamination and residual emission to attribute to the galactic soft X-ray background. We obtain ground level intensities and/or simulated lightcurves for each target and compare to X-ray data. The local 3/4 keV emission (O VII and O VIII) detected in front of shadowing clouds is found to be entirely explained by the CX heliospheric emission. No emission from the LB is needed at these energies. Using the model predictions we subtract the heliospheric contribution to the measured emission and derive the halo contribution. We also correct for an error in the preliminary analysis of the Hubble Deep Field North (HDFN).
We present a method to derive outflow velocities in the solar corona using different data sets including solar wind mass flux coming from the SWAN/SOHO instrument, electron density values from LASCO-C2 and interplanetary solar wind velocities derived
from ground-based Interplanetary Scintillation Observations (IPS). In a first step, we combine the LASCO electron densities at 6 solar radii and the IPS velocities, and compare the product to the SWAN mass fluxes. It is found that this product represents the actual mass flux at 6 solar radii for the fast wind, but not for the slow wind. In regions dominated by the slow wind, the fluxes derived from SWAN are systematically smaller. This is interpreted as a proof that the fast solar wind has reached its terminal velocity at about 6 solar radii and expands with constant velocity beyond this distance. On the contrary, the slow solar wind has reached only half of its terminal value and is thus accelerated further out. In a second step, we combine the LASCO-C2 density profiles and the SWAN flux data to derive velocity profiles in the corona between 2.5 and 6 solar radii. Such profiles can be used to test models of the acceleration mechanism of the fast solar wind.
