Search

High spectral resolution (∼80 000) and signal-to-noise observations from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project (UVES-POP) are used to study the interstellar molecular lines CN (3874 Å), CH+ (3957, 4232 Å) and CH (3886, 4300 Å) towards 74 O- and B-type stellar sightlines. Additionally, archive data are presented for 140 ELODIE early-type stellar sightlines at R = 42 000, plus 25 FEROS at R = 48 000 and 3 UVES at R > 50 000, mainly in the CH+ (4232 Å) and CH (3886, 4300 Å) transitions. Detection rates are ∼45 per cent for CN and ∼67 per cent for the other lines in the POP sample, and ∼10–15 per cent for CH+ and CH lines in the additional sample. CH and CH+ are well correlated between log[N(CH) cm−2]∼12–14, implying that these clouds are CH+-like CH and not CN-like CH. CH is also very well correlated with Na i D in the range log[N(Na i cm−2]) ∼12.2–14.2. A few sightlines show tentative velocity shifts of ∼2 km s−1 between CH and CH+, which appear to be caused by differences in component strength in blends, and hence do not provide firm evidence for shocks. Finally, we describe a search for 13CH+ in a sightline towards HD 76341. No 13CH+ is detected, placing a limit on the 13CH+ to 12CH+ ratio of ∼0.01. If a formal fit is attempted, the equivalent width ratio in the two isotopes is a factor ∼90 but with large errors. [ABSTRACT FROM AUTHOR]

We present Ca ii K and Ti ii optical spectra of early-type stars taken mainly from the ultraviolet and visual echelle spectrograph (UVES) Paranal Observatory Project, plus H i 21-cm spectra, from the Vila-Elisa and Leiden-Dwingeloo Surveys, which are employed to obtain distances to intermediate- and high-velocity clouds (IHVCs). H i emission at a velocity of −117 km s−1 towards the sightline HD 30677 ( ) with column density has no corresponding Ca ii K absorption in the UVES spectrum, which has a signal-to-noise ratio (S/N) of 610 per resolution element. The star has a spectroscopically determined distance of 2.7 kpc, and hence sets this as a firm lower distance limit towards Anti-Centre cloud ACII. Towards another sightline (HD 46185 with ), H i at a velocity of +122 km s−1 and column density of is seen. The corresponding Ca ii K spectrum has a S/N of 780, although no absorption is observed at the cloud velocity. This similarly places a firm lower distance limit of 2.9 kpc towards this parcel of gas that may be an intermediate-velocity (IV) cloud. The lack of IV Ca ii absorption towards HD 196426 ( ) at a S/N of 500 reinforces a lower distance limit of ∼700 pc towards this part of complex gp, where the H i column density is and velocity is +78 km s−1. Additionally, no IV Ca ii is seen in absorption in the spectrum of HD 19445, which is strong in H i with a column density of at a velocity of ∼−42 km s−1, placing a firm although uninteresting lower distance limit of 39 pc to this part of IV South. Finally, no high-velocity Ca ii K absorption is seen towards HD 115363 ( ) at a S/N of 410, placing a lower distance of ∼3.2 kpc towards the HVC gas at velocity of ∼+224 km s−1 and H i column density of . This gas is in the same region of the sky as complex WE ( Wakker 2001 ), but at higher velocities. The non-detection of Ca ii K absorption sets a lower distance of ∼3.2 kpc towards the HVC, which is unsurprising if this feature is indeed related to the Magellanic System. [ABSTRACT FROM AUTHOR]

We present Ca ii interstellar observations towards 20 early-type stars, to place lower distance limits to intermediate- and high-velocity clouds (IHVCs) in their lines of sight. The spectra are also employed to estimate the Ca abundance in the low-velocity gas towards these objects, when combined with Leiden–Dwingeloo 21-cm H i survey data of spatial resolution . Nine of the stars, which lie towards IHVC complexes H, K and gp, were observed with the intermediate dispersion spectrograph on the Isaac Newton Telescope at a resolution of 9000 (∼33 km s−1) and signal-to-noise ratio (S/N) per pixel of 75–140. A further nine objects were observed with the Utrecht Echelle Spectrograph on the William Herschel Telescope at and S/N per pixel of 10–25. Finally, two objects were observed in both Ca ii K and Na i D lines using the 2D COUDÉ spectrograph on the McDonald 2.7-m telescope at . The abundance of Ca ii plotted against H i column density for the objects in the current sample with heights above the Galactic plane ( z) exceeding 1000 pc is found to obey the Wakker & Mathis (2000) relation. Also, the reduced column density of Ca ii K as function of z is consistent with the larger sample taken from Smoker et al. (2003) . Higher S/N observations than those previously taken towards HVC complex H stars HD 13256 and HILT 190 reinforce the assertion that this lies at a distance exceeding 4000 pc. No obvious absorption is detected in observations of ALS 10407 and HD 357657 towards IVC complex gp. The latter star has a spectroscopically estimated distance of ∼2040 pc, although this was derived assuming the star lies on the main sequence and without any reddening correction being applied. Finally, no Ca ii K absorption is detected towards two stars along the line of sight to complex K, namely PG 1610+529 and PG 1710+490. The latter is at a distance of ∼700 pc, hence placing a lower distance limit to this complex, where previously only an upper distance limit of 6800 pc was available. [ABSTRACT FROM AUTHOR]

We present an analysis of interstellar Na i ( and 3302.98 Å), Ti ii and absorption features for 74 sightlines towards O- and B-type stars in the Galactic disc. The data were obtained from the Ultraviolet and Visual Echelle Spectrograph Paranal Observatory Project, at a spectral resolution of 3.75 km s−1 and with mean signal-to-noise ratios per pixel of 260, 300 and 430 for the Na i, Ti ii and Ca ii observations, respectively. Interstellar features were detected in all but one of the Ti ii sightlines and all of the Ca ii sightlines. The dependence of the column density of these three species with distance, height relative to the Galactic plane, H i column density, reddening and depletion relative to the solar abundance has been investigated. We also examine the accuracy of using the Na i column density as an indicator of that for H i. In general, we find similar strong correlations for both Ti and Ca, and weaker correlations for Na. Our results confirm the general belief that Ti and Ca occur in the same regions of the interstellar medium (ISM) and also that the Ti ii/Ca ii ratio is constant over all parameters. We hence conclude that the absorption properties of Ti and Ca are essentially constant under the general ISM conditions of the Galactic disc. [ABSTRACT FROM AUTHOR]

We compare existing high spectral resolution (R = λ/Δλ ∼ 40 000) Ca II K observations (λair = 3933.66 Å) towards 88 mainly B-type stars, and new observations taken using the Intermediate dispersion Spectrograph and Imaging System (ISIS) on the William Herschel Telescope at R ∼ 10 000 towards three stars taken from the Palomar­Green Survey, with 21-cm H I emission-line profiles, in order to search for optical absorption towards known intermediate- and high-velocity cloud complexes. Given certain assumptions, limits to the gas phase abundance of Ca II are estimated for the cloud components. We use the data to derive the following distances from the Galactic plane (z). (i) Tentative lower z-height limits of 2800 and 4100 pc towards complex C using lack of absorption in the spectra of HD341617 and PG0855+294, respectively. (ii) A weak lower z-height of 1400 pc towards complex WA-WB using lack of absorption in EC 09470–1433 and a weak lower limit of 2470 pc using lack of absorption in EC 09452–1403. (iii) An upper z-height of 2470 pc towards a southern intermediate-velocity cloud (IVC) with vLSR = −55 km s-1 using PG2351+198. (iv) Detection of a possible IVC in CaII absorption at vLSR = +52 km s-1 using EC 20104–2944. No associated H i in emission is detected. At this position, normal Galactic rotation predicts velocities of up to ∼ +25 km s-1. The detection puts an upper z-height of 1860 pc to the cloud. (v) Tentative H I and Ca II K detections towards an IVC at ∼ +70 km s-1 in the direction of high-velocity cloud (HVC) complex WE, sightline EC 06387–8045, indicating that the IVC may be at a z-height lower than 1770 pc. (vi) Detection of Ca II K absorption in the spectrum of PG 0855+294 in the direction of IV20, indicating that this IVC has a z-height smaller than 4100 pc. (vii) A weak lower z-height of 4300 pc towards a small HVC with vLSR = +115 km s-1 at l, b = 200°, + 52°, using lack of absorption in the Ca II K spectrum of PG 0955+291. [ABSTRACT FROM AUTHOR]

We present Westerbork Synthesis Radio Telescope H I images, Lovell telescope multibeam H I wide-field mapping, William Herschel Telescope long-slit echelle Ca II observations, Wisconsin Hα Mapper (WHAM) facility images, and IRAS ISSA 60- and 100-µm co-added images towards the intermediate-velocity cloud (IVC) at +70 km s[sup -1], located in the general direction of the M 15 globular cluster. When combined with previously published Arecibo data, the H I gas in the IVC is found to be clumpy, with a peak H I column density of ∼1.5 × 10[sup 20] cm[sup -2], inferred volume density (assuming spherical symmetry) of ∼24 cm[sup -3]/D (kpc) and a maximum brightness temperature at a resolution of 81 × 14 arcsec² of ∼14 K. The major axis of this part of the IVC lies approximately parallel to the Galactic plane, as does the low-velocity H I gas and IRAS emission. The H I gas in the cloud is warm, with a minimum value of the full width at halfmaximum velocity width of 5 km s[sup -1] corresponding to a kinetic temperature, in the absence of turbulence, of ∼540 K. From the H I data, there are indications of two-component velocity structure. Similarly, the Ca II spectra, of resolution 7 km s[sup -1], also show tentative evidence of velocity structure, perhaps indicative of cloudlets. Assuming that there are no unresolved narrow-velocity components, the mean values of log[sub l0][N(Ca II K) cm[sup -2]] ∼ 12.0 and Ca II/H I ∼2.5 × 10[sup -8] are typical of observations of high Galactic latitude clouds. This compares with a value of Ca II/H I > 10[sup -6] for IVC absorption towards HD 203664, a halo star of distance 3 kpc, some 371 from the main M15 IVC condensation. The main IVC condensation is detected by WHAM in Hα with central local-standard-of-rest velocities of l60-70 km s[sup -1], and intensities uncorrected for Galactic extinction of up to 1.3 R, indicating that the gas is partially ionized. The FWHM values... [ABSTRACT FROM AUTHOR]