תוכן
תמונות
הוסף תמונה שלך
DSS Images Other Images
מאמרים קשורים
Probing the inner halo and IVC gas through the Local Interstellar Chimney
We present an absorption study of the interstellar gas at high positivegalactic latitudes in the direction close to the axis of the LocalChimney (LC), which is an extension of the rarefied local cavity thatreaches out from the galactic disk to a z-distance of at least 250 pcinto the lower halo region. Our study includes high-resolution (R 1.7 km s-1) spectral observations of the interstellar NaI andCaII absorption lines seen towards 6 early-type stars with distancesranging from 225 to 500 pc contained within a radius of6° along the sight-line (l = 160°, b= +55°). These visible data are supplemented withfar-ultraviolet absorption measurements of the interstellar sight-linestowards two hot white dwarf stars, RE J1043+490 (d = 230 pc) and REJ1059+512 (d = 315 pc), taken with the NASA Far UltravioletSpectroscopic Explorer (FUSE) satellite.Our observations reveal interstellar gas clouds with velocities in the-20 to -60 km s-1 range that appear to be falling towards thegalactic disk. In particular, we have detected absorption with avelocity of V_helio -55 km s-1 towards two sight-lines(HD 89501 and HD 88545) that can be associated with an intermediatevelocity (IV) cloud called the IV Arch. Our observations place aprobable z-distance to this IVC of 275-320 pc, this being much nearerthan previously thought.The far UV spectra of the two hot white dwarfs show only a few (10)interstellar absorption lines, which is indicative of the very lowdensity phase of the interstellar gas contained within the LC region. Wehave derived relative elemental abundance ratios for C, N, O, Si, Ar andFe for these two sight-lines and find that the abundance patterns arevery similar to those found for other sight-lines in the local cavity.The high ionization line of OVIłambda1032 Å has beendetected towards RE J1043+490 with a column density of 7 ×1012 cm-2, which is consistent with the averagespace density of this ion recently found in the Local Bubble region.Finally, we (tentatively) propose a possible connection between theformation of the Gould Belt, the Local Bubble cavity, the Local Chimneyand the overlying IV Arch clouds.
| 3D mapping of the dense interstellar gas around the Local Bubble
We present intermediate results from a long-term program of mapping theneutral absorption characteristics of the local interstellar medium,motivated by the availability of accurate and consistent parallaxes fromthe Hipparcos satellite. Equivalent widths of the interstellar NaID-line doublet at 5890 Å are presented for the lines-of-sighttowards some 311 new target stars lying within ~ 350 pc of the Sun.Using these data, together with NaI absorption measurements towards afurther ~ 240 nearby targets published in the literature (for many ofthem, in the directions of molecular clouds), and the ~ 450lines-of-sight already presented by (Sfeir et al. \cite{sfeir99}), weshow 3D absorption maps of the local distribution of neutral gas towards1005 sight-lines with Hipparcos distances as viewed from a variety ofdifferent galactic projections.The data are synthesized by means of two complementary methods, (i) bymapping of iso-equivalent width contours, and (ii) by densitydistribution calculation from the inversion of column-densities, amethod devised by Vergely et al. (\cite{vergely01}). Our present dataconfirms the view that the local cavity is deficient in cold and neutralinterstellar gas. The closest dense and cold gas ``wall'', in the firstquadrant, is at ~ 55-60 pc. There are a few isolated clouds at closerdistance, if the detected absorption is not produced by circumstellarmaterial.The maps reveal narrow or wide ``interstellar tunnels'' which connectthe Local Bubble to surrounding cavities, as predicted by the model ofCox & Smith (1974). In particular, one of these tunnels, defined bystars at 300 to 600 pc from the Sun showing negligible sodiumabsorption, connects the well known CMa void (Gry et al. \cite{gry85}),which is part of the Local Bubble, with the supershell GSH 238+00+09(Heiles \cite{heiles98}). High latitude lines-of-sight with the smallestabsorption are found in two ``chimneys'', whose directions areperpendicular to the Gould belt plane. The maps show that the LocalBubble is ``squeezed'' by surrounding shells in a complicated patternand suggest that its pressure is smaller than in those expandingregions.We discuss the locations of several HI and molecular clouds. Usingcomparisons between NaI and HI or CO velocities, in some cases we areable to improve the constraints on their distances. According to thevelocity criteria, MBM 33-37, MBM 16-18, UT 3-7, and MBM 54-55 arecloser than ~ 100 pc, and MBM 40 is closer than 80 pc. Dense HI cloudsare seen at less than 90 pc and 85 pc in the directions of the MBM 12and MBM 41-43 clouds respectively, but the molecular clouds themselvesmay be far beyond. The above closest molecular clouds are located at theneutral boundary of the Bubble. Only one translucent cloud, G192-67, isclearly embedded within the LB and well isolated.These maps of the distribution of local neutral interstellar NaI gas arealso briefly compared with the distribution of both interstellar dustand neutral HI gas within 300 pc.Tables 1 and 2 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp:cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/411/447
| Delta a and Stroemgren photometry of stars in the Renson-catalogue of AP and AM stars
We have observed 131 stars of \cite[Renson's (1991)]{re91} catalogue ofAp and Am stars both in the Stroemgren & Maitzen's (1976) Delta asystem as a contribution to the photometric studies of the lambda 5200broad band flux depression feature in chemically peculiar stars. Withfew exceptions the probability grouping of Renson for membership in theCP2 group of peculiar stars is nicely reflected by peculiar values ofDelta a. Comparison with already available Delta a values yieldsslightly larger values due to a minor shift in the filter g_1 samplingthe depression. As found by \cite[Maitzen & Vogt (1983)]{ma83} theGeneva system peculiarity parameters correlate well with Delta a. Thisstudy demonstrates the advantageous performance of a photoelectricphotometer with a rapidly rotating filter wheel moving in a stop and gomode. Tables 3 and 4 are also available in electronic form at the CDSvia anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or viahttp://cdsweb.u-strasbg.fr/Abstract.html
| Mesures de vitesses radiales. VII. Accompagnement AU sol DU programme d'observation DU satellite Hipparcos. Radial velocities. VII. Ground based measurements for Hipparcos.
We publish 734 radial velocities of stars distributed in 28 fields of4x4deg. We continue the PPO series (Fehrenbach et al. 1987; Duflot etal. 1990 and 1992), using the Fehrenbach objective prism method.
|
הכנס מאמר חדש
לינקים קשורים
הכנס לינק חדש
משמש של הקבוצה הבאה
|
תצפית ומידע אסטרומטרי
קטלוגים וכינוים:
|
