Оглавление
Изображения
Загрузить ваше изображение
DSS Images Other Images
Публикации по объекту
New 3D gas density maps of NaI and CaII interstellar absorption within 300 pc
Aims: We present new high resolution (R > 50 000) absorptionmeasurements of the NaI doublet (5889-5895 Å) along 482 nearbysight-lines, in addition to 807 new measurements of the CaII K (3933Å) absorption line. We have combined these new data withpreviously reported measurements to produce a catalog of absorptionstowards a total of 1857 early-type stars located within 800 pc of theSun. Using these data we have determined the approximate 3-dimensionalspatial distribution of neutral and partly ionized interstellar gasdensity within a distance-cube of 300 pc from the Sun. Methods:All newly recorded spectra were analyzed by means of a multi-componentline profile-fitting program, in most cases using simultaneous fits tothe line doublets. Normalized absorption profiles were fitted by varyingthe velocity, doppler width and column density for all interveninginterstellar clouds. The resulting total column densities were then usedin conjunction with the Hipparcos distances of the target stars toconstruct inversion maps of the 3D spatial density distribution of theNaI and CaII bearing gas. Results: A plot of the equivalent widthof NaI versus distance reveals a wall of neutral gas at ~80 pc that canbe associated with the boundary wall to the central rarefied LocalCavity region. In contrast, a similar plot for the equivalent width ofCaII shows no sharply increasing absorption at 80 pc, but instead weobserve a slowly increasing value of CaII equivalent width withincreasing sight-line distance sampled. Low values for the volumedensity of NaI (nNaI < 10-9 cm-3)are generally found within 50 pc of the Sun, whereas values in the range10-8 >nNaI > 10-10cm-3 are found for sight-lines with distance >300 pc. Bothhigh and low values of the volume density of CaII (nCaII) arefound for sight-lines <30 pc, dependent on whether local gascloudlets are encountered. For distances >100 pc a value ofnCaII ~ 10-9 cm-3 is typical for mostsight-lines, indicating that the distribution of CaII bearing gas isfairly uniform throughout the general ISM. Our three maps of the 3Dspatial distribution of local neutral NaI absorption extend and improveupon the accuracy of similar maps initially presented by Lallement etal. (2003, A&A, 411, 447), with many new neutral interstellar gasfeatures (such as low neutral density gas tunnels) in the localinterstellar medium now being revealed for the first time. The maps ofthe 3D distribution of partially ionized CaII gas are the first of theirkind to be presented and exhibit many spatial similarities to those oftheir equivalent NaI absorption maps. A major finding from both sets ofmaps is that the low density Local Cavity region is surrounded by ahighly fragmented wall of higher density NaI and CaII gas clouds. Theappearance of this broken boundary may be linked to the purportedexplosive origin of the Local Cavity. Maps of the distribution of CaIIgas density reveal the presence of many partially ionized low densitycloudlets that reside within the Local Cavity, and their newly derived3D spatial contours confirm previous observations of the local gas byRedfield & Linsky (2008, ApJ, 673, 283). Both the NaI and CaII mapssuggest that the Local Cavity may contain several low densitysub-cavities that are surrounded by thin filaments of neutral and/orpartially ionized gas. However, further observations will be required toconfirm the existence of a collection of cell-like interstellarcavities. The new maps also reveal several sight-lines where CaIIabsorption is high and the corresponding NaI absorption is low, andvice-versa. Such regions are probably influenced by the effects of thelocal stellar ionization field which can significantly affect theobserved NaI/CaII column density ratio. Plots of this ratio as afunction of distance for stars located near to the galactic plane showvalues in the range 0.1 to 1.0 for sight-lines with distances <80 pc.However, ratio values of between 0.5 and 20 are typical for more distantsight-lines. The highest values of the NaI/CaII ratio are found towardsl ~ 150° in the direction of the Taurus dark clouds, with ratiovalues in the narrower range of 0.1 to 5 being found in galacticquadrant 3.Partly based on observations collected at the European SouthernObservatory, La Silla, Chile.Full Table 1 is only available inelectronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr(130.79.128.5) or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/510/A54
| Pulkovo compilation of radial velocities for 35495 stars in a common system.
Not Available
| Distances and Metallicities of High- and Intermediate-Velocity Clouds
A table is presented that summarizes published absorption linemeasurements for the high- and intermediate-velocity clouds (HVCs andIVCs). New values are derived for N(H I) in the direction of observedprobes, in order to arrive at reliable abundances and abundance limits(the H I data are described in Paper II). Distances to stellar probesare revisited and calculated consistently, in order to derive distancebrackets or limits for many of the clouds, taking care to properlyinterpret nondetections. The main conclusions are the following. (1)Absolute abundances have been measured using lines of S II, N I, and OI, with the following resulting values: ~0.1 solar for one HVC (complexC), ~0.3 solar for the Magellanic Stream, ~0.5 solar for a southern IVC,and ~solar for two northern IVCs (the IV Arch and LLIV Arch). Finally,approximate values in the range 0.5-2 solar are found for three moreIVCs. (2) Depletion patterns in IVCs are like those in warm disk or halogas. (3) Most distance limits are based on strong UV lines of C II, SiII, and Mg II, a few on Ca II. Distance limits for major HVCs aregreater than 5 kpc, while distance brackets for several IVCs are in therange 0.5-2 kpc. (4) Mass limits for major IVCs are0.5-8×105 Msolar, but for major HVCs theyare more than 106 Msolar. (5) The Ca II/H I ratiovaries by up to a factor 2-5 within a single cloud, somewhat morebetween clouds. (6) The Na I/H I ratio varies by a factor of more than10 within a cloud, and even more between clouds. Thus, Ca II can beuseful for determining both lower and upper distance limits, but Na Ionly yields upper limits.
| Radial velocities. Measurements of 2800 B2-F5 stars for HIPPARCOS
Radial velocities have been determined for a sample of 2930 B2-F5 stars,95% observed by the Hipparcos satellite in the north hemisphere and 80%without reliable radial velocity up to now. Observations were obtainedat the Observatoire de Haute Provence with a dispersion of 80Ä,mm(-1) with the aim of studying stellar and galactic dynamics.Radial velocities have been measured by correlation with templates ofthe same spectral class. The mean obtained precision is 3.0 km s(-1)with three observations. A new MK spectral classification is estimatedfor all stars. Based on observations made at the Haute ProvenceObservatory, France and on data from The Hipparcos Catalogue, ESA.Tables 4, 5 and 6 are only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr or viahttp://cdsweb.u-strasbg.fr/Abstract.htm
| The distance to the Chain A high-velocity cloud complex.
We present high-resolution (R~5km/s) NaI and CaII interstellarabsorption line spectra observed toward five B stars in the line ofsight to the high-velocity cloud complex Chain A. We have failed todetect the presence of any high-velocity (V<-100km/s) interstellarabsorption toward these stars. This null detection enables us to place anew lower limit on the distance to the Chain A complex ofz>=837+/-200pc, assuming normal gas-phase abundances of NaI and CaII.If this distance determination is typical for other high-velocityclouds, it poses problems for theories that currently argue these cloudsinteract with the galactic disk.
|
Добавить новую статью
Внешние ссылки
- - Внешних ссылок не найдено -
Добавить внешнюю ссылку
Группы:
|
Наблюдательные данные и астрометрия
| Созвездие: | Большая Медведица |
| Прямое восхождение: | 08h55m04.13s |
| Склонение: | +57°25'37.0" |
| Видимая звёздная величина: | 8.436 |
| Расстояние: | 446.429 парсек |
| Собственное движение RA: | -15.7 |
| Собственное движение Dec: | -3.8 |
| B-T magnitude: | 8.553 |
| V-T magnitude: | 8.446 |
Каталоги и обозначения:
|
