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The Nuclear Gasdynamics and Star Formation of NGC 7469
We report interferometric radio CO 2-1 and HCN 1-0 observations atresolutions of 0.7" and 2.0", respectively, and 0.085" resolutionadaptive optics K-band spectroscopy, including H2 1-0 S(1)line emission and CO 2-0 stellar absorption, of the inner few arcsecondsof NGC 7469. The CO 2-1 map shows a ring of molecular clouds (which ingeneral lie outside the compact knots seen in K-band images) and abright extended nucleus, with a bar or pair of spiral arms between them.The dynamical structure of both the radio CO 2-1 and the K-bandH2 1-0 S(1) lines at their different resolutions can bereproduced using a single axisymmetric mass model comprising threecomponents: a broad disk, a ring 4"-5" across, and an extended nucleus,which we interpret as an inner nuclear ring about 0.5" across. Thevelocity residuals between the model and the data have a standarddeviation of 25 km s-1, and no noncircular motions fasterthan this are seen, although this may be because in some cases asecondary bar is not expected to cause gas inflow. From the dynamicalmass and estimates of the stellar mass we find that theCO-to-H2 conversion is 0.4-0.8 times that for the Milky Way,following the trend to small factors that has been reported for intensestar-forming environments. The central H2 1-0 S(1) morphologyhas a strong peak at the nucleus, but this does not trace the massdistribution; the rotation curves indicate that there is no strongnuclear mass concentration. The origins of the 1-0 S(1) emission areinstead likely to lie in X-ray and UV irradiation of gas by the activegalactic nucleus rather than via processes associated with starformation. Using the 2.3 μm stellar CO 2-0 band head absorption andthe slope of the continuum, we have directly resolved the nuclear starcluster to be 0.15"-0.20" across and find that it is asymmetric. Thiscluster has an age of less than about 60 Myr and contributes 20%-30% ofthe nuclear K-band light and about 10% of the nuclear bolometricluminosity. Within a radius of ~4" gas contributes more than half thetotal mass, but in the nucleus, within a radius of 0.1", it is likelythat most of the mass is due instead to stars.The near-infrared data presented herein were obtained at the W. M. KeckObservatory, which is operated as a scientific partnership among theCalifornia Institute of Technology, the University of California, andthe National Aeronautics and Space Administration. The Observatory wasmade possible by the generous financial support of the W. M. KeckFoundation. The radio data are based on observations carried out withthe IRAM Plateau de Bure Interferometer. IRAM is supported by INSU/CNRS(France), MPG (Germany), and IGN (Spain).
| An Einstein Observatory SAO-based catalog of B-type stars
About 4000 X-ray images obtained with the Einstein Observatory are usedto measure the 0.16-4.0 keV emission from 1545 B-type SAO stars fallingin the about 10 percent of the sky surveyed with the IPC. Seventy-fourdetected X-ray sources with B-type stars are identified, and it isestimated that no more than 15 can be misidentified. Upper limits to theX-ray emission of the remaining stars are presented. In addition tosummarizing the X-ray measurements and giving other relevant opticaldata, the present extensive catalog discusses the reduction process andanalyzes selection effects associated with both SAO catalog completenessand IPC target selection procedures. It is concluded that X-rayemission, at the level of Lx not less than 10 exp 30 ergs/s, is quitecommon in B stars of early spectral types (B0-B3), regardless ofluminosity class, but that emission, at the same level, becomes lesscommon, or nonexistent, in later B-type stars.
| On the nearest molecular clouds. III - MBM 40, 53, 54, and 55
In an attempt to determine the distances to four high-latitude molecularclouds (HLCs), echelle spectra near the Na I D lines, accurate MKspectral types, and photoelectric photometry for 25 nearby stars havebeen obtained. Fairly firm distance limits may be placed on MBM 40 (dsmaller than or equal to 140 pc) and MBM 53 (d greater than or equal to110 pc and less than or equal to 155 pc), based on the presence orabsence of strong interstellar Na I absorption towards stars projectedon or near those HLCs. Weak interstellar absorption lines observedtoward many of the stars located near MBM 54 and 55 make the distancesto those clouds less certain (about 265 pc for both). Interstellar CHabsorption at 4300 A was detected in the spectrum of HD 218662, locatedbehind MBM 53 with a CH column density of 2.1 x 10 to the 13th per sqcm, thus implying a CH abundance comparable to that observed in othermolecular clouds. Morphological and velocity agreement among COemission, the Na I absorption, the 100 micron infrared cirrus emission,and the 21 cm H I emission near these HLCs suggest a close associationof the interstellar material responsible for those phenomena.
| A photometric study of wide visual double stars with significant relative proper motion
Photometric observations and uvby H-beta indices of 142 wide visualdouble stars are presented. Calibrations of the indices are used toderive MK class, color excess, absolute magnitude, effectivetemperature, and distance. The results are used to check candidatesdouble stars for the Hipparcos mission for opticity.
| A search for SH(+) and CH(+) in diffuse and translucent clouds
Results are reported from a search for SH(+) absorption at about 336 nmfrom diffuse interstellar clouds and high-latitude molecular clouds inthe direction of nine early-type stars. Two of the lines of sight in thedirection of translucent high-latitude molecular clouds were alsosearched for CH(+) absorption at 4232 nm. Both CH(+) and SH(+) arebelieved to be formed by endothermic reactions which require the passageof a shock through the diffuse cloud. SH(+), in particular, is thoughtto form as a consequence of an MHD shock. SH(+) was not detected fromany of the lines of sight, nor was CH(+) detected from either of thehigh-latitude clouds. The N(SH+) upper limits obtained are marginallyinconsistent with the presence of MHD shocks with velocities greaterthan 14 km/s, and the nondetections of CH(+) for the high-latitudeclouds are inconsistent with current shock-chemistry models.
| Radial velocity measurements. II - Ground-based observations of the program stars for the HIPPARCOS satellite
New radial velocities for 446 stars of magnitude 9.0 or brighter in 1616-sq-deg fields of the Northern Hemisphere are determined by automaticPDS measurement of 80-A/mm-dispersion spectra obtained at theObservatoire de Haute Provence using a 17-cm-diameter objective prism.The fields were selected to provide data for the input catalog of theESA Hipparcos astrometric satellite. The measurement techniques andprecision are discussed, and the results are presented in extensivetables and graphs.
| Visual multiples. VII - MK classifications
Classifications are given for 865 components of visual multiples; theyshow no systematic differences from the MK system, and the random errorsare one subclass in type and two-thirds of a luminosity class. It isfound that at least 1% of the F-type IV and V stars are weak-lined, 32%of the A4-F1 IV and V stars are Am, and 5% of the A0-A3 IV and V starsare early-type Am. Attention is called to the large fraction (55%) ofthe A3-A9 III-V stars that are of luminosity classes III or IV, unlikethe percentage (16%) at neighboring types.
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Dades d'Observació i Astrometria
| Constel·lació: | Pegasus |
| Ascensió Recta: | 23h09m22.68s |
| Declinació: | +18°44'09.3" |
| Magnitud Aparent: | 6.742 |
| Distancia: | 242.131 parsecs |
| Moviment propi RA: | 10.4 |
| Moviment propi Dec: | -16.8 |
| B-T magnitude: | 6.668 |
| V-T magnitude: | 6.736 |
Catàlegs i designacions:
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