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Stellar and Molecular Gas Kinematics Of NGC 1097: Inflow Driven by a Nuclear Spiral
We present spatially resolved distributions and kinematics of the starsand molecular gas in the central 320 pc of NGC 1097. The stellarcontinuum confirms the previously reported three-arm spiral patternextending into the central 100 pc. The stellar kinematics and the gasdistribution imply this is a shadowing effect due to extinction by gasand dust in the molecular spiral arms. The molecular gas kinematics showa strong residual (i.e., non-circular) velocity, which is manifested asa two-arm kinematic spiral. Linear models indicate that this is theline-of-sight velocity pattern expected for a density wave in gas thatgenerates a three-arm spiral morphology. We estimate the inflow ratealong the arms. Using hydrodynamical models of nuclear spirals, we showthat when deriving the accretion rate into the central region, outflowin the disk plane between the arms has to be taken into account. ForNGC 1097, despite the inflow rate along the arms being ~ 1.2 Msun yr–1, the net gas accretion rate to thecentral few tens of parsecs is much smaller. The numerical modelsindicate that the inflow rate could be as little as ~ 0.06 Msun yr–1. This is sufficient to generaterecurring starbursts, similar in scale to that observed, every 20-150Myr. The nuclear spiral represents a mechanism that can feed gas intothe central parsecs of the galaxy, with the gas flow sustainable fortimescales of a gigayear.Based on observations at the ESO Very Large Telescope (076.B-0098).
| A study of visual double stars with early type primaries. IV Astrophysical data
Astrophysical parameters (MK class, color excess, absolute magnitude,distance, effective temperature, mass, and age) are derived fromcalibrations of the uvby-beta indices for the members of 253 doublestars with O or B type primaries and faint secondaries. The photometricspectral classification is compared to the MK classes, and the agreementis very good. The derived data together with spectroscopic and JHKL dataare used for deciding which pairs are likely to be physical and whichare optical, and it is shown that 98 (34 percent) of the secondaries arelikely to be members of physical systems. For 90 percent of the physicalpairs the projected separation between the components is less than25,000 AU. A majority of the physical secondaries are late-type stars,and 50 percent of them are contracting towards the zero-agemain-sequence. Also presented are new uvby-beta data for 43 secondariesand a computer program for determining astrophysical parameters fromuvby-beta data.
| A study of visual double stars with early type primaries. II - Photometric results
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1983A&AS...51..161L&db_key=AST
| A study of visual double stars with early type primaries. I - Spectroscopic results
Attention is given to spectral peculiarities found in data on thespectral classes of 486 stars in 254 visual doublet or multiplet systemswith O or B type primaries, in order to isolate a group of very youngstars that may serve for the study of early stellar evolutioncharacteristics. It is noted that the material contains a substantialfraction of secondaries that are likely to be physical, and that severalof these may be in the premain-sequence phase of stellar evolution, orhave reached the zero-age main sequence.
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