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HD 100453: A Link Between Gas-Rich Protoplanetary Disks and Gas-Poor Debris Disks
HD 100453 has an IR spectral energy distribution (SED) which can be fitwith a power law plus a blackbody. Previous analysis of the SED suggeststhat the system is a young Herbig Ae star with a gas-rich, flared disk.We reexamine the evolutionary state of the HD 100453 system by refiningits age (based on a candidate low-mass companion) and by examininglimits on the disk extent, mass accretion rate, and gas content of thedisk environment. We confirm that HD 100453B is a common proper motioncompanion to HD 100453A, with a spectral type of M4.0V-M4.5V, and derivean age of 10 ± 2 Myr. We find no evidence of mass accretion ontothe star. Chandra ACIS-S imagery shows that the Herbig Ae star has Lx/L bol and an X-ray spectrum similar tononaccreting β Pic Moving Group early F stars. Moreover, the disklacks the conspicuous Fe II emission and excess FUV continuum seen inspectra of actively accreting Herbig Ae stars, and from the FUVcontinuum, we find the accretion rate is < 1.4 ×10–9 M sun yr–1. Asensitive upper limit to the CO J = 3–2 intensity indicates thatthe gas in the outer disk is likely optically thin. Assuming a[CO]/[H2] abundance of 1 × 10–4 and adepletion factor of 103, we find that the mass of coldmolecular gas is less than ~0.33 M J and that the gas-to-dustratio is no more than ~4:1 in the outer disk. The combination of a highfractional IR excess luminosity, a relatively old age, an absence ofaccretion signatures, and an absence of detectable circumstellarmolecular gas suggests that the HD 100453 system is in an unusual stateof evolution between a gas-rich protoplanetary disk and a gas-poordebris disk.
| A large, complete, volume-limited sample of G-type dwarfs. I. Completion of Stroemgren UVBY photometry
Four-colour photometry of potential dwarf stars of types G0 to K2,selected from the Michigan Spectral Catalogues (Vol. 1-3), has beencarried out. The results are presented in a catalogue containing 4247uvby observations of 3900 stars, all south of δ = -26deg. Theoverall internal rms errors of one observation (transformed to thestandard system) of a program star in the interval 8.5 < V < 10.5are 0.0044, 0.0021, 0.0039, and 0.0059, respectively, in V, b-y, m_1_ ,and c_1_. The purpose of the catalogue, combined with earliercatalogues, is to allow selection of a large, complete, volume-limitedsample of G- and K-type dwarfs, investigate their metallicitydistribution, and compare it to predictions of various models ofgalactic chemical evolution. Future papers in this series will discussthese subjects.
| Walraven photometry of nearby southern OB associations
Homogeneous Walraven (VBLUW) photometry is presented for 5260 stars inthe regions of five nearby southern OB associations: Scorpio Centaurus(Sco OB2), Orion OB1, Canis Major OB1, Monoceros OB1, and Scutum OB2.Derived V and (B - V) in the Johnson system are included.
| 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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