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Trimble, Virginia; Aschwanden, Markus J.
doi: 10.1086/316546pmid: N/A
The year 1999 saw the arrival of a star with three planets, a universe with three parameters, and a solar corona that could be heated at least three ways. In addition, there were at least three papers on every question that has ever been asked in astrophysics, from “Will the Universe expand forever?” to “Does mantle convection occur in one or two layers?” The answers generally were, “Yes,” “No,” and “None of the above,” to each of the questions. The authors have done their best to organize the richness around centers defined by objects, methods, and madnesses.
doi: 10.1086/316553pmid: N/A
Type‐specific luminosity functions on the M0,iB(T) magnitude system of the Revised Shapley‐Ames Catalog (RSA) are derived for distance‐limited samples of galaxies for all Hubble types and van den Bergh luminosity classes listed in the RSA. The distributions of 21 cm line widths are derived for the Sa to Sd spirals and the Sm/Im types in the same samples. The distance‐limited subsamples have been separated from the complete flux‐limited listings in the RSA using properties of Spaenhauer diagrams.Each type‐specific luminosity function is bounded on the bright and faint ends. All galaxies in the sample that have an appreciable spiral pattern are brighter than M0,iB(T) = -15 (H0 = 50). There are no dwarf spirals in this sample. Galaxies on the exponentially rising faint end of “general” luminosity functions in the recent literature called “spirals” are not galaxies with spiral arms but rather are star‐forming galaxies of Sm and Im types. The distinction is crucial in predictions of the morphological mix expected at faint apparent magnitudes and large redshifts. One of the purposes of this paper is to begin to provide the necessary morphological resolution to adjudicate the high‐redshift suggestions for an appreciable morphological evolution with look‐back time.The brightest and fastest rotating galaxies along the present‐day Hubble sequence are large‐bulge Sa types. The faintest and slowest rotators are Sd and Sm/Im galaxies. The luminosity function of E galaxies is appreciably fainter than for all spirals earlier than Sc II–III. S0 galaxies that have pronounced disk characteristics are fainter than those with “intermediate” (I) and/or “subtle” (S) S0 characteristics.Bias in the slope and zero point of the Tully‐Fisher (TF) relation in flux‐limited samples compared with distance‐limited subsamples is demonstrated using Sb and Sbc galaxies, similar to that shown for Sc galaxies in Paper VII. A fine structure in the TF correlation that varies with Hubble type and van den Bergh luminosity class is suggested for Sb and Sbc galaxies, also similar to that set out for Sc galaxies in Paper VII. The sense is that at fixed absolute magnitude the later luminosity classes (i.e., larger L numbers) for a fixed Hubble type have higher rotational velocities by ∼4% per luminosity L number. Said differently, the Sb, Sbc, and Sc galaxies with less developed spiral arms rotate faster at a given absolute magnitude. A larger sample is required to prove or disprove the trend seen in the present data.
doi: 10.1086/316548pmid: N/A
The present note updates the information published in my recent monograph on The Galaxies of the Local Group. Highlights include (1) the addition of the newly discovered Cetus dwarf spheroidal as a certain member of the Local Group; (2) an improved distance for the Sagittarius dwarf irregular galaxy (SagDIG), which now places this object very close to the edge of the Local Group zero‐velocity surface; (3) more information on the evolutionary histories of some individual Local Group members; and (4) improved distance determinations to, and luminosities for, a number of Local Group members. These data increase the number of certain (or probable) Local Group members to 36. The spatial distribution of these galaxies supports Hubble’s claim that the Local Group “is isolated in the general field.” Currently available evidence suggests that star formation continued much longer in many dwarf spheroidals than it did in the main body of the Galactic halo. It is suggested that “young” globular clusters, such as Ruprecht 106, might have formed in now defunct dwarf spheroidals. Assuming SagDIG, which is the most remote Local Group galaxy, to lie on, or just inside, the zero‐velocity surface of the Local Group yields a dynamical age ≳ 17.9 ± 2.7 Gyr. However, this value is meaningful only if the outer regions of the local Group are in virial equilibrium.
Pitman, Karly M.; Clayton, Geoffrey C.; Gordon, Karl D.
doi: 10.1086/316551pmid: N/A
The 2175 Å absorption bump, a feature often ascribed to graphite grains and ubiquitous in the spectra of sight lines through the Galactic diffuse interstellar medium, is generally weak or nonexistent for objects outside our Galaxy. Many active galaxies seem to have Small Magellanic Cloud–type dust extinction, suggesting that the presence of the bump in our Galaxy may be exceptional. Recently, it was suggested that the spectrum of the high‐ionization broad absorption line QSO UM 425 shows a 2175 Å feature. This apparent feature seen in UM 425 and the rest frame spectra of other QSOs is intrinsic to the QSO spectrum. It is the result of a relative absence of emission near 2200 Å. Thus far, no significant detection of the 2175 Å bump in a QSO has been reported.
Kerber, F.; Furlan, E.; Roth, M.; Galaz, G.; Chanamé, J. C.; ,
doi: 10.1086/316554pmid: N/A
The major purpose of the investigation presented in this paper was to prove or disprove the nature of planetary nebula (PN) candidates in the southern hemisphere, selected from the third volume of the Atlas of Galactic Nebulae by Neckel & Vehrenberg. We present imaging and spectroscopic observations of seven PNe, five of them identified for the first time. An additional object probably is an H ii region. All observed PNe represent evolved stages, their angular diameter ranging from 15″ to 170″, and exhibit low surface brightnesses.
Tuthill, P. G.; Monnier, J. D.; Danchi, W. C.; Wishnow, E. H.; Haniff, C. A.
doi: 10.1086/316550pmid: N/A
We report the first use of Michelson interferometry on the Keck I telescope for diffraction‐limited imaging in the near‐infrared JHKL bands. By using an aperture mask located close to the f/25 secondary, the 10 m Keck primary mirror was transformed into a separate‐element, multiple‐aperture interferometer. This has allowed diffraction‐limited imaging of a large number of bright astrophysical targets, including the geometrically complex dust envelopes around a number of evolved stars. The successful restoration of these images, with dynamic ranges in excess of 200∶1, highlights the significant capabilities of sparse aperture imaging as compared with more conventional filled‐pupil speckle imaging for the class of bright targets considered here. In particular, the enhancement of the signal‐to‐noise ratio of the Fourier data, precipitated by the reduction in atmospheric noise, allows high‐fidelity imaging of complex sources with small numbers of short‐exposure images relative to speckle. Multiepoch measurements confirm the reliability of this imaging technique, and our whole data set provides a powerful demonstration of the capabilities of aperture‐masking methods when utilized with the current generation of large‐aperture telescopes. The relationship between these new results and recent advances in interferometry and adaptive optics is briefly discussed.
Massey, Philip; Foltz, Craig B.
doi: 10.1086/316552pmid: N/A
Recent (1998–1999) absolute spectrophotometry of the night sky over two southern Arizona astronomical sites, Kitt Peak and Mount Hopkins, is compared to similar data obtained in 1988 at each site. The current zenith sky brightness in the range ∼3700–6700 Å is essentially identical at the two sites and is as dark now as Palomar Observatory was in the early 1970s, when it was generally considered a premier dark observing site. Converted to broadband measurements, our spectrophotometry is equivalent to B = 22.63, V = 21.45 mag arcsec−2, for the zenith night sky. The contribution of high‐pressure sodium street lights to broadband V is about 0.2 mag arcsec−2, comparable to the strong airglow O i λ5577 line. During the period from 1988 to 1998–1999, the zenith sky brightness increased only modestly, with the largest changes being seen for Kitt Peak, where the zenith sky has brightened by ≈0.1–0.2 mag arcsec−2 in the blue‐optical region. For Kitt Peak we also have both 1988 and 1999 observations at modestly large zenith distances ( ZD ≈ 60°). In the directions away from Tucson, the sky has brightened by ≈0.35 mag arcsec−2 over the intervening decade. Toward Tucson the change has been larger, approximately 0.5 mag arcsec−2. In most directions the increase in the sky brightness has lagged behind the fractional increase in population growth, which we attribute to good outdoor lighting ordinances, a fact which is further reflected in the decrease in Hg emission. However, our results emphasize the need for diligent attention as developments creep closer to our observing sites.
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