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The Complete Guide to the Herschel Objects
Sir William Herschel's contributions to astronomy during the late eighteenth century are unrivalled. His lasting legacy is his dedicated all-sky survey of star clusters and nebulae, and these objects continue to be among the most studied in the night sky. This unique book provides a complete re-examination of Herschel's entire catalogue of non-stellar discoveries, making it the most accurate and up-to-date reference of its kind. Retrace the footsteps of one of history's greatest astronomers and explore every one of Herschel's landmark discoveries, including those considered to be lost or non-existent. Read detailed notes about each object's appearance and physical characteristics, and view hundreds of photos of the most intriguing Herschel objects, along with dozens of sketches of what is visible at the eyepiece. This superb book is a must-have for amateur astronomers seeking new and exciting observing challenges, and as the ultimate reference on the Herschel objects.
eBook
Small-Scale Cosmology Independent of the Standard Model
‘Small-scale cosmology’ is a theory designed to incorporate the linear redshift versus distance relation, which is inferred from observations, into the theoretical framework independent of the global Robertson–Walker–Friedman (RWF)-type models. The motivation behind this is that the RWF cosmological models, based on the assumptions of homogeneity and a constant matter density, as well as the concept of expanding space inherent to them are not applicable on the scales of observations from which the linear Hubble law is inferred. Therefore, explaining the Hubble law as the small redshift limit of the RWF model or as an effect of expanding space is inconsistent. Thus, the Hubble linear relation between the redshift of an extragalactic object and its distance should be considered an independent law of nature valid in the range of the distances where the RWF cosmology is not valid. In general, the theory, based on that concept, can be developed in different ways. In the present paper, ‘small-scale cosmology’ is formulated as a theory operating in the (redshift–object coordinates) space, which allows developing a conceptual and computational basis of the theory along the lines of that of special relativity. In such a theory, the condition of invariance of the Hubble law with respect to a change in the observer acceleration plays a central role. In pursuing this approach, the effectiveness of group theoretical methods is exploited. Applying the Lie group method yields transformations of the variables (the redshift and space coordinates of a cosmological object) between the reference frames of the accelerated observers. In this paper, the transformations are applied to studying the effects of the solar system observer acceleration on the observed shape, distribution and rotation curves of galaxy clusters.
Journal Article
Anomalous Spectral Types and Intrinsic Colors of Young Stars
We highlight differences in spectral types and intrinsic colors observed in pre-main sequence (pre-MS) stars. Spectral types of pre-MS stars are wavelength-dependent, with near-infrared spectra being 3-5 spectral sub-classes later than the spectral types determined from optical spectra. In addition, the intrinsic colors of young stars differ from that of main-sequence stars at a given spectral type. We caution observers to adopt optical spectral types over near-infrared types, since Hertzsprung-Russell (H-R) diagram positions derived from optical spectral types provide consistency between dynamical masses and theoretical evolutionary tracks. We also urge observers to deredden pre-MS stars with tabulations of intrinsic colors specifically constructed for young stars, since their unreddened colors differ from that of main sequence dwarfs. Otherwise, V-band extinctions as much as ~0.6 mag erroneously higher than the true extinction may result, which would introduce systematic errors in the H-R diagram positions and thus bias the inferred ages.
Journal Article
The Observing Guide to the Messier Marathon
The Messier Catalogue is a list of one hundred and ten galaxies, star clusters and nebulae, and includes many of the brightest and best-known objects in the sky. Amateur astronomers can challenge their abilities by attempting to find all the objects on the list in one night, and thus complete the Messier Marathon. This book contains over 90 easy-to-use star maps to guide the observer from one object to the next, and provides tips for a successful night of observing. The book also tells the story of the eighteenth-century astronomer, Charles Messier, and how he came to compile his extensive catalogue. This complete guide to the Messier Marathon will help the amateur astronomer to observe the Messier Objects throughout the year, using a small telescope or even a pair of binoculars.
eBook
A catalog of galaxies in and around the cluster A1367. Spectral studies of several galaxies
We present a catalog of galaxies in and around the cluster A1367, together with the results of a spectroscopic study of eight faint galaxies projected onto the central part of the cluster. The observations were carried out with the Boller and Chivens spectrograph of the 2m telescope of the Guillermo Haro Observatory (Cananea, Mexico). Redshifts of eight galaxies were derived from both emission and absorption lines; the redshift for one of these, derived from H
α
, SII, OIII, and H
β
emission lines, is
z
= 0.015. The spectrum of this galaxy displays no absorption lines at
z
= 0.026, testifying that it is located between the observer and A1367.
Journal Article
The secret deep
In this fresh list, Stephen James O'Meara presents 109 new objects for stargazers to observe. The Secret Deep list contains many exceptional objects, including a planetary nebula whose last thermal pulse produced a circumstellar shell similar to the one expected in the final days of our Sun's life; a piece of the only supernova remnant known visible to the unaided eye; the flattest galaxy known; the largest edge-on galaxy in the heavens; the brightest quasar; and the companion star to one of the first black hole candidates ever discovered. Each object is accompanied by beautiful photographs and sketches, original finder charts, visual histories and up-to-date astrophysical information to enrich the observing experience. Featuring galaxies, clusters and nebulae not covered in other Deep-Sky Companions books, this is a wonderful addition to the series and an essential guide for any deep-sky observer.
eBook
Isochrones and Luminosity Functions for Old White Dwarfs
Using a new grid of models of cooling white dwarfs, we calculate isochrones and luminosity functions in the Johnson-Kron/Cousins and HST filter sets for systems containing old white dwarfs. These new models incorporate a non-grey atmosphere which is necessary to properly describe the effects of molecular opacity at the cool temperatures of old white dwarfs. The various functions calculated and extensively tabulated and plotted are meant to be as utilitarian as possible for observers so all results are listed in quantities that observers will obtain. The tables and plots developed should eventually prove critical in interpreting the results of HST's Advanced Camera observations of the oldest white dwarfs in nearby globular clusters, in understanding the results of searches for old white dwarfs in the Galactic halo, and in determining ages for star clusters of all ages using white dwarfs. As a practical application we demonstrate the use of these results by deriving the white dwarf cooling age of the old Galactic cluster M67.
Paper
The secrets of off-season globular
While the disk of the Milky Way is dense, dynamic, and rife with star formation, the halo is relatively calm. The X-ray radiation undoubtedly results from stellar material streaming from one star of a pair onto the superdense surface of its companion (be it a neutron star or a black hole), which no optical telescope will reveal. Because this slithering giant contains few bright stars for its size and little outstanding to the naked eye, observers often overlook it. While M87, the gravitational nucleus of the extensive Virgo Cluster, is one of the most thoroughly studied of its type, its total apparent brightness trumps the relatively unknown NGC 5634 by less than one magnitude. [...]that galaxy's thousands of globular clusters, visible as such only photographically, are much more celebrated than our lone globular at the opposite end of the constellation. Magnitude 9.2 NGC 5466 in Boötes is a diffuse globular with no immediate reference points, although the spectacular cluster M3 in the adjacent constellation Canes Venatici lies a cozy 5° west. While NGC 5466 is closer to the summer sky than M3, which is at the cusp of naked-eye visibility, I included it because it typifies the challenge of off-season globular clusters. Because globular clusters within the Milky Way total only about 150 objects, and because many are within the reach of portable telescopes, most observers could view more than half of them within a reasonable timespan.
Magazine Article
Gravitational waves from coalescing binaries and Doppler experiments
Doppler tracking of interplanetary spacecraft provides the only method presently available for broad-band searches of low frequency gravitational waves. The instruments have a peak sensitivity around the reciprocal of the round-trip light-time T of the radio link connecting the Earth to the space-probe and therefore are particularly suitable to search for coalescing binaries containing massive black holes in galactic nuclei. A number of Doppler experiments -- the most recent involving the probes ULYSSES, GALILEO and MARS OBSERVER -- have been carried out so far; moreover, in 2002-2004 the CASSINI spacecraft will perform three 40 days data acquisition runs with expected sensitivity about twenty times better than that achieved so far. Central aims of this paper are: (i) to explore, as a function of the relevant instrumental and astrophysical parameters, the Doppler output produced by in-spiral signals -- sinusoids of increasing frequency and amplitude (the so-called chirp); (ii) to identify the most important parameter regions where to concentrate intense and dedicated data analysis; (iii) to analyze the all-sky and all-frequency sensitivity of the CASSINI's experiments, with particular emphasis on possible astrophysical targets, such as our Galactic Centre and the Virgo Cluster.
Paper