Tooth characters of protohippine horses with special reference to species from the Merychippus zone, California

The critical review of equine tooth characters attempted in this paper is the result of a study of the protohippine horses obtained from the Merychippus Zone of the north Coalinga district, California. During the conduct of extensive excavations in this zone since 1928 by the California Institute, more than two thousand teeth of the genus Merychippus have been collected. In addition to the types represented by the equine material, a number of associated land mammals have been secured. The faunal list, which includes some fifteen species, suggests that this locality occupies a stratigraphic position approximately late middle Miocene in age. The variation displayed in the dental characters of the merychippine material from the Merychippus Zone necessitated comparisons with cheek-teeth of Equidae from practically all of the Miocene formations furnishing vertebrate remains in the Pacific Coast and Great Basin Provinces. A comprehensive study of these collections clearly demonstrates that many of the cheek-tooth characters employed in the description of type specimens of fossil horses are variable to an extent which renders them unreliable in a determination of species. The variation of these characters within a large collection also indicates that it is possible for teeth referable to a particular species to have a wider stratigraphic range than has been hitherto appreciated. The conclusion is reached that the presence of a species has less value in reaching an age determination of the strata in which it occurs than evidence furnished by an association of several species

Anchitheriine Horses from the Merychippus Zone of the North Coalinga District, California

Excavations by the California Institute of Technology in the Merychippus zone of the North Coalinga district, California, have added considerably to our knowledge of the Equidae from this horizon. In addition to a large amount of material representing the genus Merychippus, the teeth of three genera of anchitheriine horses have been found. These teeth are of value in that they furnish additional information regarding the taxonomic position and geographic distribution of several of the middle Tertiary genera known from the Pacific Coast and Great Basin provinces

Tooth characters of protohippine horses with special reference to species from the Merychippus zone, California

The critical review of equine tooth characters attempted in this paper is the result of a study of the protohippine horses obtained from the Merychippus Zone of the north Coalinga district, California. During the conduct of extensive excavations in this zone since 1928 by the California Institute, more than two thousand teeth of the genus Merychippus have been collected. In addition to the types represented by the equine material, a number of associated land mammals have been secured. The faunal list, which includes some fifteen species, suggests that this locality occupies a stratigraphic position approximately late middle Miocene in age. The variation displayed in the dental characters of the merychippine material from the Merychippus Zone necessitated comparisons with cheek-teeth of Equidae from practically all of the Miocene formations furnishing vertebrate remains in the Pacific Coast and Great Basin Provinces. A comprehensive study of these collections clearly demonstrates that many of the cheek-tooth characters employed in the description of type specimens of fossil horses are variable to an extent which renders them unreliable in a determination of species. The variation of these characters within a large collection also indicates that it is possible for teeth referable to a particular species to have a wider stratigraphic range than has been hitherto appreciated. The conclusion is reached that the presence of a species has less value in reaching an age determination of the strata in which it occurs than evidence furnished by an association of several species

The fauna of the Merychippus zone, north Coalinga District, California

The fauna from the Merychippus zone, north of Coalinga, California, was first described by J. C. Merriam in 1915. The assemblage\ud as listed by Merriam included four genera of land mammals, namely, Merychippus, Proethennops, Procamelus and Telrabelodon. As recognized by Dr. Merriam, the discovery of mammalian remains in the marginal marine series of California possesses particular significance in that it furnishes an important aid in determining the time relationships between the marginal marine deposits of the Pacific Coast and the continental formations of the Great Basin and Great Plains areas of North America. The present studies were initiated, therefore, with a view to enlarging the fauna from this horizon and to establishing more accurately the time relationships of the assemblage. Moreover, it seemed desirable to record information concerning the mode of accumulation of the fossiliferous deposits and of the ecologic conditions under which the fauna existed

The Morphology of the Expanding Ejecta of V2491 Cygni (2008 N.2)

Determining the evolution of the ejecta morphology of novae provides valuable information on the shaping mechanisms in operation at early stages of the nova outburst. Understanding such mechanisms has implications for studies of shaping for example in proto-Planetary Nebulae. Here we perform morpho-kinematical studies of V2491 Cyg using spectral data to determine the likely structure of the ejecta and its relationship to the central system and shaping mechanisms. We use Shape to model different morphologies and retrieve their spectra. These synthetic spectra are compared with observed spectra to determine the most likely morphology giving rise to them, including system inclination and expansion velocity of the nova ejecta. We find the best fit remnant morphology to be that of polar blobs and an equatorial ring with an implied inclination of 80$^{+3}_{-12}$ degrees and an maximum expansion velocity of the polar blobs of 3100$^{+200}_{-100}$ km/s and for the equatorial ring 2700$^{+200}_{-100}$ km/s. This inclination would suggest that we should observe eclipses which will enable us to determine more precisely important parameters of the central binary. We also note that the amplitude of the outburst is more akin to the found in recurrent nova systems.Comment: 9 pages, 7 figures, accepted for publication in MNRA

Hubble Space Telescope Imaging of the Expanding Nebular Remnant of the Recurrent Nova RS Ophiuchi (2006)

We report Hubble Space Telescope imaging obtained 155 days after the 2006 outburst of RS Ophiuchi. We detect extended emission in both [O III] and [Ne V] lines. In both lines, the remnant has a double ring structure. The E-W orientation and total extent of these structures (580+-50 AU at d=1.6kpc) is consistent with that expected due to expansion of emitting regions imaged earlier in the outburst at radio wavelengths. Expansion at high velocity appears to have been roughly constant in the E-W direction (v_{exp} = 3200+-300 km/s in the plane of the sky), with tentative evidence of deceleration N-S. We present a bipolar model of the remnant whose inclination is consistent with that of the central binary. The true expansion velocities of the polar components are then v = 5600+-1100 km/s. We suggest that the bipolar morphology of the remnant results from interaction of the outburst ejecta with a circumstellar medium that is significantly denser in the equatorial regions of the binary than at the poles. This is also consistent with observations of shock evolution in the X-ray and the possible presence of dust in the infrared. Furthermore, it is in line with models of the shaping of planetary nebulae with close binary central systems, and also with recent observations relating to the progenitors of Type Ia supernovae, for which recurrent novae are a proposed candidate. Our observations also reveal more extended structures to the S and E of the remnant whose possible origin is briefly discussed.Comment: 13 pages, 2 figures, accepted for publication in ApJ

Accurate Realizations of the Ionized Gas in Galaxy Clusters: Calibrating Feedback

Using the full, three-dimensional potential of galaxy cluster halos (drawn from an N-body simulation of the current, most favored cosmology), the distribution of the X-ray emitting gas is found by assuming a polytropic equation of state and hydrostatic equilibrium, with constraints from conservation of energy and pressure balance at the cluster boundary. The resulting properties of the gas for these simulated redshift zero clusters (the temperature distribution, mass-temperature and luminosity-temperature relations, and the gas fraction) are compared with observations in the X-ray of nearby clusters. The observed properties are reproduced only under the assumption that substantial energy injection from non-gravitational sources has occurred. Our model does not specify the source, but star formation and AGN may be capable of providing this energy, which amounts to 3 to 5 x10^{-5} of the rest mass in stars (assuming ten percent of the gas initially in the cluster forms stars). With the method described here it is possible to generate realistic X-ray and Sunyaev-Zel'dovich cluster maps and catalogs from N-body simulations, with the distributions of internal halo properties (and their trends with mass, location, and time) taken into account.Comment: Matches ApJ published version; 30 pages, 7 figure