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Cincinnati, OH, United States

Meier D.S.,New Mexico Institute of Mining and Technology | Meier D.S.,Astronomer | Turner J.L.,University of California at Los Angeles | Beck S.C.,Tel Aviv University | And 3 more authors.
Astronomical Journal

We present a first look at the local luminous infrared galaxy (LIRG) IRAS 04296+2923. This barred spiral galaxy, overlooked because of its location behind the Taurus molecular cloud, is among the half dozen closest (D = 29 Mpc) LIRGs. More IR-luminous than either M82 or the Antennae, it may be the best local example of a nuclear starburst caused by bar-mediated secular evolution. We present Palomar J and Pa β images, Very Large Array continuum maps from λ = 20-1.3 cm, a subarcsecond Keck Long Wavelength Spectrometer image at 11.7 μm and Owens Valley Millimeter Array CO(1-0), 13CO(1-0), and 2.7 mm continuum images. The J-band image reveals a symmetric barred spiral galaxy. Two bright, compact mid-infrared and radio sources in the nucleus mark a starburst that is energetically equivalent to ∼ 105 O7 stars, separated by <50 pc. This is probably a pair of young super star clusters, with estimated stellar masses of ∼107 M⊙ each. The nuclear starburst is forming stars at the rate of ∼12 ± 6 M⊙ yr -1, or about half of the total star formation rate for the galaxy of ∼25 ± 10M⊙yr-1. IRAS 04296+2923 is very bright in CO, and among the most gas-rich galaxies in the local universe. The 12CO luminosity of the inner half kpc is equivalent to that of the entire Milky Way. While the most intense CO emission is extended over a 15″ (2 kpc) diameter region, the nuclear starburst is confined to within 1″-2″ (150-250 pc) of the dynamical center. Based on masses obtained with 13CO, we find that the CO conversion factor in the nucleus is lower than the Galactic value, XCO Gal by a factor of three to four, typical of gas-rich spiral nuclei. The nuclear star formation efficiency (SFE) is nucMgas/SFRnuc = 2.7 × 10 -8yr-1, corresponding to a gas consumption timescale, τSF nuc ∼ 4 × 107 yr. The SFE is 10 times lower in the disk, with τSF disk∼ 3.3 × 108 yr, The low absolute SFE in the disk implies that the molecular gas is not completely consumed before it drifts into the nucleus, and is capable of fueling a sustained nuclear starburst. IRAS 04296+2923 appears to be beginning a 100 Myr period as an LIRG, during which it will turn much of its 6 × 109 M⊙ of molecular gas into a nuclear cluster of stars. © 2010. The American Astronomical Society. All rights reserved. Source

Rees L.,Astronomer
Environmental Law and Management

Population trends beyond 2050 will depend on what people now in their teens and 20s decide about the number and spacing of their children. Hundreds of millions of women are denied such a choice. There is a valuable organization called the 'Optimum Population Trust' which highlights the problems of overpopulation. And there is the key issue of the discount rate. Commercial decisions apply a discount that assigns minimal importance to what happens at the end of the century. But surely we should not value the grandchildren's welfare less than the own. It is ironic that there is only one area of policy where we do implicitly apply a zero discount rate: radioactive waste disposal, where people talk with a straight face about whether the repository would be safe for ten thousand years. Geoengineering would be an utter political nightmare: not all nations would want to adjust the thermostat the same way. Very elaborate climatic modeling would be needed in order to calculate the regional impacts of such an intervention. Source

Mansfield R.L.,Astronomer
Advances in the Astronautical Sciences

This paper presents a method of initial orbit determination (IOD) for use with short arcs of deep-space, angles-only observations. The method is then used to determine the Earth flyby path of the asteroid 2012 DA14 on 2013 February 15, as an extreme example. (The asteroid was inbound and 150-116 Earth radii distant from Earth during the time span of the observations.) The solution is obtained in geocentric coordinates, rather than heliocentric, to emphasize the significance, for Earth, of close-Earth asteroid encounters. Being founded in the work of Paul Herget, the method uses all of the available observations in the arc, not just three, as with classical IOD methods. But when only three suitably-spaced observations are available, it provides an exact, two-body fit. The method is modular with respect to the Lambert solution. It is therefore a schema or framework for preliminary orbit determination, in that any of the Lambert solutions of Gauss, Battin, Gooding, or der could be incorporated. But for the asteroid example at hand, a Lambert solution attributable Gauss, with some modifications, is used to illustrate the method. Source

Belton M.J.S.,Belton Space Exploration Initiatives | Belton M.J.S.,Astronomer

I show that the size-distribution of small scattered-disk trans-neptunian objects when derived from the observed size-distribution of Jupiter Family comets (JFCs) and other observational constraints implies that a large percentage (94-97%) of newly arrived active comets within a range of 0.2-15.4km effective radius must physically disrupt, i.e., macroscopically disintegrate, within their median dynamical lifetime. Additional observational constraints include the numbers of dormant and active nuclei in the near-Earth object (NEO) population and the slope of their size distributions. I show that the cumulative power-law slope (-2.86 to -3.15) of the scattered-disk TNO hot population between 0.2 and 15.4km effective radius is only weakly dependent on the size-dependence of the otherwise unknown disruption mechanism. Evidently, as JFC nuclei from the scattered disk evolve into the inner Solar System only a fraction achieve dormancy while the vast majority of small nuclei (e.g., primarily those with effective radius <2km) break-up. The percentage disruption rate appears to be comparable with that of the dynamically distinct Oort cloud and Halley type comets (Levison, H.F., Morbidelli, A., Dones, L., Jedicke, R., Wiegert, P.A., Bottke Jr., W.F. [2002]. Science 296, 2212-2215) suggesting that all types of comet nuclei may have similar structural characteristics even though they may have different source regions and thermal histories. The typical disruption rate for a 1km radius active nucleus is ~5×10-5disruptions/year and the dormancy rate is typically 3 times less. We also estimate that average fragmentation rates range from 0.01 to 0.04events/year/comet, somewhat above the lower limit of 0.01events/year/comet observed by Chen and Jewitt (Chen, J., Jewitt, D.C. [1994]. Icarus 108, 265-271). © 2014 Elsevier Inc. Source

Crocker A.F.,University of Massachusetts Amherst | Crocker A.F.,University of Oxford | Bureau M.,University of Oxford | Young L.M.,New Mexico Institute of Mining and Technology | And 2 more authors.
Monthly Notices of the Royal Astronomical Society

We present new mm interferometric and optical integral-field unit (IFU) observations and construct a sample of 12 elliptical (E) and lenticular (S0) galaxies with molecular gas which have both CO and optical maps. The galaxies contain 2 × 107 to 5 × 109 M of molecular gas distributed primarily in central discs or rings (radii 0.5-4 kpc). The molecular gas distributions are always coincident with distributions of optically obscuring dust that reveal tightly wound spiral structures in many cases. The ionized gas always approximately corotates with the molecular gas, evidencing a link between these two gas components, yet star formation is not always the dominant ionization source. The galaxies with less molecular gas tend to have [O iii]/Hβ emission-line ratios at high values not expected for star formation. Most E/S0s with molecular gas have young or intermediate-age stellar populations based on optical colours, ultraviolet colours and absorption linestrengths. The few that appear purely old lie close to the limit where such populations would be undetectable based on the mass fractions of expected young to observed old stars. The 8 μm polycyclic aromatic hydrocarbon (PAH) and 24 μm emission yield similar star formation rate (SFR) estimates of E/S0s, but the total infrared overpredicts the rate due to a contribution to dust heating from older stars. The radio-far-infrared relation also has much more scatter than for other star-forming galaxies. However, despite these biases and additional scatter, the derived star formation rates locate the E/S0 galaxies within the large range of the Schmidt-Kennicutt and constant efficiency star formation laws. Thus, the star formation process in E/S0s is not overwhelmingly different than in other star-forming galaxies, although one of the more reliable tracers (24 μm) points to a possible lower star formation efficiency at a given gas surface density. © 2010 The Authors. Journal compilation © 2010 RAS. Source

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