296,447 research outputs found

    Luminosity Guaranteed

    Get PDF
    This article aims to show that Williamson's anti-luminosity argument does not succeed if we presuppose a constitutive connection between the phenomenal and the doxastic. In contrast to other luminists, however, my strategy is not to critically focus on the refined safety condition in terms of degrees of confidence that anti-luminists typically use in this context. Instead, I will argue that, given a certain conception of what Chalmers calls ‘direct phenomenal concepts,’ luminosity is guaranteed even if the refined safety condition in terms of degrees of confidence is taken for granted

    The Galaxy Luminosity Function and Luminosity Density at Redshift z=0.1

    Get PDF
    Using a catalog of 147,986 galaxy redshifts and fluxes from the Sloan Digital Sky Survey (SDSS), we measure the galaxy luminosity density at z = 0.1 in five optical bandpasses corresponding to the SDSS bandpasses shifted to match their rest-frame shape at z = 0.1. We denote the bands (0.1)u, (0.1)g, (0.1)r, (0.1)i, (0.1)z with lambda(eff) = (3216; 4240; 5595; 6792; 8111 Angstrom), respectively. To estimate the luminosity function, we use a maximum likelihood method that allows for a general form for the shape of the luminosity function,fits for simple luminosity and number evolution, incorporates the flux uncertainties, and accounts for the flux limits of the survey. We find luminosity densities at z = 0.1 expressed in absolute AB magnitudes in a Mpc(3) to be (-14.10 +/- 0.15, -15.18 +/- 0.03, - 15.90 +/- 0.03, -16.24 +/- 0.03, -16.56 +/- 0.02) in ((0.1)u, (0.1)g, (0.1)r, (0.1)i, (0.1)z), respectively, for a cosmological model with Omega(0) = 0.3, Omega(Lambda) = 0.7, and h = 1 and using SDSS Petrosian magnitudes. Similar results are obtained using Sersic model magnitudes, suggesting that flux from outside the Petrosian apertures is not a major correction. In the (0.1)r band, the best-fit Schechter function to our results has phi* = (1.49 +/- 0.04) x 10(-2) h(3) Mpc(-3), M-* - 5 log(10) h = - 20.44 +/- 0.01, and alpha = - 1.05 +/- 0.01. In solar luminosities, the luminosity density in (0.1)r is (1.84 +/- 0.04) x 10(8) h L-0.1r,L-. Mpc(-3). Our results in the (0.1)g band are consistent with other estimates of the luminosity density, from the Two-Degree Field Galaxy Redshift Survey and the Millennium Galaxy Catalog. They represent a substantial change ( similar to 0.5 mag) from earlier SDSS luminosity density results based on commissioning data, almost entirely because of the inclusion of evolution in the luminosity function model

    The Protostellar Luminosity Function

    Full text link
    The protostellar luminosity function (PLF) is the present-day luminosity function of the protostars in a region of star formation. It is determined using the protostellar mass function (PMF) in combination with a stellar evolutionary model that provides the luminosity as a function of instantaneous and final stellar mass. As in McKee & Offner (2010), we consider three main accretion models: the Isothermal Sphere model, the Turbulent Core model, and an approximation of the Competitive Accretion model. We also consider the effect of an accretion rate that tapers off linearly in time and an accelerating star formation rate. For each model, we characterize the luminosity distribution using the mean, median, maximum, ratio of the median to the mean, standard deviation of the logarithm of the luminosity, and the fraction of very low luminosity objects. We compare the models with bolometric luminosities observed in local star forming regions and find that models with an approximately constant accretion time, such as the Turbulent Core and Competitive Accretion models, appear to agree better with observation than those with a constant accretion rate, such as the Isothermal Sphere model. We show that observations of the mean protostellar luminosity in these nearby regions of low-mass star formation suggest a mean star formation time of 0.3±\pm0.1 Myr. Such a timescale, together with some accretion that occurs non-radiatively and some that occurs in high-accretion, episodic bursts, resolves the classical "luminosity problem" in low-mass star formation, in which observed protostellar luminosities are significantly less than predicted. An accelerating star formation rate is one possible way of reconciling the observed star formation time and mean luminosity.Comment: 22 pages, 9 figures, accepted to Ap

    Practical Knowledge and Luminosity

    Get PDF
    Many philosophers hold that if an agent acts intentionally, she must know what she is doing. Although the scholarly consensus for many years was to reject the thesis in light of presumed counterexamples by Donald Davidson, several scholars have recently argued that attention to aspectual distinctions and the practical nature of this knowledge shows that these counterexamples fail. In this paper I defend a new objection against the thesis, one modelled after Timothy Williamson’s anti-luminosity argument. Since this argument relies on general principles about the nature of knowledge rather than on intuitions about fringe cases, the recent responses that have been given to defuse the force of Davidson’s objection are silent against it. Moreover, the argument suggests that even weaker theses connecting practical entities with knowledge are also false. Recent defenders of the thesis that there is a necessary connection between knowledge and intentional action are motivated by the insight that this connection is non-accidental. I close with a positive proposal to account for the non-accidentality of this link without appeal to necessary connections by drawing an extended analogy between practical and perceptual knowledge
    • …
    corecore