A variable growth rate modification of von Bertalanffy's equation for aquaculture

In aquaculture experiments of only a few months'duration, fish can approach their asymptotic size and growth rates may change greatly. One objective of aquaculture is to obtain a maximum economic return, and a growth model is needed to relate rate of growth to food consumption and other costs to find the optimum duration of growth cycles. Von Bertalanffy's equation is an asymptotic growth model which can be used for this purpose. A variable growth rate model was developed to describe fish growth oscillations observed in aquaculture experiments. This growth model provides improved estimates of von Bertalanffy's equation in aquaculture and can be used for an efficient evaluation of fish production during production cycles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73180/1/j.1365-2109.1994.tb00689.x.pd

Scientific Highlights of the HETE-2 Mission

The HETE-2 mission has been highly productive. It has observed more than 250 GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has localized 43 GRBs to date. Twenty-one of these localizations have led to the detection of X-ray, optical, or radio afterglows, and as of now, 11 of the bursts with afterglows have known redshifts. HETE-2 has confirmed the connection between GRBs and Type Ic supernovae, a singular achievement and certainly one of the scientific highlights of the mission so far. It has provided evidence that the isotropic-equivalent energies and luminosities of GRBs are correlated with redshift, implying that GRBs and their progenitors evolve strongly with redshift. Both of these results have profound implications for the nature of GRB progenitors and for the use of GRBs as a probe of cosmology and the early universe. HETE-2 has placed severe constraints on any X-ray or optical afterglow of a short GRB. It is also solving the mystery of "optically dark' GRBs, and revealing the nature of X-ray flashes.Comment: 10 pages, 9 figures, to appear in proc. "The Restless High-Energy Universe", Royal Tropical Institute, Amsterdam; revised text, added ref

Asteroseismology of red giants & galactic archaeology

Red-giant stars are low- to intermediate-mass ($M \lesssim 10$~M$_{\odot}$) stars that have exhausted hydrogen in the core. These extended, cool and hence red stars are key targets for stellar evolution studies as well as galactic studies for several reasons: a) many stars go through a red-giant phase; b) red giants are intrinsically bright; c) large stellar internal structure changes as well as changes in surface chemical abundances take place over relatively short time; d) red-giant stars exhibit global intrinsic oscillations. Due to their large number and intrinsic brightness it is possible to observe many of these stars up to large distances. Furthermore, the global intrinsic oscillations provide a means to discern red-giant stars in the pre-helium core burning from the ones in the helium core burning phase and provide an estimate of stellar ages, a key ingredient for galactic studies. In this lecture I will first discuss some physical phenomena that play a role in red-giant stars and several phases of red-giant evolution. Then, I will provide some details about asteroseismology -- the study of the internal structure of stars through their intrinsic oscillations -- of red-giant stars. I will conclude by discussing galactic archaeology -- the study of the formation and evolution of the Milky Way by reconstructing its past from its current constituents -- and the role red-giant stars can play in that.Comment: Lecture presented at the IVth Azores International Advanced School in Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta, Azores Islands, Portugal in July 201

GRB 010921: Discovery of the first high energy transient explorer afterglow

We report the discovery of the optical and radio afterglow of GRB 010921, the first gamma-ray burst afterglow to be found from a localization by the High Energy Transient Explorer satellite. We present optical spectroscopy of the host galaxy, which we find to be a dusty and apparently normal star-forming galaxy at z = 0.451. The unusually steep optical spectral slope of the afterglow can be explained by heavy extinction, Av > 0.5 mag, along the line of sight to the GRB. Dust with similar Av for the host galaxy as a whole appears to be required by the measurement of a Balmer decrement in the spectrum of the host galaxy

Young and Intermediate-age Distance Indicators

Distance measurements beyond geometrical and semi-geometrical methods, rely mainly on standard candles. As the name suggests, these objects have known luminosities by virtue of their intrinsic proprieties and play a major role in our understanding of modern cosmology. The main caveats associated with standard candles are their absolute calibration, contamination of the sample from other sources and systematic uncertainties. The absolute calibration mainly depends on their chemical composition and age. To understand the impact of these effects on the distance scale, it is essential to develop methods based on different sample of standard candles. Here we review the fundamental properties of young and intermediate-age distance indicators such as Cepheids, Mira variables and Red Clump stars and the recent developments in their application as distance indicators.Comment: Review article, 63 pages (28 figures), Accepted for publication in Space Science Reviews (Chapter 3 of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Age

Magnetic Field Amplification in Galaxy Clusters and its Simulation

We review the present theoretical and numerical understanding of magnetic field amplification in cosmic large-scale structure, on length scales of galaxy clusters and beyond. Structure formation drives compression and turbulence, which amplify tiny magnetic seed fields to the microGauss values that are observed in the intracluster medium. This process is intimately connected to the properties of turbulence and the microphysics of the intra-cluster medium. Additional roles are played by merger induced shocks that sweep through the intra-cluster medium and motions induced by sloshing cool cores. The accurate simulation of magnetic field amplification in clusters still poses a serious challenge for simulations of cosmological structure formation. We review the current literature on cosmological simulations that include magnetic fields and outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure

The Discovery of a Planetary Companion Interior to Hot Jupiter WASP-132 b

Hot Jupiters are generally observed to lack close planetary companions, a trend that has been interpreted as evidence for high-eccentricity migration. We present the discovery and validation of WASP-132 c (TOI-822.02), a 1.85 ± 0.10 R ⊕ planet on a 1.01 day orbit interior to the hot Jupiter WASP-132 b. Transiting Exoplanet Survey Satellite and ground-based follow-up observations, in conjunction with vetting and validation analysis, enable us to rule out common astrophysical false positives and validate the observed transit signal produced by WASP-132 c as a planet. Running the validation tools vespa and TRICERATOPS on this signal yields false-positive probabilities of 9.02 × 10-5 and 0.0107, respectively. Analysis of archival CORALIE radial velocity data leads to a 3σ upper limit of 28.23 ms-1 on the amplitude of any 1.01 day signal, corresponding to a 3σ upper mass limit of 37.35 M ⊕. Dynamical simulations reveal that the system is stable within the 3σ uncertainties on the planetary and orbital parameters for timescales of ∼100 Myr. The existence of a planetary companion near the hot Jupiter WASP-132 b makes the giant planet's formation and evolution via high-eccentricity migration highly unlikely. Being one of just a handful of nearby planetary companions to hot Jupiters, WASP-132 c carries with it significant implications for the formation of the system and hot Jupiters as a population

Broadband observations of the afterglow of GRB 000926: Observing the effect of inverse Compton scattering

GRB 000926 has one of the best-studied afterglows to date, with multiple X-ray observations, as well as extensive multifrequency optical and radio coverage. Broadband afterglow observations, spanning from X-ray to radio frequencies, provide a probe of the density structure of the circumburst medium, as well as of the ejecta energetics, geometry, and physical parameters of the relativistic blast wave resulting from the explosion. We present an analysis of Chandra X-Ray Observatory observations of this event, along with Hubble Space Telescope and radio monitoring data. We combine these data with ground-based optical and IR observations and fit the synthesized afterglow light curve using models where collimated ejecta expand into a surrounding medium. We find that we can explain the broadband light curve with reasonable physical parameters if the cooling is dominated by inverse Compton scattering. For this model, an excess due to inverse Compton scattering appears above the best-fit synchrotron spectrum in the X-ray band. No previous bursts have exhibited this component, and its observation would imply that the GRB exploded in a moderately dense (n ∼ 30 cm-3) medium, consistent with a diffuse interstellar cloud environment

GRB 010921: Strong limits on an underlying supernova from the Hubble Space Telescope

GRB 010921 was the first HETE-2 gamma-ray burst (GRB) to be localized via its afterglow emission. The low redshift of the host galaxy, z = 0.451, prompted us to undertake intensive multicolor observations with the Hubble Space Telescope with the goal of searching for an underlying supernova (SN) component. We do not detect any coincident SN to a limit 1.33 mag fainter than SN 1998bw at 99.7% confidence, making this one of the most sensitive searches for an underlying SN. Analysis of the afterglow data allows us to infer that the GRB was situated behind a net extinction (Milky Way and the host galaxy) of Av ∼ 1.8 mag in the observer frame. Thus, had it not been for such heavy extinction, our data would have allowed us to probe for an underlying SN with brightness approaching those of more typical Type Ib/c SNe